bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemically assisted ion beam etching for submicron structures
Authors: Chinn J. D. , Adesida I. , Wolf E. D.
Published: July 2002

The flexibility of broad-beam ion processing when used in conjunction with a chemistry assist technique is demonstrated. In this technique called chemically assisted ion beam etching (CAIBE), a chemically reactive gas is introduced into the sample chamber independent of the ion source which can be operated on inert or reactive gases. This allows for a wide range of independent control of the chemical and ionic fluxes not available in other dry etching techniques. Using a two component gas system of argon and xenon difluoride vapor under various operating conditions, the etched wall profiles of Si were found to be controllable. In the reactive ion beam etching mode of operation, overcut profiles with enhanced etch rates over ion milling rates were produced from Ar+ and XeF+x beams resulting from predominantly physical etching mechanisms. With the introduction of low vapor pressures of XeF2 into the sample chamber in conjunction with Ar+ ion bombardment, profiles resulted from line-of-sight ion assisted etching. Vertical walls were obtained with a collimated ion beam while profiles with directional undercutting resulted under highly divergent beam conditions. By increasing in XeF2 vapor pressure, undercut profiles from purely chemical etching were formed. Thus, by varying the partial pressure or the ion source operating conditions during an etch process, profile tailoring was accomplished.
Correction of spherical aberration in charged particle lenses using aspherical foils
Authors: van Gorkum Aart A.
Published: July 2002

The struggle to overcome spherical aberration in electron lenses has a long history. One of the weapons against this lens defect has been the use of foils, as suggested by Scherzer. Most attention was paid to the use of an electrostatic foil lens having a weak negative power and an accompanying negative spherical aberration. It was used to correct the positive spherical aberration of a magnetic lens. Some work has been devoted to the use of foils in purely electrostatic lenses, trying to create a positive lens free from spherical aberration. Flat foils and even spherical ones were used. It turned out that only weak positive lenses without spherical aberration could be created using these foils. It is shown here that a strong positive lens free from spherical aberration can be created using an aspherical foil. More specifically, the radius of curvature of the foil should increase with increasing distance from the rotation axis of the lens. The properties of these lenses are analyzed using ray tracing through numerically calculated fields. All higher order aberrations are thus taken into account. Using this type of analysis, it is proved that positive aspherical foil lenses show very little or even negative spherical aberration, depending on the geometry of the foil and/or its position in the two tube equidiameter accelerating lens.
Dopant redistribution in silicides: Materials and process issues
Authors: Cooper C. B. , Powell R. A. , Chow R.
Published: July 2002

The need to understand dopant redistribution in refractory metal silicides is important for reliable fabrication of polycide gates and other silicide-containing structures in VLSI devices. This paper will review work on dopant redistribution in silicides with emphasis on polycide structures. Of particular concern is the high-temperature sintering step required to form stable silicide and polycide structures. Results from conventional furnace sintering indicate that dopants can diffuse rapidly through certain silicides. The use of rapid thermal processing techniques to minimize dopant redistribution during the sintering step will also be reviewed. One conclusion is that our understanding of dopant redistribution in refractory metal silicides is limited and additional studies are required.
Photochemical deposition of Sn for use in molecular beam epitaxy of GaAs
Authors: Kowalczyk Steven P. , Miller D. L.
Published: July 2002

The suitability of several Sn-containing molecules (tetramethyltin, tetrabutyltin, dibutyltin dibromide, and stannic chloride) as gas phase sources of Sn for use in molecular beam epitaxy of GaAs was evaluated. In situ Auger electron spectroscopy showed that the Sn molecules absorbed at approximately the monolayer level at room temperature on GaAs (001) epilayer surfaces and pyrolytically decomposed before desorption. Capacitance–voltage and secondary ion mass spectrometry profiles demonstrated that the pyrolytic Sn deposits incorporated as an n-type dopant into newly regrown GaAs epilayers. Sn films were ultraviolet (UV) photolytically deposited on GaAs from each of these Sn-containing molecules and characterized by x-ray photoelectron spectroscopy.
X-ray characterization of single-crystal Fe films on GaAs grown by molecular beam epitaxy
Authors: Qadri Syed B. , Goldenberg M. , Prinz G. A. , Ferrari J. M.
Published: July 2002

X-ray structural studies of Fe films grown on (100)GaAs by MBE have shown very well-oriented mosaic structure originating at the interface and presumably caused by the lattice mismatch of 1.34%. The size and structure of the domains depend upon growth conditions, but at film thicknesses approaching 1 μm, the films assume the character of bulk α-phase Fe. This study has shown that although RHEED photographs indicated smooth flat MBE growth of these films, they were inadequate to explain the anomolous transport and magnetic properties. On the other hand, careful x-ray studies, especially linewidth rocking-curve measurements, have revealed a very fine grain mosaic structure which can strongly affect those properties.
Beryllium and silicon doping studies in AlxGa1−xAs and new results on persistent photoconductivity
Authors: Chand N. , Fischer R. , Klem J. , Henderson T. , Pearah P. , Masselink W. T. , Chang Y. C. , Morkoç H.
Published: July 2002

