JPH07181016A - Method and apparatus for measuring film thickness - Google Patents

Abstract

PURPOSE:To provide method and apparatus for measuring the film thickness of various materials automatically with high accuracy by transmitting the light beam, projected from a light source having a wide wavelength region, in an arbitrary wavelength region inherent to an object to be measured having a transmittance dependent on the film thickness. CONSTITUTION:A light beam having a transmittance dependent on the film thickness is projected from a light source 2, e.g. a black body furnace, having a wide wavelength range and transmitted selectively through an optical filter 3 before impinging on an object 5 to be measured and a reference object 7 having a known film thickness. The reflected lights are subjected to photoelectric conversion through detectors 6, 8 and compared with each other before the film thickness is measured at a section 9 comprising a subtractor 10, a signal processor 11, a thickness indicator 12, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a relatively simple structure capable of efficiently and automatically detecting the film thickness of a single material film or the film thickness of any material such as a thin film laminated on a base film. Film thickness measuring method and film thickness measuring device.

[0002]

2. Description of the Related Art For example, a PET film used as a packaging material has a MgO single layer thin film deposited on its surface. In order to obtain the vapor deposition characteristics of this MgO single-layer thin film and stabilize the quality of the packaging paper, it is necessary to measure the film thickness. Conventionally, as a method of measuring a thin film of this kind, a method of irradiating an object to be measured with a light beam and obtaining the film thickness from the amount of transmitted attenuated light is generally adopted. Specifically, a single-wavelength component that exhibits the transmittance that has the most dependency (correlation) with the film thickness is dispersed by a diffraction grating, and this spectral ray is irradiated to the DUT, and the transmission attenuation is photoelectrically converted. An electric output is obtained by the above method, and the film thickness is detected from this output value. In this case, in order to improve the resolution of the film thickness measurement, a means for amplifying the transmitted attenuation light amount by time integration has also been adopted for the object to be measured with a weak transmitted attenuation light amount. Also,
There has also been adopted a device that uses a laser beam as a light source and utilizes its high output characteristic to efficiently measure a film thickness.

[0003]

In the above-mentioned prior art, since the single-wavelength light beam irradiated to the object to be measured uses only a part of the transmission attenuation wavelength range of the object to be measured, a light source such as a white light source is used. In the case of a light source having a wide emission spectrum, the utilization rate of the radiant energy of the light source is low and wasted. In addition, since the diffraction grating disperses light of a specific wavelength, it is necessary to change the diffraction angle continuously to emit light of a wide range of wavelengths, but the scanning speed and the response time of the detector are limited. However, it is not practically applicable because the device structure is complicated. Further, it is possible to improve the measurement efficiency by using a single-wavelength and high-output light source such as a laser beam, but there is a problem that the wavelength region is specified similarly to the above, and the laser beam When the object to be measured has a property of being unable to withstand the amount of irradiation energy, the output of laser light must be reduced. Therefore, there is a problem that the measurement efficiency is lowered because the sensitivity must be improved by time-integrating the weak transmitted attenuation light amount. Further, in the case of laser light, there is a problem in that the wavelength range is limited and it is not possible to deal with measured objects of various materials.

The present invention solves the above problems by using a light source having a wide wavelength range and selecting light in an arbitrary wavelength range according to the material of the object to be measured. An object of the present invention is to provide a film thickness measuring method and a film thickness measuring device having a relatively simple structure and capable of efficiently and automatically detecting the film thickness.

[0005]

In order to achieve the above object, the present invention provides a method for measuring the film thickness of an object to be measured, which comprises a thin film, and which comprises a light source that emits light rays in a wide wavelength range. Among the radiated light, only the light beam in the wavelength region peculiar to the object to be measured, which shows the transmittance correlated with the film thickness, is transmitted through the optical filter, and the transmitted light beam is irradiated to the object to be measured, and the film is formed. It is characterized by a film thickness measuring method for obtaining the film thickness of an object to be measured based on the amount of transmitted attenuated light attenuated in correlation with the thickness. Further, as a device for specifically implementing this method, a device for measuring the film thickness of an object to be measured composed of a thin film, which is a light source that emits a light source in a wide wavelength range, and a transmission that correlates with the film thickness. An optical filter that transmits only a light ray in a wavelength region specific to the measured object indicating a ratio, and a film thickness of the measured object based on the transmission attenuation light amount of the transmitted light that is attenuated by passing through the measured object. The film thickness measuring device is provided with a film thickness detecting section for automatic detection and display. Further, in the present invention, a combination of a short cut filter, a long cut filter, a band cut filter and a band pass filter are adopted as the optical filter.

