WO2021085641A1

WO2021085641A1 - Polarization measurement device and ellipsometer

Info

Publication number: WO2021085641A1
Application number: PCT/JP2020/040970
Authority: WO
Inventors: 井上　喜彦; 佐藤　尚; 川嶋　貴之; 守俊加藤; ローランファーブル; 寿憲熊谷; 湧紀石田
Original assignee: 株式会社フォトニックラティス
Priority date: 2019-11-01
Filing date: 2020-10-30
Publication date: 2021-05-06
Also published as: JP2021071433A

Abstract

[Problem] To provide a polarization measurement device with which an imaging element can be disposed in an environment different from an environment in which an object to be measured is disposed. [Solution] A wave plate and a polarizer are arranged in this order from a direction in which light is incident. The wave plate is divided into regions within one plate, and each region has a plurality of axial directions. The polarizer is uniform or is divided into regions within one sheet, and each region has a plurality of axial directions. The wave plate and the polarizer are arranged in front of one end surface of a bundle fiber, and an imaging element is disposed in the rear of the other end surface of the bundle fiber. Polarization information on the incident light is converted into a light-dark distribution by causing the light to pass through the wave plate and the polarizer, and the light-dark distribution propagates to the imaging element through the bundle fiber, and is converted into an electric signal using the imaging element, thereby obtaining the polarization information. Accordingly, a position where the polarization information is acquired and a position of the imaging element are separated from each other.

Description

Polarization measuring device and ellipsometer

The present invention relates to a polarization measuring device and an ellipsometer. Specifically, the polarization measuring device and the ellipsometer according to the present invention move the image sensor that converts optical information into an electric signal away from the measurement environment to acquire and analyze the polarization information in a special environment such as in a vacuum. It is the one that realized the measurement in.

The polarization measuring device can be used as a birefringence measuring device by analyzing the polarization information of the light passing through the sample, for example. Further, in the case of a sample in which a thin film is formed on the surface, the light reflected by the sample is affected by multiple reflections in the thin film, and its polarization state changes. The thickness or refractive index of the thin film can be derived from this change in the changed state. It is known that such a polarization measuring technique can be calculated by incident the light to be analyzed on a wave plate and a polarizer, rotating them, and measuring a change in the intensity of the transmitted light.

However, when rotating the wave plate and the polarizer as described above, a rotation mechanism is required, so that there are problems such as time required for measurement, dust generation from the rotating part, and complicated mechanism. In order to solve these problems, it is possible to use a polarized image sensor that combines a region-divided polarizer, a region-divided wave plate, and an image sensor such as a CCD or CMOS for the purpose of realizing high-speed, real-time measurement of polarization information. Are known.

Japanese Patent No. 4974543 "Polarization Imaging Device" Japanese Patent No. 5118311 "Measuring device for phase difference and optical axis orientation" Japanese Patent No. 5140409 "Polarization measuring instrument, measuring system" Japanese Patent No. 5254323 "Optical strain measuring device" Japanese Unexamined Patent Publication No. 2005-114704 "Polarization Analyzer"

On the other hand, in the manufacture of semiconductors or displays, devices are made by stacking films of various materials. Since the thickness of each film affects the characteristics of the device, high-precision control is required, and the film is often formed mainly in vacuum. For example, an ellipsometer is known as a technique capable of measuring an ultrathin film of several nanometers with high accuracy, and is used for measuring the thickness of such a film. However, usually, a sample is taken out from the vacuum layer and measured, and an ellipsometer capable of measuring during the process or without breaking the vacuum has been desired.

By the way, a conventional polarized image sensor is provided with a region-divided polarizer or a region-divided wave plate and a uniform polarizer or a region-divided polarizer, and the light transmitted through them is converted into a light-dark distribution that differs depending on the polarization state. , It is converted into an electric signal by the image pickup element arranged immediately after (Fig. 1). Therefore, when it is necessary to measure the polarization in close proximity to the measurement target, it is necessary to install the image sensor in an environment with the measurement target. On the other hand, when the environment for acquiring the polarization information is, for example, a vacuum, a high temperature environment, or a special environment such as in a liquid, there is a problem that it is difficult to operate the image sensor stably.

As a means to solve this, there is a method of separating the measurement environment and the space where the polarization measurement sensor is arranged through a glass window or the like. However, when accurate positioning of the measurement position is required, or when the distance between the measurement target and the measurement sensor needs to be close, the required accuracy may not be obtained by the method of measuring through the window glass. It was.

In the present invention, the conventionally integrated region-dividing polarizer or region-dividing wave plate and an image sensor such as a CCD or CMOS are separated via a bundle fiber to create an environment different from the environment in which the measurement target is arranged. It is based on the finding that it is possible to arrange an image sensor.

