JP2007212250A - Optical element, inspection device, inspection method, and light spot position displacement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize a light spot by propagation light, and to displace the position thereof. <P>SOLUTION: An optically-axisymmetric beam part L12 having a similar shape to a section shape of a light emission surface in a plane orthogonal to the optical axis AX, and having a desired inner diameter from the optical axis and the width is emitted from the light emission surface 10A of a transparent optical element 10 having a projecting and optically-axisymmetric cone surface as the light emission surface, and a fine light spot SP is formed on the optical axis out of the optical element. The formation position of the fine light spot SP is changed by changing at least the inner diameter: R from the optical axis between the inner diameter: R from the optical axis AX and the width: Δ of the optically-axisymmetric beam part L12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical element, an inspection apparatus, an inspection method, and a light spot position displacement method.

  By propagating the laser beam to the optical fiber and emitting it from the exit end formed in a convex conical surface shape, it is condensed on the optical fiber optical axis to form a micro light spot of micron order or less, It is intended that the surface of the object is inspected by scanning the surface of the object with this light spot, or that the surface is processed with light energy.

  In addition, a conical surface with a small apex angle is formed at the exit end of the optical fiber, and a conductive thin film for leaching near-field light is formed on the conical surface, so that the propagating light propagated in the optical fiber is transmitted through the conical surface. It is also intended to perform near-high-resolution inspection by generating near-field light by total reflection and scanning the object surface with this near-field light.

  Regarding inspection using near-field light, Patent Document 1 discloses that a near-field light detection optical probe is incorporated in a normal optical microscope apparatus including an observation system using an objective lens.

  The above-mentioned “light spot formed by propagating light emitted from the convex conical surface formed at the exit end of the optical fiber” is very small, but the optical axis direction of the optical fiber (emits the central axis direction of the optical fiber). It has a long and thin shape (in the direction of a straight line extending outward from the end), and it is necessary to devise in order to acquire information on the surface orthogonal to the surface to be examined (for example, minute unevenness on the surface).

JP 2000-055818 A

  An object of the present invention is to miniaturize the light spot caused by the propagation light as described above and to displace the position thereof.

The light spot position displacement method according to the present invention is a “method of forming a minute light spot and displacing the position”, and has the following features (claim 1).
That is, from the light exit surface of the “transparent optical element having an optical axis symmetric and convex cone surface as the light exit surface”, the optical axis has a shape similar to the cross-sectional shape of the light exit surface within the plane orthogonal to the optical axis. From the optical axis symmetrical light flux portion having a desired inner diameter and width, and a minute light spot is formed on the optical axis outside the optical element. Then, by changing “at least the inner diameter from the optical axis among the inner diameter and width from the optical axis of the light beam portion symmetric with respect to the optical axis”, the formation position of the minute light spot is changed.

The “optical axis” is a spatial axis that coincides with the symmetry axis of the emitted light beam emitted from the exit end face, and the convex cone surface is rotationally symmetric with respect to this optical axis.
Since the “light exit surface” is a convex cone surface that is symmetrical with respect to the optical axis, it may be various cone surfaces with the optical axis as a rotationally symmetric axis, for example, “conical surface of an n-pyramid” with n ≧ 3. It can also be a “conical surface”. Since the light exit surface is a surface from which light is emitted, the propagating light incident on the light exit surface from the inside of the optical element must not be totally reflected. Therefore, the angle formed by the cone surface with respect to the surface orthogonal to the optical axis needs to be “an angle smaller than the total reflection angle”.

  When the light exit surface is virtually cut by a “plane perpendicular to the optical axis”, the shape on this cross section is a regular n-gon (when the cone surface is a cone surface of an n-pyramid) or a circle (the cone surface is a conical surface). ).

  Since the light exit surface is a “convex cone surface symmetrical to the optical axis”, when light is emitted from the entire light exit surface, the emitted light is “refracted in the direction toward the optical axis” by the cone surface, and the cone surface is Since it is symmetric with respect to the optical axis, it is condensed on the optical axis to form a light spot. However, since the light exiting from the light exit surface does not substantially have a focusing action in the optical axis direction, “Elongated shape in the optical axis direction”.

  However, as described above, “the optical axis is symmetrical in the plane perpendicular to the optical axis and similar to the cross-sectional shape of the light exit surface (the regular n-gon or circular shape) and having a desired inner diameter and width from the optical axis. When the light beam part is emitted, the width of the light beam part corresponds to “a part of the cone surface”. Therefore, the formed light spot is the optical axis direction formed by the light emitted from the entire light emission surface. The light spot is focused on a part of the “elongate shape”, and the light spot is “miniaturized in the optical axis direction”.

  Further, when the “distance from the optical axis” of the light beam portion is changed, the condensing position of the emitted light changes in the optical axis direction. The “desired inner diameter and width from the optical axis” of the “light beam portion symmetric with respect to the optical axis” refers to the “inner diameter and width in the optical element at the position of exit from the exit surface”.

  Therefore, the light spot formed by the propagation light emitted from the light exit surface of the optical element can be “miniaturized in the optical axis direction”, and the formation position can be displaced on the optical axis.

  The optical element according to claim 1, wherein the optical element has a shape similar to a cross-sectional shape of the light exit surface within the plane orthogonal to the optical axis (the regular n-gon or circular shape) and has a desired inner diameter and width from the optical axis. As a method of emitting the light beam portion symmetric with respect to the optical axis, the shape similar to the cross-sectional shape of the light emission surface within the plane orthogonal to the optical axis of the optical element is used as in the light spot position displacement method according to claim 2. Then, a light beam whose cross-sectional shape is adjusted to an optical axis symmetric shape having a desired inner diameter and width from the optical axis is incident on the light exit surface parallel to the optical axis direction, and is emitted from the light exit surface. Can be.

  In order to “adjust the beam cross-sectional shape” as described above, for example, a method using a liquid crystal filter or MMD (micromirror device) can be used.

  Or, the “polarization selection means for selectively transmitting a specific polarization component” on the light exit surface of the optical element “the polarization component for selective transmission changes stepwise or continuously depending on the distance from the optical axis. By changing the polarization state of the light that propagates through the optical element and travels toward the light exit surface, the polarization selection means “similar to the cross-sectional shape of the light exit surface within the plane orthogonal to the optical axis”. An optically symmetric light beam portion having a desired inner diameter and width can be emitted from the optical axis in a shape.

  As described above, the shape of the light exit surface can be a cone surface shape of a regular n-pyramid, but the ease of forming the light exit surface and the “symmetry around the optical axis” of the formed small light spot The surface of the light exit surface is preferably a “convex conical surface” (claim 5). In this case, a “light beam portion having a ring-shaped light beam cross-sectional shape having a desired inner diameter and width from the optical axis” can be emitted from the light emission surface.

  As described above, the “optical element” used in the light spot position displacement method described above has a convex cone surface that is symmetrical with respect to the optical axis as the light exit surface, and the “in-plane orthogonal to the optical axis” extends from the light exit surface. In this way, an optical axis-symmetric light beam portion having a desired inner diameter and width is emitted from the optical axis in a shape similar to the cross-sectional shape of the light exit surface, and a minute light spot is formed on the optical axis outside the optical element. The shape of the light exit surface can be a cone shape of a regular n-pyramid as described above.

  The optical element according to claim 5 has a “light axis symmetrical and convex conical surface” as a light exit surface, and selectively selects “polarization selection means for selectively transmitting a specific polarization component” on the light exit surface. The polarization component to be transmitted is provided so as to “change stepwise or continuously according to the distance from the optical axis”.

In the optical element according to claim 5, “a stepwise or continuous change of the polarization component selectively transmitted by the polarization selection unit according to the distance from the optical axis” is changed from the reference polarization component to this. The orthogonal polarization component may be “monotonically changing with the distance from the optical axis” (Claim 6), or “in the polarization selection means, the polarization component selectively transmitted according to the distance from the optical axis. The “change” may be “randomly changes with the distance from the optical axis” from the reference polarization component to the polarization component orthogonal thereto (claim 7).
“Random change” as used herein means that the change of the polarization component to be selectively transmitted according to the distance from the optical axis is “in any order with respect to the distance from the optical axis”.

  Note that the “stepwise or continuous change of the polarization component to be selectively transmitted according to the distance from the optical axis” in claim 5 changes randomly even when it changes monotonously with the distance from the optical axis. In this case, it is not necessary to cover the entire polarization change region from the “reference polarization component to the orthogonal polarization component”, and only a part of the polarization change region may be used. When a part of the polarization change region is used in this way, polarization components other than the polarization change region do not exit from the light exit surface.

