Integration of Solar Cells on Top of CMOS Chips Part I: a-Si Solar Cells

We present the monolithic integration of deep-submicrometer complementary metal-oxide-semiconductor (CMOS) microchips with copper indium gallium (di)selenide (CIGS) solar cells. Solar cells are manufactured directly on unpackaged CMOS chips. The microchips maintain comparable electronic performance, and the solar cells on top show an efficiency of 8.4 ± 0.8% and a yield of 84%, both values being close to the glass reference. The main integration issues, i.e., adhesion, surface topography, metal ion contamination, process temperature, and mechanical stress, can be resolved while maintaining standard photovoltaic processing. A tight process window is found for the manufacturing of CIGS solar cells on the CMOS side of the microchip. More process margin exists for backside integration.