JP5756733B2 - Interferometric film thickness meter - Google Patents

Description

  The present invention relates to an interference film thickness meter.

  As an apparatus for measuring the thickness of a film, an interference type film thickness meter using an optical interference phenomenon is known (see, for example, Patent Document 1). The measurement principle of the interference film thickness meter will be described. When light is irradiated onto a transparent measurement object, reflected light returns from the front surface and the back surface. At this time, each reflected light interferes and strengthens at a certain wavelength and weakens at a certain wavelength. The wavelength to be strengthened and the wavelength to be weakened are determined by the film thickness and refractive index of the film to be measured. Thereby, the film thickness is calculated from the interval between the interference fringes in the reflection spectrum.

FIG. 18 is a schematic configuration diagram of a conventional interference type film thickness meter.
The film thickness meter includes a light source 101, a light projecting optical fiber 103, a light projecting / receiving unit 105, a light receiving optical fiber 107, a spectroscope 109, and a calculation unit 111. The calculation unit 111 includes a spectral data acquisition unit 113, a power spectrum calculation unit 115, and a film thickness calculation unit 117.

  The white light emitted from the light source 101 is guided to the light projecting / receiving unit 105 by the light projecting optical fiber 103, condensed, and irradiated onto the measurement target film 119. The light reflected by the front and back surfaces of the measurement target film 119 enters the light projecting / receiving unit 105 and guided to the spectroscope 109 by the light receiving optical fiber 107. The spectroscope 109 divides the light from the light receiving optical fiber 107 to obtain a reflection spectrum, converts it into an electrical signal, and outputs it.

  The calculation unit 111 calculates the film thickness of the measurement target film 119 based on the electric signal from the spectroscope 109. The spectral data acquisition unit 113 acquires spectral spectral data based on the electrical signal from the spectral unit 109. The spectral data acquisition unit 113 outputs the spectral spectrum data to the power spectrum calculation unit 115.

  The power spectrum calculation unit 115 performs preprocessing and Fourier transform on the spectrum data and calculates a power spectrum. The power spectrum calculation unit 115 outputs power spectrum data to the film thickness calculation unit 117.

The film thickness calculator 117 calculates the film thickness of the measurement target film 119 based on the peak position of the power spectrum and the refractive index of the measurement target film 119.
The prior art in FIG. 18 calculates the film thickness of the measurement target film 119 based on the spectral spectrum of the reflected light from the measurement target film 119, but the interference type film thickness meter uses the spectral spectrum of the transmitted light from the measurement target film. The film thickness of the measurement target film can also be calculated based on the above.

FIG. 19 is a schematic configuration diagram of a conventional interference type film thickness meter. In FIG. 19, parts having the same functions as those in FIG.
The film thickness meter includes a light source 101, a light projecting optical fiber 103, a light projecting unit 121, a light receiving unit 123, a light receiving optical fiber 107, a spectroscope 109, and a calculation unit 111. The calculation unit 111 includes a spectral data acquisition unit 113, a power spectrum calculation unit 115, and a film thickness calculation unit 117.

The light projecting unit 121 and the light receiving unit 123 are arranged at a position sandwiching the measurement target film 119.
Light from the light source 101 is applied to the measurement target film 119 via the optical fiber for projection 103 and the light projecting unit 121. The light transmitted through the measurement target film 119 enters the light receiving unit 123 and is guided to the spectroscope 109 by the light receiving optical fiber 107. The spectroscope 109 obtains a transmission spectrum by dividing the light from the light receiving optical fiber 107, converts it into an electrical signal, and outputs it. The calculation unit 111 calculates the film thickness of the measurement target film 119 based on the electric signal from the spectroscope 109.

JP-A-7-280520

  For example, in a film or sheet manufacturing process made of polyimide, polyethylene, PET (Polyethylene terephthalate) or the like, an interference film thickness meter may be used for on-line measurement. In the on-line measurement, the measurement target film is continuously transferred. In this case, the measurement target film vibrates or bends. When the measurement target film vibrates or bends, the distance between the light projecting unit and the light receiving unit and the measurement target film and the angle formed by the light projecting unit, the light receiving unit, and the measurement target film change.

  First, as shown in FIG. 19, a case where the light projecting unit and the light receiving unit are separated will be described. If the focal position of the light emitted from the light projecting unit and the focal position of the light incident on the light receiving unit are separated from the measurement target film, the interference type film thickness meter cannot calculate the film thickness of the measurement target film. there were. As a result of investigating the cause, the inventors of the present application have found that when the focal position moves away from the measurement target film, the measurement spot on the measurement target film becomes large and measurement becomes impossible.

  When the measurement spot becomes large, the uniformity of the thickness of the measurement target film in the measurement spot decreases. For example, as shown in FIG. 20, when the film thickness of the measurement target film 119 is different between the measurement position A and the measurement position B in the measurement spot, the light transmitted through the measurement position A and the light transmitted through the measurement position B are transmitted to the light receiving unit. Incident. The light that has passed through the measurement position A and the light that has passed through the measurement position B have slightly different wavelengths from each other. When these lights are added together, the interference fringes are averaged out as shown in FIG. For this reason, when the focal position is away from the measurement target film, the interference film thickness meter cannot calculate the film thickness of the measurement target film.

