多晶鍺元件的研製與分析

Abstract

在本論文研究中，我們探討了多晶鍺薄膜和鍺化鎳的材料特性。藉由不同形式的結晶方法，由超高真空濺鍍系統沈積的非晶鍺會被轉變成多晶鍺薄膜。從固相結晶法(SPC)的結果，我們發現在經過500 ℃ 1小時的退火處理後，非晶鍺會轉變成多晶鍺且晶粒尺寸會達到飽和，不再隨退火時間的增加而增加尺寸。與SPC相比，金屬誘發結晶法(MIC)在鎳的幫助下可降低結晶溫度且獲得較大的晶粒尺寸。而MIC除了可以增加薄膜的結晶性之外，亦可運用於摻雜的活化，也就是金屬誘發摻雜活化(MIDA)技術。因為在MIC過程中，摻雜會因晶格重排而進入取代位，所以MIDA可在低溫下進行摻雜的活化。金屬鍺化物的使用被認為可以降低寄生電阻並解決較低的摻雜固態溶解度的問題，而我們發現形成鍺化鎳的適合溫度為300 ℃到375 ℃。此外，在本論文中，我們也製作了五種元件，從電性結果來看，我們發現多晶矽的存在可以增加多晶鍺薄膜的結晶性，而且當多晶矽是被沈積在源極和汲極端的多晶鍺薄膜的下方時，多晶矽對電性的影響是最明顯的。

In this study, material properties of poly-Ge thin films and Ni germanides were investigated. The poly-Ge thin films were formed by different crystallization schemes performed on a-Ge deposited by an ultra-high vacuum sputter. From the results of solid-phase crystallization (SPC) method, we found that a-Ge is transformed into poly-Ge at 500 ℃ for 1 hour annealing and then the grain size saturates. For metal-induced crystallization (MIC) method, the crystallization temperature can be reduced with the assistance of Ni and the grain size is bigger than that formed by SPC method. In addition to enhanced crystallization, MIC can be applied to activate dopants at low temperature, termed metal-induced dopant activation (MIDA), because dopants will be rearranged into the substitutional sites during MIC process. Germanide process is expected to reduce the parasitic resistance and alleviate the issue of low dopant solid solubility. We found that the suitable temperature to form NiGe is from 300 ℃ to 375 ℃. Besides, we also fabricate five types of devices in this thesis. From the electrical characteristics, we discovered that poly-Si can increase the crystallinity of poly-Ge and this apparent effect occurs when poly-Si is deposited under the poly-Ge film at the S/D region.