Abstract

The charge-coupled device (CCD) can be used to detect photons at wavelengths from the near UV infrared down to the x-ray region. In this paper we review the development of CCDs with respect to quantum efficiency and imaging characteristics for XUV and x-ray wavelengths. In the XUV region—15-50 nm—the CCD must be used in back-illuminated mode because the gate structures grown on the front side are completely opaque at these wavelengths. This requires that the imaging area of the backside be thinned to approximately the depth of the depletion region (about 10 µm), as the penetration technologies have been developed for thinning the device. Physical conditions in the backside surface oxide play an important role in the ability of the device to collect signal photoelectrons in the depletion region. For example, trapped positive charge creates a potential barrier that can inhibit collection of the signal photoelectrons. Ion implementation has been successfully used to modify back surface potentials, permitting useful detective quantum efficiencies throughout the XUV and soft-x-ray regions.

© 1990 Optical Society of America