JPH109819A - Distance measuring equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the distance of a sample without modifying an existing microscope by determining the positional difference of a stage with respect to an image having the maximum contrast at a specified position among a plurality of images. SOLUTION: Image picked up by means of a CCD camera 2 are stored in a frame memory 8 and a plurality of images thus stored are added 10 in units of frame and stored in an addition memory 12. An added and stored 12 secondary image is then subjected to recovery processing through a divider 13 and a spatial filter circuit 14 while the plurality of images stored in the memory 8 are compressed through a frame memory control circuit 9 to constitute an image for 1 screen. Any one of image recovered or compressed through the spatial filter circuit 14 is switched by means of signal switches 15, 19 or the like and presented on a TV monitor 5. A CPU 22 determines the position of a stage 3 corresponding to the maximum contrast value at a position designated by a pointing device 6 and then calculates the distance of a sample based on the difference thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device used for measuring, for example, the thickness of a pattern on a semiconductor wafer.

[0002]

2. Description of the Related Art Conventionally, as a distance measuring apparatus of this type, a first example, a second example, and a third example described below are generally known. The first example uses a microscope equipped with a stage that can move independently in any of the three axes of X, Y, and Z, and a scale for reading the position on each axis. In such a configuration, when there are two measurement points to be measured, one of the measurement points is focused, and the X, Y, and Z positions at that time are read from the scale and stored. Also focus on the other measurement point,
The position at that time is stored. Based on this memory content,
It is configured so that a three-dimensional distance can be calculated.

In a second example, in order to clarify the in-focus position in the first example, an optical displacement shown in Japanese Patent Application Laid-Open No. 4-25711 is optically moved in the Z direction, that is, in the optical axis direction. It is equipped with a meter.

This known optical displacement meter includes a light source, an objective lens for condensing light emitted from the light source on a surface to be measured, and an image forming device for imaging light reflected by the surface to be measured. A lens, a beam splitter for splitting the reflected light, a plurality of apertures disposed before and after the in-focus position of each reflected light split by the beam splitter, and a reflection passing through each aperture. It is provided with a plurality of light receiving elements for detecting the amounts of light, respectively, and obtains a displacement signal of the surface to be measured based on a difference between outputs of the respective light receiving elements.

In a third example, as shown in FIG. 9, a laser light source 31, a photodetector 32, a one-dimensional scanning mechanism 33, a reflecting mirror 3
4. Laser scanning microscope main body 30 including semi-reflective mirror 35
Scanning control unit 36, Z-direction movement control circuit 37,
In this example, a laser scanning microscope including an image memory 38, a computer 39, and a monitor 40 is used, and a device devised for detecting the amount of light in a minimum area of a focal plane is used.

[0006]

However, in the above-described first example, if the position in the optical axis direction is different even with respect to the measurement point within the field of view, it is necessary to focus on each measurement point. It takes time and effort.

In the second example, the above-described known optical displacement meter generally operates only at the center of the field of view, so that movement in the X and Y directions is prevented even when the measurement point is within the field of view. I will be forced.

In a third example, as shown in FIG. 10, a point light source 41 such as a laser beam or a pinhole 45 is used to detect the amount of light in a minimum area of a focal plane 44 via a projectile 42 and a lens 43. A special optical system such as a light amount detector 46 is required, and a mechanism for scanning in the X and Y directions, for example, a mechanism for driving a stage or a mechanism for moving an optical path to the input side of the lens 43 is not provided. In addition, it is expensive because such a mechanism is required.

The present invention has been made in order to eliminate the above-mentioned problems, and an object of the present invention is to provide a distance measuring apparatus capable of measuring the distance of a sample without making any change to an existing optical microscope. Is to do.

[0010]

According to a first aspect of the present invention, there is provided an optical microscope having a focusing mechanism capable of adjusting a focusing position with respect to a specimen, and a focusing mechanism provided by the focusing mechanism. A photographing means for photographing a plurality of images of the specimen while changing the position; an image storing means for storing a plurality of images photographed by the photographing means; and a plurality of images stored by the image storing means. Image addition and storage means for storing, image processing means for reading out the image added and stored by the image addition and storage means and performing a two-dimensional image restoration process, and image display for displaying the image processed by the image processing means Means, coordinate position indicating means for indicating an image of a position to be measured on the screen of the image display means, the image storage means, the image addition storage means, and the coordinate position indicating means. Central processing means for controlling and calculating; and obtaining a position of a stage corresponding to an image having a maximum contrast value among a plurality of images obtained by the photographing means at a position designated by the coordinate position designating means, and calculating a difference between them. And a focusing position detecting means for detecting a distance of the sample from the distance measuring device.

