Indium bump array fabrication on small CMOS circuit for flip-chip bonding

We demonstrate a novel method for indium bump fabrication on a small CMOS circuit chip that is to be flip-chip bonded with a GaAs/AlGaAs multiple quantum well spatial light modulator.A chip holder with a via hole is used to coat the photoresist for indium bump lift-off.The 1000 μm-wide photoresist edge bead around the circuit chip can be reduced to less than 500μm,which ensures the integrity of the indium bump array.64 × 64 indium arrays with 20 μm-high,30 μm-diameter bumps are successfully formed on a 5 × 6.5 mm2 CMOS chip.