Heat-Depolymerizable Polypropylene Carbonate as a Temporary Bonding Adhesive for Fabrication of Flexible Silicon Sensor Chips

This paper presents a method for fabrication of flexible silicon sensor chips using temporary bonding, backside thinning, debonding, and flexible packaging. Flexibility of silicon chips requires ultrathin thickness, which imposes a challenge to debonding of thinned silicon chips from carrier wafers because of the fragility of silicon. To address this problem, temporary bonding using polypropylene carbonate (PPC), a heat-depolymerizable polymer material, as bonding adhesive is developed. PPC allows damage-free detachment of ultrathin silicon chips from carrier wafers by heating after backside thinning. The method is demonstrated and applied to the fabrication of silicon stress sensor chips with thickness down to $30~\mu \text{m}$ . The measurement results show that the ultrathin silicon chips have good flexibility and function well. The processes are optimized, and the detailed parameters are reported. The preliminary results demonstrate the feasibility of the method, and show its potential application in the fabrication of flexible ultrathin silicon sensors.