Stress Effects in Boron‐Implanted Polysilicon Films

Abstract

Polycrystalline silicon films are used throughout the semiconductor industry in the fabrication of both metaloxide-semiconductor (MOS) and bipolar products. For example, in MOS products, doped polysilicon is used for gate and interconnection materials. In bipolar products, polysilicon is used for device isolation, passive resistors, or active base elements. While these films are usually used with different ranges of doping, stress measurement of doped polysilicon is not well reported. Earlier reports of thick (up to 500..mu..m) intrinsic polysilicon films gave tensile stress properties. Later reports using thinner films (4000-6000A) showed compressive stress properties. The thinner films were deposited under different conditions than the thick films, and were both intrinsic and boron diffused. The purpose of conducting this study was to determine quantitative stress measurements made on boron-implanted and annealed polycrystalline films to assess the possible effect of stress on device fabrication, such as pattern distortion and change in the electrical property of a substrate. Comparative warpage measurements were made treating various film structures as substrates. The effect of doping concentrations and annealing temperatures on the film stress was also studied. Film stress was determined using comparative warpage measurements on oxide, polysilicon, and nitride films.