電漿處理後摻雜氟之二氧化矽的特性研究

Abstract

本論文研究具有低介電常數摻雜氟二氧化矽(SiOF)之特性。SiOF 是以TEOS/O2 加入CF4 氣體的電漿化學氣相沈積法成長。SiOF 的介電常數值隨著CF4 的加入由4.09降至3.44。低濃度摻雜氟二氧化矽(CF4=200sccm)有介電常數為3.62和折射率為1.428的特性，而且它的崩潰電場，漏電流和水氣的阻擋能力跟傳統的二氧化矽(SiO2)非常相似。 當SiOF 薄膜中氟的的含量增加時，SiOF 對水氣的的阻擋能力變的較差。原因是SiOF 薄膜變得比較鬆散，以及形成Si-F2化學鍵結。這將會增加SiOF的介電常數而且會影響元件的可靠度。為了增加SiOF 阻擋水氣的能力，我們使用了N2O、NH3、O2和N2 這四種氣體來做電漿退火處理。我們發現N2O 電漿退火處理是一個最有效阻擋水氣侵入的方法。經過10分鐘N2O 電漿退火處理，SiOF 具有介電常數為3.51和折射率為1.418的特性而且可以有效的阻擋水氣侵入。N2O 電漿退火處理也可以增加崩潰電場和降低漏電流。

We have studied the properties of fluorine-doped silicon dioxide (SiOF) deposited by adding CF4 to conventional tetraehylorthosilicate (TEOS)-based plasma-enhanced chemical vapor deposition (PECVD). Dielectric constants of SiOF films are reduced from 4.09 to 3.44 by the addition of CF4. The SiOF film (CF4=200sccm) with low concentration fluorine exhibit dielectric constant and refractive index values of 3.62 and 1.428, respectively. Characteristics of breakdown field, leakage current and moisture resistance for the SiOF film (CF4=200sccm) are similar to traditional undoped oxide. As the fluorine content increases, the SiOF films become more unstable to moisture absorption. The moisture absorption of SiOF with high fluorine content are caused by the porosity and the formation of Si-F2 in the films. The absorbed water causes increase of dielectric constant and reliability problems in LSIs. In order to improve the moisture resistance of SiOF films, we would like adopt plasma annealing such as N2O, NH3, O2 and N2 as the post treatment to stabilize this film. We find that N2O-plasma annealing is effective in improving moisture resistance of the SiOF film at the expense of increased K value. The SiOF film (CF4=800sccm) after 10 min N2O plasma annealing is enough to make SiOF film highly resistant to moisture. The SiOF film (CF4=800sccm) after 10 min N2O plasma annealing exhibit dielectric constant and refractive index values of 3.51 and 1.418, respectively. The N2O plasma treatment also improved the quality of SiOF films, as indicated by the increase of the breakdown electric field and the decrease of the leakage current density. Abstract (Chinese)………………………………………………………………i Abstract (English)………………………………………………………………ii Acknowledgments (in Chinese)………………………………………………..iii Contents………………………………………………………………………...iv Table Captions………………………………………………………………….vi Figure Captions………………………………………………………………...vii Chapter 1. Introduction 1-1 General Background 1 1-2 Fluorine Doped Oxide 3 1-3 Motivation 3 Chapter 2. The Characteristics of SiOF Films 2-1 Introduction 6 2-2 Experimental 7 2-2-1 Sample Preparation 7 2-2-2 MIS Capacitor Fabrication 7 2-2-3 Thickness, Refractive Index, and FTIR Measurement 8 2-2-4 Leakage Current-Voltage (I-V) Measurement 8 2-2-5 Capacitance-Voltage Measurement 9 2-3 Results and Discussion 10 2-3-1 Film properties 10 2-3-2 Stability of films 12 2-3-3 Electrical Characteristics 14 2-4 Summary 14 Chapter 3. Plasma Annealing Effect on SiOF films 3-1 Introduction 16 3-2 Experimental 17 3-3 Results and Discussion 18 3-3-1 Thickness and Refractive Index 18 3-3-2 Dielectric Constant (K-value) and Surface roughness 19 3-3-3 Effect of N2O plasma Treatment 20 3-4 Summary 22 Chapter 4. Conclusions 24 References………………………………………………………………26