bluuebunny/crossref_metadata_2025 huggingface dataset:
Elimination of flux transients in molecular beam epitaxy
Authors: Maki P. A. , Palmateer S. C. , Calawa A. R. , Lee B. R.
Published: July 2002

The application of molecular beam epitaxy (MBE) to the growth of compound semiconductors for devices and monolithic circuits requires excellent film uniformity and reproducibility of growth conditions. Conventional conical crucible cells for group III elements typically provide excellent film uniformity but exhibit a significant flux transient upon shutter opening due to the cooling of the melt surface. Flux transients result in poor control over initial growth stoichiometry and uncertainty over the initial film parameters which limit film reproducibility. This paper reports on a unique pyrolytic boron nitride (PBN) crucible arrangement for group III elements which simultaneously provides excellent film uniformity and a low flux transient. The cell utilizes a deep PBN crucible for a large recessed melt volume and a PBN insert to maintain beam uniformity. The cell provides film thickness and doping variations of less than 2% across a 2-in.-diam wafer and a flux transient of less than 3% when the shutter is opened. The usable melt volume is 20 cm3 and the operating temperature is approximately 100 °C lower than that of the conical crucible cell. The large cell volume increases run time between cell recharging over conventional conical crucible cells. The melt location deep in the furnace provides long term temperature stability and reduces long term growth rate variations. The high material quality and low oval defect density (<500 cm−2) are comparable to conventional conical cells. The results of the measurement of film parameters are presented and the operation of the cell is described.
Arsenic passivation of GaAs and pyrolytic decomposition of organotin compounds for i
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u selected area doping of GaAs molecular beam epitaxy
Authors: Kowalczyk S. P. , Miller D. L.
Published: July 2002

Development of in situ selected area doping techniques would add a powerful new dimension to GaAs MBE technology. We report here a study of an in situ selected area doping procedure based on the following steps: (i) MBE growth of GaAs on a clean GaAs (001) substrate, (ii) adsorption of an As passivation cap which would be patterned for selected area doping, (iii) adsorption of an organotin compound, (iv) thermal desorption of the organotin compound along with the As cap in the passivated areas and with pyrolytic decomposition of the organotin compound in the unpassivated regions, and (v) regrowth of GaAs with selected area Sn incorporation into the regrowth layer. In this study we evaluated steps (iii)–(v). Steps (iii) and (iv) were investigated by means of in situ Auger electron spectroscopy, and step (v) by electrolytic C–V profiling of the carrier concentration. The organotin compounds in this study were tetrabutyltin and dibutyltin dibromide.
Interface defects and disorder in a-Si:H/a-SiNx:H superlattices
Authors: Roxlo C. B. , Abeles B. , Persans P. D.
Published: July 2002

We have examined the interfaces in amorphous silicon hydride/amorphous silicon nitride multilayers with layer thicknesses varying from 7 to 200 Å. Infrared measurements show that these interfaces are heavily hydrogenated, with 1015 cm−2 excess hydrogen atoms per interface pair. Electroabsorption spectroscopy indicates that the interfaces are charged and asymmetrical, indicating that the interface properties depend upon the order of deposition. We attribute these effects to interface defects which are induced by the severe mismatch in bond density at the interface. Raman measurements show that the interface region is highly disordered, with bond angle fluctuations of 13°. Effects due to the interface region extend 10–20 Å into the a-Si:H layers.
Selective GaAs/AlxGa1−xAs reactive ion etching using CCl2F2
Authors: Knoedler C. M. , Kuech T. F.
Published: July 2002

The reactive ion etching (RIE) of GaAs/AlxGa1−xAs heterolayers has been examined as a function of alloy composition (x=0.00–0.31) and the etching parameters of pressure, rf applied power, gas flow rate, and time using CCl2F2 as the etching gas. The information derived from this study was used to determine the GaAs to AlxGa1−xAs etch selectivities. The use of CCl2F2 promotes the formation of nonvolatile reaction products on the surface of AlxGa1−xAs, so that even for small amounts of aluminum the etch rate of AlxGa1−xAs is significantly reduced compared to GaAs. This compositional factor favors the highly selective etching of GaAs over AlxGa1−xAs. High gas pressure and flow rate and a low rf applied power also contribute to high selectivities in this system. A selectivity (GaAs to AlxGa1−xAs etch ratio) of 300 was attained for a pressure of 20 mTorr and an rf power of 500 W.
Role of Hg bonding in metal/Hg1−xCdxTe interface formation
Authors: Friedman D. J. , Carey G. P. , Lindau I. , Spicer W. E. , Wilson J. A.
Published: July 2002

We discuss the role of the weak bonding of Hg in the Hg1−xCdxTe (MCT) lattice in determining interface morphology when metal is deposited on the surface. The Ag/MCT, Cu/MCT, Al/MCT, and Cu/CdTe interfaces are studied in an ultrahigh vacuum with x-ray and ultraviolet photoemission and with low energy electron diffraction. The three metals are found to yield distinctly different interface morphologies. For Ag/MCT, the Hg instability results in diffusion of Ag 102–103 Å into the semiconductor through Hg vacancies. For Cu overlayers, the instability greatly enhances Te and Cd intermixing into the Cu for MCT compared to CdTe. The more reactive Al overlayers deplete the weakly bound Hg from the MCT surface. We compare the metal/MCT interfaces with the corresponding metal/CdTe and metal/GaAs interfaces. For the three overlayer metals on MCT the instability of the Hg bond results in interfaces with a much greater degree of intermixing than for the corresponding metal/binary semiconductor interfaces.
Raman scattering study of plasma etching damage in GaAs
Authors: Kirillov D. , Cooper C. B. , Powell R. A.
Published: July 2002

In the present work, we have applied Raman scattering to study the damage produced by etching GaAs with inert and reactive gas plasmas. (AIP)
A study of novel growth approaches to influence the growth mechanism and interface quality in heterostructures grown by molecular beam epitaxy
Authors: Singh Jasprit , Dudley S. , Bajaj K. K.
Published: July 2002

An atomic model based on Monte Carlo techniques is discussed and motivations are presented for the need of novel growth approaches for growth of high quality heterostructures. These motivations arise from recognizing the differences in cation kinetics of the two semiconductor components of the heterostructure, which may not allow high quality growth of both the components at the same temperature. Results of computer simulations on two approaches to overcome this problem are reported. The two approaches are (a) use of periodic substrate temperature pulses during growth and (b) growth interruption. Based on our simulations we propose that high quality heterostructures can be grown at low average temperature provided the substrate temperature is periodically raised for a few seconds without growth interruption.
O 1s studies of the oxidation of InP(110) and GaAs(110) surfaces
Authors: Hughes G. , Ludeke R.
Published: July 2002

Two major outstanding issues in the oxidation of InP and GaAs(110) surfaces are addressed: (1) single phase versus multiphase oxidation and (2) surface versus bulk oxidation. From the analysis of O 1s, In 4d, and P 2p core level spectra it is concluded that InP oxidizes predominantly in a single phase at room temperature. Its stoichiometry is enhanced upon annealing to give InPO4. There is no evidence for any other oxide phase for the coverage range investigated (to ∼1 monolayer of adsorbed oxygen). It appears that the oxidation is nucleated, but forms a fairly homogeneous oxide layer at the surface. GaAs(110), on the other hand, oxidizes from submonolayer oxygen coverages on into separate gallium and arsenic oxide phases. There is evidence for several oxidation states of the As. These do not consolidate upon annealing into a stoichiometric phase, but rather are reduced by the presence of GaAs to form additional gallium oxide. Reference spectra obtained from β-Ga2O3 crystals were used to confirm the absence of this oxide in the oxidized GaAs surfaces and to calibrate the oxygen uptake. The experimental results confirm the issue of subsurface oxidation prior to a monolayer uptake of oxygen.
PtSi contact metallurgy using electron-beam evaporated Pt films and different annealing processes
Authors: Chang Chin-An , Cunningham B. , Segmüller A. , Huang H.-C. W. , Turene F. E. , Sugerman A. , Totta P. A.
Published: July 2002

Pt films deposited by electron-beam evaporation onto both heated and unheated Si substrates have been used to form PtSi by different annealing sequences and ambients. Pt films deposited on substrates at 350 °C show complete formation of PtSi. Subsequent annealing at 550 °C is needed to form the protective oxide desired for device processing, with little dependence on the annealing ambients used. Pt films deposited on unheated substrates, on the other hand, show a partial formation of Pt2Si. The formation of PtSi by further annealing of such films is clearly dependent on the annealing sequence and ambient used. A three-temperature sequence at 200/300/550 °C in forming gas is shown to allow a complete reaction between Pt and Si, and to develop a surface protective oxide of excellent resistance against etching in aqua regia. PtSi films formed by single-temperature annealing at 550 °C in various ambients, however, show incomplete reactions between Pt and Si, leaving unreacted Pt and traces of Pt2Si, and a surface passivating oxide of poor resistance against aqua regia. The results on such evaporated Pt films are therefore similar to those reported earlier for the sputtered Pt. Film structures and compositions, phases formed, and Schottky diodes using different processes are analyzed and compared with those using sputtered Pt.
Material characterization of plasma-enhanced chemical vapor deposited titanium silicide
Authors: Morgan Alan E. , Stacy William T. , De Blasi Janet M. , Chen T-Y. James
Published: July 2002

Auger electron spectroscopy, Rutherford backscattering, secondary ion mass spectrometry, and transmission electron microscopy have been used to study the material properties of titanium silicide films prepared at 450 °C by plasma-enhanced CVD on polysilicon, single crystal Si, and thermally grown SiO2 substrates. Three amorphous layers are deposited, the middle one containing Ti and Si, and the outer layers Si only. A 650 °C anneal is sufficient to form a 14 μΩ cm, large grain, stoichiometric TiSi2 film of good purity. Oxidation of TiSi2/Si produces a Ti-free SiO2 layer over the silicide. However, after prolonged oxidation, voids are found in the oxide layer and the silicide film becomes discontinuous. This can be prevented by oxidizing only the excess Si remaining after TiSi2 formation. During oxidation of the silicide deposited on SiO2 substrates, TiSi2 is decomposed into TiOx and SiO2.
Electronic and optical properties of strained-layer superlattices made of semiconductor alloys
Authors: Ting D. Z.-Y. , Chang Yia-Chung
Published: July 2002

We report theoretical calculations of the electronic and optical properties of strained-layer superlattices (SLS) made up of semiconductor alloys. The SLS conduction band states are obtained by using a two-band model capable of correctly describing the band structure over the entire Brillouin zone. This allows us to study intervalley scattering among the various conduction band valleys (Γ, L, X, etc.). Our model also allows us to easily incorporate the effects of strain on the band structure. Using this model we have studied materials such as Si/GeSi SLS, and the effects of zone folding and strain on the band structure and photoabsorption are reported. We have also studied the effect of disorder scattering in SLS made of alloy semiconductors by generalizing the coherent potential approximation (CPA) to the treatment of superlattices. The results are compared with those obtained within the virtual crystal approximation (VCA) which does not include disorder scattering.
Nucleation and growth of chemically vapor deposited tungsten on various substrate materials: A review
Authors: Broadbent Eliot K.
Published: July 2002

W films produced by chemical-vapor deposition (CVD), typically via reduction of WF6, are being used for numerous applications in very large scale integrated circuit technology. Blanket and selectively deposited films require nucleation and growth on a specific underlayer material—Si, metal, or metal silicide. The compatibility of CVD W with various underlayers is reviewed for the device applications of contact/via fill, diffusion barrier, metal interconnect, and source/drain coating. Nucleation of W directly on single crystal Si can sometimes produce tunnel-defect structures at the edges or along the entire interface of the deposit. Sputtered Mo and W, and to some extent TiW and TiN, have been shown to be suitable nucleation layers for CVD W, yielding a fluorine-free interface with low-electrical contact resistance. A sputtered W/Ti adhesion bilayer is demonstrated for a blanket W deposition+etchback process. CoSi2 appears an appropriate choice where CVD W and salicide technologies are combined.
Properties of a laser-plasma x-ray source for x-ray lithography
Authors: Crawford E. A. , Hoffman A. L. , Albrecht G. F. , Sogard M. R.
Published: July 2002

We have used an advanced, near diffraction limited Nd:YAG laser, operated at 1.06 μm and employing a zig-zag slab amplifier, to generate x rays from the laser induced plasmas of a number of target materials. The x-ray conversion efficiencies were studied as a function of target material and laser parameters. We have measured the x-ray spectra, for x-ray energies above about 1 keV, and used them to evaluate this source with regard to x-ray lithography. A number of target material, resist, and mask combinations appear suitable for a lithography system capable of 0.25-μm minimum feature size.
Stability of polycrystalline silicon-on-cobalt disilicide–silicon structures
Authors: Murarka S. P. , Chang C. C. , Adams A. C.
Published: July 2002

Stability of the polycrystalline silicon–CoSi2–single crystalline silicon sandwich structures, at temperatures in the range of 600–950 °C, is investigated. It is found that at temperatures above 800 °C, the structure is unstable whenever the polycrystalline silicon is undoped or boron (in situ) doped. At temperatures >800 °C, silicon migrates to the crystalline substrate and CoSi2 migrates to surface, finally resulting in a structure where no polycrystalline silicon was left on top of the silicide in a manner analogous to solid-phase epitaxial process reported earlier in literature. However this exchange of place between polycrystalline silicon and CoSi2 did not occur when the phosphorus (in situ)-doped film was used. The structure ‘‘phosphorous (in situ)-doped polycrystalline silicon–CoSi2–single crystalline silicon’’ was stable at 900 °C in argon, nitrogen–15% hydrogen, or PBr3 doping ambients.
Electrical properties of SrF2/InP (100) diodes and SrF2 thin films
Authors: Couturier G. , Chaouki A. , Ricard H. , Barriere A. S. , Haw C.
Published: July 2002

Thin films of SrF2, with a lattice parameter close to InP, have been grown by sublimation under vacuum on the semiconductor. This paper mainly deals with the electrical properties of the metal/polycrystalline SrF2 layers/n-type InP (100) structures. For sweep rates greater than 10 Vs−1, the capacitance–voltage characteristics do not show any significant hysteresis. An important modulation of the surface potential of InP is observed. The surface state density, in the depletion and near the accumulation regions of the semiconductor is very low. For low-voltage sweep frequencies a hysteresis occurs and is interpreted in terms of low-ionic conductivity in the polycrystalline fluoride layers.
The role of order on the interface properties of Sb/GaAs(110)
Authors: Schäffler F. , Ludeke R. , Taleb-Ibrahimi A. , Hughes G. , Rieger D.
Published: July 2002

The influence of thermal annealing of Sb/GaAs(110) interfaces is studied in situ by high-resolution photoemission spectroscopy. A detailed line shape analysis of the Sb 4d core-level spectra shows that Sb deposition at room temperature (RT) does not lead to perfectly ordered growth of the first monolayer (ML), as previously assumed. Annealing at 330 °C results in a highly ordered overlayer that is desorption limited to 1 monolayer (ML). The degree of order affects the barrier height at the interface drastically: whereas RT deposition produces band bending of up to 0.6 eV on p-GaAs, annealing reduces the position of the surface Fermi level by a factor of 2 to a position 280 meV above the valence-band maximum of the GaAs. This pinning position corresponds to the maximum of the two-dimensional valence-band structure of the ordered-Sb monolayer. Band bending effects attributable to the generation of intrinsic defects in the GaAs during deposition or annealing processes were not observed.
Chemical and electronic properties of the Pt/GaAs(110) interface
Authors: McCants C. E. , Kendelewicz Tom , Bertness K. A. , Mahowald P. H. , Williams M. D. , List R. S. , Lindau I. , Spicer William E.
Published: July 2002

