KR101207684B1

KR101207684B1 - Device and method for measuring thickness of thin film

Info

Publication number: KR101207684B1
Application number: KR1020100135251A
Authority: KR
Inventors: 박현철; 임충수; 이상진; 허형준
Original assignee: 주식회사 포스코
Priority date: 2010-12-27
Filing date: 2010-12-27
Publication date: 2012-12-03
Also published as: KR20120073473A

Abstract

Even in the case of high temperature objects, a thin film thickness measuring apparatus and a thin film thickness measuring method capable of measuring a thin film thickness in real time without time delay with respect to a thin film on the surface are proposed. The proposed thin film thickness measuring apparatus includes a light source for emitting light; A filter for filtering the light emitted from the light source and transferring the light to the steel sheet on which the thin film is formed; A spectrometer for obtaining a spectrum of light reflected from the steel sheet on which the thin film is formed; And a calculating unit calculating a thickness of the thin film based on the spectrum obtained by the spectroscope, wherein the filter blocks at least one of the wavelength sections of the emitted light, and the calculating unit is blocked by the filter of the spectra obtained by the spectroscope. The heat radiation noise spectrum may be calculated using the spectrum of the section portion, and the thickness of the thin film may be calculated using the result of removing the heat radiation noise spectrum from the spectrum obtained by the spectrometer.

Description

Thin film thickness measuring device and thin film thickness measuring method {DEVICE AND METHOD FOR MEASURING THICKNESS OF THIN FILM}

The present invention relates to a thin film thickness measuring apparatus and a thin film thickness measuring method, and more particularly, a thin film thickness measuring apparatus and a thin film thickness capable of measuring a thin film thickness in real time without time delay for a thin film on a surface even in a high temperature object. It relates to a measuring method.

In order to improve the plating property of high-strength steel, the measurement of the surface oxide layer thickness of a high temperature steel sheet has become a very important issue. Currently, in Europe, we are developing a technology for measuring oxide layers online and non-contact using reflection spectroscopy and applying the pre-oxidation method to the field using them. Reflective spectroscopy technology provides a reliable method for measuring oxide layer thickness by extracting constructive and destructive interference wavelengths from an intensity spectrum of light reflected from an oxide layer on a steel plate surface.

In order to eliminate the effects of thermal radiation from high-temperature steel sheets, reflection spectroscopy has a shutter that opens and closes continuously in front of the light source's output. When the shutter is closed, only the light emitted from the thermal radiation of the hot steel sheet is collected. When the shutter is opened, the reflected light of the light emitted from the light source and the thermal radiation noise of the hot steel sheet are simultaneously measured.

Therefore, by subtracting the spectrum measured when the shutter is closed from the spectrum measured when the shutter is opened, it is possible to eliminate the effects of thermal radiation noise from the hot steel sheet. In other words, the reflection spectrum of the light source and the heat radiation noise spectrum are separated in the time domain.

However, even in the case of reflection spectroscopy, it works correctly in a stable temperature environment, but in a section where the temperature changes rapidly or is not stable, the shape of the heat radiation spectrum changes every moment, so there is a problem that the influence cannot be removed accurately.

The present invention is to solve the above problems, an object of the present invention is to provide a thin film thickness measuring apparatus and a thin film thickness measuring method capable of measuring a thin film thickness in real time with no time delay for a thin film on the surface even in high temperature objects It is.

Thin film thickness measuring apparatus according to an aspect of the present invention for achieving the above object, the light source for emitting light; A filter for filtering the emitted light emitted from the light source and transferring the filtered light to the steel sheet on which the thin film is formed; A spectrometer for obtaining a spectrum of light reflected from the steel sheet on which the thin film is formed; And a calculator configured to calculate a thickness of the thin film based on the spectrum obtained by the spectrometer.

The filter may filter the emitted light to be discontinuous light, block at least one of the wavelength sections of the emitted light, or filter the emitted light by blocking a plurality of sections of the wavelength sections of the emitted light in the form of combs. .

The calculating unit calculates a thermal radiation noise spectrum by using a spectrum of a section portion blocked by the filter among the spectra obtained by the spectrometer, and uses the result of removing the thermal radiation noise spectrum from the spectrum obtained by the spectrometer to obtain the thickness of the thin film. Can be calculated. Alternatively, the operation unit may calculate the thermal radiation noise spectrum by first interpolating a spectrum of the section portion blocked by the filter among the spectra obtained by the spectrometer, and remove the heat radiation noise spectrum from the spectrum obtained by the spectrometer. The second interpolation process may calculate the reflected light spectrum.

