- 學位論文
反應速率與均勻度對於低壓化學氣相沉積影響之研究
Study on the Influence of Reaction Rate and Uniformity during Low Pressure Chemical Vapor Deposition Process
摘要
自 1975 年，低壓化學氣相沉積 (LPCVD) 技術以熱壁爐管反應器於半導體業界占主導地位，以控制製程參數來設定晶片的多晶矽厚度均勻度目標，來達到元件一致性要求。儘管 LPCVD 爐管一個批次 61 片晶圓厚度變化只幾個百分點，但是厚度分佈還是呈現 S 型曲線且為傳質效應與表面化學反應所影響。 在過去的幾十年裡，許多研究人員一直在開發數學模型來描述各種物理和化學過程。通常使用連續方程數學模型描述 LPCVD 反應器中熱傳質傳流動。以模擬評估諸如溫度和表面化學反應等對製程的影響。而沉積速率的主要因素是溫度，它影響多晶矽表面上矽甲烷熱解和氫脫附表面化學反應。 本論文的主要目標是利用模擬技術研究 LPCVD 中涉及的關鍵製程參數，以找出 S 型曲線的根本原因所在。過程中先以實驗數據與模擬計算做比對，化學表面反應的活化能是沉積率主導因素，而沉積率又與晶圓表面薄膜均勻度完全相關，所以 LPCVD 的均勻度最終為製程中的溫度所掌控的。 實驗數據的最終結果只能以歸納法推測溫度是否為其主因但無法做定量的論述，本研究透過計算流體力學模擬證實溫度就是 S 型曲線主因而且還可以將儲存數據再進一步做定量分析。本研究所發展的模擬模型對於深入多批次晶片 LPCVD 的製程特性和影響厚度均勻性的參數掌握以及半導體反應器設計將能提供極大助益。
並列摘要
The low-pressure chemical vapor deposition (LPCVD) techniques have been utilized in the semiconductor industry since 1975 with hot wall furnace type reactor. The poly-crystalline silicon was studied to define the wafer thickness uniformity with controlling process parameters for requirement device consistence performance. The S type curve over LPCVD furnace is found in the 61 wafers in one batch run, although its thickness variation is less than a few percent per batch, which could be mass transport effect and surface reaction to dominate uniformity curve. Over the last decades many researchers have been developing mathematical models to describe the various physical and chemical processes. For gas flow with heat and mass transfer in LPCVD reactors models based on continuum equations are generally used. Simulations was conducted to assess the effects of contributing processes like temperature and surface chemical reactions. The dominate factor of the deposition rate is temperature which affects the surface chemical reactions during silane pyrolysis and hydrogen desorption on silicon surface. The purpose of the thesis is the investigate the key process parameters involved in the LPCVD in order to find the root cause of S type curve and then optimized the wafers uniformity within a batch run. The simulation studies reported the temperature gradient dominate the surface reactions. For uniformity consideration, the detail gas phase chemical model is not key factor to influence the uniformity. Focus on obtaining the knowledge required to be able to solve S type curve wafer uniformity problem using CFD and ab initio calculation are widely used to design semiconductor reactors which have advantage solving deposition uniformity problem.