Effects of Applied Loads, Effective Contact Area and Surface Roughness on the Dicing Yield of 3D Cu Bonded Interconnects

Bonded copper interconnects were created using thermo-compression bonding and the dicing yield was used as an indication of the bond quality. SEM images indicated that the Cu was plastically deformed. Our experimental and modeling results indicate that the effective contact area is directly proportional to the applied load. Furthermore, for first time, results have been obtained that indicate that the dicing yield is proportional to the measured bond strength, and the bond strength is proportional to the effective contact area. It is also shown that films with rougher surfaces (and corresponding lower effective bonding areas) have lower bond strengths and dicing yields. A quantitative model for the relationship between measured surface roughness and the corresponding dicing yield has been developed. An appropriate surface-roughness data acquisition methodology has also been developed. The maximum possible applied load and the minimum possible surface roughness are required to obtain the maximum effective contact area, and hence to achieve optimum yields (both mechanically and electrically).Singapore-MIT Alliance (SMA

Preliminary Characterisation of Low-Temperature Bonded Copper Interconnects for 3-D Integrated Circuits

Three dimensional (3-D) integrated circuits can be fabricated by bonding previously processed device layers using metal-metal bonds that also serve as layer-to-layer interconnects. Bonded copper interconnects test structures were created by thermocompression bonding and the bond toughness was measured using the four-point test. The effects of bonding temperature, physical bonding and failure mechanisms were investigated. The surface effects on copper surface due to pre-bond clean (with glacial acetic acid) were also looked into. A maximum average bond toughness of approximately 35 J/m² was obtained bonding temperature 300 C.Singapore-MIT Alliance (SMA

Quantitative analysis of the mechanical and electrical properties of Cu-Cu bonds for three-dimensional integrated circuits (3D ICs)

The increasing complexity and the scaling down of feature sizes for devices have led to the increasing dominance of interconnect delays in determining integrated circuit performance. One promising solution is to stack devices vertically, commonly known as 3D ICs. Copper is an attractive candidate for 3D applications as it can be both the bonding and interconnect material. This thesis explores the wafers bonding technique, thermocompression bonding, to create 3D ICs. This technique involves the application of pressure and temperature to forge a bond. In this work, copper thin films were used to bond two silicon substrates. Characterization of the bond process focused on the effects of bonding temperature (250oC to 400oC), applied load (400 to 10000 N) and surface roughness (total root-mean-square roughness of 1 nm to 14nm). The resultant bond was quantified using a four-point bend test technique. High bond strength was obtained and the bond quality was found to improve with increases in the bond temperature and applied load, and with decreases in the surface roughness. However, nonideality in the load-displacement behavior was observed due to variation in the bond strengths and non-uniformity in the bonding. This is attributed to process issues such as dishing and non-uniform distribution of the true contact area.Doctor of Philosophy (AMM and NS