CN101236362A - Photo-etching machine projection objective wave aberration on-line detection method - Google Patents

Photo-etching machine projection objective wave aberration on-line detection method Download PDF

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CN101236362A
CN101236362A CNA2008100570601A CN200810057060A CN101236362A CN 101236362 A CN101236362 A CN 101236362A CN A2008100570601 A CNA2008100570601 A CN A2008100570601A CN 200810057060 A CN200810057060 A CN 200810057060A CN 101236362 A CN101236362 A CN 101236362A
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slit
interferometer
projection objective
circular hole
wave aberration
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CN101236362B (en
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李艳秋
刘克
刘丽辉
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Beijing Institute of Technology BIT
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Beijing Institute of Technology BIT
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    • 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

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Abstract

The invention relates to an on-line detection method for detecting the wave aberration of a projection objective of a photoetching machine. The on-line detection, revising, and controlling are done to the wave aberration of the projection objective by integrating an interferometer device on the photoetching machine. The interferometer device is a point-diffraction interferometer or a slit-diffraction interferometer and is provided with two measuring modules: a PSI measuring module and an FTM measuring module. The PSI measuring module adopts phase shifting interferometry with high measuring precision and is mainly used to detect the error calibration in an interferometer device system; the FIM measuring module adopts fourier transform method to treat with interference fringes with high measuring speed, and is mainly used to on-line detect and control the wave aberration of the projection objective. The method improves the measuring precision without reducing the measuring speed, and improves the measuring precision and reproducibility of the interferometer device by adopting a higher quality spherical reference wave to calibrate the systematic error caused by each component of the interferometer device without reducing the contrast ratio of the interference fringes.

Description

Photo-etching machine projection objective wave aberration on-line detection method
Technical field
The present invention relates to the optical property detection method of projection optical system, particularly photo-etching machine projection objective wave aberration on-line detection method.
Background technology
Use projection aligner in the preparation process of large scale integrated circuit, the pattern on the mask is being scribbled on the silicon chip of photoresist through the projection objective reduced projection.Along with the application of resolution enhance technology such as phase shifting mask, off-axis illumination, process factor is being approached the limit of technology gradually, and is more and more higher to the requirement of the control of characteristic dimension and alignment precision.The wave aberration of projection objective, particularly senior aberration wherein are more and more outstanding to the influence of characteristic dimension departure.Therefore, be necessary to develop the on-line measuring device of projection objective wave aberration, carry out online detection of quick, high-precision wave aberration and correction.
Traditional projection objective aberration measurement method is imaged on pattern specific on the test mask plate on the image planes of projection objective usually, and the employing scanning electron microscopy measurement is developed in the picture on the silicon chip, calculates the aberration data of projection objective according to measurement result.This method need be developed to silicon chip, so Measuring Time is longer, and because the error of technologies such as gluing, development in the measuring process, measuring accuracy is lower.For fear of these problems, people have proposed to utilize the method for interferometry, dispose interferometer on litho machine, and the wave aberration of projection objective is carried out online detection.The interferometric method of the lithographic equipment supplier of main flow employing comprises in the world, point-diffraction interferometer (Point Diffraction Interferometer, PDI), slit diffraction interferometer (Line Diffraction Interferometer, LDI) and shearing interferometer (Lateral ShearingInterferometer, LSI) or the like.The method of aforementioned interferometry has advantages such as detection speed is fast, precision is high, measuring repeatability is good; And can be integrated in the litho machine system, carry out the online detection of full visual field wave aberration of projection objective, obtain the wave aberration that 36 Zernike coefficients of each visual field point are represented; And, carry out the on-line correction and the control of wave aberration according to 36 Zernike coefficients of each visual field point that detection obtains.Aforementioned interferometric method is the main developing direction of wave aberration of photo-etching machine projection objective detection technique from now on.
