Simulation of Millisecond Laser Anneal on SOI: A Study of Dopant Activation and Mobility and its Application to Scaled FinFET Thermal Processing

Abstract

This work investigates scanning laser annealing used for ultra-shallow junction (USJ) activation. We investigate the laser system via simulation to determine the peak temperature achieved in the active area during processing. We employed the Sentaurus TCAD software by Synopsys to perform a 2D simulation of a laser scans across the active area of the device, solving the heat equation in both time and space. An absorber layer is deposited on the wafer surface to enhance the absorption of incident energy and reduce SOI reflectivity. An effective absorption coefficient of α=8000cm^-1 was calculated for the absorber layer, calibrated with the experimental laser intensity. This absorption coefficient correctly predicts the silicon temperature as a function of power with any arbitrarily defined scan speed. To investigate the role of dopant activation, an SOI wafer was implanted with arsenic 25 keV, dose 3e15 /1.5e15 cm-2 and laser annealed in areas of target temperatures ranging from 850-1300°C. The sheet resistance was measured using 4-point probe showing sheet resistance improvement with increasing laser temperature. The extracted temperature cycle from the 2D heat simulation was used as an equivalent millisecond RTA in a full 3D process simulation to study dopant distribution and activation using Sentaurus Process Kinetic Monte Carlo (KMC), considering the effect of dopants, dopant clusters, and point defects. The results of this simulation demonstrate deactivation of arsenic above 1050°C, which is inconsistent with Hall measurements that suggest increasing laser temperature will increase mobility and activation. The results are analyzed versus the expected trends and suggest future improvements needed to the KMC model or the laser temperature profiles in order to describe activation kinetics in millisecond anneals within SOI.