Source: http://www.google.com/patents/US7602503?dq=5,838,906
Timestamp: 2013-12-12 06:38:09
Document Index: 546887516

Matched Legal Cases: ['Application No. 60', 'Application No. 2004', 'Application No. 93100919', 'Application No. 04000525', 'Application No. 04000525', 'Application No. 200400111', 'Application No. 200410001918', 'Application No. 04000525', 'Application No. 200400111', 'Application No. 200400111', 'Application No. 2004001', 'Application No. 04000512', 'Application No. 2004', 'Application No. 200400111']

Patent US7602503 - Methods for measuring a wavefront of an optical system - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Sign inAdvanced Patent SearchPatentsA method for measuring a wavefront of an optical system. A first step of the method includes directing electromagnetic radiation uniformly at an object plane having a first grating positioned therein. Lines of the first grating comprise a plurality of dots. A second step of the method includes projecting...http://www.google.com/patents/US7602503?utm_source=gb-gplus-sharePatent US7602503 - Methods for measuring a wavefront of an optical systemPublication numberUS7602503 B2Publication typeGrantApplication numberUS 11/708,618Publication dateOct 13, 2009Filing dateFeb 21, 2007Priority dateJan 15, 2003Fee statusPaidAlso published asCN1523448A, CN100476586C, EP1439427A2, EP1439427A3, US7268891, US20040169866, US20070153295Publication number11708618, 708618, US 7602503 B2, US 7602503B2, US-B2-7602503, US7602503 B2, US7602503B2InventorsSherman K. PoultneyOriginal AssigneeAsml Holdings N.V.Export CitationBiBTeX, EndNote, RefManPatent Citations (71), Non-Patent Citations (44), Classifications (19), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetMethods for measuring a wavefront of an optical systemUS 7602503 B2Abstract A method for measuring a wavefront of an optical system. A first step of the method includes directing electromagnetic radiation uniformly at an object plane having a first grating positioned therein. Lines of the first grating comprise a plurality of dots. A second step of the method includes projecting an image of the first grating onto a focal plane having a second grating positioned therein. A third step of the method includes measuring the wavefront of the optical system based on a fringe pattern produced by the second grating.
1. A method for measuring a wavefront of an optical system, comprising:
(a) directing electromagnetic radiation uniformly at an object plane having a first grating positioned therein, wherein lines of the first grating comprise a plurality of dots;
(b) projecting an image of the first grating onto a focal plane having a second grating positioned therein; and
(c) measuring the wavefront of the optical system based on a fringe pattern produced by the second grating.
directing electromagnetic radiation uniformly at an object plane having a first grating positioned therein, wherein lines of the first grating comprise a plurality of reflective dots.
directing electromagnetic radiation uniformly at an object plane having a first grating positioned therein, wherein lines of the first grating comprise a plurality of dots having different sizes.
projecting an image of the first grating on a focal plane having a second grating positioned therein, wherein the second grating is one of a checkerboard grating or a cross-grating.
projecting an image of the first grating on a focal plane having a second grating positioned therein, wherein the second grating includes a regular pattern of absorptive regions and transmissive regions.
orienting the first grating at a 45 degree angle with respect to the second grating.
projecting an image of the first grating on a focal plane having a second grating positioned therein, wherein a pitch of the first grating is equal to a pitch of the second grating times a magnification factor of a projection optical system.
projecting an image of the first grating onto a focal plane having a second grating positioned therein, wherein a pitch of the first grating is such that a second order diffraction pattern disappears at the focal plane.
9. The method of claim 1, wherein (b) comprises:
filling an input numerical aperture of a projection optical system with the image of the first grating.
10. A method for measuring a wavefront of an optical system, comprising:
(a) directing electromagnetic radiation uniformly at an object plane having a first grating or a second grating positionable therein, wherein lines of the first grating and lines of the second grating comprise a plurality of dots;
(b) projecting an image of one of the first grating or the second grating onto a focal plane having a third grating positioned therein; and
(c) measuring the wavefront of the optical system based on a fringe pattern produced by the third grating.
11. The method of claim 10, wherein (a) comprises:
directing electromagnetic radiation uniformly at an object plane having a first grating or a second grating positionable therein, wherein the second grating is oriented orthogonally to the first grating.
12. The method of claim 10, wherein (a) comprises:
directing electromagnetic radiation uniformly at an object plane having a first grating or a second grating positionable therein, wherein at least one of the first grating and the second grating is a reflective grating.
13. The method of claim 10, wherein (a) comprises:
directing electromagnetic radiation uniformly at an object plane having a first grating or a second grating positionable therein, wherein the plurality of dots of at least one of the first grating and the second grating comprise dots having different sizes.
14. The method of claim 10, wherein (b) comprises:
projecting an image of one of the first grating or the second grating on a focal plane having a third grating positioned therein, wherein the third grating is one of a checkerboard grating or a cross-grating.
15. The method of claim 10, wherein (b) comprises:
projecting an image of one of the first grating or the second grating on a focal plane having a third grating positioned therein, wherein the third grating includes a regular pattern of absorptive regions and transmissive regions.
16. The method of claim 10, wherein (b) comprises:
orienting one of the first grating or the second grating at a 45 degree angle with respect to the third grating.
17. The method of claim 10, wherein (b) comprises:
projecting an image of one of the first grating or the second grating on a focal plane having a third grating positioned therein, wherein a pitch of at least one of the first grating and the second grating is equal to a pitch of the third grating times a magnification factor of a projection optical system.
