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Nov 1995

Volume 13, Issue 6, pp. 2153-3113


Surface investigations by scanning thermal microscopy

M. Stopka, L. Hadjiiski, E. Oesterschulze, and R. Kassing

J. Vac. Sci. Technol. B 13, 2153 (1995); http://dx.doi.org/10.1116/1.588094 (4 pages) | Cited 7 times

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A scanning thermal microscope has been developed which is capable of imaging thermal properties of materials with high spatial resolution. First results indicate a lateral resolution less than 200 nm. The microscope employs a miniaturized thermal probe whose tip is formed as a thermocouple. The probe is laser heated to generate a thermovoltage. A sample approaching the heated tip leads to a heat flow from the tip to the cooler sample surface and thus to a decrease of the measured voltage. In the initial experiments we scanned the tip above the sample surface with open feedback loop and mapped the thermovoltage at each location of the scan range. Furthermore, we closed the feedback loop keeping the thermovoltage constant and measured the z displacement of the piezoelectric tube carrying the probe. All these measurements yield topographical as well as thermal information of the sample surface. © 1995 American Vacuum Society
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07.79.-v Scanning probe microscopes and components
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Synthesis and atomic force microscopy characterization of GeFe nanophase materials

Timothy Eastman, Jing Shi, and Da‐Ming Zhu

J. Vac. Sci. Technol. B 13, 2157 (1995); http://dx.doi.org/10.1116/1.588095 (3 pages) | Cited 1 time

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Nanocrystalline GeFe samples with Fe concentration varying from a few percent to about 86% were synthesized using an inert gas condensation method. The samples were compressed into thin disks in vacuum before exposure to air. Magnetization measurements found that the magnetization of the samples cannot be described by a simple Langevin function. Atomic force microscopy has been used to characterize the average size of the nanocrystals in the samples. For samples with a low concentration of Fe, atomic force microscopy images show distinct individual clusters with an average size of about 500 Å in diameter. For samples with a higher concentration of Fe, individual clusters cannot be distinguished, and atomic force microscope images show a mountain‐like, rugged morphology on the sample surfaces. © 1995 American Vacuum Society
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Rm Porous materials; granular materials

Scanning tunneling microscopy investigation of Co cluster growth and induced surface morphology changes on highly oriented pyrolitic graphite

H. Xu and K. Y. S. Ng

J. Vac. Sci. Technol. B 13, 2160 (1995); http://dx.doi.org/10.1116/1.588096 (6 pages)

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Co nucleation and growth on graphite were studied by scanning tunneling microscopy. Co atoms were found to adsorb preferentially on the B sites. Two‐ and three‐dimensional Co clusters were observed, distributed uniformly on the graphite surface. The internal structure of the Co cluster is quite disordered. Cluster evolution on the surface was observed in sequential images, suggesting that atom dissociation and incorporation may be one of the mechanisms for cluster migration. Co cluster‐induced superstructures were observed to localize around the clusters on the surface. The patterns of some superstructures reflect graphite’s threefold symmetry. Thermal annealing of the sample resulted in Co‐promoted etching of the graphite surface. © 1995 American Vacuum Society
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Fabrication of thickness‐controlled silicon nanowires and their characteristics

Hideo Namatsu, Yasuo Takahashi, Masao Nagase, and Katsumi Murase

J. Vac. Sci. Technol. B 13, 2166 (1995); http://dx.doi.org/10.1116/1.588097 (4 pages) | Cited 15 times

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A process for fabricating thin Si nanowires is proposed which can reduce the parasitic series resistance of the nanowire. The process includes electron cyclotron resonance plasma deposition of a SiO2 film through the openings of a patterned resist film. Since the SiO2 thickness decreases as the opening narrows, the SiO2 film can be made thinnest in the nanowire region. Therefore, during the following reactive‐ion etching, the SiO2 film in this region is removed first and the Si layer is then selectively etched. A Si nanowire fabricated through this process shows quantized conductance at temperatures as high as 200 K. © 1995 American Vacuum Society
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73.61.Cw Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Si nanostructures fabricated by electron beam lithography combined with image reversal process using electron cyclotron resonance plasma oxidation

K. Kurihara, K. Iwadate, H. Namatsu, M. Nagase, and K. Murase

J. Vac. Sci. Technol. B 13, 2170 (1995); http://dx.doi.org/10.1116/1.588098 (5 pages) | Cited 6 times

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A new image reversal process has been developed for Si nanodevice fabrication that uses electron beam lithography and electron cyclotron resonance (ECR) plasma techniques. This process is based on Si oxidation with an ECR oxygen plasma through the openings in resist mask patterns. Si on SiO2 is selectively etched by either Cl2‐based ECR plasma etching or KOH anisotropic etching by using a plasma oxide mask. ECR plasma formed silicon oxide with a thickness of 2–3 nm was found to be an excellent etch mask for these etching techniques. Highly directional ECR oxygen plasma keeps the change in the resist linewidth and edge roughness small enough for nanofabrication. Furthermore, the linewidth of reversed Si patterns can be reduced by SF6 addition to Cl2 in ECR plasma etching. This image reversal process successfully achieves 10‐nm‐scale Si wires and pillars. © 1995 American Vacuum Society
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81.65.-b Surface treatments
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

New microfabrication technique on a submicrometer scale by synchrotron radiation‐excited etching

Shingo Terakado, Takashi Goto, Masayoshi Ogura, Kazuhiro Kaneda, Osamu Kitamura, Shigeo Suzuki, Masao Nakao, and Kenichiro Tanaka

J. Vac. Sci. Technol. B 13, 2175 (1995); http://dx.doi.org/10.1116/1.588099 (4 pages)

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Synchrotron radiation‐excited etching of Si, SiC, and WO3 has been investigated using a noncontact mask with a pattern of submicrometer scale. The blank pattern of the mask was replicated on the etched surface, and highly area‐selective etching was realized at the size of ∼0.4 μm. The spatial distribution of synchrotron radiation intensity on the sample determined the depth profile of the etched region of the sample. Some adsorbate which might be redeposited etching products appeared in the vicinity of the blank pattern of the mask. © 1995 American Vacuum Society
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81.65.-b Surface treatments
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Dry development of photosensitive polyimides for high resolution and aspect ratio applications

J. Muñoz and C. Domínguez

J. Vac. Sci. Technol. B 13, 2179 (1995); http://dx.doi.org/10.1116/1.588100 (5 pages) | Cited 1 time

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A plasma developing process for photosensitive polyimide layers has been investigated as an alternative to wet development. Silylation of photoimageable polyimide by applying an organosilicon compound and subsequent ultraviolet exposure using a g‐line mask aligner equipment lead, as a consequence, to copolymerization of photoactive functional groups of silylating agents and sensitizer groups of the polyimide‐based photoresists. Development of the photoresist layer is carried out by means of oxygen‐containing plasma. Interaction of oxygen plasma with a silylated surface of polyimide leads to the formation of a silicon oxide layer that acts as a barrier giving large differences in the etching rates of the photoresist covered and not covered with organosilane. The influence of O2 plasma etching process parameters on the etching selectivity is studied. The photochemical silylation process and the dry developing method have been characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. © 1995 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Hp Lithography, masks and pattern transfer

Feasibility study of photocathode electron projection lithography

Gordon F. Saville, P. M. Platzman, George Brandes, Rene Ruel, and Robert L. Willett

J. Vac. Sci. Technol. B 13, 2184 (1995); http://dx.doi.org/10.1116/1.588101 (5 pages) | Cited 8 times

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Photocathode electron projection is an electron lithography technique that may be used to pattern semiconductors at the deep submicron level. Using a robust gold cathode, mask features in the range of 0.11–0.54 μm have been transferred to electron resist coated wafers with adequate depth of focus (≂5 μm) and large field of view (≂2 cm2). Low accelerating voltages ∼3 keV minimize proximity effects, and with a mask to wafer spacing of a few millimeters, the necessary magnetic field is ≂0.46 T. © 1995 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Ion beam modification and patterning of organosilane self‐assembled monolayers

Earl T. Ada, Luke Hanley, Sergei Etchin, John Melngailis, Walter J. Dressick, Mu‐San Chen, and Jeffrey M. Calvert

J. Vac. Sci. Technol. B 13, 2189 (1995); http://dx.doi.org/10.1116/1.588102 (8 pages) | Cited 15 times

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The patterning and modification of organosilane self‐assembled monolayers on Si native oxide surfaces by low‐ and high‐energy ion beams were investigated. The nature and extent of low‐energy (50–140 eV) Ar+ ion‐induced modification of a 2‐(trimethoxysilyl) ethyl‐2‐pyridine monolayer was studied by x‐ray photoelectron spectroscopy and by the quality of the electroless Ni patterns obtained. C(1s) and N(1s) core level x‐ray photoelectron spectroscopy indicated that the ion‐induced modification of the monolayer involved loss of the ethylpyridyl chain by sputtering and/or decomposition. The type of modification was independent of the ion energy and fluence, but the extent of modification depended on both parameters. The modification of the pyridine monolayer was monitored by the percent loss in the N(1s) peak area; modification commenced at a fluence of 5×1014 ions/cm2 and was observed for all ion energies studied. However, selective electroless metallization occurred only for monolayers that suffered ≳50% loss in the N(1s) x‐ray photoelectron spectroscopy signal. A damage saturation level of 80% N(1s) loss was indicated at an ion fluence of 9×1015 ions/cm2. A high‐energy focused ion beam lithography system was also used to evaluate the high resolution patterning of N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane, (aminoethylaminomethyl) phenethyltrimethoxysilane, and pyridine monolayers by Ga+, Si++, Au+, and Au++ ions at energies ranging from 50 to 280 keV. The highest resolution metal features obtained were 0.3‐μm‐wide gaps on phenethyltrimethoxysilane and pyridine monolayers using Ga+ and Si++ ions. Aminopropyltrimethoxysilane monolayers were found to require ten times higher ion fluences to achieve comparable results with the phenethyltrimethoxysilane and pyridine monolayers for all ions investigated. © 1995 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Observation of sidewall contamination in submicron contact holes by thermal desorption spectroscopy

