Xiao-An Fu

Characteristics of Polycrystalline β-SiC Films Deposited by LPCVD with Different Doping Concentration

The physical and electrical properties of polycrystalline -SiC were studied according to different nitrogen doping concentration. Nitrogen-doped SiC films were deposited by LPCVD(1ow pressure chemical vapor deposition) at and 2 torr using (35 sccm) and in (180 sccm) as the Si and C precursors, and in (20-100 sccm) as the dopant source gas. The resistivity of SiC films decreased from with of 20 sccm to with 100 sccm. The surface roughness and crystalline structure of -SiC did not depend upon the dopant concentration. The average surface roughness for each sample 19-21 nm and the average surface grain size is 165 nm. The peaks of SiC(111), SiC(220), SiC(311) and SiC(222) appeared in polycrystalline -SiC films deposited on substrate in XRD(X-ray diffraction) analysis. Resistance of nitrogen-doped SiC films decreased with increasing temperature. The variation of resistance ratio is much bigger in low doping, but the linearity of temperature dependent resistance variation is better in high doping. In case of SiC films deposited with 20 sccm and 100 sccm of , the average of TCR(temperature coefficient of resistance) is -3456.1 ppm/ and -1171.5 ppm/, respectively.

Nitrogen Doped Polcrystalline 3C-Sic Films Deposited by LPCVD for MEMS Applications

This paper reports our latest results in developing and characterizing low-stress, heavily- nitrogen-doped polycrystalline 3C-silicon carbide (poly-SiC) films by low pressure chemical vapor deposition. Deposition pressure and NH3 gas concentration are used to control residual stress, stress gradient and conductivity at a deposition temperature of 900degC using SiH2O2 (100%) and C2H2 (5% in H2) as the Si and C precursors. The residual stress is tensile and increases from near zero to near a maximum of 250 MPa with increasing doping concentration; the resistivity decreases from 0.14 Omega-cm to 0.006 Omega-cm in the same doping concentration range. The average TCR decreases from -2050.3 ppm/degC to -1957.0 ppm/degC over approximately the same doping concentration range. The Youngs modulus of the films is estimated at 330 GPa, assuming a Poissons ration of 0.163 for poly-SiC.

Fabrication of Micro- and Nanoscale SiC Structures Using Selective Deposition Processes

A method to fabricate nanometer scale SiC beams and nanoporous SiC shells using conventional microlithographic techniques combined with selective APCVD has been developed as an alternative to nanolithographic patterning and electrochemical etching. The process involves the selective deposition of poly-SiC films on patterned SiO 2 /polysilicon/SiO 2 thin film multilayers on (100) Si substrates using a carbonization-based 3C-SiC growth process. This technique capitalizes on significant differences in the nucleation of SiC on SiO 2 and polysilicon surfaces in order to form mechanically durable and chemically stable structures.

Stress and strain gradient control of polycrystalline SiC films

This work reports the development of very low residual stress and low strain gradient polycrystalline SiC (poly-SiC) thin films deposited by low pressure chemical vapor deposition (LPCVD). Using dichlorosilane (DCS, SiH<inf>2</inf>Cl<inf>2</inf>) and acetylene (C<inf>2</inf>H<inf>2</inf>) as precursors, it was found that the flow rate of DCS can be used to adjust the residual stress from tensile to compressive in as-deposited films. The resulting poly-SiC films, with tensile stresses lower than 50 MPa and strain gradients as low as 1.3×10⁻⁴ °m⁻¹, are well-suited for MEMS and NEMS structural materials.