KR20100085595A - Optical critical dimension metrology method and apparatus using spectral interferometry - Google Patents

Abstract

PURPOSE: An optical critical dimension metrology method and an apparatus using a spectral interferometry are provided to increase measuring speed while obtaining SE parameter through one single shot. CONSTITUTION: A first spectrometer(16) and a second spectrometer(17) are arranged. A light source(10) projects the white light. A polariscope(12) polarizes the white light from the light source to a TM polarizer and a direction of 45 degrees from the TM polarizer. A beam splitter(13) makes a polarized linear white light to a measurement object. An OCD interferometer(14) forms a light interference with a measured light reflected from the target and a reference light reflected from a reference mirror.

Description

Method and apparatus for measuring OCD using optical interference {OPTICAL CRITICAL DIMENSION METROLOGY METHOD AND APPARATUS USING SPECTRAL INTERFEROMETRY}

The present invention relates to a method and apparatus for measuring OCD using optical interference. More specifically, the vertical incident structure is introduced by introducing optical interference and spectral carrier frequency concepts so that the disadvantages of each of the vertical incident structure and the diagonal incident structure can be compensated for. The present invention relates to a method and apparatus for measuring OCD using optical interference that can improve the measurement speed by allowing the SE parameters Ψ and Δ to be acquired simultaneously with a single shot.

3D information measurement of nanopatterns has become a big issue in the semiconductor field, and its importance is increasing with the rapid development of integrated circuit (IC) technology.

As the size of semiconductors goes down to 100 nm or less, the 3D measurement of nanopatterns is facing difficulties. Recently, cross-sectional scanning electron microscopes (SEMs) and atomic force microscopes (AFMs) have made it possible to measure images of very small features.

However, SEMs and AFMs are expensive and can damage semiconductor devices, making them unsuitable for real-time monitoring of nanopattern structures on production lines. In addition, even if Top View CD-SEMs are applied to a production line, CD-SEMs information is generally not applicable to the acquisition of shape 3D data such as the height of a pattern or the angle of side walls. Recently, various optical critical dimension (OCD) measurement methods have been proposed to overcome the disadvantages of SEMs and AFMs.

On the other hand, while traditional optical imaging techniques fail to measure shapes smaller than the wavelength of the beam, OCD (also known as 'scatterometry' or 'scatterometer') metrology techniques use spectroscopic measurements of the physical parameters of the sub-wavelength repetitive structure. It allows you to extract from signatures. Among OCD measurement techniques, rigorous coupled-wave analysis (RCWA) method is usefully used to describe diffraction (or reflection) of electromagnetic waves from the surface of a lattice structure. This optical approach can be used for a variety of reasons, including nondestructive and noninvasive properties, low cost, small footprint, high accuracy, and robustness in the manufacturing environment. There is an advantage.

Representative hardware structures in the OCD measurement technology as described above are the Spectroscopic Reflectometric (SR) system and the Spectroscopic Ellipsometric (SE) system. Here, the SE system is more advantageously recognized in that it can provide higher sensitivity in the measurement of repetitive nanopatterned 3D structures than the SR system.

On the other hand, nano-pattern 3D measurement technology using OCD measurement technology requires two important improvements. One is the development of algorithms faster than the RCWA method, and the other is to improve the measurement speed of the SE parameters Ψ and Δ. The development of fast algorithms is related to improving the performance of software, and the improvement of the measurement speed is related to improving the performance of hardware.

)와 s-편광 반사 강도(s-polarized reflected intensity,

)를 동시에 측정하려는 시도가 있었다. 그러나, 위 방법은 많은 SE 어플리케이션에서 진폭 비율(Ψ)보다 높은 민감도(Sensitivity)를 제공하는 위상차(Δ)를 측정할 수 없는 단점이 있다.Among the various studies to improve the performance of the hardware, a broad spectral range in real time using an oblique incidence SE system with Wallaston prism and two spectroscopic channels over the spectral range, the p-polarized reflected intensity,

) And s-polarized reflected intensity,

) Was attempted to measure at the same time. However, this method has the disadvantage of not being able to measure the phase difference Δ, which provides a sensitivity higher than the amplitude ratio Ψ in many SE applications.

