JPH0861940A - Surface roughness inspecting device - Google Patents

Abstract

PURPOSE: To provide a surface roughness inspecting device having a simple structure, easy to be assembled, having a small size and light weight, and requiring a low cost. CONSTITUTION: A laser beam 13 is made incident slantedly on an surface to be inspected 1, and the reflected light thereof is condensed through a lens 3. In addition, regular reflected light 14 is deflected by a mirror 6 laid at a lens focal position, and made incident on the first light receiving element 7. Also, scattered light 15 generated by the surface roughness of the surface 1 is imaged on an image surface, and made incident on the second light receiving element 9. In this case, the surface roughness rms of the surface 1 can be obtained from the equation λ/(4πcosθ)}√(IS/IT), where λ represents laser beam wavelength, θ, an incidence angle on the surface 1, and IS and IT, the output current of each of the elements 7 and 9. Also, the value of θ is set to satisfy the relationships of 2θ.cosθ>λ.fs , and (θ-π/2)cosθ>λ.fs .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a highly accurate surface to which a laser beam is incident, and the reflected light is the total reflected light amount and the scattered light amount generated by the surface roughness of the tested surface. The present invention relates to an improvement of a surface roughness inspecting device that measures the surface roughness of a surface to be measured by measuring and measuring the ratio of the two.

[0002]

2. Description of the Related Art Conventionally, a roughness meter shown in FIGS. 9 and 10 has been known as a surface roughness inspection apparatus of this type.

In the roughness meter of FIG. 9, an integrating sphere is brought into contact with and fixed to the surface to be inspected, a laser beam is incident on the surface to be inspected through a first hole provided in the integrating sphere, and the specularly reflected light is integrated. Second on the sphere
Only the scattered light is detected by the integrating sphere by letting it escape to the outside of the integrating sphere through the hole of, and the surface roughness is obtained by comparing with the amount of incident light.

In the roughness meter of FIG. 10, laser light is incident on the surface to be inspected, and the light quantity distribution of specular reflection light and scattered light of the reflected light is
The surface roughness is calculated by scanning the photodetector and comparing the amounts of total reflected light and scattered light by calculation. In any case, assuming that the total reflected light amount I _T of the laser light of the wavelength λ incident on the surface to be inspected at the incident angle θ and the scattered light amount I _S generated by the surface roughness of the surface to be inspected are rms values of the surface roughness. σ
Is a well-known relationship

## EQU1 ## σ = {λ / (4πcos θ)} √ (I _S / I _T )

[0005]

In the roughness meter of FIG. 9, an integrating sphere is used to inspect the total amount of scattered light, but a second hole is provided to allow specular reflected light to escape to the outside of the integrating sphere. It is provided. In such a configuration, when the scattering angle of scattered light (the angle formed by the specularly reflected light and the scattered light) is large, the scattered light hits the inner wall of the integrating sphere and is detected by the photodetector, but when the scattering angle is small, The specularly reflected light escapes from the second hole through the second hole and is not detected as scattered light. By the way, ω is the scattering angle and ν is the spatial frequency of the surface roughness of the test surface.
given that,

Equation 2 can be calculated as ω≈ν · λ / cos θ (rad). If the light source is a He-Ne laser (λ =
0.633 μm) and the incident angle θ = 30 °, the scattering angle is 1 ° when the spatial frequency is 25 (mm ⁻¹ ).
Is. Considering the luminous flux width of the incident light, it is difficult to completely separate the scattered light and the specularly reflected light. In addition, the amount of scattered light is very small on the surface to be inspected, which is a highly accurate surface,
In the integrating sphere method, the amount of light guided to the photodetector is further reduced, so it is difficult to collect scattered light, and a high-performance detector such as a photomultimeter is required. For example, in the case of an ultra-precision cut surface such as a polygon mirror, scattered light has a minute light amount of about 2% and is difficult to collect. In addition, the integrating sphere itself is expensive.