In United States Patent (USP) 2006/0262323, propose, PDI or LDI are installed on litho machine, the wave aberration of projection objective is carried out online detection.In the aforementioned patent, the measuring principle of PDI is, places mask plate on the image planes of projection objective, is carved with diameter circular hole and bigger window less than aforementioned projection objective system diffraction limit resolution on the mask plate; Circular hole produces the ideal ball ground roll as the reference ripple to projection objective outgoing beam generation diffraction; Window does not exert an influence to the projection objective outgoing beam, and the window outgoing beam carries the information of projection objective wave aberration as test waves; Utilize the interferogram of photoelectric sensor such as CCD collecting test ripple and reference wave; Utilize interference fringe Processing Algorithm such as phase extraction, phase unwrapping and corrugated fit, calculate multinomial 36 projection objective wave aberrations that the Zernike coefficient is represented.In the aforementioned patent, LDI is similar to the principle of PDI, adopts slit to replace circular hole, utilizes slit to projection objective outgoing beam generation diffraction, produces the ideal ball ground roll as the reference ripple on the one dimension direction of space; Reference wave interferes with the test waves of carrying projection objective wave aberration information of window transmission, forms interference fringe; By twice measurement on the orthogonal space direction, obtain two width of cloth interferograms on the orthogonal directions; Utilize interference fringe Processing Algorithm such as phase extraction, phase unwrapping and corrugated fit, calculate the projection objective wave aberration that 36 Zernike coefficients are represented.
Adopt PDI or LDI interferometric method in the aforementioned patent to detect projection objective wave aberration, owing to utilize circular hole or the slit filtering of size less than aforementioned projection objective diffraction limit resolution, cause system's light intensity transmitance lower, the contrast of interference fringe is relatively poor, and noise in interferogram is bigger.Can have a strong impact on the precision of aforementioned interference fringe Processing Algorithm like this, the projection objective wave aberration repeatable accuracy that 36 Zernike coefficients that cause calculating are represented descends.Adopt Moire fringe technique to carry out the processing of interference fringe in the aforementioned patent, it is identical with the interferogram that collects that this method utilizes computer mould to draw up carrier frequency, and several simulation interferograms with fixed skew carry out phase shift and calculate, in fact belong to a kind of single width interferogram treatment technology, detection speed is very fast.
Movable phase interfere art (Phase Shifting Interferometry, PSI) be that the locking phase Detection Techniques in the Communication Theory are introduced in the interferometry, orderly phase shift is introduced in stepping by phase shifting equipment between two coherent lights of interferometer, the sampling of carrying out multi-frame interferometry figure can greatly suppress the influence of noise in interferogram, under the bad situation of interference fringe contrast, also can reach higher duplicate measurements precision.But PSI need control the phase shifting equipment stepping and gather multi-frame interferometry figure, and detection speed is relatively slow.(Fourier Transform Method is a kind of frequency domain interference fringe disposal route FTM) to the Fourier transform method, and measuring accuracy is higher, and only needs a width of cloth carrier wave figure, and detection speed is very fast, is fit to very much carry out online detection.
Summary of the invention
The technical issues that need to address of the present invention are: a kind of quick, high-precision projection objective wave aberration on-line detection method is provided.
The technical solution adopted in the present invention is: integrated interferometer device on litho machine, carry out online detection, correction and the control of projection objective wave aberration.Described interferometer is point-diffraction interference (PDI) or slit diffraction interferometer (LDI), possesses two kinds of measurement patterns: PSI measurement pattern and FTM measurement pattern.The PSI measurement pattern adopts the movable phase interfere art, and measuring accuracy is higher, is mainly used in described interferometer systematic error timing signal; The FTM measurement pattern adopts the Fourier transform method to handle interference fringe, and measuring speed is very fast, mainly uses when online detection of projection objective wave aberration and control.
The invention provides a kind of photo-etching machine projection objective wave aberration on-line detection method, the system that described method is used comprises: the light source that is used to produce projected light beam; Be used to adjust the beam lighting visual field that described light source sends and the illuminator of partial coherence factor; Mask pattern can be imaged on the projection objective on the silicon chip; Can carry described mask and pinpoint mask work stage; Can carry described silicon chip and pinpoint silicon slice workpiece platform; The interferometer of the described projection objective wave aberration of the online detection of energy.
In above system, interferometer is point-diffraction interferometer or slit diffraction interferometer.Interferometer comprises: the beam splitting arrangement that the light beam that is used for that described light source is sent carries out beam splitting, as grating; Be used to drive described beam splitting arrangement is introduced orderly phase shift between test waves and reference wave phase shifting equipment, as piezoelectric ceramics micrometric displacement platform; Be used to stipulate the object space mask plate of measured visual field point; Be used to produce picture side's mask plate that test waves and sphere reference wave and described interferometer systematic error are demarcated; Be used to gather the photoelectric sensor of described test waves and sphere reference wave interference fringe, as CCD; Be used to preserve the storer of the fringe intensity information that described photoelectric sensor gathers; Be used for arithmetical unit according to the adjustment amount of each compensator in the described interferometer systematic error of described storer data computation, described projection objective wave aberration and the described projection objective; Be used for coming aberration correction, and control the controller that described phase shifting equipment stepping realizes phase shift according to each compensator adjustment of the described projection objective of Data Control that described arithmetical unit calculates.
