Optics: measuring and testing – Lens or reflective image former testing
Reexamination Certificate
2000-09-22
2002-08-20
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Lens or reflective image former testing
C355S053000, C355S077000, C430S005000, C430S030000
Reexamination Certificate
active
06437858
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-271260, filed Sep. 24, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an aberration measuring method, an aberration measuring system and an aberration measuring mask for measuring a lens aberration in an optical system.
A lens aberration of an exposure apparatus used in a lithography process adversely affects a pattern position error, a focus error, a variation in pattern dimensions on a semiconductor device pattern. The kind of aberration can be determined, depending on whether the effect of the lens aberration relates to the pattern size or the pattern direction.
Conventional methods of evaluating astigmatism or spherical aberration using such phenomena include a Kirk method (Joseph P. Kirk, “Astigmatism and field curvature from pinbars”, SPIE Vol. 1463 (1991), P.294), a line-width abnormality value measuring method which evaluates coma aberration, and a relative displacement measuring method (Jpn. Pat. Appln. KOKAI Publication No. 11-142108).
FIGS. 1A
to
1
D show aberration measuring patterns used in the line-width abnormality value measuring method. In the line-width abnormality value measuring method, five line patterns each with an equal line width, as shown in
FIGS. 1A
to
1
D, are transferred on a wafer, and an error in line width between both endmost lines is measured by a length-measuring type scanning electron microscope (SEM). As is shown in
FIGS. 1A
to
1
D, four five-line patterns having line directions set at 0°, 45°, 90° and 135° with respect to a reference straight line
111
are provided, thereby to measure aberration in each line-width direction.
FIGS. 2A and 2B
show aberration measuring patterns used in the relative displacement measuring method. In the relative displacement measuring method, as shown in
FIGS. 2A and 2B
, two kinds of patterns with different line widths are disposed in parallel, and a relative displacement is measured by using a difference in positional displacement of each pattern width. Based on the amount of the relative displacement, an aberration is measured. The pattern shown in
FIG. 2A
is used to measure an aberration in 0° and 90° directions with respect to a reference line
121
, and the pattern shown in
FIG. 2B
is used to measure an aberration in 45° and 135° directions with respect to the reference line
121
.
With further reduction in pattern size and variation in device structure in modern technology, there arise problems of aberrations other than coma aberration. For instance, in fabrication of DRAMs, capacitors with deep trench structure have been formed. Unlike conventional line & space patterns, etc., the deep-trench type capacitor has a two-dimensional pattern. Specifically, a pattern is disposed in one direction, and another pattern is disposed in another direction. In this case, it is necessary to consider not only the effect of the pattern disposed in one direction, but also the relationship among the patterns disposed in a plurality of directions, in particular, a diffraction. Also in the case of device activation regions, etc. there is the same necessity to consider the relationship among the patterns disposed in a plurality of directions.
Specifically, in the conventional line & space pattern, etc., the sizes of patterns disposed in one direction will vary due to diffraction. This adverse effect has been observed in the prior art. In order to decrease it, a method has been proposed wherein an aberration in a projecting optical system is measured and corrected and thus a normal pattern is formed. With this aberration measurement, adequate pattern precision has been obtained in the conventional patterns.
On the other hand, in the case of the deep-trench capacitor, for instance, diffraction occurs not only between adjacent patterns disposed in one direction but also between adjacent patterns disposed in plural directions. Consequently, transferred patterns become triangular or pentagonal. It is known that this undesirable phenomenon is due to an aberration called “three-fold symmetry aberration” or “five-fold symmetry aberration” occurring in the projecting optical system.
It is known that each term of a Zernike series obtained by series-developing a Zernike function, which is obtained by expressing the lens aberration function by the function of coordinates (R, &thgr;) at a pupil plane, is represented by a radial function (zernike coefficient ZI×variable R). For instance, the term representing coma aberration is expressed by Z
2
R cos &thgr;, Z
3
Rsin&thgr;; the term representing three-fold symmetry aberration is expressed by Z
10
R
3
cos 3&thgr;, Z
11
R
3
sin 3&thgr;; and the term representing five-fold symmetry aberration is expressed by Z
26
R
5
cos 5&thgr;, Z
27
R
5
sin 5&thgr;.
There are conventional aberration measurement methods for measuring an aberration between an axial direction, and a direction perpendicular thereto, or between the axial direction and a direction at 45° or 135° thereto. However, there is no methods of measuring other aberrations. In the case of conventionally fabricated patterns, adequate pattern precision and exposure tolerance have been obtained without the need to measure such other aberrations. By contrast, in the case of modern small-sized patterns, adequate pattern precision and exposure tolerance cannot be obtained.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide an aberration measuring method, an aberration measuring system and an aberration measuring mask capable of measuring an (2n+1)-fold (n=natural number) symmetry aberration.
According to an aspect of the present invention, there is provided an aberration measuring method comprising the steps of providing an aberration mask comprising a plurality of aberration measuring pattern units each having a plurality of elemental patterns arranged in a direction of a given straight line, the aberration measuring pattern units being disposed in a given circumferential direction such that the straight line of each of the aberration measuring pattern units is cyclically shifted relative to a reference line at an angle of (&pgr;/2)/(2n+1) rad (n=natural number) in a range between 0 rad and &pgr;/2 rad; transferring pattern images of the aberration measuring mask onto a substrate to be processed, using an optical system; and detecting the transferred pattern image, thereby measuring an aberration in the direction of the reference straight line of the optical system.
According to another aspect of the invention, there is provided an aberration measuring system comprising an illumination optical system; an aberration measuring mask disposed on an optical path of light from the illumination optical system and comprising a plurality of aberration measuring pattern units each having a plurality of elemental patterns arranged in a direction of a given straight line, the aberration measuring pattern units being disposed in a given circumferential direction such that the straight line of each of the aberration measuring pattern units is cyclically shifted relative to a reference line at an angle of (&pgr;/2)/(2n+1) rad (n=natural number) in a range between 0 rad and &pgr;/2 rad; and a projecting optical system for focusing light, which has passed through the aberration measuring mask, onto a substrate to be processed.
According to still another aspect of the invention, there is provided an aberration measuring mask comprising a plurality of aberration measuring pattern units each having a plurality of elemental patterns arranged in a direction of a given straight line, the aberration measuring pattern units being disposed in a given circumferential direction such that the straight line of each of the aberration measuring pattern units is cyclically shifted relative to a reference line at an angle of (&pgr;/2)/(2n+1)
Higashiki Tatsuhiko
Kouno Takuya
Nomura Hiroshi
Finnegan, Henderson, Farabow, Garrett & Dunner,.L.L.P.
Pham Hoa Q.
LandOfFree
Aberration measuring method, aberration measuring system and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aberration measuring method, aberration measuring system and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aberration measuring method, aberration measuring system and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2911111