  Next, as shown in FIG. 18, a case where the light projecting unit and the light receiving unit are configured by a light projecting / receiving unit will be described. Also in this case, the inventors of the present application have investigated, and when the focal position of the light irradiated from the light projecting / receiving unit and the light incident on the light projecting / receiving unit is separated from the measurement target film, the light from the measurement target film is It was discovered that the measurement could not be performed due to the fact that it was not incident on.

  For example, as shown in FIG. 22, when the position of the measurement target film 119 changes from the broken line position to the solid line position and the distance between the light projecting / receiving unit 105 and the measurement target film 119 changes, reflected light (broken line) is transmitted to the light projecting / receiving unit 105. It will not be incident.

  Further, as shown in FIG. 23, when the position of the measurement target film 119 changes from the broken line position to the solid line position and the angle formed between the optical axis of the light irradiated from the light projecting / receiving unit 105 and the measurement target film 119 changes, Light (broken line) does not enter the light projecting / receiving unit 105.

  When the reflected light from the measurement target film 119 does not enter the light projecting / receiving unit 105, the interference type film thickness meter cannot calculate the film thickness of the measurement target film 119. Therefore, the conventional interference type film thickness meter has a problem that stable measurement cannot be performed in online measurement. This problem also occurs in an interference film thickness meter that calculates the film thickness of the measurement target film based on the spectral spectrum of the transmitted light from the measurement target film.

  An object of this invention is to provide the interference type film thickness meter which can perform the stable measurement in on-line measurement.

  An interference film thickness meter according to the present invention includes a light projecting unit that irradiates light to be measured from a light source, a light receiving unit that receives reflected light or transmitted light from the measurement target film, and a light projecting unit. A focal position scanning unit that scans a common focal position that is a focal position of irradiated light and that is also a focal position of light incident on the light receiving unit within a predetermined range, and spectral spectrum data of light received by the light receiving unit A spectral data acquisition unit that acquires the power spectrum, a power spectrum calculation unit that calculates a power spectrum based on the spectral spectrum data, and a film thickness calculation unit that calculates the thickness of the measurement target film based on the data of the power spectrum, A threshold value for the spectral spectrum data or the power spectrum data or both, and a data extraction unit for extracting data equal to or higher than the threshold value. That. The film thickness calculation unit outputs film thickness data corresponding to the data extracted by the data extraction unit.

  In the interferometric film thickness meter according to the present invention, the focal position scanning unit has a common focal position within a predetermined range that is a focal position of light emitted from the light projecting unit and is a focal position of light incident on the light receiving unit. Let it scan. Thereby, when the distance between the light projecting unit and the light receiving unit and the measurement target film changes, the optical axis of the light irradiated from the light projecting unit, the optical axis of the light incident on the light receiving unit, and the measurement target film Even when the angle formed is changed, appropriate light is irradiated from the light projecting unit to the measurement target film, and appropriate reflected light or transmitted light is incident on the light receiving unit from the measurement target film.

  Furthermore, in the interference film thickness meter of the present invention, the data extraction unit provides a threshold value for spectral spectrum data and / or power spectrum data, and extracts data equal to or greater than the threshold value. When the common focus position is scanned, unnecessary data is also acquired. The data extraction unit extracts only appropriate data. The film thickness calculation unit outputs film thickness data corresponding to the data extracted by the data extraction unit.

  In the interference-type film thickness meter of the present invention, the light projecting unit and the light receiving unit are formed by, for example, a light projecting / receiving unit that irradiates the measurement target film with light from the light source and receives reflected light from the measurement target film. It is configured. However, in the interference type film thickness meter of the present invention, the light projecting unit and the light receiving unit may be provided separately.

  In the interference type film thickness meter of the present invention having the light projecting / receiving unit, an example of the focus position scanning unit includes a thickness or a refractive index in the optical path between the light projecting / receiving unit and the measurement target film, or both of them. A plurality of different transparent parallel plates are sequentially inserted to change the common focus position.

  In another example of the focal position scanning unit, the common focal position is changed by rotating a mirror disposed in an optical path between the light projecting / receiving unit and the measurement target film.

  Still another example of the focal position scanning unit is that the common focal point is formed by sequentially inserting a plurality of transparent parallel plates having different thicknesses or refractive indexes or both in the optical path between the mirror and the measurement target film. Change position.

  Still another example of the focal position scanning unit includes a transparent parallel plate disposed in an optical path between the light projecting / receiving unit and the film to be measured. The common focus position is changed by rotating the shaft so that the angle formed by the transparent parallel plate changes.

  Still another example of the focal position scanning unit is configured to rotate the pair of mirrors arranged in parallel to each other in an optical path between the light projecting / receiving unit and the measurement target film, thereby rotating the common focal position. Change.

