Yield Enhancing AR Treatment Process For Large Format Space FPAs

Imaging sensors, or focal plane arrays (FPAs), designed to detect the light signature of ballistic missiles, are a critical component of the Missile Defense Agency’s (MDA) space sensor program known as the Space Tracking and Surveillance System (STSS). The need to detect a missile at the greatest distance from its intended target, drives the advancement of sensor technology toward the increased resolution afforded by large pixel count FPAs. As an example, the Air Force Research Laboratory’s (AFRL) recent HIGH STARE program will develop a 4 mega-pixel infrared FPA, a pixel count that is 16 times greater than the original infrared FPA planned for STSS. A major challenge for HIGH STARE sensor manufacturers BAE Systems and Teledyne, will be to increase the fabrication yield of large format FPAs. One concern that has been identified involves the warping of the FPA substrate during processing that can lead to failures at the assembly, or hybridization stage. This problem is particularly aggravated by stresses introduced when depositing the conventional multi-layer thin-film coatings needed for effective infrared anti-reflection (AR). Eliminating or preventing wafer stress introduced by thin-film AR coatings may become impossible when fabricating large format FPAs such as the 7x7cm HIGH STARE format. A solution to the yield limiting stress issue is proposed where thin-film AR coatings are replaced by a high-performance, radiation-resistant, stress-free AR treatment based on surface relief microstructures fabricated directly in the FPA substrate. TelAztec has been developing high performance AR microstructure technology in an ongoing MDA sponsored SBIR project that has progressed into the Phase II Transition stage. With the active participation and support of Raytheon, Teledyne, and BAE Systems, TelAztec proposes to apply its AR microstructure treatment to large format, 7x7cm CdZnTe substrates. The transmission and surface figure of the wafers will be recorded before and after application of the AR treatment to determine the amount of added stress. A wafer treated with thin-film AR coatings deposited by BAE Systems, will be tested to provide a direct comparison. Each test wafer will then be bump-bonded to a mechanical silicon ROICs to qualify the expected reduction in hybridization failures. Plans will be made to refine the AR microstructure fabrication process and to apply the process to large format functional devices during a Phase II project and into Phase III.