Doping with silicon donors and beryllium acceptors has been studied in MBE grown AlxGa1−xAs covering the entire composition range from GaAs to AlAs. The Si donor binding energy and the persistent photoconductivity were observed to depend on the alloy composition. In addition to the dominant deep donor level, a shallow donor level is observed which is postulated to be tied to the Γ minimum in the 0.25<x<0.35 range. A multivalley effective mass model has been successfully used to explain the donor binding energy. Beryllium behaves as a relatively shallow acceptor with its binding energy increasing slowly with increasing x from about 15 meV for GaAs to 41 meV for Al0.7Ga0.3As. Binding energies decrease with increasing doping densities in both cases. Excitation with light at low lattice temperatures results in a persistent increase of electron concentration in Si-doped AlxGa1−xAs and a persistent decrease of hole concentration in Be-doped alloys, while the mobility increases in both cases. This phenomenon is most pronounced in the 0.2≤x≤0.4 range and is correlated with the donor density.
Investigation of molecular beam epitaxial In0.53Ga0.47As regrown on liquid phase epitaxial In0.53Ga0.47As/InP
Authors: Nashimoto Y. , Dhar S. , Hong W. P. , Chin A. , Berger P. , Bhattacharya P. K.
Published: July 2002

Molecular beam epitaxial In0.53Ga0.47As regrown on high-purity liquid phase epitaxial In0.53Ga0.47As has been investigated. The regrown layers have been characterized by Hall measurements, low-temperature photoluminescence, and deep level transient spectroscopy. The regrown layers have properties comparable to material directly grown on InP substrates.
High rate masked etching of GaAs by magnetron ion etching
Authors: Contolini R. J. , D’Asaro L. A.
Published: July 2002

High rate masked etching of III–V materials such as GaAs and InP is needed for device processing requirements, such as via formation and chip separation. We have investigated the use of magnetron enhanced reactive ion etching to etch GaAs using photoresist as a mask. This technique gives unmasked etch rates up to 7 μm/min in GaAs. With an adequate heat sink, a photoresist mask shows little degradation for etch rates up to 1.2 μm/min with an undercut less than about 0.5 μm. Mechanisms of these results and directions for future work are presented.
Electronic structure of (001) and (111) growth axis InAs–Ga1−xInxSb strained-layer superlattices
Authors: Mailhiot C. , Smith D. L.
Published: July 2002

The electronic structure and optical properties of InAs–Ga1−xInxSb strained-layer superlattices grown along the (001) and (111) axis are investigated with the use of a realistic k⋅p theory. We assume that this superlattice is of the type II, i.e., the conduction band minimum of InAs lies at an energy below the valence band maximum of the alloy Ga1−xInxSb. We consider alloy compositions from x=0.1 to x=0.4, corresponding to lattice mismatches ranging approximately from 1% to 3%. Deformation potentials effects cause a substantial reduction of the band gap and allow the possibility to reach the technologically important 12 μm infrared region for very thin superlattices. This result is significant because type II superlattices exhibit optical matrix elements which decrease rapidly with increasing superlattice layer thickness. Reasonably large optical matrix elements can be obtained in the 12 μm region by properly tailoring the strain in the superlattice layers. In fact, optical matrix elements in InAs–Ga1−xInxSb strained-layer superlattices are shown to be comparable to those of HgTe–CdTe superlattices in the 12 μm region. Strained-layer superlattices grown along the (111) axis exhibit smaller quantum confinement energies and consequently appear to be slightly more advantageous than their (001) counterparts for optical applications. Furthermore, the presence of internal strain-induced piezoelectric fields in (111) growth-axis strained-layer superlattices produces a further reduction of the superlattice band gap. These results are significant and reveal that properly strained type II superlattices constitute a novel class of systems with useful materials properties for long-wavelength detection applications.
Localized laser chemical processing of tungsten films
Authors: Grossman W. M. , Karnezos M.
Published: July 2002

A focused argon-ion laser beam at 514 nm was used to thermally induce localized tungsten deposition from a WF6:H2 mixture. Tungsten lines were deposited on silicon wafers coated with either boron nitride (BN) or polyimide. Typical linewidths range from 0.5 to 10 μm, and the thicknesses from 0.1 to over 1 μm. Linewidth correlated most strongly with laser power, while the thickness correlated best with the laser fluence delivered to the sample. A minimum threshold laser power is needed to attain the temperature for deposition. The process is self-limiting since the deposited metal increases the surface reflectivity and thermal conductivity, thus increasing the threshold laser power. A feedback system based on measuring the reflected laser power during deposition was used to modulate the incident power and defeat the self-limiting nature of the process, thus allowing tungsten lines to be connected. Tungsten deposition and etching using other gases are reported for contrast with the deposition using WF6:H2 mixtures.
Formation of deep holes in silicon by reactive ion etching
Authors: Hirobe Kado , Kawamura Ko-ichirou , Nojiri Kazuo
Published: July 2002

Anisotropic etching for the formation of deep holes in the single crystalline silicon has been reported. This technique uses a film deposited on the sidewall to inhibit the lateral etching caused by the bombardment of ions which impinge on the silicon substrate out of the vertical direction. This film is composed of materials released from the cathode plate by ion bombardment. Using this technique, profiles appropriate for refilling with chemical vapor deposited CVD polycrystalline silicon can be obtained by adjusting the ratio of film deposition rate to silicon etch rate. It was found that this ratio can be controlled by adjusting parameters in reactive ion etching, such as self-bias voltage Vdc and gas pressure.
Characterization of a high-resolution novolak based negative electron-beam resist with 4 μC/cm2 sensitivity
Authors: Liu Hua-yu , deGrandpre Mark P. , Feely Wayne E.
Published: July 2002

