具溫度感測功能之微電阻銲接合封裝技術

Abstract

本論文針對本實驗室團隊先前所提出的新型晶圓級封裝方法進行改善。此封裝方式是在兩片晶片上設計相對應的接合結構，以電阻焊的方式進行局部加熱及瞬間液相接合（transient liquid phase bounding），形成金屬化合物，完成兩片晶圓的接合。 此封裝方法具有以下優點：（1）接合金屬的接觸面不需要事先平坦化、去氧化層。（2）本作法屬於局部加熱，局部的接合溫度可以較高而不會損壞晶片中其他位置的IC電路或是MEMS元件。（3）無須額外製作微加熱器，可以節省成本。（4）本作法結合矽晶穿孔技術（through silicon via）可進行晶圓層級的封裝，且封裝完成後的電性輸入／輸出點皆在晶圓的外露面，因此可以進行晶圓層級的測試。 由於先前設計的接合環狀結構在接合的過程中變異數過多，為了精確量化此封裝方式的特性，本研究首先將接合結構改為實心方塊，並且使用了摻雜硼的多晶矽當作溫度感測器，in-situ量測接合過程的溫度。另外，分別在真空與大氣下進行接合實驗。最後利用SEM及EDAX確認瞬間液相接合的性質，並使用拉伸試驗機確認接合強度。 實驗結果顯示：（1）本研究本研究所設計的溫度感測器，由於具有類似蕭基二極體的介面，其溫度感測係數優於一般僅使用摻雜硼的多晶矽元件高出數倍。（2）利用電阻銲方式可將接合溫度控制在230~300℃，持續加熱一小時以上可完成接合。（3）在真空中的接合效果優於在大氣中，因為在大氣中進行接合會在接合面產生氧化物。（4）在接合強度試驗的過程中發現本元件的破壞點發生在元件的絕緣層（二氧化矽）與金屬黏著層（Ti）並未發生在接合處。

This paper proposed several methods to improve the bounding property of a wafer-level packaging technology which was proposed by our research team previously. The bounding method employed in this technology is to use the conventional resistance welding to facilitate the process of transient-liquid-phase (TLP) bonding, which forms inter-metallic compounds to bound two wafers together. The advantages of this packaging technology are as follows. First, the bounding surface need not to be cleaned or flattened in advance. Second, it is a local-heating process so that IC and MEMS devices would not be damaged by the elevated bounding temperature. Third, this method does not need additional micro-heater. The space and fabrication complexity can be reduced. Finally, it can integrate the through-silicon-via (TSV) technology to implement the connection between IC devices and MEMS devices. Besides, the bounding pads can be exposed for the wafer-level testing. In the previously study, our research team used ring type bounding structure. Unfortunately, the results show that the bounding property can be easily affected by the process variation, In this research, we used solid square to replace the ring type structure. Besides, we design in-situ temperature sensors to monitor the temperature of the bounding process. The experiments were conducted both under vacuum and atmosphere to observe the influence of the environment. Lastly, we used SEM and EDAX to exam the bounding surface, and traction machine to test the bounding force. According to the experimental results, we found that the fabricated temperature sensors have higher sensitivity than the conventional born-doped polysilicon film because of its Schottky diode interface. The resistance welding method can successfully implement the TLP bounding with temperature of 230~300C. The bounding property is better in the vacuum than in the atmosphere due to the generation of metal oxide during the bounding process. Lastly, the stretching test indicates that the failure happens at the oxide and Ti interface, but not at the intended bounding surface.