KR102545519B1 - Reflective Optical System with Minimized Polarization Modulation and Spectroscopic Ellipsometer Provided Therewith - Google Patents

Abstract

The present invention relates to a reflective optical system and a spectroscopic ellipsometer having the same and, more specifically, to a reflective optical system, in which reflective surfaces are disposed to minimize polarization modulation, and a spectroscopic ellipsometer having the same. The reflective optical system with minimized polarization modulation, which includes a polarizer and an analyzer, and defines a first plane including light passing through the polarizer and a normal line of a sample surface and a second plane including light passing through the analyzer and the normal line of the sample surface, comprises: a first reflective optical system which includes a first reflective surface; and a second reflective optical system which includes a second reflective surface. Here, the first reflective surface is disposed to allow a first polarization surface, which is a p-wave polarization surface of light that has passed through the first reflective optical system, to be formed side by side with a surface that rotates the first plane in a first direction around a first reference shaft. The second reflective surface is disposed to allow a second polarization surface, which is a p-wave polarization surface of light that has passed through the second reflective optical system, to be formed side by side with a surface that rotates the second plane in a second direction around a second reference shaft. The reflective optical system according to the present invention has an advantage of minimizing polarization modulation.

Description

Reflective Optical System with Minimized Polarization Modulation and Spectroscopic Ellipsometer Provided Therewith}

The present invention relates to a reflective optical system and a spectroscopic ellipsometer having the same, and more particularly, to a reflective optical system having reflective surfaces arranged to minimize polarization modulation and a spectroscopic ellipsometer equipped with the same.

Spectroscopic ellipsometry (SE) is used as a method for deriving information such as thickness, refractive index (n), extinction coefficient (k), and optical bandgap of a semiconductor thin film. . Spectroscopic ellipsometry is an analysis method that investigates the optical properties of a material by using the property that the polarization state changes according to the refractive index or thickness of the medium after light incident on the material is reflected or transmitted through the surface.

A spectroscopic ellipsometer used in the semiconductor industry has a micro focal spot having a size of several tens of μm. To achieve this, an optical system using a transmissive or reflective optical element is configured.

A typical transmissive optical element is a lens, and the biggest problem in a transmissive optical system using a lens is a difference in spot size for each wavelength due to chromatic aberration caused by a difference in refractive index for each wavelength due to the characteristics of a transmissive material.

In the case of using a reflective optical system to avoid this, polarization change due to reflection appears as the biggest problem.

1 is a view showing a conventional elliptical spectrometer, and FIG. 2 is a view of the elliptical spectrometer shown in FIG. 1 viewed from above. As shown in FIGS. 1 and 2, the conventional reflective optical system includes a polarizer (1) for polarizing light generated from a light source, and the light passing through the polarizer (1) is measured at a spot on the surface of a sample (S). A first reflective optical system 3 including a pair of first reflective surfaces 2 for reflecting light toward, and the light reflected from the surface of the sample S toward the analyzer 7 It includes a second reflective optical system 5 including a pair of second reflection surfaces 4 for reflecting light, and an analyzer 7 for detecting the polarization state of the light reflected from the surface of the sample S.

In addition, the elliptical spectrometer transmits light passing through a light source 9 and a pair of mirrors 11 that transmit light from the light source 9 to the polarizer 1 and the analyzer 7 to a spectrometer 15. It further includes a pair of mirrors 13 that transmit.

FIG. 3 is a diagram illustrating a first polarization plane P _P,1 and a second polarization plane Pp, ₂ in the reflective optical system shown in FIG. 1 . As shown in FIG. 3, in the reflective optical system shown in FIGS. 1 and 2, the incident light (R _I ), the normal line (N) of the sample (S), and the reflected light (R _R ) form an incident surface (P _I ), The first polarization plane (P _P,1 ) and the second polarization plane (P _P,2 ) form the same plane. The first polarization plane (P _P,1 ) and the second polarization plane (P _P,2 ) pass through the p-wave polarization plane of the light passing through the first reflection type optical system 3 and the second reflection type optical system 5, respectively. means the p-wave polarization plane of one light.

Polarization, one of the unique wave properties of light, is modulated according to the optical properties of the medium, such as the complex refractive index of the medium, when it is reflected from the surface of the medium. Therefore, in the reflective optical system, polarization modulation occurs unintentionally during the reflection process on the first reflective surfaces 2 and the second reflective surfaces 4. By controlling polarization, a thin film thickness of several Å to hundreds of nm In the case of a spectroscopic ellipsometer that must measure , an unintended change in polarization causes an error in the measured value. Therefore, a method capable of canceling this polarization modulation must be considered. In particular, since polarization modulation directly affects polarization when it occurs between polarizer 1 and analyzer 7, it is very important to cancel the polarization modulation in the optical path between polarizer 1 and analyzer 7. It is important.

In the conventional reflective optical system shown in FIGS. 1 to 3 , an incident plane (P _I ), a first polarization plane (P _P,1 ), and a second polarization plane (P _P,2 ) form the same plane. However, since the phase and magnitude of the p-wave and the s-wave change differently during the reflection process, the phase and magnitude of the p-wave at the first polarization plane (P _P,1 ) are the same as those of the p-wave at the incident plane (P _I ). different from phase and size. The same goes for s waves. Accordingly, the polarized light incident on the sample S becomes polarized light having a different ellipticity coefficient from the polarized light passing through the polarizer 1. For example, when the linearly polarized light passing through the polarizer 1 is incident on the sample S, it is modulated into elliptically polarized light.

More specifically, in a spectroscopic ellipsometer using an ideal reflector as a sample and using light with a wavelength of 600 nm, the ellipticity constant obtained when there is no optical element affecting polarization between the polarizer 1 and the analyzer 7 When the size of (Δ, ψ) is (36.179, 2.435), respectively, if a micro-spot reflective optical system affecting polarization exists between the polarizer (1) and the analyzer (7), the ellipticity constant (Δ, A simulation result in which ψ) is modulated by (21.746, 1.949) is obtained. This is that the elliptic constant modulation (dΔ, dψ) (14.433, 0.486) is generated by the reflective optical system added for the micro spot. The Δ value is the phase difference between the p-wave and the s-wave incident on the target area after reflection, and the Ψ value represents the angle between the reflection coefficient ratio (tan Ψ) of the p-wave and the s-wave of the reflected light.

As a method of offsetting this polarization modulation, Korean Patent Registration No. 10-2137053 discloses a pair of reflective surfaces constituting 45 degrees with respect to the traveling direction of light, each having a polarization emitting unit and a polarization entering unit disposed at an angle of 90 degrees. A method of doing so is disclosed. In the above method, polarization modulation is canceled by making p-polarized light with respect to one reflective surface to s-polarized light with respect to the other reflective surface.

However, there is a problem that polarization modulation remains even when this method is applied. For example, in a similar way to the above method, if the polarization state is simulated by applying 90-degree reflective surfaces only to the reflective optical system between the sample and the analyzer, the ellipticity constants (Δ, ψ) become (33.851, 1.883), The elliptic constant modulation (dΔ, dψ) due to the polarization modulation is (2.328, 0.552).

The reason for this is as follows. For example, when it is assumed that 10% of the polarization modulation by the reflective surface of the reflective optical system occurs on the basis of the p-wave, 10% of the polarization modulation of the p-wave occurs in the path from the reflective surface on the polarizer side to the sample.

When light having a p-wave reference polarization modulation of 10% is incident on a sample, 10% of the polarization modulation by the sample includes 10% of the polarization modulation at the reflective surface on the polarizer side. This means that when the polarization modulation by the sample is 50%, 10% of 50%, that is, 5% additional polarization modulation occurs.

Assuming that the light reflected from the sample is incident on the reflective surface on the analyzer side rotated by 90 degrees and the p-wave is changed to an s-wave to cancel the 10% polarization modulation, this cancels out only the additional 5% of the polarization modulation caused by the polarization modulation by the sample You will be able to do it. Therefore, only a part of the 10% polarization modulation generated at the polarizer-side reflective surface can be canceled.

