| An array of powerful analytic techniques was employed to examine the microstructure of a wide variety of LPCVD polysilicon thin films processed under a multitude of conditions, and to correlate these results with macroscopic measured properties. The study utilized cross sectional TEM, AFM, X-ray, four point probe and wafer curvature to measure microstructure, surface topography, crystalline texture, resistivity and stress respectively. The examined films included as-deposited 0.45 mum films grown at 5 temperatures between 580°C and 700°C. The second group focused on films of 0.45 mum and 2.0 mum in thickness, deposited at 590°C, then implanted with boron, and annealed at one of four temperatures; 900°C, 950°C, 1050°C, or 1100°C. The third group of films consisted of polysilicon on amorphous surfaces, such as oxides, nitrides, and PSG layers in actual MEMS structures. In the course of analyzing the surface topography of films from the second group, a high density of surface grains that protruded above the plane of the surrounding surface was found. These surface grains were then studied in more detail to identify their formation mechanism. It was found that the surface grains correlated to film stress and were related to the transition from an amorphous to crystalline deposition during growth. Many of the observed microstructural features were found to have a direct impact on film properties important for MEMS applications. |
