Low-temperature wafer-level transfer bonding

In this paper, we present a new wafer-level transfer bonding technology. Th e technology can be used to transfer devices or films from one substrate wa fer (sacrificial device wafer) to another substrate wafer (target wafer). T he transfer bonding technology includes only low-temperature processes; thu s, it is compatible with integrated circuits. The process flow consists of low-temperature adhesive bonding followed by sacrificially thinning of the device wafer. The transferred devices/films can be electrically interconnec ted to the target wafer (e.g., a CMOS wafer) if required. We present three example devices for which we have used the transfer bonding technology. The examples include two polycrystalline silicon structures and a test device for temperature coefficient of resistance measurements of thin-film materia ls. One of the main advantages of the new transfer bonding technology is th at transducers and integrated circuits can be independently processed and o ptimized on different wafers before integrating the transducers on the inte grated circuit wafer. Thus, the transducers can be made of, e.g., monocryst alline silicon or other high-temperature annealed, high-performance materia ls. Wafer-level transfer bonding can be a competitive alternative to flip-c hip bonding, especially for thin-film devices with small feature sizes and when small electrical interconnections (< 3 x 3 mum(2)) between the devices and the target wafer are required.