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New Calibration Disk for Laser-based Optical Inspection Tool

IP.com Disclosure Number: IPCOM000010642D
Original Publication Date: 2002-Dec-31
Included in the Prior Art Database: 2002-Dec-31
Document File: 3 page(s) / 160K

Publishing Venue

IBM

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New Calibration Disk for Laser-based Optical Inspection Tool

Magnetic hard disks used for data storage require precision surfaces with ideally no defect or extremely low defect rate. Therefore, processed disks undergo various tests and inspections to ensure required surface conditions and cleanliness. Laser-based optical inspection tools have been widely used for surface characteristics measurement and surface inspection of disk planar surfaces in disk drive industry. Scatterometry is a common optical technique used in most laser-based inspection tool, in measuring both patterned surfaces, and isolated defects. Scatterometry-based inspection instruments are mostly tested and calibrated using a known surface pattern, or groups of spherical particles of known diameters.

Inspection tool is a scatter-type instrument that measures the change in the intensity of the low angle probe laser beam reflected off the surface under inspection to detect surface defects. A change in the intensity of reflected probe beam could be the result of "light scattering" by contaminant particles, surface imperfections, surface structural defects, or by reflectivity changes introduced by surface stain and other surface conditions. In order to use the tool in manufacturing, it needs to be calibrated using a disk surface with known surface structure, at a known position. The predefined microstructure on a calibration disk would introduce light scattering each time the probe beam hits a segment of the structure on the disk, resulting in a specific number of "pixels" interpreted as "defects". Examples of such microstructure is CO2-laser-produced continuous circular ridge on glass substrates, or continuous circular groove (with volcano-shape cross-section) on AlMg substrate produced by overlapping volcano-shape bumps.

This publication briefly describes a method for producing "calibration disk" for the optical tool using the process of laser bump formation on asputtered magnetic glass disk. In this method, a known pattern structure ofmicro-size bumps or "defects" is produced on a sputtered magnetic glass disk, using Vanadate-laser based texturing tool. The laser-produced bumps or defect pattern can be used for calibration of the tools, i.e., to adjust the tool to yield calibrated results.

In this method, the micro-size defect structure consists of few closely-spaced spirals of bumps with known height, diameter, and shape. Laser-produced bumps, or defects, can be placed tightly ad...