鍺是近幾年極受矚目的半導體元件通道材料，擁有比矽材料更高的載子遷移率，但是在N型Ge通道金屬氧化物半導體場效電晶體(MOSFET)的發展中存在著許多障礙，特別是在源極/汲極(S/D)會因為費米能階釘紮(Fermi-level pinning)的現象形成高接觸電阻值。而造成費米能階釘紮的原因是金屬與半導體接觸面太多缺陷和金屬所導致的能隙能階(MIGS)所導致。本論文是以N型Ge基板與金屬的接面做介面工程，使其介面處的缺陷減少和MIGS效應得到緩解，並進一步降低費米能階釘紮的效應而得到較低的接觸電阻值，探討其提升的元件電特性。
第一部分先使用蝕刻機台的SF6電漿在Ge的表面形成一層修補缺陷的鈍化層(passivation)，藉由改變電漿作用的時間來找出最有效的鈍化層。在經10秒的SF6電漿處理後，XPS分析發現表面的S與F元素含量分別為7.52% 與0.69%，可得到最佳接觸電阻值為3.10*10-4 Ω*cm2。另外再使用ALD沉積的TiO2氧化層做為介面層，其中分別使用不同cycle數使得介面層的厚度改變，分別為1.57nm、2.25nm、5.19nm。最佳的厚度為2.25nm作為元件的介面層，得到的接觸電阻值為2.30*10-5 Ω*cm2。最終結合兩者最佳的參數，先在Ge基板表面進行SF6電漿處理而後再沉積TiO2氧化層，但最後量測出來的結果與預期不同，從TEM和AFM看出是因為經過SF6電漿處理後Ge的表面因為蝕刻關係變得相當粗糙，接續沉積的TiO2介面氧化層反而無法有效的形成，缺陷也提高許多造成電性變得很差。
第二部分採用第一部分最佳的TiO2氧化層厚度，對其做NH3電漿處理，目的為增加TiO2氧化層中的氧空缺含量以及氮化TiO2氧化層，使其氧化層的導電性增加且進一步降低接觸電阻。實驗首先在TiO2氧化層表面做NH3電漿處理60秒，因考量氮化後TiO2氧化層會改變，故在參數上以調變TiO2氧化層厚度搭配有無使用NH3電漿處理做比對，結果從電性上發現變化不大，故在後續實驗中設計在TiO2氧化層中做均勻的混合處理，除了能使NH3電漿均勻的與TiO2氧化層完整反應，也能使氫原子鈍化TiO2/Ge介面，藉由沉積1 cycle的TiO2後進行5秒的NH3電漿處理為一個循環，連續進行12次循環後，再進行88次單純沉積循環的ALD TiO2氧化層沉積(MIX)，雖然分析後得到在TiO2氧化層變厚為2.94nm，但若有經過MIX方式的NH3電漿均勻處理仍能使逆偏電流密度值再提升0.5order，接觸電阻值為5.24*10-4 Ω*cm2，從以上的實驗得知在均勻混合的TiO2氧化層以及NH3電漿處理後能使得逆偏電流密度有效的提升，未來若能更有效的控制TiO2氧化層經NH3電漿處理後的厚度，預期能使得電性上能有再進一步的提升。

Germanium is regarded as a promising channel material owing to higher carrier mobility in recent years. However, there are many problems in the development of N-type Ge MOSFET. A high resistance contact was formed at the interface between source/drain(S/D) and metal due to the Fermi-level pinning, which caused by many defects in the metal-semiconductor contact surface and the metal-induced gap states (MIGS). In this thesis, the effects of plasma treatment on M-I-S contact structure are investigated by interface engineering between N-type Ge wafer and metal. A lower contact resistance can be achieved by reducing the defects at the interface and the MIGS effect.
In the first part, the SF6 plasma treatment was used to form a passivation layer to repair the defects at the surface of Germanium. To optimize passivation effect, the SF6 plasma treatments were applied for various time. The optimized SF6 plasma treatment time was 10 seconds, and corresponding S and F concentration were 7.52% and 0.69% from XPS analysis. The contact resistance was 3.10*10-4 Ω*cm2. In addition, ALD TiO2 interfacial layer was used to form M-I-S contact structure. TiO2 layers with a thickness of 1.57 nm, 2.25 nm and 5.19 nm were deposited by ALD. The optimum thickness of TiO2 interfacial layer was 2.25 nm and a corresponding contact resistance of 2.30*10-5 Ω*cm2 was obtained. Then both SF6 plasma treatment and TiO2 interfacial layer were applied to improve contact property of the n-Ge device. However, electrical characteristics became worse. The TEM and AFM showed that the Ge surface became rougher after SF6 plasma treatment. As a result, the defects increased and the TiO2 oxide interfacial layer couldn’t be formed effectively.
In the second part, NH3 plasma treatment was applied to the TiO2 oxide interfacial layer to increase the oxygen vacancy and form TiOxNy. The aforementioned process increased the conductivity of the oxide layer and further reduced the contact resistance. The TiO2 oxide layer was treated by NH3 plasma for 60 seconds. Because the thickness of TiO2 oxide layer might change after the plasma nitridation process, the TiO2 oxide interfacial layers with various thickness were used. However, the electrical properties were similar after the NH3 plasma treatment. Hence, a uniform mixing treatment at TiO2/Ge interface was designed to improve the electrical characteristics. First, a mixing cycle process, which was one cycle TiO2 deposition and following NH3 plasma treatment for 5 seconds, was applied. After repeating this mixing cycle process for 12 times, the TiO2 oxide layer was then deposited by following 88 ALD cycles. The process could also passivate the TiO2/Ge interface by hydrogen. Though the thickness of the resulting oxide interfacial layer increased to 2.94 nm after the uniform mixing treatment, the reverse bias current density increased by 0.5 order, and the contact resistance could reduce to 5.24*10-4 Ω*cm2.
The reverse bias current density can be effectively improved by the NH3 plasma treatment. The electrical property of Ge M-I-S contact can be further improved by optimizing thickness of the NH3 plasma treated TiO2 oxide interfacial layer.

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