無助銲劑銅銦直接接合製程及其介面反應分析

Fluxless direct bonding between Cu/In and the interfacial reaction analysis

邱于珊(Yu-Shan Chiu)

指導教授 ： 高振宏

共同指導教授 ： 重藤曉津(Akitsu Shigetou)

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2020年)

https://doi.org/10.6342/NTU202002992

摘要

未來的電子設備封裝趨勢需應用到各式材料進行封裝，因而工業中需要兼容性高且具有成本效益的接合介質。綜合以上需求，焊料被視為最簡易的接合介質。近年來，半導體產業偏好低溫接合技術，以避免殘餘熱應力導致基板產生熱損傷。因此，銦焊料憑藉著優秀的機械性能以及在高溫存儲下的高性能表現， 而被視為極有潛力的低溫焊點材料。本研究中通過固液擴散接合（SLID）探索了銅銦介金屬結構對可靠性的影響，並通過氬原子快速原子撞擊法（Ar-FAB）和水蒸氣氛中真空紫外光照射（V-VUV）的直接接合方式形成了理想的銅銦界面，該接合過程均在低溫下進行（室溫附近：低於50°C）。
經由固液擴散接合後銅銦的微觀結構，與Cu2In和Cu7In3相比，Cu11In9的形成最為快速。然而，在高溫時效後Cu11In9、Cu2In、Cu7In3，因而引起體積收縮。因此，為減少體積收縮所產生的孔洞，多階段的相變化應被避免。此外，從背向散射電子繞射分析中，Cu11In9沒有特定的晶粒排列方向，因而不同方向的機械性質得已表現出相似的特性。在本研究的下一階段中，我們通過直接接合（氬原子快速原子撞擊法和水蒸氣氛中真空紫外光照射），並在低溫時效後形成單一的Cu11In9介金屬相。
透過氬原子快速原子撞擊法和水蒸氣氛中真空紫外光照射，本研究創造了不需焊料的銅銦鎳系統且接合溫度接近室溫的接合方式。從掃描式電子顯微鏡圖像及高解析穿透式電子顯微鏡圖像中，發現在原子級別上銅銦界面緊密接合且沒有裂縫。 CuIn和CuIn2的形成證明了在氬原子快速原子撞擊法和水蒸氣氛中真空紫外光照射接合過程後，銅銦原子間產生了相互擴散的現象。其中，介金屬中的銅原子濃度百分比與擴散速率有關，而擴散速率則受氬原子快速原子撞擊法和水蒸氣氛中真空紫外光照射的接合原理影響。在150°C下時效500 小時後，銅銦介金屬轉變為Cu11In9，其剪切強度高於經由固液擴散接合後產生的銅銦介金屬。本研究結果證明氬原子快速原子撞擊法和水蒸氣氛中真空紫外光照射兩種直接接合方法均能形成緊密的銅銦界面且有良好的機械性質。

關鍵字

接合 ； 低溫焊料 ； 表面分析 ； 3D 封裝

並列摘要

For future electronic device packaging, application-oriented assembly of multiple materials is unavoidable. A compatible, compliant, and cost-effective bonding medium is needed for use in conventional industry. Therefore, solder has been regarded as a simple solution. Recently, low temperature bonding to avoid residual thermal stress and thermal damages was advocated widely in the semiconductor industries. Among the low melting temperature solder, indium solder is thought to be one of the promising candidates due to the better mechanical properties as well as the performance under high temperature storage. In this study, we explore the Cu-In IMC structure influence on reliability through solid liquid interdiffusion(SLID) first and create an ideal Cu-In interface through direct bonding such as Ar fast atom beam (Ar-FAB) and vapor-assisted vacuum ultraviolet (V-VUV), which was fluxless and low temperature bonding process (near room temperature: lower than 50 °C).
The microstructure evolution of Cu/In after SLID shows that the formation of Cu11In9 is the fastest compared with Cu2In and Cu7In3. However, Cu11In, Cu2In, Cu7In3 existed simultaneously after aging, which induced the volume shrinkage. Therefore, it’s better to form Cu11In9 individually after aging reaction. In addition, the EBSD analysis shows that the mechanical properties of Cu11In9 should exhibit similar behaviors along different directions. Therefore, we created this ideal phase with direct bonding such as FAB and V-VUV in the next step.
Using FAB and V-VUV, we created a bonding process without flux and at a very low bonding temperature for Cu/In/Ni system. From SEM images and high-resolution TEM images, the Cu/In interface was found to be adhered atomically. The formation of CuIn and CuIn2 proved that interdiffusion occurs among Cu/In atoms after FAB and V-VUV bonding process, respectively. The atomic concentration percentage of Cu in IMCs is related to the interdiffusion rate, which is based on the difference of bonding mechanism of V-VUV/FAB. After aging at 150 °C for 500 h, Cu-In IMCs transformed into Cu11In9 and the shear strength was higher than the samples bonded through SLID. The results proved that both methods created tight voidless bond interfaces of Cu-In surface.

並列關鍵字

Bonding ； low temperature solder ； 3D packaging ； surface analysis

參考文獻

[1] D. P. Seraphim, R. C. Lasky, and C.-Y. Li, Principles of electronic packaging. McGraw-Hill College, 1989.

[2] Lau, John H. "Evolution, challenge, and outlook of TSV, 3D IC integration and 3D silicon integration." 2011 international symposium on advanced packaging materials (APM). IEEE, 2011.

[3] K. Banerjee, S. J. Souri, P. Kapur, and K. C. Saraswat, “3-D ICs: A novel chip design for improving deep-submicrometer interconnect performance and systems-on-chip integration,” Proc. IEEE, vol. 89, no. 5, pp. 602–633, 2001.

[4] “Solders-Technology-Roadmap-2015.pdf.” .

[5] M. Z ou, Y. Ma, X. Yuan, Y. Hu, J. Liu, and Z. Jin, “Flexible devices: from materials, architectures to applications,” J. Semicond., vol. 39, no. 1, p. 011010, Jan. 2018.