bluuebunny/crossref_metadata_2025 huggingface dataset:
Projection ion beam lithography
Authors: Löschner H. , Stengl G. , Chalupka A. , Fegerl J. , Fischer R. , Hammel E. , Lammer G. , Malek L. , Nowak R. , Traher C. , Vonach H. , Wolf P. , Hill R. W.
Published: July 2002

Demagnifying mask-to-wafer projection with ion beams is a potential lithographic technique for high volume device production with large process latitudes. Sub-0.1 μm resolution is possible with more than 10 μm depth of focus. Furthermore, there is the possibility of an electronic alignment on-line during chip exposure with nanometer precision: ‘‘pattern lock’’ may be achieved in feedback control loops by controlling X and Y position, rotation, scale, difference in X–Y scale and trapezoidal distortion of the projected ion image by dipole, quadrupole, and hexapole fields induced in an electrostatic multipole, by axial magnetic fields generated in a solenoid, and by the fine adjustment of lens voltages. Results obtained with an advanced research type ‘‘Alpha Ion Projector’’ are presented with the focus on recent exposure latitude evaluations. Further developments of ion projection lithography are discussed concentrating on electrostatic lens optics for the realization of large exposure fields (20×20 mm2–35×35 mm2) with less than 20 nm distortion. Results of a cost of ownership model for ion projection steppers are presented.
Growth of group III nitrides on Si(111) by plasma-assisted molecular beam epitaxy
Authors: Stevens K. S. , Ohtani A. , Schwartzman A. F. , Beresford R.
Published: July 2002

Wurtzitic single-crystal GaN and polycrystalline (columnar) InGaN have been grown on the Si(111) face in an electron cyclotron resonance plasma-assisted molecular beam epitaxy process. Reflection high-energy electron diffraction shows registry of the nitride basal-plane triangular lattice with respect to the Si(111) substrate triangular network. Plan-view transmission electron microscopy images reveal crystalline or polycrystalline GaN structure depending on growth temperature. High-resolution x-ray rocking curves of the (0002) peak were as narrow as 30 min for a 0.6-μm GaN film grown on a thin AlN buffer layer at 750 °C.
Determination of AlAs mole fraction in AlxGa1−xAs using Raman spectroscopy and x-ray diffraction
Authors: Solomon G. S. , Kirillov D. , Chui H. C. , Harris J. S.
Published: July 2002

High resolution x-ray diffraction (HRXRD) is used to accurately determine the AlAs mole fraction in AlxGa1−xAs samples over the complete alloy range. The AlAs mole fraction error in the HRXRD measurement is estimated to be less than 0.0035. A small bowing in the variation of the alloy lattice constant with changing AlAs mole fraction is observed. The HRXRD characterized samples are used in Raman spectroscopy to calibrate the variation in the longitudinal optical (LO) GaAs and AlAs modes with varying alloy composition. Empirical expressions for the variation in the LO modes are found, with mole fraction errors of less than 0.03. Raman spectroscopy is a relatively simple nondestructive measurement and the expressions developed here allow for the fast determination of AlAs mole fraction in AlxGa1−xAs samples. The Raman data is compared to a theoretical dependence for a two phonon mode alloy crystal with excellent results.
Gate technology for 0.1-μm Si complementary metal–oxide–semiconductor using g-line exposure and deep ultraviolet hardening
Authors: Jeon D. Y. , Chin G. M. , Lee K. F. , Yan R. H. , Westerwick E. , Cerullo M.
Published: July 2002

A gate technology for producing 0.1-μm gate length silicon complementary metal–oxide– semiconductor (CMOS) circuits has been developed by integrating g-line exposure, resist narrowing, deep UV hardening, and dry etching of nitride and polysilicon. The 0.1-μm gate length n-channel and p-channel MOS devices have been previously processed via e-beam lithography using a chemically amplified e-beam resist. However, the e-beam technique suffers from low throughput, especially in processing complex circuits. In addition, the chemically amplified e-beam resist requires prompt processing. Thus g-line exposure and photoresist narrowing was chosen as an alternative. The resist features were narrowed from 0.5 μm down to 0.1 μm using low power O2 plasma. The profile of the narrowed resist shows that the body is thicker than the base. The narrowed resist features were then hardened by deep UV in order for the photoresist to withstand the subsequent nitride etch using CHF3 reactive ion etching (RIE). The obtained nitride profile shows a rounded top which is expected from the profile of resist features. The subsequent polysilicon etch was done using a two-step Cl2 RIE. The obtained profile of polysilicon is comparable to that previously obtained using e-beam lithography. This gate technology was used to successfully fabricate 0.1-μm circuits such as conventional unloaded CMOS ring oscillators and 2:1 frequency dividers.
Comparison measurement in the hundred nanometer range with a crystalline lattice using a dual tunneling-unit scanning tunneling microscope
Authors: Kawakatsu Hideki , Higuchi Toshiro , Kougami Hiroshi , Kawai Minoru , Watanabe Michihito , Hoshi Yasuo , Nishioki Nobuhisa
Published: July 2002

