Device Scaling Effect on the Spectral Absorptance of Wafer Front Side

Temperature non-uniformity is a critical problem in the rapid thermal processing of wafers because it leads to uneven diffusion of implanted dopants and introduces thermal stress. One cause of the problem is non-uniform absorption of thermal radiation, especially in patterned wafers, where the optical properties vary across the wafer surface. The feature size of the new generation of semiconductor devices is already below 100 nm and is smaller than the wavelength (200-1000 nm) of the flash-lamp annealing heat sources. Little is known to the spectral distribution of the absorbed energy for different patterning structures. This paper presents a parametric study of the radiative properties of patterned wafers with the smallest feature dimension down to 10 nm, considering the effects of temperature, wavelength, and angle of incidence. Two different front side topographies are considered: (1) arrays of silicon gates on a silicon substrate; and (2) arrays of oxide trenches embedded inside a silicon substrate. Various gate and trench sizes and their dimensions relative to the period are used in examining the effect of device scaling on the spectral absorptance. The rigorous coupled wave analysis and finite-difference time-domain method are employed to obtain numerical solutions of the Maxwell equations. The effective medium theory is also used to explain the trends observed in the calculated absorptance. It is found that depending on the gate size and trench size relative to the period and the wavelength, different effect (diffraction, interference, etc.) appears in the absorptance of the wafer front side