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Nov 1989

Volume 7, Issue 6, pp. 1321-2065


Silicon etching in a direct current glow discharge of CF4/O2 and NF3/O2

H.‐O. Blom, S. Berg, C. Nender, and H. Norström

J. Vac. Sci. Technol. B 7, 1321 (1989); http://dx.doi.org/10.1116/1.584532 (4 pages) | Cited 1 time

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The effect of adding oxygen to a dc discharge containing CF4 and NF3, when etching polysilicon, have been studied. It is shown that the increase in atomic fluorine concentration observed in rf discharges is absent in the measurements performed in a dc discharge. This is probably due to the inefficient dissociation of the gas molecules in a dc discharge. This indicates that oxidation reactions in the gas phase are limited. In the dc discharge it is possible to separate several mechanisms that act on the silicon surface. In the case of CF4, the added oxygen helps in keeping the silicon surface clean from polymer formation. This results in an observed maximum in etching rate and yield. For NF3 there is no need for a ‘‘cleaning’’ of the silicon surface. The rate and yield decreases monotonically for increasing oxygen concentrations.
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81.65.-b Surface treatments
52.80.Hc Glow; corona
52.40.Hf Plasma-material interactions; boundary layer effects

An investigation of the roughening of silicon(100) surfaces in Cl2 reactive ion etching plasmas by in situ ellipsometry and quadrupole mass spectrometry

D. J. Thomas, P. Southworth, M. C. Flowers, and R. Greef

J. Vac. Sci. Technol. B 7, 1325 (1989); http://dx.doi.org/10.1116/1.584533 (8 pages) | Cited 10 times

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The conditions which cause silicon roughening in Cl2 RIE plasmas are investigated. In situ ellipsometry provides a quantitative interpretation of the extent and nature of the roughening process, while mass spectrometry yields complementary information regarding the composition of the plasma. The degree of roughening is reproducible when base pressures are ≊10−5 Torr but is strongly dependent on the rf power and process pressure. Careful selection of these parameters (50 W, 100 mTorr) retains a smooth silicon surface and gradually smooths those which have been roughened. Water vapor has a very significant effect on the etching reactions. In low concentrations it induces roughening and in high concentrations it prevents any etching of silicon. We suggest that silicon oxide micromasks are not responsible for roughening. Instead we propose that hydroxyl (SiOH) groups are the more likely masking species. Roughening of silicon is efficiently prevented when the wafer is patterned with positive photoresist. It is possible that CClx (x=1–4) species can remove the micromasks to retain a smooth surface.
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81.65.-b Surface treatments
52.40.Hf Plasma-material interactions; boundary layer effects

Fabrication and characterization of Si‐coupled superconducting field effect transistors with 0.1 μm gate

Mutsuko Hatano, Fumio Murai, Toshikazu Nishino, Haruhiro Hasegawa, Tokuo Kure, and Ushio Kawabe

J. Vac. Sci. Technol. B 7, 1333 (1989); http://dx.doi.org/10.1116/1.584534 (5 pages) | Cited 4 times

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A 0.1‐μm‐gate‐length superconducting field effect transistor (FET) with a coplanar structure is realized by a self‐aligned fabrication process using electron beam lithography. A T‐shaped gate structure with an insulated sidewall makes it possible to form the spacing between the superconducting source and drain electrodes to be <0.15 μm without causing an electrical short. The characteristics of this FET measured at 4.2 K indicate that the superconducting current and normal‐state resistance can be successfully controlled by the applied gate bias.
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85.30.Tv Field effect devices
85.25.-j Superconducting devices
85.40.Hp Lithography, masks and pattern transfer

Low‐temperature highly preferred polycrystalline Si film growth on crystallized amorphous Si by reactive ion beam deposition

Hiroshi Yamada

J. Vac. Sci. Technol. B 7, 1338 (1989); http://dx.doi.org/10.1116/1.584535 (7 pages) | Cited 2 times

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Highly preferred polycrystalline Si (polysilicon) film growth on amorphous Si with ion‐assisted crystallization by reactive ion beam deposition (RIBD) at the low temperature of 550 °C was investigated. This method uses low‐energy controlled ionized species produced from electron‐cyclotron‐resonance plasma. To achieve highly preferred polysilicon film growth, a new growth process using ion‐assisted crystallization was developed as follows: After a thin amorphous Si film was deposited on an amorphous substrate at 100–150 °C and 100 eV by RIBD using SiH4, it was crystallized at 550 °C by 400‐eV H+ and H+2 irradiation using the same RIBD system. Then, a polysilicon film was grown at the same temperature and 100 eV by RIBD using SiH4. Polysilicon films grown by this process possess stronger Si(220)‐preferred growth orientation and higher Hall mobility than the films grown directly on amorphous substrates.
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81.15.Cd Deposition by sputtering

Silicon oxide deposition from tetraethoxysilane in a radio frequency downstream reactor: Mechanisms and step coverage

Nur Selamoglu, John A. Mucha, Dale E. Ibbotson, and Daniel L. Flamm

J. Vac. Sci. Technol. B 7, 1345 (1989); http://dx.doi.org/10.1116/1.584536 (7 pages) | Cited 33 times

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Isotopic labeling and step coverage studies of silicon oxide deposited from tetraethoxysilane (TEOS) have been carried out by introducing TEOS(16O) downstream from an 18O2 discharge. Rutherford backscattering (RBS) data on films deposited near 440 °C show that, on average, one Si–O bond in the original TEOS molecule is preserved in the process, while mass spectrometric results indicate only H216O and C18O16O as gaseous products of the cleavage of the remaining three Si–O bonds. Infrared analyses of films deposited at room temperature show large amounts of Si–OH in a gel‐like material, and the presence of a CO species. The results suggest a mechanism dominated by diffusion and condensation of Si–OH species that form extensive chains and preserve an Si–16O bond from the original precursor. This is followed by cross‐linking to form the final silicate network; however, Si–O bond cleavage is apparently occurring at potential cross‐linking sites via a carbonate intermediate that promotes isotopic scrambling. Step coverage is shown to be better under conditions (high temperature, low TEOS flow) that favor a low concentration of surface precursors during film growth. This is consistent with the proposed mechanism since second‐order condensation reactions of surface species under these conditions would be kinetically limited allowing effective mean free paths to increase dramatically. Experimental parameters and techniques, such as modulated chemical feeds to enhance the role of surface migration also lead to improved step coverage. However, we also conclude that perfectly conformal coverage based on similar mechanisms will inevitably lead to void formation in high‐aspect‐ratio topography because of transport limitations.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Comparison of etch rates of silicon nitride, silicon dioxide, and polycrystalline silicon upon O2 dilution of CF4 plasmas

Paul E. Riley and David A. Hanson

J. Vac. Sci. Technol. B 7, 1352 (1989); http://dx.doi.org/10.1116/1.584537 (5 pages)

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The etch rates of Si3N4, SiO2, and doped polycrystalline silicon with CF4 plasmas have been examined as a function of O2 dilution and radio frequency (rf) (13.56 MHz) power density at constant residence time (25 mTorr and 25 sccm total process gas flow rate) at 22±2 °C in a batch reactor. At fixed reactor pressure and process gas composition, the etch rates of these materials increase linearly, with different slopes, with increasing rf power density. Under the conditions studied, the etch rates of SiO2 are lower than those of the other two materials and are primarily a function of rf power for CF4 plasmas that are diluted with 0%–25% O2 by flow rate. In comparison, the etch rates of Si3N4 and doped polycrystalline silicon are functions of both rf power density and gas composition, although at each rf power level (200, 300, and 400 W) the Si3N4 etch rate reaches a plateau at an O2 dilution of ∼10%–15% by flow rate. Although the doped polycrystalline silicon etch rate exhibits similar behavior at 200 and 300 W, a steady increase in etch rate is noted at 400 W over the range of O2 dilution examined in this work. At low O2 dilutions, the Si3N4 etch rate is greater than the doped polycrystalline silicon etch rate. However, with increasing O2 dilution, the doped polycrystalline silicon etch rate exceeds the Si3N4 etch rate, with the intersections of these etch rate curves shifting to greater O2 dilution at higher rf power settings.
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81.65.-b Surface treatments
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

A reflection high‐energy electron diffraction study of (100) GaAs vicinal surfaces

S. A. Chalmers, A. C. Gossard, P. M. Petroff, J. M. Gaines, and H. Kroemer

J. Vac. Sci. Technol. B 7, 1357 (1989); http://dx.doi.org/10.1116/1.584538 (6 pages) | Cited 10 times

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The RHEED specular beam profiles produced by GaAs vicinal surfaces are examined and correlated with the surface topography. It is found that the shape of split peaks produced with the incident beam normal to step edges is a measure of surface orientation over lengths on the order of terrace widths, but is not sensitive to short range roughness on the terraces themselves. The profile produced with the incident beam parallel to step edges is sensitive to terrace roughness and can be correlated with RHEED intensity oscillation behavior. It is also found that reconstruction disorder can influence the specular beamwidth.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Density of states of quasi‐two, ‐one, and ‐zero dimensional superlattices

Hung‐Sik Cho and Paul R. Prucnal

J. Vac. Sci. Technol. B 7, 1363 (1989); http://dx.doi.org/10.1116/1.584539 (5 pages) | Cited 3 times

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A formalism is developed using the effective mass approximation to evaluate the density of states of quasi‐two, ‐one, and ‐zero dimensional semiconductor superlattices (QnD SLs). This formalism is applied to GaAs/AlGaAs systems to determine the effect of barrier size on the density of states. The calculated results show that the density of states of QnD SLs evolves from that of QnD structures to that of Q(n+1) D structures with decreasing barrier sizes, where n=0, 1, and 2.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Application of photoacid generating chemistry to photobleachable deep‐ultraviolet resist

Masayuki Endo, Yoshiyuki Tani, Masaru Sasago, Noboru Nomura, and Siddhartha Das

J. Vac. Sci. Technol. B 7, 1368 (1989); http://dx.doi.org/10.1116/1.584540 (4 pages)

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The high optical density of the conventional positive resist in the deep UV region (190 nm to 300 nm) prevents its use in the fabrication of high contrast patterns. The photobleachable deep UV resist composed of a 1,3‐dicarbonyl‐2‐diazo compound as the alkaline dissolution inhibitor and an alkaline‐soluble styrene polymer as the resin matrix, which we developed, is one promising approach to resolve these problems. Using this resist, high contrast 0.5 μm patterns were obtained with a KrF excimer laser stepper. In this paper, we have applied photoacid generators to such photobleachable resists. The photoacid generator used was triphenylsulfonium hexafluoroarsenate, and it greatly enhanced the sensitivity and contrast of the resist. The decomposition of diazo compound in the resist was significantly enhanced (and the dissolution characteristics improved) in the presence of the onium salt. This novel positive resist utilizing chemical amplification more than meets the requirements for KrF excimer laser lithography.
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85.40.Hp Lithography, masks and pattern transfer

