CN116222394A - Differential confocal axial range expansion measuring device, system and method - Google Patents
Differential confocal axial range expansion measuring device, system and method Download PDFInfo
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Abstract
The invention discloses a differential confocal axis vector range expansion measurement device, a differential confocal axis vector range expansion measurement system and a differential confocal axis vector range expansion measurement method, and belongs to the field of confocal microscopic measurement. The objective table drives the measured sample to move up and down along the axial direction to realize layer scanning, and combines the differential confocal microscopic measurement technology used by an illumination unit, a collimating lens, a digital micromirror device, a beam splitter lens, an objective lens and a focusing lens, and adjusts the axial distance of reference planes according to the multiple of the objective lens used by a measurement system, and simultaneously carries out intersection operation on a pre-focusing defocused image and a post-focusing defocused image according to the effective measurement area of each reference plane to determine the reducible image area of each reference plane.
Description
Technical Field
The invention relates to the field of confocal microscopic measurement, in particular to a differential confocal axial distance expansion measurement device, a differential confocal axial distance expansion measurement system and a differential confocal axial distance expansion measurement method.
Background
Confocal microscopy as a non-contact optical measurement method with high measurement accuracy, high resolution and unique chromatographic capability has been widely used in the fields of semiconductor detection, precision measurement, biological medicine and the like since the last century. The traditional confocal microscopic measurement technology is based on the conjugation of an illumination pinhole and an imaging pinhole for imaging, and needs to scan layer by layer when measuring the three-dimensional morphology information of the surface of a sample, and realizes axial positioning and quantification by using a peak positioning algorithm. In order to improve the axial measurement efficiency and the measurement accuracy, a plurality of scholars start from the relation curve of the axial light intensity and the axial position, and a plurality of different differential measurement methods are provided. But is limited by the axial defocus distance before/after the focus, so that the high-precision measurement range is limited, and the axial large-range measurement cannot be realized. In addition, the existing differential confocal 3D measurement method is mainly focused on improving the single-range measurement efficiency and measurement accuracy under single measurement, and lacks a processing method for axially expanding the layer scanning data. Meanwhile, with the rapid development of the semiconductor industry, the chip stacking technology has become the key of the current development, and how to ensure the compatibility of the measurement precision and the measurement range has become the key of the current measurement technology development. Therefore, a measurement method which combines axial measurement accuracy and axial measurement range is urgently needed at the present stage.
Disclosure of Invention
The invention aims to provide a differential confocal axial measuring range expansion measuring device, a differential confocal axial measuring range expansion measuring system and a differential confocal axial measuring range expansion measuring method, which can expand the differential confocal axial measuring range and realize axial wide-range measurement.
In order to achieve the above object, the present invention provides the following solutions:
a differential confocal axial extension measuring device comprises: the device comprises an illumination unit, a collimating lens, a digital micro-mirror device, a beam splitting lens, an objective table, a focusing lens and a camera;
the objective table is used for driving the tested sample to move up and down along the axial direction;
after the objective table drives the tested sample to move once along the axial direction, the illumination unit emits single beam light and reaches the digital micro-mirror device through the collimating lens; the digital micro-mirror device modulates single light into parallel point light arrays, and feeds the parallel point light arrays back, and the fed parallel point light arrays are converged on the surface of a sample to be measured through an objective lens after passing through a beam splitting lens; the collected light rays are reflected by the surface of the sample to be measured and then sequentially transmitted through the objective lens and the beam splitting lens, and are collected into the camera through the focusing lens;
the camera is used for collecting surface information of the measured sample at different axial positions; the measured sample surface information characterizes the height measurement result of the axial measuring range.
Optionally, the method further comprises: a tube mirror;
the tube lens is arranged between the beam-splitting lens and the objective lens, and the objective table, the objective lens, the tube lens, the beam-splitting lens, the focusing lens and the camera are parallel to each other; the tube lens is used for connecting the beam splitting lens and the objective lens.
