Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Reexamination Certificate
2002-08-07
2004-11-30
Nguyen, Tu T. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
Reexamination Certificate
active
06825932
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a projection exposure apparatus used to manufacture micro-device such as semi-conductor elements, liquid crystal display elements, camera elements (CCDs) and thin-film magnetic heads, by a lithographic process, and more particularly, it relates to a method for measuring optical features of an exposure apparatus such as light intensity distribution of illumination light used for transferring a pattern of a mask (for example, a reticle) onto a substrate (for example, a wafer or a glass plate) and an imaging feature of a projection optical system.
In the past, for example, when semi-conductor elements or liquid crystal display elements are manufactured by a lithographic process, there have been used projection exposure apparatuses in which a pattern on a mask or a reticle (referred to generically as “reticle” hereinafter) is projected for exposure, through a projection exposure system, onto a sensitive substrate (such as a wafer) on which photo-resist is coated. In such projection exposure apparatuses, a high accurate imaging feature is required to form a fine or minute circuit pattern with high accuracy, and, high overlapping accuracy is required to put the pattern of the reticle to be currently exposure-treated on top of the patterns formed on the substrate during exposure for formation of previous layers, in order to successively form patterns of respective layers on the same area of the substrate in a laminated manner. Thus, an imaging feature of the projection exposure apparatus for focusing the reticle pattern onto the substrate must be adjusted with high accuracy, and, to this end, various methods for evaluating the imaging feature of the projection exposure apparatus prior to exposure treatment have been proposed.
As one of the methods for evaluating the imaging feature of the projection exposure apparatus, a method in which a pattern of a test reticle on which a plurality of marks are formed is projected for exposure onto a substrate prior to actual production exposure and a developed test pattern image is observed has been utilized most popularly. However, in this method, since a preliminary exposure process and a preliminary developing process are required, longer time and much labor are required and a special device for measuring an image must be provided.
To eliminate such an inconvenience, there has been proposed a method in which a photo-electric sensor is provided on a stage on which a sensitive substrate is rested and a spatial image of a test pattern of a reticle formed through a projection optical system is directly observed on the basis of output from the sensor (for example, refer to Japanese Patent Laid-open No. 59-94032 (1984)) (U.S. Pat. No. 4,629,313). According to this method, the change in imaging feature caused by not only initial adjustment of the apparatus but also time-lapse change of the apparatus, or change in environmental conditions (such as atmospheric pressure and temperature), or absorption of illumination light of the imaging optical system, or change in conditions of the apparatus such as an illumination condition (solid angle and the like) to the reticle can easily be observed and the imaging feature can be corrected on the basis of the observed result. Recent projection exposure apparatuses include a mechanism for measuring the imaging feature of the projection optical system to carry out this method.
The following two methods for measuring the spatial image of the test pattern (referred to as “measurement pattern” hereinafter, because this test pattern is used for measuring the imaging feature) formed on the reticle by using the photo-electric sensor provided on the substrate stage are generally used in combination with the above-mentioned imaging feature measuring mechanism of the projection exposure apparatus.
In one of the above methods (first method), the spatial image of the single measurement pattern is measured while illuminating only a limited area on the reticle near the measurement pattern, and, after the measurement is finished, the setting of a blind (field stop) in the illumination system is altered and the illumination area on the reticle is switched to a limited area on the reticle near the next measurement pattern, and then, the spatial image of the next measurement pattern is measured. Similar operations are repeated.
In the other method (second method), the spatial images of the measurement patterns are successively measured while illuminating substantially the entire surface of the reticle.
Recently, as the semi-conductor elements become high density and circuit patterns become more minutely, higher resolving power and higher overlapping accuracy have been required. To this end, a plurality of measurement patterns are disposed within the reticle and the imaging feature of the projection optical system is evaluated more strictly by using the measured results of the spatial images of the measurement patterns in order to adjust the imaging feature of the projection optical system with high accuracy.
However, when the above-mentioned first method is used, although deterioration of the imaging feature due to absorption of the illumination light in the projection optical system is prevented by not illuminating the undesired areas, as the number of the measurement patterns (i.e., the number of measuring points or positions) is increased, the switching between the illumination areas imposes a bad influence upon the through-put.
On the other hand, when the above-mentioned second method is used, although there is no reduction of the through-put, since the entire surface of the reticle is illuminated by the illumination light during the measurement of all of the measurement patterns, the illumination light is absorbed by the reticle and the projection optical system, thereby worsening the imaging feature.
Further, in the exposure apparatus, light intensity distribution of the illumination light on the exposure surface is also measured.
Now, a method for measuring the light intensity distribution of the illumination light on the exposure surface in the conventional exposure apparatus will be described hereinbelow.
An illumination area is adjusted so that the illumination area of the exposure surface of the exposure apparatus becomes a maximum effective area. In general, the maximum effective area is a rectangular area or a square area having a diagonal line corresponding to a diameter of a circle slightly smaller than the maximum illumination area of a projection lens, which maximum effective area is referred to as “entire illumination area” and is used as a measurement range for seeking the light intensity distribution, for example.
A photo-electric conversion means for providing the light intensity distribution measurement is rested on the wafer stage so that a light receiving surface of the photo-electric conversion means becomes flush with an exposure surface of a wafer, and, by scan-moving the stage on which the photo-electric conversion means is rested relative to the measurement range, light intensity within the measurement range is measured by the photo-electric conversion means. The light intensity distribution within the measurement range is determined on the basis of an output value from the photo-electric conversion means and positional information of the light receiving surface from a position measuring means for measuring the position of the stage. An example of the measurement of the light intensity distribution is disclosed in Japanese Patent Publication No. 1-39207 (1989) (U.S. Pat. No. Re. 32,795), for example. Since the greater the number of different positions within the measurement range at which the light intensity is measured, the more accurate light intensity distribution can be obtained within the measurement range, the light intensity distribution is measured at various positions within the measurement range by successively shifting (or scan-moving) the photo-electric conversion means within the measurement range.
In the above-mentioned convent
Murayama Masayuki
Suzuki Kousuke
Nguyen Tu T.
Nikon Corporation
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Method for measuring optical feature of exposure apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for measuring optical feature of exposure apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for measuring optical feature of exposure apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3306025