The first aspect of the present invention relates to a polarization measuring device. The polarization measuring device is arranged in the order of the wave plate and the polarizer from the direction in which light enters. The wave plate is divided into regions within one plate, and each region has a plurality of axial directions. The polarizer is uniform or divided into regions within one sheet, and each region has a plurality of axial directions. The wave plate and polarizer are placed in front of one end face of the bundle fiber. An image sensor is placed after the other end face of the bundle fiber. As a result, the polarization information of the incident light is converted into a light-dark distribution by passing through the wave plate and the polarizer, and the light-dark distribution is propagated to the image sensor through the bundle fiber and converted into an electric signal using the image sensor. This makes it possible to acquire polarization information. As described above, in the polarization measuring apparatus of the present invention, the position of acquiring polarization information and the position of the image sensor are separated.

It is also possible to omit the wave plate in the polarization measuring device. In that case, a polarizer is used in which the regions are divided in one sheet and each region has a plurality of axial directions. The polarizer is placed in front of one end face of the bundle fiber. An image sensor is placed after the other end face of the bundle fiber. As a result, the polarization information of the incident light is converted into a light-dark distribution by passing through the polarizer, the light-dark distribution is propagated to the image sensor through the bundle fiber, and the polarization information is converted into an electric signal by using the image sensor. Can be obtained. In this way, the position where the polarization information is acquired and the position of the image sensor are separated.

The second aspect of the present invention relates to an ellipsometer. The ellipsometer is arranged in the order of the wave plate and the polarizer in the order in which the light reflected from the surface of the sample is incident and the light enters. The wave plate is divided into regions within one plate, and each region has a plurality of axial directions. The polarizer is uniform or divided into regions within one sheet, and each region has a plurality of axial directions. The wave plate and polarizer are located in front of one end face of the bundle fiber. An image sensor is placed after the other end face of the bundle fiber. As a result, the polarization information of the incident light is converted into a light-dark distribution by passing through the wave plate and the polarizer, and the light-dark distribution is propagated to the image pickup element through the bundle fiber and converted into an electric signal by using the image pickup element. The polarization information can be obtained with, and the film thickness or refractive index of the sample can be calculated from the polarization information. As described above, in the ellipsometer of the present invention, the position of acquiring polarization information and the position of the image sensor are separated.

It is also possible to omit the wave plate in the ellipsometer. In that case, a polarizer is used in which the regions are divided in one sheet and each region has a plurality of axial directions. The polarizer is placed in front of one end face of the bundle fiber. An image sensor is placed after the other end face of the bundle fiber. As a result, the polarization information of the incident light is converted into a light-dark distribution by passing through the polarizer, the light-dark distribution is propagated to the image sensor through the bundle fiber, and the polarized light is converted into an electric signal by using the image sensor. Information can be obtained. In this way, the position where the polarization information is acquired and the position of the image sensor are separated.

The region-divided polarizer is preferably a photonic crystal produced by a self-cloning method, a wire grid method, or the like. Further, the region-divided wave plate is preferably a photonic crystal produced by a self-cloning method or the like.

A self-cloning photonic crystal is manufactured by forming a multilayer film on a substrate having a concavo-convex groove shape in an arbitrary direction by a special film forming technique called a self-cloning method. A self-cloning photonic crystal refers to a polarizer having a transmission axis along the direction of the concavo-convex shape and a wave plate having an anisotropic axis along the direction of the concavo-convex shape (FIG. 2). The function as a polarizer or a wave plate can be selected by controlling the thickness of the multilayer film. Further, by changing the direction of the concave-convex groove shape of the substrate for each divided region, a region dividing element of a polarizer or a wave plate can be easily realized (FIG. 3). Since the shape and size of the region can be arbitrarily designed, the self-cloning photonic crystal is suitable as the region-dividing polarizer and the region-dividing wave plate of the present invention.

A bundle fiber has a structure in which at least three or more optical fibers are bundled (Fig. 4). In front of one end face of the bundle fiber, a region-dividing polarizer is arranged alone (FIG. 5 (a)), or a combination of a region-dividing wave plate and a uniform polarizing plate is arranged (FIG. 5). (B)), or a combination of a region-dividing wave plate and a region-dividing polarizer is arranged (FIG. 5 (c)), and the bundle fiber is brought close to or in contact with one end face. The vicinity of one end face of the bundle fiber in which the region dividing element is arranged is called a "polarization detection unit". Further, an image sensor such as a CCD or CMOS is arranged on the other end face of the bundle fiber. The end face of the bundle fiber in which the image sensor is arranged is called a "photoelectric conversion unit" in the sense that it converts an optical signal into an electric signal. One of the features of the present invention is that the polarization detection unit and the photoelectric conversion unit are separated by the bundle fiber.

