JP2008002891A - Surface state inspection device and surface state inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a surface state inspection device capable of highly precisely and rapidly detecting local non-uniformity of about several millimeters with respect to a rough surface having roughness of about several ten μm sufficiently larger than the wavelength of incident light and a difinite or above area as the rough surface of matter, and to provide a surface state inspection method. <P>SOLUTION: The surface state inspection device has a laser beam source for irradiating the surface of an inspection target and an optical system for condensing a part of the optically diffracted image from the surface of the inspection target and is constituted so as to measure the uniformity of the surface roughness of the inspection target from a change in the optically diffracted image intensity distribution from the surface of the inspection target. The incident light is incident as S polarized light at a predetermined incident angle and the diffracted light to the vicinity of the direction of a predetermined angle θ<SB>S</SB>in the incident surface from a normal line is condensed by the optical system with the number NA of apertures and the angle θ<SB>S</SB>when the change of light quantity is measured by a light intensity detector is properly set through the light flux restricting means installed in the vicinity of the near axis image surface of the optical system. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface state inspection apparatus and a surface state inspection method, and is suitable for measuring, for example, the uniformity of a rough surface (roughness) of a cylindrical surface with high accuracy.

  Conventionally, as a method of detecting the presence or absence of minute defects (scratches or foreign matter) on the surface of an object, the laser beam is focused on a fine spot, irradiated onto the surface to be inspected, and the scattered light generated from that spot A method for detecting (light diffracted light) is known.

  In addition, as a method for detecting the roughness state of the rough surface of the object surface, a method for obtaining a cross-correlation function of speckle diffraction image distribution from the object surface when the wavelength or angle of incident light is changed, or an interferometer There is known an interferometer method for detecting a phase difference by using (Patent Document 1).

  In addition, inspection apparatuses that measure the surface roughness using the characteristics of the surface material of the measurement object are known (Patent Documents 2 and 3).

On the other hand, a scanning measurement method is known in which a surface state is inspected by scanning a surface having a certain area or more with light. In this method, a surface to be measured is scanned and inspected by a combination of a deflector and a scanning optical system.
Japanese Patent Laid-Open No. 5-52540 JP 11-295240 A JP 2000-081325 A

  In recent years, as a defect present on the surface of an object, local unevenness of around millimeters has occurred on a rough surface having a roughness (irregularity) of about several tens of microns, sufficiently larger than the wavelength of incident light, and having a certain area or more. As a result, a device capable of detecting at high speed is demanded.

  At this time, if the object surface is irradiated with a fine spot light of several to several tens of microns, the diffraction image is disturbed, and it is difficult to detect a minute amount therefrom.

  The method using the speckle correlation function described above is premised on that the surface roughness is shorter than the wavelength of incident light. For this reason, it is not practical to obtain a correlation function at a large number of points in each of a wide range because of time limitations.

  Of the measurement methods described above, the interferometer method requires a complicated and precise optical system. The speckle pattern generated by the visible laser beam originating from an essentially rough surface has a random phase with a standard deviation greater than 2π. For this reason, the phase difference that is usually obtained does not contain useful information regarding the rough surface profile.

  Each of these measuring methods requires branching means for branching each polarization component, or measuring means for measuring at a plurality of positions on the surface to be inspected, and an apparatus comprising each member for detecting light and judging the result. The whole tends to be complicated.

  Although the scanning measurement method is excellent at high-speed and high-precision scanning, the entire apparatus is complicated, and the incident angle with respect to the irradiation point differs depending on the scanning angle of view. It becomes difficult.

  For this reason, it is difficult to accurately detect the relative change amount depending on the position on the surface to be scanned. If a telecentric optical system is used as the detection optical system, it is possible to make the incident angle constant, but an optical component having the same size as that of the measurement object is required, and the entire apparatus becomes large.

  The present invention has a roughness of several tens of microns that is sufficiently larger than the wavelength of incident light as a rough surface of the object surface, and can detect a rough surface having a certain area or more quickly with high accuracy. The object is to provide a surface condition inspection apparatus and a surface condition inspection method.