Korean Patent Registration No. 10-2137053

An object of the present invention is to provide a novel reflective optical system capable of minimizing polarization modulation and a spectroscopic ellipsometer equipped with the same.

In order to achieve the above object, the present invention is located between a light source and the sample surface, and a polarizer for polarizing light generated from the light source, and an analyzer for detecting the polarization state of light reflected from the sample surface. (analyzer) and defines a first plane including the light passing through the polarizer and the normal of the sample surface, and a second plane including the light passing through the analyzer and the normal of the sample surface. An optical system comprising: a first reflective surface disposed between the polarizer and the sample surface and configured to change a propagation path of light so that the light passing through the polarizer is directed to a measurement spot on the sample surface; a reflective optical system; A second reflective type including at least one second reflective surface disposed between the sample surface and the analyzer and configured to change a propagation path of light so that the light reflected from the measurement spot on the sample surface is directed toward the analyzer. A reflective optical system including an optical system in which polarization modulation is minimized is provided.

Here, in order to cancel polarization modulation due to reflection from the first reflection surface, the first reflection surface is a first polarization plane that is a p-wave polarization plane of light passing through the first reflection type optical system. The first plane is arranged to be formed parallel to a plane rotated in a first direction with respect to a first reference axis.

A part of the light passing through the first reflection type optical system based on the first polarization plane travels as a p-wave and a part as an s-wave.

And, in order to cancel the polarization modulation due to reflection from the second reflection surface, the second polarization plane, which is a p-wave polarization plane of light passing through the second reflection type optical system, forms the second plane. It is arranged to be formed parallel to a surface rotated in a second direction based on a second reference axis different from the first reference axis.

A part of the light passing through the second reflection type optical system based on the second polarization plane travels as a p-wave and a part as an s-wave.

In addition, the present invention provides a reflective optical system in which polarization modulation is minimized, wherein the first reference axis is an optical axis of light passing through the polarizer, and the second reference axis is an optical axis of light passing through the analyzer.

In addition, the first reference axis is an optical axis of light passing through the first reflection type optical system and incident on the sample surface, and the second reference axis is an optical axis of light reflected from the sample surface and incident on the second reflection type optical system. Provided is a reflective optical system in which polarization modulation is minimized.

In addition, the rotation angle between the first rotation direction and the second rotation direction is the material of the first reflection surface and the second reflection surface and the angle of incidence of light incident on the first reflection type optical system and the angle of incidence of light incident on the second reflection type optical system. Provided is a reflective optical system in which polarization modulation is minimized, characterized in that it is determined based on the incident angle of light.

In addition, the first rotation direction and the second rotation direction are opposite to each other, providing a reflective optical system in which polarization modulation is minimized.

In addition, a rotational angle in the first rotational direction and a rotational angle in the second rotational direction are the same in a reflective optical system in which polarization modulation is minimized.

In addition, the present invention provides an ellipsoidal spectrometer equipped with a reflective optical system in which the above-described polarization modulation is minimized.

The reflective optical system according to the present invention has an advantage of minimizing polarization modulation.

1 is a diagram showing a conventional ellipsometric spectrometer.
FIG. 2 is a view of the ellipsometer shown in FIG. 1 viewed from above.
FIG. 3 is a view showing a first polarization plane and a second polarization plane in the reflective optical system shown in FIG. 1 .
4 is a three-dimensional view of a reflective optical system in which polarization modulation is minimized according to an embodiment of the present invention.
FIG. 5 is a top view of the ellipsometric spectrometer including the reflective optical system shown in FIG. 4 .
FIG. 6 is a view showing a first polarization plane and a second polarization plane in the reflective optical system shown in FIG. 4 .

Hereinafter, one embodiment of the present invention will be described with accompanying drawings. However, embodiments of the present invention may be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Therefore, the shapes of elements in the drawings are exaggerated to emphasize more clear description, and elements indicated by the same reference numerals in the drawings mean the same elements.

