- 學位論文
使用有機化學氣相沉積系統成長銻化鎵磊晶層於矽基板上對互補式 金屬氧化物半導體之應用
MOCVD Growth of GaSb Material on Si Substrate for CMOS Application
摘要
矽互補式金屬氧化物半導體(Si complementary metal oxide semiconductor, Si CMOS)元件之電晶體尺寸已到很難再持續縮小的地步。五三族複合半導體(V-III compound semiconductors) 對於超高速及低耗能電晶體應用方面極具潛力，因此有希望成為未來半導體替代材料之一而受到高度重視。在五三族材料之中，銻化鎵材料(GaSb-based materials)具有高電洞遷移率(high hole mobility)、載子有效質量小(low effective mass)、可調變能帶(band engineering)等優點，因此將銻化鎵材料與砷化鎵或矽基板結合將有希望成為下一代金屬氧化物半導體。尤其是對低成本、輕量化、大面積、高效能邏輯元件來說，銻化鎵半導體材料與矽基板結合無疑是近年來相當重要的研究題目。因此，此博士論文主要聚焦在使用有機化學氣相沉積法成長高品質銻化鎵磊晶層於矽基板上對互補式金屬氧化物半導體之應用。 在此研究中，成長高品質銻化鎵於砷化鎵基板上的磊晶技術被充分論證，研究結果發現於介面差排(interfacial misfit, IMF)成長模式下沉積一層很薄銻在砷化鎵緩衝層上當作界面處理層可使銻化鎵/砷化鎵介面處獲得較佳磊晶品質；沒有這層介面處理層，銻化鎵磊晶層可能遵循Stranski–Krastanov (S-K)成長機制或S-K與介面差排交互混和機制成長於砷化鎵基板上並造成較差的介面品質，這現象可能是在成長過程中，銻化鎵/砷化鎵介面處陰離子交互混和而造成先驅物成分與介面差排分布不均勻所導致。隨著銻界面處理層的使用，介面差排序列(IMF array)能形成在銻化鎵/砷化鎵介面處進而成長高品質銻化鎵磊晶層。 高品質砷化鎵緩衝層(410nm)亦被成長在0度矽(001)基板上。在此研究中，於490度下所成長砷化鎵成核層(nucleation layer)之磊晶時間被仔細研究討論，由高解析穿透式電子顯微鏡影像圖顯示砷化鎵化合物在2D島狀形成之前是為3D島狀成長，最後形成一層均勻砷化鎵磊晶層。最佳成核層厚度約為10奈米以抑制反相疇界 (antiphase domain boundaries, APBs) 產生。這層砷化鎵成核層之均方根粗糙度(root-mean-square surface roughness)約為0.48nm，並讓隨後高溫砷化鎵層磊晶成長於其上時可獲得較低螺紋狀差排缺陷密度(threading dislocation density)與幾乎不可見反相疇界。 使用介面差排模式成長銻化鎵磊晶層於砷化鎵/矽異質結構上，由高解析穿透式電子顯微鏡與XRD倒晶格空間繪圖(reciprocal space mapping)結果可知晶格不匹配所導致的應力可被有效釋放(relaxed)。Al2O3/GaSb/GaAs/Si結構之價帶補償(valence-band offset)與導帶補償(conduction-band offset)被預測分別為2.39 and 3.65 eV。Al2O3/p-GaSb/GaAs/Si 金氧半電容(MOS capacitors)展現不錯電容-電壓(capacitance-voltage, C-V)與較低頻率發散(frequency dispersion~1.05% per decade)等特性。這些研究結果顯示在介面差排模式下所成長銻化鎵磊晶層於砷化鎵/矽結構上可被應用在下一世代金屬氧化物半導體上。
並列摘要
The continued downsizing of Si complementary metal oxide semiconductor (CMOS) devices comes to a standstill. Thus, V-III compound semiconductor has been attracting extensively as a promising alternating material due to their potential in ultra-high speed and low power consumption transistors. Among V-III materials, the integration of GaSb-based materials on GaAs or Si substrate has been considered as the next generation of CMOS devices due to its high hole mobility, low effective mass, and band engineering as combining with other V-III materials. Especially, the integration of GaSb semiconductor on Si substrates for low cost, light weight, large area and high performance logic devices has been a subject of intense investigation in recent years. Therefore, this dissertation concentrates on the growth of high quality thin GaSb epitaxial layers on Si substrates for CMOS application by using MOCVD growth method. A method for the growth of high quality GaSb epilayer on GaAs (001) substrate is demonstrated in this study. It is found that a superior GaSb/GaAs interface can be obtained by depositing a thin Sb-precursor layer on the GaAs substrate containing a GaAs buffer layer. It is suggested that the growth occurs via the interface misfit (IMF) growth mode. Without this treatment, GaSb epilayer may grow according to the Stranski–Krastanov mechanism or via a blend of the Stranski–Krastanov and IMF mechanisms, leading to an inferior GaSb/GaAs interface. This could be due to the intermixing of anions, leading to the turbulent composition and misfit dislocation distribution at the heterointerface. It appears that with the addition of a Sb layer, IMF arrays can be formed at GaSb/GaAs interface resulting in superior GaSb layer without the need for changing the growth parameters. High quality 410 nm temperature-graded GaAs buffer layer was grown on the zero off-cut Si (001)-oriented substrate. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this study. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1 × 106 cm−2 and almost invisible APDs. A fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. High-resolution transmission electron microscopy micrographs and high-resolution X-ray reciprocal space mapping indicate an entirely relaxed IMF array GaSb epilayer. The valence-band offset and conduction-band offset of the Al2O3/GaSb/GaAs/Si structure are estimated to be 2.39 and 3.65 eV, respectively. The fabricated Al2O3/p-GaSb/GaAs/Si MOS capacitors exhibited good capacitance–voltage characteristics with a small accumulation frequency dispersion of approximately 1.05% per decade. These results imply that the GaSb epilayer grown on the GaAs/Si platform in the IMF mode can be used for future complementary metal-oxide semiconductor applications.
參考文獻
延伸閱讀
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