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CD stamper bumps, perspective view


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ASM discusses SPM Automation 1998

Don Chernoff is an invited speaker at the Magnetic and Optical Media Seminar in Los Angeles, Oct. 27-29, 1998. Click here to read the MOMS abstract.

Don Chernoff will present a poster at the American Vacuum Society national meeting in Baltimore, Nov. 2-6, 1998. Click here to read the AVS abstract.

MOMS Abstract

A Process for Automating High Precision Disc Inspection using the Atomic Force Microscope

Donald A. Chernoff and David L. Burkhead

DVD manufacturing requires much tighter control of physical feature dimensions and placement than CD manufacturing. Because the feature dimensions are truly nanometer scale (T3 pits are 400 nm long, 320 nm wide, 120 nm high, with a track pitch of 740 nm), it is necessary to use nanometer inspection tools. The Atomic Force Microscope (AFM) is such a tool. It enables one to see the physical features which ultimately determine the electrical performance of the disc-player system. Defects can be measured without mixing in the effects of player optics and electronics. Masters, stampers and replicas are inspected to pinpoint root causes of quality variations. In order to make AFMs even more valuable and easier to use, we have developed the software for a very accurate, automated process for analyzing AFM images. We measure track pitch, pit height, width, length and sidewall slopes. These measurements are carried out exhaustively, measuring every complete feature in each image. It is now easy to accumulate sufficient data to report not just the mean of each parameter, but also standard deviations and cross-correlations. Some of the interesting results include track pitch variation, length jitter and the dependence of pit width on pit length. These impact electrical characteristics such as cross-talk, data jitter, signal strength and asymmetry.

This talk will be presented on Thursday Oct. 29 in the session from 1000-1130 AM. Other talks in that session are:
"Near field technology for High Density Storage", R. Hajjar, TeraStor Corp.
"An Interferometer-based Optical Recording Medium for CD-R and DVD-R", J. Mahy, Akzo Nobel Central Research.

AVS abstract

Automated, High Precision Measurement of Critical Dimensions using the Atomic Force Microscope

Session:NS-ThP (Nov. 5, 1998, 530 - 7pm)

D.A. Chernoff and D.L. Burkhead

Abstract: Atomic Force Microscopes are used in many industries for research, engineering and process control. Until now, AFM operators have usually made dimensional measurements of sub-micron features by manually placing cursors on images or cross-section plots. Time constraints and operator fatigue limit the number of measurements. This in turn limits the extent of statistical analysis. We have developed a high accuracy measurement process which overcomes these limitations.

On DVDs (Digital Versatile Discs), the smallest features are about 400 nm long, 320 nm wide, 120 nm high, with a track pitch of 740 nm. We use a specific data capture protocol and automated image analysis to measure the following parameters: track pitch1,2,3, bump height, bump width (at various threshold levels), bump length, and four sidewall slope angles. In a single 10x10 micron image of a DVD stamper, containing about 100 bumps, we tabulate about 1000 values. It is useful to pool the data from several images. In a plot of bump width vs. bump length, we see that width at half height increases from 315 nm for the shortest bumps (420 nm long) to about 380 nm for bumps longer than 1100 nm; this matches the increase seen for corresponding optical signals produced when a finished disc is played. Where sidewall angle deviates from the norm, we are able to review the image data to identify the specific nature of the defect.
1D.A. Chernoff, "Nano-metrology for the data storage industry", abstract of paper presented at AVS National Meeting 10/97, p.113
2US Patents # 5,644,512 and 5,825,670
3see also


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