4 is a three-dimensional view of a reflective optical system in which polarization modulation is minimized according to an embodiment of the present invention, and FIG. 5 is a top view of an ellipsoidal spectrometer including the reflective optical system shown in FIG. 4 .

4 and 5, the reflective optical system 20 in which polarization modulation is minimized according to the present invention includes a polarizer 21, a first reflective optical system 23, and a second reflective optical system 25 and an analyzer 27.

The polarizer 21 serves to polarize light generated from the light source 30 . For example, the polarizer 21 may convert light generated from the light source 30 into linearly polarized light in which phases of p-polarized light (p-wave) and s-polarized light (s-wave) are the same.

The first reflective optical system 23 is disposed between the polarizer 21 and the surface of the sample S. The first reflective optical system 23 is configured to change the propagation path of light so that the light passing through the polarizer 21 is directed to the measurement spot on the surface of the sample S.

The first reflective optical system 23 includes at least one first reflective surface 22a, 22b. Although the embodiment shown in FIG. 2 is illustrated as having a pair of first reflective surfaces 22a and 22b, it may include one first reflective surface or three or more first reflective surfaces. there is.

Here, the first reflective surfaces 22a and 22b are disposed to cancel polarization modulation due to reflection from the first reflective surfaces 22a and 22b.

Since the reflection coefficients of the first reflective surfaces 22a and 22b are different for p-wave and s-wave, the linearly polarized light incident on the first reflective surface 22a disposed on the upstream side of the light propagation path is elliptically polarized. turns into Further, polarization modulation occurs again in the process of being reflected again by the first reflecting surface 22b disposed on the downstream side.

In the present invention, the first polarization plane (P _P,1 ), which is the p-wave polarization plane of the light passing through the first reflection type optical system 23 , has a first plane (P ₁ ) with respect to the first reference axis (A ₁ ). Polarization modulation by the first reflective surfaces 22a and 22b is canceled by arranging the first reflective surfaces 22a and 22b to be parallel to the surface rotated in the first direction. The first plane P ₁ is a plane including an optical axis of light passing through the polarizer 21 and a normal line N of the sample S.

In the present invention, by changing the polarization modulation generated in the first reflection type optical system 23 into some p-waves and some s-waves, the polarization modulation generated by the first reflection surfaces 22a and 22b is canceled by itself, so that the sample (S) ) It is configured to maintain the polarization state of light incident on the light passing through the polarizer 21, for example, the linear polarization state.

The p-wave polarization plane refers to a plane including the direction of vibration of the p-wave and the traveling direction of light.

FIG. 6 is a diagram illustrating a first polarization plane P _P,1 and a second polarization plane P _P,2 in the reflective optical system in which polarization modulation is minimized shown in FIG. 4 .

As shown in FIG. 6 , the first reference axis A ₁ may be, for example, an optical axis of incident light passing through the polarizer 21 . The first direction may be clockwise. The rotation angle α is determined based on the material of the first reflection surfaces 22a and 22b and the angle of incidence of light entering the first reflection type optical system 23 . The rotation angle α may be, for example, 30 to 40 degrees.

Also, the first reference axis A ₁ may be an optical axis of light passing through the first reflective optical system 23 and incident on the surface of the sample S.

The rotation angle α in the first direction for forming the first reflection type optical system 23 that minimizes polarization modulation and the movement condition are the first reflection surfaces 22a and 22b constituting the first reflection type optical system 23 It is determined according to conditions such as the radius of curvature, the angle of incidence of light incident on the first reflective surfaces 22a and 22b, the material of the first reflective surfaces 22a and 22b, and the type of coating.

Some of the light passing through the first reflection type optical system 23 based on the first polarization plane (P _P,1 ) travels as a p-wave, and some travels as an s-wave.

