EP1301830A2 - Systeme et procedes pour caracteriser des systemes optiques a l'aide de reticules holographiques - Google Patents

Systeme et procedes pour caracteriser des systemes optiques a l'aide de reticules holographiques

Info

Publication number
EP1301830A2
EP1301830A2 EP01957171A EP01957171A EP1301830A2 EP 1301830 A2 EP1301830 A2 EP 1301830A2 EP 01957171 A EP01957171 A EP 01957171A EP 01957171 A EP01957171 A EP 01957171A EP 1301830 A2 EP1301830 A2 EP 1301830A2
Authority
EP
European Patent Office
Prior art keywords
reticle
grating
image
optical system
interfering
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01957171A
Other languages
German (de)
English (en)
Inventor
Matthew E. Hansen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ASML US Inc
Original Assignee
ASML US Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ASML US Inc filed Critical ASML US Inc
Publication of EP1301830A2 publication Critical patent/EP1301830A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70591—Testing optical components
    • G03F7/706—Aberration measurement
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/38—Masks having auxiliary features, e.g. special coatings or marks for alignment or testing; Preparation thereof
    • G03F1/44—Testing or measuring features, e.g. grid patterns, focus monitors, sawtooth scales or notched scales
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70283—Mask effects on the imaging process
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/70616—Monitoring the printed patterns
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70691—Handling of masks or workpieces
    • G03F7/70733—Handling masks and workpieces, e.g. exchange of workpiece or mask, transport of workpiece or mask
    • G03F7/70741—Handling masks outside exposure position, e.g. reticle libraries
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms

Definitions

  • the present invention relates to characterizing an optical system, and particularly to the rapid and precise characterization of an optical system including focus, field curvature, astigmatism, spherical, coma, and/or focal plane deviation using holographically produced reticles.
  • Photolithography is often used in the manufacture of semiconductor devices and other electronic equipment.
  • projection optics of high quality are often used to image features on a reticle onto a photosensitive substrate, such as a resist covered wafer.
  • the optical system or projection optics must be continually maintained and checked for image quality.
  • optical system or projection optics Often, the performance of an optical system or projection optics is difficult to obtain without time consuming techniques. Generally, multiple exposures are required of a photosensitive substrate at different locations in the image field and at different focus depths to characterize the optical system. The optical system is then characterized by compiling information obtained from examining the multiple processed images. Each of the many exposures and the corresponding processed images are acquired serially. Consequently, focus errors, scan errors and temporal variations to the optical system parameters during the measurement are compounded.
  • the present invention comprises a method and apparatus for obtaining optical system characterization information simultaneously by utilizing a volume of space during a relatively short time or in a single exposure.
  • a test reticle having a plurality of features with different orientations, sizes, and line types is imaged with the optical system being characterized. Either the object plane in which the reticle is positioned or the image plane in which the characterization data is obtained is tilted or angled within the corresponding three-dimensional volume of space.
  • the reticle, having a plurality of features is imaged with the optical system being characterized. In a volume of space, through a depth of focus, an envelope of feature quality through focus is thereby obtained.
  • This envelope of feature quality is simultaneously obtained by acquiring image data of the reticle in a plane that is oblique to the reticle plane.
  • the resulting image of the reticle and corresponding features are analyzed with metrology techniques, which can include an interferometric tool thereby obtaining optical system characteristics.
  • the optical system characteristics that can be obtained include focus, field curvature, astigmatism, coma, distortion, telecentricity and/or focal plane deviation, as well as information on spherical aberrations and variation of coherence.
  • the test reticle described above is produced holographically. More specifically, a holographic reticle is generated by interfering two or more beams of optical radiation to generate an interference volume having periodic interference pattern(s). The interference patterns are recorded on a reticle blank using any of the various recording techniques, such as photographic films, photo-resist, etc.
  • the geometry of the periodic interference pattens is tightly controlled by the properties of the interfering optical beams. More specifically, the geometry is controlled by the wavelength of light, the wavefront variation, and the geometry of the exposure configuration (i.e., the relative beam angle of the optical radiation before and after interference). All of these factors can be controlled much more precisely than serially written e-beam or laser writing tools. Additionally, much larger reticle areas can be written in a single pass using holographic patterning. As such, writing errors that result from stitching together e-beam sub-fields are avoided entirely.
  • an optical system is characterized quickly and in a single exposure or imaging operation.
