低壓化學沉積腔體中矽沉積速率之模擬研究

Abstract

使用直接蒙地卡羅法 (Direct Simulation Monte Carlo method) 模擬化學氣相沉積過程。參考Boyd 提出之CWS (Conservative weighting scheme) 來處理化學氣相沉積過程中的微量氣體。CWS藉由降低微量氣體的權值 (weight) 來增加它的模擬分子數，進而大量的改善了統計的不確定性。並且CWS在處理兩個權值差異很大的分子碰撞時仍能保持動量和能量的守恆。在single-cell的模擬中驗證了當權值的比例低於0.05的時候，CWS處理兩種氣體分子、三種氣體分子以及轉動內能交換的模擬結果都相當的正確並且有效率。而ECWS (Extended CWS) 在模擬氣體化學反應和表面化學反應時可以做到傳統方法所無法做到的模擬結果。最後，我們要使用ECWS來做低壓化學沉積腔體中矽的沉積模擬。

Particle simulation of silicon Chemical Vapor Deposition (CVD) process is proposed using the Direct Simulation Monte Carlo (DSMC) method. Conservative weighting scheme [Boyd, 1996] is used to deal with the trace species often involved in CVD, which is otherwise considered computationally impossible using the conventional DSMC method. This conservative weighting scheme (CWS) improves greatly the statistical uncertainties by decreasing the weighting factors of trace-species particles and ensures the conservation of both momentum and energy between two colliding particles with large difference of weighting factors. A single-cell equilibrium simulation is performed for verification of the CWS. Results show that it is most efficient and accurate for weight ratio lower than 0.05 for flows with 2 and 3 species. Rotational energy exchange using the CWS has been evaluated for mixture with 2 species. Simulations of both gas-phase reaction and surface reactions show that only Extended CWS can produce reasonable results. Finally, ECWS is used to simulate the silicon deposition in the LPCVD chamber using a supersonic jet.