In addition, W. Yang has acquired three reflection spectra, R _TE , R _TM , and R _Φ (Φ is the system polarizer angle between 0 ° and 90 °) in relation to hardware performance improvement. We have proposed a normal incidence spectroscopic metrology system that can measure SE parameters Ψ and Δ.

Here, in a vertical incidence spectrometer system, R _TE , R _TM obtained by aligning the polarization transmission axis parallel or perpendicular to the grating lens is used to calculate tan (Ψ), SE parameter, and R _Φ is cos, SE parameter. It is used to calculate (Δ). In other words, W.Yang's proposed vertical incident spectroscopy system requires three spectral data to calculate Ψ and Δ, and three measurements to acquire these three spectral data.

Accordingly, the present invention introduces the concept of optical interference and spectral carrier frequency in order to compensate for the disadvantages of the conventional vertical incidence structure in the approach for nano-pattern measurement. It is an object of the present invention to provide a method and apparatus for measuring OCD using optical interference which can improve measurement speed by allowing SE parameters? And Δ to be simultaneously acquired in a single shot).

The object is according to the invention, (a) irradiating white light; (b) linearly polarizing the white light in a direction inclined at 45 ° with respect to the TE polarization direction and the TM polarization direction in which the mutual polarization directions are perpendicular to each other; (c) the linearly polarized white light interfering with the measurement light and the reference light, respectively reflected from the measurement object and the reference mirror, to form interference light; (d) separating the interference light into the TE polarization component and the TM polarization component; (e) inputting the TE polarization component and the TM polarization component into a first spectrometer and a second spectrometer, respectively; (f) extracting TE spectral data and TM spectral data from the input TE polarization component and the input TM polarization component, respectively, to extract amplitude information and phase information for each of the TE polarization component and the TM polarization component; ; (g) calculating the amplitude ratio (Ψ) and phase difference (Δ) on the RCWA technique by applying the extracted amplitude information and the extracted phase information to a RCWA technique. It is achieved by an OCD measurement method using optical interference.

Here, the amplitude ratio Ψ and the phase difference Δ may be expressed by the RWA (Rigorous coupled-wave analysis) technique.

Where p is a reflection coefficient ratio of the RCWA technique, R _TM is a reflection coefficient of the TM polarization component, and R _TE is a reflection coefficient of the TE polarization component. It is a reflection coefficient, and δ _TM represents a phase shift of the TM polarization component, and δ _TE represents a phase shift of the TE polarization component.

In the step (c), the interference light may be formed in a state where an optical path difference between the optical path of the reference light and the optical path of the measurement light is generated so that a spectral carrier frequency is applied.

Further, in the step (f), the TE spectral data is expressed by equation

Where I _TE is the TE spectral data, k is a wave number, and h is the spectral carrier frequency defined by the optical path difference between the optical path of the reference light and the optical path of the measurement light. ), E _{r, TE} and E _{t, TE} are the reference light and the measurement light for the TE polarized light component, i _{0, TE} is a DC term for the TE polarized light component, and the γ _TE (k, pattern) is a visibility amplitude function for the TE polarization component, Φ _TE is a total phase function for the TE polarization component, and φ _TE is for the TE polarization component A phase function dependent on the nanopattern shape of the measurement object; The TM spectrum data is represented by equation

Where I _TM is the TM spectral data, E _{r, TM} and E _{t, TM} are the reference light and the measurement light for the TM polarization component, respectively, and i _{0, TM} is a DC item for the TM polarization component (DC term), the γ _TM (k, pattern) is the Visibility amplitude function for the TM polarization component, Φ _TM is the total phase function for the TM polarization component, φ _TM is expressed as a phase function dependent on the nanopattern shape of the measurement object for the TM polarization component; The amplitude information and the phase information in the step (f) include the visibility amplitude function γ _TE and the phase function φ _TE for the _TE polarization component and the phase polarization component for the TM polarization component. Visibility amplitude function γ _TM and the Phase function φ _TM ; In step (g), R _TM , R _TE , δ _TM , and δ _TE of the equation by the RCWA (Rigorous coupled-wave analysis) technique are extracted in step (f) γ _TM , γ _TE , φ _TM and φ _TE can be substituted respectively.