Optionally, the single beam of light emitted by the illumination unit is monochromatic light, polychromatic light, visible light or invisible light.
Optionally, the beam-splitting lens is a semi-transparent semi-reflective lens, or a combination of a polarizer and a polarizing beam splitter;
the objective table is a three-dimensional motion objective table and is used for driving the tested sample to move in a two-dimensional plane or a three-dimensional space.
A differential confocal axial extension measurement system, comprising: the processing unit and the differential confocal axial distance expansion measuring device;
the processing unit is used for acquiring the surface information of the measured sample at different axial positions acquired by the differential confocal axial range expansion measuring device, determining a height measuring result with a full field of view according to the surface information of the measured sample at different axial positions, and realizing axial range expansion measurement.
The differential confocal axial range expansion measurement method applies the differential confocal axial range expansion measurement system, and the differential confocal axial range expansion measurement method comprises the following steps:
according to the multiple of the objective lens in the differential confocal axial range expansion measurement system, determining the axial distance between adjacent reference planes; the reference plane is a focal plane formed by focusing the surface of the sample to be tested after the object stage drives the sample to be tested to move once along the axial direction;
the objective table drives the measured sample to axially move to each reference plane according to the axial distance;
after the measured sample moves forwards and backwards equidistantly along the axial direction from each reference plane, a pre-focal defocus image and a post-focal defocus image are obtained;
determining a differential light intensity response curve of the front and rear of the focus corresponding to the reference plane, and acquiring an effective measurement area of each axial reference plane position from the differential light intensity response curve;
according to the effective measurement area, performing intersection operation on the pre-focusing defocused image and the post-focusing defocused image, and determining a reducible image area in each reference plane;
restoring the height information of each reference plane according to the image area which can be restored in each reference plane;
and fusing the restored height information of all the reference planes to obtain a height measurement result with a full field of view.
Optionally, determining the axial distance between adjacent reference planes according to the multiple of the objective lens in the differential confocal axial distance expansion measurement system specifically includes:
when the measurement is started, determining a focal plane formed by primary focusing on the surface of a sample to be measured on the objective table as a zeroth reference plane;
determining an axial offset distance according to the multiple of the objective lens; the axial offset distance is a distance that moves axially forward or backward from the reference plane;
the axial light intensity measuring curve of the pre-calibrated zeroth reference plane is axially moved according to the axial offset distance, and a pre-focal axial light intensity response curve and a post-focal axial light intensity response curve are obtained;
subtracting the axial light intensity response curve before the coke from the axial light intensity response curve after the coke to obtain a differential light intensity response curve before the coke and after the coke corresponding to a zeroth reference plane;
determining a linear measurement area from a differential light intensity response curve between the front focus and the rear focus corresponding to the zeroth reference plane;
and determining the distance length corresponding to the linear measurement area as the axial distance between the adjacent reference planes.
Optionally, determining a differential light intensity response curve of each reference plane corresponding to the front focal point and the back focal point, and obtaining an effective measurement area of the axial position from the differential light intensity response curve, which specifically includes:
using the formula
Determining a differential light intensity response curve between the front focus and the back focus corresponding to each reference plane; wherein I is z For differential light intensity response curve, +.>
Is the response curve of the axial light intensity before focusing, +.>
Is the axial light intensity response curve after focusing, z is the axial position of the reference plane, z d A distance that moves axially forward or backward from the reference plane;
and determining a linear region from the differential light intensity response curve, and taking a distance range corresponding to the linear region as an effective measurement region of the axial position.
Optionally, according to the effective measurement area, performing intersection operation on the pre-focusing defocused image and the post-focusing defocused image, and determining an image area capable of being restored in each reference plane specifically includes:
the effective measuring range is respectively brought into a front axial light intensity response curve and a rear axial light intensity response curve to respectively obtain effective light intensity intervals before and after the coke;
and performing intersection operation on the front defocusing image part corresponding to the front effective light intensity interval and the rear defocusing image part corresponding to the rear effective light intensity interval to obtain a reducible image area in the reference plane.