Since scanning probe microscopes scan the probes mechanically along the samples, accuracy of lateral scales of acquired images is mainly determined by the calibration of the movement of the end point of the probes. A dual tunneling unit scanning tunneling microscope (DTU-STM) with an xy stage for simultaneous lateral scanning of both the sample and the scale-reference crystal was developed. It enables calibration of the lateral scale of the sample image under the assumption that the lattice spacing is constant. Accuracy and problems of the proposed method were evaluated by comparing images of graphite simultaneously or consecutively acquired with the DTU-STM. For simultaneously acquired images in the 10 nm range, calibration of drift rates of the tips to the samples, and tilt of the samples to the xy plane were found to be effective in improving the accuracy of comparison measurement to 98.9±1.5%, regardless of orientation. The accuracy marked a higher value of 99.7±0.25% in the direction of the line scan, since the effect of thermal drift is less dominant in the direction. Consecutive single-line scanning of 150 nm with a rate of 380 ms/line, at 30 min intervals, gave an accuracy of over 99.98±0.036%.
Target temperature prediction for plasma source ion implantation
Authors: Blanchard James P.
Published: July 2002

Plasma source ion implantation (PSII) is a plasma-based ion implantation technique which requires pulsed operation. Because the power incident on the implanted objects (targets) can be large, target temperatures can be quite high. Therefore, target temperature prediction can be quite useful, both in reaching high temperatures when they are desirable, and in avoiding high temperatures when they are undesirable. In this paper, a simple, time-dependent, lumped-capacity thermal model is developed for predicting temperatures in PSII targets. Two simple analytical models are used to justify the assumptions used in developing the lumped model. Comparison of the model with measured target temperatures is used to validate the assumptions of the model. The comparison is favorable.
Arsenic capping and decapping of InyAl1−yAs(100) grown by molecular beam epitaxy
Authors: Clark S. A. , Dunscombe C. J. , Woolf D. A. , Wilks S. P. , Williams R. H.
Published: July 2002

A study of the surface of InyAl1−yAs, grown lattice matched on InP(100) by molecular beam epitaxy, protected by an As cap during storage in air and subsequently annealed in ultrahigh vacuum, is presented. The surface structure and stoichiometry of the layers are investigated by low energy electron diffraction and x-ray photoemission spectroscopy. These investigations show that decapping may be achieved by annealing the sample at 390 °C to reveal an atomically clean, As-stabilized surface, exhibiting a (3×1) symmetry. It is also shown that the relative population of In and Al on or near the surface is different from that of the underlying bulk InyAl1−yAs layer and that the overall surface symmetry and stoichiometry may be further adapted by annealing to higher temperatures.
Sputtering of fibrous-structured low-stress Ta films for x-ray masks
Authors: Yoshihara Takuya , Suzuki Katsumi
Published: July 2002

In order to achieve precise control for the internal stress of x-ray absorber films, we have controlled the sputtering-gas (Xe) pressure within ±0.002 Pa (at 0.5 Pa) using a newly developed ultrahigh-vacuum sputtering system, but we found that it was difficult to reproducibly obtain sufficiently low-stress Ta films over the long term. We therefore investigated the relationship between the internal stress and substrate temperature at a low deposition pressure (0.45 Pa). It was found that internal stress changes basically toward tensile with increasing substrate temperature because of the bimetal effect, but at substrate temperature from 205 to 220 °C, the internal stress changes toward compressive with increasing temperature. We characterized Ta films deposited at various temperatures using x-ray diffraction and secondary electron microscopy and found that a film deposited at 205 °C was columnar-structure β-Ta and that one deposited at 240 °C was fibrous-structured β-Ta. Films deposited at temperatures higher than 270 °C were rough-surfaced α-Ta. For films deposited at pressures lower than 0.8 Pa and at a substrate temperature of 240 °C, the internal stress was almost constant regardless of gas pressure fluctuation. Thus, at 240 °C and 0.45 Pa, we can deposit low-stress (<5×107 N/m2) Ta films with excellent long-term reproducibility.
Impact of lens aberrations on phase-shifting masks
Authors: Kostelak R. L. , Raab E. L. , Vaidya S.
Published: July 2002

The application of phase-shifting mask (PSM) technology in a manufacturing environment will ultimately be decided by whether this technology provides sufficient enhancement to warrant the additional costs. Initial experimental results on flat wafers and in the center of the field have demonstrated that for select feature types and layouts there is considerable improvement in the process margin when PSM are employed. However, these studies did not include the impact of residual lens aberrations in the optical exposure system. This study examines the effect of lens aberrations on the application of attenuating PSM through both SPLAT-generated (simulation of projection lens aberrations via TCCs) simulation and direct aerial image monitoring using latent image metrology. To benchmark the results obtained, all the work has been compared against a binary intensity mask (BIM). The simulation study concentrated on the three major Siedel aberrations detected in current i-line steppers, namely, coma, astigmatism, and spherical aberrations. The SPLAT-generated aerial images with these selected aberrations degrade the process latitude for both BIM and attenuated PSM; however, the initial enhancement provided by the phase-shifting technique made the attenuated PSM more tolerant of the aberration. As the feature size increased and the incremental process latitude gained by the phase-shifting technique decreased, the magnitude of the degradation with the two mask types became comparable. In summary, while PSM exposed on steppers will still maintain their performance superiority over BIM, the real improvement in process margin will suffer depending upon the feature type and layout.
Characterization of a 193 nm optical lithography system for 0.18 μm and below
Authors: Grenville A. , Owen G. , Pease R. F. W.
Published: July 2002