The interaction between evaporated Pt and the GaAs (110) surface has been studied at room temperature in ultrahigh vacuum utilizing surface-sensitive soft x-ray and ultraviolet photoemission spectroscopies. Detailed curve-fitting analysis of the substrate and metal core levels indicates dissociation of the GaAs with a reaction between the Pt and the Ga and a strong reaction with the As as well. Evidence of Pt–As compound formation is observed. Above 6.67 monolayers (ML) (10 Å), a second reacted component dominates and the As-core energy shifts smoothly to a final position ∼0.3-eV-higher binding energy than As in GaAs. The reacted Ga has a well-defined energy ∼0.4 eV less bound than the Ga in GaAs. This correlates well with the calculated core level binding energy shift reported by Nogami et al. for dilute Ga in Pt. The Schottky barrier height is established by 0.67 ML and is observed to be 0.83 (0.48)±0.1 eV for n-type (p-type) substrates, in agreement with electrical measurements on much thicker diodes. The large barrier height on the n-type substrate is similar to those obtained for Au, Cu, Ag, and Pd which, like Pt have a large electronegativity. The degree of overlayer/substrate intermixing that has been observed for these metals does not indicate a strong dependence on interfacial reaction products for the barrier height.
Molecular-beam epitaxial growth of graded band-gap quaternary GaxAlyIn1−x−yAs multilayer heterostructures on InP: Application to a novel avalanche photodiode with an ultrahigh ionization ratio
Authors: Alavi K. , Cho A. Y. , Capasso F. , Allam J.
Published: July 2002

We first describe the growth of device quality compositionally graded quaternary GaxAlyIn1−x−yAs on InP by molecular-beam epitaxy (MBE). Device quality material without misfit dislocations were grown to satisfy the lattice matching condition x+y≂0.47 as closely as possible during the growth of the entire graded region. This was accomplished by keeping the In flux constant (constant cell temperature) while changing the Ga and Al cell temperatures simultaneously to keep the total Ga plus Al flux constant while grading x (and consequently y). This was done using a desktop computer and a data acquisition/control system interfaced to cell temperature controllers and shutter actuators. Next we describe growth and operation of a novel p-intrinsic-n type semiconductor (p-i-n) avalanche photodiode (APD) which incorporates such compositionally graded layers in the i region. The i layer contains a multitude of asymmetric wells with one side abrupt and the other graded, each well surrounded by (Al,In)As. This device yielded a very large hole to electron ionization ratio β/α=50 at −12-V bias and 200 Hz. This value for β/α is the highest reported in any III–V compound. Avalanche multiplication occurs when carriers heated by the electric field in the barrier layers impact ionize carriers which are dynamically stored in the wells. Due to the grading of the exit well/barrier interface and under reverse bias condition there is a substantial reduction in the density of dynamically stored electrons and there is negligible multiplication of electrons resulting in a high β/α ratio.
Growth of high quality GaAs layers directly on Si substrate by molecular-beam epitaxy
Authors: Chong Tow C. , Fonstad Clifton G.
Published: July 2002

A study of molecular-beam epitaxy growth conditions that lead to high quality GaAs epitaxial layers grown directly on (100) Si substrates without the use of superlattice buffers is reported. An initial nucleation process which involves a predeposition of As on the Si surface and an in situ thermal annealing step immediately after the initial growth is shown to yield high quality GaAs layers with only a thin buffer layer. The effect of the growth initiation temperature is investigated and an optimal value for this temperature is found that results in smooth GaAs surface morphology. GaAs layers with relatively thin buffer layers grown under optimum conditions exhibit considerably improved electrical and optical properties, with Hall mobility and photoluminescence linewidth similar to those of homoepitaxial GaAs layers.
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u chemical etching of GaAs(001) and InP(001) substrates by gaseous HCl prior to molecular-beam epitaxy growth
Authors: Contour J. P. , Massies J. , Salètes A. , Outrequin M. , Simondet F. , Rochette J. F.
Published: July 2002

I n situ chemical etching of GaAs (001) and InP (001) by gaseous HCl before molecular-beam epitaxy (MBE) growth, on substrates previously etched with H2SO4/H2O2/H2O, has been studied by different surface and interface analysis techniques. Oxide free GaAs surfaces are obtained for low HCl pressures (p≥0.1 Torr) at 25 °C. The residual adsorbed chlorine is removed at 450 °C under vacuum or As4 pressure. In contrast to what is observed for GaAs, the surface oxide layer of InP substrates is not eliminated by gaseous HCl at room temperature. Capacitance–voltage measurements recorded after MBE growth on HCl gas deoxidized GaAs substrates do not detect any electrical perturbation of the substrate/layer interface, although the ion microprobe profiles show an increase in carboneous contamination of this interface. Moreover, the growth defect density is around four times lower when a deoxidation step by HCl gas is performed before the epitaxial growth of GaAs layers.
Observation of optically detected magnetic resonance signals in AlxGa1−xAs
Authors: Spencer M. G. , Kennedy T. A. , Magno R. , Griffin J.
Published: July 2002

Optically detected magnetic resonance (ODMR) techniques which utilize weak spin effects on deep photoluminescence have been applied to MBE AlxGa1−xAs. ODMR [unlike conventional electron paramagnetic resonance (EPR)] experiments is ideally suited for thin epitaxial samples. Using this technique we have obtained results on molecular-beam epitaxy (MBE) AlxGa1−xAs grown at substrate temperatures of 570 and 620 °C. The four-line ODMR spectrum observed from AlxGa1−xAs at low x values is attributed to Ga atoms not on their normal sites. The physical defect we have ascribed to this signal is a Ga interstitial. To our knowledge this is the first observation of a self-interstitial in the GaAs–AlxGa1−xAs system. We suggest that the level ME6 observed in deep-level transient spectroscopy (DLTS) experiments on MBE grown under similar conditions is the Ga interstitial observed in the ODMR experiment. For x>0.3 the Ga spectrum is still observed but an additional single unsplit magnetic resonance line appears which might be due to oxygen.
Controlled substitutional doping of CdTe films
Authors: Bicknell R. N. , Giles N. C. , Schetzina J. F.
Published: July 2002