Yuden Teraoka, Hidemitsu Aoki, Eiji Ikawa, Takamaro Kikkawa, and Iwao Nishiyama

J. Vac. Sci. Technol. B 13, 2197 (1995); http://dx.doi.org/10.1116/1.588103 (4 pages)

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The etching contamination remaining in Al‐base SiO2 contact holes after hole fabrication followed by a series of cleaning treatments was analyzed by using thermal desorption spectroscopy. The hole aspect ratio dependence was measured for fluorinated aluminum molecules, the major desorption species. The amount of contaminant material in the holes was found to increase with the sidewall area of the holes, suggesting that the contaminant material desorbs from the bottom surface and accumulates on the SiO2 sidewall during contact hole etching. © 1995 American Vacuum Society
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81.65.-b Surface treatments
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
85.40.Ls Metallization, contacts, interconnects; device isolation

Reducing electron energy dispersion of nonformed metal–insulator–metal electron emitters using the near‐threshold drive method

Mutsumi Suzuki, Toshiaki Kusunoki, Hiroyuki Shinada, and Tomio Yaguchi

J. Vac. Sci. Technol. B 13, 2201 (1995); http://dx.doi.org/10.1116/1.588104 (5 pages) | Cited 2 times

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The energy distribution of electrons emitted from an Al/Al2O3/Au metal–insulator–metal (MIM) electron emitter is measured. The thickness of the insulator is 5.5 nm. The energy distribution becomes narrower as the operating voltage Vd decreases since the low energy tail of the distribution is cut off by the potential barrier of the surface work function ϕ of the emitter. When the emitter is operated in the nonformed state, ΔE, the full width at half‐maximum of the distribution, is 0.32 eV for Vd=5.0 V, which is slightly above ϕ of Au (4.7 eV). As Vd increases, the high‐energy tail of the distribution broadens whereas the shape of the low‐energy tail remains unchanged. For a formed MIM emitter, ΔE becomes broader by 0.15–0.2 eV more than ΔE of a nonformed emitter at each Vd; thus, operation in the nonformed state is essential to obtain good monochromaticity. The spatial distribution of the work function in the emitter surface is also measured by the retarding potential method. The variation of ϕ, which limits the ultimately attainable monochromaticity with the near‐threshold drive method, is measured as 0.05 eV. It is estimated that ΔE less than 0.2 eV could be attained by the near‐threshold drive if the insulator thickness and Vd are further reduced. © 1995 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
41.75.Fr Electron and positron beams
85.45.-w Vacuum microelectronics

Thermomechanical analysis of failure of metal field emitters

M. G. Ancona

J. Vac. Sci. Technol. B 13, 2206 (1995); http://dx.doi.org/10.1116/1.588105 (9 pages) | Cited 6 times

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An analysis of the thermomechanics of metal (chiefly molybdenum) field emitters under normal operating conditions is given. The focus is on various ‘‘intrinsic’’ phenomena and the possibilities of triggering catastrophic breakdown. The heating is found to be predominantly Nottingham in origin (as opposed to ohmic) and is not appreciable unless the currents are well beyond the normal operating regime, e.g., as might occur under arcing conditions. As a result, the increases in temperature in operating tips are generally minimal unless the heat sinking to the substrate is weak, e.g., in ultrasharp tips, in tips on long, narrow posts, and/or in tips with severely degraded thermal conductivity. Apart from these exceptions, the small temperature excursions mean that no thermal runaway, melting, thermal desorption, or other direct thermal effects occur. Thermal stresses are of course also minimal; however, Maxwell stresses can be large under normal operating conditions, approaching the yield strength under high bias conditions. © 1995 American Vacuum Society
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85.45.-w Vacuum microelectronics

Mechanisms of copper removal during chemical mechanical polishing

J. M. Steigerwald, S. P. Murarka, J. Ho, R. J. Gutmann, and D. J. Duquette

J. Vac. Sci. Technol. B 13, 2215 (1995); http://dx.doi.org/10.1116/1.588106 (4 pages) | Cited 13 times

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Schemes using chemical mechanical polishing of copper have been proposed for the patterning of interconnections in copper multilevel metallization. In this article, the phenomena involved in the removal of copper during copper chemical mechanical polishing are investigated. The concentration of chemical etchant in the polish slurry is varied to investigate the chemical component, and the applied pressure is varied to investigate the mechanical component. Two slurries, an ammonium hydroxide plus ferricyanide slurry and a nitric acid slurry, are used to polish both copper and Cu2O thin films. Removal of copper or Cu2O is hypothesized to be a result of mechanical abrasion, while the role of the chemical etchant is to dissolve the material abraded from the surface rather than to etch the material directly from the surface. © 1995 American Vacuum Society
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81.05.Bx Metals, semimetals, and alloys
85.40.Ls Metallization, contacts, interconnects; device isolation

Charges and defects in SiO2/Si systems after exposure to microwave plasmas

T. T. Chau, K. W. Chan, and K. C. Kao

J. Vac. Sci. Technol. B 13, 2219 (1995); http://dx.doi.org/10.1116/1.588107 (7 pages) | Cited 2 times

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SiO2/Si systems with the SiO2 films produced by plasma‐enhanced chemical vapor deposition (PECVD) usually have a high density of interface traps (Dit) as compared to those with the SiO2 films grown thermally because in the former the systems have been subjected to plasma radiation. To simulate the radiation effects due to microwave plasmas during the deposition of SiO2 films by PECVD, we used high‐quality thermally grown SiO2 films to form SiO2/Si systems and studied the changes of the behavior of such systems after being exposed to microwave plasmas at various device temperatures. The results show that for SiO2/Si systems without metallic electrodes, the density of electron‐trapped charges, Qot, in the SiO2 bulk and Dit are higher after plasma radiation. For SiO2/Si systems with aluminum electrodes on the oxide and the Si surfaces, the effects of plasma radiation on the values of Qot and Dit are less, indicating that aluminum electrodes act as protective layers partly screening the plasma radiation, but the penetration of vacuum ultraviolet light from the plasma to the SiO2 bulk produces electrons and holes in SiO2 bulk, which react with oxygen vacancies in the SiO–Si (nonbridging) bonds forming positive trapped charge in the SiO2 bulk and at the SiO2/Si interface. The value of Dit increases with increasing SiO2 film thickness and decreases as the device temperature is increased from 25 to 200 °C during radiation. A further increase in device temperature beyond 200 °C leads to a reverse trend, implying that the defect generation and annihilation processes take place simultaneously during plasma radiation. Annealing in a forming gas at 400 °C removes most of the radiation‐induced defects. It should be noted that under a PECVD situation the radiation damage could be much worse particularly at the beginning of the PECVD process whereas the SiO2 film is still very thin. © 1995 American Vacuum Society
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.-b Surface treatments
85.30.De Semiconductor-device characterization, design, and modeling

Gate oxide loss at the periphery of a metal–oxide–semiconductor field‐effect transistor resulting from a polysilicon gate etch with a helicon etch tool

R. Kraft and S. Krishnan

J. Vac. Sci. Technol. B 13, 2226 (1995); http://dx.doi.org/10.1116/1.588053 (4 pages) | Cited 1 time

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This article describes a study of gate oxide loss at the gate periphery of a metal–oxide–semiconductor field‐effect transistor (MOSFET) resulting from a polysilicon gate etch with a commercially available low pressure, high density plasma helicon etch tool. When the oxide is removed at the periphery of a MOSFET with the gate etch process, it is possible to damage the underlying silicon in the source and drain regions leading to device degradation or failure. Conventional oxide thickness and scanning electron microscope measurements after the gate etch have been shown to be inadequate in detecting microtrenches and microholes in the oxide at the gate periphery. To measure the integrity of the oxide at the gate periphery, a modified MOS (MMOS) capacitor test structure has been developed to measure the electrical field breakdown strength of the oxide at the gate periphery. This article describes a MMOS study of the oxide loss and underlying etch mechanisms encountered in a low pressure, high plasma density helicon etch tool. © 1995 American Vacuum Society
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81.65.-b Surface treatments
85.30.Tv Field effect devices

Analysis and Monte Carlo simulations of spontaneous etching: Cl–Si(100)‐2×1

J. R. Sánchez, C. M. Aldao, and J. H. Weaver

J. Vac. Sci. Technol. B 13, 2230 (1995); http://dx.doi.org/10.1116/1.588054 (4 pages) | Cited 2 times

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Scanning tunneling microscopy observations of the growth of Cl‐induced etch pits on Si(100)‐2×1 lend themselves to quantitative determinations of vacancy size distributions, particularly those that are linear or branched at some point along the linear pit. These result in rate constants and energy differences for the dominant etching channels. By considering nearest‐neighbor and second‐nearest‐neighbor interactions, we determine the attractive interaction energies between dimers in a row, 0.28 eV, and between dimers in adjacent rows, 0.22 eV, as well as the repulsive second‐neighbor dimers, −0.08 eV. These results are tested by means of Monte Carlo simulations. © 1995 American Vacuum Society
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments

Si1−xGex pulsed plasma etching using CHF3 and H2

D. J. Paul, V. J. Law, and G. A. C. Jones

J. Vac. Sci. Technol. B 13, 2234 (1995); http://dx.doi.org/10.1116/1.588055 (4 pages) | Cited 4 times

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Selective reactive ion etching of Si over Si1−xGex and Si1−xGex over Si has been demonstrated by using a modulation‐frequency, plasma‐etch technique which employs CHF3 and H2 as the etch precursor gases. The selective etch crossover region appears at a modulation frequency of 2–3 Hz for a duty cycle of 50%. It is suggested that the etch selectivity phenomenon arises from the relative ion‐assisted and purely chemical components of the radio frequency plasma and decaying plasma afterglow. © 1995 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.-b Surface treatments