According to the first aspect of the present invention, an image having a plurality of focal planes in the depth direction is obtained by driving the stage of the microscope in the optical axis direction and adding the sample images, thereby obtaining a measurement point. Focus adjustment is not required each time, and a plurality of measurement points within the visual field can be indicated and measured at once. Further, the captured image can be viewed on one screen at a time.

[0012]

Embodiments of the present invention will be described below. <First Embodiment> FIG. 1 is a configuration diagram of a distance measuring apparatus according to a first embodiment of the present invention.

The distance measuring apparatus according to the present embodiment has the following configuration. That is, an optical microscope 1 in which a stage 3 on which a sample (not shown) is mounted as a focusing mechanism is movable in a direction of an optical axis by a stage driving circuit 4, and an image of the sample is taken every time the height position of the stage 1 is changed. Image capturing means such as a CCD camera 2, image storing means for storing an image captured by the CCD camera 2, such as an analog signal processing circuit 7, a frame memory 8, and a plurality of images stored in the frame memory 8 as frames. Image addition and storage means for adding and storing in units, for example, an image addition means including an image adder 10 and an addition memory 12, and an image processing means for reading out an image added and stored by the addition memory 12 and performing a two-dimensional image restoration process; For example, one comprising a divider 13 and a spatial filter circuit 14 and a frame memory 8
, And compresses the image processed by the spatial memory circuit 14, or the image processed by the spatial filter circuit 14, or compressed by the frame memory control circuit 9. Image display means for displaying any one of the displayed images, for example, signal switch 15, image display memory 17, signal switch 1
9, a video signal processing circuit 20 and a television monitor 5; and a coordinate position designating means for designating an image of a position to be measured on the screen of the television monitor 5, such as a pointing device 6 and a pointing device control circuit 25. Frame memory control circuit 9, addition memory control circuit 11, pointing device control circuit 2
5, a central processing unit for performing control / calculation, for example, the CPU 22
And the position of the stage 3 corresponding to the maximum value of the contrast of the image obtained by the CCD camera 2 at the position indicated by the pointing device 6, and the focus position detection for detecting the distance of the sample from the difference therebetween. Means, for example, a RAM 23 and a CPU 22.

Hereinafter, the above configuration will be specifically described. A television monitor 5 for inputting a sample image from the CCD camera 2 as a photographing means and displaying a processed image is connected to the apparatus main body 26. Further, the pointing device 6 is connected to the apparatus main body 26 so that the pointing device 6 can indicate the coordinates of an arbitrary position on the image displayed on the television monitor 5.

The apparatus main body 26 includes a CCD camera 2, an analog signal processing circuit 7, a frame memory 8, a frame memory control circuit 9, an image data adder 10, an addition memory control circuit 11, an addition memory 12, a divider 13, a spatial filter. Circuit 14, signal switch 15, display memory control circuit 16, image display memory 17, overlay memory 18, signal switch 19, video signal processing circuit 20, stage drive I / F
A circuit 21, a CPU 22, a RAM 23, a ROM 24, and a pointing device control circuit 25 are provided.

An image output terminal of the CCD camera 2 has a CCD
An analog signal processing circuit 7 for converting a video analog signal from the camera 2 into a digital image is connected. An output (digital image data) of the analog signal processing circuit 7 is a frame memory 8 having a capacity capable of storing images for 16 screens. It is connected to the. The frame memory 8 is connected to a frame memory control circuit 9 for outputting a write address and a read address.

The digital image data stored in the frame memory 8 is connected to one input terminal of an image data adder 10 and one input terminal of a signal switch 15. The other input terminal of the image data adder 10 has an addition memory 12
Output terminals are connected.

The output terminal of the image data adder 10 is connected to the input terminal of the addition memory 12, and the image data adder 10
Inside, the addition operation of the contents of the addition memory 12 and the image input from the frame memory 8 is performed.

