DELTA-DOPED CCDS FOR ENHANCED UV PERFORMANCE Shouleh Nikzad, M.E. Hoenk, P.J. Grunthaner, R.W. T’erhune, and F.J. Grunthaner Center for Space Microelectronics Technology Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 R. Winzenread, M. Fattahi, H-F. Tseng EG&G Reticon, Surtnyvale, CA 94086. Abstract Thin, backside-illuminated CCDS are modified by growing a delta-doped silicon layer on the back surface using molecular beam epitaxy. Delta-doped CCDS exhibit stable and uniform 100% internal quantum efficiency. The process consists of growth of an epitaxial silicon layer on a fully-processed commercial CCD die in which 30% of a monolayer of boron atoms are incorporated into the lattice nominaI1y in a single atomic layer. Long term stability was tested and showed no degradation of the device quantum efficiency over sixteen months. Reduction of the reflectivity of the Si surface by deposition of Hf@ on the CCD back surface further increased the QE, with measured QE over 80% in some regions of the spectrum. We will discuss these results as well as the delta-doped CCD concept and process. Lhviolet detection with silico~m The highest UV quantum efficiency (QE) in silicon CCDS is obtained by backside-illumination of thinned devices. However, positive charge in the Si/SiOL interface creates a potential well which traps photoelectrons at the CCD back surface. The detection of ultraviolet light in Si CCDS has been a long- standing challenge, due to the short absorption length of UV photons in silicon and the existence of this potential well. To put this probIem in perspective, the absorption depth of UV photons in silicon drops to a minimum of 40 ~ at about 270 nm, and is less than 100 ~ over the range of wavelengths from 90 nm to 360 nm. In comparison, the backside potential well typically extends -0.5 vrn into the silicon lattice, preventing detection of photoelectrons produced within that region. Improvement of the UV quantum efficiency is accomplished by placing a high concentration of negative charge near the positively-charged oxide to reduce or eliminate this potential well. The negative charge must be placed as close as possible to the back surface in order to obtain the maximum possible quantum efficiency. The first solutions to this problem involved treating the back surface of the CCD by surface charging (i.e., UV-flood, biased flash-gate), resulting in reasonable or high UV quantum efficiency.l’Q However, these treatments suffer variously from problems of yield, response stability, hysteresis, and long-term reliability. Stability of the quantum efficiency has great impact on astronomical measurements, particularly in space-based applications where renewal of the back surface treatment (e.g., by exposing the device to intense UV light) is not an attractive option. Elimination of the potential well by the introduction of a thin layer of p+ doped silicon results in stable, high quantum efficiency, provided that the dopant concentration is sufficiently high and the p + layer is sufficiently thin. The first attempts at this soiution used ion implantation of the CCD back surface.3 However, the quantum efficiency obtained by ion implantation does not approach the theoretical limit. While the MBE-modification of thin CCDS is conceptually similar to ion itnplantation, there are fundamental differences in the techniques of incorporation of negative charge in the lattice, post charge- incorporation processes, and resulting performance of these processes. Because ion implantation damages the lattice and leaves many of the dopant atoms in inactive sites in the lattice, post-implantation