氧離子佈植應用在氮化鎵高電子遷移率電晶體隔離技術之探討

Abstract

本實驗的目的在於應用離子佈植隔離技術於氮化鎵高電子遷移率電晶體 (HEMTs) 之製作。離子佈植隔離技術的優點在於可發展出平坦化製程，可解決平台蝕刻隔離技術所造成蝕刻深度和形狀的問題，本研究使用氧離子佈植，在實驗中找出最佳之佈植條件及退火條件以達到最佳之元件隔絕效果。本研究是以元件間之漏電流來決定其隔絕效果。文中詳述了各個製程步驟的技術及直流特性，並研究離子佈植隔離之特性。 本實驗製作之AlGaN/GaN HEMT的閘極長度為0.3μm，閘極寬度為125μm，其直流特性具有40.1mA/mm的飽和電流密度，傳導率 (transconductance) 為39.36 mS/mm，截止電壓 (pinch-off voltage) 為-1.2 V，閘極-汲極間的崩潰電壓為84V。在使用氧離子佈植技術隔離後，元件間的漏電流為352 nA，具有很高的隔離效果。在Si3N4保護層覆蓋後，元件直流特性為30.6 mA/mm的飽和電流密度，傳導率 (transconductance) 為37.3 mS/mm，閘極-汲極崩潰電壓則昇為115V。 最後並討論經過不同退火溫度，對氧離子佈植隔絕效果之影響。同時並利用拉曼，ESCA及DCXRD 量測，觀察經過不同退火條件下，離子佈植對氮化鎵材料內部結構和鍵結之變化，以闡釋所觀察到的電性改變。

GaN-based electron devices have received much attention owing to their ability to operate at a high power level and in a high temperature environment. The GaN high electron mobility transistor (HEMT) has been developed for high frequency and high power application for power amplifiers in wireless communication. This experiment focuses on the application of ion implantation isolation technique for GaN HEMT fabrication. Device isolation serves a number of purposes. In active devices, it restricts the current flow to the desired path and electrically isolates separate devices from each other. It also reduces parasitic resistances and capacitance. Device isolation by ion implantation been widely used in III-V compounds. Implantation isolation is a planar process and has the advantages of easy control in dosage and energy, and can avoid the undercut problems using mesa etch technique. In this study, oxygen ion implantation for isolation was investigated, implantation dosage, energy and annealing conditions were experimented to achieve the optimum isolation effect between devices. The leakage current between devices was used to determine the isolation effect after implantation and annealing. Detailed process steps were described and the electrical characteristics of the devices after ion implantation isolation were also presented in this thesis. The gate length and gate width of the AlGaN/GaN HEMTs in this experiment were 0.3μm and 125μm, respectively. The energy and dosage of oxygen ion implantation were 150KeV and 5x1013cm-2 for device isolation. The devices exhibited the saturated drain current density of 40.1 mA/mm and the transconductance of 39.4 mS/mm. The pinch-off voltage was –1.2 V and the gate-to-drain breakdown voltage was 84 V. After oxygen ion implantation isolation, the leakage current between devices was 352 nA which is low enough for device isolation. After Si3N4 passivation, the devices exhibited the saturated drain current of 30.6 mA/mm and the transconductance of 37.3 mS/mm. The gate-to-drain breakdown voltage was 115 V. Finally, the influences of annealing temperature on the oxygen ion implantation isolation were studied, and Raman spectra, ESCA, and DCXRD analysis were used to explain the composition and bonding changes of the oxygen implanted GaN material after different annealing temperatures.