The step (f) may include: (f1) applying a Fast Fourier Transform (FFT) algorithm to the TE spectrum data and the TM spectrum data; (f2) removing the DC item by applying a windowing technique and a centering technique to the data passed through the step (f1); (f3) the Visibility amplitude function and the total phase of the TE polarization component by applying an Inverse Fast Fourier Transform (IFFT) algorithm to the data which has passed the step (f2). function) and extracting the Visibility amplitude function and the Total phase function for the TM polarization component.

Here, step (c) may be implemented by a Michelson interferometer.

In addition, step (d) may be implemented by Wallaston prism.

On the other hand, according to another embodiment of the present invention, the OCD measuring apparatus using optical interference, the first spectrometer and the second spectrometer; A light source for emitting white light; A polarizer for linearly polarizing the white light emitted from the light source in a direction inclined by 45 ° with respect to the TE polarization and the TM polarization direction in which the mutual polarization directions are perpendicular to each other; A beam splitter for directing the linearly polarized white light to a measurement object; An OCD interferometer for measuring light formed by reflecting the linearly polarized white light from the measurement object and reference light formed by reflecting the linearly polarized white light from the reference mirror to form interference light; A vertical linear polarization splitter disposed on the optical path of the interference light from the OCD interferometer and separating the interference light into the TE polarization component and the TM polarization component and outputting the interference to the first spectrometer and the second spectrometer, respectively; ; The amplitude ratio (Ψ) is performed by performing steps (f) and (g) of the OCD measurement method on the TE polarization component and the TM polarization component input through the first spectrometer and the second spectrometer. And it can be achieved by the OCD measuring apparatus using the optical interference, characterized in that it comprises a control unit for calculating the phase difference (Δ).

Here, the OCD interferometer may be set to generate an optical path difference between the optical path of the reference light and the optical path of the measurement light so that a spectral carrier frequency is applied.

The OCD interferometer may be implemented by a Michelson interferometer.

In addition, the vertical linearly polarized light separator may be implemented by Wallaston prism.

In addition, a CCD camera, an optical splitter disposed between the beam splitter and the wallastone prism on the optical path of the interference light, for splitting the interference light into the Willaston prism and the CCD camera, and the OCD interferometer; Replaceably provided, further comprising an applicable WSI interferometer of White-light Scanning Interferometry (WSI); The control unit controls the amplitude ratio between the TE polarized component and the TM polarized component based on the TE polarized component and the TM polarized component input through the first spectrometer and the second spectrometer while the OCD interferometer is installed. Ψ) and the OCD mode for calculating the phase difference Δ and the WSI mode for measuring the surface shape by applying image data input through the CCD camera to the white light scanning interferometry with the WSI interferometer installed. can do.

According to the present invention, the concept of optical interference and spectral carrier frequency are introduced to obtain optical interference that can improve the measurement speed by allowing the SE parameters Ψ and Δ to be simultaneously acquired in a single shot while having a vertical incident structure. Provided is a method and apparatus for measuring OCD.

Hereinafter, with reference to the accompanying drawings will be described in detail embodiments according to the present invention. First, prior to explaining the present invention, rigorous coupled-wave analysis (RCWA: RWA) related to the amplitude ratio Ψ and phase difference Δ to be obtained through the present invention. Learn how.

Spectroscopic Ellipsometric (SE) systems are recognized as the right tools for measuring 3D shapes of nanopatterns in the field of semiconductors and photonic crystals. Incident light is diffracted in positive order and negative order, and only light that is spectrally ordered zero is collected in the system. The collected light is a combination of two linearly polarized elements with a phase difference between p- and s-polarized light. Here, the polarization mode when the electric field is in a direction parallel to the diffraction grating direction is called TE mode, and the polarization mode when the electric field is in a direction perpendicular to the diffraction grating direction is called a TM mode.

The RCWA method is an analysis algorithm that uses Maxwell's equations that include boundary conditions. 1 is a diagram showing a diffraction grating shape of a one-dimensional periodic pattern in the RCWA method. The linearly polarized electromagnetic wave is incident obliquely at an angle of incidence θ.

