CN101487987B - Iris measuring apparatus and image processing process - Google Patents
Iris measuring apparatus and image processing process Download PDFInfo
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- CN101487987B CN101487987B CN2009100468203A CN200910046820A CN101487987B CN 101487987 B CN101487987 B CN 101487987B CN 2009100468203 A CN2009100468203 A CN 2009100468203A CN 200910046820 A CN200910046820 A CN 200910046820A CN 101487987 B CN101487987 B CN 101487987B
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Abstract
The invention provides a device for measuring pupil, comprising a Fourier lens, a light well, a charge coupled device and an image processing system, wherein, the light well is positioned on a focal surface at one side of the Fourier lens, the charge coupled device is positioned on the focal surface at the other side of the Fourier lens, the image processing system is connected with the charge coupled device. The invention provides a pupil measuring device of a lithography exposure system which can measure the quality of an illumination pupil on line and can diagnose the design quality and debugging error of the optical system according to appearance of the pupil.
Description
Technical field
The present invention relates to a kind of photolithographic exposure system, and be particularly related to a kind of iris measuring apparatus and image processing method in the photolithographic exposure system.
Background technology
In the photolithographic exposure system, two factors that picture quality is played a crucial role are resolution and depth of focus.So should obtain the figure that better resolution forms critical size, keep suitable depth of focus again.The off-axis illumination technology can improve depth of focus and improve resolution.Current advanced photoetching process requires to use the off-axis illumination technology, comprises ring illumination, bipolar illumination, quadrupole illuminating etc.The pupil pattern that is complementary by rational selection and exposing patterns can improve process window to greatest extent, and this just requires illuminator to have adjustable pupil pattern.
Lithography illuminating system produces the spatial intensity distribution of pupil plane inner light beam by DOE (Diffraction Optical Element), and concrete implementation is please referring to Chinese patent CN1474235.This patent provides a kind of photo-etching illuminating apparatus, and this device adopts the axicon of diffraction plate, variable focus lens package, a pair of concavo-convex complementation to produce the illumination iris of continuous variable, and this method can not lost luminous energy when changing the illumination iris pattern.Diffraction optical element DOE can carry out phase modulation (PM) to the directional light of incident, makes the light beam deviation required such as illumination iris patterns such as two utmost points, four utmost points to form in the far field.
As seen from the above description, diffraction optical element, variable focus lens package and axicon are the Primary Components that produces the illumination iris pattern, diffraction optical element can realize that it produces diffraction to light beam with the method for binary optical, makes illumination iris form required illumination pattern; The focal length of variable focus lens package is variable, can form adjustable illumination coherence factor like this; Axicon can produce the variable ring illumination of inner and outer ring by the distance of regulating two prisms.
Require to have desirable illumination iris pattern during photolithographic exposure, in the reality, owing to the designing quality of diffraction optical element, illuminator debug reason such as error, may cause the illumination iris degradation.Fig. 1 has illustrated because the optical axis of beam-pointing and illuminator when angle is arranged, can cause the ring decentraction of the ring illumination that axicon produces.
More than said pupil quality specifically be meant, actual pupil pattern that diffraction optical element produced and the difference between the design load, the illumination iris quality mainly comprises x direction pupil homogeneity in the lithography illuminating system, y direction pupil homogeneity, with four extreme direction pupil homogeneitys, in addition, the proper alignment etc. that also has ring illumination pupil inner and outer ring.X and y direction pupil homogeneity are respectively at two utmost points on x direction and y direction illuminations, are meant the difference between the two poles of the earth illumination intensity of two utmost points illumination, as shown in Figure 2.If illumination iris has the pupil of x or y direction inhomogeneous, this will cause the position deviation of optical patterning under the situation of out of focus, and can exert an influence to alignment precision, and four extreme direction pupil homogeneitys are meant the pupil capacity volume variance of illumination iris at four quadrants, the heterogeneity of four extreme direction pupils will cause can producing the ellipticalness of photoetching lines when carving the contact hole shape, in addition, the pupil quality also comprises the single extremely illumination uniformity of itself.
Summary of the invention
Problem for the pupil quality testing inconvenience that overcomes photolithographic exposure system in the prior art the invention provides a kind of iris measuring apparatus and image processing method that can conveniently detect the pupil quality
To achieve these goals, the present invention proposes a kind of iris measuring apparatus, comprising: fourier lense; Light well is positioned on the focal plane of described fourier lense one side; Charge-coupled image sensor is positioned on the focal plane of described fourier lense opposite side; Image processing system links to each other with described charge-coupled image sensor.
Optionally, described iris measuring apparatus links to each other with a control desk, is controlled the motion of described iris measuring apparatus by described control desk.
Optionally, described iris measuring apparatus is positioned over a side of a projection objective on optical path direction.
Optionally, the opposite side of described projection objective is placed a mask plate or a pupil test mask plate.
Optionally, a plurality of apertures that distribute on the described pupil test mask plate.
Optionally, the distance between the adjacent described aperture equates.
Optionally, the shape of described aperture is circular, square or triangle.
To achieve these goals, the present invention also proposes a kind of pupil image disposal route, comprises the steps: to judge the type of described pupil; Determine the center of described pupil image; Calculate the energy of described pupil; Calculate described pupil ovality, utmost point balance or proper alignment.
Optionally, said method also comprises a step-scan process, and measurement mechanism is measured the pupil quality of a plurality of apertures on the mask respectively in the two-dimensional directional step-scan of image planes, assesses it to the inhomogeneity influence of photoetching lines.
Optionally, the type of described pupil comprises circular hole illumination iris, two utmost point illumination iris, quadrupole illuminating pupil and ring illumination pupil.
The beneficial effect of a kind of iris measuring apparatus of the present invention and image processing method mainly shows: the pupil quality of the measurement illumination iris that iris measuring apparatus provided by the invention can be online, pupil image disposal route provided by the invention can be utilized the pattern of pupil to diagnose the designing quality of optical system and debug error.
Description of drawings
Fig. 1 is the structural representation of photolithographic exposure system;
Fig. 2 is the structural representation of iris measuring apparatus of the present invention;
Fig. 3 is the structural representation of mask plate of the present invention;
The ring illumination pupil plane synoptic diagram of Fig. 4 for measuring on the area array CCD of the present invention;
Fig. 5 carries out the synoptic diagram of pupil test for iris measuring apparatus of the present invention;
Fig. 6 calculates the used template synoptic diagram of pupil ellipticalness for the present invention;
Fig. 7 is a secondary illumination iris pattern synoptic diagram of the present invention;
Fig. 8 is a level Four illumination iris pattern synoptic diagram of the present invention.
Embodiment
The invention is further described below in conjunction with accompanying drawing.
Fig. 1 is the structural representation of photolithographic exposure system, the photolithographic exposure system mainly comprises light source, be used to provide illumination light, the beam Propagation system, beam Propagation is incident on the diffraction optical element (DOE), DOE goes into to inject illuminator with beam diffraction, forms needed illumination iris on the pupil of illuminator, and shines mask uniformly; Projection objective will contain the image imaging of circuit version on the silicon chip face on the mask., have conjugate relation between the pupil of illuminator and the pupil of projection objective here, carry out if will measure the pupil plane that illumination iris is difficult in illuminator or projection objective.The present invention utilizes a fourier transform lens, and the picture point a distance on the silicon chip face is formed pupil again, and the pupil of formation has the relation with the illumination iris conjugation, and the pupil quality of measuring this pupil just can be assessed the quality of illumination iris.
The present invention specifically is achieved in that
Special-purpose pupil test mask is set, the aperture of even distribution some on the mask, the shape of aperture can be circular, square, triangle etc., as shown in Figure 3.Equally, on the mask of manufacturing type, also such aperture can be set, be used as test mask.The aperture of mask is used for producing pointolite.The purpose that such mask is set is to carry out the pupil test to a plurality of points in the illuminated field, can assess the pupil quality of different illumination field of view points like this.
