KR102125624B1 - Handheld spectroscopic ellipsometer and method for measuring spectral elepsometric parameter using the same - Google Patents

Abstract

The present invention relates to a handheld spectroscopic ellipsometer that can be carried without spatial restrictions and capable of measuring spectral polarization information of a measurement object in real time, and a method of measuring spectroscopic ellipsoidal parameters using the same. The present invention enables the measurement of spectral polarization in real time, is robust against external disturbances, and provides a portable handheld spectral ellipsometer that provides a thin film and periodic nanopattern made on a free-form substrate as well as a plain surface substrate. It has measurable effects.

Description

Handheld spectroscopic ellipsometer and method of measuring spectroscopic ellipsoidal parameters using the same{HANDHELD SPECTROSCOPIC ELLIPSOMETER AND METHOD FOR MEASURING SPECTRAL ELEPSOMETRIC PARAMETER USING THE SAME}

The present invention is a handheld type spectroscopic ellipsometer, which can be carried in more detail without spatial restrictions, and is a nano-level thin film coated on a cylindrical, free-form substrate (SUBSTRATE), such as the R2R (ROLL TO ROLL) process. And a handheld spectroscopic ellipsometer capable of measuring spectral polarization information of a periodic nanopattern in real time and a method of measuring spectroscopic ellipsoidal parameters using the same.

Thin film processes ranging from several nm to several tens of nm applied to semiconductors, lithography processes, etc. are key processes that directly affect the yield of semiconductors, and various technologies for real-time monitoring, measurement, and inspection of thin film processes and patterning processes are developed. Has been used. Among them, ELIPSOMETRY technology that can measure and reflect thin film thickness and periodic nanopattern is used as the most important core technology for semiconductor process management. ELIPSOMETER is a non-permeable optical measurement method widely used to characterize the optical properties of thin films, and is particularly useful in situations where the thickness of the thin film is less than the wavelength of light.

Existing spectroscopic ellipsometers (SPECTROSCOPIC ELLIPSOMETRY) have high precision to accurately measure thin film thicknesses below nm, but there is a hassle of mechanically rotating the polarizer or phase retarder for polarization modulation. It has a limit of second level measurement speed. This slow measurement speed means that the measurement sample must be very stable and fixed for a few seconds or more to enable accurate measurement. For this reason, most of the spectroscopic ellipsometers to date have limitations that can only be used in the form of a benchtop (BENCHTOP) that operates only on a stable work table, such as a high-precision measurement analysis device.

In recent years, future nano production process technologies such as R2R to respond to the future IT industry such as flexible devices (FLEXIBLE DEVICE) have emerged, but the thin film measurement and periodic nano pattern measurement technologies that can be applied are limited by measurement speed and measurement conditions. Almost none. That is, most environments for measuring a thin film coated on a cylindrical or free-form substrate are difficult to solve with an existing benchtop type spectroscopic ellipsometer. Therefore, in a general environment, the necessity and industrial importance of a new type of spectroscopic ellipsometer capable of measuring a nano-thin film and periodic nanopattern by hand with a measuring instrument are increasing.

Korean Registered Patent No. 10-1812508 (hereinafter referred to as'prior literature') is a spectrophotometer that measures spectrally Stokes vector of white light that transmits/reflects the object to be measured at a high speed. It is about. The prior literature adopts an integrated in-line polarization interferometer in which the two beams of the interferometer have a straight parallel structure, enabling snapshot measurement of robust spectral polarization phenomena that are robust to disturbances. It has the effect of achieving measurement repeatability and accuracy.

In the prior literature, a snapshot-based spectral polarization measurement technique has been proposed to reduce the measurement time, but has a spatial limitation in which samples should be measured in the form of an existing benchtop.

Korean Registered Patent No. 10-1812508 (Invention name: All-in-one polarization interferometer and snapshot spectropolarimeter using the same, Registration date: 2017.12.20.)

An object of the present invention is to provide a handheld type spectroscopic ellipsometer that is capable of real-time spectral polarization measurement, robust to external disturbances, and portable to solve the above problems.

A handheld spectroscopic ellipsometer according to an aspect of the present invention for achieving the above object is provided in the body, the body, generates a polarized modulated wave, outputs the wave as a measurement object, and in the measurement object A spectroscopic ellipsometer that measures the spectral polarization information of the reflected wave, a handle that is provided on one side of the body, an opening through which the wave is incident and the wave is incident, and a handle capable of manipulating the spectral ellipsometer And an alignment aid for aligning the measurement position between the body and the measurement object.

The spectroscopic ellipsometer according to the present invention is a parallel light lens that converts light irradiated from a light source into parallel light, a linear polarizer that receives the parallel light and converts it into linearly polarized light, and is polarized and modulated by separating and reflecting the linearly polarized light An integrated polarization interferometer that generates the wave, the wave is directed to the measurement object at a predetermined angle of incidence, another linear polarizer linearly polarizing the wave reflected from the measurement object, and linearly polarized by the another linear polarizer to interfere A spectrometer for measuring the spectral information of the generated light, a battery disposed in the body or the handle, and supplying power to the spectroscopic ellipsometer.

The spectrometer according to the present invention is a reference area setting unit for setting a reference area of the distance between the opening and the measurement object, and the incident angle where the interference-generated light can be transmitted to the measurement object to the maximum, and the reference area It includes an information measuring unit for measuring the spectral polarization information when satisfied.

The alignment aid according to the present invention is another parallel light lens for converting the light emitted from the laser generator into another parallel light, a beam separation unit for receiving the other parallel light and splitting into two waves, the separated It includes a plane mirror for reflecting one of the two waves, and an image sensor unit for acquiring an interference fringe image between the wave reflected from the plane mirror and the wave reflected from the measurement object.

The information measuring unit according to the present invention aligns the measurement position between the body and the measurement object according to the inclination information identified through the spatial distribution of the interference fringe image, and measures the spectral polarization information when the reference region is satisfied do.

A method of measuring a spectroscopic elliptical polarization parameter using a handheld spectroscopic ellipsometer for achieving the above object is a background measuring step of measuring a background spectra with a light source blocked for a reference sample, and shutters arranged in two interferometer paths The phase difference (Δ(k)) of the spectral elliptical polarization parameters for the reference sample from the two interfered spectra using the Fourier transform method, a polarization intensity measurement step of measuring the intensity for p- and s- polarization using A phase difference extraction step of extracting, an amplitude ratio extraction step of extracting an amplitude ratio (Ψ(k)) among spectral elliptic polarization parameters for the reference sample by applying a Fourier transform method to the spectral coherence function searched according to the intensity of the polarization, and Parameters deriving optical parameters such as film thickness, material refractive index, and periodic nano-pattern 3D shape to be measured from the spectral elliptical polarization parameter phase difference (Δ(k)) and (Ψ(k)) for the reference sample It includes a derivation step.

The present invention enables the measurement of spectral polarization in real time, is robust to external disturbances, and provides a portable handheld spectral ellipsometer that provides a thin film and periodic nanopattern made on a free-form substrate as well as a flat substrate. It has measurable effects.

1 is a configuration diagram of a handheld spectroscopic ellipsometer according to the present invention.
2 is a block diagram of an integrated polarization interferometer according to the present invention.
3 is a view for explaining the measurement of spectral polarization information according to the reference area of the present invention.
4 is an embodiment of an alignment auxiliary device for maintaining a reference area according to the present invention with respect to a flat substrate.
5 is a view showing the interference spectrum of an object with a nominal thickness of SiO ₂ thin films of 100 nm and 500 nm applied to a silicon substrate.
6 is a view showing spectral ellipse parameters Δ(k) and Ψ(k) of a SiO ₂ thin film having a nominal thickness of 100 nm.
7 is a view showing spectral oval parameters Δ(k) and Ψ(k) of a SiO ₂ thin film having a nominal thickness of 500 nm.
8 is a view showing a spectral ellipse parameter Δ(k) of a SiO ₂ thin film having a nominal thickness of 1 μm at an interval of 5° from an incident angle of 45° to 70°.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the embodiments of the present invention, when it is determined that detailed descriptions of related well-known technologies may unnecessarily obscure the subject matter of the present invention, detailed descriptions thereof will be omitted.