Surface preparation of ZnSe by chemical methods

Lu‐Min Liu, Greg Lindauer, W. Brock Alexander, and Paul H. Holloway

J. Vac. Sci. Technol. B 13, 2238 (1995); http://dx.doi.org/10.1116/1.588056 (7 pages) | Cited 5 times

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The effects of several chemical treatments on ZnSe surface composition and morphology have been analyzed with scanning electron microscopy and Auger electron spectroscopy. Polycrystalline bulk and thin film ZnSe heteroepitaxed onto GaAs were used. Large variations in the etching rate and surface conditions, such as roughness, contamination, oxides, and stoichiometry, have been observed with different etchants. Contamination by carbon and oxygen was present on all the treated surfaces. Surface oxides could be thinned by dipping in HF or HF/NH4Cl, which did not etch ZnSe. Methanol with 1% bromine etched ZnSe vigorously and selectively, and resulted in a rough surface. A relatively smooth ZnSe surface resulted from etching in NH4OH/H2O2, but excess Se precipitated from this solution to form whiskers. These whiskers could be removed using CS2. No excess Se was found after etching in hot NaOH but a thicker oxide and a pitted, rough surface was observed.  A two stage etch consisting of NH4OH/H2O2 followed by CS2 is recommended for a smooth, near‐stoichiometric surface. © 1995 American Vacuum Society
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.65.-b Surface treatments

Influence of in situ argon cleaning of GaAs on Schottky diodes and metal–semiconductor field‐effect transistors

J. G. van Hassel, H. C. Heyker, and J. J. M. Kwaspen

J. Vac. Sci. Technol. B 13, 2245 (1995); http://dx.doi.org/10.1116/1.588057 (5 pages)

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The influence of in situ argon cleaning of GaAs on the electrical characteristics of Schottky diodes and metal–semiconductor field‐effect transistors (MESFETs) is investigated. The beam energy was varied from 50 to 500 eV and the characteristics were compared to wet chemically cleaned devices. The characteristics of the Schottky diodes showed a significant degradation as a consequence of damage introduced by argon cleaning. Recovery was obtained with an additional annealing step at 300 °C for diodes cleaned at energies below 125 eV. For higher energies, the samples became worse with annealing. MESFETs showed degraded performances for positive gate voltages due to a high gate leakage current. Improvement was also obtained upon annealing. © 1995 American Vacuum Society
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81.65.-b Surface treatments
85.30.-z Semiconductor devices

Etching temperature dependence of the surface composition and reconstruction for Cl2‐etched GaAs layers

N. Tanaka, M. López, I. Matsuyama, and T. Ishikawa

J. Vac. Sci. Technol. B 13, 2250 (1995); http://dx.doi.org/10.1116/1.588058 (5 pages) | Cited 3 times

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In order to understand the mechanism of the Cl2‐etching reaction with GaAs, the composition and reconstruction of in situ Cl2‐etched GaAs surfaces were studied as functions of the etching temperature. From an Auger electron spectroscopy analysis and reflection high‐energy electron‐diffraction observations, it was shown that the GaAs surface changed from As stabilized to Ga stabilized during low‐temperature (∼50 °C) etching, while it remained As stabilized during high‐temperature (150–250 °C) etching. This result can be understood by considering the temperature dependence of the desorption rate of chloride compounds. At low temperature, the desorption of Ga chlorides is more suppressed than that of As chlorides, resulting in rough Ga‐stabilized surfaces. At high temperature, the desorption of any chlorides is not suppressed. Thus, stoichiometric etching is realized, resulting in smooth As‐stabilized surfaces, which are advantageous for high‐performance microdevice fabrication. © 1995 American Vacuum Society
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.40.Hp Lithography, masks and pattern transfer

Spectroscopic ellipsometric monitoring of electron cyclotron resonance plasma etching of GaAs and AlGaAs

P. G. Snyder, N. J. Ianno, B. Wigert, S. Pittal, B. Johs, and J. A. Woollam

J. Vac. Sci. Technol. B 13, 2255 (1995); http://dx.doi.org/10.1116/1.588059 (5 pages) | Cited 5 times

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In situ real time spectroscopic ellipsometry measurements were made during electron cyclotron resonance plasma etching of radio frequency biased GaAs and AlGaAs samples. Gas mixtures used were CH4/H2/Ar, pure H2, and pure Ar. Ellipsometry provided information about damage to the surface region and AlGaAs epilayer thickness. For the methane mixture GaAs etch, damage appeared in the form of redshifted and broadened E1 and E1+Δ1 critical point features in a surface layer several tens of nm thick. The damage layer began forming within a few seconds after the start of etching, and stabilized within 1 min. Hydrogen etching caused a thicker damage layer with greater redshifting and broadening, while argon caused relatively little damage. Possible mechanisms for the redshifting are discussed. During etching of an AlGaAs/GaAs heterostructure with the methane mixture, the same redshifting and broadening effects were seen in the AlGaAs critical point structure. The AlGaAs thickness was determined from the real time data, from which an etch rate of about 20 nm/min was derived. © 1995 American Vacuum Society
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78.66.Fd III-V semiconductors
81.65.-b Surface treatments

Effects of glancing‐angle ion bombardment on GaAs(001)

J. G. C. Labanda, S. A. Barnett, and L. Hultman

J. Vac. Sci. Technol. B 13, 2260 (1995); http://dx.doi.org/10.1116/1.588060 (9 pages) | Cited 6 times

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The effect of glancing‐angle argon ion energy E (0.5–3.0 keV), dose D (0.3–10×1016 ions cm−2), flux J (0.6–5.9×1013 ions cm−2 s−1), impingement angle ϕ (6°–30°), and substrate temperature Ts (440–650 °C) on the surface morphology and crystallinity of clean and air‐exposed GaAs(001) surfaces was studied. For air‐exposed GaAs, the lowest roughness measured by atomic force microscopy was 0.3 nm at D=2.3×1016 ions/cm2, E=1 keV, and ϕ=15° for Ts=570 °C and an ≊1.5×10−5 Torr As4 overpressure. These conditions provided sufficient sputtering to remove surface contamination, as indicated by streaky, 2×4 reconstructed reflection high‐energy electron diffraction patterns and C‐ and O‐free low‐energy ion scattering spectra, while avoiding ion damage as judged by cross‐sectional transmission electron microscopy. Defect‐free epitaxial GaAs layers were grown on the sputter‐cleaned substrates. Ion bombardment of clean surfaces showed roughening at larger ϕ values, but smooth surfaces were maintained for ϕ=6°. Cross‐sectional transmission electron microscopy studies of clean bombarded surfaces showed that ion damage decreased with decreasing D, E, and ϕ, and no damage was observed over a range of conditions. Sputter yields as a function of energy and ϕ are reported. © 1995 American Vacuum Society
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61.80.Jh Ion radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.-b Surface treatments

Flux masking and thickness uniformity in molecular beam epitaxy

K. Sadra, Chih‐Hsiang Lin, and J. M. Meese

J. Vac. Sci. Technol. B 13, 2269 (1995); http://dx.doi.org/10.1116/1.588061 (7 pages)

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We suggest that properly designed masks altering the rotation‐integrated flux arriving at the substrate may be used to improve thickness uniformity in a variety of crystal growth techniques. As an illustration, we calculate the dimensions of the mask required to produce a perfectly uniform flux for a single group‐III species in single‐ and multiple‐wafer III–V molecular beam epitaxy. Estimates of the detrimental role of errors in mask machining and position are provided and schemes for correcting flux nonuniformities for multiple sources are suggested. Our results imply that flux masking can lead to significant uniformity improvements for growth on single or multiple wafers. © 1995 American Vacuum Society
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Thermal stability of AlGaAs/GaAs single quantum well structures using photoreflectance

P. J. Hughes, E. H. Li, and B. L. Weiss

J. Vac. Sci. Technol. B 13, 2276 (1995); http://dx.doi.org/10.1116/1.588062 (8 pages) | Cited 8 times

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The thermal stability of two AlGaAs/GaAs single quantum well structures was investigated using room‐temperature photoreflectance. Rapid thermal annealing between 800 and 1000 °C for times up to 180 s showed spectral ‘‘blue’’ shifts for both the ground state and higher order interband transitions of the quantum well due to Al and Ga interdiffusion across the well/barrier interface resulting in a modification of the quantum well confinement profile. The sensitivity of these transition energies to Al–Ga interdiffusion depended on both the quantum well structure and annealing conditions. The results were correlated with a theoretical model, which was developed previously to determine the effects of interdiffusion on the subband structure of quantum well samples, to give characteristics interdiffusion lengths of less than 20 Å for these annealing conditions. These interdiffusion lengths corresponded to limited interdiffusion and was confirmed from polarization sensitivity measurements where the anisotropic polarization behavior of the quantum well was maintained for these annealing conditions. The analysis of these results agrees well with the model and gives Al/Ga interdiffusion coefficients of ∼2.9×10−17 and ∼9.2×10−17 cm2/s at 900 and 1000 °C, respectively. © 1995 American Vacuum Society
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors

Photoluminescence of quantum dots fabricated using tungsten stressors

J. A. Yater, A. S. Plaut, K. Kash, P. S. D. Lin, Leigh T. Florez, James P. Harbison, S. R. Das, and L. Lebrun

J. Vac. Sci. Technol. B 13, 2284 (1995); http://dx.doi.org/10.1116/1.588063 (5 pages) | Cited 1 time

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Strain modulation of a semiconductor band gap spatially confines excitons in a near‐surface GaAs/AlGaAs quantum well. We report photoluminescence (PL) results of quantum dot arrays fabricated using tungsten stressors. Excitons are confined in a 35 meV potential well under 100 nm dot stressors, which is 2.4 times deeper than that observed using 100 nm carbon stressors. Such a confinement potential corresponds to quantum dot energy level splittings of approximately 7 meV. Arrays of dots are studied, each with individual stressors of a different size ranging from 100 to 800 nm. The lateral potential well depth, as measured by the red shift in PL signal, is dependent on the stressor width and thickness in a well‐understood manner. The integrated PL signal from the dots increases with increasing temperature, indicating increased efficiency of trapping of excitons from the quantum well into the quantum dots. Interpretation of excitation spectra, and observation of higher energy levels, are complicated by the details of the strain pattern and the near‐field coupling of radiation between the metallic stressors and the quantum well. © 1995 American Vacuum Society
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71.35.-y Excitons and related phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Metal–In80Al20Sb interface formation: An x‐ray photoelectron spectroscopy study