On the image planes of test mask, measure with the pupil proving installation.The typical structure of pupil proving installation as shown in Figure 2, iris measuring apparatus comprises an aperture 1, the conjugate image of mask aperture goes into to inject in the aperture 1, and aperture 1 is placed on the front focal plane of fourier transform lens 2, and the back focal plane of fourier transform lens 2 receives with area array CCD 3.Like this, the back focal plane of fourier transform lens becomes the relation of conjugation with the illumination iris face, measures the pupil quality on the CCD 3, and measurement data is transferred to image processing system 5, just can assess the quality of illumination iris.As shown in Figure 4, be the pattern of the ring illumination pupil that on the CCD plane, can measure.
In entire measuring device, what the pupil measuring accuracy was played a major role is the designing quality of fourier transform lens, by the Fourier optics theory as can be known, when picture point is placed on the front focal plane of fourier transform lens, will form its pupil face at the back focal plane of fourier transform lens.
Fourier transform lens requires two pairs of image conjugate position aberration corrections.The parallel beam that fourier transform lens must make infinite distance incident perfect imaging on back focal plane; The second pair of conjugate planes that must control aberration be with input face as object, corresponding picture is in infinite distance, picture side.Fourier transform lens requires the design aberration less than quarter-wave, like this, guarantees that the pupil plane of measuring is perfect illumination iris face.
Because illumination field of view has certain size, need could assess the pupil quality in the whole illuminated field like this to a plurality of point measurement pupils in the illumination field of view.This measuring method also comprises a step-scan process, measurement mechanism can step-scan on image planes, measure the pupil quality of a plurality of apertures on the mask respectively, just can assess the pupil of exposure system in whole illuminated field, the general structure synoptic diagram of native system as shown in Figure 5, light shines on the projection objective 112 by the aperture on the mask plate 111, enters iris measuring apparatus 113 of the present invention again.
Collect the pupil information of measurement point by CCD after, need analyze, to determine the pupil quality pupil.The present invention also comprises a kind of pupil image Processing Algorithm, and image processing algorithm is used for the pupil of being sampled is analyzed, to obtain illumination of two utmost points and quadrupole illuminating pupil utmost point balance, the proper alignment of ring illumination, the indexs such as homogeneity of pupil itself.
1. for traditional lighting pupil pattern, at first carry out the image de-noising, utilize the center of energy method to calculate the central point C of hot spot, with the central point of C as pupil.Be illustrated in figure 9 as and calculate the used template of pupil ellipticalness, at first the center of template is aimed at the pupil center C.Respectively with pupil image with (a) He (b) multiply each other.(a) being the template of pupil x direction printing opacity, is the template of pupil y direction printing opacity (b), calculates pupil energy in the x and y direction so respectively, and the pupil ovality is defined as pupil energy capacity volume variance in the x and y direction, with equation expression is:
According to measured x and y energy, just can calculate the pupil ovality.
2. for two utmost point illumination iris, the leading indicator that influences pupil is a utmost point balance, at first seeks the center of pupil image, tries to achieve the energy of the two poles of the earth pupil then respectively, utilizes formula
Try to achieve two aurora pupil utmost point balances.
3. for the quadrupole illuminating pupil, calculate the central point C of pupil energy earlier, cross the C point and do the separatrix, hot spot is decomposed into 4 quadrants, calculate the luminous energy size E of all quadrants respectively
1, E
2, E
3And E
4, according to formula
Calculate four aurora pupil utmost point balances.
4. for ring illumination pupil pattern, at first calculate the central point of pupil energy, utilize the mathematical morphology image processing algorithm then, seek the border of pupil inner and outer ring, seek the geometric center of inner and outer ring respectively, and the proper alignment of assessment ring illumination inner and outer ring.
5. the pupil proving installation is done two-dimentional moving along x and y direction in illumination field of view, seeks each picture point in the illumination field of view, and obtains the pupil image of each picture point, by each pupil is handled, can obtain the pupil difference of whole illumination field of view.And can assess photoetching lines homogeneity (CDU) influence that this pupil otherness is caused.
