利用低損傷中性粒子束蝕刻的方式製作出高起始電壓低磁滯的掘入式閘極增強型氮化鎵金屬-絕緣體-半導體高電子遷移率高功率電晶體

Abstract

氮化鋁鎵/氮化鎵增強型高電子遷移率電晶體已經被廣泛研究，氮化鎵具有寬能帶、高崩潰電壓、高峰值電子速率、高電子飽和速率、鍵結力與熱穩定性佳，是故氮化鎵有機會成為下一世代高功率元件的主要材料。 有些文獻中常以氧化鋁當介電層用以改變電性表現。然而多數文獻中已經證實氧化鋁/氮化鋁鎵的界面會產生高濃度的界面能階，導致載子被侷限在陷阱中以及起始電壓正向偏移的現象。 本研究使用高介電常數的二氧化铪當介電層，以及使用低損傷中性粒子束蝕刻的方式製作出高電流且可改善起始電壓穩定性的增強型金屬-絕緣體-半導體高電子遷移率電晶體，並建立其標準化製程。此結構擁有比文獻中，利用單層氧化鋁當介電層擁有更高的起始電壓穩定性。而且同時保有比較高的起始電壓，如此用以減少因為雜訊而不正常開關的情況。本實驗以傳統的增強型高電子遷移率電晶體，做蝕刻製程之參數測試，以找到對元件表現最佳化之條件。此元件擁有499 mA/mm的通道電流，70 mS/mm之互導係數，4.4 V的高起始電壓並擁有超過672 V之崩潰電壓。而此結構同時具有非常低的起始電壓偏移率(63 mV)。由於以上電性表現證實此元件適用於高功率應用上。

GaN-based devices are attractive candidates for high-power applications such as next-generation wireless base stations and power switching devices. AlGaN/GaN enhancement-mode high electron mobility transistors (HEMTs) has been extensively studied in recent years. In the past few years, some groups use Al2O3 as gate insulator to improve electrical characteristics. However, high density of interface states in Al2O3/AlGaN interface has been reported, which lead to charge trapping effect and positive threshold voltage shift. In this thesis, gate recess by neutral beam etching (NBE) system is used to fabricate E-mode SiNx/HfO2/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MISHEMTs). This structure has high threshold voltage stability by DC measurement. Additionally, this structure can achieve very high threshold voltage ( > 3V ) to avoid the mis-operation of the device. Conventional E-mode HEMT was used for process parameter evaluation to optimize etching process, and then the gate-recessed E-mode MIS-HEMT standard process was established. The device demonstrated 499 mA/mm, 70 mS/mm, 4.4 V, 11.1 Ω•mm and 672 V for channel current density, transconductance, threshold voltage, ON-resistance and breakdown voltage, respectively. Furthermore, the device shows very small △Vth about 63 mV . It indicates that the GaN E-mode MISHEMTs are promising for power switching applications.