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Multi-point First Order Drift Compensation

IP.com Disclosure Number: IPCOM000109322D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 54K

Publishing Venue

IBM

Related People

Chappelow, RE: AUTHOR [+3]

Abstract

A method is described for first-order drift compensation of lithography measurement tools. Systematic drift of measurement tool repeatability as a function of time is an example of 0th-order drift that is often compensated by a simple offset adjustment. Such techniques based only on periodic re-measurement of known targets have proved inadequate for present technologies. First-order compensation adds curve fitting of measurement system parameters as a function of time to periodic site re-measurement in order to correct measured data. The concept is extendable to higher order error compensation.

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Multi-point First Order Drift Compensation

       A method is described for first-order drift compensation
of lithography measurement tools.  Systematic drift of measurement
tool repeatability as a function of time is an example of 0th-order
drift that is often compensated by a simple offset adjustment.  Such
techniques based only on periodic re-measurement of known targets
have proved inadequate for present technologies.  First-order
compensation adds curve fitting of measurement system parameters as a
function of time to periodic site re-measurement in order to correct
measured data.  The concept is extendable to higher order error
compensation.

      The proposed first-order compensation technique includes the
following procedures.
       1. Periodically measure a number of sites.  The theoretical
minimum number required is three, but five sites are used in
practice.
       2. First-order compensation cannot be performed in real time,
but can only be performed subsequent to collecting all data.
       3. Perform compensation on six system parameters.
       4. Perform analysis to identify the correct functional form
for the six compensation functions.

      The set of all five-point drift compensation data is analyzed
according to chosen basis functions such as polynomials in x and y.
Each set of five data points yields a corresponding set of values for
the six first-order parameters.  The new set of values are curve
fitted ac...