In this case, the first interpolation process may be any one of linear interpolation and extrapolation according to Boltzmann radiation formula, and the second interpolation process may be any one of linear interpolation and extrapolation according to Boltzmann radiation formula.

According to another aspect of the invention, the step of emitting light; Filtering the emitted light and transferring the light to the steel sheet on which the thin film is formed; Acquiring a spectrum of light reflected from the steel sheet on which the thin film is formed; And calculating the thickness of the thin film based on the obtained spectrum.

The filtering may be to block at least one of the wavelength sections of the emitted light, and the calculating of the thickness of the thin film may be performed by using the spectrum of the section portion blocked by the filtering in the spectrum for the light reflected from the steel sheet. The thermal radiation noise spectrum is calculated, and the thermal radiation noise spectrum is removed from the spectrum of the light reflected from the steel sheet.

Alternatively, the calculating of the thickness of the thin film may include calculating a thermal radiation noise spectrum by first interpolating a spectrum of a section portion blocked by the filtering among spectra for light reflected from the steel sheet, and reflecting the heat radiation noise spectrum. The spectrum of light may be a step of calculating a reflected light spectrum by performing a second interpolation process on which the thermal radiation noise spectrum is removed, and calculating the thickness of the thin film based on the spectrum.

According to the present invention, since the thermal radiation noise component of the high temperature object is removed from the spectrometer's measurement spectrum by using a band pass filter, even in the case of the high temperature object, it is possible to measure the thin film thickness in real time without time delay for the thin film on the surface.

1 is a block diagram of a thin film thickness measuring apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating measuring the thickness of a thin film on a steel sheet using the thin film thickness measuring apparatus of FIG. 1.
3A to 3E are diagrams illustrating optical spectra measured in the thin film thickness measuring method according to the exemplary embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

1 is a block diagram of a thin film thickness measuring apparatus according to an embodiment of the present invention, Figure 2 is a view showing measuring the thickness of a thin film on a steel sheet using the thin film thickness measuring apparatus of FIG. Hereinafter, a description will be given with reference to FIGS. 1 and 2.

Thin film thickness measuring apparatus 100 according to an embodiment of the present invention includes a light source 110 for emitting light; A filter 120 for filtering the light emitted from the light source 110 and transmitting the filtered light to the steel sheet on which the thin film is formed; A spectrometer 130 for obtaining a spectrum of light reflected from the steel sheet on which the thin film is formed; And an operation unit 140 that calculates a thickness of the thin film based on the spectrum obtained by the spectroscope 130.

The light source 110 emits light toward the steel plate 160. The thin film 150 to measure the thickness is formed on the steel sheet 160. The thin film 150 on the steel plate 160 may be an oxide layer.

The filter 120 filters the light emitted from the light source 110 and transmits the filtered light to the steel plate 160 on which the thin film 150 is formed. The filter 120 is to separate heat radiation noise of the steel sheet 160 in real time when the emitted light is reflected from the thin film 150 and proceeds to the spectrometer 130.

To this end, the filter 120 may filter the emitted light to be discontinuous light. Alternatively, the filter 120 may block at least one section of the wavelength section of the emitted light. In this case, the filter 120 may filter the emitted light by blocking a plurality of sections of the wavelength section of the emitted light in the form of a comb.

The outgoing light filtered by the filter 120 is modulated to represent the modulation spectrum. Since some sections are filtered in the modulation spectrum, the effect of thermal radiation noise on the light reflected from the thin film 150 is clearly shown in the filtered section. This will be described further with reference to FIGS. 3A to 3E.

The spectrometer 130 acquires a spectrum of light reflected from the steel sheet 160 on which the thin film 150 is formed. Since the light reflected by the spectrometer 130 has been modulated by the filter 120 before being reflected by the thin film 150, the spectrum obtained by the spectrometer 130 already includes the modulated region. As described above, the modulated region refers to a section discontinuous or a section blocked by the filter 120.