The surface condition inspection apparatus of the present invention is
Light source means;
First light flux limiting means for limiting a light beam diameter of light emitted from the light source means;
A detection optical system that passes through the first light flux limiting means and has S-polarized light incident on the surface to be inspected, and detects light diffracted light generated from the surface to be inspected;
A second light beam limiting means disposed on the condensing surface of the detection optical system for limiting the diameter of the passing light beam;
A photodetector for detecting light that has passed through the second light flux limiting means;
A surface condition inspection apparatus for inspecting the roughness of the surface to be inspected using a signal from the photodetector,
The wavelength of light from the light source means is λ,
In the incident surface when the light from the light source means is incident on the surface to be inspected, the light beam diameter of the incident light beam on the surface to be inspected is Dp,
The effective diameter on the light incident side of the detection optical system is W,
When the distance from the conjugate point through the detection optical system to the second light beam limiting means to the entrance pupil of the detection optical system is L λ / (Dp / L) ² <W (1)
It is characterized by satisfying the following conditions.

In addition, the surface condition inspection method of the present invention,
An irradiation step in which light having a wavelength λ in parallel and S-polarized state is incident on a part of the cylindrical surface from an incident surface including a generatrix of the cylindrical surface and a central axis of the cylindrical surface;
After a part of the light diffraction image generated from the cylindrical surface is condensed by the detection optical system, the light is detected by the light detector through the light beam limiting means for limiting the light beam disposed at the light collection point of the detection optical system. An object surface inspection method including an inspection step of determining a change in intensity distribution of a diffraction image and then inspecting a surface state of the cylindrical surface;
In the incident surface, the average value of the frequency in the incident surface of the size of the surface irregularities in the irradiation region on the cylindrical surface is represented by K _j ,
Dp, the diameter of the light beam when entering the cylindrical surface
The effective diameter on the light incident side of the detection optical system is W,
L is the distance from the conjugate point through the detection optical system to the light beam limiting means to the entrance pupil position of the detection optical system.
With respect to a plurality of diffracted light distributions measured in advance from a plurality of surfaces having different average values k _j, the diffraction angle with respect to the normal line at the irradiation point that maximizes the relative intensity change is θ _m , and the relative intensity change is the largest. The incident angle of light corresponding to the diffraction angle θ _m is θ _i , the light is incident on the irradiation point at the incident angle θ _i , and the detection optical system collects light diffracted light in the angle θ _S direction with respect to the irradiation point. Light
At this time, λ / (Dp / L) ² <W (1)
1 / k _j <Dp (2)
θ _S −tan ⁻¹ {(W / 2) / L} <θ _m <θ _S + tan ⁻¹ {(W / 2) / L}
(3)
It is characterized by satisfying.

In addition, the surface condition inspection method of the present invention is:
An irradiation step in which light having a wavelength λ in parallel and S-polarized state is incident on a part of the cylindrical surface from an incident surface including a generatrix of the cylindrical surface and a central axis of the cylindrical surface;
A part of the light diffraction image generated from the cylindrical surface is condensed by a detection optical system having a numerical aperture NA, and then a light detector through a light beam limiting means for limiting a light beam arranged at a condensing point of the detection optical system. A surface state inspection method including an inspection step of detecting and detecting a change in intensity distribution of the light diffraction image, and then inspecting the surface state of the cylindrical surface,
When the diffracted light distribution in the angle θ direction from two points with different roughness and density on the cylindrical surface is I _A (θ), I _B (θ), the relative intensity change | I _B (θ) / I _A (θ) -1 |
There becomes largest diffraction angle theta _m, when the _i the angle of incidence of light theta when the diffraction angle theta _m relative change in intensity of the diffracted light distribution is maximized, the light is incident at an incident angle theta _i the irradiation point The detection optical system collects light diffracted light in the direction of angle θ _{S with} respect to the irradiation point,
At this time, θ _m −sin ⁻¹ (NA) <θ _s <θ _m + sin ⁻¹ (NA) (4)
It is characterized by satisfying.

  According to the present invention, the rough surface of the object surface has a roughness of several tens of microns that is sufficiently larger than the wavelength of incident light, and the rough surface having a certain area or more has a local nonuniformity of around millimeters. Can be detected quickly with high accuracy.

  FIG. 1 is a side view of an essential part of a surface condition inspection apparatus according to a first embodiment of the present invention. FIG. 2 is an explanatory view between the members shown in FIG. FIG. 3 is a top view of an essential part of the surface condition inspection apparatus according to the first embodiment.

  1 to 3, reference numeral 1 denotes an object to be inspected, which has a cylindrical shape. A part of the cylindrical surface (cylindrical surface) is the surface to be inspected 1a.

  Reference numeral 2 denotes a light source means, which is composed of a He—Ne laser. Reference numeral 3 denotes scattered light (light diffracted light) generated from the test surface (irradiation point) 1 c of the test object 1. Reference numeral 4 denotes a light flux limiting means (first light flux limiting means) (slit) for limiting the light 2a from the light source means 2. Reference numeral 5 denotes specularly reflected light when the light 2a from the light source means 2 is specularly reflected by the test surface 1a.

  Reference numeral 8 denotes a detection optical system having a numerical aperture NA, which condenses a part of scattered light (light diffracted light) generated from the surface 1a to be measured on the light flux limiting means (second light flux limiting means) 6.

  The test surface 1a and the light beam limiting means 6 are in a conjugate relationship or a substantially conjugate relationship.

  The light beam limiting means 6 limits the light passing through the detection optical system 8. Reference numeral 7 denotes a photodetector that detects light that has passed through the light beam limiting means 6.

The object to be inspected 1 in this embodiment has a cylindrical shape with a diameter of 30 mm (φ30 mm) and a length in the axial direction (X direction) of 400 mm, and the average value k _j of the roughness frequency of the outer surface of the cylindrical circle is 1. / (50 μm).

The light source means 2 emits light (laser) 2a having a wavelength λ of 632.8 nm, a light amount of 5 mW, and an incident beam diameter of φ1 mm (relative intensity 13.5%) on the object 1 to be inspected. The light 2 a from the light source means 2 is incident on the surface 1 a to be inspected 1 a through the slit 4 at an incident angle θ _i = 70 °.

  At this time, the spread angle of the light 2a is about 0.02 °, and can be regarded as a substantially parallel beam. Here, it is assumed that the size d of the smallest abnormal part that can detect the rough surface on the object 1 is 2 mm. The irradiation area (irradiation area) Dp in the X direction (axial direction) of the illumination light 2a to the inspection object 1 is 2 mm.

At this time, a part of the diffracted light 3 from the irradiation point 1c is emitted at an angle of θ _S = 15 ° in the regular reflection direction from the normal line 1b of the rough surface.

  In this embodiment, the light is limited by the detection optical system 8 having a focal length of 12 mm and an effective diameter W = 10 mm (NA 0.384) in which a pupil (incidence pupil) is installed at a distance L = 20 mm from the irradiation point 1c. It is collected in the photodetector 7 via the means 6. The magnification β of the condensing optical system 8 is 1.5.

  The light beam limiting means 8 is disposed on the image plane of the detection optical system 8 and its opening width H is H = 1.5 mm. In order to prevent stray light, it is desirable that light is shielded between the detection optical system 8 and the photodetector 7.

  FIG. 13 shows data obtained by converting the results measured in this example into a two-dimensional image. When observed with the naked eye or taken with an imaging means, it can be seen that abnormal portions are clearly obtained with respect to subtle differences in surface roughness that are very difficult to see.

  In this embodiment, the cylindrical surface (inspected surface) 1a of the inspection object 1 is illuminated with light (beam) 2a from the light source means 2. A part of a light diffraction image from the cylindrical surface 1a is detected by a detection optical system 8 having a predetermined NA. At this time, the uniformity of the roughness of the cylindrical surface 1a having a roughness sufficiently larger than the wavelength of the light 2a is measured from the change in the intensity distribution (light quantity) of the light diffraction image from the cylindrical surface 1a. ing.

