三維積體電路應用之超音波低溫銅柱接合研究

Abstract

因應目前電子產品多功能化的趨勢，晶片訊號處理輸入/輸出端需求數不斷增加，導致晶片封裝引線節點數密度提高和凸塊間距不斷持續縮小，因此，目前先進封裝製程均改以銅柱凸塊作為傳統錫鉛凸塊技術的取代方案。 一般銅-銅熱壓接合需要在溫度攝氏三百五十以上的高溫高壓的製程條件下才能達到高良率及優良的接合品質，然而在高溫高壓接合環境下容易導致電路性能劣化、熱應力殘留等問題，因此，為了改善此狀況，本論文選用具有低熔點特性的金屬-銦(熔點: 156.6 oC)作為低溫接合材料，並結合超音波因瞬間高速震動摩擦產生局部高溫的機制來達成整體低溫低壓的接合環境。 本研究透過剪力測試結果顯示超音波銅柱接合在溫度及壓力僅220 oC、25 N可達到平均40 MPa以上的接合強度，並經過可靠度測試(溫度循環及濕度測試)仍然保持良好的電性特徵，證明此研究方法在未來3D整合應用提供良好的接合品質和可靠度。

In response to the current trend of multi-functional electronic products, there has been a growing need for a large number of I/O counts in signal processing chips, resulting in increasing the density of the lead nodes of chip package and reducing the pitches among bumps. Therefore, the packaging industries have replaced conventional tin-lead solder bumps with Cu pillar bumps as current packaging technologies. In general, direct Cu-to-Cu thermo-compression bonding requires the process condition of high bonding temperature above 350 ⁰C and high pressure to get high yield and excellent bonding quality. Nevertheless, high temperature and pressure bonding may cause some issues to the devices, such as electrical characteristic degradation, residual thermo-stress. In order to improve the issues, this study chooses indium with low melting point of 156.6 oC as a low temperature bonding material and combines the mechanism of ultrasonic vibration, which generates local heat and ruptures the oxidative layer by friction at the bonding interface, to achieve low temperature and pressure bonding conditions. Through this study, the shear test results show that bonding strength of Cu pillar interconnects can be achieved to an average over 40 MPa under the bonding conditions of 220 ⁰C, 25 N. In addition, Cu pillar interconnects still maintain good electrical characteristics after reliability test such as TCT and unbiased HAST and prove that the low temperature Cu pillar thermosonic bonding provides good bonding quality and reliability for 3D integration applications.