Method of detecting aberrations of an optical imaging system
First Claim
1. A method of detecting aberrations of an optical imaging system, comprising the steps ofarranging a test object in the object plane of the system;
- providing a photoresist layer in the image plane of the system;
imaging the test object by means of the system and an imaging beam;
developing the photoresist layer, and detecting the developed image by means of a scanning detection device having a resolution which is considerably larger than that of the imaging system, characterized in that use is made of a test object which comprises at least one closed single figure having a phase structure, and in that the image of this figure observed by the scanning detection device is subjected to an image analysis in order to ascertain at least one of different types of changes of shape in the image of the single figure, each type of shape change being indicative of a given kind of aberration.
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Abstract
Aberrations of an imaging system can be detected in an accurate and reliable way by imaging, by means of the imaging system, a circular phase structure on a photoresist, developing the resist and scanning it with a scanning detection device which is coupled to an image processor. The circular phase structure is imaged in a ring structure and each of several possible aberrations, like coma, astigmatism, three-point aberration, etc. causes a specific change in the shape of the inner contour and the outer contour of the ring and/or a change in the distance between these contours, so that the aberrations can be detected independently of each other. The new method may be used for measuring a projection system for a lithographic projection apparatus.
96 Citations
8 Claims
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1. A method of detecting aberrations of an optical imaging system, comprising the steps of
arranging a test object in the object plane of the system; -
providing a photoresist layer in the image plane of the system;
imaging the test object by means of the system and an imaging beam;
developing the photoresist layer, and detecting the developed image by means of a scanning detection device having a resolution which is considerably larger than that of the imaging system, characterized in that use is made of a test object which comprises at least one closed single figure having a phase structure, and in that the image of this figure observed by the scanning detection device is subjected to an image analysis in order to ascertain at least one of different types of changes of shape in the image of the single figure, each type of shape change being indicative of a given kind of aberration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification