KR20090049951A - Linear focus ellipsometer - Google Patents

Abstract

The present invention relates to an ellipsometer, and more particularly, to a linear focus ellipsometer for measuring a change in polarization state of reflected light after focusing linearly on a specimen using a cylindrical optical system. To this end, the present invention comprises a light splitting unit for dividing the light generated from the light source into polarized light; A light concentrating unit irradiating the light split from the light splitting unit onto the specimen; And a light detector for detecting the light passing through the light concentrator and the light splitter after being reflected from the specimen, wherein the light concentrator is configured to linearly irradiate the split light to the specimen. Provides a linear focus ellipsometer. The linear focus ellipsometer has the effect of measuring a plurality of specimens at the same time by measuring the change in polarization state for multiple incident angles after focusing the light split in the light splitter linearly on a plurality of specimens.

Ellipsometer, Polarization Generator, Linear Focus, Light Splitter

Description

Linear focus ellipsometer {LINEAR-FOCUSED BEAM ELLIPSOMETER}

The present invention relates to an ellipsometer, and more particularly, to a linear focus ellipsometer for measuring a change in polarization state of reflected light after focusing linearly on a specimen using a cylindrical optical system.

In general, in the fields of physics, chemistry and materials, measuring the optical properties of materials and measuring the thickness of thin films is a very important factor. Particularly, various nano thin film manufacturing processes are used in the semiconductor industry. In order to evaluate the properties of the nano thin films, an ellipsometer, which is a non-destructive and non-contact real-time measuring technology, is widely used as a measuring instrument for processing.

At present, a variety of methods are well known as principles for measuring the properties of materials and the thickness of thin films. Among these, elliptical measurement has been greatly improved in performance with the development of light sources, photodetectors, computers, etc., and the application field has been greatly increased as processes using thin films and surfaces have increased.

Elliptic measurement can be divided into reflection type and transmission type. Among them, reflective ellipsometric technique for analyzing the polarization state of light reflected from the surface of the specimen with the incident angle is widely used. By measuring the change in the polarization state of the light reflected by the specimen, it can be mainly used to extract the optical characteristics of the specimen, such as refractive index or extinction coefficient, it can also be used to extract the characteristics such as the state of the specimen interface.

In the case of incidence of parallel light in the oblique direction, all the light rays are irradiated onto the specimen with the same angle of incidence, so that the angle of incidence can be controlled more accurately. However, when the size of the incident beam is reduced by using an iris, Because of the increased phenomenon, it is difficult to reduce the size of the beam irradiated to the specimen to mm or less.

In order to evaluate the various thin film manufacturing processes for semiconductor device production through measurement, the semiconductor industry has specially made and used a limited measuring area on the wafer in the range of several tens of micrometers to several tens of micrometers. In order to measure the thickness of a thin film using an ellipsometer in the measurement area limited to the micro level, a technique is used to focus parallel light incident in an oblique direction on a specimen surface using an optical system composed of a lens or a reflective mirror. . However, in this case, since light rays having a plurality of incident angles are incident on the specimen at the same time, there is a problem that it is difficult to secure and maintain the measurement accuracy rather than using parallel light in the oblique direction.

In accordance with the recent development of semiconductor device manufacturing technology, the size of the patterned line width on the wafer is expected to continue to be reduced in the semiconductor device fabrication technology in the future, so that the area of the limited measurement area should be reduced in proportion. However, in the case of the oblique focus ellipsometer described above, despite many researches and efforts to minimize the area of the beam irradiated to the specimen, the size of the oblique focus ellipsometer is no longer reduced due to aberrations and structural limitations of the focus optical system. There is a difficult problem.

In addition, when the optical system is used to focus on the surface of the specimen in the form of dots, it is necessary to measure the thickness or characteristic of one specimen and then measure the other specimen. Therefore, many specimens cannot be measured at the same time. There is a problem.

In order to solve the above problems, the present invention is the polarized state of the reflected light after the incident light in the direction perpendicular to the plane of the specimen and focused on a straight line on the surface of the specimen using a cylindrical optical system Its purpose is to provide a linear focus ellipsometer that measures the change of.

In order to achieve the above object, the present invention provides a light splitting unit for dividing light generated from a light source into polarized light; A light concentrating unit irradiating the light split from the light splitting unit onto the specimen; And a light detector for detecting the light passing through the light concentrator and the light splitter after being reflected from the specimen, wherein the light concentrator is configured to linearly irradiate the split light to the specimen. Provides a linear focus ellipsometer.

