Etching characteristics and mechanical properties of a-SiC : H thin films

Due to its chemical inertness after effusing the incorporated hydrogen as w ell as the oxygen free deposition atmosphere in combination with a depositi on temperature < 300 degreesC, amorphous silicon carbide (a-SiC:H) has gain ed much attention the recent years in microsystems technology (MST). In thi s paper, we report about etching experiments performed with a NF3/O-2 gas m ixture in a plasma enhanced process. By varying important etching parameter s as rf power, substrate temperature and total gas pressure, a maximum etch rate of 135 nm/min can be achieved. Further material parameters of the a-S iC:H thin films are determined by load deflection measurements performed at diaphragms. This technique allows to measure interferometically the film s tress a and the Young's modulus E as a function of annealing time and tempe rature T-a respectively. Choosing for the latter a temperature range betwee n 450 and 750 degreesC, the film stress changing from -400 to +490 MPa is c learly more affected than the Young's modulus having a value of 180 GPa (+/ -5%). At T-a = 550 degreesC, the intrinsic compressive nature in "as deposi ted" a-SiC:H layers changes to tensile stress. For devices, operating at te mperatures up to 650 degreesC, a postdeposition anneal at 650 degreesC for 240 min is necessary to get thermally stabilized values for c as well as E. Therefore, micromachined sensors which are in direct contact with aggressi ve media as well as high temperatures can be well protected by this passiva tion layer and, hence, increasing their lifetime substantially. (C) 2001 El sevier Science B.V. All rights reserved.