AVS1996 Session EM-WeP: Electronic Materials and Processing Poster Session II

Wednesday, October 16, 1996 5:00 PM in Ballroom A

Wednesday Afternoon

Time Period WeP Sessions | Topic EM Sessions | Time Periods | Topics | AVS1996 Schedule

EM-WeP-1 Study of MBE Grown ZnSe/GaAs(100) Interfaces with Differently Prepared GaSs Surfaces E. L\aa o\pez-Luna, J. Luyo, M. L\aa o\pez-L\aa o\pez, M. Mel\aa e\ndez-Lira, C. V\a a\zquez, I. Hern\aa a\ndez-Calder\aa o\n (CINVESTAV, Mexico) Very recently Sony demonstrated that the reduction of defect density in ZnSe based heterostructures allowed the fabrication of a diode laser with an operating lifetime longer than 100 hr [1]. Further improvement in the performance of these devices requires a precise control of the generation and propagation of defects. A large amount of them are generated at the interface between the commonly used GaAs substrate and the ZnSe layer. Intrinsic problems are: lattice mismatch, interdiffusion, and chemical reactions, which can severely affect the whole heterostructure. Here, we report our investigation on the search of an optimal preparation method of the GaAs surface to obtain high quality ZnSe layers by molecular beam epitaxy (MBE). GaAs(100) surfaces were prepared by different methods, including several ex-situ chemical treatments, and previously MBE grown GaAs buffer layers with an As cap. Once in the growth chamber, the substrates were annealed to eliminate oxides and/or the As cap. ZnSe films were grown at substrate temperatures between 285 and 350 \sup o\C with nominal film thickness in the range from a few \Ao\ to 2 \mu\m. The typical growth rate was around 1 \mu\m/hr and different Se/Zn flux ratios were employed. The optical properties of the interfaces were characterized by photoluminescence, photoreflectance, and Raman spectroscopies. Their structural properties were investigated in-situ by reflection high energy electron diffraction and afterwards by atomic force microscopy. The chemical composition of the GaAs surfaces and the resulting ZnSe/GaAs interfaces was investigated by Auger electron spectroscopy. The results will be explained in terms of the chemical and structural properties of the differently prepared GaAs surfaces and the initial formation of the ZnSe/GaAs interfaces. Partially supported by CONACyT, Mexico. 1. Compound Semic. 2, 7(1996).
EM-WeP-2 Fowler-Nordheim Stressing of Polycrystalline Si/Oxide/Si Structures: Observation of Stress-induced Defects in the Oxide/Si Interface as well as in Bulk Si J. Jiang, O. Awadelkarim (Pennsylvania State University); J. Werking, G. Bersuker, Y. Chan (Sematech) Degradation of oxide/silicon interfaces in metal-oxide-silicon (MOS) device structures is a major reliability concern for submicron complementary MOS (CMOS) technologies. This degradation occurs during CMOS processing of the devices as well as durin g their subsequent operation. The main cause of degradation is interface trap generation by electrical stress. The goal of the study reported herein was to investigate, by means of deep level transient spectroscopy (DLTS), interface trap generation by Fow ler-Nordheim (FN) stress of MOS capacitor structures. The capacitors were fabricated using a 0.5 microns CMOS process flow. The capacitor structures were subjected to constant-voltage FN stressing at temperatures between 50 K and 300 K. It was observed th at stressing at temperatures above 150 K induces a 0.20 eV-wide band of closely-spaced interface hole-traps centered at 0.55 eV above the edge of the valence band in silicon. For the same stress level, the concentration of traps in the band decreases with decreasing temperature, and the band is undetectable at stress temperatures below 150 K. However in the course of this study we discover that, in addition to generating interface traps, FN stress can induce carrier traps in bulk silicon beneath the oxide /silicon interface ; i. e., in what would be the channel region in a corresponding MOS field-effect transistor. We observe and report on two bulk-silicon defects, one of which is configurationally bistable, that are induced by FN stressing. These defects, located in silicon at 600 \Ao\ to 1000 \Ao\ below the interface, give rise to electron traps at 0.30 eV, 0.35 eV, and 0.37 eV below the conduction band. The former two traps are suggested to arise from the configurationally bistable boron-vacancy pair. T he latter trap, which is unstable above 150 K, is tentatively ascribed to the isolated vacancy.
