Laser-induced damage to silicon CCD imaging devices

Abstract

Laser-induced morphological and electrical changes to silicon CCD imaging devices were studied. The devices were polysilicon gate time delay integrating CCD arrays of 2048x96 elements. The laser source for these experiments was a Q-switched Nd:YAG laser at 1.06 μm with 10-ns pulses at a 10-Hz repetition rate focused to an approximate 400-μm spot radius. Single pulse and multiple pulse damage behavior were studied. Both CCD arrays and diagnostic structures from the wafer periphery were tested. The additional diagnostic structures included polysilicon resistors and metallic oxide semiconductor field-effect transistor (MOSFET) gates. of the measurements made, leakage current between polysilicon clock lines, drain-to-substrate and drain-to-source leakage currents, and transconductance in MOSFETs were found to be the most sensitive parameters to laser-induced change. The onset of electrical parameter changes was observed at laser fluences as low as 0.2 J/cm². Severe electrical parameter changes began at 0.5 J/cm² and continued up to the onset of severe morphological damage at 1.0 J/cm². Above this fluence, both polysilicon and aluminum interconnect lines melted and broke.