Heterogeneous integration toward monolithic 3D chip

Monolithic 3D (M3D) integration has attracted lots of attentions to continue equivalent scaling by vertically stacking transistors [1]. It allows the reduction of the interconnect delay, resulting in reduction of the power consumption of the chip, which is the attractive driving force for M3D integration. Moreover, with M3D, many other components such as digital, analog, MEMS, sensors, etc. can be heterogeneously integrated together in a single chip to provide enhanced functionality (Fig. 1). In this context, M3D concept can have additional benefit by integrating two or more different materials [2]. Heterogeneous integration of different materials combined with M3D is more powerful, because each processes with different materials don't have to share same process step and sequence, allowing us more flexible process design and it naturally has many benefits from their advantageous physical properties.