Optionally, restoring the height information of each reference plane according to the image area capable of being restored in each reference plane specifically includes:
calculating the height information of the zeroth reference plane by using a conventional differential axial measurement curve z (x, y) =k×i (x, y) +b according to the image area capable of being restored in the reference plane; wherein z (x, y) is the height information of the pixel point (x, y) on the zeroth reference plane, I (x, y) is the gray value of the pixel point (x, y), k is the slope, and b is the constant;
according to formula H n ＝z(x,y)+n×2z d Calculating height information of the reference plane; wherein H is n Height information for the nth reference plane.
Optionally, the objective table drives the tested sample to move along the axial direction unidirectionally from the zeroth reference plane according to the axial distance until the reference plane is stopped when gray information does not exist.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention discloses a differential confocal axial direction range expansion measuring device, wherein an objective table drives a measured sample to move up and down along the axial direction to realize layer scanning, and the differential confocal microscopic measuring technology used by a lighting unit, a collimating lens, a digital micromirror device, a beam splitter lens, an objective lens and a focusing lens is combined, so that the differential confocal axial direction measuring range is expanded, and the axial wide-range measurement is realized.
The invention discloses a differential confocal axial vector range expansion measurement system and a differential confocal axial vector range expansion measurement method, which are used for adjusting the axial distance between reference planes according to the multiple of an objective lens used by the measurement system, carrying out intersection operation on an out-of-focus image before focusing and an out-of-focus image after focusing according to the effective measurement area in each reference plane, determining an image area which can be truly restored in each reference plane, and expanding the differential confocal axial measurement range, realizing the axial wide-range measurement and simultaneously ensuring the axial measurement precision by combining a differential confocal measurement method with a layer scan.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a differential confocal axial direction expansion measurement device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a differential confocal axial direction expansion measurement system according to an embodiment of the present invention;
FIG. 3 is a flow chart of a differential confocal axial range expansion measurement method provided by an embodiment of the invention;
FIG. 4 is a schematic diagram of the principle of extending the axial range of parallel differential confocal axes according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a differential confocal measurement according to an embodiment of the present invention.
Symbol description: the device comprises an illumination unit-1, a collimating lens-2, a digital micro-mirror device-3, a beam splitting lens-4, a tube lens-5, an objective lens-6, a stage-7, a focusing lens-8, a camera-9 and a processing unit-10.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a differential confocal axial measuring range expansion measuring device, a differential confocal axial measuring range expansion measuring system and a differential confocal axial measuring range expansion measuring method, which can expand the differential confocal axial measuring range and realize axial wide-range measurement.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
As shown in fig. 1, an embodiment of the present invention provides a differential confocal axial extension measurement device, including: an illumination unit 1, a collimator lens 2, a digital micromirror device 3, a spectroscopic lens 4, an objective lens 6, a stage 7, a focusing lens 8, and a camera 9.
The objective table 7 is used for driving the tested sample to move up and down along the axial direction.
After the objective table 7 drives the tested sample to move once along the axial direction, the illumination unit 1 emits single beam light and reaches the digital micro-mirror device 3 through the collimating lens 2; the digital micro-mirror device 3 modulates single light into parallel point light arrays, and feeds the parallel point light arrays back, and the fed parallel point light arrays are converged on the surface of a sample to be measured through the objective lens 6 after passing through the beam splitting lens 4; the collected light is reflected by the surface of the sample to be measured and then sequentially transmitted through the objective lens 6 and the beam splitting lens 4, and is collected into the camera 9 through the focusing lens 8.
The camera 9 is used for collecting the surface information of the measured sample at different axial positions; the measured sample surface information characterizes the height measurement result of the axial measuring range.
The differential confocal axial direction expansion measuring device further comprises: and a tube mirror 5. The tube lens 5 is disposed between the spectroscopic lens 4 and the objective lens 6, and the stage 7, the objective lens 6, the tube lens 5, the spectroscopic lens 4, the focusing lens 8, and the camera 9 are parallel to each other. The tube lens 5 is used for connecting the beam-splitting lens 4 and the objective lens 6.
Specifically, the illumination unit 1 includes a point light source, and generates point illumination light. The point illumination light is directed towards the collimating lens 2, the dmd 3, which are collinear, creating an array of parallel light. The point illumination light sequentially passes through the collimating lens 2 and then reaches the digital micro-mirror device 3, the feedback point light array irradiates the objective table 7 through the beam splitting lens 4, the tube lens 5 and the objective lens 6, is reflected by the objective table 7 and then passes through the beam splitting lens 4 again, and is converged to the camera 9 through the focusing lens 8.
The single beam of light emitted by the lighting unit 1 is illustratively monochromatic light, polychromatic light, visible light or invisible light.
In one example, the beam splitting lens 4 is a half-mirror lens, or a combination of a polarizer and a polarizing beam splitter.
In another example, the stage 7 is a three-dimensional moving stage, so as to drive the sample to be measured to move in a two-dimensional plane or a three-dimensional space.
The measuring device can also be a double-camera system and a three-camera system, only the image acquisition step in the axial scanning process is influenced, and the double-camera system can acquire two images before and after the focus at the same time without controlling the objective table to axially and independently move to acquire the images; the three cameras are similar.
According to the differential confocal axial direction range expansion measuring device, the differential confocal axial direction measurement range is expanded by combining differential confocal measurement with differential layer scanning, and axial wide-range measurement is realized.
Example two
The embodiment of the invention provides a differential confocal axial distance expansion measurement system, as shown in fig. 2, comprising: the processing unit 10 and the differential confocal axial extension measuring device of the first embodiment;
the processing unit 10 is configured to obtain surface information of the measured sample at different axial positions acquired by the differential confocal axial range expansion measurement device, determine a height measurement result with a full field of view according to the surface information of the measured sample at different axial positions, and implement axial range expansion measurement.
Example III
The embodiment of the invention provides a differential confocal axial range expansion measurement method, which applies the differential confocal axial range expansion measurement system, as shown in fig. 3, and comprises the following steps:
step S1, according to the multiple of an objective lens in a differential confocal axial displacement expansion measurement system, determining the axial distance between adjacent reference planes; the reference plane is a focal plane formed by focusing the surface of the sample to be tested after the object stage drives the sample to be tested to move once along the axial direction.
Illustratively, the axial spacing determination method is:
when the measurement is started, determining a focal plane formed by primary focusing on the surface of a sample to be measured on the objective table as a zeroth reference plane;
determining an axial offset distance according to the multiple of the objective lens; the axial offset distance is a distance that moves axially forward or backward from the reference plane;
the axial light intensity measuring curve of the pre-calibrated zeroth reference plane is axially moved according to the axial offset distance, and a pre-focal axial light intensity response curve and a post-focal axial light intensity response curve are obtained;
subtracting the axial light intensity response curve before the coke from the axial light intensity response curve after the coke to obtain a differential light intensity response curve before the coke and after the coke corresponding to a zeroth reference plane;
determining a linear measurement area from a differential light intensity response curve between the front focus and the rear focus corresponding to the zeroth reference plane;
and determining the distance length corresponding to the linear measurement area as the axial distance between the adjacent reference planes.
Wherein the axial offset distances moved by the objective lenses of different multiples are different, for example: under the condition of 10 times objective lens measurement, the axial offset distance is 10 μm, and the distance length corresponding to the linear measurement area (axial effective measurement area) is 14 μm, namely, the measurement range of each differential measurement is 14 μm. Therefore, in order to enable distance measurement of the full field of view, the axial spacing of adjacent reference planes is determined to be 14 μm.
And S2, driving the tested sample to move to each reference plane along the axial direction by the objective table according to the axial distance.
