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Nov 1990

Volume 8, Issue 6, pp. 1177-2055


Properties of silicon dioxide films prepared by low‐pressure chemical vapor deposition from tetraethylorthosilicate

S. Rojas, A. Modelli, W. S. Wu, A. Borghesi, and B. Pivac

J. Vac. Sci. Technol. B 8, 1177 (1990); http://dx.doi.org/10.1116/1.584937 (8 pages) | Cited 9 times

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The 20 to 100‐nm thick tetraethylorthosilicate (TEOS)‐derived SiO2 films were deposited on silicon substrates in the 650–780 °C temperature range by low‐pressure chemical vapor deposition. The main properties of the as‐deposited and annealed films such as refractive index, etch rate, stress, step coverage, and density are reported. Infrared (IR) spectra and the electrical properties were studied as a function of process parameters including temperature, pressure, oxygen, and TEOS flow. These studies have shown that TEOS‐SiO2 films have very good thickness uniformity and conformal step coverage which can be controlled by adjusting the process pressure. IR spectra show that TEOS‐SiO2 films are deposited as stoichiometric oxides. Annealing results in the removal of absorbed water and Si–OH groups, and in an increase of the number of Si–O–Si bonds. The electrical characteristics, such as breakdown field strength for films deposited on POCl3 ‐doped polysilicon, are comparable to those of SiO2 films thermally grown at 1100 °C in dry O2 atmosphere.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.-p Physical properties of thin films, nonelectronic
78.66.-w Optical properties of specific thin films

Radio frequency plasma etching of Si/SiO2 by Cl2/O2 : Improvements resulting from the time modulation of the processing gases

S. C. McNevin

J. Vac. Sci. Technol. B 8, 1185 (1990); http://dx.doi.org/10.1116/1.584938 (7 pages) | Cited 8 times

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The etching of poly‐Si and its selectivity over gate oxide SiO2 were measured for both Cl2 and Cl2/O2 plasmas and the experimental data indicate that modulation of the processing gases increases the Si/SiO2 selectivity while decreasing the unwanted deposition. The best results to date have been Si etch rates of ∼1000 Å/min and Si/SiO2 selectivities of ∼50, and it has been demonstrated that the Si/SiO2 selectivity is critically related to the presence of photoresist. A qualitative model for these results is proposed which appears to fit these observations. In this model, hydrocarbon fragments from sputtered photoresist reduces the SiO2 to Si, with a corresponding decrease in the Si/SiO2 etching selectivity. This carbonaceous material can be removed by the oxygen before it causes etching damage to the SiO2. Oxygen, unfortunately, can also react with the etching reaction products (e.g., SiCl4 ) to form SiO2 and the Si oxy‐chlorides (Si2OCl6, Si3OCl8 ) which deposit on the wafer. The experimental evidence indicates, however, that this unwanted deposition can be minimized by alternating the Cl2 and O2 gases, rather than by running them both at a constant pressure as is typically done. Of most immediate interest is the fact that this modulation improvement can be achieved on time scales (≳1 s) which are attainable with the fairly slow residence times available in present generation hex etchers.
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81.65.-b Surface treatments
81.05.Kf Glasses (including metallic glasses)
52.75.-d Plasma devices
52.80.-s Electric discharges

Extremely high selective, highly anisotropic, and high rate electron cyclotron resonance plasma etching for n+ poly‐Si at the electron cyclotron resonance position

Seiji Samukawa, Masami Sasaki, and Yasuhiro Suzuki

J. Vac. Sci. Technol. B 8, 1192 (1990); http://dx.doi.org/10.1116/1.584939 (7 pages) | Cited 4 times

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Extremely high selective, highly anisotropic, and high rate electron cyclotron resonance (ECR) plasma etching for n+ poly‐Si is achieved at the ECR position in a newly developed ECR plasma etching system. The selectivity ratio of the n+ poly‐Si etching rate to the SiO2 etching rate is more than 100 at 5×10−4 Torr and 260 at 3×10−3 Torr in pure Cl2 gas at a substrate temperature of 30 °C. Furthermore, the selectivity ratio increases infinitely by using a Cl2/O2 gas mixture at 5×10−4 Torr. The n+ poly‐Si etching rate is more than 3000 Å/min with no radio frequency (rf) bias under the above selectivity ratio conditions. The etching selectivity is generated by low ion energy at the ECR position. The high etching rate is achieved by high ion current density at the ECR position in the plasma chamber.
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81.65.-b Surface treatments
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
52.75.-d Plasma devices

Study of sidewall passivation and microscopic silicon roughness phenomena in chlorine‐based reactive ion etching of silicon trenches

G. S. Oehrlein, J. F. Rembetski, and E. H. Payne

J. Vac. Sci. Technol. B 8, 1199 (1990); http://dx.doi.org/10.1116/1.584896 (13 pages) | Cited 38 times

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Sidewall passivation layers produced in the formation of Si trenches by HCl/O2/BCl3 reactive ion etching have been characterized by angle‐resolved x‐ray photoemission measurements and secondary electron microscopy. Electron‐shading effects observed at grazing electron emission angles and electrostatic charging of insulating portions have been used to differentiate photoemission contribution from (i) the trench sidewall film (moderately insulating), (ii) the oxide mask (highly insulating), and (iii) the Si trench bottom (conductive). The sidewall passivation film for this process is found to be a silicon oxide. Only minor amounts of chlorine are incorporated in this film. The thickness of the sidewall passivation layer depends on the width of the Si trench and ranges from ≂0.1 μm for narrow trenches to ≂0.7 μm for wide Si trenches for our conditions. The Si taper formed in this trench etching process is produced by the simultaneous formation of the sidewall film which protects the underlying Si from etching. It is also shown that microscopic silicon pillars (‘‘black silicon’’ or ‘‘grass’’) form by micromasking under process conditions where large areas of unmasked silicon are exposed. The microscopic Si pillars are protected by the same sidewall passivation film as the trench sidewalls. Islands of black silicon are observed only in large open silicon areas and separated from oxide masked areas by a characteristic distance which is free of silicon pillars. This roughness‐free distance is of the order of the mask thickness employed. Ion scattering from the sloped mask sidewalls and sputtering of involatile micromasking material can explain this observation. Our results are consistent with a mechanism in which the processes that cause the formation of the beneficial sidewall film also initiate and control the production of undesirable silicon roughness in large unmasked Si regions.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Gy Mechanical properties; surface strains

A thermochemical model for the plasma etching of aluminum in BCl3/Cl2 and BBr3/Br2

S. C. McNevin

J. Vac. Sci. Technol. B 8, 1212 (1990); http://dx.doi.org/10.1116/1.584897 (11 pages) | Cited 10 times

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This article describes a quantitative Recipe Map which has been constructed to target the controllable gas flows, wafer loading, and temperature settings predicted to result in the optimum BCl3/Cl2 and BBr3/Br2 plasma etching of aluminum for a given reactor and background oxygen pressure. The numerical predictions of this Recipe Map are based on modeling the plasma as a steady state flow system in which all thermodynamically predicted chemical reactions occur with collision limited kinetics, and where, in addition, physical sputtering removes material from the ion‐bombarded surfaces. Anisotropic etching is caused by the sputtering of deposited oxide which allows the chemical etching of the underlying Aluminum. Although this model is very simple, its numerical predictions are in good qualitative agreement with the observed Al etching dependence on the processing parameters in both single wafer and hex etchers. In particular, the effect of wafer loading can be quantitatively evaluated using simple formulas.
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81.05.Bx Metals, semimetals, and alloys
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Disintegration of TiSi2 on narrow poly‐Si lines at high temperatures

H. Norström, K. Maex, and P. Vandenabeele

J. Vac. Sci. Technol. B 8, 1223 (1990); http://dx.doi.org/10.1116/1.584898 (9 pages) | Cited 6 times

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The thermal stability of TiSi2/poly‐Si structures with narrow lines has been studied as a function of the dopants introduced into the poly‐Si (i.e. boron or arsenic) in the temperature range from 700 °C to 950 °C. The silicide layer was formed by rapid thermal processing (RTP) in nitrogen via a solid–solid reaction between titanium and poly‐Si. The integrity, upon heat treatment, of the TiSi2 film on large areas was investigated by Rutherford backscattering spectroscopy (RBS) analysis, plan‐view scanning electron microscopy (SEM), and cross‐sectional SEM studies. Electrical information about the thermal stability of the bilayer was obtained from sheet resistance measurements on Van der Pauw structures in combination with linewidth measurements of bridge resistors with a nominal width between 0.8 and 1.5 μm. To provide for statistical variation about one hundred measurements were collected for each linewidth and temperature setting. The results clearly show that the thermal stability of the bilayer is a function of the amount and type of dopants in the polysilicon, favoring the use of high levels of arsenic. Moreover, the thermal stability was observed to be affected by the linewidth, since at the temperature for onset of degradation (above 900 °C), narrow lines were found to disintegrate at a much higher rate than wider ones. Cross‐sectional SEM and TEM micrographs of the polycide lines clearly reveal the TiSi2/poly‐Si interface to suffer from bowing. The effect was observed to be more pronounced on narrow undoped and boron‐doped polycide lines. Both the narrow line disintegration and the bowing effect of polycide structures can have important implications for submicron very large scale integrated (VLSI) technologies.
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81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Stress migration resistance and contact characterization of Al–Pd–Si interconnects for very large scale integrations

Y. Koubuchi, J. Onuki, M. Suwa, S. Fukada, S. Moribe, and Y. Tanigaki

J. Vac. Sci. Technol. B 8, 1232 (1990); http://dx.doi.org/10.1116/1.584899 (7 pages) | Cited 6 times

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Stress‐induced migration resistance and contacts to silicon of Al–0.3%Pd–1%Si interconnections for submicron process integrated circuit devices have been investigated and compared to Al–0.5%Cu–1%Si. Using creep tests, Pd has been found to be an excellent additional element to Al for reducing grain boundary diffusion. Palladium improved the stress‐induced migration resistance and reduced void and hillock formation in Al–Si conductors. Aluminum palladium precipitates in Al–Pd–Si alloys were found to be formed at higher temperatures than aluminum copper compounds and may be the reason for the improvements. The contact resistance of Al–Pd–Si was found to be similar to that of Al–Cu–Si. The reliability and yield data from 1.2 μm ROM test devices using Al–Pd–Si conductors is better than that of Al–Cu–Si conductors.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Capillary‐type cluster ion source and its application for selective deposition of aluminum film