A novel novolak based negative working resist, developed by Rohm and Haas Company, has been investigated for use in direct-write electron-beam lithography. The resist has demonstrated 0.3 μm resolution at a dose of 4 μC/cm2 . It displays high-dry etching resistance similar to that of conventional diazoquinone based positive resist. Results on the characterization of the resist and the development of a process are presented. In addition, the chemical properties and reaction mechanism of the resist are discussed briefly. The effects of postexposure-bake temperature and time on the resist image parameters, sensitivity, and resolution of the resist have been investigated. Exposure latitude and development latitude of the resist is discussed. Results of proximity effect correction using the GHOST method are presented.
Characterization of ion beam etching induced defects in GaAs
Authors: Yuba Yoshihiko , Ishida Tomohiro , Gamo Kenji , Namba Susumu
Published: July 2002

Ion beam etching (IBE) of GaAs was carried out at an energy of 1 keV using Ar and CCl2F2 as a source gas and defect center induced by IBE was investigated by means of deep level transient spectroscopy and carrier profile measurements. From DLTS measurements, five different defect centers (electron traps) were resolved. They were distributed far beyond the ion range and showed different depth profiles. The deep distribution of IBE induced defects was also confirmed from the carrier profile measurement. Annealing at 500 °C was effective to reduce the observed defect centers but defect centers with a concentration between 1×1015 and 5×1016/cm3 still remained.
An improved boron nitride technology for synchrotron x-ray masks
Authors: Levy R. A. , Resnick D. J. , Frye R. C. , Yanof A. W. , Wells G. M. , Cerrina F.
Published: July 2002

This study investigates the effects of hydrogen removal on the properties of nonstoichiometric B3NH films. Total removal of the hydrogen from such films is shown to result in the production of x-ray mask membranes that are mechanically stable under synchrotron radiation. However, the phase separation that accompanies the high temperature annealing (∼1100 °C), essential for removal of all of the hydrogen, is seen to result in undesirable darkening of the film. This problem is shown to be resolved by the preparation of stoichiometric BN films under optimized deposition conditions. Although BN films are seen not to degrade optically after high temperature annealing and x-ray irradiation, their characteristic compressive stress makes them undesirable for single membrane x-ray masks. A hybrid x-ray mask structure is proposed which combines the favorable properties of stoichiometric and nonstoichiometric boron nitride films. This radiation-hard x-ray mask structure is shown to meet the mechanical stability and optical transmission requirements.
An investigation of hydrogen concentration profiles in as-deposited and annealed chemical vapor deposited SiO2 films
Authors: Xie Joseph Z. , Murarka Shyam P. , Guo Xin S. , Lanford William A.
Published: July 2002

Hydrogen concentration depth profiles in as-deposited and annealed chemical vapor deposited silicon oxide [2% P glass, 8% P glass, tetraethylorthosilicate (TEOS), phosphorous-doped TEOS and plasma oxide] films were measured using the nuclear reaction profiling technique with a 6.4 MeV 15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2 or H2/Ar were carried out. It is found that hydrogen concentration is in the range 1021–1022 per cm3 in as-deposited films. Annealing at high temperatures, even in hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.
Increased dependence of Schottky barrier height on metal work functions due to a thin-oxide layer
Authors: Schmidt M. T. , Podlesnik D. V. , Yu C. F. , Wu X. , Osgood R. M. , Yang E. S.
Published: July 2002

Ultraviolet illumination has been used to form a few monolayers of GaAs oxide in dry oxygen on both p-type and n-type GaAs(100) surfaces. Some of the oxides have been annealed to form Ga-rich oxide surfaces. Six metals with a wide range of work functions and different reactivity with the oxide layer have been used to form Schottky contacts on clean GaAs and on the thin-oxide layers. Large variations from the Schottky barrier height on clean GaAs have been observed for both doping types due to the photo-oxidation of the GaAs surfaces. The trend in Schottky barrier change is toward the ideal Schottky limit where the metal work function determines the barrier height. The GaAs Fermi level is shown to move in a much wider region of the band gap for the oxidized surfaces than for clean surfaces, however, it is still confined to a midgap region.
Structure of the (100) GaAs on GaP interface
Authors: Gerthsen D. , Ponce F. A. , Anderson G. B. , Chung H. F.
Published: July 2002

A 55-nm-thick GaAs layer has been grown on a (100) GaP substrate at a temperature of 550 °C by metal–oxide chemical vapor deposition. The morphology and the structure of the interface and the epitaxial GaAs layer has been studied by transmission electron microscopy (TEM). The growth was found to be two-dimensional without any indications of island growth. The 3.7% misfit between GaAs and GaP is partially relaxed by misfit dislocations which are located at the interface. The misfit dislocations are arranged in a regular array along the 〈110〉 directions in the interface plane. Many stacking faults and fewer microtwins are observed in the overgrown GaAs layer, whose generation is discussed. Models for the two dominant misfit dislocation types are proposed, based on high-resolution TEM results.
Recombination mechanisms in type II (GaAs/AlAs) heterostructures
Authors: Wilson B. A. , Bonner Carl E. , Spitzer R. C. , Dawson P. , Moore K. J. , Foxon C. T.
Published: July 2002

