bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanostructure fabrication in InP and related compounds
Authors: Adesida I. , Nummila K. , Andideh E. , Hughes J. , Caneau C. , Bhat R. , Holmstrom R.
Published: July 2002

Nanometer-scale gratings have been fabricated in InP and InGaAs/InP heterostructures using electron-beam lithography and reactive-ion etching in methane-hydrogen plasmas. It is shown that the slight overcut obtained in the etch profiles during a single-step etch in CH4/H2 is due to polymer formation on inert mask surfaces and edges. Intermittent removal of the deposited polymer film is shown to be effective in obtaining anisotropic profiles. Highly anisotropic 35-nm-wide InP lines at 70-nm pitch demonstrate the potential of this fabrication process. The formation of 100-nm-wide free-standing InP wires is also presented.
Fabrication of grooved glass substrates by phase mask lithography
Authors: Brock Phillip J. , Levenson Marc D. , Zavislan James M. , Lyerla James R. , Cheng John C. , Podlogar Carl V.
Published: July 2002

A phase-shifting mask without chrome opaque features can be used to print groove servo patterns for optical storage disks and provides improved contrast and resolution in printed photoresist images when used in a projection printer such as a Perkin-Elmer MicralignTM-500 mask aligner. Such a phase-shifting photomask structure can be fabricated in the following way. Onto a conventional photoresist coated chrome on fused quartz photomask blank is written a pattern of concentric lines and spaces or a spiral pattern. The photoresist is developed and the exposed chrome etched in the conventional way to yield a transmission mask pattern of twice the pitch desired in the final groove pattern. The quartz is then etched, using the photoresist/chrome and/or chrome pattern as the resist, by either a wet or dry process, to a uniform depth. The chrome is then completely removed to form a ‘‘chromeless’’ phase-shifting mask [K. K. H. Toh, G. Dao, R. Singh, H. Gaw, Proc. SPIE 1991 Symp. Microlithogr. 1463 (1991)] Phase-shifting masks of this sort have been fabricated and used successfully to print photoresist images on glass disks yielding patterned photoresist structures of 1.5, 1.2, and 1.0 μm pitch. The resulting photoresist pattern could be transferred into the glass substrate by a wet etch process to generate the desired glass etch pattern after photoresist removal. Phase-shifting masks of this design require careful dimensional control in three dimensions. One modification to the phase mask design described which simplifies the fabrication process is to alter the relative dimensions of the groove and land. If the land is made very small in relation to the groove, then the groove prints as though it were a clear feature in a transmission mask. Conversely, the land prints as though it were a chrome (‘‘dark’’) feature. The contrast obtained in the image is much larger than can be obtained from a conventional transmission mask of similar dimensions and the depth of focus was increased to >10 μm.

This ‘‘darker than dark’’ phase-shifting mask phenomenon may prove valuable in the fabrication of complex patterns [K. K. H. Toh, G. Dao, R. Singh, and H. Gaw, SPIE 1991 Symp. Microlithogr. 1463 (1991) and K. Nakagawa, M. Taguchi, and T. Ema, Fabrication of 64M DRAM with i-line Phase Shift Lithography, IEEE International Electron Devices Meeting, Dec. 9–12, 1990, San Francisco, California].
Stable low-stress tungsten absorber technology for sub-half-micron x-ray lithography
Authors: Kola R. R. , Celler G. K. , Frackoviak J. , Jurgensen C. W. , Trimble L. E.
Published: July 2002

Tungsten is attractive for very large scale integrated device metallization and as absorber for x-ray lithographic masks. To minimize distortions in an x-ray mask, intrinsic stresses in the absorber films have to be low and reproducible. We present the results of a systematic study of the microstructure and stress of rf sputter-deposited W films as a function of deposition parameters, using optical interferometry, scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Rutherford backscattering spectrometry and Auger electron spectroscopy were used for the chemical analysis of the films. By controlling the nucleating phase and mobility of the adatoms, we have produced W films with low stresses (<±50 MPa). The low-stress films have a 〈110〉 preferred orientation and a bimodal grain size distribution with large, elongated grains surrounded by small equiaxed grains. The lattice parameter and the argon content in W films increased with decreasing argon deposition pressure. It was found that a low base pressure (<10−7 Torr) is necessary to produce stable α-phase W and to eliminate the metastable β phase. Additional seed layers (Cr, SiO2 ) at the Si/W interface resulted in a small improvement in stress control of the W films. The W films were stable (no change in stress) on subsequent anneals at 200 °C for 50 h in vacuum and argon ambients.
Response surface modeling of high pressure chemical vapor deposited blanket tungsten
Authors: Clark Thomas E. , Chang Mei , Leung Cissy
Published: July 2002

Chemical vapor deposited (CVD) blanket tungsten has been studied at high pressure (80 Torr) in a single-wafer cold wall reactor using response surface modeling methods. Deposition factors studied include temperature (430–490 °C), H2 partial pressure (6–30 Torr), WF6 partial pressure (1–2 Torr), and the gas inlet to wafer surface separation (200–600 mils). Quadratic models were generated for deposition rate, resistivity, sheet resistance uniformity, film stress, step coverage, reflectance, and WF6 conversion. The models were examined for consistency with previously reported results for CVD tungsten films, and were used to construct contour plots that aided a deposition process optimization search for a plug application. Optimization requirements for step coverage and sheet resistance Rs uniformity resulted in significant constraints on the usable factor space, while requirements for deposition rate, resistivity, stress, WF6 conversion, and reflectance were largely met throughout the original factor space. The resulting optimized factor space was found to be relatively large and offered additional opportunities for fine tuning of the process. Finally, data from replicated trials showed the high pressure CVD blanket tungsten process to be highly reproducible.
The influence of Sb as a surfactant on the strain relaxation of Ge/Si(001)
Authors: Thornton J. M. C. , Williams A. A. , Macdonald J. E. , van Silfhout R. G. , van der Veen J. F. , Finney M. , Norris C.
Published: July 2002