  • holographically patterned reticles can print linewidths that are much smaller than current reticle writing tools.
  • phase shifts in periodic structures can be precisely controlled.
  • Phase shift structures are valuable in the characterization of odd optical aberrations that produce feature shifts in the image plane.
  • the reticle is in a different plane than the plane from which data is acquired in image space.
  • the perpendicular from the reticle and/or image plane interceptor be non-collinear with the axis of the optical system.
  • FIG. 1A is a schematic illustration of a photolithographic system.
  • FIG. 2 is a perspective view of the reticle or object space.
  • FIG. 4 is a plane view illustrating a test reticle having a plurality of periodic structures or patterns thereon.
  • FIG. 5B is a plane view illustrating another type of grating or periodic pattern or structure.
  • FIG. 7 is a block diagram illustrating high-level method steps of an embodiment of the present invention.
  • FIG. 8A schematically illustrates a volume of space.
  • FIG.8B is a schematic plane view of an image formed on a photosensitive substrate.
  • FIG. 10A is a schematic plane view illustrating a reticle.
  • FIG. 10B is a schematic plane view illustration a portion of a reticle pattern.
  • FIG. 11 A is a schematic plane view of another embodiment of a portion of a pattern on a reticle.
  • FIG. 11B is a schematic perspective view illustrating detection of astigmatism based upon the embodiment illustrated in FIG. 11 A.
  • FIG. 14 is a perspective graphical view of an interferometer map illustrating detection of distortion or aberrations of an optical system in an embodiment of the present invention.
  • FIG. 15 is a graph illustrating the different distortions or aberrations that can be detected with an embodiment of the present invention.
  • FIGS . 16A-D graphically illustrate, in perspective, the different distortions or aberrations illustrated in FIG. 15.
  • FIG. 17 is a plane view of a photosensitive substrate illustrating an embodiment of the present invention used to obtain best focus of an optical system.
  • FIG. 18 is a graph illustrating detection of spherical aberrations in an embodiment of the present invention.
  • FIG. 19 A is a schematic plane view illustrating an embodiment of the present invention for determining optimum placement of a reticle for enhanced imaging.
  • FIG. 19B is a schematic plane view of a reticle utilized in the embodiment of the present invention illustrated in FIG. 19 A.
  • the Littrow angle is the angle at which electromagnetic radiation from the interferometer retro-diffracts to return to the interferometer.
  • the peaks of an intensity map acquired by the phase-shifting interferometer are the points of best focus of the optical system being characterized. These peaks comprise a ridge in the direction of the y axis. The meandering of this ridge in the direction of the x axis as the field is traversed in the direction of the y axis represents the field curvature.
  • the robustness of this procedure relies on its ability simultaneously to acquire intensity data at points throughout the volume of space 620. Calibration, scaling, and extraction of data are straightforward. This method uses the intensity of the retro-diffraction.
  • the image quality will vary along the depth of focus for the different linewidths. Accordingly, an envelope representing the image quality as a function of the depth of focus for each different linewidth section will shift depending upon any spherical aberrations.
  • different reticle portions can be utilized having different line patterns over portions of the reticle to detect a variety of different aberrations at different locations in the field. These different portions of reticle patterns can be incorporated in a single reticle to simultaneously detect and measure the field curvature and different aberrations.
  • FIG. 14 is a perspective view of an interferometric analysis or map of a resist covered or photosensitive substrate exposed with the image of a basket weave or interlaced or cross periodic pattern or grating.
  • an analysis could be performed by viewing the pattern in real time by using a demodulating device (such as demodulating device 24 as shown in FIG. IB).
  • the basket weave or cross periodic pattern or grating is a reticle having orthogonal lines over the entire field.
  • the entire field of the optical system can be characterized by exposing a reticle over the field onto a tilted photosensitive substrate.
  • the photosensitive substrate should be tilted so that the entire field falls within the depth of focus of the optical system. Because of the tilt, the x axis in FIG.
  • M' lies on the midpoint of a line 1333 midway between line A-A' and line
  • FIG. 18 illustrates the use of an embodiment of the present invention to detect spherical aberrations.
  • Curve or line 1402 represents the resist depth as a function of focus. Due to a tilt through focus when exposing a photosensitive substrate, the periodic pattern or grating formed on the photosensitive substrate by the processed resist has a varying depth. The depth is greatest at best focus and becomes smaller as focus degrades.