A method previously employed for characterizing lithographic performance independent of resist processing has been applied to Markle–Dyson optics working at 0.7 NA and 193 nm to demonstrate diffraction limited imaging down to 0.15 μm resolution. Excellent agreement is shown between theory and experimentally measured modulation as a function of spatial frequency, defocus, and numerical aperture. We have also measured both tangential and sagittal field curvatures and found close correlation with simulation. No loss of contrast was observed inside the semicircular field of 2 mm diameter. Reflective 1× masks required for the experiment were patterned in silicon on fused silica down to 0.12 μm linewidths. To characterize the projection optics further, we have printed 0.16 μm features in resist using no resolution enhancement techniques.
Characterization of an expanded-field Schwarzschild objective for extreme ultraviolet lithography
Authors: Kubiak G. D. , Tichenor D. A. , Ray-Chaudhuri A. K. , Malinowski M. E. , Stulen R. H. , Haney S. J. , Berger K. W. , Nissen R. P. , Wilkerson G. A. , Paul P. H. , Bjorkholm J. E. , Fetter L. A. , Freeman R. R. , Himel M. D. , MacDowell A. A. , Tennant D. M. , Wood O. R. , Waskiewicz W. K. , White D. L. , Windt D. L. , Jewell T. E.
Published: July 2002

The performance of a new 10×-reduction Schwarzschild system for projection imaging at 13.4 nm wavelength is reported. The optical design is optimized to achieve 0.1 μm resolution over a 0.4 mm image field of view, an increase in area of a factor of 100 over previous designs. An offset aperture, located on the convex primary, defines an unobscured 0.08 numerical aperture. The system is illuminated using extreme ultraviolet (EUV) radiation emitted from a laser plasma source and collected by an ellipsoidal condenser. A 45° turning mirror is used to relay the collected EUV radiation onto a near-normal reflecting mask. Multiple sets of primary and secondary elements were fabricated, matched, and clocked to minimize the effects of small figure errors on imaging performance. Optical metrology indicates that the wave-front error within the subaperture used is within a factor of 2 of the design value. Images recorded in poly(methyl methacrylate) and ZEP 520 (Nippon Zeon) resists reveal good imaging fidelity over much of the 0.4 mm field with equal line/space gratings being resolved to 0.1 μm.
Imaging of extreme ultraviolet lithographic masks with programmed substrate defects
Authors: Nguyen K. B. , Mizota T. , Haga T. , Kinoshita H. , Attwood D. T.
Published: July 2002

Extreme ultraviolet lithographic masks with programmed defects on the mask substrates have been imaged to study substrate defects printability. The imaging was performed with a 2-aspherical-mirror system operating at 14 nm wavelength. Results showed that 25 nm thick substrate defects caused observable distortions of resist patterns. Defects of sizes approximately half the minimum resolvable features resulted in 15%–20% variations in resist linewidths. However, since the imaging system was operating at a reduced resolution due to misalignments of the optics, the effect of the defects may have been partially concealed by the phase front distortions caused by mirror misalignments. The defects are difficult to observe under a scanning electron microscope.
Yaw compensation for an electron-beam lithography system
Authors: Innes Robert
Published: July 2002

Recent experience with the wayless planar stage designed by IBM shows that accurate e-beam lithography is possible in the Write-on-the-FlyTM mode with varying stage yaw. The metrology equations necessary to compensate for yaw and axial misalignment of the interferometers with respect to the laser beam are introduced for plane mirror interferometers of the double-beam type. Geometric equations are derived for various errors of setup of the column, lasers, and interferometers, and for relative positioning errors of the distance and yaw interferometers. The rotation of beam electron deflections and the required yaw-induced electron-beam offset are updated within 10 μs using digital signal processors. The offsets for each coordinate sufficient for Write-on-the-Fly lithography are constants to be determined by calibration in terms of the form: const×sin(yaw), const×(interferometer reading)×sin(yaw), and (interferometer reading+const) ×[1−cos(yaw)]. The optimum choice of the definition of the zero point of yaw and the effect of this choice on both the form of the metrology equations and the calibration procedures are discussed.
Nanometer-scale patterning of high-T
c superconductors for Josephson junction-based digital circuits
Authors: Wendt J. R. , Plut T. A. , Corless R. F. , Martens J. S. , Berkowitz S. , Char K. , Johansson M. , Hou S. Y. , Phillips J. M.
Published: July 2002

A straightforward method for nanometer-scale patterning of high-Tc superconductor thin films is discussed. The technique combines direct-write electron beam lithography with well-controlled aqueous etches and is applied to the fabrication of Josephson junction nanobridges in high-quality, epitaxial thin-film YBa2Cu3O7. We present the results of our studies of the dimensions, yield, uniformity, and mechanism of the junctions along with the performance of a representative digital circuit based on these junctions. Direct current junction parameter statistics measured at 77 K show critical currents of 27.5 μA±13% for a sample set of 220 junctions. The Josephson behavior of the nanobridge is believed to arise from the aggregation of oxygen vacancies in the nanometer-scale bridge.
Dynamic corrections in MEBES 4500
Authors: Pearce-Percy Henry , Prior Richard , Abboud Frank , Benveniste Albert , Gasiorek Leonard , Lubin Michael , Raymond Frederick
Published: July 2002

Some systematic errors of the mebes raster scan lithography system are examined and how significant accuracy improvements can be achieved is demonstrated. The accuracy improvements result from error compensation hardware and software applying corrections that are either a function of time (write scan position) or of position on the substrate. Error analysis shows the following correctable errors to be among the largest error sources in the mebes iv: electronic noise, stage z runout, deflection alignment drift, mask flatness, and clamping distortion, and scan nonlinearity. These errors contribute to placement/overlay accuracy and to butting accuracy. The dynamic corrections implemented are automatic write scan correction, which reduces deflection alignment errors, scan linearity measurement and correction, grid correction, and height detection and correction, which reduce cassette height and mask flatness errors. With these corrections implemented, system performance improves dramatically.
Overlay enhancement with product-specific emulation in electron-beam lithography tools
Authors: Puisto Denise , Sturans Maris , Lawliss Mark
Published: July 2002

Electron-beam image–placement errors, commonly expressed as registration and overlay errors, are becoming increasingly critical as the device dimensions shrink into the subhalf-micrometer range. Contributors to image-placement errors include: (1) system limitations, i.e., noise and minimum exposure increment or least-significant bit (LSB); (2) column and resist charging; (3) substrate and carrier clamping; (4) resist stress; (5) thermal effects; and (6) mask-processing effects. This article attempts to quantify the magnitude of positional errors attributable to these effects using experimental data from x-ray membrane exposures under various conditions; when possible, a comparison to theoretical data is made. Although the image–placement errors from many of the previously mentioned contributors are typically very repeatable, they are difficult to eliminate. Methods such as discharge layers, decreased exposure time, and alternate resist systems can minimize the effects but may cause other problems such as defects due to an increased number of processing steps. A new method has been developed to address the repeatable errors. Pattern-specific errors for a particular exposure are measured, and a calibration known as product-specific emulation (PSE) is formed. This article explains the method used to accumulate the PSE data and demonstrates results on some dense product patterns.
Address data reduction and lithography performance of graybeam writing strategies for raster scan mask generation
Authors: Muray Andrew , Abboud Frank , Raymond Frederick , Berglund C. N.
Published: July 2002

Graybeam (GB) writing methods [Muray, Abboud, and Raymond, J. Vac. Sci. Technol. B 11, 2390 (1993)], including the new combination of graybeam plus per pixel deflection (GBPPD), were first investigated last year as a method for improving throughput on an e-beam raster scan machine. These techniques were shown to produce pattern edge placement resolution equivalent to writing at a smaller address unit, thereby improving throughput. The GB and GBPPD writing techniques are further investigated to address data reduction and lithographic performance. Accurate simulations and lithography on two-dimensional test patterns for GBPPD writing are presented.
Surface imaging by silylation for low voltage electron-beam lithography
Authors: Böttcher M. , Bauch L. , Stolberg I.
Published: July 2002

Electron-beam lithography with low voltage electrons offers a number of advantages. Low voltage electrons have short penetration depths. Therefore, backscattering from the substrate which causes the proximity effect as well as radiation damage in the substrate are potentially minimized or excluded. As a consequence, a top surface imaging resist technology should be applied. The surface imaging by silylation was combined with low voltage electron exposure using 1.8-, 3-, and 5-keV electrons. Resist structures down to 50 nm are shown.
Tungsten etching in pulsed SF6 plasmas
Authors: Petri R. , Kennedy B. , Henry D. , Sadeghi N. , Booth J.-P.
Published: July 2002

Tungsten etching in pulsed plasmas has been investigated in a helicon plasma source reactor. The time dependence of the fluorine atom concentration has been measured using the time-resolved actinometry technique and related to the etch rate. According to our observations, it appears that fluorine adsorption on the tungsten substrate surface continues in the post-discharge period until the surface saturates. Moreover, it appears that two etching regimes exist. For short discharge off periods, the etching is limited by the fluorine adsorption ability of the surface, whereas for long periods, the etching is limited by the desorption rate of the etch products. Experiments were performed at different substrate temperatures and plasma gas pressures. An empirical model has been developed, in good agreement with the experimental data.
Acid generation process by radiation-induced reaction in chemically amplified resist films
Authors: Watanabe T. , Yamashita Y. , Kozawa T. , Yoshida Y. , Tagawa S.
Published: July 2002

A new interpretation of the acid generation process in novolak resin systems is reported. To investigate the acid generation process in chemically amplified resist, a novolak resin system with an acid generator (PAG) was employed. In order to analyze the acid generation process, the visible absorption characteristics from a conventional spectrophotometer, and nanosecond and millisecond pulse radiolysis systems, were analyzed. For m-cresol novolak with triphenylsulfonium triflate, it was hypothesized that acid would be generated during exposure; however, it is asserted that a protonated intermediate was generated during exposure and that acid was generated during exposure, and more acid was formed during PEB. The yield of the acid during PEB, rather than that of the protonated intermediate during exposure, was strongly influenced by the presence of triphenylamine. A comparison of the experimental result for m-cresol novolak which contains PAG with that for p-cresol novolak which also contains PAG indicates that the time range of acid generation may be dependent on the base resin system.
Combined lithographies for the reduction of stitching errors in lithography
Authors: Koops Hans W. P. , Kretz Johannes , Weber Markus
Published: July 2002

