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An improved pattarn formation method for misalignment measurement in stepping exposure process

IP.com Disclosure Number: IPCOM000013670D
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-18

Publishing Venue

IBM

Abstract

Disclosed is an improved pattern formation method for overlay measurements to accurately measure stitching overlay misalignment for photolithographic exposures on the same layer. In conventional misalignment measurements, first a larger square shape is formed on the initial layer, and a smaller square shape is formed on a subsequent layer as shown in Fig. 1. The difference in position of the subsequent pattern from the center of the first pattern indicates the overlay misalignment. The amount of vertical misalignment of the subsequent pattern to the first pattern is given by (Y1-Y2)/2, in Fig. 1. The amount of horizontal misalignment can be found in a similar manner. The conventional method does not work though for misalignment measurements between exposures on the same level because only the smaller square shape remains after both shapes are exposed and developed. Our previous disclosed pattern in the disclosure JA8-97-0616, which can be used to measure the misalignment between exposures on the same level, is shown in Fig. 2. The pattern shown in Fig. 2 is formed by exposing the two patterns, labeled "A" and "B" shown in Fig. 3 where pattern "A" is exposed prior to "B". The method of calculating the misalignment from exposure "A" to "B" is shown in Fig. 2. To understand the disclosed misalignment method, in Fig. 3 note that the inner square is defined by exposure "A" and the outer shape is defined by exposure "B". The pattern, indeed, can give us quick and accurate misalignment measurement, however, sometimes abnormal pattern shown in Fog. 4 is formed by high-viscosity-etchant. It is difficult for the high-viscosity-etchant to etch off the material between exposed pattern "A" and "B" due to a narrow gap. Making the dimension larger can solve the etching problem, however, the accurate measurement is achieved by using a high-powered optical microscope having a magnification of 1000 or more, Therefore the smaller the dimension is, the better the measurement accuracy become. Our disclosed pattern, which can improve the pattern formation easily, is shown in Fig. 5. The pattern shown in Fig. 5 is formed by exposing the two patterns, labeled "A" and "B" shown in Fig. 6 where pattern "A" is exposed prior to "B". The method of calculating the misalignment from exposure "A" to "B" is shown in Fig. 5. To understand the disclosed misalignment method, in Fig. 6 note that the inner square is defined by exposure "B" and the outer shape is defined by exposure "A". 1 2 3