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

Abstract

This paper reports our latest results in developing and characterizing low-stress, heavilynitrogen-doped polycrystalline 3C-silicon carbide (poly-SiC) films by low pressure chemical vapor deposition. Deposition pressure and NH 3 gas concentration are used to control residual stress, stress gradient and conductivity at a deposition temperature of 900ºC using SiH 2 Cl 2 (100%) and C 2 H 2 (5% in H 2 ) 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 Ω-cm to 0.006 Ω-cm in the same doping concentration range. The average TCR decreases from -2050.3 ppm/°C to -1957.0 ppm/°C over approximately the same doping concentration range. The Young's modulus of the films is estimated at 330 GPa, assuming a Poisson's ration of 0.163 for poly-SiC.

Stress and strain gradient control of polycrystalline SiC films

“…In this paper, poly-SiC was deposited in a highthroughput, resistively-heated, horizontal LPCVD furnace which is capable of processing fifty 150 mm-diameter wafers [1,2]. The films were deposited on (100) silicon (Si) wafers (with and without SiO 2 thin film passivation) at 900°C using DCS (100%) and C 2 H 2 (5% in H 2 ) as precursors.…”

“…DCS flow rate was varied from 18 to 54 sccm, while C 2 H 2 flow rate was fixed at 180 sccm. Deposition pressure and temperature were fixed at 2 Torr and 900°C, respectively, while deposition time was fixed at 2 hours, based on our previous work [1,2]. Poly-SiC films were deposited without additional dopant gases in order to focus this study on the effect of the DCS flow rate on the deposited film stress and strain gradient.…”

“…Significant progress in both scientific understanding and practical control of the stress and strain gradient of poly-SiC films has been made since we first reported the effect of deposition pressure and NH 3 doping concentration on the residual stress of poly-SiC films [1,2]. A number of MEMS and NEMS devices have been fabricated using these low tensile stress poly-SiC films, including for example SiC capacitive pressure sensors [3], SiC strain gauge sensors [4], and SiC nano-switches [5].…”

Room-Temperature Wet Etching of Polycrystalline and Nanocrystalline Silicon Carbide Thin Films with HF and HNO[sub 3]

“…Because of its high melting point, 1 chemical inertness, [2][3][4] extreme hardness, 5 fracture toughness, 6 wear resistance, 7 and adhesion reduction qualities 8 polycrystalline 3C-SiC ͑poly-SiC͒ is a material of choice for harsh environment applications. The emergence and development of uniform poly-SiC thin films 9 with controllable residual stress, [10][11][12] strain gradient, 10,13 and electrical resistivity [14][15][16] have allowed the surface micromachining of micro-and nanoelectromechanical systems with poly-SiC as a structural layer or a coating. [17][18][19] While its chemical inertness makes poly-SiC well suited for harsh environment applications, it also makes poly-SiC difficult to remove, in particular, selectively over other thin films for patterning.…”