X-RAY-ABSORPTION NEAR-EDGE STRUCTURE IN THE QUANTUM EFFICIENCY OF X-RAY CHARGE-COUPLED-DEVICES

We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate structure, namely, phosphorus doped polysili con, silicon dioxide, and silicon nitride. The x-ray transmission of t hese films shows large oscillations with small changes in energy in th e vicinity of the following absorption edges: nitrogen K (400 eV), oxy gen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a CCD in the soft x-ray range deviates s ignificantly from simple model predictions based on Henke et at. (1993 ) mass absorption coefficients. The measurements covered the range of energies from 60 to 3000 eV, using synchrotron beamlines at the Advanc ed Light Source (ALS; Berkeley), Physikalisch-Technische Bundesanstalt BESSY (Berlin), the Synchrotron Radiation Center (SRC; University of Wisconsin-Madison). Our model of the CCD response includes near edge x -ray absorption structure and predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector at the BESSY synchrotron confirmed our model predictions for both frontside and backside illuminated CCDs . (C) 1998 Society of Photo-Optical instrumentation Engineers. [S0091- 3286(98)01910-2].