  • the asymmetry in curve or line 1402, identified at region 1404, is representative of spherical aberrations. Accordingly, the present invention can be applied to detect spherical aberrations in an optical system.
  • FIGS. 19 A and 19B illustrate another embodiment of the present invention for determining initial placement of a reticle in the optical system for obtaining optimized imaging.
  • a photosensitive substrate 1522 is exposed by a reticle 1516.
  • the image of the reticle is presented for viewing in real time by using a demodulating device (such as demodulating device 24 as shown in FIG. IB).
  • the reticle is tilted out of an x-y object plane about the x axis.
  • the photosensitive substrate 1522 is preferably out of the x-y plane about the y axis.
  • the position at which the locus of best focus position for each different linewidth cross represents the preferred position for the reticle to minimize aberrations, and in particular spherical aberrations.
  • the intersection of lines 1502 and 1504 represents the optimum position for the reticle 1506 to minimize spherical aberrations.
  • Line 1506 represents the location or plane of optimum position for the positioning of the reticle 1516 to obtain the best image or minimum spherical aberrations. For example, as illustrated along the left longitudinal edge of the photosensitive substrate in FIG. 19A, if the reticle 1516, in FIG.
  • the present invention can also obtain full field data in seconds, a relatively short time. This is an important feature in lithographic tools using deep UV and beyond because of the small line sizes and thermally varying time constants.
  • the ability of the present invention to utilize a full field exposure in a single shot eliminates alignment timing errors due to the scanning acquisition of data.
  • the use of the plurality of different feature sets having multiplexed feature orientations, sizes, and line types allows for the determination of focus position, astigmatism, field curvature and depth of focus. Additionally, the present invention can yield information on coma, spherical, and variation of coherence.
  • the present invention in consisting of multiplexed periodic features that are imaged by the imaging system to be tested and a lithographic recording process, including a metrology tool to analyze the printed images makes possible the rapid characterization of an optical system.
  • the feature sets can be a group or isolated variant line types, shapes, sizes and orientations.
  • the present invention images these feature sets through and beyond the depth of focus of the imaging system in a single exposure.
  • the envelope or feature quality through focus is printed and analyzed. This analysis can consist of full depth of focus data evaluation, as in the case of auto-correlation and cross-correlation analysis. Alternatively, the analysis can identify envelope maxima or minima asymmetry or slope. This is contrary to the prior techniques that analyze individual features at pre-determined and consequently non-optimum discrete focal positions.
  • the quality of particular feature sets through focus can be used to determine flat focus, field curvature, astigmatism, spherical aberration, partial coherence, distortion and coma, depending upon the feature type orientation and/or size selected.
  • astigmatism different line orientations can be interlaced down the field and read by a dark field or interferometric microscope.
  • different line orientations can be interlaced across the field and read by an interferometric microscope or atomic force microscope.
  • the features can be read using a full field interferometer.
  • a test reticle with a plurality of periodic patterns and other structures is used to characterize an optical system (such as a lens) under test.
  • an optical system such as a lens
  • the optical system 18 is imaged with the pattern on the test reticle 16, resulting in image data that is recorded on the substrate 22.
  • the substrate 22 is examined to retrieve image data that is subsequently processed to determine parameters for the optical system including: focus, field curvature, astigmatism, coma, focal plane deviation, spherical aberration, and coherence variation.
  • test reticle 16 Since the test reticle 16 is used to test the quality of the optical system 18, it is preferable that the patterns on test reticle 16 be as accurate as possible so that a true characterization can be made. More specifically, it is important that the lines and spaces of the gratings (e.g., see FIG. 4) on the test reticle have accurate dimensions and placement. If the grating are not accurate, then it is difficult to determine if aberrations recorded on the substrate 22 are caused by the optical system 18 or by the test reticle 16.
  • Conventional means for making reticles, including test reticles include e-beam writing tools and laser writing tools. These conventional techniques typically write sub-fields of a larger pattern that are subsequently stitched together to create the larger composite field pattern. When the sub-fields are stitched together, reticle writing errors can occur. At sub- 100 nm linewidths in very high numerical aperture (VHNA) lithographic tools, these writing errors have become a limiting factor in the ability to test optical imaging systems.
  • VHNA very high numerical aperture
  • the laser 2002 generates coherent optical radiation 2004.