We have investigated by the use of surface x-ray diffraction the initial strain relaxation of Ge on Si(001) when a ‘‘surfactant’’ layer of Sb [0.7 monolayers (ML)] is present. Due to the high sensitivity of the technique to lateral strain in the overlayer, we have been able to observe directly the onset of strain relaxation at a coverage of 9–10 ML. This strain relief proceeds gradually as a function of coverage, but unlike the case without an Sb surfactant, it was not possible to relax the overlayer fully. No bulklike Ge was seen even up to a coverage of ≊55 ML. Concurrent specular reflectivity measurements also showed that the overlayer formed in a layer-by-layer mode up to the same level. These results differ quite markedly from those obtained without the surfactant layer, where several stages of island formation and strain relaxation are seen. They show dramatically how the modification of surface energies by the presence of a surfactant can affect the morphology of, and strain in, a lattice mismatched overlayer. In addition, they are direct confirmation that the initial strain relaxation mechanism in operation when a surfactant is not present is the formation of coherent Ge islands, rather than that of dislocations.
Photoassisted organometallic vapor-phase epitaxy of CdTe
Authors: Liu B. , Hicks R. F. , Zinck J. J. , Jensen J. E. , Olson G. L.
Published: July 2002

A mathematical model has been developed which describes the transport phenomena and elementary reaction kinetics encountered during photoassisted organometallic vapor-phase epitaxy of cadmium telluride. Dimethylcadmium and dimethyltellurium in helium carrier gas are fed to a horizontal, square duct containing a substrate heated to 165 °C. The organometallic compounds are photodissociated in the gas by illumination with 248 nm photons from a continuous-wave laser. Average deposition rates predicted by the model agree to within 10% of those measured experimentally. The numerical simulations reveal that the growth rate is controlled by the photolysis rate of the organometallic compounds. This results in a linear dependence of the growth rate on dimethylcadmium pressure and laser power. The simulations further indicate that elemental tellurium deposits with cadmium telluride over a wide range of operating conditions. The elemental tellurium is avoided by operating below 20 Torr total pressure, by illuminating the gas directly above the substrate, and by feeding two–four times more dimethylcadmium than dimethyltellurium. Under these conditions, the flux of methyl radicals to the surface is sufficient to etch away the excess tellurium. The model has also been used to identify an illumination geometry suitable for obtaining uniformly thick CdTe films.
Application of reflection electron microscopy in cross-sectional study of multilayer semiconductor devices
Authors: Peng L.-M. , Jiang J. , Du A. Y. , Zhou Joe X.
Published: July 2002

Reflection electron microscopy (REM) has been applied, for the first time, to study the cross-sectional structures of multilayer semiconductor devices. An example is given of a GaAs/AlxGa1−xAs multiple quantum wells infrared detector. The technique was used during the device fabrication process as an in-line monitoring method to provide a direct and precise dimensional measurement of a fabricated mesa so as to reach an optimum fabrication condition. The REM results are compared with those deduced from electrical measurements of the fabricated devices and a complete consistency is obtained.
Observation of the instability of TixGay alloys with respect to GaAs at elevated temperatures
Authors: Kniffen Margaret L. , Helms C. Robert
Published: July 2002

The metallurgical reactions occurring at the Ti–GaAs interface between 600 and 850 °C were examined using Auger depth profiling. Between 600 and 720 °C titanium will react with gallium arsenide to form a uniform TixGay /TiAs/GaAs layered structure, similar to that which formed upon annealing Ti–GaAs contacts at much lower temperatures [J. Vac. Sci. Technol. A 5, 1511 (1987); J. Vac. Sci. Technol. A 6, 1473 (1988)]. However above 800 °C the dominant reaction products are a titanium arsenide phase and liquid gallium. This result has significant implications for the development of thermally stable contacts to gallium arsenide using titanium-based metallizations.
Trilayer lift-off metallization process using low temperature deposited SiNx
Authors: Lothian J. R. , Ren F. , Pearton S. J. , Chakrabarti U. K. , Abernathy C. R. , Katz A.
Published: July 2002

A trilevel resist scheme using low temperature (≤50 °C) deposited SiNx rather than Ge for the transfer layer has been developed. This allows use of an optical stepper for lithographic patterning of the emitter-base junctions in GaAs/AlGaAs heterojunction bipolar transistors where a conventional lift-off process using a single level resist often leads to the presence of shorts between metallizations. The plasma-enhanced chemically vapor deposited (PECVD) SiNx shows a slightly larger degree of Si–H bonding compared to nitride deposited at higher temperature (275 °C), and is under compressive stress (∼5×1010 dyn cm−2) which is considerably relieved upon thermal cycling to 500 °C (∼1.5×1010 dyn cm−2 after cooldown). This final stress is approximately a factor of 2 higher than conventional PECVD SiNx cycled in the same manner. The adhesion of the low temperature nitride to the underlying polydimethylglutarimide base layer in the trilevel resist is excellent, leading to high yields in the lift-off metallization process. These layers are etched in electron cyclotron resonance discharges of SF6 or O2, respectively, using low additional dc bias (≤−100 V) on the sample. Subsequent deposition of the HBT base metallization (Ti/Ag/Au) and lift-off of the trilevel resist produces contacts with excellent edge definition and an absence of shorts between metallization.
Near-surface residue formation in CF4/H2 reactive ion etching of silicon
Authors: Potter Gregg E. , Morrison G. H. , Charvat Peter K. , Ruoff Arthur L.
Published: July 2002

Surface residues and near-surface damage present in the surface and near-surface regions of Si after reactive ion etching with CF4, CF4+H2, and CHF3 were investigated with secondary ion mass spectrometry, laser ellipsometry, x-ray photoelectron spectroscopy, and cross-sectional transmission electron microscopy. Specifically, the change in the thickness and composition of the deposited residues with changes in the backfill gas chemistry was investigated. A fluorocarbon (FC) residue was found to develop on all etched samples, with thicknesses ranging from a few angstroms to microns. Two regimes of FC deposition were identified, where (a) a steady-state FC layer quickly develops during etching, and the net FC deposition rate drops to zero thereafter, and (b) the FC deposition continues at a constant rate throughout the etch. F was found to diffuse to the Si surface to form a fluorinated Si layer between the deposited FC layer and the bulk Si. This layer was taken to be the reaction layer resulting from diffusion-limited kinetics in this etch system. The diffusion of F or C into the near-surface region of Si was not observed to change with increasing H2 additions. A simple quantitative model was developed based on rate-limiting Fickian diffusion through the deposited FC layer. The model was found to agree well the available etch rate data. Si etching with CHF3 was found to behave similiarly to CF4+H2 etching in the steady-state FC layer regime.
The growth and characterization of Si1−yCy alloys on Si(001) substrate
Authors: Eberl K. , Iyer S. S. , Tsang J. C. , Goorsky M. S. , Legoues F. K.
Published: July 2002

We have prepared Si1−yCy alloy layers on Si (001) substrates using solid-source molecular-beam epitaxy. The lattice mismatch between diamond and Si is about 50%. Thus, a Si1−yCy (y=0.02) alloy has a mismatch of about 1% with respect to Si assuming Vegard’s law. Transmission electron microscopy (TEM) shows the layers to be pseudomorphic. Growth temperatures between Tg=500–550 °C are suitable for Si1−yCy layers with y≤0.05 for a growth rate of about 0.2 nm/s. Raman spectra show a distinct phonon mode at 600 cm−1, which is characteristic of substitutional carbon in Si. The Raman spectra show no evidence of silicon carbide precipitates, nor are precipitates observed in the cross-sectional TEM micrographs. This is consistent with the lattice constant measurements by x-ray diffraction. Amorphous growth occurs for lower substrate temperatures or significantly higher carbon concentration. That means, with increasing y in the Si1−yCy alloy layer the substrate temperature must be increased moderately. We have also studied the thermal stability of Si1−yCy strained-layer superlattices and find that the layers are stable to about 800 °C (for y=0.015). The ability to grow high-quality Si1−yCy alloy layers and Si1−yCy/Si superlattices adds a new dimension to Si-based band-gap engineering with the possibility for integration of a potential wide band-gap semiconductor into Si technology.
Effect of molecular-beam epitaxy growth conditions on GaAs–AlGaAs heterojunction bipolar transistor performance: Beryllium incorporation and device reliability
Authors: Streit Dwight C. , Oki Aaron K. , Velebir James R. , Stolt Kjell S. , Umemoto Donald
Published: July 2002

We have studied the effect of molecular-beam epitaxy (MBE) growth conditions on the performance and reliability of npn GaAs–AlGaAs heterojunction bipolar transistors (HBTs). Wafers grown under normal conditions yield devices with high current gain, but suffer premature failure due to interstitial beryllium diffusion from the base into the graded AlGaAs emitter. Wafers grown with high arsenic/gallium flux ratio and reduced substrate temperature during base deposition have high current gain, and are extremely reliable. Mean time to failure, as defined by a 10% reduction in original current gain, is ≳ 108 h at 125 °C junction temperature for devices grown using conditions optimized for device reliability. We believe the ability to produce high reliability HBTs by MBE is vital to future applications of this technology.
Near band-edge photoluminescence from Si1−xGex/Si superlattices grown by molecular-beam epitaxy
Authors: Steiner T. D. , Hengehold R. L. , Yeo Y. K. , Godbey D. J. , Thompson P. E. , Pomrenke Gernot S.
Published: July 2002

Sharp, well-resolved near band-edge photoluminescence (PL) has been observed from long-period Si1−xGex/Si superlattices grown by molecular-beam epitaxy, including PL from a 120 Å Si/40 Å Si1−xGex sample. The sharp PL is due to shallow bound excitons (BE), and consists of a no-phonon (NP) line as well as phonon-assisted lines. The exciton binding energies obtained from the temperature dependence of the BE(NP) lines are in the range of 4–6 meV.
Monolayer coverage dependence for the surface photovoltage of Si(100)/Na
Authors: Hamawi A. , Walldén L.
Published: July 2002

