Effects of Nanoscale Patterns on the Spectral Absorptance of Wafers

Abstract

This paper presents a parametric study of the radiative properties of patterned wafers with a polysilicon gate array on the Si substrate, considering the effect of wavelength and polarization. While the gate sizes are very small compared to wavelength, the results show rather unusual phenomena. The absorptance calculated by effective medium theory (EMT) is in agreement with finite-difference time-domain (FDTD) in the cases with small gate and period sizes. With the increase of period and decrease of the ratio of the gate width to the pattern pitch, both EMT and FDTD results for TM mode approach to pure silicon since the grating effect diminishes. Besides, the TE absorptance curve separates from that of plain Si at the wavelength equals to the grating period, this is because the gate can interact with its neighboring region by diffraction and the diffraction effects are weak, when the wavelength is small. It also shows a slight increase in the gate height can drastically increase the absorptance and the increased gate height shifts the peak absorptance to longer wavelength. This work is of great importance for optimization of advanced annealing techniques in semiconductor manufacturing.