bluuebunny/crossref_metadata_2025 huggingface dataset:
AlGaAs/Ge/GaAs heterostructures grown by molecular beam epitaxy
Authors: Wang Y. , Baruch N. , Wang W. I. , Cheney M. E. , Huang C. I. , Scherer R. L.
Published: July 2002

We report the comparison studies of molecular beam epitaxial growth of AlGaAs/Ge/GaAs heterostructures on differently oriented GaAs substrates. We have investigated the molecular beam epitaxial growth of Ge on GaAs, and GaAs and AlGaAs on Ge epitaxial layers with the aim of obtaining device-quality interfaces of AlGaAs and GaAs epilayers on Ge which are free of antiphase domains. Our results show that the junctions grown on (311)B oriented substrates have better electrical characteristics than those grown on (100) oriented substrates. This is due to the absence of antiphase domains and less interface charge in heterostructures grown on (311)B substrates.
Atomically controlled growth of GaAs/NiAl/GaAs structures by molecular-beam epitaxy
Authors: Hirono S. , Tanimoto M. , Inoue N.
Published: July 2002

The morphology of molecular-beam epitaxy (MBE) grown GaAs/NiAl/GaAs structures using scanning tunneling microscopy (STM) was investigated. Improving the flatness of the NiAl layer is achieved by improving the wettability of NiAl on GaAs by using a Ni template and increasing the island density by low-temperature growth. This method gives a continuous, flat NiAl film with a mean roughness of one monolayer. A GaAs overlayer with a roughness of two monolayers or less is obtainable by using low-temperature migration enhanced epitaxy (MEE).
Migration enhanced epitaxy and optical properties of ZnSe/CdSe digital alloy quantum wells
Authors: Short S. W. , Luo H. , Xin S. , Yin A. , Pareek A. , Dobrowolska M. , Furdyna J. K.
Published: July 2002

We report the growth of ZnSe/CdSe digital alloy quantum wells by migration enhanced epitaxy. The well regions are imbedded in barriers of ZnSe, and are composed of various periods of 1 monolayer (ML) of CdSe and 3 ML of ZnSe, thus having an effective Cd concentration of 25%. The time and sequence of successive shutter openings was varied during growth, and the effects on layer coverage were investigated using reflection high-energy electron diffraction oscillations, photoluminescence, photoluminescence excitation, and optical absorption.
Study of lattice-mismatched (In,Ga)As/GaAs heterostructures on the unconventional (110) GaAs surface
Authors: Sun Decai , Towe Elias , Bennett Brian R.
Published: July 2002

Structural and optical properties of strained (In,Ga)As/GaAs heterostructures grown on (110) GaAs substrates intentionally misoriented by 6° toward the (111)B surface have been investigated. Photoluminescence and double-crystal x-ray diffraction data show that high-quality (In,Ga)As/GaAs quantum wells can be grown on the (110) vicinal surface.
Gated chromium volcano emitters
Authors: Pogemiller J. E. , Busta H. H. , Zimmerman B. J.
Published: July 2002

By reversing the bias of a field emitter with a volcano-shaped gate, it is demonstrated that emission occurs from the rim of the gate. The gate-to-emitter distance of this structure is defined by the thickness of the insulating film between the electrodes and not by expensive photolithographic techniques. By enlarging the gate diameter to printed circuit board-type dimensions, in principle, low cost, large area field emitter arrays can be fabricated. The process is being demonstrated on a silicon substrates and initial emission data are being presented. The article concludes by demonstrating one transfer path of this technology onto an inexpensive glass substrate.
Characterization of gridded field emitters
Authors: Huang M. , Mackenzie R. A. D. , Godfrey T. J. , Smith G. D. W.
Published: July 2002

A system combining field emission microscopy, field ion microscopy, atom probe, and current–voltage (I–V) measurement facilities has been developed to study gridded field emitter devices, either in the form of single tips or arrays. (I–V) measurement results, field emission images, and field ion images of a single tip and an array of 1500 tips are presented here, of which field ion images of the gridded emitters are reported for the first time. The first atom probe results from a gridded array are also given here, demonstrating that chemical composition analysis of gridded field emission cathodes is possible.
Chemical vapor deposition and plasma-enhanced chemical vapor deposition carbonization of silicon microtips *
Authors: Zhirnov V. V. , Givargizov E. I.
Published: July 2002

Silicon microtips for field emission applications were coated with thin silicon carbide layers by chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD) at temperatures of 800 to 1200 °C using propane or a methane/propane mixture as carbon sources. Coatings from 4 to 30 nm thick were obtained. Scanning electron microscopy and Auger electron spectroscopy were used to investigate the morphology and composition of the carbonized tips. Both silicon carbide and pure carbon coatings could be formed depending on the process parameters used. Sharp carbonized tips were obtained by PECVD using propane flow concentrations.
Epitaxy and scanning tunneling microscopy image contrast of copper–phthalocyanine on graphite and MoS2
Authors: Ludwig C. , Strohmaier R. , Petersen J. , Gompf B. , Eisenmenger W.
Published: July 2002