A new way of lithography is presented, which makes use of overlapping address fields to expose patterns by conventional or unconventional lithographies and uses the overlap area to position subsequent pattern areas with high accuracy by image processing. Dot marks are generated by beam induced deposition in the overlap areas at the end of the exposure process of each field. Then the sample is moved to the next field. The marks are searched by taking a highly magnified image scan in a reduced area. The mark position is evaluated by processing of this image to determine the new position of the sample. The position is obtained in the address scale used for exposure with an accuracy of ±1 address steps, which makes it possible to stitch the adjacent pattern in the next field with this precision. Having a ‘‘coarse’’ field or stage positioning means with 1-μm precision is now sufficient to obtain patterns, which are stitched with an accuracy of 1 nm by using an address field of ≳14 bit for the overlapping fields and by sacrificing an area of <1% of the address area for the mark detection in the overlap region. The method is especially applicable to nanolithography with instruments and processes that allow inspection of the mark without destroying the lithography area. In this case, only the mark area of the size of a few pixels is lost for the patterning within the fields. This is especially valid for scanning probe lithographies and beam induced deposition lithography methods.
High-resolution definition of buried InGaAs/InP wires by selective thermal intermixing
Authors: Kerkel K. , Oshinowo J. , Forchel A. , Weber J. , Laube G. , Gyuro I. , Zielinski E.
Published: July 2002

Buried InGaAs/InP wire structures with widths down to 30 nm by using a new and simple fabrication technique have been developed. The key point is the local removal of the InP top barrier layer of an InGaAs/InP quantum well using high-resolution electron-beam lithography and selective wet chemical etching. The patterned sample is then subjected to a rapid thermal annealing step. The InGaAs surface quantum wells, formed in the etched parts of the samples, display an enhanced interdiffusion compared to conventional quantum wells covered with an InP cap layer. This leads to a local increase of the band gap, which confines the carriers to the InP covered regions. The wires show sharp photoluminescence emission bands even for the smallest wire widths and a significant increase of the emission intensity due to carrier capture from the vertical and lateral barriers.
Advances in near field holographic grating mask technology
Authors: Tennant D. M. , Dreyer K. F. , Feder K. , Gnall R. P. , Koch T. L. , Koren U. , Miller B. I. , Vartuli C. , Young M. G.
Published: July 2002

We report progress on several practical issues of near field holographic (NFH) printing for optoelectronic applications. In particular, we report on the following: adaptation of the mask making process to large area holographically generated grating masks; evaluation of a commercially available UV contact aligner modified to allow routine NFH printing; use of mask copies to avoid excessive wear on original masks; options for reducing the writing time for e-beam generated grating masks; and the application of e-beam generated grating masks to a DFB six-laser array with 200-GHz frequency channel separation.
Optical second harmonic generation: A probe of atomic structure and bonding at Si–SiO2 interfaces, and other chemically modified Si surfaces
Authors: Emmerichs U. , Meyer C. , Bakker H. J. , Wolter F. , Kurz H. , Lucovsky G. , Bjorkman C. E. , Yasuda T. , Ma Yi , Jing Z. , Whitten J. L.
Published: July 2002

Optical second harmonic generation (SHG) is a highly surface-sensitive probe for studying crystalline Si surfaces because the inversion symmetry is broken and electric dipole optical SHG processes forbidden in the bulk are allowed. The polarized optical SHG from a perfectly oriented Si surface is inherently anisotropic, varying periodically as the in-surface projection of the polarization vector of the incident laser is rotated about a normal to the surface. The harmonic contributions to the angular anisotropy from the surface are characteristic of the surface bonding, and are modified by misorientation, chemical termination, as well as thermal treatments. This paper reviews the results of our previously reported optical SHG studies on Si(111) wafers with misorientations of 0°–5°±0.5° in the [112̄] direction for Si–H or Si–O terminated surfaces. Azimuthal anisotropy data are compared with an empirical model for the SHG intensity that is based on (i) the nonlinear response of anharmonic oscillators, and (ii) a phenomenological theory of azimuthal anisotropies expected for different surface orientations. This model is used as a framework for estimating ’’effective‘‘ resonance energies from single wavelength experiments, and in particular, for providing insights into the microscopic mechanisms that can contribute to the changes in these resonance energies with respect to different processing conditions. For example, important differences between thermally grown and plasma-oxidized interfaces are identified, and correlations between SHG and electrical performance of the Si–SiO2 interfaces are discussed.
Surface chemistry evolution during molecular beam epitaxy growth of InGaAs
Authors: Evans K. R. , Kaspi R. , Ehret J. E. , Skowronski M. , Jones C. R.
Published: July 2002

Temperature-programmed desorption (TPD) measurements are carried out in a molecular beam epitaxy (MBE) growth chamber on pseudomorphic GaAs/In0.22Ga0.78As(125 Å)/GaAs single quantum wells in various stages of growth, using a line-of-sight mass spectrometer for quantitative desorption analysis. The presence of surface-segregated indium is inferred from the appearance of a relatively low binding energy (Eb≊1.5 eV) peak in the indium TPD spectra. Integration of this TPD peak provides a quantitative measure of the surface-indium population ΘIn. By incorporating the TPD experiment as a subroutine in the MBE growth program, systematic variations of growth parameters are effected and their influence on ΘIn established. Detailed composition profiles are calculated and found to be in excellent agreement with previous results [Nagle et al., J. Cryst. Growth 127, 550 (1993)]. We find that both the bottom (InGaAs on GaAs) and top (GaAs on InGaAs) interfaces are graded over as much as 10 monolayers, with the bottom interface being indium-poor, due to the sacrificial buildup of ΘIn, and the top interface being characterized by segregation of indium into the GaAs cap, due to relatively slow incorporation of ΘIn into the lattice after closing the indium shutter. A more ‘‘squarelike’’ bottom interface is obtained by predeposition of a thin indium layer just before InGaAs growth, while a more ‘‘squarelike’’ top interface is obtained by ‘‘flash-off’’ of ΘIn just after InGaAs growth. It is believed that the combination of predeposition plus flash-off produces a more truly square InGaAs/GaAs quantum well than that obtained by more standard MBE growth approaches.
Planar lenses for field-emitter arrays
Authors: Tang Cha-Mei , Swyden Thomas A. , Ting Antonio C.
Published: July 2002

Experimental data is analyzed for a method of collimating and focusing electron beams emitted from field-emitter arrays (FEAs) where the focusing electrode is co-planar or nearly co-planar with the gate electrode. The focusing mechanism is provided by the fringe field formed along the edge of the gate electrode due to the potential difference between the grid and the substrate or the gate and another lens electrode. The concept is verified by EGUN2 simulations. Experiments performed to verify the theory and focusing of electron beams emitted from FEAs were observed. Emission data from 1×1, 1×100 and 2×100 arrays, located within long thin strips of gate electrodes are reported. Without focusing lenses, emission patterns on screen should have been approximately circular. However, elongated emission patterns were consistently observed, indicative of one-dimensional focusing.
Plasma-induced damage of GaAs pn-junction diodes using electron cyclotron resonance generated Cl2/Ar, BCl3/Ar, Cl2/BCl3/Ar, and SiCl4/Ar plasmas
Authors: Shul R. J. , Lovejoy M. L. , Hetherington D. L. , Rieger D. J. , Klem J. F. , Melloch M. R.
Published: July 2002

Plasma-induced etch damage often degrades the electrical and optical performance of III–V high-density integrated circuits and photonic devices. We have investigated the etch-induced damage of electron cyclotron resonance (ECR) generated plasmas on the electrical performance of mesa-isolated GaAs pn-junction diodes. Cl2/Ar, BCl3/Ar, Cl2/BCl3/Ar, and SiCl4/Ar ECR plasmas at ion energies ranging from 10 to 200 eV were studied. Diodes fabricated under low dc-bias (≤100 V) etch conditions yielded low reverse-bias currents which were comparable to wet-chemical-etched devices. As the dc bias was increased, the diodes showed significantly higher reverse-bias currents indicating plasma-induced sidewall damage of the pn-junction. Variations in diode reverse-bias leakage currents are reported as a function of plasma parameters and chemistries.
Global and stochastic space-charge effects in ion beam lithography
Authors: Petillo John J. , Mondelli Alfred A.
Published: July 2002

Ion projection lithography (IPL) is a candidate technology for meeting expected circuit design rules (less than 0.18 μm) for future generations of semiconductor devices. The Advanced Lithography Group (ALG), a consortium of industrial and U. S. government laboratories and universities, is developing IPL technology with funding from the Advanced Research Projects Agency (ARPA) and the state of Maryland. A prototype IPL device, the ALG-1000, is being developed to demonstrate the capability of IPL to meet future requirements for pattern overlay. To realize IPL technology requires control of space charge effects in the ion optical column. Due to the length of the IPL system (several meters), the precision of the calculation to predict distortion at the wafer plane becomes difficult to perform. Including the effects of the space charge is even more difficult. Both global and stochastic space-charge phenomena occur. This article presents a system of computer models that allows simulations of both global and stochastic space-charge effects. In particular, the models will be used on the ion beam projector in the ALG-1000 device. The calculations are carried out using a self-consistent equilibrium ray tracing code, where the applied fields are calculated from the actual lens column geometry. For global space charge, the model also includes optimization of the lens electrode voltages to minimize pattern distortion at the wafer plane.
Contrast formation in focused ion beam images of polycrystalline aluminum
Authors: Barr D. L. , Brown W. L.
Published: July 2002

Focused ion beam secondary electron images of polycrystalline aluminum films are valuable in revealing the grain structure of the films with great clarity on a scale of <50 nm. The contrast mechanism for focused ion beam images in crystalline materials was identified ten years ago as due to crystalline channeling of the ion beam. To our knowledge there has been no report which quantifies this mechanism either with respect to the magnitude of the intensity changes or their angular dependence. The ‘‘critical angles’’ of the angular dependence are expected to depend on the source of the secondary electrons, which may be different than the channeled angular dependence of backscattering or sputtering, for example, because of the difference in the distance of approach between the ion and a target atom at which the physical mechanism of interest takes place. The experiment described here quantifies the change in intensity and angular width in the case of channeled 30 keV Ga ions in aluminum thin films. This has been accomplished through a novel combination of focused ion beam images and electron backscatter diffraction measurements. Results of these experiments, and their possible implications for metallurgical imaging, will be discussed.
Multicusp sources for ion beam lithography applications
Authors: Leung K. N. , Herz P. , Kunkel W. B. , Lee Y. , Perkins L. , Pickard D. , Sarstedt M. , Weber M. , Williams M. D.
Published: July 2002