M. Ogura, M. Komuro, K. Shimizu, and A. Yabe

J. Vac. Sci. Technol. B 8, 1239 (1990); http://dx.doi.org/10.1116/1.584900 (3 pages)

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Cluster ions of acetone and triisobutylaluminum (TIBA) are generated from an apex of a capillary tube with an inner diameter of 5 μm and outer diameter of 20 μm, based on the atomization of a semiconductive liquid in high electrostatic field. Ion emission has an onset at a threshold voltage of around 2 kV, which is nearly equal to the value calculated from Taylor’s argument. The averaged charge‐to‐mass ratio of these cluster ions is determined to be 4.0–4.7 Coulomb/kg from a time‐of‐flight method. Spatially selected chemical vapor deposition of aluminum films is realized by the cluster ions of TIBA.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
79.90.+b Other topics in electron and ion emission by liquids and solids and impact phenomena (restricted to new topics in section 79)

A unified line‐of‐sight model of deposition in rectangular trenches

T. S. Cale and G. B. Raupp

J. Vac. Sci. Technol. B 8, 1242 (1990); http://dx.doi.org/10.1116/1.584901 (7 pages) | Cited 21 times

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The integro‐differential equations which describe free molecular flow in long rectangular trenches in the absence of deposition and to both low pressure chemical vapor deposition (LPCVD) and physical vapor deposition (PVD) are derived. A pseudosteady state assumption is implicit in the formulation, i.e., the feature dimensions change slowly relative to the time required for the flux to redistribute in response to the changes. Numerical solution of the governing equations provides film and deposition rate profiles as a function of deposition time until the trench is completely filled. Solutions are discussed for selected values of the sticking coefficient from zero to unity. The calculated film profiles are consistent with empirical results which typically show poor uniformity in PVD and step coverage increasing with decreasing sticking coefficient in LPCVD. Film profiles compare well with Monte Carlo based simulations of deposition processes.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
02.60.Cb Numerical simulation; solution of equations

Rapid thermal processing systems: A review with emphasis on temperature control

Fred Roozeboom and N. Parekh

J. Vac. Sci. Technol. B 8, 1249 (1990); http://dx.doi.org/10.1116/1.584902 (11 pages) | Cited 15 times

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This paper highlights the basic principles of rapid thermal processing (RTP) systems and the important areas of concern. The basic system characteristics, the fundamental physics involved, and the techniques for temperature measurement and control are extensively reviewed. We summarize the options currently available for 15 RTP equipment manufacturers and point out the latest developments in RTP system design and temperature measurement. Some novel options for temperature control (optical, fiber optical, and photoacoustic) are included.
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85.40.Hp Lithography, masks and pattern transfer
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

A Zn predeposition technique applied to GaAs/AlGaAs heterobipolar transistors

Y. Shimamoto, K. Itakura, and D. Ueda

J. Vac. Sci. Technol. B 8, 1260 (1990); http://dx.doi.org/10.1116/1.584903 (4 pages)

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A Zn predeposition technique has been developed for forming the extrinsic base regions of HBTs. Zn ions are implanted in a shallow region of the p‐base region, followed by a quick diffusion using rapid thermal annealing (RTA) at a relatively low temperature of 650 °C. The resultant heavily doped extrinsic base region has less defects at the vicinity of the p‐base region than those obtained from conventional Be or Mg ion implantation. Experimentally fabricated HBTs using the new technique have shown more than twice the current gain than reference devices fabricated through Be ion implantation owing to reduced recombination centers in the extrinsic base region.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Pq Bipolar transistors
85.40.Hp Lithography, masks and pattern transfer

High‐temperature growth of Si‐doped AlGaAs by molecular‐beam epitaxy

Junji Saito and Kazuo Kondo

J. Vac. Sci. Technol. B 8, 1264 (1990); http://dx.doi.org/10.1116/1.584904 (6 pages) | Cited 2 times

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We studied the growth rate, AlAs mole fraction, surface morphology, and electrical properties of Si‐doped AlxGa1−xAs (0≤x≤0.3) layers grown by molecular‐beam epitaxy at substrate temperatures from 620 to 770 °C. From the dependence of the growth rates and the AlAs mole fraction on the substrate temperature, we showed that the equilibrium partial pressure of Ga, Al, and As molecules at the growth surface governs the growth rates and the AlAs mole fraction of the epitaxial layers grown at these temperatures. This paper also deals with the growth mechanism of the smooth surface morphology of AlxGa1−xAs grown between 700 and 750 °C using the bonding energy of Al–As and Ga–As. Above 700 °C, the free electron concentration and the mobility of the Si‐doped AlxGa1−xAs epitaxial layers were reduced. In particular, the electron concentration and the mobility of AlxGa1−xAs were significantly decreased by intervalley scattering because of incremented AlAs mole fraction. Secondary ion mass spectroscopy showed us that carbon incorporation into the AlxGa1−xAs increased with substrate temperature. We discuss the substrate temperature dependence of mobility and concentration of a two‐dimensional electron gas in selectively doped GaAs/N‐AlxGa1−xAs heterostructures at 77 K.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Temperature dependence of current conduction in barrier‐enhanced, carbon delta‐doped GaAs diodes

A. Katz, S. J. Pearton, F. Ren, and C. R. Abernathy

J. Vac. Sci. Technol. B 8, 1270 (1990); http://dx.doi.org/10.1116/1.584905 (4 pages)

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The temperature dependencies of Schottky barrier height, ideality factor, and reverse bias breakdown voltage are reported for Ti/Pt/Au contacts on n‐type GaAs containing zero, one, or two near‐surface, carbon δ‐doped (p=7×1019 cm−3) layers, each ∼50 Å wide. Arrhenius plots of the total current flowing under forward bias in each structure yield effective barrier heights of 0.73, 0.91, and 0.65 eV, respectively, as the transition is made from barrier enhancement (reduced thermionic emission) to barrier lowering (increased tunneling). Both the ideality factor and breakdown voltage degrade with increasing measurement temperature.
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85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Use of hydrogenated chlorofluorocarbon mixtures for reactive ion etching of In‐based III–V semiconductors

S. J. Pearton, W. S. Hobson, U. K. Chakrabarti, G. E. Derkits, and A. P. Kinsella

J. Vac. Sci. Technol. B 8, 1274 (1990); http://dx.doi.org/10.1116/1.584906 (11 pages) | Cited 6 times

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The reactive ion etching (RIE) of InP, InAs, InSb, InGaAs, and AlInAs in CHCl2F —or CHClF2 —based discharges was investigated as a function of plasma power density, pressure, and gas composition. For 0.56 W cm−2, 4 mTorr discharges the etch rates are in the range 125 Å min−1 (AlInAs) to 390 Å min−1 (InAs). These are comparable to the etch rates obtained with C2H6/H2 RIE under similar conditions. All of these materials exhibit smooth surface morphologies over a wide range of RIE parameters. Carrier compensation is observed to depths of ∼2000 Å in n‐type InP for high power density (1.3 W cm2) etching, but lower powers yield surfaces that display reasonable Schottky diode behavior for evaporated Au contacts. Thin (20–30 Å) residue layers containing 3–9 at. % Cl and 1–3 at. % F (24 at. % for AlInAs) are present after the dry etching, although this contamination can be removed by solvent cleaning. The formation of a high concentration of AlF3 on AlInAs provides a natural etch stop for removal of InGaAs layers in AlInAs/InGaAs heterojunction bipolar transistor structures.
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81.65.-b Surface treatments

Susceptor and proximity rapid thermal annealing of carbon‐implanted InP

A. Katz and S. J. Pearton

J. Vac. Sci. Technol. B 8, 1285 (1990); http://dx.doi.org/10.1116/1.584907 (6 pages)

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AuGe contacts to n‐type layers formed by carbon implantation into semi‐insulating InP substrates demonstrate superior performance on material activated by annealing within an enclosed SiC‐coated graphite susceptor (700 °C, 10 s), compared to the more conventional proximity approach. This superiority is due to the better substrate surface morphology achieved. Activating the implants within the graphite susceptor eliminates P outdiffusion and formation of pits. In addition, annealing within the susceptor provides much better protection against edge degradation and slip formation.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer

Photoresist etching in a hollow cathode reactor

M. Gross and C. M. Horwitz

J. Vac. Sci. Technol. B 8, 1291 (1990); http://dx.doi.org/10.1116/1.584908 (6 pages) | Cited 2 times

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The submicron photoresist patterning capabilities of hollow cathode and asymmetric diode (‘‘reactive ion etch’’) reactors are compared here. Confined hollow cathodes etch more than 15 times faster than a diode at a given target voltage, at pressures of 2 Pa and below. Etch directionality has been studied using measurements of undercut in deep submicron patterns. Low‐pressure hollow cathode etch anisotropy is similar to that obtained in a diode reactor, at all target voltages. At high target voltages both reactor designs result in less than a few percent of total undercut and sidewall bowing using 0.7‐μm period, 3‐μm‐thick structures. This level of bowing is often seen in submicron etched apertures; we show how such bowing is affected by mask sidewall slope, and by the aspect ratio of etched structures. We review theories of sidewall bowing, concluding that electrostatic deflection and ion reflection from mask edges cause most of the sidewall bowing under our low‐pressure conditions.
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81.65.-b Surface treatments
52.80.-s Electric discharges
85.40.Hp Lithography, masks and pattern transfer
84.47.+w Vacuum tubes

An edge‐defined technique for fabricating submicron metal–semiconductor field effect transistor gates