Described interferometer possesses two kinds of measurement patterns: carrying out described interferometer systematic error timing signal, adopting the PSI measurement pattern; When carrying out online detection of described projection objective wave aberration and control, adopt the FTM measurement pattern.Wherein the PSI measurement pattern adopts the movable phase interfere art, utilizes the stepping of described phase shifting equipment to obtain multi-frame interferometry figure, and measuring accuracy is higher; The FTM measurement pattern adopts the Fourier transform method to handle interference fringe, only needs to gather a width of cloth interferogram, and measuring speed is very fast.
Described interferometer has system calibrating error function, can demarcate the systematic measurement error that interferometer itself is introduced.
Described picture side mask plate has the wave aberration detecting element and systematic error is demarcated element.The wave aberration detecting element of described picture side mask plate is made up of circular hole (or slit) and window; The size of circular hole (or slit) less than
Figure S2008100570601D00041
Produce reference wave; Fenestra is of a size of
Figure S2008100570601D00042
Produce test waves; Wherein λ is the wavelength of described light source, NA iFor projection objective as number formulary value aperture, σ is the partial coherence factor of described illuminator, f is the spatial frequency range of the projection objective emergent pupil wave aberration measured of described interferometer.
The systematic error of described picture side mask plate is demarcated element and is made up of two circular holes (or slit); First circular hole (or slit) is identical with the circular hole (or slit) of wave aberration detecting element on the picture side mask plate, size less than The size of second circular hole (or slit) less than
Figure S2008100570601D00052
Be used for producing the higher spherical wave reference ripple of quality, to demarcate the systematic error of described interferometer.
Described photo-etching machine projection objective wave aberration on-line detection method may further comprise the steps: at the illumination field of view and the partial coherence factor of the described illuminator of litho machine adjusted that described interferometer is housed, make described interferometer can collect the higher interference fringe of contrast; Under the PSI measurement pattern, utilize the systematic error on the described picture side mask plate to demarcate element, the systematic error of demarcating described interferometer; Under the FTM measurement pattern, utilize the wave aberration detecting element of described picture side mask plate, carry out the online detection of described projection objective wave aberration; Utilize the controller of described interferometer, finish the aberration correction of described projection objective automatically.
With respect to detection method in the United States Patent (USP) 2006/0262323, the present invention adopts the interferometer with two kinds of measurement patterns to carry out the online detection of wave aberration: carrying out interferometer systematic error timing signal, adopting the PSI measurement pattern; When carrying out online detection of projection objective wave aberration and control, adopt the FTM measurement pattern.Under the prerequisite that does not reduce detection speed, improved measuring accuracy.In addition, the interferometer systematic error scaling method that the present invention proposes, under the prerequisite that does not reduce the interference fringe contrast, adopt the higher sphere reference wave of quality to demarcate the systematic error that each components and parts of interferometer are caused, improved the measuring accuracy and the repeatability of interferometer itself.
Description of drawings
Fig. 1 is according to the litho machine of the embodiment of the invention and the structural representation of interferometer;
Fig. 2 is beam splitting arrangement 201 synoptic diagram according to the embodiment of the invention 1;
Fig. 3 is object space mask plate 203 synoptic diagram according to the embodiment of the invention 1;
Fig. 4 is picture side's mask plate 204 synoptic diagram according to the embodiment of the invention 1;
Fig. 5 is beam splitting arrangement 201 synoptic diagram according to the embodiment of the invention 2;
Fig. 6 is object space mask plate 203 synoptic diagram according to the embodiment of the invention 2;
Fig. 7 is picture side's mask plate 204 synoptic diagram according to the embodiment of the invention 2;
Embodiment
The invention will be further described below in conjunction with the drawings and specific embodiments.
Fig. 1 is according to the litho machine of the embodiment of the invention and the structural representation of interferometer.The chief component of litho machine 100 is: light source 101, illuminator 102, mask plate 103, mask work stage 104, projection objective 105, silicon chip 106 and silicon slice workpiece platform 107.The chief component of interferometer is: beam splitting arrangement 201, phase shifting equipment 202, object space mask plate 203, as square mask plate 204, photoelectric sensor 205, storer 206, arithmetical unit 207 and controller 208.Integrated interferometer device 200 on litho machine 100 is realized the online detection of wave aberration, correction and control to projection objective 105 in the litho machine 100.
