Influence of material morphology on fabrication of large format IRFPA

Abstract

Material characteristics of InSb wafer and Si wafer are fundamental factors to fabricating qualified infrared focal plane array (IRFPA). Parallelism and flatness of wafer are critical to yield and reliability of large format IRFPA. Influence of materials’ parallelism and flatness on indium bump growing, flip-chip bonding and back thinning in the fabrication of large format IRFPA is analyzed. Parallelism of material brings additional nonuniformity to IRFPA. Parallelism after back thinning is only determined by the parallelism of readout integrated circuit (ROIC) and isn’t affected by that of detector. Influence of material flatness is non-contacting or bad-contacting during flip-chip bonding, which results in bad pixels of IRFPA. According to actual fabrication condition of IRFPA, flatness of one single detector and ROIC chip should be better than 1 µm. Parallelism of ROIC chip should be better than 2 μm. Optical flat is the most convenient approach for InSb material morphology test. Utilizing higher indium bump and press in flip-chip bonding, designing larger contact metal under indium bumps or fabricating indium bumps with smaller diameter in center, selecting distribution of chips on wafer are put forward to reduce influence of morphology. Yield of large format IRFPA is improved.