Tungsten

About: Tungsten is a research topic. Over the lifetime, 35225 publications have been published within this topic receiving 456213 citations. The topic is also known as: W & element 74.

Properties of low-pressure CVD tungsten silicide for MOS VLSI interconnections

Abstract: Low-pressure chemical vapor deposition of tungsten silicide has been done and the properties of the deposited films have been studied to determine the process compatibility and suitability to form gate electrodes and interconnections in MOS VLSI applications. The silicide was deposited on single-crystal silicon and on oxidized silicon with and without a coating of polycrystalline silicon film. Auger analysis of the As-deposited films showed absence of any contaminants in it. X-ray diffraction and transmission electron microscopy showed that As-deposited films were microcrystalline with grains smaller than 30 A and upon annealing became polycrystalline WSi 2 with hexagonal structure at 500°C and tetragonal structure at or above 600°C with a corresponding decrease in resistivity from 600-900 µΩ . cm to 35-60 µΩ . cm depending upon anneal temperature and time. No appreciable change in the thickness of the silicide was found during the high-temperature anneals. Silicon-rich silicide films remained stable, smooth, and free of cracks through high-temperature anneals and oxidations, and their adherence to the wafer remained excellent. On the other hand, metal-rich films had overall inferior properties. Thermal oxidation of WSi 2 on polysilicon in dry oxygen in the temperature range of 900 to 1100°C was found to be similar to that of silicon except the linear regime of oxidation was extremely rapid and the entire process could be modeled by a parabolic equation X^{2) = Bt with an activation energy of 1.7 eV. MOS capacitors were fabricated with silicide and polycide gate electrodes. Polysilicon thickness variation from 0 to 5000 A had no adverse effect on the electrical characteristics or mechanical integrity of the devices. In all cases, low values of N f (1 × 1010-7 × 1010cm-2) and N it ( \sime 8 MV/cm) were obtained.

In situ stress measurement of refractory metal silicides during sintering

Abstract: The stress of thin film tantalum silicide, titanium silicide, and tungsten silicide was measured in situ during sintering. These refractory metal silicide films were cosputtered on oxidized silicon, quartz, and sapphire substrates. The films were heated to 910 °C, annealed for 30 min, and cooled down to room temperature. Throughout the heat treatment cycle, the film stress was measured at short intervals by measuring the curvature of the film/substrate couple with a laser beam. It was demonstrated that the intrinsic stress of these silicides is negligible at 910 °C. The final room temperature stress of these silicides, after high temperature sintering, is mainly thermal stress which originates from the difference in thermal expansion coefficients between the films and the substrates. The final stress ranged from 8×108 to 2×109 Pa depending on the silicide and the substrate material. The biaxial elastic moduli were found to be 3.4×1011 Pa for TaSi2.4, 3.9×1011 Pa for TaSi1.4, and 2.2×1011 Pa for TiSi2.4. T...