bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive ion etching for submicron structures of refractory metal silicides and polycides
Authors: Zhang M. , Li J. Z. , Adesida I. , Wolf E. D.
Published: July 2002

Refractory metal silicides and n+ polysilicon/silicides are of particular interest for VLSI gate and interconnection technology. Reactive ion etching experiments have been conducted on sputter-deposited films of MoSi2, CVD n+ polysilicon, and thermal SiO2 using admixtures of SF6 with O2. The influence of partial pressure and total pressure on profile control and etch selectivity has been determined. Highly anisotropic etching of n+ polysilicon and MoSi2 was obtained using a gas mixture of SF6 plus 50% oxygen. Examples of 0.2μ anisotropically etched structures of silicides and n+ polysilicon/silicide stacked films have been realized using electron beam lithography and one step dry etching. Mechanisms of profile control involved in the SF6/O2 system are discussed. In addition, exploratory reactive ion etching studies using SiF4/Cl2 gas mixtures for these materials and TaSi2 have been carried out.
High resolution patterning of silicon by selective gallium doping
Authors: Berry I. L. , Caviglia A. L.
Published: July 2002

High resolution patterns have been fabricated in 〈100〉 silicon by doping selected areas with gallium utilizing an ion microprobe. These doped regions are used as an etch mask for subsequent anisotropic etching of silicon. The etching was performed in a KOH:IPA solution at 80–90 °C. The resulting etch rate of the doped silicon is approximately inversely proportional to the gallium impurity concentration. At high doping concentrations an etch rate difference of greater than 1000:1 has been measured between the virgin silicon and the doped regions. Using this technique features as small as 30 nm have been produced.
Optical monitoring for rate and uniformity control of low power plasma-enhanced CVD
Authors: Dautremont-Smith W. C. , Lopata J.
Published: July 2002

Plasma-enhanced CVD requires close control of the plasma power density for reproducibility of both deposition rate and spatial uniformity in a radial-flow reactor. Frequently the low rf power levels needed are not adequately controlled by the output power control of the relatively high power rf generator found in most commercial multipurpose plasma etch/deposition systems. This paper describes very simple and inexpensive broadband optical monitoring of the plasma emission for improved control sensitivity. The technique has the advantage of directly monitoring the plasma intensity, avoiding effects of variable power transmission losses between the rf generator and the plasma. Application to the control of low power plasma-enhanced CVD of ‘‘SiO2’’ from Ar:SiH4:N2O plasmas, where the monitor signal is almost entirely due to near infrared Ar emission, is described.
Resist patterning and x-ray mask fabrication employing focused ion beam exposure and subsequent dry etching
Authors: Kuwano Hiroki , Takaoka Hedetoshi , Ozawa Akira
Published: July 2002

A lithographic method using focused ion beam exposure and subsequent dry etching is examined. The lithographic mechanism is also investigated. Employing resist patterns formed by this method, an x-ray mask is prepared. It is shown that Ga ion exposed regions of polymer resists act as an in situ mask during the O2 reactive ion etching dry development of unexposed regions. Gallium distribution and its chemical shift in a resist after exposure or development are measured by XPS. The surface gallium atoms of resist exposed to oxygen plasma are changed to Ga2O3, which covers the resist surface and acts as in situ masks against the oxygen plasma. The feasibility of the lithographic method is demonstrated by a preparation of submicron pattern x-ray masks.
GHOST solubility rate ratio: A new parameter for characterization of positive electron resists
Authors: Rissman Paul , Owen Geraint
Published: July 2002

Positive electron beam resists can be characterized by the GHOST solubility ratio parameter Srg defined as the ratio of the solubility at the nominal exposure dose Qe to the solubility at the GHOST correction dose, [ηe/(1+ηe)]xQe. This parameter removes the development time ambiguity inherent in resist characterization by means of a thickness remaining vs dose curve, and eliminates the experimental difficulty in characterization of resist based on measurements of unexposed solubility rate. Modeling data indicate that the Srg parameter is a good measure of resist performance. GHOST proximity effect correction results on PMMA exposed at doses from 10 to 200  μC/cm2 illustrate experimentally the dependency of feature quality on the value of Srg. The Srg method is a general technique for resist characterization, and is valid whether or not proximity effect correction is used. This parameter has been used to compare the performance of PMMA, EBR-9, CP-3 and Microposit 2400. Electrical test measurements show that GHOST works with low Srg, Microposit 2400.
Evidence of crystallographic etching in (100)GaAs using SiCl4 reactive ion etching
Authors: Li J. Z. , Adesida I. , Wolf E. D.
Published: July 2002

Etch rate and etch profile characteristics of (100)GaAs in SiCl4 reactive ion etching have been studied in the pressure range of 2–110 mTorr. Pronounced crystallographic or orientation dependent etching effects were observed at moderate pressures around 20 mTorr at lower power densities. Etch profiles became vertical at lower pressures. Therefore, pattern profiles with perfectly vertical sidewalls or with sidewalls defined by crystallographic planes can be realized merely by changing the etch conditions. The addition of argon to the etch gas increased the edge sharpness of the vertical profiles and eliminated any trace of orientation dependent etching. Sawtooth gratings and submicrometer structures with high aspect ratios have been fabricated.
Focused Ga+ beam direct implantation for Si device fabrication
Authors: Hamadeh H. , Corelli J. C. , Steckl A. J. , Berry I. L.
Published: July 2002

