三五族高載子遷移率電晶體與其臨界電壓調變之研究

Investigation of III-V High Electron Mobility Transistors and the Approaches of the Threshold-voltage Modulation

張立成(Li-Cheng Chang)

指導教授 ： 吳肇欣

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201903688

摘要

本篇論文主要探討三五族化合物半導體高載子遷移率電晶體之臨界電壓調變以及其相關特性之分析。在本篇論文中，主要利用兩種策略來調變元件之臨界電壓以達到增強型元件，分別為鰭狀通道的應用以及氟離子摻雜技術。首先，我們將鰭狀通道應用於窄能隙之砷化銦鎵異質結構上。元之最窄鰭寬為54奈米，對應的臨界電壓為0.56伏，且從平面元件微縮至最窄鰭寬時，臨界電壓往正調變了2.98伏。藉由此結果可知鰭狀通道對於調變臨界電壓是有效的。而電性圖也顯示隨著較窄的鰭狀通道具有較明顯的閘極漏流，此為鰭狀通道側壁漏流所致。另一方面，我們也將鰭狀通道應用在寬能隙之氮化鎵上。如同砷化銦鎵元件，氮化鎵之元件顯現出相同之臨界電壓調變趨勢。如同預期，寬能隙的氮化鎵具有較低的閘極漏流，此乃歸因於較寬能隙的材料具有較高的蕭特基能障。另一方面，為了能更了解鰭狀通道元件之開關機制，亦使用了三維度之泊松-飄移擴散載子模型進行模擬。由通道中之載子濃度分布可看出鰭狀通道中的載子除了傳統的縱向分佈調變外，亦會呈現橫向分佈的調變；而能帶圖的模擬也可觀察到鰭狀通道的能帶較平面元件更早被拉起。由此模擬結果可發現，當鰭狀通道的寬度到達一定程度時，元件將提早被關閉，我們將此現象稱為「提早關閉效應」。
另一方面，我們也藉由氟離子摻雜的技術將氮化鎵金氧半高載子遷移率電晶體之臨界電壓進行調變。由實驗可看出5分鐘之氟離子處理可使元件之臨界電應調整至1.15伏。藉由脈衝與直流偏壓的量測，我們可看到元件之臨界電壓皆會產生永久性的正向偏移，此偏移可再藉由固定負偏壓將元件之臨界電壓重置。由此結果我們可知，元件中缺陷之放射時間常數非常的長，可以被視為是氧化層中的邊緣缺陷，而此邊緣缺陷乃肇因於熱退火處理時，氟離子擴散所導致之結果。

關鍵字

三五族化合物半導體 ； 氮化鎵 ； 砷化銦鎵 ； 高載子遷移率電晶體 ； 臨界電壓 ； 增強型元件 ； 鰭狀通道 ； 氟離子摻雜 ； 側壁 ； 蕭特基能障 ； 泊松-飄移擴散載子模型 ； 提早關閉效應 ； 氟離子摻雜 ； 脈衝量測 ； 邊緣缺陷 ； 放射時間常數

並列摘要

This dissertation mainly focuses on the strategies of threshold-voltage (Vth) modulation to achieve E-mode operation for III-V high-electron-mobility transistors (HEMTs). First one is to form the fin-shaped channel on HEMT with the Schottky-gate which is called “Schottky-gate Fin-HEMT”. For the InGaAs device, Vth can be adjusted to 0.56 V with fin width (Wfin) of 54 nm. The positive Vth shift can be observed with the Wfin scaling and the total movement of Vth from planar to 54-nm-Wfin device is +2.98 V. However, with the Wfin scaling, the gate leakage also becomes significant which is caused by the sidewall leakage. AlGaN/GaN Schottky-gate Fin-HEMT also exhibits the same trend of the Vth modulation with lower gate leakage due to the higher bandgap of GaN. In order to further investigate the ON/OFF switching mechanism, simulation with the 3-dimensional Poisson and drift-diffusion model is applied. For the fin device, carrier concentration in channel is modulated both vertically and laterally. On the other hand, band diagram suggests that it is pulled up more rapidly than the planar device. These results indicate that once the fin is narrow enough, channel can be pinched off earlier than the planar device which can be regarded as “early pinch-off effect”.
Second approach to modulate the Vth is to utilize the fluorine-doped technique to form the F-doped MIS-HEMT. Positive Vth of 1.15 V with 5-minute F-plasma is achieved. Through the pulsed I-V and DC stress measurement, a retentive Vth shift is observed which can be recovered through a negative bias. This result indicates that the trap in the gate oxide is characterized by long emission time constant which can be regarded as border trap and is caused by the F diffusion during the annealing.

並列關鍵字

III-V ； InGaAs ； GaN ； HEMT ； threshold voltage ； E-mode ； Fin-HEMT ； Schottky ； sidewall ； Poisson and drift-diffusion model ； early pinch-off effect ； fluorine-doped ； pulsed I-V ； border trap ； emission time constant

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