Influence of Atmosphere on Ultrasonic Bonding of Silicon to Metal

对几种金属箔（Au、Ag、Al、Cu、Ni、Fe）进行了超声键合。在金属键合相似的情况下，取得了良好的键合效果。然而，在不同金属结合的情况下，只有少数金属箔的组合才能实现良好的结合。金属箔与银箔的结合很差。其次，测试了金属箔与硅片的键合能力，并与Au箔和Al箔进行了良好的键合。在Si与Al箔结合的情况下，结合强度（剪切强度）存在较大的分散。由于结合面上的氧化层可能导致Si/Al箔结合强度的大散射，因此将Si和Al箔浸泡在酸和碱中去除氧化层。将硅在HF水溶液中浸泡24 h，将铝箔在不同含量（0 ~ 10 kmol/ m3）的NaOH溶液中浸泡时间（0 ~ 10 min）。在氢氧化钠溶液中浸泡Si对Si与Al箔的键合特性没有影响，但随着NaOH溶液中浸泡Al越多，各键合条件下的最小键合强度增加，键合强度的散射减小。溶液中NaOH含量和浸泡时间对键合性能的影响不明显。在NaOH溶液中浸泡时，扫描电镜观察到铝箔的氧化层上有许多小孔，认为这是由于超声振动时氧化层容易从金属箔表面脱落所致。然后，在2 Pa的压力下进行了Si与Al箔的超声波键合，但强度没有增加，强度的散射也没有减少。通过溅射在Si表面形成Au膜，然后在空气气氛下将Au膜与Al箔结合。结合强度随Au膜厚度的增加而增加。断裂发生在Au薄膜与Si衬底之间的界面处，其结合强度取决于Au箔的强度和Si/Al界面的强度。从这些结果可以预期，通过对Si和金属表面进行表面处理可以提高Si/金属箔结合的结合强度。少

Ultrasonic bonding was carried out with some kinds of foil (Au, Ag, Al, Cu, Ni, Fe). In the case of similar metal bonding, good bonding was carried out. However, in the case of dissimilar metal bonding, only a few combination of metal foil enabled good bonding. The bonding of metal foil with Ag foil was very poor. Next, the bonding ability of metal foil to Si wafer was examined and good bonding was obtained with Au foil and Al foil. In the case of bonding of Si to Al foil, there was large scatter in bonding strength (shear strength). Since large scatter in strength of Si/Al foil bonding might be caused by oxide layer on the bonding face, Si and Al foil were immersed in acid and alkali to remove oxide layer. Namely, Si was immersed in HF water solution for 24 h, and Al foil was immersed in NaOH solution of different content (0 - 10 kmol/m_3) for different times (0 - 10 min). Immersion of Si in HF solution gave no influence on bonding character of Si to Al foil, but after immersion of Al … More foil in NaOH solution, minimum bonding strength increased at each bonding condition and scatter of bonding strength decreased. There was no clear influence of NaOH content in solution and immersion time on bonding character. Since many small holes were observed on the oxide layer of Al foil during immersion in NaOH solution through SEM, it was thought that the increase in bonding strength was caused by easy detachment of oxide layer from the surface of metal foil during ultrasonic vibration. Then, the ultrasonic bonding of Si to Al foil was done under a pressure of 2 Pa, but no increase in the strength and no decrease in scatter of the strength was obtained. Au film was formed on Si surface by spattering, and then the bonding of Au film to Al foil was done under air atmosphere. The bonding strength increased with increasing thickness of Au film. The fracture occurred at an interface between Au film and Si substrate, and the bonding strength was dependent on the strength of Au foil and the strength of Si/Al interface. From these results, it was expected that the bonding strength of Si/metal foil bonding increases through surface treatment of Si and metal surface. Less