A focused ion beam (FIB) has been used for Si submicron device fabrication. p-n junctions and two terminal resistors were fabricated using a 60 keV Ga+ ion beam of diameter as small as 0.2 μm. Typical resistor dimensions were 50–160 μm in length and 0.2–0.5 μm in width. The Ga+ dose ranged from 5E13 to 5E14 Ga/cm2. I–V measurements showed the correct dependence of resistance on resistor length, width, and impurity concentration. We have studied the broadening of lines implanted in Si and SiO2 using a fixed ion beam diameter as a function of dose level. Selective etch (H3PO3 at 180 °C for Si and HF for SiO2) and SEM analysis showed an increase of 50%–75% in linewidth as the dose was increased by an order of magnitude.
Topographical limitations to the metallization of very large scale integrated structures by bias sputtering: Experiments and computer simulations
Authors: Bader H. P. , Lardon M. A.
Published: July 2002

Aluminum deposition by radio-frequency bias sputtering on grooves and holes with aspect ratios (depth to width) in the range of 0.5–1.0 was studied experimentally and by computer simulation. The structures with an aspect ratio of up to 0.5 were planarized. Aspect ratios larger than about 0.6 however led to the buildup of cavities within the grooves and holes. This limitation for narrow structures with vertical sidewalls was observed experimentally and was in excellent agreement with the results of the profile simulations. The critical aspect ratio may be increased by using a higher bias potential and slope angles of less than 90°.
Characterization of a low voltage, high current density electron probe
Authors: Kinalidis Christodoulos , Wolfe J. C.
Published: July 2002

A low voltage, high current density electron probe has been constructed. Electrons are extracted at 7 keV from a zirconiated tungsten cathode operated in the Schottky emission mode, pass through a two-lens collimated optical system, and are decelerated by a retarding field at the sample. The spot size was shown to be independent of landing energy for several working distances. Peak current densities of 4.3×103 A/cm2 were obtained.
The field solutions for multipole electrostatic deflectors
Authors: Jiang Xin-rong , Na Zhao-feng
Published: July 2002

A unified and simple solution method for the field distribution is described for two kinds of multipole electrostatic deflectors. First of all, having given the conditions how to obtain the uniform field distribution for the deflectors, six forms of the deflectors are calculated for the uniform field adjusting parameters, the uniform field degrees, etc. Secondly, using the uniform field conditions, the field distribution of the deflectors near the optical axis can be greatly simplified, with the result that the distribution can be simply determined by only the electric field E(z), F(z) on optical axis and their second order derivatives. Thirdly, the field parameters of the deflectors are computed by the finite difference method and other numerical methods for Fourier function coefficients, electric field on the optical axis, etc. Finally, an approximate formula for the electric field distribution on optical axis for the deflectors is put forward. The values of the formula are close to those of the numerical calculation in various geometric dimensions of the deflectors.
Gallium clusters from a liquid metal ion source
Authors: Barr D. L.
Published: July 2002

Gallium ion clusters Ga+n with n ranging up to 30 have been measured from liquid gallium ion sources using a time-of-flight spectrometric technique. The observations were made as a function of total ion emission current, angle of emission, and temperature of the liquid metal. Under all conditions Ga+ is the overwhelmingly dominate species emitted. The cluster data reveal several remarkable features. First, emission of clusters tends to be very low below 2 μA emission current, to rise steeply with current to 10 or 20 μA and decrease for higher current. Second, within the range examined, clusters with n=8 and 15 have particularly low abundances. Third, the energy distributions of the resolvable clusters are bimodal with characteristic peaks at approximately 30 and 120 eV below the source potential. Fourth, the angular distributions of the clusters are more nearly axial than that of the primary species. The temperature of the liquid metal has no noticeable effect on cluster emission over the range examined. A possible model for cluster formation will be discussed.
Electron-beam lithography system using a quadrupole triplet
Authors: Okayama Shigeo
Published: July 2002

A variable spot-shaping system using an electrostatic quadrupole triplet has been developed to provide a more flexible pattern generation without loss of beam current accompanying a change of dimension of the shaped beam. The quadrupole electron-beam lithography system (QEBS) consists of a LaB6 electron gun, magnetic illuminating lenses, square apertures, an electrostatic quadrupole triplet, and an octopole deflector. The high precision electrostatic quadrupole triplet has been newly developed for this system. The length of the shaped beam can be varied from 0.3 to 30 μm for a rectangular beam and from 1 to 200 μm for a linear beam by adjusting the excitation voltages of the second and the third quadrupoles. The excitation voltages of the quadrupole triplet are controlled by floating digital/analog (D/A) converters with high voltage amplifiers and high-precision dc voltage sources. Preliminary parttern exposures demonstrate that the QEBS is suitable for forming fine line patterns.
Characterization and optimization of low-pressure chemical vapor deposited tungsten silicide using screening and response surface experimental designs
Authors: Clark Thomas E.
Published: July 2002

