KR100747044B1 - Thickness and Shape Measurement System - 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 reference mirror disposed at an inclined angle with respect to a direction perpendicular to a path of incident light; An optical interference unit having a light splitting unit for separately irradiating the light from the light source to the measurement object and the reference mirror, and an interference filter disposed between the reference mirror and the light splitting unit to transmit light having a predetermined interference wavelength range A module; A spectroscope having a wavelength dispersion range including the interference wavelength range, and for 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 the light in the wavelength range excluding the interference wavelength range among the wavelength ranges of the light formed in the imaging unit, the information on the calculated thickness and the light in the imaging unit It characterized in that it comprises a control unit for calculating information on the shape of the object to be measured according to the spatial-carrier phase measurement methods (based on the light within the interference 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 measurement system according to 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.

FIG. 3 is a diagram illustrating light measured by the thickness and shape measurement system of FIG. 1.

* 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

The present invention relates to a thickness and shape measurement system, and more particularly, to a thickness and shape measurement system that can reduce the manufacturing cost while reducing the time required to measure the thickness and shape.

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 the data for analyzing the measured data.

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 costs while reducing the time required to measure thickness and shape.

The object is, according to the present invention, a thickness and shape measurement system having a light source for emitting light, the system comprising: a reference mirror disposed at an angle with respect to a direction perpendicular to a path of incident light; An optical interference unit having a light splitting unit for separately irradiating the light from the light source to the measurement object and the reference mirror, and an interference filter disposed between the reference mirror and the light splitting unit to transmit light having a predetermined interference wavelength range A module; A spectroscope having a wavelength dispersion range including the interference wavelength range, and for 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 the light in the wavelength range excluding the interference wavelength range among the wavelength ranges of the light formed in the imaging unit, the information on the calculated thickness and the light in the imaging unit And a control unit for calculating information on the shape of the measurement object according to spatial-carrier phase measurement methods based on light in the interference wavelength range. Can be achieved by

Here, it is preferable that the upper limit of the said interference wavelength range of the said interference filter matches the upper limit of the said wavelength dispersion range of the said spectral part.

The optical interference module may include any one of a Michelson interference module, a Linnik interference module, and a Mirau interference module.

(여기서, d는 상기 두께에 대한 정보이고, k1 및 k2는 인접하는 두 최대점에 대한 전파상수이고, n(k1) 및 n(k2)은 각각 k1 및 k2 에서의 복소 굴절률의 흡수 계수이다)에 의해 상기 두께에 대한 정보를 산출할 수 있다.And, the control unit is an equation

(Where d is information on the thickness, k1 and k2 are propagation constants for two adjacent maximum points, and n (k1) and n (k2) are absorption coefficients of complex refractive indices at k1 and k2, respectively) The information on the thickness can be calculated.

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

Thickness and shape measuring apparatus according to 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 spectroscope 40 ), An imaging unit 50, and a control unit 60.

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.

The light reflected by the beam splitter 20 and directed toward the measurement object 200 mounted on the measurement unit 100 is incident on the interference module 30. Here, for example, the interference module 30 according to the present invention uses a Michelson interference module 30.

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 20 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 of a predetermined interference wavelength range. In the present invention, the interference filter 32 selectively transmits only light having a wavelength of 630 nm to 633 nm. 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 630 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 reference mirror 34 is disposed at an angle inclined with respect to the direction perpendicular to the path of incident light. Accordingly, the controller 60 can obtain a spatial carrier frequency used when calculating the shape information using spatial-carrier phase measurement methods to be described later. .

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 and incident to the light splitter 31 is input to the spectrometer 40 through the light splitter 31 and the beam splitter 20. .

The spectroscope 40 spectroscopy light incident in a wavelength dispersion range including an interference wavelength range of the interference filter 32. Here, the upper limit of the interference 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 interference 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. Here, light incident from the beam splitter 20 passes through the diffraction grating 41 and is reflected from the beam splitter 42 to be 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 a wavelength of 630 nm to 633 nm, which is the interference 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 630 nm other than the interference 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.

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 630 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 based on the information on the light of the 630nm ~ 633nm of the image formed through the image forming unit 50 and the thickness calculated through the [Equation 1], the spatial-carrier phase measurement method Information on the shape of the measurement target 200 is calculated according to carrier phase measurement methods.

Hereinafter, a process in which the controller 60 calculates information on the shape of the measurement object 200 according to spatial-carrier phase measurement methods will be described.

First, the information on the thickness and shape in the white light scanning interferometry (WSI) satisfies [Equation 2].

[Equation 2]

Here, E _r and E _t are wavefront functions of the light reflected from the reference mirror 34 and the measurement target 200, respectively, and ψ (d) represents the phase change by the thin film 202 of the measurement target 200. .

라 가정하면, 형상에 대한 정보 h는 [수학식 3]에 의해 산출된다.here,

Assume that the shape information h is calculated by Equation 3 below.

[Equation 3]

Here, k ₀ represents the transmission wavelength of the interference filter 32.

Here, φ (x), which is a total phase function, is calculated according to spatial-carrier phase measurement methods. That is, as described above, the spatial carrier having a high frequency in the interference fringe between the light reflected from the reference mirror 34 and the light reflected from the measurement target 200 by tilting the reference mirror 34 of the interference module 30 by a predetermined angle. Spatial carrier frequency is formed and applied to spatial-carrier phase measurement methods.

That is, when the concept of spatial carrier frequency of spatial-carrier phase measurement methods is introduced in [Equation 1], it is expressed as in [Equation 4].

[Equation 4]

Here, when i ₀ (x) and γ (x) of Equation 4 are replaced with a (x) and b (x), respectively, and a spatial carrier frequency f ₀ is applied, the interference signal I (x) may be expressed as shown in [Equation 5].

[Equation 5]

이다.here,

to be.

In addition, the controller 60 performs a Fast Fourier Transform on Equation 5 to obtain a frequency characteristic function represented by Equation 6.

[Equation 6]

Here, A (f _x ) denotes a dc component according to the fast Fourier transform of a (x), and C (f _x ) includes φ (x) information, which is a total phase function according to the fast Fourier transform of c (x). Done.

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

As shown in Equation 6, the dc components A (f _x ) and C (f _x -f ₀ ) can be separated by the spatial carrier frequency f ₀ , and the phase function φ (x) can be separated. Filter C (f _x -f ₀ ) to get it.

By that do the following, the control unit 60 is C (f _x) performing centering (Centering), and centering the C (f _x) to re-reverse fast Fourier transform (Inverse Fast Fourier Transform) for a, c (x) Can be obtained.

And the control part 60 calculates the information about the shape of the measurement target 200 by calculating (phi) (x) using the calculated c (x).

 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, according to the present invention, there is provided a thickness and shape measurement system that can reduce manufacturing costs while reducing the time required to measure thickness and shape.

Claims (4)

A thickness and shape measurement system having a light source that emits light, A reference mirror disposed at an inclined angle with respect to a direction perpendicular to a path of incident light; An optical interference unit having a light splitting unit for separately irradiating the light from the light source to the measurement object and the reference mirror, and an interference filter disposed between the reference mirror and the light splitting unit to transmit light having a predetermined interference wavelength range A module; A spectroscope having a wavelength dispersion range including the interference wavelength range, and for 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 the light in the wavelength range excluding the interference wavelength range among the wavelength ranges of the light formed in the imaging unit, the information on the calculated thickness and the light in the imaging unit And a control unit configured to calculate information on the shape of the measurement object based on spatial-carrier phase measurement methods based on light within the interference wavelength range. The method of claim 1, The upper limit value of the said interference wavelength range of the said interference filter is the same as the upper limit value of the said wavelength dispersion range of the said spectral part. The method according to claim 1 or 2, The optical interference module may include any one of a Michelson interference module, a Linnik interference module, and a Mirau interference module. The method of claim 3, The control unit is

(Where d is information on the thickness, k1 and k2 are propagation constants for two adjacent maximum points, and n (k1) and n (k2) are absorption coefficients of complex refractive indices at k1 and k2, respectively) Calculating the information on the thickness by the thickness and shape measurement system.

Images