EM-WeP-3 Low Energy Cathodoluminescence Spectroscopy of SiO\sub 2\ Nanoparticles X. Yang, L. Brillson, K. Law (Xerox Wilson Center for Research and Technology) We have performed low energy cathodoluminescence (CLS) and photoluminescence (PLS) spectroscopy measurements on nanometer scale particles of SiO\sub 2\. Ultra small particles with sizes ranging from 7-16 nm prepared by flame-hydrolysis provided very high surface to bulk ratios and thereby large surface signals. These materials are commonly used as "charge control agents" in contact charging of xerographic toner. We investigated both hydrophobic and hydrophilic SiO\sub 2\ specimens under ultra high vacuum (UHV) conditions in order to control surface chemical adsorption. CLS and PLS yielded evidence for energy levels deep in the band gap of these materials. A set of spectral peaks appeared at ca. 1.2-1.3, 1.7-1.9, and 2.75-2.95 eV in both hydrophobic and hydrophilic SiO\sub 2\. The appearance of these features at energies well below the band edge of SiO\sub 2\ (8.9 eV) is indicative of traps in the band gap which may play a role in the charge transfer process. We observed a strong intensity dependence of the 2.75-2.95 eV features on incident electron beam energy, increasing with more surface (1 keV) vs. bulk (2 keV) excitation. This feature also displayed an increase with hydrophilicity, with particle size, as well as with additional surface chemical treatment. The 2.75-2.95 eV feature increase with larger hydrophobic particle size suggests that chemical conditions as well as surface area contribute to the peak intensity. Furthermore, particle size also affects peak energies as well, indicative of quantum size effects. We observe peak shifts in both hydrophilic and hydrophobic specimens from 2.75 to 2.8-2.85 eV as particle size diminishes from 16 to 7 nm. These are the first observations of electronic phenomena associated with chemical and size properties in these SiO\sub 2\ nanoparticles. In addition, they provide significant evidence for deep levels in wide band gap insulating SiO\sub 2\ playing role in triboelectric contact charging.
EM-WeP-4 An Infrared Study of H\sub 8\Si\sub 8\O\sub 12\ Spherosiloxane Clusters on Si (100) J. Eng, Jr. (Columbia University); L. Struck (National Institute of Standards & Technology); B. Bent (Columbia University); M. Banaszak-Holl (University of Michigan); S. Lee (Brown University); K. Raghavachari (Bell Laboratories); J. Bender (Brown University); Y. Chabal (Bell Laboratories) Due to the demand in the microelectronics industry for thin, well-defined SiO\sub 2\ layers on Si, there has been great interest in understanding the local structure at the Si/SiO\sub 2\ interface. Recently, studies using x-ray photoelectron spectroscopy (XPS) have been performed in which spherosiloxane clusters (H\sub 8\Si\sub 8\O\sub 12\) were chemisorbed onto a clean Si(100) surface to provide a model of the Si/SiO\sub 2\ interface which could be used to calibrate the Si(2p) core level shifts.[M. Banaszak-Holl et al., PRL 72, 2441 (1993)]. The controversial interpretation of these XPS experiments rejects the conventional assignments of the Si(2p) core level shifts and questions the validity of previous Si/SiO\sub 2\ interface models. At the core of the controversy is disagreement about the cluster adsorption geometry. In this work, the adsorption geometry and thermal behavior of H\sub 8\Si\sub 8\O\sub 12\ clusters on clean, chemically-oxidized, and hydrogen-passivated Si(100) surfaces has been studied by external reflection infrared (IR) spectroscopy. The entire frequency range from 330-3000 cm\super -1\ has been examined using Si(100) samples with a buried CoSi\sub 2\ layer to improve the sensitivity for external reflection by a factor of 10. Importantly, the IR spectra show that the cluster attaches to the clean surface through one vertex, consistent with the geometry proposed on the basis of XPS studies. The competition between water and cluster adsorption on the Si(100) surface has also been studied to rule out contamination. The results of the IR experiments are considered in the context of the XPS experiments and density functional calculations of the same system.