  • the splitter 2006 splits the optical radiation 2004 into two or more beams 2008a,b.
  • Two beams 2008a,b are shown for ease of illustration. However, multiple beams 2008 could be generated, where the number of beams is dependent on the type of interference pattern that is desired.
  • the resulting beams 2011a,b have wavefronts that generate a desired interference pattern during subsequent beam interference.
  • the specific type of wavefront for each beam 2011 depends on the specific interference pattern that is desired.
  • Exemplary wavefronts include but are not limited to: cylindrical wavefronts, planer wavefronts, spherical wavefronts, etc. Specific wavefront combinations and associated interference pattens are discussed further herein.
  • the beams 2011a,b interfere to produce an interference volume 2012 having an associated interference pattern.
  • FIG. 20 illustrates two beam interference for ease of illustration. However, the scope of the invention includes multiple beam interference, where the number of beams depends on the type of interference pattern that is desired.
  • an optical system is tested using the holographic test reticle, such as the optical system 18 that was described in FIG.l.
  • holographic patterning is more accurate than e-beam techniques because the resulting interference pattern is determined by the wavelength of light, the wavefront variation of the interfering beams, and the geometry of the exposure configuration. All of these factors can be controlled more accurately than in conventional e-beam and laser writing techniques, and thereby reducing reticle writing errors that are associated with conventional techniques.
  • the periodic structures e.g., grating
  • the linewidth pitch uniformity can be precisely controlled, and therefore distortion is minimized.
  • variable pitch patterns can be produced with great accuracy. Therefore, an optical system can be tested over a precisely-controlled continuum of linesizes, line orientations, and pattern pitches.
  • phase shifts in periodic structures can be precisely controlled. Phase shifted gratings are useful for the characterization of odd optical aberrations in optical systems, which produce feature shifts in the image plane.
  • holographic patterning can print linewidths that are much smaller than the current reticle writing tools, including e-beam and laser writing tools. For example, e-beam techniques are currently limited to 100 nm and above, whereas holographic patterning can print linewidths that are sub-lOOnm and as low as 50 nm.
  • FIG. 22A illustrates an example of holographic reticle patterning (or writing) based on interference of two spherical beams.
  • optical expanders 2204a,b receive optical radiation beams 2202a and 2202b.
  • the expanders 2204a,b manipulate the beams 2202a,b to have expanding spherical wavefronts, represented as beams 2206a and 2206b.
  • the beams 2206a and 2206b interfere to produce an interference volume 2208 having a substantially linear grating pattern as shown.
  • the linear grating pattern is recorded on a reticle blank 2210.
  • the linewidth and spacing of the grating pattern (also called pitch uniformity) are tightly controlled by the wavelength of the beams, and the angle at which the beam interference occurs.
  • the optical wavelength is extremely accurate and stable. Therefore, the pitch uniformity of the resulting grating is also very accurate and stable, and improved over that achieved with e-beam or laser writing techniques.
  • spherical expanding beams are illustrated to create linear gratings for example purposes only, and are not meant to be limiting.
  • Other embodiments will be understood by those skilled in the arts.
  • long path length quasi-plane wave beams can be used to improve the pitch uniformity.
  • additional optics can be utilized to collimate the beams to produce plane waves.
  • linear gratings can be produced by interfering collimated light.
  • FIG. 22B illustrates a simulation associated with an interference pattern 2212 that is produced by spherical two beam interference.
  • the simulation represents the change in pitch uniformity over the pattern 2212.
  • the box 2214 in the center of the interference pattern 2212 highlights an area having constant pitch uniformity. In other words, the linewidths and spaces are substantially constant within the box 2214.
  • the box 2216 highlights an area of the pattern 2212 having a variable (but controlled) pitch uniformity. More specifically, the linewidths and spaces in the box 2216 are increasing, but at a known and controlled rate. This is known as a chirped grating. Similarly, other parts of the pattern 2212 have linewidths and spacing that are decreasing at a controlled rate.
  • FIGS. 23A-E illustrate holographic reticle patterning for generating an interference pattern having a chirped grating.
  • chirped gratings have a series of continuously variable lines and spaces, as further illustrated in FIGS. 23B-E.
  • Chirped gratings are useful for determining image distortion of an optical systems over multiple linewidths and spacings, without requiring multiple exposures.
