| 摘要: | 氮化鎵（GaN）薄膜材料是目前全世界半導體材料研究的熱點，金屬有機化學氣相沉積法（MOCVD）技術由於具有外延層(epitaxial layer)均勻性較好、材料純度高等優點，為現今LED磊晶產業用於生長氮化鎵的重要製程技術。
本研究利用有限元素分析法(FEM)，建立表面吸附之化學反應機制，為使生長速率計算更接近實際製程，同時考慮物種由於質傳與表面反應造成的反應消耗，利用數值模擬，藉由Langmuir熱力學定理計算氣相反應後各物種在晶圓表面上的吸附速率，並以MMG作為主要的吸附物種，主要的反應式共有3條。
首先，利用不同腔體模型建立表面吸附模型，與文獻之實驗結果進行對比驗證，證明本研究之物理模型的準確性，并探討影響表面反應速率的主要參數如溫度(550-1050℃)對薄膜生長速率的影響。接著探討製程參數如TMG/H2氣體流量(25-75 slpm)、載盤轉速(500-1800 rpm) 以及腔體壓力(30-90Torr) 對薄膜生長速率及均勻性的影響。
模擬結果顯示，增加進氣流量使薄膜生長速率變快，但會降低薄均勻性；增加載盤轉速可提高濃度梯度，使薄膜生長速率增加，但高轉速下容易造成載盤中心的濃度堆積；增加腔體腔力可明顯提升薄膜生長速率，使載盤中心與外側的生長速率差異變小，但高壓下，容易造成腔體流場不穩定。
接下來使用考慮實際入口之原始三維腔體模型，對基本幾何參數與入口幾何參數進行設計，結果顯示腔體直徑為177mm，h/D為0.51時， 能夠達到較好的薄膜生長速率及均勻性；增加viewport外環氫氣進氣口能夠有效改善物種在viewport下方的聚集現象，當vH2:vTMG =4時viewport下方的渦流消失。
最後，藉由優化入口幾何設計以得到更佳的均勻性結果，結果顯示圓環形切割slot jet（入口3）能夠增強中心區域的擴散並減少中環區域的物種濃度從而達到更好的均勻性。;GaN is a remarkable semiconductor material in the current investigation. Because of the unique advantages of high purity, good quality, and suitable method for high mass production with a large deposition area, the films are produced by MOCVD. At present, MOCVD technique has been widely applied to manufacture GaN films.
This study uses the FEM method, builds the mechanism of chemical adsorption based on the Langmuir isotherm. After comparing the adsorption rate of the different species, MMG is entered into the major consideration, as the result, the MMG molecule which deposited on the wafer surface is mostly generated by 3 gas reaction processes.
Firstly, the study modifies the temperature variation from 550 to1050℃，makes the comparison with the experimental results, and investigates the effect of varying these manufacturing parameters, such as gas flow rate (25-75 slpm) , rotation rate of wafer carrier (500-1800 rpm), and chamber pressure (30-90 Torr), on the growth rate and film thickness uniformity.
The results indicate that the increase of gas flow rate improves the growth rate of the film but makes deterioration of uniformity. Moreover, enhancing the chamber pressure and wafer carrier rotation rate can accelerate the diffusion speed of specie to get a better growth rate and film thickness uniformity. However, higher speed and higher pressure lead to the instability in the flow field.
After that, we considers the real gas inlets of the 3D model of Veeco D180 chamber, design of the basic geometry and then the study of optimization of the gas inlets was done. The result presents that when the radius is 177mm, ratio of h/D is 0.51, the film thickness uniformity is better. The setting of the hydrogen inlet can effectively improve the species aggregation below the viewport, and the vertical below the viewport will disappear when vH2:vTMG =4.
Finally, the study of optimization of the gas inlets was done. The results shows the inlet design with circle arrangement will enhance the diffusion of gas and also reduce the uniformity of the film. |
