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Proceedings Paper

Low dark current, back-illuminated charge coupled devices
Author(s): R. C. Westhoff; B. E. Burke; H. R. Clark; A. H. Loomis; D. J. Young; J. A. Gregory; R. K. Reich
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Paper Abstract

Dark current for back-illuminated (BI) charge-coupled-device (CCD) imagers at Lincoln Laboratory has historically been higher than for front-illuminated (FI) detectors. This is presumably due to high concentrations of unpassivated dangling bonds at or near the thinned back surface caused by wafer thinning, inadequate passivation and low quality native oxide growth. The high dark current has meant that the CCDs must be substantially cooled to be comparable to FI devices. The dark current comprises three components: frontside surface-state, bulk, and back surface. We have developed a backside passivation process that significantly reduces the dark current of BI CCDs. The BI imagers are passivated using molecular beam epitaxy (MBE) to grow a thin heavily boron-doped layer, followed by an annealing step in hydrogen. The frontside surface state component can be suppressed using surface inversion, where clock dithering reduces the frontside dark current below the bulk. This work uses surface inversion, clock dithering and comparison between FI and BI imagers as tools to determine the dark current from each of the components. MBE passivated devices, when used with clock dithering, have dark current reduced by a factor of one hundred relative to ion-implant/laser annealed devices, with measured values as low as 10-14 pA/cm2 at 20°C.

Paper Details

Date Published: 27 January 2009
PDF: 11 pages
Proc. SPIE 7249, Sensors, Cameras, and Systems for Industrial/Scientific Applications X, 72490J (27 January 2009); doi: 10.1117/12.817051
Show Author Affiliations
R. C. Westhoff, MIT Lincoln Lab. (United States)
B. E. Burke, MIT Lincoln Lab. (United States)
H. R. Clark, MIT Lincoln Lab. (United States)
A. H. Loomis, MIT Lincoln Lab. (United States)
D. J. Young, MIT Lincoln Lab. (United States)
J. A. Gregory, MIT Lincoln Lab. (United States)
R. K. Reich, MIT Lincoln Lab. (United States)

Published in SPIE Proceedings Vol. 7249:
Sensors, Cameras, and Systems for Industrial/Scientific Applications X
Erik Bodegom; Valérie Nguyen, Editor(s)

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