The roughness meter of FIG. 10 has a structure in which the detector (light receiving element) is scanned in a hemispherical or semicircular shape to integrate the amount of received light, which causes an increase in the size of the device and makes a measurement. It takes time and cannot measure in real time. Further, there is a problem that it is necessary to control the measurement position with high accuracy, and it is difficult to perform repeated measurement to obtain data reliability.

For this reason, the present inventor has previously filed Japanese Patent Application No. 5-489.
In No. 16, we proposed a surface roughness inspection device that is extremely simple in structure, easy to assemble, compact, lightweight, and low cost. 6 and 7 show the surface roughness inspecting apparatus, wherein 1 is the surface to be inspected of the object, 2 is a half mirror for making laser light incident on the surface to be inspected, and 3 is light reflected from the surface to be inspected. A lens 4 is an aperture plate placed on the focal plane 5 of the lens, and 6 is a mirror which is located at the focal position of the condenser lens in the aperture of the aperture plate and which deflects the specular reflection light component from the surface to be inspected. , 7 is a first light receiving element composed of a photodiode for detecting a specular reflection light component, 8 is an image plane of the surface 1 to be inspected, 9 is a second photodiode which is provided on the image plane and is composed of a photodiode for detecting a scattered light component. Light receiving elements 10, 10 are amplifiers, and 12 is a data output circuit.

In the above structure, when the parallel laser light 13 is incident on the surface 1 to be inspected through the half mirror 2, the reflected light is condensed by the lens 3. The specularly reflected light 14 of the reflected light is deflected by the mirror 6 arranged at the focal position of the lens 3 and enters the first light receiving element 7. The scattered light 15 generated due to the surface roughness of the surface 1 to be inspected passes on the focal plane 5 of the lens away from the spot of the specularly reflected light, so that it is not reflected by the mirror 6 and is reflected on the image plane 8 as the surface to be inspected. Since the image of No. 1 is formed, it is incident on all the light receiving elements 9 installed therein.

In the above structure, the focal plane 5 of the lens 3 has
A Raunhofer diffraction image of the surface to be inspected 1 (see FIG. 7) appears. Here, only the specular reflection light from the surface of the surface to be inspected 1 and the scattered light 16 a of the extremely low frequency component of the spatial frequency of the surface shape (undulation) of the surface to be inspected 1 are deflected by the mirror 6. The scattered light 16b that has been deflected by the mirror 6 and its holding portion 6a or has not contributed to the image formation of the image plane 8 is due to the high frequency component (surface roughness) of the surface shape of the surface 1 to be inspected. Therefore, by reducing the size of the opening of the mirror 6 and its holding portion 6a to a size close to the converging spot of specular reflection light, specular reflection light and scattered light can be separated. The upper limit of the spatial frequency that can be detected is determined by the aperture of the diaphragm plate 4 on the focal plane 5. In that case, the aperture of the lens 3 and the like need to be sufficiently larger than the aperture of the diaphragm plate 4.

[0010] Here, if the positive reflected light 14 receives detected by the first light receiving element 7 light quantity I _o, and light quantity I _S detected by the second light receiving element 9 for receiving the scattered light, the detected scattered light The ratio of to the total reflected light can be approximately represented by I _S / (I _S + I _o ). Further, when I _S is sufficiently small, there is no practical problem even if I _S / I _o .

FIG. 8 shows the apparatus of FIG. 6 in which a lens 17 is provided behind the lens 3 and a second light receiving element 9 is provided on the image plane 8 of the surface 3 to be inspected by the lens 3 and the lens 17. is there. In the case of this configuration, the surface to be inspected 1 and the second light receiving element 9
Although the position of 1 has a conjugate relationship with the lens 3 and the lens 17, it is easy to reduce the absolute value of the lateral magnification of this lens system, so there is an advantage that a small one can be selected.

[0012] Thus, according to the device of the above-mentioned prior application, the above-mentioned problems of the prior art can be solved, but there is still room for improvement. That is, although the half mirror 2 is used to make the laser light 13 vertically incident on the surface 1 to be inspected, with such a configuration, the half mirror 2 depends on the scattering angle of the laser light.
There will be a difference in transmittance. Further, when the support portion and the mirror support frame are provided as the structure of the mirror 6 that reflects only the specular reflection light component 14, the scattered light is partially shielded at this portion. An object of the present invention is to further solve the problems of the prior application device.

