一噴灑頭式MOCVD反應器之性能數值模擬分析

Abstract

本文利用計算流體力學(Computational Fluid Dynamics)數值方法來分析一垂直噴灑頭式反應器內金屬有機化學氣相沉積(MOCVD)之熱流場與化學反應變化。參考模型由經濟部矽基氮化鎵LED科專計畫與工研院所共同開發之噴灑頭反應器。透過商用軟體ANSYS FLUENT來模擬化固態電子材料氮化鎵(GaN)在反應器內晶圓表面的化學沉積速率。其模擬的目的在於建立一方便調整製程各項參數之模型，提供驗證以及最佳化設計，幫助半導體產業研究分析，來改良薄膜沉積均勻度，並降低工業化生產製造之成本。在操作設定上使用有限體積法以及SIMPLE演算法，求解穩態之連續方程式、動量方程式、能量方程式與質量傳輸方程式，可由反應腔體內部顯示出熱流場變化、與濃度擴散之情況。最後在反應器內透過模擬氣相及表面化學反應方程式，來計算薄膜沉積速率，透過改變反應器內的參數設定如: 壓力、轉速等性質後，分析薄膜沉積之均勻性。結果顯示，在低壓的狀態下，熱流場分布均勻將使得化學反應獲得較好的沉積速率，並且利用轉速可以將濃度擴散均勻的分佈在反應器中，可幫助GaN在獲得更好的均勻度。

Computational fluid dynamics (CFD) is widely used in the semiconductor for analyzing and designing chemical vapor deposition (CVD) reactors. The CVD process is studied by various CFD simulations between 2d and 3d conditions to grow gallium-nitride (GaN) film, a sequence of reactions between gas-phase and surface-reaction which take a great influence to depositing film uniformity. The showerhead type MOCVD model is based on Ministry of Economic Affairs, R.O.C. and I.T.R.I. developing LED GaN on silicon program. This research uses CFD commercial software: ANSYS FLUENT to calculate flow, heat transfer and species transport in a vertical CVD chamber. Discretization is made by using finite volume method and the system of discretized algebra equations are solved by SIMPLE algorithm. In order to know GaN growth conditions and deposition rate, we have observed that different pressure and rotation speed caused flow and heat transfer changing in the reactor by using numerical simulation. The 2D model was design of axisymmetric, uniform gas inlet into the chamber with different conditions in this study. The results performed that the heated susceptor may cause the buoyancy effect and recirculation above the wafers. And the 3D reactor model includes of chemical gas-phase and surface-reaction mechanism. Simulation results showed the effect of important parameters, such as operating pressure, susceptor temperature, rotating speed, inlet to susceptor distance, on GaN film growth. Compare with 2d and 3d model, we found out that low pressure and high rotation speed providing better flow distribution and uniform deposition rates. These characters help stabilizing the flow and heat transfer in the chamber meanwhile they also cause the stable species transport in the reactor.