The first successful doping of CdTe films is reported. These doped epilayers were prepared using a new technique, photoassisted molecular-beam epitaxy, in which the substrate is illuminated during the film deposition process. Illumination was found to produce immediate and favorable changes in the electrical properties of the films such that highly conducting epilayers resulted.
Formation of submicron isolation region in GaAs by Ga focused ion beam implantation
Authors: Nakamura K. , Nozaki T. , Shiokawa T. , Toyoda K. , Namba S.
Published: July 2002

Highly resistive regions formed by Ga focused ion beam (FIB) were investigated. The submicron isolation region can be formed into n-GaAs layers by Ga FIB single line implantation with the conductive layer carrier concentration up to 1×1018 cm−3 and with the annealing temperature up to 900 °C. Using Ga FIB raster scanning implantation, the resistivity of the highly resistive region was evaluated to be more than 2×104 Ω cm for doses around 1×1014 cm−2. Exceeding this dose, n-type carrier generation was observed for S-doped layers, while p-type carrier generation was observed for Si-doped layers. No highly resistive region could be observed for p-GaAs layers. For conventional Ga unfocused ion beam (UIB), similar results were obtained.
Radiation damage effects in boron nitride mask membranes subjected to x-ray exposures
Authors: Johnson W. A. , Levy R. A. , Resnick D. J. , Saunders T. E. , Yanof A. W. , Betz H. , Huber H. , Oertel H.
Published: July 2002

The effects of radiation damage with 1 to 3 keV x-rays on hydrogenated boron nitride films prepared by LPCVD have been investigated. It is shown that both the surface and bulk film properties of these materials are modified and may potentially limit the use of this material as a membrane in an x-ray mask structure. Specifically, it is shown that growths will form on exposed boron nitride surfaces irradiated in oxygen-containing ambients; optical transmission of irradiated films will degrade with the cumulative absorbed dose; the tensile stress of an x-ray mask membrane will decrease and introduce pattern distortions depending upon the irradiation dose/flux and exposure geometries. A model to evaluate the observed pattern distortions and a mechanism to explain the observed stress changes of the hydrogenated boron nitride films are proposed.
Aryloxy-poly(phosphazenes) as negative-working, oxygen reactive ion etching resistant resist materials
Authors: Hiraoka H. , Chiong Kaolin N.
Published: July 2002

In bilayer and multilayer resist processes only silicon-containing polymers have been studied most extensively as oxygen etch barrier layers. We wish to report the aryloxy-poly(phosphazenes) can be used as an oxygen etch barrier layer with a very small etch rate and can be imaged under e-beam, x-ray, and UV exposure in the presence of a sensitizer; a sensitivity of 20 mJ/cm2 at 254 nm and that of 55 mJ/cm2 at 4.4 Å of x-ray were obtained, and for 25 keV electron beam exposures, a sensitivity of 0.7 μC/cm2 was obtained. These poly(phosphazenes) can be removed readily by CF4–reactive ion etching (RIE) or by aqueous and organic solvents.
Optical properties of InP doping superlattices grown by metal organic chemical vapor deposition
Authors: Gal M. , Viner J. M. , Taylor P. C. , Yaun J. S. , Stringfellow G. B.
Published: July 2002

Recently we have reported the first InP superlattice grown by the organometallic vapor phase epitaxy (organometallic vapor phase epitaxy or metal organic chemical vapor deposition) technique. These samples were grown in an atmospheric pressure reactor using trimethylindium and phosphine in a hydrogen ambient. The n- and p-type dopants were diethyltellurium and dimethylzinc, respectively. Several experiments indicate that the interfaces between the n and p regions in these structures are sharp and of high quality. The peak energy and the line shape of the photoluminescence spectra depend on the excitation intensity just as predicted theoretically. In addition, the time decay of the luminescence contains distinct steps, indicating the existence of subbands due to quantum size effects. The first photoreflectance (PR) measurements have also been performed on these doping superlattices. These measurements show that the photoexcited carriers modulate the subband levels in a very predictable fashion. The observed PR line shapes are well explained by photomodulation of the subbands in the conduction band. These line shapes have been fit accurately with a simple model, which accounts for the dependence of the spectrum on the power of the exciting light and on the layer thickness. The agreement between the model calculations, which assume a parabolic well to describe the quantized subbands of the electrons, and the experimental line positions suggests that the interfaces are sharp and that the compensated regions between n and p layers are narrow.
A comparison of different methods for removal of damage caused by reactive sputter etching of silicon
Authors: Östling M. , Petersson C. S. , Norström H. , Buchta R. , Blom H-O.
Published: July 2002

The influence of etch time and power density on damage introduced in silicon by reactive sputter etching has been investigated. The induced damage was characterized by Schottky barrier height measurements, backscattering–channeling technique, and transmission electron microscopy. The study also comprises three methods for removal of the damage. It was found that the surface could be fully restored by means of thermal oxidation or plasma oxidation followed by a HF dip. These results were verified both by electrical measurements and by backscattering–channeling technique. The rapid thermal annealing treatment seems to fully restore the surface etched at a power density of 0.5 W/cm2 or lower. For higher power densities, the surface is not fully restored, but a considerable improvement is found.
Clearing resist from alignment mark areas using an excimer laser
Authors: Seeger D. E. , Rosenfield M. G.
Published: July 2002

