JP4433371B2 - Image measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image measuring apparatus that measures an image of an overlay pattern on a silicon wafer.
[0002]
[Prior art]
In a photolithography process for manufacturing a semiconductor device, exposure is performed on a wafer through a circuit pattern formed on a reticle or a mask. At this time, prior to exposure, an overlay mark on the wafer is detected by observing the wafer surface using an observation device, and relative alignment between the mask and the wafer is performed based on the detection result. This alignment is performed by measuring the amount of overlay deviation between the mask pattern projected in the exposure process and the base pattern using an image measuring device.
[0003]
In addition, in order to align the resist pattern that has undergone the exposure process and the development process and the circuit pattern formed on the substrate in the previous pattern formation process, a mark indicating the reference position of each circuit pattern and the reference of the resist pattern A mark indicating the position is used as an overlay mark.
[0004]
In this case, the overlay mark is irradiated with illumination light, and the reflected light from the overlay mark is imaged on a predetermined surface via an objective lens or the like, imaged by a CCD camera or the like, image processing is performed, Measure misalignment.
[0005]
[Patent Literature]
JP-A-7-151514 [0006]
[Problems to be solved by the invention]
In this image measuring apparatus, an image is acquired by a CCD camera using a positioning completion signal indicating completion of positioning of a stage on which a wafer is placed and a focusing signal indicating completion of autofocus as trigger signals.
[0007]
However, vibrations generated when the stage is moved or the wafer transfer mechanism is operated are transmitted to the CCD camera, and the CCD camera vibrates.
[0008]
When an image is acquired while the CCD camera is vibrating, the acquired image is blurred even though positioning and autofocus are completed. In addition, when the plurality of acquired images are integrated and the position of the overlay mark is measured, a plurality of images with different image positions are integrated due to the shaking of the CCD camera.
[0009]
As a result, there is a problem that the edge of the overlay mark is blurred and accurate image measurement cannot be performed.
[0010]
The present invention has been made in view of such circumstances, and its problem is to accurately detect a part of the overlay mark without being affected by the movement of the stage, the operation of the wafer transfer mechanism, etc. An object of the present invention is to provide an image measurement device capable of performing image measurement.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention according to claim 1 is an image measuring apparatus for measuring an image of an overlay mark on a wafer, a stage on which the wafer is placed, and an enlarged image in which the overlay mark is enlarged. A microscope optical system, an imaging unit that captures an enlarged image of the overlay mark, a vibration detection unit that detects vibration of the imaging unit, and an edge of the enlarged image of the overlay mark with respect to the vibration at a plurality of accelerations A storage unit for storing a density change state of a part, and a part of an enlarged image of the overlay mark, and the enlargement based on the detected vibration state of the imaging unit and the stored density change state of the edge part. And an image correction unit that corrects the edge position of the image.
[0012]
According to a second aspect of the present invention, in the image measuring apparatus according to the first aspect, the image correction unit corrects deterioration of an image of an edge of the overlay mark .
[0013]
According to a third aspect of the present invention, in the image measurement device according to the first aspect, the image measurement apparatus further includes an image acquisition timing control unit that controls an image acquisition timing of the imaging unit based on a detection result of the vibration detection unit. The timing control unit converts the detection result of the vibration detection unit into an acceleration component, and outputs a control signal that causes the imaging unit to start image acquisition when the vibration acceleration is equal to or less than a predetermined value.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a block diagram of an image measuring apparatus according to an embodiment of the present invention.
[0021]
This image measurement apparatus includes a stage 20, a microscope optical system 30, a CCD camera (imaging unit ) 40, an image storage unit 41, an image processing unit 42, an acceleration sensor (vibration detection unit ) 50, and a timing control unit. (Image acquisition timing control unit ) 60 and an arithmetic control unit 10 are provided.
[0022]
A stage 20 on which a wafer (measuring object) 5 is placed is placed on a surface plate 21 and is movable in the X direction, the Y direction, and the Z direction. A predetermined signal based on a control signal from the arithmetic control unit 10 is provided. Move to position.
[0023]
The microscope optical system 30 is configured integrally with the CCD camera 40. The microscope optical system 30 forms an image of an overlay mark (not shown) exposed on the wafer 5 on the imaging surface of the CCD camera 40. The microscope optical system 30 is disposed on the optical axis.
[0024]
The CCD camera 40 is a TV camera using a CCD. An image of the overlay mark magnified by the microscope optical system 30 is formed on the imaging surface of the CCD camera 40. The CCD converts an optical image of light intensity into a video signal corresponding to the intensity and outputs it. The CCD camera 40 captures an image of the overlay mark based on an imaging trigger signal (control signal) 60a from the timing controller 60.
[0025]
The microscope optical system 30 and the CCD camera 40 are supported by a support member 22 fixed to the surface plate 21.
[0026]
The image storage unit 41 captures and stores the overlay mark image data captured by the CCD camera 40 as an image signal 40a.
[0027]
The image processing unit 42 receives an image signal 41a, which is image data output from the image storage unit 41, and performs image processing such as image integration and image correction. When the image processing is completed, the image processing unit 42 outputs a processing end signal 42a. Although not shown, the image processing unit 42 includes an image correction unit (image correction unit) that corrects an image acquired by the CCD camera 40.
[0028]
The acceleration sensor 50 converts the vibration generated by the movement of the stage 20 or the operation of a wafer transfer mechanism (not shown) and the like and transmitted to the CCD camera 40 via the support member 22 as indicated by a waveform arrow, into an acceleration component, The vibration signal 50a is output. As the acceleration sensor 50, for example, a piezoelectric type is used. The piezoelectric sensor is small and light, and has a feature that a measurement frequency range of about 5 Hz to 20 kHz can be obtained.
[0029]
The timing control unit 60 receives the vibration signal 50 a output from the acceleration sensor 50. The timing controller 60 monitors the vibration signal 50a and outputs an imaging trigger signal 60a for starting image acquisition to the CCD camera 40 based on the monitoring result.
[0030]
Further, the timing control unit 60 has a vibration memory 61. The vibration memory 61 stores the vibration signal 50a as a vibration recording signal 60b.
[0031]
Further, the timing control unit 60 outputs a result of processing based on a mode control signal 10a described later as a result transmission signal 60c.
[0032]
The arithmetic control unit 10 outputs an image processing control signal 10b for outputting arbitrary image data as an image signal 41a from among a plurality of image data stored in the image storage unit 41.
[0033]
The arithmetic control unit 10 also determines the timing for outputting the imaging trigger signal 60a to the CCD camera 40, and outputs a mode control signal 10a for selecting a mode for acquiring an image.
[0034]
Hereinafter, an image acquisition method in each mode will be described.
[0035]
2A and 2B are diagrams illustrating image acquisition timing according to the first image acquisition mode, FIG. 2A is a diagram illustrating an output waveform of the acceleration sensor, and FIG. 2B is a diagram illustrating image acquisition timing. .
[0036]
The arithmetic control unit 10 outputs the image processing control signal 10b to the image processing unit 42, outputs the mode control signal 10a to the timing control unit 60, and sets the timing control unit 60 to the first image acquisition mode.
[0037]
The timing control unit 60 monitors a vibration signal 50 a that is an output of the acceleration sensor 50.
[0038]
The timing control unit 60 outputs an imaging trigger signal 60a to the CCD camera 40 after the acceleration is attenuated to approximately 0 (below a value that does not affect the image acquisition) (see FIG. 2A).
[0039]
The CCD camera 40 acquires an image of the overlay mark based on the imaging trigger signal 60a.
[0040]
The acquired image is stored in the image storage unit 41 and is integrated by the image processing unit 42.