At first set forth the principle of work of litho machine 100.The light that light source 101 sends is through after the illuminator 102, and illumination is on mask plate 103, and by projection objective 105, in the mode of stepping-scanning, reduced projection realizes the transfer of pattern on the silicon chip 106 that scribbles photoresist with the pattern on the mask plate 103.Light source 101 is a quasi-molecule laser source, and for example, wavelength is about the ArF excimer laser of 193nm or the KrF excimer laser that wavelength is about 248nm.Illuminator has the field stop of regulating the illumination field of view size and adjusts the illuminating bundle distribution, thereby adjusts the aperture diaphragm of illumination section coherence factor.In addition, illuminator also comprises a large amount of other optical elements, as fly_eye lens array etc., and the comparatively ideal homogeneity that has on mask plate 103 of throwing light on like this.The mask plate 103 that is carved with circuit pattern to be transferred is supported and is driven by mask work stage 104; The silicon chip 106 that scribbles photoresist is supported and is driven by silicon slice workpiece platform 107.Mask plate 103 and silicon chip 106 are positioned on the optical conjugate face of projection objective 105.Mask work stage 104 and silicon slice workpiece platform 107 be with different synchronization of rate scanning motions, with the mode of stepping-scanning pattern with mask plate 103, by projection objective 105 accurately projection transfer on the silicon chip 107 that scribbles photoresist.The wave aberration of projection objective 105, particularly senior aberration wherein can have a strong impact on the control accuracy of the pattern characteristics size of transfer.
Embodiment 1
In the present embodiment, integrated interferometer 200 based on the point-diffraction interference principle carries out online detection to the wave aberration of projection objective 105 on litho machine 100.As shown in Figure 1, interferometer 200 structurally is made up of 200a and 200b two parts: 200a is integrated on the mask work stage 104, and 200b is integrated on the silicon slice workpiece platform 107.Set forth the principle of work of interferometer in the present embodiment below.The light beam that light source 101 sends at first passes through illuminator 102 shapings, shine on the beam splitting arrangement 201, in the present embodiment, beam splitting arrangement 201 is a binary raster, adopt the preparation of electron beam exposure chrome mask plate, base material is a fused quartz, and light blocking layer is a crome metal, be carved with 1: 1 periodic structure of dutycycle on the chromium layer, as shown in Figure 2.Light beam forms several orders of diffraction by behind the periodic structure of binary raster on object space mask plate 203.Phase shifting equipment 202 is a piezoelectric ceramics micrometric displacement platform, is used for driving binary raster stepping on perpendicular to the direction of grating line, thereby introduces phase differential in the senior diffraction light of binary raster.
Object space mask plate 203 is supported and is driven by mask work stage 104, the same electron beam exposure chrome mask plate that adopts prepares, base material is a fused quartz, light blocking layer is a crome metal, be carved with a circular hole 209a and a bigger window 209b on the chromium layer, as shown in Figure 3, be used for selecting two specific orders of diffraction time to enter projection objective as test waves and reference wave.Circular hole 209a plays filter action to incident beam, eliminates illuminator 102 grades and is positioned at object space mask plate 203 aberration that optical element caused before, and diffraction produces spherical wave and enters projection objective to be measured 105.The diameter d of circular hole 209a oSatisfy formula (1), less than the resolution of incident beam diffraction limit.
d o ≤ λ 2 NA o σ - - - ( 1 )
In the formula (1), λ is the wavelength of light source 101, NA oBe the object space numerical aperture of projection objective 105, σ is the partial coherence factor of illuminator 102, can calculate by formula (2).
σ = NA il NA o - - - ( 2 )
In the formula (2), NA IlBe the numerical aperture of illuminator 102 in mask plate 103 sides.By formula (1), (2) as can be seen,, can increase the diameter of circular hole 209a, improve system's transmitance of interferometer by reducing the σ of illuminator 102, thus the contrast of the interference fringe that raising photoelectric sensor 205 collects.
The width of window 209b influences its transmitted beam light intensity, thereby influences the contrast of interference fringe.Should select the optimal width of window 209b according to the contrast of interference fringe.
Be positioned on the optical conjugate face of projection objective 105 as square mask plate 204 and object space mask plate 203.Picture side's mask plate 204 is supported and is driven by silicon slice workpiece platform 107, the same electron beam exposure chrome mask plate that adopts prepares, and base material is a fused quartz, and light blocking layer is a crome metal, be carved with wave aberration detecting element 210 and systematic error on the chromium layer and demarcate element 211, as shown in Figure 4.