The light from the light source means 2 is a substantially parallel beam and is incident in an S-polarized state at an angle θ _i with respect to the normal 1b at the irradiation point 1c, with the plane (XY plane) including the generatrix of the cylindrical surface and the central axis as the entrance plane is doing.

In order to make it incident with S-polarized light, for example, there is a method using a polarizing plate. Diffuse reflected light that diffuses in the direction of the angle θ _s from the normal line 1 b in the incident surface is collected by the detection optical system 8. Then, the light quantity change is measured by the photodetector 7 through the light beam limiting means 6 disposed in the vicinity of the paraxial image plane of the detection optical system 8.

  The roughness uniformity of the surface 1a is obtained based on the signal from the photodetector 7 obtained at this time.

Here, λ is the wavelength of the light 2a from the light source means 2.
k _j is an average value of the frequency in the surface direction of the unevenness of the surface in the irradiation area Dp of the light 2a.
Let Dp be the projected dimension of the incident beam diameter of the light 2a (the diameter at which the normalized intensity is 13.5%) in the direction of the cylindrical surface on the surface 1a.
L is a distance from the pupil position of the detection optical system 8 to the irradiation point 1c on the surface of the object 1 to be inspected.
Let W be the effective diameter of the detection optical system 8.
Let θ _{s be} the angle of diffusely reflected light from the normal 1b in the incident plane.
Let θ _m be the diffraction angle with respect to the normal 1b at the irradiation point 1c, where the relative intensity change is greatest for a plurality of diffracted light distributions measured in advance from a plurality of surfaces having different average values k _j .

Here, when the diffracted light distribution in the angle θ direction from two points with different roughness and density on the cylindrical surface is I _A (θ), I _B (θ), the relative intensity change PL is PL = | I _B (Θ) / I _A (θ) -1 | (5)
It is. The diffraction angle θ _m is an angle at which the value of the relative intensity change PL is the largest.

The incident angle θ _i is the beam incident angle at the diffraction angle θ _{m at which} the relative intensity change PL is the largest.

At this time, λ / (Dp / L) ² <W (1)
1 / k _j <Dp (2)
θ _S −tan ⁻¹ {(W / 2) / L} <θ _m <θ _S + tan ⁻¹ {(W / 2) / L}
(3)
1 or more of these are satisfied.

Alternatively, light is incident on the irradiation point at an incident angle θ _i , and the NA detection optical system 8 condenses the light diffracted light in the angle θ _S direction with respect to the irradiation point.

At this time, θ _m −sin ⁻¹ (NA) <θ _s <θ _m + sin ⁻¹ (NA) (4)
Meet.

  If each member is set so as to satisfy the conditional expressions (1), (2), (3) or the conditional expression (4), it can be applied to regions of different roughness in the rough surface of the inspected surface 1a. The diffraction pattern when a highly coherent laser beam is incident changes significantly compared to the diffraction pattern from other uniform portions.

In this embodiment, by a large diffraction angle theta _m of particular change therein is measured to be included in the acceptance angle theta _s in the condensing optical system 8, slight difference in the roughness of the inspected surface 1a even more It is detected with high sensitivity (high accuracy).

At this time, the size of the irregularities on the surface to be inspected 1a is sufficiently larger than the wavelength of the light 2a. For this reason, the irradiated region (projection in the cylindrical surface generatrix direction (X direction) on the surface of the beam diameter of the light 2a) Dp is equal to or less than 1 / k _j indicating the order of the surface direction of the unevenness. A small number of irradiated irregularities work like a curved mirror. As a result, as shown in FIG. 4, the pattern of the diffraction image (speckle image) 41 is greatly disturbed.

It is preferable to obtain a diffraction image as shown in FIG. Therefore, in order to reduce the particle size of the speckle and make the entire envelope smooth and stable, it is necessary to irradiate a region including a certain number of irregularities on the surface to be inspected 1a. That is, it is necessary to irradiate the light 2a with a region Dp (1 / k _j <Dp) sufficiently larger than 1 / k _j indicating the size of the unevenness.