[0013]

In order to achieve the above object, the first invention is that laser light is incident on a surface to be inspected and the amount of scattered light generated by the surface roughness of the surface to be inspected is measured. In a surface roughness inspection device that measures the surface roughness of the surface to be inspected,
A lens that collects the reflected light from the surface to be inspected, a deflection unit that is arranged at the focal position of the lens and that deflects the specular reflected light component, and a first light receiving element that detects the specular reflected light component,
A second light receiving element which forms an image of the surface to be inspected and which is provided on the image surface of the imaging optical system including the lens, and which detects a scattered light component; Is configured so as to be incident obliquely.

In a second aspect based on the first aspect, the incident angle θ of the laser beam with respect to the surface to be inspected is the laser beam wavelength λ,
2θ · cosθ as maximum value fs of spatial frequency to be measured
> Λ · fs and (θ−π / 2) cos θ> λ · fs.

According to a third aspect of the present invention, in the first or second aspect of the invention, the all-transparent plate centered on the deflecting means is arranged at a predetermined angle with respect to the light reflected from the surface to be inspected. Is characterized by.

In a fourth aspect based on the third aspect, the deflecting means of the total transparent plate is a total reflection film that reflects specularly reflected light, and the scattered light transmitting portion other than the total reflection film has angle dependence. The anti-reflection film is provided.

A fifth aspect of the present invention is a surface roughness measuring method for measuring a surface roughness of a surface to be inspected by injecting a laser beam onto the surface to be inspected and measuring an amount of scattered light generated by the surface roughness of the surface to be inspected. In the inspection device, a lens that focuses the light reflected from the surface to be inspected,
Deflection means disposed between the lens and its focal position for deflecting the specular reflection light component, transmission preventing means for preventing transmission of the specular reflection light component at the focal position, and first detecting the specular reflection light component. 1 and a second light receiving element for detecting a scattered light component provided on the image surface of the imaging optical system including the lens for forming an image of the surface to be inspected, It is characterized in that the laser beam is obliquely incident on the inspection surface.

In a sixth aspect based on the fifth aspect, the deflecting means is a half mirror, and the transmission preventing means is a transmission preventing pattern provided at the center of a transparent plate provided perpendicularly to the optical axis. It is characterized by

[0019]

In the apparatus of the first to fourth inventions, the laser light is obliquely incident on the surface to be inspected, and the first light receiving element outputs the output signal according to the specular reflection light component to the second light receiving element. Generates an output signal corresponding to the scattered light component, and the surface roughness of the surface to be inspected is obtained from these signals. In the devices of the fifth and sixth inventions, the specular reflection light component is deflected by the deflecting means arranged between the lens and its focal position, and the transmission of the specular reflection light component is prevented at the focal position.

[0020]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows an embodiment of the surface roughness inspection apparatus of the present invention. The same reference numerals as those in FIG. 6 represent the same or similar apparatuses. In particular, in the apparatus of this embodiment, the laser beam 13 is oblique to the surface 1 to be inspected. The half mirror 2 is not necessary because the light is incident. In this case, it is preferable to set the incident angle θ of the laser light according to the following equation.

Equation 3] 2θ · cosθ> λ · fs ( θ-π / 2) cosθ> λ · fs wavelengths where lambda is the laser beam, fs is the maximum value of the spatial frequency to be measured (e.g., fs = 500 (mm ^{- 1} ) degree)

Next, the grounds for establishing the above equation will be described. In the present invention, FIG. 11 shows an angular relationship between incidence and reflection of laser light on the surface to be inspected. Here, when the incident angle of incident light on the surface to be inspected: θ (rad) and the spatial frequency of surface roughness of the surface to be inspected: ν (1 / mm), the scattering angle of scattered light (from specularly reflected light to scattered light Angle ω (rad) is

Ω = ν · λ / cos θ (0 ≦ ν ≦ f _s (1). ± 1st order light is generated as scattered light. Surface roughness is measured by the surface roughness inspection device of the present invention. In order to do this, let ω _max be the angle of the scattered light to be measured (detected),

Ω _max = f _s · λ / cos θ (2) Therefore, the scattering angle of the optical system is -ω _max ~ ω
It is necessary to detect all scattered light in the _max range.

