应用于3D集成的高密度Cu/Sn微凸点键合技术

High Density Cu/Sn Microbump Bonding Technology for 3D Integration

摘要:

3D-IC技术被看作是应对未来半导体产业不断增长的晶体管密度最有希望的解决方案,而微凸点键合技术是实现3D集成的关键技术之一.采用电镀工艺制作了直径为50μm、间距为130μm的高密度Cu/Sn微凸点,分析了不同预镀时间及电流密度对Cu微凸点形成质量的影响,并使用倒装焊机实现了高密度Cu/Sn微凸点的键合.利用直射式X射线、分层式X射线对键合样片进行无损检测,结果表明键合对准精度高,少量微凸点边缘有锡被挤出,这是由于锡层过厚导致.观察键合面形貌,可以发现Cu和Sn结合得不够紧密.进一步对键合面金属间化合物进行能谱分析,证实存在Cu6Sn5和Cu3Sn两种物质,说明Cu6Sn5没有与Cu充分反应生成稳态产物Cu3Sn,可以通过增加键合时间、减少Sn层厚度或增加退火工艺来促进Cu3Sn的生成.

Abstract:

3D-IC technology is supposed to be the most promising solution for the growing transistor density in semiconductor industry,and microbump bonding is one of the key technologies for realizing 3D stacking.In this paper,high density Cu/Sn microbumps of 50μm in diameter and 130μm in pitch were fabricated by electroplating,and the influence of different pre-electroplating time and current density on the quality of copper bumps were analyzed.Then high density Cu/Sn microbump bonding were performed by using a flip chip bonding equipment.Radiography and laminography were carried out for nondestructive detecting of the bonding samples,and the results show that the bonding alignment accuracy is quite high,while a small amount of Sn is squeezed out at the edge of the bumps owing to the excessive thickness of the Sn layer.By observing the bonding interface morphology,it is found that the Cu layer and the Sn layer are not tightly combined with voids exist at the interface.The spectral analysis is utilized to confirm the ingredients of the bonding intermetallic compounds,and the results prove that the intermetallic compounds are composed of Cu3Sn and Cu6Sn5,indicating the bonding reaction of Cu6Sn5 and Cu is inadequate to the stable and planar intermetallic compound Cu3Sn.The formation of Cu3Sn can be promoted by increasing the bonding time,decreasing the thickness of Sn layer or introducing the anneal process.