[0041]
According to the first mode, the image is acquired after the vibration is attenuated to a value that does not affect the image acquisition. Therefore, the image acquired by the CCD camera 40 is blurred, or a plurality of acquired images are integrated. When an image of the position of the overlay mark is measured, a plurality of images having different image positions are not integrated, and the edge of the overlay mark is not blurred.
[0042]
3A and 3B are diagrams illustrating image acquisition timing according to the second image acquisition mode, in which FIG. 3A is a diagram illustrating an output waveform of the acceleration sensor, and FIG. 3B is a diagram illustrating image acquisition timing. .
[0043]
The arithmetic control unit 10 outputs the image processing control signal 10b to the image processing unit 42, outputs the mode control signal 10a to the timing control unit 60, and sets the timing control unit 60 to the second image acquisition mode.
[0044]
The timing control unit 60 monitors a vibration signal 50a (acceleration) that is an output of the acceleration sensor 50.
[0045]
The timing controller 60 outputs an imaging trigger signal 60a to the CCD camera 40 when the acceleration is attenuated to a predetermined value or less (see FIG. 3A).
[0046]
Further, the vibration transmitted to the CCD camera 40 is attenuated while performing a predetermined natural vibration. Therefore, the imaging trigger signal 60a is sent to the CCD camera 40 in synchronization with the timing when the acceleration of the vibration detected by the acceleration sensor 50 becomes zero. You may make it output.
[0047]
The CCD camera 40 acquires an image of the overlay mark based on the imaging trigger signal 60a.
[0048]
The acquired image is stored in the image storage unit 41, and the vibration signal 50a is stored in the vibration memory 61 as the vibration recording signal 60b in synchronization with the image acquisition.
[0049]
The acquired images are integrated by the image processing unit 42.
[0050]
According to the second mode, an image is acquired when the acceleration is attenuated to a predetermined value or less. Therefore, the image acquired by the CCD camera 40 is blurred, or a plurality of acquired images are integrated to position the overlay mark. When an image is measured, a plurality of images having greatly different image positions are not accumulated, and blurring of the edge of the overlay mark can be greatly improved.
[0051]
4A and 4B are diagrams illustrating image acquisition timing according to the third image acquisition mode. FIG. 4A is a diagram illustrating the output waveform of the acceleration sensor, and FIG. 4B is a diagram illustrating the timing of image acquisition. .
[0052]
The arithmetic control unit 10 outputs the image processing control signal 10b to the image processing unit 42, outputs the mode control signal 10a to the timing control unit 60, and sets the timing control unit 60 to the third image acquisition mode.
[0053]
After the wafer positioning and autofocus are completed, the timing control unit 60 starts to acquire the overlay mark image. In synchronization with this image acquisition, the vibration signal 50a is stored in the vibration memory 61 as the vibration recording signal 60b.
[0054]
After acquiring all the images, the vibration recording signal 60b stored in the vibration memory 61 is referred to using the arithmetic control unit 10 and the timing control unit 60, and the vibration recording signal whose acceleration is attenuated to a predetermined value or less. The image corresponding to 60b is selected from the image storage unit 41.
[0055]
The selected image is integrated by the image processing unit 42.
[0056]
According to the third image acquisition mode, only an image whose acceleration is attenuated to a predetermined value or less is used for measurement. Therefore, an image acquired by the CCD camera 40 is blurred, or a plurality of acquired images are integrated to form an overlay mark. When the position of the image is measured, a plurality of images having greatly different image positions are not accumulated, and blurring of the edge of the overlay mark can be greatly improved.
[0057]
According to this embodiment, the edge of the overlay mark can be reliably detected and accurate image measurement can be performed without being affected by the movement of the stage or the operation of the wafer transfer mechanism.
[0058]
Of the first to third image acquisition modes, in the second image acquisition mode and the third image acquisition mode, no image is acquired in a state where the acceleration is almost zero. The edge of the projected image (projection waveform) deteriorates.
[0059]
Therefore, the edge correction described below is performed so that more reliable image measurement can be performed.