  In still another example of the focal position scanning unit, a plurality of lenses having different focal lengths are sequentially inserted in an optical path between the light projecting / receiving unit and the measurement target film to change the common focal position.

  Still another example of the focal position scanning unit sequentially inserts a plurality of wedge substrates having different wedge angles or inclined surfaces or both in the optical path between the light projecting / receiving unit and the measurement target film. Then, the common focus position is changed.

  Still another example of the focal position scanning unit includes two wedge substrates arranged in an optical path between the light projecting / receiving unit and the measurement target film. The two wedge substrates have the same wedge angle and the inclined surfaces are opposed to each other. The focal position scanning unit changes the common focal position by moving the focal position scanning unit so that the total thickness of the two wedge substrates positioned in the optical path is changed.

  In the interference-type film thickness meter of the present invention, the light projecting unit and the light receiving unit are disposed, for example, at positions sandwiching the measurement target film. In this configuration, the light receiving unit receives transmitted light from the measurement target film. In this configuration, the focus position scanning unit moves the light projecting unit and the light receiving unit with respect to the measurement target film while maintaining the distance and angle between the light projecting unit and the light receiving unit, for example. Change position.

  The focal position scanning unit is not limited to the configuration examples given above. In the interference film thickness meter of the present invention, the focal position scanning unit may have any configuration as long as the common focal position can be scanned within a predetermined range.

  In the interference type film thickness meter of the present invention, an example of the data extraction unit provides the threshold value for the received light intensity in the spectral data.

  In another example of the data extraction unit, the threshold value is provided for the difference between the maximum value and the minimum value of the received light intensity in the spectral data.

  Yet another example of the data extraction unit provides the threshold value at the peak height in the power spectrum data.

  In the interferometric film thickness meter according to the present invention, the focal position scanning unit has a common focal position within a predetermined range that is a focal position of light emitted from the light projecting unit and is a focal position of light incident on the light receiving unit. Let it scan. Further, the data extraction unit provides a threshold value for the spectral spectrum data and / or the power spectrum data, and extracts data equal to or higher than the threshold value. The film thickness calculation unit outputs film thickness data corresponding to the data extracted by the data extraction unit.

  Thereby, the interference type film thickness meter of the present invention can measure the film thickness of the measurement target film even if the measurement target film vibrates or bends. Therefore, the interference type film thickness meter of the present invention can perform stable measurement in online measurement. However, the use of the interference type film thickness meter of the present invention is not limited to online measurement. The interference type film thickness meter of the present invention can also be applied to film thickness measurement of a measurement target film disposed at a predetermined position.

It is a schematic block diagram for demonstrating one Example of an interference-type film thickness meter. It is a schematic perspective view for demonstrating the light projection / reception probe, the focus position scanning part, and the measurement object film | membrane which comprise the Example of FIG. It is the schematic for demonstrating a mode that a common focus position is changed in the Example of FIG. It is a wave form diagram for demonstrating data extraction operation | movement when a data extraction part provides a threshold value to the light reception intensity in spectral spectrum data. It is a wave form chart for explaining data extraction operation when a data extraction part provides a threshold for the difference between the maximum value and the minimum value of the received light intensity in the spectral data. It is a wave form chart for explaining data extraction operation when a data extraction part provides a threshold in peak height in data of power spectrum. It is a graph which shows an example of the film thickness measurement result by the Example of FIG. It is a graph which shows an example of the film thickness measurement result by a prior art. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the structure and operation | movement of the focus position scanning part in another Example. It is a schematic block diagram for demonstrating the further another Example of an interference-type film thickness meter. It is the schematic for demonstrating a mode that a common focus position is changed in the Example of FIG. It is a schematic block diagram of the conventional interference type film thickness meter. It is a schematic block diagram of the conventional interference type film thickness meter. It is the schematic for demonstrating the malfunction of the conventional interference type film thickness meter of FIG. It is the schematic for demonstrating the malfunction of the conventional interference type film thickness meter of FIG. It is the schematic for demonstrating the malfunction of the conventional interference type film thickness meter of FIG. It is the schematic for demonstrating the malfunction of the conventional interference type film thickness meter of FIG.

  FIG. 1 is a schematic configuration diagram for explaining an embodiment of an interference film thickness meter. FIG. 2 is a schematic perspective view for explaining the light projecting / receiving probe, the focal position scanning unit, and the measurement target film constituting this embodiment.

  The film thickness meter includes a light source 1, a light projecting optical fiber 3, a light projecting / receiving probe 5, a focal position scanning unit 7, a light receiving optical fiber 9, a spectroscope 11, and a calculation unit 13. The light projecting / receiving probe 5 constitutes a light projecting / receiving unit, a light projecting unit, and a light receiving unit in the interference film thickness meter of the present invention. The calculation unit 13 includes a spectral data acquisition unit 15, a power spectrum calculation unit 17, a film thickness calculation unit 19, and a data extraction unit 21.