Therefore, the spectrum acquired by the spectroscope 130 may reflect the influence of the heat radiation noise of the steel sheet 160, which is a high-temperature object, when reflected from the thin film 150, and the influence may extend to the modulated region. However, the emission light spectrum does not appear in the region where the output light is filtered and modulated, and only the spectrum due to thermal radiation noise of the steel sheet 160 appears in the modulated region. Therefore, when the spectrum obtained by the heat radiation noise of the modulated region is removed from the spectrum obtained by the spectroscope 130, the reflected light spectrum from which the heat radiation noise effect is removed can be obtained.

The calculating unit 140 calculates the thickness of the thin film based on the spectrum obtained by the spectrometer 130. The calculation unit 140 is a signal processor that removes the thermal radiation noise spectrum from the spectrum obtained by the spectrometer 130 to obtain the reflected light spectrum and calculates the thickness of the thin film based thereon. This will be described further with reference to FIGS. 3A to 3E.

The calculation unit 140 calculates the thickness value by measuring the offset and reinforcement for each wavelength caused by the interference of the incident light and the reflected light. In principle, it is possible to calculate the thickness when the n and k values of the material are known, but when it is not known, it can be calculated indirectly using model equations such as Cauchy or Sellmeier. This method has the advantage that it is possible to measure the thickness of a relatively thick film and can be measured easily and quickly. In addition, it is possible to measure very narrow areas so that the thickness can be measured on a fine pattern.

When the light emitted from the light source 110 is incident on the thin film 150, the light reflected from the surface of the thin film 150 and the interface between the steel plate 160 is measured by the spectrometer 130. Since the reflected waves are coherent light emitted from the same light source, the reflected waves show interference and mutually reinforce and cancel interference depending on the wavelength. Therefore, the reflectance seems to be different depending on the wavelength. The reflectance R for each wavelength in the multi-film may be expressed as a function of refractive index, extinction coefficient and thickness depending on the wavelength. That is, the measured reflected light shows an inherent reflectance distribution according to the wavelength depending on the thickness of the thin film and the properties of the thin film. Therefore, the calculation unit 140 may obtain the characteristics and thickness of the thin film from the reflectance according to the wavelength.

After the reflected light is separated for each wavelength by the grating in the measuring device, the reflected light is converted into an electrical signal by the CCD, and converted into a digital signal to interpret the data in the calculator 140. Although the calculator 140 is not illustrated in FIG. 2, the calculator 140 does not need to be determined relative to the light emitted by the light source 110, the filter 120, and the spectrometer 130. The measuring device 100 may be located at any position.

3A to 3E are diagrams illustrating optical spectra measured in the thin film thickness measuring method according to the exemplary embodiment of the present invention. Figure 3a is an emission light spectrum that is the spectrum of the emitted light emitted from the light source, Figure 3b is a modulated spectrum of the output light is modulated through the filter, Figure 3c is a modulated light is reflected from the thin film is incident on the spectrometer obtained by the spectroscope 3D and 3E show the spectra obtained by the spectroscope, which is the spectrum of the light, respectively, separated into a heat radiation noise spectrum and a reflected light spectrum.

The outgoing light spectrum of FIG. 3A is modulated in a filter and represented as a modulation spectrum as shown in FIG. 3B. Referring to FIG. 3B, it can be seen that some sections of the emission light spectrum are blocked. The outgoing light spectrum is thus modulated with the spectrum of discontinuous light. The area blocked by the filter is called a modulated area.

The light modulated by the filter is reflected by the thin film and incident on the spectrometer to represent the spectrum obtained by the spectrometer. The spectrum acquired by the spectrometer of FIG. 3C reflects the influence of thermal radiation noise of the hot steel sheet. The spectrum obtained from the spectrometer is a mixture of a discontinuous thermal radiation noise spectrum and a discontinuous reflected light spectrum.

The calculating unit calculates a thermal radiation noise spectrum by using a spectrum of a modulated region, which is a section blocked by a filter, from the spectrum obtained by the spectrometer. The calculator may calculate a thermal radiation noise spectrum by first interpolating a spectrum of the modulated region among the spectra obtained from the spectrometer. Such interpolation may be performed using extrapolation according to linear interpolation or Boltzmann radiation formula.

When the thermal radiation noise spectrum of FIG. 3d is calculated, the calculator may obtain the reflected light spectrum by removing the thermal radiation noise spectrum of FIG. 3d from the spectrum obtained by the spectrometer of FIG. 3c. At this time, the heat radiation noise spectrum is removed from the spectrum obtained by the spectroscope, and then the second interpolation may be performed to obtain the reflected light spectrum. Even at this time, interpolation may be performed using extrapolation according to linear interpolation or Boltzmann radiation formula.

When the reflected light spectrum as shown in FIG. 3E is obtained, the thickness of the thin film is calculated using the calculation unit as described above.

According to another aspect of the invention, the step of emitting light; Filtering the emitted light and transferring the light to the steel sheet on which the thin film is formed; Obtaining a spectrum of light reflected from the steel sheet on which the thin film is formed; And calculating a thickness of the thin film based on the obtained spectrum.

The filtering may be to block at least one of the wavelength ranges of the emitted light, and the calculating of the thickness of the thin film may include thermal radiation noise using a spectrum of the portion of the section blocked by the filtering of the spectrum of the light reflected from the steel sheet. It can be performed using the result of calculating the spectrum and removing the thermal radiation noise spectrum from the spectrum for the light reflected from the steel sheet. Alternatively, the calculating of the thickness of the thin film may be performed by first interpolating a spectrum of the section portion blocked by the filtering of the spectrum of the light reflected from the steel sheet to calculate a thermal radiation noise spectrum, and the spectrum of the light reflected from the steel sheet. The method may include calculating a reflected light spectrum by performing a second interpolation process on which the thermal radiation noise spectrum is removed, and calculating a thickness of the thin film based on the calculated spectrum.

The invention is not to be limited by the foregoing embodiments and the accompanying drawings, but should be construed by the appended claims. In addition, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible within the scope of the present invention without departing from the technical spirit of the present invention.

100 Thin Film Thickness Measuring Equipment
110 light source
120 filters
130 spectrometer
140 steel plate
150 thin film

Claims

A light source for emitting light;
A filter for filtering the emitted light emitted from the light source and transferring the filtered light to the steel sheet on which the thin film is formed;
A spectrometer for obtaining a spectrum of light reflected from the steel sheet on which the thin film is formed; And
And a calculation unit calculating a thickness of the thin film based on the spectrum obtained by the spectrometer.
The filter cuts at least one section of the wavelength section of the emitted light,
The calculating unit calculates a heat radiation noise spectrum using a spectrum of a section portion blocked by the filter among the spectra obtained by the spectrometer, and removes the heat radiation noise spectrum from the spectrum obtained by the spectrometer, Thin film thickness measuring apparatus, characterized in that for calculating the thickness.

delete

The method of claim 1,
The calculating unit calculates the thermal radiation noise spectrum by first interpolating a spectrum of a section portion blocked by the filter among the spectra obtained from the spectrometer,
And a second light interpolation process of the spectrum obtained by removing the thermal radiation noise spectrum from the spectrum obtained by the spectrometer to calculate the reflected light spectrum.

The method of claim 3,
The first interpolation process is any one of linear interpolation and extrapolation according to Boltzmann radiation formula,
The second interpolation process is a thin film thickness measuring apparatus, characterized in that any one of linear interpolation and extrapolation according to Boltzmann radiation formula.

Emitting light;
Filtering the emitted light and transferring the light to the steel sheet on which the thin film is formed;
Acquiring a spectrum of light reflected from the steel sheet on which the thin film is formed; And
Calculating a thickness of the thin film based on the obtained spectrum;
The filtering blocks at least one of the wavelength sections of the emitted light.
The calculating of the thickness of the thin film may be performed by calculating a thermal radiation noise spectrum using a spectrum of a section portion blocked by the filtering of the spectrum for the light reflected from the steel sheet, and in the spectrum for the light reflected from the steel sheet. The thickness of the thin film is calculated using the result of removing the thermal radiation noise spectrum.

delete

The method of claim 5,
The calculating of the thickness of the thin film may include calculating a thermal radiation noise spectrum by first interpolating a spectrum of a section portion blocked by the filtering among spectra for light reflected from the steel sheet.
The thickness of the thin film thickness measuring method, characterized in that for calculating the reflected light spectrum by a second interpolation process of the spectrum from the spectrum of the light reflected from the steel sheet to remove the thermal radiation noise spectrum.