分子束磊晶成長氧化釔/砷化鎵之介面及其電性研究

Interfacial Electrical Properties of MBE-Y2O3/GaAs MOS capacitors

蘇毓凱(Su, Yu Kai)

指導教授 ： 洪銘輝 ； 黃倉秀

國立清華大學/工學院/材料科學工程學系/碩士(2013年)

摘要

以矽和氧化矽為材料所製作的互補式金氧半場效電晶體(MOSFETs)其元件微縮遇到材料本質特性上的限制，導致電子元件的效能無法繼續提升。因砷化鎵具有遠高於矽的載子遷移率，若能成功被應用在反轉式金氧半場效電晶體能將元件效能進一步提升。若能以砷化鎵為半導體，而氧化釔做為高介電材料，則此系統具有高的能帶偏移，好的熱穩定性，並且有潛力形成良好且具有低缺陷密度的介面。
本實驗先利用分子束磊晶成長高品質的砷化鎵，再接著用分子束磊晶成長高介電材料氧化釔於砷化鎵上，成長過程皆在高真空中進行。
經過900oC快速高溫氮氣退火60秒後，再將製作好的MOSCAPs在400oC做氮氫混合氣體(forming gas)退火5分鐘，電性量測結果得到一個小的積聚電容值頻率分散(5%-12.4%)於量測頻率100赫茲到1000千赫茲，顯示出良好的介面電性。進一步用低頻電容法分析得到V型的介面缺陷分佈，在介面能帶中間區域得到一個低的缺陷密度1×10^12 eV^(-1)cm^(-2)，靠近能帶邊緣缺陷密度為1×10^13 eV^(-1)cm^(-2)。此外，利用變溫的電導方法得到缺陷密度為3-5×10^11 eV^(-1)cm^(-2)位在高於價帶0.4-0.6 eV處。從低頻電容-電壓圖形和高溫(100oC)量測100赫茲到1000千赫茲的電容-電壓圖形可得知此系統在介面能帶中間區域並沒有高峰形狀的缺陷密度分佈。
實驗的結果顯示出此系統有良好的特性，氧化層/半導體界面具有低的缺陷密度和良好的熱穩定性，有潛力實現高效能且低耗能的反轉式金氧半場效電晶體。

關鍵字

分子束磊晶 ； 高介電常數閘極介電質 ； 金氧半場效電晶體 ； 三五族化合物半導體 ； 砷化鎵 ； 氧化釔 ； 氧化鋁

並列摘要

The scaling of Si-based MOSFETs is approaching limitation, GaAs has highly potential to be a candidate for n-channel MOSFETs. MBE-Y2O3 as gate dielectric on GaAs attracts our attention because of its high dielectric constant of ~16, relatively high band offset, high thermodynamic stability, and possibility of formation sharp interface with low Dit value.
In-situ MBE-Y2O3 on p- and n-GaAs without using interfacial passivation layers and chemical treatments between oxide/GaAs interface were performed in a multi-chamber UHV-MBE system.
The MOSCAPs of MBE-YAO/MBE-Y2O3/GaAs were initially post deposition annealed at 900oC for 60s in nitrogen ambient followed by post metallization annealing at 400oC for 5 minuet in forming gas, which has shown small frequency dispersion 4.6% (100Hz-1MHz) at accumulation region for p-MOSCAPs, and 12.4% for n-MOSCAPs. Further, the Dit(E) spectra within the GaAs band gap were extracted by applying Terman, QSCV, temperature-dependent conductance methods for MBE-YAO/MBE-Y2O3/GaAs MOSCAPs. The Dit’s extracted from QSCV exhibits a V-shaped Dit(E) distribution without discernible peak. The Dit near midgap is given by ~1×10^12 eV^(-1)cm^(-2), and high D_it~1×10^13 eV^(-1)cm^(-2) located at near conduction and valence band edge are observed. The Dit’s extracted from temperature-dependent conductance method gives D_it~3-5×10^11 eV^(-1)cm^(-2) lying 0.4-0.6 eV above the valence band edge. Moreover, the inversion-like humps, which is an indication of Dit(E) peak feature causing insufficient Fermi-level movement, are not observed in QSCV measurement and high-temperature (373K) C-V characteristics.
The study shows the high potential of MBE-Y2O3/GaAs system to realize enhance mode MOSFETs due to its low Dit in midgap region and excellent thermodynamic stability after RTA to 900oC for S/D activation.

並列關鍵字

molecule beam epitaxy ； High-k gate dielectirc ； MOS ； III-V ； GaAs ； Y2Oe ； Al2O3

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