Monolayers of copper–phthalocyanine (Cu–Pc) on highly oriented pyrolytic graphite (HOPG) and MoS2 prepared by organic molecular beam epitaxy have been investigated by scanning tunneling microscopy. On both substrates there exist well defined preparation conditions leading to ordered two-dimensional arrays of flat lying molecules. On HOPG they form a close-packed structure with a nearly quadratic unit cell, whereas on MoS2 we found two phases, one close-packed and one rowlike phase. This rowlike phase can be explained by a long range interaction due to an adsorbate induced superstructure of the substrate, which also can be seen in the scanning tunneling microscopy images. In images with submolecular resolution, the molecules appear different on the two substrates. On MoS2 they look like a four-leaved clover, on graphite they show a more detailed inner structure.
Analysis and Monte Carlo simulations of spontaneous etching: Cl–Si(100)-2×1
Authors: Sánchez J. R. , Aldao C. M. , Weaver J. H.
Published: July 2002

Scanning tunneling microscopy observations of the growth of Cl-induced etch pits on Si(100)-2×1 lend themselves to quantitative determinations of vacancy size distributions, particularly those that are linear or branched at some point along the linear pit. These result in rate constants and energy differences for the dominant etching channels. By considering nearest-neighbor and second-nearest-neighbor interactions, we determine the attractive interaction energies between dimers in a row, 0.28 eV, and between dimers in adjacent rows, 0.22 eV, as well as the repulsive second-neighbor dimers, −0.08 eV. These results are tested by means of Monte Carlo simulations.
Ohmic contacts on p-In0.53Ga0.47As prepared by Zn implantation into Pd-based metallizations
Authors: Ressel P. , Strusny H. , Vogel K. , Würfl J. , Fritzsche D. , Kräutle H. , Kuphal E. , Mause K. , Trapp M. , Richter U.
Published: July 2002

A new technique is presented for the fabrication of low-resistivity Ohmic contacts on p-In0.53Ga0.47As doped below 1×1019 cm−3 consisting of dopant implantation into the contact metal and subsequent rapid thermal annealing. Zn-implanted and annealed Pd/Au/Pt/Au, Pd/LaB6/Au, and Pd/Ge contacts exhibit drastically lowerer contact resistivity in comparison to corresponding systems prepared without implantation. A resistivity decrease by approximately one and a half orders of magnitude is observed in cases of Pd/Au/Pt/Au and Pd/LaB6/Au contacts. The lowest value is found for Pd/Au/Pt/Au on p-In0.53Ga0.47As doped to 4×1018 cm−3 with 1×10−6 Ω cm2, whereas 1–2×10−5 Ω cm2 is obtained for Pd/Ge contacts on p-In0.53Ga0.47As doped to 7×1018 cm−3. The elemental redistribution and the interface morphology of annealed contacts have been studied with backside secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. No contact penetration and a planar interface are found in the case of Pd/Ge, whereas significant penetration of contact components into the semiconductor and nonplanarity of the interface are observed in Pd/Au/Pt/Au and Pd/LaB6/Au contacts. In contacts annealed at conditions for minimal resistivity the penetration depth is 200 and 105 nm, respectively. Implanted Zn is redistributed toward the contact interface during thermal processing. Thus the resistivity lowering is attributed to enhanced p-doping by Zn, which diffused from the contact into the underlying semiconductor. Residual implantation damage is discussed as the essential cause of the comparably high resistivity of implanted and annealed Pd/Ge contacts.
Atomic force microscopy study of III–V materials etched using an electron cyclotron resonance source
Authors: Thomas S. , Pang S. W.
Published: July 2002

GaInAs, InP, and GaAs are etched in a Cl2/Ar plasma generated by an electron cyclotron resonance source. Analysis using scanning electron microscopy shows no difference in GaInAs surface morphology before or after etching in a Cl2/Ar plasma. However, a significant increase in the mean surface roughness of GaInAs from 0.2 to 1.9 nm after etching is detected by atomic force microscopy. The mean surface roughness of GaAs also increases from 0.2 to 1.0 nm after etching. X-ray photoelectron spectroscopy was used to measure atomic concentrations on the etched surface. The results show that the increased roughness of etched GaInAs is related to residual etch products that consist of O and Cl. Using atomic force microscopy, the mean surface roughness was measured to be 1.8 nm at 0.5 mTorr and it increased to 2.7 nm at 5 mTorr. The degradation in GaInAs surface morphology with increasing pressure caused an increase in the specific contact resistivity. Etching related roughness can be minimized by using high radio-frequency power, low pressure, and low Cl2% in Ar. Increasing the ion density by increasing the microwave power allows InP to be etched at 2.7 μm/min with a Cl2/Ar plasma at 30 °C. A smooth surface obtained at 500 W microwave power has a mean surface roughness of 1.7 nm and the InP stoichiometry remains nearly constant after etching. For a lower microwave power of 100 W, the mean surface roughness increases to 4.3 nm, and the surface is characterized by large islands. An H2O rinse immediately following the etch is able to remove residual etch products as indicated by a decrease in the surface roughness as well as the Cl and O concentrations on the surface.
A novel design for a small retractable cylindrical mirror analyzer
Authors: McIlroy D. N. , Dowben P. A. , Knop A. , Rühl E.
Published: July 2002

In this paper we will review the performance of a ‘‘miniature’’ single pass cylindrical mirror analyzer (CMA) which we have used successfully in a variety of experiments. The underlying premise behind this CMA design was to minimize spatial requirements while maintaining an acceptable level of instrumental resolution. While we are presenting the results of a single pass cylindrical mirror analyzer, improvements on the present design, such as going to a double pass design, will undoubtedly improve the instrumental resolution.
Observation of sidewall contamination in submicron contact holes by thermal desorption spectroscopy
Authors: Teraoka Yuden , Aoki Hidemitsu , Ikawa Eiji , Kikkawa Takamaro , Nishiyama Iwao
Published: July 2002

