Abstract: Au–W(Ti)/n‐GaAs diodes were constructed for the purpose of examining the thermal stability of the metal–GaAs interface and the integrity of the W(Ti) diffusion barrier. The evaluation procedure consisted of using measurements of the Schottky barrier height and other electrical parameters as a function of annealing temperatures. Barrier heights, Vb(Io), determined by measurement of the zero voltage current intercept, Io, were found to increase with annealing temperatures up to 600°C. Values determined by the measurement of forward current activation energies were in agreement with Vb(Io) up to 500°C. Above 500°C, however, this method was not applicable, due to the onset of excess forward current at low voltages. This current was accompanied by evidence of gold interdiffusion, compensation, and high electric field strength in the depletion layer. Direct identification of the excess current source, however, was not accomplished.

Abstract: Thin film structures comprising a layer of aluminum and a material having a tendency to interact with aluminum are separated by an intermediate layer of aluminum having a high aluminum oxide content. The intermediate layer prevents said interaction by acting as a diffusion barrier. Preferred embodiments are directed to silicon semiconductor metallization structures, including Schottky barrier contacts, which comprise a bottom layer of tantalum, or other transition metal, or a metal silicide in contact with a silicon substrate, an intermediate layer of aluminum having a high aluminum oxide content and a top layer of aluminum. The intermediate layer functions as a diffusion barrier between aluminum and the metal, metal silicide or silicon. The preferred embodiments of the invention also includes the process for forming such structures preferably comprising: depositing pure tantalum under high vacuum in evaporation apparatus, substituting aluminum for tantalum in the evaporation apparatus and bleeding-in water, air or oxygen to form the aluminum oxide-rich intermediate aluminum layer and then returning to the high vacuum to deposit pure aluminum. The invention is also applicable to FET or CCD structures where a diffusion barrier for aluminum is required.

Abstract: The ORMAK vacuum liner is constructed of stainless steel, overcoated with a thin platinum diffusion barrier and a final layer of gold. Gold was selected as the vacuum surface because it is chemically inert to the adsorption of common gases. However, gold surfaces do adsorb hydrocarbons, and carbon (along with oxygen) was the principal plasma contaminant during the first two years of ORMAK operation. Upon switching discharge cleaning gases from hydrogen to oxygen, carbon levels dropped until carbon is no longer a significant contaminant. Residual hydrocarbons can now be controlled by either hydrogen or oxygen discharge cleaning. The principal measured plasma contaminant in ORMAK is now oxygen. Samples taken from the ORMAK liner and analyzed by Auger electron spectroscopy reveal the presence of iron and oxygen. There is evidence from a SXAPS (Soft X-ray Appearance Potential Spectroscopy) probe of iron and chromium diffusion from the stainless steel through the gold surface in spite of the platinum diffusion barrier. The Fe and Cr provide surface oxidation sites, and SXAPS analysis shows that these metals exist as oxides. In order to investigate tokamak impurity problems further, the ISX (Impurity Study Experiment) tokamak is presently under construction. It will provide a cleaner and more flexible vacuum system in which to conduct studies of surfaces and plasma impurities. The operating characteristics will be much the same as those of ORMAK (with ohmic heating) in terms of size, plasma current, and plasma temperature.

Abstract: The process according to this invention makes it possible to produce a silicon nitride diffusion barrier on a semiconductor substrate, such as III-V semiconductor substrate and particularly a GaAs substrate, the produced diffusion barrier being efficient at temperatures as high as 900° C during a long period. It comprises the following steps: (a) chemical deoxidation of the substrate, (b) thermal treatment at 400° C, (c) 1st cathode sputtering step in a nitrogen atmosphere with a cathode made of silicon, (d) ionic etching to reduce the thickness of nitride layer produced in c), (e) 2nd cathode sputtering step similar to the first one. It is useful for III-V semiconductors having to be treated at high temperature, as for instance to be annealed after ion implantation.

Abstract: Carbon fibers in contact with nickel suffer a pronounced loss of strength at temperatures above 600°C as a result of surface attack by the nickel (at temperatures of 800–900°C and treatment times of 10–20 h) or recrystallization (during heating for more than l h at 1000°C). There is no unique correlation between fiber structure and strength. A zirconium nitride coating fails to prevent carbon fibers from reacting with nickel. A titanium carbide coating reduces, even at high temperatures, the strength loss experienced by carbon fibers by decreasing the rate of dissolution of the material of the fibers in nickel and by slowing down the fiber recrystallization process.