CN116518852A - Three-dimensional displacement measurement system based on digital grating - Google Patents
Three-dimensional displacement measurement system based on digital grating Download PDFInfo
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- CN116518852A CN116518852A CN202310429658.3A CN202310429658A CN116518852A CN 116518852 A CN116518852 A CN 116518852A CN 202310429658 A CN202310429658 A CN 202310429658A CN 116518852 A CN116518852 A CN 116518852A
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- 238000001259 photo etching Methods 0.000 description 3
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- 238000004556 laser interferometry Methods 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
Abstract
The invention discloses a three-dimensional displacement measurement system based on a digital grating, and belongs to the technical field of semiconductor integrated circuit manufacturing. The three-dimensional displacement measurement system includes: XY direction measuring mechanism, Z direction measuring mechanism and industrial computer. The invention utilizes the property of even arrangement of camera pixel points, and provides a digital grating structure, wherein the digital grating is formed by simulating equidistant rows or columns of a camera into a light transmission area and a light non-transmission area, overlapping the equidistant rows or columns of the camera with an image formed by an optical one-dimensional or two-dimensional grating on the surface of the camera to form moire fringe images which can be used for measurement, and searching for periods with equal light intensity in the rows and the columns respectively as alignment points so as to calculate three-dimensional displacement information; the invention has the advantages of environmental interference resistance of the grating type measuring system, lower cost, higher flexibility, simple and efficient whole use, realization of high-precision and high-speed displacement measurement and positive influence on improvement of integrated circuit manufacturing equipment.
Description
Technical Field
The invention relates to a three-dimensional displacement measurement system based on a digital grating, belonging to the technical field of semiconductor integrated circuit manufacturing.
Background
With the continuous shrinking of critical dimensions of very large scale integrated circuits, it is very challenging to manufacture integrated circuits, and the most critical process for manufacturing chips is photolithography. Due to the continuous improvement of lithography precision and productivity, higher and stricter requirements are put on the positioning precision and speed of the wafer table. The positioning accuracy of the wafer table is ensured by a feedback control system. A six-dimensional displacement measurement system measures the current position of the wafer table and transmits the position information to a feedback control device. The device adjusts according to the deviation of the current position and the ideal position, so that the wafer table is near the ideal position. It can be seen that the displacement measurement system is very important in the lithography machine, and its measurement accuracy is a precondition for ensuring the positioning accuracy of the wafer table. In the lithography technique, six-degree-of-freedom displacement measurement is essentially achieved by a plurality of X, Y, Z three-dimensional displacement measurement systems.
Three-dimensional displacement measurement systems in advanced lithography machines are mainly divided into two types: laser interferometry systems and grating measurement systems. Laser interferometry systems are widely used in Extreme Ultraviolet (EUV) lithography and various Deep Ultraviolet (DUV) lithography based on laser interference effects. The measurement accuracy of the interferometer depends on the laser wavelength, when the temperature and humidity, the air pressure and the air flow in the environment change, the error can be increased, and the error caused by the environment is usually nonlinear error and is difficult to eliminate by a later measurement means, so that another measurement system is mostly adopted in the immersion type DUV photoetching machine of an advanced node: a grating type displacement measuring system. The grating measuring system takes the grating distance of the grating as a measuring reference, and meanwhile, the distance between the measuring equipment and the object to be measured is greatly shortened, so that the dependence on the environment is greatly reduced, but the cost is increased when high-precision measurement is realized.
In summary, the existing lithography machine displacement measurement system has at least the following disadvantages: (1) When the laser interferometer is used for a three-dimensional displacement measurement system in a photoetching machine, the influence of environmental disturbance is large, nonlinear errors which cannot be eliminated in the later period exist, and the laser interferometer is not suitable for being used in an advanced immersion photoetching machine; (2) The grating type measuring system has high use cost and complex expansion freedom degree, and the optical structure of the grating type measuring system needs to be changed.
Disclosure of Invention
The invention utilizes the property of uniform arrangement of pixel points of CCD or CMOS camera, and provides a digital two-dimensional grating structure, which is characterized in that equidistant rows and columns of the camera are simulated into a light transmission area and a light non-transmission area, moire fringe images which can be used for measurement are formed by overlapping images formed by the optical two-dimensional grating on the surface of the camera, periods with equal light intensity in the rows and the columns are respectively searched as alignment points, displacement information in two directions is calculated, the image processing is carried out by utilizing the overlapping grating structure, a moire fringe signal curve is generated, and the alignment points of the curve are tracked, so that long-stroke measurement can be realized. In addition, the stacked grid structure can be used for Z-direction long-travel measurement by combining an optical triangulation method or other optical principles.
