Introduction

We have developed fully depleted, back-illuminated CCD imagers fabricated on high-resistivity, n-type silicon for scientific applications (see Fig. 1, [1]). Since first described by Holland et al. [2], the virtues of such a CCD have been well established. The typical thickness of 200-300 ^m results in good near-infrared Quantum Efficiency (QE) and greatly reduces fringing [3]. The Point Spread Function (PSF) is well defined and is determined by the transit time of photo-generated holes in an electric field that extends throughout the thickness of the device. Under full depletion conditions, the PSF is directly proportional to the thickness of the CCD and

inversely proportional to the square-root of the substrate bias used [1]. The PSF of a relatively thick, fully depleted CCD can be superior to that observed with a conventional thinned CCD if the latter has a significant field-free region at the backside of the device [4]. Since the CCD is p-channel, the radiation hardness due to bulk damage from protons in the space environment is improved significantly [5] when compared to conventional n-channel CCDs due to the lack of phosphorus-vacancy formation in the channels.

Figure 1. Schematic view of LBNL CCD showing the clock electrodes on the front surface and the bias voltage applied to the rear. These devices are operated fully depleted to achieve good PSF.

In this paper we describe efforts to fabricate fully depleted, back-illuminated CCDs on 150 mm diameter wafers. Three fabrication process flows that are under investigation to produce high performance CCDs are discussed. In addition, we report results to date on high-voltage compatible CCDs of particular interest to the proposed SuperNova/Acceleration Probe (SNAP) satellite [6].

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