The number of researchers using imaging devices in their work continues to increase rapidly. Disciplines including astronomy, biology, chemistry, physics and manufacturers of imaging devices, optical components and complete optical systems are recognising the enormous potential. Further Developments in Scientific Optical Imaging brings together the latest information on commercial and academic research, development and applications in scientific optical imaging, from state-of-the-art devices to exciting explorations in space. Topics range from a new generation of CCDs, through spectroscopic applications of CTDs, to improved image processing and new applications for microscopy and spectroscopy. Experts from around the world provide overviews of important aspects of optical imaging, such as design considerations, device fabrication and integration, and data reduction. Comprehensive and international in coverage, this book will be welcomed by developers, manufacturers and users of this technology in universities, observatories and businesses around the world.
Further Developments in Scientific Optical Imaging
By M. Bonner DentonThe Royal Society of Chemistry
Copyright © 2000 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-784-0Contents
Advancements in Small-pixel, Video-rate, Backside-illuminated Charge-coupled Devices J R. Tower, 1,
New Developments in Three-dimensional Imaging with Optical Microscopes C.D. Mackay, 7,
Megacam: A Wide-field Imager for the MMT Observatory B.A. McLeod, M. Conroy, T.M. Gauron, J.C. Geary, and M.P. Ordway, 11,
Signal Processing for the S.A.O. Megacam J.C. Geary, 18,
Advances in Scientific-quality Detectors at JPL: Hybrid Imaging Technology M. Wadsworth, T. Elliott, and G. Atlas, 24,
Integrating Elemental and Molecular Imaging J R. Schoonover, G.J Havrilla, and P.J. Treado, 31,
CCDs for the Instrumentation of the Telescopio Nazionale Galileo R. Cosentino, G. Bonanno, P. Bruno, S. Scuderi, C. Bonoli, F. Bortoletto, M. D 'Alessandro, and D. Fantinel, 40,
Spectral Imaging with a Prism-based Spectrometer J.M. Lerner, 53,
Combining Linear and Neural Processing in Analytic Instruments — Or When to Switch On Your Neurons N.M. Allinson, B. Pokric, E.T. Bergström, and D.M. Goodall, 64,
ICIMACS: How We Go from 0.3 to 3 µ with 1 to 40 Amplifiers B. Atwood, J.A. Mason, D.P. Pappalardo, K. Duemmel, R. W Pogge, and B. Hartung, 80,
Electro-optical Characterizations of the CID 17PPRA, CID 38SG, CID 38Q-A, and CID 38Q-B Q.S. Hanley, J.B. True, and M.B. Denton, 83,
Development of a Back-illuminated 4096 x 4096 15-Micron Pixel Scientific CCD M. Lesser and R. Bredthauer, 111,
ROLIS: A Small Scientific Camera System for the Rosetta Lander H. Michaelis, T Behnke, M. Tschentscher, H.-G. Grothues, and S. Mottola, 118,
Detection of Isolated Manmade Objects Using Hyperspectral Imagery W.F. Kailey and M. Bennett, 132,
High Speed Scientific CCDs — II J Janesick, J Pinter, J McCarthy, and T. Dosluoglu, 142,
High-speed Array Detectors with Sub-electron Read Noise CD. Mackay, 160,
Practical Considerations for LN2-cooled, O-ring-sealed, Vacuum-insulated Dewars for Optical and IR Detectors B. Atwood and T P. 0 'Brien, 176,
Pharmaceutical Reaction Monitoring by Raman Spectroscopy J G. Shackman, J H. Giles, and M.B. Denton, 186,
Subject Index, 202,
CHAPTER 1
ADVANCEMENTS IN SMALL-PIXEL, VIDEO-RATE, BACKSIDE-ILLUMINATED CHARGE-COUPLED DEVICES
John R. Tower
Samoff Corporation CN 5300 Princeton, NJ 08540-5300
1 ABSTRACT
Sarnoff Corporation has developed a CMOS-CCD process technology that has enabled the development of a new generation of backside-illuminated charge-coupled devices (CCDs). The new devices achieve high quantum efficiency (QE), combined with high modulation transfer function (MTF) performance, at pixel sizes down to 6.6 microns. This new generation of CCDs also provides excellent noise performance at video readout rates. To permit the realization of large-format devices, photocomposition (stitching) has also been demonstrated within this new process technology.
