4H-SiC閘極介電層之特性研究

Study on Thermally-Grown Gate Oxide in 4H-SiC MOSFETs

陳尚駿(Shang-Chun Chen)

指導教授 ： 黃智方

國立清華大學/電機資訊學院/電子工程研究所/碩士(2007年)

摘要

碳化矽為適合應用於高功率元件的寬能帶半導體材料，又因其寄生氧化層為二氧化矽使其可製作MOS結構。但是卻因為材料特性限制，在氧化生長二氧化矽時，二氧化矽與碳化矽基板界面時會產生碳沉積，使得MOSFET的界面捕捉電荷密度提高，降低遷移率。而欲有效改善界面品質，可透過變化氧化環境、在氧化後予以熱退火等等來達成。
本篇論文透過不同環境熱氧化生長二氧化矽於4H-碳化矽上，分別為以溼氧、乾氧熱氧化生長二氧化矽，在氧化鋁、鐵環境的乾氧生長，及嘗試以鉑作為催化氧化之試驗，以此五種不同氧化條件之氧化層製作MOSFET，探討其電性之比較，希望建構較佳的碳化矽氧化製程，以利未來應用於高功率元件中。此外，本篇論文也同時探討了氧化層中移動電荷對與不同基板接地位置對於MOSFET臨界電壓的影響，以及不同溫度下MOSFET遷移率的變化，在高溫下遷移率與界面捕捉電荷有相關性，最後比較五種氧化層之漏電流。

關鍵字

碳化矽 ； 閘極介電層 ； MOSFET ； 遷移率 ； 界面捕捉電荷

並列摘要

Silicon carbide is one of wide bandgap semiconductors so that it is feasible to high power applications. Besides, the native oxide of silicon carbide is silicon dioxide. That makes it possible to construct MOS structure devices in SiC. However, there are carbon deposit in the interface during thermal oxidation. The deposited carbon increases interface trap density, and decreases channel mobility of MOSFETs. Some methods like changing oxidation environment and post annealing etc. improve the interface quality efficiently.
In this paper, silicon dioxide are thermally grown on 4H-SiC substrate by different oxidation conditions. They are dry, wet ambient oxidation, dry ambient in alumina and iron environment, and platinum catalyzed oxidation testing oxidation. Then fabricating MOSFETs on them respectively to measure and discuss their electronic performances. Moreover, some effects of MOSFET are discussed in this work. Including threshold voltage varied by mobile charges effect and body contact position effect, channel mobility varied with elevated temperature, and leakage current comparison between these five dielectrics.

參考文獻

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