  The light source 1 is realized by, for example, a white LED (Light Emitting Diode). The white light emitted from the light source 1 is guided to the light projecting / receiving probe 5 by the light projecting optical fiber 3. The white light guided to the light projecting / receiving probe 5 is applied to the measurement target film 23 via a condensing lens (not shown) provided on the light projecting / receiving probe 5 and the transparent parallel plate 7 a of the focal position scanning unit 7. .

  The light reflected from the front and back surfaces of the measurement target film 23 enters the light projecting / receiving probe 5 through the transparent parallel plate 7 a and guided to the spectroscope 11 by the light receiving optical fiber 9. The spectroscope 11 spectrally separates the light from the light receiving optical fiber 9 to obtain a reflection spectral spectrum, converts it into an electrical signal, and outputs it. The wavelength range of the spectroscope 11 is approximately 400 nm (nanometers) to 700 nm, for example. The light receiving element of the spectroscope 11 is, for example, a CCD (Charge Coupled Device). The spectroscope 11 measures the reflection spectrum at 2 kHz, for example.

  The calculation unit 13 calculates the film thickness of the measurement target film 23 based on the electrical signal from the spectroscope 11. The spectral data acquisition unit 15 acquires spectral spectral data based on the electrical signal from the spectral unit 11. The spectral data acquisition unit 15 outputs the spectral data to the power spectrum calculation unit 17 or the data extraction unit 21 or both.

  The power spectrum calculation unit 17 performs preprocessing and Fourier transform on the spectrum data and calculates a power spectrum. The power spectrum calculation unit 17 outputs the power spectrum data to the film thickness calculation unit 19 or the data extraction unit 21 or both.

  The data extraction unit 21 provides threshold values for the spectral spectrum data from the spectral data acquisition unit 15 and / or the power spectrum data from the power spectrum calculation unit 17, or both, and extracts data that is equal to or greater than the threshold value.

  The film thickness calculation unit 19 calculates the film thickness of the measurement target film 23 based on the peak position of the power spectrum and the refractive index of the measurement target film 23. The film thickness calculation unit 19 outputs film thickness data corresponding to the data extracted by the data extraction unit 21.

  As shown in FIGS. 1 and 2, the focal position scanning unit 7 includes a plurality of transparent parallel plates 7a, a rotating plate 7b, and a motor 7c. In this embodiment, seven transparent parallel flat plates 7a are provided. The seven transparent parallel plates 7a have the same refractive index and different thicknesses. The thicknesses of the seven transparent parallel flat plates 7a are, for example, 1 mm (millimeter), 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm. The transparent parallel plate 7a is made of, for example, borosilicate crown glass (refractive index is about 1.52).

  The rotating plate 7b has eight openings on the circumference centered on the rotating shaft. The transparent parallel plates 7a are arranged one by one in the opening of the rotating plate 7b. The transparent parallel plate 7a is not disposed at one of the openings of the rotating plate 7b.

  The motor 7c rotates the rotating plate 7b. By rotating the rotating plate 7b, an opening where the transparent parallel plate 7a is not disposed and the seven transparent parallel plates 7a are sequentially inserted into the optical path between the light projecting / receiving probe 5 and the measurement target film 23. Thereby, the focal position scanning unit 7 is the focal position of the light emitted from the light projecting / receiving probe 5 with respect to the reference position of the measurement target film 23 and the focal position of the light incident on the light projecting / receiving probe 5. The common focus position is scanned within a predetermined range in the optical axis direction.

  FIG. 3 is a schematic diagram for explaining how the common focal position is changed in this embodiment. This state will be described with reference to FIGS.

  When the rotating plate 7b is rotated by the motor 7c and an opening in which the transparent parallel plate 7a is not disposed is disposed in the optical path between the light projecting / receiving probe 5 and the measurement target film 23 (no parallel plate), the light projecting / receiving probe 5 The focal point of the light incident on is located at the reference position of the measurement target film 23. The distance between the light projecting / receiving probe 5 and the reference position is, for example, 27 mm.

  When the transparent parallel flat plate 7a having a relatively small thickness is disposed in the optical path between the light projecting / receiving probe 5 and the measurement target film 23 (parallel flat plate (thin)), the focal point of the light incident on the light projecting / receiving probe 5 is the reference position. To the plus (+) side.

  When a transparent parallel plate 7a having a relatively large thickness is arranged in the optical path between the light projecting / receiving probe 5 and the measurement target film 23 (parallel plate (thickness)), the focal point of the light incident on the light projecting / receiving probe 5 is the reference position. Is further moved to the plus (+) side.

In this way, the focus of the light incident on the light projecting / receiving probe 5 is moved with respect to the reference position, and the common focus position is changed.
When the focal point of the light incident on the light projecting / receiving probe 5 is in the vicinity of the measurement target film 23, appropriate reflected light enters the light projecting / receiving probe 5.

The operation of the data extraction unit will be described with reference to FIGS. 1 and 4 to 6.
FIG. 4 is a waveform diagram for explaining the data extraction operation when the data extraction unit sets a threshold value for the received light intensity in the spectral data.