The grating period L is generally expressed as a combination of several regions with various different refractive indices. Here, f is a filling factor of the lattice period obtained by the floor area of the lattice. All structures can be divided into an incident area (area I), a grating or pattern area and an exit area (area II). The electric field can be obtained from the Maxwell's equation by using the boundary conditions of the lattice region. In this lattice region 0 <z <d, the periodic dielectric function is extended to a Fourier series having a period L, as shown in [Equation 1].

[Equation 1]

Where ε _h is the h th Fourier element of the dielectric function in the lattice region.

On the other hand, in the TE mode, the electric fields of the regions I and II can be expressed as [Equation 2].

[Equation 2]

Here, E _{inc, y} is an incident normalized electric field, and K _xi is determined from the Floquet state and is defined by Equation 3.

&Quot; (3) &quot;

Here, k ₀ is a wave number determined by 2π / λ ₀ , and λ ₀ is a wavelength of light in free space. In Equation 2, R _i is the normalized electric-field amplitude of the i-th backward diffracted (reflected) wave in region I, and Ti is the i-th in region II. Normalized electric-field amplitude of the forward diffractied (reflected) wave. Applying the Maxwell's equation in the lattice domain and matching boundary conditions at the interfaces of the three domains determines the amplitudes Ri and Ti of the diffraction wave.

In the OCD measurement method, since i = 0, i.e., only R ₀ , R _TE in Equation 4 corresponds to R ₀ in TE mode. Equally, it can be obtained using the case where R _{TM in} Equation 4 is also i = 0 in the TM mode. These two reflection coefficients (R _TE and R _TM ) can be expressed as two SE parameters Ψ, Δ and [Equation 4].

&Quot; (4) &quot;

Here, δ _TE and δ _TM are phase shifts of the TE polarization mode and the TM polarization mode, respectively. In addition, tan Ψ can be obtained from an amplitude ratio between the TE polarization mode and the TM polarization mode. And, the phase difference Δ between the TE polarization mode and the TM polarization mode can be obtained by the difference between δ _TE and δ _TM .

Hereinafter, the OCD according to the present invention for obtaining δ _TE and δ _TM , R _TE and R _TM in order to calculate Ψ and Δ to be finally obtained in [Equation 4] defined by the RCWA method as described above. The measuring method and apparatus will be described in detail.

2 is a diagram showing the configuration of an OCD measuring apparatus according to the present invention. Referring to FIG. 2, the OCD measuring apparatus according to the present invention includes a first spectrometer 16 and a second spectrometer 17, a light source 10, a polarizer 12, and a beam splitter 13. (Beam splitter), OCD interferometer 14, the vertical linear polarizer splitter 15 and the control unit.

The light source 10 irradiates white light. Here, the light source 10 may be provided in various forms for emitting white light, and the white light irradiated from the light source 10 becomes parallel light while passing through the convex lens 11 disposed on the light path.

The white light passing through the convex lens 11 passes through the polarizer 12 disposed between the beam splitter 13 and the convex lens 11, wherein the white light passing through the polarizer 12 is perpendicular to each other. We have a linearly polarized light with a 45 ° tilt for both the p- and s-polarized phosphors. Here, the polarization that is horizontal with the line direction of the grating pattern formed on the measurement object 100 among the p-polarized light and the s-polarized light is TE polarized light, and the polarized light that is perpendicular to the line direction of the grating pattern is called TM polarized light. -Polarization is TM polarization and s-polarization is TE polarization. The white light passing through the polarizer 12 is incident on the beam splitter 13, is reflected from the beam splitter 13 toward the OCD interferometer 14, and is emitted from the beam splitter 13.

The OCD interferometer 14 is disposed on the optical path between the beam splitter 13 and the measurement object 100. Here, the OCD interferometer 14 is the light emitted from the polarizer 12 and reflected from the measurement object 100 and the reference light formed from the polarizer 12 and reflected from the reference mirror 14c interfere with each other to interfere To form light.

In the present invention, as shown in FIG. 2, the Michelson interferometer type is applied to the OCD interferometer 14, and the Mach-zehnder interferometer is also applicable.

