A Low-Temperature Nickel Silicide Process for Wafer Bonding and High-Density Interconnects

Wafer-scale heterogeneous integration provides a viable pathway for the development of highly capable microsystems. However, it remains challenging to integrate die-and wafer-level components with a high-density interconnects while minimizing the system volume and within the temperature restrictions imposed by integrated circuits. Advancements in CMOS have motivated the development of low-temperature and low-resistance metal-silicon alloys or silicides. Nickel silicide (NiSi) is a CMOS-compatible material that forms at temperatures and anneal times within the thermal budget of commercial CMOS die and can be implemented with a wide range of nickel and silicon thin-film processing methods. We describe here the development of a 3-D integration strategy utilizing NiSi formation to generate both mechanical bonding and electrical interconnection between wafers. Specifically, we show that our NiSi-based wafer-bonding process is effective below 400 °C, at very short anneal times (minutes), and with a variety of thin-film processing methods. This NiSi-based process offers a robust approach for creating heterogeneously integrated microsystems in a CMOS-compatible fashion.