Further, the speckle particle size is represented by λ / (Dp / L) ² where L is the distance from the position of the diffraction image shown in FIG. Must be at least this particle size.

  As the particle size is smaller than the opening W, the overall diffraction image distribution becomes smoother and the stability of measurement increases.

  When the beam diameter is increased to some extent, there is a method in which a convergent or divergent beam is used, and the position of the rough surface of the surface to be inspected 1a is adjusted to a position where an appropriate irradiation spot is formed. In that case, the wavefront of the irradiated beam becomes a wavefront having a larger curvature as the beam waist diameter is smaller. At this time, the geometric incident angle cannot be made constant in the irradiation region Dp.

  Therefore, it is desirable to set the beam waist diameter to a value that is equivalent to the irradiation diameter of the light 2a, that is, a value that provides a substantially parallel beam.

  As a result, the incident beam 2a becomes a plane wave, and a constant incident angle can be ensured throughout the irradiation region Dp, and diffracted light with different conditions can be prevented from being generated.

  Regarding the incident direction, it is assumed that the rough surface to be inspected as a surface to be inspected is not a flat surface but a cylindrical surface as shown in FIG. At this time, when the light 2a is incident so that the incident surface is a surface perpendicular to the axis of the cylindrical surface 91, the cylindrical surface 91 has a function of a convex mirror, and the diffraction pattern is greatly spread in the incident surface.

Further, the incident angle θ _i varies depending on the incident position of the light 2a on the irradiation surface 1a, and the diffracted light under different conditions is mixed and the detection sensitivity is lowered. For this reason, as shown in FIG. 7, the incident surface is set to coincide with the plane 102 including the generating line 101 and the axis 102 of the cylindrical surface, and the incident angle is constant in the entire irradiation area Dp of the light 2a in the incident surface 102. To be.

  Furthermore, in order to ensure the S / N of the measurement value in the photodetector 7, the polarization state of the incident beam is S-polarized light that increases the absolute value of the reflectance.

  For the detection direction, as an example of examining the change in roughness from the change in diffraction image distribution using the same method, the entire area of the diffraction distribution is scanned with a photodetector, and the spatial distribution corresponding to the spatial low frequency and the spatial high frequency are scanned. There is an example in which the light intensity is measured at two points of the section and obtained from the ratio (FIG. 8, 18th SICE Scientific Lecture Proceedings p157).

In this method, there is a case where there is no change or a very small result depending on how the diffracted light distribution shape is changed. On the other hand, in the present embodiment, the condition that the diffraction angle θ _{m at} which the sensitivity is maximized when the state of the rough surface changes is included in the capturing angle θ _s of the condensing optical system 8, that is, the conditional expression ( 3) or a specific one-direction θ _S that satisfies the conditional expression (4).

As shown in FIG. 9, the diffraction angle θ _m is a relative intensity change (diffracted light) with respect to a plurality of diffracted light distributions measured in advance at a certain beam incident angle condition with respect to a plurality of surfaces having different average values k _j. Intensity) is the diffraction angle at which PL is the largest. As shown in FIG. 11, the incident angle θ _i is determined so that the relative intensity change PL at the diffraction angle θ _m becomes the largest.

  Next, a second embodiment of the present invention will be described.

In this embodiment, when the angle θs of the diffuse reflected light is the diffuse reflected light intensity E (k _j , θ _S ) to the angle, k ₁ <k ₂ ,
E (k ₁ , θ _S ) <E (k ₂ , θ _S )
Each member is set to have such an angle.

Under the conditions of this embodiment, as shown in FIG. 9, when the average value k _j of the unevenness frequency is larger (when the unevenness density is “dense”, the abnormal part) I _B (θ) is small. Compared to (normal part) I _A (θ), the diffraction distribution represented by the Fourier transform of the concavo-convex surface has a lower spatial low-frequency component (a direction close to the regular reflection direction) and a stronger spatial high-frequency component. Become.