The etching contamination remaining in Al-base SiO2 contact holes after hole fabrication followed by a series of cleaning treatments was analyzed by using thermal desorption spectroscopy. The hole aspect ratio dependence was measured for fluorinated aluminum molecules, the major desorption species. The amount of contaminant material in the holes was found to increase with the sidewall area of the holes, suggesting that the contaminant material desorbs from the bottom surface and accumulates on the SiO2 sidewall during contact hole etching.
Preparation of InSb substrates for molecular beam epitaxy
Authors: Liu W. K. , Yuen W. T. , Stradling R. A.
Published: July 2002

Several chemical cleaning procedures for InSb(100) substrates were studied. Nomarski microscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy were used to assess their credibility for use in molecular beam epitaxial growth of high quality films. The most satisfactory substrate surface was prepared using a modified CP4A etchant (HNO3:CH3COOH:HF:DI H2O at 2:1:1:10). This etchant was found to produce a flat surface with low defect density and a passivating layer consisting mainly of easily removable Sb oxide.
Optimization of reactive ion etching of Al0.48In0.52As in CH4/H2 by the experimental design method
Authors: Carpi Enio L. , Van Hove M. , Alay J. L. , Van Rossum M.
Published: July 2002

The use of methane/hydrogen for reactive ion etching (RIE) of III–V compounds offers several advantages when compared to other chemistries. It shows a widespread use for etching of InP, GaAs, and related compounds for fabrication of optoelectronic devices, transistors, and mesoscopic systems. In the present work the etching of Al0.48In0.52As lattice matched to InP has been optimized by an experimental design technique by measuring the etch rate, the dc self-bias, and the polymer formation as function of the following process parameters: total flow, methane content, pressure, and rf power. Results show that interactions between process parameters cannot be disregarded. The optimized process parameters are 90 sccm, 13.2% of CH4 in H2, 60 mTorr, and 100 W. At this setup the process is diffusion limited, showing a maximum etch rate at 60 mTorr and strong sputtering action. Atomic force microscopy (AFM) shows that the trench quality is better compared to wet phosphoric based chemistry [2.07 nm root mean square (rms) versus 4.65 nm rms]. X-ray photoelectron spectroscopy shows, when compared to a wet-etched reference, a strong surface depletion of arsenic ([As]ref/[As]etch=15) and an increase in the aluminum and indium concentration ([Al]ref/[Al]etch=0.2; [In]ref/[In]etch=0.3). Before etching the surface consists mainly of indium oxide, aluminum oxide, pure As, and a small amount of arsenic oxide. After etching aluminum oxide is still present but the other oxides are being replaced by InAs compounds.
Coherence of large gratings and electron-beam fabrication techniques for atom-wave interferometry
Authors: Rooks Michael J. , Tiberio Richard C. , Chapman Michael , Hammond Troy , Smith Edward , Lenef Alan , Rubenstein Richard , Pritchard David , Adams Scott
Published: July 2002

We describe the fabrication of slotted, free-standing structures used as amplitude gratings in a separated-beam interferometer. Improvements in electron-beam writing techniques have allowed us to compensate for electron-beam system drift, making practical the exposure of 800×800 μm gratings with period as small as 0.14 μm. Alignment marks are used for periodic drift compensation. Finite element analysis of fracture formation in silicon nitride films gives us a tool for the prediction of structural failure in arbitrarily shaped free-standing structures.
Resist planarization over topography using ion implantation
Authors: Wong Vincent V. , Yasaka Anto , Smith Henry I.
Published: July 2002

We present a novel application of ion implantation for obtaining planar films of resist on substrates with deep topography (≥1 μm). The motivation of this work comes from the fabrication of laterally coupled distributed feedback lasers, where lateral gratings need to be patterned adjacent to the sidewalls of a deep ridge waveguide. We demonstrate this process using both boron and phosphorous ion species implanted into polymethylmethacrylate (PMMA, 950 K) resist. The ion energies in our experiments ranged from a few tens of keV to approximately 1 MeV at a typical dose of 1013 cm−2. Experimental results show that the developed depth of the PMMA can be controlled very accurately. Furthermore, post-implant x-ray lithographic exposures show no deleterious effects of the implant on the PMMA characteristics. Lateral gratings (Λ=406 nm) were fabricated on 1.1-μm-high ridge waveguides in InP/InGaAlAs/InGaAsP by CH4/H2 reactive-ion etching. This process is equally applicable for other applications where lithography on substrates with significant topography is required.
Intrafield linewidth variances in 0.25 μm i-line lithography
Authors: Liu Hua-Yu , Yu Crid , Gleason Bob
Published: July 2002

We have studied variations of the widths of polysilicon lines patterned to nominal dimensions of 0.25 μm with an i-line stepper. The analysis is based on measurements of electrical resistance of the etched polysilicon patterns. Systematic dependence of linewidths on exposure field coordinates accounts for a large fraction of their total variance. We have expressed the systematic intrafield variance as a sum of three terms: one attributed to the stepper, another to the reticle, and a third to both. The systematic intrafield dependence is most significant for small isolated lines; this term alone had a 3σ value of 25 nm at a nominal dimension of 0.25 μm.
Ultrahigh resolution chirped distributed feedback gratings fabricated by electron-beam lithography using bent waveguides for low-cost photonic components
Authors: Hillmer H. , Burkhard H. , Seebald E. , Kiesel K.
Published: July 2002

