應用DSMC法分析垂直式旋轉基座LPCVD 之熱流場及薄膜沈積模擬

Abstract

本研究使用直接模擬蒙地卡羅法(Direct Simulation Monte Carlo method, DSMC) 模擬垂直式旋轉基座 LPCVD 反應腔體內之熱流場模式。主要是為配合國科會半導體製程設備產學計畫(銅化學氣相沈積系統之研製及其製程開發)以及後續銅膜沈積研究的實驗提供預測數據以提供新一代半導體製程設備設計之參考。本文主要探討在不同的撞擊係數（sticking coefficient）、反應活化能、基座溫度分布情況與載氣種類等操作條件下，對整個反應腔體內的熱流場與沈積特性的影響。在載氣模擬的部份，以往的研究大多僅侷限於單原子氣體（即不考慮旋轉自由度），本文將討論雙原子氣體對沈積特性的影響。此外，以微觀的角度根據銅源在基板表面的化學反應，在化學反應式部份加入副產物，讓整個模擬程式更接近實際的銅化學氣相沈積。最後，將使用CFX-4.1軟體模擬所獲得的腔體流場結果和DSMC法作一比較，以了解分子流和連續流在過渡區模擬結果的異同。 預測結果顯示，當撞擊係數越小沈積均勻度越好但是會降低整個沈積速率；在較高的活化能下進行薄膜沈積，由於反應屬於「表面反應限制範圍(reaction control limitation)」，因而比低活化能進行下的薄膜（屬「傳輸限制範圍(diffusion control limitation)」）能得到較佳的均勻性，但沈積率較慢，此和實驗的結果相同；對於同樣大小的粒子而言，因為雙原子氣體比單原子氣體具有更好的傳熱效率，所以雙原子載氣可以得到較快速的沈積率（約增加5%）；由於較輕（小）的粒子的傳輸能力較好，因而沈積率會比較重的粒子還快；本模擬中，若加入副產物模式，可以得到模擬的沈積率約38 nm/min，此結果與許多相關的實驗數據相當接近；CFX-4.1的方法雖然有用slip-flow的邊界條件，但仍然無法呈現一些在稀薄氣體裡特有的現象，不過可得到與DSMC法相同的流場趨勢。

This thesis analyzes the flow and thermal field in a vertical LPCVD chamber with rotating susceptor by using the DSMC method. Complying with the requirements of project "Development of Cu-CVD Technology and Fabrication" supported by the National Science Council of Taiwan, this work aims at exploring the Cu-deposition characteristics of various operating parameters, including the sticking coefficient (Sc), activation energy, temperature distribution on the susceptor, and different carrier gases. For the simulation of using different carrier gas, it quarries the difference between the gases with rotational energy and without any internal mode. For being closer to real situation, the simulation of chemical reaction including the by-products is also carried out. The predicted results show that the uniformity becomes worse and the deposition rate becomes greater with an increase of Sc. For the case of higher activation energy 4.0 kcal/mole, it belongs to the reaction control regime and can obtain an even film. If the masses for two carrier gases are similar, the one with considering rotational energy has the faster deposition rate because of the greater heat transfer capability. The faster deposition rate can be achieved by using a lighter carrier gas such that the precursor can be easier to reach the substrate. The deposition rate obtained by the by-product model in the present study is about 38.0 nm/min, which is close to the one obtained by experiment. The uniformity of film thickness is found sensitive to the distribution of temperature. Finally, a comparison of using DSMC and CFX-4.1 methods is given. It is found that some of the special phenomena in rarefied gas can not be reproduced by the CFX method, even it sets the slip condition at the solid boundary. However, both methods can obtain the similar trends in the transition flow regime.