Time-resolved photoluminescence spectra and decay data are presented for a series of type II (GaAs/AlAs) samples with different GaAs layer thicknesses. Low-temperature delayed spectra reveal that the spectral lines shift gradually to lower energy with delay, and that the shift extends to ms time scales. At 6 K the decay curves of the type II emission contain power-law and exponential components with rates ∼103 s−1, indicating significant Γ–X mixing, both by random and nonrandom processes. Both rates increase with temperature. The dependence of the decay rates and spectra on the GaAs layer thickness is examined. Models of the recombination mechanisms are discussed in the context of these new results.
The effect of phosphorous and sulfur treatment on the surface properties of InP
Authors: Iyer R. , Chang R. R. , Dubey A. , Lile D. L.
Published: July 2002

Insulated gate electronic devices on InP and related III–V compound semiconductors have not to date achieved a level of performance adequate for commercial exploitation. This in part is believed to be due to the noncongruent dissociation of the group V element upon heating. In order to minimize such surface effects on InP, we have investigated two broad approaches; one involving the creation of an excess overpressure of phosphorous to suppress the anion loss; and one involving the creation of an ideal interface analogous to the SiO2/Si system by sulfurization. In situ photoluminescence, measured during annealing in a phosphorous ambient in a mass spectrometer equipped low-pressure chemical vapor deposition growth chamber, shows that surface degradation may be retarded by appropriate use of gaseous phosphorous. A phosphorous-rich interfacial oxide, grown prior to SiO2 growth, similarly appears to considerably improve the interface of InP metal–insulator–semiconductor (MIS) structures as seen by C–V analysis. Sulfurized InP MIS structures treated in (NH4)2Sx, show excellent interface quality as judged by high-frequency and quasistatic C–V measurements. MIS field effect transistors fabricated using the benefits of these surface treatments show large transconductances and stabilities approaching those of thermal SiO2/Si with <5% variation in drain current over a 12 h test period.
Valence-band offset and interface formation in ZnTe/GaSb(110) studied by photoemission using synchrotron radiation
Authors: Wilke W. G. , Horn K.
Published: July 2002

We report on a photoemission study of the ZnTe/GaSb(110) heterojunction prepared under ultrahigh vacuum conditions. Upon deposition of ZnTe on a cleaved GaSb(110) surface by molecular-beam epitaxy, a reacted layer is formed, which is characterized by the liberation of Sb atoms from the substrate, and the reaction between Ga and Te. The thickness of this layer is dependent on the temperature of the substrate, and is on the order of one monolayer under optimum conditions. The ZnTe overlayers show good crystalline order as evidenced by low-energy electron diffraction and valence level photoemission. Taking into account band bending upon interface formation, we derive a valence-band offset of −0.34 eV. This result is compared with theoretical predictions as well as experimental data based on band offset transitivity. The determination of ionization energies for both substrate and overlayer demonstrates the failure of the electron affinity rule in predicting heterojunction valence-band offsets.
Patterned growth of gallium arsenide on silicon
Authors: Matyi R. J. , Shichijo H. , Tsai H. L.
Published: July 2002

The molecular-beam epitaxial (MBE) growth of GaAs on silicon through openings in an oxide or nitride mask is an attractive alternative to the conventional full wafer deposition of GaAs on silicon for the monolithic integration of GaAs and Si devices. We have investigated techniques for the patterned growth of GaAs on Si and have found that single-crystal GaAs regions of high-crystalline quality can be successfully grown on silicon substrates. When the MBE growth is performed through holes in a mask onto the original planar silicon surface, the GaAs transformed from polycrystalline to single-crystal growth directly above the termination point of the wet etched oxide mask. Postgrowth annealing was found to drastically change the defect structure by causing single-crystal overgrowth of the mask, an elimination of the transition region defects, and significant grain growth in the remaining polycrystalline GaAs. Growth within etched trenches in the Si substrate also produced GaAs of good crystalline quality, although the defect density was higher than that observed in the GaAs grown on the original Si surface. Postgrowth annealing of the trench grown GaAs again led to a reduction in the number of structural defects and a dramatic change in defect morphology. Reasonable performance has been obtained from devices fabricated on both types of patterned GaAs.
Study of molecular-beam epitaxy GaAs1−xSbx (x<0.76) grown on GaAs(100)
Authors: Zhao J. H. , Li A. Z. , Jeong J. , Wong D. , Lee J. C. , Milliman M. L. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

Lattice mismatched 0.5 to 1-μm-thick GaAs1−xSbx epilayers were grown on (100) n-type GaAs by molecular-beam epitaxy (MBE) throughout the whole composition range and characterized for Sb content up to 0.76. The Sb incorporation coefficient is found to be 0.42 at a substrate temperature of 480 °C. The epilayer quality was examined by x-ray diffraction, photoluminescence, and photoresponse. The relationship between energy band gap of GaAs1−xSbx and Sb content at room temperature is found to be in good agreement with the result of Nahory et al. and that at 77 K is established and can be reasonably described by the estimated one from the binary band gaps of GaAs and GaSb at 77 K and the ternary band gaps of GaAs1−xSbx at 300 K. Both majority electron and hole traps in GaAs1−xSbx epilayers were characterized.
Resist contrast enhancement in high resolution electron beam lithography
Authors: Chiong Kaolin Grace , Rothwell Mary Beth , Wind Shalom , Bucchignano Jim , Hohn Fritz J. , Kvitek Richard
Published: July 2002

