JP2011180113A - Measurement of film thickness, and measurement of refractive index of diamond-like carbon thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure, with use of near-infrared light, the film thickness and refractive index of a DLC thin film formed on outer and inner surfaces of a substrate of any shape, such as planar shape, cylindrical shape, and free shape. <P>SOLUTION: A product of film thickness and an refractive index is calculated by the vertically reflected interference spectrum measurement, by using as a light source, the range of wavelengths of near-infrared light, in which a diamond-like carbon thin film containing a graphite component is translucent. Furthermore, the refractive index of an identical point on a sample to be subjected to interference measurement is determined, by using an identical light source, to measure a Brewster's angle that is determined solely by the refractive index of a reflective substance, using slope incidence and reflection measuring gauge. As a result, an accurate film thickness is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an apparatus capable of simultaneously measuring the film thickness and refractive index of a diamond-like carbon thin film using near infrared rays.

  The conventional film thickness measuring device for deposited thin film 1) Based on the color comparison of reflected light from a standard sample with a known thickness, 2) Create a part that is not partially deposited, and mechanically create the resulting step. 3) Measuring the thickness of the exposed ring-shaped thin film by microscopic inspection, 4) In the reflection spectrum of light in the visible light region There is one that obtains the product of the film thickness and the refractive index from analysis of the generated interference fringes.

  Although the method 1) is a non-contact method, the film thickness of the standard sample needs to be measured in advance by other methods, and the thickness is estimated by color judgment. I cannot expect accuracy. The methods 2) and 3) are a kind of destructive inspection, and are methods that partially destroy the measurement object. Although the method 4) is a non-contact method, only a transparent substance can be measured in the wavelength range of light used. The measurement result gives the product of the film thickness and the refractive index, and the refractive index of the substance is known in advance by another method, or a literature value or the like is used.

  Diamond-like carbon thin film (called DLC film) is known for its high hardness and low coefficient of friction. By depositing it on processing tools, automotive parts, polishing jigs, etc. Even with hard materials, the mechanical performance of the material to be deposited can be dramatically improved. Measurement of the thickness of the diamond-like carbon thin film is extremely important in determining the performance of the deposited components.

The composition of diamond-like carbon thin film varies depending on the production method and application. Generally, a diamond component and a graphite component coexist, and the mixing ratio is changed depending on the required thin film performance. Diamond is transparent with a broad spectrum from visible to infrared. However, most of the diamond-like carbon thin films that are practically used are black. The optical absorption has a strong wavelength dependence in the presence of the graphite component. It is known that it is opaque in the visible light region (400 to 800 nm), and in the course of studying the present invention, it was found to be translucent in the near infrared (1000 to 2000 nm).
An opaque film cannot be measured by the interference measurement method which is a non-contact measurement method using a light source in the visible light region.

  Furthermore, since a diamond-like carbon thin film adjusts a component according to a manufacturing method or a use application, it is known that the refractive index has various values. Accordingly, since the product of the film thickness and the refractive index is measured in the measurement using the above-described interferometry, accurate refractive index measurement is indispensable for accurate film thickness calculation.

JP 2000-352506 A

JP 2008-020318 A

However, according to the existing technology described above, accuracy is not achieved by the method of measuring by comparison with the standard sample, and the sample is destroyed by optical measurement by mechanical measurement or grinding, which is a non-contact method. Optical interference measurement using a range light source cannot measure because the diamond-like carbon thin film absorbs light strongly. Moreover, since the refractive index of the diamond-like carbon thin film varies greatly depending on the production lot and usage, the accuracy in the interferometric method cannot be obtained.
Therefore, the present invention obtains the product of the film thickness and the refractive index by an interferometry method using a light source in the near-infrared region where the diamond-like carbon thin film has been found to have transparency. It is an object of the present invention to provide an apparatus that directly measures the refractive index of the same sample point to which the interferometry method is applied and gives an accurate film thickness as a result.

The composition of diamond-like carbon thin film varies depending on the production method and application. Generally, a diamond component and a graphite component coexist, and the mixing ratio is changed depending on the required thin film performance. Diamond is transparent with a broad spectrum from visible to infrared. However, many diamond-like carbon thin films are black. Its optical absorption has a strong wavelength dependence due to the presence of the graphite component, and is known to be opaque in the visible light range (400 to 800 nm), but is translucent in the near infrared (1000 to 2000 nm). It turned out to be.
A light source in the visible light range cannot be used in the interferometric method that is the non-contact measuring method.

  Furthermore, since the diamond-like carbon thin film adjusts components depending on the production method and application, its refractive index has various values. Accordingly, since the product of the film thickness and the refractive index is measured in the measurement using the above-described interferometry, accurate refractive index measurement is indispensable for accurate film thickness calculation.

In order to solve the above-described problems, the first aspect of the present invention provides a film thickness by vertical reflected light interference spectrum measurement characterized in that near-infrared light having a semi-transparent wavelength region is used as a light source in the interferometry method. It is a device that can calculate the product of the refractive index.
In addition, the second invention is a tilted reflectometer that determines the refractive index at the same point of the target sample to be subjected to interference measurement, and the Brewster angle determined only by the refractive index of the reflecting material (the reflectance of the p-polarized component of incident light is zero) The refractive index can be determined by measuring the angle).
It is a measuring apparatus characterized by measuring the exact film thickness of a diamond-like carbon thin film by combining both.

  According to the first invention or the second invention, the reflection interference waveform for the near infrared rays can be easily collected regardless of the mixing ratio of graphite, and the product of the film thickness and the refractive index can be easily obtained. In addition, since the refractive index at the same point can also be measured, an accurate film thickness can be calculated as a result.

An embodiment of the first invention is shown. An embodiment of the first invention and the second invention is shown. It is a perspective view which shows one Example of this 1st invention and 2nd invention.

  One embodiment of the first invention is shown in FIG. Near-infrared light from a white light source 2 in the near-infrared region is irradiated directly or vertically through a lens 3 onto a substrate 1 on which a diamond-like carbon thin film (hereinafter referred to as DLC film) to be measured is attached. The reflected light from the surface of the DLC film and the substrate below the DLC film is branched by the mirror 4 and the spectral intensity of the reflected light is measured with a near-infrared spectrometer. The two types of reflected light interfere with each other in the spectroscope and form intensity peaks and valleys in the reflected spectrum. The wavelength interval between adjacent peaks and peaks, peaks and valleys, or valleys and valleys in the spectrum is determined only by the product of the thickness of the DLC film and the refractive index. Therefore, it is possible to calculate the product of the film thickness and the refractive index from these measured values.

One embodiment of the first and second inventions is shown in FIG. The measurement target is the substrate 1 with a DLC film. The measurement embodiment of the product of the film thickness and refractive index of the DLC film by the near-infrared white light source 2, the coaxial composite optical fiber 3, and the near-infrared spectrometer 4 is the same as the description of FIG. FIG. 2 also shows an embodiment of the second invention. The light from the white light source 5 is applied to the sample through a polarizing plate 9 and a lens 8 housed in the optical system holding cylinder 7 from a direction inclined by an incident angle q ₁ from the vertical direction of the sample surface. The polarizing plate 9 is installed so as to transmit only the p-polarized component of the light from the white light source. The reflected light from the sample substrate is reflected in the direction of the reflection angle q ₂ , but the incident angle and the reflection angle measured from the vertical direction of the sample substrate by the law of reflection are equal (q ₁ = q ₂ ). Similar to the incident optical system, the reflected light is guided to the near-infrared spectrometer 7 through the lens 8 and the polarizing plate 9 housed in the optical system holding cylinder 7, and the reflected light intensity of the p-polarized component is measured.

A drive system that can change the incident angle and the reflection angle while maintaining the same angle is used. For example, the incident light angle is about 45 degrees to about 75 degrees, for example, every 2 degrees, the reflected light intensity (the spectroscope can measure all the spectral ranges in which the spectroscope detector has sensitivity within the spectral range of the white light source. Measure). When the angle dependence of the reflection intensity at the same wavelength is plotted from the measured reflection spectrum, the angle at which the reflected light intensity is lowest can be obtained. The angle is called the Brewster angle and is a numerical value determined only by the refractive index of the DLC film on the substrate. Accordingly, the refractive index can be calculated from the value of the angle at which the reflection intensity is lowest.
When the wavelength for data processing is changed, the wavelength dependency of refractive index (referred to as refractive index dispersion) can also be obtained.

  FIG. 3 shows an example of realizing the above embodiment. The substrate with the DLC film is placed on the measurement sample stage 1. The sample stage is provided with a driving mechanism for adjusting the position and angle of the sample in order to ensure the detailed position and directionality of the sample substrate. The vertical reflection optical system (incident / exit composite optical fiber) for film thickness measurement can be fixed by inserting it into the incident / reflected optical fiber mounting port 2 for film thickness measurement. No near infrared light source or near infrared spectrometer is shown. The optical system for refractive index measurement is attached to the irradiation optical fiber attachment port 3 for refractive index measurement. The white light source to be connected to the fiber is not shown. The light receiving optical system for measuring the reflected light intensity is attached to the reflective light receiving fiber attachment port 4 for refractive index measurement. The near infrared spectrometer to be connected to the fiber is not shown. Each mounting port is fixed to the incident angle variable driving base 5 or the light receiving angle variable driving base 6. Each drive base can be driven by a single ball screw drive system (not visible because it is on the back side of the figure) connected to the simultaneous drive motor 7.

  The DLC film dramatically improves the mechanical properties of the material to be deposited by depositing it on the surface of processing tools, automobile parts, polishing jigs, etc. It is very important to measure accurately and quickly. This device can semi-automatically make precise and simple measurement and can greatly contribute to the efficiency improvement at the work site.

Claims (4)

Using a white light source in the wavelength range of 1000 nm to 2100 nm, the product of film thickness and refractive index is measured using the spectral interference effect of the reflected light from the diamond-like carbon thin film, and diamond-like carbon at the same sample position as the reflection interference method An apparatus for measuring a refractive index of a thin film by a Brewster angle measurement method. 2. The apparatus according to claim 1, wherein a broadband white light source having a wavelength range of 800 nm to 2500 nm is used. 2. The apparatus according to claim 1, wherein polarized monochromatic light in a visible light region (400 nm to 700 nm) or a near infrared light region (700 nm to 2100 nm) is used as a light source for refractive index measurement. 2. The apparatus according to claim 1, wherein a polarized laser beam in a visible light region (400 nm to 700 nm) or a near infrared light region (700 nm to 2100 nm) is used as a light source for refractive index measurement.

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