Showing papers by "Veena Misra published in 1993"

Characterization of Thin Silicon Oxynitride Films Prepared by Low Pressure Rapid Thermal Chemical Vapor Deposition

Abstract: Thin silicon oxynitride (Si-N-O) films have been deposited using low pressure rapid thermal chemical vapor deposition (RTCVD), with silane (SiH[sub 4]), nitrous oxide (N[sub 2]O), and ammonia (NH[sub 3]) as the reactive gases. Structural and kinetic studies indicate that an increase in the NH[sub 3]/N[sub 2]O flow rate ratio leads to an increase N/O atomic ratio and a decreased Si-N-O deposition rate for constant SiH[sub 4] and N[sub 2]O flow rates. Experimental results show that RTCVD Si-N-O films with high throughput at low thermal budget, uniform composition, and atomically flat interface can be achieved using a SiH[sub 4]/NH[sub 3]/N[sub 2]O gas mixture. Electrical characterization of poly Si/Si-N-O/Si capacitors demonstrates that for NH[sub 3]/N[sub 2]O flow rate ratios ranging from 20 to 100%, the mid-gap interface trap densities of the deposited Si-N-O films are [<=]2 [times] 10[sup 10] eV[sup [minus]1] cm[sup [minus]2] and Fowler-Nordheim electron-tunneling rather than Frenkel-Poole thermal-emission is the dominant conduction mechanism in the thin RTCVD Si-N-O films.

Thin oxynitride film metal‐oxide‐semiconductor transistors prepared by low‐pressure rapid thermal chemical vapor deposition

Abstract: Thin silicon oxynitride (Si‐O‐N) films have been deposited using low‐pressure rapid thermal chemical vapor deposition (RTCVD) with silane (SiH4), nitrous oxide (N2O), and ammonia (NH3) as the reactive gases. Metal‐oxide‐semiconductor transistor transconductance measurements showed decreasing peak gm values but improved high field degradation characteristics. This is consistent with previous work on thermally nitrided oxides and suggests that the films are perhaps under tensile stress. Hot carrier stress at maximum substrate current was performed with the Si‐O‐N films displaying larger threshold voltage shifts when compared to furnace SiO2 indicating the possible existence of hydrogen related traps.

Elemental analyses of hypervelocity microparticle impact sites on Interplanetary Dust Experiment sensor surfaces

Abstract: The Interplanetary Dust Experiment (IDE) had over 450 electrically active ultra-high purity metal-oxide-silicon impact detectors located on the six primary sides of the Long Duration Exposure Facility (LDEF). Hypervelocity microparticles (approximately 0.2 to approximately 100 micron diameter) that struck the active sensors with enough energy to break down the 0.4 or 1.0 micron thick SIO2 insulator layer separating the silicon base (the negative electrode), and the 1000 A thick surface layer of aluminum (the positive electrode) caused electrical discharges that were recorded for the first year of orbit. The high purity Al-SiO2-Si substrates allowed detection of trace (ppm) amounts of hypervelocity impactor residues. After sputtering through a layer of surface contamination, secondary ion mass spectrometry (SIMS) was used to create two-dimensional elemental ion intensity maps of microparticle impact sites on the IDE sensors. The element intensities in the central craters of the impacts were corrected for relative ion yields and instrumental conditions and then normalized to silicon. The results were used to classify the particles' origins as 'manmade,' 'natural,' or 'indeterminate.' The last classification resulted from the presence of too little impactor residue, analytical interference from high background contamination, the lack of information on silicon and aluminum residues, or a combination of these circumstances. Several analytical 'blank' discharges were induced on flight sensors by pressing down on the sensor surface with a pure silicon shard. Analyses of these blank discharges showed that the discharge energy blasts away the layer of surface contamination. Only Si and Al were detected inside the discharge zones, including the central craters of these features. Thus far a total of 79 randomly selected microparticle impact sites from the six primary sides of the LDEF have been analyzed: 36 from tray C-9 (Leading (ram), or East, side), 18 from tray C-3 (Trailing (wake), or West, side), 12 from tray B-12 (North side), 4 from tray D-6 (South side), 3 from tray H-11 (Space end), and 6 from tray G-10 (Earth end). Residue from manmade debris was identified in craters on all trays. (Aluminum oxide particle residues were not detectable on the Al/Si substrates.) These results were consistent with the IDE impact record which showed highly variable long term microparticle impact flux rates on the West, Space and Earth sides of the LDEF which could not be ascribed to astronomical variability of micrometeorite density. The IDE record also showed episodic bursts of microparticle impacts on the East, North, and South sides of the satellite, denoting passage through orbital debris clouds or rings.

Effects of oxygen doping on properties of microcrystalline silicon film grown using rapid thermal chemical vapor deposition

Abstract: An oxygen doped microcrystalline silicon (μc-Si) deposition process is developed by mixing small amounts of nitrous oxide (N2O) with silane (SiH4) in a rapid thermal chemical vapor deposition (RTCVD) reactor. The effects of oxygen doping on the properties of RTCVD μc-Si films are studied. Experimental results show that the RTCVD process provides high deposition rates for μc-Si and polycrystalline silicon (polySi) films at elevated deposition temperatures and pressures. The surface roughness of the RTCVD μc-Si films can be significantly reduced compared to that of conventional LPCVD polySi films. Steep side walls can be realized due to the small grain size of the μc-Si films. The sheet resistance of BF2 doped μc-Si films is slightly higher than that of BF2 doped polySi films, whereas sheet resistances of P and As doped μc-Si films are much higher than those of the corresponding P and As doped polySi films. Measurements of the catastrophic breakdown strength of metal-oxide-semiconductor (MOS) capacitors indicate that the quality of gate electrodes fabricated using μc-Si is improved relative to that of MOS capacitors fabricated using polySi gate electrodes.

