Inline Bondwave Monitoring for Direct Bonding, Process Optimization and Impact on Post-Bond Distortion

Direct wafer bonding is essential in semiconductor manufacturing, with bondwave propagation dynamics influencing the overall bond quality. The main factor impacting bondwave velocity dynamics are substrate rigidity, fluid viscosity and adhesion energy between the two surfaces. The latter, which depends on substrates properties and process parameters, is key and should be controlled and monitored for fusion bonding applications. The use of an inline infrared (IR) monitoring within an automated fusion bonding equipment, EVG ® 850LT, facilitates real-time defect detection, root cause analysis, and bond re-workability. The equipment, which features a sealed bonding chamber equipped with an IR camera and a reflective chuck, together with a plasma chamber for pre-processing enables the assessment of various process conditions. Post-bond distortions are then evaluated using high-resolution metrology. Bondwave monitoring use-cases, a detailed analysis of bondwave speed impact on bonded stack distortion and the influence of diverse process parameters on bondwave propagation are presented or discussed in the current paper.