Wave aberration detecting element 210 as square mask plate 204 comprises circular hole 210b and window 210a.The outgoing beam of window 209b is through behind the projection objective 105 on the object space mask plate 203, incide on the circular hole 210b, this incident beam is the instrument aberration information of carrying projection objective 105 not, also carry the aberration information of illuminator 102 components and parts such as grade simultaneously, after circular hole 210b filtering, diffraction produces the sphere reference wave.The diameter d of circular hole 210b I1Satisfy formula (3), less than the resolution of incident beam diffraction limit, NA iBe projection objective 105 picture number formulary value apertures.
d i 1 ≤ λ 2 NA i σ - - - ( 3 )
The outgoing beam of circular hole 209a is through behind the projection objective 105 on the object space mask plate 203, incide on the window 210a, this incident beam only carries the aberration information of projection objective 105, window 210a does not make a difference to it, produce test waves and interfere, on photoelectric sensor 205, form interference fringe with the sphere reference wave that circular hole 210b diffraction produces.The width w of window 210a iThe spatial frequency f that depends on projection objective emergent pupil wave aberration to be measured, as the formula (4).
w i 1 = 2 fλ NA i - - - ( 4 )
The systematic error of picture side's mask plate 204 is demarcated element 211 and is made up of two circular holes.The diameter of circular hole 211b satisfies formula (3), with the diameter d of circular hole 210b I1Identical, to window 209b outgoing beam generation diffraction, the sphere reference wave of generation is also identical.The diameter d of circular hole 211a I2Satisfy formula (5), resolution less than projection objective 105 diffraction limits, to circular hole 209a outgoing beam generation diffraction, produce the higher sphere reference wave of quality, interfere with the sphere reference wave that circular hole 211b produces, on photoelectric sensor 205, form interference fringe, demarcate the systematic error of interferometer 200.
d i 1 ≤ λ 2 NA i σ - - - ( 5 )
Photoelectric sensor 205 can adopt the ccd sensor that is operated in the deep ultraviolet wave band, is integrated in the silicon slice workpiece platform 107, is used for surveying interference fringe, the strength information of recording interference fringe, and be kept in the storer 206.Arithmetical unit 207 has the interference fringe processing, systematic error is demarcated and area of computer aided is debug series of algorithms such as algorithm, wave aberration according to each visual field point of fringe intensity information calculations projection objective of each visual field point of projection objective of storage in the storer 206, and the adjustment amount of each compensator of projection objective, debug aberration correction by 208 pairs of projection objectives of controller again.
When using wave aberration detecting element 210 to detect the wave aberration of projection objective 105, interferometer 200 adopts the FTM measurement pattern, utilizes the Fourier transform method, extracts phase information from the strength information of interference fringe.The Fourier transform method is a kind of frequency domain interference fringe disposal route, and key step comprises: the denoising of interference fringe and continuation; Two-dimension fourier transform obtains the striped frequency spectrum; Filter filtering also moves to the frequency domain center; Calculate the wrapped phase on corrugated at last by inverse Fourier transform.By phase unwrapping, the wrapped phase on corrugated is expanded into continuous phase place, obtain the wave aberration of this visual field point of projection objective, and fit algorithm table with the corrugated and be shown as 36 Zernike coefficients.The FTM measurement pattern only needs a width of cloth interferogram just can calculate the wave aberration that 36 Zernike coefficients of 105 1 visual field points of projection objective are represented, detection speed is very fast; By selecting denoising preferably and continuation algorithm, algorithm filter and phase-unwrapping algorithm, FTM can reach very high measuring accuracy.Use wave aberration detecting element 210 detected wave aberration W 1, not only comprise the wave aberration W of projection objective 105 PO, also comprise the systematic error of interferometer 200, as the formula (6).
W 1＝W PO+W R1+W T1+W T2+W S (6)
In the formula (6), W R1Being the residual aberration of sphere reference wave after the circular hole 210b filtering, mainly is because the fused quartz substrate that circular hole 210b processing circularity deficiency and light beam see through as square mask plate 204 causes; W T1Being the residual aberration of spherical wave after the 209a filtering of hole, mainly is because circular hole 209a processing circularity deficiency and light beam see through the fused quartz substrate of object space mask plate 203 causes; W T2When seeing through window 210a for test light, the error that is caused by fused quartz substrate as square mask plate 204; W SBe the systematic error that interferometer 200 each components and parts are caused, mainly comprise system's how much comas of interferometer 200, the processing of grating 201 and debug error and the special sensor 205 of photoelectricity debug aberration that error causes etc.The said system error can exert an influence to the measuring accuracy of interferometer.