We present an efficient method to define arbitrarily chirped distributed feedback gratings giving differences between neighboring effective distributed feedback pitch lengths in the range of subinteratomic distances. Using bent waveguides superimposed on homogeneous distributed feedback grating fields, distributed feedback gratings with arbitrary chirping in the axial direction can be generated by appropriate bending functions. The bending functions are generated by high resolution electron-beam lithography on a set of masks which can be frequently reused for a low-cost production process. We describe the design principles to enhance the device yield per wafer by defining specific unit cells which are reproduced as often as necessary to obtain full coverage of the wafer. The method can be applied to several crystalline, amorphous, or polycrystalline solid-state materials such as inorganic or organic semiconductors, inorganic or organic dielectrics, glass, and polymers. Our method will be demonstrated for distributed feedback grating based photonic inorganic semiconductor devices.
Direct comparison of cross-sectional scanning capacitance microscope dopant profile and vertical secondary ion-mass spectroscopy profile
Authors: Huang Y. , Williams C. C. , Smith H.
Published: July 2002

The scanning capacitance microscope (SCM) has been shown to be useful for quantitative 2D dopant profiling near the surface of silicon. An atomic force microscope is used to position a nanometer scale tip at a silicon surface, and local capacitance change is measured as a function of sample bias. A new feedback method has been recently demonstrated in which the magnitude of the ac bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. The applied ac bias voltage as a function of position is then input into an inversion algorithm to extract the dopant density profile. The new feedback approach allows for the use of a quasi-1D model in the inversion algorithm. Since there are no alternative 2D dopant profiling techniques which are well established at present, evaluation of the quantitative character of 2D SCM measured profiles has been a challenge. To avoid this obstacle, we have developed sample preparation methods which allow direct comparison of lateral SCM measured profiles on cleaved wafers (cross-sectional plane) with vertical secondary ion-mass spectroscopy (SIMS) profiles. The direct comparison of inverted SCM data and SIMS profiles indicates that quantitative 2D dopant profiling can be achieved by the SCM on a nanometer scale.
Emission current saturation of the p-type silicon gated field emitter array
Authors: Hirano Takayuki , Kanemaru Seigo , Itoh Junji
Published: July 2002

Current–voltage (I–V) characteristics, current stability, and capacitance–voltage (C–V) characteristics of p-type Si gated field emitter arrays (FEAs) have been measured. Emitter tips were made on a p-type Si substrate with a resistivity of 100 Ω cm. From experimental results, emission current saturation was found to occur beyond ∼2 μA and an inversion layer was found to be present under the gate. The emission current was also found to be much more stable than n-type Si FEAs. A model to explain the present I–V characteristics was derived, based on current limitation by thermal carrier generation in depletion layers under both the tips and the gate. In this model, the inversion layer acts as an n-channel gathering the thermally-generated electrons under the gate and supplies them to the tips. A concept for a new FEA capable of actively controlling the emission current is proposed.
Annihilation of monolayer holes on molecular beam epitaxy grown GaAs surface during annealing as shown by in situ scanning electron microscopy
Authors: Inoue Naohisa , Morimoto Keizo , Araki Tsutomi , Ito Taichiro , Homma Yoshikazu , Osaka Jiro
Published: July 2002

The behavior of monolayer-deep holes on the surface of (001) GaAs grown by molecular beam epitaxy during post-growth annealing is observed by in situ scanning electron microscopy. Most small holes disappear immediately after growth in the same way as the islands. However, it is found that some are left for a long time and form big holes with each other. These residual big holes are elongated in the [110] direction initially. They extend in the [110] direction and coalesce with each other, but, at the same time, they shrink in the [1–10] direction and become elongated in the [110] direction. Finally they shrink in both directions and disappear. It takes about 10 min for all the holes to disappear, which is much longer than the growth interruption period usually employed to smooth heterointerfaces. The anisotropic behavior of big holes are discussed in relation to the reported growth anisotropy.
Silicon metal-oxide-semiconductor field-effect transistor with gate structures defined by scanned probe lithography
Authors: Hagedorn M. S. , Litfin D. D. , Price G. M. , Gordon A. E. , Higman T. K.
Published: July 2002

We report on the use of scanned probes to define nanolithographic features in the controlling gate structures of silicon metal-oxide-semiconductor field-effect transistors (MOSFETs). By using an atomic force microscope (AFM) with conducting tips (either Ti coated Si3N4 or heavily doped Si cantilevers) in conjunction with surface adsorbed water, we define oxide structures by anodization which are used as masks for subsequent etching. These patterns consist of such things as constrictions and gratings in the gate. When combined with thin oxides, the pattern of the gate is mirrored in the higher mobility MOSFET inversion layer. Pattern transfer into the gate is accomplished by either direct anodization of the gate material (titanium) or by anodization of sacrificial resists consisting of plasma-deposited organosilicon polymers from methylsilane precursors. The AFM anodization of titanium has been thoroughly described in the literature, and the AFM anodization of the plasma-deposited organosilicon is thought to be a similar mechanism but the organosilicon is also photo-oxidizable when exposed to deep-UV radiation in the presence of oxygen. Using these two methods (direct anodization of gate material and anodization of sacrificial resists) enables AFM lithography to be carried at virtually any step in the process flow. In this way, nanostructure definition can be carried out as a last step in a standard process or may be inserted earlier. Completed devices and their characteristics will be shown.
Study on elliptical polarization illumination effects for microlithography
Authors: Jeon Seong-Ho , Cho Bae-Doo , Lee Kyeong-Woon , Lee Sung-Muk , Baik Ki-Ho , Ahn Chang-Nam , Yim Dong-Gyu
Published: July 2002