[0006]

A light beam from a light source such as a black body furnace having a wide wavelength range is wavelength-selected by an optical filter and outputs a light beam in a wavelength range peculiar to an object to be measured, which has a dependency on film thickness and transmittance. The light beam is applied to, for example, the object to be measured and a reference object made of the same material as the object to be measured, becomes a transmission attenuation light beam, is input to the detector, and is photoelectrically converted into a detection signal and a reference detection signal. These two signals are compared and subtracted by the subtractor of the film thickness detection unit, and measured and displayed by the signal processing device and the thickness indicator. By using a combination of cut filters and a bandpass filter, it is possible to selectively extract light rays in an arbitrary wavelength range and measure the film thickness of the object to be measured. This enables effective use of light rays and increases measurement sensitivity.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing the overall structure of a first embodiment of the present invention,
FIG. 2 is a front view of a chopper rotator, which is one of the constituent elements of the embodiment, FIGS. 3 and 4 are configuration diagrams showing the overall structure of the second and third embodiments of the present invention, and FIG. 5 is a wavelength and spectral transmittance. And FIG. 6 is a diagram showing the relationship between the spectral radiance indicating the radiation dose and the wavelength, and FIGS. 7 to 18 are specific examples of the optical filter and a method of selecting a desired wavelength region according to the specific example. It is a diagram for explaining.

(Embodiment 1) As shown in FIG. 1, the film thickness measuring apparatus 1 of this embodiment is roughly classified into a light source 2 and an optical filter 3.
A chopper rotator 4, a detector 6 for the DUT 5,
It comprises a detector 8 for the reference measurement object 7, a subtractor 10 constituting the film thickness detection unit 9, a signal processing device 11, a thickness indicator 12, and the like. In addition, a parabolic mirror piece 13 formed from a part of the parabolic mirror is arranged near the light source 2.

The light source 2 emits light rays in a wide wavelength range, and a thermal radiator such as a black body furnace (black body / Planck radiator) is applied. The black body furnace is shown in FIG.
As shown in (1), it has a predetermined radiance in a wide wavelength range from ultraviolet to far infrared. The relationship curve between the spectral radiance and the wavelength shown in FIG. 6 changes with temperature as a parameter.

The optical filter 3 will be described in detail later,
The light source 2 selectively transmits light rays in a wavelength region showing a transmittance having a correlation with the film thickness, out of light rays having a wide range of wavelengths from the light source 2, and is set depending on the material of the DUT 5. The optical filter 3 includes a combination of a short cut filter that cuts only a short wavelength region, a long cut filter that cuts only a high wavelength region, and a band cut filter that cuts only a specific wavelength region, or a specific wavelength region. A bandpass filter that transmits only light is used.

The chopper rotator 4 is, as shown in FIG.
It is composed of a chopping blade 15 rotated by a motor 14 and a synchronous counter 16 which is engaged with the chopping blade 15 and counts the rotation cycle thereof. Chopping feather 15
As shown in FIG. 2, the circumference is divided into four equal parts, and the openings 17 and the reflecting mirror parts 18 are alternately formed in the part of the quarter circumference.

The object to be measured 5 is formed by depositing a MgO single layer thin film on a PET film, for example. When light passes through the DUT 5, the light is absorbed and attenuated. The spectral transmittance (%) and the wavelength (μm) have a relationship as shown in FIG. This diagram differs depending on the material of the thin film of the DUT 5 and is unique. As shown in FIG. 5, the sample thickness of the curve A indicated by the solid line is the thinnest, the curve A of the dotted line is the second thinnest, and the curve C of the one-dot chain line is the thickest. Generally, the smaller the thickness is, the higher the transmittance is, but as shown in FIG. 5, it varies depending on the wavelength. In this case, there is a positive correlation between the film thickness and the transmittance only in the wavelength regions indicated by α and β. Therefore, the optical filter 3 having the structure that selects the wavelength regions of α and β is most efficient. On the other hand, the reference measurement object 7 is made of the same material as the measurement object 5, and its film thickness is known in advance.