Via photoemission, a strong coverage dependence is observed for the surface photovoltage (SPV) of Si(100) (n-doped, 2 Ω cm) held at low temperature (∼70 K) upon adsorption of monolayer amounts of Na. At low coverage light from the source used for photoemission produces nearly flatbands (SPV ∼0.5 eV), while at high monolayer coverages the SPV is small with the changeover occurring in a small coverage interval. In nearly the same coverage range, the surface region obtains metal character as judged from the photoemission intensity at the Fermi edge. Information about the coverage is obtained from the quantum well like states observed for multiatomic layer thick Na films.
Study of phonons and long-range order in Si–Ge superlattices using empirical interatomic potentials
Authors: Khor K. E. , Das Sarma S.
Published: July 2002

It is known that existing empirical potentials for semiconductors do not give good phonon spectra. They fail particularly in the aspect of transverse acoustical (TA) flattening. In this work we develop an empirical potential for the Si–Ge system which incorporates long-range interactions and accurately reproduces the phonon spectra, including TA flattening, of Si and Ge. This potential is based on our earlier theoretical work on a universal interatomic potential for semiconductors, which employs very few parameters. The validity of our potentials has already been confirmed in previous work where we have shown that elastic constants, cohesive energies, excess energies, equilibrium structural, and lattice parameters for several different monolayer superlattices are in very good agreement with the available first principles and experimental results. Long-range interactions are considered to be important in the understanding of superlattice phonons. A potential which can predict equilibrium structures accurately (which is essential for phonon studies), and at the same time calculate accurate phonon frequencies should be useful. We report on the results of the application of the potentials to the study of phonon spectra of Si–Ge strained layer superlattices. We also apply the potentials to the study of RH1 and RH2 long-range ordering in Si–Ge systems.
Formation of SiO2/GaAs(100) interfaces by electron stimulated oxidation of ultrathin Si overlayers: Subcutaneous oxidation processes
Authors: Palomares F. J. , Alonso M. , Soria F.
Published: July 2002

Recent studies of chemical vapor deposition of SiO2 films on GaAs substrates show the existence of subcutaneous oxidation processes which degrade the electrical properties of the interface. To form SiO2/GaAs interfaces this work presents a different approach based on a direct writing technique that consists in the growth of the SiO2 film by electron beam stimulated oxidation of ultrathin Si layers deposited onto the GaAs(100) surfaces. Modeling of the interface chemical evolution is performed by a detailed quantitative analysis of the Auger intensities. Subcutaneous oxidation is found to play an important role for Si films as thin as 1 monolayer (ML), and its kinetics is discussed by comparison with that of the SiO2 growth. However, while a Ga oxide film clearly appears below the Si oxide layer for 1 Si ML deposits, no signs of Ga oxidation are found for Si films 2.5 ML thick, that providing an estimate for discussing the minimum thickness required to grow abrupt SiO2/GaAs interfaces.
Use of diffracted light from latent images to improve lithography control
Authors: Hickman K. C. , Gaspar S. M. , Bishop K. P. , Naqvi S. S. H. , McNeil J. R. , Tipton G. D. , Stallard B. R. , Draper B. L.
Published: July 2002

As the microelectronics industry strives to achieve smaller device design geometries, control of linewidth, or critical dimension (CD), becomes increasingly important. Currently, CD uniformity is controlled by exposing large numbers of samples for a fixed exposure time which is determined in advance by calibration techniques. This type of control does not accommodate variations in optical properties of the wafers that may occur during manufacturing. In this work, a relationship is demonstrated between the intensity of light diffracted from a latent image consisting of a periodic pattern in the undeveloped photoresist and the amount of energy absorbed by the resist material (the exposure dose). This relationship is used to simulate exposure control of photoresist on surfaces having slight variations in optical properties, representative of those found in operating process lines. We demonstrate that linewidth uniformity of the developed photoresist can be greatly improved when the intensity of diffracted light from the latent image is used to control the exposure dose. Samples include a variety of photoresist materials and substrates with a wide range of optical properties. To verify the experimental observations, diffractions from the latent image grating structures is modeled using rigorous coupled wave analysis. The modeling is used to predict the diffraction from a latent image as a function of the substrate optical properties and the parameters of the latent image (i.e., linewidth, sidewall angle). Good agreement is obtained between theoretical and experimental observations. Conversely, the inverse problem is solved in which the parameters of the diffracting structure (the latent image) are determined from a measurement of the diffracted power. Therefore, the diffracted power can be monitored for the purpose of determining when the latent image will produce the proper CD upon development.
Comparison of the geometric structure and electron reflectivity of A/B-NiSi2/Si(111) and U/F-Si(111)-7×7 interfaces
Authors: Kubby J. A. , Greene W. J.
Published: July 2002

The electron reflectivity of A/B-NiSi2/Si(111) metal–semiconductor interfaces are compared to the structurally related U/F-Si(111)-7×7 interfaces. The twist of the lattice about the surface normal for type-B NiSi2/Si(111) and faulted Si(111)-7×7 is found to increase the electron reflectivity in both systems, leading to the formation of standing-wave states between the surface and twist interfaces.
GaInAs/InP and GaInP/GaAs (100) interfaces: An ultraviolet photoelectron spectroscopy study
Authors: Landesman J. P. , Garcia J. C. , Massies J. , Jezequel G. , Maurel P. , Hirtz J. P. , Alnot P.
Published: July 2002