EM-WeP-5 Characterization of Metal Films on Doped Silicon Carbide Epilayers W. Collins (Fisk University); D. Larkin (NASA Lewis Research Center); M. George (Fisk University); J. Petit (NASA Lewis Research Center); D. Shi, A. Burger (Fisk University) Tantalum and Aluminum contacts on CVD SiC films were studied to examine variations in the chemical, morphological and electrical properties of the samples. Nitrogen and aluminum doped substrates were prepared to give n-type and p-type SiC epilayers respectively. These preparations were examined by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and by scanning tunneling microscopy (STM). Samples were studied both before and after the deposition of the metal films to compare differences between SiC(p++)/metal and SiC(n++)/metal contact interfacial properties. Variations in the surface composition and morphologies were compared to the (I-V) behavior of the samples. Correlations were also made to the adhesion of the metals to n+ and p+ epilayers. The metals generally have been found to have good adherence to the n+ epilayer while metal films deposited on p+ epilayers have had poor adherence. AFM images revealed nanometer sized clusters, attributed to excess Si on the n+ epilayers, while no clusters were observed on the p+ epilayers. XPS studies of the as-prepared samples indicated that the n+ epilayers had higher concentrations of oxides which may enhance adhesion.
EM-WeP-6 Observation of a Complex Structure for Se on Ge(100) Surface: a Photoelectron Holographic Image Study J. Wu, M. Keeffe, G. Lapeyre (Montana State University) The atomic structure for a 0.3 monolayer (ML) of Se on single-domain Ge(100) 2x1 is determined by the small-cone photoelectron holographic imaging (PHI) technique [1,2], in conjunction with low-energy electron diffraction (LEED). The 4\supere 0\ vi cinal cut Ge (100) surface was cleaned by several cycles of Ar\super +\ sputtering and annealing up to about 875\super 0\ C, and showed the sharp single-domain 2x1 LEED pattern. The Se coverage was obtained by deposition of ZnSe onto the substrate at room temperature followed by annealing to about 525\super 0\ C to desorb all the Zn from the surface. Then a well order 1x2 LEED pattern was formed, i.e. the two-by direction is perpendicular to the two-by direction on the clean surface. Energy-dependent phot oelectron diffraction spectra for the Se 3d core-level emission were collected by employing constant-initial-energy spectroscopy (CIS) for a set of emission directions. The small-cone holographic inversion gives an image in real space for atoms near the S e emitter. The image is complex and it is evaluated in terms of two types of adsorption sites. A model is proposed in which two types of regions coexist on the surface. One is that the Se adsorption breaks the Ge dimer bonds and occupies bridge sites on the Ge surface. The other is regions where the Se displaces the surface Ge atoms occupying bridges sites to the second-layer Ge atoms. This occurs in alternating rows. * Supported by ONR/DEPSCOR 1. H. Wu and G. J. Lapeyre, Phys. Rev. B51, 14549 (1995). 2. H. Wu, G. J. Lapeyre, H. Huang and S. Y. Tong, Phys. Rev. Lett. 71, 251 (1993).