While lithography tooling continues to advance to achieve the resolution and overlay requirements of most advanced devices, resist science, and technology proceed with material advancements and process enhancements to ultimately achieve the sensitivity and contrast required. In this paper, we report approaches of modifying a single layer resist system to achieve the characteristics of a bilayer resist system without the complexity of a multilayer process.The top surface of the single layer resist is made less sensitive to electron beam exposure and development effects. One of the methods used consists of desensitizing the top surface of a positive resist which operates on the chemical amplification principle, prior to exposure. The desensitization step is achieved by controlling the post-apply bake condition during resist film preparation. Proper bake control of this resist provides the exposed regions with an initial dissolution rate which is three times slower than that in the resist bulk. This surface modification process forms a thin layer of augmented resist that is less sensitive to beam interaction. Linewidth control is enhanced by delayed lateral erosion of the resist patterns. Very high resolution images are delineated using one development step which eliminates the complexity of a multilayer resist process. While scattering effects through the resist bulk are essentially unchanged, the beam resist interaction on the top surface is greatly altered. The slow dissolution rate in the top surface relative to the resist bulk results in a higher resist contrast and a more controllable process. Moreover, this technique provices a system with very little resist bias and leads to significant advantages as dimensions shrink. These contrast enhancement techniques and possible mechanisms for the relatively slow dissolution of the resist surface are related to image edge acuity. Using these techniques on single layer resist systems, subquarter micron dimensions have been obtained with good linewidth control which is much enhanced and less complex as compared to the multilayer resist processes.
Mechanism of ion beam induced deposition of gold
Authors: Dubner A. D. , Wagner A.
Published: July 2002

Gold films were deposited on quartz crystal microbalances (QCM) by decomposing C7H7F6O2Au [dimethyl gold hexafluoroacetylacetonate, or DMG(hfac)] with a 5 keV argon ion beam. A model for ion beam induced deposition is presented which relates the net deposition yield to the gas adsorption, the decomposition cross section, and the sputtering yield. The deposition rate was measured in situ as a function of ion current, gas pressure, and substrate temperature using the QCM. The deposition yield (mass deposited per incident ion) increased with increasing gas pressure and decreasing substrate temperature. The QCM was also used to measure the adsorption of DMG(hfac). The results demonstrated that the variation in deposition yield with temperature and pressure was proportional to the number of DMG(hfac) molecules adsorbed per cm2. Based on the observed correlation between deposition yield and adsorption, a decomposition cross section for 5 keV argon ions of 2×10−13 cm2 was estimated.
Elastic stress domains on the Si(100) surface
Authors: Vanderbilt David , Alerhand O. L. , Meade Robert D. , Joannopoulos J. D.
Published: July 2002

It is proposed that surfaces of crystals that reconstruct with broken orientational symmetry and exhibit an anisotropic stress tensor are unstable to the formation of elastic stress domains. The ground state of such a surface is not uniform, but corresponds to a mosaic pattern of the different domains. This result is applied together with microscopic calculations of surface stress to study the Si(100) surface. A structural transition from single-layer to double-layer steps for vicinal Si(100) surfaces is also studied.
Photoluminescence characterization of SimGen superlattices
Authors: Kallel M. A. , Arbet V. , Karunasiri R. P. G. , Wang K. L.
Published: July 2002

SimGen strained monolayer superlattices (SMS) have been fabricated by molecular beam epitaxy (MBE) and characterized using photoluminescence. Symmetrically strained structures with different periodicities have been grown on top of Si1−xGex alloy buffer layers. Luminescence peaks below the Si energy bandgap have been observed. Superlattices on top of Si buffers with different substrate orientations have been prepared with thicknesses below the critical values in order to avoid generation of misfit dilocations. Energy band diagrams constructed based on the deformation potential and the envelope function approximation are used to explain the experimental results.
Surface structures of the (Al,Ga)Sb system
Authors: Piao J. , Beresford R. , Wang W. I.
Published: July 2002

We have studied the surface structures of GaSb, AlGaSb, and alternating GaSb/AlSb layers using 10-kV reflection electron diffraction. Above 540 °C, the Sb-stabilized surface (1×3) patterns change to c(8×2), a Ga-stabilized surface. Because the c(8×2) surface has been observed on all other III–V arsenides, phoshpides, and antimonides, it is now clear that the c(8×2) metal-stabilized surface is common to all III–V compounds, suggesting that bond pairing occurs on all III–V semiconductor surfaces and is a universal reconstruction mechanism. The smooth, sharp transitions observed in the growth of alternating GaSb and AlSb layers show that atomically smooth interfaces can be formed in this system. In contrast, for the AlAs overgrowth on GaAs, transient structures associated with a Ga surface layer can be observed.
Thermodynamic analysis of the W–F–Si–H and W–F–Si–H–Cl systems
Authors: Rode Edward J. , Harshbarger William R.
Published: July 2002