The output terminal of the addition memory 12 is connected to a divider 13
, And the other input terminal of the divider 13 receives the image addition number signal from the CPU 22, and the divider 13 processes the signal into an appropriate data value. An output terminal of the divider 13 is connected to an input terminal of a well-known spatial filter circuit 14, and in the spatial filter circuit 14, image restoration processing and the like are performed. Specifically, for example, a previously calculated integrated point image intensity distribution (integrated of all point image intensity distributions in a state in which a point is infinitely separated from a focused state) is inversely converted. Then, an image recovery process is performed, and an in-focus image can be obtained over the entire in-focus plane of each of the plurality of added images.

Here, the spatial filter circuit 14 will be described with reference to FIG. The spatial filter circuit 14 has 3 ×
It consists of a matrix of 3 to 7 × 7 (in FIG. 2, 3 × 3
In each row, data latch circuits 51 to 53 for sequentially latching pixel data of a corresponding line are provided in series. The pixel data latched by each of the latch circuits 51 to 53 is supplied to a corresponding one of the multipliers 5 provided.
A predetermined coefficient is multiplied by 4-56. Coefficients set in these multipliers 54 to 56 are stored in coefficient registers 57 to 5.
9 and the corresponding coefficient latch circuits 61
６３63 to the multiplication units 54〜56. Pixel data of the corresponding line is input to the rows 50, 70, and 90 of each stage, and the pixel values latched by the data latch circuits 51 to 53 and the coefficients stored in the corresponding coefficient registers 57 to 59 are stored. Is input to the adder 100. Then, the adder 100 adds all the input products,
The sum is used as the output of the spatial filter circuit 14.

The spatial filter circuit 14 performs edge enhancement, averaging, noise removal, and the like on an input image by changing a coefficient value stored in a coefficient register in a matrix, and processes the processed image. Can be output as

The output terminal of the spatial filter circuit 14 is connected to one input terminal of a signal switch 15 and the signal switch 15
The output terminal of the frame memory 8 is connected to the other input terminal of the frame memory 8 so as to switch between the added and filtered image output from the spatial filter circuit 14 and the unprocessed image from the frame memory 8. It is possible. The output terminal of the signal switch 15 is connected to the image display memory 1
7 input terminal. The image display memory 17
Is connected to a display memory control circuit 16 which outputs a read address and a write address to the image display memory 17 or the overlay memory 18.

An output terminal of the overlay memory 18 and an output terminal of the image display memory 17 are respectively connected to input terminals of a signal switch 19, and the output of the image display memory 17 or the overlay memory 18 is controlled by the signal switch 19.
Is selected and sent to the video signal processing circuit 20, where it is processed into a video signal by the video signal processing circuit 20, and this is output and displayed on the television monitor 5.

The measurement operation can be assisted by writing into the overlay memory 18 shape data such as an arrow indicating the coordinate position of the pointing device 6 and character data indicating the coordinates of the current stage.

The CPU 22 is connected to the frame memory control circuit 9, the addition memory control circuit 11, and the display memory control circuit 16 via the internal bus, and through these, the frame memory 8, the addition memory 12, the image display memory 17, It is connected to an overlay memory 18.

Further, the CPU 22 is connected to the image data adder 10, the divider 13, the spatial filter circuit 14, the stage drive I / F circuit 21, the RAM 23, the ROM 24, and the pointing device control circuit 25 via an internal bus. ing. The stage drive I / F circuit 21 is the microscope 1
Is connected to the stage drive circuit 4.

Next, the operation of the first embodiment configured as described above will be described. An image of a sample placed on the stage 3 is captured by a CCD camera 2 attached to a microscope 1, and this sample image signal is converted into a digital signal by an analog signal processing circuit 7, and is converted into image data as a frame memory control circuit. Along with the write address and read address generated from 9, they are sequentially stored in the frame memory 8.

The image data adder 10 adds the image data read from the addition memory 12 and the image data read from the frame memory 8 by the addition memory control circuit 11. The added image data is stored at the write address of the addition memory 12 generated by the addition memory control circuit 11. The image data read from the addition memory 12 is processed into an appropriate data value by the next divider 13 and input to the spatial filter circuit 14. In the spatial filter circuit 14, two rows up to a matrix of 7 rows × 7 columns
A two-dimensional image processing is performed, and a restoration process of the output image of the divider 13 is performed.

The spatial filter circuit 14 calculates the integrated point image intensity distribution on the light receiving element determined by the numerical aperture of the exit of the imaging optical system of the microscope 1, the pupil function of the imaging optical system, the wavelength of the imaging optical system, and the like. The filter characteristics of the spatial filter circuit 14 are changed according to the spread and the relative relationship with the size of the light receiving element of the CCD camera 2. To change the spatial filter characteristics,
Change one or both of the filter coefficients or filter size.