1 is a configuration diagram of a handheld spectroscopic ellipsometer according to the present invention. 1 shows a front view of a spectroscopic ellipsometer. Referring to FIG. 1, the handheld spectroscopic ellipsometer can be largely composed of a body 100 and a handle 400. The body 100 is provided with a spectroscopic ellipsometer that generates a polarized modulated wave, outputs a wave to a measurement object, and measures spectral polarization information of the wave reflected from the measurement object. The spectroscopic ellipsometer includes a light source 210, a parallel light lens 220, a linear polarizer 230, an integrated polarization interferometer 240, an imaging lens 250, another linear polarizer 260, and a spectrometer 270. can do.

The light source 210 uses a white light source, and it is also possible to use other types of light sources. The light generated from the light source 210 is transmitted to the optical fiber, and the light spread from the optical fiber is irradiated to the parallel light lens 220. The parallel tube lens 220 converts the received light into parallel light. The parallel light converted by the parallel light lens 220 is output to the linear polarizer 230, and the linear polarizer 230 converts the received parallel light into linear polarization. The parallel light is linearly polarized in the 45° direction by the linear polarizer 230.

The integrated polarization interferometer 240 separates and reflects linearly polarized light to generate a polarized wave. The linearly polarized light is separated into a first wave and a second wave by the integrated polarization interferometer 240, and the separated wave is reflected by the mirror. Here, the first wave may be P-polarized light and the second wave may be S-polarized light. The configuration of the integrated polarization interferometer 240 will be described in detail with reference to FIG. 2. Referring to FIG. 2, the integrated polarization interferometer 240 may include a polarization separation unit 241, a first mirror 242, and a second mirror 243. The polarization separation unit 241 is a device that separates linearly polarized light into a first wave (P-polarized light) and a second wave (S-polarized light). The polarization separation unit 241 transmits the first wave (P-polarized light), enters the first mirror 242, and reflects the second wave (S-polarized light) and enters the second mirror 243. The first mirror 242 and the second mirror 243 are integrally attached to the polarization separation unit 241 to maintain strong advantages against disturbance due to external vibration.

The wave output from the integrated polarization interferometer 240 is directed to the measurement object at a predetermined incident angle. Another linear polarizer 260 linearly polarizes the wave reflected from the measurement object. The wave is linearly polarized by another linear polarizer in the direction of 45°, causing interference. The generated light is incident on the spectrometer 270 through the imaging lens 250.

The spectrometer 270 measures spectral polarization information of the light with which interference has occurred. The present invention characterizes a thin film of an object to be measured using only a single channel spectrometer to produce a handheld type. The use of a single channel spectrometer has the advantage of reducing cost and miniaturizing the device. The thin film can be characterized based on a change in polarization state of a monochromatic plane wave reflected by the surface of the measurement object at an incident angle.

The measurement principle of spectral polarization information uses Jones-matrix formalism, and it is assumed that the polarized light in Jones-matrix formalism is ideal. The Jones vector E _in input to the integrated polarization interferometer 240 is as follows.

Here, k denotes a wave number representing 2π/λ, i ² = −1, u and v denote the amplitude of the incident beam. η and ξ represent the phase of the light wave along the x-axis and y-axis, respectively.

The matrix of the optical device is as follows.

Here, J _Pol , J _BS , J _M , and J _ThinF are _related to a polarizer, a non-polarized beam splitter, a reflective mirror surface, and a Jones matrix of a measurement object. φ and m represent the azimuth angle of the polarizer and the complex reflection coefficient of the mirror used in the integrated polarization interferometer 240. r _p , r _s and δ _p , δ _s are reflectance and phase changes for p- and s- polarized light. The output electric field E _out of the integrated polarization interferometer 240 is as follows.

E _out (k) = E ₁ (k)+E ₂ (k)

Here, E ₁ (k) and E ₂ (k) are complex waves shifted through the p- and s- polarization paths, respectively. u', ξ'and v', η'represent the unknown amplitude and phase conditions of E ₁ (k) and E ₂ (k). The spectrum measured by the spectrometer 270 can be described as follows.

I(k) = (E ¹ _sp (k)+E ² _sp (k))(E ¹ _sp (k)+E ² _sp (k))

Here, E _sp ^1,2 (k) represents the wave of the measurement object for the p-polarization component and the s-polarization component at the entrance of the spectrometer 270 and can be represented as follows.

