Browse Prior Art Database

Accurate Two Dimensional Measurement of Overlays

IP.com Disclosure Number: IPCOM000089720D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Rottman, HR: AUTHOR [+2]

Abstract

New laser-controlled image repeaters have become available which permit stepping of masks with tolerances which equate those of the measurement machines. Therefore, the reduction of overlay errors to meet more critical device specifications is practically impossible.

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Accurate Two Dimensional Measurement of Overlays

New laser-controlled image repeaters have become available which permit stepping of masks with tolerances which equate those of the measurement machines. Therefore, the reduction of overlay errors to meet more critical device specifications is practically impossible.

A method and special test patterns are provided for accurate self- measurement of image repeaters. This approach can also be extended to future applications (E-beam and X-ray lithography), which will impose even greater restrictions than photolithographic methods.

Determination of overlay or registration errors is achieved by printing an array of measurement targets M in close proximity to a corresponding set of reference targets R. Accurate comparison measurements then can be made by a high magnification measuring microscope (S.D. is less than or = 20 nm) without resorting to measurement machines. As a consequence, tolerances or errors of the measurement machine, such as yaw, table orthogonality, temperature, and table and microscope interaction, are avoided.

Figs. 1 and 2 show typical 10X target patterns. As an example, consider the stepping errors between two image repeaters. For this purpose, a resist-coated chrome plate is stepped on an image repeater #1 using 10X pattern R. After completion, the 1X plate is transferred to image repeater #2, and the same array is stepped again, using 10X target pattern M. Since the set of lines of target R covers a substantial area (~ 0.5 nm), placement tolerance...