以低壓有機金屬化學氣相沉積於矽基板上成長氮化鎵磊晶薄膜

Abstract

此論文，主要利用三種不同方法利用低壓有機金屬化學氣相沉積設備，成長氮化物於6吋矽基板上，並對氮化物半導體異質結構磊晶成長於矽基板上做一探討。 首先第一種方法，藉由 MOCVD方法，以多層氮化鋁與結合漸變氮化鋁鎵層為緩衝層，已可將高品質氮化鎵薄膜成功的成長於6吋矽基板上。緩衝層的結構、薄膜品質與厚度為成長高品質不會龜裂之氮化鎵層於矽基板上之主要關鍵。使用不同溫度下成長之多層氮化鋁並結合漸變氮化鋁鎵層為緩衝層，藉由此緩衝層的張應力降低與遞增的壓應力氮化鎵層，以獲得成長0.5微米厚度無龜裂氮化鎵薄膜於6吋矽基板上。 第二種方法，氮化鎵成長於多層氮化鋁與結合漸變氮化鋁鎵層為緩衝層，藉由調變氮化鋁中之鋁成份，由0調變至66%，藉有調變氮化鋁鎵中的鋁成份，藉以用來緩和因氮化鎵與矽基板於磊晶成長所產生的應力。以高解析度X光繞射對於氮化鎵薄膜進行對稱與非對稱的ω/2θ分析與倒置晶格圖譜分析氮化鋁鎵中鋁成份組成與氮化鎵薄膜所導致的應力之間關係。發現適當的設計氮化鋁鎵層中的鋁成份能有效的緩和氮化鎵與矽基板成長時所產生的應力，並成功的應用多層氮化鋁與結合漸變氮化鋁鎵層為緩衝層於6吋矽基板上磊晶成長為裂痕之氮化鎵薄膜。 最後，第三個方法，以氮化鋁為成核緩衝層並結合兩步驟不同成長條件長晶，低應力，低差排密度氮化鎵成功的成長於圓型圖案化矽基板上。拉曼量測顯示氮化鎵成長於圖案化矽基板具有有效降低薄膜內部應力。以PL對氮化鎵薄膜進行量測，PL曲線具有往短波長位置偏移(blueshift)可以更明顯證明氮化鎵成長薄膜張應力被圖案化矽基板部份釋放。可以相信因晶格不匹配與熱膨脹系數差異過大所產生的應力，可藉由多晶面向的氮化鋁緩衝層與此邊界產生的差排密度，有助於將氮化鋁上成長的氮化鎵薄膜釋放應力，進而獲得於圖案化矽基板上成長無龜裂之氮化鎵薄膜。

In this thesis, the heterostructure growth of GaN on Si substrate by Low-pressure metal-organic chemical vapor deposition (LP-MOCVD) is studied. The investigation focuses on the growth of GaN on 6 “ Si (111) wafer. There different approaches werw including in this study. In the first approach, high quality GaN film was successfully grown on 150 mm Si (111) substrate by MOCVD method using multilayer AlN combined with the graded AlGaN layer as buffer. The buffer layer structure, film quality and film thickness are critical for the growth of the crack free GaN film on Si (111) substrate. Using multilayer AlN films grown at different temperatures combined with graded Al1-xGaxN film as the buffer, the tensile stress on the buffer layer was reduced and the compressive stress on the GaN film was increased, as a result, high quality 0.5 μm crack-free GaN epitaxial layer was successful grown on 6” Si substrate. In the second aaproach, the GaN film was grown on Si substrate using multilayer AlN/AlxGa1-xN buffer by low pressure metal organic chemical vapor deposition (MOCVD) method. The AlxGa1-xN films with Al composition varying from 0~ 0.66 was used to accommodate the stress induced between GaN and Si substrate during GaN growth. The correlation of the Al composition in the AlxGa1-xN films with respect to the stress induced in the GaN film grown was studied using high resolution X-ray diffraction including symmetrical and asymmetrical ω/2θ scans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1-xN buffer layer, crack-free GaN film can be successfully grown on 6” Si (111) substrates using multilayer AlN and AlxGa1-xN buffer layers Finally, in the third approach, low stress, low defect density GaN film was successful grown on circle array patterned Si (111) substrate using AlN as the nucleation buffer followed by two steps growth of the GaN film. Raman measurement shows a reduction of the in plane biaxial stress for the GaN film grown on patterned substrate. The slight blueshift of the band edge PL peaks further provides the evidence that the tensile stress in the GaN film was relaxed in the patterned Si substrate. It’s believed that the grain boundaries of the polycrystalline AlN buffer layer and the dislocations in the GaN film grown helped to relieve the stress induced by the lattice and the thermal coefficient mismatches during growth.