氮化鋁鎵/氮化鎵高電子遷移率電晶體之可靠度分析與閘極氧化製程優化

Abstract

本論文首先將介紹氮化鎵高電子遷移率電晶體的原理與結構，並介紹磊晶層中所存在的缺陷。緊接著介紹氮化鎵的電流崩塌效應，連結此效應與材料中缺陷的關係，並量測不同的鈍化層對電流崩塌效應的影響，其中SiO2作為鈍化層造成的電流崩塌約為19.07%，SiN作為鈍化層造成的電流崩塌效應約為15.02%，可看出不同的鈍化層對於電流崩塌的抑制效果有所差異；其次為使用不同尺寸元件的電流崩塌效應會隨著LGD而改變。 其次，我們將使用兩種不同的表面處理方法，分別是紫外光臭氧處理技術與氧電漿表面處理技術，其中紫外光臭氧處理技術成功在直流導通電性僅有約15~20%的下降，閘極漏流便減少了約2~3個數量級；氧電漿技術則將漏流降了3~4個數量級，然而導通電流卻大幅降低，因此，在後續製程我們將對其進行優化。 最後，我們優化了氧電漿表面處理技術，解決了前述導通電流大幅下降的問題，並且比較不同製程瓦數與不同製程時間的元件之電性，最後通過此方法做出開關比達到6個數量級以上的電晶體元件。

This paper provides an overview of the principles and structures of Gallium Nitride (GaN) high electron mobility transistors (HEMTs) and discusses the defects commonly found in epitaxial layers. It also explores the current collapse phenomenon in GaN HEMTs, establishing a correlation with material defects. Various passivation layers are studied to evaluate their impact on current collapse, with SiO2 causing a reduction of approximately 19.07% and SiN causing a reduction of approximately 15.02%. These results demonstrate the varying effectiveness of different passivation layers in mitigating current collapse. Furthermore, the paper investigates the dependence of current collapse on gate-drain distance (LGD) for devices of different sizes. In the subsequent section, two different surface treatment techniques, namely ultraviolet (UV) ozone treatment and oxygen plasma surface treatment, are employed. UV ozone treatment successfully reduces the DC on-resistance by approximately 15-20% while decreasing gate leakage current by about 2-3 orders of magnitude. On the other hand, oxygen plasma treatment reduces gate leakage current by 3-4 orders of magnitude but results in a substantial decrease in the on-state current. Consequently, optimization of the oxygen plasma treatment process is carried out in the subsequent processing steps. In the final section, the optimized oxygen plasma surface treatment is applied, resolving the issue of significant on-state current reduction. The paper compares the electrical characteristics of devices fabricated using different processing parameters, ultimately achieving an improvement in the on-off ratio by more than 6 orders of magnitude for GaN HEMT devices.