大面積過渡金屬硫化物異質結構成長及原子層蝕刻技術之開發

Abstract

在本論文中，我們透過預濺鍍過渡金屬再硫化方式成長出大面積的二硫化鉬薄膜，且經由控制濺鍍金屬時間，可以於準確控制10 層以下二硫化鉬薄膜之層數。對於較厚的鉬金屬膜，經硫化後雖可成長出層數大於 10 層之二硫化鉬薄膜，但在薄膜下方則包覆著鉬氧化物。此結果說明了，在硫化的過程中，兩種成長機制將同時發生，其一為平面二硫化鉬薄膜的成長，其二為鉬氧化物因高溫在表面的移動。此外，經過依序濺鍍過渡金屬鉬和鎢且依序硫化的方式，可以成功的製備出二硫化鉬/二硫化鎢二維晶體異質結構薄膜，轉印此二維晶體異質結構薄膜至預成長 300 奈米二氧化矽的矽基板上，透過此方式，即可製作出背閘極場效電晶體，其元件特性更勝於二硫化鉬背閘極場效電晶體。此結果表明了，二維晶體異質結構的堆疊可以克服了單一二維晶體先天上的限制並且仍然保有著二維晶體的優點，為一種具有前瞻性的材料。此外在此論文中，我們亦完成了二硫化鉬與二硫化鎢的的原子層蝕刻，對於二硫化鎢/二硫化鉬異質結構薄膜，透過重複的氧電漿蝕刻並進行再硫化之方式，可以達到上方二硫化鎢之選擇性蝕刻。另外透過重複原子層蝕刻之技術來製備二硫化鎢/二硫化鉬異質結構電晶體，可以使得源/汲電極直接接觸到二硫化鉬通道，此結果表明，二維晶體異質結構的等效選擇性蝕刻可以通過重複原子層蝕刻技術來實現，這是二維晶體異質結構元件製作上極為重要的一步。

In this thesis, we have demonstrated that large-area molybdenum disulfide (MoS2) can be prepared by sulfurizing the pre-deposited transition metal films. Good layer number controllability up to 10 layers of the MoS2 film is also achieved by controlling the sputtering times of the pre-deposited transition metal films. For the sample with thicker Mo films, although MoS2 films with the layer number larger than 10 can be obtained, clusters of multi-layer 2D crystals covering Mo oxides are obtained for the sample. The results suggest that two growth mechanisms of planar MoS2 formation and Mo oxide segregation would take place simultaneously during the sulfurization procedure. After sequential transition metal deposition and sulfurization procedures of Mo and tungsten (W), MoS2/WS2 2D crystal hetero-structures can be established. After transferring the hetero-structure film to a 300 nm SiO2/Si substrate, a bottom-gate transistor with enhanced field-effect mobility is obtained. The results have revealed that the establishment of different hetero-structures is a promising approach to overcome the limit of individual 2D crystals and still maintain their advantage. The atomic layer etchings of MoS2 and WS2 are demonstrated in this paper. By repeated oxygen plasma etchings and a final re-sulfurization procedure, multi-layer WS2 can be selectively etched off from the WS2/MoS2 hetero-structure. A WS2/MoS2 hetero-structure transistor is fabricated with source/drain electrodes contacted directly to the MoS2 channel by using the repeated atomic layer etching technique. The results have revealed that the equivalent selective etching effect for two-dimensional crystal hetero-structures can be achieved by repeating the atomic layer etching procedure, which is an important step for the device fabrication of 2D crystal hetero-structures.