The image data output from the signal switch 15 is stored in the image display memory 17 according to the write address generated by the image display memory control circuit 16.

When reading out images one by one from the frame memory 8 by the frame memory control circuit 9, the image can be compressed in the vertical and horizontal directions by thinning out pixels and lines.
Then, the image display memory control circuit 16 sets the storage address of the image display memory 17 to the number of compressed pixels and the number of lines, and shifts each image to the right as shown in FIG. 16 images taken from the frame memory 8 can be displayed on the display memory 17 at one time.

The image data read from the image display memory 17 at the read address generated by the image display memory control circuit 16 and the supplementary information data read from the overlay memory 18 are converted by the signal switch 19 into supplementary information. The data is preferentially selected, and the video signal processing circuit 20
Is converted into a video signal, and is displayed on the television monitor 5 together with the image.

The CPU 22 controls the frame memory control circuit 9
To read and write the frame memory 8, and read and write the addition memory 12 through the addition memory control circuit 11.
Image display memory 1 through image display memory control circuit 16
7 and the overlay memory 18 are read and written. Also, C
The PU 22 appropriately controls the three frame memory control circuits 9, the addition memory control circuit 11, and the display memory control circuit 16, and sets the spatial filter circuit 14
Dimensional image processing coefficients can be set. The program recording the operation of the CPU 22 or the variables and the like necessary for the operation are as follows:
It is stored in the RAM 23 or the ROM 24.

The CPU 22 detects the movement amount of the designated point on the plane from the pointing device 6 connected through the pointing device control circuit 25, and indicates the coordinate position corresponding to the movement amount in the form of an arrow or the like (supplementary information data).
Is written in the overlay memory 18, the coordinates on the screen can be designated.

The CPU 22 includes a stage drive I / F circuit 2
The stage 3 can be driven up and down through 1 and the position of the stage 3 can be read from the stage drive circuit 4.

The operation of the apparatus main body 26 in the apparatus main body 26 is controlled by the CPU 22. Device body 2
6, a method of measuring the thickness of a pattern formed on a silicon wafer in a pattern inspection process of a semiconductor wafer will be described.

An example will be described in which the height difference between the measurement points P0 to P2 of the patterns having different thicknesses as shown in FIG. 4 is measured. First, a description will be given of a method of capturing an image in which a plurality of surfaces are focused in the optical axis direction.

In general, when a high magnification objective lens is used in an optical microscope, the depth of focus becomes shallow, and the contrast of an unfocused image becomes low as shown in FIG.
Therefore, a contrast value in the case of low contrast is obtained in advance from the optical performance of the microscope to be used, and the threshold value of the contrast is determined in advance. The contrast is obtained while moving the stage 3 in the direction of the optical axis, and the position where the threshold is reached is set as the image capturing position.

Alternatively, the operator may determine the image capturing position while checking the image captured by the CCD camera 2 on the television monitor 5. The contrast measurement line (contrast calculation area) is as shown in FIG. 6, and is calculated by the following formula (1), for example.

[0040]

(Equation 1)

In the case of a semiconductor wafer, the film thickness of a pattern formed from a silicon surface can be roughly determined by the thickness and the number of layers to be overlapped. Then, the number of images to be added to the moving amount of the stage 3 in the optical axis direction is determined. Therefore, an addition image is generated in the addition memory 12 in accordance with the determined moving amount of the stage 3 in the optical axis direction and the number of images to be added from the image capturing position. The added image is divided by the divider 13 into image data by the number of added images, subjected to recovery processing such as edge enhancement by the spatial filter circuit 14, sent to the image display memory 17, and displayed on the television monitor 5.
The image of the entire specimen is grasped by the image in which the plurality of surfaces in the optical axis direction are focused.

Next, a measurement point to be measured is specified on the screen of the television monitor 5 using the pointing device 6. The area for which the contrast is to be obtained is limited around the measurement point designated in this way. The measurement area is X, as shown in FIG.
The range is set to sufficiently include the pattern in the Y direction. Then, the stage 3 is returned to the initial image capturing position, and while moving the stage 3 with the minimum controllable amount of movement, the contrast value of the measurement point and the moving position of the stage 3 are set to R each time the stage 3 moves.
Record in AM23. The CPU 22 determines the end point of the movement of the stage 3 based on a mechanical movement limit point or a contrast value and a threshold value.