In addition, to achieve the above object, the present invention is a polarizing unit for polarizing the light generated from the light source; A light splitting unit dividing the light polarized from the polarizing unit; A light concentrating unit irradiating the light split from the light splitting unit onto the specimen; A polarization detector for detecting a specific polarization state from the light passing through the light concentrator and the light splitter after being reflected from the specimen; And a photodetector configured to detect light passing through the polarization detector, wherein the photoconcentrator provides a linearly focused ellipsometer for linearly irradiating the split light onto the specimen.

The linear focus ellipsometer further includes an aperture for passing only a part of the light split from the light splitter, and the aperture is located between the light splitter and the light focusing unit.

The light concentrator may be configured using a cylindrical optical system for linearly concentrating light on the specimen, and the cylindrical optical system may be configured using at least one of a semi-cylindrical lens, a semi-cylindrical mirror, and a curved mirror. .

The light splitter may include a polarization splitter or a non-flat splitter, and the linear focus ellipsometer may include a linear polarizer between the light splitter and the light concentrator. It further comprises.

The light source may be a white light source or a monochromatic light source. When the white light source is used as the light source, the linear focus ellipsometer further includes a band pass filter for passing light in a specific wavelength range.

The linear focus ellipsometer may further include a compensator for changing a phase of the light between the light splitter and the light concentrator, according to a polarization state of light split into the light splitter.

The photodetector may include a 2D image measuring device including a plurality of pixel units.

The linear focus ellipsometer according to the present invention changes the polarization state of the reflected light with respect to multiple incidence angles after focusing the light split in the light splitter linearly on a plurality of specimens using a light concentrator configured using a cylindrical optical system. By measuring, the optical properties of the specimen, that is, in the case of the thin film specimen, the information on the thickness and the refractive index of the thin film can be obtained simultaneously for a plurality of specimens. This saves time and effort in measuring the optical properties of many specimens.

The terminology used in the present invention is a general term that is currently widely used as possible, but in certain cases, the term is arbitrarily selected by the applicant, in which case the meaning of the term is described in the detailed description of the invention. It should be understood that the present invention in terms of terms other than these terms.

Hereinafter, with reference to the accompanying drawings a preferred embodiment of the present invention that can specifically realize the above object, the present invention is not limited or limited by the above embodiments.

1 shows a structure of a linear focus ellipsometer according to a first embodiment of the present invention. Referring to FIG. 1, the linear focus ellipsometer has a light source 10, a polarization generator 20, a light splitter 30A, an aperture 50, a light concentrator 60, a polarization detector 80, and a light. The detection unit 90 and the calculation processing unit 100 are included.

The polarization generator 20 makes the parallel light emitted from the light source unit 10 into a specific polarization state. The light splitter 30A splits a part of the light passing through the light source 10. Some of the divided light passes through the light concentrator 60 positioned under the light splitter 30A. The light concentrator 60 refracts a part of the divided light to linearly irradiate the specimen 70 linearly.

Optionally, some of the light split by the light splitter 30A may pass through the aperture 50 before passing through the light concentrator 60. The aperture 50 blocks the outer portion of the light divided by the light splitter 30A and allows only the central portion to reach the light concentrator 60. The shape and structure of the aperture 50 and the light concentrator 60 will be described later.

The light reflected from the specimen 70 passes through the light concentrator 60 and the light splitter 30A, and then passes through the polarization detector 80 that filters out a specific polarization state. Then, the light passing through the polarization detector 80 is input to the photodetector 90, and the photodetector 90 measures the intensity of the input light. The photodetector 90 is composed of a unit pixel, and information obtained from the unit element is transferred to the operation unit 100 and stored as a digital signal.

2 shows a structure of a linear focus ellipsometer according to a second embodiment of the present invention. Referring to FIG. 2, the linear focus ellipsometer includes a light source unit 10, a light splitter 30B, a light concentrator 60, a light detector 90, and a calculator 100.

As described above, the light emitted from the light source unit 10 is partially reflected or transmitted through linearly polarized light in the light splitter 30B. Some of the light split from the light splitter 30B is linearly irradiated onto the specimen 70 through the light concentrator 60. Then, the light reflected from the specimen 70 is input to the light detector 90 for detecting the parallel light filtered in a specific polarization state while passing through the light concentrator 60 and the light splitter 30B as a unit device. The calculating unit 100 corrects the intensity of the light detected by the light detecting unit 90 to perform arithmetic processing. Compared with the linear focus ellipsometer described with reference to FIG. 1, the linear focus ellipsometer described with reference to FIG. 2 indicates that the light splitter 30B includes the functions of the polarization generator 20 and the polarization detector 80. will be.

The calculation unit 100 (for example, a computer) analyzes the waveform of the voltage or current detected by the photodetector 90, thereby the optical properties of the specimen 70 or the thickness and optical constant of the thin film. And the like.

In order to arbitrarily adjust the polarization state of the light incident on the specimen 70, a compensation unit 40 selectively changing the phase of the traveling wave according to the polarization state between the light splitter 30B and the light concentrator 60. You can install it. In addition, an aperture 50 for preventing the outer portion of the light split by the light splitter 30B from reaching the light concentrator 60 is provided between the light splitter and the light concentrator 60 or the compensation unit. It may optionally be additionally installed between the 40 and the light concentration unit 60.

The compensator 40 is a phase difference of transmitted light when the polarized light is perpendicular to the plane of the compensator 40 when the direction of polarization is parallel to the optical axis of the compensator 40. There is a characteristic with a value.

In the case where the linear focus ellipsometer includes the compensator 40 and / or the aperture 50, some of the light split from the light splitter 30B is the compensator 40 and / or the aperture 50. After passing through), the light is input to the light concentrator 60, and the light reflected from the specimen 70 passes through the light concentrator 60, the aperture 50 and / or the compensator 40, and then the light splitter. Delivered to 30B.

In addition, in FIG. 2, the light splitter 30B may be configured using a light splitter for polarization. If the light splitter 30B is configured as a non-polarized light splitter instead of a polarized light splitter, a linear polarizer may be provided between the non-polarized light splitter and the compensator 40.

The light source unit 10 may use a white light source, such as a tungsten-halogen lamp, an Xe discharge lamp, and a monochromatic light source, such as a laser, which are generally used as a light source. When a white light source is used, a band pass filter for passing light having a specific wavelength range must be installed at the rear end of the light source unit 10 or the front end of the light detector 90.

The light emitted from the light source unit 10 is made of parallel light using a reflection and refraction optical system, and part of the light is reflected by the light splitter 30B, and the polarization direction of the light is inside the light splitter 30B. It has a characteristic that is aligned in the x-axis direction parallel to the inclined reflective surface of the.

The photodetector 90 has a plurality of unit devices and corresponds to a charge coupled device capable of measuring a two-dimensional image. Information obtained from each unit element of the photodetector 90 is transferred to the operation unit 100 and stored as a digital signal.

The positions of the light source unit 10 and the light detector 90 described with reference to FIGS. 1 and 2 are exemplary, and the linear focus ellipsometer having the positions of the light source unit 10 and the light detector 90 that are different from each other has the same function. When carried out is included in the present invention.

Hereinafter, the device principle of the present invention for implementing the light concentrator 60 of the linear focus ellipsometer described above will be described in detail.

3A and 3B illustrate light concentrating units for linearly irradiating light onto a specimen by using a semi-cylindrical lens according to an embodiment of the present invention. 3A is a perspective view of the light concentrator 60, and FIG. 3B shows the light concentrator 60 viewed from the front (x-axis). Referring to FIGS. 3A and 3B, the light split by the light splitters 30A and 30B passes through 51. The aperture 51 has a rectangular shape having a rectangular hole in the center portion, and a part of the light split from the light splitting portions 30A and 30B is transmitted to the light concentrating portion 60 through the rectangular hole. It is interrupted by the aperture 51. As described above, the aperture 51 is optional, and the light split by the light splitters 30A and 30B may be directly transmitted to the light concentrator 60 without passing through the aperture 51. The rectangular hole in the center of the aperture 51 is exemplary, and the present invention includes an aperture 51 having various types of holes.

Light concentrating portion 60 may be composed of a semi-cylindrical lens 61, the semi-cylindrical lens 61, the outer peripheral surface adjacent to the aperture 51 is formed of a semi-circular curved surface, the outer peripheral surface adjacent to the specimen 70 is It is formed into a rectangular cross section. Therefore, the light transmitted to the semi-cylindrical lens 61 is linearly concentrated on the specimen 70 after being refracted while passing through the semi-cylindrical lens 61. As shown in FIG. 3B, the light passing through the semi-cylindrical lens 61 is reflected by the specimen 70 at the same reflection angle Φ as the incident angle Φ, and then refracted while passing through the semi-cylindrical lens 61 again. It is delivered to the aperture 51.

