First Demonstration of Heterogeneous IGZO/Si CFET Monolithic 3D Integration with Dual Workfunction Gate for Ultra Low-power SRAM and RF Applications

In this work, we demonstrate vertically stacked heterogeneous dual-workfunction gate complementary FET (CFET) inverters and 6T-SRAM with n-type IGZO and p-type polysilicon channels for the first time. The dual-workfunction gate structure with adjusted gate biasing allows the adjustment of channel potential to match the threshold voltage of transistors for CMOS and SRAM operation. High-frequency IGZO RF devices with p-type silicon isolation are fabricated simultaneously with the same process. Novel etching process based on fluorine-based gas with an extremely high-etching selectivity between the source/drain metal and the IGZO facilitates the definition of the source/drain region. IGZO surface treated with fluorine-based gas during over-etching step allows a low leakage current shallow passivation layer to optimize direct current characteristics.