  The “polarization selection means provided on the light exit surface” in the optical element according to any one of claims 5 to 7 is configured by “a structure that forms a periodic shape change that is ½ or less of an incident light wavelength”. (Claim 8), in that case, the structure having a periodic shape change of 1/2 or less of the incident light wavelength can be formed of "conductive material" (Claim 9). As the conductive material, “Au (gold) or Al (aluminum)” is suitable (claim 10).

  The “light emitting surface” in the optical element according to any one of claims 5 to 10 is a surface for emitting light propagating in the optical element (referred to as “propagating light”), and the light of the optical element. Of course, the entire area of the light emitting portion can be formed as a single light emitting surface, but the present invention is not limited to this, and the light emitting surface is surrounded by the “region including the optical axis” of the optical element. The “conical surface having a smaller apex angle than the light exit surface” is formed as the near-field light exudation surface, and the near-field light exudation surface is covered with the “conductive film for near-field light exudation”. (Claim 11).

  Thus, when the optical element has “a light exit surface and a near-field light exit surface surrounded by the exit surface”, the light spot formed by the propagation light emitted from the light exit surface is referred to as “propagation light spot. ”To distinguish it from spots with near-field light.

  In the optical element according to the eleventh aspect, the polarization selecting means provided on the light exit surface is constituted by “a conductive material having a periodic shape change of ½ or less of the incident light wavelength” (claim 9, 10) The conductive material can be the same as “the material of the conductive film for leaching near-field light” (claim 12).

  The optical element according to any one of claims 5 to 10 can be an "optical fiber probe in which a light exit surface is formed as an exit end face shape of an optical fiber" (claim 13), claim 11 or 12 The described optical element can also be an “optical fiber probe in which a light exit surface and a near-field light bleed surface are formed as an exit end face shape of an optical fiber” (claim 14).

  The “polarized light selection means” is not limited to the “structure having a periodic shape change equal to or less than ½ of the incident light wavelength” described above, but can also be composed of an organic birefringent film or a multilayer film.

The inspection apparatus according to the present invention is an “apparatus for optically inspecting a surface to be inspected” and includes a light source, an optical element, a light spot position displacement unit, a scanning unit, and a detection unit.
The “light source” emits light for inspection. As the light source, various laser light sources such as semiconductor lasers and LED light sources can be suitably used. The light source can also be “one whose emission wavelength can be switched to multiple wavelengths”.

  The “optical element” propagates light from a light source and emits the propagated light from a light exit surface that is symmetric with respect to the optical axis, and is one according to any one of claims 5 to 14.

  "Light spot position displacement means" is a means for displacing the position of a minute light spot formed by propagating light emitted from an optical element on the optical axis, and polarization of light incident on the light emission surface of the optical element from a light source. It is a means to change the direction.

“Detecting means” is means for detecting return light from the surface to be detected as inspection light.
“Return light from the test surface” is scattered light or reflected light from the test surface, but can be “guided to the detecting means via the optical element”.

  In the inspection apparatus according to claim 15, the optical fiber probe according to claim 13 can be used as the optical element (claim 16), or the optical fiber probe according to claim 14 can be used (claim 17). When the optical fiber probe according to the fourteenth aspect is used as an optical element, the scanning unit can switch between “scanning surface scanning using a propagation light spot” and “scanning surface scanning using near-field light”. In the case of the inspection means according to claim 17, it is preferable that "the emission wavelength of the light source can be switched".

The inspection method of the present invention is an inspection method for optically inspecting a surface to be inspected using the inspection apparatus according to any one of claims 15 to 17 (claim 18).
The inspection method according to claim 19 is the inspection method according to claim 18, wherein the formation position of the propagation light spot is set very close to the test surface, and the light spot is scanned while scanning the test surface with the propagation light spot. The polarization direction of the light incident on the light exit surface of the optical element from the light source is changed by the position displacing means, and the `` light spot position where the return light detected by the detecting means has the maximum intensity '' is covered for each sampling position of the test surface The inspection method can be acquired as height information of the inspection surface.

In this specification, “inspection” means that the state of the test surface is optically scanned and “the state of the test surface is optically observed” or “optical measurement is performed on the test surface. In addition to the case of “performing”, the case of “performing the surface to be inspected with light energy” is also included.
For example, in the inspection apparatus according to any one of claims 15 to 17, while the inspection light passing through the surface to be detected is detected and monitored by the detecting means, the light energy of the propagating light spot or the near-field light is detected. Processing on the inspection surface can also be performed.

  In the inspection apparatus according to claim 15, the optical element has the “optical axis symmetric and convex cone surface” described above as the light exit surface, and the light exit surface is “perpendicular to the optical axis”. A small light spot on the optical axis outside the optical element by injecting an optical axis symmetric beam portion having a desired inner diameter and width from the optical axis in a shape similar to the cross-sectional shape of the light exit surface within the surface. It is also possible to configure an inspection apparatus using a device that can form the above-mentioned, for example, “a light exit surface having a regular n-pyramidal pyramid surface shape”.

  As described above, according to the present invention, since the propagation light spot can be miniaturized in the optical axis direction, the resolution in the optical axis direction in the inspection using the propagation light spot is improved. In addition, since the position of the propagating light spot can be displaced in the optical axis direction without displacing the optical element in the optical axis direction, Acquisition of “information” is facilitated.

Hereinafter, embodiments will be described.
FIG. 1 is a view for explaining one embodiment of a light spot position displacement method according to claims 1, 2, and 4. In FIG. 1A, reference numeral 10 denotes an “optical element”. This optical element 10 is an optical element that forms only a propagation light spot and does not generate near-field light.

  The optical element 10 is a “transparent body”, and a parallel light beam L is incident from above in FIG. 1A, and the incident surface has a planar shape perpendicular to the optical axis AX. The surface opposite to the incident surface (the surface on the lower side in FIG. 1A) is formed as a “convex conical surface”, and the vicinity of the top is shielded by the light shielding film 10B, and the conical surface portion on the outside thereof. Is the light exit surface 10A. The inclination angle: θ of the light exit surface 10A with respect to a plane orthogonal to the optical axis AX is referred to as the “taper angle” of the light exit surface.

As shown in FIG. 1A, when a parallel light beam L is incident from the incident surface side of the optical element 10, the incident light beam propagates through the optical element 10 as propagation light L1, and exits from the light exit surface 10A. It becomes the emitted light L2. When the exit light L2 exits from the light exit surface 10A, it is refracted by the action of the taper angle of the light exit surface 10A. Thus, the light is “thinly condensed” on the optical axis AX.
In FIG. 1A, the part indicated by the symbol SPL is a “light collection region by the emitted light L2.”

  In this condensing region, the propagation light L1 propagating through the optical element 10 is emitted light L2 and condensed in a “spot shape that is long in the optical axis direction”. I will call it.

  FIG. 1B is a diagram for explaining the formation of a “propagating light spot” by the optical element 10. When a light beam L10 having a “ring-shaped light beam cross section with the optical axis as the central axis” is made incident from the incident surface of the optical element 10, the incident light beam passes through the optical element 10 with a “hollow cylinder-shaped” light beam L11. When the light is emitted from the light exit surface 10A as the light beam L12, the light is condensed on the optical axis AX to form a minute light spot SP. This minute light spot SP is a “propagating light spot”.

  In FIG. 1B, assuming that the distance from the optical axis AX of the incident light beam L10 to the optical element 10 is “inner diameter: R” and the width of the ring-shaped light beam cross section is “width: Δ”, these are used as parameters. : When R is changed, the formation position of the propagation light spot SP is displaced in the vertical direction on the optical axis AX in FIG. Further, the change of the width Δ changes the “size of the propagation light spot SP in the optical axis AX direction”. The displacement region in the optical axis AX direction of the propagating light spot SP is equal to the length of the condensing spot SPL by the propagating light in the optical axis direction.

  Accordingly, a “hollow cylindrical light beam” incident on the light exit surface 10A, that is, an optical axis symmetric light beam portion L10 having a desired inner diameter: R and width: Δ from the optical axis AX is emitted from the light exit surface 10A. By emitting as L12, the propagation light spot SP can be formed as a “fine light spot”, and by changing the inner diameter: R of the light beam L10, the position of the propagation light spot SP can be displaced in the optical axis AX direction. By changing the width: Δ, the “size in the optical axis direction” of the propagation light spot SP can be adjusted.

  When a laser light source is used as the light source, the incident light beam generally has “a light intensity distribution symmetrical to the optical axis”. In this case, if the light intensity distribution at the position R from the optical axis is P (R), the light intensity when the light beam L10 having the inner diameter R and the width Δ is condensed as the propagation light spot SP. Is approximately 2πR · Δ · P (R), so changing the width: Δ corresponds to changing the light intensity of the propagation light spot SP, and therefore propagating by changing the width: Δ. The light intensity of the light spot SP can be adjusted.

In order to obtain the hollow cylindrical incident light beam L10, for example, the following may be performed.
The light shielding member F shown in FIG. 1C has a light shielding property, and a transmission portion F1 having a desired inner diameter (R) and width (Δ) is formed in a ring shape. Specifically, for example, the light shielding member F can be realized by forming a metal light shielding film on “a portion excluding the transmission portion F1” on one side of a transparent glass plate.

  A parallel light beam L from a light source is incident on such a light shielding member F as shown in FIG. 1 (d), and a hollow cylindrical light beam transmitted through a ring-shaped transmission part is formed by lenses 13 and 15. The light beam diameter is adjusted to a size suitable for the size of the incident surface of the optical element 10 and is incident on the optical element 10 by a focal “beam diameter reducing optical system”.

  A plurality of kinds of light shielding members such as the light shielding member F are prepared with different “inner diameters and widths of the ring-shaped transmission portions”, and these are incorporated in the turret and arranged in the optical path of the incident light L by rotating the turret. By switching the members, the inner diameter and width of the light beam L10 incident on the light exit surface 10A of the optical element 10 can be switched.

  In addition, by using a liquid crystal shutter device, a micromirror device, or the like and switching the inner diameter and the width of the hollow cylindrical light beam, the formation position of the propagation light spot can be displaced in the optical axis direction.

  That is, the method described above with reference to FIG. 1 is a method of forming a minute light spot SP and displacing the position, and is an optical having an optical axis symmetry and a convex cone surface as the light exit surface 10A. From the light exit surface 10A of the element 10, the shape is similar to the cross-sectional shape of the light exit surface in a plane orthogonal to the optical axis AX, and the optical axis is symmetric with the desired inner diameter: R and width: Δ from the optical axis AX. The light beam portion L12 is emitted to form a minute light spot SP on the optical axis outside the optical element, and at least light of the distance: R and width: Δ from the optical axis AX of the light beam portion L12 symmetric to the optical axis. This is a light spot position displacement method (claim 1) in which the formation position of the minute light spot SP is changed by changing the distance from the axis: R.

  Further, an optical axis-symmetrical shape having a desired inner diameter: R and width: Δ from the optical axis AX with a “shape similar to the cross-sectional shape of the light exit surface 10A” in a plane orthogonal to the optical axis AX of the optical element 10. The light beam L10 having the light beam cross-sectional shape adjusted is incident on the light exit surface 10A in parallel with the optical axis AX direction, and exits from the light exit surface 10A (claim 2). The light exit surface 10A of the optical element 10 is a conical surface, and a ring-shaped light beam portion L12 having a desired inner diameter: R and width: Δ is emitted from the light exit surface 10A. 4).

  Although the case where the light exit surface shape of the optical element is a conical shape has been described above, the above also applies to the case where the light exit surface shape is not a conical surface and is an optically symmetric n pyramid (n ≧ 3). It will be easily understood that “the position where the propagation light spot is formed can be displaced in the optical axis direction” in the same manner as in FIG.

  To add a little, the light shielding film 10B provided in the vicinity of the optical axis including the optical axis of the light emitting surface is for blocking the emission of the light beam in this portion. This is for separating the position of the “condensing spot SPL” from the “apex position of the cone surface”. If the light shielding film 10B is not formed, the condensing spot SPL by propagating light is formed in contact with the vertex position.

  Although the condensing spot SPL by the propagating light may be in contact with the “apex position of the light exit surface”, it is considered that the optical element 10 is displaced relative to the test surface when scanning the test surface. In order to prevent the tip of the optical element from contacting the surface to be examined, the formation position of the condensing spot SPL (this is the displacement area width of the propagating light spot) is from the tip of the optical element 10. It is better to be “a certain distance”, and for this purpose, the light shielding film 10B is preferably formed to an appropriate size.

  As the taper angle: θ of the light exit surface described above is reduced, the formation position of the condensed spot SPL by the propagating light is further away from the tip of the optical element 10 on the optical axis. Since the taper angle: θ is equal to the incident angle of the light beam L10 on the light exit surface 10A inside the optical element, even if the taper angle: θ is large, it cannot be greater than the total reflection angle.

  In the embodiment of FIG. 1, the “condensing spot SPL by propagating light” can be formed by blocking the incident parallel light beam L from the light source side and making all the light beams enter the optical element 10. To do this, for example, the liquid crystal shutter device may be fully opened, or the light shielding member may be retracted from the optical path of the incident light beam.

  FIG. 2 is a view for explaining one embodiment of the light spot position displacement method according to the first, third, and fourth aspects. In FIG. 2A, reference numeral 20 denotes an “optical element”. This optical element 20 is also an “optical element that forms only a propagating light spot” and does not generate near-field light.

  The optical element 20 is a “transparent body”, and a parallel light beam (not shown) is incident from above in FIG. 2A, and the incident surface has a planar shape perpendicular to the optical axis AX. . The surface opposite to the incident surface (the lower surface in FIG. 2 (a)) is formed as a “convex conical surface”, its top portion is shielded by the light-shielding film 20B, and the outer portion is light-emitted. It is the surface 20A. The inclination angle θ of the light exit surface 20A with respect to a plane orthogonal to the optical axis AX: θ is referred to as the “taper angle” of the light exit surface. The taper angle: θ is less than the total reflection angle, as in the case of the optical element 10 in FIG.

Polarization selection means 20C is formed on the light exit surface 20A.
FIG. 2C illustrates the state in which the optical element 20 is viewed from the lower side of FIG. On the exit surface side, a light shielding film 20B is formed in a region in the vicinity of the optical axis including the optical axis, and a polarization selection means 20C is provided so as to surround the light shielding film 20B.

  In this example, the polarization selection means 20C is divided into a plurality (N) of annular regions 20A1, 20A2, 20A3, 20A4,. These annular zones are set with polarization characteristics so as to “selectively transmit specific polarization components”, and the polarization directions of the “polarization components to selectively transmit” (each rectangular shape shown in FIG. 2C). Is indicated by a “double-sided arrow” in the innermost ring region 20A1 from the “left-right direction” to the “vertical direction” in the outermost ring region 20AN according to the distance from the optical axis. It is changing gradually and gradually.

  As shown in FIG. 2B, a parallel light beam LF having a circular cross section is made incident on the optical element 20. At this time, the incident light beam LF is polarized into linearly polarized light. In FIG. Assume that the double-sided arrow drawn in LF is the polarization direction of the incident light beam LF. In this example, the polarization direction matches the polarization component that is selectively transmitted by the annular zone 20A4 in the polarization selection means 20C.

  Then, the linearly polarized parallel light beam LF incident on the optical element 20 propagates in the optical element AX direction, and the light beam portion incident on the light shielding film 20B is blocked. Further, in the light beam part incident on the light exit surface 20A, the part (of the parallel light beam LF out of the parallel light beam LF) incident on the part of the annular zone 20A4 where the linear polarization direction of the parallel light beam LF matches the “polarized light component to be selectively transmitted”. Only the hollow cylindrical light beam portion having the annular zone as the bottom surface) is refracted out of the optical element and emitted as a light beam LA4 to form a propagation light spot SP.

Accordingly, if the polarization direction of the linearly polarized light in the parallel light beam LF incident on the optical element 20 is changed, the “ring zone region for selectively transmitting the polarized light beam” is switched, and accordingly, formed on the optical axis AX. The position of the propagating light spot SP is displaced in the optical axis direction.
In this way, the position of the propagation light spot can be displaced.
If a parallel light beam incident on the optical element 20 of FIG. 2 is incident in a “circularly polarized state”, a “condensing spot SPL by propagating light” can be formed. In order to execute this, a quarter-wave plate may be inserted into the optical path of the parallel light flux in the linearly polarized state to convert it into circularly polarized light.

  The method described with reference to FIG. 2 is a method of forming a minute light spot SP and displacing the position of the light spot SP, and the light emission of the optical element 20 having an optical axis symmetric and convex cone surface as a light emission surface. From the surface 20A, a shape similar to the cross-sectional shape of the light exit surface 20A in a plane orthogonal to the optical axis AX, and a desired inner diameter (inner diameter from the optical axis of the zone regions 20A1 to 20AN) and width (ring The width of the belt regions 20A1 to 20AN) is emitted to form a small light spot SP on the optical axis AX outside the optical element 20, and the light beam portion LA4 having the optical axis symmetry is formed. This is a light spot position displacement method (Claim 1) that changes the formation position of the minute light spot SP by changing at least the distance from the optical axis AX among the distance and width from the optical axis AX.

  In addition, the polarization selection means 20C that selectively transmits a specific polarization component to the light exit surface 20A of the optical element 20 “the polarization component that selectively transmits changes stepwise according to the distance from the optical axis AX. By changing the polarization state of the light that propagates through the optical element 20 and travels toward the light exit surface 20A, the polarization selection means 20C causes a “cross section of the light exit surface within the plane orthogonal to the optical axis AX. A light beam portion LA4 having a desired inner diameter and width is emitted from the optical axis AX with a shape similar to the shape "(Claim 3), and the light exit surface 20A of the optical element 20 is a conical surface. A light beam portion LA4 having a ring-shaped light beam cross section having a desired inner diameter and width is emitted from the light exit surface 20A (claim 4).

  The region width of each of the annular regions 20A1 to 20AN is such that, for example, the intensity of the propagating light spot SP is “substantially constant regardless of the formation position” in consideration of the light intensity distribution in the incident light beam LF. Can be set to

  In addition, instead of forming the zonal region concentrically, the width of the zonal region is narrowed to form a `` helical shape '', and the polarization direction of the `` polarized light component selectively transmitted '' along with the spiral rotation is `` By setting “shifted by a small angle”, the polarization component to be selectively transmitted can be “changed continuously according to the distance from the optical axis”.

  Even when the shape of the light exit surface of the optical element 20 is not a conical surface but an n-pyramid (n ≧ 3) that is symmetric with respect to the optical axis, It will be readily understood that “can be done”.

  The optical element 20 shown in FIG. 2 has a convex conical surface that is symmetrical with respect to the optical axis as the light exit surface 20A, and a polarization selection means 20C that selectively transmits a specific polarization component to the light exit surface 20A. (5), the polarization component to be transmitted is changed stepwise according to the distance from the optical axis.

  In addition, the stepwise change of the polarization component selectively transmitted in the polarization selection means 20C of the optical element 20 according to the distance from the optical axis AX is a reference polarization component (polarization component in the annular zone 20A1). To the polarization component orthogonal to this (polarization component in the annular zone 20AN) changes monotonously with the distance from the optical axis (Claim 6). Not limited to such an example, the “change in the polarization component selectively transmitted according to the distance from the optical axis” in the polarization selection means is changed from the reference polarization component to the polarization component orthogonal to the optical axis. You may make it change at random with the distance from (Claim 7).

  In the polarization selection means, the stepwise change of the selectively transmitted polarization component according to the distance from the optical axis is monotonous with the distance from the optical axis, from the reference polarization component to the polarization component orthogonal to this. In the adjacent annular zone, the polarized light components that are selectively transmitted tend to be in directions close to each other, and in this case, the incident light flux and the light from the specific annular zone are included in the adjacent annular zone. It is conceivable that some light flux is easily emitted from the band region and the shape of the propagating light spot is slightly blurred in the optical axis direction. Such a problem can be effectively avoided if the “corresponding change” is changed randomly with a distance from the optical axis from a reference polarization component to a polarization component orthogonal thereto.

The polarization selection means 20C provided on the light exit surface 20A can be constituted by a “structure that forms a periodic shape change that is ½ or less of the incident light wavelength” (Claim 8). It is preferable to form it with a conductive material, particularly Au or Al.
The optical elements 10 and 20 described above can also be configured as “an optical fiber probe in which a light emission surface is formed as an emission end face shape of an optical fiber”.

FIG. 3 is a diagram for explaining one embodiment of the “inspection apparatus”.
The inspection apparatus in FIG. 3 can be implemented as, for example, “a near-field optical microscope that measures optical physical properties in a minute region of a sample that is an object to be inspected”.
The inspection apparatus includes a light source 31 that emits laser light, a drive power source 31 a that drives the light source 31, a beam splitter 32 that is disposed in the optical path of the laser light emitted from the light source 31, and laser light that has passed through the beam splitter 32. A half-wave plate 38a, a quarter-wave plate 38b disposed in the optical path, an adjusting unit 38 for adjusting these wave plates, and the light transmitted through the wave plates 38a and 38b in the test object 2 An optical fiber probe 30 that irradiates the surface 2a, a photodetector 34 that detects return light from the surface 2a to be detected, a probe control unit 35, an image processing unit 36, an image display unit 37A, and a control means 100 are provided. The control means 100 is constituted by a microcomputer or the like and controls the entire apparatus.

  The optical fiber probe 30 is an optical fiber having a core 301 and a clad 302 surrounding the core 301. The optical fiber probe 30 includes a propagation part 303 for propagating laser light, and a probe part 304 formed at an emission side end of the propagation part 303. Have The probe unit 304 includes a near-field light extruding unit 304b and a normal propagation light emitting unit 304a.

  The core 301 and the clad 302 are each made of silicon dioxide glass, and the composition is controlled so that the refractive index of the clad 302 is lower than that of the core 301 by adding germanium, phosphorus, or the like.

  The normal propagation light exit part 304a is formed by forming a polarization selection means on a “light exit surface” formed in a conical surface as the exit end face shape of the optical fiber, and the near-field light exuding part 304b is surrounded by the light exit surface. In this way, the surface of the near-field light bleed surface formed in “a sharp conical surface with a smaller apex angle than the light exit surface” is coated with the “conductive film for leaching near-field light” ( Claim 11).

  That is, the optical fiber probe 30 is an “optical element (claim 14)” in which a light exit surface and a near-field light exudation surface are formed as the exit end face shape of the optical fiber.

The light source 31 is driven by a driving power source 31a and emits laser light having a predetermined wavelength. The emitted laser light is in a linearly polarized state, and part of it is transmitted through the beam splitter 32 and then transmitted through the half-wave plate 38a and the quarter-wave plate 38b.
The half-wave plate 38a and the quarter-wave plate 38b are rotatable around the optical axis of the transmitted light, and their positions are controlled by driving by the adjusting means 38 to control the polarization of the laser beam (the polarization of the laser beam). Control to change the orientation of the surface). Since the polarization control of the laser light is thus performed, the polarization direction of the laser light emitted from the light source 31 may be arbitrary.

  The laser light transmitted through the half-wave plate 38 a and the quarter-wave plate 38 b is incident on the core 301 of the optical fiber probe 30 and propagates through the core 301 of the propagation unit 303 as a single mode wave. If the light propagation part 303 of the optical fiber probe 30 is long and the light propagation part 303 is bent, “the polarization state of the propagating laser light is disturbed by the bending of the light propagation part 303 (linearly polarized light becomes elliptical)”. By adjusting the position of the / 4 wavelength plate 38b, "the correction of the disturbance of the polarization state" is performed, and the laser light incident on the probe unit 304 is adjusted to linearly polarized light.

As described above, the ¼ wavelength plate 38b “corrects the disorder of the polarization state of the propagating laser light due to the bending of the light propagation portion 21”, so that the optical fiber probe is configured so as not to disturb the polarization state. Is unnecessary and can be omitted. In such a case, the polarization state of the laser light can be adjusted by rotating the light source 31.
It should be noted that high-speed polarization control can be realized by using other polarization control means, for example, “liquid crystal polarization modulation element” instead of the half-wave plate 38 a, and using the liquid crystal drive means instead of the drive means 38.

Here, the state of the probe unit will be described with reference to FIG.
4A shows a state where the probe portion 304 of the optical fiber probe 30 is viewed from below in FIG. The probe unit 304 includes a normal propagation light emitting unit 304a and a near-field light exuding unit 304b, and a core end surface corresponding to the normal propagation light emitting unit 304a is a “light emitting surface” from which normal propagation light is emitted. The core end surface corresponding to the near-field light exuding portion 304b is a “near-field light exuding surface”.

The near-field light exudation surface is formed in a “pointed conical surface”, and a “conductive film for near-field light exudation” is formed on the surface as a conductive thin film made of Au, Ag, Al, or the like.
First, the “taper angle: θ” is defined for the light exit surfaces of the optical element 10 of FIG. 1 and the optical element 20 of FIG. 2, but the taper angle is similarly applied to the optical fiber probe 30 of FIG. The light exit surface and the near-field light exit surface are defined.

  The taper angle of the light exit surface is given by “90 ° −α1 / 2”, where “vertical angle of the conical surface forming the light exit surface” is α1. This is hereinafter referred to as the taper angle of the light exit surface: θ1. For the near-field light bleed surface, the apex angle of the “conical surface forming the near-field light bleed surface” is α2, and “θ2 = 90 degrees−α2 / 2” is defined as “taper angle of the near-field light bleed surface: θ2.”

  The normally propagating light is parallel to the center line of the core 301 of the optical fiber probe 30, and the taper angles θ1 and θ2 are incident angles of the laser light on the light exit surface and the near-field light bleed surface, respectively. The taper angle: θ1 is “greater than 0 and less than the total reflection angle”, and the taper angle: θ2 is “greater than the total reflection angle and less than 90 degrees”.

The normal propagation light exit unit 304a is formed by forming a polarization selection unit on the light exit surface.
That is, the polarization selecting means is divided into a plurality (N) of concentric annular zone regions 4a1, 4a2, 4a3, 4a4,... 4aN-1, 4aN. These annular zones are set with polarization characteristics so as to “selectively transmit specific polarization components”, and the polarization directions of the “polarization components to selectively transmit” (each rectangular shape shown in FIG. 4A). Is indicated by a “double-sided arrow” in the innermost ring region 4a1 from the “horizontal direction” to the “vertical direction” in the outermost ring region 4aN according to the distance from the optical axis. It is changing gradually and gradually.

  FIG. 4B is a view for explaining the configuration of individual annular zones constituting the polarization selection means formed on the light exit surface of the optical fiber probe. In FIG. 4B, reference numeral 3041 denotes a “light exit surface”, and a fine grid structure FD that is “a structure having a periodic shape change of ½ or less of the incident light wavelength” is conductive on the light exit surface. It is made of material.

  In the grid structure FD, “conductive materials having a rectangular cross-sectional shape” having a width: w and a height: h are arranged at a pitch: p, and the pitch: p is an incident light wavelength (normally incident from a light source, The wavelength of the light propagating through the optical fiber as propagating light) is 1/2 or less. The “rectangular cross-sectional shape” is uniform in a direction orthogonal to the drawing of FIG.

  When “linearly polarized light having a wavelength of 2p or more” is incident on such a periodic shape change, the polarization plane of the incident linearly polarized light (vibration surface of the electric field) becomes “pitch direction (in FIG. 4B) of the grid structure FD. The transmissivity is maximum when it is parallel to the “left-right direction”, and the transmissivity is 0 when the polarization plane of the incident linearly polarized light is orthogonal to the pitch direction of the grid structure.

  As a specific example, the parameters of the grid structure FD are, for example, taper angle: θ1 = 11 degrees, the conductive material forming the grid structure FD is Au (gold), the pitch: p = 200 nm, and the width: w. = 100 nm, height: h = 150 nm, when linearly polarized light having a wavelength of 633 nm is incident, the incident light has a polarization plane parallel to the pitch direction and orthogonal to the pitch direction. The extinction ratio is about 100.

  For example, when the taper angle is θ1 = 11 degrees, the conductive material forming the grid structure FD is Al, the pitch is p = 300 nm, the width is w = 200 nm, and the height is h = 200 nm, the wavelength is 633 nm. When linearly polarized light is incident, the extinction ratio of the emitted light is about 10,000 when the polarization plane of incident light is parallel to the pitch direction and when orthogonal to the pitch direction.

  That is, by changing the pitch direction in the grid structure FD, the polarization direction of the “polarized light component to be selectively transmitted” can be changed, so that “in the annular zones 4a1 to 4aN shown in FIG. If the “pitch direction of the grid structure” is set to the direction of “double-sided arrow” in each rectangular shape in FIG. 4A, the polarization direction of the “polarized light component to be selectively transmitted” is the innermost annular zone. It is possible to realize a state that changes monotonously and stepwise according to the distance from the optical axis from the “left-right direction” in the region 4a1 to the “vertical direction” in the outermost annular zone region 4aN.

  FIG. 4C shows a state in which the polarization plane of the incident light LI is “parallel to the polarization component selectively transmitted through the annular zone 4a1”. At this time, the light beam propagates by the light beam emitted from the annular zone 4a1. A light spot SP (4a1) is formed. The position where the propagation light spot SP (4a1) is formed is relatively close to the tip of the optical fiber probe.

  FIG. 4D shows a state in which the plane of polarization of the incident light LI is “parallel to the polarization component selectively transmitted through the annular zone 4aN”. At this time, a propagation light spot SP (4aN) is formed by the light flux emitted from the annular zone region 4aN. The position where the propagation light spot SP (4aN) is formed is relatively far from the tip of the optical fiber probe. “DL” in the figure indicates the size of the “region displaceable in the optical axis direction” of the propagation light spot SP. “DL” is a “variable range of working distance” when the propagating light spot SP is displaced in the optical axis direction.

  As shown in FIG. 4A, in the annular zones 4a1 to 4aN, the “polarized component that is selectively transmitted” is monotonously rotated from the innermost annular zone 4a1 toward the outermost annular zone 4aN. ing. This state is shown in FIG.

  The horizontal axis of FIG. 4 (e) is the “polarization state according to the distance from the optical axis” of the optical fiber probe, and the greater this is, the more the ring zone region is located on the outer side. The “polarization component” on the vertical axis indicates that the polarization component of the annular zone 4a1 is 0 and the polarization component of the outermost zone 4aN is 1. In the drawing, the polarization component is drawn so as to increase continuously from 0, but since the polarization component is constant for each annular region, it actually has a step-like change.

  FIG. 4 (f) shows that when the annular zone changes from 4a1 to 4aN, the position of the formed propagation light spot (condensing position on the vertical axis) changes gradually away from the tip of the optical fiber probe. It shows a state. If the upper limit of the displacement region on the vertical axis is D1 (state of FIG. 4D) and the lower limit is D2 (state of FIG. 4C), the upper limit: D1 is the polarization component (FIG. 4A) of the annular region 4aN. ), The lower limit: D2 is the polarization component of the annular zone 4a1 (in the left-right direction of FIG. 4A, represented by the symbol “P2” in the diagram). Correspond. The intermediate distance between the upper limit: D1 and the lower limit: D2 is D3, and the corresponding polarization component is represented by the symbol “P3”.

  Eventually, the position of the propagation light spot can be changed in the optical axis direction by adjusting the direction of the polarization plane of the linearly polarized light incident on the propagation light emitting section 304a. This action is the same as the action of the polarization selection means 20C in the optical element 20 described with reference to FIG. 2, and the polarization selection means 20C in the optical element 20 is the same as the polarization selection means of the optical fiber probe 30 being described. “Each of the zone regions 20A1 to 20AN is configured by a“ grid structure ”as shown in FIG. 4B, and the pitch direction is set to the direction of“ double-sided arrow ”in each rectangular shape of FIG. For example, the polarization direction of the “polarized light component to be selectively transmitted” depends on the distance from the optical axis from the “horizontal direction” in the innermost zone region 20A1 to the “vertical direction” in the outermost zone region 20AN. Thus, it is possible to realize a monotonous and stepwise change state.

  The polarization control function of the grid structure FD is dependent on the “wavelength of incident light”. In general, a polarization control function can be realized by using “a high reflectance (for example, 80% or more)” as a conductive material having a grid structure. As a specific example in the visible wavelength band, the wavelength is 600 nm or more when the conductive material constituting the grid structure is Au, and the wavelength is 700 nm or less when the conductive material is Al.

  In addition, you may fill with the "dielectrics other than air" between the grids of the grid structure FD in FIG.4 (b) for the mechanical strength improvement of a grid structure.

  The distance D between the condensing spot SPL caused by the propagation light emitted from the normal propagation light exit part 304a and the tip of the near-field light exudation part 304b can be controlled by adjusting the taper angle θ1 of the light exit surface.

  FIG. 5A shows the relationship between the taper angle: θ1 and the distance: D of the conical surface forming the light shooter surface. FIG. 5A shows the case where the refractive index of the core 301 is 1.53 and the emission side medium is air, and the taper angle: θ1 = 50 degrees corresponds to the total reflection angle, and the taper. Angle: The distance D increases as θ1 becomes smaller, and when θ1 becomes smaller than 20 degrees, the normal propagation light spot is collected at a position about several hundred nm to several um away from the tip of the optical fiber probe. . This is because the smaller the taper angle θ1, the smaller the refraction angle at the light exit surface.

  The distance D is also dependent on the ratio B: A of the diameter B of the near-field light extruding portion 304b in the probe portion 304 of the optical fiber probe and the diameter A of the normal propagation light emitting portion 304a: B / A. This dependency relationship is shown in FIG. As can be seen from this figure, it is understood that the normal propagation light spot can be formed at a “position sufficiently away from the tip of the optical fiber probe” by setting the diameter ratio: B / A to 0.25 or less.

  Increasing the diameter ratio: B / A means increasing the diameter: B of the near-field light oozing portion 304b, but the conical taper angle of the near-field light oozing portion: θ2 is “the total reflection angle or more. Therefore, when the diameter B is increased, the height of the conical shape is increased to approach the normal propagation light spot, and thus the distance D is decreased.

Next, the near-field light exuding part 304b will be described.
As described above, the near-field light exuding portion 304b is arranged on the near-field light extruding surface formed in a conical surface shape having a taper angle: θ2 at the distal end portion of the optical fiber probe 30. Formed.