The light beam incident on the polarization detection unit is converted into a spatial distribution of the amount of transmitted light according to the polarization information by the region-divided polarizer alone or the combination of the region-divided wave plate and the polarizing plate. The amount of light converted into the spatial distribution becomes the distribution of the amount of light transmitted by each optical fiber of the bundle fiber, is transmitted to the end face of the bundle fiber on the photoelectric conversion unit side, and is converted into an electric signal by the image sensor. The light amount distribution information converted into an electric signal can be calculated by software to know the polarization information incident on the polarization detection unit.

The ellipsometer of the present invention may further have a configuration in which a reflection mirror is arranged so as to guide light to the sample, whereby a wave plate and a polarizer are arranged in the same direction as the light emission position (the ellipsometer of the present invention). FIG. 10).

By using a polarization measuring device in which bundle fibers are interposed between region-divided polarizer wavelength plates, it is possible to arrange the image sensor in atmospheric pressure and atmosphere regardless of the environment in which the observation target is installed. For example, the polarization information of a light beam transmitted or reflected from a measurement target installed in a vacuum is measured using an image sensor installed in the atmosphere via a bundle fiber drawn from the inside of the vacuum chamber to the outside. Becomes possible.

Therefore, by using the polarization measuring device of the present invention, only optical components having high environmental resistance such as region dividing elements and bundle fibers are arranged in a special environment such as in a vacuum, in a liquid, or in a high temperature environment. Electronics application parts such as image pickup devices and light sources with low environmental resistance can be installed in an atmospheric environment to enable polarization measurement in a special environment.

FIG. 1 shows a configuration example of a conventional polarization imaging sensor. FIG. 2 is a schematic view of a self-cloning photonic crystal and its substrate. FIG. 3 is a schematic view of a region-divided self-cloning photonic crystal and its substrate. FIG. 4 is a schematic view of the bundle fiber. FIG. 5 is a device configuration diagram of a polarization measuring device including a bundle fiber between a polarization detecting unit and a photoelectric conversion unit. The polarization detector includes a single region-dividing polarizer (FIG. 5 (a)), a combination of a region-dividing polarizer and a uniform polarizing element (FIG. 5 (b)), and a combination of a region-dividing polarizer and a region-dividing polarizer (FIG. 5 (b)). It consists of any of FIG. 5 (c)). FIG. 6 is a configuration example of a suitable polarization measuring device of the present invention. FIG. 7 shows an example of arrangement of the region-divided wave plate, the inorganic polarizer, and the image sensor arranged at both ends of the bundle fiber. FIG. 8 is a configuration example of an ellipsometer using the polarization measuring device of the present invention. FIG. 9 is a comparison graph of measurement results of a conventional ellipsometer and an ellipsometer using the polarization measuring device of the present invention. FIG. 10 is a configuration example of an ellipsometer in which the light source is arranged on the same side as the polarization measuring device. FIG. 11 is a configuration example of a birefringence measuring device that combines a transmitted light source and the polarization measuring device of the present invention.

Hereinafter, a mode for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to the forms described below, and includes those which are appropriately modified by those skilled in the art from the following forms to the extent obvious to those skilled in the art.

[1. Basic configuration]
FIG. 6 is an example of a device configuration of a polarization measuring device including a polarization detection unit including a region-divided wave plate and a polarizer, a bundle fiber, and a photoelectric conversion unit including an image sensor. As shown in FIG. 6, a light ray (measurement light) transmitted or reflected through the measurement target transmits the region-divided wave plate and the uniform inorganic polarizing element substantially vertically in this order, and is also substantially perpendicular to the bundle fiber end face. The polarization detection unit is configured so as to be incident on. Further, the image sensor is arranged on the end face on the opposite side of the bundle fiber. The light amount distribution information transmitted by the bundle fiber is converted into an electric signal by the image sensor, and the polarization information can be acquired by the software that calculates and analyzes this. In addition, in order to detect the ellipticity with high sensitivity even when the light beam to be measured is close to linearly polarized light, it is desirable that the polarization detection unit is a combination of a region-divided wave plate and a uniform inorganic polarizer.

FIG. 7 is a component configuration example of the polarization detection unit used in the present invention. Each region of the region-divided wave plate matches the arrangement of each fiber constituting the bundle fiber. Further, the polarization detection unit has a configuration in which an inorganic polarizer having a uniform transmission axis is inserted between the region-divided wave plate and the bundle fiber.

The region-divided wave plate is preferably a photonic crystal (self-cloning type photonic crystal) produced by the self-cloning method. Further, a wave plate made of quartz or the like may be divided and combined according to the arrangement of each fiber constituting the bundle fiber.

Further, when the polarization state to be measured is close to circularly polarized light, the polarization detection unit may be configured only by the region-divided polarizing element instead of the combination of the region-divided wave plate and the inorganic polarizing element.

[2. Ellipsometer for measuring the film thickness of the object to be measured in the vacuum chamber]
FIG. 8 shows an arrangement example of the ellipsometer of the present invention. As the light source, one in which one end of an optical fiber is connected to a laser light source, the fiber tip is arranged at a position where light is obliquely irradiated to the measurement target, and a polarizing plate is arranged at the fiber tip is used. By doing so, it is possible to keep the polarization state of the light irradiating the measurement target constant without worrying about bending of the fiber or the like. The light emitted from the optical fiber generally spreads, but for example, by connecting a fiber type collimator lens using graded index fiber to the optical fiber and attaching a polarizer to the tip, collimated light with a constant polarization state is irradiated. can do.

Next, the polarization detection unit of the polarization measuring device of the present invention is arranged on the optical path of the irradiation light reflected on the surface to be measured. When the light rays transmitted through the region-divided wave plate pass through the polarizer, they are converted into a light-dark pattern corresponding to the polarization state of the reflected light. The light-dark pattern is transmitted to the image sensor arranged in the photoelectric conversion unit via the bundle fiber, and is converted into an electric signal here. By calculating the obtained electrical signal with software, it is possible to know the polarization information of the light beam incident on the polarization detection unit. By comparing and calculating the obtained polarization information with the simulation results, an ellipsometer that acquires information on the film thickness and refractive index of the thin film provided on the measurement target is realized.

The prototype device was able to obtain the same measurement results as when the measurement target was placed in the atmosphere even when the measurement target was placed in the vacuum chamber. As the mechanism for introducing the bundle fiber into the vacuum, a commercially available mechanism may be used.

Further, in the present embodiment, since a bundle fiber in which a plurality of optical fibers are arranged in two rows is used as shown in FIG. 7, the region division wavelength made of a self-cloning photonic crystal divided into regions corresponding to this arrangement is used. A board was used. However, the bundle fiber is not limited to the two-row arrangement as shown in FIG. Self-cloning photonic crystals divided into regions according to the arrangement of bundle fibers of various arrangements may be used. Further, when the number of fibers bundled in the bundle fiber is large, a necessary light / dark pattern is required even if the area is divided into a region irrelevant to the arrangement of the fibers by using a region dividing element divided into a region sufficiently larger than the arrangement of the fibers. Can be obtained.

Polarization measurement requires at least 4 pieces of information. That is, it can be realized if there is a wave plate in four directions. Even if there are multiple directions, there is no problem if the parameters at the time of calculation are changed. Further, the patterns in four directions may be arranged periodically. The diameter of one bundle fiber used in the trial is 220 μm. The portion (core) through which light propagates has a diameter of 200 μm. Therefore, the pattern of the photonic crystal to be mounted may be 200 μm or more in diameter. For example, one region of the wave plate may be placed on a plurality of fibers.

In the case of a wave plate having only four directions, if the incident light has a spatial intensity distribution, it is necessary to take into account the amount depending on the intensity of the calculation. On the other hand, in the incident light, wave plates in four directions having an area sufficiently smaller than the incident range of the light are arranged periodically or randomly, and the outputs corresponding to each of the four directions obtained on the image sensor are averaged. Therefore, it is possible to perform a measurement that is not easily affected by the intensity distribution of the beam.
In addition, the bundle fibers are not always arranged in the same manner at the entrance and the exit, and the arrangement may be interchanged inside. Even in such a case, it is possible to change the polarization direction of the first incident light and know in advance which output corresponds to which wave plate from the change in intensity. Polarization can be calculated using that information. This operation can be performed before vacuuming.

FIG. 9 shows the result of comparing the output result of the ellipsometer of the present invention with the measurement result of a commercially available ellipsometer (SE101 manufactured by Photonic Lattice). As shown in FIG. 9, according to the ellipsometer of the present invention, results equivalent to those on the market were obtained.

[3. A small ellipsometer with the light source placed on the same side as the bundle fiber for polarization measurement]
In FIG. 10, an optical fiber connected to a laser light source is arranged along a bundle fiber for polarization measurement, and a light beam emitted from the optical fiber is bent by a small mirror and irradiated to a measurement target, which is equivalent to a normal ellipsometer. This is an example of realizing an optical system. In order to arrange the polarization detection unit in the same direction as the light emission position, a reflection mirror is arranged so as to guide the light emitted from the tip of the optical fiber to the sample. With this configuration, the light source constituting the ellipsometer and the polarization measuring unit can be integrated, and the unit placed close to the measurement target can be miniaturized. In this case, the polarization state of the light emitted from the fiber may change due to the reflection mirror, but this can be corrected by grasping it in advance.

[4. Polarized light measuring device for transmitted light]
As shown in FIG. 11, the birefringence of the measurement target can be known by measuring and calculating the change in the polarization information of the light beam transmitted through the measurement target. Therefore, the birefringence measuring device can be configured by combining the polarization measuring device of the present invention with a transmission light source. FIG. 11 shows an example of the device configuration. In the case of the birefringence measuring device, the light source does not have to be a laser, and for example, an LED can be used. In the case of a birefringence measuring device, the light source is arranged with a polarizer and a 1/4 wave plate in order from the side where light enters so that the light source is circularly polarized light, and the transmission axis of the polarizer and the axis of the 1/4 wave plate are 45. It is necessary to shift the degree.

The polarization measuring device of the present invention can be used in all situations where the installation environment of the observation target is different from the atmosphere such as in vacuum or liquid. In particular, in an ellipsometer that measures the polarization state of light rays reflected from the surface of a measurement target installed in a vacuum, it is necessary to bring the polarization detection unit close to the sample. However, when the polarization detection unit is installed in a vacuum, the present invention The ellipsometer according to the above can be preferably used.

Claims

The wave plate and the polarizer are arranged in this order from the direction in which the light enters.
The wave plate is divided into regions within one plate, and each region has a plurality of axial directions.
The polarizer is uniform or is divided into regions within one sheet, and each region has a plurality of axial directions.
The wave plate and the polarizer are placed in front of one end face of the bundle fiber.
An image sensor is placed after the other end face of the bundle fiber.
The polarization information of the incident light is converted into a light-dark distribution by passing through the wave plate and the polarizer, and the light-dark distribution is propagated to the image sensor through the bundle fiber and converted into an electric signal using the image sensor. Polarization information can be obtained by
A polarization measuring device in which the acquisition position of polarization information and the position of the image sensor are separated.
There is a polarizer in which the regions are divided in one sheet and each region has multiple axial directions.
The polarizer is placed in front of one end face of the bundle fiber
An image sensor is placed after the other end face of the bundle fiber.
The polarization information of the incident light is converted into a light-dark distribution by passing through the polarizer, the light-dark distribution is propagated to the image sensor through the bundle fiber, and the polarized light is converted into an electric signal by using the image sensor. You can get information,
A polarization measuring device in which the acquisition position of polarization information and the position of the image sensor are separated.
The light reflected from the surface of the sample is incident, and the wave plate and the polarizer are arranged in this order from the direction in which the light enters.
The wave plate is divided into regions within one plate, and each region has a plurality of axial directions.
The polarizer is uniform or is divided into regions within one sheet, and each region has a plurality of axial directions.
The wave plate and the polarizer are placed in front of one end face of the bundle fiber.
An image sensor is placed after the other end face of the bundle fiber.
The polarization information of the incident light is converted into a light-dark distribution by passing through the wave plate and the polarizer, and the light-dark distribution is propagated to the image pickup element through the bundle fiber and converted into an electric signal by using the image pickup element. By doing so, polarization information can be obtained, and the film thickness or refractive index of the sample can be calculated from the polarization information.
An ellipsometer in which the position where the polarization information is acquired and the position of the image sensor are separated.
There is a polarizer in which the regions are divided in one sheet and each region has multiple axial directions.
The polarizer is placed in front of one end face of the bundle fiber
An image sensor is placed after the other end face of the bundle fiber.
The polarization information of the incident light is converted into a light-dark distribution by passing through the polarizer, the light-dark distribution is propagated to the image sensor through the bundle fiber, and the polarized light is converted into an electric signal by using the image sensor. You can get information,
An ellipsometer in which the position where the polarization information is acquired and the position of the image sensor are separated.
The polarization measuring apparatus according to claim 1 or 2, wherein the region-divided wave plate or the polarizer is made of a photonic crystal.
The ellipsometer according to claim 3 or 4, wherein the region-divided wave plate or the polarizer is composed of a photonic crystal.
The ellipsometer according to claim 4 or 6, wherein a reflection mirror is arranged so as to guide light to the sample, whereby the wave plate and the polarizer are arranged in the same direction as the emission position of the light. ..