The Fabrication by using Surface MEMS of 3C-SiC Micro-heaters and RTD Sensors and their Resultant Properties

Abstract

The electrical properties and the microstructure of nitrogen-doped poly 3C-SiC films used for micro thermal sensors were studied according to different thicknesses. Poly 3C-SiC films were deposited by LPCVD (low pressure chemical vapor deposition) at <TEX>$900^{\circ}C$</TEX> with a pressure of 4 torr using <TEX>$SiH_2Cl_2$</TEX> (100%, 35 sccm) and <TEX>$C_2H_2$</TEX> (5% in <TEX>$H_2$</TEX>, 180 sccm) as the Si and C precursors, and <TEX>$NH_3$</TEX> (5% in <TEX>$H_2$</TEX>, 64 sccm) as the dopant source gas. The resistivity of the poly SiC films with a 1,530 <TEX>${\AA}$</TEX> thickness was 32.7 <TEX>${\Omega}-cm$</TEX> and decreased to 0.0129 <TEX>${\Omega}-cm$</TEX> at 16,963 <TEX>${\AA}$</TEX>. The measurement of the resistance variations at different thicknesses were carried out within the <TEX>$25^{\circ}C$</TEX> to <TEX>$350^{\circ}C$</TEX> temperature range. While the size of the resistance variation decreased when the films thickness increased, the linearity of the resistance variation improved. Micro heaters and RTD sensors were fabricated on a <TEX>$Si_3N_4$</TEX> membrane by using poly 3C-SiC with a 1um thickness using a surface MEMS process. The heating temperature of the SiC micro heater, fabricated on 250 <TEX>${\mu}m$</TEX><TEX>${\times}$</TEX>250 <TEX>${\mu}m$</TEX> <TEX>$Si_3N_4$</TEX> membrane was <TEX>$410^{\circ}C$</TEX> at an 80 mW input power. These 3C-SiC heaters and RTD sensors, fabricated by surface MEMS, have a low power consumption and deliver a good long term stability for the various thermal sensors requiring thermal stability.