EM-WeP-7 Comparison of Dry Etch Chemistries for SiC G. McDaniel, S. Pearton, P. Holloway (University of Florida, Gainesville); F. Ren (Bell Laboratories); J. Grow, M. Bhaskaran (New Jersey Institute of Technology) SiC has generally been plasma etched in polymer-forming chemistries such as CHF\sub 3\/O\sub 2\ or CF\sub 4\/O\sub 2\, often with addition of H\sub 2\ to achieve acceptable surface morphologies. We find that under high ion density conditions gases such as SF\sub 6\, ICl, IBr and Cl\sub 2\ produce smooth surfaces which are free of hydrogen passivation effects. Etch rates in excess of 2,000\Ao\/min are achieved in Electron Cyclotron Resonance SF\sub 6\/O\sub 2\ or SF\sub 6\/Ar discharges with low additional rf chuck powers (100-150W). The rates are somewhat lower with Cl\sub 2\, I\sub 2\ or Br\sub 2\ chemistries. Ion-induced damage is evident from Hall measurements for SiC exposed to rf powers >150W under ECR conditions and >250W under reactive ion etch conditions. A major annealing stage is evident at ~700/super o/C, with an activation energy of ~3.5eV, but there is significant damage remaining even after 1050\super o\C annealing. Hydrogen passivation is a problem only in p-type SiC, and is removed by annealing at 400-450\super o\C under N\sub 2\ ambients. This is strongly correlated with SIMS measurements on deuterated samples annealed at different temperatures.
EM-WeP-8 Damage Investigation in AlGaAs and InGaP Exposed to High Ion Density Ar and SF/sub 6/ Plasmas J. Lee, K. Lee, R. Stradtmann, C. Abernathy, S. Pearton (University of Florida, Gainesville); W. Hobson (Bell Laboratories) Both electrical and optical properties of AlGaAs and InGaP were changed by exposure to high density Ar and SF/sub 6/ plasmas. Capacitance-Voltage measurements, photoluminescence and sheet resistance measurements were used to characterize the degradation of the materials caused by the plasmas as a function of microwave power, rf power, exposure time and chamber pressure. The results showed n-type InGaP suffered more damage than p-type InGaP by the Ar plasmas, while the reverse was true for AlGaAs. Annealing of the damaged semiconductors needed high temperature (for example, ~750/super o/C for InGaP), which is not suitable for typical III-V semiconductor processing because the high temperature may cause thermal degradation. Electron cyclotron resonance SF/sub 6/ plasma produce more surface states than reactive ion etching (i. e. rf power only) condition. Both C-V measurements and photoluminescence data showed rf power (>50W) and pressure(< 2mTorr) to play main roles in introducing electrical and optical degradation of both AlGaAs and InGaP under ECR condition, while there was little change as a function of rf power in the RIE case. Minimal overetching time of SF/sub 6/ plasmas is necessary to avoid severe damage in the materials during opening the windows for the active semiconductors from photoresist, dielectric or metal layers.
EM-WeP-9 High Resolution Electron Energy-Loss Spectroscope Study of Clean and Hydrogenated MBE-grown GaAs(111)A and GaAs(111)B Surfaces J. Wu, G. Lapeyre (Montana State University) The polar GaAs(111) surfaces are of interest because they can occur in novel electro-optic devices and as "side walls" in patterned device structures. Well controlled Molecular Beam Epitaxy (MBE) grown surfaces need to be used for surface studies instead of sputter etched and annealed surfaces. MBE grown GaAs(111)A and GaAs(111)B surface are transferred into UHV for investigation with High Resolution Electron Energy-Loss Spectroscope (HREELS), X-ray Photoemission Spectroscope (XPS), Ultra-violet Photoemission Spectroscope (UPS), and Low Energy Electron Diffraction (LEED). The Si-doping produces p-type material for GaAs(111)A growth and n-type for GaAs(111)B growth, and both surfaces have a 2x2 reconstruction. The HREELS results from the clean A and B surfaces show the same Fuchs-Kleiwer surface optical phonon energy at 35.5 meV, but different free carrier loss plasmon features because of different properties for holes and electrons. The HREELS spectra for the atomic hydrogen exposed B surfa ce has both As-H and Ga-H stretch mode losses, while only Ga-H stretch mode appears in the spectra of GaAs(111)A. The latter can be explained by the Ga-vacancy buckling model. From the HREELS and XPS data, it is found that hydrogen exposed B surface shows As erosion, but it does not occur on the GaAs(111)A surface. Neither surface prepared by sputter etch and annealing showed erosion.
EM-WeP-10 Hydrogen Molecules in Crystalline Silicon Treated with Atomic Hydrogen Studied by Raman Spectroscopy N. Fukata, S. Sasaki (University of Tsukuba, Japan); K. Murakami (University of Tsukuba., Japan); K. Ishioka, M. Kitajima (National Research Institute of Metals, Japan); S. Fujimura (Fujitsu Ltd., Japan) We present the first observation of hydrogen molecules in crystalline silicon by using Raman scattering spectroscopy. Hydrogenation was performed by exposing samples at 333-873K to hydrogen atoms from a hydrogen plasma. We observed a Raman line at around 4155 cm\sup -1\ for the samples after the hydrogen atom treatment at 473-873K (Figure). This is the vibrational line of the hydrogen molecule. A rotational line of the hydrogen molecule was also detected. The vibrational line of the deuterium molecule was observed at around 2990 cm\sup -1\ for the samples treated in a deuterium plasma. The results demonstrate the existence of hydrogen molecules in crystalline silicon. INSERT FIGURE HERE
EM-WeP-11 XPS and ISS Analysis of (NH\sub 4\)\sub 2\S\sub x\- and Ethanethiol- Treated InP (100) Surfaces G. Herdt, M. Al-Jassim (National Renewable Energy Laboratory) Surface passivation and stabilization of InP remains an important issue in fabrication of devices with this material. Treatment of InP surfaces with sulfur-containing compounds appears to be a promising means of passivating the surface, but many details of the surface chemistry of these systems remain unreported in the literature. In the present work, x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to characterize InP (100) surfaces treated with (NH\sub 4\)\sub 2\S\sub x\ and ethanethiol. XPS core level spectra and valence bands for these systems are quite comparable, indicating a similar surface chemistry and suggesting that alkanethiols may provide an alternative means of passivating the InP surface. Further evidence of the similarity of these systems is provided by ISS compositional depth profiles of the near surface region. The stability of InP treated with these compounds is also discussed.
EM-WeP-12 Characterisation of a High Intensity Hydrogen Plasma for Materials Processing. G. Brussaard, G. Brinkman, P. van de Ven, M. Sanden, J. van der Mullen, D. Schram (Eindhoven University of Technology, The Netherlands) A cascaded arc plasma is used as a remote source for plasma treatment of solid state materials. The ion and electron densities as well as temperatures are determined by Langmuir probe measurements. Microwave interferometry measurements are performed as a double check on the probe measurements. Two photon Laser Induced Fluoresence and active actinometry are performed to determine neutral atom densities. Since ion temperatures are low (0.1-1 eV) and no substrate bias is applied, no io-induced substrate damage is expected. To verify this, AFM is used to measure the surface roughness of crystalline silicon before and after plasma treatment. To rule out possible pollution of the plasma by tungsten or copper from the plasma source diamond and crystalline silicon samples are investigated after exposure to the plasma. RHEED and SIMS measurements are carried out to determine the effect of pollution on the surface of the samples. Results show that ion densities in the plasma can be varied between 10\super 15\ and 10\super 18\ m\super -3\. Temperatures are low (0.1-1 eV). Neutral atom densities up to 10\super 21\ m\super -3\ have been achieved. No significant surface damage or pollution is detected.
EM-WeP-13 UV Laser Induced Formation of Silicon Dioxide Films from R-silsesquioxane J. Sharma, D. Berry, R. Composto, H. Dai (University of Pennsylvania) We have found that when spin-coated films of R-silsesquioxane (ClCH\sub 2\CH\sub 2\SiO\sub 1.5\) on Si (100) are irradiated by pulsed UV laser (193 nm), they undergo transformation to silicon dioxide with very small amounts of residual carbon, hydrogen, and chlorine. It has been found previously by Berry et. al. that spin-coated films of R-silsesquioxane on Si(100) transform to silicon dioxide when annealed at a temperature of 300-400 degrees C. The first question that we addressed in our study was whether the UV laser-induced process was photochemical or thermal. After resolving this, we focussed on the mechanism of the process; whether it was due to direct absorption in which the thin film molecules are directly excited and undergo chemical reaction, or if it was substrate mediated in which the substrate molecules absorb the incident light efficiently and then dissipate the absorbed energy in some form to the thin film molecules, which then undergo chemical transformation. In our investigation, we utilized various techniques such as Rutherford Backscattering spectrometry, Ellipsometry, Infrared and UV-VIS optical absorption. We compared the previously reported thermal process with the photochemical process in terms of carbon content, refractive index, and change in thickness of the thin films.