The specific technical scheme is as follows:
a first object of the present invention is to provide a three-dimensional displacement measurement system comprising: XY direction measuring mechanism, Z direction measuring mechanism and industrial computer;
the XY direction measurement mechanism includes: a first camera, a first light source, and a reflective two-dimensional grating; the first light source emits light to irradiate the surface of the reflective two-dimensional grating to form periodic reflected light to image on the first camera lens, and the first camera transmits image data to the industrial personal computer for image processing;
the Z-direction measuring mechanism includes: the device comprises a second light source, a projection objective, a transmission grating, a reflecting mirror component, a detection lens cone and a second camera; the light emitted by the second light source is telecentric light beam after passing through the projection objective lens, periodically passes through the transmission grating, passes through the reflection mirror component and the object to be detected, and then is imaged on the second camera through the detection lens barrel, and the second camera transmits the acquired image data to the industrial personal computer for image processing.
Optionally, the transmission grating is an amplitude type one-dimensional grating.
Optionally, the mirror assembly includes: the first reflecting mirror and the second reflecting mirror are respectively positioned at two sides of the object to be detected, are higher than the upper surface of the object to be detected and have the same height, and the reflecting surfaces are opposite.
The second object of the present invention is to provide a three-dimensional displacement measurement method, which is implemented based on the three-dimensional displacement measurement system described in any one of the above, wherein the industrial personal computer collects physical grating images collected by the camera, and generates a grating overlapping effect with a digital grating formed by itself according to a similar period to form a signal that can be used for measurement, and when the sample to be measured is displaced, the industrial personal computer calculates and obtains displacement in three directions X, Y, Z through the change of the digital grating period, and the correspondence between the digital grating period and the position is obtained through early calibration;
the calculation method of the digital grating period comprises the following steps:
dividing an image into a plurality of equal and mutually independent bright areas and dark areas according to camera pixels, numbering the images in sequence from the upper part to the lower part of the image, respectively calculating and recording the light intensity accumulated values of the bright areas and the dark areas in each numbered area, and if a certain number exists, the accumulated value of the light intensity of the bright areas is equal to the accumulated value of the light intensity of the dark areas, and then, the value of the number is called as an alignment point.
Optionally, the method for calculating the digital grating period further includes:
recording the light intensity of the bright area and the light intensity of the dark area in each digital grating area, calculating the difference value of the light intensity of the bright area and the light intensity of the dark area in each digital grating area, and thus, the numbered area with the light intensity difference value of 0 is an alignment point, if no point which is exactly 0 exists actually, fitting by using a polynomial function, finding the zero point position of the function, and marking the transverse sitting position of the zero point position as the alignment point.
Optionally, the method adopts an incremental measurement method to realize long-stroke displacement measurement, and the incremental measurement method comprises the following steps:
by selecting a proper system, at least two or more alignment points exist in each dimension digital grating, the incremental measurement method judges which alignment points disappear at the previous moment by making difference between the alignment points measured at the current moment and the alignment points recorded at the previous moment, and updates displacement information by tracking the alignment points which do not disappear, and after each measurement is completed, all the alignment points and the position information are recorded, so that the iteration of the position information and the alignment point information is completed, and long-stroke displacement measurement is realized.
A third object of the present invention is to provide an XY direction displacement measurement method, which realizes the measurement of XY direction displacement by using the three-dimensional displacement measurement method described in any one of the above.
A fourth object of the present invention is to provide a height displacement measurement method, which uses any one of the above three-dimensional displacement measurement methods to measure displacement in the Z direction.
The invention has the beneficial effects that:
the invention utilizes the property of uniform arrangement of pixel points of a CCD or CMOS camera, provides a digital two-dimensional grating structure, not only has the advantage of environmental interference resistance of a grating type measuring system, but also has lower cost and higher flexibility compared with the grating type measuring system based on a diffraction principle, and the measuring precision is related to the magnification of the camera, thereby realizing high-precision high-speed displacement measurement and having positive influence on improving integrated circuit manufacturing equipment.