Erratum: Use of Raman spectroscopy to characterize strain III–V epilayers: Application to InAs on GaAs(001) grown by molecular‐beam epitaxy [J. Vac. Sci. Technol. B 7, 365 (1989)]

Alain C. Diebold, S. W. Steinhauser, and R. P. Mariella

J. Vac. Sci. Technol. B 7, 1372 (1989); http://dx.doi.org/10.1116/1.584541 (1 page)

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Abstract Unavailable
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68.60.Bs Mechanical and acoustical properties
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
78.30.Fs III-V and II-VI semiconductors
99.10.Cd Errata

Erratum: Effect of disorder on the Al/GaAs(001) interface [J. Vac. Sci. Technol. B 7, 742 (1989)]

S. K. Donner, K. P. Caffey, and Nicholas Winograd

J. Vac. Sci. Technol. B 7, 1372 (1989); http://dx.doi.org/10.1116/1.584542 (1 page)

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Abstract Unavailable
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Nq Composition and phase identification
99.10.Cd Errata

The future costs of semiconductor lithography

Robert W. Hill

J. Vac. Sci. Technol. B 7, 1387 (1989); http://dx.doi.org/10.1116/1.584543 (4 pages) | Cited 2 times

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A method for comparing the costs for photoprocessing high volume semiconductor logic and memory wafers is presented. Industry lithographic trends and process structures are discussed and a cost model is applied. Some typical results obtained with optical tooling and x‐ray synchrotron based lithography are discussed for 1/2 μ ground rules. The model consists of two sections; exposure costs and process costs per level. Both areas are addressed and discussed. Equivalent yield has been assumed for all processes. Normalized results done with the model are presented and discussed. Net conclusions are that photo process costs are as great or greater than the exposure costs, and that x‐ray technology with a synchrotron source becomes competitive with optical technologies for large volume applications because of process simplicity. Optical technologies will continue to be used by many manufacturers because of their lower initial investment and evolutionary nature.
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85.40.Hp Lithography, masks and pattern transfer

Use of two‐dimensional protein crystals from bacteria for nonbiological applications

D. Pum, M. Sára, and U. B. Sleytr

J. Vac. Sci. Technol. B 7, 1391 (1989); http://dx.doi.org/10.1116/1.584544 (7 pages) | Cited 2 times

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This paper gives an overview on the structure, chemistry, self‐assembly, and technical application potentials of crystalline bacterial cell surface layers (S layers). These structures represent ideal model systems for studying self‐assembly processess on the nanometer level. Since S layers reveal no pore size distribution they can be used for the production of a completely new type of ultrafiltration membrane. Chemical modification allows specific adaption of the S‐layer surface either for ultrafiltration purposes or for coating with monolayers of biologically active molecules (e.g., enzymes). As supports for covalent attachment of macromolecules, S‐layer membranes might be usable for specific and rapid determination of substances by enzymatic or immunogenic methods. S‐layer structures can also be used as supports for Langmuir–Blodgett films. Finally it can be expected that as the architecture and function of more complex biological systems, particularly membranes, become better known, novel concepts will influence the design and fabrication of molecular machines and electronic devices.
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87.15.B- Structure of biomolecules
87.10.-e General theory and mathematical aspects
87.16.D- Membranes, bilayers, and vesicles

Nanoelectronics: Fanciful physics or real devices?

J. N. Randall, M. A. Reed, and G. A. Frazier

J. Vac. Sci. Technol. B 7, 1398 (1989); http://dx.doi.org/10.1116/1.584545 (7 pages) | Cited 16 times

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Remarkable advances in microfabrication technology have allowed physicists to probe into the size regime where quantum mechanical effects begin to dominate transport. When 1D conducting wires made from two‐dimensional electron gases (2DEGs) approach the same size as the deBroglie wavelength of electrons, electronic transport is determined by transmission through a small number of ‘‘waveguide modes’’ of the 1D channel. Low temperature experiments in this size regime show significant wavefunction interference effects. A number of devices based upon these physical phenomena have been proposed. Quantum localization has also been explored in perpendicular electronic transport through heteroepitaxial structures, the simplest case being one‐dimensional resonant tunneling structures that exhibit strong quantum interference up to room temperature. Three‐terminal devices that directly modulate this interference have been demonstrated. Ultimate scaling limitations of heterojunction tunneling devices will only be confronted in the limit of three‐dimensional confinement, i.e., ‘‘quantum dots.’’ The implementation of these discrete electronic state structures in a quantum IC architecture will be discussed.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
73.20.Fz Weak or Anderson localization

Electron beam lithography: Its applications

F. J. Hohn

J. Vac. Sci. Technol. B 7, 1405 (1989); http://dx.doi.org/10.1116/1.584546 (7 pages) | Cited 6 times

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This paper addresses the various aspects of e‐beam lithography as they relate to device fabrication at and below 0.25 μm. These dimensions will eventually be necessary for the fabrication of 256 MB DRAM chips. It is important to evaluate how key components in lithography have to be integrated to provide this necessary early learning. E‐beam lithography tools today may consist of Gaussian round and variable shape beam systems. The understanding of the performance of the tool goes hand in hand with directly related issues such as electron‐resist interaction, proximity effect correction, etc. Since each of these parameters can be optimized independently, but not simultaneously as a complete set, tradeoffs will have to be made. The discussion will therefore focus on compromises between critical issues such as beam profile, throughput, image quality, process latitude, degree of accuracy in proximity effect correction, and overall process engineering for very high resolution lithography. All of these aspects are strategically important components in support of device technology research. The implementation of an ‘‘integrated e‐beam lithography’’ operation as it relates to fully scaled and partially scaled device programs will be discussed. Current work on device fabrication below 0.25 μm demonstrates the capability of integration of all sectors of e‐beam lithography to provide early research work for ULSI device technology.
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85.40.Hp Lithography, masks and pattern transfer

Nanometer X–Y positioning stages for scanning and stepping

Anwar Chitayat

J. Vac. Sci. Technol. B 7, 1412 (1989); http://dx.doi.org/10.1116/1.584547 (6 pages) | Cited 2 times

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This paper describes new developments in X–Y stages for scanning or stepping and use in vacuum. The requirement for high dynamic stiffness is analyzed as to its effects on positioning accuracy in dynamically moving stages (scanning) and on settling time for stepping applications. Novel solutions are described to increase the accuracy and stability of the X–Y stages to perform in the nanometer range: (1) the use of piezoelectric locking systems to directly lock the product to the beam producing source (to reduce vibration to the subnanometer level), (2) through‐the‐chamber wall linear motor drives, where the X–Y stages are located inside the vacuum chamber and linear motor drives are located outside the vacuum chamber, (3) the use of low friction ways with a mirror surface finish so that high smoothness and extremely constant velocity is achieved, and (4) how the combination of these new techniques has resulted in practical systems for nanometer fabrication and inspection.
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06.60.Sx Positioning and alignment; manipulating, remote handling

Piezo locking stage for nanometer electron‐beam lithography

E. Kratschmer, S. A. Rishton, H. E. Luhn, D. P. Kern, and T. H. P. Chang

J. Vac. Sci. Technol. B 7, 1418 (1989); http://dx.doi.org/10.1116/1.584548 (4 pages)

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A piezo‐actuated locking stage is described, which minimizes stage mechanical vibrations relative to the column in a nanometer electron beam lithography system capable of using large 5‐in. diameter substrates. The performance of the piezo locking stage is compared to the performance of a laser position servo system with a resolution of about 5 nm. The measurements show that mechanically locking the stage with respect to the objective lens is far more effective than the servo loop in suppressing mechanical vibrations. With the stage locked, total beam position noise with respect to the substrate has been measured as 2.5‐nm peak‐to‐peak compared to 10‐nm peak‐to‐peak total noise for the servo loop within a bandwidth of 0.25 to 200 Hz. A more detailed analysis of the beam position noise shows that the piezo locking stage reduces the noise component which is caused by mechanical vibrations to 0.4‐nm rms.
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85.40.Hp Lithography, masks and pattern transfer

A 1:1 electron stepper

A. Delong and V. Kolar̆ík

J. Vac. Sci. Technol. B 7, 1422 (1989); http://dx.doi.org/10.1116/1.584549 (4 pages) | Cited 3 times

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A new approach to the design of a 1:1 electron stepper has been suggested. A metal‐insulator–metal (MIM) cathode is used in place of the photoemission one. The mechanism of the electron emission from the MIM cathode is markedly different from that of photoemission. In the MIM cathode the electrons from the base metal layer move through the thin dielectric layer, in which a strong electric field is generated (about 7×108 V m−1), into the outer thin metal layer. Those electrons that have enough energy remaining after scattering in the dielectric and outer thin metal layer (to overcome the work function barrier of the outer metal layer) will escape into the vacuum. Compared to photoemission, the described mechanism has some advantages if considered for use in electron projection lithography. For example, an emission current density of the order of 10−4 A cm−2; the cathode can be easily and quickly switched on and off with the image of the mask and independently of the orientation marks; and finally, the possibility of preparing cathodes outside the vacuum chamber of the stepper and their storing. To verify the advantages of the MIM cathode and experimental 1:1 electron stepper has been constructed and orientation experiments have been evaluated.
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85.40.Hp Lithography, masks and pattern transfer
73.40.Rw Metal-insulator-metal structures

Advanced direct write electron beam lithography for GaAs monolithic microwave integrated circuit production

L. K. Hanes and A. Morris

J. Vac. Sci. Technol. B 7, 1426 (1989); http://dx.doi.org/10.1116/1.584550 (5 pages)

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Direct write electron beam lithography has been used for several years to pattern submicrometer and sub‐half‐micrometer gates for GaAs monolithic microwave integrated circuit (MMIC) devices. The e‐beam systems used at this process step have generally been vector scan Gaussian beam machines operated in a step and write exposure mode. These systems have very low throughput and are better suited to research and development environments than large volume production. In order to meet the production requirements at the new Raytheon Monolithic Microwave Center, we have sought to adapt the Perkin–Elmer advanced electron beam lithography equipment (AEBLE)‐150 system for use on GaAs. Results of early usage of the AEBLE system for direct write GaAs will be presented. Eightfold improvement in throughput for typical MMIC devices compared to results obtained on an earlier model e‐beam machine will be shown. Both metalized (by liftoff) and etched alignment markers have been used; alignment strategy and a comparison of these alignment marks will be discussed. Results from the AEBLE demonstrating sub‐half‐micrometer lighography on GaAs will be presented. System issues related to handling GaAs wafers and areas in need of improvement will be briefly discussed.
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85.40.Hp Lithography, masks and pattern transfer

Detection of low‐contrast fiducial marks for electron beam direct write

J. G. Garofalo and R. L. Kostelak

J. Vac. Sci. Technol. B 7, 1431 (1989); http://dx.doi.org/10.1116/1.584551 (7 pages)

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Precise registration to substrate fiducial marks is crucial to high density, fine‐line device fabrication. Mark detectability is a function of both the mark contrast with respect to its surrounding substrate and also its interior topography. Since the accuracy and speed of detection of any scheme is related to the signal‐to‐noise ratio (SNR) of the mark image presented to the detection filter, one is compelled to develop higher contrast marks in order to enhance the effective SNR and thereby keep pace with the more stringent registration requirements of today’s processes. Unfortunately, some higher contrast marks, being developed by more advanced processes, are characterized by a rather severe interior topography. Standard edge detectors are hampered by the apparent interior ‘‘edges’’ of such marks. Another complication arises from the pulsed type data acquisition scheme used on the AT&T in‐house EBES4 system that demands high bandwidth detection electronics. This prohibits the reduction of the detection noise power spectral density by low‐pass filtering operations. While this acquisition architecture has the potential for accurate mark location with little electron beam induced mark degradation or errors due to charging, the detection filter must cope with a relatively strong noise energy content. To register to both low contrast and moderate contrast ‘‘rough terrain’’ marks under these circumstances, a two‐stage matched filter has been developed. This variant of the standard matched filter was designed to improve its edge localization characteristics. The approach incorporates computationally intensive signal processing algorithms executed on special purpose hardware. Our detection system consists of a custom digitizer that feeds a VMEbus based array processor. The digitizer is equipped with a large, fast memory buffer so that scan data may be processed as a new scan is being acquired. This parallelism results in detection times commensurate with high throughput. Detection accuracy from chrome marks has been investigated using three detection techniques. Optimum ‘‘‖mean‖+3σ’’ overlay errors of ≤0.06 μm were achieved by utilizing the two‐stage filter.
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85.40.Hp Lithography, masks and pattern transfer

A fast Monte Carlo beam simulator using exact Coulomb scattering

Vernon Beck, Michael Gordon, and Timothy Groves

J. Vac. Sci. Technol. B 7, 1438 (1989); http://dx.doi.org/10.1116/1.584552 (5 pages) | Cited 2 times

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The space charge interaction in a beam can be approximated by summing the scattering between all possible pairs of electrons in the beam. An efficient algorithm is presented for the exact solution to the two‐body Coulomb scattering problem. This algorithm is incorporated into a Monte Carlo program to simulate the effects of space charge in electron‐beam lithography systems. The results of this algorithm are compared to those obtained using a numerical integration of the Coulomb interaction for the N‐body problem. We demonstrate that this approach accurately models the detailed physics for beam currents common to many state‐of‐the‐art e‐beam lithography systems.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Electron‐beam proximity printing of half‐micron devices

K. Meissner, W. Haug, S. Silverman, and S. Sonchik

J. Vac. Sci. Technol. B 7, 1443 (1989); http://dx.doi.org/10.1116/1.584553 (5 pages)

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Electron‐beam proximity printing (EBP), a lithographic shadow projection method, has demonstrated the capability to print structures with dimensions below 0.5 μm, to achieve level‐to‐level overlay better than 50 nm (1σ) and to perform with very high throughput. Four sequential EBP mask levels have been exposed and functional n‐type metal–oxide semiconductor (NMOS) devices have been produced. This paper describes the overall process as well as the operation of the EBP tool. It presents process and lithography data for these devices and shows that the overlay capability exceeds the requirements for half‐micron ground rules. EBP has the unique capability to continuously change the direction of the electron beam and so to laterally displace the image of mask structures on the wafer. This feature makes it possible to correct distortions of the IC pattern in the mask (e.g., magnification, rotation, higher‐order distortions) to adapt a new pattern level to one former level already on the wafer and to achieve a fast precise pattern alignment independent of the precision of the stage step. The achievable level‐to‐level overlay was predicted through both calculation of the mask and tool dependent errors and simulation of the EBP correction feature. This theoretical result was confirmed with experimental data from the processed half‐micron devices. Both the theoretical prediction and the method to measure the level‐to‐level overlay will be described.
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85.40.Hp Lithography, masks and pattern transfer

Optimized eight‐inch extraction system for reactive ion beam etching

D. Korzec and J. Engemann

J. Vac. Sci. Technol. B 7, 1448 (1989); http://dx.doi.org/10.1116/1.584510 (6 pages) | Cited 2 times

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A methodology of ion extraction system optimization is proposed, taking into account the influence of the ion density variation in plasma at the plasma sheath. Software tools for extraction grids design and machining have been developed, allowing compensation for the current, divergence, and deflection of a single beamlets. Simulation was used to predict the properties of the three‐grid single beamlet. The measurement of the radial ion saturation current density distribution in plasma using a double Langmuir probe for an axial magnetic field up to 16 mT, vacuum chamber pressure ranging from 4×10−5 to 2×10−3 and rf power from 100 to 900 W has been performed. These distributions were used to calculate the grid compensation functions. An extraction system was optimized for the reference magnetic field in the air coil B=7.20 mT, vacuum chamber pressure p=2.0×10−4 mbar, rf power Prf=500 W, and net acceleration voltage Vnet=300 V with argon as a working gas. The ion current density distributions for optimized and nonoptimized extraction systems have been measured and compared with predictions of the model. A maximum detectable variation in the ion current density across the 8 in. target can be reduced to < 3%.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative

Maskless selected area processing

G. W. Rubloff

J. Vac. Sci. Technol. B 7, 1454 (1989); http://dx.doi.org/10.1116/1.584511 (8 pages) | Cited 3 times

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Although conventional (mask‐based) lithography will continue to dominate selected area processing in microelectronics, two approaches aimed at ‘‘maskless’’ patterning are playing major roles in applications and in research. (i) Self‐aligned processes add (or modify) material in simple spatial relation to an already existing pattern, based on selective surface chemistry or topographic structure. Because they simplify processing by eliminating lithography steps, self‐aligned processes are already exploited whenever possible. (ii) Direct beam processes can be used to deposit, etch, or modify material as needed, either by scanning of microbeams or projection of broad, patterned beams of photons, ions, or electrons, and a diverse set of support and special applications has been identified. Broader applications of maskless processing may arise from combinations of self‐aligned and direct beam processes, motivated in part by the advantages of in situ, integrated, dry/vacuum processing, but progress is dependent on better understanding and control of underlying chemistry and physics in order to achieve high quality materials and structures.
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85.40.Hp Lithography, masks and pattern transfer

Comparison of damage in the dry etching of GaAs by conventional reactive ion etching and by reactive ion etching with an electron cyclotron resonance generated plasma

R. Cheung, Y. H. Lee, K. Y. Lee, T. P. Smith, D. P. Kern, S. P. Beaumont, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 7, 1462 (1989); http://dx.doi.org/10.1116/1.584512 (5 pages) | Cited 9 times

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We have developed a high‐resolution etch for GaAs in an electron cyclotron resonance‐radio frequency (ECR‐rf) hybrid reactor using CCl2F2/He as the etch gas. Surface contamination from the gas and from the electrodes was found to affect the etching process as well as etched substrate. Surface damage studies using Schottky diode and x‐ray photoelectron spectroscopy analysis and sidewall damage characterization using room‐temperature conductance measurements of n+‐GaAs quantum wires indicate that very little damage is caused by ECR‐rf reactive ion etching compared with conventional rf reactive ion etching (RIE). In addition, the small residual damage after ECR‐rf RIE is measured to increase with etching time.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

A focused ion beam vacuum lithography process compatible with gas source molecular beam epitaxy

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

J. Vac. Sci. Technol. B 7, 1467 (1989); http://dx.doi.org/10.1116/1.584513 (4 pages) | Cited 14 times

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We demonstrate a direct‐write lithography process for InP wafers in which a finely focused Ga+ ion beam is used to form the pattern which is then transferred into the substrate by dry etching. The result is a patterned substrate which is suitable for epitaxial growth. We have combined the ion beam writing and dry etching in a common vacuum chamber with a gas source molecular beam epitaxy (GSMBE) system. GaInAs/InP heterostructures grown on the in situ patterned substrates show excellent morphology and high luminescence efficiency. Surface relief on the order of 1000–2000 Å has been produced with this process using a 20 keV Ga+ ion beam. Lateral resolution is limited by the ion beam diameter, 2000 Å.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Etching of GaAs for patterning by irradiation with an electron beam and Cl2 molecules

K. Akita, M. Taneya, Y. Sugimoto, H. Hidaka, and Y. Katayama

J. Vac. Sci. Technol. B 7, 1471 (1989); http://dx.doi.org/10.1116/1.584514 (4 pages) | Cited 12 times

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Etching of GaAs for patterning by an electron beam (EB) and Cl2 molecules is described. When a GaAs substrate is exposed to a 10 keV EB and Cl2 molecules, etching of GaAs is observed only in the EB‐scanned area. Etch rates are obtained as a function of substrate temperature. Morphologies of the etched surface are rather smooth and the photoluminescence intensity indicates that this etching process introduces much less damage to the sample than some processes using ions.
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81.65.-b Surface treatments

Energy dependence and depth distribution of dry etching‐induced damage in III/V semiconductor heterostructures

R. Germann, A. Forchel, M. Bresch, and H. P. Meier

J. Vac. Sci. Technol. B 7, 1475 (1989); http://dx.doi.org/10.1116/1.584515 (4 pages) | Cited 32 times

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We have investigated the depth distribution, energy dependence, and the effect of the angle of incidence of ion beam etching (IBE) induced damage. Our technique is based on the partial etching of the upper GaAlAs barrier of a GaAs single quantum well (SQW) layer. The optical emission of the SQW at low temperatures is used as a local probe for the created damage. The dependence of the quantum efficiency on the etch depth can be described by a Gaussian depth distribution with a typical decay length of 5.6 nm and a non‐Gaussian long range tail. Our measurements show a strong dependence of the dry etch damage on the angle of incidence of the ion beam and on the sample orientation.
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61.80.Jh Ion radiation effects
85.40.Hp Lithography, masks and pattern transfer

Selective metalorganic reactive ion etching of molecular‐beam epitaxy GaAs/AlxGa1−xAs