S. A. Clark, S. P. Wilks, R. H. Williams, A. D. Johnson, and C. R. Whitehouse

J. Vac. Sci. Technol. B 13, 2289 (1995); http://dx.doi.org/10.1116/1.588064 (4 pages)

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The formation of intimate, atomically clean, In–In80Al20Sb interfaces has been investigated using x‐ray photoelectron spectroscopy. The attenuation of the substrate (Sb) core levels showed anomalous behavior; increasing for the first few monolayers of In deposited. This is interpreted in terms of a reaction between chemisorbed In on the c(8×2) reconstructed In‐rich In80Al20Sb surface and deposited In, to produce clustering, so enhancing the substrate signals emanating from bulk In80Al20Sb. The incremental deposition of In brought about incremental shifts of the In core level binding energies, related to changes in the chemical environment of the In. For the other bulk core levels examined, no further shifts were resolved, indicating that the Fermi level at the In80Al20Sb surface is pinned prior to metallization. © 1995 American Vacuum Society
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68.35.Fx Diffusion; interface formation
73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures

Implant isolation of InxAl1−xN and InxGa1−xN

C. B. Vartuli, S. J. Pearton, C. R. Abernathy, J. D. MacKenzie, and J. C. Zolper

J. Vac. Sci. Technol. B 13, 2293 (1995); http://dx.doi.org/10.1116/1.588065 (4 pages) | Cited 5 times

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N‐type layers of InxAl1−xN and InxGa1−xN were implanted with multiple energy N+, F+, or O+ ions at doses in the range 5×1012–5×1014 cm−2, and subsequently annealed up to 900 °C. Increases in sheet resistance of up to factors of ∼104 were achieved in In0.75Al0.25N after implantation at the higher doses, followed by annealing at 600–700 °C. The behavior for InxGa1−xN followed the same trend, with somewhat lower increases in sheet resistance. The implantation creates deep acceptor states in the upper part of the band gap of both types of material, rather than at midgap, which is the optimum situation for implant isolation. © 1995 American Vacuum Society
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61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.61.Ey III-V semiconductors

Ohmic contacts on p‐In0.53Ga0.47As prepared by Zn implantation into Pd‐based metallizations

P. Ressel, H. Strusny, K. Vogel, J. Würfl, D. Fritzsche, H. Kräutle, E. Kuphal, K. Mause, M. Trapp, and U. Richter

J. Vac. Sci. Technol. B 13, 2297 (1995); http://dx.doi.org/10.1116/1.588066 (9 pages) | Cited 1 time

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A new technique is presented for the fabrication of low‐resistivity Ohmic contacts on p‐In0.53Ga0.47As doped below 1×1019 cm−3 consisting of dopant implantation into the contact metal and subsequent rapid thermal annealing. Zn‐implanted and annealed Pd/Au/Pt/Au, Pd/LaB6/Au, and Pd/Ge contacts exhibit drastically lowerer contact resistivity in comparison to corresponding systems prepared without implantation. A resistivity decrease by approximately one and a half orders of magnitude is observed in cases of Pd/Au/Pt/Au and Pd/LaB6/Au contacts. The lowest value is found for Pd/Au/Pt/Au on p‐In0.53Ga0.47As doped to 4×1018 cm−3 with 1×10−6 Ω cm2, whereas 1–2×10−5 Ω cm2 is obtained for Pd/Ge contacts on p‐In0.53Ga0.47As doped to 7×1018 cm−3. The elemental redistribution and the interface morphology of annealed contacts have been studied with backside secondary ion mass spectroscopy and cross‐sectional transmission electron microscopy. No contact penetration and a planar interface are found in the case of Pd/Ge, whereas significant penetration of contact components into the semiconductor and nonplanarity of the interface are observed in Pd/Au/Pt/Au and Pd/LaB6/Au contacts. In contacts annealed at conditions for minimal resistivity the penetration depth is 200 and 105 nm, respectively. Implanted Zn is redistributed toward the contact interface during thermal processing. Thus the resistivity lowering is attributed to enhanced p‐doping by Zn, which diffused from the contact into the underlying semiconductor. Residual implantation damage is discussed as the essential cause of the comparably high resistivity of implanted and annealed Pd/Ge contacts. © 1995 American Vacuum Society
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73.40.Cg Contact resistance, contact potential
85.30.-z Semiconductor devices

100 years of x rays: Impact on micro‐ and nanofabrication

Henry I. Smith

J. Vac. Sci. Technol. B 13, 2323 (1995); http://dx.doi.org/10.1116/1.588067 (6 pages) | Cited 7 times

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In November of 1895 Wilhelm C. Röntgen observed fluorescence caused by invisible rays emanating from a discharge tube. This discovery of x rays was not a mere happenstance; Röntgen was a highly skilled experimentalist, well prepared to launch a series of clever experiments and startle the world with the announcement of ‘‘a new kind of ray.’’ The practice of medicine was transformed, and the era of modern physics inaugurated. X rays have proven essential to the probing of atomic, molecular, and solid‐state structures. X‐ray astronomy has revealed some of the most exotic and violent phenomena in the universe, including the black holes. X‐ray microscopy provides information complementary to what is obtainable from optical and electron microscopies. In micro‐ and nanolithography x rays provide high quality aerial images and simple processing, in part because of an absence of spurious scattering, something that Röntgen himself observed. However, application in ultralarge scale integrated (ULSI) manufacturing is still uncertain for a variety of reasons, primarily because ultraviolet optical‐projection lithography continues to satisfy commercial needs. X‐ray lithography may find application in areas outside the ULSI industry, for example in optoelectronics, flat‐panel displays, and magnetic data storage. It has the intrinsic resolution to reach the practical limits of the lithographic process, around 20 nm. However, to approach this limit diffraction blurring must be avoided by reducing the mask–sample gap below 5 μm, which may not be acceptable in manufacturing. In this event, and in order to retain the lithographic qualities of 1 nm wavelength radiation, projection with Fresnel zone plate arrays could be employed. © 1995 American Vacuum Society
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41.50.+h X-ray beams and x-ray optics
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Process and device technologies for 1 Gbit dynamic random‐access memory cells

Toru Kaga, Makoto Ohkura, Fumio Murai, Natsuki Yokoyama, and Eiji Takeda

J. Vac. Sci. Technol. B 13, 2329 (1995); http://dx.doi.org/10.1116/1.588068 (6 pages) | Cited 9 times

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This article discusses the technological issues involved with continuing the miniaturization of dynamic random‐access memory cells into the gigabit era. Ever‐smaller giga‐generation dynamic random‐access memory cells require three‐dimensional high‐charge density capacitors with high‐ϵ insulating films, leading to the need for further improvements in lithographic resolution for ever‐smaller, higher aspect ratio memory cells, and planarization technologies for reducing the memory‐cell height. This article demonstrates two technologies for meeting these two requirements: high acceleration energy electron‐beam lithography and KrF excimer‐laser phase‐shift photolithography, and plate‐wiring merge technology. Metal–insulator–metal 1.6 nm Ta2O5 CROWN capacitors and single Si3N4 spacer OSELO isolation technology for an experimental 1 Gbit dynamic random‐access memory chip are also discussed. © 1995 American Vacuum Society
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Toward accurate metrology with scanning force microscopes

Yves Martin and H. Kumar Wickramasinghe

J. Vac. Sci. Technol. B 13, 2335 (1995); http://dx.doi.org/10.1116/1.588069 (5 pages) | Cited 5 times

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Scanning force microscopes (SFMs) have become valuable instruments for inspection of surfaces on a submicron scale in the semiconductor industry. Their ability to track the position of a surface with an accuracy of the order of 1 nm opens the door to applications in micro‐ or nanometrology. Standard SFMs, using a conical shaped tip, are being applied to measurements of the height or depth of shallow features, such as via holes or small lines and trenches, that cannot readily be characterized by scanning electron microscopy or optical techniques. Recent technical developments of the SFM have provided new capabilities for accurate measurement of the line and trench width using a flared tip and an improved scanning and tracking method for the tip. Laboratory tests as well as industrial tests have revealed that repeatability in measuring critical dimensions approaches 1 nm. If careful attention is given to issues of calibration, particularly for the motion of the tip and for dimensioning of the tip itself, SFM techniques may attain accuracies that approach their measurement precision. © 1995 American Vacuum Society
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Excimer laser assisted etching of AlGaAs and GaAs

Shinichiro Takatani, Seiji Yamamoto, Hiroyuki Takazawa, and Kozo Mochiji

J. Vac. Sci. Technol. B 13, 2340 (1995); http://dx.doi.org/10.1116/1.588070 (4 pages) | Cited 3 times

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Laser assisted etching of AlGaAs and GaAs by chlorine using ArF and KrF excimer lasers was investigated. The etching rate of AlGaAs was shown to be larger than that of GaAs. Quadrupole mass spectroscopy analysis of the etching products for KrF assisted etching showed intense Ga+ and As+ signals from AlGaAs. It is suggested that a laser‐induced neutral atom desorption process is enhanced in the AlGaAs etching. Hall measurements of a shallow channel heterostructure sample and GaAs Schottky diode characterization demonstrated the low damage of the etching process. The etching profile was examined by scanning electron microscopy and feasibility for field effect transistor gate recess etching was shown. © 1995 American Vacuum Society
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81.65.-b Surface treatments
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
85.30.Tv Field effect devices

Selective reactive ion etching of InGaAs and InP over InAlAs in SiCl4/SiF4/HBr plasmas

S. K. Murad, S. P. Beaumont, M. Holland, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 13, 2344 (1995); http://dx.doi.org/10.1116/1.588071 (6 pages) | Cited 10 times