EM-WeP-14 Interface Engineered SiN\sub x\/InP/InGaAs HIGFET Technology M. Tazlauanu, J. Currie, A. Yelon, R. Masut, S. Chetlur, P. Mihelish (Ecole Polytechnique Montreal, Canada) In the past few years there has been considerable interest in developing InP/InGaAs Heterojunction Insulated Gate (HIG)FET for microwave and photonic applications. MIS like structures, using dielectrics such as SiN\sub x\, has been hampered by a large density of traps at InP/insulator interface. Recently, it has been shown that an ultra thin (10-50 \Ao\) Interface Control Layer (ICL) at the insulator/semiconductor junction can be used to engineer device quality low trap interfaces with good uniformity and reproducibility. Our group has developed a robust photo electrochemically induced In-S monolayer coverage. We have investigated the physics of formation of these layers, identified the mechanism of trap reduction/passivation and studied the characteristics of the interface engineered ICL MIS structures. XPS and electrochemical studies show the illumination dependence of the S coverage, explained by charge transfer interactions at the InP/electrolyte interface. The In-S layers reduce trap densities to the low 10\super 11\ cm\super -2\eV\super -1\. range and result in completely "unpinned" C-V behavior in bulk n-InP indirect plasma SiN\sub x\ MIS structures. Doped channel ICL SiN\sub x\/InP/InGaAs/InP HIGFETs have been fabricated and show excellent drain I-V characteristics with transconductance of 150 mS/mm and measured current gain cut-off frequency of 5-10 GHz. We have constructed simple integrated circuits using these devices such as buffer amplifiers with a gain of 7-10 dB at 3 GHz and sample and hold circuits that operate at 2 GHz clock frequency.
EM-WeP-15 SIMS Study of Silicon Surface Preparation and the Polystrene/Silicon Interface Y. Strzhemechny, R. Kumar (Queens College of CUNY); J. Schachter (Bronx High School of Science); S. Schwarz (Queens College of CUNY); M. Rafailovich, J. Sokolov (State University of New York, Stony Brook) We routinely employ secondary ion mass spectrometry (SIMS) to obtain depth profiles in polymer films on silicon substrates. Deuterated polymer blend components are typically used to monitor diffusion, segregation, and ordering (with a depth resolution of ~10 nm) within the film and at the silicon surface. In some cases, the diffusion and segregation behavior near the silicon surface is influenced by the extent of surface oxidation. There is also concern that remnant moisture on the surface may influence the redistribution of blend components. We therefore investigate here the effect of standard cleaning procedures on the polystyrene/silicon interface. Deuterated etches are employed to allow us to detect remnant moisture from the cleaning/etching steps, and to indicate the level of hydrogen termination at the silicon surface. Samples are annealed for various times, after the silicon is spin-coated by polystrene, to examine the motion of constituents from the interface. The SIMS data indicate that the surface is effectively terminated by approximately one monolayer of hydrogen after an HF etch step, and by a thin oxide layer after an HCl/peroxide etch. There is no evidence of remnant moisture. Interfacial deuterium and oxygen are stable under the annealing conditions employed (up to 190 C in vacuum). SIMS results also indicate a thin fluorine rich layer just below the silicon surface. The redistribution of deuterium, oxygen, and fluorine under a variety of etching and annealing conditions will be reported. The results are largely in accord with recent surface vibrational studies of silicon wafer cleaning.
