JP2008002892A - Surface condition inspection apparatus and surface condition inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface condition inspection apparatus and a surface condition inspection method which can inspect local nonuniformity with a size of nearly a millimeter on a rough surface of an object having roughness with a size of a few tens of micrometers, which is sufficiently larger than the wavelength of incident light, and having an area of more than a certain level with high precision and quickly. <P>SOLUTION: The inspection apparatus includes a laser light source for irradiating the surface of an object to be inspected and an optical system having a predetermined numerical aperture NA for collecting part of an optical diffraction image from the surface to measure the roughness uniformity of the surface of the cylindrical member having roughness sufficiently larger than the wavelength of the laser light using changes in optical diffraction image intensity distribution from the surface. The incident light is made incident with P-polarized light at an angle of θi and is collected by the optical system having a means for selecting only the P-polarized component of diffracted light in the direction with a predetermined angle θs with respect to the normal in the plane of incidence. A change in the amount of light is measured by an optical intensity detector through a beam restriction means in the vicinity of a paraxial image surface of the optical system. The incident angle θi, the angle θs, and the numerical aperture NA are appropriately set. <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 the speckle diffraction image distribution generated from the object surface when the wavelength or incident angle of incident light is changed, An interferometer method for detecting a phase difference by a meter is known (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). In Patent Document 2, P-polarized illumination light is incident on a surface to be inspected from a linear light source, and specularly reflected light is detected in the Brewster angle direction. The light from the surface to be inspected is detected separately by branching the P component and the S component, and the abnormal portion of the surface to be inspected is detected from the component ratio.

  Patent Document 3 separately detects S and P components of scattered light in a Brewster angle direction by entering a laser beam having an S component and a P component from a certain incident angle into a surface to be inspected. Thus, the surface roughness is evaluated from the strength ratio.

  Patent Document 3 also proposes a method in which P-polarized light is incident, the scattered light intensity is detected in two directions, the Brewster angle direction and a different direction, and the surface roughness is obtained from the ratio. .

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 measurement methods requires branching means for branching each polarization component, or measurement means for measuring at a plurality of positions on the surface to be inspected, and the entire apparatus composed of each member for detection and judgment is complicated. There was a tendency to become.

  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 P-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;
P-polarized component selection means for selecting and transmitting the P-polarized component in the light incident side of the detection optical system or in the optical path between the detection optical system and the photodetector;
A surface condition inspection apparatus that inspects 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 P-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;
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,
The incident angle of light when irradiating the cylindrical surface is θ _i ,
When the Brewster angle of the surface material of the cylindrical surface is θ _B , the photodetector selects only the P-polarized component from the light diffracted light generated in the angle 2θ _B −θ _i direction from the cylindrical surface. Detecting via the selection means,
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 luminous flux when entering the cylindrical surface,
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 light beam limiting means to the entrance pupil position of the detection optical system is L, θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°],. (2)
1 / k _j <Dp, (3)
λ / (Dp / L) ² <W (1)
It is characterized by satisfying.

The surface condition inspection method of the present invention is
An irradiation step in which light having a wavelength λ in parallel and P-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,
The incident angle of light when irradiating the cylindrical surface is θ _i ,
When the Brewster angle of the surface material of the cylindrical surface is θ _B , the photodetector has a P-polarized component selection unit that selects only the P-polarized component from the light diffracted light generated in the angle θ _S direction from the cylindrical surface. When detecting through
θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°], (2)
2θ _B −θ ₁ −sin ⁻¹ (NA) <θ _S <2θ _B −θ ₁ + 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. Reference numeral 9 denotes a P-polarized component selection means, which is composed of a polarizing plate, and allows only P-polarized light to pass through the light incident from the detection optical system 8.

  The light beam restricting means 6 restricts the light passing through the P polarization component selecting means 9. Reference numeral 7 denotes a photodetector that detects light that has passed through the light beam limiting means 6.

  In this embodiment, the roughness of the object surface (surface to be inspected) is measured by detecting that the P-polarized component of the scattering intensity at the scattering Brewster angle changes according to the roughness of the dielectric surface.