In addition, the optical part of the three-dimensional measurement system is not based on interference and diffraction principles, and the whole light path structure is concise by combining the reflection type with an image processing algorithm, and the subsequent processing of the measurement data is embodied in an excellent algorithm design, so that the optical structure is not required to be changed when the multi-dimensional measurement is realized, the measurement cost can be reduced, and the whole use is simple and efficient.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and 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 the three-dimensional displacement measurement system of the present invention.
Fig. 2 is a Z-directed schematic view of the displacement measurement system of the present invention.
Fig. 3 is a diagram of an image and digital raster image detected by a camera of the present invention.
FIG. 4 is a plot of a function fit solution alignment of the present invention.
Fig. 5 is a chart of alignment point recordings at the time of long-stroke measurement according to the present invention.
FIG. 6 is a schematic diagram of the construction of the XY direction measurement system of the present invention.
Fig. 7 is a two-dimensional raster embodiment of the present invention.
Fig. 8 is a view of a two-dimensional grating of the present invention imaged on a camera surface.
Fig. 9 is a diagram of a modulation method of a two-dimensional digital grating according to the present invention, wherein (a) is a modulation diagram in an X direction and (b) is a modulation diagram in a Y direction.
Wherein 1-a first camera; 2-a light source; 3-reflective two-dimensional gratings; 4-LED light sources; 5-projection objective; 6-amplitude type one-dimensional grating; 7-two mirrors; 8-detecting lens barrel; 9-a second camera; 10-industrial personal computer.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the embodiments of the present invention will be described in further detail with reference to the accompanying drawings.
Embodiment one:
the present embodiment provides a three-dimensional displacement measurement system including: XY direction measuring mechanism, Z direction measuring mechanism and industrial computer;
the XY direction measurement mechanism includes: a first camera, a first light source, and a reflective two-dimensional grating; the method comprises the steps that a reflective two-dimensional grating is placed on the surface of an object to be detected, a first light source emits light to illuminate the surface of the reflective two-dimensional grating, periodic reflected light is formed to form images on a first camera lens, and the first camera transmits image data to an industrial personal computer for image processing;
the Z-direction measuring mechanism includes: the device comprises a second light source, a projection objective, a transmission grating, a reflecting mirror component, a detection lens cone and a second camera; light emitted by the second light source is telecentric light beam after passing through the projection objective lens, periodically passes through the transmission grating, passes through the reflection of the reflecting mirror component and the object to be detected, and then is imaged on the second camera through the detection lens barrel, and the second camera transmits collected image data to the industrial personal computer for image processing.
Embodiment two:
the present embodiment provides a three-dimensional displacement measurement system, referring to fig. 1, the system includes: XY direction measuring mechanism, Z direction measuring mechanism and industrial computer.
Wherein the XY direction measuring mechanism includes: the method comprises the steps that a first camera 1, a light source 2 and a reflective two-dimensional grating 3 attached to the surface of an object to be detected are adopted, after light emitted by the light source 2 strikes the surface of the reflective two-dimensional grating 3, the reflective two-dimensional grating 3 periodically reflects light to form cross bright stripes to be imaged on the camera 1 with a matched lens, the camera 1 transmits image data to an industrial personal computer 10 to conduct image processing, digital grating periods in the X direction and the Y direction are obtained, when the reflective two-dimensional grating 3 moves in the X direction or the Y direction, the digital grating periods in the X direction and the Y direction are changed, and displacement in the X direction and the Y direction is calculated.
The Z-direction measuring mechanism includes: the system comprises an LED light source 4, a projection objective 5, an amplitude type one-dimensional grating 6, two reflectors 7 for adjusting light paths, a detection lens barrel 8 and a second camera 9, wherein the light source emitted by the LED light source 4 is parallel light after passing through the projection objective 5, periodically passes through the amplitude type one-dimensional grating 6, is reflected by the two reflectors 7 and an object to be detected, is imaged on the second camera 9 through the detection lens barrel 8, finally image data acquired by the second camera 9 are transmitted to an industrial personal computer 10, the industrial personal computer 10 calculates a digital grating period through image processing, when the object to be detected changes in height, the image can generate corresponding displacement on the second camera 9, the displacement on the second camera 9 can enable the digital grating period calculated by the industrial personal computer 10 to change, and the linear relation between the change in height and the change in the digital grating period can be known through calibration, so that when the industrial personal computer 10 detects the change in the digital grating period, the change in the height of the object to be detected can be reversely calculated.
