利用四氟化碳電漿處理於多晶矽及氮電漿處理於二氧化鉿閘極介電層之低溫多晶矽薄膜電晶體之研究

Abstract

近年來低溫多晶矽薄膜電晶體由於在主動陣列顯示器的應用而吸引很多注意，然而莫爾定律通常限制於微影技術，越小的線寬需要更更短波長的光源，因此很難一直永遠微縮下去。當閘極氧化層非常薄而小於1.4奈米時會由於直接穿隧的漏電而造成不可避免的閘極漏電流。因此近年來高介電常數的物質常常被廣泛應用在閘極材料上，進而提升它的閘極品質而降低漏電流。在眾多高介電常數的材料當中，二氧化鉿有高介電常數(25-30)、足夠大的能帶而且和多晶矽有很好的熱穩定性等優點，因此二氧化鉿被認定為是最有前瞻性高介電常數材料。實驗中，我們將二氧化鉿用在低溫多晶矽薄膜電晶體上當作是對照組，而再外加由四氟化碳電漿的前處理和氮電漿的後處理作為觀察組(我們稱雙重電漿處理)。我們不僅討論二氧化鉿用於低溫多晶矽薄膜電晶體的基本電性外，更進一步深入探討可靠度的問題，例如: 閘極正偏壓應力、閘極正偏壓應力高溫應力、閘極負偏壓應力和熱載子效應。而在結果中不管是用哪一種方法量測二氧化鉿用於低溫多晶矽薄膜電晶體的可靠度，雙重電漿處理的觀察組皆比沒電漿處理的對照組特性要好，原因可能是四氟化碳電漿的前處理可以修補介面品質而氮電漿的後處理可以修補二氧化鉿閘極的內部缺陷。

In recent years, high performance low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) have been attracted much attention due to the increasing applications in active matrix display (AMLCDs). However, the scaling to Moore’s law are limited to the lithography, the more minimum feature size as we need to pattern, the shorter wavelengths of light we must to achieve, so it is impossible to scale down forever. It is terrible that gate oxide is so thin (1.4 nm) which caused an intolerable gate leakage due to direct tunneling current. Therefore, high-k gate dielectric material has been extensively studied in recent year, which could effectively reduce leakage current and improve device performance. There are many high-k dielectric materials had been used before, hafnium oxide (HfO2) is considered one of the promising high-k gate material due to its high permittivity (25-30), wide energy bandgap and thermal stability with poly-Si. The HfO2 LTPS-TFTs were used as without treatment sample and combined with dual plasma treatment because of the combination of pre-deposition plasma fluorination and post-deposition plasma nitridation. We discussed not only the basic electrical characteristics but also reliability properties such as positive-bias stress instability (PBI), positive-bias temperature instability (PBTI), negative-bias stress instability (NBI) and hot carrier stress (HCS). No matter how the stress mechanism applies, the dual plasma treatment LTPS-TFTs exhibits a superior performance than without treatment. It might be that fluorine incorporation can improve the interface quality and nitrogen also can repair defects at bulk dielectric to decrease the leakage current.