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Simplified Phase Mask Design for Optical Servo

IP.com Disclosure Number: IPCOM000119455D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 1 page(s) / 43K

Publishing Venue

IBM

Related People

Brock, PJ: AUTHOR [+3]

Abstract

Several current optical disk configurations require a ca. 1.5 micron pitch radial groove pattern in the surface which supports the information carrying layers. A phase shifting mask can be constructed by etching in a quartz mask substrate concentric rings of the same width as the alternate land features. Phase shifting masks of this design require careful dimensional control in 3 dimensions. If the dimensions are not carefully controlled, the desired photoresist pattern is not obtained. For example, if the dimension of the mask groove is too large or if the bottom of the groove is rough, an alternating pattern of groove dimensions is obtained in the photoresist. Grooves etched from such a pattern would not be optimal for use as the servo pattern for an optical disk. (Image Omitted)

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Simplified Phase Mask Design for Optical Servo

      Several current optical disk configurations require a ca. 1.5
micron pitch radial groove pattern in the surface which supports the
information carrying layers.  A phase shifting mask can be
constructed by etching in a quartz mask substrate concentric rings of
the same width as the alternate land features.  Phase shifting masks
of this design require careful dimensional control in 3 dimensions.
If the dimensions are not carefully controlled, the desired
photoresist pattern is not obtained.  For example, if the dimension
of the mask groove is too large or if the bottom of the groove is
rough, an alternating pattern of groove dimensions is obtained in the
photoresist.  Grooves etched from such a pattern would not be optimal
for use as the servo pattern for an optical disk.

                            (Image Omitted)

      An improved modification to the phase mask design is to alter
the relative dimensions of the groove and land.  If the land is made
very small in relation to the groove, then the groove prints as
though it were a clear feature in a transmission mask.  Conversely,
the land prints as though it were a chrome ("dark") feature.  The
contrast obtained in the image is much larger than can be obtained
from a conventional transmission mask of similar dimensions.  A
transmission mask of 1.6 mm pitch with regions of varying
clear/chrome dimensions of 0.7mm / 0.9mm to 1.0mm /...