The formation of GaInAs/InP and GaInP/GaAs (100) lattice-matched heterostructures grown by metalorganic molecular-beam epitaxy (MOMBE) was investigated in situ by ultraviolet photoelectron spectroscopy, using a He discharge lamp. Both direct (Ga0.47In0.53As grown on InP or Ga0.5In0.5P grown on GaAs) and inverse interfaces were investigated, with overlayer thicknesses in the range 1 to 10 monolayers (MLs). The Ga-3d and In-4d core-level (CL) spectra were measured with the He ii radiation (hν=40.8 eV), allowing highly surface sensitive measurements. We first show that the GaInAs and GaInP surfaces immediately after MOMBE growth display In segregation, leading to 100% In composition at both surfaces. A simple model indicates that this In segregation is limited to the first monolayer of ternary material. We have then studied the Ga/In atomic profiles at the various heterostructures studied. Both direct interfaces are abrupt in this respect. The situation is not so simple for the inverse interfaces. In the case of GaAs grown on GaInP, an In layer is detected at the growing GaAs surface, coming from a Ga/In exchange reaction at the first step of the growth of this heterostructure. The equivalent thickness of this InAs-like layer could be measured and is shown to depend crucially on the growth temperature in the range 480–550 °C. For inverse interfaces in the system InP/GaInAs, we sometimes observe Ga diffusion in the InP layer, but this is not systematic, and the driving growth parameter for this phenomenon could not be identified.

Taking into account these chemical configurations of the interfaces, we have undertaken a determination of the valence band offsets (VBOs) from the shifts of CL spectra. For GaInAs/InP, interfaces, we find a value of 440±50 meV for the direct case, in very good agreement with both experimental and calculated values, whereas for the inverse case we obtain a VBO of 260±50 meV. This strong asymmetry is discussed in parallel with the chemical asymmetry observed previously, in particular the fact that the inverse interfaces involve the growth of an InP layer on an In-segregated GaInAs surface. For GaInP/GaAs interfaces, we obtain values for the VBO very close to zero for both heterostructures. This behavior is discussed in connection with the observation that interfaces in this system are not well-known and published values for the VBO cover almost the entire band gap difference.
Reflection high-energy electron diffraction studies of the growth of InAs/Ga1−xInxSb strained-layer superlattices
Authors: Collins D. A. , Fu T. C. , McGill T. C. , Chow D. H.
Published: July 2002

We have used reflection high-energy electron diffraction to study the surface periodicity of the growth front of InAs/GaInSb strained-layer superlattices (SLSs). We found that the apparent surface lattice spacing reproducibly changed during layers which subsequent x-ray measurements indicated were coherently strained. Abrupt changes in the measured streak spacings were found to be correlated to changes in the growth flux. The profile of the dynamic streak spacing was found to be reproducible when comparing consecutive periods of a SLSs or different SLSs employing the same shuttering scheme at the InAs/GaInSb interface. Finally, when the interface shuttering scheme was changed, it was found that the dynamic streak separation profile also changed. Large changes in the shuttering scheme led to dramatic differences in the streak separation profile, and small changes in the shuttering scheme led to minor changes in the profile. In both cases, the differences in the surface periodicity profile occured during the parts of the growth where the incident fluxes differed.
Covered electrode HgCdTe photoconductor under high illumination levels
Authors: Fenigstein A. , Schacham S. E. , Finkman E.
Published: July 2002

The issue of thermal imaging systems exposed to large photon fluxes is of great practical importance, as it is encountered while observing a scenery which includes ‘‘hot’’ sources. High illumination level phenomena appear when excess carrier density is comparable or larger than majority carrier density in the bulk. This state can be reached quite easily in n-type HgCdTe detectors due to the moderate doping levels (typically ≤1015 cm−3). A modified expression for the current responsivity is derived, suitable for use at both high and low illumination levels. The quasineutrality assumption is verified; thus the ambipolar equation can be applied to describe high illumination behavior. Photoconductive detectors with and without covered electrodes are measured and analyzed. It is shown that under high illumination levels (1) the dominating recombination mechanism is the phonon assisted Auger process, and (2) the relative photoresponse for a covered electrode structure decreases monotonously with increasing covered electrode length. This is in contrast to low illumination levels where an optimum responsivity is reached. Thus, covered electrode photoconductors provide benefits at both ends of the power spectrum.
Reduced metal–insulator semiconductor tunneling in metalorganic chemical vapor deposition HgCdTe(111)Te films
Authors: Koestner R. , Lopes V. , Korenstein R. , Oguz S. , Kreismanis V. , Ehsani H. , Bhat I.
Published: July 2002

Metal–insulator semiconductor tunnel currents in metalorganic chemical vapor deposition (MOCVD) HgCdTe(111)Te layers are measured to be comparable to those found in high quality liquid phase epitaxy HgCdTe(111)Te. These tunnel currents are found to increase if CdTe rather than lattice-matched CdZnTe substrates are chosen or if the (001) growth orientation is selected. The rotational twins that generally form with (111) oriented HgCdTe growth by MOCVD are not detectable in more than 60% of the films characterized in this work. These results mark an important step towards the use of MOCVD HgCdTe heterostructure or heterojunction films for high performance infrared focal plane arrays.
Ion mill damage in n-HgCdTe
Authors: Elkind J. L.
Published: July 2002