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A new selective reactive ion etching (RIE) process has been developed for etching InGaAs and InP over InAlAs using a mixture of SiCl4/SiF4/HBr gases. Optical emission spectroscopic (OES) investigation showed that the dominant emitting species in the plasma are HBr+, Br, and Br2, with weaker emission from SiBr and SiHBr. Using a flow rate of SiCl4/HBr of 6/15 SCCM, a pressure of 100 mTorr, and with a dc bias of 180 V, the etch rates of InGaAs and AlInAs can be as high as 200 nm/min at room temperature with good surface morphology. The formation of bromosilanes or chlorosilanes of the form (SiHxBry, SiHxCly) in the plasma is believed to be responsible for the etching In‐containing compounds through the formation of indiumbromosilanes and indiumchlorosilanes. The selectivity of etching InGaAs and InP over InAlAs is obtained by the addition of SiF4 to the mixture of SiCl4/HBr, which is thought to be due to the formation of an etch stop layer of AlF3 on the AlInAs layer. Using a flow rate ratio of SiCl4/SiF4/HBr of 5/6/25 SCCM, a dc bias of ≤70 V, and a pressure of 100 mTorr, the selectivity was extraordinary high for this material system a minimum of (600:1). The etching was stopped on a 5‐nm‐thick AlInAs layer for at least 60 min. These values of selectivity are an order of magnitude higher than the reported values in the literature. Moreover, this RIE process (SiCl4/SiF4/HBr) etches silicon nitride, and NiCr very slowly. Structures in InP have been etched as deep as 6 μm with very little erosion to the mask which was a very thin layer (100 nm thick) of either Si3N4 or NiCr. The dry etch damage was evaluated using Hall effect measurements made on a high electron mobility transistors material structure. This structure had a 7 nm InGaAs capping layer. Etching the 7 nm cap layer had very little effect on the value of the sheet carrier concentration and the mobility even after 7 min of continuous bombardment of the active layers by selective etching of the 7 nm capping layer. © 1995 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.-b Surface treatments
85.30.De Semiconductor-device characterization, design, and modeling

Atomic force microscopy study of III–V materials etched using an electron cyclotron resonance source

S. Thomas and S. W. Pang

J. Vac. Sci. Technol. B 13, 2350 (1995); http://dx.doi.org/10.1116/1.588072 (5 pages) | Cited 3 times

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GaInAs, InP, and GaAs are etched in a Cl2/Ar plasma generated by an electron cyclotron resonance source. Analysis using scanning electron microscopy shows no difference in GaInAs surface morphology before or after etching in a Cl2/Ar plasma. However, a significant increase in the mean surface roughness of GaInAs from 0.2 to 1.9 nm after etching is detected by atomic force microscopy. The mean surface roughness of GaAs also increases from 0.2 to 1.0 nm after etching. X‐ray photoelectron spectroscopy was used to measure atomic concentrations on the etched surface. The results show that the increased roughness of etched GaInAs is related to residual etch products that consist of O and Cl. Using atomic force microscopy, the mean surface roughness was measured to be 1.8 nm at 0.5 mTorr and it increased to 2.7 nm at 5 mTorr. The degradation in GaInAs surface morphology with increasing pressure caused an increase in the specific contact resistivity. Etching related roughness can be minimized by using high radio‐frequency power, low pressure, and low Cl2% in Ar. Increasing the ion density by increasing the microwave power allows InP to be etched at 2.7 μm/min with a Cl2/Ar plasma at 30 °C. A smooth surface obtained at 500 W microwave power has a mean surface roughness of 1.7 nm and the InP stoichiometry remains nearly constant after etching. For a lower microwave power of 100 W, the mean surface roughness increases to 4.3 nm, and the surface is characterized by large islands. An H2O rinse immediately following the etch is able to remove residual etch products as indicated by a decrease in the surface roughness as well as the Cl and O concentrations on the surface. © 1995 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.65.-b Surface treatments

Diffusion and channeling of low‐energy ions: The mechanism of ion damage

Ching‐Hui Chen, Debora L. Green, and Evelyn L. Hu

J. Vac. Sci. Technol. B 13, 2355 (1995); http://dx.doi.org/10.1116/1.588073 (5 pages) | Cited 22 times

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A simple model, including both channeling and diffusion effects, has been developed for the understanding of the mechanism of low‐energy ion‐induced damage. This model provided much better agreement with our experimental data, and yields a value for the effective diffusivity of defects during ion bombardment as ∼3×10−15 cm2/s. The numerical results support our experimental data that diffusion of defects, even at room temperature, plays an important role in determining the profile of ion‐induced damage and suggests that some enhancement of defect diffusion occurs during ion bombardment. In addition, since the majority of defects are located in the near‐surface region (within ∼50 Å of the surface), even modest etch removal of the surface can dramatically alter the damage profile. Therefore, surface removal has also been considered in our model to find the influence of etch rate on the ion damage profile. © 1995 American Vacuum Society
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61.80.-x Physical radiation effects, radiation damage
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

A comparative study of Cl2 and HCl gases for the chemically assisted ion beam etching of InP

C. Youtsey and I. Adesida

J. Vac. Sci. Technol. B 13, 2360 (1995); http://dx.doi.org/10.1116/1.588074 (6 pages) | Cited 7 times

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Chemically assisted ion beam etching using an Ar ion beam and Cl2 and HCl gases was investigated for the etching of high quality facets in InP. The etch rate, anisotropy, and surface morphology for the Cl2 and HCl processes are compared for different conditions of substrate temperature and reactive gas flow rate. Elevated substrate temperatures above 150 °C were required due to the low volatility of InClx reaction products below this temperature. At higher substrate temperatures, etch rates in the range of 1–5 μm/min using Cl2 and 200–500 nm/min using HCl were obtained. Vertical etch profiles were obtained above 200 °C for Cl2 and above 300 °C using HCl. The HCl process provided very smooth etched surfaces under most conditions investigated. Surface analysis using Auger electron spectroscopy and secondary ion mass spectroscopy techniques was conducted. Auger electron spectroscopy indicated surface depletion of In using Cl2, HCl resulted in increased depletion of P. Secondary ion mass spectroscopy depth profiles carried out using deuterium gas indicated diffusion of deuterium greater than 10 μm at a process temperature of 325 °C, while a postetch anneal at 325 °C/10 min was demonstrated to reduce the level of deuterium near the surface. © 1995 American Vacuum Society
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81.65.-b Surface treatments
82.80.-d Chemical analysis and related physical methods of analysis

Plasma development of a silylated bilayer resist: Effects of etch chemistry on critical dimension control and feature profiles

Richard S. Hutton, Craig H. Boyce, and Gary N. Taylor

J. Vac. Sci. Technol. B 13, 2366 (1995); http://dx.doi.org/10.1116/1.588075 (6 pages) | Cited 8 times

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We have previously described a positive‐tone, silylated, dry‐developed bilayer resist process for which 0.2 μm features with an aspect ration of 4.5 were obtained using deep‐UV (248 nm) exposure. The plasma development of the resist is comprised of two steps: an initial etch with a mixture of Ar and Cl2 to remove the thin layer of silylated resist in the exposed regions followed by pattern transfer using an oxidative plasma. In this process feature profiles with minimal undercut were obtained when CO2 was used instead of O2 in the pattern transfer step. We have investigated the mechanism of these etching processes using x‐ray photoelectron spectroscopy (XPS) and trilevel resist processing and found that there was little deposition and that the selectivity of the silylated resist decreased by a factor of 2 in the CO2 plasma compared to the O2 plasma. The lower selectivity leads to increased erosion of the silicon‐containing mask and reduced critical dimension (CD) control. In order to obtain good CD control and further improve the feature profiles we have evaluated other etching gases which are considered to undergo sidewall deposition during the pattern transfer step, including SO2 and mixtures of O2 with N2 and SO2. Using trilevel resist structures, the degree of lateral etching was determined for each plasma. The extent of deposition in each plasma was monitored through surface analysis using XPS. In the silylated bilayer resist, the feature profiles are significantly influenced by the etching rates, selectivities, and degree of overetch which were studied by varying the etcher power levels, and etching times. In this article we will discuss the results of these studies and show how 0.2 μm features with nearly vertical sidewalls were obtained. © 1995 American Vacuum Society
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication of ultrasmall magnets by electroplating

W. Xu, J. Wong, C. C. Cheng, R. Johnson, and A. Scherer

J. Vac. Sci. Technol. B 13, 2372 (1995); http://dx.doi.org/10.1116/1.588076 (4 pages) | Cited 16 times

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We use high voltage electron beam lithography followed by electroplating to define small metal features on semiconductor substrates. These have been used to form high resolution etch masks, dense nanomagnet arrays, and highly anisotropic metal nanostructures. To reproducibly obtain uniform arrays of such structures, we have developed an end‐point detection technique, which is based on in situ observation of the electrodeposition process. © 1995 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Plasma passivation of etch‐induced surface damage on GaAs

K. K. Ko and S. W. Pang

J. Vac. Sci. Technol. B 13, 2376 (1995); http://dx.doi.org/10.1116/1.588077 (5 pages) | Cited 2 times

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Various plasma passivation techniques for removal of etch‐induced damage on GaAs have been studied. It was found that a Cl2 plasma generated with an electron cyclotron resonance source can efficiently remove dry etch‐induced damage with minimal etching of the GaAs. Complete recovery of the electrical characteristics of both the Schottky diodes and unalloyed transmission lines was found with a 30 s Cl2 plasma passivation at 25 °C. The chlorine reactive species used for passivation were generated with 50 W microwave power at 2 mTorr without any rf power applied at the stage. The Cl2 passivated surface was thermally stable up to 450 °C. Similar recovery was also observed for diodes passivated with a N2 plasma. Compared to Cl2, however, N2 plasma passivation requires a higher temperature (350 °C) and higher microwave power (500 W). Capacitance–voltage measurements show that the presence of H2 in the plasma during passivation results in dopant depletion near the surface, but the dopants can be reactivated after annealing at temperature ≥450 °C for 3 min. Plasma passivation with H2S was found to result in a partial recovery of the electrical characteristics for the etched diodes and transmission lines. Annealing at 300 °C is also required after H2S plasma passivation to desorb the excess S on the GaAs surface. Changes in the defect density as a function of the conditions used for passivation have been correlated to Schottky diode characteristics. © 1995 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.-b Surface treatments

Analysis of InP etched surfaces using metalorganic chemical vapor deposition regrown quantum well structures

