J. Phys. IV France 03 (1993) C3-457-C3-464
Direct writing of piezoresistive silicon resistors using laser-induced CVDH. MOILANEN, L. LEPPÄVUORI and A. UUSIMÄKI
Microelectronics and Material Physics Laboratories, University of Oulu, Linnanmaa, 90570 Oulu, Finland
Laser-induced chemical vapour deposition (LCVD), using a movable focused Ar+ laser beam (1 W, 514.5 nm), was used for direct, maskless writing of strain sensitive silicon resistors for the fabrication of prototype pressure sensors on a silicon on sapphire (SOS) and sapphire substrates from the mixed ratio of 0.1% B2H6 in the reactive gas SiH4. The strain sensitive resistors, approximately 300 µm long, were deposited, with in situ measurement of their resistance. The width of the deposited stripes were about 10 µm, and lines over 1 µm thick were written at speeds of 50 µm/s. The resistivity of the stripes was 7-10 mΩcm. The LCVD processing pressure was typically 100 mbar. In the case of silicon-on-sapphire (SOS) diaphragms (thickness of 330 µm) longitudinal gauge factors of 40-80 were observed when the direction of the resistors was parallel to the -type epitaxial direction. The gauge factor of 13 was measured when the resistor was deposited parallel to the -type direction. Polycrystalline deposition on the sapphire substrate (thickness of 530 µm) gave gauge factors of 31-48. Temperature coefficients of resistance (O°C...70°C) of silicon stripes were -500...- 2200 (SOS) and -2300...-2900 ppm/°C (sapphire), respectively.
© EDP Sciences 1993