以鉿薄膜緩衝層及氧化鋯鉿堆疊改善鍺金氧半電晶體之電特性

Improved Electrical Characteristics of Ge MOSFETs with Hf film Buffer Layer and ZrHfO stacks

陳廷鈞(Chen,Ting Chun)

指導教授 ： 張廖貴術

國立清華大學/原子科學院/工程與系統科學系/碩士(2015年)

摘要

鍺相較於矽而言，電子的遷移率可提升兩倍、電洞的遷移率可以提升至四倍，故利用純鍺基板以及high-k材料來達成超薄等效氧化層厚度，以及更高的載子遷移率對於通道電流傳輸可以大大改善。但鍺半導體材料製程也存在許多困難，在400℃下產生易揮發氣體不耐高溫且容易水解，鍺擴散造成的漏電流以及氧化鍺的介面工程皆是我們致力於改善的目標。因此，我們希望藉由鉿薄膜緩衝層來改善介面，並且使用高介電係數的材料氧化鋯來改善電特性，最後再利用不同的熱退火處理來優化鍺金氧半電晶體的電特性。
本論文的研究以使用純鍺基板，於ALD (Atomic Layer Deposition System)中堆疊不同的high-k以提升鍺基板元件的特性，其中第一部分，使用氮氧化鉿(HfON)做為high-k材料製作電晶體，並且在介面GeO2與氮氧化鉿中間沉積一層薄的鉿薄膜緩衝層(Hf film Buffer Layer)探討其電性上的改變。實驗結果可以發現，介電層為氮氧化鉿含鉿薄膜緩衝層，其等效反轉氧化層厚度(Tinv)為7 Å，閘極漏電流則維持在2x10-3 A/cm2，並且有更大的驅動電流以及較高的載子遷移率以及改善介面。從XRD圖中也可以推測，high-k層中的HfON因為Ge的擴散，增進形成一介電係數非常高的Tetragonal phase。
第二部分中，延續第一部分提到的鉿薄膜緩衝層來改善GeO2與介電層的介面，並且摻入二氧化鋯(ZrO2)材料進入high-k層中，比較ZrO2與HfON以及交互堆疊層在電性上的差異。實驗結果可以發現，在介電層摻入材料二氧化鋯的結構不論是下層HfON上層ZrO2或者兩者交互堆疊成的HfO-ZrO co-deposition，在電性上都表現的比單層介電層HfON來的突出。另外我們也發現使用單層的介電層材料HfON在元件的可靠度特性上都會比堆疊層要來的好。
第三部分中，延續上兩部分所得到的結果，利用鉿薄膜緩衝層以及下層HfON上層ZrO2作介電層製作電晶體元件，最後比較燒結(Sinter) 、微波退火(Microwave annealing)及雷射退火(Laser annealing)其在電特性上的差異。實驗結果可以發現，利用雷射退火可以增加元件的驅動電流，而微波退火主要可以改善介面進而降低元件的關閉電流。

關鍵字

鍺金氧半電晶體 ； 鉿薄膜緩衝層 ； 氧化鋯 ； 微波退火 ； 雷射退火

並列摘要

Ge possesses two times electron mobility and .four times hole mobility compared to Si. Using Ge substrate and high-k material to obtain ultra-thin EOT, to achieve high mobility and drain current. However, using Ge material will face many challenges. It is easy for Ge oxide to be volatilized and hydrolyzed at 400°C. Ge out-diffusion induced gate leakage and Ge oxide quality is our first priority which is needed to be improved immediately. First, Hf film buffer layer can improve the interfacial layer. ZrO with a higher dielectric constant is used to achieve ultra-thin EOT and improve electrical characteristics of Ge MOS devices. At last, different annealing processes is performed to optimize electrical characteristics of Ge MOSFETs.
In this thesis, different high-k materials are deposited by an ALD on Ge substrate to improve the electrical characteristics of MOS device. In the first part, HfON is used as a high-k material. An Hf film buffer layer is deposited between HfON and GeO2, and the change of electrical characteristics is discussed. One can conclude that if HfON with Hf film buffer layer is chosen as a high-k material, 0.7 nm EOT can be achieved, and gate leakage is about 2x10-3 A/cm2. Moreover, it has higher drain current and mobility due to improved interfacial layer. Ge out diffusion into HfON can enhance tetragonal phase, resulting in a higher dielectric constant.
In the second part, ZrO2 and HfON are integrated as high-k dielectric stacks, and the electrical characteristic are discussed as well. The Hf film buffer layer as studied in the first part is also used. HfON/ZrO2 and HfO-ZrO co-deposition exhibit better electrical characteristic than that of single HfON layer. However, it is found that the reliability of single HfON layer is better than that with high-k dielectric stacks.
In the third part, the Hf film buffer layer and HfON/ZrO2 stack are applied to Ge MOSFETs. Difference annealing processes such as sinter, microwave annealing, and laser annealing are compared. In conclusion, laser annealing can improve drain current of Ge MOSFETs. Interface quality can be improved by microwave annealing, and then off current is reduced.

並列關鍵字

Ge MOSFET ； Hf-rich buffer ； ZrO2 ； Microwave annealing ； Laser annealing

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