An increasingly important problem in various lithographies is accurate alignment. Detection of alignment marks can be obscured by different resist coatings covering the marks. To circumvent this problem, a technique has been developed to clear resist from alignment mark areas. The technique uses ablative photodecomposition (APD) with an excimer laser to clear the resist thereby facilitating alignment. A potential problem using APD for semiconductor processing is the well-known phenomenon of debris formation. It has already been shown that only a small percentage of the products derived from ablation are volatile and that large amounts of solid debris are formed under a variety of ablation conditions. Though some postablation wafer cleaning techniques may be possible, these involve extra process steps and are therefore undesirable. The technique described here uses a localized vacuum system to collect the debris. A marked improvement in debris containment has been demonstrated using this system. The alignment mark clearing technique has been implemented in a prototype tool consisting of an automated x,y stage driven by linear motors for wafer positioning, a personal computer driven laser shutter to control the number of laser pulses, alignment optics, and the vacuum system for debris containment. The wafer is loaded on the stage after which alignment is performed using an off-axis alignment system. The software removes wafer rotation and controls stage positioning and laser output to ablate the desired number of alignment marks. The prototype tool has been used to clear alignment marks for both optical and electron beam alignment systems.
Fabrication of fully scaled 0.5-μm n-type metal–oxide semiconductor test devices using synchrotron x-ray lithography: Overlay, resist processes, and device fabrication
Authors: Silverman J. P. , DiMilia V. , Katcoff D. , Kwietniak K. , Seeger D. , Wang L. K. , Warlaumont J. M. , Wilson A. D. , Crockatt D. , Devenuto R. , Hill B. , Hsia L. C. , Rippstein R.
Published: July 2002

Functional, fully scaled n-type metal–oxide semiconductor (NMOS) circuits with 0.5-μm ground rules have been fabricated using synchrotron radiation x-ray lithography for all device levels. The exposures were done at the vacuum ultraviolet storage ring of the National Synchrotron Light Source at Brookhaven National Laboratory using a mask/wafer aligner developed at IBM Research. The system is capable of step-and-repeat exposures covering 125-mm wafers. The mask and wafer are held in a near-vertical plane and a scanning dark-field alignment technique is used to register mask to wafer with a proximity gap of 40 μm. A scanning mirror in the beamline sweeps the x-ray beam up and down over the exposure area to achieve uniform exposure over the 25×25 mm2 exposure field used for this experiment. Exposures were done in 20 Torr of helium to provide cooling for the mask. Both positive and negative tone single-layer resists were used. The mask set consists of four light-field masks patterned on silicon substrates with electroplated gold absorbers; patterns were written by a vector scan electron beam lithography system. The performance of the aligner on both test wafers and device wafers is discussed, with emphasis on overlay and linewidth control. The repeatability of the alignment and the overall level-to-level overlay are described. Characteristics of the fabricated devices are also presented.
Measurement techniques for submicron resist images
Authors: Rosenfield Michael G.
Published: July 2002

Low-voltage scanning electron microscopes (SEM’s) are primarily used for submicron metrology and inspection of resist images and other processing levels in the fabrication of integrated circuits. The optical confocal laser scanning microscope (CLSM) has recently been introduced as another system for submicron metrology. In this paper, the important issues of submicron resist metrology are investigated. It is shown that SEM based metrology systems can be used to measure the top widths of 0.5-μm-thick resist features with an accuracy of 0.02 μm or better, down to ∼0.1 μm, the smallest pattern used in this study. The measurement precision of the SEM was actually better than 0.015 μm, 3σ. The precision was found to be influenced by charging effects and the quality of the SEM signal. The 325-nm wavelength CLSM was able to make measurements of similar accuracy down to 0.5–0.35 μm using a careful choice of focus height and measurement threshold. Changing the substrate from Si to 0.27-μm oxide/Si resulted in a significant change in the measurement offset for the CLSM, but had little effect on the SEM measurements. The measurement precision of the CLSM was typically below 0.025 μm, 3σ. The CLSM precision was influenced by small variations in focus height. The accuracy and precision of both systems were dependent on the correct utilization of the measurement algorithms and careful calibration of the measurement signals.
Study on oxygen behavior during Ti/Si and Ti/SiO2 interactions
Authors: Li Bing-Zong , Zhou Shi-Fang , Hong Feng , Jiang Guo-Bao , Liu Ping , Zhang Ai-Ming , Chao Ming
Published: July 2002

For practical titanium silicide device application the oxygen behavior in the solid phase interaction is important to study. The Ti/Si and Ti/SiO2 interaction by the NH3 plasma assisted thermal annealing and oxidation of Ti/SiO2 and TiSi2/Si in a wet oxygen ambient were investigated by Auger electron analysis. The characteristic Auger spectral line shapes of Ti, O, and Si and their changes in compounds were measured. The experiment clearly demonstrated the oxygen snowplow effect during TiSi2 and TiN growth, and a stable SiO2 can be grown on TiSi2/Si directly or through a layer of TiO2.
TiSi2 strap formation by Ti–amorphous-Si reaction
Authors: van Houtum H. J. W. , Bos A. A. , Jonkers A. G. M. , Raaijmakers I. J. M. M.
Published: July 2002