  The conductive film material for leaching near-field light is different from the conductive material of the grid structure FD formed on the light exit surface and constituting “periodic shape change of 1/2 or less of the incident light wavelength”. A material may be used, but it is preferable to use the same material in order to improve the productivity of the optical fiber probe. By making these the same material, film is formed simultaneously on the near-field light bleed surface and light exit surface of the tip of the optical fiber, and then fine processing such as ion beam etching on the conductive film covering the light exit surface portion. By forming the grid structure, the conductive film for leaching near-field light and the grid structure forming the polarization selection means can be formed in a continuous process.

  Of the laser light propagating in the core 301, a light beam portion in the vicinity of the optical fiber optical axis is incident on the near-field light extruding surface. The near-field light exudation surface has a conical surface shape with a taper angle: θ2, and the taper angle: θ2 is “more than the total reflection angle and less than 90 degrees”. It is totally reflected on the surface, and part is exhaled as “evanescent light” on the “conductive film for leaching near-field light”, coupled with the surface plasmon of the conductive film, to the tip of the near-field light oozing part 304 b A near-field light spot (hereinafter referred to as “near-field light spot”) that propagates toward the surface and is coupled with the surface plasmon localized at the tip is formed.

  Incidentally, the symbol NFS in FIG. 4D illustrates the “near-field light spot” in an explanatory manner. Since the near-field light spot is not “propagating light”, even if it is generated, it is not observed alone.

  The material of the “conductive film for leaching near-field light” may be any material as long as it is conductive. However, the effect of enhancing near-field light by surface plasmons is obtained, and the chemical stability is excellent. To “Au thin film”.

The intensity of the near-field light spot generated, in general, there is wavelength dependence as shown in FIG. 6 (a), the wavelength of FIG. 6 (a): λ21~λ22 range (maximum: 1/2 of the P ₀ By selecting a wavelength region that is equal to or greater than the value (P ₁ ), a near-field light spot with good intensity can be formed.

  When the conductive film for leaching near-field light is an “Au thin film”, it is preferable to select light having a wavelength that falls within a wavelength band of about 480 nm to 700 nm.

The light intensity of the near-field light spot also has “taper angle: dependence on θ2”.
FIG. 6 (b) shows a general tendency of the near-field light exudation surface with respect to the tapered angle: θ2 of the conical surface, and the taper angle: θ2 indicates a range of “θa to θb (maximum light intensity). By selecting the angle of “value: half of P0: range in which P1 is equal to or greater)”, the light intensity of the near-field light spot can be improved. For example, when the conductive film for leaching near-field light is an “Au thin film”, when the incident light wavelength is 532 nm, the taper angle θ2 is preferably about 45 to 55 degrees.

  The polarization selection means of the normal propagation light emitting portion 304a of the optical fiber probe 30 shown in FIG. 3 is configured with an Au grid structure, and the conductive film of the near-field light oozing portion 304b is an Au thin film.

  As described above, when both the grid structure FD forming the polarization selection means and the conductive film for leaching near-field light are made of Au, a wavelength of 600 nm or more is used to form a propagating light spot with a polarization component that is selectively transmitted. In order to form a near-field light spot with good intensity, light having a wavelength of about 500 nm is preferable. That is, it is preferable that the wavelength of the light emitted from the light source is different between the case where the inspection is performed using the propagation light spot SP and the case where the inspection is performed using the near-field light.

  For this reason, the light source 31 in the embodiment of FIG. 3 can switch the emission wavelength to, for example, 633 nm and 532 nm, depending on whether the inspection is performed by “propagating light spot” or “near-field light”. (Semiconductor lasers with different wavelengths are selected by switching).

That is, in the optical fiber probe 30 described with reference to FIGS. 3 to 6, the conical surface having a smaller apex angle than the light emitting surface is close to the region including the optical axis so as to be surrounded by the light emitting surface. An optical element formed as a field light bleed surface, the near field light bleed surface covered with a conductive film for leaching near field light (claim 11), and a polarization selection means FD provided on the light exit surface The conductive material is made of a conductive material having a periodic shape change of ½ or less of the incident light wavelength, and the conductive material is the same as the material (Au) of the conductive film for leaching near-field light. Item 12).
An optical fiber probe in which a light exit surface and a near-field light bleed surface are formed as the exit end face shape of the optical fiber (claim 14).

  Returning to FIG. 3, a laser beam having a wavelength suitable for the inspection is emitted depending on whether the inspection by the propagation light spot or the inspection by the near-field light is performed, and the emitted laser light is as described above. Then, the light enters the probe portion 304 of the optical fiber probe 30.

  When an inspection is performed using the propagation light spot, a “propagation light spot” is formed, and the surface 2a of the inspection object 2 is scanned by the propagation light spot. Further, when an inspection using near-field light is performed, a “near-field light spot” is formed, and the surface 2a to be measured is scanned.

These scans are performed by controlling the probe controller 35 by the control means 100.
The light reflected by the scanned surface 2a to be scanned (even in the case of the near-field light constituting the near-field light spot, becomes reflected light when reflected by the tested surface 2a) is “returned light”. The light enters the core portion 301 of the optical fiber probe 30, passes through the quarter-wave plate 38 b and the half-wave plate 38 a, is reflected by the beam splitter 32, enters the photodetector 34, and is detected.

  The photodetector 34 photoelectrically converts the received return light to generate a luminance signal. A scanned image is created by the image processing unit 36 based on the generated luminance signal and displayed on the image display unit 37A.

In general, in the inspection of the surface 2a to be tested, first, “low-resolution inspection” is performed by scanning with a propagation light spot, and an inspection area for performing “high-resolution inspection” is specified based on the inspection result. Is inspected with a light spot by near-field light.
In the inspection apparatus shown in FIG. 3, the “surface shape inspection” of the surface 2a to be inspected can be performed by displacing the position of the propagation light spot in the optical axis direction.

  First, “low-resolution inspection using a propagating light spot” will be described.

  Returning to FIG. 3, the optical fiber probe 30 is configured as described above, and the vicinity of the probe unit 304 is attached to the probe control unit 35. The probe control unit 35 is a known one configured by, for example, a “three-axis actuator” or the like, and is a “direction in which the probe unit 304 of the optical fiber probe 30 is brought close to and away from the test surface 2a (up and down direction in the drawing). ”And a function of displacing in two directions orthogonal thereto.

  In the low-resolution inspection, the distance between the tip (tip) of the near-field light extruding portion 304b of the optical fiber probe 30 and the test surface 2a is set to “a distance suitable for scanning with a propagation light spot (several hundred nm to several μm)”. ”And scanning with a propagating light spot is performed. The “distance suitable for scanning with a normal propagation light spot” is experimentally specified in advance and stored in the memory of the control means 100.

  The laser light having a linearly polarized light component emitted from the light source 31 is transmitted through the beam splitter 32, and the polarization is adjusted by the half-wave plate 38a and the quarter-wave plate 38b driven by the adjusting means 38, and the optical fiber. At this time, the polarization state of the laser beam incident on the optical fiber probe 30 is determined by the position of the propagation light spot emitted from the normal propagation light emitting unit 304a and formed on the optical axis. It is adjusted so that the position of a distance suitable for scanning with a spot (this distance is experimentally determined in advance and stored in the memory of the control means 100 and used as a control parameter).

  In this state, the control means 100 controls the probe control unit 35 to perform two-dimensional scanning of the test surface 2a. First, the probe control unit 35 adjusts the interval between the probe unit 304 and the test surface 2a so that the interval becomes the “distance suitable for scanning with the propagation light spot SP”. Then, the propagation light spot formed at the position of the distance from the tip of the probe unit 304 forms a scanning spot on the surface 2a to be measured.

  In this state, when the probe control unit 35 scans the probe unit 304 two-dimensionally, the surface 2a to be measured is scanned two-dimensionally by the propagation light spot. Then, as described above, the light reflected by the surface to be examined is returned as light and detected by the photodetector 34, and a scanned image is displayed on the image display unit 37A. Based on the image displayed on the image display unit 37A, the inspector can measure and observe the details of the surface 2a to be inspected and execute the low-resolution inspection.

  At this time, a near-field light spot is formed at the tip of the near-field light exuding portion 304b, but the tip and the test surface 2a are separated from each other by several hundreds of nanometers to several μm, and the near-field light spot is not covered. Since it does not interact with the inspection surface 2a, the exudation near-field light does not affect the inspection by the propagation light spot. Therefore, the inspection using the propagation light spot can be performed at a high S / N ratio without being affected by the exuding near-field light.

