Abstract: The continued increase in the cost of precious metals such as palladium and gold has stimulated increased interest in the development of lower cost, but equally reliable, substitutes for noble metal thin film conductor systems such as Ti-Pd-Au. This paper discusses a Ti-Cu-Ni-Au (TCNA) substitute which eliminates the use of Pd and reduces the thickness of gold necessary for a .005 ohms per square sheet resistance from 5µm to \leq 2µm. The reduction in gold thickness can result in considerable cost savings. The TCNA films were deposited by plating, i.e., electron gun evaporation of Ti and Cu followed by the plating of Cu-Ni-Au. The results of TCNA film aging and resistor aging with TCNA at 150°C and 250°C, bondability, adherence, corrosion resistance in air + dry and wet (5% RH) HCl, SO 2 , and NO 2 environments, solderability, and humidity testing (85°C, 85% RH) under bias for encapsulated and unencapsulated TCNA conductors have been found to be comparable to the Ti-Pd-Au system. Nickel in the range of 1 µm if non-porous is a barrier to the diffusion of copper to the gold surface at the temperatures (150-350°C) and times of interest in bilevel Hybrid Integrated Circuit (H lC) fabrication. In addition to its role as a diffusion barrier, nickel also acts as a corrosion inhibitor like Pd in the Ti-Pd-Au system.

Abstract: The strengths of thermocompression bonds made between gold plated copper lead frames and gold metallized thin film circuits decrease in time when aged at 200-300°C in air or vacuum unless there is a diffusion barrier (such as nickel) between the copper and gold. After pulling bonds to destruction, failure modes and failed surfaces were characterized by scanning electron microscopy, Auger spectroscopy, electron microprobe, stylus probe, and X-ray diffraction. The failed surface on the substrate side of the bond was very rough, appearing to consist of "mountains" of almost pure Cu resting on a relatively smooth layer of grains, identified as Cu 3 Au, where the Cu 3 Au regions were Visible in the valleys between the copper mountains. The mating failed surface on the lead side of the bond was similarly rough, but with only a few scattered grains of Cu 3 Au evidently pulled out from the opposite surface. Oxidation, pore formation (Kirkendall effect), and ordered phase formation were considered as possible mechanisms for the degradation. Oxidation was ruled out by the observation that bonds degraded as fast in vacuum as in air. Ordered phase formation was judged more likely than pore formation as the primary mechanism. A parameter, \tau , to describe the time required for measurable degradation was defined as the time for the average 90° peel strength of a 0.25 X 0.75 mm lead to decrease from six or seven pounds to four pounds. This parameter was found to be temperature activated with an activation energy of 0.8 eV. Since ordering and pore formation are both dominated by interdiffusion, \tau was extrapolated to lower temperatures using the diffusion coefficient measurements of Pinnel and Bennett, resulting in a value of ten years at 50°C. However, with a 5000A ± 2500A nickel diffusion barrier between the copper lead and the gold plate, the value of \tau extrapolated to 50°C was considerably greater than 40 years, as desired in Bell System equipment.

Abstract: Using Schottky barrier measurements on n−GaAs diodes metallized with Au/W and Pt/W films, we have shown that thin films of W (∼3000 A) offer an excellent barrier to diffusion of both Au and Pt atoms at temperatures up to 500 °C. These properties of W are utilized in a Schottky barrier metallization scheme consisting of Au/W/(PtGa/PtAs2)/n−GaAs, where (a) the thin sintered Pt layer provides a large φB (due to PtAs2 at the GaAs interface) and a metallurgically stable conductor−semiconductor interface, (b) the W layer acts as a diffusion barrier, and (c) the outer Au layer provides thermocompression bondability.