Low-pressure chemical vapor deposited WSiX has been characterized and optimized through the use of screening and modeling experimental designs. In the screening study, the effects of temperature, pressure, gas flow rates, and a predeposition treatment were determined for a list of properties which included deposition rate, resistivity, stress, stoichiometry, oxidation rate, particle generation, and resistance to chemical attack. Over the process domain covered, temperature, WF6 flow rate, and SiH4 flow rate were found to affect deposition rate, resistivity, film stress, and stoichiometry while stoichiometry was also affected by pressure. WSiX films produced in the screening study ranged in stoichiometry from X=2.1 to 3.0. The oxidation rate of these samples was found to be insensitive to deposition conditions and unrelated to the as-deposited stoichiometry. As-deposited and annealed film stress were found to decrease linearly with increasing silicon content of the as-deposited films. Similarly, the as-deposited and postannealed resistivity of WSiX films were found to be a function of the initial stoichiometry. Manufacturability related properties such as particle generation, chemical resistance, and uniformity measures involving sheet resistance, resistivity, and film thickness were found to be largely insensitive to the process factors studied. Response surface models were developed for deposition rate, annealed resistivity, annealed stress, and stoichiometry and were used to guide the final process optimization. The optimized process window was relatively large and yielded WSiX films with an annealed (950 °C, 30 min) resistivity of ∼75 μΩ cm, an as-deposited Si/W atom ratio of ∼2.5, annealed tensile stress of ∼1.2×1010 dyne/cm2, and deposition rates of 9 to 10.5 Å/s.
Maskless selected area processing
Authors: Rubloff G. W.
Published: July 2002

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.
Electron beam lithography: Its applications
Authors: Hohn F. J.
Published: July 2002

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.
Low distortion, large area ion beam proximity printing for GaAs field effect transistors and monolithic microwave integrated circuits
Authors: Sen Sudipto , Stumbo D. P. , Fong F-O. , Damm G. A. , Engler D. W. , Wolfe J. C. , Randall John N.
Published: July 2002

We have fabricated a gate-level stencil mask for GaAs field effect transistors with 1000 gates and 1-cm2 silicon foil area. Stress relief distortion was not significant relative to the measurement error of 25 nm(1σ). The results suggest that thermal distortion is also negligible for power densities less than 10 mW/cm2 . This corresponds to a PMMA exposure time of 12 s for 120-keV H+3 ions.
High resolution germanium zone plates and apertures for soft x-ray focalometry
Authors: Tennant D. M. , Raab E. L. , Becker M. M. , O’Malley M. L. , Bjorkholm J. E. , Epworth R. W.
Published: July 2002

Circular Fresnel zone plates, apodized linear zone plates, and a variety of apertures have been fabricated in smooth germanium films deposited on boron doped silicon membranes. Zone widths as small as 60 nm have been fabricated in absorbing layers from 0.25 to 0.5 μm thick. These results were achieved using electron beam lithography in a trilevel resist followed by reactive ion etching to transfer the patterns. These optical elements are key components in a soft x-ray ‘‘focalometer’’ currently being tested at the NSLS at Brookhaven National Laboratories. The focalometer is a system which can be used to determine the imaging properties of an optical element. In this work it has been used to evaluate the imaging properties of a convergent mirror both before and after a multilayer reflective coating was applied. Results of knife edge scans of images formed by a spherical mirror using 14 nm radiation are reported. The multilayer coating applied to the mirror is found to have only a small effect on these scans.
X-ray mask distortion analysis using the boundary element method
Authors: Ohki Shigehisa , Yoshihara Hideo
Published: July 2002

The influence of absorber and membrane stresses on x-ray mask distortions were examined both by simulation and experiments. The boundary element method was used for the numerical simulation of the distortions. Investigations were focused on the distortions appearing in the bulk-Si etching step of the subtractive x-ray mask fabrication method. Distortion measurements were performed using two types of masks in order to investigate the distortions caused by only the membrane stress and both the absorber and membrane stresses, separately. The simulated results show good agreement with the experimental results. Some guidelines to suppress the process-induced distortions were derived by the simulation. The value of the product of stress and thickness of the membrane must be restricted to within 10×104 dyn/cm in order not to deform the Si frame. Pattern position shift is almost suppressed when the membrane stress is nearly equal to the absorber stress. The membrane stress should be controlled to values slightly larger than the absorber stress. If the mask is constructed of a 1 mm thick, 3 in. diam Si frame having a 23×23 mm window region with a Ta stress of 1×108 dyn/cm2 , the SiN membrane stress should be controlled in the region of 1–4×108 dyn/cm2 . This condition limits the shift in position of patterns arranged within the window region to less than 0.03 μm (3σ).
Distortion measurement of embedded absorber (silicon membrane) and conventional (diamond membrane) x-ray masks
Authors: Maluf Nadim I. , Pease R. Fabian W. , Windischmann Henry
Published: July 2002