D. G. Yu, B. P. Keller, A. L. Holmes, E. L. Hu, and S. P. DenBaars

J. Vac. Sci. Technol. B 13, 2381 (1995); http://dx.doi.org/10.1116/1.588078 (5 pages) | Cited 2 times

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We have studied a wide variety of wet and dry etching methods for InP substrates and subsequent surface treatments in preparation for regrowth. To evaluate these processes, a multiple quantum well heterostructure consisting of InGaAs quantum wells of varying widths was regrown on these etched surfaces by metalorganic chemical vapor deposition. This heterostructure was chosen so that we could use low temperature photoluminescence to determine etch damage propagation from the surface. We have found that the photoluminescence intensity of regrown quantum wells close to CH4/H2/Ar reactive‐ion‐etched surfaces is greater than for quantum wells grown the same distance from wet etched surfaces. This technique provides isolation of the characteristics of the etch and clean‐up procedure. © 1995 American Vacuum Society
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78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.-b Surface treatments
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Atomic force microscopy investigations of dry etched gate recesses for InGaAs/InAlAs‐based high‐electron‐mobility transistors using methane–hydrogen reactive ion etching

Halit C. Duran, William Patrick, and Werner Bächtold

J. Vac. Sci. Technol. B 13, 2386 (1995); http://dx.doi.org/10.1116/1.588079 (4 pages) | Cited 3 times

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A methane–hydrogen (CH4/H2) reactive ion etching process has been developed for selective gate recess etching of lattice‐matched InGaAs/InAlAs/InP high‐electron‐mobility transistors without the need for additional ashing or annealing steps after dry etching. An atomic force microscope was used for accurate studies of the morphology of the etched 0.2 μm gate recess. We found that dry etching does not alter the surface roughness significantly for low methane concentrations. Direct current and microwave measurements showed uniform device parameters with a peak transconductance gmmax of 700 mS/mm and a unity current gain frequency ft of 170 GHz. © 1995 American Vacuum Society
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Reactive ion etching lag on high rate oxide etching using high density plasma

Takeshi Akimoto, Hidetaka Nanbu, and Eiji Ikawa

J. Vac. Sci. Technol. B 13, 2390 (1995); http://dx.doi.org/10.1116/1.588006 (4 pages) | Cited 11 times

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In this article, reactive ion etching (RIE) lag effect dependence on total gas flow in contact hole etching is first investigated at a high oxide etch rate using high density plasma. We used surface wave coupled plasma apparatus, which achieves a high density of over 1011 cm−3 and a high oxide etch rate of over 1 μm/min. In the high gas flow etching process, a strong RIE lag is observed. However, the low gas flow etching process suppresses the RIE lag. Total gas flow dominates the RIE‐lag effect, and the oxygen of the etching product plays an important role for reducing the RIE‐lag effect. © 1995 American Vacuum Society
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81.65.-b Surface treatments
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Reactive ion etching for microelectrical mechanical system fabrication

Ivaylo W. Rangelow and Hans Löschner

J. Vac. Sci. Technol. B 13, 2394 (1995); http://dx.doi.org/10.1116/1.588007 (6 pages) | Cited 19 times

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The suitability of reactive ion etching for the fabrication of microelectro mechanical systems (MEMS) has been evaluated by characterizing the change of lateral dimensions versus depth in etching deep structures in silicon. Fluorine, chlorine, and bromine containing gases have provided the basis for this investigation. A conventional planar RIE (reactive ion etching) reactor has been used, in some cases with magnetic field enhancement or an inductive coupled plasma source and low substrate temperature. For RIE based on Cl2 or Cl2/HBr plasma a slightly ‘‘positive’’ (top wider than bottom) slope is achieved when etching structures with a depth of several 10 μm, whereas a ‘‘negative’’ slope is obtained when etching with an SF6 /CCl2F2‐based plasma. A pattern transfer with vertical walls is obtained for RIE based on SF6 (with O2 added) when maintaining the substrate at low temperature (≊−70 °C). Further optimization of plasma chemistries and RIE procedures should result in runouts on the order of 0.1/100 μm depth in Si as well as in organic materials. © 1995 American Vacuum Society
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07.10.Cm Micromechanical devices and systems
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.-b Surface treatments
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Fabrication and characterization of platinum nanocrystalline material grown by electron‐beam induced deposition

H. W. P. Koops, A. Kaya, and M. Weber

J. Vac. Sci. Technol. B 13, 2400 (1995); http://dx.doi.org/10.1116/1.588008 (4 pages) | Cited 51 times

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The technique of electron‐beam induced deposition allows three‐dimensional structures to be generated on the nanometer scale. This is achieved in a scanning electron microscope equipped with a lithography attachment that enables separate position and time control for every pixel. By decomposing adsorbed molecules with the electron beam, structures are created on arbitrarily chosen substrates with nm precision under computer control. Deposits containing metallic nanocrystallites can be produced using organometallic precursor materials. The decomposition of cyclopentadienylplatinum (IV)‐trimethyl (CpPtMe3) results in platinum single crystals with a 2 nm diameter embedded in a carbon‐containing amorphous matrix. The metal content of deposits can be adjusted by choosing an appropriate acceleration voltage and beam current for deposition. The growth rate of deposits from CpPtMe3 is superior to that of frequently used organogold compounds. Tips can be deposited with growth rates up to 150 nm/s. This property is in favor of a higher throughput for nanofabrication. The deposition cross section for this precursor molecule is estimated at 1×10−16 cm2. The electrical resistivity of material deposited at room temperature is measured by a two‐point technique and amounts to 1–100 Ω cm depending on the current employed for deposition. The technique is applied to generate fields of dot marks visible in the optical microscope for metrology purposes. These dot arrays can be fabricated on the surface of finished three‐dimensional structures without additional treatments like resist deposition or development. © 1995 American Vacuum Society
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Space charge effects in projection charged particle lithography systems

L. R. Harriott, S. D. Berger, J. A. Liddle, G. P. Watson, and M. M. Mkrtchyan

J. Vac. Sci. Technol. B 13, 2404 (1995); http://dx.doi.org/10.1116/1.588009 (5 pages) | Cited 16 times

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Charged particle image projection lithography systems have been proposed and are currently under development for design rules of 0.18 μm and below. Although charged particle projection lithography systems do not suffer from diffraction as a limit to spatial resolution as in photolithography, image degradation due to the effects of mutual repulsion of particles in the beam, space charge, will ultimately limit the performance of these systems. Space charge effects increase with increasing beam current. The uncorrectable image blur caused by space charge effectively reduces the dose latitude in projection charged particle lithography and therefore limits the ultimate throughput of such systems. We will describe the effects of space charge in charged particle projection lithography systems using a model we have previously developed. We will compare the predictions of the model with experimental data for an ion projection system and predict the performance of electron and ion beam systems under development. The predictions for image blur caused by space charge are used to calculate the dose latitude as a function of beam current and thus throughput for the SCALPEL(R) electron beam lithography system. © 1995 American Vacuum Society
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Global and stochastic space‐charge effects in ion beam lithography

John J. Petillo and Alfred A. Mondelli

J. Vac. Sci. Technol. B 13, 2409 (1995); http://dx.doi.org/10.1116/1.588010 (5 pages) | Cited 3 times

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Ion projection lithography (IPL) is a candidate technology for meeting expected circuit design rules (less than 0.18 μm) for future generations of semiconductor devices. The Advanced Lithography Group (ALG), a consortium of industrial and U. S. government laboratories and universities, is developing IPL technology with funding from the Advanced Research Projects Agency (ARPA) and the state of Maryland. A prototype IPL device, the ALG‐1000, is being developed to demonstrate the capability of IPL to meet future requirements for pattern overlay. To realize IPL technology requires control of space charge effects in the ion optical column. Due to the length of the IPL system (several meters), the precision of the calculation to predict distortion at the wafer plane becomes difficult to perform. Including the effects of the space charge is even more difficult. Both global and stochastic space‐charge phenomena occur. This article presents a system of computer models that allows simulations of both global and stochastic space‐charge effects. In particular, the models will be used on the ion beam projector in the ALG‐1000 device. The calculations are carried out using a self‐consistent equilibrium ray tracing code, where the applied fields are calculated from the actual lens column geometry. For global space charge, the model also includes optimization of the lens electrode voltages to minimize pattern distortion at the wafer plane. © 1995 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Study of space‐charge devices for focused ion beam systems

Li Wang, Jon Orloff, and Tiantong Tang

J. Vac. Sci. Technol. B 13, 2414 (1995); http://dx.doi.org/10.1116/1.588011 (5 pages) | Cited 1 time

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Axisymmetric and nonaxisymmetric electron space‐charge lenses and spherical aberration correctors are studied theoretically. Many interesting features of the space‐charge devices are revealed by considering some simple, but physically reasonable models. It is shown that a number of simple space‐charge distributions can compensate for a large range of positive spherical aberrations. Several numerical examples are presented in some detail. © 1995 American Vacuum Society
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41.85.Gy Chromatic and geometrical aberrations

Coulomb effect in cell projection lithography

Yasunari Sohda, Yasuhiro Someda, Norio Saitou, and Hiroyuki Itoh

J. Vac. Sci. Technol. B 13, 2419 (1995); http://dx.doi.org/10.1116/1.588012 (5 pages) | Cited 8 times

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Beam blurring due to Coulomb effects is very important in cell projection lithography. This article reports on Coulomb effects in cell projection lithography by simulation and experiment, and shows some important results. First, the Coulomb effect in a single cell is substantially uniform in conventional cell projection optics. Second, refocusing is effective in reducing the space charge effect even in Koehler illumination with a Gaussian crossover. Third, the optimum cell size in the case of a large aperture percentage depends on the ratio of the total exposure time in the peripheral circuit to the total settling time in the memory cell mat. In addition, a modified mask technique is proposed to decrease the influence of Coulomb effects on throughput. © 1995 American Vacuum Society
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41.85.Ew Particle beam profile, beam intensity
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Magnetic funnels for projection electron lithography

