Measurement of the residual stress distribution in the 3D-stacked electronic modules by embedded strain sensors

In this study, micro-scale strain sensors were embedded in a silicon chip to measure the variation of the local stress distribution around thin film interconnections used for 3D semiconductor modules. Piezoresistive effect of single crystal silicon was applied to the sensors. The stress sensitivity at room temperature was 1.3 MPa/Ω. Even though the stress sensitivity varied as a strong function of temperature, it was confirmed that this sensor can measure the stress distribution quantitatively in the temperature range from room temperature to 8°C at most. And the variation of the residual stress in electroplated copper thin films during heat treatment was investigated from the viewpoint of the change of stress amplitude during a thermal cycle. From the obtained results, it was confirmed that the recrystallization occurred when the films were annealed at only 200°C, and the change of the micro textue of the films caused the change of their residual stress. Therefore, it is very important to control the micro texture during electroplating for assuring long term reliability of interconnections.