About the influence of deposited nitride layers on oxide precipitation after RTA pre-treatment

摘要

In order to elucidate the influence of stress and in-diffused nitrogen on oxide precipitation after rapid thermal annealing (RTA), we carried out experiments with one-side and double-sided nitride layers accompanied by simulation models which help to understand the behavior of intrinsic point defects, nitrogen, and strain. We found that the presence of a nitride layer of any thickness, within the rage which we investigated, in direct contact with the silicon surface is sufficient to markedly change the precipitation behavior of interstitial oxygen after RTA at 1175 and 1250℃. The presence of the nitride layer during the stabilization and growth of the oxide precipitates is not of any influence on the precipitation behavior. Therefore, the RTA of wafers covered with silicon nitride is the crucial step controlling the bulk microdefect (BMD) depth profiles. A 10 nm oxide between silicon substrate and nitride layer prevents any change of the BMD depth profile. Only in a direct contact with the nitride layers the vacancy supersaturation, which enhanced the oxide precipitation compared to wafers without nitride layers, was generated. Nitrogen peaks below the silicon surface generated by in-diffusion of nitrogen during RTA lead lo an enhanced oxygen precipitation only for RTA at 1250 ℃ and not for RTA at 1175 ℃. We propose a model based on very tiny coherent a-Si_3N_4 precipitates generated at nitrogen-vacancy (NV) complexes which can act as nucleation sites for oxygen precipitation. Because the stability of NV seems limited to temperatures above 1200 ℃, it would not be effective for RTA at 1175℃. RTA treatment of silicon wafers with one-sided nitride layers at 1250℃ leads to very sharp and small defect denuded zones in subsequent annealing and would be suitable for proximity gettering. The depth of the denuded zone is nearly independent of the thickness of the nitride layer.