4A and 4B illustrate light concentrating units for linearly irradiating light onto a specimen by using a curved mirror according to an embodiment of the present invention. 4A is a perspective view of the light concentrator 60, and FIG. 4B shows the light concentrator 60 as viewed from the front (x-axis). 4A and 4B, the light split by the light splitters 30A and 30B passes through 52. The aperture 52 has the same or similar structure and function as the aperture 51 shown in FIGS. 3A and 3B. As described above, the aperture 52 is optional, and the light split in the light splitters 30A and 30B may be directly transmitted to the light concentrator 60 without passing through the aperture 52.

The light concentrator 60 may be configured as a rectangular curved mirror 62, and the curved mirror 62 is formed as a concave curved surface having an outer circumferential surface adjacent to the aperture 52, and is installed obliquely on the specimen 70. do. Thus, the light transmitted to the curved mirror 62 is linearly concentrated on the specimen 70 after being reflected by the curved mirror 62. As shown in FIG. 4B, the light reflected by the curved mirror 62 is reflected by the specimen 70 at the same reflection angle Φ as the incident angle Φ, and then reflected by the curved mirror 62 to be unfolded 52. Is delivered.

5A and 5B illustrate light concentrating units for linearly irradiating light onto a specimen using a semi-cylindrical mirror and a curved mirror according to an embodiment of the present invention.

FIG. 5A is a perspective view of the light concentrator 60, and FIG. 5B shows the light concentrator 60 as viewed from the front (x-axis). Referring to FIGS. 5A and 5B, the light split by the light splitters 30A and 30B passes through 53. The aperture 53 has the same or similar structure and function as the apertures 51 and 52 shown in FIGS. 3A and 3B or 4A and 4B. As described above, the aperture 53 is optional, and the light split in the light splitters 30A and 30B may be directly transmitted to the light concentrator 60 without passing through the aperture 53.

The light concentrating part 60 may be composed of a semi-cylindrical mirror 64 and a rectangular curved mirror 63, and the curved mirror 63 is formed of a curved surface having a convex outer circumferential surface adjacent to the aperture 53. ) Is installed obliquely, the semi-cylindrical mirror 64 forms a curved surface of the outer peripheral surface adjacent to the aperture 53 is convex. Therefore, the light passing through the aperture 53 is reflected by the semi-cylindrical mirror 64, and then again reflected by the curved mirror 63 is linearly concentrated on the specimen 70. As shown in FIG. 5B, the light reflected by the curved mirror 66 is reflected by the specimen 70 at the same reflection angle Φ as the incident angle Φ, and then again the curved mirror 62 and the semi-cylindrical mirror 64. Reflected by and delivered to the aperture (53).

The configuration of the light concentrator 60 described above is exemplary, and the present invention also includes any type of light concentrator 60 for irradiating light linearly to the specimen 70.

6 is a view illustrating a reflection path of light in a specimen according to an embodiment of the present invention in detail, and FIG. 7 corresponds to an intensity of light measured by unit elements of a light detector according to an embodiment of the present invention. A two-dimensional video signal is shown.

As described above, light having a specific polarization state passing through the light concentrator 60 is reflected by the specimen 70 at the same reflection angle Φ as the incident angle Φ and then transmitted to the light concentrator 60. Referring to FIG. 6, light incident at 70A is reflected at 70C at 72C of the specimen 70, and light incident at 70B is reflected at 70A at 72C of the specimen 70. Reflected at 70C, which is the same path, at 72C of the specimen 70. In the same principle, the light incident on 71A is reflected at 71C at the 73C position of the specimen 70, the light incident at 71B is reflected at 71A at the 73C position of the specimen 70, and the light incident at 71C is reflected on the specimen ( At position 73C of 70) is reflected to 71C which is the same path. The light reflected from the specimen 70 is transmitted to the photodetector 90 through the light concentrator 60 and the light splitters 30A and 30B.

6 and 7, the intensity distribution of light measured by the unit elements of the photodetector 90 can be seen. When light having a specific polarization state is incident to 70A, the light is reflected by the specimen 70B to 70B, and then only the polarization components parallel to the y-axis are filtered while passing through the light splitters 30A and 30B. Then, the point 90B of the two-dimensional image signal acquired by the photodetector 90 is reached and detected by the unit element of the photodetector 90 as an electrical signal such as a voltage or a current corresponding to the light intensity. do.