Before measurement, the differential confocal axial range expansion measurement system is utilized to focus the surface of the measured sample, and the focal plane is used as a zeroth reference plane. And the object stage drives the tested sample to move along the axial direction unidirectionally from the zeroth reference plane according to the axial distance until the reference plane is stopped when gray information does not exist. Judging that gray information does not exist in the current reference plane: the gray information of the reference plane and the front/rear plane is zero.
After the sample to be measured moves to each reference plane, steps S3 to S6 are performed.
And S3, after the sample to be measured moves forwards and backwards equidistantly along the axial direction from each reference plane, acquiring a pre-focus defocus image and a post-focus defocus image.
The reference plane is taken as an axial reference zero point, the reference plane is respectively moved forwards/backwards by the same distance (axial offset distance), the forward movement can obtain a front focal image of the current reference plane, and the backward movement can obtain a back focal image of the current reference plane.
And S4, determining a differential light intensity response curve of the front and the back of the focus corresponding to each reference plane, and acquiring an effective measurement area of the axial position from the differential light intensity response curve.
In the confocal measurement system, the function relation between the axial light intensity and the axial defocus is that
The corresponding differential curve can be obtained by axially shifting the axial light intensity response curve before/after focusing and subtracting.
The principle of parallel differential confocal axial range expansion is shown in figure 4. In fig. 4, the ordinate Normalizedlight intensity indicates the normalized light intensity, the first reference plane: first pre-focal curve represents the First pre-focal axial light intensity response curve, first differential curve represents the First differential light intensity response curve, and First post-focal curve represents the First post-focal axial light intensity response curve. A second reference plane: second-focal curve represents the Second pre-focal axial intensity response curve, second differential curve represents the Second differential intensity response curve, and Second post-focal curve represents the Second post-focal axial intensity response curve. Third reference plane: the Third pre-focal curve represents the Third pre-focal axial intensity response curve, third differential curve represents the Third differential intensity response curve, and the Third post-focal axial intensity response curve.
The specific acquisition process of the effective measurement area is as follows:
using the formula
Determining a differential light intensity response curve between the front focus and the back focus corresponding to each reference plane; wherein I is z For differential light intensity response curve, +.>
Is the response curve of the axial light intensity before focusing, +.>
Is the axial light intensity response curve after focusing, z is the axial position of the reference plane, z d A distance that moves axially forward or backward from the reference plane;
and determining a linear region from the differential light intensity response curve, and taking a distance range corresponding to the linear region as an effective measurement region of the axial position.
As shown in the differential light intensity response curve of fig. 5, there is a linear region (linear) in the axial measurement curve after the differential, such as a dashed box in the middle position. It can be seen that the axial offset distances moved by the objective lenses of different multiples are different, and the axial offset distance is 10 μm under the condition of measuring the objective lens of 10 times. Whereas its axial effective measurement is only + -7 μm. The two dotted boxes on both sides in fig. 5 represent image areas where no true measurement height information is possible in the effective measurement gray scale section before/after focus, respectively.
And S5, performing intersection operation on the pre-focusing defocused image and the post-focusing defocused image according to the effective measurement area, and determining a reducible image area in each reference plane.
Illustratively, the determination of the image area in each reference plane that can be restored (truly restored) is:
the effective measurement range is brought into the front/back axial light intensity response curve, so that the corresponding light intensity interval can be found in the front/back axial light intensity response curve, but the gray scale interval can find solutions of two different axial ranges in the front/back axial light intensity response curve because of the unilateral symmetry property of the light intensity axial response curve. And the real solution can be subjected to intersection operation through gray scale areas meeting the real solution in the front image and the rear image. Restored in each reference plane is an image area that is truly measurable relative thereto.
And S6, restoring the height information of each reference plane according to the restored image area in each reference plane.
Calculating the height information of the zeroth reference plane by using a conventional differential axial measurement curve z (x, y) =k×i (x, y) +b according to the image area capable of being restored in the reference plane; wherein z (x, y) is the height information of the pixel point (x, y) on the zeroth reference plane, I (x, y) is the gray value of the pixel point (x, y), k is the slope, and b is the constant;
according to formula H n ＝z(x,y)+n×2z d Calculating height information of the reference plane; wherein H is n Height information for the nth reference plane.