Ion milling, a process believed to introduce interstitial mercury deeply into and type convert vacancy-doped p-HgCdTe, is shown to produce long-range isotropic damage in n-Hg1−xCdxTe (x=0.22). This damage is characterized by a bias-dependent dark current in metal–insulator semiconductor devices. Previous work has shown that ion milling also produces a moderate reduction in photoconductive response, a few micrometers below the ion-milled surface without reducing minority-carrier lifetime, and this is also presented here. It is determined that the severity of ion-mill damage can be reduced with a bake, either at 100 or 185 °C. The thermal decomposition of an anodic oxide, which is also believed to introduce interstial mercury deeply into and type convert vacancy-doped p-HgCdTe, is found to induce exactly the same changes in n-HgCdTe as obtained by ion milling. Since these two, rather different, processes both produce very deep type conversion in vacancy-doped p-HgCdTe, and also produce identical long-range electrical changes in n-HgCdTe, it is concluded that both processes share the same damage mechanism which includes the production and diffusion of interstitial mercury.
Schottky barrier induced injecting contact on wide band gap semiconductors
Authors: Liu Y. X. , Wang M. W. , McCaldin J. O. , McGill T. C.
Published: July 2002

A new method is proposed by which a minority carrier injecting contact or ohmic contact can be attained in wide band gap II–VI semiconductors. The basic principle is to use a forming process, i.e., an applied electric field at an elevated temperature in the Schottky contact, to spatially separate dopants from compensating centers. In this way, the ratio of dopants to compensating centers can be greatly increased at the semiconductor surface. Upon cooling, the dopant concentrations are frozen to retain a large net concentration of dopants in a thin surface layer, resulting in a depletion layer that is sufficiently thin to allow tunneling injection. Calculations of band profiles, distributions of doping concentrations, and current–voltage characteristics are performed on Al doped ZnTe, in which Al donors complex with doubly negatively ionized Zn vacancies to produce total compensation. The results indicate that the doping concentration and the total band bending during the forming process are the crucial factors for achieving injecting contacts. For Schottky barrier heights above 1 eV, doping concentrations as high as 1020 cm−3 are needed.
Erbium doping of molecular-beam epitaxially grown InSb on InP
Authors: Heremans J. , Partin D. L. , Morelli D. T. , Thrush C. M.
Published: July 2002

The transport properties of molecular-beam epitaxially grown InSb films doped with Er (atom densities NEr from 4.3×1016 cm−3 to 3.6×1020 cm−3) are reported at temperatures between 40 and 400 K. Er is a donor in InSb films grown under Sb to In flux ratios smaller than 1.1. At a flux ratio Sb/In=1.06, 25 atoms of Er give one extrinsic electron. The maximum extrinsic electron concentration achievable is ∼1.8×1017 cm−3, obtained for NEr≳4×1018 cm−3. Magnetoresistance measurements at 4.2 K show evidence for spin–disorder scattering of the electrons. The low-temperature (T<150 K) electron mobility increases with doping concentration up to rare-earth densities of 1×1018 cm−3; at higher rare-earth concentrations, the mobility decreases again. At room temperature, the mobility decreases monotonically with increasing Er concentration. We note the analogy between these results and the observations made on HgSe:Fe, a system in which the carrier mobilities might be enhanced by impurity charge ordering.
Structure and defect characterization of epitaxial CoSi2 on Si(001) formed using an amorphous Co75W25 sputtered layer
Authors: La Via F. , Spinella C. , Reader A. H. , Duchateau J. P. W. B. , Hakvoort R. A. , van Veen A.
Published: July 2002

The structure evolution and the defects present in epitaxial CoSi2 formed using the solid-state reaction between an amorphous Co75W25 sputtered layer and Si(001) have been studied by transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), positron annihilation and resistivity measurements. By employing anneals between 500 and 600 °C, Co diffuses out of the amorphous alloy into the substrate to form a CoSi2 layer. After the anneal, the remaining amorphous alloy on top of the silicide has been removed by a selective wet etch. It has been found that the greater part (∼68%) of the so-formed CoSi2 film is epitaxial and that a high density of vacancy-type defects (2.6×1019/cm3) is present in the material. A second anneal at a higher temperature has been performed to improve the quality of the silicide. This results in a decrease of the RBS minimum yield and the residual resistivity to values of ∼25% and 2.6 μΩ cm, respectively. Only a few grains of twinned CoSi2 could be detected after the second anneal. By plan-view TEM and RBS dechanneling energy dependence measurements, a total projected length of dislocation lines of ∼1.7×106 cm/cm2 has been estimated. By positron annihilation a density of 1.1×1018 vacancies/cm3 has been measured.
Through-wafer via fabrication in gallium arsenide by excimer laser projection patterned etching
Authors: Foulon François , Green Mino
Published: July 2002

Through-wafer vias, in high density, can be fabricated in GaAs by excimer laser projection patterned etching in a chlorine atmosphere. The via, if circular of diameter (B), decreases in diameter (A) with depth (W), according to the relation A≊B−0.65W. This corresponds to a sidewall slope of ∼18°. Etch rates up to 3 μm/min using a 20 Hz laser (248 nm) have been obtained, with good sidewall quality; the technique would appear to be suitable as a manufacturing method.
Scanning tunneling microscopy study of deoxygenated and de-ionized water rinsed GaAs(111)-B surfaces
Authors: Fukuda T. , Hirota Y.
Published: July 2002