Using system error calibration element 211 is demarcated the interferometer system error, can improve the accuracy of detection of interferometer effectively.Carrying out the systematic error timing signal, owing to adopt circular hole 211a to replace window 210a, cause system's transmitance to descend, there is bigger noise in the interferogram that photoelectric sensor 205 collects, the contrast of interference fringe will directly be influenced, need to adopt the PSI measurement pattern, utilize the movable phase interfere art to carry out high-precision separating mutually and calculate, suppress the interferogram The noise.Simultaneously, under the PSI measurement pattern, it is d that systematic error demarcation element 211 has adopted diameter I2The circular hole 211a systematic error of demarcating interferometer 200, eliminated circular hole 210b diameter d under the FTM measurement pattern I1Increase the influence of the reference wave quality decline that is caused, thereby improved the measuring accuracy and the repeatability of interferometer 200.
Movable phase interfere is realized by following steps in interferometer 200: at first utilize controller 208 to drive silicon slice workpiece platform 107 and move, make circular hole 211a and 211b aim at separately incident beam respectively, photoelectric sensor 205 can collect the higher interferogram of contrast, and is stored in the storer 206; Phase shifting equipment 202 drives gratings 201 stepping on perpendicular to the direction of grating 201 grooves, thereby introduces phase differential in the senior diffraction light of binary raster; Utilize photoelectric sensor 205 to gather interferogram, be stored in the storer 206; Repeat above step, the interferogram of several phase shifts of row storage; Utilize multi-frame interferometry figure phase extraction algorithms to separate phase, obtain the wrapped phase on corrugated; By phase-unwrapping algorithm, the wrapped phase on corrugated is expanded into continuous phase place, and fit algorithm table with the corrugated and be shown as 36 Zernike coefficients.The corrugated phase place W that above step calculates 2Be the corrugated phase differential between the diffraction spherical wave of circular hole 211a and circular hole 211b, as the formula (7).
W 2＝W R1+W R2+W T3+W S (7)
In the formula (7), W R2Residual aberration for sphere reference wave after the circular hole 211a filtering; W T3For light beam through circular hole 211a diffraction after, the error that is caused as the fused quartz substrate of square mask plate 204 through approximate, can be thought W T3≈ W T2
Interferometer 200 systematic errors are demarcated and are passed through W 1And W 2Corresponding Zernike coefficient subtract each other and finish, the projection objective 105 wave aberration W that finally recorded, as the formula (8).
W?W 1?W 2≈W PO-W R2+W T1 (8)
After the systematic error demarcation, eliminated the systematic error W of interferometer 200 S, only comprise error W among the testing result W R2And W T1Because circular hole 211a diameter d I2Diameter d less than circular hole 210b I1, higher through the sphere reference wave quality that produces after the circular hole 211a filtering, can release W R2＜W R1, further improved the measuring accuracy of interferometer 200.
The step of the photo-etching machine projection objective wave aberration on-line detection method that present embodiment proposes is summarized as follows:
1) illumination field of view and the partial coherence factor σ of adjusting illuminator 102 make interferometer 200 can collect the higher interference fringe of contrast;
2) under the PSI measurement pattern, utilize as the systematic error of square mask plate 204 and demarcate element 211, demarcate the systematic error of interferometer 200;
3) under the FTM measurement pattern, utilization is as the wave aberration detecting element 210 of square mask plate 204, carry out the online detection of projection objective 105 full visual field wave aberrations, obtain the wave aberration that 36 Zernike of projection objective 105 each visual field points represent, and the adjustment amount of projection objective 105 each compensators;
4) utilize the controller 208 of interferometer 200, finish the aberration correction of projection objective 105 automatically.
Embodiment 2
In the present embodiment, integrated interferometer 200 based on the slit diffraction principle of interference carries out online detection to the wave aberration of projection objective 105 on litho machine 100.Slit diffraction interferometer in the present embodiment is similar with the point-diffraction interferometer principle among the embodiment 1, similar, systematic error scaling method and wave aberration detection method are similar, difference have following some.
On the interferometer measurement principle, present embodiment adopts the circular hole among the slit replacement embodiment 1, utilize slit to projection objective outgoing beam generation diffraction, on the one dimension direction of space, produce the ideal ball ground roll as the reference ripple, by twice measurement on the orthogonal space direction, obtain the wave aberration of projection objective;
On the structure of interferometer 200, the difference of present embodiment and embodiment 1 has the following aspects:
1) beam splitting arrangement 201 is a binary raster, and the groove direction is mutually orthogonal both direction, as shown in Figure 5.
