Dopant Diffusion Simulation in Thin-SOI
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Dopant Diffusion Simulation in Thin-SOI Hong-Jyh Li, Robin Tichy, Jonathon Ross*, Jeff Gelpey*, Ben Stotts**, Heather Galloway** and Larry Larson International SEMATECH, 2706 Montopolis Dr., Austin, TX 78741 *Vortek Industries Ltd, 605 West Kent Avenue, Vancouver, BC Canada V6P 6T7 **Southwest Texas State University, San Marcos, Texas
ABSTRACT As the top Si layer is thinned, the dopants’ diffusion in the confined Si layer in SOI wafer with respect to different thermal treatments needs to be better understood. Boron, BF2 with/without Ge pre-amorphization were implanted into bulk Si and SOI wafers with 530 Å Si and 1475A BOX. Samples were annealed using both spike (Impulse) anneal and Flash anneal. Simulations of dopant diffusion is used to resolve apparent differences in dopant profiles that resulted for SOI in contrast with bulk Si samples. Result suggests that the implantation damage difference between SOI and bulk Si makes the B diffusion in SOI higher than in bulk Si. INTRODUCTION As the technology of semiconductor devices evolves, the scaling of traditional CMOS devices might approach barriers that make the scaling economically or physically infeasible. New starting materials such as SOI (Silicon-On-Insulator) have been attracting attention recently as approaches to overcome these barriers. To further improve the device characteristics using SOI, it is necessary to optimize the top Si layer thickness [1]. To achieve better control over short and narrow channel effects in today’s SOI technology, doping in the confined Si layer needs to be better understood especially for the implanted boron in p-typed device due to its transient enhanced diffusion (TED) [2]. In bulk Si substrate, B TED has been extensively studied and it has been well recognized that B TED is caused by the excess Si interstitials resulted from the implant process. B interacts with the nearby Si interstitial and forms a lower energy migration pathway in Si than the case without Si interstitial. Previous work on B diffusion in SOI [3] described the interstitial kinetics between SOI and bulk Si cases. Si interstitials can recombine with vacancies at the top surface; however, the buried oxide serves to keep the excess interstitials from diffusing away from the surface region into the bulk substrate. The level of interstitial supersaturation in SOI relative to the bulk material will depend on the relative strength of these two processes in removing excess interstitials from the near-surface region. Recent modeling study [4] on B diffusion with spincoated B source diffused at 860 oC showed that B diffusion was retarded as compared to the bulk Si case and the retardation is enhanced near the oxide box interface. Interestingly, oxideenhanced-diffusion [5] was not observed in their study. This diffusion retardation was explained
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by the undersaturation of Si interstitials in the Si layer due to the larger recombination velocity of interstitial at the oxide box. As ion implantation is the prevailing technique to dope Si, it is interesting
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