矽鍺在複晶矽薄膜電晶體上的應用

Abstract

在本論文中，我們提出一個矽鍺間隙壁的新結構來降低複晶矽薄膜電晶體的漏電流。我們利用超高真空化學氣相沉積（Ultra High Vacuum Chemical Vapor Deposition, UHVCVD）矽鍺在複晶矽表面沉積但在氧化矽表面不沉積的特性，選擇性的在複晶矽閘級側邊橫向沉積矽鍺間隙壁（SiGe spacer）。此製成具有製程簡單、製成溫度與傳統低溫複晶矽薄膜電晶體接近和矽鍺間隙壁是自我對準等優點。由實驗結果，我們發現這個新結構的矽鍺間隙壁的確能有效降低在汲極端空乏區的電場。與傳統的複晶矽薄膜電晶體比較之下，我們的新結構能降低漏電流的產生、使轉折效應不明顯並且在元件可靠度方面也有顯著的改善。 另外為了整合主動式液晶顯示器上的周邊電路，複晶矽薄膜電晶體必須要有較大的驅動的電流跟較高的崩潰電壓。而使用超薄通道元件雖然可以得到較大的驅動電流但是卻會伴隨著較大的源極、汲極接觸電阻、較大的寄生串聯電阻還有較小的崩潰電壓等等會降低元件性能的問題發生。為了克服這些問題，我們提出一個利用選擇性矽鍺沉積來製作薄通道但是卻有較厚源極、汲極元件的新製程．與先前製作薄通道但是卻有較厚源極、汲極元件的製程比較之下，此製成具有不需額外光罩、自我對準製程和與傳統複晶矽薄膜電晶體製成相容的優點．由實驗結果，我們的新結構能提高導通電流、具有較大的崩潰電壓、降低源極、汲極的電阻和降低漏電流的特性。

In this dissertation, we proposed two different novel polycrystalline-silicon thin-film transistors (poly-Si TFTs) to improve device performance. Firstly, a new SiGe spacer with lightly-doped drain (LDD) structure was fabricated to reduce the anomalous leakage current of poly-Si TFTs. The SiGe spacer was selectively grown in ultra-high vacuum chemical vapor deposition (UHVCVD) system at 550°C. The resultant SiGe spacer TFTs features a self-aligned LDD region and no additional masks are required, which is ideally suitable for AMLCD applications. Our experimental results show that device performance such as kink-effect, leakage current and reliability are improved with SiGe spacer TFTs, compared to conventional counterparts. To integrate peripheral circuits on AMLCD, higher drive current and breakdown voltage are necessary. To this end, another novel TFTs with SiGe raised source/drain TFTs (SiGe RSD TFTs) was proposed. The SiGe RSD TFTs feature an ultra-thin channel and a thick S/D region. Ultra thin channel is beneficial for higher drive current and lower leakage current. However, ultra thin film suffers from a poor S/D resistance, which degrades device performance. In our work, SiGe raised S/D regions were selectively deposited in UHVCVD system to overcome this problem. With SiGe RSD TFTs, device performances such as turn-on current, leakage current, and breakdown voltage are superior to those with conventional TFTs. Moreover, the process is simple and no additional masks are necessary, which is consistent with conventional fabrications.