A new electron cyclotron resonance (ECR) plasma CVD system has been developed in order to obtain high deposition rates. By using this system, hydrogenated amorphous silicon (a-Si:H) films have been prepared at a deposition rate of 1.0. μ m/min. The utilization efficiency of SiH4 gas is 16% under such conditions. Films prepared at 1.0 μ m/min have high photoconductivity (σ ph) of 10-6 S/cm and low dark conductivity (σ d) of 10-12 S/cm, leading to a high photosensitivity of σ ph/σ d=106. Both high microwave power and high SiH4 gas flow rates are essential to the high rate deposition of sufficiently photosensitive a-Si:H films. Annealing at 300° C improves the photosensitivity up to σ ph/σ d=107.

High and low bandgap amorphous silicon thin film alloys (a-Si:Al, a-Si:Se, a-Si:S, and a-Si:Ga) were prepared by plasma-enhanced chemical vapor deposition. It was found that Al and Ga amorphous silicon alloys are low bandgap materials whereas a:SiS and a:SiSe are high bandgap semiconductors. The optical band gap of these systems could be changed from 1.0 eV to 2.0 eV, depending on the alloying element and its concentration in the film. The dark to light conductivity ratio was measured. The elemental content and distribution was analyzed by the SIMS and EPMA techniques. The results show that some of the amorphous silicon alloys studied are promising materials for multi-bandgap photovoltaic devices.

In glow discharge deposition (GD) of a-Si:H alloys, the concentration of electronically-active defects increases as the incorporation of bonded hydrogen in polymerized dihydride groups, (SiH2)n increases. Since the fraction of dihydride groups increases strongly with decreasing substrate temperature (Ts), the incorporation of these bonding groups can only effectively be reduced by restricting Ts to about 230°C or higher. We have found that a-Si:H films produced by remote Plasma Enhanced Chemical Vapor Deposition (remote PECVD) are qualitatively different than the GD films in the following ways: 1) the amount of bonded hydrogen for Ts > 100°C is less by about a factor of two; and 2) the fraction of polyhydride bonding is also significantly less than the monohydride fraction for Ts > 100°C. We develop a statistical model that provides a basis for translating any process-dependent representation of data for the polyhydride fraction into a universally-obeyed scaling relationship in which the independent variable is [H]. The agreement between the statistical model and the experimental data, replotted as a function of [H], supports our observation that the fraction of polyhydride bonding is not determined simply by Ts, but is a function of the particular reaction pathways in the deposition process chemistry.

Methods to prepare diamond thin films by means plasma chemical vapor deposition are reviewed. The various techniques available to date are compared with respect to their deposition rates, deposition area, quality and homogeneity of the material produced, and their specific advantages and drawbacks. The deposition rates of both thermally induced and plasma induced CVD methods correlate well with the gas temperature in the reaction zone supporting the hypothesis that the large quantities of diamond precursor species necessary for high deposition rates are formed in a hot spot of the deposition system.

The early stages of thin film deposition from the rf glow discharge of SiH4 or SiH4 + NH3 have been studied by analysing the structure of silicon based multiiayers consisting of hydrogenated amorphous silicon (a-Si:H, 10 – 200 A thick) and stoichiometric silicon nitride (a-Si3N4:H, 25 – 250 A) alternating layers. The x-ray diffraction, its rocking curve and x-ray interference of the multilayers have shown that the amorphous silicon/silicon nitride interface is atomically abrupt and the surfaces of the respective layers are atomically flat regardless of substrate materials. This indicates that the precursors impinging onto a substrate from the gas phase homogeneously cover the growing surface and the layer by layer growth proceeds on atomic scale. In the plasma deposition of the covalently bonded semiconductors and insulators, the island formation on a substrate surface at the beginning of the thin film growth is very unlikely.

We have deposited thin films of silicon dioxide, SiO2, and amorphous silicon, a- Si, by remote Plasma-Enhanced Chemical-Vapor Deposition (Remote PECVD), and have extended this process to the deposition of silicon suboxides, SiOx, 0<x<2. Heterostructures, comprised of alternating layers of SiO 2, and SiOx, x∼1, have been deposited by electronically controlling the flow of charged particles from the plasmageneration region into the deposition chamber, without interrupting the flow of process gases. We discuss the electrical properties of these heterojunction structures.

A wide area disc shaped plasma source of 20cm in diameter generated by a ring shaped cathode electron beam is used to decompose Trimethylgallium (TMGa) and Trimethylarsenic (TMAs). Volume photo-absorption of VUV photons and sensitized atom-molecule collisions with excited species and radicals can all assist dissociation of the organometallic feedstock reactants. In addition, the excited radical flux and VUV impingement on the film may also assist heterogeneous surface reactions and increase surface mobility of absorbed species. Mass spectrometry studies using deuterium as a replacement for hydrogen as a trace gas allowed for the elicidation of decomposition pathways of TMGa and TMAs. Byproducts of hydrogen and helium plasmas were also studied.

The native oxides of Ge and GaAs have long been known to preclude the formation of suitable MIS structures. In situ cleaning of Ge and GaAs surfaces has been achieved at 300–375 °C using a novel technique employing hydrogen that is dissociated using a remote Ar discharge. Such a technique circumvents the problems of cross contamination introduced from a directly excited hydrogen discharge due to erosion of the quartz tube walls by the active hydrogen. Reconstructed surfaces characteristic of clean Ge and GaAs surfaces have been observed with Reflection High Energy Electron Diffraction (RHEED) following such a treatment. Auger and X-ray Photoelectron Spectroscopy (XPS) analyses show that such a treatment removes both oxygen and carbon contamination from the surface. XPS window scans on the Ga-3d and the As-3d peaks show that the treatment is successful in removing oxygen bonded to both Ga and As on the GaAs surface.

Following the in situ cleaning, excellent MIS structures on Ge and GaAs have been realized with a novel structure that utilizes an ultra-thin Si interlayer (1.5 nm) between the insulator-oxide and the clean semicondutor surface. The Si interlayer prevents any sub-cutaneous oxidation of the underlying semiconductor while exploiting the advantages of the excellent Si-SiO2 interface. The entire structure is fabricated in a single-chamber remote plasma CVD unit.

We have begun a detailed study of the physical properties of Si3 N4 films deposited at low temperatures using a PECVD process based on dilution of reactive gases with inert carrier gas [1] in order to investigate their feasibility for use as post-implant encapsulants and/or device passivation layers for GaAs. The films and substrates are analyzed by ion channeling, ellipsometry, IR spectrometry, ESR, RBS, and SEM to evaluate implantationinduced substrate and interface damage as well as the films’ optical properties, surface morphology, stoichiometry, uniformity, stress, and electrical trapping characteristics. Following furnace or RTA annealing they are recharacterized, adding SIMS to evaluate As diffusion into the films. Both Schottky and ohmic contacts are then formed and used to measure Hall mobility, trap density and 1/f noise. Preliminary results of these studies are presented and compared with those obtained using other techniques such as wafer-to-wafer As entrapment, arsine overpressure, or conventional CVD.

Thin films of chalcogenide glasses GeSeywere prepared by PECVD for lithographic applications. Their structure and morphology were characterized by EXAFS and electron microscopy. EXAFS studies enabled comparison of the structures of thin films and those of homologous bulk glasses. Morphology studies by SEM and TEM revealed an heterogeneous structure explained by a phase separation: these glasses consist of microdomains whose size varies with the overall GeSey composition.

Surface modifications of thin polyimide films (100–2000 A˚) in downstream microwave CF4/NF3/Ar plasmas and radio-frequency (RF) CF4 plasmas have been studied in situ by Fourier transform infrared (FTIR) reflection-absorption spectroscopy. The downstream microwave plasma treatment produced significant surface fluorination in terms of polyfluorinated alkyl and aryl compounds as well as acyl and benzoyl fluorides. The depth of fluorination was approximately 500 Å. Similar changes in polymer surface functionalities were observed for RF plasma surface modifications, but the depth of fluorination was reduced to 30Å because of ion-bombardment. The interface between the tungsten film and polyimide surfaces has been characterized by ex situ FTIR reflection-absorption technique through the silicon side of Si/polymer/W structures. The observed spectral changes relative to polyimide-gold interfaces were interpreted in terms of interactions of tungsten with functionalities of the polyimde backbone. Tungsten deposited by both sputtering and plasma enhanced chemical vapor deposition (PECVD) showed significant chemical interactions, strongest for PECVD tungsten.