V. J. Law, G. A. C. Jones, D. A. Ritchie, D. C. Peacock, and J. E. F. Frost

J. Vac. Sci. Technol. B 7, 1479 (1989); http://dx.doi.org/10.1116/1.584516 (4 pages) | Cited 6 times

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We report on a metalorganic reactive‐ion etch (MORIE) methane and hydrogen process for the selective etching of GaAs, AlxGa1−xAs and GaAs/AlxGa1−xAs heterostructures, grown by molecular‐beam epitaxy (MBE). Etch rates, degree of selectivity, and loading effects are examined as a function of aluminium mole fraction(x=0.0–1.0), gas flow rates, pressure, and applied rf power. The etch process employs a specially prepared positive photoresist which can withstand high rf powers (1.1 W cm−2) with plasma potentials of −600 Vdc at 1.3 Pa and prolonged etch times (> 200 min) with little mask erosion, while maintaining a high degree of anisotropy in the etch process. The etch rate ratio of GaAs over AlxGa1−xAs is shown to be a strong function of the methane molecular concentration and by selecting a high methane flow rate, i.e., a low chamber residence time, favorable etch rate ratios are obtained. AlxGa1−xAs layers can either be etched through or an etch‐stop achieved, before the onset of plasma polymerisation. This process has been successfully used for etching micron and submicron size mesas and GaAs/AlxGa1−xAs heterostructures, with linear etch rates (Ro) of up to 45 nm min−1 to a depth of 7 μm for GaAs and 0–10 nm min−1 for Al0.3Ga0.7As, depending upon the plasma conditions used.
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81.65.-b Surface treatments

The influence of ion scattering on dry etch profiles

J. Pelka, M. Weiss, W. Hoppe, and D. Mewes

J. Vac. Sci. Technol. B 7, 1483 (1989); http://dx.doi.org/10.1116/1.584517 (5 pages) | Cited 9 times

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A simulation study is presented using a new version of the simulation program ADEPT (advanced simulation of dry‐etching process technology), which is a subset of the process simulator COMPOSITE. Based on some aspects of plasma physics, a model was developed that allows for the calculation of important properties of a collisional sheath by Monte Carlo methods. These properties have great influence on the anisotropy of dry‐etch processes. Angle/energy spectra of ions and fast neutrals can be gained from the model and can be used as input data for profile simulation. A simulation study is presented showing several profile phenomena. A short discussion is included on sidewall protection by polymer deposition, and on surface diffusion.
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81.65.-b Surface treatments
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Kinetic theory of bombardment induced interface evolution

Charles W. Jurgensen and Eric S. G. Shaqfeh

J. Vac. Sci. Technol. B 7, 1488 (1989); http://dx.doi.org/10.1116/1.584518 (5 pages) | Cited 7 times

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An interface evolution equation has been formulated to describe bombardment‐induced etching by an axisymmetric angular distribution of energetic particles where the yield per incident particle is assumed to be a function of its energy and its angle relative to the surface normal. These assumptions result in a nonlinear integro differential equation, but this equation reduces to a partial differential equation in several important special cases. At points that are not shadowed by a remote part of the surface, the interface evolution equation reduces to a nonlinear hyperbolic conservation law. Such equations have been applied to bombardment‐induced etching by a monodirectional beam with angle‐dependent yields; however, this form of equation applies more generally to raised isolated convex regions (e.g., etching masks) regardless of the angular distribution of the incident particles or the angle dependence of the yield. The essential qualitative feature of the solution in these cases is the spontaneous evolution of facet edges (slope discontinuities) from smooth initial conditions. Shadowing by remote parts of the surface may occur in concave regions (e.g., trenches) where it results in proximity effects.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Selective reactive ion etching for short‐gate‐length GaAs/AlGaAs/InGaAs pseudomorphic modulation‐doped field‐effect transistors

A. A. Ketterson, E. Andideh, I. Adesida, T. L. Brock, J. Baillargeon, J. Laskar, K. Y. Cheng, and J. Kolodzey

J. Vac. Sci. Technol. B 7, 1493 (1989); http://dx.doi.org/10.1116/1.584519 (4 pages) | Cited 4 times

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Selective reactive ion etching of GaAs on AlGaAs in SiCl4/SiF4 plasma is reported. A selectivity ratio of 350:1 has been obtained at low power. A small decrease in the saturation current of gateless MODFET structures has been observed after etching the GaAs cap layer and has been ascribed to be due to low‐power ion damage of the AlGaAs layer. This process was applied to the fabrication of 0.2 μm T‐gate pseudomorphic MODFET’s. The dc and microwave performance of reactive‐ion‐etched devices and wet‐etched devices were identical. However, for these short‐gate‐length devices a threshold voltage standard deviation of 30 mV was obtained for the reactive‐ion‐etched devices as compared to 230 mV for the wet‐etched devices.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Effects of chromium on the reactive ion etching of steep‐walled trenches in silicon

N. I. Maluf, S. Y. Chou, J. P. McVittie, S. W. J. Kuan, D. R. Allee, and R. F. W. Pease

J. Vac. Sci. Technol. B 7, 1497 (1989); http://dx.doi.org/10.1116/1.584520 (5 pages) | Cited 6 times

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Formation of vertical‐walled, high‐aspect‐ratio, narrow trenches in silicon is often required in submicron VLSI semiconductor processing. Present trench etching processes suffer from undercutting of the mask and sloped or bulged sidewalls; and when using chlorine‐based reactive ion etching (RIE), there is frequently enhanced etching at the bottom corners of the trench. We report here the effects of chromium on the RIE of silicon. We found that, compared to using a SiO2 mask only, using a mask consisting of a chromium layer on top of SiO2, in a Cl2:SiCl4:N2 etching gas mixture, improves the trench sidewall angle relative to the vertical from 8° to 2°, and almost eliminates the enhanced etching at the bottom corners. Furthermore, we found that, by etching a sample partially covered with chromium in a Cl2:SiCl4:N2 gas mixture, the trench shape in the areas not covered with chromium depends on how far the trench is from the edge of the chromium layer. Those areas, within 1 cm of the edge of the chromium layer, showed quite steep sidewall angles that degraded (to 8°) at greater distances (few cm). Similarly, the size of the grooves due to the enhanced etching at the bottom corners is reduced as the trench gets closer to the edge of the chromium layer. It appears that the beneficial effect of the chromium is an indirect chemical action, based on the suppression of the concentration of neutrals or the formation of an inhibitor layer, rather than direct physical masking.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Thermal distribution and the effect on resist sensitivity in electron‐beam direct write

Nicholas K. Eib and Richard J. Kvitek

J. Vac. Sci. Technol. B 7, 1502 (1989); http://dx.doi.org/10.1116/1.584521 (5 pages) | Cited 7 times

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Thermal sensitivity measurements of diazoquinone/novolac (DQN), poly‐olefin sulfone/novolac (SNS), and an acid catalyzed/proprietary resin (XPR) were made by gently exposing coated wafers at 10−9 amp/cm2 on a cooled/heated stage in our e‐beam exposure tool. The results were characterized by the influence of exposure temperature on blanket‐exposure‐dissolution rates and developed image profiles. Three‐dimensional Monte Carlo absorbed‐energy‐density calculations have been combined with ANSYS finite‐element‐thermal analysis to estimate the time evolution of temperature profiles on silicon wafers, silicon membranes, and SiO2 wafers at 50 keV. Lithographic modeling system (LMS) has then combined the predicted thermal fronts with the experimentally measured resist response to predict the effects on image profiles. Thermal proximity effects in 2 μm wide lines are negligible on Si wafers, 3–5% on Si membranes, and two to three times worse on SiO2 substrates.
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85.40.Hp Lithography, masks and pattern transfer
81.40.Rs Electrical and magnetic properties related to treatment conditions

Proximity correction for electron beam lithography using a three‐Gaussian model of the electron energy distribution

S. J. Wind, M. G. Rosenfield, G. Pepper, W. W. Molzen, and P. D. Gerber

J. Vac. Sci. Technol. B 7, 1507 (1989); http://dx.doi.org/10.1116/1.584522 (6 pages) | Cited 10 times

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Accurate proximity correction has proven essential for the patterning of submicron features using electron beam lithography. The use of a two‐Gaussian model, which accounts for the finite beam size and forward scattering in the resist as well as backscattering, has demonstrated widespread success. It has been shown, however, that in certain instances, such as for features of order 100 nm or less or for exposure on high atomic number substrates, the two‐Gaussian expression is unable to adequately fit the absorbed energy distribution in the resist. Suggested modifications, such as the addition of a third Gaussian term to account for large angle electron scattering, or the inclusion of an exponential term which may account for an increased absorption rate in high Z materials, have resulted in improved fits. This paper describes a study to determine the improvement gained in exposed features by including additional Gaussian terms in the expression for the absorbed energy distribution in the resist. A very high resolution probe (beam diameter ∼20 nm FWHM) is used so that forward scattering effects in the resist may be separated from the primary beam distribution. PMMA is exposed on Si and GaAs substrates at 25 keV using proximity correction parameters generated by curvefitting the three‐Gaussian model and the two‐Gaussian model to the absorbed energy distributions. The three‐Gaussian model is seen to provide improved proximity correction particularly in the 100 nm size scale.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Hp Lithography, masks and pattern transfer

A program for Monte Carlo simulation of electron energy loss in nanostructures

S. Johnson and N. C. MacDonald

J. Vac. Sci. Technol. B 7, 1513 (1989); http://dx.doi.org/10.1116/1.584523 (6 pages) | Cited 1 time

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A Monte Carlo program named simulation of electron energy loss (SEEL) has been developed to simulate electron trajectories in submicron scale electronic structures. The accuracy of the program at low energies is investigated, and the simulation techniques described. The backscattered electron energy spectra have been taken for Au and Al using an Auger electron spectrometer with a cylindrical mirror energy analyzer. For a beam energy of 1.5 keV, simulated electron energy distributions follow the experimental distributions down to 0.1 keV, showing relatively good agreement with experimental results at low electron energies.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Conducting polyanilines: Discharge layers for electron‐beam lithography

