KR20060087714A - System for measurement of thickness and surface profile - Google Patents

Abstract

The present invention relates to thickness and shape measurement systems. The thickness and shape measurement system according to the present invention comprises a light source for emitting light; A light having a reference mirror, a light splitting unit for separately irradiating light from the light source to a measurement object and the reference mirror, and an interference filter disposed between the reference mirror and the light splitting unit and transmitting light in a multi-wavelength range An interference module; A spectroscope having a wavelength dispersion range including the multi-wavelength range and spectroscopy light reflected from the measurement object and light reflected from the reference mirror; An imaging unit in which light spectroscopically formed by the spectroscope is formed; The information on the thickness of the measurement target is calculated based on light in a wavelength range excluding the multi-wavelength range among the wavelength ranges of the light formed on the imaging unit, and the information on the calculated thickness and the light formed on the imaging unit And a control unit for calculating information on the shape of the measurement target based on the light within the multi-wavelength range. Accordingly, the manufacturing cost can be reduced while reducing the time required for measuring thickness and shape.

Description

Thickness and Shape Measurement System {SYSTEM FOR MEASUREMENT OF THICKNESS AND SURFACE PROFILE}

1 is a view showing the configuration of a thickness and shape system according to a first embodiment of the present invention,

FIG. 2 is a diagram illustrating an example of a measurement object whose thickness and shape are measured according to the thickness and shape measurement system of FIG. 1.

3 is a view analyzing light measured by the thickness and shape measurement system of FIG.

FIG. 4 is a graph illustrating a process of calculating information about a shape in the thickness and shape measuring system of FIG. 1.

5 is a view showing the configuration of a thickness and shape measurement system according to a second embodiment of the present invention,

FIG. 6 is a diagram illustrating an example of a single plate of the thickness and shape measurement system of FIG. 5.

* Explanation of symbols for the main parts of the drawings

10: light source 20: beam splitter

30: interference module 31: interference filter

34: reference mirror 40: spectroscopic portion

50: imaging unit 60: control unit

70: single plate 80: plate driving unit

The present invention relates to a thickness and shape measurement system, and more particularly, a thickness and shape measurement system which can reduce manufacturing costs while reducing the time required for measuring thickness and shape, and can provide various measurement modes. It is about.

In general, there is a process of applying a transparent thin film layer on the surface of the opaque metal layer in the semiconductor manufacturing process, several methods for measuring the information about the thickness and the surface shape of the transparent thin film layer has been proposed.

As a method of measuring the thickness of the transparent thin film layer and its surface shape, White-light Scanning Interferometry (WSI) has been proposed, and 2π- of the conventional Phase Shifting Interferometry (PSI) has been proposed. Overcoming the ambiguity (2π ambiguity), it is possible to measure the rough surface or the measuring surface having a high step with high resolution.

The basic measurement principle of white light scanning interferometry utilizes the short coherence length characteristic of white light. This uses the principle that the interference signal is generated only when the reference light and the measurement light separated by the beam splitter, which is an optical splitter, experience almost the same optical path difference.

Therefore, when the measured object is observed in the direction of the optical axis by the transmission means such as the PZT actuator at small intervals of several nanometers, the interference signal at each measuring point in the measuring area is observed, the optical path difference of each point is equal to the reference mirror. At this point, a short interference signal is generated.

When the generation position of the interference signal is calculated at all measurement points in the measurement area, information on the three-dimensional shape of the measurement surface is obtained, and the thickness and shape of the thin film layer are measured from the obtained three-dimensional information.

On the other hand, there is a method of measuring the thickness of the transparent thin film layer and its surface shape using an Acoustic Optics Tunable Filter (AOTF). In the method using the acoustooptic modulation filter, the acoustooptic modulation filter selectively transmits light of a specific wavelength band, thereby obtaining the same effect as the PZT actuator in the white light scanning interferometry to move the measurement object by minute intervals in the optical axis direction.

Examples of the two methods as described above are disclosed in Korean Patent Laid-Open Publication No. 2000-0061037 and Korean Patent Publication No. 2004-0004825, which will not be described in detail.

However, the above two methods for measuring the thickness and shape of the thin film layer have a long measurement time, a large amount of measured data, a problem that takes a lot of processing time of data for analyzing the measured data has been raised. .