Incidentally, with respect to the scattered light of the + 1st-order light in FIG. 11, if the scattered light is in the direction in which it overlaps with the incident light, the scattered light cannot be detected. Therefore,

It is necessary that ω _max <2θ (3). In addition, the scattered light of the −1st order light cannot be measured when it is parallel to the surface of the test surface,

It is necessary that ω _max <(π / 2) −θ (4).

Substituting equation (2) into equation (3), f _s · λ <2θ · cos θ (5) Substituting equation (2) into equation (4), f _s · λ <((π / 2 ) −θ) cosθ (6), and the above equation holds.

FIG. 2 shows another embodiment of the present invention in which a transparent plate 21 is provided so as to be tilted with respect to the optical axis with the focal point of the lens 3 as the center. The transparent plate 21 is configured, for example, as shown in FIG.
The total reflection film 2 that reflects the specularly reflected light component 14 is provided in the center thereof.
1a is provided by a predetermined mask pattern, and the scattered light transmitting portion other than the total reflection film has an angle-dependent antireflection film 21.
b is provided.

FIG. 4 shows another embodiment of the present invention, in which 22 is a half mirror as a deflecting means for the specular reflection light component 14, and the half mirror 22 is provided between the lens 3 and its focal position. ing. The specular reflection light component 14 reflected by the half mirror 22 is focused on the light receiving element 7 by the lens 18. A transparent plate 23 is provided perpendicular to the optical axis with the focal point of the lens 3 as the center. As shown in FIG. 5, the transparent plate 23 is provided with a transmission preventing pattern (light absorbing film or the like) 23a at its central portion (focal point position) and prevents reflection of scattered light components vertically incident on other portions. A film 23b is provided.

[0026]

As described above, according to the present invention, the total reflection light from the surface to be inspected is divided into the specular reflection light component and the scattered light component, which are detected by the light receiving element, and the laser light is emitted. Since the light is incident on the surface to be inspected at an angle, it is possible to eliminate the need for the half mirror used in the prior application device to make the laser light incident vertically on the surface to be inspected. It is not necessary to consider the transmittance distortion due to the measurement, reliable measurement is possible, and the scattered light component due to the spatial frequency f _s reaches the second light receiving element without any trouble. Further, since the scattered light component is not blocked by the supporting portion of the mirror as the deflecting means, it is possible to effectively use the minute scattered light amount. Further, even when the deflecting means is formed of a reflective film, instability such as reflectance and transmittance is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of the present invention.

FIG. 3 is a configuration diagram of a transparent plate in the embodiment of FIG.

FIG. 4 is a schematic configuration diagram showing still another embodiment of the present invention.

5 is a configuration diagram of a transparent plate in the embodiment of FIG.

FIG. 6 is a configuration diagram of a surface roughness inspection device of the prior application.

FIG. 7 is an explanatory diagram of a Raunhofer diffraction image that appears on the focal plane.

FIG. 8 is a configuration diagram of another surface roughness inspection apparatus of the prior application.

FIG. 9 is an explanatory diagram of a configuration of a conventional surface roughness meter.

FIG. 10 is an explanatory diagram of a configuration of another conventional surface roughness meter.

FIG. 11 is a diagram showing an angular relationship between incidence and reflection of laser light on a surface to be tested in the present invention.

