JP2588679Y2 - Surface roughness inspection device - Google Patents

Description

[Detailed description of the invention]

[0001]

The present invention relates to a laser beam incident on a surface to be measured, which is a high-precision surface, and the amount of scattered light generated by the total amount of reflected light and the surface roughness of the surface to be reflected. The present invention relates to an improvement of a surface roughness inspection apparatus for measuring the surface roughness of a surface to be measured by measuring the surface roughness of the surface to be measured by measuring the ratio of the two.

[0002]

2. Description of the Related Art Conventionally, a roughness meter shown in FIGS. 4 and 5 has been known as this type of surface roughness inspection apparatus.

In the roughness meter shown in FIG. 4, an integrating sphere is brought into contact with and fixed to a 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. 2nd ball
Then, only the scattered light is detected by the integrating sphere by letting it out of the integrating sphere through the hole, and compared with the amount of incident light to determine the surface roughness.

In the roughness meter shown in FIG. 5, a laser beam is incident on a surface to be measured, and the distribution of the amount of regular reflection light and scattered light of the reflected light is measured by scanning a photodetector, and the total reflection light amount is measured. By calculating the amount of scattered light, the surface roughness is determined. In any case, the total quantity of reflected light I _T Les <br/> laser light of wavelength λ incident at an angle θ to the test _surface, when the amount of scattered light I _S generated by the surface roughness of the test surface, The rms value σ of the surface roughness is
As a known relationship,

(Equation 1) Required from.

[0005]

In the roughness meter shown in FIG. 4, an integrating sphere is used to inspect the total amount of scattered light. In the case of the roughness meter shown in FIG. A second hole is provided for escape to In such a configuration, if the scattering angle of the scattered light (the angle between the regular reflection light and the scattered light) is large,
The scattered light hits the inner wall of the integrating sphere and is detected by the photodetector. However, when the scattering angle is small, the scattered light escapes from the second hole through which the specularly reflected light escapes and is not detected as scattered light. By the way, if the scattering angle is ω and the spatial frequency of the surface roughness of the test surface is ν,

(Equation 2) Can be calculated as Assuming that 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 ) . Considering the light beam width of the incident light, it is difficult to completely separate the scattered light and the specularly reflected light. Furthermore,
Although the amount of scattered light is very small on the surface to be measured, which is a high-precision surface, the amount of light guided to the photodetector is further reduced in the integrating sphere method. Is required. For example, in the case of an ultra-precision cut surface such as a polygon mirror, the amount of scattered light is a very small amount of about 2%, and is difficult to collect. In addition, the integrating sphere itself is expensive.

The roughness meter shown in FIG. 5 has a configuration in which a detector (light receiving element) is scanned in a hemispherical or semicircular shape and the amount of received light is integrated. It is time consuming and does not allow real-time measurements. In addition, there is a problem that it is necessary to control the measurement position with high accuracy, and it is difficult to perform repeated measurements to obtain data reliability.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized, light-weight, low-cost surface roughness inspection apparatus which is extremely simple in structure and easy to assemble.

[0008]

According to the present invention, a laser beam is incident on a surface to be measured which is a high-precision surface, and the reflected light is scattered light generated by the total amount of reflected light and the surface roughness of the surface to be measured. In a surface roughness inspection device that measures the surface roughness of the surface to be measured by measuring the amount of light and calculating the ratio between the two, a lens that collects the reflected light from the surface to be measured and a lens that focuses the light A deflecting unit arranged to deflect the specular reflected light component, a first light receiving element for detecting the specular reflected light component, and an imaging optical system including the lens for forming an image of the surface to be measured . A second light receiving element for detecting a scattered light component provided on the image plane is provided.

[0009]

According to the above construction, the output of the first light receiving element for detecting a specularly reflected light component on the surface to be inspected and the second light receiving device for detecting a scattered light component provided on the image surface of the surface to be inspected are provided. The surface roughness of the test surface is determined from the output of the element.

[0010]

1 and 2 show an embodiment of the present invention. 1 and 2, reference numeral 1 denotes a surface to be inspected of a subject;
Is a half mirror for allowing laser light to be incident on the surface to be measured, 3 is a lens for condensing light reflected from the surface to be measured, 4 is a diaphragm plate located on the focal plane 5 of the lens, and 6 is an aperture of the diaphragm plate. So,
A mirror disposed at the focal position of the condenser lens for deflecting a specularly reflected light component from the surface to be measured; 7, a first light receiving element comprising a photodiode for detecting the specularly reflected light component; A surface 9 is a second light receiving element provided on the image plane and composed of a photodiode for detecting a scattered light component.
0 and 11 are amplifiers, and 12 is a data output circuit.

