Automating wafer-level test of uncooled infrared detectors using wafer-prober

Fraunhofer IMS develops and fabricates far-infrared focal plane arrays (IRFPA) using microbolometers with a pixel pitch of 17μm technology realized on top of a 0.35 μm CMOS readout integrated circuit (ROIC). The microbolometers are encapsulated by a Chip-Scale-Package (CSP) to ensure a high quality vacuum level. The CSP is realized by placing an infrared transparent lid above a solder frame surrounding the microbolometer array. To concept a wafer-level test it is very challenging to implement highly accurate electrical stimuli and a far infrared radiation source (black body) while affecting the wafer-prober handling by a non-flat wafer surface, due to the infrared transparent lids of the CSP. Accordingly, wafer-level test has been developed based on a PC which controls, by using a test program, the wafer handling of a prober, the electrical stimuli of a test hardware, and the far-infrared radiation such as the optical stimuli. Thus, the most important electro-optical parameters of IRFPAs will be measured at wafer-level: Noise Equivalent Temperature Difference (NETD), responsivity, and the percentage of the defective pixels.