介電質化學機械研磨理論與應用方面之研究

Abstract

為了消除階梯覆蓋的差異,同時也為了減少不必要的熱預算,低溫且全面的 平坦化技術在未來的積體電路製程中是非常重要的.由於化學機械研磨平 坦化技術之精巧度可達此一要求,故具有實際應用之價值. 本論文首先探 討不同方法製備的氧化層特性.由化學機械研磨,紅外線光譜分析及毫微刻 痕測試發現,對未摻雜雜質的氧化層而言,蝕刻率,矽-氧鍵結密度和硬度三 者之間有一比例關係;但對摻雜雜質之氧化層而言,雜質之種類及數量對氧 化層之化學本質及研磨過程中之化學反應有重大作用,導致上述之比例關 係消失.另薄膜應力對材料之抗裂性及耐磨性的效應亦被仔細的探討.本論 文接下來以研磨顆粒和晶圓表面薄膜之物理接觸為基礎,推導出材料磨損 之數學模式,並經實驗證明其可行性.本模式除了和普雷斯特方程式相同的 預測蝕刻率和承受壓力及磨盤轉速成正比關係外;進一步地,本模式首次考 慮研磨襯墊,研磨顆粒及晶圓表面薄膜三者之機械性質對蝕刻率之影響.化 學機械研磨製程對晶圓而言,是一個高汙染製程.本論文分別評估化學和機 械方法對微粒子去除之效果.實驗結果發現,增加浸洗液之鹼度或正向壓 力,將有助於去除晶圓表面之微粒子.實際上,微粒子比較不容易沾在較硬 之薄膜上;但一旦沾上,就較不易去除.運用化學機械研磨技術,具圖形落差 之晶圓表面薄膜,可以得到全面的平坦化.此時若在軟的介電層上覆蓋一薄 膜層,則圖形逆轉現象可用來檢測蝕刻終點.最後,本論文並對傳統平坦方 法及化學機械研磨對元件特性變化做一完整比較.根據本論文之研究,化學 機械研磨技術,確實可用於未來的半導體製程中. The application of chemical mechanical polishing (CMP) to planarize pre-metal and inter-metal dielectrics is very pro- mising for future circuit interconnections due to its ability to eliminate step coverage variation and to reduce unnecessary thermal budget for planarization.In this thesis,the charac- teristics of oxide films related to film's preparation methods were studied. CMP,FTIR spectra,and nanoindentation data showed that the removal rate and the Si-O bond density scale with the hardness of undoped oxide films. This does not hold for doped oxide films however because the type and content of doping species have considerable impact on film's chemical structure and the reaction is mediated by local conditions of contact during CMP. The role of the sign and magnitude of film's pre- existing stress on crack resistance during indentation and on CMP removal rate were also discussed. The wear mechanism of dielectrics during CMP was inves- tigated based on the mode of particle/substrate contact. A polish model is proposed,which is supported by experimental evidence. The removal rate is found to be directly proportional to polishing pressure and wafer velocity as expected from the Preston's equation based on glass polishing. Of particular importance in the model is the incorporation of the effects of a mechanical factor (Hardness/ modulus) into the contact scheme between the pad, the slurry- carried particle,and the wafer during mass removal. Both cleaning mechanics and chemistry were independently studied to better understand post-CMP cleaning process. Increases in the pH of the immersing solution as well as in buffing pressure could enhance the efficiency of particle removal.Particles appeared to have difficulty attaching on or being removed from a harder surface of the dielectric film. Excellent planarity achieved by CMP is demonstrated for patterned wafers. Here, inversion patterns are indenified for the composite dielectrics formed by a thin hard film on the top