Application of the multicusp source for ion projection lithography is described. It is shown that the longitudinal energy spread of the positive ions at the extraction aperture can be reduced by employing a magnetic filter. The advantages of using volume-produced H− ions for ion beam lithography are also discussed.
Investigation of n- and p-type doping of GaN during epitaxial growth in a mass production scale multiwafer-rotating-disk reactor
Authors: Yuan C. , Salagaj T. , Gurary A. , Thompson A. G. , Kroll W. , Stall R. A. , Hwang C.-Y. , Schurman M. , Li Y. , Mayo W. E. , Lu Y. , Krishnankutty S. , Shmagin I. K. , Kolbas R. M. , Pearton S. J.
Published: July 2002

n- and p-doped GaN thin films have been epitaxially grown on c-sapphire substrates by metal-organic chemical-vapor deposition in a production scale multiwafer-rotating-disk reactor. The in situ doping was performed with material having a low background carrier concentration of n∼mid-1016 cm−3. Biscyclopentadienyl magnesium (Cp2Mg) and disilane (Si2H6) were used as the precursors for the p and n dopants, Mg and Si, respectively. The effect of mole flow on material, electrical, and optical properties was studied. We observed that both n- and p-type doped GaN exhibited an excellent surface morphology, even with a high mole flow of doping precursors. After the Mg-doped GaN was annealed in a N2 ambient at ∼700 °C for 30–60 min, the highly resistive GaN was converted into p-type GaN with a low resistance of 0.1–1.0 Ω cm. Transmission electron microscopy showed that the defect density on the annealed Mg-doped GaN is only 4×109 cm−2 which is of the same order as undoped GaN (1.5×109 cm−2). One of the best p-GaN samples has a Hall carrier concentration of 5.2×1018 cm−3 and a hole mobility of 20 cm2/V s, which are the best values reported in the literature to date. The photoluminescence spectra of p-GaN show a strong band edge at 430 nm with a full width at half-maximum of 300 meV at room temperature.
Intrinsic asymmetry between the [011] and [011̄] crystallographic directions in the In0.52Al0.48As/InP matched system
Authors: Peiró F. , Cornet A. , Morante J. R.
Published: July 2002

We have examined by transmission electron microscopy In0.48Al0.52As layers grown by molecular beam epitaxy on (100) InP substrates. The characterization of the nature of the crystal defects (dislocations and stacking faults) observed in the layers, and the study of their asymmetric distribution in the 〈011〉 directions point towards the differentiation of two mechanisms for defect nucleation and therefore towards two models explaining the observed anisotropy depending on the growth temperature (Tg). Then, for low Tg (300 °C) we have observed a {11̄1}-microtwinned structure whose origin has been explained taking into account the limited kinetics of III atoms during the growth and the differences in the propagation speed of the surface steps during the molecular beam epitaxy growth. For growth temperatures in the 440–530 °C range, the defect densities decrease monotonically, being threading dislocations and stacking faults on the (11̄1) and (111̄) planes the prevalent type of defects. The asymmetry of fault densities between the {11̄1} and {111} planes have been discussed on the basis of the different mobilities of the partial dislocations bordering the faults.
Thin-film interferometry of patterned surfaces
Authors: Maynard Helen L. , Hershkowitz Noah
Published: July 2002

The use of thin-film interferometry to determine the thickness of thin films is extended from unpatterned to patterned films. We developed a two-color thin-film interferometer which is robust and suitable for shop-floor use. With this new diagnostic, the etch rates of both the masking film and the underlying layer can be monitored. Several approaches to analyzing the thin-film interferometry data from patterned samples are explored including a mechanistic model, a simplified sine wave model, and fast Fourier transforms. The relative advantages and disadvantages of each technique are described. Both the mechanistic and sine wave models are complicated by the fact that they are nonlinear functions of the etch rates. It was therefore useful to examine maps of the mean squared error of the fit of data to the sine wave model. The analysis techniques are applicable to samples that have one or more thin films, are patterned with features that are larger than the wavelength of light, λ, and where at least a thickness λ of each film is etched away. The analysis techniques are demonstrated on laboratory data sets of the etching of photoresist-masked oxide films on silicon wafers.
Silicon surface cleaning by oxidation with electron cyclotron resonance oxygen plasma after contact hole dry etching
Authors: Sakuma K. , Machida K. , Kamoshida K. , Sato Y. , Imai K. , Arai E.
Published: July 2002