  When scanning the probe unit 304 in a direction parallel to the surface with respect to the test surface 2a, the height of the probe unit 304 with respect to the test surface 2a is made constant so that control in the optical axis direction is not required during inspection. Thus, coupled with the distance between the probe tip and the propagation light spot: about several hundred nm to several um, high-speed scanning becomes possible, leading to a significant reduction in measurement time.

  Furthermore, compared with the conventional near-field light measurement, since the measurement range per measurement point is wide, a wide range of measurement can be realized with the same number of measurement points and the same number of measurement lines (scanning lines).

  Furthermore, compared with the case where the light emitted from the optical fiber probe 30 is not condensed, more return light from the measured surface 2a can be obtained, and as a result, a high-contrast measurement result can be provided to the user. .

  Next, “a high-resolution inspection region for performing a more detailed inspection” is specified based on “optical property information of the surface 2a to be measured” obtained from the image displayed on the image display unit 37A, and the optical fiber probe 30 is placed in the region. “Position alignment” is performed by horizontally moving, and “high-resolution inspection using a near-field light spot” is performed only on the region concerned.

  That is, the probe control unit 35 is controlled by the control unit 100 to change the distance between the tip of the probe unit 304 of the optical fiber probe 30 and the test surface 2a. In this state, scanning is performed in two directions parallel to the test surface 2a, thereby scanning the test surface 2a with a near-field light spot. “Amount of change in the distance between the tip of the optical fiber probe 30 and the test surface 2a” associated with the switching from the low-resolution inspection to the high-resolution inspection is experimentally determined in advance and converted into data and stored in the memory of the control means 100. It is used as a parameter for the switching control.

  In a state where the near-field light spot is formed, the probe control unit 35 moves the probe unit 304 in a direction approaching the surface 2a to be measured. When the distance between the tip of the near-field light extruding portion 304b and the test surface 2a is ¼ or less of the wavelength of the laser light emitted from the light source 31, the near-field light from the near-field light spot is detected on the test surface 2a. , And a “very small light spot” of near-field light is formed on the test surface 2a.

  The near-field light that forms the light spot is reflected by the test surface 2a, guided as inspection light to the photodetector 34 through the core 301, and used for "high-resolution inspection of the test surface 2a" in the same manner as described above. It is made.

  The photodetector 14 photoelectrically converts the inspection light by the received near-field light to generate a luminance signal. Based on the generated luminance signal, a “scanned image” is created by the image processing unit 16 and displayed on the image display unit 17A. The inspector can measure and observe the details of the surface 2a to be inspected based on the image displayed on the image display unit and perform a high resolution inspection.

  When moving the probe unit 304 in the direction parallel to the test surface 2a toward the high-resolution inspection region, if the "height with respect to the test surface 2a" of the tip of the probe unit 22 is constant, during the inspection Displacement control in the proximity / separation direction is not required, and faster scanning is possible in combination with the distance (about several hundred nm to several μm) between the propagation light spot and the tip of the probe described above. Thus, the measurement time can be greatly shortened.

  As described above, the inspection apparatus according to the embodiment shown in FIG. 3 is an apparatus for optically inspecting the surface 2a to be inspected 2 and propagates light from the light source 31 and the light source. And the position of a minute light spot ("propagation light spot") formed by the propagation light emitted from the optical element 30 and the optical element 30 that emits the propagation light from the light exit surface that is symmetric with respect to the optical axis. A light spot position displacing means for displacing the scanning surface, a scanning means 35 for scanning the test surface 2a of the test object with a minute light spot, and a detection means 34 for detecting the return light from the test surface 2a as the inspection light. , 36, and 37A, and the optical element 30 is the optical element (optical fiber probe) according to claim 14, and the light spot position displacing means is incident from the light source 31 to the light exit surface of the optical element 30. Means for changing the polarization direction of light 8,38A, a 38b (claim 15).

  Further, the optical fiber probe 30 is the one according to the fourteenth aspect, and the scanning means 35 is capable of switching between the test surface scanning by the propagation light spot and the test surface scanning by the near-field light (claim 17). Therefore, the inspection described above is the inspection method according to claim 18.

  Hereinafter, the surface shape inspection of the test surface 2a will be described.

  First, the half-wave plate 38a and the quarter-wave plate 38b are driven by the adjusting means 38, and the polarization state of the laser beam incident on the optical fiber probe 30 is changed to the polarization state P3 in FIG. The spot condensing position is set to be the condensing position: D3 (condensing position: intermediate position between D1 and D2) in FIG. 4F, and this position is set as the “reference position of the propagation light spot”. .

  In this state, the probe control unit 35 adjusts the distance between the probe unit 304 and the test surface 2a so that the light collection position D3 where the propagation light spot is formed as described above coincides with the test surface 2a.

  Subsequently, the polarization state of the incident light is set to the polarization state P1 in FIG. 4 (f), and the condensing position of the propagation light spot is set to the end portion: D1 of the region: D1 to D2. In this state, the preparation process ends.

  Next, “scanning of the inspection area” is performed by the probe control unit 35. In this scanning, “a plurality of sampling positions: SP1, SP2,... SPi,. The propagation light spot is sequentially moved to the set sampling position. Sampling position: SPi is specified by the two-dimensional coordinates (X, Y) of the inspection region.

  Then, every time a new sampling position: SPi comes to the scanning position, the polarization state of the incident light is sequentially switched from P1 to P2 in FIG. It is changed in the range of ~ D2. The intensity of the return light: PW accompanying the change of the condensing position is stored in the memory as received light data: PW (Dx) in relation to the condensing position: Dx in the areas: D1 to D2.

  When the light reception data: PW (Dx) is obtained for all sampling positions, the control means 100 extracts “propagation light spot condensing position: D (SPi)” having the highest return light intensity for the light reception data for each sampling position: SPi. To do. When the converging position of the propagation light spot is changed, “the return light is maximized” is when the propagation light spot is condensed on the surface of the test surface 2a. : Record again as data on the unevenness (shape information) of the test surface 2a in SPi.

  The surface of the surface to be inspected 2a generally has “small unevenness”, but when the shape information: D (SPi) is obtained for each sampling position: SPi as described above, the sampling position: SPi is Since it is specified by the two-dimensional coordinates (X, Y), the uneven shape of the inspection surface in the inspection region is known for each sampling position, and thus, the surface shape inspection of the surface 2a to be detected is executed. Can do. A set of shape information: D (SPi) stored in the memory can be image-processed to display the three-dimensional shape of the test surface 2a on the image display unit 37A.

  When the probe unit 304 is scanned in a direction parallel to the surface with respect to the test surface 2a, the height of the probe unit 304 with respect to the test surface 2a is made constant so that control in the optical axis direction can be performed during the inspection. And the distance between the probe tip and the propagation light spot: about several hundred nm to several um, high-speed scanning becomes possible, leading to a significant reduction in measurement time.

  That is, in the “surface shape inspection method” described above, the position of the propagation light spot is set very close to the test surface 2a, and the position of the light spot is displaced while scanning the test surface 2a with the propagation light spot. By changing the polarization direction of the light incident on the light exit surface of the optical element from the light source by means, the light spot position where the return light detected by the detecting means has the maximum intensity for each sampling position: SPi of the test surface 2a: D An inspection method for acquiring (SPi) as height information of a surface to be inspected (claim 19).

  The scanning of the test surface 2a may be performed by fixing the probe unit 304 of the optical fiber probe 30 and displacing the test object 2, or the tip of the probe unit 304 and the test surface 2a. Is switched by “displacement of the object 2 to be inspected (displacement in the vertical direction in FIG. 1)”, and two-dimensional scanning by the near-field light spot or the propagation light spot is performed by the displacement of the probe unit 304. May be. That is, scanning can be executed by three-dimensional relative displacement between the test surface and the probe unit (optical element).

  It should be noted that if the “polarization state can be electrically modulated” instead of the half-wave plate 38a, for example, a liquid crystal polarization element, and the polarization state is electrically changed, the polarization state can be adjusted. By adopting a configuration that performs modulation using "electrical liquid crystal drive means" without using a mechanical moving part, high-speed modulation without a mechanical moving part is possible, and the converging position displacement of the propagating light spot is high-speed. Therefore, the above surface shape inspection can be realized at high speed.

  The optical element 20 shown in FIG. 2 can be configured as an optical fiber probe, and this optical fiber probe can be used in place of the optical fiber probe 30 in FIG. In this case, high-resolution inspection using a near-field light spot cannot be performed, but the low-resolution inspection and surface shape inspection can be performed. Further, the optical element 10 shown in FIG. 1 is configured as an optical fiber probe, and using such an optical fiber probe and the above-described turret of the light shielding member F, a liquid crystal shutter device, a micromirror device, etc., a hollow cylindrical light beam By switching between the inner diameter and the width, it is possible to configure an inspection apparatus capable of performing the low-resolution inspection and the surface shape inspection.

