Stresses in 3C-SiC films grown on Si substrates

Abstract

C-Sic films were grown epitaxially on Si(OO1) substrates by an atmospheric pressure chemical vapor deposition method. The stresses in the films were determined by Raman spectroscopy and compared to data from load-deflection measurements on similar films. The films are tensile as grown and have a stress of 0.3 GPa, which is lower than the reported values for similar films. A possible explanation for the lower stresses as well as other observed trends is suggested. A. Introduction In order for 3C-Sic films epitaxially grown on Si substrates to be used in devices, it is important that the stresses in the films be well understood and controlled, as these stresses determine the flatness and usability of these wafers, as well as other subsequent device characteristics. These stresses do not arise from the lattice mismatch of 20%, but rather from the thermal mismatch of 8% and other factors. The lattice mismatch is accommodated within the first monolayer by the formation of misfit dislocations. However, the thermal coefficient mismatch cannot be avoided and the stresses develop as the film-substrate system cools down after growth. While a number of explanations have been offered in the past for these stresses in chemical vapor deposition (CVD) grown films (l), there is no clear quantitative explanation that explains all the data. B. Experimental Results The films were grown in an atmospheric pressure CVD (APCVD) reactor and the details of the growth have been previously reported (2). The stresses were measured by micro- Raman spectroscopy and compared with data on films grown in the same reactor and measured by a load-deflection technique (3). The calculations of stress are based on the work of Feng et al. (4). It is well known that stresses cause a shift in the Raman peaks. These stresses can be estimated from the shifts in the LO (longitudinal optical) and TO (transverse optical) phonon positions. The peak positions for the films are tabulated in Table 1. From these values, the stress was determined. A stress of 0.3M0.2 GPa was measured in a 0.3 pm thick film grown in the APCVD reactor at 1360 "C. This value of stress is lower than the values on similar films obtained by the load-deflection technique (3). These films were all grown in the same reactor under identical conditions. The resolution of the micro-Raman measurements was lower than that of the load deflection technique and that could explain the higher stress value measured by Raman spectroscopy. It has already been established in the SiC/Si system, that there are no stresses due to the film-substrate lattice mismatch, because of the presence of misfit dislocations with the appropriate spacing at the interface. Thus, any residual stresses are due to the thermal mismatch and other intrinsic stresses. The thermal mismatch stresses (of) can be calculated for each film orientation, using