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Optical Disk Alignment Technique

IP.com Disclosure Number: IPCOM000036274D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 51K

Publishing Venue

IBM

Related People

Major, JC: AUTHOR [+2]

Abstract

This article describes a concept in applying a currently used method to orient and course align silicon wafers to an optical disk application. To exploit an exposure method developed for patterning optical disks on a Perkin-Elmer 500/600 exposure tool, it is necessary to align the pattern concentric to the ID bore of the disk. A conceptual method is described as modified from the standard silicon wafer application. Disadvantages of the current method as well as the advantages of the new method are discussed.

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Optical Disk Alignment Technique

This article describes a concept in applying a currently used method to orient and course align silicon wafers to an optical disk application. To exploit an exposure method developed for patterning optical disks on a Perkin-Elmer 500/600 exposure tool, it is necessary to align the pattern concentric to the ID bore of the disk. A conceptual method is described as modified from the standard silicon wafer application. Disadvantages of the current method as well as the advantages of the new method are discussed.

An optical disk has a pattern consisting of a series of concen

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tric grooves that define tracks upon which data is read or written on. These grooves provide a read-back signal, called a tracking error signal (TES). This signal is processed by the electronics in an optical disk drive system that allows the laser head to follow a given track. These grooves are imprinted in photoresist that has been spun on to the disk substrates by projection exposure. The photoresist is developed and etched on the glass disk substrate. Once the subsequent thin-film layers are deposited on the grooved disk, data can be stored on the tracks as defined by the grooves. For the laser head to track, the TES is used to make corrections in the servo so that the laser head will react to following a given track. Due to laser head mass and reaction time, a maximum error between the disk ID bore and the groove pattern must not be exceeded. Many tolerances add up to account for the total error allowed in an assembled disk. A component of this total error is a tolerance that must be maintained at the grooving level that will not exceed approximately 40% of the total error. This article defines a method by which an alignment can be made in a noncontact fashion that meets a tolerance, at the grooving level, consistent to meeting the maximum allowable error.

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At the grooving level it has been determined that a total tolerance of 20 micrometers from disk ID bore center to groove pattern center must be maintained. This tolerance is defined during the projection photolithography process when the disk is imprinted with the pattern prior to etching. As a result, an alignment must occur between the nominal position of the projected image and the glass disk. The mask which contains an image of the groove pattern is aligned to a standard, called a tooling disk. This tooling disk was created with very little error of no more than 2 micrometers of error as defined above. The alignment is done optically using the Perkin-Elmer 500/600 (P-E) alignment system. This alignment can be done with an accuracy of 0.5 micrometer or better. Once the tooling disk is aligned, all subsequent disks must be placed with a total tolerance not to exceed 17.5 micrometers, so that the total is no more than 20 micrometers. Disks with nonuniform ID bores exceeding a tolerance of +/- 10 micrometers in diameter and a total out of round...