WO2017200226A1 - Device for measuring three-dimensional shape using multi-wavelength optical scanning interferometer - Google Patents

Abstract

The present invention relates to a device for measuring a three-dimensional shape using a multi-wavelength optical scanning interferometer, comprising: a light source for irradiating light of at least two or more different wavelength bands; a light separator for separating the light irradiated from the light source; a sample disposed at the lower end of the light separator and irradiated with light reflected from the light separator; a reference mirror unit disposed on a path of the light transmitted through the light separator, and providing the number of reference beams which corresponds to the number of wavelength bands of the beams; and a measurement unit for receiving a measurement beam reflected from the sample and the reference beams reflected from the reference mirror unit, and separating a received image according to wavelength band.

Description

3D shape measurement device using multi-wavelength optical scanning interferometer

The present invention relates to a three-dimensional shape measuring apparatus using a scanning interferometer, and more particularly, to a technology that can significantly reduce the measurement time by greatly reducing the scan length in the height direction of the object using a multi-wavelength light source. It is about.

In order to detect defects such as flat panel displays, semiconductors and fine precision parts, it is necessary to inspect the surface of an object and measure three-dimensional thickness and / or shape, and interferometer methods are generally used. It is possible to obtain the thickness and / or solid shape of the object by generating and analyzing the interferometer pattern on the surface of the object to be measured.

One method for this is white light scanning interferometry (WSI). The white light scanning interferometry, which has been actively studied since 1990, was developed to overcome the phase ambiguity of phase-shifting interferometry and can be measured at several nm resolution even for shapes having a large step of several μm. Has the advantage.

1 is a general optical system configuration diagram of a white light scanning interferometer, and includes a light source 10, a light separator 20, a reference mirror 30, a measurement sample 40, and a measurement unit 50.

The white light irradiated from the light source 10 is separated into the measurement light and the reference light by the optical separator 20, and irradiated onto the surface of the measurement sample 40, which is the measurement plane, and the surface of the reference mirror 30, which is the reference plane, respectively. The light reflected from each side generates an interference signal through the same optical path.

As shown in FIG. 1, when the measurement sample is observed at an interference signal at one measuring point while moving at a small interval in the optical axis direction (z-axis direction), as shown in the figure, the position difference between the measuring point and the reference plane is a short distance within the interference length. In other words, the interference signal appears only at the point where the measurement path occurs at the same optical path difference as that of the reference plane. Therefore, by acquiring the interference signal for all the measurement points in the measurement area and setting the optical axis direction position at the vertex of each interference signal as the height value, it is possible to realize the three-dimensional solid surface shape of the measurement plane with respect to the reference plane.

Another method for measuring the height direction of an object may be a method of observing an interference signal at one measuring point while moving the reference mirror 30 at a small interval from side to side.

Since the shape measurement method using the conventional white light scanning interferometer has to be scanned in the height direction over the entire measurement height, the scanning time becomes longer, the inspection speed is delayed, and the moving length for moving the measurement sample or the reference mirror becomes longer. A problem arises in that the cost of the service increases.

The present invention is proposed to solve the problems of the prior art as described above, by using a light source of different wavelengths to separate the height measurement area for each light source to reduce the scan time and the moving length for the scan.

According to an aspect of the present invention for achieving the above object, a light source for irradiating light of at least two different wavelength bands, an optical separator for separating the light emitted from the light source, disposed at the bottom of the optical separator A reference mirror unit disposed on the sample irradiated with the light reflected by the optical separator, the path of the light transmitted by the optical separator, and providing a reference light corresponding to the number of wavelength bands of the light; It provides a three-dimensional shape measuring apparatus using a multi-wavelength optical scanning interferometer, characterized in that for receiving the measurement light and the reference light reflected from the reference mirror, and separating the received image for each wavelength band.

The measurement unit is preferably a color image sensor.

The reference mirror may include a first optical filter that reflects light of a first wavelength band or more, a first reference mirror disposed at a position to which the light reflected by the first optical filter is irradiated to provide a first reference light, and the second reference mirror. It may include a second reference mirror disposed at a position where the light passing through the light filter is irradiated to provide a second reference light.

In addition, the reference mirror is a distance between the optical splitter and the first optical filter c, the distance between the first optical filter and the first reference mirror a, the distance between the first optical filter and the second reference mirror b, When the distance between the top of the sample is ℓ ₁ and the distance between the optical separator and the middle point of the sample height is ℓ ₂ ,

ℓ ₁ = c + a

ℓ ₂ = c + b

It is preferable to be installed in a position that satisfies the relationship.

The reference mirror unit may include a first optical filter that reflects light of a first wavelength band or more, a first reference mirror that is disposed at a position to which the light reflected by the first optical filter is irradiated to provide a first reference light, and the first reference mirror A second optical filter disposed on a path of light passing through the optical filter to reflect light above a second wavelength band lower than the first wavelength band, and disposed on a path of light passing through the second optical filter The second reference mirror may provide a reference light, and the third reference mirror may be disposed at a position at which the light reflected by the second light filter is irradiated to provide a third reference light.

In addition, the reference mirror is a distance between the optical splitter and the first optical filter l _a , the distance between the first optical filter and the first reference mirror l _R , the distance between the first optical filter and the second optical filter l _b , ℓ _B the distance between the second optical filter and the second reference mirror, ℓ _G the distance between the second light filter and the third reference mirror, ℓ ₁ , the distance between the optical splitter and the top of the sample ℓ ₁ , 2/3 of the optical separator and the sample height. When the distance between the points ℓ ₂ and the distance between the optical splitter and the third point of the sample height ℓ ₃ ,

ℓ ₁ = ℓ _a + ℓ _b + ℓ _B

ℓ ₂ = ℓ _a + ℓ _b + ℓ _G

ℓ ₃ = ℓ _a + ℓ _R

It is preferable to be installed in a position that satisfies the relationship.

According to the present invention, as the scan time is significantly reduced, the inspection time is shortened and thus the yield is remarkably improved.

In addition, as the moving distance of the sample or the reference mirror for scanning is reduced, the manufacturing cost of the drive system is reduced, thereby reducing the manufacturing cost.

1 illustrates an optical system structure of a conventional white light scanning interferometer.

2 shows an optical system structure of a white light scanning interferometer using multiple wavelengths according to the first embodiment of the present invention.

3 is a view for conceptually explaining a method of measuring the height of a sample using light sources having two different wavelengths.

4 shows an optical system structure of a white light scanning interferometer using multiple wavelengths according to a second embodiment of the present invention.

Hereinafter, with reference to the drawings will be described in detail a preferred embodiment of the present invention.

2 shows an optical system structure of a multi-wavelength optical scanning interferometer according to the present invention, including a light source 100, an optical separator 200, a reference mirror 300, a sample 400, and a measurement unit 500. It is composed. In FIG. 2, the PC measuring the height of the object by using the result measured by the measuring unit 500 and the driving system for moving the object or the reference mirror are omitted for simplicity.

The light source 100 emits two different wavelengths, that is, the first light and the second light of different colors. In FIG. 2, the first light and the second light are red light and blue light. Red and blue LEDs are described by way of example.

The optical separator 200 separates the irradiated light into the reference light and the measurement light, and when the separated reference light and the measurement light are reflected and returns to each other, serves to create interference light as a function of the conventional optical separator 200. Is the same member.

The reference mirror 300 is provided to provide the reference light, and includes an optical filter 310, a first reference mirror 320, and a second reference mirror 330.

The optical filter 310 is positioned on the path of transmitted light transmitted by the optical separator 200 to transmit only light of a specific wavelength band. In the embodiment of FIG. 2, the light filter 310 transmits light having a wavelength shorter than that of red light and starts from the red band. The filter member having the characteristic of reflecting light may be used. Accordingly, the red light of the red light and the blue light emitted from the light source 100 is reflected by the optical filter 310 to be irradiated to the upper first reference mirror 320, and the blue light passes through the optical filter 310 to form a second second light source. The reference mirror 330 is irradiated.

The first reference mirror 320 is installed at a position to which the light reflected by the light filter 310 is irradiated to provide a reference light for the first light. Here, in the present embodiment, the first light is red light. The position where the first reference mirror 320 is installed is the sum of the distance c between the optical separator 200 and the optical filter 310 and the distance a between the optical filter 310 and the first reference mirror 320. It may be a point to be the distance (L ₁ ) between the optical separator 200 and the top of the sample.

The second reference mirror 330 is installed at a position to which the light passing through the optical filter 310 is irradiated to provide a reference light for the second light. In the embodiment of FIG. 2, the second light is blue light. The position where the second reference mirror 330 is installed is the sum of the distance c between the optical separator 200 and the optical filter 310 and the distance b between the optical filter 310 and the second reference mirror 330. It may be a point to be the distance (L ₂ ) between the optical separator 200 and the intermediate point of the sample height.

Referring to the drawings, the installation positions of the first and second reference mirrors 320 and 330 for generating the reference light are summarized as follows.