Chemical vapor deposition of WSi2 was studied through thermodynamic equilibrium calculations for the W–F–Si–H and W–F–Si–H–Cl systems. The calculations were made with a computer program that minimizes the Gibbs free energy by Langrangian multiplier techniques. The parameter range for these system analyses were: temperature 473 to 1073 K, pressure from 50 to 500 mTorr, and Si/W ratios of 3 to 1000. 21 gas phase species and eight solid species were included in the calculations for the W–F–Si–H system and 39 gas phase species and 15 solid species were considered for the W–F–Si–H–Cl system. At the equilibrium condition, H2, SiF4, and SiF2H2 are the most prominent gaseous species for the W–F–Si–H system while WSi2 and Si are formed in the solid phase. For the W–F–Si–H–Cl system, WSi2 and Si are formed in the solid phase, while H2, SiCl4, HCl, SiF4 and SiHCl3 are the most prominent gas phase species. The SiCl2 intermediate plays a key role in the surface activated reaction for this system.
Use of hydrogenated chlorofluorocarbon mixtures for reactive ion etching of In-based III–V semiconductors
Authors: Pearton S. J. , Hobson W. S. , Chakrabarti U. K. , Derkits G. E. , Kinsella A. P.
Published: July 2002

The reactive ion etching (RIE) of InP, InAs, InSb, InGaAs, and AlInAs in CHCl2F —or CHClF2 —based discharges was investigated as a function of plasma power density, pressure, and gas composition. For 0.56 W cm−2, 4 mTorr discharges the etch rates are in the range 125 Å min−1 (AlInAs) to 390 Å min−1 (InAs). These are comparable to the etch rates obtained with C2H6/H2 RIE under similar conditions. All of these materials exhibit smooth surface morphologies over a wide range of RIE parameters. Carrier compensation is observed to depths of ∼2000 Å in n-type InP for high power density (1.3 W cm2) etching, but lower powers yield surfaces that display reasonable Schottky diode behavior for evaporated Au contacts. Thin (20–30 Å) residue layers containing 3–9 at. % Cl and 1–3 at. % F (24 at. % for AlInAs) are present after the dry etching, although this contamination can be removed by solvent cleaning. The formation of a high concentration of AlF3 on AlInAs provides a natural etch stop for removal of InGaAs layers in AlInAs/InGaAs heterojunction bipolar transistor structures.
A scanning electron microscope for trench observation
Authors: Saito Kenichi , Yoshizawa Masahiro , Wada Kou
Published: July 2002

A new objective lens structure is proposed for observing the bottom of submicron trenches with a low-voltage scanning electron microscope. By placing a magnetic coil close to the specimen, and using it to apply a strong magnetic field to the specimen, electron beam current is increased under high spatial resolution of secondary electron (SE) images. This increase in current increases the SEs coming out of a trench, and this makes it possible to observe the bottom of the trench more clearly. An experimental system is constructed, and submicron trenches are observed. The experimental results show that the proposed structure enables clear bottom observation of trenches 0.6 μm wide by 5 μm deep.
Properties of silicon dioxide films prepared by low-pressure chemical vapor deposition from tetraethylorthosilicate
Authors: Rojas S. , Modelli A. , Wu W. S. , Borghesi A. , Pivac B.
Published: July 2002

The 20 to 100-nm thick tetraethylorthosilicate (TEOS)-derived SiO2 films were deposited on silicon substrates in the 650–780 °C temperature range by low-pressure chemical vapor deposition. The main properties of the as-deposited and annealed films such as refractive index, etch rate, stress, step coverage, and density are reported. Infrared (IR) spectra and the electrical properties were studied as a function of process parameters including temperature, pressure, oxygen, and TEOS flow. These studies have shown that TEOS-SiO2 films have very good thickness uniformity and conformal step coverage which can be controlled by adjusting the process pressure. IR spectra show that TEOS-SiO2 films are deposited as stoichiometric oxides. Annealing results in the removal of absorbed water and Si–OH groups, and in an increase of the number of Si–O–Si bonds. The electrical characteristics, such as breakdown field strength for films deposited on POCl3 -doped polysilicon, are comparable to those of SiO2 films thermally grown at 1100 °C in dry O2 atmosphere.
Growth temperature and substrate orientation dependences of moving emission and ordering in Ga0.52 In0.48 P
Authors: DeLong M. C. , Taylor P. C. , Olson J. M.
Published: July 2002

The excitation intensity and temperature dependences of the photoluminescence (PL) from Ga0.52 In0.48 P grown by organometallic vapor phase epitaxy on GaAs substrates have been investigated as a function of the epilayer growth temperature and the substrate misorientation from (100). The energy band gap is dependent on substrate temperature during growth but is effectively independent of substrate misorientation. A strong excitation intensity dependence of the PL is found to be a function of both substrate orientation and growth temperature. We postulate that the strong dependence of PL emission energy on excitation intensity in some samples may result from the sizes, shapes, and orientations of ordered domains.
Transition metal–GaP(110) interfaces: The roles of impurity states and metallicity
Authors: Ludeke R. , Prietsch M. , McLean A. B. , Santoni A.
Published: July 2002