For example, in the case of the white light scanning interference method, a PZT actuator moves a measurement object in a direction of an optical axis to a pixel by several hundreds of nanometers at a small interval of several nanometers (nanometer). The time required is long, and accordingly the amount of data becomes large.

In addition, the method using the acoustic optical modulation filter has a disadvantage that an expensive acoustic optical modulation filter should be used.

Accordingly, it is an object of the present invention to provide a thickness and shape measurement system that can reduce manufacturing time while reducing the time required to measure thickness and shape and can provide various measurement modes.

According to the present invention, there is provided a thickness and shape measurement system having a light source for emitting light, comprising: a reference mirror, a light splitting unit for separately irradiating light from the light source to a measurement object and the reference mirror, and An optical interference module disposed between a reference mirror and the optical splitter and having an interference filter transmitting light in a multi-wavelength range; A spectroscope having a wavelength dispersion range including the multi-wavelength range and spectroscopy light reflected from the measurement object and light reflected from the reference mirror; An imaging unit in which light spectroscopically formed by the spectroscope is formed; The information on the thickness of the measurement target is calculated based on light in a wavelength range excluding the multi-wavelength range among the wavelength ranges of the light formed on the imaging unit, and the information on the calculated thickness and the light formed on the imaging unit It can be achieved by the thickness and shape measurement system, characterized in that it comprises a control unit for calculating information on the shape of the measurement object based on the light in the multi-wavelength range.

Here, the spectroscope includes: a diffraction grating in which light reflected from the measurement object and light reflected from the reference mirror pass and are spectroscopically; It may include a beam splitter for transmitting or reflecting the light passing through the diffraction grating toward the image forming portion.

And a blocking plate disposed between the reference mirror and the light splitting unit, at least one of the interference filter and the blocking plate is disposed on an optical path between the reference mirror and the light splitting unit. / Or further comprises a plate drive for moving the blocking plate; When the blocking plate is disposed on an optical path between the reference mirror and the light splitter, the controller may measure the thickness of the measurement object based on light formed in the imaging unit.

And the interference filter and the blocking plate are provided in one single plate; The driving unit may move the single plate such that any one of the interference filter and the blocking plate provided on the single plate is disposed on an optical path between the reference mirror and the light splitter.

The driving unit is provided to move the single plate such that the interference filter and the blocking plate are not disposed on an optical path between the reference mirror and the light splitting unit. When the interference filter and the blocking plate are not disposed on the optical path between the reference mirror and the light splitter, the controller may measure the shape of the measurement object based on light formed in the imaging unit. Can be.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Thickness and shape measurement apparatus according to a first embodiment of the present invention, as shown in Figure 1, the light source 10, the beam splitter 20 (Beam splitter), the interference module 30, the measuring unit 100 , The spectrometer 40, the imaging unit 50, and the controller 60 may be included.

The light source 10 emits monochromatic light, such as white light, and may use a tungsten-halogen lamp of approximately 70 W. Here, the light emitted from the light source 10 is connected to one side of the optical fiber 11 in the outgoing direction.

The optical fiber 11 transmits light incident through one side to the other side. The other side of the optical fiber 11 is fixed by the fixing member 12. Here, a pinhole is provided at the center of the fixing member 12 so that the other side of the optical fiber 11 may be connected. The light emitted through the pinholes extends around the pinholes.

The first convex lens 13 is disposed between the fixing member 12 and the beam splitter 20. Here, the light emitted from the optical fiber 11 is aligned at a constant width while passing through the first convex lens 13.

The light transmitted through the first convex lens 13 is incident on the beam splitter 20 positioned at a predetermined distance from the first convex lens 13. Here, the beam splitter 20 may have a form of a non polarized cube that can separate incident light at a ratio of approximately 50:50. Here, since the reflection angle of the beam splitter 20 is about 45 degrees with respect to the incident direction of light, the reflected light is reflected perpendicularly to the incident direction.

Light reflected by the beam splitter 20 and directed toward the measurement object 200 is incident on the interference module 30. Here, for example, the interference module 30 according to the present invention uses the interference module 30 in the form of a Michelson interference module.

The interference module 30 may include an optical splitter 31, a reference mirror 34, and an interference filter 32.

The light splitter 31 irradiates the light emitted from the light source 10 and incident on the interference module 30 through the beam splitter 20 to the measurement object 200 and the reference mirror 34. The light splitter 31 may be a beam splitter in the form of a non-polarized cube.