GaAs(111)-B (arsenic terminated) surfaces prepared by rinsing with running deoxygenated and de-ionized water (DODIW) were investigated by scanning tunneling microscopy in ultrahigh vacuum. After annealing the sample, As-rich 2×2 reconstruction was found between 415 and 500 °C. Above 500 °C, Ga-rich √19×√19-like structures were also found around As desorbed triangular valleys. Although details of the reconstructions were slightly different from molecular-beam epitaxially grown surfaces, similar temperature dependence proved that DODIW-treated surfaces were effectively passivated against oxidation.
Lift-off process for noble metals
Authors: Domanský Karel , Petelenz Danuta , Janata Jiří
Published: July 2002

A two-layer lift-off process using aluminum and an inorganic dielectric for patterning noble metals is described. It produces a smoothly sloped metallization pattern and is compatible with the deposition temperatures up to 350 °C. The metal layers can be deposited either by evaporation or by sputtering. It is particularly useful in applications requiring thick metallization.
New silicon-rich silylating reagents for dry-developed positive-tone deep-ultraviolet lithography
Authors: Wheeler David R. , Hutton Skip , Stein Susan , Baiocchi Frank , Cheng May , Taylor Gary
Published: July 2002

Disilanes are used as silylating reagents for near-surface imaging with deep ultraviolet (248 nm) light. A relatively thin imaging layer of a photocross-linking resist is spun over a thicker layer of hard-baked resist which functions as a planarizing layer and antireflective coating. Photoinduced acid generation and subsequent heating cross-links exposed areas and renders them impermeable to an aminodisilane which reacts with the unexposed regions. Subsequent O2 reactive-ion etching affords a positive-tone image in the resist. The use of disilanes introduces a higher concentration of silicon into the polymer than is possible with silicon reagents that incorporate only one silicon atom per reactive site. The higher silicon content in the silylated polymer increases etching selectivity between exposed and unexposed regions and thereby increases the contrast. We have resolved high-aspect ratio, 0.25 μm line and space patterns with 248 nm light in a stepper with a numerical aperture=0.48.
Effect of low-solubility surface layer on development of AZ-PF514
Authors: Krasnoperova Azalia A. , Turner Stephen W. , Ocola Leo , Cerrina Franco
Published: July 2002

Effect of prebake conditions on dissolution of Hoechst AG positive chemically amplified resist AZ-PF514 has been studied. It was shown that the dissolution of the resist was nonlinear, with the retardation time strongly dependent on prebake conditions. Plasma etching of the top layer of the resist has been proposed in order to eliminate undesirably long development retardation time of the high temperature baked resist. It was shown that the roughness of the developing resist film was caused by the surface layer of low solubility.
Dissolution rate properties of three-component deep-ultraviolet positive photoresists
Authors: Thackeray James W. , Denison Mark , Fedynyshyn Theodore H. , Georger Jacque , Mori J. Michael , Orsula George W.
Published: July 2002

This article describes the optical and dissolution properties of Shipley three-component positive deep-ultraviolet (DUV) resists. These properties are optimized to provide higher resolution resists. These resists have higher B values than diazonaphthoquinone-novolak (DQN) resists, but because of chemical amplification, their C values are 200 times smaller. Due to the higher B values of these resists, resolution can only be improved through increased dissolution selectivity. Through increased blocking, the dissolution selectivity can be as high 16 000, a value that is 10 times that of DQN resists. However, these high selectivities have practical limitations, due to increased tendency to cap, and slower photospeed. A simple equation is derived for the dissolution rate as a function of extent conversion. The catalytic chain length can be extracted from these simulations, and, under the processing conditions described in this study, is shown to be in the range of 56–78 for all the resists studied. Using experimentally derived optical and dissolution parameters, the lithographic imaging of these resists can be modeled using PROLITH/2 (a product of Finle Technologies, Inc.) lithographic modeling software. With some assumptions, reasonable agreement between the modeled and real images are seen. Finally, a high-resolution DUV positive resist, Megaposit■ XP-3036, is described that has linearity to 0.275 μm and an Es of 86 mJ/cm2.
Patterning issues of 256MB dynamic random access memory x-ray masks
Authors: Koek B. , Jennings B. , Grant R.
Published: July 2002

Optical UV lithography has probably the best chance to become the production technique for 256MB complexity devices [M. Rothschild, Proceedings of the 37th International Symposium on Electron, Ion, and Photon Beams, Orlando, FL, 26–29 May, 1992 (unpublished). N. Nomura et al., Microcircuit Engineering Conference, Erlangen, Germany, Date 1992 (unpublished)]. X-ray lithography (XRL) is still a promising alternative, but this technology is in an earlier state of development [S. Yoshida, MicroProcess Conference, Kawasaki, Japan, Date 1992 (unpublished)]. Many research centers are putting effort into this to accelerate the development. Maskmaking is one of the critical issues in XRL. With increasing pattern complexity, not only the accuracy of the lithographic tool, but the whole path from computer-aided design conversion to lithography tool optimization to exposure becomes important. 256MB complexity pattern data have been converted by using both a flattening and a hierarchical convertor. The total conversion time from both convertors is similar. By maintaining the hierarchy during the fracturing, the hierarchical convertor has more flexibility for pattern manipulation. The Leica Cambridge EBPG5-HR was optimized and the exposure time of a 256MB complexity mask was less than 7 h. Four masks were exposed and fully analyzed. After correcting for substrate drift in the first two exposures, the overlay between the second pair of masks was 41 nm (3σ). Pattern placement in all masks was better than 25 nm (3σ).
Fabrication and optical properties of InGaAs/InP quantum wires and dots with strong lateral quantization effects
Authors: Ils P. , Michel M. , Forchel A. , Gyuro I. , Klenk M. , Zielinski E.
Published: July 2002

High-quality In0.53Ga0.47As/InP quantum wires and dots have been fabricated using high-voltage electron-beam lithography and wet chemical etching. Using poly(methyl- methacrylate) resist, gold lift-off, and wet chemical etching, dot structures with geometrical diameters down to ∼30 nm and wires with lateral widths down to 16 nm have been obtained. The wire structures were studied optically by means of photoluminescence spectroscopy and show strong optical emission even for the smallest geometrical widths and without overgrowth. The weak decrease of the quantum efficiency with decreasing wire width indicates that there is no significant damage at the sidewalls of the wires, which is in contrast to previous studies on dry-etched structures. The photoluminescence energy of the In0.53Ga0.47As/InP wires is independent of the wire width down to ∼60 nm. For smaller widths an increasing blue shift of the photoluminescence energy up to 60 meV is observed displaying a strong lateral quantization.
Optimization of aerial image quality
Authors: Turner S. , Cerrina F.
Published: July 2002

In this study, a metric of aerial image quality for two dimensional images is presented. Modeling is used to predict feature shape. The metric then imposes ‘bounds of acceptable deviation’ on the feature perimeter, and measures the exposure latitude which these bounds allow. The figure of merit is applied to the optimization of mask parameters for x-ray lithography of a 0.25 μm contact hole. The findings of this trial are presented.
Time-of-flight electron spectrometer for voltage measurements on integrated circuits
Authors: Dinnis A. R. , Khursheed A.
Published: July 2002

The basis of the method is to measure the time taken for secondary electrons emitted from the specimen to reach a detector situated some way up the electron-optical column. This time depends on the potential of the point on the surface from which the electrons are emitted. Measurements previously reported by the authors were carried out on small specimens inserted into the final lens bore of a conventional scanning electron microscope. The work has now been extended so that measurments can be made on integrated circuit chips in standard dual-in-line packages. It has therefore been demonstrated that the technique is useful for voltage-contrast diagnostics on real specimens.
Metrology for replicated x-ray masks using an electron-beam machine
Authors: Luciani L. , Di Fabrizio E. , Grella L. , Baciocchi M. , Figliomeni M. , Gentili M. , Mastrogiacomo L. , Maggiora R. , Kraspenova A. , Reilly M.
Published: July 2002

In this article, electron-beam metrology is applied to the dimensional control of an x-ray mask replication process for a feature size down to 0.15 μm. This task was accomplished by using an e-beam writer in the metrological mode. Backscattered electrons resulting from the e-beam scanning on mask gold absorbers are collected by an annular channel plate detector and the metrological information is extracted by means of a custom linewidth algorithm. Statistical samples of data are collected for each gold absorber feature, both for master and replicated masks. Masks are inspected by taking measurements point by point, in each spatial location of the layout. Then, the gold features replicated by experimental chemically amplified x-ray negative resists, are directly compared to the master mask ones. All the relevant statistical parameters for either master or replica masks were obtained by this method. The metrology experiment allowed the study of an x-ray mask replica process for linewidth control within 50 nm in the range of 0.15–2 μm feature sizes. Moreover, mask absorbers as small as 0.15 μm were inspected with a precision of 15 nm (3σ) by this method.
Investigation of the longitudinal and lateral distribution of implantation induced damage in GaAs/InGaAs heterostructures
Authors: Kieslich A. , Doleschel H. , Faller F. , Forchel A. , Stoffel N. G.
Published: July 2002

Ar+ ion implantations on unpatterned and patterned GaAs/InGaAs samples were carried out to study the depth and the lateral spread of the damage profile. The photoluminescence emission intensity from quantum wells located at different positions in the layer structure was used as a local probe for the induced damage. An unexpected wide range of the damage profile is observed which can be explained in terms of accidental capture of ions into channels. Implantation along the axial channels of the zinc-blende crystal leads to an additional increase of the longitudinal damage range. It is shown that the lateral damage distribution under the implantation masks of ions implanted in a random direction is clearly broader than that of ions implanted along the [110] axis.
Reactive ion etching-induced damage studies and application to self-aligned InP/InGaAs heterojunction bipolar transistor technology
Authors: Chau Hin-Fai , Pavlidis Dimitris , Brock Tim
Published: July 2002

A self-aligned InP/InGaAs heterojunction bipolar transistor (HBT) technology which makes use of a combination of CH4/H2/Ar reactive ion etching (RIE) and wet chemical etching to reduce the base-emitter separation is described. Surface damage and contamination induced by the CH4/H2/Ar discharge can, if not properly removed, degrade the current gain or lead to device failure. Surface analysis techniques, such as electron spectroscopy for chemical analysis and secondary ion mass spectrometry have been used to examine dry-etched surfaces. Submicron I-bar structures with varying InP air-bridge channel widths were defined by electron beam lithography and used for the analysis of vertical sidewall damage. Based on these studies, a RIE process has been defined and incorporated in the development of a self-aligned HBT technology. By eliminating the damaged regions and creating an overhang in the emitter layer using wet chemical etching, damage-free self-aligned HBTs with excellent characteristics were fabricated and their properties are reported.