18. The method of claim 10, wherein (b) comprises:
projecting an image of one of the first grating or the second grating onto a focal plane having a third grating positioned therein, wherein a pitch of at least one of the first grating and the second grating is such that a second order diffraction pattern disappears at the focal plane.
19. The method of claim 10, wherein (b) comprises:
filling an input numerical aperture of a projection optical system with the image of one of the first grating or the second grating. Description
CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 10/750,986, entitled �Transmission Shear Grating In Checkerboard Configuration For EUV Wavefront Sensor,� and filed on Jan. 5, 2004, now U.S. Pat. No. 7,268,891, which claims the benefit of U.S. Provisional Application No. 60/440,050, filed Jan. 15, 2003, the entirety of which is incorporated by reference herein.
As chip manufacturers have been able to use shorter wavelengths of light, they have encountered a problem in that the shorter wavelength light is absorbed by the glass lenses that are intended to focus the light. Due to the absorption of the shorter wavelength light, the light fails to reach the silicon wafer. As a result, no circuit pattern is created on the silicon wafer. In an attempt to overcome this problem, chip manufacturers developed a lithography process known as Extreme Ultraviolet Lithography (EUVL). In this process, a glass lens can be replaced by a mirror.
SUMMARY OF THE INVENTION The present invention is directed to a transmission shear grating and checkerboard configuration for EUV wavefront sensor that substantially obviates one or more of the problems and disadvantages of the related art.
The wavefront can be measured when imaging is not being performed.
In order to measure the wavefront, the reticle stage is moved, such that one of the gratings 203 in the source module 103 on the reticle stage is placed in the optical path, rather than the reticle 102 itself. The wafer stage is also moved such that the wavefront sensor is positioned to receive an image of the source module grating 203. The CCD detector 202 below the 2-D grating 201 then receives and measures the transmitted radiation. The reticle stage can then be moved to place a different diffraction grating in the optical path, so as to measure the wavefront with an orthogonal orientation of the source module grating 203.
As noted above, the pitch of the 2-D grating 201 is chosen in one embodiment to provide a shear ratio of 1/30 th, where the CCD detector 202 is in the fringe plane (i.e., below the focal plane of the system), and �sees� a pattern of fringes (an interferogram) or a number of overlapping circles, as will be discussed further below. The shear ratio is a measure of the overlap of two circles, where a shear ratio of zero represents perfect overlap. Note also that it is desirable for the CCD detector 202 to �see� only the zeroth order and the + and −1st order diffraction images, and to eliminate the + and −2nd order on diffraction images. For this purpose, the use of a checkerboard grating with square transmission and reflection areas, as shown in FIG. 3, is believed to be optimal. Furthermore, the first grating 103 is constructed to aid in eliminating unwanted orders. It is important, however, that whichever pattern of transmission and reflection areas is used, that it be a regular pattern that forms a 2-D grating. It will be appreciated however that other shapes, in addition to square shapes, are possible, e.g., circular reflective areas, or circular transmissive areas, etc., as long as the pattern is regular.
FIG. 7 illustrates the wavefront fringes (412 in FIG. 4) as seen by the CCD detector 202. As shown in FIG. 7, in the upper right-hand photograph, sheared fringes for a single object space slit are shown, where the slit is positioned in front of an incoherent, diffuse source that fills the maximum numerical aperture and smoothes any wavefront inhomogeneities. The bottom right-hand figure shows a fringe visibility function 601, with zeroth order and first order diffraction patterns. Wavefront fringes are formed by interference of 0th order with +1st order and with −1st order diffractions at the PO pupil.
The 50% duty cycle on the grating 201 makes all even orders of the diffraction pattern invisible. At the bottom left of FIG. 7, the image space shearing grating 201 is shown, with a shear ratio of 0.5.
FIGS. 8-11 illustrate exemplary wavefronts as seen by the CCD detector 202, for different shear ratios.
In one embodiment, the diameter of the dots, for the parameters discussed above (6.4 μm for 4� magnification, 0.25 output numerical aperture, 0.0625 input numerical aperture, 13.5 nm source) is between 70 and 120 nm, preferably close to 70 nm.
When the reflective dots are placed randomly within the grating lines, speckle appears in the fringe pattern, as well as a bright spot at the center. The bright center can be eliminated by making the reflective dots of random height with a standard deviation of many times the wavelength (i.e., OPD many times π plus a fraction). When dots are placed in regular pattern, the overlapping fringe artifacts in the fringe plane can likewise be eliminated (but causing speckle) by making the dots of random height with an optical path difference standard deviation of many times π. However, the fringe artifacts may have less impact on fringe analysis.
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C., "White Light Extended Source Shearing Interferometer," Applied Optics, vol. 13, No. 1, Jan. 1974, pp. 200-202.Classifications U.S. Classification356/515International ClassificationG03F7/20, G02B5/18, G01B9/02, G01J9/02, G01B11/24, H01L21/027, G01M11/02Cooperative ClassificationG03F7/7085, G03F7/706, G01J2009/0219, G03F7/70591, G02B5/1838, G01J9/0215European ClassificationG03F7/70L6, G03F7/70L6B, G03F7/70P4, G02B5/18H, G01J9/02DLegal EventsDateCodeEventDescriptionMar 7, 2013FPAYFee paymentYear of fee payment: 4Feb 21, 2007ASAssignmentOwner name: ASML HOLDING N.V., NETHERLANDSFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:POULTNEY, SHERMAN K.;REEL/FRAME:019018/0692Effective date: 20040406RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google