2 INTRODUCTION
Sarnoff, formerly RCA Laboratories, began work on CCD development in 1971. The backside-illuminated CCD work at RCA dates back to 1978. The backside-illuminated process that has now been employed for over twenty years utilizes whole wafer thinning with backside lamination to a glass support substrate. The back surface is implanted and then furnace annealed to provide stable, high quantum efficiency from < 400nm to > 1,000 nm.
Over the past few years, Samoff has been moving toward a more unified processing approach across our imaging products. Recently, we have integrated aspects of our double polysilicon spectroscopic CMOS-CCD process with our backside-illuminated, triple polysilicon CCD process. We have also moved the majority of our products to Canon 5X lithography to achieve tighter design rules. This paper will summarize the present state-of-the-art at Sarnoff.
3 PROCESS TECHNOLOGY
The new generation of backside-illuminated devices is processed in a triple polysilicon, single-level metal process technology with aluminum metallization. The process technology supports full CMOS circuitry in a twin well configuration. Standard oxide thicknesses are employed for pixel sizes > 12 microns, and scaled, thin oxides are employed for pixel sizes < 12 microns. The CMOS/CCD process supports CMOS-quality electrostatic discharge (ESD) pad protection.
A number of process options have been incorporated into the process flow. Pixel or horizontal register buried blooming drain structures can be implemented to achieve anti-blooming. Buried contacts can be realized to reduce the floating diffusion capacitance. This floating diffusion stray capacitance reduction increases the output sensitivity and reduces the amplifier equivalent noise.
To achieve high-speed clocking of vertical register gates, metal-to-poly strapping contacts have been demonstrated for pixel sizes down to 8 microns. These small geometry contacts are the enabling technique for achieving 1 MHz vertical clock rates on CCDs with > 50-mm-long gates at an 8-micron pixel pitch.
To produce very long linear array devices, Sarnoff has developed photocomposition (stitching) capability on the Canon 5X stepper. Employing stitching, Sarnoff has demonstrated > 60-mm-long devices. Figure 1 shows a long linear array produced with stitching. Figure 2 shows the excellent registration and feature size fidelity achieved with stitching. The figure indicates the stitch boundary location. The poly 2 gates at the top of the figure are 4 microns in width. The stitch boundary is difficult to detect, with typical panel-to-panel misalignments of 0.1 micron.
4 IMPROVEMENTS IN QUANTUM EFFICIENCY
The major advantage of backside illumination is the high quantum efficiency that can be achieved, particularly at wavelengths below 550 nm. With 100% optical fill factor and no gates to absorb short wavelength photons, backside-illuminated devices can approach ideal silicon quantum efficiency. Figure 3 indicates measured QE for the best non-AR coated devices peaking at 80%. With the AR coatings now being developed, the peak QE should be > 90%. Furthermore, as indicated in Figure 3, the AR coatings can be tailored to peak the QE in the band of interest.
5 IMPROVEMENTS IN DYNAMIC RANGE
As the pixel size is reduced, the dynamic range is compressed due to reduction in full well capacity. To maximize the dynamic range for small pixel devices we have 1) increased the area charge capacity (e/µm2) of the pixel, and 2) decreased the amplifier noise floor. The measured improvement in full well will be discussed first. Two small pixel designs have been fabricated with standard buried channel implants and enhanced, high capacity implants. The measured full-well results are indicated in Table 1. The criteria for full well is the maximum charge that can be transferred without extended-edge-response charge-transfer efficiency (CTE) degradation. The Nova 8-micron pixel results indicate that > 1.5 X improvement in full well can be achieved moving from the standard implant to the high capacity implants. The charge density is > 9,000 e/µm2 for the improved Nova device. The Mark V 6.6-micron pixel design does not exhibit charge densities as high as the Nova design. By layout changes, the design can be optimized further to provide higher charge capacity. However, as is, this charge capacity is excellent for such a small pixel device.
To achieve a full...