W. A. Strifler and B. D. Cantos

J. Vac. Sci. Technol. B 8, 1297 (1990); http://dx.doi.org/10.1116/1.584909 (3 pages)

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A new technique has been developed to fabricate submicron gates in GaAs metal–semiconductor field effect transistors (MESFETs) using simple contact lithography. The technique employs a multiple layer resist structure and angle evaporation to define a conformal aluminum mask above the wafer surface. The gate length of the aluminum mask is well controlled by an evaporation angle and a resist thickness. The pattern transfer to the wafer surface is compatible with a recessed gate technology. In a production environment, the process is capable of producing quarter‐micron MESFETs with less than ±150 Å (1σ) gate length variation across a 2‐in. wafer.
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85.30.Tv Field effect devices
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Improved resolution of an i‐line stepper using a phase‐shifting mask

Tsuneo Terasawa, Norio Hasegawa, Toshihiko Tanaka, Souichi Katagiri, and Toshiei Kurosaki

J. Vac. Sci. Technol. B 8, 1300 (1990); http://dx.doi.org/10.1116/1.584910 (9 pages) | Cited 4 times

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Improved resolution of an available i‐line (365 nm) stepper using a phase‐shifting mask is discussed. The resolution investigated here is not only for periodic lines but also for isolated spaces and hole patterns. To reduce the sizes of isolated space images for printing fine single spaces on a wafer, two additional line apertures with widths smaller than the critical dimension of the stepper lens are placed on each side of the main aperture of the mask. The optical phase of light passing through the main aperture and those through additional apertures are opposite. The additional apertures play a role in reducing the bright feature size to less than the line spread function of the lens. Similarly, printing a fine hole is accomplished by using a main aperture surrounded by four additional apertures. The intensity distribution on the wafer surface is simulated by comparing the images obtained with a phase‐shifting mask and those obtained with a conventional transmission mask. Printing fine patterns are performed using an i‐line stepper with a numerical aperture (NA) of 0.42. A pattern of 0.3 μm lines and spaces, 0.3 μm isolated spaces, and 0.4 μm hole patterns are resolved using the phase‐shifting mask. The process latitudes and the effects of variations in the optical phase of the additional apertures are also investigated. The image simulations and experimental results suggest that the phase‐shifting mask improve not only resolution but also exposure latitude and focus latitude. Furthermore, it is found that it is possible to control the position of the best focal plane by changing the optical phases of the additional apertures.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Coherent point source electron beams

Hans‐Werner Fink, Werner Stocker, and Heinz Schmid

J. Vac. Sci. Technol. B 8, 1323 (1990); http://dx.doi.org/10.1116/1.584911 (2 pages) | Cited 3 times

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The concept of a point source for electrons in view of quantum mechanical experiments is described. The engineering of such atomic electron emitters is discussed and recent experiments in holography with low energy electrons are presented.
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41.75.Fr Electron and positron beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors
42.40.-i Holography

Soft x‐ray projection lithography

N. M. Ceglio, A. M. Hawryluk, D. G. Stearns, D. P. Gaines, R. S. Rosen, and S. P. Vernon

J. Vac. Sci. Technol. B 8, 1325 (1990); http://dx.doi.org/10.1116/1.584912 (4 pages) | Cited 4 times

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Recent advances in x‐ray optics have made possible the practical consideration of soft x‐ray projection imaging for the fabrication of high density integrated circuits.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments
42.79.Wc Optical coatings

Imaging surface atomic structure by means of Auger electrons

Arthur T. Hubbard, Douglas G. Frank, Oliver M. R. Chyan, and Teresa Golden

J. Vac. Sci. Technol. B 8, 1329 (1990); http://dx.doi.org/10.1116/1.584913 (6 pages)

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It has recently been demonstrated that the surface atomic structure of single crystals, monolayers, and thin films can be imaged by means of Auger electrons. Angular distribution Auger microscopy (ADAM) produces subatomic resolution images of atomic structure by measuring and displaying the complete angular distribution of low‐energy Auger electrons emitted from atoms near the surface of a substrate or thin film. Auger angular distributions contain the silhouettes of surface atoms backlit by emission from atoms located deeper in the solid, revealing the relative positions of atoms near the surface. High‐energy Auger electrons have a larger escape depth and are therefore less surface sensitive but contain crystallographic information, particularly the locations of channels in the crystal. Consequently, ADAM is a powerful new technique for the characterization of semiconductor surfaces and epitaxial thin films, and also for fundamental studies of electron physics provided that certain important experimental criteria are met. Described here are recent applications of ADAM to probing the structures of single‐crystal surfaces and thin films.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
79.20.Fv Electron impact: Auger emission
68.37.-d Microscopy of surfaces, interfaces, and thin films
68.55.-a Thin film structure and morphology

A novel electron‐beam exposure technique for 0.1‐μm T‐shaped gate fabrication

N. Samoto, Y. Makino, K. Onda, E. Mizuki, and T. Itoh

J. Vac. Sci. Technol. B 8, 1335 (1990); http://dx.doi.org/10.1116/1.584914 (4 pages) | Cited 5 times

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This article reports on a novel fabrication technique for T‐shaped short gates using double‐layer electron‐beam(EB) resist system, which provides uniform gate length across 2‐in. wafers. In the proposed novel fabrication technique, a 1‐μm PMMA(I)/0.25‐μm PMMA(II) (HI/LOW MW) double‐layer resist system is adopted to fabricate T‐shaped gates. To avoid the influence of scattered electrons, the bottom PMMA(II) resist is EB‐exposed through the top opening with an acceleration of 50 or 25 kV and a single‐path line dose of 0.8–2.0 nC/cm. The top opening has been formed with a 25‐kV Gaussian electron beam at a 120 μC/cm2 dosage. The developed technique has accomplished T‐shaped gates with 70‐nm minimum footprint and 0.1–0.2‐μm T‐shaped gates, whose yield is over 80% on wafers.
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85.40.Hp Lithography, masks and pattern transfer

High aspect ratio asymmetric gate structures employed in novel self‐aligned high electron mobility transistor technology

M. A. Thompson, L. M. Jelloian, L. D. Nguyen, and U. K. Mishra

J. Vac. Sci. Technol. B 8, 1339 (1990); http://dx.doi.org/10.1116/1.584915 (4 pages) | Cited 3 times

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We report on the development and fabrication of high aspect ratio asymmetric gate structures defined by electron beam lithography. The asymmetric gate or ‘‘gamma’’ gate, as it is referred to, has substantially lower resistance compared to gates fabricated by more conventional techniques. The improved gate resistance is achieved by having an increased cross section (∼3×) over conventional T‐shaped gates, which is provided by the asymmetric fabrication scheme. Concurrently, the gamma gate has been incorporated into a self‐aligned high electron mobility transistor process, in which its asymmetric shape can be used to define the gate to source and gate to drain spacings independently. The unique tailoring capabilities of this fabrication technique, enables specific gate to source (Lgs), gate to drain (Lgd), and source to drain (Lsd) dimensions independent of the gate length (Lg). Devices fabricated using this technique, had an Lg of 0.10 μm, an Lgs of 0.20 μm, and an Lgd of 0.90 μm. The total Lsd self‐aligned dimension was 1.20 μm, with a resultant aspect ratio of 12:1 for a given Lg of 0.10 μm.
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85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

All‐level electron‐beam lithography for trench isolated nano‐metal–oxide semiconductor devices

Asanga H. Perera and J. Peter Krusius

J. Vac. Sci. Technol. B 8, 1343 (1990); http://dx.doi.org/10.1116/1.584916 (5 pages)

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An electron beam lithography based fabrication technology using highly anisotropic reactive ion etching (RIE) has been developed for the fabrication of exploratory 200 nm metal–oxide semiconductor field effect transistors (MOSFETs), designed to overcome scaling limitations below 0.5 μm. A Cambridge Instruments EBMF 10.5 vector scan system operated at 20 keV and field size of 1.6384 mm is employed. A pattern overlay accuracy of 75 nm (3σ) was obtained using 5×5×1.5 μm2 pit marks etched into the Si substrate. The fabrication process uses four resist systems: a polyimide/PECVD SiO2 based trilayer resist, P[MMA/MAA], the negative novalac resist SAL601‐ER7, and a newly developed positive novalac e‐beam resist SYSTEM‐9, which offers contrasts up to 13.9 and a moderate sensitivity of 29 μC/cm2. This integrated electron beam lithography for device fabrication at 0.2 μm and below, allows a throughput of 2–3 wafer/h writing 256 fields/wafer and a maximum data density (exposed area/total area) of 41%.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices
07.68.+m Photography, photographic instruments; xerography
41.75.Fr Electron and positron beams

Fabrication of closely spaced quantum dot diodes

J. N. Randall, M. A. Reed, and Y.‐C. Kao

J. Vac. Sci. Technol. B 8, 1348 (1990); http://dx.doi.org/10.1116/1.584917 (5 pages) | Cited 6 times

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Quantum dot devices have been proposed as the basic structure for an integrated circuit technology with extremely high functional density [R. T. Bate, Sci. Am. 258, 96 (1988)]. Electronic transport has been reported through quantum dot diodes which are resonant tunneling devices with lateral dimensions small enough to produce zero‐dimensional (0D) confinement effects [M. A. Reed, J. N. Randall, R. J. Aggarwal, R. J. Matyi, T. M. Moore, and A. E. Wetsel, Phys. Rev. Lett. 60, 535 (1988); G. Faini, A. Ramdane, F. Mollot, and H. Launois, (to be published) NATO Workshop Spain 1990; S. Tarucha, Y. Hirayama, T. Saku, and T. Kimura, Phys. Rev. B 41, 5459 (1990)]. We seek improvements in the switching characteristics of these 0D tunneling devices as well as processing techniques to fabricate them very close together in an attempt to study field coupling between dots. We will discuss the processing issues involved with fabricating very closely spaced quantum dot diodes. We are building pairs of quantum dot diodes which are approximately 1500 angstroms in diameter and spaced a few hundred angstroms apart. e‐beam lithography is used to define the dot patterns. The use of nonalloyed InGaAs contacts, which is essential to providing ohmic‐type contacts of this small diameter, [J. N. Randall, C. H. Yang, Y. C. Kao, and T. M. Moore, J. Vac. Sci. Technol. B 7, 2007 (1989); P. Gueret, P. Buchmann, K. Daetwyler, and P. Vettiger, Appl. Phys. Lett. 55, 1735 (1989)], presents complications for the reactive ion etching of these structures. The task of independently contacting two very small and closely spaced contacts requires high resolution lithography and accurate re‐alignment techniques. The e‐beam lithography techniques used to accomplish this task will be presented. Finally some transport measurements through isolated quantum dot diodes will be presented.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
73.40.Gk Tunneling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.40.Hp Lithography, masks and pattern transfer

