Physical Model for Surface Annihilation of Silicon Interstitials during Annealing

Abstract

Surface annihilation is the main mechanism through which implantation defects are annealed out from Si wafer. Surface annihilation possibility of silicon interstitials has obvious impact on total diffusion of dopant as well as junction depth. In this paper, a model on variation of surface annihilation possibility for silicon interstitials is proposed. By considering the surface annihilation rate and desorption rate and surface defect point, the analytical model for effective surface annihilation possibility is developed and verified. The impact of surface annihilation possibility on enhanced diffusion is simulated.interstitials [2]. However it is still not very clear how the surface annihilation possibility change with surface conditions. Some model is needed to predict the surface behavior. In this paper, we presented a new analytical model on Si surface annihilation possibility. In this model, mechanism of absorption and desorption of Si interstitials at surface is considered. Change of surface structure is taking into account. The model is verified by the experimental results [3]. Simulation on Si isotopes diffusion and B diffusions considering surface annihilation possibility is discussed. Physical Model 1. IntroductionEnhanced diffusion of B has been investigated a lot for shallow junction formation. It is suggested that surface annihilation and reflection of Si interstitials has obvious impact on the enhancement of B diffusion [1][2], because B diffusion is assisted by Si interstitials. This is more important in shallow junction formation, where doping region is only about several nm beneath the surface. For high dose ultra-low energy implantation, density of implantation damage is very high. The role of surface annihilation is more important. There has been investigation on how the interaction between surface and defects impacts B diffusion and junction depth [1] [2]. There is also experimental result indicates that variation of physical and chemical surface conditions induces change of surface ability of annihilating Si The present work seeks to develop a kinetic model for surface annihilation of point defects under variation of surface structure. The annihilation rates of point defects were quantified through an effective annihilation probability S defined as the probability that a point defect encountering the surface actually incorporates there and is removed from the bulk [4]. As bulk point defects such as interstitial atoms and vacancies can approach and react from below in the same way that gases approach surfaces from above, our model is analogous to the precursor model used to describe adsorption rates in gas-surface chemistry [5], in which adsorbates move substantial distances parallel to the surface before incorporation. Recent quantum calculations show that the formation energy for silicon interstitials is much lower in the subsurface layers near the surface than in the bulk, which suggests the accumulation of silicon interstitials 1-4244-