Fabrication of GaSb Channel PMOSFETs with HfO2 as Gate Dielectric and Ni-GaSb Alloy as Source/Drain
|關鍵字:||銻化鎵;P型場效電晶體;氫氣電漿處理;二氧化鉿;GaSb;PMOSFET;hydrogen plasma treatment;HfO2|
|摘要:||在此篇論文中，我們首先於原子層沉積化學氣相沉積(atomic layer deposition, ALD)之前利用氫氣電漿處理製作出以二氧化鋯為介電材料之銻化鎵p型金屬-氧化物-半導體電容 (pMOSCAP)。我們發現在做氫氣電漿處理之後不僅電容調節(modulation of capacitance)提升其漏電流也得以被抑制住。我們使用博戈隆方法(Berglund method)及電導方法(conductance method)萃取介面能態密度。經過組成氣體退火(forming gas anneal)之後介面能態密度來到約5x1012 eV-1cm-2。透過X射線光電子能譜儀(XPS)，我們瞭解到氫電漿處理能夠去除銻化鎵的原生氧化層。此外，我們發現一旦使用氫電漿處理後銻化鎵的表面變得平滑。
最後，我們成功展示以二氧化鉿為閘極介電材料及鎳-銻化鎵為源極和汲極之銻化鎵通道p型場效電晶體(pMOSFET)。雖然源極電流的開關電流比達到將近4個數量級，我們也發現因大的接面漏電流而使汲極開關比極低。此外，透過分離電容法(split CV method)萃取出極低的電洞遷移率 (~22cm2V-1s-1)。另外，我們也討論p型金氧半場效電晶體製程的缺點，問題及取捨。|
In this thesis, we firstly fabricated HfO2/GaSb p-MOSCAPs by utilizing hydrogen plasma treatment prior to HfO2 deposition. We found that not only modulation of capacitance was increased but also leakage current was suppressed after performing hydrogen plasma treatment. We used Berglund method and conductance method to extract interface states density (Dit). Dit value of 5x1012 eV-1cm-2 was achieved after performing forming gas annealing. By X-ray photoelectron spectroscopy (XPS), we realized that the native oxides of GaSb could be eliminated by hydrogen plasma treatment. Moreover, as confirmed in atomic force microscopy (AFM), we found that the surface of GaSb was smoother once hydrogen plasma treatment was applied. Secondly, we successfully formed Ni-GaSb alloy at 250℃ for 1 minute by rapid thermal annealing (RTA). Strong Schottky behavior was observed in the I-V characteristic of Ni-GaSb/n-GaSb junction, which had large Ion/Ioff (~103 ) and low ideal factor (~1.2). Nevertheless, large junction reverse current was observed at high annealing temperature or long annealing time. As annealing temperature reached higher than 350℃, various crystal orientation of NiSb was formed and also agglomeration was observed, leading to large junction leakage current. NiSb was formed at 250℃ for annealing time longer than 5 minutes as well. Besides, we found that Ni, Ga and Sb would diffuse during annealing process. Finally, we successfully fabricated GaSb channel PMOSFETs with HfO2 as gate dielectric as well as Ni-GaSb as S/D. Although on/off ratio (~4 orders) of source current was achieved, extremely low on/off ratio of drain current was also observed owing to large junction leakage current. Besides, ultra-low hole mobility (~22cm2V-1s-1) was extracted by means of split CV method. Also, we discussed the drawbacks, problems and trade-off of the process we adopted for fabricating PMOSFETs.
|Appears in Collections:||Thesis|