In0.53Ga0.47As/InP quantum wires: Fabrication and magnetotransport studies

A. Menschig, B. Roos, R. Germann, A. Forchel, K. Pressel, W. Heuring, and D. Grützmacher

J. Vac. Sci. Technol. B 8, 1353 (1990); http://dx.doi.org/10.1116/1.585076 (4 pages)

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We have fabricated In0.53 Ga0.47 As/InP quantum wires with geometrical widths down to 80 nm by high resolution electron beam lithography and dry etching. The magnetotransport measurements display four distinct features: (1) The Shubnikov–de Haas oscillations show for narrow wires (<200 nm) a strong deviation from the 1/B periodicity. (2) Over the complete magnetic field range there are nonperiodic universal conductance fluctuations superimposed on the resistance curve. (3) At very low magnetic fields we observe a large negative magetoresistance, which decreases with increasing wire width. (4) In narrow wires we observe a distinct magnetoresistance peak at magnetic fields of about 1 T.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
81.65.-b Surface treatments

Nanostructure fabrication in InP and related compounds

I. Adesida, K. Nummila, E. Andideh, J. Hughes, C. Caneau, R. Bhat, and R. Holmstrom

J. Vac. Sci. Technol. B 8, 1357 (1990); http://dx.doi.org/10.1116/1.585077 (4 pages) | Cited 17 times

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Nanometer‐scale gratings have been fabricated in InP and InGaAs/InP heterostructures using electron‐beam lithography and reactive‐ion etching in methane‐hydrogen plasmas. It is shown that the slight overcut obtained in the etch profiles during a single‐step etch in CH4/H2 is due to polymer formation on inert mask surfaces and edges. Intermittent removal of the deposited polymer film is shown to be effective in obtaining anisotropic profiles. Highly anisotropic 35‐nm‐wide InP lines at 70‐nm pitch demonstrate the potential of this fabrication process. The formation of 100‐nm‐wide free‐standing InP wires is also presented.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Focused ion beam micromachined three‐dimensional features by means of a digital scan

H. Ximen, R. K. DeFreez, J. Orloff, R. A. Elliott, G. A. Evans, N. W. Carlson, M. Lurie, and D. P. Bour

J. Vac. Sci. Technol. B 8, 1361 (1990); http://dx.doi.org/10.1116/1.585078 (5 pages) | Cited 6 times

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Focused ion beam micromachining (FIBM) is a promising new technique capable of forming optical quality surfaces in semiconductor laser materials. A beam of 25 keV Ga+ ions focused to a 50–250 nm spot can sputter materials from a wafer surface providing a method for fabricating submicron features, such as diode laser output mirrors and coupled cavity oscillating mirrors. To date, all mirrors fabricated by traditional FIBM have been made up of lines or rectangles (i.e., fabricated by straight line scans). However, straight line scans cannot be satisfactorily used for many kinds of applications. In order to fabricate arbitrary structures such as curves and intersecting lines, a fully digitized, nonlinear, three‐dimensional (3D) and variable‐speed scan strategy, which can produce desired structures with arbitrarily curved paths in a plane and arbitrary depth profiles, has been developed. This strategy has been implemented using a FIB system with an IBM‐compatible computer to fabricate ‘‘V’’, micro‐‘‘V’’ and parabolic mirrors in GaAs lasers. A simple computer simulation of FIBM in 3D space, which is based upon a Gaussian current distribution for the ion beam, has been developed to demonstrate the difference between the two scan strategies, i.e., with and without variable‐scan speed. The aim of the 3D simulation is software support for the computer controlled FIB micromachining of various 3D structures on semiconductor diode laser devices.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Fabrication of coupled quantum dot arrays with a 100–150 nm period

K. Y. Lee, D. P. Kern, K. Ismail, R. J. Haug, T. P. Smith, W. T. Masselink, and J. M. Hong

J. Vac. Sci. Technol. B 8, 1366 (1990); http://dx.doi.org/10.1116/1.585079 (5 pages) | Cited 2 times

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This paper demonstrates a novel method for fabricating two‐dimensional lateral surface superlattices. The technique involves etching a grid into a GaAs/GaAlAs modulation‐doped heterostructure using a mask consisting of an array of 50‐nm diam Ni/Au dots with a 100–150 nm period. Bias applied to a Schottky gate deposited over the structured surface varies the coupling strength between dots. The devices can be tuned to operate in the superlattice (weak and strong coupling) or the quantum dot (no coupling) regimes. Low‐temperature characterization of the superlattices fabricated specifically for transport and capacitance measurements reveal novel magnetic field effects.
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85.40.Hp Lithography, masks and pattern transfer
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.30.Tv Field effect devices
81.65.-b Surface treatments

Optical properties of InGaAs/InP semiconductor nanostructures

J. S. Weiner, Y. L. Wang, H. Temkin, L. R. Harriott, R. A. Hamm, and M. B. Panish

J. Vac. Sci. Technol. B 8, 1371 (1990); http://dx.doi.org/10.1116/1.585080 (3 pages)

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We have studied the optical properties of buried InGaAs/InP nanostructures fabricated by in situ focused gallium ion beam writing, dry etching, and overgrowth by gas source molecular beam epitaxy. Due to the small size and buried nature of these structures, cathodoluminescence imaging and spectroscopy are the most suitable techniques for studying them. We have determined the dose dependence of their optical properties and have fabricated fully buried quantum wires. We find high quantum efficiency of optical emission from structures as small as 2000 Å in lateral extent. With improvements in the in situ processing it should be possible to fabricate fully buried nanostructures as small as a few hundred angstroms in laterial dimensions.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
85.60.-q Optoelectronic devices
78.60.Hk Cathodoluminescence, ionoluminescence

Merging focused ion beam patterning and optical lithography in device and circuit fabrication

James E. Murguia, Christian R. Musil, Mark I. Shepard, Henri Lezec, Dimitri A. Antoniadis, and John Melngailis

J. Vac. Sci. Technol. B 8, 1374 (1990); http://dx.doi.org/10.1116/1.585081 (6 pages) | Cited 1 time

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Combining optical lithography and focused ion beam (FIB) patterning in direct‐write device and circuit fabrication by generating large features optically and small features with the FIB can significantly reduce beam writing time. Our approach to FIB pattern definition is ideally suited for alignment to optically patterned features and takes full advantage of the lithographic and implantation capabilities of the FIB. Optical and FIB patterns are designed simultaneously in the very large scale integrated layout tool magic, [magic, Report No. UCB/CSD 85/225 University of California, Berkley (March 1985)]. We have developed a software package magtofib [James E. Murguia, Christian Musil, Mark Shepard, Sasan Zamani, magtofib, Massachusetts Institute of Technology (1989)] which takes its input from the magic data file and converts it to FIB stage and beam commands. The FIB is aligned by operating in scanning ion microscope mode and finding the centroid of an optically produced die alignment mark. Since the coordinate systems of a typical optical reticle, stepper, and of the FIB are, in general, nonorthogonal and rotated with respect to the wafer, the alignment error increases as one moves away from the alignment point. To place features 1 cm apart to an accuracy of 0.1 μm, calibration must be better than one part in 105. This precision is achieved with a linear transformation calculated from three alignment crosses on the pattern perimeter which transform computer aided design layout coordinates into wafer coordinates. The transformation is calculated once per wafer. The patterning tools have been demonstrated using three types of alignment marks and two resists, on a variety of devices, as well as x‐ray masks. The alignment accuracy is ±0.1 μm. In addition, we report a process to combine optical and FIB lithography on the same layer using the same positive UV resist (KTI 820) as a negative FIB resist.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.30.-z Semiconductor devices
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Vacuum lithography for three‐dimensional fabrication using finely focused ion beams

L. R. Harriott, H. Temkin, Y. L. Wang, R. A. Hamm, and J. S. Weiner

J. Vac. Sci. Technol. B 8, 1380 (1990); http://dx.doi.org/10.1116/1.585082 (5 pages) | Cited 5 times

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Three‐dimensional nanostructure fabrication for optoelectronic and quantum‐effect devices can benefit from the greatly improved surface layer quality and low contamination offered by all vacuum processing. Ultrathin epitaxial layers can be grown with excellent uniformity and interface quality with techniques such as molecular beam epitaxy (MBE) to produce two‐dimensional confinement structures. What has been lacking is a lateral patterning method which is compatible with dimensions required for quantum confinement and the high vacuum crystal growth environment. Surface contamination and damage produced during processing become a much more serious problem with feature sizes in the range of 100 nm and below. The usual lithographic processes involve exposure to produce a chemical change in a polymer resist with photons or electrons resulting in a pattern but also introduce surface contamination incompatible with epitaxial overgrowth. A number of high resolution vacuum compatible patterning techniques are possible with finely focused ion beams due to their unique ability to deliver momentum as well as energy to a target. We have developed in situ patterning process for InP‐based compounds in which a focused ion beam is used to pattern a very thin (20–30 Å) surface oxide layer. The mask pattern is then transferred into the substrate by dry etching of a Cl2 atmosphere at 200 °C with or without the assistance of a broad area Ar ion beam. Results of experiments exploiting the oxide masking for the pattern formation on InP will be presented, including in situ formation and removal of the mask, and regrowth performed on patterned layers.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.60.-q Optoelectronic devices