[Explanation of symbols]

 1 Test Surface of Subject 2 Half Mirror 3 Condenser Lens 4 Aperture Plate 5 Focal Plane 6 Mirror 6a Mirror Holder 7 First Light-Receiving Element 8 Image Surface 9 Second Light-Receiving Element 13 Laser Light 14 Specular Reflection Light Component 15 Scattered light component 21,23 Transparent plate 22 Half mirror

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[Procedure amendment]

[Submission date] July 27, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

In a second aspect based on the first aspect, the incident angle θ of the laser beam with respect to the surface to be inspected is the laser beam wavelength λ,
2θ · cos as the maximum value fs of the spatial frequency to be measured
It is characterized in that θ> λ · fs and ( π / 2−θ ) cos θ> λ · fs.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

[0020]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows an embodiment of the surface roughness inspection apparatus of the present invention. The same reference numerals as those in FIG. 6 represent the same or similar apparatuses. In particular, in the apparatus of this embodiment, the laser beam 13 is oblique to the surface 1 to be inspected. The half mirror 2 is not necessary because the light is incident. In this case, it is preferable to set the incident angle θ of the laser light according to the following equation.

Equation 3] 2θ · cosθ> λ · fs ( π / 2θ) eosθ> λ · fs wavelengths where lambda is the laser beam, fs is the maximum value of the spatial frequency to be measured (e.g., fs = 500 (mm ^{- 1} ) degree)

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

Next, the grounds for establishing the above equation will be described. In the present invention, FIG. 11 shows an angular relationship between incidence and reflection of laser light on the surface to be inspected. Here, when the incident angle of incident light on the surface to be inspected: θ (rad) and the spatial frequency of the surface roughness of the surface to be inspected: ν (1 / mm), the scattering angle of scattered light (from specularly reflected light to scattered light Up to) ω (rad) is

Ω = ν · λ / cos θ (0 ≦ ν ≦ f _s ) (1) As the scattered light, ± first-order light is generated. When the angle of scattered light measured (detected) to measure the surface roughness with the surface roughness inspection device of the present invention is ω _max ,

Is a [number 5] _{ω max = f s · λ /} cosθ (2). Therefore, as an optical system, the scattering angle is -ω _max ~
It is necessary to detect all scattered light in the range of ω _max .

Claims (6)

[Claims] 1. A surface roughness inspecting apparatus for measuring a surface roughness of a surface to be inspected by injecting a laser beam onto the surface to be inspected and measuring an amount of scattered light generated by the surface roughness of the surface to be inspected, A lens that collects the reflected light from the surface to be inspected, a deflection unit that is arranged at the focal position of the lens and that deflects the specular reflected light component, a first light receiving element that detects the specular reflected light component, and A second light receiving element for forming an image of the surface to be inspected, the second light receiving element being provided on the image surface of the imaging optical system including the lens, and detecting a scattered light component; A surface roughness inspection device characterized in that it is configured to be incident obliquely. 2. The incident angle θ of the laser beam with respect to the surface to be inspected
Is the laser light wavelength λ, the maximum value f of the spatial frequency to be measured
_s as 2θ · cosθ> λ · f _s and (θ-π / 2) cosθ
> Λ · f _s , wherein:
Surface roughness inspection device according to. 3. The surface according to claim 1, wherein an all-transparent plate having the deflecting means arranged at the center is arranged at a predetermined angle with respect to the reflected light from the surface to be inspected. Roughness inspection device. 4. The deflecting means of the totally transparent plate is a total reflection film that reflects specularly reflected light, and an angle-dependent antireflection film is provided in a scattered light transmitting portion other than the total reflection film. The surface roughness inspection device according to claim 3. 5. A surface roughness inspection apparatus for measuring the surface roughness of a surface to be inspected by injecting a laser beam onto the surface to be inspected and measuring the amount of scattered light generated by the surface roughness of the surface to be inspected, A lens that focuses the reflected light from the surface to be inspected, a deflection unit that is arranged between the lens and the focal position thereof and that deflects the specular reflected light component, and prevents transmission of the specular reflected light component at the focal position. A scattered light component provided on an image plane of an image forming optical system including a transmission preventing unit, a first light receiving element for detecting the specular reflection light component, and the lens for forming an image of the surface to be inspected is provided. A second light receiving element for detecting, and is configured so that the laser light is obliquely incident on the surface to be inspected. 6. The deflecting means is a half mirror, and the transmission preventing means is a transmission preventing pattern provided at the center of a transparent plate provided perpendicularly to the optical axis. Surface roughness inspection device.