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Method for Measuring Semiconductor Lithographic Tool Focus and Exposure

IP.com Disclosure Number: IPCOM000039580D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Chappelow, RE: AUTHOR [+3]

Abstract

An automated technique for selecting the optimum focus and exposure settings for a semiconductor photolithographic exposure system and for evaluating the performance of the associated focus and exposure control subsystem of the semiconductor photolithographic exposure system is presented. The reported technique is faster and more accurate than visual techniques which rely on operator judgement and faster and less costly than techniques that employ scanning electron microscopes. The technique is based on a quantitative evaluation of the characteristics of developed photoresist images and their edge slopes on a semiconductor wafer in exposed photoresist material.

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Method for Measuring Semiconductor Lithographic Tool Focus and Exposure

An automated technique for selecting the optimum focus and exposure settings for a semiconductor photolithographic exposure system and for evaluating the performance of the associated focus and exposure control subsystem of the semiconductor photolithographic exposure system is presented. The reported technique is faster and more accurate than visual techniques which rely on operator judgement and faster and less costly than techniques that employ scanning electron microscopes. The technique is based on a quantitative evaluation of the characteristics of developed photoresist images and their edge slopes on a semiconductor wafer in exposed photoresist material. The images and their edge characteristics are quantified through the use of a special pattern of phase grid compatible images, a phase grid measurement system and analysis method. The procedure for utilizing this technique on photographic exposure systems begins by exposing a two-dimensional array of special patterns of phase grid compatible images, as shown in Fig. 1. The pattern consists of rows and columns of lines which have a width equal to half of a specified pitch. The array is arranged such that focus varies from pattern to pattern along one axis, and the exposure varies from pattern to pattern along the other axis. The phase grid measurement system, which operates on a reflected light principle, is used to evaluate the array of special patterns. The amount of light reflected from the photoresist image patterns depends on the size and edge slope of the image patterns as well as on the reflectivity of the photoresist on the wafer. The photoresist image size and edge slope is dependent on both focus and exposure parameters. Fig. 2 shows the effects of focus and exposure on the photoresist image. Fig. 2a shows a cross-section of a developed photoresist image which is correctly exposed and in focus. In this figure, the width of the photoresist image is equal to half the pitch of the images, the edge slope is approximately vertical and the image top surface meets the edges at a right angle. Fig. 2b shows a developed positive photoresist image which is overexposed, but in focus. In this figure, the width of the p...