The effects of broadband 250 nm illumination on process latitude

Birol Kuyel and Harry Sewell

J. Vac. Sci. Technol. B 8, 1385 (1990); http://dx.doi.org/10.1116/1.585083 (7 pages)

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The effects on lithography of the spectral bandwidth of the illumination used in an optical step‐and‐scan projection aligner have been studied J. Buckley and C. Karatzas, SPIE 1088, 424 (1989). An illumination bandwidth of 240–255 nm is compared with a single wavelength of 248 nm representing mercury–xenon lamp and excimer‐laser spectra, respectively. Linewidth control for resist‐thickness variations, resist‐profile effects, and linewidth stability on topography are reported. The experimental results on critical‐dimension variations were obtained from tests run on a deep‐UV 0.35 numerical aperture (NA) 4× step‐and‐scan system using the Shipley XP89‐142 negative resist system, and on a 0.35 NA 5× excimer stepper using both SNR248 and XP89‐142 (SNR248‐3×) resist. An HP 8450 photospectrometer was used to study resist reflectivity variations with wavelength and thickness. Both SEM and electrical‐probe measurements are reported. It is demonstrated that resist thickness variations cause larger critical‐dimension variations in monochromatic exposures than in broadband exposures. It is shown that the critical‐dimension variation due to resist‐thickness variation over topography reduces the process window, particularly in the case of monochromatic illumination. It is also demonstrated that the full benefit of the spectral width of the broadband illumination is only achieved when the illumination source spectrum, the deep‐UV filter‐transmission characteristics, and the resist transmission are all matched.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
78.66.Qn Polymers; organic compounds

Electronically wired petri dish: A microfabricated interface to the biological neuronal network

M. D. Eggers, D. K. Astolfi, S. Liu, H. E. Zeuli, S. S. Doeleman, R. McKay, T. S. Khuon, and D. J. Ehrlich

J. Vac. Sci. Technol. B 8, 1392 (1990); http://dx.doi.org/10.1116/1.585084 (7 pages) | Cited 2 times

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Presented is the design, fabrication, and evaluation of 72‐channel microcircuit electrode arrays (biochips) built to interface neurons and computers. Contributions include a detailed mathematical model of the electrode/electrolyte interface and subsequent electrode design optimization (in terms of maximum signal‐to‐noise ratio). Electrode impedance measurements were obtained with the electrodes submerged in electrolytic neural solution. Large sample results indicate a 7% discrepancy between theoretical and measured impedances. In addition to the engineering efforts, biological cell culturing techniques were developed to enable the growth of synaptically interconnected, electrically excitable cells on the biochip. Both dissociated invertebrate neurons and clonal mammalian cell systems were employed. Together these contributions enabled microvolt signals to be recorded from individual neurons grown and synaptically interconnected on the biochip surface. Also recorded were neuronal responses to on‐chip stimulation. Consequently, the biochip technology presented represents a step towards a long‐term, noninvasive, multisite electrical stimulation and recording capability necessary for extracting the mechanisms governing the way living neural networks connect, integrate, and self‐organize.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
89.20.Ff Computer science and technology

Scattering matrix analysis of electron transport in disordered Aharonov–Bohm interferometers and ballistic constrictions

M. Cahay, S. Bandyopadhyay, and H. R. Frohne

J. Vac. Sci. Technol. B 8, 1399 (1990); http://dx.doi.org/10.1116/1.585085 (5 pages) | Cited 4 times

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We present a fully quantum‐mechanical analysis of phase‐coherent electron transport in disordered semiconductor nanostructures. The analysis is based on a scattering matrix formalism which allows us to simulate the effects of interface roughness scattering, as well as scattering from point defects and defect clusters. Using this technique, we have studied quantum conduction in electrostatic Aharonov–Bohm interferometers and narrow ballistic constrictions of submicron dimensions.
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72.10.-d Theory of electronic transport; scattering mechanisms
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.80.Ng Disordered solids
85.30.-z Semiconductor devices

First order distributed feedback gratings (92.5–105 nm period) for GaInP/AlGaInP lasers emitting in the visible range

M. Korn, T. Körfer, A. Forchel, and P. Roentgen

J. Vac. Sci. Technol. B 8, 1404 (1990); http://dx.doi.org/10.1116/1.585086 (4 pages) | Cited 1 time

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The fabrication of first order gratings for distributed feedback (DFB) GaInP/AlGaInP laser structures with periods in the range of 100 nm will be reported. The laser structures were pumped optically and show single mode emission at 639 and 651 nm with coupling coefficients of 151 cm−1. Due to the principally nonexisting radiation mode loss first order DFB lasers will show lower thresholds than the yet demonstrated third order DFB lasers with three times coarser grating periods. The gratings fabricated by e‐beam lithography and dry etching techniques show strong feedback and moderate damaging of the waveguide properties.
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42.79.Dj Gratings
42.60.-v Laser optical systems: design and operation
41.75.Fr Electron and positron beams

Electron‐beam lithography and chemically assisted ion beam etching for the fabrication of grating surface‐emitting broad‐area AlGaAs lasers

R. C. Tiberio, G. A. Porkolab, J. E. Johnson, W. J. Grande, L. C. Rathbun, E. D. Wolf, H. G. Craighead, R. J. Lang, A. Larsson, S. Forouhar, and J. Cody

J. Vac. Sci. Technol. B 8, 1408 (1990); http://dx.doi.org/10.1116/1.585087 (4 pages) | Cited 1 time

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We report on the fabrication and characterization of broad‐area, grating‐coupled, distributed Bragg reflector, surface‐emitting, AlGaAs/GaAs laser diodes. Electron‐beam lithography and chemically assisted ion‐beam etching (CAIBE) were used to fabricate both first‐order (120‐nm period) and second‐order (240‐nm period) gratings. Gratings were patterned by exposing PMMA resist using 50‐keV electrons in a JEOL 5DIIU direct write electron‐beam lithography system. The resist image was transferred into the AlGaAs layer by CAIBE. CAIBE was performed using chlorine gas in conjunction with a 500‐eV argon‐ion beam in a modified Technics Plasma GmbH RIB 160 etcher. Surface‐emitting lasers using second‐order gratings were fabricated on AlGaAs/GaAs asymmetric separate confinement double heterostructure layers grown by liquid‐phase epitaxy. Wet chemical etching was used to remove the upper cladding layer, exposing the waveguide in selected areas. Gratings were then etched into the waveguide to produce surface emitting window regions. The far‐field light intensity pattern shows a lateral angular spread of 2.4° for a 50‐μm‐wide stripe. This lateral angular distribution is the lowest reported for a broad‐area (not array) grating surface‐emitter.
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81.65.-b Surface treatments
42.55.Px Semiconductor lasers; laser diodes
41.75.Fr Electron and positron beams
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Structural control and the optimization of chlorinated styrene‐based electron resists

D. R. Brambley, R. G. Jones, Y. Matsubayashi, and P. Miller Tate

J. Vac. Sci. Technol. B 8, 1412 (1990); http://dx.doi.org/10.1116/1.585088 (6 pages) | Cited 4 times

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A large number of chlorinated styrene‐based resists has been prepared, both by the copolymerization of methylstyrene with chloromethylstyrene, and by the direct chlorination of methylstyrene polymers. These resists have been characterized, and Inokuti’s equation has been applied to the lithographic data to obtain radiation chemical yields which have been related to polymer structure and composition. Inokuti’s theory has also been used to predict the dependence of lithographic performance on polymer parameters. Qualitative and quantitative agreement between these predictions and experimental observations has been demonstrated in several polymer systems, and this theory has been shown to provide useful pointers to resist optimization. A number of comparatively high sensitivity polymers have been found which do not undergo chain scission on irradiation and which accordingly exhibit high contrasts. From this range of polymers several well‐suited for use as electron resists have been selected.
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization
36.20.-r Macromolecules and polymer molecules

Resist profile simulation for photoresist composition optimization

Tohru Ushirogouchi, Yasunobu Onishi, and Tsukasa Tada

J. Vac. Sci. Technol. B 8, 1418 (1990); http://dx.doi.org/10.1116/1.585089 (5 pages) | Cited 1 time

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Monte Carlo dissolution simulation and dissolution properties related to resist composition were studied. Using these results, a composition assembling resist profile simulator (CARPS) has been developed. This simulator makes it possible to optimize the resist composition.
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85.40.Hp Lithography, masks and pattern transfer
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
82.35.-x Polymers: properties; reactions; polymerization

Modeling and simulation of a deep‐ultraviolet acid hardening resist

Richard A. Ferguson, John M. Hutchinson, Chris A. Spence, and Andrew R. Neureuther

J. Vac. Sci. Technol. B 8, 1423 (1990); http://dx.doi.org/10.1116/1.585090 (5 pages) | Cited 7 times

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A modeling methodology for a class of resist materials that rely on the acid catalyzed crosslinking of the resin matrix during a post‐exposure bake is presented. This methodology is used to derive a complete and quantitative model for a production worthy deep‐ultraviolet (UV) resist, Shipley XP‐8843 (also known commercially as SNR 248). The modeling is based on the chemical and physical mechanisms which determine resist behavior during the exposure, post‐exposure bake, and development processes. The IR absorption bands near 990 and 1070 cm−1 are used to monitor the extent of crosslinking during the bake as a function of bake temperature, bake time, and photogenerated acid concentration. The post‐exposure bake model consists of a primary crosslinking reaction with an order of 1.42 in photo‐generated acid and an acid loss reaction to account for dose dependent saturation of the crosslinking. Resist development is modeled by relating the dissolution rate to the extent of crosslinking during the post‐exposure bake and to the number of sites on the crosslinking agent (six for melamine). Good correlation is obtained between simulated development profiles and experimental results with several post‐exposure bake conditions.
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85.40.Hp Lithography, masks and pattern transfer
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Synthesis and lithographic characterization of poly(4‐t‐butoxycarbonyloxystyrene‐sulfone)

J. M. Kometani, O. Nalamasu, E. Reichmanis, R. S. Kanga, L. F. Thompson, and S. A. Heffner

J. Vac. Sci. Technol. B 8, 1428 (1990); http://dx.doi.org/10.1116/1.585091 (4 pages)

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Poly(4‐t‐butoxycarbonyloxystyrene‐sulfone) was synthesized by a thermally induced radical copolymerization of 4‐t‐butoxycarbonyloxystyrene and sulfur dioxide using AIBN as the initiator. The effect of polymerization conditions such as temperature, monomer feed ratio, and monomer concentration on the copolymer molecular weight and composition was studied. Additionally, the lithographic performance of the matrix polymer was evaluated for various copolymer compositions and molecular weights.
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82.35.-x Polymers: properties; reactions; polymerization

Positive photoresist process simulation over nonplanar substrates

Eytan Barouch, Brian Bradie, Uwe Hollerbach, and Steven A. Orszag

J. Vac. Sci. Technol. B 8, 1432 (1990); http://dx.doi.org/10.1116/1.585092 (5 pages) | Cited 1 time

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A three‐dimensional computational simulator of nonplanar substrates coated with positive photoresists is presented. The model includes four major steps: projection printing, exposure, post‐exposure baking (PEB), and dissolution. Projection printing is based on Hopkins’ classical work. The exposure model employs the full nonlinear wave equation coupled with the photoactive compound (PAC) bleaching rate equation. These equations are solved using a spectral element iterative scheme. The PEB is treated as a material diffusion equation employing ideas introduced by Mack and the dissolution algorithm is our LEAD (least action dissolution) algorithm modified for nonplanar substrates. Several realistic examples are presented displaying final profiles at various dissolution times.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.30.Tv Field effect devices

New compensation method for avoiding proximity resist heating in variably shaped electron beam lithography

Ken Nakajima, Toshiyuki Honda, and Hiroshi Matsumoto

J. Vac. Sci. Technol. B 8, 1437 (1990); http://dx.doi.org/10.1116/1.585093 (4 pages) | Cited 1 time

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A horizontal‐mode resist heating is proposed and a suitable method for avoiding it in variably shaped electron beam lithography is described. The horizontal thermal diffusion through a top layer resist between electron beam shots cannot be neglected when using a high current density electron beam, a high speed deflector amplifier, and a multiple layer resist because these cause a horizontal‐mode resist heating (labeled ‘‘proximity resist heating’’) which depends on the pattern size and on the time interval between shots. A method, suitable to avoid this resist heating, is proposed where the pattern size dependent optimum repetition number of exposures for each pattern is used. There is a slight throughput degradation of typically 10%–20% increase.
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85.40.Hp Lithography, masks and pattern transfer
79.20.Kz Other electron-impact emission phenomena

Multicomponent Langmuir–Blodgett resists for optical lithography

Laura L. Kosbar, Curtis W. Frank, and R. Fabian W. Pease

J. Vac. Sci. Technol. B 8, 1441 (1990); http://dx.doi.org/10.1116/1.585094 (6 pages) | Cited 1 time

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We have used Langmuir–Blodgett (LB) techniques to prepare very thin (≤1000 Å), uniform organic films, and we have investigated their potential use in lithographic applications. Resist films were prepared using novolac and poly (p‐hydroxystyrene) resins and both near and deep UV sensitive photoactive compounds (PAC). LB resist films formed from mixtures of polymer and PAC behaved lithographically in a similar fashion to spin cast films. LB films as thin as 300 Å were sufficient to protect 500 Å of chromium during wet chemical etching. As few as three monolayers of PAC deposited on the top surface of a spin cast novolac film was sufficient to protect up to ∼1 μm of film from dissolving. Investigation of the ‘‘sphere of influence’’ of PAC molecules by controlling their distribution throughout the film indicates that strong interactions may exist between consecutive LB layers of PAC.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Exposure characteristics of high‐resolution negative resists

Kaolin Grace Chiong, Shalom Wind, and David Seeger

J. Vac. Sci. Technol. B 8, 1447 (1990); http://dx.doi.org/10.1116/1.585095 (7 pages) | Cited 8 times

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Positive and negative resist systems are both essential in the microfabrication of experimental devices. While numerous positive resists have been shown to have high‐resolution, negative resists were considered to have poor contrast and resolution. In this paper, the electron‐beam exposure characteristics of several negative resist systems including epoxy novolac‐type systems [K. J. Stewart, M. Hatzakis, J. M. Shaw, and D. E. Seeger, J. Vac. Sci. Technol. B 7, 1734 (1989); M. Hatzakis, K. Stewart, J. Shaw, and S. Rishton, Microelectron. Eng. 11, 487 (1990)] and two selected vendor resist systems have been investigated. These resist exposure characteristics are related to resist resolution, image profile, edge acuity, and process latitude. The sensitivity of various resists to slight exposures which may be caused by electron scattering in electron‐beam lithography or mask diffraction in optical or x‐ray lithography varies from resist to resist. The resist system that is least sensitive to these slight exposure effects offers the highest resolution. High‐resolution images down to 0.25‐μm lines and spaces were delineated only in resist systems with a gamma value higher than 2.5. Resist images of 50 nm dimensions in 0.4‐μm‐thick resist films have been obtained from the epoxy novolac system with vertical sidewalls and good edge acuity. In addition, results of high‐voltage electron‐beam exposures showed that residues between small shapes are substantially reduced. Similarly, cleanly resolved features were obtained when a high‐contrast mask is used in x‐ray synchrotron exposures.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

Process optimization of the advanced negative electron beam resist SAL605

Theodore H. Fedynyshyn, Michael F. Cronin, Louis C. Poli, and Christine Kondek

J. Vac. Sci. Technol. B 8, 1454 (1990); http://dx.doi.org/10.1116/1.585096 (7 pages) | Cited 7 times

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Electron beam lithography requires a high resolution resist system capable of maintaining tight linewidth tolerances. These tolerances require a resist process which yields the greatest process latitude. SAL601‐ER7 is an example of an electron beam resist which has demonstrated the ability to provide submicron resolution coupled with high resist sensitivity. This paper will focus on developing an optimized process for a new advanced negative electron beam resist (ANR), SAL605 which also utilizes a chemically amplified crosslinking system. The SAL605 electron beam resist is a next generation version of SAL601‐ER7, and as such has many of the same processing requirements. The effect of developer normality and development time on sensitivity and linewidth control with MF‐312 based developers will be presented. The effect of post‐exposure bake (PEB) temperature and time with respect to sensitivity and linewidth control will also be presented. We will show that there are processing windows for submicron resolution which give high sensitivity as well as a large exposure latitude.
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07.68.+m Photography, photographic instruments; xerography
41.75.Fr Electron and positron beams
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Characterization of novel sulfonic acid photogenerating 2‐nitrobenzyl ester derivatives

F. M. Houlihan, T. X. Neenan, E. Reichmanis, J. M. Kometani, L. F. Thompson, T. Chin, and R. S. Kanga

J. Vac. Sci. Technol. B 8, 1461 (1990); http://dx.doi.org/10.1116/1.585097 (5 pages)

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The thermal stability of 2‐nitrobenzyl sulfonate esters was dramatically increased by the introduction of an electron withdrawing, sterically bulky group (Br, CF3 ) at the ortho position of the benzyl moiety. This enhancement in thermal stability allowed synthetic access to thermally stable, photogenerators of acids based on more powerful organic acids which are useful in formulating deep‐UV resists having sensitivities approaching those of the more traditional onium salt‐based materials.
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68.60.Dv Thermal stability; thermal effects
85.40.Hp Lithography, masks and pattern transfer
82.30.Nr Association, addition, insertion, cluster formation
81.65.-b Surface treatments

Methylated poly(4‐hydroxystyrene): A new resin for deep‐ultraviolet resist application

Dennis R. McKean, William D. Hinsberg, Thomas P. Sauer, Grant Willson, Richard Vicari, and Douglas J. Gordon

J. Vac. Sci. Technol. B 8, 1466 (1990); http://dx.doi.org/10.1116/1.585098 (4 pages) | Cited 1 time

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Positive photoresists which function on the basis of dissolution inhibition are the mainstay of optical lithographic technology at long wavelength. Described in this paper is a new type of material which permits the dissolution inhibition mechanism to be extended to deep‐UV wavelengths. Methylated poly(4‐hydroxystyrene) resins are prepared by a copolymerization reaction which results in a final product whose dissolution properties can be defined by the ratio of the two monomers used in the reaction. The deep‐UV optical absorbance of the methylated resin is about one‐half the absorbance of novolac at 248 nm which makes these materials attractive for application in deep‐UV resist formulations. Binary photoresists using diazo compounds as dissolution inhibitors have been prepared with the methylated poly(4‐hydroxystyrene) as the host resin. These materials function very similarly to the familiar diazonaphthoquinone/novolac photoresists at long wavelength. For deep‐UV application, both binary and three component resists have been evaluated. The three component system has high sensitivity (<5 mJ/cm2 ) and contrast (γ>3). The high contrast is due in part to the induction effect observed from dissolution data. Projection printed images have steep wall profiles indicative of high contrast photoresists.
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization
78.40.Ha Other nonmetallic inorganics

Comparison of exposure, bake, and dissolution characteristics of electron beam and optically exposed chemically amplified resists

