Response surface modeling of high pressure chemical vapor deposited blanket tungsten

Abstract

Chemical vapor deposited (CVD) blanket tungsten has been studied at high pressure (80 Torr) in a single-wafer cold wall reactor using response surface modeling methods. Deposition factors studied include temperature (430–490 °C), H2 partial pressure (6–30 Torr), WF6 partial pressure (1–2 Torr), and the gas inlet to wafer surface separation (200–600 mils). Quadratic models were generated for deposition rate, resistivity, sheet resistance uniformity, film stress, step coverage, reflectance, and WF6 conversion. The models were examined for consistency with previously reported results for CVD tungsten films, and were used to construct contour plots that aided a deposition process optimization search for a plug application. Optimization requirements for step coverage and sheet resistance Rs uniformity resulted in significant constraints on the usable factor space, while requirements for deposition rate, resistivity, stress, WF6 conversion, and reflectance were largely met throughout the original factor space. The resulting optimized factor space was found to be relatively large and offered additional opportunities for fine tuning of the process. Finally, data from replicated trials showed the high pressure CVD blanket tungsten process to be highly reproducible.