The detectors 6 and 8 have a photoelectric conversion function of emitting an electric signal corresponding to the amount of transmitted attenuated light that has passed through the object to be measured 5 and the reference object to be measured 8.

As described above, the film thickness detecting section 9 has the subtracter 1
0, a signal processing device 11 and a thickness indicator 12.
The detectors 6 and 8 and the synchronous counter 16 are connected to the subtractor 10, and electric signals from them are input. Specifically, the subtractor 10 monitors the rotation synchronization signal of the chopping blade 15 output from the synchronization counter, detects the switching timing of the DUT 5 or the reference measurement object 7, and determines the difference in the amount of transmitted attenuation light between the two. Is calculated and output as an electric signal to the next stage side. In addition, the signal processing device 11 is connected to the calculator 10, and the calculator 1 is connected to the calculator 10.
The film thickness signal is generated by referring to a look-up table calculated in advance based on the calculated value of 0. Further, the thickness indicator 12 displays the film thickness value based on the film thickness signal.

Next, a film thickness measuring method by the film thickness measuring device 1 of the first embodiment will be described. A light ray (H1) having a spread of a certain radiation angle θ is emitted from the light source 2. The ray (H1) hits the parabola mirror piece 13 and is reflected to be a parallel ray (H2).
become. The parallel ray (H2) passes through the optical filter 3 to select the ray (H3) in the specific wavelength region. The light ray (H3) travels straight from the opening 17 in parallel by the chopping blade 15 of the chopper rotator 4 (H3).
4) and the reflecting mirror 18 divides the light beam into a light beam (H5) whose optical path is changed in a right angle direction. The ray (H4) and the ray (H5) are divided at a time ratio of 1: 1. The rotation counter 16 of the chopper rotator 4 outputs a rotation synchronization signal S5 to the subtractor 10. The light ray (H4) irradiates the DUT 5 and becomes a transmission attenuated light ray (H6) which is attenuated depending on its film thickness. On the other hand, the light ray (H5) irradiates the reference measurement object 7 and becomes a transmission attenuated light ray (H7). The transmission attenuated rays (H6) and (H7) enter detectors 6 and 8 and are converted into electric outputs corresponding to the intensities of these rays, and a detection signal S1 and a reference detection signal S2 are output. The rotation synchronization signal S5, the detection signal S1, and the reference detection signal S2 are input to the subtractor 10. The rotation synchronization signal S5 is for controlling the switching timing of the detection signal S1 and the reference detection signal S2. The subtractor 10 subtracts the reference detection signal S2 from the detection signal S1 and inputs the subtraction signal S3 to the signal processing device 11. The signal processing device 11 refers to the spectral transmission characteristics of the DUT 5 for the input subtraction signal S3 from the wavelength sensitivity characteristics of the detectors 6 and 8 with reference to a look-up table, and calculates the subtraction signal S3 with the film thickness. The signal S4 is converted and input to the thickness indicator 12. The thickness indicator 12 displays a film thickness value corresponding to the film thickness signal S4.

When the material of the object to be measured 5 is changed, the light source 2 is used as it is, and the optical filter 3 and the reference object to be measured 7 are used.
The lookup table in the signal processing device may be exchanged. That is, since the shape of the curve showing the relationship between the spectral transmittance and the wavelength shown in FIG. 5 changes depending on the material of the DUT 5, it is necessary to select the wavelength region having the spectral transmittance that depends on the film thickness. become. That is, the film thickness can be measured as it is by changing the transmission region by the optical filter 3. It should be noted that there is no problem in measuring single layers and thin films made of a single material, but when measuring thin films laminated on a base film, the measurement wavelength range should be selected after considering the spectral transmittance characteristics of the base material. Need to do. Further, in the case of the first embodiment, the light beams (H4) and (H5) are switched by the chopper rotator 4, and the amounts of light incident on the detectors 6 and 8 become equal.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention. This film thickness measuring device 1a uses a semi-transmissive mirror 19 instead of the chopper rotator 4 of the first embodiment, and other configurations are the same as those of the first embodiment, and detailed description thereof will be omitted. Normally, the semi-transmissive mirror 19 has wavelength dependence, and care must be taken when the film thickness needs to be measured over a wide wavelength range. Further, since the intensity of the light beam applied to the semi-transmissive mirror 19 is divided into two, the amount of light incident on the detectors 6 and 8 is halved.
However, the film thickness can be measured according to this embodiment without synchronously controlling the chopper rotator. Optical filter 3
The light ray (H3) from is transmitted by the semi-transmissive mirror 19 (H4).
And the ray (H5) is split 1: 1. Hereinafter, in the same manner as in the above-described embodiment, the DUT 6, the reference measured object 7, and the detector 6,
The detection signal S1 and the reference detection signal S2 that have passed through 8 enter the film thickness detection unit 9 side, and film thickness measurement and display are performed.