N. N. Tam, R. A. Ferguson, A. Titus, J. M. Hutchinson, C. A. Spence, and A. R. Neureuther

J. Vac. Sci. Technol. B 8, 1470 (1990); http://dx.doi.org/10.1116/1.585099 (6 pages)

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Fourier‐transform infrared (FTIR) spectrometry and dissolution rate measurements are used to compare chemical–physical mechanisms in electron beam and deep‐ultraviolet (UV) optical exposure of a chemically amplified negative crosslinking resist, Shipley XP‐8843 (SNR‐248). In contrast to optical exposure, up to 20% of the maximum extent of reaction by the melamine crosslinking agent, as measured by the change in peak‐to‐peak absorbance of the infrared (IR) spectrum at 990–1070 cm−1, was observed after electron beam exposure at nominal exposure doses of 0.5–3 μC/cm2. For both electron‐beam and optical exposure, the kinetics of the acid‐catalyzed crosslinking reactions during the postexposure bake (PEB) were similar and the saturation value of the crosslinking reaction measured by the FTIR was identical. A plot of the dissolution rate versus the degree of crosslinking for normal lithographic doses was single‐valued and tended to follow comparable data for optical exposure. When doses >5 μC/cm2 are used without a PEB, the slowing of the dissolution rate is less than expected from IR spectral change. Contrary to typical electron beam exposed negative resists, slightly underexposing small features produced a reentrant profile apparently owing to the high contrast of this resist.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Silylation processes based on ultraviolet laser‐induced crosslinking

M. A. Hartney, M. Rothschild, R. R. Kunz, D. J. Ehrlich, and D. C. Shaver

J. Vac. Sci. Technol. B 8, 1476 (1990); http://dx.doi.org/10.1116/1.585100 (5 pages) | Cited 2 times

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This report describes a positive‐tone silylation process which results from crosslinking by exposure of novolac‐based resists to deep‐UV excimer laser irradiation. Comparison of 193 and 248 nm irradiation shows that the former leads to more efficient crosslinking. The dependence of silylation on time, temperature and pressure was studied in order to investigate the mechanism of the diffusion process. Evidence of both standard diffusion and non‐Fickian behavior was found. Additionally, diffusion of the silylating agent in patterned resist was determined to be anisotropic.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Gas phase silylation in the diffusion enhanced silylated resist process for application to sub‐0.5 μm optical lithography

Ki‐Ho Baik, L. Van den hove, A. M. Goethals, M. Op de Beeck, and B. Roland

J. Vac. Sci. Technol. B 8, 1481 (1990); http://dx.doi.org/10.1116/1.585101 (7 pages) | Cited 2 times

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The diffusion enhanced silylated resist (DESIRE) process has been presented as one of the most attractive surface imaging technologies for advanced optical lithography. It has been shown that the silylation step, usually carried out in a hexamethyldisilazane (HMDS) ambient, is one of the more critical steps in the process. In this paper an in‐depth study of the silylation is presented. Several alternative mono‐ and polyfunctional silylating agents are evaluated for application in the DESIRE process. DMSDMA, TMSDMA, and TMDS are promising candidates, showing several advantages over HMDS. For the case of HMDS and TMDS, the kinetics of the silylation are additionally studied using Rutherford backscattering spectroscopy, Auger electron spectroscopy, and infrared measurements for various process conditions. In an earlier study we have reported lateral swelling for silylation with HMDS resulting from volume expansion of the silylated resist. Because of the reduced volume expansion and/or the lower silylation temperature, these alternative silylating agents reduce the swelling and surface roughness. It has been observed that the silylation process window can be greatly increased by optimizing the presilylation bake.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

The silylation processes for positive and negative deep ultraviolet resists

S. M. Sviridov, M. R. Timerov, K. A. Valiev, L. V. Velikov, and D. Yu. Zaroslov

J. Vac. Sci. Technol. B 8, 1488 (1990); http://dx.doi.org/10.1116/1.585102 (5 pages) | Cited 1 time

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In this report the experimental results of the resist silylation and O2‐plasma development are presented. The Soviet commercial novolac based photoresists of both positive and negative type and gas phase silylation in hexamethyldisilazane (HMDS) were used. The flood exposure of the resist films was made by Hg lamp or KrF laser. It is found that the silylated resist film mass growth (per resist surface square) must exceed 15×10−6 g/cm2 to provide the formation of the etching barrier layer under O2‐plasma development. The silylation kinetic is shown to be linear at first period. The dependence of the initial silylation rate on the experimental conditions was studied and results are discussed. Under the silylation of the highly crosslinked resist films the induction effect was observed. For both positive and negative processes the silylation conditions providing selective O2‐plasma development are determined. To enhance the contrast of O2‐plasma development the three‐stage procedure was elaborated.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

Plasma‐deposited organosilicon thin films as dry resists for deep ultraviolet lithography

M. W. Horn, S. W. Pang, and M. Rothschild

J. Vac. Sci. Technol. B 8, 1493 (1990); http://dx.doi.org/10.1116/1.585103 (4 pages) | Cited 8 times

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Organosilicon thin films have been formed by plasma enhanced chemical vapor deposition and employed as deep‐UV photoresists. Films 20–200 nm thick were deposited from liquid organosilicon sources onto carbon‐based planarizing layers and patterned in projection with a 193 nm excimer laser. At fluences below ∼5 mJ/cm2/pulse, exposure to 193 nm radiation induced oxygen incorporation into the film. Following either a wet or dry development step, negative‐tone imaging was achieved, with the remaining photooxidized film being highly resistant to the O2 reactive ion etching employed in the subsequent pattern transfer step. At higher fluences, ∼15 mJ/cm2, positive‐tone imaging by self‐development was obtained for single‐pulse exposures.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Hp Lithography, masks and pattern transfer

Silylated acid hardened resist process: A deep ultraviolet surface imaging technique

Edward K. Pavelchek, John F. Bohland, James W. Thackeray, George W. Orsula, Susan K. Jones, Bruce W. Dudley, Stephen M. Bobbio, and Peter W. Freeman

J. Vac. Sci. Technol. B 8, 1497 (1990); http://dx.doi.org/10.1116/1.585104 (5 pages) | Cited 3 times

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A deep ultraviolet surface imaging technique using a silylated acid hardened resist (SAHR) is described. The resist, Shipley XP‐8928, contains a meta, para‐cresol novolak resin which has a high optical absorbance in the deep ultraviolet (DUV). This reduces complications from substrate reflections and restricts the image to the near‐surface regions. The exposed regions, which become crosslinked, are less susceptible to vapor silylation by agents such as trimethylsilyldiethylamine (TMSDEA). The unexposed regions may be easily silylated. An anisotropic oxygen reactive ion etching is used to transfer the surface image through the bulk of the resist. This paper discusses the kinetics of silylation with TMSDEA, the resulting silicon distributions in the film before and after etch, and the lithographic performance of the process. Silicon distribution throughout the film is determined by Rutherford backscattering spectrometry and illustrated by stained cross sections. It is found that the film surface saturates at a Si content of 9–10 wt. %, and further silylation results in a sharp front at this concentration moving deeper into the film. The rate at which the front moves is determined by the temperature, pressure and the degree of crosslinking. The etch barrier formed at the surface of the resist has been investigated by x‐ray photoelectron spectroscopy. This indicates that the surface oxidation of both carbon and silicon is increased, while the silicon concentration is unchanged from unetched samples. This process is capable of producing 0.5 μm line/space pairs when exposed by a 0.35 numerical aperture (NA) lens at 248 nm with as little as 7 mJ/cm2. These features can be produced with flat tops and steep sidewalls. Isolated lines with very high aspect ratios can be produced.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.40.Hp Lithography, masks and pattern transfer

Application of Plasmask R  resist and the DESIRE process to lithography at 248 nm

Richard S. Hutton, Robert L. Kostelak, Omkaram Nalamasu, Avi Kornblit, Susan McNevin, and Gary N. Taylor

J. Vac. Sci. Technol. B 8, 1502 (1990); http://dx.doi.org/10.1116/1.585105 (7 pages) | Cited 3 times

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Plasmask resist and its associated dry development process called DESIRE constitute one product which has incorporated surface imaging for lithography at 436 and 366 nm. Based on its performance at these wavelengths, Plasmask 150U resist is predicted to have a resolution limit of ∼0.3 μm at 248 nm with a 0.38 NA lens. Using best focus exposures of 1.5‐μm thick films we have examined a variety of factors that influence the resolution and sensitivity of Plasmask 150U resist at 248 nm. These include standard processing steps as well as silylation with hexmethyldisilazane, plasma development conditions and equipment, and various descum techniques. Processing without a descum step resolved 75° profile, 0.3 μm line and space patterns at high exposure doses, but always afforded a grassy residue. Use of Ar sputter etching to remove ∼2200 Å from unexposed areas prior to plasma development afforded vertical profile 0.3‐μm resolution patterns with no grassy residue.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
78.70.-g Interactions of particles and radiation with matter

Reduction imaging at 14 nm using multilayer‐coated optics: Printing of features smaller than 0.1 μm

J. E. Bjorkholm, J. Bokor, L. Eichner, R. R. Freeman, J. Gregus, T. E. Jewell, W. M. Mansfield, A. A. Mac Dowell, E. L. Raab, W. T. Silfvast, L. H. Szeto, D. M. Tennant, W. K. Waskiewicz, D. L. White, D. L. Windt, et al.