  In general, when light enters an object surface, there is an incident angle (Brewster angle) at which the reflectance of P-polarized light becomes zero.

Here, when the refractive index of the incident medium is N ₀ and the refractive index of the substance on the object surface is N ₁ , the Brewster angle θ _B is tan θ _B = N ₁ / N _0.
It becomes.

Here, in the scattering Brewster angle direction (the direction of 2θ _B from the incident light beam), if the surface roughness is large (the unevenness density is low), the P-polarized component increases, and the surface roughness is small (the unevenness density is low). High), the P-polarized component becomes small. 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, since the Brewster angle θ _B of the surface material of the object to be inspected 1 is 60 °, a part of the diffracted light 3 from the irradiation point 1c is 2θ _B − in the regular reflection direction from the normal line 1b of the rough surface. Observed at an angle of θ _i = 50 °.

  The light in this direction is captured by the detection optical system 8 with 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. The light is collected by the photodetector 7 through the P-polarized component selection means 9 and the light flux limiting means 6.

  The P polarization component selection means 9 may be at any position in the optical path from the detection optical system 8 to the photodetector 7. The magnification β of the detection optical system 8 is 1.5, and the width H of the light beam limiting means 6 arranged on the image surface of the surface to be inspected 1a is H = 1.5 mm. In order to prevent stray light from entering the photodetector 7, the space between the detection optical system 8 and the photodetector 7 is shielded.

  FIG. 13 shows two-dimensional image data obtained in this embodiment. The abnormal part is clear against the difference in surface roughness.

  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 a P-polarized state at an angle θ _i with respect to the normal line 1b at the irradiation point 1c with the plane (XY plane) including the generatrix and the central axis of the cylindrical surface as the incident plane. is doing. When the Brewster angle of the surface material is θ _B , diffuse reflected light in the direction of the predetermined angle 2θ _B −θ _i from the normal line 1b within the incident surface is collected by the detection optical system 8 and is P-polarized light Only the components are selected by the P-polarized component selection means 9. Then, the change in the amount of light is measured by the photodetector 7 through the light beam limiting means 6 in which the light of the P-polarized component is arranged 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 _B be the Brewster angle of the surface material of the object 1 to be inspected.

At this time, λ / (Dp / L) ² <W (1)
θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°], (2)
1 / k _j <Dp (3)
One or more of the following conditions are satisfied.

  When each member is set so as to satisfy one or more of conditional expressions (1), (2), and (3), it is possible to coherence in a region having a different roughness in the rough surface of the surface to be inspected 1a. The diffraction pattern when a high laser beam is incident changes significantly compared to the diffraction pattern from other uniform portions.

  In this embodiment, by measuring the change in the light intensity of the P-polarized component in the Brewster scattering direction, a slight difference in roughness of the surface to be inspected 1a can be detected with higher sensitivity (high accuracy). ing.

In addition, in the present embodiment, the optical detector 7, the light diffracted lights generated from the cylindrical surface 1 at an angle theta _S direction may be detected through the P-polarized component selection unit 9 to select only the P polarized light component.

At this time, θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°], (2)
2θ _B −θ ₁ −sin ⁻¹ (NA) <θ _S <2θ _B −θ ₁ + sin ⁻¹ (NA)
(4)
You may make it satisfy | fill.

  This also provides the same effect as described above.

The size of the unevenness on the surface of the surface 1a to be inspected in this embodiment is sufficiently larger than the wavelength of the light 2a. For this reason, the irradiation region (projection in the cylindrical surface generatrix direction (X direction) on the surface of the beam diameter of the light 2a) Dp is equivalent to 1 / k _j indicating the order of the surface direction of the unevenness. A small number of 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. In other words, it is necessary to irradiate the light 2a with a region Dp sufficiently larger than 1 / k _j indicating the size of the unevenness.

  In the present embodiment, the above-described conditional expression (3) is satisfied.

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.