Distortion of x-ray masks remains an important issue in the development of x-ray lithography. In x-ray masks employing the embedded absorber structure, the absorber material is deposited selectively in the trenches at an elevated temperature. Thermal stresses develop upon cooling the mask due to the mismatch in the coefficients of linear expansion between the absorber and the membrane resulting in distortions. Such x-ray masks were fabricated with 0.45 μm thick tungsten absorber and 2.5 μm thick silicon membrane; the tungsten was deposited by chemical vapor deposition (CVD) at 300 °C. The resulting in-plane-distortions (IPD) were experimentally measured by using a special purpose mask consisting of equal lines and spaces and a large array of fine crosses; the IPD was found by measuring the locations of these crosses at the beginning and the completion of the mask processing. It was found that the maximum IPD is 0.27 μm over a 7.5×7.5 mm2 square die for a typical value of fractional absorber coverage (FAC) of 50%. The results are in agreement with the calculations obtained from a previously developed analytical model suggesting that the distortions are entirely due to thermal stresses, predictable and correctable. Large IPD can be greatly reduced by using a membrane whose Young’s modulus is much larger than that of the absorber. A conventional mask was fabricated by patterning 0.2 μm thick evaporated tungsten on a 1.5 μm thick diamond membrane; it was found that the distortions were reduced to less than 0.07 μm over a 7.5×7.5 mm2 square die in spite of the large intrinsic stress (500 MPa) in the evaporated absorber.
An electron beam line probe with variable aspect ratio
Authors: Brodie A. D.
Published: July 2002

This paper presents a concept for using a line source in combination with quadrupole lenses, operated with a stigmatic focus, to produce a variable aspect ratio line probe. Using a quadrupole doublet and triplet the aspect ratio of a line probe may be varied from 1:1 to 100:1 with high resolution. The quadrupole lenses were considered in two locations: near the source as in conventional shaping optics and as a final lens. The first order optical properties and third order aberrations were calculated to show the feasibility of this concept.
A study of deposited charge from electron beam lithography
Authors: Cummings K. D.
Published: July 2002

This paper presents results from a study of pattern placement errors due to substrate charging in fixed spot direct write electron beam lithography. Experimental results indicate charging-induced errors of over 0.5 μm can occur on a grounded Si substrate. Several theoretical models of the charge distribution are presented. Beam deflection due to the monopole field of the accumulated charge predominate over dipole fields in our system and electrons deposited in the Si substrate create negligible pattern placement errors. Finally, about half of the electrons initially trapped in the resist remain there many hours after exposure.
Charging effects on trilevel resist and metal layer in electron-beam lithography
Authors: Itoh Hiroyuki , Nakamura Kazumitsu , Hayakawa Hajime
Published: July 2002

Charging effects of trilevel resist on a W layer have been investigated with an electron beam lithography system. The tungsten layer was deposited before the resist and the charge-induced beam deflections were measured for several thick W layers. A test pattern was employed consisting of an array 21×21 cross marks in a 3 mm field. The charging effects show different dependencies on W thickness between 20 and 30 keV because of the W backscattering. To evaluate the correlation between the charging and the backscattering process in W and trilevel resist, reflected electron signals were detected from the developed resist marks. The resist mark signal has a double sloped inverse peak characteristic due to backscattering from the W layer and absorption by the resist mark. As a result, the charge-induced beam deflections and the intensity of backscattered electrons are increased in proportion to W thickness. The authors will discuss the electron distribution caused by the electron beam and sample material interacting using these experimental approaches and numerical simulations of electron beam scattering.
Atomic structure of ordered copper adlayers on single-crystalline gold electrodes
Authors: Magnussen O. M. , Hotlos J. , Beitel G. , Kolb D. M. , Behm R. J.
Published: July 2002

We have investigated submonolayer electrodeposits of copper on the three low-index planes of gold in situ by STM. The atomic structure of the clean electrode surfaces and of different ordered Cu adsorbate layers were resolved. For submonolayer Cu coverages on Au(111) and Au(100), deposited under potential control from sulfuric acid solutions, various ordered structures were observed, where the Cu adatoms are arranged in hexagonal or quasihexagonal lattices. The larger Cu-Cu distances in these structures, as compared to the pseudomorphic (1×1) Cu islands formed in vacuum deposits even at low coverages, demonstrate the structure determining role of the coadsorbed anions. For Cu deposition on Au(110) only a (1×1) Cu adlayer was observed. These results are in good agreement with recent ex situ LEED data.
Photon emission scanning tunneling microscope
Authors: Berndt R. , Schlittler R. R. , Gimzewski J. K.
Published: July 2002

