B. Semmache

Rapid thermal processing of piezoresistive polycrystalline silicon films: An innovative technology for low cost pressure sensor fabrication

Abstract Rapid thermal processing is evaluated as a low cost and flexible single wafer technology to develop SOI pressure sensors, allowing the fabrication of polycrystalline piezoresistors on thermally grown silicon dioxide with a turnaround time of a few minutes. The growth kinetics and the microstructure of polysilicon films obtained by rapid thermal chemical vapour deposition using an argon-silane gas mixture are investigated as a function of the process pressure and temperature. Polysilicon films deposited at 5 mbar and at temperatures lower than 750 °C exhibit high compressive stresses and grain sizes of about 30 nm due to a high level of oxygen contamination. At 1 mbar the lower oxygen contamination enables to deposit well crystallized films, with residual tensile stresses comparable to those of classical low pressure chemical vapour deposition polysilicon and with grain sizes reaching 55 nm. Longitudinal gauge factors of boron-implanted piezoresistors patterned on polysilicon films deposited at 5 mbar and 720 °C show a maximum of 20–22 in the 2×10 19 -4×10 19 cm −3 doping range. Longitudinal gauge factors of 25–32 are measured for piezoresistors made from boron-diffused polysilicon deposited at 5 mbar and 850 °C, thus illustrating the flexible capabilities of rapid thermal processing for the silicon microsystem technology.

Physical properties of RT-LPCVD and LPCVD polysilicon thin films: application to emitter solar cell

This investigation was implemented in the framework of a novel all-low thermal budget polysilicon emitter solar cells fabrication technology. A comparative study of structural and electrical properties of thin silicon layers deposited by silane pyrolysis in a classical hot-wall furnace (LPCVD) and a cold-wall RTP reactor (RT-LPCVD) has been made. Deposition conditions and rapid thermal anneals were varied in order to improve the physical properties of RT-LPCVD polysilicon films. The structural properties have been characterized by means of grazing X-ray diffraction and cross-sectional TEM analysis. Sheet resistivity measurements performed on POCl/sub 3/-doped and subsequently rapid thermal annealed films showed the feasibility of low resistivity films particularly when the polysilicon layers are initially deposited in the amorphous state. Finally, RTCVD polysilicon emitter solar cells with various thicknesses were tested by spectral photo-response analysis.