Optics: measuring and testing – Lens or reflective image former testing
Reexamination Certificate
1999-12-15
2001-11-27
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Lens or reflective image former testing
C355S053000
Reexamination Certificate
active
06323945
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coma aberration automatic measuring mark used for measuring only a coma aberration of various aberrations of a lens system used in a reduction projection exposure, and a method for measuring the coma aberration by using the coma aberration automatic measuring mark.
One important factor is to quickly and simply measure a coma aberration of a reduction projection lens system. Now, a prior art method for measuring the coma aberration of the reduction projection lens system will be described with reference to
FIGS. 1A and 1B
.
As shown in
FIG. 1A
, a prior art coma aberration automatic measuring mark is constituted of a plurality of strip-shaped patterns L
1
L
2
, L
3
, L
4
and L
5
arranged in parallel to one another and separately from one another, at a pitch which is about a double of a wavelength of an exposure light. A line width of a projected pattern of each of the strip-shaped patterns L
1
, L
2
, L
3
. L
4
and L
5
is measured by for example a length measuring SEM (scanning electron microscope), and the amount of coma aberration is calculated from a difference in the line width between the strip-shaped patterns L
1
and L
5
positioned at opposite side ends of the projected coma aberration automatic measuring mark, as shown in
FIGS. 1A and 1B
.
FIG. 1A
illustrates a case having no coma aberration, and
FIG. 1B
illustrates a case having a coma aberration.
FIG. 1C
illustrates a case having a spherical aberration.
In the prior art, however, when the coma aberration is very large, it is not possible to carry out an automatic measurement utilizing an image processing, and therefore, the coma aberration must be measured manually, with the result that the measurement needs a considerable time. Therefore, adjustment of the reduction projection lens system cannot be smoothly performed, and a satisfactory degree of reproduction cannot be obtained because of the manual measurement. In addition, it is difficult to separate the coma aberration from the other aberrations occurring in the reduction projection lens system.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a coma aberration automatic measuring mark used for automatically measuring the coma aberration with a high degree of reproduction, and a method for measuring the coma aberration by using the coma aberration automatic measuring mark.
The above and other objects of the present invention are achieved in accordance with the present invention by a coma aberration automatic measuring mark comprising a first-order diffraction grating composed of a plurality of elongated isosceles triangle patterns which are so arranged that the axis of symmetry passing on the center of each elongated isosceles triangle is parallel to one another, that a half of the elongated isosceles triangle patterns are located in a direction opposite to that of the remaining half of the elongated isosceles triangle patterns, and the elongated isosceles triangle patterns are located separately from one another, in a direction perpendicular to the axis of symmetry passing on the center of each elongated isosceles triangle, and at a pitch diffracting a measuring coherent light.
Specifically, the pitch diffracting the measuring coherent light is about a double of a lens design wavelength.
In an embodiment of the coma aberration automatic measuring mark, the elongated isosceles triangle patterns includes a first group of elongated isosceles triangle patterns and a second group of elongated isosceles triangle patterns, which are located in symmetry to each other, in connection with a line which is positioned between the first group of elongated isosceles triangle patterns and the second group of elongated isosceles triangle patterns and which is perpendicular to the axis of symmetry passing on the center of the elongated isosceles triangle.
This coma aberration automatic measuring mark is adapted for not only a measurement of a coma aberration but also a measurement of a telecentric property of an optical axis.
According to a second aspect of the present invention, there is provided a method for measuring a coma aberration by using a coma aberration automatic measuring mark, wherein the coma aberration automatic measuring mark comprising at least two first-order diffraction gratings each of composed of a plurality of elongated isosceles triangle patterns which are so arranged that the axis of symmetry passing on the center of each elongated isosceles triangle is parallel to one another, that a half of the elongated isosceles triangle patterns are located in a direction opposite to that of the remaining half of the elongated isosceles triangle patterns, and the elongated isosceles triangle patterns are located separately from one another, in a direction perpendicular to the axis of symmetry passing on the center of each elongated isosceles triangle, and at a pitch diffracting a measuring coherent light, the at least two first-order diffraction gratings being located separately from each other in a direction of the axis of symmetry passing on the center of the elongated isosceles triangle, in such a manner that the elongated isosceles triangle patterns included in the at least two first-order diffraction gratings are in symmetry to each other, in connection with a line which is positioned between the at least two first-order diffraction gratings and which is perpendicular to the axis of symmetry passing on the center of the elongated isosceles triangle, and
wherein the method includes the steps of scanning the at least two first-order diffraction gratings by the measuring coherent light, measuring a relative distance between diffraction lights generated by the at least two first-order diffraction gratings, and comparing the measured relative distance with a distance between the at least two first-order diffraction gratings.
Specifically, a distance between the at least two first-order diffraction gratings located in symmetry to each other is set to a distance which is sufficiently longer than a wavelength of a measuring coherent light and which is on the order which can make negligible an Abbe error occurring in a coordinate measuring system and a distortion occurring in a reduction projection lens.
This method can be used for measuring a telecentric property of an optical axis, in place of measuring the coma aberration.
Here, the triangular patterns constituting the coma aberration automatic measuring mark are not limited to the elongated isosceles triangle patterns, but are sufficient if the triangular patterns are elongated triangular patterns which can be so located that a half of the elongated triangular patterns are located in a direction opposite to that of the remaining half of the elongated triangular patterns, and the elongated triangular patterns are located in parallel to each other and separately from one another, at a pitch diffracting a measuring coherent light, in a direction substantially perpendicular to the long axis that extends from the vertex between two long sides of three sides of the elongated triangle to the shortest side of the three sides of the elongated triangle, perpendicularly to the shortest side of the elongated triangle.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.
REFERENCES:
patent: 4814829 (1989-03-01), Kosugi et al.
patent: 4908656 (1990-03-01), Suwa et al.
patent: 5300786 (1994-04-01), Brunner et al.
patent: 5402224 (1995-03-01), Hirukawa et al.
patent: 5615006 (1997-03-01), Hirukawa et al.
patent: 6088113 (2000-07-01), Kim
patent: 10-232185 (1998-09-01), None
patent: 10-260108 (1998-09-01), None
patent: 11-297614 (1999-10-01), None
NEC Corporation
Pham Hoa Q.
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