The analysis of photons emitted from the tip–surface region of an STM has produced new information on local dissipative processes in tunneling. A key objective to extend our work to a general spectroscopic and microscopic method is to collect and detect photons as efficiently as possible and here we describe our experimental arrangements, one of which incorporates an ellipsoidal mirror and the other a lens system to collect the photons. The systems operate in UHV and have in situ sample and tip transfer facilities. Examples of a variety of photon spectroscopy modes including photon spectra, isochromat spectra, angular distributions, and photon mapping are presented.
Current status of direct growth of CdTe and HgCdTe on silicon by molecular-beam epitaxy
Authors: Sporken R. , Chen Y. P. , Sivananthan S. , Lange M. D. , Faurie J. P.
Published: July 2002

CdTe and HgCdTe can be grown directly on Si(100) substrates by molecular-beam epitaxy. The layers grow in the (111)B orientation. Single domain films are always obtained on Si(100) 8° off toward [011], whereas single and double domain films were obtained on nominal Si(100). A possible reason for the formation of these domains is discussed based on a microscopic model of the CdTe/Si interface. The structural quality of the layers is determined by double crystal x-ray rocking curves. The narrowest rocking curves are obtained on single-domain films grown on nominal Si(100) substrates; a full width at half-maximum (FWHM) of only 230 arcsec was measured, compared to 460 arcsec on the best layer with two domains. For HgCdTe layers grown on CdTe/Si, rocking curves with 110 arcsec FWHM were measured; these layers are n-type with electron mobilities above 5×104 cm2 V−1 s−1 at 23 K for a Cd mol % of 26%.
Novel approach to zero-magnification x-ray mask replication
Authors: Wells G. M. , Krasnoperova A. , Haytcher E. A. , Engelstad R. , Cerrina F. , Fair R. , Maldonado J.
Published: July 2002

A technique for replicating x-ray masks with no magnification of the master mask pattern has been developed. This technique uses a raster scanning pattern with a synchrotron x-ray source to eliminate pattern magnification due to the source divergence. Kinematic mounts were employed to reduce clamping induced distortions in the mask replication process and the metrology tool. Finite element analysis of the thermal response of the clamped master and replicate masks during exposure indicates the temperature increase of the two membranes during exposure is matched, so that thermal distortions are not transferred to the printed pattern.
Proximity effect reduction in x-ray mask making using thin silicon dioxide layers
Authors: Rhee Kee W. , Ma David I , Peckerar Martin C. , Ghanbari R. A. , Smith Henry I.
Published: July 2002

A novel method is reported for reducing the proximity effect in high-resolution electron beam patterning of high atomic number materials such as tungsten. The method involves interposing a thin (50–400 nm) layer of SiO2 between the resist and the underlying high-Z substrate. Examples are shown in which gratings of 0.2 μm lines with a 0.5 μm period were written without proximity effect compensation. Optimal intermediate layer thickness for the best resolution of the gratings is determined to be 200 nm. A Monte Carlo model of electron scattering including inelastic processes has been implemented to interpret our experimental results. The model presented shows that having the low atomic number SiO2 layer between the resist and the tungsten prevents the fast secondary electrons being generated at the surface of the tungsten from propagating back into the resist, suggesting a mechanism for proximity effect reduction. The results presented here have important practical applications for x-ray mask making.
Improvement of the quality of InGaAs/InP quantum wires due to epitaxial overgrowth
Authors: Bergmann R. , Menschig A. , Lehr G. , Kübler P. , Hommel J. , Rudeloff R. , Henle B. , Scholz F. , Schweizer H.
Published: July 2002

Using high-resolution electron beam lithography and a dry etching process, we fabricated InGaAs/InP quantum wires down to a geometrical wire width of 65 nm. In order to reduce surface recombination and surface depletion effects, the quantum wires were buried in an epitaxial layer of InP by low-pressure metalorganic vapor phase epitaxy (LPMOVPE). By optical studies and magnetotransport measurements, an overall improvement of the wire properties due to the epitaxial overgrowth is demonstrated. The quantum efficiency determined from luminescence experiments increased by two orders of magnitude for 65 nm wide quantum wires. Magnetotransport measurements yield an improvement of transport properties in overgrown wires. This article presents a recently developed in situ etching and overgrowth process in the LPMOVPE reactor which reduces the surface effects.
Single layer chemically amplified resist processes for device fabrication by x-ray lithography
Authors: Seeger D. , Viswanathan R. , Blair C. , Gelorme J. , Conley W.
Published: July 2002

Resist systems using synchrotron radiation x-ray lithography for the fabrication of 0.25 μm (Leff) devices has been investigated [R. Viswanathan et al. (unpublished)]. In this study, a chemically amplified negative crosslinking IBM resist, CGR [W. Conley and J. Gelorme, J. Vac. Sci. Technol. B 10, XXXX (1992)], for use on the contact level was the focus. Linewidth control and contrast curves of this system have been studied as a function of a number of parameters including changes in formulations. Mask limited resolution to 0.25 μm feature size (line/space array) has been achieved using a 40 μm mask-to-wafer gap. More important for device fabrication, reproducibility of exposure latitude and resist bias has been demonstrated and will be discussed. Data on the effect of postapply and postexposure bake conditions on the process will also be presented. It is of interest to note that this resist shows little change in linewidth with respect to postexposure bake temperature. This resist system was modeled using aerial images generated from xmas and a thresholding resist development model. The model indicates that the wall profiles for this resist should be somewhat more tapered for isolated spaces than for isolated lines or line/space arrays and is verified experimentally. It is believed that this is related to the slope of the aerial image at the dose used and not inherent to the resist system. A positive resist was also looked at for application on the polysilicon level. A process that has been previously described was used [(a) A. Katnani, Proc. SPIE XX, XXX (1992); (b) D. Seeger, R. Wood, J. Gelorme, and K. Stewart, KTI Interface ’89 (unpublished), p. 351; (c) R. Wood, C. Lyons, R. Mueller, and J. Conway, KTI Interface ’88 (unpublished), p. 341.] and looked at linewidth control across device wafers. Line widths for the polysilicon gates were measured across topography, across field, and from field-to-field and will be described in detail.
Antireflective MoSi photomasks
Authors: Chiba Akira , Matsuda Shuichi , Watakabe Yaichiro
Published: July 2002

Antireflective MoSi (AR-MoSi) photomasks which are produced by applying a thin layer of MoSi oxide directly over the conventional MoSi layer on a quartz substrate has been developed. The thin layer of MoSi oxide is deposited using magnetron dc sputtering. The reflectivity and optical density of the thin layer are not affected by H2SO4 at 120 °C. The layer reflectivity is changed by varying the oxygen partial pressure ratio in argon gas and the layer thickness. To obtain minimum reflectivity, the mechanism of antireflection was studied by using a model of multipath interference with absorption of light. Experimental and theoretical results are in good agreement and show a minimum reflectivity of 6.4% for a 40–60 nm thick MoSi oxide layer. By exposing the photomask, it was found that the AR-MoSi photomask has practicable resolution performance comparable to conventional photomasks.
Characteristics of an improved chemically amplified deep-ultraviolet positive resist
Authors: Nalamasu Omkaram , Kometani Janet , Cheng May , Timko Allen G. , Reichmanis Elsa , Slater Sydney , Blakeney Andrew
Published: July 2002

Chemically amplified positive resist formulations have been shown to exhibit high photospeed, excellent resolution, and tolerance to process parameters such as softbake, exposure, postexposure bake, developer concentration, and temperature. Many chemically amplified positive resists, however, adhered poorly to some substrates (e.g., Si3N4), required considerable optimization of the etch process to achieve desired etch selectivities and were sensitive to airborne basic contaminants. Many chemically amplified negative resists while not as sensitive to contaminants in the clean room air, show retrograde wall angles especially on antireflection coatings, demonstrate poor latitude in defining contact holes and are difficult to strip after pattern transfer steps. In this article we discuss our efforts toward designing new deep-ultraviolet (UV) matrix resins and resist formulations as well as efforts toward defining an optimized process. The optimized resist process demonstrates 0.25 μm line and space (L/S) and 0.30 μm contact hole resolution in 0.8 μm thick resist films with a GCA deep-UV exposure tool. The resist also exhibits excellent adhesion on most semiconductor substrates (e.g., Si, polysilicon, SiO2, Si3N4), thermal stability to at least 140 °C, an order of improvement in postexposure delay latitude over that of CAMP1 (poly t-butoxycarbonyloxystyrene-sulfone formulated with photoacid generators) and etch selectivity comparable to that of novolac based resists. In addition, the polymers developed were designed for ease of manufacture with regard to reproducibility, low metal concentration, and cost.
Gate technology for 89 GHz vertical doping engineered Si metal–oxide semiconductor field effect transistor
Authors: Jeon D. Y. , Tennant D. M. , Kim Y. O. , Yan R. H. , Lee K. F. , Early K.
Published: July 2002

The gate definition performed on a vertical doping engineered metal–oxide semiconductor field effect transistor is described. The fabricated gates were as narrow as 0.15 μm. For writing narrow gates, e-beam lithography and a chemically amplified negative resist SAL603 were used. The alignment between the gate level and underlying Nikon-printed levels was made using 0.8 μm deep trenched marks. The gate patterning was done with reactive ion etching (RIE) in CHF3 gas to etch a nitride layer which serves as a gate etch mask and subsequently in a Cl2 gas used to etch the polysilicon gate. A sidewall spacer was formed with a two step etch using CF4 RIE and CHF3 RIE after deposition of a 2000 Å TEOS film. After metallization the n-channel devices have measured excellent device characteristics.
Overlay performance of x-ray steppers in IBM Advance Lithography Facility
Authors: Progler C. J. , Chen A. C. , Gunther T. A. , Kaiser P. , Cooper K. A. , Hughlett R. E.
Published: July 2002

