由多區域溫度回授控制有機金屬化學氣象沉積製程晶圓溫度均勻度最大化

Abstract

MOCVD (Metal Organic Chemical Vapor Deposition)製程中，有許多因素會影響晶圓品質，如晶圓溫度均勻度等，快速熱過程(RTP)是用以高溫製造單片半導體晶圓的過程[1]-[6]，加熱晶圓時必須使用非均勻能量通量進行加熱，晶圓在高溫操作時會有邊界效應，故須使用非均勻熱通量以提升溫度均勻度，提升晶圓表面溫度均勻度為此研究之目標，藉由設計模型參考(Model Reference)由多區域回授控制以達到承載盤上晶圓溫度均勻度最大化[7]-[10]。 控制晶圓表面溫度均勻度的方法有很多，如模型預測控制(MPC)[11]，線性二次高斯控制(LQG)[12]，內模控制(IMC)[13]，隨時變最佳化控制(time-varying optimal control)[14]。離線控制器基於承載盤上每個區域受限數量的熱傳模型做設計[15]-[18]，此離散模型是建立於熱傳基礎理論與有限元素模型結合，加熱器分段控制對應之點，提供不同的功率回授控制並調整PID控制器中之參數使得暫態過衝量最小化[19]-[22]，建立有限元素模型，並成功的在COMSOL軟體中寫入PID回授控制式，溫度偵測點測得溫度後將回授至加熱器進行功率調整控制，使得溫度均勻度得以提升，線圈間獨立控制操作，並成功的驗證控制器效能，使未經控制之晶圓表面溫度最大溫差12.5°C，經過控制後而達到4°C內，模擬結果顯示晶圓表面溫度變化有效的控制在0.4% (1000±4°C)。

During the process of metal organic chemical vapor deposition, many of reasons will affects the quality of the wafers, such like non-uniformity in the temperature distribution of a wafer in a MOCVD process, rapid thermal processing (RTP) is used for single-wafer processes at high-temperature in semiconductor manufacturing [1]-[6], in order to achieve a nearly uniform wafer temperature distribution for multizone system by applying a non-uniform heat flux [7]-[10], it is well-known that a non-uniform flux is required because of wafer edge effect. The study aims at maximizing temperature uniformity of wafers in a MOCVD process by designing a model-reference controller. The strategy for automatically control wafer temperature uniformity for multizone lamp systems has well researched, at least five different solutions have been proposed, including MPC control [11], LQG control [12], IMC control [13], time-varying optimal control [14]. The controller is designed off-line based on a discretized heat transfer model of a susceptor in a limited number of annual zones [15]-[18]. The discretized model is established by fundamental heat transfer theory and an associated finite element model, and apply non-uniform heat flux to the wafers form a closed loop and feedback the temperature by the probe, tune the parameter to minimizing the transient without large overshoot [19]-[22]. Finally, established finite element model is used again in successfully build a feedback closed loop control system in COMSOL, set up three points as a temperature probe points each point are control by its own zone heat controller, feedback the temperature to the heater and again until the temperature distribution is nearly uniform, each part of the heat controller are independently manipulated and successfully validating the effectiveness of the controller designed. The maximum temperature difference is 12.5°C, and after controlled the temperature is under 4°C. Simulation data show that temperature variation of the wafer is effectively controlled within 0.4 percent (1000±4 °C).