ℓ ₁ = c + a

ℓ ₂ = c + b

The measurement unit 500 is for receiving the measurement light reflected from the sample 400 and the first and second reference light reflected from the reference mirror 300, and a color image sensor capable of capturing both red and blue light may be provided. Used.

The measurement unit 500 separates the captured image into an image for the first light source (red light) and an image for the second light source (blue light), and provides the image to the PC, and the PC is provided by the measurement light and the reference light for the first light source. The height of the object is calculated by analyzing the generated interference image and the interference image generated by the measurement light and the reference light for the second light source.

At this time, the interference image for the first light source is used to measure the height from the middle point to the top of the sample, and the interference image for the second light source is used to measure the height from the bottom to the middle point of the sample.

Therefore, according to the present invention, if the object is moved only as much as half of the height of the object, the upper and lower portions are separately scanned by the two light sources of the object, thereby reducing the scanning time by half.

3 is a view for conceptually explaining the object height measuring method according to a first embodiment of the present invention.

As shown in FIG. 3, the half height at the top of the sample is treated as the scan area of the first light source, and the half height at the bottom thereof is the scan area of the second light source. Therefore, the height of the top half is measured by the first light source, and the bottom half height is measured by the second light source while the sample is moved upward for height measurement.

For example, if the height h ₁ of the first point in the lower region moves the sample by Δh _1, the path difference between the measurement light of the second light source and the reference light is the same, so that an interference signal appears. Set the position to the height value.

In addition, the height (h ₂ ) of the second point in the upper region is equal to the path difference between the measurement light of the first light source and the reference light when the sample is moved by Δh _2, so that an interference signal appears. Will be set to the height value.

4 shows an optical system structure of a multi-wavelength optical scanning interferometer according to a second embodiment of the present invention. Similar to the first embodiment, the light source 100, the optical splitter 200, the reference mirror 300, Comprising a sample 400 and the measuring unit 500, the PC for measuring the height of the object using the results measured by the measuring unit 500 and the drive system for moving the object or the reference mirror is simple to explain. Omitted for

The light source 100 emits three different wavelengths, that is, first to third lights of different colors. In FIG. 4, the first to third lights are red light, green light, and blue light. The red LED, the green LED, and the blue LED that occur are described as an example.

The reference mirror 300 is for providing reference light, and includes a first light filter 310, a first reference mirror 320, a second light filter 340, a second reference mirror 330, and a third reference light. It is configured to include a mirror (350).

The first optical filter 310 is the same member as the first embodiment and is a filter member that reflects light in a red light abnormal band. Accordingly, the red light of the light emitted from the light source 100 is reflected by the optical filter 310 and irradiated to the first reference mirror 320, and the blue light and the green light pass through the optical filter 310 to form a second second light source. The optical filter 340 is irradiated.

The first reference mirror 320 is installed at a position to which the light reflected by the light filter 310 is irradiated to provide a reference light for the first light. Here, in the present embodiment, the first light is red light. The position where the first reference mirror 320 is installed is the distance L _a between the optical separator 200 and the optical filter 310 and the distance L _R between the optical filter 310 and the first reference mirror 320. The sum may be a point such that the distance (L ₃ ) between the optical separator 200 and a point near 1/3 of the sample height.

The second optical filter 340 is a member that is positioned on the path of transmitted light transmitted by the first optical filter 310 to transmit only light of a specific wavelength band. In the second embodiment, light of a wavelength band shorter than green light is transmitted. A filter member having a property of reflecting light above the green band may be used. Therefore, the green light is reflected by the second optical filter 340 from the light passing through the first optical filter 310 is irradiated to the upper third reference mirror 350, the blue light passes through the second optical filter 340. The second reference mirror 330 of the rear end is irradiated.

The second reference mirror 330 is installed at a position where the light transmitted through the second optical filter 310 is irradiated to provide the reference light for the second light. In the second embodiment, the second light is blue light. The position where the second reference mirror 330 is installed is a distance ℓ _a between the optical splitter 200 and the first optical filter 310, and the distance between the first optical filter 310 and the second optical filter 340 ( ℓ _b) and the second optical filter 340 and the point at which the sum of the distance (ℓ _B) between the second reference mirror 330 such that the distance (ℓ ₂₎ between the optical splitter 200 and the top near the point of sample one Can be.

