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OPTICAL LENS TESTING USING OPTICAL TRANSFER FUNCTION DATA AND IMAGE SIMULATION

IP.com Disclosure Number: IPCOM000006456D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2002-Jan-04
Document File: 2 page(s) / 118K

Publishing Venue

Motorola

Related People

Whitson G. Waldo: AUTHOR

Abstract

Lithography is one of the gating technologies restricting the evolution to larger integrated circuits with more densely packed finer features. The image transfer from a mask or reticle onto the wafer has components of image quality (i.e., the shape and size of the imaged features) and image placement (i.e., the overlay of the previous layers with the current one). The printing equip- ment includes steppers, scanners, and step-and-scan machines. Manufacturing engineering attempts to exer- cise control of the printers within design tolerances so it is critical to evaluate new equipment performance comprehensively to confmn that it can enter manufac- turing withii specfication and without contributing imag- ing defects.

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MOTOROLA INC. Technical Developments Volume 15 May 1992

OPTICAL LENS TESTING USING OPTICAL TRANSFER FUNCTION DATA AND IMAGE SIMULATION

by Whitson G. Waldo

  Lithography is one of the gating technologies restricting the evolution to larger integrated circuits with more densely packed finer features. The image transfer from a mask or reticle onto the wafer has components of image quality (i.e., the shape and size of the imaged features) and image placement (i.e., the overlay of the previous layers with the current one). The printing equip- ment includes steppers, scanners, and step-and-scan machines. Manufacturing engineering attempts to exer- cise control of the printers within design tolerances so it is critical to evaluate new equipment performance comprehensively to confmn that it can enter manufac- turing withii specfication and without contributing imag- ing defects.

  The current technology for testing printers calls for experimental testing of image quality and placement. Image quality for certain aberrations such as defocus and astigmatism can be characterized easily with empirical methods. However, for aberrations such as coma, spher- ical and chromatic aberration are much more diicult to test empirically. Image placement testing can be done experimentally quite well, for most aberrations except coma. Image placement errors include intrafield and intertield errors. Intratield errors are those which are systematic from field to field, including lens positional aberrations such as 3rd and 5th order distortion. Intetield errors include alignment and wafer grid errors caused from stage systematic and random errors. The analysis of multiple image field placement deviation values using a least squares fit to a geometrical model allows charac- terization of the individual errors. One such model is
dx = TX - Ry + Mx + Kxx2 + Kyxy + xrzD3 +xr'D5 (1) dy = Ty + Rx + My +Kyy2 + Kxxy +yr2D3 + itiD (2)

where ti = x2 + y*. In the model, dx and dy are the component image displacement values at various field positions, T is translation, R is rotation, M is magnitica- tion, K is keystone, D, is 3rd order distortion, and D, is 5th order distortion. For interfield modeling, the key-

stone and distortion terms are dropped. For i&afield errors, residuals to the model are interpreted as either gauge capability errors or random point errors (perhaps with contriiutions from coma). For intertield errors, resid- uals are ascribed to stage imprecision or alignment sig- nal processing errors. While it is relatively easy to quantify displacement errors every lmm in a field, it is much more difficult to certify image quality with this level of thoroughness since experimental methods generally rely on SEM analysis of linewidths and resist profiles. How- ever, as difficult as a lmm grid is, this might be too coarse a scale for complete testing of image quality for advanced lithographic applications.

  A...