The second convex lens 33 and the third convex lens for condensing the light emitted from the light splitter 31 on the light path emitted from the light splitter 31 toward the measurement object 200 and the reference mirror 34. 35 is disposed.

The interference filter 32 is disposed between the light splitter 31 and the second convex lens 33. Here, the interference filter 32 selectively transmits light in the multi wavelength range. In the present invention, the interference filter 32 selectively transmits only light in the multi-wavelength range of 550 nm to 633 nm will be described as an example. Here, of course, the interference filter 32 may be disposed between the second convex lens 33 and the reference mirror 34.

Light having a wavelength of 550 nm to 633 nm passing through the interference filter 32 is reflected by the reference mirror 34 through the second convex lens 33 and then passes through the second convex lens 33 and the interference filter 32. Towards the partition 31.

The light passing through the third convex lens 35 causes a change in its wavelength when reflected from the measurement target 200. Here, the change in the wavelength of the light reflected from the measurement target 200 has information on the thickness and shape of the measurement target 200.

As shown in FIG. 2, the measurement target 200 has a predetermined opaque metal pattern 201 formed on a plate surface such as a wafer, and a transparent thin film 202 is coated on the metal pattern 201 and the plate surface. have. Here, the unexplained reference number RS of FIG. 2 is a reference plane in the thickness and the formation measurement.

On the other hand, the light reflected from the measurement target 200 and the reference mirror 34 respectively and incident on the light splitter 31 is input to the spectrometer 40 through the light splitter 31 and the beam splitter 20. .

The spectrometer 40 spectroscopy light incident in a wavelength dispersion range including the multi-wavelength range of the interference filter 32. Here, the upper limit of the multi-wavelength range of the interference filter 32 may coincide with the upper limit of the wavelength dispersion range of the spectrometer 40. As described above, when the multi-wavelength range of the interference filter 32 is 633 nm, the upper limit of the wavelength dispersion range of the spectroscope 40 is also approximately 633 nm. In the present invention, the wavelength dispersion range of the spectrometer 40 is described as an example that 400nm ~ 633nm.

The spectrometer 40 may include a diffraction grating 42, a beam splitter 41, and a fourth convex lens 43.

The light incident on the diffraction grating 42 from the beam splitter 20 passes through the diffraction grating 42 and is spectroscopically directed to the beam splitter 41. The light from the diffraction grating 42 is reflected from the beam splitter 42 and directed to the image forming unit 50. Here, light having a wavelength that does not go from the beam splitter 42 to the image forming section 50 is absorbed by the blocking member 44 and then disappears.

Here, reference numeral 43, which is not shown in FIG. 1, is a convex lens that collects light directed toward the blocking member 44 as the blocking member.

Light spectroscopically distributed by the spectroscope 40 in the wavelength dispersion range of 400 nm to 633 nm is formed in the imaging unit 50. The imaging unit 50, for example, forms a light focused by the fourth convex lens provided in the spectroscope 40, scans the formed light, and extracts each piece of information.

Here, the light having the wavelength range of 550 nm to 633 nm, which is the multi-wavelength range of the interference filter 32, of the light spectroscopically detected at the wavelength of 400 nm to 633 nm by the spectroscope 40 is measured with the light reflected from the reference mirror 34. Corresponding to a wavelength range in which interference between light reflected from the object 200 occurs, the information about the shape of the measurement object 200 is included. The light having a wavelength of 400 nm to 550 nm other than the multi-wavelength range among the light spectroscopically detected at a wavelength of 400 nm to 633 nm includes information on the thickness of the measurement object 200 as light reflected from the measurement object 200.

3 is a graph in which the control unit 60 analyzes the light spectroscopically analyzed by the spectroscope 40 and formed in the imaging unit 50 in units of wavelength. Here, the x-axis of the graph of FIG. 3 is the coordinate of one line measured with respect to the measurement object 200, and the λ-axis is the coordinate of the wavelength of light. As shown in FIG. 3, the wavelength range and the shape including the information on the thickness of the light formed by the image forming unit by using the selective transmission of the light by the interference filter 32 of the interference module 30 is included. It can be divided into a wavelength range including.

Hereinafter, a process of calculating information on the thickness and shape of the measurement target 200 based on the information included in the light formed through the imaging unit 50 will be described with reference to FIG. 3.

First, the controller 60 analyzes light having a wavelength of 400 nm to 550 nm among the light formed through the imaging unit 50, and calculates information on the thickness of the measurement target 200 by using Equation 1 below. .

[Equation 1]

Where d is information on thickness, k ₁ and k ₂ are propagation constants for two adjacent maximum points, and n (k ₁ ) and n (k ₂ ) are the complex refractive indices of k ₁ and k ₂ , respectively. Absorption coefficient.

Then, the control unit 60 is calculated based on the light of 550nm ~ 633nm of the light formed through the image forming unit 50 and the information on the thickness calculated through the equation (1).

Hereinafter, the process of the controller 60 to calculate the information on the shape of the measurement target 200 by using the concept of the spectral carrier frequency. Here, the overall phase function φ (k) may be defined as a function of k through the following process using the concept of Spectral Carrier Frequency based on the interference information of the light formed through the imaging unit 50.

First, information on thickness and shape in spectral scanning profilometry satisfies [Equation 2].

[Equation 2]

Here, if I ₀ (k), ψ (k) is replaced with a (k) and b (k), and the spectral carrier frequency h ₀ is applied, the interference signal I (k) is expressed as shown in [Equation 3]. Can be.

[Equation 3]

이다.here,

to be.

Here, h ₀ plays a role of applying a high spectral carrier frequency to φ (k) under the assumption that the overall phase function φ (k) changes very slowly with respect to k.

On the other hand, if FFT (Fast Fourier Transform) is used, a frequency characteristic function transformed into the Spectral frequency f _k region of Equation 4 can be obtained. Here, the physical unit of f _k represents a length that is the inverse of the propagation constant k.

[Equation 4]

Where A (f _k ) represents the dc component as a result of the FFT of a (k), and C (f _k ) contains the total phase function φ (k) information that is ultimately obtained as the FFT result of c (k). do.

C * (f _x ) represents a conjugate of C (f _x ).

As in Equation 4, the dc component A (f _k ) and C (f _k -h ₀ ) by the Spectral carrier frequency h ₀ can be separated, and C to obtain the overall phase function φ (k) (f _k -h ₀ ) should be filtered.

FIG. 4 is a diagram illustrating an experiment result obtained by filtering an interference signal by FFT and filtering by a rectangular window. And center as C (f _k ) as approximately as possible. Actually, it is not known exactly how much the Spectral carrier frequency h ₀ is applied, but in the process of applying h ₀ to h (x, y) and centering again, a dummy h of h _d is actually added, but h _d and h _{Since 0} is a constant for modes x and y, it does not cause measurement error in obtaining positional shape information of h (x, y).

Then, by finally inverting the centered C (f _k -h _d ) by Inverse Fast Fourier Transform (IFFT), Equation 5 including a dummy h _d can be obtained.

[Equation 5]

In this way, when the total phase function? (K) is calculated, the shape information h (x) can be obtained through Equation (6).

[Equation 6]

In the above-described embodiment, the multi-wavelength range of the interference filter 32a has been described as an example of 550 nm to 630 nm, but it may vary depending on the characteristics of the thickness and shape of the measurement target 200.

Hereinafter, the thickness and shape measurement system according to the second embodiment of the present invention will be described in detail with reference to FIG. 5. Here, in the description of the thickness and shape measurement system according to the second embodiment of the present invention, the same reference numerals are used for the same configuration as the above-described first embodiment, and description thereof will be omitted as necessary.

The thickness and shape measurement system according to the second embodiment of the present invention further includes a blocking plate 71 and a driving unit 80.

The blocking plate 71 is disposed between the reference mirror 34 of the interference module 30 and the light splitter 31. In addition, the driver 80 may include the interference filter 32a and / or such that at least one of the interference filter 32a and the blocking plate 71 is disposed on an optical path between the reference mirror 34 and the light splitter 31. Or the blocking plate 71 is moved.

When the blocking plate 71 is disposed between the reference mirror 34 and the light splitter 31 by the driver 80, the light from the light splitter 31 to the reference mirror 34 is blocked.

The blocking plate 71 has a characteristic of absorbing all incident light. Accordingly, the light incident on the blocking plate 71 is not reflected, and the light formed by the imaging unit 50 includes only the light reflected from the measurement target 200. Therefore, when the blocking plate 71 is disposed between the reference mirror 34 and the light splitter 31, the controller 60 controls the measurement object 200 based on the light formed by the imager 50. Information about the thickness is calculated.

Accordingly, the user arranges one of the blocking plate 71 and the interference filter 32a by the driving unit 80 between the reference mirror 34 and the light splitter 31, thereby measuring the object to be measured according to the two measurement modes. 200 can be measured. For example, when the interference filter 32a is disposed between the reference mirror 34 and the light splitter 31, the thickness and shape of the measurement target 200 can be simultaneously measured as in the first embodiment described above. It becomes.

On the other hand, when the blocking plate 71 is disposed between the reference mirror 34 and the light splitter 31, only the thickness of the measurement target 200 is measured, but the range of wavelengths of light for thickness measurement becomes wider. More accurate thickness measurements are possible, and the range of measurable thicknesses is also widened.

Here, the driving unit 80 may move the blocking plate 71 and the reference mirror 34 out of the optical path between the mode reference mirror 34 and the light splitter 31. In this case, the light reflected from the measurement target 200 and the light reflected from the reference mirror 34 generate interference in the entire wavelength range, so that information about the shape of the measurement target 200 may be obtained. Will be.

FIG. 6 illustrates an example in which the blocking plate 71 and the reference mirror 34 are provided in one single plate 70. As shown in the figure, the interference filter 32a is installed in the first through hole 73 on the substantially plate-shaped single plate 70, and the second through hole 72 is formed at one side. In addition, one region forms a blocked blocking plate 71 region. Accordingly, the driving unit 80 moves the single plate 70 in the plate direction to move the single plate 70, the interference filter 32a, and the second through hole 72 to the reference mirror 34 and the light splitter ( By selectively positioning on the optical path between 31), the measurement mode can be changed.

A method of calculating information on thickness and / or shape based on light formed through the imaging unit 50 in each measurement mode of the thickness and shape measurement system according to the second embodiment is the first embodiment described above. Corresponding to the method for calculating the information on the thickness and shape in the bar, the description thereof will be omitted.

In the above-described embodiments, the interference module 30 is provided as a Michelson interference module as an example. In addition, the present invention can be applied to other interference modules such as Linnik interference modules and Mirau interference modules.

Although some embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that modifications may be made to the embodiment without departing from the spirit or spirit of the invention. . And the scope of the invention will be defined by the appended claims and equivalents thereof.

As described above, the present invention provides a thickness and shape measurement system that can reduce manufacturing costs while reducing the time required for measuring thickness and shape, and can provide various measurement modes.

Claims (5)

A thickness and shape measurement system having a light source that emits light, A light having a reference mirror, a light splitting unit for separately irradiating light from the light source to a measurement object and the reference mirror, and an interference filter disposed between the reference mirror and the light splitting unit and transmitting light in a multi-wavelength range An interference module; A spectroscope having a wavelength dispersion range including the multi-wavelength range and spectroscopy light reflected from the measurement object and light reflected from the reference mirror; An imaging unit in which light spectroscopically formed by the spectroscope is formed; The information on the thickness of the measurement target is calculated based on light in a wavelength range excluding the multi-wavelength range among the wavelength ranges of the light formed on the imaging unit, and the information on the calculated thickness and the light formed on the imaging unit And a control unit for calculating information on the shape of the measurement object based on light in the multi-wavelength range. The method of claim 1, The spectroscopic section, A diffraction grating, through which light reflected from the measurement object and light reflected from the reference mirror pass and are spectroscopically; And a beam splitter that transmits or reflects the light passing through the diffraction grating toward the image forming portion. The method of claim 2, A blocking plate disposed between the reference mirror and the light splitter, and the interference filter and / or such that at least one of the interference filter and the blocking plate is disposed on an optical path between the reference mirror and the light splitter And a plate driver for moving the blocking plate; When the blocking plate is disposed on an optical path between the reference mirror and the light splitter, the controller measures the thickness of the measurement object based on light formed in the imaging unit. Measuring system. The method of claim 3, The interference filter and the blocking plate are provided in one single plate; Wherein the driving unit moves the single plate such that any one of the interference filter and the blocking plate provided on the single plate is disposed on an optical path between the reference mirror and the light splitting unit. . The method of claim 4, wherein The driving part is provided to move the single plate such that the interference filter and the blocking plate are not disposed on an optical path between the reference mirror and the light splitting part; The controller is configured to measure the shape of the measurement target based on light formed in the imaging unit when the interference filter and the blocking plate are not disposed on the optical path between the reference mirror and the light splitter. Thickness and shape measurement system, characterized in that.

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