B. Semmache et al., RAPID THERMAL-PROCESSING OF PIEZORESISTIVE POLYCRYSTALLINE SILICON FILMS - AN INNOVATIVE TECHNOLOGY FOR LOW-COST PRESSURE SENSOR FABRICATION, Sensors and actuators. A, Physical, 46(1-3), 1995, pp. 76-81
Rapid thermal processing is evaluated as a low cost and flexible singl
e wafer technology to develop SOI pressure sensors, allowing the fabri
cation of polycrystalline piezoresistors on thermally grown silicon di
oxide with a turnaround time of a few minutes. The growth kinetics and
the microstructure of polysilicon films obtained by rapid thermal che
mical vapour deposition using an argon-silane gas mixture are investig
ated as a function of the process pressure and temperature. Polysilico
n films deposited at 5 mbar and at temperatures lower than 750 degrees
C exhibit high compressive stresses and grain sizes of about 30 nm du
e to a high level of oxygen contamination. At 1 mbar the lower oxygen
contamination enables to deposit well crystallized films, with residua
l tensile stresses comparable to those of classical low pressure chemi
cal vapour deposition polysilicon and with grain sizes reaching 55 nm.
Longitudinal gauge factors of boron-implanted piezoresistors patterne
d on polysilicon films deposited at 5 mbar and 720 degrees C show a ma
ximum of 20-22 in the 2x10(19)-4x10(19) cm(-3) doping range. Longitudi
nal gauge factors of 25-32 are measured for piezoresistors made from b
oron-diffused polysilicon deposited at 5 mbar and 850 degrees C, thus
illustrating the flexible capabilities of rapid thermal processing for
the silicon microsystem technology.