The first camera 1 and the second camera 9 are synchronized, so that real-time three-dimensional displacement information of an object to be measured at any moment can be obtained, and the specific calculation method is as follows:
fig. 2 is a schematic diagram of a three-dimensional displacement measurement system for Z-direction measurement according to the present embodiment, where the basic principle is an optical triangulation method, and the left side is a projection objective system, and a transmission grating image (transmission grating: grating is equally spaced and divided into a light-transmitting area and a light-non-transmitting area) customized in the earlier stage is imaged on the upper surface of an object to be measured, reflected and imaged on the upper surface of the object to be measured in a detection lens barrel on the right side, spot information is received by a detection camera, an image is obtained, and then the image is processed by an algorithm to obtain a digital grating period of the image at the current position, where a linear relationship exists between the value of the digital grating period and an actual height value, and the value of the digital grating period can be converted into the actual height value through earlier stage calibration, so that no additional device is required.
The digital grating is an image processing algorithm for realizing subdivision pixels, an image is divided into a plurality of equal and mutually independent bright areas and dark areas, and the bright areas and the dark areas are numbered sequentially from the upper part to the lower part of the image, as shown in fig. 3, fig. 3 is an actual image received by a camera, wherein the smallest square part represents the pixels of an area array camera, the dark part is a transmission grating transmission part (the light intensity of the part is larger), the accumulated light intensity values of the bright areas (I, II, III, IV) and the dark areas (the upper two rows in each area) in each numbered area are respectively calculated and recorded, if a certain number exists, the accumulated light intensity value of the bright areas is equal to the accumulated light intensity value of the dark areas, the numbered value is called an alignment point or a digital grating period, the corresponding relation is formed between the actual displacement and the measured alignment point during calibration, the corresponding relation is found, and the alignment point can be converted into the actual height value according to the corresponding relation obtained during the previous calibration.
Normally, if there is no perfect area, the light intensity of the area will be perfectly divided equally, when in actual use, the light intensity of the bright area and the light intensity of the dark area in each digital grating area are recorded, the difference value is calculated and used as the light intensity difference value of each digital grating area, so that the numbered area with the light intensity difference value of 0 is an alignment point, if there is no point with the perfect value of 0 in actual use, the number area is drawn, and the zero point position of the function is found by polynomial function fitting, and the transverse sitting of the zero point position is marked as the alignment point.
In addition, the measurement method provided in this embodiment is an incremental measurement method, if the digital grating method does not adopt incremental displacement measurement, a very serious nonlinear change occurs after a small distance is moved, which is determined by the optical property and the physical principle thereof, the algorithm changes the measurement algorithm into an incremental one by recording the change of the state of the alignment point, the defect caused by the physical property is repaired from the angle of the algorithm, the long-stroke high-precision measurement is realized, and how to realize the incremental wide-range measurement will be specifically described below.
When measuring the alignment points, generally, there is more than one alignment point, as shown in fig. 4, but the non-incremental measuring method only tracks the position change information of one alignment point, ignores the overall change, performs verification and comparison by using the information of two alignment points in an incremental way, when one alignment point is about to disappear from an image, tracks the other alignment point in time, and records the information of the alignment point at each moment for the next moment to use, thereby realizing long-stroke measurement.
The measuring device for the X and Y directions is shown in fig. 6, wherein 1 is a camera and a lens matched with the camera, and is only used for displaying the image of the grating on the surface of the camera, wherein the magnification of the lens is selected in relation to the precision required by measurement, 2 is a light source, 3 is a reflective two-dimensional grating, if the image is modulated by the digital grating selected when the measuring device for the Z direction in fig. 3 is continuously used, the modulation method can only carry out one-dimensional measurement, and in order to be capable of measuring the displacement information of the X and Y directions, the modulation method of the digital grating needs to be changed.
In the two-dimensional grating modulation method shown in fig. 9, two kinds of modulation are respectively carried out on the images measured by a camera, the a image is marked as modulation in the X direction, when the difference operation is carried out on the bright area and the dark area of the digital grating to obtain an alignment point, the light intensity fluctuation in the Y direction is counteracted, the alignment point in the X direction is measured, the alignment point in the Y direction can be measured by the b image, the two directions are separately calibrated and calculated, and the alignment point variation in the X direction and the alignment point variation in the Y direction can be obtained, and finally the displacement in the X direction and the displacement in the Y direction are converted.