More specifically, referring to FIG. 2, the white light emitted from the beam splitter 13 passes through the iris 14b (Iris) and then enters the beam splitter 14a. Here, the beam splitter 14a of the OCD interferometer 14 reflects part of the incident white light to the reference mirror 14c and transmits the remaining part to the measurement object 100. Then, the measurement light reflected from the surface of the measurement object 100 and the reference light reflected from the reference mirror 14c are incident on the beam splitter 14a and interfere with each other, thereby forming interference light, which is formed on the upper portion of the OCD interferometer 14. The light is emitted toward the beam splitter 13 arranged. Here, the concept of an optical carrier frequency (h) is applied to the OCD interferometer 14 according to the present invention, which will be described later. The interfering light emitted from the OCD interferometer 14 is directed through the beam splitter 13 to the vertical linearly polarized light separator 15.

The vertical linear polarization separator 15 is disposed on the optical path of the interference light from the OCD interferometer 14, which separates the interference light into a TE polarization component and a TM polarization component whose mutual polarization directions are perpendicular to each other. Here, the vertical linear polarization of the TE polarization component and the TM polarization component respectively form interference light, and the vertical linear polarization separator 15 separates the TE polarization component and the TM polarization component. The TE polarization component and the TM polarization component separated by the vertical linear polarization separator 15 are input to the first spectrometer 16 and the second spectrometer 17, respectively. A condenser lens 16a for condensing the TE polarization component and the TM polarization component toward the first spectrometer 16 and the second spectrometer 17, respectively, in front of the first spectrometer 16 and the second spectrometer 17. , 16b).

Here, in the present invention, the vertical linear polarization separator 15 is provided as a wallastone prism as an example. In addition, a polarizing beam splitter 13 may be used.

The controller extracts the TE spectrum data and the TM spectrum data from the TE polarization component and the TM polarization component respectively input through the first spectrometer 16 and the second spectrometer 17. The controller calculates amplitude information and phase information for each of the TE polarization component and the TM polarization component.

Hereinafter, a method in which the controller extracts the TE spectral data and the TM spectral data from the TE polarization component and the TM polarization component to calculate amplitude information and phase information for each of the TE polarization component and the TM polarization component will be described in detail.

First, the optical carrier frequency introduced into the above-described OCD interferometer 14 will be described. As shown in FIG. 3, the measurement object 100 has a distance difference from the virtual reference plane by h. Here, h may be defined as an optical path difference (OPD) between the optical path of the reference light and the optical path of the measurement light, and a unit (m) that is a distance unit is used.

At this time, when h becomes '0', since the optical carrier frequency becomes 0, the OCD interferometer 14 is set so that h has a constant value for the application of the optical carrier frequency. In the present invention, an example in which the OCD interferometer 14 is set to have a h of about 10 to 20 µm is used.

Due to the introduction of the optical carrier frequency concept as described above, the TE spectral data and the TM spectral data for the TE polarization component and the TM polarization component input through the first spectrometer 16 and the second spectrometer 17 are respectively [ Equation 5] and [Equation 6].

[Equation 5]

&Quot; (6) &quot;

In Equations 5 and 6, I _TE and I _TM are TE spectral data and TM spectral data, respectively, and k is a wave number. h is the spectral carrier frequency as described above, E _{r, TE} and E _{t, TE} are the reference light and the measurement light for the TE polarized light component, respectively, and E _{r, TM} and E _{t, TM} are the Reference light and measurement light. And i _{0, TE} and i _{0, TM} are DC terms for TE polarization component and TM polarization component, and γ _TE (k, pattern) and γ _TM (k, pattern) are TE polarization component and Visibility amplitude function for the TM polarization component. Φ _TE and Φ _TM are total phase functions for the TE polarization component and the TM polarization component, respectively, and φ _TE and φ _TM are the measurement targets for the TE polarization component and the TM polarization component, respectively. Phase function dependent on the grid pattern shape of.

4 is a diagram illustrating TE spectral data and TM spectral data obtained as a result of measurement on a sample pattern. Here, the graph shown in FIG. 4 shows the TE spectrum data and the TM spectrum obtained from the measurement object 100 having a lattice pattern having a lattice spacing, fill factor and height of 1000 nm, 0.5, and 55 nm, respectively. The data is shown.

Hereinafter, a process of calculating amplitude information and phase information for each of the TE polarization component and the TM polarization component using the TE spectrum data and the TM spectrum data as shown in FIG. 4 will be described.