[0060]
5A shows a projection waveform of an image with almost zero acceleration, FIG. 5B shows a projection waveform of an image with acceleration 2x, and FIG. 5C shows a projection waveform of an image with acceleration 2x. FIG.
[0061]
FIG. 5 shows a projection waveform when scanning is performed in the x direction (see FIG. 1).
[0062]
FIG. 5A shows a projection waveform with sharp edges that are not affected by vibration. The edge of the overlay mark is clear (no blur), and image measurement with good reproducibility of the projection waveform can be performed.
[0063]
FIG. 5B and FIG. 5C are projection waveforms in which the edge deteriorates due to the influence of vibration. The edge of the overlay mark is rounded, and image measurement with good reproducibility of the projection waveform cannot be performed. As can be seen from FIGS. 5B and 5C, edge degradation is proportional to amplitude and acceleration.
[0064]
Therefore, the edge inclination with respect to the acceleration is stored in advance as data in a memory (not shown), and for example, the edge of the projection waveform is corrected by the center value of the edge inclination corresponding to the acceleration obtained by the acceleration sensor 50 at the time of image acquisition. To do. This edge correction is performed by the image correction unit of the image processing unit 42.
[0065]
As a result, the edge of the overlay mark is cleared, and image measurement with good reproducibility of the projection waveform can be performed.
[0066]
【The invention's effect】
As described above, according to the present invention, it is possible to reliably detect a part of the overlay mark and perform accurate image measurement without being affected by the movement of the stage or the operation of the wafer transfer mechanism. .
[Brief description of the drawings]
FIG. 1 is a block diagram of an image measuring apparatus according to an embodiment of the present invention.
2A and 2B are diagrams illustrating image acquisition timing according to a first image acquisition mode, in which FIG. 2A illustrates an output waveform of the acceleration sensor, and FIG. 2B illustrates image acquisition timing; FIG.
3A and 3B are diagrams illustrating image acquisition timing according to a second image acquisition mode, in which FIG. 3A illustrates an output waveform of an acceleration sensor, and FIG. 3B illustrates image acquisition timing; FIG.
4A and 4B are diagrams illustrating image acquisition timing according to a third image acquisition mode. FIG. 4A illustrates an output waveform of the acceleration sensor, and FIG. 4B illustrates image acquisition timing. FIG.
5A is a diagram showing a projection waveform of an image with almost zero acceleration, FIG. 5B is a diagram showing a projection waveform of an image with acceleration 2x, and FIG. 5C is an image with acceleration 2x. It is a figure which shows the projection waveform of.
[Explanation of symbols]
5 Wafer 10 Operation control unit
20 stages
30 microscope optical system 40 CCD camera (imaging part )
50 acceleration sensor (vibration detection unit)
60 a timing control section (image acquisition timing controller)

Claims (3)

An image measuring apparatus for measuring an overlay mark on a wafer,
A stage on which the wafer is placed;
A microscope optical system for creating an enlarged image in which the overlay mark is enlarged;
An imaging unit that captures an enlarged image of the overlay mark;
A vibration detection unit for detecting vibration of the imaging unit;
A storage unit for storing a density change state of an edge portion of the enlarged image of the overlay mark with respect to the vibration at a plurality of accelerations ;
An image correction unit that corrects the edge position of the magnified image based on the detected vibration state of the imaging unit and the stored density change state of the edge using a part of the magnified image of the overlay mark. An image measuring device characterized by comprising.   The image measurement apparatus according to claim 1, wherein the image correction unit corrects deterioration of an image of an edge of the overlay mark. An image acquisition timing control unit that controls the image acquisition timing of the imaging unit based on the detection result of the vibration detection unit;
The image acquisition timing control unit converts the detection result of the vibration detection unit into an acceleration component, and outputs a control signal for causing the imaging unit to start image acquisition when the vibration acceleration is equal to or less than a predetermined value. The image measurement apparatus according to claim 1.

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