Mechanical properties of silicon carbide films for X-ray lithography application

Hydrogenated amorphous silicon carbide a-SixC1-x:H films of various compositions (0.4 less-than-or-equal-to x less-than-or-equal-to 0.7) were deposited using a plasma-enhanced chemical vapour deposition technique. The as-deposited films are under high compressive stress (1 GPa). The control of the stress relaxation is an important stage in the X-ray mask technology. The stress of the a-Si(x)C1-x:H films is measured by the wafer bow technique, whereas the resonance frequency and the bulge techniques are used to measure the stress of the a-Si(x)C1-x:H free-standing membranes. These three methods give similar results and it is pointed out that the wafer bow technique can be used with confidence to determine the stress of a-Si(x)C1-x:H films intended to X-ray membrane processing. From the bulge method, the biaxial Young's modulus E/(1 - v) of the a-SixC1-x:H membranes is also deduced. Values of 200 +/- 25 GPa are obtained for a-Si(x)C1-x:H films at x = 0.4 and 0.5 film compositions. At x = 0.67, E/(1 - v) is reduced by a factor of about two. The structure and composition of the a-Si(x)C1-x:H films were investigated by means of elastic recoil detection, X-ray diffraction, and Fourier transform infrared absorption techniques. It is shown that the biaxial Young's modulus increases with the Si-C bond density in the film.