Marie Angelopoulos, Jane M. Shaw, Richard D. Kaplan, and Stanley Perreault

J. Vac. Sci. Technol. B 7, 1519 (1989); http://dx.doi.org/10.1116/1.584524 (5 pages) | Cited 11 times

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This paper describes the use of electrically conducting polyanilines as discharge layers for electron‐beam (e‐beam) lithography. The emeraldine oxidation state polyaniline is a soluble material which can be doped by various cationic reagents, most commonly protonic acids, to afford conductivity on the order of 10° Ω−1 cm−1. The conducting polyanilines are incorporated as thin interlayers (2000 Å) in a multilayer resist system consisting of a planarizing underlayer (2.8 μm) and the imaging resist (1.2 μm) on top. We find that various acid‐treated polyanilines eliminate charging during e‐beam patterning of the resist, i.e., zero pattern displacements are observed as compared to the case where a conducting interlayer is not incorporated into the resist system. In the latter case placement errors greater than 5 μm are observed as a result of charging. A minimum conductivity of 10−4 Ω−1 cm−1 is required for the polyaniline interlayers in order to observe zero pattern displacement. In addition, we have simplified the doping reaction for polyaniline by inducing the conductivity photochemically or by e‐beam exposure with the use of onium salts. This process resulted in the development of a new photo and e‐beam conducting resist material.
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85.40.Hp Lithography, masks and pattern transfer

Proximity effect correction for an electron beam direct writing system EX‐7

Takayuki Abe, Naotaka Ikeda, Hideo Kusakabe, Ryoichi Yoshikawa, and Tadahiro Takigawa

J. Vac. Sci. Technol. B 7, 1524 (1989); http://dx.doi.org/10.1116/1.584525 (4 pages)

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A new proximity effect correction software system has been developed, which is characterized by the usage of an approximate correction dose formula. The arrayed shot method was developed and a hierarchical data format was used to compact the amount of EB data. An inversion method has also been developed and a hierarchical pattern layout structure was used to accelerate the correction calculation speed. The proximity effect correction system has been installed into a high voltage electron beam direct writing system EX‐7 and has been applied to some LSI patterns. The calculation time for correction was about 0.7 h for a 4 MDRAM and about 1 h for a 20 k gate array by using a 14 MIPS computer. The amount of EB data was about 40 Mbytes for the DRAM and about 50 Mbytes for the gate array.
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85.40.Hp Lithography, masks and pattern transfer

High‐performance electron beam lithography for 0.5 μm semiconductor device fabrication

T. Sakashita, N. Nomura, K. Hashimoto, T. Koizumi, K. Harafuji, A. Misaka, N. Sawada, and K. Kawakita

J. Vac. Sci. Technol. B 7, 1528 (1989); http://dx.doi.org/10.1116/1.584526 (4 pages)

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High‐performance electron beam (e‐beam) lithography is applied for fabricating contact holes with submicron size, using a new trilayer resist process. This technology consists of proximity effect correction software and the H+ ion shower irradiation technique onto a trilayer resist. The proximity effect correction software based on a dose modulation method was developed to control the dimensional accuracy of submicron patterns, by using the calculation of the double Gaussian exposure intensity distribution (EID) function. The dimensional accuracy of 0.5 μm contact hole and line and space patterns were kept within 0.05 μm. The H+ ion shower irradiation technique was adopted to decrease the charging problem. Ion shower was irradiated onto the bottom layer of the trilayer resist at 40 keV, 1×1016 ions/cm2. The sheet resistance of the bottom layer resist was decreased from 1013 Ω/ to 107 Ω/ by the H+ ion shower irradiation. The field butting error due to the charging problem was improved to 0.1 μm/3σ, and also the overlay accuracy was improved to 0.12 μm/3σ. When this high performance e‐beam lithography was applied to fabricate 0.5 μm size contact holes, the yield of the 106 contact hole chains was improved to 90% by using selectively deposited W film on the bottom of the contact holes.
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85.40.Hp Lithography, masks and pattern transfer

Investigation of the charging effect on thin SiO2 layers with the electron beam lithography system

Hiroyuki Itoh, Kazumitsu Nakamura, and Hajime Hayakawa

J. Vac. Sci. Technol. B 7, 1532 (1989); http://dx.doi.org/10.1116/1.584527 (4 pages) | Cited 3 times

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The charging problem of a dielectric layer during direct exposure with an electron beam lithography system is investigated. Electron beam irradiation on a wafer with a dielectric layer such as SiO2 often causes charge buildup. This excessive accumulation of charge on the sample disturbs placement accuracy, and results in overlay errors. In order to analyze this charging problem, a metrology software package is used to measure the placement error of the exposed patterns on a target plane. Tested sample wafers are deposited with 0.2–1.5 μm SiO2, and then coated with 1 μm resist for exposure. To evaluate the charging dependence on electron beam current, a variable‐shaped electron beam lithography system which can easily change beam current is used. The results indicate that nongrounding 0.2 and 0.5 μm SiO2 do not show charge‐induced placement errors while 1 and 1.5 μm SiO2 show a definite placement error due to charging. On 1.5 μm Sio2 results indicate an electrostatic breakdown of SiO2, and no charging error is observed after breakdown. These pattern distortions due to charging are evaluated by a statistical analysis, and they are approximated by a simplified equation. To prevent charging, a mechanical contact with the substrate has proven to be effective. This grounding method, using a conductive diamond tip, shows excellent grounding ability.
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85.40.Hp Lithography, masks and pattern transfer

Charging effects from electron beam lithography

K. D. Cummings and M. Kiersh

J. Vac. Sci. Technol. B 7, 1536 (1989); http://dx.doi.org/10.1116/1.584528 (4 pages) | Cited 9 times

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This paper discusses initial results from a study of pattern placement errors due to substrate charging in fixed spot direct write electron beam systems. Experimental results obtained from small crosses written with 20 keV electrons near large pads indicate charging‐induced errors of 0.2 μm can occur over 1 mm away from the pad. We present a simple theory that describes the placement errors for large cross‐pad separations. The theory suggests that the substrate–electron interaction is strong and long range. Finally, we give some insights on how 50 keV electrons effectively reduce charging effects.
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85.40.Hp Lithography, masks and pattern transfer

Simulation of electron beam exposure of submicron patterns

Jo A. McMillan, Sylvester Johnson, and Noel C. MacDonald

J. Vac. Sci. Technol. B 7, 1540 (1989); http://dx.doi.org/10.1116/1.584529 (6 pages) | Cited 2 times

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Analytical and Monte Carlo electron beam radial exposure distributions (REDs) are compared for accuracy in predicting proximity effects in submicron lithographic patterns. A proximity effect simulation tool (PRESTO) has been developed to convolve the desired pattern with the RED obtained from a companion Monte Carlo program for the simulation of electron energy loss (SEEL) or an empirical RED which is an analytical fit to experimental results. Together, SEEL and PRESTO are shown to simulate the electron beam exposure of submicron size patterns using a focused Gaussian electron beam system. PRESTO generates the electron distribution for the pattern by simulating the exposure of the resist for each pixel. Once the energy distribution has been determined equienergy density contours for the exposure of a given shape can be plotted. The ability of PRESTO and SEEL to accurately simulate the exposure of patterns with 0.25 μm design rules is demonstrated. Comparisons are made of the simulation results obtained when double Gaussian, triple Gaussian and SEEL approximations are used for the REDs. We also show that these two programs can be used to evaluate the sensitivity of the radial exposure distribution and proximity effects for multilevel substrates, for varying topography, and for different exposure conditions.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Exploratory test structures for characterization of electron‐beam lithography

Nelson Tam, Hiroshi Nozue, David Yu, and Andrew R. Neureuther

J. Vac. Sci. Technol. B 7, 1546 (1989); http://dx.doi.org/10.1116/1.584530 (6 pages)

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Electrical testing of electron beam lithography was carried out on the AEBLE‐150 in a simulation‐calibrating approach to quantitatively study the impact of dose, maximum beam current, and substrate atomic number. The recording thin‐film stacks consist of a resist coated thin Ti layer, a thin CVD oxide layer, and a substrate material of polyimide, Si, Mo, or W. The patterns were written using a negative‐working chemical amplification resist Shipley SAL‐601/ER‐7. Electrical data for lines, arrays, serpentine squares, and shorting structures on Si and Mo substrates show no significant dependence on feature orientation or the maximum beam current of the exposure tool. Data from exposures up to five times normal show a lateral line edge growth of about half the Bethe range on Si. On Mo the dose to correctly size a 0.5 μm line drops from 5 to 3 μC/cm2 and the edge growth is much larger than the Bethe range in Mo. Simulation of backscatter electron effects and of the resist profile time evolution were used in the design and interpretation of the experiment.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Thermal effects in electron beam lithography

E. H. Mulder, K. D. van der Mast, and A. C. Enters

J. Vac. Sci. Technol. B 7, 1552 (1989); http://dx.doi.org/10.1116/1.584531 (4 pages)

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At the Delft University of Technology, an electron beam (e‐beam) writer is being designed, which uses a constant 10 μA beam current at 100 kV and shape sizes of 0.1×0.3 to 1.0×1.0 μm. The brightness of the source is modulated to keep the probe current constant. The maximum current density will be 3.3 104 A/cm2. Therefore, thermal effects are a primary concern. High‐energy electrons lose most of their energy at depth in the substrate. The exposure times are, due to the high current density, too short to make thermal diffusion from the bulk significant. Therefore, only the local energy deposition in the resist and the contributions from previously exposed points influence the temperature rise. Presently, the writing speed of lithography systems is restricted by the resist sensitivity. The lower limit to the dose for writing is determined by the statistical noise in the number of electrons, to define the smallest detail. For 0.1 μm lines, the ideal sensitivity of the resist is 0.1 C/m2, thus allowing a writing speed of 1 cm2 /s. Using the ideal resist on silicon, the temperature rise caused by one exposure was calculated to be less than 17 K, at the edge of the exposed point. The heating is higher for low accelerating voltages, since the penetration depth is smaller and the direct energy loss is higher.
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85.40.Hp Lithography, masks and pattern transfer

Proximity‐effect correction in electron‐beam lithography

P. Vermeulen, R. Jonckheere, and L. Van Den Hove

J. Vac. Sci. Technol. B 7, 1556 (1989); http://dx.doi.org/10.1116/1.584488 (5 pages) | Cited 1 time

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A survey is given of the dose correction method we have developed to compensate for the proximity effect. Accurate values for the parameters of the double Gaussian function have been obtained with the doughnut method. A self‐consistent correction method has been implemented that is not limited to rectangles, which is successful in correcting polygons by splitting them into trapezoids and computing the interactions between these trapezoids. By applying a clustering technique, the speed of this correction software has been remarkably increased. Furthermore, programs have been developed to perform different fracturing strategies on the input pattern. Also the influence of the various fracturing methods on the quality of the correction can be checked by software. In this way, time consuming experiments can be avoided.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Stress‐free and amorphous Ta4B or Ta8SiB absorbers for x‐ray masks