The room temperature formation of GaP(110) interfaces with the transition metals (TM) vanadium and yttrium were studied by photoemission spectroscopy. Both the evolution of band bending and the interface chemical reactivity were deduced from the Ga 3d and P 2p core level emission spectra for a metal coverage range of ∼0.003 to 50 Å. Free Ga is generated through a TM–Ga exchange reaction; it disperses in both metals with increasing coverages and with a noticeable tendency toward surface segregation. Two phosphorous reaction components were observed for both metals, one of which was attributed to free P, the other to TM–P bonding. Band gap emission attributed to an impurity state derived from the V 3d level was observed for coverages as low as 0.01 Å. A metallic Fermi edge developed at 1 Å of V, but required a thickness of ∼30 Å for Y. However, metallic character was observed in the replaced Ga for Y coverages ≳3 Å. The band bending for both metals on n-GaP is characterized by a near-constant value of the Fermi level EF close to midgap for a broad coverage range to ∼1 Å, followed by a rapid drop of EF with onset of metallicity in the V. For Y, this decrease extended to coverages beyond 20 Å, consistent with the delayed onset of metallicity for this system. Schottky barrier heights of 1.33 eV (V) and 1.24 eV (Y) were measured. For coverages below the onset of metallicity EF appears to be determined by the observed TM-induced impurity states in the gap. The previously described delocalization model successfully accounts for both the observed drop in EF with onset of metallicity and Schottky barrier heights for a number of metals, including V and Y.
Application of Plasmask R  resist and the DESIRE process to lithography at 248 nm
Authors: Hutton Richard S. , Kostelak Robert L. , Nalamasu Omkaram , Kornblit Avi , McNevin Susan , Taylor Gary N.
Published: July 2002

Plasmask resist and its associated dry development process called DESIRE constitute one product which has incorporated surface imaging for lithography at 436 and 366 nm. Based on its performance at these wavelengths, Plasmask 150U resist is predicted to have a resolution limit of ∼0.3 μm at 248 nm with a 0.38 NA lens. Using best focus exposures of 1.5-μm thick films we have examined a variety of factors that influence the resolution and sensitivity of Plasmask 150U resist at 248 nm. These include standard processing steps as well as silylation with hexmethyldisilazane, plasma development conditions and equipment, and various descum techniques. Processing without a descum step resolved 75° profile, 0.3 μm line and space patterns at high exposure doses, but always afforded a grassy residue. Use of Ar sputter etching to remove ∼2200 Å from unexposed areas prior to plasma development afforded vertical profile 0.3-μm resolution patterns with no grassy residue.
Investigations of undeveloped e-beam resist with a scanning tunneling microscope
Authors: Marrian C. R. K. , Dobisz E. A. , Colton R. J.
Published: July 2002

A scanning tunneling microscope (STM), operated in vacuum in the field emission mode, has been used to observe the latent image written with a focussed 50 kV e-beam in a polydiacetylene negative resist. The ability to study the latent image in the undeveloped resist allows the resolution degradation caused by the exposure process to be separated from that occurring during the resist development step. The minimum linewidth observed in the resist is close to 80 nm in both the developed and undeveloped resist. This linewidth is significantly greater than that expected on the basis of the 50 kV e-beam probe size, electron scattering, and secondary electrons. The results indicate that the resolution degradation occurs during the exposure process rather than during post-exposure processing. This implies that swelling during development is not the critical problem it is with other negative resists. The quality and accuracy of the STM observations is discussed together with descriptions of related surface modifications created in situ with the STM.
Tunneling between localized states in GaAs/AlGaAs resonant tunneling diodes with spacer layers
Authors: Jogai B. , Huang C. I. , Koenig E. T. , Bozada C. A.
Published: July 2002

We have observed singularities in current–voltage data that indicate charge quantization in the accumulation layer of resonant tunneling diodes with thick spacer layers. The electrons are strongly localized between the artificial barrier formed by the lightly doped emitter spacer layer and the first metallurgical barrier. Tunneling occurs between these states and those confined to the quantum well. We presume this process to be the source of negative differential resistance in the single- and double-well samples we have fabricated.
Improved breakdown voltage in molecular beam epitaxy HgCdTe heterostructures
Authors: Koestner R. J. , Goodwin M. W. , Schaake H. F.
Published: July 2002

We present recent progress in the development of metal–insulator–semiconductor (MIS) heterostructure detectors grown by molecular beam epitaxy (MBE); these heterostructure films should significantly improve the available well capacity for MIS long wavelength infrared (LWIR) detectors. Recent MBE grown HgCdTe(112)Te heterostructures show a 4× increase in available charge capacity and a 2× decrease in net donor density relative to our MBE HgCdTe(001) layers. To obtain full advantage of the MIS heterostructure however, another 2.5× increase in the MWIR breakdown field (0.8–2.0 V/μm) and a 2× decrease in the MWIR donor density (1×1015–5×1014cm−3) is necessary. Since the MWIR breakdown field does not appear to be limited by compositional micro-inhomogeneities or by compound twin defects in the MBE HgCdTe layers, we suspect either dopant micro-inhomogeneities or native point defects are responsible for the significant tunnel currents measured in our MWIR MBE HgCdTe.
Laser-assisted scanning tunneling microscopy
Authors: Völcker M. , Krieger W. , Suzuki T. , Walther H.
Published: July 2002

Infrared laser radiation is coupled via the tip into the tunneling junction of a scanning tunneling microscope. Rectification and difference frequency generation of the laser light caused by the nonlinearity in the current-voltage characteristic of the junction are observed. Images with atomic resolution are obtained either by recording the rectified signal or by measuring the intensity at the difference frequency when the tip is scanned across the surface. These images are compared with others obtained in the conventional way by observing the tunneling current.
Helium radio-frequency-plasma GaAs device isolation: Application to an in-plane gated quantum wire transistor
Authors: Ingram S. G. , Simpson P. J. , Law V. J. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