This report describes the formation of a TiSi2 strap in combination with the self-aligned titanium silicide (salicide) technology. The TiSi2 strap is formed by reaction of amorphous silicon (a-Si) with the underlying Ti layer. It was determined that sputter deposition of the Ti and a-Si had to be done in one deposition cycle, otherwise interface contamination would prevent the Ti–a-Si reaction and give rise to extensive silicon diffusion from the active areas. Since TiSi2 straps are formed over diffusion areas as well as over oxide surfaces, the influence of the substrate on the Ti/a-Si reaction was determined. It was found that for straps deposited on oxide substrate the properties of the silicide layer formed were determined by the Ti/a-Si atomic ratio. A titanium-rich strap resulted in a high-resistivity silicide layer due to TiSi compound formation. Stoichiometric straps formed low-resistivity TiSi2 layers with a thin-TiN top layer and silicon-rich straps also resulted in a low-resistivity TiSi2 layer but with a silicon enrichment at the surface. On a mono-Si substrate no influence of the sputtered Ti/a-Si atomic ratio could be found. Only low-resistivity TiSi2 layers were formed. In case of silicon-rich Ti/a-Si ratio the excess silicon disappears from the layer and regrows onto the Si substrate. The roughness of TiSi2 straps, mainly observed for stoichiometric or silicon-rich straps on oxide substrates, was found to be related to the presence of argon (and probably hydrogen) incorporated in the layer during sputter deposition. Special attention was paid to strap formation at oxide/diffusion area edges. Possible void formation by local silicon consumption could not be detected. Strap/TiSi2 salicide transitions are also very smooth and showed no substrate defects.
The use of vector scanning for producing arbitrary surface contours with a focused ion beam
Authors: Crow G. , Puretz J. , Orloff J. , DeFreez R. K. , Elliott R. A.
Published: July 2002

A new method of using focused ion beams to micromachine contoured surfaces in solids is described. Instead of using a raster scan with a uniform scan rate, the new technique, called vector scanning, uses a nonuniform scan rate which is varied in a manner related to the profile of the desired sputter crater. A simple relationship between the scan rate and the desired surface contour has been derived and used to develop an algorithm for the deflecting voltages needed to micromachine slanted surfaces of the type desired for the production of surface emitting semiconductor lasers, and sinusoidal surfaces which may be used as optical diffraction gratings.
Si metal–oxide semiconductor field effect transistor with 70-nm slotted gates for study of quasi-one-dimensional quantum transport
Authors: Scott-Thomas J. H. F. , Kastner M. A. , Antoniadis D. A. , Smith Henry I. , Field Stuart
Published: July 2002

We have fabricated dual-gate Si metal–oxide semiconductor field effect transistor devices in which the lower gate is slotted and the upper gate, separated by 45 nm of SiO2, is planar. By appropriate adjustment of the potentials on the two gates, the field lines from the upper gate are pinched, creating an inversion layer about one-half the slot width. The resist patterning was done by x-ray lithography, using a mask that combined crystallographic-template/sidewall-shadowing techniques with UV lithography. The slotted lower gate was produced by lift-off. The metallization was a sandwich structure of Cr/W/Cr which permitted high-temperature annealing. Very high mobilities, ∼15 000 cm2 /V s at 4.2 K, were achieved as a result. The combination of high mobility and extremely narrow inversion channel (∼30 nm) yields very clear structure in the conductance as a function of gate voltage, which cannot be accounted for by either localization effects or universal conductance fluctuations. Although these oscillations may be related to one-dimensional subband effects, the magnetic field independence of the oscillations is not understood. At very high (12 T) magnetic fields an anomalous magnetoresistance has been seen.
Reactive ion etching of epitaxial ZnSe thin films
Authors: Clausen E. M. , Craighead H. G. , Schiavone L. M. , Tamargo M. C. , de Miguel J. L.
Published: July 2002

Using mixtures of boron trichloride and argon, we show it is possible to reactive ion etch epitaxial thin films of ZnSe grown on GaAs. Optimum etching conditions were determined by the application of a model generated from the multiple linear regression of the independent variables affecting the etching process. These variables included the power, pressure, gas composition, and time of etch. Optimum etching conditions produced etched structures with straight sidewalls and smooth surfaces. Photolithographically defined structures included both micrometer sized stripes and pixel arrays. Cathodoluminescence was measured from the surfaces of these etched structures and from the surface of unetched material at room temperature. Luminescence intensities of broad flat etched surfaces are shown not to be degraded by the etching process. This suggests the possibility of efficient etched light emitting structures.
The (001) surface of molecular-beam epitaxially grown GaAs studied by scanning tunneling microscopy
Authors: Pashley M. D. , Haberern K. W. , Woodall J. M.
Published: July 2002

In order to better understand the mechanism of molecular-beam epitaxy (MBE) growth on GaAs(001), it is essential to know the structure of the arsenic rich (2×4)/c(2×8) surface where growth usually begins and ends. We have studied this surface with the scanning tunneling microscope (STM). The specimens were grown by MBE and arsenic capped prior to transfer to the STM. In the STM chamber the arsenic capping was removed by heating to ∼450 °C. The STM images show that the (2×4) unit cell consists of three arsenic dimers and a missing dimer to give the 4× periodicity, resulting in an arsenic coverage of 0.75 monolayers. The surface consists of small domains of both (2×4) and c(2×8) reconstructions. The c(2×8) structure is made up from the basic (2×4) units. The STM images also show other features which may be important in the growth mechanism. The most striking of these are small islands one step up and small holes one step down, typically only a few unit cells in size. The step height corresponds to the spacing between arsenic planes. The raised islands are made up of complete unit cells, and can be as small as one (2×4) unit cell wide in the 4× direction. This shows the three dimers of a (2×4) unit cell to be a very stable structure, either in the plane when it is bordered by missing dimers, or on a raised island when bordered by a step edge.
Reactively sputtered WSiN film suppresses As and Ga outdiffusion
Authors: Asai Kazuyoshi , Sugahara Hirohiko , Matsuoka Yutaka , Tokumitsu Masami
Published: July 2002