First, a Fast Fourier Transform (FFT) algorithm is applied to the TE spectrum data and the TM spectrum data. FIG. 5 is a diagram illustrating amplitude data in a spectral frequency domain obtained by applying a fast Fourier transform algorithm to TE spectrum data and TM spectrum data.

Then, by applying the windowing technique, only the object term is selected, and the object peak in the frequency domain is centered in the region where the frequency is 0, thereby conjugating the conjugate term. Remove a DC term that contains).

Then, the Inverse Fast Fourier Transform (IFFT) algorithm is applied to the Visibility amplitude function γ _TE and phase function φ _TE and TM polarization components for the _TE polarization component. Visibility amplitude function γ _TM and Phase function φ _TM are extracted.

Γ _TM and γ _TE extracted in this process become desired amplitude information, and φ _TM and φ _TE become desired phase information. Here, γ _TM and γ _TE mean visibility of an interference fringe, and may be expressed as shown in Equation 7 below. That is, the visibility amplitude function is expressed as the product of the absolute value of the reflection coefficient of the reference light and the absolute value of the reflection coefficient of the measurement light.

[Equation 7]

Further, φ _TM and φ _TE mean a difference between the phase shift of the measurement light and the phase shift of the reference light, which may be expressed as in Equation (8).

[Equation 8]

6 is a graph showing γ _TE and φ _TE for the TE polarization component, and FIG. 7 is a graph showing γ _TM and φ _TM for the TM polarization component, respectively.

Substituting γ _TM , γ _TE , φ _TM and φ _TE extracted through the above process into R _TM , R _TE , δ _TM , and δ _TE of [Equation 4], the amplitude ratio is finally SE parameter. (Ψ) and phase difference (Δ) can be obtained.

Here, the spectral carrier frequency h is reflected in the 2kh items in [Equation 5] and [Equation 6], and is canceled when calculating the phase difference Δ so that accurate measurement of the h value is unnecessary in the present invention.

8 is a diagram showing graphs of the amplitude ratio Ψ and the phase difference Δ calculated through the above process, respectively. 8 shows the amplitude ratio Ψ and the phase difference Δ calculated using the conventional RCWA method, and the graph indicated by the dotted line shows the amplitude ratio calculated through the OCD measuring method according to the present invention. Ψ) and phase difference Δ. It can be seen from FIG. 8 that the same results as the conventional RCWA method are obtained through the OCD measuring method according to the present invention.

Through the above configuration, the present invention can simultaneously measure the SE parameters Ψ and Δ in a single shot. More specifically, by applying the vertical incidence structure, the complexity of the structure of the existing oblique incidence structure is improved, and phase information can be extracted by using optical interference through the OCD interferometer 14, and in addition, spectroscopic The concept of carrier frequency and the application of a pair of spectrometers make it possible to obtain SE parameters Ψ and Δ simultaneously in a single shot.

Hereinafter, another embodiment of the OCD measuring device according to the present invention will be described with reference to FIGS. 9 and 10. Here, the OCD measuring apparatus shown in FIGS. 9 and 10 is provided in a form capable of measuring the surface shape according to the White-light Scanning Interferometry (WSI) together with the OCD measurement as described above. That is, in addition to the configuration shown in FIG. 2, the CCD camera 32, the light splitter 30, and the WSI interferometer 20 may be further included.

The WSI interferometer 20 is provided to be replaced with the OCD interferometer 14, and is provided in a form that can be applied to the white light scanning interferometry. 9 illustrates an example in which the OCD interferometer 14 is applied, and FIG. 10 illustrates an example in which the OCD interferometer 14 is removed and the WSI interferometer 20 is applied. Here, the WSI interferometer 20 and the OCD interferometer 14 are applied to the interferometer of the magnification suitable for the white light scanning interferometry and OCD measurement, respectively, and the magnification of the OCD interferometer 14 for the OCD measurement is usually the magnification of the WSI interferometer 20. Lower than

The light splitter 30 is disposed between the beam splitter 13 and the Willaston prism on the optical path of the interfering light. Then, the interfering light is split into a Willaston prism and a CCD camera 32 and outputted.

In accordance with the above configuration, the controller operates in one of an OCD mode for OCD measurement and a WSI mode for application of the white light scanning interference method.