By above-mentioned illumination iris measurement mechanism, the function that can be achieved as follows:
1. be provided with down at certain sigma (illumination coherence factor), measure the pattern of illumination iris, utilize the homogeneity of the methods analyst illumination iris of Digital Image Processing, indexs such as utmost point balance can be assessed the performance of diffraction optical element.
2. by under one group of sigma scope, measuring the pupil pattern, can detect the zooming range of zoom lens, and can diagnose the error of debuging of optical system.
3. the proper alignment of the inner and outer ring by measure annular illumination, and measure in conjunction with the illumination heart far away, best incident beam direction can be sought.
Measure illumination iris by the difference in illumination field of view, can measure the pupil difference of whole illumination field of view.And can assess the CDU influence that this pupil otherness is caused.
Though the present invention discloses as above with preferred embodiment, so it is not in order to limit the present invention.The persond having ordinary knowledge in the technical field of the present invention, without departing from the spirit and scope of the present invention, when being used for a variety of modifications and variations.Therefore, protection scope of the present invention is as the criterion when looking claims person of defining.
Claims (8)
1. iris measuring apparatus is characterized in that comprising:
Fourier lense;
Light well is positioned on the focal plane of described fourier lense one side;
Charge-coupled image sensor is positioned on the focal plane of described fourier lense opposite side;
Image processing system links to each other with described charge-coupled image sensor;
Described iris measuring apparatus is positioned over a side of a projection objective on optical path direction, the opposite side of described projection objective is placed a mask plate.
2. according to the described a kind of iris measuring apparatus of claim 1, it is characterized in that described iris measuring apparatus links to each other with a control desk, is controlled the motion of described iris measuring apparatus by described control desk.
3. according to the described a kind of iris measuring apparatus of claim 1, it is characterized in that a plurality of apertures that distribute on the described mask plate.
4. according to the described a kind of iris measuring apparatus of claim 3, it is characterized in that the distance between the adjacent described aperture equates.
5. according to the described a kind of iris measuring apparatus of claim 3, the shape that it is characterized in that described aperture is circular, square or triangle.
6. the pupil image disposal route that use is installed according to claim 1 is characterized in that comprising the steps:
The image processing system of described device is judged the type of described pupil;
Described image processing system is determined the center of described pupil image;
Described image processing system calculates the energy of described pupil;
Described image processing system calculates described pupil ovality, utmost point balance or proper alignment.
7. according to the described a kind of pupil image disposal route of claim 6, it is characterized in that also comprising a step-scan process, measurement mechanism is measured the pupil quality of a plurality of apertures on the mask respectively in the two-dimensional directional step-scan of image planes, assesses it to the inhomogeneity influence of photoetching lines.
8. according to the described a kind of pupil image disposal route of claim 6, it is characterized in that the type of described pupil comprises circular hole illumination iris, two utmost point illumination iris, quadrupole illuminating pupil and ring illumination pupil.
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| CN2009100468203A CN101487987B (en) | 2009-02-27 | 2009-02-27 | Iris measuring apparatus and image processing process |
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| CN102566289A (en) * | 2010-12-20 | 2012-07-11 | 上海微电子装备有限公司 | Method for testing diaphragm of illumining system of photoetching equipment |
| US9091650B2 (en) * | 2012-11-27 | 2015-07-28 | Kla-Tencor Corporation | Apodization for pupil imaging scatterometry |
| CN107870522B (en) * | 2016-09-26 | 2020-06-16 | 上海微电子装备（集团）股份有限公司 | Imaging optical path device and detection control method of imaging optical path device |
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Address after: 201203 Zhangjiang High Tech Park, Shanghai, Zhang Dong Road, No. 1525 Patentee after: Shanghai microelectronics equipment (Group) Limited by Share Ltd Address before: 201203 Zhangjiang High Tech Park, Shanghai, Zhang Dong Road, No. 1525 Patentee before: Shanghai Micro Electronics Equipment Co., Ltd. |