This article describes the overlay performance of the Suss XRS200/3 synchrotron compatible x-ray steppers installed in the IBM Advanced Lithography Facility. The Suss XRS200/3 uses a video-based brightfield microscope alignment system. The overall performance of the stepper was described previously. This article will specifically focus on the test, optimization, and performance of the alignment system. In the Suss alignment system, the quality of optics and test methods of the optical assembly was a critically important factor in achieving the 110 nm overlay quoted previously. A detailed discussion is given on the selection and characterization of these alignment optics, along with the subsystem level tests used to ensure performance of the complete imaging assembly prior to and after installation on the main stepper body. The overlay test methodology and data obtained during the acceptance testing is also discussed in detail. The exposure testing was designed to measure a full range of performance of the stepper. Indeed, overlay ranged from 50 nm (mean plus three sigma) on the very best levels to in excess of 150 nm on the most difficult. Sensitivity of the alignment system to small film thickness changes was tested along with alignment precision as a function of alignment mark depth or signal contrast.
X-ray mask replication using square synchrotron radiation illumination
Authors: Reilly M. , Wells G. M. , Guo J. , Wallace J. P. , Edwards N. , Cerrina F. , Melngailis J.
Published: July 2002

X-ray masks are an expensive part of the x-ray lithographic technology. The overall mask making process can be simplified and the cost reduced by a judiciously applied replication process. It is desirable that the copy has negligible feature bias and minimal placement distortion. It should therefore be produced by a process that has the greatest possible latitude with respect to dose and gap. In this article, it is described how these conditions are met. The latitude requirement is met by engineering the exposure system so that the source has a prescribed amount of spatial incoherence. This technique is an extension of the zero magnification method used by Wells et al. [J. Vac. Sci. Technol. B 10, 3221 (1992)]. This approach is particularly well suited for synchrotron-based x-ray lithography.
X-ray stepper aiming at 0.2 μm synchrotron orbital radiation lithography
Authors: Uchida Norio , Kuwabara Osamu , Ishibashi Yoriyuki , Kikuiri Nobutaka , Hirano Ryoichi , Nishida Jun , Nishizaka Takeshi , Kikuchi Yukiko , Yoshino Hisakazu
Published: July 2002

A vertical x-ray stepper has been developed for 0.2 μm synchrotron orbital radiation lithography. The key features of this prototype stepper are a new gap setting algorithm, an optical heterodyne alignment system, and a newly developed fine motion mask stage. Gap setting is executed so as to make the mask and wafer parallel to the travel plane of the wafer x–y stage so that only one gap setting per wafer is required. The gap setting accuracy between 20 and 50 μm gaps is better than ±1.5 μm (3σ) for each exposure position. The optical heterodyne alignment signal obtained by detecting the diffraction beams from two checkerboard gratings has a detectable resolution of better than 0.01 μm and has only a small dependence of ±0.02 μm on gap variation. The alignment signals are fed back to the mask stage which can align the mask and wafer with a resolution of 5 nm. In exposure experiments, 0.15 μm lines and spaces were printed on a negative resist (SAL 601) and a 0.05 μm overlay accuracy has been obtained.
Etched-quartz fabrication issues for a 0.25 μm phase-shifted dynamic random access memory application
Authors: Ferguson R. , Martino R. , Budd R. , Hughes G. , Skinner J. , Staples J. , Ausschnitt C. , Weed J.
Published: July 2002

A 0.25 μm pattern from a dynamic random access memory application is used to assess the impact of an etched-quartz fabrication process on the lithographic performance of an actual phase-shifted circuit design. A new measurement tool called the aerial image measurement system is used to quantify the effects of an isotropic wet etch following the quartz reactive-ion etching step on the printability of the phase-shifted pattern at two values of partial coherence. The presence of significant transmission and phase errors, in part a result of optical scattering from the edges and/or corners of the etched-quartz trench, reduced the potential benefits obtained from phase shifting. At the optimum postetch conditions for a partial coherence of 0.36, only 65% of the ideal depth-of-focus was obtained. Transmission errors were reduced from greater than 25% with no postetch treatment to less than 5% with wet-etch depths in excess of 1100 Å. However, large phase errors, between 20° and 60°, were present for all postetch conditions, and were strongly dependent on the partial coherence. Optimization of depth-of-focus required a nominal wet-etch depth of 1200 Å for σ=0.6, but only a 900 Å depth at σ=0.36. Large variations in the phase error as a function of the postetch treatment conditions were attributed to electromagnetic resonance phenomena between the sidewalls of the etched-quartz trench.
Evaluation of depth-of-focus in photolithography at 193 and 248 nm for feature sizes of 0.25 μm and below
Authors: Rothschild M. , Doran S. P. , Barouch E. , Hollerbach U. , Orszag S. A.
Published: July 2002

The aerial image of alternative exposure systems was calculated in order to determine process latitude in photolithography at 0.25 μm and below. A fast software package was used for both simple and complex mask patterns. The depth-of-focus (DOF) was obtained with the aid of exposure–defocus plots at 193 and 248 nm. The numerical aperture and degree of spatial coherence were varied over a wide range. The effects of annular illumination were also studied. It was shown that for most geometries the DOF at 193 nm exceeds that of 248-nm systems. Only for equal lines and spaces does a 248-nm tool with annular illumination possess a DOF comparable to that of a conventionally illuminated 193-nm system.
Simulation of x-ray generation based on electron trajectory calculation
Authors: Koshishiba H. , Yoshimura M. , Nakagawa Y.
Published: July 2002