More specifically, in the case where it is intended to operate in the OCD mode, it is measured while the OCD interferometer 14 is installed. At this time, the control unit is based on the TE polarization component and the TM polarization component input through the first spectrometer 16 and the second spectrometer 17, through the above-described process between the TE polarization component and the TM polarization component The amplitude ratio Ψ and the phase difference Δ are calculated. Interference light is transmitted to the CCD camera 32 by the optical splitter 30 even in the OCD mode. In the OCD mode, the control unit does not operate the CCD camera 32.

On the other hand, when the WSI mode is to be operated, the measurement is performed with the WSI interferometer 20 installed. At this time, the controller measures the surface shape by applying the image data input through the CCD camera 32 to the white light scanning interference method. Even in the WSI mode, the interfering light is emitted by the light splitter 30 toward the Willaston prism and transmitted to the first spectrometer 16 and the second spectrometer 17. In the WSI mode, the control unit may control the first spectrometer 16. ) And the second spectrometer 17 are not operated. Here, the method for measuring the surface shape by the white light scanning interference method is a well-known technique, and thus a detailed description thereof will be omitted.

Through the above configuration, it is possible to measure the aberration shape according to OCD measurement and white light scanning interferometry only by replacing the interferometer in one measuring equipment. Unexplained reference numeral 31 in FIGS. 9 and 10 is a condenser lens for focusing interference light with the CCD camera 32, and unexplained reference numerals 20a, 20b and 20c in FIG. 10 are beam splitters constituting the WSI interferometer 20. FIG. , Lenses and reflective mirrors.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a view for explaining a conventional RCAW technique,

2 is a diagram illustrating a configuration of an OCD measuring apparatus using optical interference according to the present invention,

3 is a view for explaining the concept of the spectral carrier frequency in the OCD measuring method according to the present invention,

4 to 8 are graphs for explaining the OCD measuring method according to the present invention,

9 and 10 are views showing the configuration of an OCD measuring device according to another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

10 light source 12 polarizer

13 beam splitter 14 OCD interferometer

15 vertical linearly polarized separator 16 first spectrometer

17: second spectrometer

Claims (12)

(a) irradiating white light; (b) linearly polarizing the white light in a direction inclined at 45 ° with respect to the TE polarization and the TM polarization directions in which the mutual polarization directions are perpendicular to each other; (c) the linearly polarized white light interfering with the measurement light and the reference light, respectively reflected from the measurement object and the reference mirror, to form interference light; (d) separating the interference light into the TE polarization component and the TM polarization component; (e) inputting the TE polarization component and the TM polarization component into a first spectrometer and a second spectrometer, respectively; (f) extracting TE spectral data and TM spectral data from the input TE polarization component and the input TM polarization component, respectively, to extract amplitude information and phase information for each of the TE polarization component and the TM polarization component; ; (g) calculating the amplitude ratio Ψ and phase difference Δ on the RCWA technique by applying the extracted amplitude information and the extracted phase information to a rigid coupled-wave analysis (RCWA) technique. OCD measurement method using optical interference. The method of claim 1, The amplitude ratio Ψ and the phase difference Δ are expressed by the RWA (Rigorous coupled-wave analysis) technique.

Where p is a reflection coefficient ratio of the RCWA technique, R _TM is a reflection coefficient of the TM polarization component, and R _TE is a reflection coefficient of the TE polarization component. Is a reflection coefficient, and δ _TM represents a phase shift of the TM polarization component, and δ _TE represents a phase shift of the TE polarization component. OCD measurement method using optical interference. The method of claim 2, In the step (c), the interference light is formed in a state where an optical path difference between the optical path of the reference light and the optical path of the measurement light is generated so that a spectral carrier frequency is applied. How to measure OCD. The method of claim 3, In the step (f) The TE spectrum data is expressed by Equation

Where I _TE is the TE spectral data, k is a wave number, and h is the spectral carrier frequency defined by the optical path difference between the optical path of the reference light and the optical path of the measurement light. ), E _{r, TE} and E _{t, TE} are the reference light and the measurement light for the TE polarized light component, i _{0, TE} is a DC term for the TE polarized light component, and the γ _TE (k, pattern) is a visibility amplitude function for the TE polarization component, Φ _TE is a total phase function for the TE polarization component, and φ _TE is for the TE polarization component A phase function dependent on the nanopattern shape of the measurement object; The TM spectrum data is represented by equation

Where I _TM is the TM spectral data, E _{r, TM} and E _{t, TM} are the reference light and the measurement light for the TM polarization component, respectively, and i _{0, TM} is a DC item for the TM polarization component (DC term), the γ _TM (k, pattern) is the Visibility amplitude function for the TM polarization component, Φ _TM is the total phase function for the TM polarization component, φ _TM is expressed as a phase function dependent on the nanopattern shape of the measurement object for the TM polarization component; The amplitude information and the phase information in the step (f) include the visibility amplitude function γ _TE and the phase function φ _TE for the _TE polarization component and the phase polarization component for the TM polarization component. Visibility amplitude function γ _TM and the Phase function φ _TM ; In the step (g), R _TM , R _TE , δ _TM , and δ _TE in the equation by the RCWA (Rigorous coupled-wave analysis) method are included in the γ _TM , γ _TE , φ _TM and φ _TE are substituted respectively, the method of measuring OCD using optical interference. The method of claim 4, wherein Step (f), (f1) applying a Fast Fourier Transform (FFT) algorithm to the TE spectral data and the TM spectral data; (f2) removing the DC item by applying a windowing technique and a centering technique to the data passed through the step (f1); (f3) the Visibility amplitude function and the total phase of the TE polarization component by applying an Inverse Fast Fourier Transform (IFFT) algorithm to the data which has passed the step (f2). extracting the Visibility amplitude function and the Total phase function for the TM polarization component and the TM polarization component. 6. The method according to any one of claims 1 to 5, Step (c) is a method for measuring OCD using optical interference, characterized in that implemented by a Michelson Interferometer (Michelson Interferometer). 6. The method according to any one of claims 1 to 5, The step (d) is OCD measurement method using optical interference, characterized in that implemented by Wallaston prism (Wollaston prism). In the OCD measuring apparatus using optical interference, A first spectrometer and a second spectrometer; A light source for emitting white light; A polarizer for linearly polarizing the white light emitted from the light source in a direction inclined by 45 ° with respect to the TE polarization and the TM polarization direction in which the mutual polarization directions are perpendicular to each other; A beam splitter for directing the linearly polarized white light to a measurement object; An OCD interferometer for measuring light formed by reflecting the linearly polarized white light from the measurement object and reference light formed by reflecting the linearly polarized white light from the reference mirror to form interference light; A vertical linear polarization splitter disposed on the optical path of the interference light from the OCD interferometer and separating the interference light into the TE polarization component and the TM polarization component and outputting the interference to the first spectrometer and the second spectrometer, respectively; ; The step (f) and the method of measuring OCD according to any one of claims 1 to 4 for the TE polarization component and the TM polarization component input through the first spectrometer and the second spectrometer and a control unit for calculating the amplitude ratio Ψ and the phase difference Δ by performing step g). The method of claim 8, The OCD interferometer is configured to generate an optical path difference between the optical path of the reference light and the optical path of the measurement light so that the spectral carrier frequency (Spectral carrier frequency) is applied. 10. The method of claim 9, The OCD interferometer is OCD measurement apparatus using optical interference, characterized in that implemented by a Michelson Interferometer (Michelson Interferometer). 10. The method of claim 9, The vertical linearly polarized light separator is OCD measuring apparatus using optical interference, characterized in that implemented by Wallaston prism (Wollaston prism). 10. The method of claim 9, With CCD camera, An optical splitter disposed between the beam splitter and the wallastone prism on the optical path of the interference light to split and output the interference light to the Willaston prism and the CCD camera; Replaceable with the OCD interferometer, further comprising an applicable WSI interferometer of White-light Scanning Interferometry (WSI); The control unit controls the amplitude ratio between the TE polarized component and the TM polarized component based on the TE polarized component and the TM polarized component input through the first spectrometer and the second spectrometer while the OCD interferometer is installed. Ψ) and the OCD mode for calculating the phase difference Δ and the WSI mode for measuring the surface shape by applying image data input through the CCD camera to the white light scanning interferometry with the WSI interferometer installed. OCD measuring apparatus using optical interference, characterized in that.

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