Abstract: Steel is the most economical substrate for the deposition of silicon. At temperatures used for the chemical vapor deposition of silicon, however, a barrier layer must be used to prevent the diffusion of iron from the substrate into the silicon layer. Tungsten was found to be ineffective as a diffusion barrier when silicon was deposited by the thermal decomposition of silane at 900/sup 0/C and above. Borosilicate deposited by the oxidation of a silicon-diborane mixture was found to be an effective barrier at temperatures up to 1150/sup 0/C. Silicon layers deposited at low temperatures and high rates consist of small crystallites with a strong preferred (110) orientation, while those deposited at high temperatures and low rates consist of larger crystallites with more random orientation. Silicon p--n junctions deposited on borosilicate/steel substrates show poor electrical characteristics because of the high concentration of grain boundaries, and solar cells have low conversion efficiencies.

Abstract: A diffusion barrier and separation substance for metal parts which adjoin each other in an oxygen-free, inert and preferably a helium-containing atmosphere such as used in a closed-cycle high temperature reactor or gas turbine comprises first and second adjoining metal parts with a hexagonal boron nitride placed between said parts. The hexagonal boron nitride is applied to the boundary surface of the metal parts in an aqueous or organic suspension prepared as a pasty, putty-like or brushable liquid substance. The substance contains from 5 to 50% of boron nitride, from 0.5 to 30% of binders and from 2 to 6% of swelling agents and 50 to 90% liquid suspension medium. The suspension medium may advantageously contain an anti-corrosive agent and in addition the formed protective film is burned from 0.25 to 3 hours at a temperature of from 100° to 500° C.

Abstract: 1. A study was made of the oxidation kinetics exhibited by hard alloys with an without titanium nitride coatings during exposure for periods of 30–180 min to an air atmosphere at temperatures of 700–1000°C. 2. It is shown that the growth of scale on unimpregnated VK and TK hard alloy specimens is a linear function of time, and falls with rise in the TiC and Co contents of the alloys. Externally, the scale is cross-shaped, which is indicative of unilateral diffusion of the components of air (oxygen) toward the scale/alloy interface. 3. It has been established that titanonitriding increases the oxidation resistance of a hard alloy, depending on its composition, three- to fivefold when the temperature is raised to 1000°C. On titanonitrided T30K4 alloy no scale formation is observed at any of the oxidation temperatures or duration investigated. This may be due to the creation in the course of oxidation of a TiNxOy diffusion barrier.

Abstract: A radio frequency powered ion plating process was used to apply the diffusion barriers of aluminum oxide, yttrium oxide, hafnium oxide and titanium carbide to a substrate tungsten fiber. Each of the coatings was examined as to its effect on both room temperature strength and tensile strength of the base tungsten fiber. The coated fibers were then overcoated with a nickel alloy to become single cell diffusion couples. These diffusion couples were exposed to 1093 C for 24 hours, cycled between room temperature and 1093 C, and given a thermal anneal for 100 hours at 1200 C. Tensile testing and metallographic examinations determined that the hafnium oxide coating produced the best high temperature diffusion barrier for tungsten of the four coatings.

Abstract: The method of preparing thin films—about 500 to 2000 A thick—by thermal decomposition of organometallic compounds has been applied to produce gold films useful as reflectors or as selective absorbers of radiant energy. In either case the gold films deposited on metallic substrates are stabilised by an intermediate diffusion barrier of refractory oxide which permits operation at elevated temperatures.

Abstract: Reactions in rf sputtered W-Pt-W-A,u films on oxidized and unoxidized Si substrates have been analyzed using a micro-spot scanning Auger spectroscopy and microscopy technique. The analysis shows that the W-Pt-W-Au films on Si substrates have undergone three annealing stages resulting in gold-silicon eutectic formation and migration. Stage I (450°C, 12 hours) was characterized by the formation of Si rich globular regions on the Au film. During Stag,,, II (450°C, 24 hours) the entire unreacted gold film was consumed. Finally, during Stage III (550°C, 24 hourS) gold and the liquid phase eutectic migrated toward the metal-Si interface. For W-Pt-W-Au on oxidized Si substrates, the diffusion barrier of W-Pt-W was observed to be effective up to 550°C tot 24 hours.