AVS 59th Annual International Symposium and Exhibition
    Electronic Materials and Processing Thursday Sessions
       Session EM-ThP

Paper EM-ThP8
Simulation of Millisecond Laser Anneal on SOI: A Study of Dopant Activation and Mobility and its Application to Scaled FinFET Thermal Processing

Thursday, November 1, 2012, 6:00 pm, Room Central Hall

Session: Electronic Materials and Processing Poster Session
Presenter: T. Michalak, University at Albany-SUNY
Authors: T. Michalak, University at Albany-SUNY
J. Herman, University at Albany-SUNY
M. Rodgers, University at Albany-SUNY
D. França, University at Albany-SUNY
C. Borst, University at Albany-SUNY
Correspondent: Click to Email
Next generation CMOS requires high activation and hyper-abrupt junction formation for low sheet resistance and device performance. The primary method of doping, ion implantation, provides excellent spatial control of dose. A high temperature anneal (>1000° C) is required to remove defects introduced from ion implantation and to electrically activate the implanted specie. A “diffusionless anneal” by which dopant is activated without significantly diffusing, would be ideal for ultra-shallow junction (USJ) formation. This work investigates one such technique, laser annealing, which uses a scanning laser to locally heat the wafer surface. 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 scanning across the active area of the device, solving the heat equation in both time and space (Fig 1). An absorber layer is deposited on the wafer surface to encourage the absorption of optical power and consequent heating of the wafer surface. An effective absorption coefficient of α=8861 cm-1 was calculated for the absorber layer, calibrated with the experimental laser intensity of 52526 W/cm2 required to melt silicon at a scan speed of 150 mm/s which lies within the range for amorphous carbon stated in literature (Fig 2). This absorption coefficient correctly predicts the silicon temperature as a function of power with any arbitrarily defined scan speed (Fig 3). To investigate the role of dopant activation, an SOI wafer was implanted at 25 keV, dose 3e15 cm-2 and laser annealed in stripes of target temperatures ranging from 1100-1300 ºC. The sheet resistance was measured on wafer showing Rs improvement with increasing laser temperature (Fig 4). The extracted temperature cycle from the 2D heat simulation was used as an equivalent millisecond RTA in a full 3D finFET process simulation to study dopant distribution and activation using Sentaurus Process Kinetic Monte Carlo (KMC), considering the effect of dopant clusters and point defects. The results of this simulation, supplemented with Hall mobility measurement and secondary ion mass spectroscopy (SIMS), show that there is no further activation of arsenic with increasing laser temperature (~ 25%) which suggests healing of the implant crystal damage may be reducing sheet resistance. As well, an electrical device simulation of the finFET was performed to compare device performance between RTA and laser annealing (schematic Fig 5). Simulation results show a theoretical improvement in drive current with the laser process over standard RTA.