銅腐蝕抑制劑對銅保護機制在化學機械研磨之研究

Abstract

半導體製程在技術節點進入0.18m後，內連結金屬就以鋁材改為銅材，而多層金屬內連節隔離層也改為低介電材料，化學機械研磨(Chemical-Mechanical Planarization，CMP)因而成為重要的製程之一。本論文研究酸性Cu 研磨液在銅與介電層研磨反應，而其主要以去離子水、氧化劑與抑制劑(Inhibitor)所組成。雖然高濃度的蝕刻抑制劑(Benzotriazole, BTA)可以在銅表面形成鈍化層來幫助控制表面研磨，但是也會造成在晶圓表面產生有機物殘留而形成缺陷。本研究便以化合物A(長鏈形酮基化合物)來減少BTA濃度，卻仍具有銅鈍化層效用，進而減少有機物殘留與控制銅研磨率等問題。 本文以不同濃度的BTA與化合物A混合，分別對銅導電層與介電層作研磨，得到銅與介電層的研磨率與研磨選擇比。並且利用電化學方式來驗證銅在研磨液中的氧化反應機制，最後再對研磨後的晶圓做缺陷測量。綜合研磨率、缺陷測量與電化學反應等方式去證化合物A在酸性Cu CMP研磨液作用機制是否達到預期研磨效果與有機物殘留減量。 實驗結果顯示，化合物A確實可以減少BTA使用量，銅金屬表面藉由BTA與化合物A形成鈍化層保護，減少氧化劑、研磨粒子與異物對銅表面反應與刮傷。介電層表面屬疏水性，化合物A直接黏著在介電層表面，形成鈍化保護層，來提高研磨選擇比，可以調整銅與介電材料的平坦化效果。提高酸性清潔液濃度雖可達到較好的有機物清除效果，但也會造成銅表面的粗糙度變差，化合物A的添加可以減少了有機物數量，也不需提高酸性清潔液濃度清除有機物。

When the technology node of semiconductor evolved to below 0.18um, the interconnect metal and dielectric materials were replace by copper (Cu) and low K dielectrics respeetwely. Chemical-mechanical planarization (CMP) hence becomes one of the key processes in manufactory flow of semiconductor. This study focuses on the improvement of Cu CMP defects induced by the acidic CMP slurry. The typical alkaline CMP slurry contains DI water, oxidizer and inhibitor (benzotriazole, BTA). Although high concentration of BTA inhibitor may protect Cu film and suppress Cu reacting rate, it also induces organic residues on the Cu surface. By introducing new additive A, the usage of BTA inhibitor can be effectively decrease without sacrificing the benefits and performance of Cu CMP slurry. In this study, CMP slurry solutions containing various contents of additive A are prepared and they are applied to CMP process to analyze their removal rates and selectivities. Electrochemistry was adopted to investigate the oxidization reaction of Cu in CMP slurry. Finally, all the polished wafers in this study were examined and made a comprehensive review to understand whether additive A is capable of polishing performance improvement. The experimental results, indicated that additive A can reduce the usage of BTA. Cu surface can be passivated by BTA and additive A, reducing surface reaction by oxidants and scratches caused by abrasives. The dielectric surface, which is hydrophobic, could be covered by additive A. The selectivity could be controlled by the passivation of additive A to enhance the planarization performance. Although using high concentration clean agent can provide better clean efficiency for organics, it can also induce worse roughness of Cu surface. The addition of component A reduces the usage of organics, which also indicates that it is unnecessary to use a high concentration clean agent to remove the organics.