bluuebunny/crossref_metadata_2025 huggingface dataset:
Extended x-ray absorption fine structure and x-ray diffraction study of strain and bond distortions in epitaxial semiconductor layers
Authors: Woicik J. C. , Bouldin C. E. , Cross J. O. , Sorensen L. B. , King C. A.
Published: July 2002

Extended x-ray absorption fine structure and x-ray diffraction have determined the strain and bond distortions in epitaxial GexSi1−x on Si(001). In a 31% Ge, 340 Å pseudomorphic GexSi1−x film, the Ge–Ge and Ge–Si first-neighbor bond lengths have been found to be 2.44±0.02 and 2.38±0.02 Å, respectively. The lattice parameter perpendicular to the GexSi1−x/Si(001) interface has been found to be a⊥=5.553±0.002 Å. These results show that the bond length strain in epitaxial semiconductor layers appears primarily in the second and higher coordination shells, rather than in the nearest-neighbor bond lengths which remain the same as in the unstrained materials. A microscopic model is presented which accounts for these findings.
Investigations of dry etching in AlGaInP/GaInP using CCl2F2/Ar reactive ion etching and Ar ion beam etching
Authors: Hommel J. , Moser M. , Geiger M. , Scholz F. , Schweizer H.
Published: July 2002

We report on investigations of dry etching in GaInP/AlGaInP. As a method of dry etching we used CCl2F2/Ar reactive ion etching (RIE) and Ar ion beam etching (IBE). The suitability of these two methods for microstructure technology with respect to etch rates in investigated. First data on damage resulting from application of these two dry etching techniques in GaInP/AlGaInP are presented. The degree of damage was detected by performing photoluminescence measurement.
Metal-less x-ray phase-shift masks for nanolithography
Authors: White V. , Cerrina F.
Published: July 2002

In this article the theoretical and experimental results of metal-less x-ray phase-shift masks are reported. Features of 40 nm have been printed using gaps on the order of 5–10 μm, and lines of 0.1 μm have been printed with gaps of 30 μm with synchrotron radiation. A first prototype has been constructed of 2.75 μm of PMMA patterned on 0.8 μm Si3N4. They can be created out of a variety of low-Z materials. The model predicts a mask contrast between 5–6. Among its advantages is its ability to form nanometer lines without actually having to write them directly, because, with this technique, only the edges of the features are patterned on the mask where the two phases destructively interfere. In addition, the images do not degrade with increasing gap as quickly as a standard metal masks, resulting in a larger process window.
Ultrahigh vacuum in situ fabrication of three-dimensional semiconductor structures using a combination of particle beams
Authors: Jones G. A. C. , Ritchie D. A. , Linfield E. H. , Thompson J. H. , Hamilton A. R. , Brown K.
Published: July 2002

Focused ion beams have been combined with molecular-beam epitaxy (MBE) in two new in situ processes to produce semiconductor structures. First, a high-energy focused Ga ion beam has been used, during MBE growth interruption, to produce high-quality, vertically isolated ohmic contacts to a two-dimensional electron gas grown in close proximity to an underlying n+ layer. Second, using a focused Sn ion source within the MBE growth chamber, high-quality, electrically active, selected area, n-doped GaAs structures have been grown. In this case, a very low incident energy ion beam (≤50 eV) was used in order to prevent ion damage occurring to the crystal. This was achieved using retarded field ion optics.
Analytical description of backscattered electron signal for high-resolution metrology
Authors: Di Fabrizio E. , Luciani L. , Grella L. , Baciocchi M. , Gentili M. , Mastrogiacomo L. , Maggiora R. , White V.
Published: July 2002

Backscattered electron (BE) signals obtained by scanning fine features with a focused electron beam were studied. A commercial electron beam lithography machine (EBMF10 of Leica Cambridge) equipped with a channel plate detector was exploited for this purpose. The collected signal profile, and in particular the effect of the electron emission from the sidewalls of the feature under inspection (sidewall electrons, SWE) were studied. The variables we investigated include feature material and beam accelerating voltage. The effect of SWE on the BE signal was clarified by making use of Monte Carlo simulations. In particular it was possible to separate the SWE contribution from the global BE signal. Further, a novel analytical representation of the BE signal including the SWE effect was implemented. By this method, a precise linewidth measurement routine was developed and applied for metrology at different voltages on fine metal features of different materials. The application of this method to the metrology of submicron features (down to 0.2 μm) showed an intrinsic accuracy of better than 5% of the actual linewidth value.
Resist etching kinetics and pattern transfer in a helicon plasma
Authors: Jurgensen C. W. , Hutton R. S. , Taylor G. N.
Published: July 2002

We describe the first commercial etching system based on a helicon ion source and characterize it for etching organic films in an oxygen plasma. This single wafer etching system achieves a throughput of at least 30 fully processed 5 in. wafers per hour, which is comparable to the throughput of batch reactors. The etching chamber is equipped with a 13.56-MHz 2500-W helicon source, four low-field magnets to shape the plasma and support the helicon wave mode, and a 600-W radio-frequency chuck with He backside heat exchange and a temperature range from −50 to +125 °C. Etching rates and uniformity were measured on unpatterned resist-coated wafers, while trilayer resist patterns were used to study pattern transfer effects. Under nearly optimum conditions we obtain an etching rate of 1.31 μm/min, a throughput ≥30 wafers/h, nonuniformity ≤± 3%, selectivity ≊70 relative to SiO2 and nearly vertical etching profiles for all types of features having dimensions down to 0.25 μm. We describe the effect of process variables on etching rate, uniformity, selectivity, and etching profiles. We present a model based on multicomponent adsorption kinetics that fits the observed dependence of etching rate on the process variables. This etching system is being applied to several advanced lithographic schemes including dry-developed resists, bilayer lithography, and pattern transfer through organic antireflective coatings and planarizing layers.
Growth of β-SiC film on Si substrate by surface reaction using hydrocarbon gas and Si molecular beams in ultrahigh vacuum
Authors: Kim Kinam , Choi Si-Don , Wang K. L.
Published: July 2002