  Now, as shown in FIG. 6, when the incident light 2a is mainly composed of a P-polarized component, the central axis of the incident light 2a satisfies the Brewster angle with respect to the normal 2d of the surface of the minute portion with the uneven portion. And In this case, the reflected light intensity with respect to the incident light 2a is very small.

  As a result, as shown in FIG. 7, in the broad diffuse reflection (diffraction) distribution, a portion having a darker brightness than the surroundings is generated. FIG. 8 is a graph showing the angle dependence of the reflectance with respect to the P-polarized light and S-polarized light components on the surface of a certain inspection surface.

  When the surface to be inspected has a low unevenness density (the value of K is small), that is, when the number of unevennesses in the beam irradiation region Dp is small (smooth), the ratio of the light beam that satisfies the Brewster angle is reduced, which is dark. The brightness of the part becomes brighter.

  Conversely, when the unevenness density is high (the value of k is large), that is, when the number of unevennesses in the beam irradiation region Dp is large, the ratio of the light beam that satisfies the Brewster angle increases, so the brightness of the dark part becomes darker. .

  In this embodiment, by measuring this change, a portion where the unevenness density has changed with respect to the surrounding normal portion is detected.

  Regarding the beam 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 91 as shown in FIG. At this time, when the light 2a is incident so that the incident surface is in a plane coinciding with the cross section of the cylindrical surface 91, the cylindrical surface 91 has a function of a convex mirror, and the diffraction pattern greatly spreads in the incident surface.

  As a result, the proportion of light rays that satisfy the Brewster angle in the diffraction image is reduced, and the detection sensitivity is lowered.

  For this reason, as shown in FIG. 10, the incident surface of the light 2a is set to coincide with the plane 102 including the generatrix 101 and the axis 102 of the cylindrical surface, and within the incident surface 102, the entire irradiation area Dp of the light 2a is constant. The incident angle condition is satisfied.

  In the present embodiment, a simpler configuration is realized by measuring at one specific location that satisfies the Brewster angle with respect to the incident angle.

  FIG. 11 illustrates the result of the relative change amount (diffracted light intensity ratio) PL of the detected light amount when an area including an abnormal part such as a defect on the inspection surface is scanned with light in the direction of the axis 102 of the cylindrical surface 91. FIG.

Here, the relative change amount PL is the relative change amount PL = | the light amount of the abnormal portion / the light amount of the normal portion−1 |
It is.

  Here, since the roughness of the abnormal portion is “rough” compared to the surrounding area, the ratio of the light beam that satisfies the Brewster angle is reduced, and the detected light amount is increased from the surrounding area. Thereby, even a slight change in roughness can be detected as a change amount of several tens of percent.

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

  In Example 2, a cylindrical surface is used as the surface to be inspected, and the roughness on the cylindrical surface is measured.

  In the second embodiment, as shown in FIG. 12, while rotating the cylindrical surface 1 at a constant angular velocity, the cylindrical surface 1 or the measuring unit SB of the light source and the measuring device SB has a constant velocity 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 (5)
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 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 third embodiment of the present invention will be described.

  In Example 3, the light from the laser light source is branched into a plurality of lights by one or two or more semi-transparent mirrors, and irradiated to a plurality of positions on one cylindrical surface or a plurality of cylindrical surfaces at the same time. 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 fourth embodiment of the present invention will be described.

  In this example, the change in the intensity distribution of the light diffraction image from the surface when the position of the light irradiated on the surface on the object to be inspected is changed, so that the surface of the surface sufficiently larger than the wavelength of the light is cylindrical. Roughness uniformity is measured. At this time, the incident light is a substantially parallel beam, and the plane including the generatrix and the central axis of the cylindrical surface is the incident surface.

Light is incident as P-polarized light at an angle θ _i with respect to the normal line at the irradiation point on the cylindrical surface. Only the P-polarized light component is selected by the P-polarized light component selecting means for the diffuse reflected light in the direction of the predetermined angle 2θ _B −θ _i from the normal line within the incident surface. The light from the P-polarized component selection means is collected by the detection optical system, and the change in the amount of light is measured by the photodetector through the light beam limiting means provided near the paraxial image plane of the detection optical system.