The data extraction unit 21 determines whether or not the received light intensity is greater than or equal to the threshold for the spectral data input from the spectral data acquisition unit 15.
When the received light intensity in the spectral data is equal to or higher than the threshold value, the data extraction unit 21 treats it as extracted data.
When the received light intensity in the spectral data is smaller than the threshold value, the data extraction unit 21 treats it as excluded data.

The data extraction unit 21 outputs spectral spectrum data determined to be extraction data to the power spectrum calculation unit 17. The power spectrum calculation unit 17 performs Fourier transform on the extracted spectral spectrum data to obtain power spectrum data. The power spectrum calculation unit 17 outputs power spectrum data to the film thickness calculation unit 19. The film thickness calculator 19 calculates the film thickness of the measurement target film 23 based on the power spectrum data, and outputs the film thickness data.
Thereby, the calculating part 13 can obtain only film thickness data when appropriate reflected light is incident on the light projecting / receiving probe 5.

  FIG. 5 is a waveform diagram for explaining the data extraction operation when the data extraction unit provides a threshold value for the difference between the maximum value and the minimum value of the received light intensity in the spectral data.

The data extraction unit 21 determines whether or not the difference between the maximum value and the minimum value of the received light intensity is greater than or equal to the threshold for the spectral data input from the spectral data acquisition unit 15.
When the difference between the maximum value and the minimum value of the received light intensity in the spectrum data is equal to or greater than the threshold value, the data extraction unit 21 handles the extracted data.
When the difference between the maximum value and the minimum value of the received light intensity in the spectral data is smaller than the threshold value, the data extraction unit 21 treats it as excluded data.

The subsequent film thickness calculation operation of the calculation unit 13 is the same as the operation described with reference to FIG.
Thereby, the calculating part 13 can obtain only film thickness data when appropriate reflected light is incident on the light projecting / receiving probe 5.

  FIG. 6 is a waveform diagram for explaining the data extraction operation when the data extraction unit sets a threshold value for the peak height in the power spectrum data.

  The power spectrum calculation unit 17 obtains a power spectrum based on the spectrum data input from the spectrum data acquisition unit 15. The power spectrum calculation unit 17 outputs power spectrum data to the data extraction unit 21.

The data extraction unit 21 determines whether the peak height of the power spectrum data input from the power spectrum calculation unit 17 is greater than or equal to a threshold value.
When the peak height in the data of the power spectrum is equal to or greater than the threshold value, the data extraction unit 21 treats it as extracted data.
When the peak height in the data of the power spectrum is smaller than the threshold value, the data extraction unit 21 treats it as excluded data.

The data extraction unit 21 outputs the power spectrum data determined to be the extraction data to the film thickness calculation unit 19. The film thickness calculation unit 19 calculates the film thickness of the measurement target film 23 based on the extracted power spectrum data, and outputs the film thickness data.
Thereby, the calculating part 13 can obtain only film thickness data when appropriate reflected light is incident on the light projecting / receiving probe 5.

  In the data extraction operation described with reference to FIGS. 4 to 6, the data extraction unit 21 uses only one threshold value, but the present invention is not limited to these. The data extraction unit 21 may perform the data extraction operation by combining the three types of data extraction operations using a plurality of threshold values among the three types of threshold values. Thereby, the extraction accuracy of appropriate data is improved.

  FIG. 7 is a graph showing an example of a film thickness measurement result according to the embodiment of FIG. FIG. 8 is a graph showing an example of a film thickness measurement result according to the prior art of FIG. The vertical axis in FIGS. 7 and 8 represents a film thickness value (unit: μm (micrometer)). The horizontal axis of FIG.7 and FIG.8 shows the position (a unit is mm) of a measurement object film | membrane.

  Regarding the position of the measurement target film, the reference position is a focal position when a transparent parallel plate is not disposed in the optical path between the light projecting / receiving probe and the measurement target film. The position of the measurement target film at the reference position is 0 mm. The position of the measurement target film was set to −1 mm, the reference position, +1 mm, +2 mm, and +3 mm (see FIG. 2 for the plus direction and the minus direction with respect to the reference position).

The sample of the measurement target film is a PET film having a film thickness of about 12 μm.
In the embodiment of FIG. 1, the focal position scanning unit 7 rotates the rotating plate 7b at a speed of 15 Hz by driving the motor 7c.

  In the conventional interference type film thickness meter of FIG. 18, the focal point of the light incident on the light projecting / receiving unit 105 is fixed at the reference position. Therefore, as shown in FIG. 8, the conventional interference type film thickness meter was able to measure the film thickness of the sample at the reference position. However, if the position of the film to be measured is deviated by 1 mm from the reference position, the conventional interference type film thickness meter cannot measure the film thickness.

  The interference type film thickness meter of the embodiment of FIG. 1 scans the focal position of light incident on the light projecting / receiving probe 5 within a predetermined range by the operation of the focal position scanning unit 7. Thereby, as shown in FIG. 7, the interference type film thickness meter of the example was able to measure the film thickness of the measurement target film at the reference position, +1 mm, and +2 mm.

