利用氟離子電漿處理製作出高效能增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體

Abstract

本論文探討了利用氟離子電漿處理，製作出高效能增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體。在閘極下方施打氟離子電漿處理，有效地移轉空乏型元件的工作範圍，成功將元件特性轉移為增強型操作模式。在經過氟離子電漿處理後，元件的臨界電壓(threshold voltage)呈現出0.7 V的增強型特徵。此增強型元件展現出高達580 mA/mm的源極飽和電流密度與185 mS/mm的最大轉導係數。脈衝電性量測也顯示出氟離子電漿處理在經過10分鐘的高溫退火後，對於磊晶結構的緩衝層具有相當小的傷害；此外，氟離子電漿處理的增強型元件也透露出源極電流密度與臨界電壓間，兩者的相抵得失。為了進一步增進氟離子電漿處理後增強型元件的臨界電壓，我們製作了氮化鋁鎵/氮化鎵金氧半高電子遷移率電晶體，並且選用原子層沈積系統沈積出氧化鋁薄膜。搭配16 nm氧化鋁當作閘極氧化層，成功將增強型元件的臨界電壓調變至5.2 V，並且擁有高達12.7 V的閘極起始電壓(turn-on voltage)；其元件電性表現方面則展現出520 mA/mm的飽和電流密度與100 mS/mm的最大轉導係數。 另一方面，我們也成功利用氟離子電漿處理，製作出增強型高崩潰電壓氮化鋁鎵/氮化鎵高電子遷移率電晶體。在漏電流密度達到1 mA/mm即為元件崩潰的定義下，元件均呈現出大於200 V的崩潰電壓。此外，其單一元件總輸出電流高達900 mA，並且在源極偏壓至200 V的情況下，僅出現150 μA/mm漏電流密度。上述元件特性，可以顯示出氟離子電漿處理，在未來高功率電子元件應用中，具有相當高的發展與應用潛力。

Enhancement mode (E-mode) AlGaN/GaN HEMTs utilizing Fluorine plasma treatment is investigated in this study. The Fluorine-plasma technique effectively converted the device from conventional depletion mode (D-mode) into E-mode operation. The threshold voltage of the AlGaN/GaN HEMT shifted to +0.7 V after F-treatment. A maximum drain current density of 580 mA/mm was measured at VG = 4 V, and peak transconductance was around 185 mS/mm at VG = 2.5 V. The pulsed ID-VD measurement shows the damages caused by Fluorine plasma treatment in the GaN buffer layer was removed after 400 ℃ annealing for 10 min. In addition, the F-ion treated E-mode HEMTs revealed a tradeoff between threshold voltage and current density. To increase the threshold voltage without sacrificing the current density, an E-mode ALD-Al2O3/AlGaN/GaN MIS-HEMT was fabricated to further increase the threshold voltage. An AlGaN/GaN HEMT with high threshold voltage of 5.2 V was demonstrated as truly normally-off operation along with high turn-on gate voltage of 12.7 V due to the insertion of a 16-nm Al2O3 layer under Schottky gate. The device also demonstrated a maximum drain current density of 520 mA/mm at VG = 11 V without large gate leakage and with a peak transconductance of 100 mS/mm. E-mode high-breakdown-voltage (HBV) AlGaN/GaN HEMTs were also developed. The developed devices have a breakdown-voltage higher than 200 V were achieved, as defined by drain (or gate) leakage current up to 1 mA/mm. The F-treated E-mode HBV HEMT demonstrated an output current as high as 900 mA under 3-V gate bias, and the device also showed a low leakage current of 150 μA/mm at VD= 200 V. The above results indicate such F-treated E-mode devices developed are promising for future power electronic applications.