  • holographic reticle configuration 2300 depicts an off-axis cylindrical and plane wave beam combination, which is useful for generating interference patterns that have a chirped grating.
  • Radiation beams 2310a,b having planer wavefronts, are projected onto the bottom of a reticle 2306, as shown.
  • a mirror 2302 projects radiation beams 2304a,b onto the reticle 2306 at angles ⁇ and ⁇ , relative to the beams 2310a,b.
  • the beams 2304a,b preferably have a cylindrical wavefront, and meet at a point 2308.
  • the beams 2310a,b and 2304a,b interfere to produce an interference volume having a chirped grating pattern, where the characteristics of the chirped grating are dictated by the geometry of the cylindrical divergence and the interfering beam wavelengths.
  • FIGS.23B-E illustrate exemplary chirped gratings. More specifically, FIG. 23B illustrates a cylindrical zone plate grating 2312, where the linewidths and spacings are a maximum at the center of the grating, and decrease from the center of the grating to the edge of the grating. FIG. 23C illustrates a reverse cylindrical zone plate grating 2314, where the linewidths and spacings are a minimum at the center of the grating and increase to maximum at edges of the grating.
  • FIG. 23D illustrates interlaced chirped grating 2316 composed of multiple chirped gratings 2318a-e.
  • the interlaced grating 2316 is generated by taking multiple exposures of the component gratings 2318, and moving the reticle blank in the y-direction between exposures.
  • the interlaced grating 2316 enables image distortion to be measured at multiple field points of the optical system under test, simultaneously.
  • FIG. 23E illustrates a circular zone plate array.
  • holographically generated chirped gratings are dictated by the geometry and wavelength of the interfering beams.
  • the holographically generated chirped gratings are continuous and smoothly varying across their extent.
  • discrete patterning methods typically vary the linewidth and pitch of a grating as a function of scanned, rastered, or pixelated patterning. These discrete serial methods suffer from temporal variations in patterning beam location, stage location, and stitching accuracies.
  • FIG. 23F illustrates focus determination of an optical system using the interlaced chirped grating 2316. More specifically, focus curves 2320a-e are generated by imaging an optical system under test (such as optical system 18 in FIG.1) using the interlaced chirped grating 2316. Each curve 2320 represents the depth of focus ( in the z-direction of FIG. 1 A) that corresponds to the linewidths in the adjacent grating 2318. One of the linewidths in the gratings 2318 is arbitrarily selected to provide a reference focus (such as linewidth 2322), and the depth of focus for the other linewidths are plotted relative to the reference focus, as shown.
  • a reference focus such as linewidth 2322
  • FIG. 24 illustrates an atomic force micrograph of an actual cross-grating 2400 that was patterned on a holographic test reticle.
  • the cross grating 2400 is viewed at an angle of 45 degrees, and has two sets of orthogonal lines (i.e., 2-fold geometry).
  • FIG. 25 illustrates a holographic hex pattern 2500 having lines in three different orientations (i.e., 3-fold symmetry), and therefore allowing image distortion at these orientations to be measured simultaneously. This allows the image distortion of an optical system to be measured at these three orientations, simultaneously.
  • the invention is not limited to 3-fold symmetry, as n-fold symmetry will be discussed below.
  • FIG. 26 illustrates a polygonal grating 2600 that is the result interfering combining multiple plane wave beams.
  • the grating 2600 is composed of intersecting lines in the x-y plane that intersect at the relative angles of 0, 45, 90, and 135 degrees.
  • the invention is not limited to this geometry.
  • multi-beam interference can be used to generate complex sub- micron geometries on a reticle that have 2-fold, 3-fold, 4-fold, and in general n-fold geometries.
  • These n-fold patterns can be used to probe optical system parameters that are dependant on line orientation.
  • the advantage of producing these pattens holographically is that the spatial relationships between the periodic structures are tightly constrained. Additionally, these n-fold patterns are valuable in decoupling the collection of distortion, coma, or other image shifting aberrations that are separable as azimuthally-dependent asymmetric aberrations in the pupil plane of the optical system.
  • the intersecting lines in the grating 2400 have a sinusoidal amplitude whose intensity varies according to the function : [sin (x+y) * sin (x-y) * sin (x) * sin (y)] 2 .
  • Other intensity distributions could be used, including binary on-off lines, as will be understood by those skilled in the arts. These other amplitude functions are within the scope and spirit of the present invention.
  • FIG. 27 illustrates a zone plate array 2700, which takes the n-fold geometry to the limit.
  • Zone plate array 2700 includes circles having variable linewidths and spacings (i.e., chirped). Because of the circular orientation of array 2700, image distortion for all possible line orientations can be measured simultaneously, and with a single test reticle.
  • the zone plate array 2700 is generated by combining/interfering two beams of optical radiation so as to create a spherical beam.
  • FIG. 28 illustrates holographic patterned gratings 2802-2806, which collectively depict examples of pitch change and phase change for periodic gratings. More specifically, gratings 2802 and 2804 depict pitch change because the linewidths and spacings (i.e., pitch) of the grating 2802 are much smaller than the pitch of the grating 2804. Gratings 2804 and 2806 depict phase change because the lines of the grating 2806 are shifted in the x-direction relative to the lines in the grating 2804.
  • FIG. 29 A illustrates a reticle with a holographic pattern having a constant pitch grating with a varying duty cycle.
  • a reticle 2900 has a constant pitch grating 2902.
  • the duty cycle of grating 2902 is a 1 : 1 line- to-space ratio
  • the duty cycle of grating 2902 is a 3:1 line-to-space ratio.
  • Having such a holographic pattern with a constant pitch on one reticle 2900 allows the entire pattern to be interferometrically interrogated at a single diffraction angle.
  • aberrations can be identified and decoupled based on the various induced image shifts and focus shifts produced as a function of the line-to-space duty cycle.
  • FIGS. 29B and 29C illustrate how the holographic pattern of reticle 2900 is formed.
  • FIG. 29B illustrates a uniform grating pattern 2908.
  • FIG. 29C illustrates a pattern with variation in exposure intensity 2910.
  • exposure intensity is greater at a bottom portion 2912 and lesser at a top portion 2914.
  • Exposure intensity between bottom portion 2912 and top portion 2914 varies continuously in a gradual transition between the values of these two portions 2912, 2914.
  • Holographic reticle pattern 2900 is formed by superimposing uniform grating pattern 2908 on the pattern with variation in exposure intensity 2910.
  • any of a variety of duty cycle patterns could be produced by superimposing a pattern with a variation in exposure intensity on a uniform grating pattern.
  • the pattern with the variation in exposure intensity is not limited to one in which the exposure intensity transitions from a high value to a low value across the span of the pattern.
  • FIG. 30 illustrates a phase control system 3000 for creating a controlled phase shift, such as the phase shift between the grating 2804 and 2806 in FIG.28.
  • the control system 3000 includes optical detectors 3004 and 3006, a control input 3008, and a difference module 3010.
  • the control system 3000 can be operated in a fringe locking capacity, and/or can be used to implement an intentional grating phase shift, based on the control signal 3008.
  • the optical detectors 3004 and 3006 are placed to measure light intensity at different points of a holographic interference pattern 3002, resulting in intensity signals 3005 and 3007.
  • the detectors 3004 and 3006 are optical detector diodes or equivalent devices that generate an electrical signal that is proportional to the intensity of the detected light.
  • the difference module 3010 receives the intensity signals 3005 and 3007, and the control signal 3008.
  • the difference module 3010 determines a difference signal 3011 by adding the control signal 3008 to the intensity signal 3005, and then subtracting the intensity signal 3007.
  • the control signal 3008 is substantially zero, and therefore the difference signal 3011 represents the difference between the light intensity that is measured by the detectors 3004 and 3006. If the difference signal 3011 is approximately zero, then the detectors 3004 and 3006 are receiving approximately the same light intensity, and therefore are monitoring the same corresponding location on each fringe. If the difference signal 3011 is not approximately zero, then the detectors 3004 and 3006 are not straddling an equivalent portion of a light fringe.
  • the difference signal 3011 is used to control a mirror, or a crystal, or another optic device (not shown) that phase shifts one of the interfering beams that was used to create the interference pattern 3002. If the difference signal 3011 is approximately zero, then no action is taken. If the difference signal 3011 is not zero, then an interfering beam is phase shifted in order to phase shift the interference (or fringe) pattern 3002. For fringe locking, the fringe pattern 3002 is phase shifted so that the detectors 3004 and 3006 will detect equivalent intensities of light, and therefore drive the difference signal 3011 to approximately zero. Fringe locking is useful for making small corrections due to vibrations, and other random disturbances, etc. In contrast to fringe locking, an intentional phase shift can be introduced in the fringe pattern 3002, even when signals 3005 and 3007 are equal, by introducing a non-zero control signal 3008, as discussed further below.
  • the phase control system 3000 can be incorporated into a reticle writing system 3100 to write a holographic test reticle having gratings with a controlled relative phase shift.
  • the reticle writing system 3100 is similar to the system 2000 (FIG. 20), with the addition of the phase controller 3000 and the phase shifting device 3102.
  • the phase controller 3000 analyzes the interference volume 2012, and generates the difference signal 3011 based on the interference volume 2012 and the control signal input 3008, as discussed above.
  • the difference signal 3011 controls the phase shifting device 3102 in the manipulation optics 2010, which phase shifts the beam 2011a and thereby produces a phase shift in the interference volume 2012 that is based on the control signal 3008.
  • the interference volume 2012 can be phase shifted by various amounts by changing the control signal 3008.
  • the phase shifting device 3102 can be a mirror, a crystal, or another optic device that is useful for phase shifting an optical beam.
  • Other specific embodiments for the device 3102 include the following: a reflective, refractive, or diffractive array; an electro-deformable device; an acousto-optic device; anano-actuated optic device such as, but not limited to, a piezo-driven mirror or a bimorph-driven mirror; a nano-def ormable mirror array that is reflective, diffractive, or refractive ; a MEMS mirror array; an electro-deformable hologram; and an electronic fringe-locking system.
  • phase shifted gratings can be generated using the system 3100, by exposing the reticle blank multiple times using different voltages for the control signal 3008.
  • Flowchart 3200 (FIG. 32) describes the generation of multiple phase shifted gratings in further detail.
  • step 3202 the voltage of the control signal 3008 is set to a reference voltage.
  • step 3204 a reticle blank is exposed with a holographic interference volume to record a reference grating that corresponds to the reference voltage.
  • step 3206 the reticle blank is moved in a direction that is perpendicular to the desired phase shift of the grating. For example, in FIG.28, if grating 2804 was printed first, then the reticle would be moved in the y direction, to print the grating 2806.
  • step 3208 the voltage of the control signal 3008 is changed to effect a phase shift in the holographic interference volume
  • step 3210 the reticle blank is re-exposed with the (phase shifted) holographic interference volume to record a grating that is phase shifted relative to the reference grating that was generated in step 3204.
  • the steps 3206-3210 can be repeated multiple times to generate multiple gratings having a relative phase shift. Using this technique, extremely accurate phase shifts between gratings can be realized. In embodiments, a phase-shift of minute fractions of a linewidth can be achieved. For sub-micron linewidths, it is possible to achieve a controlled phase shift in the angstrom range.
  • test reticles that are described herein are preferably utilized to test optical systems.
  • the optical system 18 is imaged with a test reticle 16, where the test reticle 16 can be a holographically generated test reticle.
  • the resulting image data is recorded on a photosensitive substrate 22, which can be subsequently analyzed to extract information that characterizes the optical system 18.
  • the resulting image data can be presented for viewing in real time by using a demodulating device.
  • the photosensitive substrate 22 is analyzed using interferometric techniques to determine properties of the optical system under test.
  • the resulting interferogram represents changes in a phase front of light that is interferometrically diffracted off the exposed substrate 22.
  • FIG.33 illustrates an example interferogram 3300 that represents a phase front of the diffracted light for a 3 x 3 field array of an optical device under test.
  • the interferogram 3300 is composed of nine blocks (corresponding to a 3 x 3 array) that are delineated by homs, such as exemplary hom 3302.
  • Each block is characterized by a tilt and piston, which quantify the aberrations and distortion in the array field of the optical system under test.
  • Non-uniform distortion parameters can be analyzed based on local pistons and tilts. More specifically, the tilt refers to the angle of the block and represents the magnification of the reflected light and the telecentricty of the optical system under test.
  • the piston refers to the height of the block and represents translation differences of the reflected phase front and therefore phase shift caused by the optical system under test.
  • the distortions and aberrations for an optical system can be plotted vs. optical linewidth.
  • graph 3400 (FIG. 34) illustrates coma induced distortion vs. optical linewidth.
  • Other optical system characteristics can be quantified and plotted vs. optical linewidth. These include, but are not limited to: Zemike aberrations, focus, field curvature, astigmatism, coma, distortion, telecentricity, focal plane deviation, spherical aberrations, and coherence variation.