The measurement procedure of the spectroscopic elliptical polarization parameters Ψ(k) and Δ(k) in which the optical parameters of the thin film structure can be derived is as follows.

First, the background spectrum with the light source blocked is measured. The intensity for p- and s- polarization is measured using a shutter placed in the path of the two interferometers. Here, the intensity for p- and s- polarization is needed when searching for the spectral coherence function extraction. Considering the interference spectrum of an untargeted object as a reference, the measurement when placing a thin film object is expressed as follows.

Where γ is related to the spectral coherence function. Φ ^ref (K) and Φ ^obj (k) correspond to the spectral phase function for the reference and thin film objects. A _ref ^DC (k)=α ² +β ² , A _obj ^DC (k)=(αr _p ) ² +(βr _s ) ² , A _ref ^AC (k)=αβ and A _obj ^AC (k)=αβr _p r _s denotes the DC and AC conditions of the non-target-shaped interference spectrum and the interference spectrum when thin film objects are respectively disposed.

From the two interfered spectra, Δ(k) can be extracted from the spectroscopic elliptical polarization parameters using the Fourier transform method as follows.

△(k)=Φ ^obj (k)- Φ ^ref (k) = δ _p (k)-δ _s (k)

In order to obtain the amplitude ratio Ψ(k) among the spectroscopic polarization parameters, it is necessary to extract a spectrum coherence function that is not changed by the measured thin film object. The spectral coherence function is obtained in the spectral domain by applying FFT to the reference spectrum as follows.

The spectral elliptical polarization parameter Ψ(k) is extracted as follows.

Here, α and β are related to the intensity of light measured using a shutter. From the measured spectral elliptical polarization parameters Ψ(k) and Δ(k), optical parameters of a thin film structure such as film thickness, material refractive index, and periodic nano-pattern 3D shape can be derived.

Meanwhile, the spectrometer 270 may include a reference region setting unit 271 and an information measuring unit 272. The reference area setting unit 271 is a device in which the reference area of the distance and the incident angle between the opening 300 and the measurement object to which the interference-generated light can be transmitted to the object to be measured is maximized. The information measuring unit 272 is a device that measures spectral polarization information when a reference region is satisfied. Measurement of the spectral polarization information according to the reference area will be described later with reference to FIG. 3.

Referring again to FIG. 1, the body 100 is provided with an opening 300 through which a wave output from the spectroscopic ellipsometer is emitted to the outside or a wave reflected from a measurement object is incident.

One side of the body 100 is provided with a handle 400 for a handheld. The handle 400 may be provided with a controller 410 for manipulating the spectroscopic ellipsometer.

A battery 500 for supplying power to the spectroscopic ellipsometer is disposed in the body 100 or the handle 400. 1 is an example in which the battery 500 is provided in the body 100, and can be used as a portable type as the power supply means is provided in the body 100.

3 is a view for explaining the measurement of the spectral polarization information according to the reference area of the present invention.

The reference region of FIG. 3 is an embodiment when the incident angle is 45° and the reference height is 1 cm. Here, the reference height means the distance between the opening 300 and the object to be measured. The reference area is a condition in which interference-generated light can be transmitted to the object to be measured to the maximum, and it can be designed to be changed depending on the installation structure, chip, device size, and external environment of the spectroscopic ellipsometer. Also, the reference region may have some error range. For example, if the error range is ±1%, the incident angle of the reference region is 44.55° to 45.55°, and the reference height is 0.99cm to 1.01cm.

Looking at the'reference area satisfaction' of FIG. 3, it can be seen that the wave output from the integrated polarization interferometer 240 satisfies the reference height of 1 cm between the incident angle of 45° and the distance between the opening 300 and the measurement object.

On the other hand, looking at the'reference area dissatisfaction' of FIG. 3, the wave output from the integrated polarization interferometer 240 is output at an incident angle of 40°, and the reference height and the predetermined distance difference as the body 100 is inclined at a certain angle. (△x) occurs and the reflection angle is also different, so that the reflected light does not reach the light-receiving part properly.

The spectrometer 270 measures spectral polarization information in real time when the reference region is satisfied. 3, the spectral polarization information is accurately measured in the case of'satisfaction of the reference region', whereas the spectral polarization information is not accurately measured in the case of'satisfaction in the reference region'.

On the other hand, the handheld spectroscopic ellipsometer of the present invention may include a notification unit for notifying the user whether the reference area is satisfied by visual, auditory or the like.

4 is an embodiment of an alignment auxiliary device for maintaining a reference area according to the present invention with respect to a flat substrate. 4 shows a side view of the spectroscopic ellipsometer. Referring to FIG. 4, since the optical elements constituting the alignment auxiliary device form an optical path perpendicular to each other with the optical elements constituting the spectroscopic ellipsometer, the alignment auxiliary device can be simultaneously installed with the spectroscopic ellipsometer Do. The alignment aid may include a laser generator 610, another parallel light lens 620, a beam splitter 630, a planar mirror 640, another imaging lens 650, and an image sensor 660. .

The laser generator 610 is a device that outputs a laser beam. Another parallel light lens 620 is a device that receives light output from the laser generator 610 and converts it into another parallel light. The beam splitter 630 is a device that receives another parallel light and separates it into two beams. The transmitted wave separated by the beam separation unit 630 is transmitted and is incident on the plane mirror 640, and the reflected wave is reflected and incident on the measurement object. On the other hand, the object to be measured is made of a reflective sample such as a semiconductor wafer, a cylindrical or free-form substrate.

The image sensor unit 660 acquires an interference fringe image between the wave reflected from the plane mirror 640 and the wave reflected from the measurement object. The interference fringe image obtained by the image sensor unit 660 may be displayed so that the user can visually identify it, and tilt information may be determined. The user can more easily determine the state of satisfaction of the reference area of the information measuring unit 272 using the tilted display information and give the device a measurement command accurately.

The information measuring unit 272 also stores and analyzes the spatial distribution of the interference fringe image, and also includes a function to automatically recognize the inclination of the spectroscopic ellipsometer, and the body and the body according to the measured inclination information. When the measurement positions between the measurement objects are aligned and the reference area is satisfied, the spectral polarization information can be automatically recognized and measured.

Hereinafter, the operability of the hand-held spectroscopic ellipsometer will be verified through FIGS. 5 to 8. The validity of FIGS. 5 to 8 was performed with a uniform Si0 ₂ thin film having a nominal thickness of 100 nm, 500 nm, and 1 μm deposited on two different thin film structures, the Si wafer. On two different samples of SiO ₂ thin films on a silicon (Si) substrate, the performance of a handheld spectroscopic ellipsometer is demonstrated by measuring the phase difference and amplitude ratio for each wavelength, which are the spectroscopic polarization parameters. The bare silicon (Si bare) wafer was placed at an angle of incidence of 45°, and a reflection spectrum for p- and s-polarized light was measured using a shutter.

5 is an interfered spectrum of bare silicon (Si bare) and SiO ₂ thin film objects having nominal thicknesses of 100 nm (a) and 500 nm (b). Here, the solid line is the interference spectrum of Si bare, and the dotted line is the interference spectrum of the SiO ₂ thin film object.

6 is a spectroscopic ellipsometry parameters of the SiO ₂ thin film has a nominal thickness of 100nm, Figure 7 is a spectral ellipsometry parameters of the SiO ₂ thin film has a nominal thickness of 100nm. 6A and 7A are spectral elliptical polarization parameters Δ(λ), and (b) are spectral elliptical polarization parameter amplitude ratios Ψ(λ). The solid line represents the measured spectroscopic elliptical polarization parameter, and the dotted line is the result obtained by the phase delay rotary spectral ellipsoid.

The spectral elliptical polarization parameters Ψ(k) and Δ(k) shown in FIGS. 6 and 7 are extracted based on a Fast Fourier Transform method.

Referring to FIGS. 6 and 7, it can be seen that the spectral oval polarization parameter measured by the device proposed by the present invention and the result values measured by the conventional phase delay rotary spectral oval polarizer are similar. The thickness of the SiO ₂ thin film for the two measured samples was determined to be 110.02 nm and 512.33 nm, respectively, and this value is consistent with the value obtained from the phase delay rotary spectral ellipsometer. However, some errors are generated, but the exact rotation angle of the polarization optics is not manually aligned or is caused by some systematic errors in signal processing performed in the spectral Fourier domain.

8 is a spectral ellipse parameter Δ(k) of a SiO ₂ thin film with a nominal thickness of 1 μm at an interval of 5° from an incident angle of 45° to 70°. 8(a) is an experimental result measured with the device proposed by the present invention, and (b) is a result obtained by a phase delay rotary spectral ellipsometer. In (b) of FIG. 8, phase jumping occurs in the wavelength range of 465 nm-480 nm and 580 nm-615 nm, which is a phenomenon that is caused by an incident angle of 70 degrees close to the Brewster angle.

The preferred embodiments of the present invention have been shown and described above, but the present invention is not limited to the specific embodiments described above.

100: body 210: light source
220: parallel light lens 230: linear polarizer
240: integrated polarization interferometer 241: polarization separation unit
242: first mirror 243: second mirror
250: imaging lens 260: another linear polarizer
270: spectrometer 271: reference area setting unit
272: information measuring unit 300: opening
400: handle 410: controller
500: battery 610: laser generator
620: another parallel light lens 630: beam separation
640: plane mirror 650: another imaging lens
660: image sensor unit

Claims (8)

Body; A parallel light lens that converts the light irradiated from the light source into parallel light, a linear polarizer that receives the parallel light and converts it into linear polarization, and separates and reflects the linear polarization to polarize and modulate the generated wave at a predetermined incident angle An integrated polarization interferometer outputting to, another linear polarizer for linearly polarizing the wave reflected from the measurement object, and a spectrometer for linearly polarized by the other linear polarizer to measure the spectral polarization information of the generated interference, A spectroscopic ellipsometer provided in the body;
An opening through which a wave generated by the integrated polarization interferometer is emitted, and a wave reflected from the measurement object is incident;
A handle provided on one side of the body and capable of manipulating the spectroscopic ellipsometer; And
A handheld spectroscopic elliptical polarization measuring device comprising a; alignment aid for aligning the measurement position between the body and the measurement object.
delete The spectrometer of claim 1, wherein
A reference area setting unit in which a reference area of a distance between the opening and the measurement object, and the incident angle, at which the interference-generated light can be maximally transmitted to the measurement object, is set; And
A handheld spectroscopic ellipsometer measuring device comprising; an information measuring unit for measuring the spectral polarization information when the reference area is satisfied.
According to claim 3, The alignment aid
Another parallel light lens for converting the light output from the laser generator to another parallel light;
A beam splitter that receives the other parallel light and separates it into two waves;
A plane mirror for reflecting one of the separated two waves; And
And an image sensor unit for acquiring an interference fringe image between the wave reflected from the plane mirror and the wave reflected from the object to be measured.
According to claim 4,
The information measurement unit is characterized in that the measurement position between the body and the measurement object is aligned according to the inclination information identified through the spatial distribution of the interference fringe image and measures the spectral polarization information when the reference area is satisfied. Handheld spectroscopic ellipsometer.
According to claim 1,
A handheld spectroscopic ellipsometer that is disposed within the body or handle and further includes a battery that supplies power to the spectroscopic ellipsometer.
A method for measuring a spectroscopic elliptical polarization parameter using the handheld spectroscopic ellipsometer of claim 1
A background measurement step of measuring a background spectra with a light source blocked for the reference sample;
A polarization intensity measurement step of measuring intensity for p- and s-polarized light using shutters disposed in two interferometer paths;
A phase difference extraction step of extracting a phase difference (Δ(k)) among spectral elliptic polarization parameters for the reference sample from the two interfered spectra using a Fourier transform method; And
And an amplitude ratio extraction step of extracting an amplitude ratio (Ψ(k)) among spectral elliptic polarization parameters for the reference sample by applying a Fourier transform method to the spectral coherence function retrieved according to the intensity of the polarization. Spectroscopic elliptical polarization parameter measurement method.
The method of claim 7,
From the phase difference (Δ(k)) and amplitude ratio (Ψ(k)) of the spectroscopic polarization parameters for the reference sample, optical parameters such as film thickness, material refractive index and periodic nano-pattern 3D shape to be measured are derived. A method of measuring a spectral elliptical polarization parameter further comprising a parameter deriving step.

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