[Back]

U. Schmid, M. Eickhoff, Ch. Richter, G. Krötz, D. Schmitt-Landsiedel:
"Etching Characteristics and Mechanical Properties of a-SiC:H Thin Films";
Sensors and Actuators A: Physical, Vol. 94 (2001), 1-2; 87 - 94.

Due to its chemical inertness after effusing the incorporated hydrogen as well as the oxygen free deposition atmosphere in combination with a deposition temperature <300°C, amorphous silicon carbide (a-SiC:H) has gained much attention the recent years in microsystems technology (MST). In this paper, we report about etching experiments performed with a NF3/O2 gas mixture in a plasma enhanced process. By varying important etching parameters 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-SiC:H thin films are determined by load deflection measurements performed at diaphragms. This technique allows to measure interferometically the film stress σ and the Young´s modulus E as a function of annealing time and temperature Ta, respectively. Choosing for the latter a temperature range between 450 and 750°C, the film stress changing from −400 to +490 MPa is clearly more affected than the Young´s modulus having a value of 180 GPa (± 5%). At Ta=550°C, the intrinsic compressive nature in "as deposited" a-SiC:H layers changes to tensile stress. For devices, operating at temperatures up to 650°C, a post-deposition anneal at 650°C for 240 min is necessary to get thermally stabilized values for σ as well as E. Therefore, micromachined sensors which are in direct contact with aggressive media as well as high temperatures can be well protected by this passivation layer and, hence, increasing their lifetime substantially.

http://dx.doi.org/10.1016/S0924-4247(01)00691-4