And S7, fusing the restored height information of all the reference planes to obtain a height measurement result with a full field of view.
And fusing the image areas restored by the plurality of different axial reference planes to realize the height measurement of the whole area in the view field, namely realizing the differential confocal axial three-dimensional range extension measurement.
Fusion: the step superposition method is adopted for fusion, and besides the height information restored by adopting the conventional differential confocal measurement principle relative to the reference plane, the step S6 can be used for finding that the distance between the current reference plane and the zeroth reference plane is required to be added during fusion. After fusion, a height measurement with a full field of view is obtained.
The differential confocal axial range expansion measurement method is realized based on an information theory and is specifically embodied in the following places:
the first individual now controls the axial spacing of the different reference planes, which need to be adjusted according to the objective lens multiple used by the measurement system;
the second individual now needs an image intersection operation process of extracting the effective measurement area in each reference plane when performing range expansion measurement, namely when two or more reference planes are needed;
the third individual now determines when to complete the information of the measurement while performing the span extension measurement.
The existing differential confocal 3D measurement method is mainly focused on improving the single-range measurement efficiency and measurement accuracy under single measurement, and lacks a processing method for axially expanding the layer scanning data. According to the differential confocal axial direction range expansion measurement method, the differential confocal axial direction measurement range is expanded by combining the differential confocal measurement method with the differential layer scanning, and the axial large-range measurement is realized.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (10)
1. The utility model provides a differential confocal axial vector journey expands measuring device which characterized in that includes: the device comprises an illumination unit, a collimating lens, a digital micro-mirror device, a beam splitting lens, an objective table, a focusing lens and a camera;
the objective table is used for driving the tested sample to move up and down along the axial direction;
after the objective table drives the tested sample to move once along the axial direction, the illumination unit emits single beam light and reaches the digital micro-mirror device through the collimating lens; the digital micro-mirror device modulates single light into parallel point light arrays, and feeds the parallel point light arrays back, and the fed parallel point light arrays are converged on the surface of a sample to be measured through an objective lens after passing through a beam splitting lens; the collected light rays are reflected by the surface of the sample to be measured and then sequentially transmitted through the objective lens and the beam splitting lens, and are collected into the camera through the focusing lens;
the camera is used for collecting surface information of the measured sample at different axial positions; the measured sample surface information characterizes the height measurement result of the axial measuring range.
2. The differential confocal axial extension measurement apparatus of claim 1, further comprising: a tube mirror;
the tube lens is arranged between the beam-splitting lens and the objective lens, and the objective table, the objective lens, the tube lens, the beam-splitting lens, the focusing lens and the camera are parallel to each other; the tube lens is used for connecting the beam splitting lens and the objective lens.
3. The differential confocal axial travel expansion measurement device of claim 1, wherein the single beam of light emitted by the illumination unit is monochromatic light, polychromatic light, visible light or invisible light.
4. The differential confocal axial travel expansion measurement device of claim 1, wherein the beam-splitting lens is a half-transparent half-reflective lens, or a combination of a polarizer and a polarizing beam splitter;
the objective table is a three-dimensional motion objective table and is used for driving the tested sample to move in a two-dimensional plane or a three-dimensional space.
5. A differential confocal axial extension measurement system, comprising: a processing unit and the differential confocal axial extension measurement apparatus of any one of claims 1-4;
the processing unit is used for acquiring the surface information of the measured sample at different axial positions acquired by the differential confocal axial range expansion measuring device, determining a height measuring result with a full field of view according to the surface information of the measured sample at different axial positions, and realizing axial range expansion measurement.