  The film thickness of the sample at the reference position was calculated based on spectral spectrum data obtained when the aperture where the transparent parallel plate 7a is not disposed is disposed in the optical path between the light projecting / receiving probe 5 and the sample. The film thickness of the sample at the position of +1 mm was calculated based on the spectral data when the transparent parallel plate 7a having a thickness of 3 mm was placed in the optical path between the light projecting / receiving probe 5 and the sample. The film thickness of the sample at the position of +2 mm was calculated based on spectral spectrum data obtained when the transparent parallel flat plate 7a having a thickness of 6 mm was disposed in the optical path between the light projecting / receiving probe 5 and the sample.

  As described above, the interference film thickness meter of the embodiment of FIG. 1 can calculate the film thickness of the measurement target film even when the position of the measurement target film is shifted from the reference position.

  In the embodiment of FIG. 1, the focal position when the aperture where the transparent parallel plate 7a is not arranged is arranged in the optical path of the light projecting / receiving probe 5 is used as the reference position of the measurement target film 23. However, the reference position is limited to this. Not. In the present invention, the reference position of the measurement target film may be any position as long as the position of the measurement target film where appropriate reflected light or transmitted light enters the light receiving unit from the measurement target film when the common focal position is scanned. Good.

  Further, in the embodiment of FIG. 1, the plurality of transparent parallel plates 7a having different thicknesses are used, but the plurality of transparent parallel plates may have the same thickness and different refractive indexes. The plurality of transparent parallel flat plates may have different thicknesses and refractive indexes. Moreover, the transparent parallel plate may be arrange | positioned at all the openings of the rotating plate 7b.

By the way, if there is a defect such as a flaw in the film to be measured, the measurement light does not return from the defective part, so the film thickness data is lost.
Since the interference type film thickness meter of the present invention extracts only the data from which the measurement light returns, there is also an effect that the measurement excluding such a defect is possible.

  FIG. 9 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  The focal position scanning unit 25 changes the common focal position by rotating a mirror 25a disposed in the optical path between the light projecting / receiving probe 5 and the measurement target film 23 by a driving mechanism (not shown). By the operation of the focal position scanning unit 25, the angle formed between the optical axis of the light incident on the mirror 25a and the measurement target film 23 with respect to the reference position of the measurement target film 23 changes. The mirror 25a is composed of, for example, a tilt mirror or a polygon mirror created by MEMS (Micro Electro Mechanical Systems).

  FIG. 10 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in still another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  The focal position scanning unit 27 is a combination of the focal position scanning unit 7 shown in FIG. 1 and the focal position scanning unit 25 shown in FIG. The focal position scanning unit 27 includes a plurality of transparent parallel plates 7a, a rotating plate 7b, a motor 7c, a mirror 25a, and a drive mechanism (not shown) that rotates the mirror 25a. Further, the focal position scanning unit 27 includes a drive mechanism (not shown) that rotates the arrangement positions of the rotating plate 7b and the motor 7c in accordance with the rotation of the mirror 25a. The optical axis of the light from the mirror 25a and the plane of the transparent parallel plate 7a make an angle of 90 degrees.

With the operation of the focal position scanning unit 27, the angle formed by the measurement target film 23 and the optical axis of the light incident on the light projecting / receiving probe 5 with respect to the reference position of the measurement target film 23, and the light incident on the light projecting / receiving probe 5 The focal length changes.
In this embodiment, the rotating plate 7b and the motor 7c are rotated in accordance with the rotation of the mirror 25a, but the arrangement positions of the rotating plate 7b and the motor 7c may be fixed. In this case, the angle formed by the optical axis of the light from the mirror 25a and the plane of the transparent parallel plate 7a changes.

  FIG. 11 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in still another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  The focal position scanning unit 29 passes through a transparent parallel flat plate 29 a disposed in the optical path between the light projecting / receiving probe 5 and the measurement target film 23, and is transparent parallel to the optical axis of light from the focal point of the light incident on the light projecting / receiving probe 5. The common focus position is changed by rotating the drive mechanism (not shown) so that the angle formed by the flat plate 29a is changed. The focal length of the light incident on the light projecting / receiving probe 5 is changed by the operation of the focal position scanning unit 29.

  FIG. 12 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in still another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  The focal position scanning unit 31 rotates a pair of mirrors 31a and 31b arranged in parallel to each other in the optical path between the light projecting / receiving probe 5 and the measurement target film 23 by a driving mechanism (not shown). , Change the common focus position. The focal length of the light incident on the light projecting / receiving probe 5 is changed by the operation of the focal position scanning unit 31. The mirrors 31a and 31b are composed of, for example, a tilt mirror or a polygon mirror created by MEMS.

  FIG. 13 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in still another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  The focal position scanning unit 33 sequentially inserts a plurality of lenses 33a having different focal lengths into the optical path between the light projecting / receiving probe 5 and the measurement target film 23 and an opening 33b in which no lenses are arranged, thereby providing a common focal point. Change position. The focal position scanning unit 33 is realized, for example, by disposing the lens 33a instead of the transparent parallel plate 7a in the focal position scanning unit 7 shown in FIG. The focal length of the light incident on the light projecting / receiving probe 5 is changed by the operation of the focal position scanning unit 33. A lens may be disposed in all the openings of the rotating plate. Further, the plurality of lenses arranged on the rotating plate may be only a convex lens or only a concave lens.

  FIG. 14 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in still another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  In the focal position scanning unit 35, a plurality of wedge substrates 35a and wedge substrates having different wedge angles or inclined surfaces or both of them are arranged in the optical path between the light projecting / receiving probe 5 and the measurement target film 23. The common focal position is changed by sequentially inserting the non-opening 35b. The focal position scanning unit 35 is realized, for example, by arranging a wedge substrate 35a in place of the transparent parallel plate 7a in the focal position scanning unit 7 shown in FIG. By the operation of the focal position scanning unit 35, the focal length of the light incident on the light projecting / receiving probe 5 and the angle formed between the optical axis of the light incident on the wedge substrate 35a and the measurement target film 23 are changed. In addition, the wedge board may be arrange | positioned at all the openings of a rotating plate.

  FIG. 15 is a schematic configuration diagram for explaining the configuration and operation of a focal position scanning unit in still another embodiment. In this embodiment, the configuration other than the focal position scanning unit is the same as that of the embodiment described with reference to FIG.

  The focal position scanning unit 37 includes two wedge substrates 37 a and 37 b disposed in the optical path between the light projecting / receiving probe 5 and the measurement target film 23. The two wedge substrates 37a and 37b have the same wedge angle and are inclined to face each other. The focal position scanning unit 37 is moved by a drive mechanism (not shown) so that the total thickness of the wedge substrates 37a and 37b located in the optical path of the light incident on the light projecting / receiving probe 5 is changed, thereby the common focal position. To change. The focal length of the light incident on the light projecting / receiving probe 5 is changed by the operation of the focal position scanning unit 37.

  In the said Example, although the light projection / reception probe 5 is used as a light projection part and a light-receiving part, a light projection part and a light-receiving part may be provided separately.

  Further, in the above embodiment, the thickness of the film to be measured is obtained by obtaining the spectrum of the reflected light from the film to be measured, but the interference type film thickness meter of the present invention uses the transmitted light that has passed through the film to be measured. The film thickness of the measurement target film may be obtained by obtaining a spectrum.

  FIG. 16 is a schematic configuration diagram for explaining still another example of the interference film thickness meter. In FIG. 16, parts having the same functions as those in FIG. A detailed description of the portion performing the same function as in FIG. 1 is omitted.

  The film thickness meter includes a light source 1, a light projecting optical fiber 3, a light projecting unit 39, a light receiving unit 41, a light receiving optical fiber 9, a spectroscope 11, a calculation unit 13, and a focal position scanning unit 43. The calculation unit 13 includes a spectral data acquisition unit 15, a power spectrum calculation unit 17, a film thickness calculation unit 19, and a data extraction unit 21.

  The light projecting unit 39 and the light receiving unit 41 are arranged at positions sandwiching the measurement target film 23. The focal position of the light emitted from the light projecting unit 39 and the focal position of the light incident on the light receiving unit are set to the same position (common focal position). The optical axis of the light emitted from the light projecting unit 39 and the optical axis of the light incident on the light receiving unit are arranged on the same straight line.

  White light emitted from the light source 1 is guided to the light projecting unit 39 by the light projecting optical fiber 3. The white light guided to the light projecting unit 39 is applied to the measurement target film 23 via a condenser lens (not shown) provided in the light projecting unit 39.

  The light transmitted through the measurement target film 23 enters the light receiving unit 41 and is guided to the spectroscope 11 by the light receiving optical fiber 9. The spectroscope 11 spectrally separates the light from the light receiving optical fiber 9 to obtain a reflection spectral spectrum, converts it into an electrical signal, and outputs it. The calculation unit 13 calculates the film thickness of the measurement target film 23 based on the electrical signal from the spectroscope 11.

  FIG. 17 is a schematic diagram for explaining how the common focal position is changed in this embodiment. This situation will be described with reference to FIGS.

  The focal position scanning unit 43 moves the light projecting unit 39 and the light receiving unit 41 relative to the measurement target film 23 while maintaining the distance and angle between the light projecting unit 39 and the light receiving unit 41. As a result, the common focal position that is the focal position of the light emitted from the light projecting unit 39 and the focal position of the light incident on the light receiving unit 41 is scanned within a predetermined range. For example, the focal position scanning unit 43 moves the light projecting unit 39 and the light receiving unit 41 in a direction parallel to the optical axis of the light emitted from the light projecting unit 39 and the light incident on the light receiving unit 41.

As shown in FIG. 16, the focal point of the light emitted from the light projecting unit 39 and the light incident on the light receiving unit 41 is moved with respect to the reference position, and the common focal position is changed.
When the focus of the light irradiated from the light projecting unit 39 and the light incident on the light receiving unit 41 is in the vicinity of the measurement target film 23, appropriate reflected light enters the light receiving unit 41.

  As mentioned above, although the Example of this invention was described, material, a shape, arrangement | positioning, a dimension, etc. are examples, This invention is not limited to these, In the range of this invention described in the claim Various changes can be made.

DESCRIPTION OF SYMBOLS 1 Light source 5 Projection / reception probe 7, 25, 27, 29, 31, 33, 35, 37, 43 Focus position scanning part 7a, 29a Transparent parallel plate 15 Spectral data acquisition part 17 Power spectrum calculation part 19 Film thickness calculation part 21 Data Extraction unit 23 Measurement target films 25a, 31a, 31b Mirror 33a Lens 35a Wedge substrates 37a, 37b Wedge substrate 39 Light projecting unit 41 Light receiving unit

Claims (14)

A light projecting unit that irradiates the measurement target film with light from the light source;
A light receiving unit that receives reflected light or transmitted light from the measurement target film; and
A focal position scanning unit that scans a common focal position that is a focal position of light emitted from the light projecting unit and is also a focal position of light incident on the light receiving unit within a predetermined range;
A spectral data acquisition unit for acquiring spectral spectral data of light received by the light receiving unit;
A power spectrum calculation unit for calculating a power spectrum based on the spectral spectrum data;
A film thickness calculator that calculates the film thickness of the measurement target film based on the data of the power spectrum;
A threshold value is provided for the spectral spectrum data or the power spectrum data or both, and a data extraction unit for extracting data equal to or higher than the threshold value, and
The film thickness calculation unit is an interference type film thickness meter that outputs film thickness data corresponding to the data extracted by the data extraction unit.   2. The interference type according to claim 1, wherein the light projecting unit and the light receiving unit are configured by a light projecting / receiving unit that irradiates the measurement target film with light from the light source and receives reflected light from the measurement target film. Film thickness meter.   The focal position scanning unit sequentially inserts a plurality of transparent parallel plates having different thicknesses, refractive indexes, or both into the optical path between the light projecting / receiving unit and the measurement target film, and changes the common focal position. The interference type film thickness meter according to claim 2.   The interference type film thickness meter according to claim 2, wherein the focal position scanning unit changes the common focal position by rotating a mirror disposed in an optical path between the light projecting / receiving unit and the measurement target film. .   The focal position scanning unit sequentially inserts a plurality of transparent parallel plates having different thicknesses, refractive indexes, or both in an optical path between the mirror and the measurement target film, and changes the common focal position. Item 5. The interference type film thickness meter according to Item 4.   The focal position scanning unit includes a transparent parallel plate disposed in an optical path between the light projecting / receiving unit and the measurement target film, and an optical axis of light from a focal point of light incident on the light projecting / receiving unit and the transparent parallel plate. The interference type film thickness meter according to claim 2, wherein the common focus position is changed by rotating the flat plate so that an angle formed by the flat plate is changed.   The focal position scanning unit changes the common focal position by rotating a pair of mirrors arranged in parallel with each other in an optical path between the light projecting and receiving unit and the measurement target film. The interferometric film thickness meter described in 1.   The interference according to claim 2, wherein the focal position scanning unit sequentially inserts a plurality of lenses having different focal lengths into an optical path between the light projecting / receiving unit and the measurement target film to change the common focal position. Formula film thickness meter.   The focus position scanning unit sequentially inserts a plurality of wedge substrates having different wedge angles or inclined surfaces or both of them into the optical path between the light projecting / receiving unit and the measurement target film, and The interference type film thickness meter according to claim 2, wherein the focal position is changed. The focal position scanning unit includes two wedge substrates arranged in an optical path between the light projecting / receiving unit and the measurement target film,
The two wedge substrates have the same wedge angle and the inclined surfaces are opposed to each other,
The interference-type film thickness meter according to claim 2, wherein the focal position scanning unit changes the common focal position by moving the focal position scanning unit so that a total thickness of the two wedge substrates located in the optical path is changed. The light projecting unit and the light receiving unit are arranged at positions sandwiching the measurement target film,
The light receiving part receives transmitted light from the measurement target film,
The focus position scanning unit moves the light projecting unit and the light receiving unit with respect to the measurement target film and changes the common focus position while maintaining a distance and an angle between the light projecting unit and the light receiving unit. The interference type film thickness meter according to 1.   The interference type film thickness meter according to any one of claims 1 to 11, wherein the data extraction unit provides the threshold value to the received light intensity in the spectral data.   The interference type film thickness meter according to any one of claims 1 to 11, wherein the data extraction unit provides the threshold value in a difference between a maximum value and a minimum value of received light intensity in the spectral spectrum data.   The interference type film thickness meter according to claim 1, wherein the data extraction unit provides the threshold value at a peak height in the data of the power spectrum.

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