Low-energy ion bombardment has been used for isolation to define an in-plane gated quantum wire transistor in a GaAs/AlAs heterostructure. The two-dimensional electron gas (2DEG) was 17 nm below the GaAs/vacuum interface, with a mobility at 1.2 K of 7.97×105 and 6.3×105 cm2 V−1 s−1 at a sheet carrier concentration of 6.45×1011 and 5.98×1011 cm−2 with and without illumination, respectively. Optimum gate isolation was achieved using a 6 min exposure to a helium radio-frequency (rf) plasma at 5.7 Pa (43 mTorr), with a dc bias of −150 V. Electrical measurements show that the application of a suitable gate bias produces conductance changes in the device, with evidence for one-dimensional (1D) ballistic transport at 1.2 K.
Band structure effects in interband tunnel devices
Authors: Ting D. Z.-Y. , Yu E. T. , McGill T. C.
Published: July 2002

We report on a calculation of transport in InAs/GaSb/AlSb-based interband tunnel structures using a realistic band structure model. The results are compared with calculations using a two-band model which includes only the lowest conduction band and the light-hole band. We find that for device structures containing GaSb quantum wells, the inclusion of heavy-hole states can introduce additional transmission resonances and substantial hole-mixing effects. These effects are found to have a significant influence on the current–voltage characteristics of interband devices.
Ballistic electron emission spectroscopy of metals on GaP(110)
Authors: Ludeke R. , Prietsch M. , Samsavar A.
Published: July 2002

Ballistic electron emission spectroscopy (BEES), a technique based on the scanning tunneling microscope (STM), was used to measure Schottky barrier heights of metals on cleaved n-type GaP(110). The threshold voltages V0 for current detection in the semiconductor were found to be uniform to within ±0.02 V over the sample surface for any given metal on GaP. A transport model for the current Ic crossing the barrier, that includes both nonclassical transmission across the metal–semiconductor interface and electron scattering in the metal, yields Ic∝(V−V0)5/2 near threshold. The value of V0 extracted from the data, which represents the Schottky barrier height, depends somewhat on the details of the transport model. Our best estimates of the Schottky barrier heights, within ±0.03 eV, are 1.07 (Mg), 1.11 (Ni), 1.14 (Bi), 1.25 (Cu), 1.31 (Ag), and 1.46 eV (Au).
The growth of cubic CdS on InP(110) studied i
n s
i
t
u by Raman spectroscopy
Authors: Zahn D. R. T. , Maierhofer Ch. , Winter A. , Reckzügel M. , Srama R. , Thomas A. , Horn K. , Richter W.
Published: July 2002

CdS was deposited onto clean cleaved InP(110) by molecular beam epitaxy (MBE) using a growth rate of 0.2 monolayers/min and a substrate temperature of 440 K (510 K). Raman spectra were taken in situ of the clean InP surface and after each evaporation step using an Ar+ ion laser as a light source. Due to this resonant excitation scattering signals originating from the CdS deposition are observed at coverages as low as 2 monolayers (ML). The number of phonon peaks observed and their selection rules reveal that the cubic modification is present. The spectra are dominated at all coverages by the longitudinal optical (LO) and 2LO phonon scattering intensities and the variation of the 2LO/LO intensity ratio with CdS deposition indicates changes in the electronic structure of the growing CdS. Another spectral feature in the Raman spectra is attributed to a chemically reacted layer at the interface most likely consisting of an In–S compound. The intensity of this feature is found to depend critically on the growth parameters, in particular the substrate temperature, but also on the operating time of the MBE cell. The amount of reaction at the interface also influences the critical CdS film thickness and the development of the 2LO/LO ratio. The results are discussed taking complementary photoluminescence, x-ray diffraction, and photoemission data into account.
Characterization of a permanent magnet electron cyclotron resonance plasma source
Authors: Mantei T. D. , Dhole S.
Published: July 2002

Experimental details and results are presented for a permanent magnet electron cyclotron resonance plasma source matched to a multipolar confined process chamber. A Nd–Fe–B magnet structure provides a resonant axial magnetic field with no electrical or cooling input power, replacing the more typical current driven coils. Plasma parameter and etch characterization measurements in Ar and SF6 are presented for the pressure range 0.1–1.0 mTorr and input microwave power levels 100–500 W.
Exposure characteristics of alternate aperture phase-shifting masks fabricated using a subtractive process
Authors: Kostelak R. L. , Pierrat C. , Garofalo J. G. , Vaidya S.
Published: July 2002

Exposure characteristics of an alternate aperture phase-shifting mask fabricated using a subtractive process will be discussed. The subtractive process, where the phase-shifted regions are etched into a layer below the chromium, is attractive because it allows for the use of conventional chromium-on-quartz blanks, as well as providing more processing flexibility. However, recent results using a subtractive fabrication process have determined that a linewidth variation of ∼0.05 μm exists between features imaged with etched and nonetched regions of the alternate aperture pattern. This article examines some of the potential causes for this linewidth variation, including mask linewidth control, surface roughness, contamination during phase-shift forming etch step, and sidewall profile and position. Results indicate that the sidewall profile and position are critical parameters in defining the wafer feature size. The impact of phase is also investigated. The wafer feature size depends on the depth of the quartz etch and accurate endpointing of the phase-shift depth is essential for maintaining critical dimension uniformity across all features imaged with a phase-shifting mask.