(Third Embodiment) A film thickness measuring apparatus 1b according to the present embodiment.
Is characterized in that only one detector is used and errors due to variations in the sensitivity of the detector are avoided. Further, as a structure different from the film thickness measuring devices 1 and 1a of FIGS. 1 and 3, a semi-transmissive mirror 19 and a chopper rotator 4 are used together. In this case, the chopper rotator 4 is the object to be measured 5 and the reference. It is arranged on the rear side of the measurement object 7. The light ray (H4) transmitted through the semi-transmissive mirror 19 is transmitted through the DUT 5 and becomes a transmission attenuation light ray (H6), which is applied to the chopper rotator 4.
On the other hand, the light beam (H5) reflected by the semi-transmissive mirror 19 is transmitted through the reference measurement object 7 to become a transmission attenuation light beam (H7), and is further applied to the chopper rotator 4 via the reflecting mirrors 20 and 21. The transmission light ray (H6) or (H
Either of 7) enters the single detector 6 and the detection signal S1
Alternatively, it alternates with the reference detection signal S2 and is sent to the film thickness detection unit 9 side. Thereby, almost the same film thickness measurement as described above can be performed.

Next, the structure and operation of the optical filter 3 will be described. A case will be described in which the light source 2 whose relationship between the wavelength and the spectral radiance is shown by the curve A in FIG. 7 is used. The relationship between the spectral transmittance (%) and the wavelength (μm) as shown in FIG. 5 is obtained according to the material and composition of the film thickness of the DUT 5, and the light source light in the wavelength range α, β is assumed. The case of measuring the film thickness will be described. First, as shown in FIG. 8, a portion from the wavelength corresponding to the left end of the wavelength region α in FIG. 7 to the origin is cut by a shortcut filter, and the other portion is set as a transmission region. Next, using a long cut filter, as shown in FIG. 9, the long wavelength side is cut from the right end of the wavelength region β, and the other portion is set as a transmission region. Next, as shown in FIG. 10, a band cut filter is used to cut between the right end of the wavelength region α and the left end of the wavelength region β, and the other portion is set as the transmission region. By combining the shortcut filter, the long cut filter and the band cut filter shown in FIGS. 8, 9 and 10, the optical filter 3 having the transmission region shown in FIG. 11 can be formed.

In the DUT 5 in which MgO is vapor-deposited on the PET film, the attenuation of the amount of transmitted light is observed depending on the film thickness of MgO in the infrared wavelength range of 16.1 μm to 25 μm. When the light source 2 having the spectral radiance characteristic shown in FIG. 12 is adopted, the optical filter 3 in the wavelength region corresponding to MgO is formed as follows. That is, as shown in FIG. 13, a short cut filter for cutting wavelengths of 16.1 μm or less and a wavelength of 25 μm as shown in FIG.
By combining a long cut filter that cuts m or more, the optical filter 3 having a transmission region only in the wavelength region of 16.1 μm to 25 μm is formed. Figure 1
3. As shown in FIG. 14, the respective transmittances are T1 and T2.
Wavelength 16.1μm to 25μ by cutting with
Light rays having the spectral radiance of FIG. 15 between m can be formed from the optical filter 3. Note that, in FIG. 15, T1 × T2 is added to the luminance of FIG. 12 in the wavelength range of 16.1 μm to 25 μm.

The optical filter for selecting a light beam having the same spectral radiance characteristic as shown above (shown in FIG. 18) is not limited to the above-mentioned type, but a wavelength of 16.1 μm to 25 μm.
A bandpass filter having a transparent region between them may be used. When a light ray having the characteristic shown in FIG. 16 is transmitted by a bandpass filter having the characteristic shown in FIG. 17, a light ray having the spectral radiance characteristic shown in FIG. 18 is directly obtained.