Gordon F. Saville, P. M. Platzman, and Long‐Poe Ku

J. Vac. Sci. Technol. B 13, 2424 (1995); http://dx.doi.org/10.1116/1.588013 (4 pages) | Cited 1 time

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Electrons moving in inhomogeneous magnetic fields, which are slowly varying, behave like beads on a string. Because of this a converging magnetic funnel (MF) can be used to reduce an electron image in a way which is physically very different from a conventional lens. We analyze and numerically simulate the trajectories of electrons in a realizable MF. We show that such magnetic configurations are generally capable of projecting and reducing several cm2 images with features in the 0.1 μ range. Distortions are <10−6, there is good depth of focus (≥1 μm), and spot sizes (≤20 nm) are achievable. © 1995 American Vacuum Society
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41.85.Ct Particle beam shaping, beam splitting

In‐line holography using low‐energy electrons and photons: Applications for manipulation on a nanometer scale

Heinz Schmid, Hans‐Werner Fink, and Jürgen Kreuzer

J. Vac. Sci. Technol. B 13, 2428 (1995); http://dx.doi.org/10.1116/1.588014 (4 pages) | Cited 8 times

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An in‐line holography setup is used to obtain electron and photon holograms of high magnification from various samples. Electron holograms are obtained using the coherent beam of low‐energy electrons that originates from the electron point‐source tip. Light optical holograms are generated for comparison using a divergent laser beam. In both cases the numerical reconstruction of the holograms yields the wave front at the sample. The low‐energy electron point source microscope has been modified by incorporating an additional tip for manipulating the sample under observation. With this manipulating tip, individual nanometer‐sized wires have been contacted, and an electrical current has been passed through carbon fibers as well as through carbon nanotubes while the holographic electron pattern has been observed in situ. © 1995 American Vacuum Society
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.40.-i Holography
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Micromachined field emission cathode with an integrated heater

John H. Das and Noel C. MacDonald

J. Vac. Sci. Technol. B 13, 2432 (1995); http://dx.doi.org/10.1116/1.588015 (4 pages) | Cited 3 times

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We report on the fabrication and operation of integrated micromachined and suspended field emission cathode tips. The emitter tips are suspended at the center of a silicon beam using multiple patterning methods of high aspect ratio silicon structures using a single layer silicon dioxide etch mask. The integrated, suspended silicide microheater is used to clean and to activate the cathodes. The silicon tips are subsequently modified to improve their emission properties. The modified cathodes exhibit a significantly lower turn on voltage of about 50 V (∼100 V for silicon cathodes), and need no chemical tip cleaning prior to emission. A much larger emission current with reduced emission noise has been observed when a single tip is cycled through the tip forming process. © 1995 American Vacuum Society
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Improved emission stability of carburized HfC〈100〉 and ultrasharp tungsten field emitters

Ming L. Yu, Brian W. Hussey, Ernst Kratschmer, T. H. Philip Chang, and William A. Mackie

J. Vac. Sci. Technol. B 13, 2436 (1995); http://dx.doi.org/10.1116/1.588016 (5 pages) | Cited 3 times

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We have evaluated the cold‐field‐emission characteristics of HfC〈100〉 and ultrasharp tungsten emitters. We found that proper acetylene treatment improved both the angular current confinement and the emission stability of thermally cleaned HfC〈100〉 tips. Stable emission exceeding 10 μA/sr for over 1 h and angular confinement to a 3° semicone angle have been observed. The improvements are probably related to the modified work function and surface chemical composition induced by the acetylene treatment at the tip apex. Carburization of W〈100〉 and W〈111〉 tips also significantly improved the emission current stability. This study indicates the usefulness of surface processing in the development of cold‐field emitters. © 1995 American Vacuum Society
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79.70.+q Field emission, ionization, evaporation, and desorption
81.65.-b Surface treatments
85.45.-w Vacuum microelectronics

Field emission properties of self‐shielded tungsten sources

W. K. Lo, M. Skvarla, C. W. Lo, H. G. Craighead, and M. S. Isaacson

J. Vac. Sci. Technol. B 13, 2441 (1995); http://dx.doi.org/10.1116/1.588017 (4 pages) | Cited 2 times

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The electron emission properties of self‐shield W tips were studied by field emission microscopy and spectroscopy. Self‐shielded tips were formed by focused ion beam milling an annular depression on the apex of an electrochemically etched W〈111〉 tip. The resultant tip structure consists of a flat bottomed crater (the outer rim of which forms the shielding electrode) with a central protrusion (the emitter). In situ processing consisted of moderate thermal flashing and partial buildup. Significantly greater angular emission current densities were measured, as compared to both unshielded W〈111〉 built‐up tips and standard W〈310〉 tips. Energy analysis of the emitted electrons showed no deviations from normal W〈111〉 emission. Self‐shielding may offer a generally applicable method for increasing the brightness of field emission sources in a variety of electron optical instruments. © 1995 American Vacuum Society
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Lens and deflector design for microcolumns

M. G. R. Thomson and T. H. P. Chang

J. Vac. Sci. Technol. B 13, 2445 (1995); http://dx.doi.org/10.1116/1.588018 (5 pages) | Cited 6 times

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The designs of the deflector and the final focusing lens for an electron beam microcolumn are constrained by the extremely small physical size (less than 4 mm overall), and the low energy of the beam (1 keV). Electrostatic lenses are more suitable than magnetic lenses because their field strengths are more practical. For simplicity of construction, the deflector is also electrostatic. It must be designed in concert with the focusing lens to achieve the largest possible deflection field at these low beam energies. Strategies have been developed to optimize the performance of symmetric and unsymmetric Einzel lenses together with deflection systems. The lens and deflector dimensions are varied subject to constraints which ensure that the final design can be fabricated, and nonlinear constraints on the voltages and fields ensure that operation is practical. The properties of symmetric and unsymmetric Einzel lenses have been evaluated. Immersion lenses (in which the beam energy is higher in the column than at the target plane) have also been considered, although they may not be practical in a microcolumn. Another key factor for high performance is the alignment tolerances, since fabrication errors may be a more significant fraction of the lens bore than for conventional lenses. The aberrations produced by misalignment have been predicted for the different lens types, and designs can be selected which can tolerate electrode misalignments of approximately 1 μm for the probe sizes and working distances of interest. The field which can be covered with a prelens double‐deflection system is analyzed, and strategies for improving the deflection field are discussed. © 1995 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
41.85.-p Beam optics

Beam position stabilization by suppression of electrons reentering the electron‐beam column

Junichi Kato, Hirofumi Morita, Kenichi Saito, and Nobuo Shimazu

J. Vac. Sci. Technol. B 13, 2450 (1995); http://dx.doi.org/10.1116/1.588019 (5 pages)

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The electron trap proposed in this paper provides high beam positioning stability. It keeps reflected electrons and secondary electrons from reentering the column from the specimen. The effect of the trap is evaluated numerically and experimentally, and the results show that it can reduce beam positioning drift by a factor of 6. © 1995 American Vacuum Society
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41.85.-p Beam optics
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Compression of field‐emission angular distribution using a cathode shield

M. G. R. Thomson

J. Vac. Sci. Technol. B 13, 2455 (1995); http://dx.doi.org/10.1116/1.588020 (4 pages) | Cited 2 times

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A conventional field‐emission electron gun consists of a pointed cathode and an extraction electrode at a positive potential which produces a strong electric field at the cathode surface. Electrons are field‐emitted from the cathode, pass through an axial hole in the extractor electrode, and must then be accelerated to full energy. The field emission current density at the cathode surface is very sensitive to changes in the electric field strength. The distribution of electric field on the end of the cathode can be changed by an additional nearby electrode if its size is not large compared to the cathode radius. A cylindrical shield electrode has been proposed which surrounds the cathode, and for convenience can be at the same potential as the cathode. This configuration has been examined theoretically using second‐order finite element analysis. The results of this analysis show that the change in distribution of the electric field on the cathode will depend upon the relative dimensions of the cathode and the shield, and, for a significant change in emission distribution, the shield radius must not be larger than approximately five times the cathode radius. The addition of the shield leaves the virtual source size unchanged, so the brightness of the source is approximately proportional to the axial current density. It has been suggested that combined cathodes and shields can be fabricated by ion milling to form a pointed cathode in the end of a shield. © 1995 American Vacuum Society
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Field emission from carbide film cathodes

W. A. Mackie, Tianbao Xie, and P. R. Davis

J. Vac. Sci. Technol. B 13, 2459 (1995); http://dx.doi.org/10.1116/1.588021 (5 pages) | Cited 8 times

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We report here on experiments with the deposition of ZrC onto individual prefabricated W and Mo emitters and on field emission arrays using Mo and Si emitters. With observed field emission current densities greater than 1×108 A/cm2 and work functions approximately 1 eV lower than Mo or W, carbides make good candidates for low voltage microelectronic field emitter arrays. In addition, evaporation of ZrC films onto Mo and W single field emitter cathodes improves their emission stability and greatly improves beam confinement. Mo and W field emitters were individually fabricated and an appropriate quantity of ZrC was evaporated onto the emitter surface from a high‐purity ZrC evaporation source. Several emitters prepared by this method have been tested. The uniformity of the emission pattern was checked by in situ field emission microscopy, both before and after carbide deposition, in order to verify that the surface of the emitter had been cleaned and smoothed. The deposited film was subjected to a variety of heating treatments, each of which was followed by examination of the emission pattern and determination of I–V characteristics. The results of these experiments indicate that work function reductions of the order of 1 eV can be achieved by the deposition of ZrC films onto W or Mo field emitters. The observed emission patterns indicate that the lowest film work functions occur on and around the (100) planes of the underlying Mo or W emitter. Beam confinement is therefore possible with carbide film deposition on Mo or W field emission cathodes. We also report on experiments with ZrC film deposition onto field emitter arrays with Mo and Si emitters. In the case of ZrC on a Spindt array of Mo cathodes we observed a decrease of operating voltage from 122 to 68 V for 100 μA emission current following ZrC deposition. The ratio of the Fowler–Nordheim slope for the ZrC layer to that for the cathode before deposition was approximately 0.68. These results seem consistent and very promising for the use of ZrC film on field emitters and field emitter arrays. © 1995 American Vacuum Society
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Design of a high voltage electron gun for lithography applications

Paul F. Petric

J. Vac. Sci. Technol. B 13, 2464 (1995); http://dx.doi.org/10.1116/1.588022 (4 pages)

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A development project was undertaken at IBM to meet the needs of production e‐beam lithography at increased beam energies up to 100 kV. The project was divided into two separate development efforts. The first part, which is the topic of this article, dealt with the gun vacuum and its overall design. The second half dealt with the high voltage design. This article describes the design of the overall gun and its vacuum system and the initial results of testing as they pertain to the vacuum system of the gun and its operation with the integral ion pump design. © 1995 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Miniature Schottky electron source

H. S. Kim, M. L. Yu, E. Kratschmer, B. W. Hussey, M. G. R. Thomson, and T. H. P. Chang

J. Vac. Sci. Technol. B 13, 2468 (1995); http://dx.doi.org/10.1116/1.588023 (5 pages) | Cited 10 times

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A miniature Schottky electron source has been developed and evaluated for applications in a new generation of scanning tunneling microscope aligned field emission microcolumns. Both the physical dimensions and the heating power of this source have been significantly reduced from a conventional source of the same kind. Operating parameters for such a source in a microcolumn environment in terms of emission characteristics, suppressor operating range, etc., have been evaluated. Test results show that very good emission stability at ≥100 μA emission current over several hours, and axial angular current densities in excess of 100 μA/sr can be obtained. Energy distributions have been measured using a carefully calibrated analyzer, and the results show a full width at half‐maximum of 0.4 to 0.76 eV for a 0.3 μm radius Schottky source operating over an angular current density range of 1 to over 100 μA/sr. A significant change in the shape of the energy distribution was observed over this range of operation, indicating evidence of tunneling currents at the high angular current density regime. © 1995 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
85.45.-w Vacuum microelectronics

Resolution analysis in electron‐beam cell projection lithography system

Hiroshi Yamashita, Kenichi Tokunaga, Yoshikatu Kojima, Hiroshi Nozue, and Eiichi Nomura

J. Vac. Sci. Technol. B 13, 2473 (1995); http://dx.doi.org/10.1116/1.588024 (5 pages) | Cited 6 times

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We have experimentally analyzed the resolution in electron‐beam cell projection lithography systems. The results indicated that the Coulomb interaction effect and the proximity effect are critical issues for resolution because of the larger beam current compared with the conventional variable‐shaped beam. We achieved a practical resolution of 0.18 μm, which is enough for 1 Gbit dynamic random access memory (DRAM) fabrication, by adjusting the beam current. We have also found that there is some interaction between the individual line beams (streams). Also, the beam profile degradation in cell projection lithography systems depends not only on the beam current but also on the distance between the streams. Therefore, in order to obtain higher resolution, these effects must be considered more carefully than in the case of conventional variable‐shaped beam lithography systems. A resolution of less than 0.15 μm, which is required for Gbit level DRAM fabrication, can then be available in cell projection lithography systems. © 1995 American Vacuum Society
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Performance enhancements on IBM’s EL‐4 electron‐beam lithography system

R. Butsch, W. A. Enichen, M. S. Gordon, T. R. Groves, J. G. Hartley, J. W. Pavick, H. C. Pfeiffer, R. J. Quickle, J. D. Rockrohr, and W. Stickel

J. Vac. Sci. Technol. B 13, 2478 (1995); http://dx.doi.org/10.1116/1.588025 (5 pages) | Cited 5 times

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IBM’s latest electron‐beam mask maker, EL‐4, is installed at IBM’s Advanced Mask Facility in Essex Junction, Vermont. The EL‐4 system is a 75 kV variable‐shaped‐beam lithography system designed to produce 1X or NX masks for 0.25 μm lithography ground rules, extendable to 0.13 μm. It is currently producing NIST‐style x‐ray membrane masks with pattern sizes up to 50×50 mm2. After a brief description of the EL‐4 tool and its operating features, the article describes the recently implemented new writing subsystem, provides an overview of the tool software structure, and presents measurement data from masks recently produced on the tool. © 1995 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Error budget analysis of the SCALPEL(R) mask for sub‐0.2 μm lithography

J. Alexander Liddle, Harold A. Huggins, and G. Patrick Watson

J. Vac. Sci. Technol. B 13, 2483 (1995); http://dx.doi.org/10.1116/1.588378 (5 pages) | Cited 9 times

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In this article we derive the design constraints, and hence the fabrication requirements, for the SCALPEL(R) mask for sub‐0.2 μm design rules. These are determined by the Semiconductor Industry Association (SIA) advanced mask specifications, in combination with the likely error budget of an advanced pattern generator. Further constraints are imposed by the overall SCALPEL system error budget. We demonstrate that the mask is not only technically feasible to construct, but also that it can be fabricated at an acceptable cost. © 1995 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Experimental evaluation of an electron‐beam pulse modulated blanker (160 MHz) for next‐generation electron‐beam raster scan systems

Andrew Muray, Dave Colby, Robin Teitzel, and Mark Gesley

J. Vac. Sci. Technol. B 13, 2488 (1995); http://dx.doi.org/10.1116/1.588379 (5 pages) | Cited 1 time

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The simplicity of raster scan architecture has several benefits for mask‐making production tools, the most important being accuracy. Nevertheless, building patterns on a grid resolution determined by the writing address of the raster scan mask generator places limitations on pattern edge locations, or equivalently, on throughput. A method of getting around this throughput bottleneck is pixel‐level dose modulation, i.e., graybeam. In this article, a new driver technology in combination with the MEBES(R) 4500 blanker operating at 160 MHz is experimentally evaluated for real‐time dose modulation by pulse width variation. Measurements of the rise and fall time of the blanker driver using various input data vectors (i.e., combinations of various pulse width signals) and a beam current modulation transfer function for the blanker are presented. Contributions from electronic artifacts such as electronic jitter are measured. Finally, these measurement results are used to determine the preliminary performance of a graybeam system. © 1995 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Patterning accuracy improvement of the electron beam direct writing system EX‐8D

R. Yoshikawa, K. Hattori, H. Wada, S. Magoshi, H. Sunaoshi, A. Ando, T. Yamaguchi, S. Mikami, S. Nishimura, H. Housai, S. Hashimoto, and T. Takigawa

J. Vac. Sci. Technol. B 13, 2493 (1995); http://dx.doi.org/10.1116/1.588380 (5 pages)

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To improve patterning accuracy, a feedback compensation technique for the magnetic field was applied to EX‐8D. The beam position deviation induced by low‐frequency ambient magnetic field changes and 50 Hz magnetic interference has been minimized by using a feedback system for the interference source signals. As the result of the feedback technique and magnetic shielding applied to EX‐8D, the subfield position deviation measured on written patterns has been improved to be 22 nm as a 3σ value without room shielding. The main deflection calibration method was also improved by utilizing an axially displaceable mark together with a fixed‐height mark. On the fixed mark, the main deflection coefficients were determined with no concern to height sensor outputs. Height‐dependent coefficients were then calibrated by evaluating the field size for various heights using the axially displaceable mark. The calibration accuracy was estimated to be 9.7 nm at the main field edge. It was also confirmed that height‐dependent coefficients would be calibrated accurately enough by the use of a piezodriven mark. As a result, a stripe stitching error of less than 30 nm has been obtained. © 1995 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

An electron‐beam microcolumn with improved resolution, beam current, and stability

E. Kratschmer, H. S. Kim, M. G. R. Thomson, K. Y. Lee, S. A. Rishton, M. L. Yu, and T. H. P. Chang

J. Vac. Sci. Technol. B 13, 2498 (1995); http://dx.doi.org/10.1116/1.588381 (6 pages) | Cited 18 times

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We have built and tested a 1 keV electron‐beam microcolumn that focuses 1 nA of beam current into a 10 nm full width half‐maximum beam diameter at a working distance of 1 mm. The electron source is a miniaturized Zr/O/W Schottky field emitter with 150 μA/sr angular emission current density operating at about 1800 K at a distance of only 100 μm from a silicon membrane extractor electrode. The actual microcolumn is 3.5 mm long assembled mainly from silicon membrane electrodes. Improved einzel lens design and fabrication allowed the operation of this beam focusing element in the accelerating mode. Spherical and chromatic aberrations were reduced by factors of about 2–3, respectively, as compared to the retarding lens mode. Excellent beam current stability with less than 1% variation over several hours has been observed. © 1995 American Vacuum Society
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41.85.-p Beam optics
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.45.-w Vacuum microelectronics

A background dose proximity effect correction technique for scattering with angular limitation projection electron lithography implemented in hardware

G. Patrick Watson, Steven D. Berger, J. Alexander Liddle, and Warren K. Waskiewicz

J. Vac. Sci. Technol. B 13, 2504 (1995); http://dx.doi.org/10.1116/1.588382 (4 pages) | Cited 6 times

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A background dose proximity effect correction procedure is proposed that utilizes the unique way image contrast is formed in scattering with angular limitation projection electron lithography (SCALPEL(R)). An electron beam is selectively scattered by a thin, high atomic number layer patterned on a membrane mask. Some of the scattered radiation, which is normally blocked at an aperture to form contrast at the wafer, is allowed to pass through the system optics. Nominally dark regions of the mask are therefore allowed to expose the resist on a wafer. However, because the scattered radiation enters the projection system at relatively large angles, it is subjected to system aberrations and is improperly focused at the wafer. This dispersed radiation mimics the natural long range backscatter exposure emanating from the intentionally exposed regions, and ideally results in a constant background exposure in the resist—similar to the GHOST background correction technique used in direct‐write applications. However, unlike the direct‐write correction, both the primary exposure and the correction exposure are achieved at the same time. Throughput is not reduced by the correction. Although the correction dose profile may not resemble the form of the long range backscatter energy deposition in the resist, the deviations of background exposure are small for mask patterns of practical interest, in comparison with the variation of uncorrected exposures of the same pattern. © 1995 American Vacuum Society
Show PACS
41.85.Ew Particle beam profile, beam intensity
85.40.Hp Lithography, masks and pattern transfer

Enhancing a hierarchical, parallel electron beam data conversion processor toward 1 Gbit memory lithography

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