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Browse Prior Art Database

Photolithographic Process Control by Optical Phase Monitoring of Latent Images in Photoresist

IP.com Disclosure Number: IPCOM000107556D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 134K

Publishing Venue

IBM

Related People

Bayer, T: AUTHOR [+2]

Abstract

This article describes a method of interferometrically determining the exposure dose of photoresist on silicon wafers and a measurement apparatus for in situ exposure endpoint monitoring in lithographic exposure tools. Another potential application is measuring the critical dimensions of latent image patterns exposed on the wafer prior to resist development.

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This is the abbreviated version, containing approximately 52% of the total text.

Photolithographic Process Control by Optical Phase Monitoring of Latent Images in Photoresist

       This article describes a method of interferometrically
determining the exposure dose of photoresist on silicon wafers and a
measurement apparatus for in situ exposure endpoint monitoring in
lithographic exposure tools.  Another potential application is
measuring the critical dimensions of latent image patterns exposed on
the wafer prior to resist development.

      Known approaches aiming at the development of such a monitoring
system are based on a method determining the unexposed photoactive
component (PAC) concentration in photoresist by absorptivity
measurements.  A serious limitation of that method is that such
measurements in the actinic range of the spectrum are impossible
without additionally exposing the resist.  Another drawback of the
prior art method which requires special monitor wafers, since the
illuminating light spot has a diameter of several millimeters, is
that it is unsuitable for heavily structured wafers.

      The exposure monitoring technique described in this article is
based on sensing optical phase variations between two coherent laser
beams reflected on a resist-coated wafer. One beam is focused on an
exposed and the other on an unexposed resist area.  Changes of the
optical resist parameters occurring during exposure lead to a
continuous increase in the optical phase difference.  Hence, the
total energy absorbed by the resist can be determined by measuring
the phase difference occurring between the two beams.  A monitoring
system utilizing this principle could be employed for in situ
monitoring the exposure dose in a lithographic tool.  As the laser
spots sensing the wafer can be focused to about 1 mm diameter, a high
lateral resolution is obtained.  Such an exposure endpoint monitoring
system is suitable for densely structured production wafers.
Moreover, a sensor working on this principle could be integrated as
an edge detector in a linewidth measurement instrument for measuring
pattern dimensions of latent images on wafers.  This involves
scanning the latent image by two laser sensing spots spaced by d
(Fig. 1).  A linewidth measuring tool using this principle offers the
advantage of controlling critical dimensions on exposed wafers prior
to resist development.  Measuring such critical dimensions of latent
images in resist allows checking the quality of the exposure tool
prior to resist development, i.e., at an earlier stage of the
lithographic process.

      Fig. 2 illustr...