The growth of β-SiC on Si(111) substrate was performed with a two-step growth method in a molecular-beam epitaxy (MBE) system using a C2H2 gas source and a Si solid source: an initial optimal carbonization process followed by MBE. The properties of SiC film were analyzed with in situ Auger electron spectroscopy, reflection high-energy electron diffraction, and x-ray photoemission spectroscopy and with ex situ Fourier transform infrared and ellipsometry. In the surface carbonization, the reacted surface showed a change from the β-SiC structure to a carbon-absorbed SiC structure with the increase in carbonization time. A carbonization time of 10 min, a substrate temperature of 875 °C, and a growth pressure of 1.6×10−6 Torr were found to be optimal for the surface carbonization. The growth of SiC was conducted at 900 °C for 30 min with a 0.8 Å/s Si beam flux and a 1.6×10−6 Torr of growth pressure and the films obtained showed single crystalline β-SiC. However, thick films obtained with high growth rates showed polycrystalline structures.
Resonant magnetotunneling of GexSi1−x resonant tunneling structures grown at extremely low temperature by molecular-beam epitaxy
Authors: Chern C. H. , Tijero J. M. G. , Wang K. L. , Wang S. J.
Published: July 2002

Resonant tunneling structures of GexSi1−x double barrier quantum wells were grown at different temperatures by molecular-beam epitaxy. Previously, the growth of very thick coherently strained GexSi1−x layers at extremely low temperature and low pressure was reported. Following this technique, strained well GexSi1−x resonant tunneling diodes with high Ge concentration are fabricated. For a strained structure with a higher Ge concentration, it is expected to have higher band offsets and lighter effective masses. A smaller leakage current and a better peak to valley ratio were found for the samples grown at low temperature. From magnetotunneling measurements, the effective masses of heavy and light holes under strain were obtained.
Gas-source molecular-beam epitaxial growth of InGaAsP for 1.3 μm distributed Bragg reflectors
Authors: Silvestre P. , Hafich M. J. , Vogt T. , Nanda A. , Robinson G. Y. , Dudley J. J. , Bowers J. E. , Jones K. M. , Al-Jassim M. M.
Published: July 2002

High-quality InGaAsP films were grown on (100) InP substrates by gas-source molecular-beam epitaxy for use in distributed Bragg reflectors (DBR) operating at the wavelengths of 1.1–1.4 μm. By adjusting the inlet pressures of the feedstock gases AsH3 and PH3, precise control of the InGaAsP film composition was reproductively obtained, as evidenced by lattice mismatch of ≤ 5 × 10−4 and band-gap wavelength variation of ≤10 nm. The InGaAsP films exhibited x-ray diffraction peak widths as small as 21 arcsec and a low-temperature photoluminescence peak width of 4.6 meV. Using 35.5 periods of alternating quarter wavelength layers of InGaAsP (1.15 μm composition) and InP, a DBR with a maximum reflectivity of 96±2% at the wavelength of 1.31 μm is demonstrated.
Monoenergetic positron beam, positron lifetime, and Hall-effect measurements in III–V epilayers grown at low temperatures by molecular beam epitaxy
Authors: Hozhabri N. , Hyer R. C. , Sharma S. C. , Ma J. Y. , Pathak R. N. , Alavi K.
Published: July 2002

A monoenergetic positron beam has been utilized to depth profile defects in GaAs and in low temperature GaAs buffer layers (LTBL) grown by molecular beam epitaxy. Doppler broadening spectra were measured as a function of positron implantation depth and analyzed in terms of positron diffusion and annihilations of free and trapped positrons. Positron lifetime spectra were measured for the LTBL samples for temperatures in the range 10–295 K. These spectra show two temperature-dependent components resulting from the annihilations of free positrons and of positrons trapped in vacancy-type shallow defects. We have performed Hall-effect and low magnetic field temperature dependent resistivity measurements on the LTBL samples and have determined that the defect activation energy is =0.78 eV. The magnetic field dependence of the Hall data for the LTBL samples shows several interesting new features including sharp stepwise increases for every 700 G between 3.5 and 6 kG.
Molecular-beam epitaxial growth and characterization of erbium-doped GaAs and AlGaAs
Authors: Evans K. R. , Taylor E. N. , Stutz C. E. , Elsaesser D. W. , Colon J. E. , Yeo Y. K. , Hengehold R. L. , Solomon J. S.
Published: July 2002

An exploratory study of the molecular-beam epitaxial growth and characterization of Er-doped GaAs and AlGaAs is described. Information regarding incorporation rate, diffusion, and surface riding of Er is obtained via secondary ion mass spectrometry and reflective electron diffraction measurements. Low temperature photoluminescence (PL) measurements near 1.54 μm show emission from multiple Er sites in AlGaAs:Er and GaAs:Er. Substrate temperature is found to affect PL spectra in a complicated manner. The dependence of Er-center PL intensity on Er concentration is very nonlinear and peaks at [Er]≊1019 cm−3. GaAs:Er samples with [Er]=6×1018 cm−3 are p type with room temperature hole concentrations of 2–5×1016 cm−3. Co-doping with Er and Si dramatically reduces electron concentration from that obtained with Si only, while the presence of Si reduces the Er-center PL intensity.
Oxidation of silicon in an oxygen plasma generated by a multipolar electron cyclotron resonance source
Authors: Sung K. T. , Pang S. W.
Published: July 2002

Silicon dioxide films with breakdown field strength ≳12 MV/cm and fixed charge density ∼3×1010 cm−2 were grown using an oxygen plasma generated by an electron cyclotron resonance source at 16 °C. This oxidation temperature is much lower than previously reported plasma oxidation of silicon, while the breakdown field and fixed charge density for these oxides are comparable to thermally grown oxide at high temperature. The oxidation rate was studied as a function of microwave power, pressure, rf power, source to sample distance, and oxidation time. The oxidation rate increases with microwave power but decreases with source distance and rf power. At pressure <5 mTorr, the oxidation rate increases rapidly with decreasing pressure. The oxide thickness increases with the oxidation time but the oxidation rate decreases. These oxide films were found to have oxygen to silicon ratio of 2 using x-ray photoelectron spectroscopy. From the ellipsometry measurements, these films show a refractive index around 1.47. These results indicate that high quality oxide films with properties that are similar to that of thermal oxide can be grown at low temperature.
Electromodulation study of GaAs with excess arsenic
Authors: Warren A. C. , Woodall J. M. , Kirchner P. D. , Yin X. , Guo X. , Pollak Fred H. , Melloch M. R.
Published: July 2002

The authors have used contactless electromodulation (photoreflectance and contactless electroreflectance) to determine the electric field distributions in thin films of as-grown and annealed low temperature GaAs with excess arsenic. The molecular-beam epitaxy fabricated structures used in this study consisted of an n+ (p+) buffer layer with an undoped (U) region followed by an as-grown low-temperature (LT) layer or an annealed low-temperature (ALT) layer. The four types of sequences investigated were LTUN, LTUP, ALTUN, and ALTUP. From the Franz–Keldysh oscillations originating in the electric field in the U region it was possible to show that the Fermi level in LT-GaAs is consistent with a single deep donor at 0.4 eV below the conduction band whereas the ALTUN and ALTUP indicated a common Fermi level pinning position 0.67 eV below the conduction band. Thus, the controlling mechanism in the ALT material is indeed that of Schottky barrier controlled pinning on metallic As precipitates. These results are consistent with previously reported measurements for these materials.
Point defects and defect–impurity interaction in CdxHg1−xTe and other II–VI semiconductors: Facts and conjectures
Authors: Marfaing Y.
Published: July 2002

Several aspects concerning the role of point defects and defect–impurity interaction in II–VI semiconductors are reviewed. First, the properties of the cation vacancy in CdxHg1−xTe are re-examined in the light of two experiments (mass-loss measurements, positron lifetime) which point out to a large concentration of vacancy-type defects compared to the hole carrier density. The possibility for the cation vacancy to be a negative-U center and the formation of divacancies are discussed. Second, the case of donor-vacancy pairs is considered. A model of impurity compensation is given which accounts for the doping limits observed in a number of semiconductors in terms of a fundamental energy parameter (dangling bond energy).
Deep submicron contact fabrication by electron beam direct writing with intraproximity effect correction
Authors: Hashimoto Kazuhiko , Misaka Akio , Nomura Noboru
Published: July 2002

Electron beam (EB) direct-writing lithography with intraproximity effect correction has been developed for fabricating contact holes having deep submicron size. The dimensional accuracy of contact holes is strongly influenced by the intraproximity effect. In delineating contact hole patterns by using EB direct writing, it is necessary to increase the exposure dose a great deal. This is because the effect of backscattered electrons on the smaller hole patterns is decreasing. It was found that the forward scattering parameter in proximity function should be optimized in order to obtain high dimensional accuracy for contact holes with the minimum feature size of 0.2 μm. The accuracy within ±0.03 μm was realized for contact holes with their dimensions from 1.0 to 0.2 μm at the same time by using present intraproximity effect correction and noncharging trilayer resist process. When this high-performance EB direct writing was applied to fabricate 0.2 μm size contact holes, the yield of the 104 contact hole chains was improved to over 95% by using selectively deposited W film on the bottom of the contact holes.
Electrical characterization of pseudomorphic GaAs/InGaAs/AlGaAs and AlGaAs/InGaAs/AlGaAs modulation doped field effect transistor-type heterostructures grown by molecular-beam epitaxy
Authors: Moreira M. V. Baeta , Py M. A. , Gailhanou M. , Ilegems M.
Published: July 2002

We studied the influence of the indium composition y, growth temperature Ts and InGaAs quantum-well channel thickness dch on the 300 and 77 K Hall electrical properties of pseudomorphic modulation doped field effect transistor (MODFET)-type heterostructures grown by molecular-beam epitaxy. In agreement with Nguyen et al., we find an optimum channel thickness of 90 Å for an indium composition y=0.25 of the channel. Significant improvements in sheet resistivity ρs and in carrier concentration nso were obtained by using AlGaAs doped barriers on both sides of the pseudomorphic channel. We were thus able to obtain a two-dimensional electron gas sheet density nso as high as 4.0×1012 cm−2 at 77 K, which is among the highest values ever reported for MODFETs on GaAs.
Measurements of critical point energies in the conduction band structure of Si1−xGex
Authors: Morar J. F. , Batson P. E.
Published: July 2002

The energies of the Δ1 and L1 conduction band minima and the L3 saddle point have been measured in Si1−xGex (x=0.0–0.95) alloys using spatially resolved electron energy-loss spectroscopy. Measurements were carried out in a scanning transmission electron microscope at a spatial resolution of better than 2 nm on specimens grown in a SiGe molecular-beam epitaxy system on Si(100) substrates. As observed in photoluminescence measurements, the Δ1 and L1 bands are seen to cross at a Ge content of approximately 85%. L3 and Δ1 maintained a nearly constant energy separation independent of alloy composition. In contrast, L1 and Δ1 approach each other rapidly with increasing Ge content. Based on these results, this technique can be used to identify the composition of thin Si1−xGex alloys with a lateral resolution of better than 2 nm.
Strategies for shallow junction and profile formation
Authors: Hill Chris
Published: July 2002

The main strategies for shallow doped layer formation in semiconductors are outlined and the physicochemical characteristics of two of these, direct implantation and diffusion from overlayers, are described. The changing implementation of these techniques is discussed in the context of bipolar and metal–oxide semiconductor silicon integrated circuit fabrication technologies as these have progressed to submicron geometries and ultra-large-scale integration densities. The crucial shallow one and two dimensional doped regions thus fabricated are presented as important and difficult challenges for state-of-the-art compositional analysis techniques.
Quantitative depth profiling resonance ionization mass spectrometry of GaAs/AlGaAs heterojunction bipolar transistors
Authors: Downey S. W. , Emerson A. B. , Kopf R. F.
Published: July 2002

Resonance ionization mass spectrometry of neutral atoms sputtered from GaAs/AlGaAs materials, used for heterojunction bipolar transistors (HBT), provides quantitative information about the dopant position near interfaces. The results help elucidate beryllium dopant migration because they are free of matrix effects common in secondary ionization mass spectrometry. HBT performance is shown to be associated with Be location. Quantitative analysis of Be is possible across the AlGaAs/GaAs interface without extensive use of standards. The magnitudes of dopant (Be) and matrix (Al) signals are related in proportion to their concentration.
Poisson-based analysis of spreading resistance profiles
Authors: Mazur R. G.
Published: July 2002

This paper discusses carrier diffusion-induced problems that occur in profiling certain silicon structures with the spreading resistance technique. Such structures include p- and n-wells, lightly doped epitaxial layers and very thin epitaxial or diffused layers. Various methods for resolving carrier diffusion problems are discussed. A new method, which we call SRP2, is introduced. In the SRP2 process, the Poisson equation is used to calculate a spreading resistance profile from an assumed dopant profile (usually deduced from conventional spreading resistance analysis or generated by a process simulator such as suprem or predict); the calculated spreading resistance profile is then compared to a measured profile to ‘‘proof-test’’ the assumed dopant profile. Examples of the SRP2 process will be shown for CMOS p- and n-wells and for several other layers, including thin epitaxial and very shallow source-drain layers. The limits of Poisson-based analysis for ultra-shallow layers will be discussed.
Study of (InAs)m(GaAs)n short-period superlattice layers grown on GaAs substrates by molecular-beam epitaxy
Authors: Jang Jung-Geau , Miller D. L. , Fu Jianming , Zhang Kai
Published: July 2002

A series of (InAs)m(GaAs)n short-period superlattice layers with m=0.87, 1, 1.15, or 2 and n=3, 5, 6, 7, or 8 were grown about 0.3 μm thick on GaAs substrates by migration enhanced epitaxy. Changes in reflection high-energy electron diffraction (RHEED) patterns indicate that the surface is roughened by InAs layers, but becomes smooth by deposition of GaAs layers. Large or nonintegral m induces more surface roughening, while large n is more effective in smoothing. For most samples, RHEED patterns became spotty beyond some total superlattice thickness depending on m and n. The positions and full width at half-maximums of the zeroth-order superlattice peaks of x-ray diffraction are correlated to the observations in RHEED. We conclude that strain-induced interface roughening is one of the major causes to short-period superlattice imperfections, and that nonintegral InAs layers significantly affect the roughening.
Very low damage etching of GaAs
Authors: Murad S. K. , Wilkinson C. D. W. , Wang P. D. , Parkes W. , Sotomayor-Torres C. M. , Cameron N.
Published: July 2002

A very low damage, anisotropic and selective reactive ion etching process has been developed using SiCl4 for etching GaAs which stops on extremely thin GaAlAs layer (4 monolayers 1.13 nm thick). Using low rf powers of ≤15 W, and hence low dc biases of 40 to ≤70 V, pressures of 8 mTorr and flow rates of 4–6 sccm, the damage was kept to a minimum value while maintaining very good anisotropy. Both the surface and sidewall damage were measured and the results were confirmed by evaluation of the performance of a metal–semiconductor field effect transistor (MESFET) with a recessed gate. Raman scattering studies of the etched surface of a heavily doped GaAs layer show that the surface damage thickness is only 3–4 nm after 2 min of etching. The damage depth increases and saturates at 9 nm after 4 min of etching (etch rate of ∼100 nm/min).

Conductance measurements [S. Thoms, S. P. Beaumont, C. D. W. Wilkinson, J. Frost, and C. R. Stanley, in Microcircuit Engineering, edited by H. W. Lehman and Ch. Bleicher (North Holland, Amsterdam, 1986), p. 249] of narrow wires formed in n+-GaAs by etching at dc biases of 40–70 V show that the sidewall damage is negligible (1 nm/sidewall) after the first 2 min of etching. This value increases to 5 nm/sidewall after 3 min etching and to 12 nm/sidewall after 5 min. This is far lower than the value 18 nm/sidewall obtained by etching for 2 min at dc biases of 200 V. Control of the transconductance of the GaAs MESFETs by wet recess etching is difficult. Dry etching to a thin stop layer is a better method, provided it is damage-free. A ratio of etching rates of GaAs: Ga0.7Al0.3As of ≳10 000:1 on a 4 monolayer thick Ga0.7Al0.3As was obtained. On existing FET device wafers with a 5 nm GaAlAs stop layer, after 2 min etching which is sufficient to come to the stop layer, the transconductance was 4.02 mS, after 5 min etching was 3.67 mS and after 12 min was 2.05 mS. Optical emission spectroscopy revealed that the dominant emitting species in the plasma are Si, SiCl, SiCl2, and Cl. The variation of emission intensity of these species with power reveals clearly the presence of two distinct etch mechanisms, one below and one above 15 W (0.066 W/cm2) power density.

The etch rate does not increase monotonically with power.
Broad area, intense electron beam source for high resolution, high throughput semiconductor lithography
Authors: Hsu T-Y. , Hadizad P. , Liou R.-L. , Baik M. , Roth G. , Frank K. , Gundersen M. A.
Published: July 2002

Electron beam lithography using a robust, high current density (≳10 A/cm2), high brightness (≳1010 A/m2 rad2), broad area (≳1 cm diam) electron beam source is reported. The electron beam is produced during the hollow cathode discharge phase of a backlighted thyratron. The generated beam propagates in soft vacuum (<200 mTorr) and is collimated using cylindrical dielectric waveguides, resulting in uniform intensity over an area exceeding ∼1 cm2, along with a small divergence angle (<1.5°). Masked lithography for replication of fine line structures has been achieved, demonstrating the potential for a high throughput (∼30–40 wafers/h), high resolution (<0.25 μm) lithography system that is competitive with more complex x-ray and short wavelength optical systems.
Gas phase etching of Si(111)-(7×7) surfaces by oxygen observed by scanning tunneling microscopy
Authors: Donig F. , Feltz A. , Kulakov M. , Hessel H. E. , Memmert U. , Behm R. J.
Published: July 2002

Structural and mechanistic aspects of the initial stages of gas phase etching of Si(111)-(7×7) surfaces, by reaction with O2 at temperatures between 910 and 1070 K, were investigated by scanning tunneling microscopy. On smaller terraces, the reaction is found to proceed via a step flow mechanism, where Si is effectively removed at the edges of retracting terraces. On very large terraces, nucleation and growth of vacancy islands contribute in addition. The data lead to a reaction mechanism involving the formation of volatile SiO on the terraces, by reaction of O adatoms and Si surface atoms, subsequent vacancy diffusion, and finally the annihilation of vacancies at step edges or in vacancy islands. The temperature dependence of the resulting step structures, ranging from irregular and nearly dendritic forms at ∼910 K via faceted steps at ∼970 K to rounded shapes above 1000 K, results from step pinning by oxide nuclei and annealing effects at higher temperatures.
New technique for computation and challenges for electron-beam lithography
Authors: Huang Xiaokang , Bazán Greg , Bernstein Gary H.
Published: July 2002

In this article, the basic concepts of our recently proposed computing architecture based on Coulomb coupling of nanofabricated structures, called quantum cellular automata (QCA) are reviewed and fabrication issues critical to the new technology are discussed. The QCA fabrication will require an extremely high level of lithographic control. To this end, the proximity effects in making very high density patterns with poly(methylmethacrylate) (PMMA) and electron-beam lithography have been experimentally investigated. A triple Gaussian model was used to simulate the experimental data. By using a 50 keV electron beam, sub-40 nm pitch gratings, double lines, and dot grids were successfully fabricated on Si and SiO2/Si bulk wafers with single-level PMMA and lift-off.
Elimination of in-process multilevel interconnect stress voids through optimization of plasma enhanced chemical vapor oxide deposition parameters
Authors: Grivna Gordon , Leathersich Cathy , Shin Hank , Cowden William G.
Published: July 2002

Glass dielectric films produced by plasma enhanced chemical vapor deposition (PECVD) have been demonstrated, depending on the deposition conditions, to absorb varying amounts of moisture over time with a commensurate increase in compressive stress level. When these films were used as interlayer dielectrics in a multilevel Al-1.5%Cu metal system, a strong correlation between the dielectric moisture absorption/desorption, stress drift, and metal stress void formation was observed. A statistical optimization of a PECVD deposition process is presented which eliminated in-process metal line voiding.
Growth of AlGaAs and AlGaAs/GaAs heterostructures on misoriented (110)GaAs and a normal incidence type-II AlAs/AlGaAs quantum well infrared photodetector
Authors: Ho Pin , Martin Paul A. , Yu Larry S. , Wang Y. H. , Li Sheng S.
Published: July 2002

High-quality AlGaAs and AlGaAs/GaAs heterostructures have been successfully grown on (110) GaAs at high temperatures by molecular-beam epitaxy (MBE). Al0.25Ga0.75As/GaAs high electron mobility transistors with an 18 nm spacer layer yielded 77 K Hall electron mobilities of 6.2×104 and 5.6×104 cm2/V s with sheet charge densities of 4.4×1011 and 5.5×1011 cm−2 at growth temperatures of 680 and 710 °C, respectively. A normal incidence type-II quantum well infrared photodetector (QWIP) using an indirect AlAs/Al0.5Ga0.5As system grown on misoriented (110)GaAs by MBE has been demonstrated for the first time. A peak wavelength of 12.7 μm, attributed to intersubband transitions, with a cutoff wavelength of 15 μm was obtained. This QWIP also showed a multispectral response from visible (0.5 μm) to far-infrared wavelength (18 μm).
Effect of crystalline defects on electrical properties of heavily Si-doped strain-relaxed In0.5Ga0.5As layers grown by molecular beam epitaxy on GaAs
Authors: Chang James S. C. , Patterson George A.
Published: July 2002

Heavily Si-doped, strain-relaxed In0.5Ga0.5As layers are often used as contact layers on N+ GaAs to form nonalloyed ohmic contacts. The present work studies the electrical properties of such In0.5Ga0.5As layers grown on undoped GaAs buffer layers by molecular beam epitaxy both as-grown and after anneals at temperatures between 300 and 430 °C. It is found that in the as-grown condition, there is a region of about 150 Å extending into the In0.5Ga0.5As layer contiguous to the In0.5Ga0.5As/GaAs interface where both the electron concentration and mobility decrease toward the interface. With postgrowth anneal, the electron concentration in this region will be further reduced and the width of the region will be increased. The associated activation energy is estimated to be 0.99±0.41 eV. This phenomenon can be fully explained in terms of defect structural changes during anneal. This work provides strong evidence to indicate that the as-grown In0.5Ga0.5As layers are not in thermodynamic equilibrium and will continue to relax when thermal energy is provided.
Surface stoichiometry and interface formation during molecular-beam epitaxy of strained InAs/AlxGa0.48−xIn0.52As heterostructures
Authors: Tournié Eric , Ploog Klaus H. , Hohenstein Matthias
Published: July 2002

We show that the surface stoichiometry of the film—i.e., cation- or anion-stable surface—provides a unique means to control the interface formation and sample quality during molecular-beam epitaxy of strained InAs films buried in an AlxGa0.48−xIn0.52As matrix lattice matched to InP substrates. When the highly (3.2%) strained InAs films are grown under As-stable conditions, islanding occurs which leads to defected interfaces. On the contrary, under In-stable conditions islanding of the InAs films is prevented and high quality strained interfaces are obtained.
Geometry and mode of growth of alkali metal/Si(100)2×1 interfaces
Authors: Soukiassian P. , Spiess L. , Schirm K. M. , Mangat P. S. , Kubby J. A. , Tang S. P. , Freeman A. J.
Published: July 2002

The atomic structure of alkali metal (Na,K)/Si(100)2×1 interfaces is investigated by the combination of (i) core-level and valence-band photoemission spectroscopies using synchrotron radiation, (ii) scanning tunneling microscopy, (iii) polarization-dependent photoemission extended x-ray absorption fine-structure (PEXAFS) experiments, and (iv) ab initio all-electron total energy DMol molecular force calculations. The experimental data were taken with extreme care concerning surface preparation and cleanliness. We use the unique ability of PEXAFS to measure the distances between the nearest neighbors of both adsorbate and substrate atoms which allows a double-checking of interatomic distances. We also probe the fine structural changes of the Si(100)2×1 surface and found that the Si-Si dimer is relaxed upon K and Na deposition. We do not find any Na-Na distance consistent with any double layer models. The experimental Na-Si, Si-Na, Si-Si, and Si-K distances are in excellent agreement with the ab initio DMol calculations performed on very large clusters (up to 77 atoms) which also provide the adsorption energy for each site. The results clearly demonstrate that the alkali atoms are adsorbed on a single site, the cave, and form one-dimensional linear chains separated by a distance of 7.68 Å and parallel to the Si dimer rows. The growth and occurrence of a second Na or K layer are clearly related to the presence of very low level of impurities which demonstrates the extreme sensitivity of the atomic structure of these interfaces to the presence of foreign atoms.
Interface roughness in Ge/Si superlattices
Authors: Headrick R. L. , Baribeau J.-M.
Published: July 2002

Interface roughness in a (GenSim)p superlattice has been observed with a root mean square height of 3.0 Å and a lateral correlation length of 0.4 μm. The roughnesses at different Ge–Si interfaces are not independent, but rather the terrace structure of the substrate is identically replicated, forming a superlattice with vertically correlated (conformal) interface roughness. A staircase structure characteristic of atomic layer steps separated by ∼1 μm is observed on the same heterostructure. Vertically correlated roughness occurs because at the low growth temperature used (350 °C) step motion on the surface is negligible.
Laboratory setup for projection electron lithography and a Monte Carlo simulation of scattering mask transmission
Authors: Miller Peter D. , Gibson J. Murray , Bleeker Arno J. , Liddle J. Alex
Published: July 2002

The progress in two areas related to scattering contrast with angular limitation projection electron lithography (SCALPEL) is reported. First, the simple modifications which have been made to convert a transmission electron microscope into a scientific SCALPEL tool, to be used for making repeated, scaled nanostructures and mesoscopic devices are discussed. Preliminary electron optical calculations for this setup predict resolution of ∼0.005 μm for a range of demagnifications. Second, a Monte Carlo simulation of the angular distribution of electrons scattered by thin solid films is described. The simulation is intended to help select the optimum materials for use in a scattering mask. It was found that for germanium (atomic number Z=32), available parameterless single-scattering distributions do not adequately describe the experimentally measured distributions. As a result, an experimentally based simulation has been adopted whose single-scattering angular distribution is directly measured. It was found that this small experimental investment significantly improves the simulation’s accuracy.
Blue/green ZnSe–ZnCdSe light-emitting diodes and photopumped laser structures grown by molecular beam epitaxy on ZnSe substrates
Authors: Ren J. , Eason D. B. , Yu Z. , Sneed B. , Cook J. W. , Schetzina J. F. , El-Masry N. A. , Yang X. H. , Song J. J. , Cantwell Gene , Harsh William C.
Published: July 2002

The first ZnSe–ZnCdSe double-heterostructure light-emitting diodes (LEDs) and photopumped laser structures on ZnSe substrates have been successfully grown by molecular beam epitaxy. The LEDs emit bright blue/green electroluminescence at room temperature, with the emission peak centered at 492 nm. Photopumped laser emission was also observed from ZnSe–ZnCdSe multiple-quantum-well structures grown on ZnSe substrates. The cleaved-cavity devices display stimulated emission in the deep-blue spectral region near 477 nm at 10 K and at 478.8 nm at 80 K.
Some doping results in ZnSe grown by molecular beam epitaxy
Authors: Li L. K. , Wang W. I. , Gaines J. M. , Petruzzello J. , Marshall T.
Published: July 2002

Comparison studies of N-doping of ZnSe for (100) and (311)A orientations have been performed. The C–V measurements indicated that the doping level of the samples grown on (311)A is higher than that of the samples on (100). Doping experiments using Zn3As2 as As-doping source evaporated by a Knudsen effusion cell also have been performed. Low-temperature photoluminescence measurements revealed evidence of shallow acceptor bound excitons, indicating that some of the As is being incorporated as shallow levels. It is also pointed out that group V monomers such as As and P are promising p-type dopants.
Modulated arsenic molecular-beam epitaxial growth of In0.48Al0.52As
Authors: Chou S. T. , Cheng K. Y.
Published: July 2002

A modulated As molecular-beam epitaxy method is utilized to grow high-quality In0.48Al0.52As epilayer at a low substrate temperature, which is compatible to the optimal In0.47Ga0.53As growth condition. The reflection high-energy electron diffraction intensity oscillations recorded during modulated As beam epitaxy shows that a persistent layer-by-layer growth mode is maintained throughout the epitaxy process. The high electron mobility, high photoluminescence (PL) intensity, and narrow PL linewidth have confirmed the low defect generation/incorporation during the modulated As beam epitaxy of the In0.48Al0.52As. The effect of interface smoothing is confirmed by the extremely narrow 77 K PL linewidth of an In0.47Ga0.53As/In0.48Al0.52As quantum well stack heterostructure grown by this method.
Film interface control in integrated processing systems*
Authors: Granneman E. H. A.
Published: July 2002

A number of system concepts in which the integrity of substrate surface and film interfaces are preserved are discussed. This includes stand-alone tools with internal clean air or nitrogen facilities with wafer transfer between such tools in clean containers (‘‘minienvironments’’) and single-wafer and batch-type cluster systems in which the processing and wafer transfer modules are physically connected. Depending on the cleanliness requirements, wafer transfer and processing are done in pure atmospheric nitrogen, low-pressure nitrogen, or vacuum. An analysis is given in which the ambient requirements are related to surface reactivity, wafer transfer time, and acceptable surface contamination level. Trade-offs in terms of capital cost, throughput, flexibility, and film quality are analyzed. A number of different system concepts combining wafer preclean, thin oxide growth, and poly-Si deposition processes are analyzed in terms of their economical performance. It appears that single-wafer systems have a logistic advantage in terms of short cycle time and wafer inventory; however, the cost per wafer of batch-type systems is considerably lower than single-wafer ones. It is shown that the optimum choice between (fast, high-temperature) single-wafer and (slow, low-temperature) batch-type systems in terms of process performance depends on physical parameters such as activation energy and the occurrence of undesired, competing, processes.
Photoluminescence studies of interstitial Zn in InP due to rapid thermal annealing
Authors: Hsu J. K. , Juang C. , Lee B. J. , Chi G. C.
Published: July 2002

Deep donor to acceptor transitions between interstitial and substitutional Zn in InP are investigated in this study via the photoluminescence technique. Interstitial Zn is to be fully activated when treated by rapid thermal annealing process at 600 °C. When treated at 400 °C, however, interstitial Zn is partially activated so that medium distance deep donor-to-acceptor transitions become less available. This medium distance transition is estimated to be in a range between 35 and 60 Å.
Nitrogen plasma source ion implantation of aluminum
Authors: Walter K. C.
Published: July 2002

Nitrogen plasma source ion implantation has been applied to pure aluminum and aluminum alloy 7075 (Al–Cu–Mg–Zn). Nitrogen implantation modified the surface properties through transformation of the surface to aluminum–nitride (AlN). A uniformly thick (∼0.15 μm), polycrystalline (∼30 nm grain size) and continuous AlN layer was formed on both pure aluminum and 7075. Knoop microhardness tests showed an increase in surface hardness at low loads. Pin-on-disk wear tests showed nitrogen implantation decreased the wear rates by a factor of ∼10 for alloy 7075. This study demonstrates significant modification of the tribological properties of an aluminum surface can be accomplished using nitrogen plasma source ion implantation.
Model for expanding sheaths and surface charging at dielectric surfaces during plasma source ion implantation
Authors: Emmert G. A.
Published: July 2002

