使用Ti作為黏著層在微銲點介面反應最終端行為之研究

Abstract

近年來，隨著數位通訊與智慧手機的進步，輕量、薄型化、多功能的消費性電子產品變為半導體業的主要發展走向。為了達到高密度堆疊與異質整合之目標，以矽穿孔與微銲點為主體架構之三維晶片整合是微電子封裝最具潛力的發展方向。其中，微銲點體積與傳統覆晶銲點有近三個數量級之差異，空間限制效應不僅將使得微銲點會在短時間內演變為與傳統大尺寸銲點迥然不同的微觀形貌，亦因接點進入微米尺度而凸顯放大特殊的微觀物理現象。過去對於封裝接點之研究僅聚焦在界面反應前中期之形貌發展，對銲錫完全耗盡且轉變為全介金屬接點後的界面反應終端行為及其對可靠度之影響一直以來是疏於探討的領域，至今對於微米尺度接點之顯微組織演變、介金屬粗化合併機制、界面剝離等終端行為的瞭解仍不夠完備。基於評估三維晶片整合封裝可靠度之需求，對微銲點界面反應最終端行為及微銲點界面強度的完整瞭解至關重要，亦是當今微電子封裝產業密切關注的議題。 在上述提到的問題中，最重要的議題是作為連接使用的微銲點將會很容易導致全介金屬化合物焊點。並且再更進一步，潤濕層的完全消耗將會使介金屬化合物 (IMC) 與黏著層直接接觸，可能會帶來嚴重的可靠性問題。因此，在本研究中，通過在 200 °C 時效處理研究了 Ti 黏著層與 Cu-Sn IMCs 的界面終端反應。經過 0到 72 小時的熱時效處理後，儘管微銲點全部轉變為介金屬化合物結構 (IMC)，但它們對 Ti 黏著層仍表現出很強的附著力。此外，Cu和Sn之間擴散速率的差異會導致時效過程中引起孔洞的形成。這些孔洞會隨著銅層的耗盡而發展到銲點的中心，然而，它們既不影響 IMC 與黏著層之間的附著，也不降低銲點的強度。總而言之，使用 Ti 作為黏著層與使用 Cr 相比，將會有與 IMC 更好的附著行為。

In recent years, with the advancement of digital communication and smartphones, lightweight, miniaturization, and multi-functional consumer electronic products have become the main development trend in the semiconductor industry. Aiming to realize the goal of high-density stacking and heterogeneous integration, three-dimensional chip integration with TSV and micro joints is the most potential development of microelectronic packaging. Among them, almost three orders of magnitude are different in the volume of the micro joint and the traditional solder joint. The space confinement effect will not only make the micro joint evolve into a microscopic morphology that is completely different from the traditional large-size solder joint in a short period of reaction time, but also amplification of special microphysical phenomena by such micrometer-scale joints. In the past, the research on solder joints only focused on the morphology development in the early and middle stages of the interfacial reaction. The terminal behavior of the interfacial reaction after the solder is completely exhausted and transformed into a full-intermetallic joint and its reliability have been incomplete. Based on the need to evaluate the reliability of 3D chip integrated packaging, a complete insight into the terminal behavior of interfacial reaction and the strength of the micro joint is crucial. It is a topic that is closely watched by the microelectronic industry today. According to the problems mentioned above, the most important issue is the easy formation of full-intermetallic structure in micro joints. Furthermore, complete depletion of the wetting layer will bring the intermetallic compound (IMC) directly adjacent to the adhesion layer, potentially causing serious reliability problems. Therefore, in this research, the terminal behavior of interfacial reaction between Cu-Sn IMCs and the Ti adhesion layer is investigated by 200 °C aging. After thermal aging from 0 to 72 hours, although they were all converted to an IMCs structure, the micro joints show strong adhesion to the Ti adhesion layer, which has a significant difference from the Cr system that spalled the IMCs from the substrate. Additionally, the voids formation in the aging period was found owing to the unbalance diffusion in Cu-Sn IMCs. As the Cu layer depleted, the development of these voids would proceed to the whole bump. However, they neither influence the adhesion between the IMCs and the Ti layer nor reduce the strength of the micro joint. In conclusion, the Ti adhesion layer will have better adhesion properties with Cu-Sn IMCs than the Cr system.