Characterization of Oxygen-Doped and Non-Oxygen-Doped Polysilicon Films Prepared by Rapid Thermal Chemical Vapor Deposition

Abstract: PolySi films deposited with and without oxygen doping using rapid thermal chemical vapor deposition (RTCVD) have been investigated. Experimental results show that RTCVD systems can be used to provide high deposition rates ( 900-1000 A/min at 700 °C) for both oxygen-doped and non-oxygen-doped polySi films. The surface roughness of the RTCVD polySi film is about half that of conventional LPCVD polySi films. The surface roughness and grain size of the RTCVD polySi film can be further reduced using oxygen doping. The catastrophic breakdown strength for capacitors using oxygen-doped polySi electrodes are improved compared with the breakdown strength for capacitors using non-oxygen-doped polySi electrodes. Electrical resistivities of B, P and As doped samples of polySi films with oxygen doping are found to be larger than those of polySi films without oxygen doping. Resistivities of silicides formed on the oxygen-doped polySi samples are approximately the same for those of silicides formed on non-oxygen-doped polySi samples.

Control of Si-SiO2 Interface Properties in MOS Devices Prepared by Plasma-Assisted and Rapid Thermal Processes

Abstract: This paper describes the preparation of silicon-based metal oxide semiconductor, MOS, devices, capacitors and field effect transistors, FETs, using deposited oxide dielectrics. A critical aspect of the device fabrication process is the way the Si-SiO2 interface is formed; e.g., either before, during, or after the oxide deposition. We have studied different methods of fabricating Si-SiO2 heterostructures, and have concluded that the implementation of independently controllable and sequential process steps for (i) interface formation, and (ii) oxide deposition consistently yields MOS devices with electrical properties that are superior to those of devices fabricated under other processing conditions which include specifically interface formation during the oxide deposition.

Selective Removal of Silicon-Germanium: Chemical and Reactive Ion Etching

Abstract: The use of both chemical and reactive ion etching for the selective removal of SixGe1-x alloys with respect to both silicon and silicon dioxide has been investigated. We have found that a solution of NH4OH:H2O2:H2O is effective in selectively etching the SixGe1-x films with respect to both of these materials. The chemical composition of the substrate surface after removal of insitu doped SixGe1-x films was evaluated using EDS and SIMS. Diffusion from insitu doped Si0.7Ge0.3, followed by selective removal, was used to demonstrate self-aligned npn dopant profiles with narrow base widths. Reactive ion etching of SixGe1-x alloys was investigated using SF6, CF4, and Cl2 based chemistries. Pressure, power, and gas flow ratios were optimized to provide the least isotropic etch possible for SixGe1-x films containing approximately 40% Ge. Selectivity and degree of anisotropic etching were determined as a function of Ge content for samples with 0% to 100% Ge. Samples were analyzed using SEM and ellipsometry. Highest selectivities were achieved using SF6 and O2.

Gate Quality Oxides Prepared by Rapid Thermal Chemical Vapor Deposition

Abstract: As the feature size of MOSFET devices shrink, issues such as thermal budget associated with controlling channel doping profiles and oxide growth kinetics raise concerns about using thermally grown furnace oxides for deep-submicron device applications. To address these concerns, we have developed a new RTCVD oxide process using a gas system of silane and nitrous oxide. The RTCVD oxides are deposited in a lamp-heated, cold wall, RTP system. Deposition rates ranging from 55 A/min. to 624 A/min. can be achieved at 800°C with silane nitrous oxide flow rate ratio of 2% and total pressure ranging from 3 to 10 Torr. The results indicate that this RTCVD process can be used to deposit both thin gate and thick isolation insulators for single wafer processing. Deposition rates of the RTCVD oxides exhibit a nonlinear dependence on the total deposition pressure. Electrical characterization of the as-deposited RTCVD oxides shows a mid-gap interface trap density of < 5×1010 eV−1 cm−2 and an average breakdown field of 13MV/cm. AES, RBS and TEM analyses have been used to study surface cleaning effects on the silicon-silicon dioxide interface quality and to determine the chemical composition of the RTCVD oxides. The results show that RTCVD oxides with stoichiometric composition and atomic flat silicon-silicon dioxide interface can be achieved using silane nitrous oxide flow rate ratio of <2%. I–V characteristics and transconductance degradation under hot carrier stress for MOSFET’s using as-deposited RTCVD gate oxides have been found to be comparable to those of MOSFET’s using thermal gate oxides.

A Dual-Function UHV-Compatible Chamber for i) Low-Temperature Plasma-Assisted Oxidation, and ii) High-Temperature Rapid Thermal Processing of Si-Based Dielectric Gate Heterostructures

Abstract: A combination of i) low-temperature, 300–400°C, plasma-assisted oxidation to form the SiO2/Si interfaces, and ii) 800°C rapid thermal chemical vapor deposition, RTCVD, to deposit SiO2 thin films have been used to fabricate gate-oxide heterostructures. This sequence separates SiO2/Si interface formation by the oxidation process from the deposition of the bulk oxide layer by RTCVD. These two processes were performed in situ and sequentially in a single-chamber, ultraclean quartz reactor system. We have studied the chemistry of the interface formation process by Auger electron spectroscopy, AES, and the electrical properties of MOS devices with Al electrodes by C-V techniques.