Plasma source ion implantation utilizes negative high voltage pulses applied to targets immersed in a plasma. This produces an expanding sheath which accelerates ions into the target. A model for expanding sheaths at dielectric surfaces is developed; the significant differences between this and metal targets are the finite dielectric constant of the material and accumulation of charge in the nonconducting material. A model is developed for an expanding sheath at a dielectric surface and applied to a polyethylene sheet as an example. The most significant effect is the reduction of the energy at which ions are implanted in the material because of charging at the surface of the polyethylene.
Atomic desorption and readsorption of chlorine on a Si(111) 7×7 surface with a scanning tunneling microscope
Authors: Baba Masakazu , Matsui Shinji
Published: July 2002

This article reports on the selective atomic desorption of Cl atoms adsorbed on an Si(111) 7×7 surface by field evaporation using a scanning tunneling microscope (STM). After using the STM to study the reaction of the Cl on the surface, the STM tip is placed on the adsorbed Cl, and a positive voltage pulse is applied to the sample. This results in selective atomic desorption of Cl from the sample surface. Although both desorption and readsorption are observed at a low pulse voltage of 4–6 V, only desorption occurs at a high pulse voltage of over 6 V. When a negative pulse voltage is applied to the sample, the Cl and metallic atoms are desorbed from the tip surface by field evaporation.
Thermal stability of highly Sb-doped molecular beam epitaxy silicon grown at low temperatures: Structural and electrical characterization
Authors: Thomsen E. V. , Hansen O. , Harrekilde-Petersen K. , Hansen J. L. , Shiryaev S. Y. , Nylandsted Larsen A.
Published: July 2002

The structural and electrical properties of highly Sb-doped molecular beam epitaxy grown silicon have been investigated as function of rapid thermal annealing (RTA) temperature. Doping levels of 3×1020 cm−3 were obtained using low temperature epitaxy (LTE) performed at a growth temperature of 300 °C. Ion channeling and transmission electron microscopy (TEM) measurements showed that the as-grown samples were of very high quality. The combination of Hall-effect profiling and Rutherford backscattering spectroscopy revealed an electrically active Sb fraction of 0.8. Short time RTA processing improved the electron mobility and the activation: RTA at 600 °C for 10 s yielded unity activation and RTA at 800 °C gave mobilities matching phosphorus doped bulk values, thus significantly exceeding previously reported values for highly doped LTE material. A degradation of the crystalline quality was observed for higher RTA temperatures: RTA at 1000 °C for 10 s reduced both the Sb-substitutional fraction and electrical activation to 0.6 due to precipitation of Sb, and lead to the formation of a high density of dislocation loops as observed by TEM. A large fraction of the precipitates decorated these dislocation loops. Mesa isolated diodes were fabricated to evaluate the use of LTE material for device production. Current–voltage measurements on these diodes revealed high quality junctions with low reverse currents and near-ideal forward characteristic.
Potential distribution measurement of thin InGaAs resistors using scanning tunneling potentiometry
Authors: Tanimoto Masafumi , Arai Kunihiro
Published: July 2002

Scanning tunneling potentiometry was successfully applied to evaluate thin InGaAs resistors with 30 nm spatial resolution. Measured potential distributions show large potential drops at the edge of and near the contacts. The observed potential drops at the edge of the contacts are attributed to Schottky barrier formation at the metal/InGaAs interface due to the low impurity concentration of InGaAs (n=1×1018 cm−3). The potential drops observed near the contacts reflect the nonlinear carrier transport properties in InGaAs. They are ascribed to the carrier accumulation and/or depletion due to the carrier velocity dependence on the electric field. These potential drops well explain the measured current-saturation feature at low electric field.
Comparison of advanced plasma sources for etching applications. III. Ion energy distribution functions for a helicon and a multipole electron cyclotron resonance source
Authors: Gibson G. W. , Sawin H. H. , Tepermeister I. , Ibbotson D. E. , Lee J. T. C.
Published: July 2002

As part of our research effort in evaluating the etching performance of high density plasma sources, we measured ion energy distribution functions near the wafer surface for a helicon and a multipole electron cyclotron resonance source (ECR). The following two salient results stand out: first is the remarkable similarity in behavior of the two sources which was also observed in previous studies comparing etching rates, profile control, and Langmuir probe diagnostics; and second is the surprising level of coupling between the applied rf bias and the bulk plasma. For both sources, the ion flux increases strongly with source power, decreases by 20%–40% as the reactor pressure increases from 2.0 to 5.0 mTorr, and is weakly modified by the applied rf bias. The mean ion energy is strongly influenced by the applied rf-bias and is relatively insensitive to source power and pressure. The ion flux exhibits high uniformity for both sources, with the helicon exhibiting slightly better uniformity. However, we note that instabilities in the ECR discharge from mode jumps caused by different operating conditions and changing reactor wall conditions, such as temperature, result in poorer uniformity. The behavior of ions with respect to applied source and rf-bias powers follows roughly the trends expected of quiescent, high density plasmas in contact with a rf-biased electrode (i.e., independent control of ion flux and mean ion energy). However, there exist subtle effects upon the ion flux, such as bimodal energy distributions, brought about by the coupling of the rf-bias power into the bulk plasma. This coupling may be an essential parameter in wafer platen design that must be addressed in order to obtain high etching rate uniformity.