[0022]

According to the present invention, the following remarkable effects are obtained. 1) Since a light source having a wide wavelength range can be used to efficiently select a light beam in a wavelength range corresponding to an object to be measured, the film thickness measurement sensitivity of various objects to be measured is improved. 2) A light ray in a wavelength range having a dependency (correlation) with the film thickness can be easily and accurately created by changing the combination of optical filters. This allows highly accurate film thickness measurement. 3) Since the film thickness is measured by comparing the measured object with a known reference measured object, highly accurate measurement can be performed. 4) Since the film thickness is obtained by automatic measurement, the measurement efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an overall structure of an embodiment (Embodiment 1) of the present invention.

FIG. 2 is a front view of the chopper rotator in the embodiment of FIG.

FIG. 3 is a configuration diagram showing the overall structure of another embodiment (Embodiment 2) of the present invention.

FIG. 4 is a block diagram showing the overall structure of still another embodiment (Embodiment 3) of the present invention.

FIG. 5 is a spectral transmittance diagram of a sample with film thickness as a parameter.

FIG. 6 is a diagram showing a spectral radiance of a light source applied to the present invention.

FIG. 7 is a diagram for explaining a wavelength region of an optical filter.

FIG. 8 is a diagram showing a transparent region of a shortcut filter.

FIG. 9 is a diagram showing a transmission region of a long cut filter.

FIG. 10 is a diagram showing a transmission region of a band cut filter.

FIG. 11 is a diagram showing the spectral radiance of a light source beam that has passed through the cut filter of FIGS. 7 to 9;

FIG. 12 is a diagram for explaining an optical filter having a wavelength region between wavelengths of 16.1 μm and 25 μm.

FIG. 13 is a transparent region (16.
(1 μm or more).

FIG. 14: Transmission area of the long-cut filter (25 μm
The following).

FIG. 15 is a spectral radiance diagram of a light source beam that has passed through the cut filters of FIGS. 13 and 14;

FIG. 16 is a diagram for explaining the contents of a bandpass filter.

FIG. 17 is a transmission region (16.1 μm) of the bandpass filter.
m to 25 μm).

18 is a spectral radiance diagram of a light source beam that has passed through the bandpass filter of FIG.

[Explanation of symbols]

 1 film thickness measuring device 1a film thickness measuring device 1b film thickness measuring device 2 light source 3 optical filter 4 chopper rotator 5 measured object 6 detector 7 reference measured object 8 detector 9 film thickness detecting section 10 subtractor 11 signal processing device 12 Thickness Indicator 13 Parabola Mira Piece 14 Motor 15 Chopping Blade 16 Synchronous Counter 17 Opening 18 Reflector 19 Semi-Transparent Mirror 20 Reflector 21 Reflector

Claims (4)

[Claims] 1. A method for measuring the film thickness of an object to be measured, which comprises a thin film, wherein the transmittance of light emitted from a light source that emits light in a wide wavelength range is correlated with the film thickness. Only the light beam in the wavelength region peculiar to the measured object is transmitted through an optical filter, the transmitted light beam is irradiated to the measured object, and the measured object is based on the amount of transmitted attenuated light attenuated in correlation with the film thickness. A film thickness measuring method, characterized in that the film thickness is determined. 2. An apparatus for measuring the film thickness of an object to be measured, which comprises a thin film, the light source emitting a light ray in a wide wavelength range, and the object to be measured which exhibits a transmittance correlated with the film thickness. An optical filter that transmits only light rays in the wavelength region of
A film thickness measuring device, comprising: a film thickness detecting section for automatically detecting and displaying a film thickness of the object to be measured based on a transmission attenuation light amount of a transmitted light beam that has been transmitted through the object to be measured and attenuated. 3. The optical filter is a combination of a short cut filter that cuts off a low wavelength region, a long cut filter that cuts off a high wavelength region, and a band cut filter that cuts off only a specific wavelength, or only a specific wavelength region. The film thickness measuring method according to claim 1, wherein the film thickness measuring method is one of a band-pass filter that transmits light. 4. The optical filter is a combination of a short cut filter that cuts off a low wavelength region, a long cut filter that cuts off a high wavelength region, and a band cut filter that cuts off only a specific wavelength, or only a specific wavelength region. The film thickness measuring device according to claim 2, wherein the film thickness measuring device is one of a band-pass filter that transmits light.