  At this time, as a relative change amount, a high-frequency component having a small absolute amount becomes larger, and even a slight change in the rough surface state can be detected with high sensitivity.

In FIG. 9, I _A (θ) is a diffracted light distribution when the roughness is rough (normal portion and the average value K _j is small).

I _B (θ) is a diffracted light distribution when the roughness is dense (abnormal part and average value K _j is large).

The angle θ _s when detected by the detection optical system 8 is I _B (θ) / I _A (θ) <1.
It is an angle that satisfies

The relative intensity change PL in the above-described conditional expression (5) is as shown in FIG. 10. Relative intensity change PL = | light quantity of abnormal part / light quantity of normal part−1 |
= | I _B (θ) / I _A (θ) -1 | (5)
It is.

  Next, a third embodiment of the present invention will be described.

In this embodiment, the beam incident angle θ _i is a certain average value k ₁ , k ₂ (k ₁ <k ₂ ).
E (k ₂ , θ _S ) / E (k ₁ , θ _S )
Is set so that the angle becomes substantially maximum.

With respect to the incident angle θ _i , the relative intensity change PL described in the previous section can be maximized by setting an appropriate beam incident angle θ _i at an average value k _j that is a condition of a certain rough surface. The change in contrast of the measurement result when the incident angle θ _i is changed is as shown in FIG.

  Next, a fourth embodiment of the present invention will be described.

  In Example 4, a cylindrical surface is used as the surface to be inspected, and the roughness on the cylindrical surface is measured.

  In the fourth embodiment, as shown in FIG. 12, while rotating the cylindrical surface 1 at a constant angular velocity, the cylindrical surface 1 or the measurement unit SB of the light source and the measuring device is at a constant speed in the axial direction (X direction) of the cylindrical surface 1. Is moving in parallel. Then, two-dimensional measurement values of the cylindrical surface 1 are obtained by detecting the reflected light from the cylindrical surface 1 and measuring the light quantity at regular intervals.

At this time, Δ is the distance between the measurement points on the cylindrical surface 1.
Δ <Dp (6)
It is said.

  As a result, it is possible to scan the entire area of the measurement target surface under exactly the same incident angle and irradiation area dimensions, and it is possible to detect a precise relative change amount depending on the position.

  In addition, data can be obtained with higher spatial resolution than the beam irradiation area.

  In particular, as shown in FIG. 12, by moving the cylindrical surface 1 in the axial direction (X direction), the incident surface is set to coincide with the plane including the generatrix and the axis of the cylindrical surface 1. Measurement is carried out under the same conditions for the whole.

  Next, a fifth embodiment of the present invention will be described.

  In Example 5, the light from the laser light source is branched into a plurality of lights by one or two or more semi-transparent mirrors, and simultaneously irradiated to a plurality of positions or a plurality of cylindrical surfaces of one cylindrical surface. The light quantity is measured simultaneously with the corresponding measuring instruments.

  In this embodiment, the scanning optical system is used to shorten the measurement time, which is suitable for measuring at a higher speed.

  In this embodiment, high-speed measurement is facilitated without rotating the cylindrical surface at high speed. In particular, the measurement time per unit area is shortened by simultaneously irradiating light to a plurality of locations or a plurality of measurement target surfaces of a single measurement target and measuring diffused light therefrom.

  At this time, since the incident light is substantially parallel, it is not necessary to prepare a large number of light sources, and the light emitted from a single (or a plurality of minimum required) light source is branched by an optical element having a semi-transparent function. By doing so, it leads to each irradiation point. Further, the axial movement of the cylindrical surface can be realized by a single (or a plurality of minimum necessary number) means.

  Next, a sixth embodiment of the present invention will be described.

The aperture width in the axial direction of the cylindrical surface 1 of the light flux limiting means 6 provided on the paraxial image plane of the condensing optical system 8 is H, the width of the smallest nonuniform roughness region to be detected is d, and the detection optics Let β be the paraxial lateral magnification of the system. At this time,
H ≦ β · d (7)
Is satisfied.