In the illustrated first reflection type optical system 23 in which polarization modulation is minimized, the first reflection surfaces 22a and 22b transmit a p wave appearing in the first polarization plane P _P,1 to minimize polarization modulation. For , it is divided into some p-waves and some s-waves, and after being reflected from the sample (S), some p-waves before reflection from the sample (S) are reflected as some s-waves, and some s-waves before reflection from the sample (S) are reflected as some p-waves designed to be

Ideally, the polarized light passing through the first reflective optical system 23 may be the same polarized light as the polarized light incident on the first reflective optical system 23 . For example, if linearly polarized light enters the first reflective optical system 23, the light passing through the first reflective optical system 23 becomes the same linearly polarized light.

The p-wave polarization planes of the light passing through the polarizer 21 and the light passing through the first reflective optical system 23 are different from each other as the first plane (P ₁ ) and the first polarization plane (P _P,1 ), but the ellipticity coefficient becomes the same polarization. For example, if the light passing through the polarizer 21 is linearly polarized light, the light passing through the first reflective optical system 23 also becomes linearly polarized light with only a different plane of p-polarization.

The sample S may be a sample S having a substrate and a plurality of thin film layers sequentially formed on the substrate. The substrate may be a glass substrate or a semiconductor substrate. The thin film layers may be layers constituting electronic devices such as semiconductor devices, display devices, and solar cells. The thin film layers may be semiconductor, dielectric or metal layers. When polarized light is incident on the sample (S), the polarization state of the reflected light is changed according to the optical characteristics of the sample (S). That is, the sample S reflects polarized light that is changed according to optical and structural characteristics such as refractive index and thickness of the thin film layers constituting the sample S and the substrate.

The second reflective optical system 25 is disposed between the surface of the specimen S and the analyzer 27 . The second reflective optical system 25 is configured to change the traveling path of light so that the light reflected from the measurement spot on the surface of the sample S is directed toward the analyzer 27 .

The second reflective optical system 25 includes at least one second reflective surface 24a, 24b. Although the embodiment shown in FIG. 2 is illustrated as having a pair of second reflective surfaces 24a and 24b, one second reflective surface may be provided or three or more second reflective surfaces may be provided. there is.

Here, the second reflective surfaces 24a and 24b are disposed to cancel polarization modulation due to reflection from the second reflective surfaces 24a and 24b.

Polarization modulation occurs because the reflection coefficients of the second reflection surfaces 24a and 24b for the p-wave and the s-wave are different from each other.

When polarized light whose polarization modulation is not canceled is incident on the analyzer 27, the polarization modulation by the sample S and the polarization modulation by the second reflecting surfaces 24a and 24b are mixed, making accurate measurement difficult.

In the present invention, the second polarization plane (P _P, 2 ), which is the p-wave polarization plane of the light passing through the second reflection type optical system 25, is based on the second reference axis (A ₂ ) relative to the second plane (P ₂ ). The polarization modulation by the second reflective surfaces 24a and 24b is canceled by arranging the second reflective surfaces 24a and 24b to be parallel to the surface rotated in the second direction. The second plane P ₂ is a plane including light passing through the analyzer 17 and a normal line N of the surface of the sample S. The second plane P ₂ is not parallel to the first plane P ₁ , but is preferably parallel to the maximum.

As shown in FIG. 6 , the second reference axis A ₂ may be, for example, an optical axis of reflected light passing through the analyzer 27 . The second direction may be counterclockwise. The rotation angle β is determined based on the material of the second reflection surfaces 24a and 24b and the angle of incidence of light entering the second reflection type optical system 25 . The rotation angle β may be, for example, 30 to 40 degrees. If the first reflective surfaces 22a, 22b and the second reflective surfaces 24a, 24b are made of the same material, the rotational angle α in the first rotational direction and the rotational angle β in the second rotational direction are may be of the same size.

Also, the second reference axis A ₂ may be an optical axis of light reflected from the surface of the sample S and incident on the second reflection type optical system 25 .

Some of the light passing through the second reflection type optical system 25 based on the second polarization plane (P _P,2 ) travels as a p-wave, and some travels as an s-wave.

Ideally, the polarized light passing through the second reflection type optical system 25 may be the polarized light incident on the second reflection type optical system 25 and modulated only by the sample S.

As shown in FIG. 5 , the elliptical spectrometer 100 further includes a light source 30 and a spectrometer 40 .

The light source 30 is a device that generates light irradiated onto the sample S, and can generate light in a wavelength band ranging from far infrared to near infrared.

The spectrometer 40 operates according to a predetermined exposure time according to an external trigger signal and measures the amount of light passing through the reflective optical system 20 . Spectrometer 40 may include a charge-coupled device.

In addition, the elliptical spectrometer 100 includes a pair of mirrors 31 that transmit light emitted from the light source 30 to the polarizer 21 and a pair of mirrors 31 that transmits light passing through the analyzer 27 to the spectrometer 40. It further includes a mirror 41 of

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific embodiments described above, and is common in the art to which the present invention pertains without departing from the gist of the present invention claimed in the claims. Of course, various modifications and implementations are possible by those with knowledge of, and these modifications should not be individually understood from the technical spirit or perspective of the present invention.

100: elliptical spectrometer
P _P,1 : 1st polarization plane
P _P,2 : Second polarization plane
P _I : entrance plane
P ₁ : first plane
P ₂ : second plane
A ₁ : first reference axis
A ₂ : 2nd reference axis
20: reflective optical system
21: polarizer
23: first reflective optical system
25: second reflective optical system
27: analyzer
30: light source
40: spectrometer

Claims (7)

It is located between the light source and the sample surface, and includes a polarizer for polarizing the light generated from the light source and an analyzer for detecting the polarization state of the light reflected from the sample surface, which passes through the polarizer. A reflective optical system defining a first plane including light passing through and a normal line of the sample surface, and a second plane including light passing through the analyzer and a normal line of the sample surface,
A first reflective type including at least one pair of first reflective surfaces disposed between the polarizer and the surface of the sample and configured to change a propagation path of light so that the light passing through the polarizer is directed to a measurement spot on the surface of the sample. optics,
A second reflector disposed between the sample surface and the analyzer and including at least one pair of second reflection surfaces configured to change a propagation path of light so that light reflected from a measurement spot on the sample surface faces the analyzer. Including a type optical system,
In order to reduce polarization modulation due to reflection in the first reflection type optical system, a first polarization plane, which is a p-wave polarization plane of light passing through the first reflection type optical system, uses the first plane as a first reference. The first reflection surfaces are arranged so as to be parallel to a surface rotated in a first direction with respect to an axis,
Some of the light passing through the first reflection type optical system based on the first polarization plane travels as p-waves, and some travels as s-waves;
In order to reduce polarization modulation due to reflection in the second reflection type optical system, a second polarization plane, which is a p-wave polarization plane of light passing through the second reflection type optical system, has the second plane different from the first reference axis. The second reflective surfaces are disposed parallel to a surface rotated in a second direction with respect to a second reference axis,
A reflection type optical system with minimized polarization modulation, characterized in that a part of the light passing through the second reflection type optical system with respect to the second polarization plane proceeds as a p wave and a part proceeds as an s wave. According to claim 1,
The first reference axis is an optical axis of light passing through the polarizer, and the second reference axis is an optical axis of light passing through the analyzer. According to claim 1,
The first reference axis is an optical axis of light passing through the first reflection type optical system and incident on the sample surface, and the second reference axis is an optical axis of light reflected from the sample surface and incident on the second reflection type optical system. A reflective optical system in which polarization modulation is minimized. According to claim 1,
The angle of rotation in the first direction and the second direction is a ratio between the material of the first and second reflection surfaces and the angle of incidence of light incident to the first reflection type optical system and the light incident to the second reflection type optical system. A reflective optical system in which polarization modulation is minimized, characterized in that it is determined based on the angle of incidence. According to claim 1,
The reflective optical system with minimized polarization modulation, characterized in that the first direction and the second direction are opposite to each other. According to claim 5,
A reflective optical system with minimized polarization modulation, characterized in that the rotation angle in the first direction and the rotation angle in the second direction are the same. An ellipsoidal spectrometer having a reflective optical system in which the polarization modulation of any one of claims 1 to 6 is minimized.

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