Browse Prior Art Database

Vertical Position Sensing with Rotating Pinhole Confocal Optics

IP.com Disclosure Number: IPCOM000105987D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Abraham, DW: AUTHOR [+2]

Abstract

Disclosed is a method for determining the height of a surface without moving the sample or inspection optics, whereby a moving pinhole array is used to measure the amount of light passing through the slits at a sequence of axial distances from the focusing lens, and thereby infer the height of the sample.

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Vertical Position Sensing with Rotating Pinhole Confocal Optics

      Disclosed is a method for determining the height of a surface
without moving the sample or inspection optics,  whereby a moving
pinhole array is used to measure the amount of light passing through
the slits at a sequence of axial distances from the focusing lens,
and thereby infer the height of the sample.

      There are many instances in which the height of a sample under
an objective lens is of interest, but for various reasons movement of
either the lens or sample is either impossible or undesirable.  A
variety of height measurement schemes exist for these applications,
each with unique advantages and problems.  As a monitor of some
process, such as laser ablation, the height measurement must be
non-invasive.  This requirement makes many conventional autofocus
schemes impractical.  Likewise, methods requiring illumination of
patterns on the sample, or tilt dependence to determine depth, are
often ruled out because of the small lateral size of the ablation.
Chromatically aberrated objectives have also been employed to provide
an axial spread in focus, although this may often be ruled out, since
it sets requirements on the objective lens that may not be possible
to meet for other reasons.  Another requirement often encountered is
that the measurement of surface height be made quickly.  For example,
in the laser delete process the data must be acquired between pulses
of the excimer laser,...