以電漿沈積法成長摻雜氟之低介電常數二氧化矽應用於內層介電材料之特性研究

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 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 的加入而由 3.8 降至 3.2. 矽氟化學鍵是利用傅利葉轉換紅外線光 譜儀(FTIR)測量. 由於矽氟鍵造成SiOF薄膜的離子偏極化減少,因此導致 低介電常數.當SiOF薄膜中氟的含量增加時,SiOF對水氣的阻擋能力變得較 差.原因是SiOF薄膜變得比較鬆散,以及形成Si-F2化學鍵結.我們以快速退 火(RTA)研究SiOF薄膜的熱穩定性.SiOF薄膜中的氟含量會隨RTA溫度的增 加而減少,然而在低水氣吸附的情形下,RTA溫度達到600C 時介電常數仍然 相同. SiOF薄膜經過RTA處理後,原子力顯微鏡(AFM)的照片顯示出薄膜表 面粗糙程度的減少以及緻密化.為了增加SiOF介電常數的穩定性,表面氮化 處理是需要的.N2O電漿退火處理是一個阻擋水氣侵入的有效方法.經N2O電 漿退火處理過的SiOF薄膜,它的介電常數幾乎不隨時間而改變. We have studied the properties of fluorine-doped silicon dioxide (SiOF)deposited by adding CF4 to conventional tetraethylorthosilicate(TEOS)-basedplasma-enhanced chemical vapor deposition (PECVD). Dielectric constants of SiOF films are reduced from 3.8 to 3.2 by the addition of CF4. Si-F bond formation in the films is detected by chemical bonding structural studies using Fourier Transform Infrared Spectroscopy (FTIR). Low dielectric constants are caused by Si-F bond formation. The reduction of the dielectric constant apparently results from a decrease of the ionic polarization. As thefluorine content increases, the SiOF films becomes more unstable to moistureabsorption. The moisture absorption of SiOF with high fluorine content are caused by the porosity and formation of Si-F2 in the films. The thermal stability of SiOF films is investigated by rapid thermal annealing (RTA). The fluorine contents of SiOF films decrease with increasing RTA temperature.However, the dielectric constants of the SiOF films remain the same up to 600C under low moisture absorption condition. Atomic force microscopic(AFM)pictures reveal the densification and the reduction in surface roughness ofSiOF films after RTA treatments. In order to stabilize dielectric constants of SiOF films which increase with the increase of moisture absorption, a surface oxynitridation is required. We find that N2O-plasma annealing in an effective way to block moisture. The dielectric constants of SiOF films treated by the N2O-plasma annealing rarely change.