  As described above, the “selective transmission of the polarization component that is selectively transmitted according to the distance from the optical axis in a stepwise or continuous manner” changes monotonously with the distance from the optical axis. Even in the case of changing randomly, it is not necessary to cover the entire polarization change region from “a reference polarization component to a polarization component orthogonal thereto”, and only a part of the polarization change region may be used.

  For example, in the embodiment shown in FIG. 3, the normal propagation light emitting section 304a has polarization selecting means formed on the light exit surface as shown in FIG. 4 (a), and the polarization selecting means is concentric. Dividing into N ring zones 4a1, 4a2, 4a3, 4a4,... 4aN-1, 4aN, the polarization direction of the “polarized light component to be selectively transmitted” is the “left-right direction” in the innermost zone zone 4a1. To the “vertical direction” in the outermost ring zone region 4aN changes monotonously and stepwise according to the distance from the optical axis.

  In this case, for example, if the annular zone 4aN is omitted and the polarization selecting means is configured by the annular zones 4a1 to 4aN-1, the annular zone 4aN shown in FIG. The polarization component (the linearly polarized light in the vertical direction in the figure) "does not exit from the light exit surface (normal propagation light exit section).

  Therefore, when performing near-field light inspection, if near-field light is generated by the “polarized light component that does not exit from the normal propagation light emitting portion” as described above, the inspection light is free from noise of the propagation light. Therefore, the S / N ratio of the inspection by the near-field light can be made extremely good.

FIG. 7 shows a modification of the optical fiber probe.
In this example, in the near-field light exudation portion 304b1 in the probe portion of the optical fiber probe, the entire near-field light exudation surface is not covered with the “conductive film for near-field light exudation”. The top of the conical surface forming the exudation surface is exposed. Even when such an optical fiber probe is used, a high-intensity near-field light spot due to exuded near-field light can be obtained. In FIG. 7, reference numeral 340a indicates a normal propagation light emitting portion, and reference numeral 3401 indicates a light emitting surface.

  1 and the optical element 20 of FIG. 2 have a taper angle: θ conical light emitting surfaces 10A and 20A, and a light emitting surface that forms the probe portion 304 at the tip of the optical fiber probe of FIG. The conical surface shape of the near-field light extruding surface having taper angles θ1 and θ2 can be formed by, for example, “wet etching process using an aqueous solution of hydrofluoric acid” disclosed in JP-A-7-26059.

  The sizes of the optical elements 10 and 20 and the optical fiber probe 30 can be appropriately set. For example, in the case of the optical fiber probe 30, a core diameter: several μm, for example, 4 μm can be used. The diameters of 20 and 20 can be appropriately selected. Further, the number of ring zones: N can be appropriately selected as a value of 2 or more. Of course, these numerical values do not limit the invention.

It is a figure for demonstrating the displacement of the condensing position of a propagation light spot. It is a figure for demonstrating the displacement of the condensing position of a propagation light spot. It is a figure for demonstrating one Embodiment of an inspection apparatus. It is a figure for demonstrating the characteristic part in embodiment of FIG. It is a figure for demonstrating the characteristic of the normal propagation light emission part of an optical fiber probe. It is a figure for demonstrating the characteristic of a near-field light exudation part. It is a figure for demonstrating the modification of an optical fiber probe.

Explanation of symbols

2 Test object 2a Test surface 31 Light source 32 Beam splitter 30 Optical fiber probe 34 Photo detector 38a 1/2 wavelength plate 38b 1/4 wavelength plate

Claims (19)

A method of forming a minute light spot and displacing the position,
The optical axis has a shape similar to the cross-sectional shape of the light exit surface in a plane perpendicular to the optical axis from the light exit surface of the transparent optical element having a convex cone surface symmetrical to the optical axis as the light exit surface. From which an optical axis symmetric light beam portion having a desired inner diameter and width is emitted to form a minute light spot on the optical axis outside the optical element,
The light spot position displacement characterized by changing the formation position of the minute light spot by changing at least the inner diameter from the optical axis among the inner diameter and width from the optical axis of the light beam portion symmetrical to the optical axis. Method. The light spot position displacement method according to claim 1,
A light beam whose shape is similar to the cross-sectional shape of the light exit surface within a plane perpendicular to the optical axis of the optical element and whose light beam cross-sectional shape is adjusted from the optical axis to an optical axis symmetric shape having a desired inner diameter and width. A method of displacing a light spot, wherein the light is incident on the light exit surface parallel to the optical axis direction and exits from the light exit surface. The light spot position displacement method according to claim 1,
A polarization selection means for selectively transmitting a specific polarization component to the light exit surface of the optical element so that the polarization component to be selectively transmitted changes stepwise or continuously according to the distance from the optical axis. Provided,
By changing the polarization state of the light that propagates through the optical element and travels toward the light exit surface, the polarization selection means makes the shape similar to the cross-sectional shape of the light exit surface within the plane orthogonal to the optical axis, A method of displacing a light spot position, wherein an optical axis symmetric light beam portion having a desired inner diameter and width is emitted from the optical axis. In the light spot position displacement method according to any one of claims 1 to 3,
A light spot position characterized by emitting a light beam portion having a ring-shaped light beam cross-sectional shape having a desired inner diameter and width from the optical axis from the light emission surface of the optical element having a conical surface. Displacement method. It has an optical axis symmetry and a convex conical surface as a light exit surface,
A polarization selection means for selectively transmitting a specific polarization component is provided on the light exit surface so that the polarization component to be selectively transmitted changes stepwise or continuously according to the distance from the optical axis. An optical element. The optical element according to claim 5, wherein
In the polarization selection means, the stepwise or continuous change of the polarization component to be selectively transmitted according to the distance from the optical axis is the distance from the optical axis from the reference polarization component to the polarization component orthogonal thereto. And an optical element that changes monotonously. The optical element according to claim 5, wherein
Changes in the polarization component to be selectively transmitted according to the distance from the optical axis in the polarization selection means change randomly with the distance from the optical axis from the reference polarization component to the orthogonal polarization component. An optical element characterized by the above. The optical element according to any one of claims 5 to 7,
An optical element characterized in that the polarization selection means provided on the light exit surface has a structure that makes a periodic shape change that is 1/2 or less of the incident light wavelength. The optical element according to claim 8.
An optical element characterized in that a structure having a periodic shape change of 1/2 or less of an incident light wavelength is formed of a conductive material. The optical element according to claim 9, wherein
An optical element, wherein the conductive material is Au (gold) or Al (aluminum). The optical element according to any one of claims 5 to 10,
A conical surface having a smaller apex angle than the light exit surface is formed as a near-field light exudation surface in a region including the optical axis so as to be surrounded by the light exit surface. An optical element characterized by being coated with a conductive film for exudation. The optical element according to claim 11, wherein
The polarization selection means provided on the light exit surface is made of a conductive material having a periodic shape change of 1/2 or less of the incident light wavelength, and the conductive material is a conductive material for leaching near-field light. An optical element characterized by being the same as the material of the film. The optical element according to any one of claims 5 to 10,
An optical element comprising an optical fiber probe having a light exit surface formed as an exit end face shape of an optical fiber. The optical element according to claim 11 or 12,
An optical element characterized by being an optical fiber probe in which a light exit surface and a near-field light exudation surface are formed as the exit end face shape of an optical fiber. An apparatus for optically inspecting a surface to be inspected,
A light source;
An optical element for propagating light from the light source, and emitting the propagating light from an optically symmetric light exit surface;
A light spot position displacing means for displacing the position of a minute light spot formed by propagating light emitted from the optical element on the optical axis;
Scanning means for scanning the test surface of the test object with the minute light spot;
Detecting means for detecting return light from the test surface as inspection light,
The optical element is the optical element according to any one of claims 5 to 14,
The inspection apparatus, wherein the light spot position displacing means is a means for changing a polarization direction of light incident on the light exit surface of the optical element from the light source. The inspection apparatus according to claim 15,
14. An inspection apparatus according to claim 13, wherein the optical element is one according to claim 13. The inspection apparatus according to claim 15,
The optical element is according to claim 14,
An inspection apparatus, wherein the scanning means is capable of switching between a scanning of a test surface by a propagation light spot and a scanning of a test surface by near-field light.   An inspection method for optically inspecting a surface to be inspected using the inspection apparatus according to any one of claims 15 to 17. The inspection method according to claim 18, wherein
Set the formation position of the propagation light spot very close to the test surface,
While scanning the test surface with the propagating light spot, the light spot position displacement means changes the polarization direction of the light incident on the light exit surface of the optical element from the light source,
An inspection method characterized in that, for each sampling position on the test surface, a light spot position at which the return light detected by the detection means has a maximum intensity is acquired as height information of the test surface.

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