Detection of Interfacial Gas Bubbles in Wafer Bonded Silicon with Different Surface Treatments

Designing a surface treatment process that generates high-strength bonding at low annealing temperatures with high overall process yields has been hampered by the development and growth of gas bubbles trapped at the bonded interface. This paper compares three methods for detecting and quantifying gas bubble defects in wafer-bonded silicon subjected to different surface treatments: ( i ) scanning acoustic microscopy (SAM), ( ii ) IR transmission (IRT) imaging, and ( iii ) IR photoelasticity [using the grey-field polariscope (IR-GFP)]. The SAM and IR-GFP are shown to detect the same defects, which are not possible to visualize with IRT, even with a modified optical train. In addition, the magnitude of the residual stress fields associated with each defect was quantified using IR-GFP shear stress imaging. Residual stresses are found to vary by more than a factor of 2, depending on the wafer pretreatment. These results also indicate that residual stress levels from interfacial gas bubbles are similar to those reported for particles trapped at the bond interface.