Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2001-12-21
2004-03-30
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000
Reexamination Certificate
active
06714282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates to a position detecting method, an optical characteristic measuring method and unit, an exposure apparatus, and a device manufacturing method, and more specifically to a position detecting method for detecting the positions of a plurality of features in an image formed on the image plane of an optical system, an optical characteristic measuring method and unit for measuring an optical characteristic of an optical system to be examined using the position detecting method, an exposure apparatus comprising the optical characteristic measuring unit, and a device manufacturing method using the exposure apparatus.
2. Description of The Related Art
In a lithography process for manufacturing semiconductor devices, liquid crystal display devices, or the like, exposure apparatuses have been used which transfer a pattern (also referred to as a “reticle pattern” hereinafter) formed on a mask or reticle (generically referred to as a “reticle” hereinafter) onto a substrate, such as a wafer or glass plate (hereinafter, generically referred to as a “substrate” as needed), coated with a resist through a projection optical system. As such an exposure apparatus, a stationary-exposure-type projection exposure apparatus such as the so-called stepper, or a scanning-exposure-type projection exposure apparatus such as the so-called scanning stepper is mainly used.
Such an exposure apparatus needs to accurately project the pattern on a reticle onto a substrate with high resolving power. Therefore, the projection optical system is designed to have a good optical characteristic with various types of aberrations being reduced.
However, it is difficult to make a projection optical system completely as is planned in design, and various types of aberrations due to various factors remain in a projection optical system actually made. Therefore, the optical characteristic of the projection optical system actually made is not the same as planned in design.
Various technologies for measuring the optical characteristic, related to aberration, of the actually made projection optical system as an optical system to be examined have been suggested, and of those technologies a wave-front aberration measuring method is attracting attentions, which comprises (a) making a spherical wave produced by a pinhole incident on the optical system to be examined, (b) producing parallel rays of light from light that has passed through the optical system to be examined and forms a pinhole image and dividing the wave front thereof into a plurality of portions, (c) making each of the portions (hereinafter, called “divided wave-front portions”) form a spot image, and (d) calculating wave-front aberration due to the optical system based on measured positions where the spot images are formed.
A wave-front aberration measuring unit using this method may comprise a micro-lens array, in which a plurality of micro lenses are arranged along a two-dimensional plane parallel to the ideal wave front of the parallel rays of light, as a wave-front dividing device for dividing the incident light and making each of the divided wave-front portions form a spot image. The wave-front aberration measuring unit picks up the spot images by a pick-up device such as CCD and calculates wave-front aberration based on deviations of the spot images' positions, which are detected from the pick-up result, from positions planned in design.
Since such a wave-front aberration measuring unit with the micro-lens array can pick up the spot images formed by the divided wave-front portions at one time, the unit is excellent in terms of quickly measuring wave front aberration.
As a premise of measuring wave front aberration, the tilts of the divided wave-front portions, if any, can be considered linear. Therefore, the wave front is preferably divided into as small portions as possible in order to accurately measure the wave front aberration.
However, as the divided wave-front portions become smaller, the distances between the spot images formed through the micro lenses of the micro-lens array become short. As a result, in view of the whole image including the spot images the position of the spot image formed through a micro lens is influenced by the spot images formed through its neighboring micro lenses. That is, cross-talks between spot images, especially between spot images adjacent to each other, are not negligible, which cause the shapes of the spot images to be distorted relative to the original shape thereof, so that the positions of the spot images obtained from the pick-up result are displaced from the real positions thereof by their respective neighboring spot images.
When spot images near a given spot image are symmetrically arranged around the given spot image, the influences from the neighboring spot images cancel each other, so that the displacement of the given spot image does not occur. Meanwhile, when spot images near a given spot image are asymmetrically arranged around the given spot image, the influences from the neighboring spot images do not cancel each other, and at least parts of the influences remain, so that the given spot image is displaced. Therefore, when spot images near a given spot image are asymmetrically arranged around the given spot image, the accuracy in detecting the real position of the given spot image decreases. Especially, no spot image exists on one side in a specific direction of a spot image present in the periphery of the whole image corresponding to the periphery of the pupil, so that the asymmetry of the arrangement of spot images is large in the periphery. Therefore, the accuracy in detecting positions of such a spot image is affected to a great extent with causing the measurement accuracy in measuring wave front aberration to decrease.
DISCLOSURE OF INVENTION
This invention was made under such circumstances, and a first purpose of the present invention is to provide a position detecting method which can accurately detect the real positions of a plurality of features even when cross-talks are present between the plurality of features formed on the image plane.
Moreover, a second purpose of the present invention is to provide an optical characteristic measuring method and unit which accurately detects the optical characteristic of an optical system to be examined.
Furthermore, a third purpose of the present invention is to provide an exposure apparatus that can accurately transfer a given pattern onto a substrate.
Moreover, a fourth purpose of the present invention is to provide a device manufacturing method which can manufacture highly integrated devices having a fine pattern thereon.
According to knowledge obtained from the study by the inventor of this invention, it is possible to make an optical system including the micro-lens array, which is used for measuring wave front aberration, as planned in design, and when the optical system is made as planned in design, the whole image data on the image plane when real spot images are assumed to be present in estimated positions can be accurately calculated based on the optical model of the optical system, in which whole image data spot images assumed to be present in the estimated positions are superposed. This invention was made on the basis of such knowledge.
According to a first aspect of the present invention, there is provided a position detecting method with which to detect positions of a plurality of features in an image formed on an image plane by a predetermined optical system, the position detecting method comprising calculating initial estimated feature positions of the plurality of features using a specific algorism based on the image formed on the image plane; calculating image information on the image plane using a model for the predetermined optical system in view of the features being formed in respective current estimated feature positions; calculating comparison feature positions using the specific algorism based on the image information; correcting the current estimated
Nguyen Henry Hung
Nikon Corporation
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