Minoru Sugawara, Masato Kobayashi, and Yoh‐ichi Yamaguchi

J. Vac. Sci. Technol. B 7, 1561 (1989); http://dx.doi.org/10.1116/1.584489 (4 pages) | Cited 3 times

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We have succeeded in obtaining practical x‐ray absorber films, Ta4B and Ta8SiB, using an rf magnetron sputtering method. The internal stress of these films can be controlled precisely within ±1.0×107 N/m2. The stress has thermal stability at 350 °C. The stress is also quite insensitive to the film thickness and substrates used. These excellent stress properties are attributed to the amorphous structure of the film. The amorphous structure also ensures quarter‐micron pattern fabrication. Densities of 15.3 g/cm3 for Ta4B and 15.6 g/cm3 for Ta8SiB are high enough to yield sufficient contrast for x‐ray exposures.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Dynamical method for the thermomechanical study of thin membranes

B. S. Berry, W. C. Pritchet, and C. E. Uzoh

J. Vac. Sci. Technol. B 7, 1565 (1989); http://dx.doi.org/10.1116/1.584490 (5 pages) | Cited 8 times

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An apparatus has been built for the dynamic mechanical analysis of thin membranes, such as those of interest for x‐ray lithographic masks. Frequency and damping measurements have been made over the temperature range 100–700 K, using vibrational modes in the range 1–10 kHz. The measurements are made at pressures below 10−5 Torr to remove atmospheric loading and damping effects and thereby reveal the intrinsic membrane behavior. Stress and differential thermal expansion results are presented for B‐doped Si membranes and a PMDA/ODA polyimide membrane, prepared on Si wafers. Annealing behavior observed during thermal cycling of the Si(B) membranes has led to the discovery that the membrane stress can be varied reversibly over a wide range by the introduction and removal of hydrogen.
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81.70.-q Methods of materials testing and analysis
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)

Pilot production of half‐micron x‐ray masks

Gregory Hughes, Gary Doyle, Gordon Foss, and Nick Gorbachenko

J. Vac. Sci. Technol. B 7, 1570 (1989); http://dx.doi.org/10.1116/1.584491 (5 pages) | Cited 1 time

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The key specifications for 0.5‐μ x‐ray mask have been achieved in a pilot production operation. A poly(butene‐1‐sulfane) (PBS), Cr patterning process has been used as the top layers of a trilevel stencil in which to plate the opaque gold absorber. The following specifications were exceeded: registration <0.08 μ (3 σ), linewidth control <0.06 μ (3 σ), and defect density <20/cm2.
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85.40.Hp Lithography, masks and pattern transfer

Thermal and mechanical model of x‐ray lithography masks under short pulse irradiation

Iqbal Shareef, Juan R. Maldonando, and David Katcoff

J. Vac. Sci. Technol. B 7, 1575 (1989); http://dx.doi.org/10.1116/1.584492 (8 pages)

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The purpose of this paper is to present computer simulations of x‐ray mask heating by fast x‐ray pulses. In particular, results will be presented of temperature distributions in an x‐ray mask during exposure to x‐ray pulses generated by a hot plasma. Three mask structures were studied: (i) Si–Au absorber, (ii) Si–polyimide–Au absorber, and (iii) Si–W absorber. The transient thermal analysis results were obtained using finite element modelling techniques (CAEDS and NASTRAN). The x‐ray exposure was assumed to have taken place in a helium atmosphere with a 40‐μ gap between the mask and the wafer, which was assumed to be a heat sink at constant temperature. The temperature distributions obtained above were subsequently used as input in order to study possible mechanical deformation of the membrane. Again, finite element techniques were used and solutions were obtained by static stress methods. Results indicate a maximum temperature rise on the mask of the order of 18 °C for a 20‐ns exposure by a 10 mJ/cm2 x‐ray pulse. The maximum temperature was obtained at the end of the x‐ray pulse. The temperature decayed quickly, reaching initial ambient temperature after about 10 ms. Mechanical analysis showed that maximum deformation, which was due to maximum temperature differences in the mask layers, also occurred at the end of the pulse. The analysis indicates that there is need for experimental study of x‐ray mask distortion during exposure to short x‐ray pulses (from a laser plasma or similar source) when the pulse amplitude reaches 10 mJ/cm2.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Sub‐100‐nm x‐ray mask technology using focused‐ion‐beam lithography

W. Chu, A. Yen, K. Ismail, M. I. Shepard, H. J. Lezec, C. R. Musil, J. Melngailis, Y.‐C. Ku, J. M. Carter, and Henry I. Smith

J. Vac. Sci. Technol. B 7, 1583 (1989); http://dx.doi.org/10.1116/1.584493 (3 pages) | Cited 6 times

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In the past, nearly all x‐ray nanolithography (i.e., sub‐100‐nm linewidths) employed the CK x‐ray line at 4.5 nm. This, in turn, necessitated near‐zero gaps (to avoid diffraction) and carbonaceous masks (e.g., polyimide, which is subject to distortion). In order to use x‐ray replication in the fabrication of multilevel devices and circuits that cover large areas (∼a few cm2) and have feature sizes well below 100 nm, we have turned to the CuL line at 1.3 nm. Masks consist of 1–1.5 μm thick Si or Si3N4 membranes and Au absorber patterns, 200 nm thick, which provide 10 db contrast. Focused‐ion‐beam‐lithography (FIBL) with Be++ ions at 280 keV was used to produce quantum‐effect‐device patterns with minimum linewidths of ∼50 nm. These were replicated using the CuL line, indicating that photoelectrons are not a serious problem. The FIBL process [exposure of 300 nm‐thick polymethylmethacrylate (PMMA), followed by Au electroplating] is high yield and much simpler than a trilevel electron‐beam‐lithography process designed to give comparable results. This is the first time FIBL has been used to make x‐ray masks at sub‐100‐nm linewidths. Along with the device patterns, linear‐zone‐plate alignment marks were also written on the masks, to be aligned to corresponding marks on the substrate via an optical alignment scheme.
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85.40.Hp Lithography, masks and pattern transfer

Electron scattering effects in master mask fabrication by single layer process for submicron x‐ray lithography

M. Gentili, A. Lucchesini, P. Lugli, G. Messina, A. Paoletti, S. Santangelo, A. Tucciarone, and G. Petrocco

J. Vac. Sci. Technol. B 7, 1586 (1989); http://dx.doi.org/10.1116/1.584494 (5 pages) | Cited 2 times

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A single layer process in electroplated master mask making is discussed. The results of a Monte Carlo simulation are utilized in order to calculate the proximity function and compare theory with experimental test patterns. Silicon membranes are utilized (2 μm thick) and the variables investigated are resist thickness (10 000 and 5000 Å), metallic layer plating base (varying thickness) and electron accelerating voltage (20–40 kV). The results show quantitatively how high resolution patterns mainly depend on forward scattering in the resist (thus on resist thickness) and backscattering from the metallic layer. In particular, 500 Å of Au plating base may hinder the possibility of high resolution, which can be improved by lowering either the thickness or the Z of the metallic layers. Finally the possibility of obtaining high‐contrast master masks down to 0.3 μm linewidth by a single layer process is demonstrated.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Ion implant compensation of tensile stress in thick silicon nitride films for x‐ray masks

D. Qingyun, Z. Liankui, C. Mengzhen, and M. Junru

J. Vac. Sci. Technol. B 7, 1591 (1989); http://dx.doi.org/10.1116/1.584495 (3 pages)

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High‐energy ion implantation can compensate the tensile stress in thick silicon nitride films. We investigated the relationship between the compensated stress in the silicon nitride films and ion implantation parameters like ion energy, dose, and kind of ions, as well as the influence of different annealing temperatures. We developed the technique of stress compensation for silicon‐nitride films and applied it in making silicon nitride x‐ray masks. As a result of the application, we have made x‐ray masks as large as 40×40 mm. Finally, we present an elementary description of the mechanism of the stress compensation.
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61.72.up Other materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Characterization of thin boron‐doped silicon membranes by double‐crystal x‐ray topography

David I. Ma, Syed B. Qadri, Martin C. Peckerar, and Mark E. Twigg

J. Vac. Sci. Technol. B 7, 1594 (1989); http://dx.doi.org/10.1116/1.584496 (6 pages) | Cited 1 time

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Heavily boron‐doped silicon transparent membranes and x‐ray masks were examined using double‐crystal x‐ray topography. The topographs revealed the strain distribution in two dimensional (2D) pattern. Slip bands and Frank–Read sources were observed. The stress variation across the membrane was confirmed using the Stoney’s stress analysis by laser beam reflecting technique. Surface strain versus bulk strain were also analyzed by choosing (224) and (115) reflecting planes. Deposition of patterns on a bare membrane did not alter the overall strain pattern of the membrane, which was apparently determined by the warpage of the silicon supporting ring. Local deformations associated with gold absorber features were visible and their associated strain fields were measured.
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81.70.-q Methods of materials testing and analysis
62.20.M- Structural failure of materials

Large‐area silicon–nitride mask technology for x‐ray lithography

Dong Qingyun, Zhang Liankui, Chen Mengzhen, and Ma Junru

J. Vac. Sci. Technol. B 7, 1600 (1989); http://dx.doi.org/10.1116/1.584497 (3 pages) | Cited 1 time

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This paper describes a technology for making large area silicon‐nitride x‐ray masks. We did extensive work for optimizing the LPCVD deposition process. Choosing proper deposition parameters, we obtained silicon‐nitride layers with low tensile stress. Using the ion implantation stress compensation technique, the stress of the silicon nitride was reduced until the desirable value was reached. The key parameters of the silicon‐nitride mask are satisfactory for the needs of x‐ray masks used to fabricate VLSI devices. Because the silicon‐nitride film is stoichiometric, a good stability of the mask is expected; tests of its stability to x‐ray radiation are being continued at IMT.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Proximity correction for electron‐beam patterning on x‐ray mask blanks

K. Reimer and S. Pongratz

J. Vac. Sci. Technol. B 7, 1603 (1989); http://dx.doi.org/10.1116/1.584498 (4 pages) | Cited 3 times

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A limiting factor in electron‐beam (e‐beam) lithography is the proximity effect. In the special case of x‐ray mask making, Monte Carlo calculations and resist profile simulations show that the proximity effect can be almost entirely eliminated by using 100 keV electrons for the resist exposure. To verify the theoretical results of the simulation, experiments with available electron energies of 20 and 50 keV were conducted, with good agreement. The poor efficiency of 100 keV electrons results in decreasing resist sensitivity. Electrons passing through the membrane hit holder parts behind it. The x‐ray radiation generated in this way was able to expose the resist from the backside of the membrane. A diffuse image of the holder parts could be seen in the resist.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Step‐and‐scan lithography using reduction optics

Jere D. Buckley, Daniel N. Galburt, and Charles Karatzas

J. Vac. Sci. Technol. B 7, 1607 (1989); http://dx.doi.org/10.1116/1.584499 (6 pages) | Cited 2 times

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Scanning 1:1 optical lithography has a long record of success that has been greatly abetted by the relatively straightforward nature of 1:1 ring‐field optics and by the fact that mask and wafer can be mounted to a common scanning carriage. However, as lithography requirements progress into the submicron regime, there is strong motivation to employ reduction optics in order to keep the difficulty of the mask‐making task within reasonable bounds. A new ‘‘step‐and‐scan’’ lithography tool achieves this goal and combines the best features of scanners and steppers by sequentially scanning 20×32.5‐mm subfields. Key features of this system are a ring‐field projection system, with a 4:1 reduction ratio, and a scanning system in which the reticle and wafer are carried by separate stages driven at different but precisely synchronized velocities.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Ls Scanners, image intensifiers, and image converters
42.79.Pw Imaging detectors and sensors

Short‐wavelength annular‐field optical system for imaging tenth‐micron features

O. R. Wood, W. T. Silfvast, and T. E. Jewell

J. Vac. Sci. Technol. B 7, 1613 (1989); http://dx.doi.org/10.1116/1.584500 (3 pages) | Cited 4 times

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We have found that the 1:1 Offner annular‐field system can provide high‐resolution imaging in the extreme ultraviolet (XUV) when used at numerical apertures (NA’s) around 0.1. For example, when illuminated with radiation at wavelengths shorter than 15 nm, a 0.0835‐NA system with a 233.6‐mm‐diam primary mirror should be able to image 0.1‐μm lines and spaces in a 100‐micron‐wide, 50‐mm‐radius ring‐shaped field at high contrast.
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42.30.Va Image forming and processing
42.15.Eq Optical system design
42.87.-d Optical testing techniques
42.79.Ls Scanners, image intensifiers, and image converters
42.79.Pw Imaging detectors and sensors

The coherence factors of excimer laser radiation in projection lithography

K. A. Valiev, L. V. Velikov, G. S. Volkov, and D. Yu. Zaroslov

J. Vac. Sci. Technol. B 7, 1616 (1989); http://dx.doi.org/10.1116/1.584501 (4 pages) | Cited 1 time

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The spatial coherence of the excimer laser radiation seriously affects the quality of the images being reproduced by diffraction limited optics in photolithography. It is shown that the coherence parameters of excimer laser radiation exceed the necessary level in 102–103 times. To decrease the coherence down to the optimal level a fly’s eye element is used. The concept of Kirchhoff integrals has been applied to calculate the mutual intensity function transformation by the illuminator of the projection system equipped with fly’s eye element.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Bh Lenses, prisms and mirrors
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Approaches to deep ultraviolet photolithography utilizing acid hardened resin photoresist systems

James W. Thackeray, George W. Orsula, John F. Bohland, and Andrew W. McCullough

J. Vac. Sci. Technol. B 7, 1620 (1989); http://dx.doi.org/10.1116/1.584502 (4 pages)

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This paper describes continuing efforts in the development of acid hardened resin (AHR) resist systems for use in deep UV photolithography. The paper is composed of two sections. The first section deals with further evaluation of a conventional negative‐tone deep‐UV resist, XP‐8843. A study of delay time between exposure and postexposure bake was carried out over a 62 min period. In particular, the linewidth versus exposure curve was generated at 2, 32, and 62 min delay times. Representative SEM cross sections at each time interval were also compared. The authors conclude that no significant time effect is evident, indicative that acid diffusion does not play a role in the 62 min time frame. The effect of defocus on sidewall angle has been evaluated over a 1.8 μ focal range as well. The sidewall angle varied from 85° to 89° reentrant over the entire focal range. Finally, results for XP‐8843 at 1.4 μ coating thickness are shown. The second section introduces the silylated AHR (SAHR) process, whereby a highly absorbing resist, such as SAL601‐ER7, is treated with hexamethyldisilazane. The exposed, crosslinked areas show virtually no reactivity with HMDS, and the unexposed areas incorporate 8.0% silicon in the film. In this manner, subsequent dry etching leads to a positive tone image.
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85.40.Hp Lithography, masks and pattern transfer

Aluminum oxides as imaging materials for 193‐nm excimer laser lithography

S. W. Pang, R. R. Kunz, M. Rothschild, R. B. Goodman, and M. W. Horn

J. Vac. Sci. Technol. B 7, 1624 (1989); http://dx.doi.org/10.1116/1.584503 (5 pages) | Cited 1 time

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Aluminum oxide films deposited over amorphous carbon(a‐C:H) planarizing layers have been investigated as imaging layers for 193‐nm excimer laser lithography. The AlOx films were deposited by ion beam deposition, e‐beam evaporation, or sputter deposition. The films have been analyzed by Auger electron spectroscopy and x‐ray photoelectron spectroscopy. Depending on the deposition conditions, AlOx films with compositions varying from metallic to fully oxidized Al can be formed. The optical appearance of these films varies from highly reflective for metallic Al to highly transparent for fully oxidized layers. Using pulsed 193‐nm radiation from an ArF excimer laser, the single‐pulse self‐development threshold energy is similar for films with different compositions when the film reflectivity is taken into account. It was found that pure Al films and highly oxidized Al films do not provide good adhesion on a‐C:H layers and have a tendency to peel during laser exposure. In contrast, films with intermediate compositions consisting of a mixture of Al and aluminum oxides provide good adhesion, high etch resistance during O2 reactive ion etching, and submicrometer resolution when exposed with the 193‐nm excimer laser. Features as small as 0.1 μm have been patterned on these films in projection, and can be transferred through a 1‐μm‐thick a‐C:H planarizing layer with vertical profiles.
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85.40.Hp Lithography, masks and pattern transfer
42.55.Lt Gas lasers including excimer and metal-vapor lasers
78.66.-w Optical properties of specific thin films
68.55.-a Thin film structure and morphology

Controlled‐ambient photolithography of polysilane resists at 193 nm

R. R. Kunz, M. Rothschild, D. J. Ehrlich, S. P. Sawan, and Y. G. Tsai

J. Vac. Sci. Technol. B 7, 1629 (1989); http://dx.doi.org/10.1116/1.584504 (5 pages) | Cited 3 times

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Various polysilanes have been examined as self‐developed photoresists at 193 nm and the benefits of imaging these materials in controlled, reactive ambients have been determined. Plasticization of the irradiated polymer due to reaction with oxygen is avoided when dry, oxygen‐free ambients are employed. In addition, the redeposition of silicon from the ablated polysilane, which is prevalent in a one‐pulse imaging mode, is greatly reduced when NF3 or CF2Cl2 are used as exposure ambients. Laser desorption mass spectrometry indicates that thermally activated decomposition of the polysilanes at fluences >100 mJ/cm2 causes more extensive fragmentation of the desorbed molecules. This results in the formation of higher volatility products upon halogenation.
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85.40.Hp Lithography, masks and pattern transfer

X‐ray lithography: On the path to manufacturing

John Warlaumont

J. Vac. Sci. Technol. B 7, 1634 (1989); http://dx.doi.org/10.1116/1.584505 (8 pages) | Cited 2 times

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X‐ray lithography has been an active area of research and development for the last 20 years, and recent spectacular results using complete, integrated x‐ray lithography systems have demonstrated, at the research level, the viability of x‐ray lithography, and have shown that x–ray lithography is on the path to manufacturing. This paper presents IBM’s recent successful development of a synchrotron‐radiation‐based x‐ray lithography system. The individual components of the system are described, along with a brief description of available alternate components. Measurements of the lithographic performance of the integrated system are presented, and the use of this system for the fabrication of fully‐scaled 0.5 μm CMOS circuits is described.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of 0.5 μm n‐ and p‐type metal–oxide semiconductor test devices using x‐ray lithography

G. Zwicker, W. Windbracke, H. Bernt, D. Friedrich, H.‐L. Huber, E. Krullmann, M. Pelka, P. Lange, P. Hemicker, and P. Staudt‐Fischbach

J. Vac. Sci. Technol. B 7, 1642 (1989); http://dx.doi.org/10.1116/1.584506 (6 pages)

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Partially scaled 0.5 μm NMOS and PMOS test devices have been fabricated using synchrotron radiation x‐ray lithography for all four levels. All exposures were done at the IMT lithography lab at the BESSY storage ring in Berlin, using the Suss MAX I x‐ray stepper. The four levels of each device have been processed with the new Hoechst RAY/PF x‐ray sensitive resist. A total overlay accuracy of 130 nm (1σ) in x and y direction for all aligned levels and an overall linewidth variation of 23 nm (1σ) across a 100 mm wafer have been achieved. Reproducible NMOS and PMOS processes have been carried out in the CMOS process line of the institute, using gateoxide thicknesses between 15 and 10 nm, appropriate channel implants, and a spacer technology. Electrical results of functional test transistors with effective gate lengths down to 0.25 μm will be presented.
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85.40.Hp Lithography, masks and pattern transfer

Soft x‐ray reduction lithography using multilayer mirrors

H. Kinoshita, K. Kurihara, Y. Ishii, and Y. Torii

J. Vac. Sci. Technol. B 7, 1648 (1989); http://dx.doi.org/10.1116/1.584507 (4 pages) | Cited 42 times

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A soft x‐ray lithograpy using multilayer mirrors for demagnifying optics and a reflecting mask has been designed and studied experimentally. In this system, a wavelength of 45–130 Å has been selected based on the optical characteristics, the exposed depth of the resist film, and the reflectivity of the multilayer mirror. To obtain a replication pattern resolution of 0.2 μm, the numerical aperture required is estimated to be greater than 0.0125 or 0.0325 for a wavelength of 50 or 130 Å, respectively. These values show that the multilayer optics using two mirrors can be realized to replicate a 0.2 μm pattern. The experiments were performed on the SR beamline BL‐1 of the KEK‐PF storage ring. The Schwarzschild demagnifying optics with a ring field were designed and fabricated. Demagnified exposure patterns of less than 0.5 μm have been obtained using a reflecting mask. The feasibility of the soft x‐ray reduction method using multilayer mirrors has been confirmed. Furthermore, new telecentric optics are proposed to realize a practical reduction lithography system.
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85.40.Hp Lithography, masks and pattern transfer

A vertical stepper for synchrotron x‐ray lithography

S. Ishihara, M. Kanai, A. Une, and M. Suzuki

J. Vac. Sci. Technol. B 7, 1652 (1989); http://dx.doi.org/10.1116/1.584508 (5 pages) | Cited 3 times

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A newly developed synchrotron x‐ray stepper installed at a port of an electron storage ring of the NTT Synchrotron Facility1–3 is described. The stepper exposes wafers in a normal atmosphere to vertically scanned synchrotron x rays with continuous alignment control throughout the exposure. The key devices of the stepper are a vertical x–y stage and an optical‐heterodyne alignment system. The x–y stage fully utilizes air lubricated ceramic components including air bearing lead screws and achieves 5 nm motion precision over a 200 mm stroke. The optical‐heterodyne alignment system detects both lateral and gap displacements between the mask and wafer gratings with accuracies of 10 and 100 nm, respectively. After wafer step positioning using a laser interferometer, alignment between the mask and wafer is executed using the optical‐heterodyne signal. In several exposure experiments, alignment capability is estimated to be better than ±0.14 μm as a 3σ value of machine repeatability. Also, several applications to device fabrication confirmed that the vertical stepper is feasible in quarter‐ to half‐micron x‐ray lithography.
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07.85.-m X- and γ-ray instruments
29.20.dk Synchrotrons
85.40.Hp Lithography, masks and pattern transfer

Thermal effects in x‐ray masks during synchrotron storage ring irradiation

Y. Vladimirsky, J. Maldonado, R. Fair, R. Acosta, O. Vladimirsky, R. Viswanathan, H. Voelker, F. Cerrina, G. M. Wells, M. Hansen, and R. Nachman

J. Vac. Sci. Technol. B 7, 1657 (1989); http://dx.doi.org/10.1116/1.584509 (5 pages) | Cited 2 times

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This paper presents theoretical model and experimental results on radiation heating and thermally induced distortions in x‐ray masks. The temperature rise of the mask membranes during x‐ray irradiation was measured using metal resistors fabricated directly on the mask. A method was developed to calculate thermal wave effects: thermal distortions of the printed image due to the nonuniformity of temperature distribution in the mask membrane during scanning of the x‐ray beam. Experimental results for the thermal wave effects are presented; they indicate that the effects are noticeable only during operation in a vacuum environment. The effects are negligible during normal operation in a helium atmosphere.
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85.40.Hp Lithography, masks and pattern transfer

Application of synchrotron x‐ray lithography to fabricate fully scaled 0.5 μm complementary metal–oxide semiconductor devices and circuits

L. K. Wang, J. Silverman, D. Seeger, E. Petrillo, V. DiMilia, D. Katcoff, K. Kwietniak, R. Acosta, K. Petrillo, S. Brodsky, I. Babich, O. Vladimirsky, H. Voelker, R. Viswanathan, J. Warlaumont, et al.

J. Vac. Sci. Technol. B 7, 1662 (1989); http://dx.doi.org/10.1116/1.584477 (5 pages) | Cited 3 times

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High performance fully scaled 0.5 μm complementary metal–oxide semiconductors very large scale integrated (CMOS VLSI) circuits have been fabricated using synchrotron x‐ray lithography technology. X‐ray lithography is employed at all levels to attain a minimum feature size of 0.5 μm. The wafer exposures are done at the VUV storage ring from the National Synchrotron Light Source, Brookhaven National Laboratory. A stepper built at IBM Yorktown Heights is used at the beamline to perform the wafer exposures. All the lithography levels are aligned to the prefabricated 0.5 μm deep silicon trench zero level with an overlay less than 0.1 μm (1σ) between levels. Single level resists (both positive and negative) are used throughout the entire CMOS process. Linewidth control better than 0.01 μm and alignment tolerance less than 0.10 μm are accomplished. The patterning of this x‐ray lithography mask is accomplished through a vector scan electron beam direct writing system. Masks made of boron doped silicon membranes with electroplated gold are used as the absorber. An average linewidth variation less than 0.2 μm can be attained for the (25 mm)2 field size masks. A retrograded N well 0.5 μm CMOS process is used to exercise the fabrication of x‐ray lithography VLSIs. In the (25 mm)2 testsite, CMOS devices, ring oscillators and fully scaled 0.5 μm CMOS SRAM (static random access memory) are densely populated to exercise this technology. In this experiment CMOS devices and ring oscillators are successfully fabricated. The device characteristics are essentially the same as those fabricated using other lithography methods. A fully scaled 0.5 μm 61 stage inverter ring oscillator was measured at a delay of 95 ps/stage when operating at a 3.5 volts power supply. Radiation effects on the fabricated CMOS devices are studied. With the final 400 °C hydrogen ambient annealing, there is no apparent difference on the device characteristics in comparison to the same devices fabricated using optical lithography.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Radiation damage study of bipolar devices in x‐ray lithography

L. C. Hsia and I. Magdo

J. Vac. Sci. Technol. B 7, 1667 (1989); http://dx.doi.org/10.1116/1.584478 (4 pages) | Cited 2 times

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The radiation damage of bipolar transistors has been investigated using the vacuum ultraviolet (VUV) storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The bipolar devices under investigation were exposed to the x‐ray radiation in the range of 1–2 keV. The device parameters were measured before and after irradiation, and were measured again after the devices were annealed in forming gas at 400 °C for 30 min. The study shows that x‐ray radiation degrades the common emitter current gain. At small collector currents, the current gain is reduced by about 20%. This change is primarily due to the interface states generated by irradiation at the interface between Si and SiO2 in the base region. Upon annealing, current gain recovers its initial value. The C–V (capacitance–voltage) measurements on MOS capacitors indicate that x‐ray radiation increases interface state density from its initial order of magnitude of 1010/cm2 eV to 1012/cm2 eV. The C–V curves also clearly indicate the generation of positive trapped charges in the silicon oxide. Upon annealing, the interface state density is reduced back to its initial value.
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85.30.Pq Bipolar transistors
85.40.Hp Lithography, masks and pattern transfer

An electron beam measurement and inspection technique for x‐ray masks using conductive organic layer

H. Watanabe, H. Nikoh, Y. Takasu, and Y. Todokoro

J. Vac. Sci. Technol. B 7, 1671 (1989); http://dx.doi.org/10.1116/1.584479 (4 pages)

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An electron beam (e‐beam) measurement and inspection technique for x‐ray masks using a conductive organic layer has been developed. This technique consists of spin coating of a conductive organic layer, scanning e‐beam probe, detecting the backscattered and secondary electron signals, and removing the conductive layer. By using this technique, x‐ray masks are successfully measured and inspected without charging problems. The behavior of incident electrons was also investigated.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Evaluation of polycrystalline silicon membranes on fused silica for x‐ray lithography masks

L. E. Trimble and G. K. Celler

J. Vac. Sci. Technol. B 7, 1675 (1989); http://dx.doi.org/10.1116/1.584480 (5 pages) | Cited 2 times

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Single crystalline Si films, heavily doped with boron for etch selectivity and often counterdoped with Ge to reduce stresses, are now commonly used as membranes in x‐ray masks. We have investigated preparation and properties of much simpler membrane structures, consisting of undoped polycrystalline Si films deposited either on oxidized Si wafers or on fused silica substrates. The latter case is particularly simple since concentrated HF that is used for etching the fused silica substrate, does not attack Si. Therefore, after coating both sides of a fused silica substrate with polycrystalline Si, a window is opened in Si on one side by simple lithography, and the wafer is immersed in HF to complete the process. Stress of the membranes can be tuned by adjusting deposition conditions, annealing temperature, and choice of high temperature glass instead of silica for the substrate. Data from three polycrystalline membranes indicate a higher fracture strength and a larger effective elastic modulus than in equivalent single crystalline Si structures. However, optical transparency is lower because of light scattering by grain boundaries.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Low‐stress tantalum absorbers deposited by sputtering for x‐ray masks

Yukio Iimura, Hiroyuki Miyashita, and Hisatake Sano

J. Vac. Sci. Technol. B 7, 1680 (1989); http://dx.doi.org/10.1116/1.584481 (4 pages) | Cited 6 times

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A method for fabricating stable and low‐stress tantalum films, suitable for absorbers of x‐ray masks, by dc‐bias, rf magnetron sputtering is presented. The superiority of Xe over Ar as a working gas is demonstrated. The stress‐vs‐bias‐voltage curve has a plateau, where the film stresses are low and constant over the bias voltage ranging from −15 to 20 V. The plateau stresses vary linearly with both the working Xe pressure and the substrate temperature with slopes of 1.2×1010 dyn/cm2 Pa and 8.6×106 dyn/cm2 deg, respectively. By control of the pressure and the temperature, stresses of (3±2)×108 dyn/cm2 are achieved. The Ta film which is stable under a heat treatment up to 300 °C is obtainable when it is deposited at 220 °C and then annealed at 220 °C for 1 h. The density of the films is (15.0±0.5) g/cm3. By x‐ray diffraction the films are found to be in a mixture of the α‐Ta phase and the β‐Ta phase. Ta patterns of 0.15 μm in width were fabricated.
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81.15.Cd Deposition by sputtering
85.40.Hp Lithography, masks and pattern transfer

High resolution x‐ray lithography using surface‐protected development

Taro Ogawa, Kozo Mochiji, Hiroshi Shiraishi, and Takeshi Kimura

J. Vac. Sci. Technol. B 7, 1684 (1989); http://dx.doi.org/10.1116/1.584482 (4 pages) | Cited 1 time

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A new process utilizing a dissolution‐blocking layer on a resist surface is proposed for improving developed pattern shape of x‐ray lithography. A thin self‐developing polymer layer which is coated onto a positive resist almost completely achieves this purpose. This layer can be efficiently decomposed and vaporized by x‐ray exposure. As a result, after x‐ray exposure, this layer never interferes with development of the exposed portion, while the layer remaining blocks dissolution of the unexposed portion during development. This enhances the development rate ratio between unexposed and exposed portions, thus developed pattern shape is greatly improved. This surface‐protected development process has been evaluated for improving the developed pattern shape of novolac based positive resist (NPR). Poly(2‐methylpentene–1‐sulfone) (PMPS), which is also used as the dissolution inhibitor of the NPR resist, is selected as the dissolution‐blocking layer. Application of the post‐exposure baking is the key process for improvement of developed pattern shape, because the PMPS layer remaining on the unexposed portion is densified and begins to oppose development, while development of the exposed portion is accelerated by thermal decomposition of the remaining PMPS both on and in the NPR. With this process, 0.3 μm high‐aspect‐ratio patterns of single‐layer NPR can be successfully fabricated at a dosage lower than one‐third of that for the current process.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of surface acoustic wave devices by using x‐ray lithography

Nobuyuki Yoshioka, Atsushi Sakai, Hiroaki Morimoto,