三維積體電路之銅/鈦接合及其應用之研究

Abstract

本論文研究在三維積體電路中的共鍍金屬接合研究。利用不同金屬 (例如:銅/鈦)間的共鍍，首先研究製程條件最佳化，探討不同金屬間的 擴散機制。同時，發現在氮氣的環境進行退火下，熔點高的元素會往矽 基板方向做擴散，以銅/鈦共鍍金屬為例，鈦會往矽基板方向擴散。但 若在大氣環境下進行退火，則鈦會到表面與氧氣反應，在表面形成氧化 鈦。以此條件在大氣環境下進行接合並定義極佳結構尺寸，可自動形成 鈦的附著層，讓銅有更高更穩定的附著性，並減少了製程步驟；而部分 鈦擴散到表面氧化形成的緻密氧化鈦，可自動形成保護銅的結構，防止 銅表面氧化而形成氧化銅，以增進銅的可靠性。最後，根據最佳的製程 條件，進行銅/鈦接合結構相關的材料分析及強度測試，並進行包括接 觸電阻等電性的量測，與傳統的銅接合結構進行比較。研究結果發現， 銅/鈦接合結構不僅有半導體製程與可靠度上的優勢，同時也符合三維 積體電路製程中接合的強度與電性需求，在三維積體電路相關應用上具 有十分的潛力。

This thesis focuses on researches of co-sputtering metal bonding in three-dimension integrated circuits (3DIC). Several co-sputtering metal species, such as copper (Cu) and titanium (Ti), are investigated. The corresponding bonding conditions are optimized as well. It is found that metal atoms with higher melting point will diffuse to the silicon substrate side under nitrogen ambient. The diffusion mechanism of co-sputtering metals has been discussed. For co-sputtering Cu/Ti metals, Ti atoms diffuse to the silicon substrate side under nitrogen ambient. However, Ti atoms diffuse to the surface of bond structure to react with oxygen and form Ti oxides if under atmosphere. Therefore, when Cu/Ti interconnects bond at the atmosphere, the Ti adhesion layer is self-formed under Cu and the process step is reduced. Some Ti atoms react with oxygen on the surface to form compact Ti oxides, which prevent Cu oxidation and improve the structure reliability. Finally, the material analysis, bonding strength, contact resistances of Cu/Ti bonding structures are investigated based on the best bonding parameters. According to our researches, the co-sputtering Cu/Ti bonding has the advantages of less fabrication steps and better reliability. The bonded structures meet the requirements of the bond strengths and electrical performance in 3D IC. This novel bonding technology has a high potential for the applications of 3D IC.