Finally, only two cameras (the camera in the Z-direction measuring system and the camera in the XY-direction measuring system) are required to be subjected to drawing synchronization, and the three-dimensional displacement of the object to be measured at a certain moment can be obtained.
In the above description, the object to be measured refers broadly to various objects to be measured and displacement tables for carrying samples to be measured, for example: in the semiconductor field, the sample is a silicon wafer, and the sample stage is a workpiece stage; in the biological field, the sample is a microorganism on a slide, and the sample stage is a displacement stage below the sample stage.
Some steps in the embodiments of the present invention may be implemented by using software, and the corresponding software program may be stored in a readable storage medium, such as an optical disc or a hard disk.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (8)
1. A three-dimensional displacement measurement system, the three-dimensional displacement measurement system comprising: XY direction measuring mechanism, Z direction measuring mechanism and industrial computer;
the XY direction measurement mechanism includes: a first camera, a first light source, and a reflective two-dimensional grating; the first light source emits light to irradiate the surface of the reflective two-dimensional grating to form periodic reflected light to image on the first camera lens, and the first camera transmits image data to the industrial personal computer for image processing;
the Z-direction measuring mechanism includes: the device comprises a second light source, a projection objective, a transmission grating, a reflecting mirror component, a detection lens cone and a second camera; the light emitted by the second light source is telecentric light beam after passing through the projection objective lens, periodically passes through the transmission grating, passes through the reflection mirror component and the object to be detected, and then is imaged on the second camera through the detection lens barrel, and the second camera transmits the acquired image data to the industrial personal computer for image processing.
2. The three-dimensional displacement measurement system of claim 1, wherein the transmission grating is an amplitude-type one-dimensional grating.
3. The three-dimensional displacement measurement system of claim 1, wherein the mirror assembly comprises: the first reflecting mirror and the second reflecting mirror are respectively positioned at two sides of the object to be detected, are higher than the upper surface of the object to be detected and have the same height, and the reflecting surfaces are opposite.
4. The three-dimensional displacement measurement method is characterized in that the measurement method is realized based on the three-dimensional displacement measurement system according to any one of claims 1-3, the industrial personal computer collects physical grating images acquired by a camera and generates a grating overlapping effect with a digital grating formed by the industrial personal computer according to a similar period to form a signal which can be used for measurement, a digital grating period is obtained through calculation of the measurement signal, when a sample to be measured is displaced, the industrial personal computer obtains X, Y, Z displacement in three directions through calculation of the change of the digital grating period, and the corresponding relation between the digital grating period and the position is obtained through early calibration;
the calculation method of the digital grating period comprises the following steps:
dividing an image into a plurality of equal and mutually independent bright areas and dark areas according to camera pixels, numbering the images in sequence from the upper part to the lower part of the image, respectively calculating and recording the light intensity accumulated values of the bright areas and the dark areas in each numbered area, and if a certain number exists, the accumulated value of the light intensity of the bright areas is equal to the accumulated value of the light intensity of the dark areas, and then, the value of the number is called as an alignment point.
5. The three-dimensional displacement measurement method according to claim 4, wherein the method for calculating the digital grating period further comprises:
recording the light intensity of the bright area and the light intensity of the dark area in each digital grating area, calculating the difference value of the light intensity of the bright area and the light intensity of the dark area in each digital grating area, and thus, the numbered area with the light intensity difference value of 0 is an alignment point, if no point which is exactly 0 exists actually, fitting by using a polynomial function, finding the zero point position of the function, and marking the transverse sitting position of the zero point position as the alignment point.
6. The three-dimensional displacement measurement method according to claim 5, wherein the method employs an incremental measurement method for realizing long-stroke displacement measurement, the incremental measurement method comprising:
the incremental measuring method judges which alignment points disappear at the previous moment by making difference between the alignment points measured at the current moment and the alignment points recorded at the previous moment by selecting a proper system, updates displacement information by tracking the alignment points which do not disappear, records all the alignment points and position information after each measurement is completed, and completes iteration of the position information and the alignment point information, thereby realizing long-stroke displacement measurement.
7. An XY direction displacement measurement method, characterized in that the measurement of XY direction displacement is achieved by the three-dimensional displacement measurement method according to any one of claims 4 to 6.
8. A height displacement measurement method, characterized in that measurement of displacement in the Z direction is achieved by using the three-dimensional displacement measurement method according to any one of claims 4 to 6.
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