高溫適用之氮化鎢T型閘極氮化鋁鎵/氮化鎵高速電晶體之製程開發與材料分析

Abstract

本研究成功地研發出以氮化鎢為T型閘極材料的氮化鋁鎵/氮化鎵之高電子移動率電晶體。經由有基金屬化學氣相沉基法成長氮化鋁鎵/氮化鎵高速電晶體結構，並開發新的元件製作技術，尤其側重於蝕刻技術及耐高溫之金屬電極之開發。本論文一開始探討氮化鎵磊晶成長，藉由探討低溫孕核層的升溫退火過程，達到孕核的最佳化。所成長的氮化鎵薄膜，以低溫光激光光譜量測其能帶結構。 發現激子放射的能帶分裂現象，以低溫光激光光譜所量測到氮化鎵價帶的能帶結構可用電子自旋耦合效應解釋，並與而與理論相符合。在氮化鋁鎵/氮化鎵異質結構中，清楚觀察到二維電子氣在低溫下的次能帶躍遷現象；並探討次能帶結構與鋁含量、間隔層厚度的變異情形。誘導耦極電漿及光化學輔助蝕刻技術也在本論文中有深入的探討，藉由蕭基二極體的特性分析，達到蝕刻參數的最佳化。應用複合式蝕刻技術，可以有效地降低表面損傷的情形，並將該技術成功地應用在電晶體閘極的製作上。除此之外，也開發高溫電極材料。氮化鈦鎢及氮化鎢在氮化鎵上皆可形成的蕭基接觸，但因鈦原子的易擴散性，高溫下的蕭基二極體特性以氮化鎢為優。最後，利用上述所開發出之蝕刻技術及耐高溫電極材料，成功地製作出之0.7微米氮化鎢T型閘極氮化鋁鎵/氮化鎵異質接面高速電晶體可在高達至少攝氏330度下仍運作正常。

AlGaN/GaN HEMTs (high electron mobility transistor) with WNx T-gate for high temperature applications were revealed. The materials growth of AlGaN/GaN HEMT structures and device fabrication techniques were developed, especially for high temperature applications including metallization and etch techniques. This dissertation starts with the epitaxy of the GaN. The recrystallization process was optimized by the ramping rate. The PL of the GaN at low temperatures was discussed in details that showed the fine structure of the valence band. The 2DEG related intersubband emissions of the AlGaN/GaN heterostructures were observed at low temperatures. The effects of the Al compositions and spacer thickness on the energy levels of the subbands in the triangular well of the AlxGa1-xN/GaN heterostructures were discussed. The ICP (Inductively coupled plasma) and PEC (photo-ehanced chemical) etch were also investigated in this dissertation. Schottky diodes characteristics were as indexes in optimizing the parameters. By applying the hybrid ICP and PEC etch, it is possible to minimize the surface damages after etch. The hybrid etch technique was than applied to fabricate the HEMTs in this dissertation. The metallizations, the Ohmic electrode and the Schottky electrode, for high temperature applications were also studied. The TiWNx and WNx were used as Schottky contact materials. The materials analysis showed that the Ti atoms in TiWNx were easy to diffuse into the GaN. As a result, the WNx was the better choice in fabricating Schottky electrode. The thermal stability of the Ti/Al/Pt/Au Ohmic contact and the WNx Schottky contact to GaN were proven to working well at high temperatures. Using the etch techniques and the metallization techniques developed here, the WNx T-gate HEMTs were carried out. According to the DC characteristics at high temperatures, the WNx T-gate AlGaN/GaN HEMTs showed high thermal stabilities that were very suitable for high temperature applications.