開發以 ANSYS-Fluent 為架構之數值模擬法探 討行星式 MOCVD 反應腔體內之三維氣體流場

Development of ANSYS-Fluent-based Numerical Approaches for Studies of Three-dimensional Gas Flows in a Planetary MOCVD Reactor

蔡禹昇(YU-SHENG CAI)

指導教授 ： 何正榮

國立中央大學/工學院/機械工程學系/博士(2015年)

摘要

隨著製程技術的持續進步與應用面的不斷推新， LED 現已是重要的半導體主流產品之一。商業量產上 LED 的製造方式主要採用金屬有機物化學氣相沉積法。其製程方式主要是通入前驅氣體三甲基鎵和氮氣在晶圓表面藉由高溫載台產生熱裂解，化學反應後沉積一層氮化鎵。氮化鎵的生長過程除了要能調控複雜的化學反應外，如何掌握熱流場使反應源能大面積且均勻地分佈在生長之晶圓表面，也是重要的關鍵。因此對於反應腔體內部熱流場的精準控制，一直是金屬有機物化學氣相沉積法的製程良率與產能提升相當重要因素。
本文以 Aixtron Planetary Reactor G2 以及 G3 反應室作為暫態模擬研究之三維模型，以模擬軟體 ANSYS-Fluent 的架構下進行網格分割及熱流場分析。過往文獻雖然也有專注於行星式的模擬研究，但是卻都沒有將腔體內部的速度場與數值顯完整地呈現出來，因此本文的研究動機即是致力於開創出一種能適用於任何 Planetary Reactor 的模擬方式，以滑移網格的構思出發取代繁雜的動態網格，不需要每個模擬的時間步長 (time step) 都重製網格一次，可大幅度縮減計算時間與計算量，接續透過 Mesh motion 與自行撰寫 Code，清楚地呈現出行星式反應腔體內部完整的動態速度場、流線圖與溫度分佈。因此本文最後以 G2 & G3 腔體進行各三種不同的模擬參數搭配下，成功模擬出各個參數下腔體內部的熱流場分佈情形，其中在高腔壓下形況下會使腔體內部流場不穩定產生渦流，流量過小也會產生渦流，再透過反應源於晶圓上濃度的分佈計算出各個參數下薄膜成長率的變化，論證出無法採用僅公轉下的長率，預測加入自轉後的長晶成長率分佈。

關鍵字

有機金屬化學氣像沉積法 ； 計算流體力學 ； 氮化鎵 ； 行星式反應腔體 ； 三甲基鎵

並列摘要

With the continuous increase in applications and reduction in price, light emitting diodes (LEDs) has been emerged to be one of the major semiconductor devices. Commercially, growing thin films for an LED is mainly accomplished in an MOCVD (metal organic chemical vapor deposition) chamber. Taking the GaN thin film for example, both the precursor gases of trimethyl gallium and nitrogen are introduced into the reactor through designated inlets, they then flow over a high-temperature susceptor. The high temperature induces the pyrolysis and chemical reactions of the precursor gases and the reactant of GaN is eventually deposited on the surface of wafers, which are placed on the susceptor. For growing a large area and high-quality GaN thin film, a uniformly thermal flow field on the susceptor surface is essential because this is the prerequisite for producing uniform chemical reactions. Consequently, through understandings of the reactor’s thermal flow and, furthermore, a well control of it, is critical to the low-cost and high-yield fabrication.
This study aims to develop new User Defined Functions within the framework of ANSYS-Fluent Software for simulating three-dimensional thermal and flow fields in the G2 and G3 Aixtron Planetary Reactors. Many works for analyzing the quality and growth rate of the deposited film through simulating flows of gases in a reactor chamber have been published. Part of them was specifically for planetary reactors. However, most of these calculations were performed by approximating the reacting chamber as axial symmetry in geometry and these were, in fact, two-dimensional cases. The complete temperature distributions, detailed flow patterns and velocity fields in a planetary reactor were not accessible in these works, not to mention the transient phenomena, which affect significantly the early-stage chemical reactions and the initial nucleations. In addition, the flow in a planetary reactor is intrinsically three dimensional. To avoid the complexity and time-consuming process in re-meshing at each time step, the technique of dynamic meshes, which is relatively straightforward to the planetary-motioned boundary conditions in ANSYS Fluent, is not used. Instead, the slide mesh technique is employed in this study. Through self-developed User Defined Functions, we demonstrate the present approach is able to simulate gas flows in a planetary chamber and the detailed dynamics of thermal and flow can be authentically captured. Finally, we demonstrate the dynamics of gas flows for three different operating conditions in both Axitron G2 and G3 chambers, respectively, and their corresponding local growth rates are calculated and discussed.

並列關鍵字

MOCVD ； Fluent ； GaN ； Planetary Reactor ； TMGa

參考文獻

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