The third reference mirror 350 is installed at a position to which the light reflected by the second light filter 320 is irradiated to provide a reference light for the third light. In a second embodiment, the third light is green light. The position where the third reference mirror 350 is installed is the distance L _a between the optical splitter 200 and the first optical filter 310, and the distance between the first optical filter 310 and the second optical filter 340 ( so that the sum of l _b ) and the distance l _G between the second optical filter 340 and the third reference mirror 330 is the distance l ₂ between the optical splitter 200 and a point about two thirds of the sample height. It may be a point.

Referring to the drawings, the installation positions of the first to third reference mirrors 320, 330, and 350 for generating the reference light are summarized as follows.

ℓ ₁ = ℓ _a + ℓ _b + ℓ _B

ℓ ₂ = ℓ _a + ℓ _b + ℓ _G

ℓ ₃ = ℓ _a + ℓ _R

The measurement unit 500 is for receiving the measurement light reflected from the sample 400 and the first to third reference lights reflected from the reference mirror 300, and is a color image capable of capturing all of red light, green light, and blue light. The sensor is used.

The measuring unit 500 separates the captured image into an image for the first light source (red light), an image for the second light source (blue light), and a third light (green light), and provides the image to the PC, and the PC is provided to the first light source. Height of the object by analyzing the interference image generated by the measurement light and the reference light, the interference image generated by the measurement light and the reference light for the second light source, and the interference image generated by the measurement light and the reference light for the third light source Calculate

At this time, the interference image for the first light source is used to measure the height from the bottom point of the sample to about one third of the sample, and the interference image for the third light source is two thirds to one third of the sample. An interference image for the second light source is used to measure the height from the 2/3 height point of the sample to the top point of the sample.

Therefore, according to the second embodiment of the present invention, if the object is moved by only one third of the object height, the scan time is 1/3 because the upper part, the middle part and the lower part of the object are separately scanned by three light sources. The effect is reduced by three times.

Although the present invention has been described in connection with the above preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

Claims (6)

A light source for irradiating light of at least two different wavelength bands; An optical separator for separating light emitted from the light source; A sample disposed at a lower end of the optical separator and irradiated with light reflected from the optical separator; A reference mirror disposed on a path of light transmitted by the optical splitter and providing a reference light of a number corresponding to the number of wavelength bands of the light; And a measuring unit configured to receive the measurement light reflected from the sample and the reference light reflected from the reference mirror, and to separate the received image for each wavelength band. The method of claim 1, The measuring unit is a three-dimensional shape measurement apparatus using a multi-wavelength optical scanning interferometer, characterized in that the color image sensor. The method of claim 1, The reference mirror portion A first optical filter reflecting light above the first wavelength band;  A first reference mirror disposed at a position to which light reflected from the first optical filter is irradiated to provide a first reference light; And a second reference mirror disposed at a position to which the light passing through the second optical filter is irradiated to provide a second reference light. The method of claim 3, wherein The reference mirror portion The distance between the optical splitter and the first optical filter c, the distance between the first optical filter and the first reference mirror a, the distance between the first optical filter and the second reference mirror b, the distance between the optical splitter and the sample top ₁ , where the distance between the splitter and the midpoint of the sample height is ℓ ₂ , ℓ ₁ = c + a ℓ ₂ = c + b 3D shape measurement apparatus using a multi-wavelength optical scanning interferometer, characterized in that installed in a position that satisfies the relationship. The method of claim 1, The reference mirror portion A first optical filter reflecting light above the first wavelength band;  A first reference mirror disposed at a position to which light reflected from the first optical filter is irradiated to provide a first reference light; A second optical filter disposed on a path of light passing through the first optical filter and reflecting light of a second wavelength band lower than the first wavelength band; A second reference mirror disposed on a path of light passing through the second optical filter to provide a second reference light; And a third reference mirror disposed at a position to which the light reflected by the second optical filter is irradiated to provide a third reference light. The method of claim 5, The reference mirror portion The distance between the optical splitter and the first optical filter is a _a , the distance between the first optical filter and the first reference mirror is _R , the distance between the first optical filter and the second optical filter is _{b b} , 2 the distance between the reference mirror ℓ _B , the distance between the second optical filter and the third reference mirror ℓ _G , the distance between the optical splitter and the top of the sample ℓ ₁ , the distance between the optical splitter and 2/3 of the sample height ℓ ₂ , When the distance between the optical separator and one third of the sample height is ℓ ₃ , ℓ ₁ = ℓ _a + ℓ _b + ℓ _B ℓ ₂ = ℓ _a + ℓ _b + ℓ _G ℓ ₃ = ℓ _a + ℓ _R 3D shape measurement apparatus using a multi-wavelength optical scanning interferometer, characterized in that installed in a position that satisfies the relationship.

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