本研究探討MOCVD製程中生長AlN薄膜的複雜化學機制和傳輸現象，研究發現間歇性噴流設計對降低製程中氣相微粒(Particle)產生及增加沉積速率有良好的影響，可透過寄生反應及物種擴散速率作很好的解釋，特別是在高溫和高壓條件下生長速率降低的機制。TMAl與NH3混合反應後會產生TMAl:NH3之加合物，加合物之熱裂解反應路徑所產生之二聚體(dimer)及三聚體(trimer)會形成無法貢獻長率之n-聚體(n>3)及氣相微粒，使反應氣體利用效率降低，是造成增加溫度及壓力使生長效率降低的主要原因。 為了探討在生長AlN薄膜時所產生之寄生反應，本研究先建立在入口處反應氣體TMAl、NH3及載氣H2同時混合之穩態模型，與文獻之實驗結果進行比對驗證，並探討在不同溫度、壓力、反應前驅物流量及載氣流量對薄膜生長速率的影響。 接著本研究透過氣體脈衝方法[Pulsed Injection (PI) Method]，在持續供應載氣H2的情況下控制反應源氣體TMAl及NH3噴入反應腔體間隔時間(0-0.3秒)，以抑制TMAl與NH3混合所產生之寄生反應，藉此減少聚合物及Particles之生成，提高反應源氣體使用效率。研究發現隨著反應源氣體進入反應腔體之間隔時間增加， TMAl與NH3的混合可以有效的抑制，主要反應路徑由TMAl:NH3熱裂解轉變為TMAl自身熱裂解反應，TMAl熱裂解所產生之Al*與NH3自身反應所產生的NH2*表面物種會成為主要物種，透過表面摘取反應吸附成為AlN薄膜。研究結果顯示，當氣體脈衝間隔時間為0.2秒時，可以有效降低Particles形成，並將沉積速率保持在大致相同的值，Al含量也因此增加，提高晶體品質。反應氣體間隔時間不能為無限大，會減少氣體停留時間，使沉積率下降。 ;In this study, a complicated chemical mechanism and mass transport phenomena of growing AlN films in metal organic chemical vapor deposition prosess were disscussed. It is found that the pulsed MOCVD design has a good effect on reducing particle generation and increase the deposition rate. It can be explained by the parasitic reactions and diffusion rate, especially the mechanism of reducing the growth rate under high temperature and high pressure. The mixture of TMAl and NH3 will produce TMAl:NH3 adducts. The dimer and trimer which produced from the TMAl:NH3 adduct-derived route will form n-mers (n>3) and particles deposit on the walls and do not contribute to the growth. The reduction of the utilization efficiency of the reaction gas is the main reason that cause the decrease of the deposition rate. In order to study the parasitic reaction of growing AlN films. The steady state model of TMAl, NH3 and H2 mixed gas at the inlet was established, and compared with the experimental results of the literature. The effects of temperature, pressure, precursor flow rate and carrier gas flow rate were discussed. The precursors were injected into the reaction chamber by pulsed injection (PI) method. Interval times of (0-0.3s) were inserted between TMAl and NH3 supplied. The carrier gas H2 was continuously supplied to supress parasitic reactions. With the increase of interval time, the mixing of TMAl and NH3 could be effectively suppressed, and the TMAl polysis path becomes the main growth pathway. The Al atoms from TMAl pyrolysis and NH2 molecules from NH3 self reaction will become the main surface species and adsorbed into AlN film with abstration reaction. The result shows that 0.2 second is the best interval times, that particle formation can be reduced effectively. It is found that the pulsed injection method not only can kept the deposition rate at almost same value, but also improve the crystal quality. The interval time width cannot be indefinitely large, it will reduce the gas residence time and decrease the deposition rate.
