| 摘要: | 金屬有機化學氣相沉積法(Metal Organic Chemical Vapor Deposition, MOCVD)具有良好的磊晶薄膜均勻性及大量生產等優點，為LED製程主要的磊晶技術。MOCVD設備中進氣系統為一相當關鍵的模組，其中近耦合噴淋式反應腔體因該機台具有較低的腔體高度和如蓮蓬頭般的多孔洞進氣系統設計，使得流場穩定和物種分佈均勻，具有較寬的製程裕度，並能減少金屬有機化合物的使用量，不過這樣的設計卻容易使進氣系統噴嘴處阻塞。本研究將利用數值模擬探討噴嘴處因反應物種吸附所造成的阻塞情況，模擬一個直徑20 cm的腔體，並考量腔體內的熱流場、質量傳輸現象及化學反應，調整進氣流速及進氣比例，觀察反應物種吸附率的變化，最後進行進氣噴嘴的改良設計。
首先探討進氣流速以及進氣比例的改變對於噴嘴處吸附率的影響，研究發現當TMG進氣比例越高，噴嘴處吸附率和載盤長率皆會增加；隨著進氣流速增加，噴嘴處的吸附率降低，而載盤上的長率呈現線性成長的趨勢。此外，結果顯示造成噴嘴處阻塞的主要吸附物種為TMGNH3。
接著對進氣噴嘴進行改良設計，在不影響載盤上磊晶薄膜成長的基準之下，探討噴嘴處反應物種吸附情形。在進氣噴嘴倒角的情況下，載盤上的長率僅減少約0.4%，而噴嘴處的吸附率也減少約5.3%，有助於改善噴嘴處阻塞的情況。最後在同心圓進氣設計的結果可以發現，噴嘴處吸附率降低約36.3%，但是載盤長率因為多通入大量H2的影響而減少約22.6%，必須提高TMG進氣比例才能將原有的長率補回。不過增加同心圓進氣設計之後，對稱軸附近的長率變的較不均勻，需要適當調整對稱軸附近的H2進氣管流速，長率才會趨於均勻的狀態。因此，同心圓進氣噴嘴設計也是能改善噴嘴處阻塞的情況。
;Metal organic chemical vapor deposition(MOCVD) has good epitaxy film uniformity and is suitable for mass production. It is the main fabrication process for the LED. MOCVD equipment, the source gas inlet system is very critical. The close coupled showerhead(CCS) is one the important inlet system design. It uses multiple holes, to make the flow uniform and stable, and thus increase uniformity of the deposit film. The process has large processing margin and can reduce the amount of the metal organic compound. The CCS design, however, is easy to cause clogging of the inlet orifices. In this thesis, we numerical simulate the clogging rate of the orifices of a CCS reactor due to adsorption of the reactive species. The simulation takes accounts of fluid dynamics, heat and mass transports, and chemical reactions, and the flow, temperature, and species distributions are obtained. The deposition rate and the adsorption rate then can be calculated to evaluate the deposition performance and the clogging degree. Finally, a modified inlet system design is proposed.
In the study, we first, consider the flow rate effects on the inlet nozzle adsorption rate. It is found that the higher proportion of TMG in the inlet gas source, the higher the adsorption rate at the inlet nozzle and the higher the growth rate at the susceptor. When the flow rate increases, the adsorption rate at inlet nozzle decreases, but the growth rate at susceptor enhances. Furthermore, the results show the main species causing nozzle clogging is TMGNH3.
In the inlet nozzle design, the chamfered nozzle and the concentric nozzle designs are studied. In the case of the chamfered nozzle, the growth rate on the susceptor reduces 0.4%, while the adsorption rate at the nozzle reduces 5.3%. The effectiveness of using chamfers are not remarkable. In the concentric inlet design, it is found that the adsorption rate at the nozzle reduces 36.3%, while the growth rate on the susceptor decreases 22.6% due to the dilution of additional H2. Also, the growth rate near the symmetry axis becomes less uniform. By adjusting the flow rate of the H2 in the concentric nozzles, the situation can be alleviate. Overall, the concentric inlet nozzle design is promising in reducing the nozzle clogging. |