2) phase shifting equipment 202 is a two-dimensional piezoelectric pottery micrometric displacement platform, is used for driving binary raster stepping on perpendicular to two orthogonal directionss of grating line, thereby introduces phase differential in the senior diffraction light of binary raster.
3) the chromium layer of object space mask plate 203 is carved with slit and window on the direction of two quadratures, as shown in Figure 6, is used for selecting two specific orders of diffraction time to enter projection objective as test waves and reference wave.The width of slit 209c and 209e satisfies formula (1), with the diameter d of circular hole 209a oIdentical, in twice measurement, on the one dimension direction of space, produce spherical wave respectively and enter projection objective to be measured 105.The width of window 209d and 209f influences its transmitted beam light intensity, thereby influences the contrast of interference fringe, should select the optimal width of window 209d and 209f according to the contrast of interference fringe.The length L of 209c, 209d, 209e and 209f oIdentical, should be longer as far as possible, make the transmitted beam light intensity increase, thereby improve the contrast of interference fringe.
4) the wave aberration detecting element 210 as square mask plate 204 is carved with slit and window on the direction of two quadratures, as shown in Figure 7, carries out twice meter and calculate the wave aberration of projection objective 105 on the direction of quadrature.The width of slit 210d and 210f satisfies formula (3), with the diameter d of circular hole 210b I1Identical, in twice measurement, on the one dimension direction of space, produce the sphere reference wave respectively.The width of window 210c and 210e satisfies formula (4), with the width w of window 210a iIdentical, depend on the spatial frequency f of projection objective emergent pupil wave aberration to be measured.The length L of 210c, 210d, 210e and 210f iIdentical, satisfy formula (9), m is the multiplying power of projection objective 105 in the formula.
L i＝L om (9)
5) as the systematic error of square mask plate 204 demarcate element 211 by the slit on two groups of orthogonal directionss to forming, as shown in Figure 7, on the direction of quadrature, carry out the systematic error of twice measurement demarcation interferometer 200.The width of slit 211d and 211f satisfies formula (3), and is identical with the width of slit 210d and 210f, and the sphere reference wave that produces in the measurement of twice orthogonal directions is also identical.The width of slit 211c and 211e satisfies formula (5), with the diameter d of circular hole 211a I2Identical, on the one dimension direction of space, produce the higher sphere reference wave of quality, the systematic error of demarcating interferometer 200.
When detecting the wave aberration of projection objective 105, present embodiment adopts the FTM measurement pattern equally, utilizes the Fourier transform method, extracts phase information from the strength information of interference fringe.Difference is, present embodiment need carry out twice measurement on the direction of quadrature, calculate the phase gradient on corrugated on two orthogonal directionss, adopt differential Zernike polynomial expression corrugated to fit the wave aberration W that algorithm obtains the projection objective 105 that 36 Zernike coefficients represent again 1
When demarcating the systematic error of interferometer 200, present embodiment adopts the PSI measurement pattern equally, utilizes the movable phase interfere art to carry out high-precision separating mutually and calculates, and suppresses the interferogram The noise.Difference is that present embodiment need carry out twice measurement on the direction of quadrature, calculate the phase gradient on corrugated on two orthogonal directionss, and adopts differential Zernike polynomial expression corrugated to fit algorithm to obtain the corrugated phase place W that 36 Zernike coefficients are represented 2Pass through W again 1And W 2Corresponding Zernike coefficient subtract each other the projection objective 105 wave aberration W that finally recorded.

Claims (6)

1. photo-etching machine projection objective wave aberration on-line detection method is characterized in that: said method comprising the steps of:
1) goes up integrated interferometer (200) at litho machine (100), the wave aberration of projection objective (105) is carried out online detection based on the point-diffraction interference principle;
2) illumination field of view and the partial coherence factor σ of adjusting illuminator (102) make interferometer (200) can collect the higher interference fringe of contrast;
3) be carved with a circular hole (209a) and a bigger window (209b) on object space mask plate (203) the chromium layer, be used for selecting two specific orders of diffraction time to enter projection objective (105) as test waves and reference wave;
4) be carved with wave aberration detecting element (210) and systematic error on the chromium layer as square mask plate (204) and demarcate element (211), wave aberration detecting element (210) comprises circular hole (210b) and window (210a), and systematic error is demarcated element (211) and formed by two circular holes (211a) with (211b);
5) interferometer (200) is adjusted to the PSI measurement pattern, utilizes as the systematic error of square mask plate (204) and demarcate element (211), demarcate the systematic error of interferometer (200);
6) interferometer (200) is adjusted to the FTM measurement pattern, utilization is as the wave aberration detecting element (210) of square mask plate (204), carry out the online detection of the full visual field of projection objective (105) wave aberration, obtain the wave aberration that 36 Zernike of each visual field point of projection objective (105) represent, and the adjustment amount of each compensator of projection objective (105);
7) utilize the controller (208) of interferometer (200), finish the aberration correction of projection objective (105) automatically.
