三維積體電路異質整合之聚醯亞胺材料應用於銅/錫與銅/銅非對稱混合接合研究

Abstract

為了追求更小的封裝架構及高性能表現，晶圓接合技術在三維積體電路中扮演極其重要的角色。微凸塊的尺寸與間距需持續進行微縮以達到2.5D/3D的高密度整合，然而，這將造成接合完畢後狹窄間距內的底膠填充越來越困難。結合金屬材料與高分子材料的混合接合技術可以同時達到電性的互連與結構的機械支撐。隨著黃光微影技術的進步，感光型高分子材料將可填滿金屬線間的微小孔隙。此外，傳統用於去除金屬表面殘留的化學機械研磨或鑽石切削加工技術可以被跳過並且透過有機材料的曝光顯影所取代。 本篇論文成功開發出兩種混合接合平台：第一種為結合銅/錫接合技術的「金屬優先」混合接合方式。非對稱混合接合結構的概念被提出以避免錫在高分子材料的固化製程中受到影響；第二種為結合銅/銅接合技術的「高分子優先」混合接合方式。為了避免銅金屬在高溫下的嚴重氧化，高分子材料的旋塗與固化提早於金屬薄膜沉積前完成。金屬與高分子材料可以依照高彈性的厚度比例同時達到良好的接合成果，並且妥善利用高分子接合來填充金屬線間的額外面積能大幅提升結構的機械強度。 本研究中完成的兩種混合接合結構皆呈現良好的電性表現與通過可靠度測試的高穩定特性。基於介電材料的感光優勢、優異的接合質量、靈活的製程彈性、高結構機械強度、良好的電性與穩定性，此二種混合接合平台展現未來應用於三維異質整合的卓越潛力。

Wafer bonding technology plays an important role to pursue small form factor and high performance for 3D integration. However, in order to achieve high density 2.5D/3D integration, the dimension and pitch of micro bumps continue to scale down. It becomes more and more difficult to fill the narrow gaps with underfill material after bonding. Hybrid bonding technique combining metal and polymer can achieve simultaneous formation of electrical interconnection and mechanical support. Photosensitive polymer is used to fill the gaps between the metal lines through the process of lithography. In addition, chemical mechanical polishing or fly cutting process, which is a conventional way of removing the residue on metals, can be skipped and replaced by the development of exposed polymer. Two types of hybrid bonding platforms are successfully developed in this thesis. The first one is “metal first” hybrid bonding combined with solder bonding. Solder may be affected during the curing process of polymer. Thus an asymmetry hybrid bonding structure is proposed to overcome this issue. The second topic is “polymer first” hybrid bonding combined with Cu/Cu bonding. Polyimide is coated and cured on the bottom wafer before metal sputtering to avoid copper oxidation at high temperature. Metal and polymer can be well bonded simultaneously with wide integration flexibility through various polymer to metal thickness ratios. The mechanical strength of bonded structure is substantially improved with the good use of polymer bonding filling in the extra areas between metal lines. Both of the hybrid-bonded structures show good electrical characteristics and pass several reliability tests. With the advantages of dielectric photosensitivity, excellent bonding qualities, high process flexibilities, strong mechanical strength, good electrical performance and high stability after the reliability tests, these two hybrid bonding structures have the outstanding potential to be used in future 3D heterogeneous applications.