利用直接模擬蒙地卡羅法模擬陣列式蒸鍍源有機發光二極體薄膜沉積之研究

Abstract

近年來，由於有機發光二極體(OLED)相關研究引起極大的關注，與液晶顯示器相比不需背光源且具有更好的亮度、高對比度與可饒性。OLED薄膜沉積製程是利用物理氣相沉積法。腔體內部為真空狀態，其連續流體的假設已不成立。除了試誤法外，模擬不僅提供製程過程的設計，也能變更相關操作條件。直接模擬蒙地卡羅法(DSMC)是一種particle-based的方法。在統計上，只要足夠大的模擬分子數量，對於求解波茲曼方程式中，它被視為是最為有效和準確的方法。 在論文中，我們使用了平行化混和非結構網格DSMC的程式(名為PDSC++)。利用PDSC++程式進行模擬薄膜沉積過程中，陣列式蒸鍍源以餘弦分佈n=5之條件進行模擬。為了降低模擬網格與計算時間，我們提出與驗證可簡化陣列式蒸鍍源的等效面積法(LEAM)。本研究目的為改變蒸鍍源與基板間的距離，進而探討其材料利用率，以及薄膜均勻度與該距離之關係。 首先，我們證明使用LEAM法，可將10x10陣列式蒸鍍源簡化為單一蒸鍍源。此簡化過程中，可使網格數目大幅減少，並且得到相同的蒸鍍速率 與相近的不均勻度，其值分別為0.13%與0.19%。 在論文第二部分中，我們利用PDSC++程式模擬真實物理薄膜沉積的製程，利用LEAM來簡化其模擬蒸鍍面積為5x5cm2的陣列式蒸鍍源(由台灣工業技術研究院所設計)。此模擬之陣列式蒸鍍源相同，改變蒸鍍源與基板間距離為20mm、50mm與100mm，其模擬結果顯示，不均勻度分別為23.73%、18.14%與8.16%。根據上述結論，我們提出改進設計，將陣列式蒸鍍源外圍單位蒸鍍源面積增加，稱為不均勻陣列式蒸鍍源。在蒸鍍源與基板間距離為50mm與100mm，不均勻度降低為8.16%與7.45%。

Recently, organic light emitting diode (OLED) related research has attracted tremendous attention because it does not need a backlight source, unlike liquid crystal display (LCD), and can be flexible with good brightness and high contrast. OLED thin film is often deposited using physical vapor deposition in a vacuum chamber, in which continuum flow assumption fails. In addition to trial-and-error method, simulation can be an important tool in optimizing the design of processing chamber and related operating conditions. The direct simulation Monte Carlo (DSMC) method applies no more than collision kinetics in directly and statistically simulating the Boltzmann equation using a large number of pseudo particles, which each particle represents a large number of real molecules. In this thesis, we apply a previously developed parallel DSMC using an unstructured grid, named PDSC++, to simulate the deposition process within a vacuum chamber with a complex geometry. The stream of atoms evaporating from the patterned source surface are modelled using the cosine law distribution with n=5. To reduce the computational cost, a lumped equivalent area method (LEAM) for lumping a periodic array of evaporating sources into a single source with the same area is proposed and verified. Study of conversion efficiency and uniformity at the substrate by changing the gap distance between source and substrate is performed. In the first stage, we prove that a patterned 10x10 array of sources can be lumped into a single source using the LEAM, which can dreamatically reduce the number of cells and thus computational cost. The LEAM preserves not only the deposition rate with the same value as , but also predicts a similar non-uniformity distribution as 0.13% and 0.19% for for 10x10 array and single source respectively. In the second stage, a physcial vapor deposition process is simulated using the PDSC++, in which the LEAM is implemented to a 5x5 cm2 source in a realistic vacuum chamber designed by Industrial Technology Research Institute (ITRI), Taiwan. The predicted non-uniformity is 23.73%, 18.14% and 8.16% for different gap distances of 20 mm, 50 mm and 100 mm, respectively. Based on the above results, an improved design of non-uniform array pattern is proposed, in which the area density of source size increases from central to edge region. The non-unifromity of the deposited film is found to decrease down to 8.16% and 7.45% at gap distance 50 mm and 100 mm, respectively, with essentially the same deposition rate.