Abstract

A focus tracking system for direct wafer steppers has been tested and its operation simulated on computer to account for transducer fabrication limitations. The focus condition of the projection lens was determined by sensing the contrast level in the backprojected image of a test grating object mounted in a plane conjugate to the reticle plane. To permit continuous focus tracking, the test grating was illuminated with red light from a solid-state light emitting diode to prevent exposure of UV-sensitive photoresists. The contrast sensor consisted of a pair of large area silicon photodiodes with grating windows arranged so that the diodes viewed complementary space and bar projected fields of the test grating. The projection lens used in these tests was a 40× microscope objective having a numerical aperture of 0.95. The focus sensing range was found to be better than 1.6 μm, and the focus sensitivity was <0.1 μm.

© 1986 Optical Society of America

Full Article  |  PDF Article
OSA Recommended Articles
Design of gradient-index lens systems for disc format cameras

J. Brian Caldwell and Duncan T. Moore
Appl. Opt. 25(19) 3351-3355 (1986)

Operations using fringe projection

Marcelo Michalski, Hector J. Rabal, and Mario J. Garavaglia
Appl. Opt. 25(23) 4338-4342 (1986)

References

You do not have subscription access to this journal. Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Cited By

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Figures (12)

You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Tables (1)

You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Equations (45)

You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Metrics

You do not have subscription access to this journal. Article level metrics are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription