CN110763686B - Defect detection device and method for transparent sample - Google Patents
Defect detection device and method for transparent sample Download PDFInfo
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Abstract
The invention discloses a defect detection device and a defect detection method for a transparent sample. The device comprises a light source, an objective table, an objective lens, a grating plate and an image acquisition device which are sequentially arranged along a light path; the light source is used for generating an illumination light beam; the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; the object stage is used for bearing a transparent sample; the objective lens is positioned on one side of the bearing surface of the objective table; the central axis of the transparent sample is not coincident with the central axis of the objective lens; the grating plate comprises a plurality of gratings, and the grating periods of the gratings are different; the device further comprises a treatment device for acquiring a first interference image and a second interference image, and acquiring the phase distribution of the transparent sample according to the first interference image and the second interference image. The embodiment of the invention eliminates the interference between the transparent sample and the self in the interference pattern, eliminates the repeated image and is easier to extract the refractive index distribution of the transparent sample.
Description
Technical Field
The embodiment of the invention relates to the field of optical detection, in particular to a defect detection device and a defect detection method for a transparent sample.
Background
The detection of micron and nanometer scale defects based on three-dimensional machine vision plays an important role in the processing industry. In general, defects on the micrometer scale are easily detected using conventional machine vision techniques. However, if it is a sub-micron defect in a transparent sample, it is difficult to find, and this problem is a critical problem in optical element inspection such as a microlens array. It is therefore necessary to develop new machine vision methods for detecting these invisible defects. In general, small optical elements are manufactured mainly by a plastic molding method. In the process of the plastic mold method, the refractive index of the optical element may be changed due to the cooling rate and pressure, and thus it is necessary to detect such a change in refractive index.
Liquid immersion, ellipsometry, white light scanning interferometry have all been proposed for detecting refractive index changes in optical elements. However, none of these methods is suitable for defect detection of optical elements on the micrometer scale. To detect defects in the optical elements on the micrometer scale, a digital holographic method may be used, which may be based on michelson or mach-zehnder interferometers. However, these interferometers tend to be too complicated in optical path structure. The shearing interference has a simple optical path structure and is easy to integrate into a detection system, but because the shearing interference is a self-reference interferometry technology, a hologram obtained by the shearing interference has a repeated image formed by sample and self interference in addition to a direct current item and a virtual image existing in a common hologram, the quality of a real image to be acquired is reduced by the repeated image, and the refractive index distribution information of an object is difficult to extract.
Disclosure of Invention
In order to solve the above problems, the present invention provides a defect detection apparatus and a defect detection method for a transparent sample, which can eliminate interference between the transparent sample and itself in an interference pattern, eliminate a repeated image, and facilitate extraction of refractive index distribution of the transparent sample.
In a first aspect, an embodiment of the present invention provides an apparatus for detecting defects of a transparent sample, where the apparatus includes:
the light source, the objective table, the objective lens, the grating plate and the image acquisition device are sequentially arranged along the light path;
the light source is used for generating an illumination light beam, and the radius of the illumination light beam is R; the objective table is used for bearing a transparent sample, the diameter of the transparent sample is 2R, and the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; the objective lens is positioned on one side of the bearing surface of the objective table; the central axis of the transparent sample is not coincident with the central axis of the objective lens; the grating plate is positioned on the focal plane of the objective lens, the grating plate comprises a plurality of gratings, the grating periods of the gratings are different, the illumination light beam generates diffraction after passing through the grating plate, and the zero-order diffraction and the first-order diffraction in the diffraction generate interference; the image acquisition device is used for acquiring a first interference image when the transparent sample is carried on the object stage for detection and a second interference image when the transparent sample on the object stage is removed;
further comprising processing means for determining a minimum grating period suitable for said transparent sample based on the radius R of said transparent sample and the radius R of said illumination beam
And maximum grating period
(ii) a The processing device is electrically connected with the image acquisition device and is used for respectively calculating a first phase distribution and a second phase distribution according to the first interference image and the second interference image, acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution, and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
In a second aspect, an embodiment of the present invention further provides a method for detecting defects of a transparent sample, where the method includes:
acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; and determining the minimum grating period suitable for the transparent sample according to the radius R of the transparent sample and the radius R of the illumination light beam
And maximum grating period
；
Placing the transparent sample on an objective table, wherein the central axis of the transparent sample is not coincident with the central axis of the objective lens;
arranging a grating plate with a preset grating period on the focal plane of an objective lens; the grating plate comprises a plurality of gratings, and the grating periods of the gratings are different; the preset grating period is greater than or equal to the minimum grating period
Less than or equal to the maximum grating period
；
Obtaining a first interference image of the transparent sample, and obtaining a first phase distribution according to the first interference image;
removing the transparent sample, obtaining a second interference image after the grating plate is irradiated by the illumination light beam, and obtaining a second phase distribution according to the second interference image;
acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
According to the embodiment of the application, the transparent sample is placed on the objective table, the diameter of the transparent sample is not larger than the radius of the illumination light beam, and the central axis of the transparent sample is not overlapped with the central axis of the objective lens, so that the illumination light beam passing through the transparent sample is divided into two parts, one part contains information of the transparent sample, and the other part does not contain the information of the transparent sample; by selecting a grating period equal to or greater than the minimum grating period
And is less than or equal to the maximum grating period
The grating ensures that the part of the zero-order diffraction light containing the transparent sample information, which is generated after passing through the grating plate, is not overlapped with the part of the first-order diffraction light containing the transparent sample information, and the whole part of the zero-order diffraction light containing the transparent sample information is overlapped with the part of the first-order diffraction light not containing the transparent sample information, so that the interference between the transparent sample and the grating is eliminated in the interference pattern, the repeated image is eliminated, the refractive index distribution of the transparent sample is easier to extract, and the defect distribution condition of the transparent sample can be obtained according to the refractive index distribution. Meanwhile, the grating plate comprises a plurality of gratings, and the grating periods of the gratings are different, so that different gratings can be flexibly selected according to the size of the transparent sample.
Drawings
Fig. 1 is a schematic structural diagram of a defect detection apparatus for a transparent sample according to an embodiment of the present disclosure;
FIG. 2 is a schematic flow chart of a method for detecting defects of a transparent sample according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of light spots of zero-order diffracted light and first-order diffracted light generated by the probe beam and the reference beam after passing through the grating according to the embodiment of the present invention;
FIGS. 4-6 are schematic diagrams of light spots of zero-order diffracted light and first-order diffracted light at three shearing distances in the embodiments of the present application;
fig. 7 is a schematic structural diagram of a grating plate according to an embodiment of the present disclosure;
FIG. 8 is a schematic structural diagram of another apparatus for detecting defects of a transparent sample according to an embodiment of the present disclosure;
FIG. 9 is a schematic flow chart of another method for detecting defects of a transparent sample according to an embodiment of the present disclosure;
fig. 10 is a schematic flowchart of a method for obtaining a complex amplitude distribution of a first interference reconstructed image according to a complex amplitude distribution of reference light and a light intensity distribution of the first interference image according to an embodiment of the present application;
fig. 11 is a flowchart illustrating a method for calculating a first phase distribution according to a complex amplitude distribution of a first interference reconstruction image according to an embodiment of the present application.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Fig. 1 is a schematic structural diagram of a defect detection apparatus for a transparent sample according to an embodiment of the present disclosure. As shown in fig. 1, the detection apparatus 100 includes:
the light source 110, the objective table 120, the objective lens 130, the grating plate 140 and the image acquisition device 150 are sequentially arranged along the optical path;
the light source 110 is used for generating an illumination beam, and the radius of the illumination beam is R; the objective table 120 is used for bearing the transparent sample 160, the diameter of the transparent sample 160 is 2R, and the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample 160; the objective lens 130 is located on the carrying surface side of the objective table 120; the central axis of the transparent sample 160 is not coincident with the central axis of the objective lens 130; the grating plate 140 is located on the focal plane of the objective lens 130, and the grating plate 140 includes a plurality of gratings, and grating periods of the gratings are different; the illumination beam generates diffraction after passing through the grating plate 140, and the zero-order diffraction and the first-order diffraction in the diffraction generate interference; the image acquisition device 150 is used for acquiring a first interference image when the transparent sample 160 carried on the object stage 120 is detected and a second interference image when the transparent sample 160 on the object stage 120 is removed;
further comprising processing means 170, the processing means 170 being adapted to determine a minimum grating period suitable for the transparent sample 160 based on the radius R of the transparent sample 160 and the radius R of the illumination beam
And maximum grating period
(ii) a The processing device 170 is electrically connected to the image acquisition device 150, and is configured to calculate a first phase distribution and a second phase distribution from the first interference image and the second interference image, respectively, obtain a phase distribution of the transparent sample from the first phase distribution and the second phase distribution, and calculate a refractive index distribution of the transparent sample 160 from the phase distribution of the transparent sample 160.
Wherein, when the region of the zero-order diffraction beam containing the transparent sample information and the region of the first-order diffraction beam containing the transparent sample information generated after the illumination beam passes through the grating plate are tangent, the corresponding grating period is the maximum grating period
The region of the zero-order diffraction beam containing the transparent sample information and the region of the first-order diffraction beam containing the transparent sample information are not overlapped, and the corresponding grating period is the minimum grating period when the region of the zero-order diffraction beam containing the transparent sample information is tangent to the edge of the first-order diffraction beam
。
Specifically, fig. 2 is a schematic flow chart of a method for detecting defects of a transparent sample according to an embodiment of the present invention. The defect detection method shown in fig. 2 is a flow for detecting defects of a transparent sample by using the device shown in fig. 1, and comprises the following specific steps:
210, obtaining the radius R of an illumination light beam according to the radius R of a transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample, and determining the minimum grating period suitable for the transparent sample according to the radius R of the transparent sample and the radius R of the illumination light beam
And maximum grating period
；
Specifically, the illumination beam diffracts after passing through the grating plate 140, wherein each level of diffraction beam is composed of two parts, namely a region containing transparent sample information and a region not containing transparent sample information. When the part of the zero-order diffraction beam containing the transparent sample information is circumscribed with the region of the first-order diffraction beam containing the transparent sample information, the corresponding grating period is the maximum grating period
(ii) a The region of the zero-order diffraction beam containing the transparent sample information and the region of the first-order diffraction beam containing the transparent sample information are not overlapped, and the grating period corresponding to the inscribing of the region of the zero-order diffraction beam containing the transparent sample information and the region of the first-order diffraction beam not containing the transparent sample information is the minimum grating period
。
220, placing a transparent sample on an objective table, wherein the central axis of the transparent sample is not coincident with the central axis of the objective lens;
the light source is a He-Ne laser having a wavelength of 632.8nm, a semiconductor laser having a wavelength of 532nm, or the like.
The light source is turned on, the central axis of the transparent sample is enabled not to coincide with the central axis of the objective lens, and considering that the diameter 2R of the transparent sample is smaller than the radius R of the illumination light beam, a part of the illumination light beam penetrates through the transparent sample and is incident to the objective lens, the part of the illumination light beam is called a probe light beam, the other part of the illumination light beam is directly incident to the objective lens without passing through the transparent sample and is called a reference light beam, the probe light beam and the reference light beam are converged to the grating plate through the objective lens to generate diffraction, interference patterns with alternate light and shade are generated, and the distribution of the refractive index of the sample to be measured can be obtained by analyzing the interference of zero-order diffraction light and first-order diffraction light.
Grating diffraction equation:
wherein the content of the first and second substances,pis the period of the grating and is,θis the angle between the diffracted light and the optical axis,λis the wavelength of the illumination light beam and,mis the order of diffraction. When m =1, the grating period can be calculated according to the wavelength of the illumination light beam and the included angle between the first-order diffracted light and the optical axis:
FIG. 3 is a schematic diagram of light spots of zero-order diffracted light and first-order diffracted light generated by the probe beam and the reference beam after passing through the grating according to the embodiment of the present invention. As shown in FIG. 3, the spot 210 of zero order diffracted light is centered on the optical axis with a grating period of:
wherein the content of the first and second substances,Sthe center of the spot of the zero-order diffracted light and the center of the spot of the first-order diffracted lightThe distance between, i.e. the shearing distance,his the distance of the image capture device from the grating 230. It can be seen that the smaller the grating period, the larger the shearing distance.
Fig. 4-6 are schematic diagrams of light spots of the zero-order diffracted light and the first-order diffracted light at three shearing distances in the embodiment of the present application. As shown in fig. 4, the shearing distance isS 1 The region 211 of the zero-order diffracted light carrying the transparent sample information overlaps with the region 221 of the first-order diffracted light carrying the transparent sample information; as shown in fig. 5, the shearing distance is increasedS 2 The region 211 carrying transparent sample information by the zero-order diffracted light is tangent to the region 221 carrying transparent sample information by the first-order diffracted light, and the region 211 carrying transparent sample information by the zero-order diffracted light falls in the region 222 not carrying transparent sample information by the first-order diffracted light; as shown in fig. 6, the shearing distance is increased againS 3 The region 211 in which the zero-order diffracted light carries transparent sample information does not overlap the region 221 in which the first-order diffracted light 220 carries transparent sample information, and the regions 211 in which the zero-order diffracted light carries transparent sample information are all tangent to the regions 222 in which the first-order diffracted light does not carry transparent sample information.
S 3 >S 2 >S 1 When the shearing distance isS 1 When the distance separating the light spot 210 of the zero-order diffraction light and the light spot 220 of the first-order diffraction light is too small, the region of the zero-order diffraction light carrying the transparent sample information interferes with the region of the first-order diffraction light carrying the transparent sample information, a repeated image is generated, and at the moment, the grating with a smaller grating period needs to be replaced to obtain a larger shearing distanceS 2 (ii) a When the shearing distance isS 2 When the light source is used, the area of the zero-order diffraction light carrying the transparent sample information is just not interfered with the area of the first-order diffraction light carrying the transparent sample information, and the area of the zero-order diffraction light carrying the transparent sample information is just interfered with the area of the first-order diffraction light not carrying the transparent sample information, so that the influence of repeated images is eliminated, and the light is continuously replaced at the momentObtaining larger shearing distance by using grating with smaller grating periodS 3 (ii) a When the shearing distance isS 3 When the area of the zero-order diffraction light carrying the transparent sample information does not interfere with the area of the first-order diffraction light carrying the transparent sample information, and the area of the zero-order diffraction light carrying the transparent sample information just interferes with the area of the first-order diffraction light not carrying the transparent sample information, the influence of repeated images can still be eliminated. However, if the shearing distance is further increased, the region where the zero-order diffracted light carries the transparent sample information cannot be totally interfered with the region where the first-order diffracted light does not carry the transparent sample information, and a part of the transparent sample information is lost. Therefore, all information of the transparent sample is obtained while eliminating the influence of the repeated image, and the shearing distance must be equal to or more thanS 2 Is less than or equal toS 3 That is to say thatS 2 And S3The minimum and maximum shearing distances for the transparent sample, respectively.
With continued reference to FIGS. 5 and 6, the minimum shearing distance S2And a maximum shearing distance S3Respectively as follows:
wherein the content of the first and second substances,ris the radius of the transparent sample and,Ris the radius of the illumination beam.
The minimum grating period can be obtained by combining the formulas (4) and (5) with the formula (3)p min And maximum grating periodp max ：
Respectively calculating the minimum grating period suitable for the transparent sample according to the formulas (6) and (7)
And maximum grating period
。
230, placing the grating plate with the preset grating period on the focal plane of the objective lens; the grating plate comprises a plurality of gratings, and the grating periods of the gratings are different; the preset grating period is greater than or equal to the minimum grating period
Less than or equal to the maximum grating period
；
Selecting a grating period equal to or less than the maximum grating period
Greater than or equal to the minimum grating period
The grating can obtain and eliminate the interference between the transparent sample and the grating, and simultaneously obtain all the information of the transparent sample, and eliminate the influence of repeated images. Transparent samples of different sizes correspond to different maximum grating periods
And minimum grating period
The grating plate comprises a plurality of gratings, the grating periods of the gratings are different, and the gratings can be used for transparent samples with different sizesDifferent grating periods are chosen.
240, obtaining a first interference image of the transparent sample, and obtaining a first phase distribution according to the first interference image;
250, removing the transparent sample, obtaining a second interference image after irradiating the grating plate by the illumination beam, and obtaining a second phase distribution according to the second interference image;
260, obtaining a phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
obtaining the complex amplitude distribution of the first interference reconstruction image through low-pass filtering, angular spectrum propagation and inverse Fourier transform according to the complex amplitude distribution of the first interference image and the reference beam, and obtaining a first phase distribution according to the complex amplitude distribution of the first interference reconstruction image, namely the first phase distribution when a transparent sample exists on an object plane
(ii) a Removing the transparent sample, illuminating the same grating with the illuminating beam to obtain a second interference image, obtaining the complex amplitude distribution of the second interference reconstruction image through the same operation according to the complex amplitude distribution information of the second interference image and the reference beam, and obtaining a second phase distribution according to the complex amplitude distribution of the second interference reconstruction image, namely the second phase distribution when no transparent sample exists on the object plane
。
Calculating the phase distribution of the transparent sample according to the formula (8)
：
270, calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
The refractive index distribution of the transparent sample was calculated according to equation (9):
wherein the content of the first and second substances,
is the phase distribution of the transparent sample,
for the thickness variation profile of the transparent sample,
the wavelength of the illumination beam.
According to the defect detection device for the transparent sample, the transparent sample is placed on the objective table, the diameter of the transparent sample is not larger than the radius of the illumination light beam, and the central axis of the transparent sample is not coincident with the central axis of the objective lens, so that one part of the illumination light beam passing through the transparent sample contains information of the transparent sample, and the other part of the illumination light beam does not contain information of the transparent sample; by selecting a grating period equal to or greater than the minimum grating period
And is less than or equal to the maximum grating period
The grating ensures that the part of the zero-order diffraction light containing the transparent sample information, which is generated after passing through the grating plate, is not overlapped with the part of the first-order diffraction light containing the transparent sample information, and the whole part of the zero-order diffraction light containing the transparent sample information is overlapped with the part of the first-order diffraction light not containing the transparent sample information, so that the interference between the transparent sample and the grating is eliminated in the interference pattern, the repeated image is eliminated, the refractive index distribution of the transparent sample is easier to extract, and the submicron defect of the transparent sample can be obtained from the refractive index distribution. Meanwhile, the grating plate comprises a plurality of gratings, and the light of each gratingThe grating periods are different, so that different gratings can be flexibly selected according to the size of the transparent sample.
Optionally, with continued reference to FIG. 1, stage 120 includes a transparent region, and transparent sample 160 is placed in the transparent region. Because the illumination light beam is incident to the transparent sample 160 after passing through the object stage 120, the transparent sample 160 is placed in the transparent area, so that the illumination light beam passes through the transparent area and irradiates to the transparent sample 160, the illumination light beam received by the transparent sample 160 is not affected, the light beam emitted by the transparent sample 160 is ensured to contain the transparent sample information and the information of the object stage 120, and the accuracy of the detection result is ensured.
Optionally, a plurality of the gratings are arranged on the grating plate in M rows and N columns; the grating plate is movable in a plane parallel to the stage in a row direction and a column direction.
Fig. 7 is a schematic structural diagram of a grating plate according to an embodiment of the present application. As shown in fig. 7, a plurality of gratings 951 on the grating plate 950 are arranged in M rows and N columns, the grating period increases from left to right along the row direction, the grating period increases from top to bottom along the column direction, the grating period of the first column grating of the ith row is greater than the grating period of the nth column grating of the i-1 row, i is greater than or equal to 2 and less than or equal to M, and i is a positive integer; meanwhile, the grating plate 950 is fixed on a grating displacement stage (not shown in the figure) which is movable in a row direction and a column direction in a plane parallel to the stage, so that the grating plate 950 can be moved in the row direction and the column direction.
According to the grating plate arranged according to the rule, the grating plate is arranged according to the rule, other grating plates do not need to be replaced aiming at transparent samples of different sizes, the grating with the required grating period can be found quickly and accurately only by moving the grating plate, and the flexibility of the device is improved. The embodiment of the application only provides a structure of the grating plate, and actually, the arrangement of the gratings on the grating plate can be in other modes, which is not limited in the application.
Fig. 8 is a schematic structural diagram of another defect detection apparatus for a transparent sample according to an embodiment of the present application. As shown in fig. 8, the detection apparatus 200 includes:
the light source 110, the beam expander 180, the reflector 190, the objective table 120, the objective lens 130, the grating plate 140 and the image acquisition device 150 are sequentially arranged along the light path;
the beam expander 180 is located between the light source 110 and the mirror 190; the reflector 190 is used for reflecting the illumination beam emitted from the light source 110 to the stage 120 after passing through the beam expander 180.
Specifically, when the beam radius R of the illumination beam emitted by the light source is small or the diameter 2R of the transparent sample is large and the beam radius R is smaller than the diameter 2R of the transparent sample, the beam expander 180 can expand the beam radius of the illumination beam, so that the beam radius R of the illumination beam is not smaller than the diameter 2R of the transparent sample, and the defect detection of the transparent sample is performed smoothly. The mirror 190 can change the propagation path of the illumination beam, and when the position of the transparent sample 160 on the stage 120 is changed, the path of the illumination beam can be changed to satisfy the defect detection condition by changing the angle of the mirror 190 without moving the light source.
Illustratively, a linearly polarized He — Ne laser having a wavelength of 632.8nm was selected as the light source, and the output power thereof was 2 mW; the transparent sample is an aspheric collimating objective lens, the radius of the aspheric collimating objective lens is 0.8mm, and the thickness of the aspheric collimating objective lens is 500 mu m; the spot radius of the expanded illumination beam of the beam expander is 4 mm; the right side of the transparent sample coincides with the right boundary of the illumination beam; the distance between the grating and the image acquisition device is 500mm, and the minimum grating period is calculated according to the formulas (6) and (7)
And maximum grating period
65.9 μm and 98.9 μm, respectively; selecting a grating with a grating period of more than or equal to 65.9 mu m and less than or equal to 98.9 mu m; the image acquisition device selects a CCD camera which has 8-bit dynamic range, pixels are 2048 × 2048, and the pixel size is 7.4 μm × 7.4 μm; the magnification of the objective lens is 2, and the numerical aperture is 0.055.
Based on the same inventive concept, the embodiment of the present invention further provides a defect detection method for a transparent sample, which is applicable to any one of the aforementioned defect detection apparatuses for transparent samples, as shown in fig. 2. The method has the beneficial effects of the corresponding device.
Fig. 9 is a schematic flowchart of another method for detecting defects of a transparent sample according to an embodiment of the present disclosure. As shown in fig. 9, the method specifically includes the following steps:
210, obtaining the radius R of an illumination light beam according to the radius R of a transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample, and determining the minimum grating period suitable for the transparent sample according to the radius R of the transparent sample and the radius R of the illumination light beam
And maximum grating period
；
220, placing a transparent sample on an objective table, wherein the central axis of the transparent sample is not coincident with the central axis of the objective lens;
230, placing the grating plate with the preset grating period on the focal plane of the objective lens; the grating plate comprises a plurality of gratings, and the grating periods of the gratings are different; the preset grating period is greater than or equal to the minimum grating period
Less than or equal to the maximum grating period
；
910, obtaining the light intensity distribution of the first interference image of the transparent sample;
specifically, referring to FIG. 5 or FIG. 6, the complex amplitude distribution of the region 211 where the zero-order diffracted light carries the information of the transparent sample isO 1 The complex amplitude of the areas 212 where the zero-order diffracted light does not carry information on the transparent sample isR 1 The first order diffracted light carries the region 221 complex amplitude distribution of the transparent sample information asO 2 The complex amplitude of the first order diffracted light in the areas 222 not carrying information on the transparent sample isR 2 The light intensity distribution of the generated first interference image can be expressed as:
wherein the content of the first and second substances,
in the form of a direct current term,
is a virtual image and is a virtual image,
is a real image.
920, obtaining the complex amplitude distribution of the first interference reconstruction image according to the complex amplitude distribution of the reference beam and the light intensity distribution of the first interference image;
specifically, fig. 10 is a schematic flowchart of a method for obtaining a complex amplitude distribution of a first interference reconstructed image according to a complex amplitude distribution of reference light and a light intensity distribution of the first interference image according to an embodiment of the present application. As shown in fig. 10, the method specifically includes:
921, removing a direct current item and a virtual image of the light intensity in the first interference image through a filtering algorithm to obtain the light intensity distribution of the first real image;
namely, the DC item of the light intensity distribution in the first interference image is removed by utilizing a low-pass filtering algorithm
And virtual images
Leaving only the real image
Since only the real image is related to the phase distribution of the transparent sample,therefore, noise can be reduced and effective information can be extracted. Thus, the light intensity distribution of the first real image is obtained as:
922, the complex amplitude distribution of the reference beam and the light intensity distribution of the first real image are superposed to obtain the complex amplitude distribution of the first interference reconstruction image.
According to the complex amplitude distribution of the reference beam and the light intensity distribution of the first real image, the reference beam is the part of the illumination beam which is directly incident to the objective lens without passing through the transparent sample
Representing the complex amplitude distribution of the reference beam, resulting in a complex amplitude distribution of the first interferometric reconstructed image:
wherein the content of the first and second substances,
is the complex amplitude of the reference beam.
930, calculating the first phase distribution from the complex amplitude distribution of the first interference reconstructed image;
specifically, fig. 11 is a flowchart illustrating a method for calculating a first phase distribution according to a complex amplitude distribution of a first interference reconstructed image according to an embodiment of the present application. As shown in fig. 11, the method specifically includes:
931, obtaining frequency domain complex amplitude distribution of the first interference reconstruction image transmitted to an image plane by using an angular spectrum transmission algorithm;
that is, the frequency domain complex amplitude distribution of the first interference reconstruction image propagated to the image plane is calculated by formula (13):
wherein the content of the first and second substances,
is the frequency domain complex amplitude distribution of the filtered image,
is composed ofxThe spatial frequency of the direction of the light,
is composed ofyThe spatial frequency of the direction of the light,kin terms of the wave number, the number of waves,drepresenting the propagation distance.
932, obtaining a spatial domain complex amplitude distribution of the first interference reconstruction image transmitted to an image plane by utilizing inverse Fourier transform;
namely, the frequency domain complex amplitude distribution of the first interference reconstruction image after being transmitted to the image plane is obtained through inverse Fourier transform according to the formula (14):
933, extracting a real part and an imaginary part in the spatial domain complex amplitude distribution of the first interference reconstruction image, and calculating the first phase distribution.
Namely, extraction
The first phase distribution is calculated according to equation (15):
wherein the content of the first and second substances,
an imaginary part of the spatial complex amplitude distribution of the image is reconstructed for the first interference,
the real part of the spatial domain complex amplitude distribution of the image is reconstructed for the first interference.
250, removing the transparent sample, obtaining a second interference image after irradiating the grating plate by the illumination beam, and obtaining a second phase distribution according to the second interference image;
removing the transparent sample, and allowing the illuminating beam to pass through the grating plate, wherein the grating on the grating plate is the same as the grating selected when the transparent sample exists, so that the light intensity distribution of the second interference image is obtained; removing the direct current item and the virtual image of the light intensity in the second interference image through a filtering algorithm to obtain a second real image; superposing the complex amplitude distribution of the reference beam and the light intensity distribution of the second real image to obtain the complex amplitude distribution of the second interference reconstruction image; converting the spatial domain complex amplitude distribution of the second interference reconstruction image into frequency domain complex amplitude distribution through Fourier transform; obtaining the frequency domain complex amplitude distribution of the second interference reconstruction image transmitted to the image plane according to the frequency domain complex amplitude distribution of the second interference reconstruction image by using an angular spectrum transmission algorithm; obtaining the spatial domain complex amplitude distribution of the second interference reconstruction image transmitted to the image plane by utilizing inverse Fourier transform; and extracting a real part and an imaginary part in the space-domain complex amplitude distribution of the second interference reconstruction image, and calculating a second phase distribution.
260, obtaining a phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
270, calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
Calculating the phase distribution of the transparent sample according to the formula (8)
Since the phase difference is determined by the optical path difference and the refractive index distribution, and the thickness variation distribution of the transparent sample is known, the refractive index distribution of the transparent sample is calculated according to the formula (9).
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A defect detecting apparatus for a transparent sample, comprising:
the light source, the objective table, the objective lens, the grating plate and the image acquisition device are sequentially arranged along the light path;
the light source is used for generating an illumination light beam, and the radius of the illumination light beam is R; the objective table is used for bearing a transparent sample, the diameter of the transparent sample is 2R, and the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; the objective lens is positioned on one side of the bearing surface of the objective table; the central axis of the transparent sample is not coincident with the central axis of the objective lens; the grating plate is positioned on the focal plane of the objective lens, the grating plate comprises a plurality of gratings, the grating periods of the gratings are different, the illumination light beam generates diffraction after passing through the grating plate, and the zero-order diffraction and the first-order diffraction in the diffraction generate interference; the image acquisition device is used for acquiring a first interference image when the transparent sample is carried on the object stage for detection and a second interference image when the transparent sample on the object stage is removed;
further comprising processing means for determining a minimum grating period suitable for said transparent sample based on the radius R of said transparent sample and the radius R of said illumination beam
And maximum grating period
(ii) a The processing device is electrically connected with the image acquisition device and is used for respectively calculating a first phase distribution and a second phase distribution according to the first interference image and the second interference image, acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample; wherein the maximum grating period
The grating period corresponds to the grating period when the part of the zero-order diffraction beam containing the transparent sample information is circumscribed with the region of the first-order diffraction beam containing the transparent sample information; the minimum grating period
The area of the zero-order diffraction beam containing the transparent sample information and the area of the first-order diffraction beam containing the transparent sample information are not overlapped, and the grating period corresponding to the inscribing of the area of the zero-order diffraction beam containing the transparent sample information and the area of the first-order diffraction beam not containing the transparent sample information is obtained.
2. The defect detection apparatus of claim 1, further comprising:
a beam expander and a mirror;
the beam expander is positioned between the light source and the reflector; the reflector is used for reflecting the illumination light beams emitted by the light source to the objective table after passing through the beam expander.
3. The defect inspection apparatus of claim 1, wherein the stage comprises a transparent region, and the transparent specimen is disposed in the transparent region.
4. The apparatus for detecting defects of a transparent sample according to claim 1, wherein a plurality of the gratings are arranged on the grating plate in M rows and N columns;
the grating plate is movable in a plane parallel to the stage in a row direction and a column direction.
5. A method for detecting defects of a transparent sample, comprising:
acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; and determining the minimum grating period suitable for the transparent sample according to the radius R of the transparent sample and the radius R of the illumination light beam
And maximum grating period
(ii) a Wherein the maximum grating period
The grating period corresponds to the grating period when the part of the zero-order diffraction beam containing the transparent sample information is circumscribed with the region of the first-order diffraction beam containing the transparent sample information; the minimum grating period
A grating period corresponding to the case that the region of the zero-order diffraction beam containing the transparent sample information and the region of the first-order diffraction beam containing the transparent sample information are not overlapped, and the region of the zero-order diffraction beam containing the transparent sample information is internally tangent to the region of the first-order diffraction beam not containing the transparent sample information;
placing the transparent sample on an objective table, wherein the central axis of the transparent sample is not coincident with the central axis of the objective lens;
arranging a grating plate with a preset grating period on the focal plane of an objective lens; the grating plate comprises a plurality of gratings, and the grating periods of the gratings are different; the preset grating period is more than or equal toAt the minimum grating period
And is less than or equal to the maximum grating period
；
Obtaining a first interference image of the transparent sample, and obtaining a first phase distribution according to the first interference image;
removing the transparent sample, obtaining a second interference image after the grating plate is irradiated by the illumination light beam, and obtaining a second phase distribution according to the second interference image;
acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
6. The defect detection method of claim 5, wherein obtaining the first interference image of the transparent sample from which the first phase distribution is obtained comprises:
acquiring the light intensity distribution of the first interference image of the transparent sample;
acquiring the complex amplitude distribution of a first interference reconstruction image according to the complex amplitude distribution of the reference beam and the light intensity distribution of the first interference image;
and calculating the first phase distribution according to the complex amplitude distribution of the first interference reconstruction image.
7. The method of claim 6, wherein the obtaining the complex amplitude distribution of the first interference reconstructed image according to the complex amplitude distribution information of the reference light and the first interference image comprises:
removing the direct current item and the virtual image of the light intensity in the first interference image through a filtering algorithm to obtain the light intensity distribution of a first real image;
and superposing the complex amplitude distribution of the reference beam and the light intensity distribution of the first real image to obtain the complex amplitude distribution of the first interference reconstruction image.
8. The defect detection method of claim 6, wherein said calculating the first phase distribution from the complex amplitude distribution of the first interferometrically reconstructed image comprises:
obtaining frequency domain complex amplitude distribution of the first interference reconstruction image transmitted to an image plane by using an angular spectrum transmission algorithm;
obtaining the spatial domain complex amplitude distribution of the first interference reconstruction image transmitted to the image plane by utilizing inverse Fourier transform;
and extracting a real part and an imaginary part in the spatial domain complex amplitude distribution of the first interference reconstruction image, and calculating the first phase distribution.
9. The defect detection method of claim 5, wherein the refractive index profile of the transparent sample is calculated using the following formula:
wherein λ is the wavelength of the illumination beam,xis a coordinate in the x direction and is,yis a coordinate in the y direction and is,din order to be able to travel a distance,
is the phase distribution of the transparent sample,
is the thickness variation distribution of the transparent sample.
10. The defect detection method of claim 5, wherein the minimum grating period is determined by calculation using the following formulap min And stationThe maximum grating periodp max ：
Wherein λ is the wavelength of the illumination beam,his the distance between the image acquisition device and the grating plate.
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