MECHANISMS FOR LASER-INDUCED FUNCTIONAL DAMAGE TO SILICON CHARGE-COUPLED IMAGING SENSORS

We measured the functional degradation of silicon CCD photodetector ar rays when subjected to Nd:YAG laser irradiation at 1.06 mum by 10-ns p ulses. Operational tests such as dark leakage, point-spread function, and modulation transfer function were developed for testing individual pixels and applied to the testing of locally laser-damaged CCD arrays . Testing revealed that the primary failure mechanism was the spreadin g of the point-spread function in the direction of clocked charge moti on that resulted from a decreased depth of potential wells within the laser-damaged spot. Lesser degradation was observed at pixels near the damaged spot that were served by clock lines that traversed the damag e spot. This damage behavior was correlated with decreased breakdown v oltage and increased leakage current between adjacent clock lines. Sub sequent morphological and TEM examination of similarly constructed chi ps indicated that laser heating of the polysilicon clock lines led to degradation of the adjacent isolation oxide between clock lines. Funct ional damage occurred at locations where two clock lines were very clo se to each other, and the thin oxide layer separating them was subject ed to high temperatures that resulted from melting of the neighboring polysilicon.