The vector image code (VIC) consisting of the vector transmission cross coefficient (TCC) and Fourier transform of the mask function is widely applied to simulate the effects of polarization in microlithography. Until now studies were restricted to the effects of linear polarization. This linear polarization illumination predicts a larger contrast gap between TE polarization and TM polarization as the numerical aperture increases or the critical dimension decreases. In this article, we have studied the effects of elliptical polarization illumination (EPI) as a new method in order to decrease these contrast gaps. We improved VIC by adopting EPI including circular polarization. As a result of using the improved VIC, EPI shows that the contrast and the contrast gap can be tuned by adjusting the angle of polarization and the ratio of the ellipticity. The simulation result also shows that the higher the ratio of ellipticity the lower the contrast gap but at the expense of lowering the contrast somewhat. If this new EPI is adopted into microlithography, the contrast gap can be decreased while the contrast to a specified direction of the mask pattern can be kept high.
Atmospheric metrology using the air turbulence compensated interferometer
Authors: Henshaw Philip D. , DeGloria Donald P.
Published: July 2002

Air turbulence affects the performance of the helium-neon interferometer used to control the wafer stage of stepper or step and scan lithography systems. In this article we describe the principles of operation and performance characterization of an air turbulence compensated interferometer (ATCI) designed to address these problems. Collinear combination of a two-wavelength compensation system using second harmonic interferometry with the existing HeNe interferometer used for length measurement provides a highly accurate system with real-time compensation for air turbulence. We characterized the performance of the ATCI system by measuring compensation performance in the presence of four different atmospheres.
Minimizing alignment error induced by asymmetric resist coating
Authors: Chen Xun , Pease R. F. W.
Published: July 2002

Asymmetric alignment signal is a major problem in optical lithography. Perhaps the most unavoidable source of such asymmetry is the resist profile covering the alignment marks. Such asymmetry can arise from the spin coating process. We describe a new technique of using TM polarized light and Brewster angle illumination to minimize the reflection from the top resist surface and hence minimize alignment error induced by asymmetric resist coating. A basic model is developed to describe the optical effect of the resist coating and to calculate the alignment signals. The results show that the Brewster angle illumination technique can reduce the alignment error more than tenfold when using standard marks such as 16 μm period gratings. Nearly error-free alignment can be achieved even on wafer marks that are covered by asymmetric resist, if the alignment marks are suitably designed.
0.1μm complementary metal–oxide–semiconductors and beyond
Authors: Toriumi Akira
Published: July 2002

The size of metal–oxide–semiconductor field effect transistors has been drastically miniaturized to achieve higher performance according to the scaling law. One micron complementary metal–oxide–semiconductor (CMOS) technology is no longer at the frontier of device research; it is being optimized as a real device. The scaling law has been partly modified but the overall direction of device technology is still following that scenario. This article will first review some key messages that have been learned from 0.1μm CMOS development in our laboratories. In the sub-0.1μm era, there will be a strong demand for new device physics and technologies, including new materials, for a new electronics paradigm. As an example of the new devices, silicon single electron tunneling devices will be discussed here in terms of their gradual assimilation into the current silicon ultralarge scale integration world.
Fabrication of back-gated complementary metal-oxide semiconductor devices using mixed and matched optical and x-ray lithographies
Authors: Yang Isabel Y. , Antoniadis Dimitri A. , Smith Henry I.
Published: July 2002

A novel silicon-on-insulator-based technology called silicon-on-insulator-with-active-substrate (SOIAS) [I. Y. Yang, C. Vieri, A. Chandrakasan, and D. A. Antoniadis, in International Electron Device Meeting (IEEE, Washington, DC, 1995), p. 877] was developed for high performance and low power electronic systems, which takes advantage of established silicon processes such as chemical mechanical polishing, wafer bonding, and the various lithographic tools used for deep submicrometer patterning. This article demonstrates the fabrication of deep submicrometer back-gated complementary metal-oxide semiconductor devices and simple circuits on SOIAS substrates using optical and x-ray lithographies with our mix-and-match strategy [I. Y. Yang, S. Silverman, J. Ferrera, K. Jackson, J. Carter, D. A. Antoniadis, and H. Smith, J. Vac. Sci. Technol. B 13, 2741 (1995)].
Fabrication and investigation of nanostructures and their application in new laser devices
Authors: Griesinger U. A. , Kronmüller S. , Geiger M. , Ottenwälder D. , Scholz F. , Schweizer H.
Published: July 2002

In this article, techniques for the realization of exactly positioned nanostructures are presented and the properties of nanometer scale optic laser devices based on GaInAs/GaInAsP/InP heterostructure are discussed. The fabrication of nanometer scale optic devices requires the precise control of the confinement length of carriers as well as the confinement length of photons, which are different by one order of magnitude. Both requirements can be met by the application of high resolution electron beam lithography in combination with low damage etching techniques and planar epitaxial overgrowth. Lateral structures down to 15 nm with high optical quality at periods around 240 nm suitable for distributed feedback (DFB) devices have been obtained. For the first time, these nanofabrication techniques allow the realization of a new class of semiconductor lasers: gain coupled wire and dot DFB lasers. The reduced dimensionality of the active area shows significant improvements of the gain values and the laser thresholds. The precise definition of dot arrays (array size up to some 100 μm) allows the fabrication of a new device: a gain coupled dot DFB laser, consisting of dots forming a two-dimensional DFB grating.
Fabrication of Si double barrier structure
Authors: Yuki K. , Hirai Y. , Morimoto K. , Morita K. , Uenoyama T.
Published: July 2002

We have observed an oscillation in the current density–voltage (J–V) characteristics caused by resonant tunneling phenomena by means of a newly developed Si-based double barrier structure (DBS). In the DBS fabrication, a thin single-crystal Si plate is used as a quantum well on SIMOX (separation by implanted oxygen) substrate. In order to obtain the Si quantum well, an anisotropic wet chemical etching followed by thermal oxidation is performed. Particularly, a novel advanced shaped etching mask is used to form an extremely thin Si plate. The width of the plate exceeds the resolution limitation of lithography. Accordingly, a quantum well with a width of 9 nm has been successfully obtained. The electrical characteristics of the sample that has around 40 nm wide quantum well and 1.6 nm thick SiO2 barriers are investigated. Oscillation peaks are observed in the J–V characteristics at 4.0 K. The observed peaks are in good agreement with the calculated resonant tunneling diode model.
Reduced nonradiative recombination in etched/regrown AlGaAs/GaAs structures fabricated by in situ processing
Authors: Kohmoto S. , Nambu Y. , Asakawa K. , Ishikawa T.
Published: July 2002

Effectiveness of in situ processing, which combines Cl2 gas etching with subsequent molecular beam epitaxy regrowth in an ultrahigh vacuum environment, is quantitatively evaluated with nonradiative carrier recombination velocity, S, of etched/regrown AlGaAs/GaAs heterointerfaces. When AlGaAs is in situ regrown on Cl2 gas-etched flat GaAs surface, the S value is as low as 1.3×103 cm/s. This value is lower than that of air-exposed/regrown (or ex situ processed) interfaces, thus representing the essential superiority of in situ processing over ex situ. Buried GaAs/AlGaAs multiquantum-well (MQW) mesa-stripes are also fabricated by in situ Cl2 gas-etching/regrowth. The S value at the MQW mesa-sidewall regrown with AlGaAs is 6.0×103 cm/s, which is reduced by more than one order of magnitude from that of a nonburied case.
Optimal filtering of scanning probe microscope images for wear analysis of smooth surfaces
Authors: Schouterden K. , Lairson B. M. , Azarian M. H.
Published: July 2002

A procedure for removing cumulative drift and white noise from scanning probe microscope images has been constructed. Smooth amorphous carbon overcoats on superpolished hard disk media in particular were examined using a scanning probe microscope. The surfaces typically had a ∼1 nm rms roughness over a scan length of 10 μm. The low roughness yielded a relatively low signal to noise ratio in the unfiltered image. While a conventional filter removes a great deal of noise, an optimal Fourier (Wiener) filter that more selectively removes noise from the image is discussed. White noise and drift were modeled and their contributions to the power spectrum are estimated, resulting in an open clamshell-shaped two-dimensional filter. The effect of the filter was demonstrated by subjecting filtered images of unworn and worn areas to a smooth surface to second derivative calculations in different directions. Anisotropy in the wear process associated with the wear direction is apparent in the optimally filtered images.
Scanning force microscopy study of the surface topography of thin BaTiO3 films deposited by pulsed laser ablation
Authors: Zhang J. , Szabadi M. , Hess P.
Published: July 2002

The surface topography of thin single-crystal BaTiO3 films deposited on SrTiO3(100) and YBCO(001)/LaAlO3(100) substrates, and thin polycrystalline films deposited on MgO(100) was studied using scanning force microscopy in air. Films 0.37, 0.26, and 0.39 μm thick were grown on the SrTiO3(100) substrate at 750 °C at oxygen pressures of 0.7, 7, and 70 Pa, respectively. Films 0.47, 0.26, and 0.25 μm thick were deposited on the SrTiO3(100) substrate at the temperatures of 550, 750, and 850 °C, respectively, at an oxygen pressure of 7 Pa. Films 0.20 and 0.10 μm thick were grown on MgO(100) and YBCO(001)/LaAlO3(100) substrates, respectively, at 750 °C and 7 Pa. Scanning force microscopy images show that, for the deposition temperature of 750 °C, when the oxygen pressure is increased from 0.7 to 7 and 70 Pa, the surface topography of the BaTiO3 films changes from flat to islandlike three-dimensional growth (Volmer–Weber mode), and the corresponding rms surface roughness values are 1.2, 3.4, and 6.4 nm. With an increase of the deposition temperature from 550 to 750 and 850 °C, the surface topography changes from corrugated to rectangular grain, and the corresponding surface roughness values are 1.2, 3.4, and 3.4 nm for an oxygen pressure of 7 Pa. The films on the MgO(100) substrate consist of two kinds of grains, and the corresponding surface roughness value is 1.0 nm. The film on the YBCO(001)/LaAlO3(100) substrate is composed of uniform hemispherical grains, and the corresponding surface roughness value is 29 nm due to the roughness of the bare substrate of 31 nm.
High rate reactive ion etch and electron cyclotron resonance etching of GaAs via holes using thick polyimide and photoresist masks
Authors: Shul R. J. , Lovejoy M. L. , Word J. C. , Howard A. J. , Rieger D. J. , Kravitz S. H.
Published: July 2002

High rate etching of through-substrate via holes are essential to many GaAs electronic and photonic device applications. The backside via holes are relevant to monolithic microwave integrated circuits for low inductance grounding and increased circuit complexity. Via holes have also become important to photonic devices such as transmission modulators and vertical cavity surface emitting lasers (VCSELs) fabricated on absorbing substrates. We have investigated and compared reactive ion etch (RIE) and electron cyclotron resonance (ECR) etch results for GaAs via holes patterned with either photodefinable polyimide masks or conventional thick photoresist masks. We report GaAs etch rates for 5 min plasma exposures of ∼8000 nm/min in a RIE-generated Cl2/BCl3/SiCl4 plasma and ∼3200 nm/min in a Cl2/BCl3 ECR-generated plasma.
Etching of high aspect ratio microcavity structures in InP
Authors: Ying F. , Juan W. H. , Pang S. W.
Published: July 2002

Etching of InP using an electron cyclotron resonance source in a Cl2/Ar plasma has been investigated for the fabrication of microcavity laser structures. Fast, smooth, and reproducible etching was achieved with etch rates of 2.14 μm/min. It was found that the etch profile depended on the Cl2 concentration in the Cl2/Ar plasma. Vertical etch profile was obtained for Cl2 concentration ⩽15%. Hard-baked photoresist and Ni have been used as etch masks. Typical etch rate of hard-baked photoresist was 0.10 μm/min and etch selectivity between InP and photoresist was 21. Typical etch rate of Ni was 13 nm/min with a selectivity of 165. The etched InP surface was smoother for samples with photoresist mask. For samples with Ni mask, the etched surface became rougher when narrower or deeper trenches were etched. With optimized etch conditions, high aspect ratio microstructures in InP that were 0.75 μm wide and 10.7 μm tall were fabricated with nearly vertical profile and smooth etched surface using photoresist mask. Similarly, arrays of microcavities of 1 μm in diameter and 4.5 μm tall have been formed.
Selective Si and SiGe epitaxial heterostructures grown using an industrial low-pressure chemical vapor deposition module
Authors: Bodnar S. , de Berranger E. , Bouillon P. , Mouis M. , Skotnicki T. , Regolini J. L.
Published: July 2002

Low-temperature epitaxial growth of Si and Si1−xGex (referred to as SiGe, hereafter) has been obtained using an industrial, 200 mm, single wafer chemical vapor deposition module operating at reduced pressure. Epitaxial Si and heteroepitaxial SiGe deposition with Ge content ⩽30% have been studied for buried channel applications in (PMOSFET) devices or as base for heterojunction bipolar transistors (HBTs). The dependence of Si and SiGe deposition rates on filling ratio and exposed windows and their evolution with the addition of HCl to the gas mixture are investigated. In contrast to selective Si growth where the global loading effect decreases slowly with temperature, the growth rate of SiGe at low temperature is strongly dependent on the oxide coverage. The addition of HCl into the gas mixture allows minimizing the dependence of the SiGe growth rate on both oxide coverage and window size. The effect of the addition of HCl on Ge and dopants incorporation is investigated on bare and/or device wafers. Results on facet formation and orientations are also presented for selective Si and SiGe growths. Finally, we report basic electrical results on selective Si epitaxial and SiGe heteroepitaxial structures, which have been integrated in PMOSFET and HBT devices.
Imaging characteristics of poly(methyl methacrylate) at vacuum ultraviolet wavelengths
Authors: Ferincz I. E. , Tóth Cs. , Young J. F.
Published: July 2002

We report the depth versus exposure characteristics of poly(methyl methacrylate) (PMMA) in the vacuum ultraviolet (VUV) region from 59 to 128 nm. Calculated absorption coefficients of the PMMA are also presented. The depth of the features on the PMMA were in the range of 20–80 nm created by 1–50 mJcm−2exposures and were measured with an atomic force microscope (AFM). We found that the AFM can reliably measure depth differences of only 2 nm. The sensitivity of the AFM permits exposures to be reduced for high resolution microscopy and holography even in the case of highly absorbing films.
Electrical optimization of plasma-enhanced chemical vapor deposition chamber cleaning plasmas
Authors: Sobolewski M. A. , Langan J. G. , Felker B. S.
Published: July 2002

Fluorinated gas discharges are widely used by the semiconductor industry in etching and chamber cleaning applications, but the performance of these discharges varies in unpredictable ways, for unknown reasons believed to be electrical in origin. To investigate possible mechanisms for this behavior, we have measured the electrical characteristics of NF3/Ar, CF4/O2/Ar, and C2F6/O2/Ar chamber cleaning plasmas at 6.7–267 Pa in a 13.56 MHz, capacitively coupled, parallel-plate reactor, using radio-frequency current and voltage probes and optical emission spectroscopy. From the measurements, power losses in the external circuitry surrounding the discharge were determined. Furthermore, using the measurements and equivalent circuit models, the mechanisms by which power was absorbed within the discharge itself were investigated. Power was absorbed most efficiently at particular values of the discharge impedance. These optimal impedances occur in the middle of a transition from capacitive impedances at low pressures to resistive impedances at high pressures. These results illustrate that the plasma impedance is a useful parameter for monitoring and optimizing plasma processes in highly electronegative gases.
KrF laser epitaxy of silicon germanium alloy layers by irradiation of Si(1−x)Gex/Si (100) structures
Authors: Larciprete R. , Grimaldi M. G. , Borsella E. , Cozzi S. , Martelli S. , Pieretti S. , Vianey I.
Published: July 2002

KrF excimer laser pulses at 248 nm were used to irradiate Ge and SiGe films grown on Si (100) by ultrahigh vacuum chemical vapor deposition (CVD) or to assist the CVD growth itself. In both cases the laser energy density was sufficiently high (0.5 J/cm2) to melt the whole CVD film. The CVD growth either without or with laser assistance, as well as the post-growth irradiation were monitored by online single wavelength ellipsometry, which allowed to follow in real time the modification of the film morphology induced by the laser treatment. Effective smoothing of the surface islands upon laser irradiation was revealed in every case. Particularly, for the laser-assisted CVD growth, the influence of the laser irradiation modality on the surface microroughness during growth was evidenced and the irradiation condition for optimal surface planarization identified. The microstructural properties of the SiGe layers were investigated by high resolution x-ray diffraction and Rutherford backscattering spectrometry. In the case of the laser-assisted CVD growth, the solidification of alloys exhibiting excellent epitaxial quality and graded Ge profiles was attained. The alloys resulted fully strained for Ge content of 5 at %. This growth technique which allows to design the Ge profile inside the alloyed layer, by adjusting precursor gas fluxes and laser irradiation conditions, results particularly attracting for the production of compositionally graded SiGe film, to be applied as buffer layers in SiGe based devices.
Plasma-assisted chemical vapor deposition growth of SiC on Si(100): Morphology and electronic structure
Authors: Bittencourt C. , De Seta M. , Evangelisti F.
Published: July 2002

We have investigated the structure and the electronic properties of thin SiC films grown on Si(100) by plasma-assisted chemical vapor deposition from CH4 diluted in H2. It was found that the growth proceeds through the nucleation of cubic and relaxed crystalline SiC islands preferentially oriented in the (100) direction. The average island size increases with carbonization time up to a maximum size consisting of ∼300 nm lateral width and ∼100 nm height. We were able to determine the valence band discontinuity although the SiC overlayers were clusterlike and did not cover uniformly the Si substrate. The found value is 0.77±0.08 eV.
Electrical properties and uniformity of two dimensional electron gases grown on cleaned SiGe virtual substrates
Authors: Paul D. J. , Ahmed A. , Pepper M. , Churchill A. C. , Robbins D. J. , Wallis D. J. , Pidduck A. J.
Published: July 2002

The low temperature electrical properties of modulation-doped two dimensional electron gases (2DEGs) in the SiGe system were studied. The effects on the electrical properties of removing the substrate from the growth chamber after the growth of the virtual substrate, chemically cleaning the virtual substrate, and then growing the modulation-doped structure on a thin SiGe buffer were investigated. The results demonstrate that the carrier density and mobility decrease as the regrowth interface is moved closer to the 2DEG. The uniformity of the regrown wafers was also investigated. A monotonic increase in carrier density and a decrease in mobility were observed towards the edge of the wafers. Appropriate mechanisms will be discussed.
77 K far-infrared hot-electron multi-quantum-well detectors
Authors: Jacobs E. S. , Waldman J. , Goodhue W. D.
Published: July 2002

The responsivity to long wavelength (513 and 1253 μm) far-infrared (FIR) radiation and the root mean square noise voltage has been measured for one bulk GaAs and two GaAs/AlGaAs multiquantum-well (MQW) hot-electron photodetectors as a function of temperature from 4.49 to 77 K. From these data the noise-equivalent power (NEP) was determined for each device over the same temperature range. The MQW detectors were measured to have 77 K responsivities and NEPs that were one to two orders of magnitude better than those measured using the high purity bulk GaAs sample. To the best of our knowledge, these are the first measurements which show that hot electron MQW detectors are able to outperform bulk GaAs detectors at 77 K. Furthermore, the photoresponse of the MQW structures showed a much slower temperature dependent rolloff as compared to the bulk device, which implies a potential for applications at temperatures above 77 K. Detection of nanosecond pulses of 496 μm FIR radiation by one MQW detector and the bulk GaAs is additional evidence of hot-electron photoconductivity.
Eu:CaF
2
layers on p-Si(100) grown using molecular beam epitaxy as materials for Si-based optoelectronics
Authors: Chatterjee T. , McCann P. J. , Fang X. M. , Johnson M. B.
Published: July 2002

Eu:CaF 2 layers have been grown epitaxially on Si using molecular beam epitaxy (MBE) with the intent of realizing an electrically pumped optical source on Si. Here we present an atomic force microscopy study of the morphological features of MBE-grown Eu:CaF2 on p-type Si(100) substrates and a study of electroluminescence (EL) from EL devices fabricated from these layers. The surface morphologies of the MBE-grown layers show an increased density of faceted features with increase in epilayer Eu content. X-ray photoelectron spectroscopy (XPS) data reveal the emergence of satellite peaks around the regular Eu XPS peaks in Eu:CaF2 layer with high Eu content. The characteristics of EL devices fabricated on these layers is presented and a possible EL mechanism is discussed.