J. Vac. Sci. Technol. B 8, 1509 (1990); http://dx.doi.org/10.1116/1.585106 (5 pages) | Cited 35 times

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We demonstrate high resolution reduction imaging in the soft x‐ray spectral region using multilayer‐coated reflective optics. In particular, a Schwarzschild objective was used at 20:1 reduction with 14 nm radiation to image line and space features from a transmission mask onto a resist‐coated silicon wafer with a resolution better than 0.1 μm. The mirrors of the objective were coated with Mo/Si multilayers to provide nearly 40% reflectance at near‐normal incidence for the 14 nm radiation. Our results demonstrate that multilayer coatings are capable of enhancing the reflectance of optical components at soft x‐ray wavelengths without significantly degrading their imaging performance.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Wc Optical coatings
78.66.-w Optical properties of specific thin films
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
07.85.-m X- and γ-ray instruments

Development of centrally controlled synchrotron radiation lithography beamline system

J. Nishino, M. Kawakami, T. Yanagisawa, and K. Okada

J. Vac. Sci. Technol. B 8, 1514 (1990); http://dx.doi.org/10.1116/1.585107 (5 pages)

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The centrally controlled beamline system for synchrotron radiation lithography has been investigated using the SORTEC storage ring(l GeV). From a practical standpoint, the recently built beamlines aim at attaining a centrally controlled beamline system, which is also serially interfaced with the storage ring. In operating the beamlines, not only local control, but also a central control notion is adopted. The central beamline control system comprises a beamline main computer and a programmable sequence controller (PSC) link. The local beamline control system consists of a PSC, a control panel, and a personal computer. The beamline main computer collects each beamline status datum through the PSC link, receiving the storage ring data from the main computer of the 1 GeV synchrotron radiation (SR) source. A novel oscillating mirror mechanism is proposed, in which the mirror chamber, driven by a combination of a cam mechanism and pulse motor installed in air, is oscillated to scan the mirror, thus producing high reliability and compact design. In addition, a practical beamline structure is offered which fulfills system vacuum protection and protects operators from radiation exposure.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Reflective systems design study for soft x‐ray projection lithography

Tanya E. Jewell, J. Michael Rodgers, and Kevin P. Thompson

J. Vac. Sci. Technol. B 8, 1519 (1990); http://dx.doi.org/10.1116/1.585108 (5 pages) | Cited 7 times

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We have investigated several all‐reflective designs which have potential application for soft x‐ray projection lithography. The resolution goal for all designs was 0.1 μm or better. Different design aspects including usable field size, distortion, obscuration, number of mirrors, surface shape (spherical versus aspheric), and system packaging were explored. Trade‐off studies were made between three types of systems: strip field scanning systems, and large field nonscanning systems with both curved and flat mask. Several candidate unobscured designs with 0.1 μm resolution are presented.
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07.68.+m Photography, photographic instruments; xerography
07.85.-m X- and γ-ray instruments

The first x‐ray lithography beamline at Hefei National Synchrotron Radiation Laboratory

Shinan Qian, Guihe Li, Zewen Liu, Qianhong Chen, Dikui Jiang, Wanpo Liu, Ya Kan, and Yonggang Su

J. Vac. Sci. Technol. B 8, 1524 (1990); http://dx.doi.org/10.1116/1.585109 (5 pages)

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An x‐ray lithography beamline, the first of six planned at Hefei National Synchrotron Radiation Laboratory (HESYRL), was completed and installed in the summer of 1989. A scanning mirror, the key optical component of the beamline, is used to cut off shorter wavelength light and to expand the vertical dimension of the exposure beam. It is oscillated by a stepping motor, while an in situ Moiré fringe grating system measures the uniformity of the motor speed. Downstream after the front end section of the beamline, a Be window is used to block longer wavelength light. A laser alignment system is used to align the beamline with a He‐Ne laser. A special exposure shutter controlled by a second stepping motor can define the exposure time. An exposure chamber in which the vacuum can reach 5×10−7 Torr is located 7 m downstream from the synchrotron radiation source. Since the chamber does not include a vacuum window, a differential pumping system has been installed upstream from the exposure chamber. Test results of simulation experiments are presented and a plan for the first XRL experiments is given in the paper.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

Absolute flux measurements for x‐ray lithography beamlines

F. Baszler, M. Hansen, and F. Cerrina

J. Vac. Sci. Technol. B 8, 1529 (1990); http://dx.doi.org/10.1116/1.585110 (6 pages)

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A calorimeter is calibrated for use as an absolute radiometer for synchrotron radiation x‐ray lithography (XRL) beamlines. Results of the characterization of two beamlines are reported and compared with theory. Photodiodes and a film detector were calibrated against the calorimeter and the performances of these ordinary radiometers are presented. Using the methods described in this paper an absolute flux reading was obtained with accuracies believed to be better than ±2%. The experimental results are compared with the prediction of a theoretical model called transmit. The code is used to predict the performance of XRL beamlines and is very suitable for ‘‘what if’’ types of scenarios.
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06.20.F- Units and standards
07.60.Dq Photometers, radiometers, and colorimeters
07.20.Fw Calorimeters
85.40.Hp Lithography, masks and pattern transfer

Novel process using x‐ray lithography for T‐shaped gate patterns

Nobuyuki Yoshioka, Takeshi Fujino, Hiroaki Morimoto, Yaichiro Watakabe, and Haruhiko Abe

J. Vac. Sci. Technol. B 8, 1535 (1990); http://dx.doi.org/10.1116/1.585111 (4 pages)

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A fabrication process capable of forming T‐shaped gates useful for high‐performance GaAs field‐effect transistor devices by exposing a single‐layer resist with x rays is proposed in this work. The x‐ray mask used in this method has absorber patterns with T‐shaped cross sections, which are made up of two absorber layers. This method makes good use of the fact that the x‐ray transmittance of materials such as resists and mask absorbers is higher than the ultraviolet/visible light transmittance used in photolithography. In order to confirm the practicality of this method, T‐shaped patterns were formed experimentally using the positive resist XPB and an exposure system with an electron‐excited x‐ray tube (Pd target). The x‐ray mask was fabricated by patterning two layers of W‐Ti alloy absorber on a BN/polyimide membrane using an electron direct writing technology. It is demonstrated that the T‐shaped pattern can be formed easily by using the proposed process.
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85.40.Hp Lithography, masks and pattern transfer
07.68.+m Photography, photographic instruments; xerography

A new perspective on proximity printing: From ultraviolet to x ray

B. J. Lin

J. Vac. Sci. Technol. B 8, 1539 (1990); http://dx.doi.org/10.1116/1.585112 (8 pages) | Cited 1 time

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Proximity printing is characterized in terms of linewidth variations in the gap–exposure (E–G) space. The usable E–G regions of all feature shapes and sizes on a given mask design have to be superimposed and the common region defines the depth of focus as well as the working distance for a given exposure latitude and linewidth tolerance. In this paper, the E–G diagrams are constructed and studied for 0.25, 0.35, and 0.5 μm x‐ray features at mask‐to‐wafer gaps between 10 and 80 μm, or equivalently, 2.5, 3.5, and 5 μm features for 250‐nm‐deep‐UV light at mask‐to‐wafer gaps between 4 and 20 μm. The types of illumination include collimated light, finite source size, and ghost line suppression. Linewidth tolerances of ±25 and ±16 nm for perfect and imperfect masks are examined. The effects of 50 nm positive and negative print biases are studied. The depth of focus and working distance are given for five representative lithographic features consisting of equal lines and spaces, isolated line openings, isolated opaque spaces, holes, and islands as well as for only the three long features.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Sensitivity/resolution variables in x‐ray chemically amplified resists exposed to synchrotron radiation

J. W. Taylor, C. P. Babcock, D. C. Mancini, D. Plumb, R. J. Olsen, and T. Fedynyshyn

J. Vac. Sci. Technol. B 8, 1547 (1990); http://dx.doi.org/10.1116/1.585113 (4 pages)

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New formulations of chemically amplified negative‐image photoresists show sensitivities to x rays on the order of 100 mJ/cm2 or less and printed minimum linewidths of 0.25 μm or smaller under electron‐beam conditions. Under x‐ray exposure, both the resist sensitivity and the contrast are responsive to the processing variables of post‐exposure bake temperature, post‐exposure bake time, developer normality, and developing time. Initial data are presented for Shipley XP‐8933B and several experimental resists to illustrate the major relationships between the listed variables for x‐ray exposure. Under optimum conditions all resists produce minimum linewidths of 0.4 μm or better.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
07.85.-m X- and γ-ray instruments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Aerial image formation in synchrotron‐radiation‐based x‐ray lithography: The whole picture

J. Z. Y. Guo, G. Chen, V. White, P. Anderson, and F. Cerrina

J. Vac. Sci. Technol. B 8, 1551 (1990); http://dx.doi.org/10.1116/1.585114 (6 pages) | Cited 3 times

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The problem of the image formation in a proximity x‐ray lithography (XRL) system has been addressed several times in the past, while a full description of the system has never been implemented for the case of a synchrotron radiation source. It is then necessary to (a) define exactly the properties of source, optical system and mask on the image and (b) correlate the different terms into a common ground. We first discuss the degree of coherence of the synchrotron source in term of the the broadband soft x‐ray spectrum and of the partial degree of coherence of the source (finite size) on the linewidth control and the processing latitude (broadening). The effect of the optical system is fully taken into account. We propose a new image calculation method based on fast Fourier transform. On the basis of the result of the aerial image calculation, we discuss the possibility of using a uniform bias on the mask pattern to improve linewidth control in the submicrometer feature range. The result shows that for printing 0.25‐μm features, the synchrotron‐radiation‐based XRL is an ideal tool when the gap is set correctly and that typical wafer topography can be handled without any problem.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

X‐ray mask repair with focused ion beams

A. Wagner, J. P. Levin, J. L. Mauer, P. G. Blauner, S. J. Kirch, and P. Longo

J. Vac. Sci. Technol. B 8, 1557 (1990); http://dx.doi.org/10.1116/1.585115 (8 pages) | Cited 20 times

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The application of focused ion beams to the repair of defects in x‐ray masks is described. An image of the defective region on the mask is obtained using the ion beam in a manner analogous to a scanning electron microscope. Opaque defects are removed by physical sputtering of extra absorber. Clear defects are repaired by ion‐beam‐induced decomposition of an organometallic compound to form an opaque film on the substrate. Examples illustrating the repair process and demonstrating submicron spatial resolution are presented. The effect of ion channeling on imaging and opaque repair is also described.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

A 100‐nm patterned x‐ray mask technology based on amorphous SiC membranes

A. M. Haghiri‐Gosnet, F. Rousseaux, B. Kebabi, F. R. Ladan, C. Mayeux, A. Madouri, D. Decanini, J. Bourneix, F. Carcenac, H. Launois, B. Wisniewski, E. Gat, and J. Durand

J. Vac. Sci. Technol. B 8, 1565 (1990); http://dx.doi.org/10.1116/1.585116 (5 pages) | Cited 8 times

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