6. The differential confocal axial range expansion measurement method is characterized in that the differential confocal axial range expansion measurement method is applied to the differential confocal axial range expansion measurement system according to claim 5, and comprises the following steps:
according to the multiple of the objective lens in the differential confocal axial range expansion measurement system, determining the axial distance between adjacent reference planes; the reference plane is a focal plane formed by focusing the surface of the sample to be tested after the object stage drives the sample to be tested to move once along the axial direction;
the objective table drives the measured sample to axially move to each reference plane according to the axial distance;
after the measured sample moves forwards and backwards equidistantly along the axial direction from each reference plane, a pre-focal defocus image and a post-focal defocus image are obtained;
determining a differential light intensity response curve of the front and rear of the focus corresponding to the reference plane, and acquiring an effective measurement area of each axial reference plane position from the differential light intensity response curve;
according to the effective measurement area, performing intersection operation on the pre-focusing defocused image and the post-focusing defocused image, and determining a reducible image area in each reference plane;
restoring the height information of each reference plane according to the image area which can be restored in each reference plane;
and fusing the restored height information of all the reference planes to obtain a height measurement result with a full field of view.
7. The differential confocal axial range expansion measurement method according to claim 6, wherein the axial distance between adjacent reference planes is determined according to the multiple of the objective lens in the differential confocal axial range expansion measurement system, and specifically comprises:
when the measurement is started, determining a focal plane formed by primary focusing on the surface of a sample to be measured on the objective table as a zeroth reference plane;
determining an axial offset distance according to the multiple of the objective lens; the axial offset distance is a distance that moves axially forward or backward from the reference plane;
the axial light intensity measuring curve of the pre-calibrated zeroth reference plane is axially moved according to the axial offset distance, and a pre-focal axial light intensity response curve and a post-focal axial light intensity response curve are obtained;
subtracting the axial light intensity response curve before the coke from the axial light intensity response curve after the coke to obtain a differential light intensity response curve before the coke and after the coke corresponding to a zeroth reference plane;
determining a linear measurement area from a differential light intensity response curve between the front focus and the rear focus corresponding to the zeroth reference plane;
and determining the distance length corresponding to the linear measurement area as the axial distance between the adjacent reference planes.
8. The differential confocal axial range expansion measurement method of claim 6, wherein determining a differential light intensity response curve of each reference plane corresponding to the front and back of the focus, and obtaining an effective measurement area of the axial position from the differential light intensity response curve, comprises:
using the formula
Determining a differential light intensity response curve between the front focus and the back focus corresponding to each reference plane; wherein I is z For differential light intensity response curve, +.>
Is a response curve of the axial light intensity before the focus,
is the axial light intensity response curve after focusing, z is the axial position of the reference plane, z d A distance that moves axially forward or backward from the reference plane;
and determining a linear region from the differential light intensity response curve, and taking a distance range corresponding to the linear region as an effective measurement region of the axial position.
9. The differential confocal axial range expansion measurement method according to claim 6, wherein the intersection operation is performed on the pre-focus defocus image and the post-focus defocus image according to the effective measurement region, and the determination of the image region that can be restored in each reference plane specifically comprises:
the effective measuring range is respectively brought into a front axial light intensity response curve and a rear axial light intensity response curve to respectively obtain effective light intensity intervals before and after the coke;
and performing intersection operation on the front defocusing image part corresponding to the front effective light intensity interval and the rear defocusing image part corresponding to the rear effective light intensity interval to obtain a reducible image area in the reference plane.
10. The differential confocal axial extension measurement method of claim 7, wherein restoring the height information of each reference plane according to the image region that can be restored in each reference plane specifically comprises:
calculating the height information of the zeroth reference plane by using a conventional differential axial measurement curve z (x, y) =k×i (x, y) +b according to the image area capable of being restored in the reference plane; wherein z (x, y) is the height information of the pixel point (x, y) on the zeroth reference plane, I (x, y) is the gray value of the pixel point (x, y), k is the slope, and b is the constant;
according to formula H n ＝z(x,y)+n×2z d Calculating height information of the reference plane; wherein H is n Height information for the nth reference plane.
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