Correlation of ellipsonometric modeling results to observed grain structure for OPO film stacks

One significant, but potentially variable, parameter in the deposition and subsequent processing of polysilicon is its microstructure. The purpose of this work was to correlate the model parameters, in this case, percentage volume fraction of polysilicon phase components, generated by regression of model dispersion using the Bruggerman effective media approximation to data acquired by the spectroscopic ellipsometry technique. Several samples are prepared, consisting of SiO₂/undoped poly-Si/SiO₂ film stacks in order to measure their as-deposited average grain sizes. Ellipsonometric data is obtained for the center site of each sample, which are then compared to AFM results from similar samples. Various grain geometry approximations are applied, along with the assumption that the polysilicon structure may be modeled to consist of three components; crystalline Si in a continuous amorphous Si matrix, and voids. A mathematical relationship is established between the percentage concentration of crystalline silicon and the mean grain size for the two cases of equiaxed and columnar microstructures. Results indicate good correlation with AFM measured grain sizes. Additional work is required to further demonstrate the correlation, and develop software applications to enable in-line product monitoring