EM-WeP-16 Control of Fermi-Level Pinning in Dry Etched (100) GaAs using In Situ Chlorine Passivation O. Glembocki (Naval Research Laboratory); K. Ko, E. Berg, S. Pang (University of Michigan); C. Stutz (Wright Patterson Laboratories) #The electronic properties of processed GaAs depend critically on the nature of the Fermi-level pinning at the surface. It is known that the pinning can be modified by changing the surface stoichiometry. In this study, we have used photoreflectance spectroscopy in combination with Auger electron spectroscopy to study the behavior of the Fermi-level pinning in (100) GaAs that is etched using an electron cycltron resonace (ECR) source and subsequently passivated in-situ with low energy energy reactive chlorine species. We show that in samples etched by ECR and exposed to ambient conditions, the Fermi-level pins near mid gap. We also observe that the midgap pinning is associated with the presence of excess As at the GaAs/oxide interface. In-situ exposure of the etched surfaces to low energy atomic chlorine is shown to signficantly reduce the Fermi-level pinning in p-GaAs. This reduction is associated with reduced As at the GaAs/oxide interface. These results clearly show that the Fermi-level pinning in ambient GaAs depends on the stoichiometry of the GaAs/oxide interface and that it can be controlled through chemical means. Our results for the Fermi-level pinning and it's changes will be discussed in terms of existing models for the Fermi-level pinning at surfaces and interfaces.
EM-WeP-18 Surface Chemistry of N-containing Precursor Dimethylhydrazine on Cu Y. Sun, J. White, A. Kamath, D. Kwong (University of Texas, Austin) Driven by microelectronics technology, CVD processes for copper metallization are being sought. One hurdle to their use is the propensity of copper to diffuse into neighboring materials. Nitrides, such as TiN and TaN, form good barrier layers inhibiting copper interdiffusion. Thus, many different CVD routes to nitrides are under investigation. This paper focuses on the surface chemistry of an N-containing precursor, dimethylhydrazine (DMH) on Cu. DMH both adsorbs and decomposes on clean Cu at room temperature. N-N, C-N and N-H bonds are cleaved resulting in the immediate desorption of N\sub 2\, H\sub 2\ and CH\sub 4\ and leaving DMH species that, during subsequent heating, lead to N\sub 2\ and CH\sub 4\ desorption. There is evidence that CH3 groups dehydrogenate to form methylene, CH2, which inserts into C-N bonds and leads to C\sub 3\H\sub 8\NH\sub 2\. Some of the latter undergoes beta-hydrogen elimination to form C\sub 3\H\sub 6\NH\sub 2\. The 300 K reactivity of a clean Cu surface is reduced by repeated CMH doses and temperature programmed desorption (TPD); under passivated conditions, no products desorb during DMH adsorption and, in TPD after DMH adsorption, parent desorption dominates, but there are additional products. At dosing temperatures above 400 K, DMH decomposition is evidenced during adsorption, but the decomposition pathway differs from that on the clean surface. Passivation is attributed to the alteration of active surface sites by small amounts of retained reaction products, presumably containing C, the concentration of which lie below XPS detection limits. The passivated surface exhibits a stable, but low, reactivity. The initial clean surface reactivity is recovered by heating to 900 K or higher. Preliminary results demonstrate TiN film growth, using TiCl\sub 4\ and DMH as precursors, at temperatures between 600 and 700 K. Supported by the National Science Foundation Science and Technology Centers Program, CHE8920120.
EM-WeP-19 Solution and Gas-Phase Sulfide Passivation of GaAs(110) Surface B. So, R. kim (The Chinese University of Hong Kong) # Recently, gas-phase polysulfide passivated GaAs(110) surface was studied and a sulfide assisted reordering process was observed (JVST A14 May/Jun 1996). Unlike the solution-phase treatment, which involves the dissolution/etching step, the gas-phase treatment is a surface adsorption/reaction process. The reaction mechanisms in both gas- and solution-phase treatment are therefore expected to be different. Hence, the present study aims at comparing the surface morphology and chemical structures of solution sulfide and gas-phase polysulfide treated GaAs(110), using in-situ low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, UHV scanning tunneling microscopy, air scanning force microscopy and thermal desorption. Both treatments were performed in a nitrogen glove box that connected directly to the loadlock of the UHV multi-technique system. Oxygen was unavoidably present on the solution treated surface but it was not observed on the gas-phase treated surface by XPS. Because of the dissolution/etching step in the solution treatment, the solution treated surface was less smooth than that of the gas-phase treatment. The dissolution of As in the solution treatment also gave a relative low surface As/Ga ratio (0.8) while that of the gas-phase treated surface had a 1:1 ratio. A diffused oblique LEED pattern could be observed directly on the solution treated surface while such a pattern could only be observed on the gas-phase treated surface after annealed to 400oC (with As/Ga ratio = 0.9). The differences of surface As/Ga ratio and smoothness suggested that the gas-phase treatment gave a more ordered surface.
EM-WeP-20 Compositional Characterization of Very Thin SiO\sub 2\/Si\sub 3\N\sub 4\/SiO\sub 2\ Stacked Films by XPS and TOF-SIMS Techniques S. Santucci, L. Lozzi, M. Passacantando, L. Ottaviano (Universit\ag a\ dell'Aquila, Italy); G. Moccia, R. Alfonsetti (Consorzio Eagle - Texas Instruments, Italy) Thin film structures with thickness less than 10 nm composed by stacked layers of SiO2/Si3N4/SiO2 were grown onto silicon wafers by thermal oxidation and Chemical Vapour Deposition (CVD). The effects of the sintering in hydrogen ambient of the whole structure have been studied performing depth profiles by ion gun bombardment and using the X-ray Photoelectron Spectroscopy (XPS) and the Time Of Flight-Secondary Ion Mass Spectroscopy (TOF-SIMS) to obtain the compositional data of the films. The results, for this kind of ultrathin multilayers, have evidenced that if we adopt to quantify the XPS results the "Auger parameter method", we obtain an available sensitivity to evidence the changes on the silicon oxide composition at the Si/SiO2 interface of the investigated layers, imputable to the sintering in hydrogen. Moreover, with this method we obtained a considerable depth resolution improvement with respect to the conventional depth profiling techniques without any problem of anomalous diffusion, which on the contrary affects the SIMS measurements. The work to relate the electrical performances of these multilayered insulating structures with their composition was also done.
EM-WeP-22 A Comparison between UPS and RHEED Intensity Oscillations during Si Epitaxial Growth on Si(100) Y. Enta, H. Irimachi, M. Suemitsu (Tohoku University, Japan); N. Miyamoto (Tohoku Gakuin University, Japan) We have recently reported that the ultraviolet-photoelectron- spectroscopy (UPS) intensities from the surface state of Si(100) periodically oscillate during Si growth using either Si\sub 2\H\sub 6\ gas or Si solid source. Because the photoelectron-energy dependence of the amplitudes of these oscillations agreed well with a difference UPS spectrum between 2x1 and 1x2 clean surfaces, the UPS intensity oscillation was ascribed to the alternation between the 2x1 and the 1x2 surface reconstructions during the growth. This paper describes a comparative study between the UPS and the reflection high-energy electron diffraction (RHEED) intensity oscillations, and presents a more direct support for this interpretation. Well-defined single-domain surfaces were prepared by depositing a Si buffer layer and by repetetive annealings at 1000 C. The epitaxial growth of Si was conducted using Si\sub 2\H\sub 6\ gas. Clear RHEED intensity oscillations wsere observed at gas pressures between 5x10\super -8\ and 1x10\super -6\ Torr, and at substrate temperatures between 450 and 600 C. The oscillation period of the half-order diffraction spots were twice as long as that of the specular-beam spot. As is generally known, this is due to the fact that the half-order oscillation reflects the alternation of the surface reconstructions between 2x1 and 1x2, which provides a period corresponding to two-monolayer growth. The period of UPS intensity oscillation was found to be in good agreement with that of the half-order diffraction spots under the same growth conditions. This result strongly supports our previous proposal that the UPS intensity oscillation originates from the alternation of the surface reconstructions.

Time Period WeP Sessions | Topic EM Sessions | Time Periods | Topics | AVS1996 Schedule