利用光電子能譜分析二硫化鉬在元件中的異質介面

Abstract

本實驗利用光電子能譜儀(PES)探討了不同摻雜劑對二硫化鉬(MoS2)的影響，使用的摻雜劑主要為鹼金族(IA)以及鹵素(VIIA)組成的鹽類，主要利用熱蒸鍍的方式對MoS2進行摻雜，而所有摻雜劑與MoS2間沒有化學鍵結的發生，其中，發現BiI3和KCl對MoS2摻雜後會使Mo 3d與S 2p的特徵峰往低束縛能的方向偏移；NaI和KI對MoS2摻雜後則會使Mo 3d與S 2p的特徵峰往高束縛能的方向偏移；LiCl和KBr對MoS2摻雜後Mo 3d與S 2p的特徵峰則維持不變。另外，利用電性分析去驗證，發現MoS2通道與BiI3和KCl進行摻雜後，電晶體的臨界電壓(Vt)往正偏壓的方向偏移，且載子遷移率(μ)以及開電流(Ion)皆有降低的趨勢；MoS2通道與NaI和KI進行摻雜後，電晶體的臨界電壓(Vt)則是往負偏壓的方向偏移，而載子遷移率(μ)以及開電流(Ion)皆有上升的趨勢。透過上述實驗結果可以得出，BiI3和KCl對MoS2具有電洞摻雜的效果；NaI和KI對MoS2具有電子摻雜的效果；而LiCl和KBr對MoS2則沒有明顯的摻雜效應，這些結果證實可以藉由摻雜劑去調節通道載子的濃度，可以應用在未來元件的製造上。 除了摻雜劑與MoS2的關係，本實驗還探討了直接利用ALD生長高介電材料是否會對MoS2造成破壞，透過XPS能譜發現，Mo 3d與S 2p會因為前驅物導致Mo-S斷鍵而產生MoxSy的訊號，其中y/x < 2。為了避免前驅物在製程中破壞MoS2，本實驗使用鋁(Al)與鈦(Ti)作為金屬種子層阻絕前驅物與MoS2間的接觸，其中Al和Ti都會使Mo 3d與S 2p往高束縛能的方向偏移，並且Ti在厚度1nm就可以杜絕前驅物對MoS2的破壞，接著在具有1nm Ti種子層的MoS2上用ALD生長氧化鋁(Al2O3)與二氧化鉿(HfO2)，兩者皆會使Mo 3d與S 2p往高束縛能的方向偏移，同時也沒有MoxSy的訊號，確認1nm Ti種子層可以在ALD製程中有效的保護MoS2。另外，利用電性分析去驗證，發現在MoS2通道沉積Ti 1nm種子層後，電晶體的臨界電壓(Vt)往負偏壓的方向偏移，且載子遷移率(μ)以及開電流(Ion)皆有上升的趨勢，再利用ALD生長氧化鋁(Al2O3)與二氧化鉿(HfO2)後，電晶體的臨界電壓(Vt)也會往負偏壓的方向偏移，同時載子遷移率(μ)以及開電流(Ion)也會隨著上升。透過上述實驗結果可以得出，利用Ti作為種子層可以有效的保護MoS2在ALD製程中的破壞，同時也確認無論是Ti、Al、Al2O3、HfO2都對MoS2有電子摻雜的效果，這些結果對於未來在製作上閘極元件中有很大的幫助。

This study utilized photoelectron spectroscopy (PES) to investigate the effects of various dopants on molybdenum disulfide (MoS2). The primary dopants used were salts composed of alkali metals (IA) and halogens (VIIA), and doping was conducted using thermal evaporation. It was found that there were no chemical bonds formed between the dopants and MoS2. Specifically, doping MoS2 with BiI3 and KCl caused the Mo 3d and S 2p peaks to shift towards lower binding energy, while doping with NaI and KI caused these peaks to shift towards higher binding energy. Doping with LiCl and KBr did not alter the Mo 3d and S 2p characteristic peaks. Electrical analysis confirmed that doping MoS2 channels with BiI3 and KCl caused the transistor's threshold voltage (Vt) to shift towards positive bias, with a decrease in carrier mobility (μ) and on current (Ion). Conversely, doping with NaI and KI shifted the threshold voltage (Vt) towards negative bias, with an increase in carrier mobility (μ) and on-current (Ion). These results indicate that BiI3 and KCl have P-type doping trend for MoS2, NaI and KI have N-type doping trend, and LiCl and KBr show no significant doping effects for MoS2. These findings confirm that dopants can be used to adjust the channel carrier concentration, which is valuable for future device fabrication. In addition to the relationship between dopants and MoS2, the study also explored whether directly growing high-κ materials using atomic layer deposition (ALD) would damage MoS2. XPS spectra revealed that Mo 3d and S 2p signals indicated Mo-S bond breaking due to the precursors, forming MoxSy signals with y/x < 2. To prevent precursor damage to MoS2 during the process, aluminum (Al) and titanium (Ti) were used as metal seeding layers to block the contact between the precursors and MoS2. Both Al and Ti caused Mo 3d and S 2p to shift towards higher binding energy. We have determined that a 1nm Ti seeding layer can effectively prevent damage to MoS2 from precursors. By utilizing atomic layer deposition (ALD) to grow aluminum oxide (Al2O3) and hafnium dioxide (HfO2) on MoS2 with a 1nm Ti seed layer, we observed shifts in the Mo 3d and S 2p peaks towards higher binding energy, without the production of MoxSy signals. This confirms that the 1nm Ti seeding layer effectively protects MoS2 during the ALD process. Electrical analysis indicated that depositing a 1nm Ti seeding layer on the MoS2 channel resulted in a negative shift in the transistor's threshold voltage (Vt), along with increases in carrier mobility (μ) and on-current (Ion). Further, utilizing ALD to grow Al2O3 and hafnium dioxide HfO2 continued to shift the threshold voltage (Vt) negatively, with additional increases in carrier mobility (μ) and on-current (Ion). These results demonstrate that using Ti as a seed layer not only effectively protects MoS2 from damage during the ALD process but also confirms that Ti, Al, Al2O3, and HfO2 all exhibit N-type doping effects on MoS2. These findings provide significant insights for the fabrication of future top-gate devices.