When the stage 3 reaches the end point of the movement,
Since the RAM 23 stores the stage position for each measurement point and the contrast value at that time as shown in FIG. 8, the position (Z0) of the stage 3 corresponding to the maximum contrast value is recorded.
Plane and Z1 plane) are obtained, and the height of the measurement point is obtained from the difference between the positions of these tages 3. Naturally, the distance in the three-dimensional space can be calculated by using the plane coordinates of each measurement point.

As described above, according to the present embodiment, an arbitrary image point within the visual field can be specified at a time by creating an image that is focused on a plurality of surfaces in the optical axis direction of the measurement image in advance. There is no need to move the optical axis.

In addition, by independently setting the area for calculating the contrast for each measurement point, the contrast depending on the measurement point can be obtained more accurately, and the accuracy of determining the focus position can be improved.

<Modification of Embodiment> In the above-described embodiment, the vertical and horizontal calculation regions are used when calculating the contrast.
Although the horizontal contrast measurement line is selected, a diagonal measurement line may be used.

Although the calculation of the contrast is performed based on the equation (1), the present invention is not limited to this. Further, the stage position can be read from the stage drive circuit 4 of the microscope 1. However, if there is no mechanism capable of reading the stage position, the moving amount may be measured by a rotary encoder or the like when moving the stage 3. Good.

The length in the X and Y directions on the screen of the television monitor 5 may be obtained by calibrating the length per pixel on the television monitor 5 with a sample whose length is known in advance. .

Although the stage on which the sample is mounted is moved as a focusing mechanism for adjusting the focus position of the sample, an optical system such as an objective lens may be moved without moving the stage.

[0050]

According to the present invention, it is possible to provide a distance measuring apparatus capable of measuring the distance of a specimen without making any change to an existing optical microscope.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a distance measuring device according to the present invention.

FIG. 2 is a view for explaining functions of the spatial filter circuit of FIG. 1;

FIG. 3 is a diagram for explaining functions of a display memory control circuit 16 of FIG. 1;

FIG. 4 is a diagram for explaining the operation of the distance measuring device in FIG. 1;

FIG. 5 is a diagram showing a relationship between an image contrast and an optical axis in an optical microscope.

FIG. 6 is a view for explaining a contrast calculation area in FIG. 1;

FIG. 7 is an explanatory diagram of a case where a measurement region is limited using the pointing device of FIG. 1;

FIG. 8 is a view for explaining the measurement principle of FIG. 1;

FIG. 9 is a diagram showing a schematic configuration of a conventional laser scanning microscope.

FIG. 10 is a view for explaining the problem in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Microscope, 2 ... CCD camera, 3 ... Stage, 4 ... Stage drive circuit, 5 ... TV monitor, 6 ... Pointing device, 7 ... Analog signal processing circuit, 8 ... Frame memory, 9 ... Frame memory control circuit, 10 ... Image data adder, 11 addition memory control circuit, 12 addition memory, 13 divider, 14 spatial filter circuit, 15 signal switcher, 16 display memory control circuit, 17 image display memory, 18 overlay Memory: 19: Signal switcher, 20: Video signal processing circuit, 21: Stage drive I / F circuit, 22: CPU, 23: RAM, 24: ROM, 25: Pointing device control circuit, 26: Device body.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H01L 21/66 G03B 3/00 A

Claims (2)

[Claims] 1. An optical microscope having a focusing mechanism capable of adjusting a focus position with respect to a sample, an imaging means for shooting a plurality of images of the sample while changing a focus position by the focusing mechanism, and the imaging Image storage means for storing a plurality of images taken by means, image addition and storage means for adding and storing a plurality of images stored by the image storage means, and images added and stored by the image addition storage means Image processing means for reading the image and performing a two-dimensional image restoration process; image display means for displaying the image processed by the image processing means; and a coordinate position for indicating an image at a position to be measured on the screen of the image display means. Instruction means; the image storage means; the image addition storage means; a central processing means for controlling and calculating the coordinate position instruction means; Focusing position detecting means for determining a position of a stage corresponding to an image having a maximum contrast value among a plurality of images obtained by the photographing means at a position, and detecting a distance of the sample from a difference therebetween. A distance measuring device characterized by the above-mentioned. 2. The distance measuring apparatus according to claim 1, further comprising an image forming unit configured to compress a plurality of images stored by the image storing unit and form an image for one screen.