  • non-uniform distortion parameters can be detected as a function of variation in linewidth.
  • a non-linear phase front can be realized on a single holographic reticle by using a chirped grating structure.
  • Graph 3400 shows as an example of how image shifts can occur as a function of linewidth and aberration type.
  • Graph 3400 and similar graphs prepared for other optical system characteristics are prepared from data obtained at the best focus position of the photolithographic system.
  • the magnitude of the image offsets are greatly influenced by the partial coherence (PC) of the optical illumination used to image the lithographic features.
  • FIGS. 35A and 35B illustrate how partial coherence affects the image offsets.
  • Graph 3500A (FIG. 35A) illustrates image shift as a function of focus for a variety of linewidths where the partial coherence of the optical illumination is 0.6.
  • Graph 3500B (FIG.
  • 35B illustrates image shift as a function of focus for a variety of linewidths where the partial coherence of the optical illumination is 0.3.
  • comparing the relative shift differences due to the different partial coherence conditions is another method of deconvolving higher order aberrations from lower order ones.
  • Table 3600 (FIG. 36) illustrates this pattern.
  • Table 3600 illustrates the relationship between linewidth and order of diffraction for different diffraction angles.
  • the diffraction angles are represented as letters. For example, consider a reticle that has linewidths with dimensions of 100 nm, 200 nm, 300 nm, 400 nm, and 600 nm. In this case, the second order diffraction of the 200 nm linewidth would be at the same angle as the first order diffraction of the 100 nm linewidth.
  • the third order diffraction of the 600 nm linewidth would be at the same angle as the first order diffraction of the 200 nm linewidth.
  • a reticle with a set of linewidths can be measured for relative image shifts at the same interferometric angle. Under test conditions, this allows for all data to be collected at a single sample angle. This improves the speed at which tests can be conducted. It also improves the robustness and sensitivity of the data collected.

Abstract

L'invention concerne un système optique caractérisé en ce qu'il est obtenu rapidement et aisément en une seule phase d'acquisition par obtention de données-image dans un volume d'espace image. Un réticule et un plan image sont positionnés obliquement l'un par rapport à l'autre, de sorte qu'un réticule ayant une pluralité de jeux de caractéristiques dessus, y compris des configurations ou des réseaux gravés périodiques, soit représenté dans un volume d'espace, y compris la profondeur de foyer. Des instruments métrologiques sont utilisés pour analyser l'image détectée ou enregistrée dans un volume d'espace à travers la profondeur de foyer en une seule étape ou exposition afin de déterminer les caractéristiques d'imagerie d'un système optique. Le foyer, la courbure de champ, l'astigmatisme, les déviations de plan sphérique, de coma et/ou de plan focal peuvent être déterminées. L'invention s'applique notamment à la fabrication de semi-conducteurs et aux techniques photolithographiques qu'elle implique, et permet de caractériser rapidement un système optique en une seule exposition, avec une qualité de données extrêmement améliorée et une couverture continue de l'ensemble de l'espace des paramètres. Dans certains modes de réalisation, le réticule d'essai est produit par holographie, en faisant interférer au moins deux faisceaux de rayonnement optique. Le modèle d'interférence qui en résulte est enregistré sur un réticule et est utilisé pour tester le système optique. La géométrie du modèle d'interférence holographique est étroitement surveillée par les propriétés des faisceaux en interférence et s'avère de ce fait nettement plus précise que les techniques traditionnelles d'écriture de réticules.
EP01957171A 2000-07-19 2001-07-19 Systeme et procedes pour caracteriser des systemes optiques a l'aide de reticules holographiques Withdrawn EP1301830A2 (fr)

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AT414285B (de) * 2004-09-28 2006-11-15 Femtolasers Produktions Gmbh Mehrfachreflexions-verzögerungsstrecke für einen laserstrahl sowie resonator bzw. kurzpuls-laservorrichtung mit einer solchen verzögerungsstrecke
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KR100886897B1 (ko) 2009-03-05
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KR20020072531A (ko) 2002-09-16
KR100956670B1 (ko) 2010-05-10
WO2002006899A3 (fr) 2002-06-20
JP2004504634A (ja) 2004-02-12
JP4599029B2 (ja) 2010-12-15
WO2002006899A2 (fr) 2002-01-24

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