Published online by Cambridge University Press: 22 February 2011
The deposition conditions used to form polysilicon layers are determined to a large extent by the geometry of the reactor used to deposit the films. The structure of the films and the electrical behavior of devices incorporating the polysilicon layers are, in turn, influenced by the deposition conditions. Operation in the reaction-rate limited regime is necessary for film uniformity in a high-volume reactor; this is achieved by operating at low temperatures and low pressures. The temperature gradient often used in this reactor changes the structure of the deposited films, and cannot be used for devices which depend sensitively on the structure. Diffusion in polysilicon is influenced by the grain boundaries and, consequently, depends sensitively on the deposition conditions. The electrical properties of devices with their active layers within the polysilicon layer itself depend strongly on the structure of the polysilicon. Even conventional MOS transistors in which the polysilicon serves only as a conducting electrode can be affected by the structure of the polysilicon. Therefore, the deposition conditions of the polysilicon films and the resulting structure must be considered to obtain the desired electrical properties in the devices being fabricated.