The relative change of the diffraction distribution by irradiation point 1c, and more when measured by a sensitive condition, in many cases must be the incident angle theta _i of the light to a very large angle in excess of 70 °. At this time, the size of the spot diameter of the light irradiated on the irradiation target surface is extended in the axial direction of the cylindrical surface.

  For example, when the beam diameter is 1 mm and the incident angle is 70 °, the irradiation area Dp extends to 2.9 mm.

  At this time, when the minimum size d of the abnormal part to be detected such as unevenness in the irradiation region is about 1 mm, the diffraction image is a mixture of components from the normal part and the abnormal part, and from the abnormal part. It is not possible to obtain only this information with high sensitivity.

  In order to solve this, the width H of the opening of the light beam limiting means 6 such as a slit or pinhole installed on the image plane of the detection optical system 8 is set to a value corresponding to the required spatial resolution.

  For example, when the size of the smallest abnormal part that must be detected is d [mm] and the paraxial lateral magnification of the detection optical system 8 is β, the width H [ mm] needs to be equal to or less than β · d.

  As a result, even when the irradiation area exceeds the necessary resolution, by limiting the luminous flux, only a diffracted light that satisfies various conditions and has necessary information can be captured, and a spatially sensitive system can be realized.

  In this embodiment, the surface roughness on the cylindrical surface is measured with high accuracy by satisfying conditional expression (7).

The principal part side view of Example 1 of this invention Explanatory drawing between each member of Example 1 of this invention The principal part top view of Example 1 of this invention Explanatory drawing of the diffraction image generated from the surface to be inspected when the irradiation beam diameter is 0.1 mm Explanatory drawing of the diffraction image generated from the surface to be inspected when the irradiation beam diameter is 0.5 mm Explanatory drawing when the beam incident surface is incident so that it is perpendicular to the axis of the cylindrical surface Explanatory drawing when light enters the cylindrical surface Explanatory drawing about conventional measurement position Illustration of diffraction image distribution due to roughness of rough surface Explanatory diagram of diffraction image distribution ratio due to changes in rough surface state Explanatory drawing of measurement results when scanned in the axial direction of the cylindrical surface Explanatory drawing of an embodiment using a scanning method Illustration of 2D imaging data of measurement results

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cylindrical rough surface 2 ... Laser light source 3 ... Diffracted light 4 ... Light beam limiting means 1
5 ... Regular reflection direction 6 ... Light flux limiting means 2
7 ... photodetector 8 ... detection optical system

Claims (8)

Light source means;
First light flux limiting means for limiting a light beam diameter of light emitted from the light source means;
A detection optical system that passes through the first light flux limiting means and has S-polarized light incident on the surface to be inspected, and detects light diffracted light generated from the surface to be inspected;
A second light beam limiting means disposed on the condensing surface of the detection optical system for limiting the diameter of the passing light beam;
A photodetector for detecting light that has passed through the second light flux limiting means;
A surface condition inspection apparatus for inspecting the roughness of the surface to be inspected using a signal from the photodetector,
The wavelength of light from the light source means is λ,
In the incident surface when the light from the light source means is incident on the surface to be inspected, the light beam diameter of the incident light beam on the surface to be inspected is Dp,
The effective diameter on the light incident side of the detection optical system is W,
When the distance from the conjugate point through the detection optical system to the second light beam limiting means to the entrance pupil of the detection optical system is L, λ / (Dp / L) ² <W
The surface condition inspection apparatus characterized by satisfying the following conditions. An irradiation step in which light having a wavelength λ in parallel and S-polarized state is incident on a part of the cylindrical surface from an incident surface including a generatrix of the cylindrical surface and a central axis of the cylindrical surface;
After a part of the light diffraction image generated from the cylindrical surface is condensed by the detection optical system, the light is detected by the light detector through the light beam limiting means for limiting the light beam disposed at the light collection point of the detection optical system. A surface state inspection method including an inspection step for determining a change in the intensity distribution of the diffraction image and then inspecting the surface state of the cylindrical surface,
In the incident surface, the average value of the frequency in the incident surface of the size of the surface irregularities in the irradiation region on the cylindrical surface is represented by k _j ,
Dp, the diameter of the light beam when entering the cylindrical surface
The effective diameter on the light incident side of the detection optical system is W,
L is the distance from the conjugate point through the detection optical system to the light beam limiting means to the entrance pupil position of the detection optical system.
With respect to a plurality of diffracted light distributions measured in advance from a plurality of surfaces having different average values k _j, the diffraction angle with respect to the normal line at the irradiation point that maximizes the relative intensity change is θ _m , and the relative intensity change is the largest. The incident angle of light corresponding to the diffraction angle θ _m is θ _i , the light is incident on the irradiation point at the incident angle θ _i , and the detection optical system collects light diffracted light in the angle θ _S direction with respect to the irradiation point. Light
At this time, λ / (Dp / L) ² <W
1 / k _j <Dp
θ _S −tan ⁻¹ {(W / 2) / L} <θ _m <θ _S + tan ⁻¹ {(W / 2) / L}
The surface condition inspection method characterized by satisfy | filling. An irradiation step in which light having a wavelength λ in a parallel and S-polarized state is incident on a part of a cylindrical surface from an incident surface including a generatrix of the cylindrical surface and a central axis of the cylindrical surface;
A part of the light diffraction image generated from the cylindrical surface is condensed by a detection optical system having a numerical aperture NA, and then a light detector through a light beam limiting means for limiting a light beam arranged at a condensing point of the detection optical system. A surface state inspection method including an inspection step of detecting and detecting a change in intensity distribution of the light diffraction image, and then inspecting the surface state of the cylindrical surface,
When the diffracted light distribution in the angle θ direction from two points with different roughness and density on the cylindrical surface is I _A (θ), I _B (θ), the relative intensity change | I _B (θ) / I _A (θ) -1 |
There becomes largest diffraction angle theta _m, when the _i the angle of incidence of light theta when the diffraction angle theta _m relative change in intensity of the diffracted light distribution is maximized, the light is incident at an incident angle theta _i the irradiation point The detection optical system collects light diffracted light in the direction of angle θ _{S with} respect to the irradiation point,
At this time, θ _m −sin ⁻¹ (NA) <θ _s <θ _m + sin ⁻¹ (NA)
The surface condition inspection method characterized by satisfy | filling. Angle theta _s when said detecting optical system for detecting light diffracted light, diffuse reflection light intensity in the the angle _{θ s E (k j, θ} S) is located average k _1, k ₂ values (k ₁ <k ₂ )
E (k ₁ , θ _S ) <E (k ₂ , θ _S )
The surface condition inspection method according to claim 2 or 3, wherein The incident angle θ _{i of the} light is an average value k ₁ , k ₂ (k ₁ <k ₂ ).
E (k ₂ , θ _s ) / E (k ₁ , θ _s )
The surface condition inspection method according to claim 4, wherein the angle is a maximum angle. While rotating the cylindrical surface at a constant angular velocity, the cylindrical surface and incident light are relatively translated at a constant speed in the axial direction of the cylindrical surface, and the photodetector is used at regular intervals. By measuring the amount of light, the two-dimensional surface state on the cylindrical surface is inspected. At this time, the distance Δ between the measurement points on the cylindrical surface is
Δ <Dp
The surface condition inspection method according to any one of claims 2 to 5, wherein   In the irradiation step, different areas on the cylindrical surface are illuminated with light, respectively, and in the inspection step, light diffracted light generated from different areas on the cylindrical surface is detected to detect the light on the cylindrical surface. The surface state inspection method according to claim 2, wherein the surface state of a plurality of regions is inspected. In the incident surface, the width through which the light beam of the light beam limiting means passes is H, and the paraxial lateral magnification when the condensing optical system forms an image of a part of the cylindrical surface on the light beam limiting device surface is β , Where d is the minimum length of the irregularities to be detected on the cylindrical surface, H ≦ β · d
The surface condition inspection method according to claim 2, wherein: