Oxygen and Nitrogen Incorporation during CW Laser Recrystallization of Polysilicon

Abstract

The incorporation of nitrogen and oxygen in polysilicon has been examined by SIMS. The analysis, combined with C-V measurements and ion implantation, has been used to correlate the incorporation of the two species with the fixed-charge density at the back polysilicon/SiO₂ interface. Laser recrystallization with a silicon-nitride encapsulation layer results in the inclusion of 2–4 × 10¹⁷ cm⁻³ nitrogen atoms in the polysilicon; if an oxide capping layer is used, the nitrogen level observed is at the background of the SIMS system (~10¹⁵ cm⁻³). Either type of capping layer results in 3–4 × 10¹⁸ cm⁻³ oxygen atoms being incorporated into the polysilicon. Implantation of nitrogen into the polysilicon before recrystallization increases the fixed-charge density N_f,b) at the back interface, while implanted oxygen decreases N_f,b. The high N_f,b found with a nitride capping layer is attributed to deposition of nitrogen or SiN_X at the back interface.