This paper evaluates reactively sputtered WSiN films as an annealing cap for GaAs substrate. WSiN film successfully suppresses As and Ga outdiffusion. The WSiN/SiO2 /SiN/substrate multilayer annealing cap reconfirms this. As and Ga accumulate in the WSiN/SiO2 interface after annealing at 800 °C for 20 min. The accumulated As peak concentration is estimated to be 1019 atoms/cm3 . X-ray diffraction shows WSiN film remains in an amorphous phase, exhibiting no recrystallized grain boundary. Film stress only changes by one-half before and after annealing. These characteristics are very different from other refractory metals such as WN and WSi which change from amorphous to crystalline phase after annealing. It is therefore concluded that reactively sputtered WSiN films prevent As and Ga outdiffusion and form a good annealing cap for GaAs.
Photoemission study of near-surface band gap states in a-Si:H
Authors: Winer K. , Ley L.
Published: July 2002

We use total yield photoelectron spectroscopy in combination with the Kelvin probe to study changes in the work function and the distribution of occupied band gap states upon boron doping and oxidation of amorphous hydrogenated silicon (a-Si:H) surfaces. We observe 3×1011 occupied surface states/cm2 in clean undoped a-Si:H in an 0.4-eV wide band centered 5.0 eV below the vacuum level, which we ascribe to intrinsic surface defects. Incorporation of boron removes these states and exposes the intrinsic valence band tail, which is exponential over four orders of magnitude in the density of states. In contrast to c-Si, where adsorbed oxygen decreases the large intrinsic surface state density (4×1014 states/cm2 ) on the clean, cleaved surface, the relatively low density of intrinsic surface states on a-Si:H allows the observation of oxygen-induced surface band gap states. The origin of these states is discussed.
Selective reactive ion etching of tungsten films in CHF3 and other fluorinated gases
Authors: Pan W. S. , Steckl A. J.
Published: July 2002

The use of reactive ion etching (RIE ) with fluorinated gas plasmas, such as SF6, CF4, CBrF3, and CHF3 mixed with oxygen, to achieve selective patterning of tungsten films is reported. The etch rates of W, Si, and SiO2 were measured as a function of oxygen percentage in fluorinated gas plasmas under various conditions. Experiments on selectivity indicate that a CHF3/70%O2 mixture under 20 sccm, 200 W, 20 mTorr etching conditions results in W:Si and W:SiO2 etch rate ratios of 1.6:1 and 1.8:1, respectively. Optimized W:Si and W:SiO2 selectivity ratios 4:1 and 4.8:1 have been obtained at 60 mTorr/150 W and 260 mTorr/200 W plasma conditions. For reverse selectivity, the optimum W:SiO2 etch rate ratio measured is 1:4.6 in pure CHF3 gas. The optimum W:Si reverse selectivity of 1:11.6 is obtained with an SF6/5%O2 mixture plasma. A vertical-to-lateral etch ratio of 4:1 was measured with CHF3/70%O2, 200 W, 10 mTorr, 20 sccm. The etching mechanisms of tungsten due to chemical and physical processes in various fluorocarbon gases under the RIE mode have been investigated and the role of etching species such as fluorine, bromine, and oxygen is discussed.
New achievements in Hg1−xCdxTe grown by molecular-beam epitaxy
Authors: Sivananthan S. , Lange M. D. , Monfroy G. , Faurie J. P.
Published: July 2002

A review of our recent achievements in the growth of Hg1−xCdxTe by molecular-beam epitaxy is presented here. The influences of the substrate temperature, the crystallographic orientation, and the nature of the substrate on the properties of Hg1−xCdxTe are discussed in detail. We show that to grow high-quality material with good uniformity in terms of the alloy composition and the doping by crystal stoichiometry deviation, the substrate temperature should be between 180 °C and Tmax. We report mobilities as high as 5.0×1205 cm2 V−1 s−1 for n-type layers and 1.2×103 cm2 V−1 s−1 for p-type layers, achieved by precisely controlling the growth parameters. We illustrate that the Hg condensation coefficient is influenced by the crystallographic orientation. Our results show that for Hg1−xCdxTe grown on both the (111)B and the (100) faces of CdTe or GaAs the Hall mobilities are very high and comparable. We report our important achievement of the successful growth of 2-in.-diam Hg1−xCdxTe films on GaAs(100), with Δx/x̄ as low as 0.7% for x̄=0.218 (Δx is the standard deviation and x̄ is the mean value), Δt/t̄ as low as 0.6% for the layer thickness, excellent uniformity in the doping, an high electron or hole mobility. This illustrates the excellent control that our group has achieved toward the growth of this material by molecular-beam epitaxy.
Ion beam assisted etching of SiO2 and Si3N4
Authors: Xu Zheng , Gamo Kenji , Namba Susumu
Published: July 2002

Ion beam assisted etching (IBAE) of SiO2 and Si3N4 is described which employs inert gas ion beam and gas mixtures based on XeF2 and H2. Etching rates of SiO2 and Si3N4 were measured as functions of various parameters such as gas pressure, mixing ratio of XeF2 to H2, ion dose, ion species, and irradiation angle. Significant enhancements up to 100 and 40 times larger than physical sputtering were achieved for SiO2 and Si3N4, respectively. Etching selectivity of the SiO2 to Si was varied from 0.07 to 6 depending on the gas mixing ratio. These results allow etching rates as well as selectivity of SiO2 to Si to be tailored to specific requirements. Simulation is performed to show the cross-sectional profiles formed by focused ion beam and to calculate the ion dose implanted into substrates. Auger analysis and surface morphology are mentioned.