2, the method for claim 1 is characterized in that: the diameter d of circular hole (209a) oSatisfy formula (1), less than the resolution of incident beam diffraction limit:
d o ≤ λ 2 N A o σ - - - ( 1 )
Wherein, λ is the wavelength of light source (101), NA oBe the object space numerical aperture of projection objective (105), σ is the partial coherence factor of illuminator (102), and computing formula is:
σ = NA il NA o - - - ( 2 )
Wherein, NA IlBe the numerical aperture of illuminator (102) in mask plate (103) side;
The diameter d of circular hole (210b) I1Satisfy formula (3), less than the resolution of incident beam diffraction limit, NA iFor projection objective (105) as number formulary value aperture:
d i 1 ≤ λ 2 NA i σ - - - ( 3 )
The width w of window (210a) iThe spatial frequency f that depends on projection objective emergent pupil wave aberration to be measured, as the formula (4):
w il = 2 fλ NA i - - - ( 4 )
The diameter of circular hole (211b) satisfies formula (3), with the diameter d of circular hole (210b) I1Identical, the diameter d of circular hole (211a) I2Satisfy formula (5), less than the resolution of projection objective (105) diffraction limit.
d i 2 ≤ λ 2 NA i - - - ( 5 )
3, the method for claim 1, it is characterized in that: under the FTM measurement pattern, by reducing the σ of illuminator (102), can increase the diameter of circular hole (209a) and circular hole (210b), improve system's transmitance of interferometer (200), thereby improved the contrast of the interference fringe that photoelectric sensor (205) collected when wave aberration is online to be detected; Under the PSI measurement pattern, it is d that systematic error demarcation element (211) has adopted diameter I2Circular hole (211a) systematic error of demarcating interferometer (200), eliminated circular hole under the FTM measurement pattern (210b) diameter d I1Increase the influence of the reference wave quality decline that is caused, thereby improved the measuring accuracy and the repeatability of interferometer (200).
4, the method for claim 1 is characterized in that: this method can also adopt based on the interferometer of slit diffraction principle of interference (200), and the wave aberration of projection objective (105) is carried out online detection; Object space mask plate (203) the chromium layer of interferometer (200) is carved with slit (209c) and slit (209e) on the direction of two quadratures, and window (209d) and window (209f); Be carved with wave aberration detecting element (210) and systematic error on picture side's mask plate (204) chromium layer of interferometer (200) and demarcate element (211); Wave aberration detecting element (210) is by slit (210d) on two orthogonal directionss and slit (210f), and window (210c) and window (210e) composition; To forming, wherein one group of slit is to being slit (211c) and slit (211d) by the slit on two groups of orthogonal directionss for systematic error demarcation element (211), and another group slit is to being slit (211e) and slit (211f).
5, method as claimed in claim 4 is characterized in that: the width of slit (209c) and slit (209e) satisfies formula (1), with the diameter d of circular hole (209a) oIdentical; The width of slit (210d) and slit (210f) satisfies formula (3), with the diameter d of circular hole (210b) I1Identical; The width of window (210c) and window (210e) satisfies formula (4), with the width w of window (210a) iIdentical; The width of slit (211d) and slit (211f) satisfies formula (3), and is identical with width (210f) with slit (210d); The width of slit (211c) and slit (211e) satisfies formula (5), with the diameter d i of circular hole (211a) 2Identical.
6, method as claimed in claim 4, it is characterized in that: under the FTM measurement pattern, by reducing the σ of illuminator (102), can increase the width of slit (209c), slit (209e), slit (210d) and slit (210f), improve system's transmitance of interferometer (200), thereby improved the contrast of the interference fringe that photoelectric sensor (205) collected when wave aberration is online to be detected; Under the PSI measurement pattern, it is d that systematic error demarcation element (211) has adopted width I2Slit (211c) and slit (211e) systematic error of demarcating interferometer (200), eliminated slit under the FTM measurement pattern (210d) and slit (210f) width d I1Increase the influence of the reference wave quality decline that is caused, thereby improved the measuring accuracy and the repeatability of interferometer (200).
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