Gary A. West

Chemical vapor deposition of cobalt silicide

We have deposited polycrystalline cobalt silicide films by chemical vapor deposition using Co2(CO)8 or HCo(CO)4 as the Co source and SiH4 or Si2H6 as the Si source. The Co:Si ratio of the films is controlled by changing the deposition temperature, and CoSi2 stoichiometry is obtained at 300 °C using SiH4 or at 225 °C when Si2H6 is the Si precursor. Carbon or oxygen contamination of the films is <0.5 at. % at deposition temperatures above 200 °C. Resistivities of films deposited near CoSi2 stoichiometry are typically 200 μΩ cm and drop to 40 μΩ cm upon annealing at 900 °C.

CO2 laser‐induced chemical vapor deposition of titanium silicide films

We have developed a CO2 laser‐induced chemical vapor deposition (CVD) process to deposit films of titanium silicide from a gaseous mixture of SiH4 and TiCl4. Such films are suitable for gate electrodes, interconnects, and contacts on present and future generations of very large scale integrated circuits. Films deposited at a 400 °C substrate temperature are amorphous and have a resistivity of 300 μΩ cm. Annealing at 800 °C converts the films to polycrystalline TiSi2 with a resistivity of 20 μΩ cm. The initial film composition can be varied by changing the SiH4/TiCl4 gas ratio. The CO2 laser induces thermal chemical reactions in the CVD reactor. Observed gas phase reaction products are those predicted by thermodynamics.

Excimer laser‐induced chemical vapor deposition of titanium silicide

A pulsed ArF excimer laser has been used to deposit thin conductive films of titanium silicide on silicon and silicon oxide substrates. The films are deposited from a gas mixture of titanium tetrachloride and silane by initiating photochemical reactions near the heated substrate. The resistivity, composition, crystal structure, and morphology of the films vary as a function of gas composition and substrate temperature. Films deposited at 400 °C, with SiH4/TiCl4 mole ratios of ∼2, have resistivities of 300 μΩ cm, which drop to 20–30 μΩ cm on annealing at 650–700 °C. At higher deposition temperatures (450–550 °C) the films have resistivities of ∼110 μΩ cm and show similar annealing behavior. The as‐deposited films are a mixture of amorphous and a metastable Ti‐Si crystalline phase. On annealing they convert to polycrystalline TiSi2. Films deposited at 400–450 °C are smooth and show conformal step coverage. The film roughness increases at higher deposition temperatures.

A comparison of the Eu3+ temperature dependent emission lifetimes in Sc2O3, Y2O3 and Gd2O3 host crystals

Abstract Emission lifetimes have been measured for europium-doped crystals of cubic scandia, yttria and gadolinia from room temperature to 1000°C. The temperature dependence of the lifetimes were accurately fit with an energy gap model.

Boron Diffusion In Silicon From Ultrafine Boron-Silicon Powder

A CO2 laser pyrolysis technique has been used to prepare ultrafine (< 0.1p diameter) boron-silicon powders with different boron concentrations. These powders have been used as a spin-on boron diffusion source for silicon wafers. The spin-on colloidal suspension is prepared by mixing the powder with a thermally degradable polymer binder, polymethyl-methacrylate (PMMA), and an organic vehicle, cyclohexanone. Thin, uniform films are spun-on using a standard photoresist spinner. Two different procedures are followed in diffusing the boron from the boron-silicon powder. In the first process, the boron is diffused by heating the wafer in an argon ambient (1000-1260°C). The excess dopant layer is removed by oxidation (02) and subsequent etching (HF). In the second process, the powder is first converted to a borosilicate glass layer by oxidation, followed by diffusion in an argon ambient. Some experiments using commercially available boron nitride powder as a diffusion source are also discussed.

Laser-Induced Deposition of Gold Micropatterns from Metallopolymer Thin Films: A Photochemical Approach

The deep ultraviolet (250 nm) photopatterning of spin-on films of polymeric Au mercaptide results in formation of adherent Au patterns. Fxcimer laser projection patterning and standard contact printing techniques give excellent pattern resolution on the micron scale. Laser direct write produces lines at very fast writing speeds. Exposed areas are less soluble than unexposed areas, i.e. the film behaves as a negative photoresist. Bakeout of developed patterns at 250°C yields good purity Au micropatterns up to 500 A thick. Mechanistic information about pattern formation is gained from uv-visible, infrared, and mass spectrometric monitoring of the photolysis process, and from Auger analysis of films. Adherent patterns are apparently formed by photochemical cleavage of Au-S bonds followed by evaporation of a small amount of free mercaptide. The loss of ligand in the exposed areas renders them less soluble than unexposed film. Thermal decomposition of both photolyzed and unphotolyzed films has the same result of volatilizing all film material except Au.

Titanium silicide ultrafine powder: CO2 laser generation and thin-film applications

A continuous wave carbon dioxide laser has been used to produce ultrafine (∼50 nm) titanium silicide powder by homogeneous nucleation from the gas phase of a mixture of titanium tetrachloride and silane. Depending on the process conditions, titanium subhalides (TiCl3, TiCl2) and silicon are also present in the powder. Thin films (1– 4 μm) have been prepared on alumina and silicon substrates by spraying a suspension of the powder on the substrate and subsequently sintering it in vacuum. Dense films can be prepared by sintering powders containing 25– 40 wt. % excess silicon at 950–1050 °C. The resistivity which has been achieved after densification of 2– 4‐μm‐thick films is 80–90 μΩ cm.