In the above configuration, when the parallel laser light 13 enters the surface 1 to be measured via the half mirror 2, the reflected light is condensed by the lens 3. Of the reflected light, the regular reflection light 14 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 test surface 1 passes on the lens focal plane 5 at a position distant from the spot of the specularly reflected light. Image one image
Therefore, all light is incident on the light receiving element 9 installed there.

In the above configuration, the focal plane 5 of the lens 3 is
A Raunhofer diffraction image of the test surface 1 (see FIG. 2) appears. Here, only the specularly reflected light from the surface of the test surface 1 and the scattered light 16 a of the extremely low frequency component of the spatial frequency of the surface shape (undulation) of the test surface 1 are deflected by the mirror 6. The scattered light 16b that has not been deflected or deflected by the mirror 6 and its holding portion 6a and contributed to the image formation on the image plane 8 is due to a high-frequency component (surface roughness) of the surface shape of the test surface 1. 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 the regular reflection light , it becomes possible to separate the regular reflection light and the scattered light. Note that the upper limit of the detectable spatial frequency is determined by the aperture of the diaphragm plate 4 in the focal plane 5. In that case, the aperture and the like of the lens 3
It is necessary that the opening is sufficiently larger.

Here, if the light amount I _o detected by the first light receiving element 7 receiving the specularly reflected light 14 and the light amount I _S detected by the second light receiving element 9 receiving the scattered light, the detected scattered light Is approximately represented by I _S / (I _S + I _o ). Further, if I _S is sufficiently small, I _S / I _o
There is no practical problem.

FIG. 3 shows another embodiment of the present invention. This embodiment is different from the above embodiment in that a rear portion of the lens 3 is provided.
A lens 17 is provided, and a surface to be inspected by the lens 3 and the lens 17 is provided.
A second light receiving element 9 is provided on one image plane 8 . In the case of this configuration, the positions of the test surface 1 and the second light receiving element 9 are
The lens 3 and the lens 17 form a conjugate relationship.
It is easy to reduce the absolute value of the horizontal magnification of the lens system
In, there is an advantage that can be selected smaller.

[0015]

As described above, since the total reflection from the surface to be inspected is divided into specular reflection and scattered light, and each is detected by the light receiving element, the following effects can be obtained. (1) It is possible to provide a small and light-weight and low-cost surface roughness inspection apparatus which is extremely simple in structure and easy to assemble. (2) Since the scattered light detection is performed on the image plane of the surface to be detected, all the scattered light transmitted through the outer periphery of the diaphragm and the mirror and its holding portion without being shaken can be easily detected. (3) Real-time measurement is possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a surface roughness inspection apparatus showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a Raunhofan diffraction image appearing on a focal plane.

FIG. 3 is a configuration diagram of a surface roughness inspection apparatus showing another embodiment of the present invention.

FIG. 4 is a diagram illustrating the configuration of a conventional surface roughness meter.

FIG. 5 is a diagram illustrating the configuration of another conventional surface roughness meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test surface of a test object 2 Half mirror 3 Condensing lens 4 Aperture plate 5 Focal plane 6 Mirror 6a Mirror holding part 7 First light receiving element 8 Image plane 9 Second light receiving element 10, 11 Amplifier 12 Data output circuit 13 Parallel laser light 14 Regular reflection light 15 Scattered light 16a Scattered light as extremely low frequency component 16b Scattered light as high frequency component (surface roughness) 17 Second lens

Claims (1)

(57) [Scope of request for utility model registration] 1. A surface roughness inspection apparatus for measuring a surface roughness of a test surface by irradiating a laser beam to the surface to be measured and measuring an amount of scattered light generated by the surface roughness of the test surface. A lens that condenses the reflected light from the surface to be measured, a deflecting unit that is disposed at a focal position of the lens and deflects the specular reflected light component, a first light receiving element that detects the specular reflected light component, Imaging optics including the lens for forming an image of a test surface
A second light receiving element provided on an image plane of the system for detecting a scattered light component.