無電鍍鎳對於晶片直接接合的應用

Abstract

三維積體電路堆疊透過垂直堆疊多層的積體電路使得摩爾定律得以延伸，以滿足現代對於電子產品高效能、多功能、低功率消耗以及較小體積的要求。然而，傳統上用於垂直堆疊的銲錫凸塊在晶片微縮的趨勢下會面臨一些物理上的挑戰，例如最小線寬的限制以及對抗電遷移效應的可靠性議題等。電鍍銅凸塊在上述所提的兩點議題上相較於傳統銲錫凸塊擁有較好的表現。因此電鍍銅凸塊有應用在微小線寬的潛力。然而，電鍍銅凸塊的常見接合方式為熱壓接合，是一種需要在高溫施加壓力的接合方式，施加高溫以及壓力會產生一些可靠性議題，像是熱應力、機械應力以及介面的剝落等。 在本研究中，我們致力開發了一新穎的接合技術能在低溫與無施加壓力的條件下進行接合，此接合技術整合了無電鍍技術與微流體技術。在此技術中，晶片被放置於以PDMS為材質的微流道中，底部以玻璃片作為支撐，微流道透過矽膠管與定量幫浦連接，形成一個微流體系統。定量幫浦使我們能夠準確的控制通過微流道內的無電鍍液之流動。 此技術擁有低操作溫度、無須施加壓力等優點，可潛在性地增加電子產品的可靠性。進一步的研究顯示操作溫度以及流速對於無電鍍的結果有影響。此外，微流體無電鍍製程在適當的上鍍參數之下，能夠接合晶片之間的銅柱。我們對成功完成接合的晶片以掃描式電子顯微鏡觀察以無電鍍結合的銅柱。我們將結合的銅柱截面使用聚焦離子束進行觀察。

3D ICs enables the extension of Moore’s law by vertical stacking of multiple layers of integrated circuits to meet electronic device requirements such as higher performance, increased functionality, lower power consumption, and smaller footprint. However, conventional solder bump is faced with challenges such as pitch limit and electromigration reliability as the chip dimensions are scaled down. Cu pillar bump provides advantages over conventional solder bump in terms of above-mentioned concerns. Thus, Cu pillar bump is a candidate for fine pitch applications. Nevertheless, common boding methods of Cu pillar bump requires high operating temperature and bonding pressure. And, both of which may cause reliability concerns such as thermal stress, mechanical stress, and interfacial delamination. In this study, we developed an innovative bonding process that requires low temperature and pressureless bonding conditions. The bonding technique incorporates electroless plating process and microfluidic system. Chips were placed between a glass plate and a PDMS microchannel. And, silicone tubes were used to connect the PDMS microchannel and a syringe pump, forming a microfluidic system. The syringe pump allows us to precisely control the flow of electroless bath through the microchannel. This bonding process has the advantages of low operating temperature and pressureless condition, which can potentially improve the reliability of electronic packaging. The investigation shows that both operating temperature and flow condition have important influence on the plating results. Furthermore, the microfluidic electroless process is able to bond Cu pillars between chips with proper plating parameters. The bonded chips were analyzed by Scanning Electron Microscope (SEM) and Optical Microscope (OM). Finally, focused in beam (FIB) was used to observe the cross-sectional image of bonded Cu pillars.