  Thereby, the uniformity of the surface roughness is obtained.

Here, d is the width (mm) of the smallest abnormal region to be detected.
Let H be the width (mm) of the opening of the light beam limiting means.
Let β be the paraxial lateral magnification when the detection optical system forms an image of a part of the cylindrical surface on the light beam limiting means 6.

At this time, λ / (Dp / L) ² <W (1)
θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°], (2)
1 / k _j <Dp (3)
H ≤ β · d, (6)
Meet.

  When the relative change in the diffraction distribution due to the irradiation point is measured under a more sensitive condition, it is often necessary to make the incident angle of light very large such that it exceeds 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 extends to 2.9 mm.

  At this time, if the size of the abnormal part such as unevenness in the irradiation area is about 1 mm, the diffraction image is a mixture of components from the normal part and the abnormal part, and only the information from the abnormal part is sensitive. I can't get well.

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

  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.

  Conditional expressions (1), (2), (3), and (6) are specified for the above reasons, and satisfy conditional expressions (1), (2), (3), and (6). By specifying each member, the surface roughness on the cylindrical surface is measured with high accuracy.

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 of diffuse reflection satisfying Brewster condition on rough surface Explanatory drawing of diffraction image distribution of P polarization component Explanatory diagram of reflectance characteristics by polarization component of surface material 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 Illustration of measurement result example when scanned 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 surface 2 ... Laser light source 3 ... Diffracted light 4 ... 1st light beam limiting means 5 ... Regular reflection direction 6 ... 2nd light beam limiting means 7 ... Light Detector 8... Detection optical system 9... P polarization component selection means

Claims (6)

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 P-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;
P-polarized component selection means for selecting and transmitting the P-polarized component in the light incident side of the detection optical system or in the optical path between the detection optical system and the photodetector;
A surface condition inspection apparatus that inspects 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 P-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;
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,
The incident angle of light when irradiating the cylindrical surface is θ _i ,
When the Brewster angle of the surface material of the cylindrical surface is θ _B , the photodetector selects only the P-polarized component from the light diffracted light generated in the angle 2θ _B −θ _i direction from the cylindrical surface. Detecting via the selection means,
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 luminous flux when entering the cylindrical surface,
The effective diameter on the light incident side of the detection optical system is W,
Θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°], where 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.
1 / k _j <Dp,
λ / (Dp / L) ² <W
The surface condition inspection method characterized by satisfy | filling. An irradiation step in which light having a wavelength λ in parallel and P-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,
The incident angle of light when irradiating the cylindrical surface is θ _i ,
When the Brewster angle of the surface material of the cylindrical surface is θ _B , the photodetector has a P-polarized component selection unit that selects only the P-polarized component from the light diffracted light generated in the angle θ _S direction from the cylindrical surface. When detecting through
θ _i ≠ θ _B , θ _i ≧ 2θ _B −90 [°],
2θ _B −θ ₁ −sin ⁻¹ (NA) <θ _S <2θ _B −θ ₁ + sin ⁻¹ (NA)
The surface condition inspection method characterized by satisfy | filling. While rotating the cylindrical surface at a constant angular velocity, the cylindrical surface and the incident light are relatively translated at a constant speed in the axial direction of the cylindrical surface, and the light quantity is measured with the photodetector at regular intervals. The two-dimensional surface condition on the cylindrical surface is inspected by performing the above, and the distance Δ between the measurement points on the cylindrical surface is
Δ <Dp
The surface condition inspection method according to claim 2 or 3, wherein   In the irradiation step, different areas on the cylindrical surface are illuminated with light, and in the inspection step, light diffracted light generated from the different areas on the cylindrical surface is detected, and a plurality of light beams on the cylindrical surface are detected. 5. The surface state inspection method according to claim 2, wherein the surface state of the region is inspected. In the incident surface, H is a width through which the light beam of the light beam limiting unit passes, and β is a paraxial lateral magnification when the detection optical system forms an image of a part of the cylindrical surface on the light beam limiting unit surface. When 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 any one of claims 2 to 5, wherein: