高功率電子應用之氮化鎵半導體於矽基板的元件製作與特性研究

Abstract

氮化鎵系列高電子遷移率電晶體與大尺寸矽基板之整合，除了具備大電流輸出與高崩潰電壓之特性外，更有低製造成本之優勢。因此成為了下一世代高功率電子元件的新寵兒。本論文將著重於矽基板上的氮化鎵系列電晶體元件製造技術，利用高品質閘極絕緣層改良元件特性以降低電流衰退現象。另一方面，開發無金閘極結構來提升元件在高溫操作下的熱穩定性。論文首先是使用氧化鋁/氮化鋁複合絕緣層對金屬-絕緣體-半導體氮化鋁鎵/氮化鎵電晶體特性改善之研究。實驗結果發現插入氮化鋁絕緣層可使元件的臨界電壓遲滯僅有200mV的正負變化。除此之外，該元件在汲極電壓100V、15小時的可靠度試驗下，汲極電流仍可保持定值。論文第二部分成功整合了閘極掘入技術與第一部分研究成果，成功製作出具備低臨界電壓遲滯效應之常關式金屬絕緣半導體氮化鎵電晶體。該常關式元件擁有1.5V之臨界電壓和高電流密度420mA/mm，並同時具備汲極開關電流比值~109以及高崩潰電壓600V。論文第三部分則是利用氮化鎢與銅金屬，成功製作出可應用在高功率電子中的無金閘極結構之氮化鋁鎵/氮化鎵電晶體，該元件之電流特性與傳統鎳/金閘極結構元件相比幾乎不相上下。同時，該元件在汲極電壓200V、42小時長時間的可靠度試驗下，依舊保有原來的特性表現。我們更將此元件進行2500C的退火處理達一個小時，並觀察其電流和蕭特基接觸特性變化。研究發現無金閘極結構之元件在升降溫之後亦能保有相當良好之特性。

The integration of GaN-based High Electron Mobility Transistors (HEMTs) and a large diameter Si substrate are promising candidates for next-generation high power device applications owing to the high current, high breakdown, and low fabrication cost. This thesis focuses GaN-based HEMTs on Si with low current collapse by high quality gate insulator and development of gold free gate structure with high thermal stability. First of all, the stable electrical properties of Al2O3/AlN/AlGaN/GaN metal-insulator-semiconductor (MIS-HEMTs) by using an Al2O3/AlN stack layer as the gate insulator layer were investigated. The device exhibits a small threshold voltage hysteresis of ~200mV. Additionally, no obvious changes in the drain current were observed for the device during the drain voltage stress of 100V for 15 h. Secondly, a gate recessed normally-OFF Al2O3/AlN/AlGaN/GaN MIS-HEMT with low threshold voltage hysteresis is demonstrated. The device exhibits a threshold voltage of +1.5 V, with current density of 420mA/mm, an OFF-state breakdown voltage of 600V and high ON/OFF drain current ratio of ~109. Finally, a GaN HEMT with WNX/Cu gate for high power application is developed. The direct current (DC) characteristics of the device are comparable to a conventional Ni/Au gated GaN HEMT. The results of a high voltage stress test indicated that the device was stable after 200 V stress was applied for 42 hours. Additionally, the WNX/Cu gated GaN HEMTs exhibits no obvious change for DC characteristics and Schottky barrier height before and after 2500C annealing for 1 hour.