In the same way, when light in a specific polarization state enters 70B, 71A, and 71B, the light is reflected from the specimen 70 to 70A, 71B, and 71A, respectively, and then passes through the light splitters 30A and 30B, and is parallel to the y-axis. Only ingredients are filtered out. Then, the point 90A, 91B, 91A of the two-dimensional image signal obtained by the photodetector 90 is reached, and the unit elements of the photodetector 90 are electrically connected to each other such as a voltage or a current corresponding to the light intensity. It is detected by a signal. As shown in FIG. 7, it can be seen that the two-dimensional image signal measured by the light detector 90 is displayed in a form parallel to the x-axis direction. Therefore, when a plurality of specimens are placed in the x-axis direction, there is an advantage that a plurality of specimens can be measured at the same time.

As described above, the present invention has been described by specific embodiments such as specific components and the like, but the embodiments and the drawings are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from such description.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and all the things that are equivalent to or equivalent to the claims as well as the following claims will belong to the scope of the present invention. .

1 is a diagram showing the structure of a linear focus ellipsometer according to a first embodiment of the present invention.

2 is a diagram showing the structure of a linear focus ellipsometer according to a second embodiment of the present invention.

3A and 3B are diagrams illustrating a light concentration unit for linearly irradiating light onto a specimen using a semi-cylindrical lens according to an embodiment of the present invention.

4A and 4B are diagrams illustrating a light concentrator for linearly irradiating light onto a specimen using a curved mirror according to an embodiment of the present invention.

5A and 5B are diagrams illustrating a light concentrator for linearly irradiating light onto a specimen by using a semi-cylindrical mirror and a curved mirror according to an embodiment of the present invention.

6 is a view showing in detail the reflection path of the light in the specimen according to an embodiment of the present invention.

7 is a diagram illustrating a 2D video signal signal corresponding to the intensity of light measured by the unit elements of the photodetector according to an exemplary embodiment of the present invention.

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

10: light source

20: polarization generator

30A, 30B: Light division

40: compensation unit

50: aperture

60: light concentration

70: Psalm

80: polarization detector

90: photodetector

100: arithmetic processing unit

Claims (10)

A light splitting unit dividing the light generated from the light source into polarized light; A light concentrating unit irradiating the light split from the light splitting unit onto the specimen; And After reflecting from the specimen, including a light detector for detecting the light passing through the light concentrator and the light splitter, The light focusing unit is a linear focus ellipsometer, characterized in that for linearly irradiating the split light to the specimen. Polarizing unit for polarizing the light generated from the light source; A light splitting unit dividing the light polarized from the polarizing unit; A light concentrating unit irradiating the light split from the light splitting unit onto the specimen; A polarization detector for detecting a specific polarization state from the light passing through the light concentrator and the light splitter after being reflected from the specimen; And Including a light detector for detecting the light passing through the polarization detector, The light focusing unit is a linear focus ellipsometer, characterized in that for linearly irradiating the split light to the specimen. The ellipsometer of claim 1 or 2, wherein the linear focal ellipsometer And an aperture for passing only a part of the light split from the light splitter, wherein the aperture is located between the light splitter and the light concentrator. The method according to claim 1 or 2, The light focusing unit includes a linear optical ellipsometer, characterized in that it comprises a cylindrical optical system for linearly concentrating light on the specimen. The method of claim 4, wherein The cylindrical optical system is a linear focus ellipsometer, characterized in that it comprises at least one of a semi-cylindrical lens, a semi-cylindrical mirror, a curved mirror. The method of claim 1, The light splitter may include a polarizer splitter or a non-flat splitter, and the linear focus ellipsometer may include a linear polarizer between the light splitter and the light concentrator. Linear focus ellipsometer, characterized in that it further comprises. The method according to claim 1 or 2, The light source is a linear focus ellipsometer, characterized in that the white light source or monochromatic light source. The method of claim 7, wherein In the case of using a white light source as the light source, the linear focus ellipsometer further comprises a band pass filter for passing light of a specific wavelength range. The ellipsometer of claim 1 or 2, wherein the linear focal ellipsometer And a compensator for changing a phase of the light between the light splitting unit and the light concentrating unit according to the polarization state of the light split into the light splitting unit. The photodetector of claim 1, wherein the photodetector A linear focus ellipsometer comprising a two-dimensional image measuring device consisting of a plurality of unit elements (pixels).

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