A continuous x-ray generation simulator is proposed for analyzing x-ray generation processes at the target of a microfocus x-ray tube. The cross section for braking radiation shown by Heitler is integrated by the numerical method and introduced into the Monte Carlo calculation on electron scattering. In addition to electron trajectories, the x-ray generation points and energies of x rays are calculated through the use of random numbers. By calculating the distribution of x-ray generation points for a reflective-type target and a thin film target, the thin film target is demonstrated to be necessary in obtaining a minute focal spot size. A prototype x-ray imaging system was therefore developed using a thin film target to achieve a high resolution of 1 μm. Electron beams are focused to within 0.8 μm by two magnetic lenses and applied to a two layer film target consisting of 1 μm thick tungsten and 10 μm thick beryllium.
Critical passivation ledge thickness in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Liu William , Harris James S.
Published: July 2002

Npn AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are fabricated to examine the critical passivation ledge thickness needed to prevent current gain degradation due to extrinsic base surface recombination current. The current gains of these molecular-beam epitaxially grown HBTs with Be-doped base layers are measured as the passivation ledge is gradually etched away. Experimental results indicate that partial passivation is achieved with a ledge thickness of 300 Å and a maximum current gain is measured with a ledge thickness of 900 Å. The ideality factor values of the base currents at various etch depths are also examined and compared with published results.
Cryogenic and high temperature operation of Al0.52In0.48P/In0.2Ga0.8As high electron mobility transistors
Authors: Kuo J. M. , Chan Y. J.
Published: July 2002

The cryogenic and high temperature characterization of Al0.52In0.48P/In0.2Ga0.8As high electron mobility transistors (HEMTs) with 1 μm-long gates, grown by gas-source molecular-beam epitaxy is being reported. Bias-stress measurements at 77 K in the dark showed only 18 mV threshold voltage shift, confirming that trapping effects are negligible in this material system. Successful operation of these HEMTs at temperatures up to 300 °C has been achieved. These results suggest that AlInP/InGaAs HEMTs have potential for cryogenic and high temperature applications.
Continuous writing method for high speed electron-beam direct writing system HL-800D
Authors: Kawano Masamichi , Mizuno Kazui , Yoda Haruo , Sakitani Yoshio , Andou Kimiaki , Saitou Norio
Published: July 2002

Hitachi has developed a new e-beam direct writing system named HL-800D [Y. Sakitani, H. Yoda, Y. Shibata, T. Yamazaki, and K. Ohbitu, J. Vac. Sci. Technol. B 10, 2759 (1992)]. This system has been developed for mass production of ultra-large scale integrated circuits such as a 256M-DRAM manufactured with high accuracy and high throughput. To achieve a productive level of throughput, this system employs a continuous writing method with variable stage speed. In the method, an e-beam traces a moving wafer stage accurately using deflections during continuous writing, and the wafer stage moves with the most suitable speed depending on the writing pattern density. The continuous writing method makes considerable improvement in throughput compared with a conventional ‘‘step and repeat’’ stage moving method. Stitching accuracy is confirmed by test writing.
Proximity effects in low-energy electron-beam lithography
Authors: Stark T. J. , Edenfeld K. M. , Griffis D. P. , Radzimski Z. J. , Russell P. E.
Published: July 2002

In this work, the accuracy with which patterns can be delineated in electron-beam lithography has been characterized in terms of the range of the electrons relative to the pattern size being produced. In addition, the interdependence of the minimum feature size, film thickness, and beam energy have been investigated for low-beam energy exposures. Palladium acetate has been used as a model resist, and beam energies ranging from 1 to 30 keV have been used for exposures. The results indicate that the proximity effect can be eliminated by reducing the range of the electrons below the minimum feature width and that the thickness of the imaging layer must be less than 2/3 of the electron range for adequate exposure. The loss of resolution due to increased probe size at low beam energies has also been investigated.
Intelligent design splitting in the stencil mask technology used for electron- and ion-beam lithography
Authors: Behringer U. , Engelke H.
Published: July 2002

Over the last ten years, projection lithography techniques have been developed for exposing sub-half-micron patterns by electron- or ion-beam irradiation. Most of these systems use a mask with physical holes, the so-called ‘‘stencil’’ or ‘‘transmission’’ mask, to avoid scattering of the corpuscular beam by the atomic lattice of the mask material. This article presents a topological solution of the well-known mask stencil problem. The basic idea is to synthesize a pattern by overlaying the projected images of a pair of complementary half-patterns. Partitioning ground rules are summarized which ensure manufacturability and mechanical stability of the two complementary half-patterns. All the steps necessary for implementing the ground rules in APL2 (a programming language) are given. They comprise generation and selection of cutting vectors, partitioning of the shape network into meshes, and distribution to two different mask levels. The method is applicable to arbitrary polygonal sets. No double exposures are generated.