A simple technique for cleaning a silicon surface after contact hole etching is proposed for obtaining stable p+ silicon contact characteristics for very large scale integrated interconnections. The contaminated layer of the silicon contact surface after dry etching is first oxidized with electron cyclotron resonance (ECR) oxygen plasma and then the surface oxide is removed by wet etching with diluted HF. X-ray photoemission spectroscopy and secondary-ion-mass spectroscopy analyses show that one of the main reasons for the instability of the p+ silicon contact is fluorine contamination, which can be removed controllably by ECR oxygen plasma treatment followed by wet etching. This surface oxidation technique with ECR oxygen plasma is, therefore, an effective way to obtain stable and low-resistance p+ contact characteristics.
Fabrication and properties of visible-light subwavelength amorphous silicon transmission gratings
Authors: Deng Wenyong , Chou Stephen Y.
Published: July 2002

We present the first fabrication and investigation of visible-light subwavelength transmission gratings in high refractive index materials (e.g., amorphous silicon) on silica substrates. The gratings have periods ranging from 100 to 800 nm in 50 nm increments, a thickness of 180 nm (very thin), and they were fabricated using electron-beam lithography and reactive ion etching. Because of the high index, we have observed, for the first time, strong polarization dependence in light transmittance. The polarization effect was found to greatly depend on the ratio of grating period to wavelength, having the largest variation when the period is near half of the wavelength. The largest transmission difference for the polarization parallel and perpendicular to the grating fingers was found to be 12 dB. This observation contradicts the behavior manifested in subwavelength transmission gratings in low index materials, where the transmittance is essentially independent of the light polarization and the grating period. Rigorous electromagnetic theory has been used to model the gratings and agrees with experiments.
Improved Fowler–Nordheim equation for field emission from semiconductors
Authors: Jensen K. L.
Published: July 2002

Typical qualitative experimental characterizations of current versus voltage [I(V)] for field emitters fundamentally rely on the Fowler–Nordheim (FN) equation relating the current density J to the field at the surface F. The particular form of the J(F) relationship is due to taking the zero temperature limit of a linearized Wentzel–Kramers–Brillouin (LWKB) analysis, which works well for metals, but for semiconductors it is unsatisfactory, as LWKB does not correctly calculate the energy distribution of the emitted electrons, because the electron energy is too close to an extremum of the potential barrier, especially at high fields. Consequently, estimations of the current density from semiconductors can be substantially in error. We show how to modify the WKB approach so as to minimize its deviation from the exact solution of Schrödinger’s equation, resulting in a modified WKB equation, and from it, a modified FN relation. J(F) will be compared for different semiconductors, and a comparison with metals is given.
Scanning tunneling microscope investigations of lead–phthalocyanine on MoS2
Authors: Strohmaier R. , Ludwig C. , Petersen J. , Gompf B. , Eisenmenger W.
Published: July 2002

Monolayers of the nonplanar organic molecule lead–phthalocyanine (PbPc) on MoS2 have been prepared by organic molecular beam epitaxy and investigated with video scanning tunneling microscopy. Three different crystallographic phases have been observed. Two of them, the close packed and the rowlike phase, have already been observed in an earlier study of the planar Cu–Pc. With PbPc we have now observed an additional phase, where three close packed rows alternate with one or two isolated single rows. In contrast to Cu–Pc, in submolecularly resolved images the PbPc appear in two different states, with either a dark or a bright center. This is attributed to the nonplanar molecular geometry, which allows the formation of two different adsorption geometries, the Pb above or below the molecular plane. In video sequences the transition from one state into the other could be observed.
Scanning tunneling microscopy of Sr adsorption on the Si(100)-2×1 surface
Authors: Bakhtizin R. Z. , Kishimoto J. , Hashizume T. , Sakurai T.
Published: July 2002

The Sr-induced ordered superstructures on the Si(100)-2×1 surface have been studied using ultrahigh vacuum scanning tunneling microscopy and low-energy electron diffraction (LEED) for metal coverages (θ) below one monolayer (ML). At very low coverages (θ≤0.01 ML) Sr atoms adsorb as isolated atoms or small clusters. At submonolayer coverages of ∼θ≥0.12 ML we have observed the alkali-earth metal chains, even at room temperature, that run perpendicular to the substrate dimer rows. It is found that the Sr rows form areas of (2×3) order for coverages θ about 1/3 ML after annealing at 800 °C whereas a (1×3) phase grows on top of this with θ≥1.0 ML coverage in agreement with LEED data. It was also observed that the (2×3) phase formation is critical to the Sr coverage and to the annealing temperature as well. The relationship between the (2×3) and (1×3) ordered structures has been investigated as a function of Sr coverage and annealing temperature.
Cu metallization using a permanent magnet electron cyclotron resonance microwave plasma/sputtering hybrid system
Authors: Gorbatkin S. M. , Poker D. B. , Rhoades R. L. , Doughty C. , Berry L. A. , Rossnagel S. M.
Published: July 2002

A permanent magnet electron cyclotron resonance microwave plasma source has been coupled to a copper sputter target to produce ionized copper fluxes for submicron integrated circuit metallization. A custom launcher assembly allows the use of microwave powers up to 5 kW in a metal deposition environment to produce plasma densities ≳1012 cm−3, well above the cutoff density at 2.45 GHz of ∼1×1011 cm−3. Six hundred nm, 1.1:1 aspect ratio features have been filled with copper, and 250 nm, 6:1 aspect ratio features have been successfully lined. Copper ionization fractions for the conditions used for lining and filling, determined by a combination of Langmuir probe measurements and optical emission spectroscopy, are between 10% and 35%.