JP5268061B2 - Board inspection equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate inspecting apparatus capable of inspecting a large substrate at a high speed. <P>SOLUTION: The substrate inspecting apparatus includes inspection heads 2 and 3 scanning the surface of a substrate to be inspected by an inspection beam and receiving the light emitted from the substrate, a drive device for moving the inspection heads in a first direction and the second direction crossing the first direction at a right angle and a signal processor for detecting a flaw on the basis of the output signals output from the inspection heads. The inspection heads are equipped with inspection beam emitting devices 11 and 15 for emitting inspection beams, an object lens 23 for projecting the inspection beams toward the substrate, the differential interference optical system 22 arranged in the light path between the inspection beam emitting devices and the object lens, a first light detecting means 27 for detecting the interference beam synthesized by the differential interference optical system and the beam deflector 20 arranged in the light path between the inspection beam emitting devices and the object lens and periodically deflecting the inspection beams to the second direction. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a substrate inspection apparatus suitable for inspecting defects of various substrates, and more particularly to a substrate inspection apparatus suitable for defect inspection of a large glass substrate.

  The present invention also relates to a light detection device suitable for detecting scattered light.

  In a manufacturing process of a liquid crystal display device or a plasma display device, various patterns are formed on a glass substrate by a photolithography method using a photomask. In this manufacturing process, if there are defects such as foreign matter, scratches, and voids in the photomask, a defect image is projected onto the substrate, resulting in a problem that the manufacturing yield is significantly reduced. Therefore, defect inspection of a glass substrate used for manufacturing a photomask is extremely important from the viewpoint of improving the manufacturing yield of various devices.

As an inspection apparatus for detecting a defect in a glass substrate, a laser scattering inspection apparatus is known (for example, see Patent Document 1). In this known inspection apparatus, a laser beam is projected obliquely with respect to a glass substrate to be inspected, scattered light from the glass substrate is received using two photodetectors, and from the two photodetectors. In accordance with the form of the output signal, foreign matter present on the front side of the glass substrate and foreign matter present on the back side are discriminated.
JP 2003-294653 A

  The above-described laser scattering type inspection apparatus is an inspection apparatus that is effective for detecting defects due to adhesion of foreign substances existing on the surface of a glass substrate. However, a defect in a photomask or a glass substrate needs to detect not only foreign substances existing on the front and back surfaces but also shallow scratches (sleeks) and minute irregularities (pits) formed on the surface of the glass substrate. However, since it is difficult for scattered light to be generated from these fine scratches, the laser scattering type inspection apparatus has a drawback that it is difficult to detect it as a defect. In addition, when a thin foreign film with a gently changing film thickness is formed on the substrate surface, only minute scattered light is generated from the thin film, so that defects caused by thin film foreign substances cannot be detected in the same manner. There is. Furthermore, if there are bubbles or a local refractive index distribution inside the glass substrate, the exposure light is scattered, which causes a decrease in device manufacturing yield. Therefore, there is a strong demand for the development of an inspection apparatus that can detect voids, which are internal defects of a glass substrate, with high sensitivity.

  In recent years, with the increase in size of devices, the original size of the photomask is also increased, and the size of the eighth generation photomask is increased to 1.22 m × 1.4 m. Therefore, with the increase in size of glass substrates, it is an urgent task to develop a defect inspection apparatus that can inspect large photomasks and glass substrates at high speed.

  When optically detecting a substrate defect, it is necessary to generate a focus error signal using an autofocus mechanism and to perform focus control on the scanning beam during inspection. However, when performing defect inspection on various substrates on which no pattern is formed, it is extremely difficult to form a focus error signal because the reflected light from the substrate does not contain bright and dark contrast components. On the other hand, when an accurate focus error signal cannot be generated, the focus of the scanning beam is deviated from the substrate surface, resulting in a problem that the accuracy of defect inspection is significantly reduced.

  An object of the present invention is to realize a substrate inspection apparatus that can inspect various large substrates at high speed.

  Another object of the present invention is to realize a substrate inspection apparatus capable of simultaneously detecting not only foreign substances existing on the surface of the substrate but also pits and sleeks on the surface of the substrate and voids existing inside the substrate in one inspection process. It is in.

  Another object of the present invention is to realize a substrate inspection apparatus capable of performing accurate focus control even on a substrate on which a pattern is not formed.

A substrate inspection apparatus according to the present invention described as a reference example scans the surface of a substrate to be inspected with an inspection beam and receives light emitted from the substrate, and the inspection head in a first direction (X direction) and A substrate inspection apparatus comprising: a drive device that moves in a second direction (Y direction) orthogonal to the first direction; and a signal processing device that detects a defect based on an output signal output from the inspection head. The inspection head is
Inspection beam generator for generating inspection beam, objective lens for projecting inspection beam toward substrate, differential interference optical system disposed in optical path between inspection beam generator and objective lens, and differential interference optical system A first light detecting means for receiving the interference beam synthesized by the first beam detecting means, and a beam deflector arranged in an optical path between the inspection beam generating device and the objective lens to periodically deflect the inspection beam in the second direction. With the equipment,
The substrate surface is scanned with the inspection beam by the beam scanning in the second direction by the beam deflecting device, and the movement of the inspection head in the first direction and the movement in the second direction.

  The present invention realizes a substrate inspection apparatus that inspects various large substrates such as a glass substrate, a quartz substrate, or a substrate having a surface formed with a halftone film or a light-shielding film at high speed. In order to achieve this object, in the present invention, not only the inspection head that projects the inspection beam toward the substrate is scanned in the X and Y directions, but also the inspection head is equipped with a third scanning mechanism, and the inspection beam is mainly used. XY scanning is performed while scanning in a direction orthogonal to the scanning direction (X direction). Thus, by scanning the inspection beam as well as the two-way scanning of the inspection head, it becomes possible to perform defect inspection at a higher speed, and the time required for the inspection of a large substrate can be greatly shortened. Further, in the present invention, since the differential interference optical system is mounted on the inspection head, it is possible to clearly detect a minute defect having a depth of about several nanometers existing on the substrate surface.

  In a preferred embodiment of the substrate inspection apparatus according to the present invention, the inspection beam generator generates an inspection beam having an elliptical cross section whose major axis extends in the first direction on the substrate surface, and the axis of rotation of the beam deflection apparatus Is set to be parallel to the major axis of the incident inspection beam, and the substrate surface is periodically scanned in the second direction by an elliptical inspection beam whose major axis extends in the first direction. It is characterized by. Thus, by performing high-speed scanning using an elliptical inspection beam whose major axis extends in the main scanning direction, the inspection time required for inspection of a large substrate can be significantly reduced.

The substrate inspection apparatus according to the present invention is a substrate inspection apparatus for simultaneously inspecting a large substrate fixedly arranged in a vertical shape so that the substrate surface extends in the vertical direction from both sides thereof,
First and second inspection heads arranged so as to face each other with the substrate to be inspected therebetween;
A first driving device that moves the first and second inspection heads in synchronization with the first direction in the vertical plane, and a second drive that moves the first and second inspection heads in synchronization with the second direction orthogonal to the first direction. Equipment,
A signal processing device that performs defect detection based on output signals output from the first and second inspection heads,
The first and second inspection heads include an inspection beam generator that generates an inspection beam, an objective lens that projects the inspection beam onto the substrate surface, and an optical path between the inspection beam generator and the objective lens. A differential interference optical system disposed on the substrate, first light detection means for receiving an interference beam reflected by the substrate surface and synthesized by the differential interference optical system via the objective lens, the inspection beam generating device, and the objective lens , A beam deflecting device that periodically deflects the inspection beam in the second direction, a second light detecting means for detecting backscattered light reflected by the substrate surface, and the substrate passing therethrough And a third light detecting means for detecting the forward scattered light ,
The third light detection means of the first inspection head is mounted on the second inspection head, the third light detection means of the second inspection head is mounted on the first inspection head,
Surfaces on both sides of the substrate are simultaneously two-dimensionally scanned by movement of the first and second inspection heads in the first direction and beam scanning in the second direction orthogonal to the first direction by the beam deflecting means,
The signal processing device mainly detects uneven defects present on the substrate surface based on an output signal from the first light detection means, and mainly detects a defect on the substrate surface based on an output signal from the second light detection means. The present invention is characterized in that an existing foreign matter defect is detected, and an internal defect mainly present in the substrate is detected based on an output signal from the third light detection means .

  When a large glass substrate having a size of 2 m × 2 m is inspected, if the inspection is performed for each side, there is a problem that the time required for the inspection becomes long. Therefore, in the present invention, a large substrate is fixedly disposed in a vertical shape, and the inspection head is disposed so as to face each other with the substrate interposed therebetween. Then, the two inspection heads are moved in the X direction and the Y direction within the vertical plane in synchronization with each other. Thus, by inspecting from both sides of the substrate using two inspection heads, the inspection time can be greatly shortened.

In the substrate inspection apparatus according to the present invention, first and second inspection head includes a third light detection means for detecting the forward scattered light transmitted through the substrate, respectively, a third light detection of the first inspection head The means is mounted on the second inspection head, the third light detection means of the second inspection head is mounted on the first inspection head,
The forward scattered light generated by the inspection beam emitted from the first inspection head is detected by the third light detection means mounted on the second inspection head, and is generated by the inspection beam emitted from the second inspection head. The forward scattered light is detected by third light detection means mounted on the first inspection head .

  Internal defects caused by bubbles or refractive index distribution existing inside the substrate can be detected as forward scattered light. This forward scattered light is detected by the third light detection means arranged on the opposite side across the substrate. In this case, if the third light detecting means is provided as an independent optical head, the structure of the substrate inspection apparatus becomes considerably complicated. Therefore, in the present invention, the third light detection means is mounted on the second inspection head that is arranged on the opposite side across the substrate and moves in synchronization. In this way, if the third photodetecting means is mounted on the inspection head located on the opposite side of the substrate, it is possible to simultaneously detect internal defects of the substrate only by moving the two inspection heads synchronously. Become.

Another substrate inspection apparatus according to the present invention scans the surface of a substrate to be inspected with an inspection beam and receives the reflected light emitted from the substrate, and displaces the inspection head in the optical axis direction orthogonal to the substrate surface. Comprising: a head driving device; and a signal processing device for detecting a defect based on an output signal output from a light detection means mounted on the inspection head, wherein the inspection head comprises:
An inspection beam generator for generating an inspection beam, an objective lens for projecting the inspection beam toward a substrate to be inspected, a light detection means for receiving a reflected beam reflected by the substrate surface, and an output signal from the light detection means A focus detection apparatus that detects a focus state of the inspection beam with respect to the substrate surface and an autofocus mechanism that generates a focus control signal for controlling the focus state of the inspection beam with respect to the substrate surface.

  Since the reflected light from the glass substrate on which no pattern is formed does not contain bright and dark luminance components, it is difficult to detect the focus state of the inspection beam with respect to the substrate surface. On the other hand, in an inspection apparatus in which an illumination beam emitted from a laser light source is converted into an elliptical beam by an optical element having a focusing function in only one direction and the substrate surface is scanned by the elliptical beam, the optical element that forms the elliptical beam is It also functions as an astigmatism element. That is, in the substrate inspection apparatus, the cross-sectional shape of the reflected beam incident on the light detection means changes according to the focus state of the inspection beam on the substrate surface. In view of this characteristic, a focus detection device is formed that detects the focus state of the inspection beam based on an output signal from the light detection means that receives the reflected beam emitted from the substrate surface. The best focus position of the inspection head is detected based on the focus detection signal output from the focus detection device, and the in-focus point of the autofocus mechanism is set to the detected best focus position. If comprised in this way, even if it is a case where the glass substrate etc. in which the pattern is not formed are test | inspected, a defect inspection can be performed in a favorable focus state.

A photodetection device according to the present invention is a photodetection device that detects scattered light generated on the surface of an object to be inspected,
A condensing element that condenses the scattered light generated from the object to be inspected, a photomultiplier that receives the scattered light emitted from the condensing element, and a mirror optical that makes the scattered light emitted from the condensing element enter the photomultiplier And having a system
The condensing element has a light incident opening through which scattered light generated by the inspection object enters, a light emitting opening through which scattered light exits, and a light incident opening having a larger opening diameter than the light incident opening; It is characterized by comprising a cylindrical body having a reflective inner peripheral surface formed between the opening and the light exit opening.

  According to the present invention, the inspection head on which the inspection optical system is mounted is moved in the main scanning direction (X direction) and the sub scanning direction (Y direction) while scanning the inspection beam in the sub scanning direction. It is possible to inspect the substrate surface at high speed. As a result, it is possible to greatly reduce the inspection time of a large glass substrate having a size of 2 m × 2 m. Moreover, since the inspection optical system uses a differential interference optical system, it is possible to accurately detect a fine uneven defect having a depth of about several nanometers.

  FIG. 1 is a diagram showing an example of an optical system mounted on an inspection head of a substrate inspection apparatus according to the present invention. In this example, it is assumed that a defect inspection is performed on a 2000 mm × 2000 mm large glass substrate or quartz substrate 1. The glass substrate 1 is fixedly arranged in a vertical shape so that the substrate surface extends in the vertical direction. The inspection heads 2 and 3 having the same configuration are arranged on both sides of the glass substrate 1 so as to face each other, and both surfaces of the glass substrate 1 are inspected simultaneously. The two inspection heads 2 and 3 move in synchronization with each other in the X direction (direction perpendicular to the paper surface) and the Y direction (up and down direction in the paper surface), and simultaneously scan both surfaces of the glass substrate 1. Further, the inspection heads 2 and 3 are arranged so as to be movable along the optical axis direction of the objective lens, and the optical axis of the objective lens according to a focus control signal output from the autofocus mechanism by a driving device (not shown). Displace in the direction. For clarity of illustration, only one inspection optical system is shown.

  The configuration of the inspection optical system mounted on the inspection heads 2 and 3 will be described. An inspection beam is generated from the laser light source 11. As the laser light source 11, for example, a solid laser that generates a laser beam having a wavelength of 532 nm is used. The inspection beam emitted from the laser light source passes through the Faraday isolator 12 that prevents return light noise, is converted into an expanded parallel light beam by the collimator lens 13, is reflected by the right-angle prism 14, and enters the cylindrical lens 15. The cylindrical lens 15 is a lens having focusing properties in one direction, and an incident inspection beam is converted into an elliptical cross section. The major axis of the elliptical beam emitted from the cylindrical lens is set to a direction orthogonal to the paper surface. Note that it is also possible to generate an elliptical or strip-shaped beam using a diffraction grating instead of a cylindrical lens.

  The inspection beam emitted from the cylindrical lens 15 enters the dichroic mirror 18 through the polarization beam splitter 16 and the imaging lens 17. The dichroic mirror 18 has a characteristic of reflecting an inspection beam having a wavelength of 532 nm and transmitting a focus detection beam of an autofocus mechanism having a wavelength of 670 nm, which will be described later. The inspection beam reflected by the dichroic mirror 18 enters the mirror surface of the polygon mirror 20 as parallel light through the fθ lens 19. The polygon mirror 20 is composed of, for example, a polygon mirror having 16 reflecting surfaces, and its rotational axis is set to be parallel to the major axis of the incident elliptical beam. A drive circuit (not shown) is connected to the polygon mirror 20 and rotates at a predetermined rotation speed by a drive signal from the drive circuit. In this example, the beam deflection direction of the polygon mirror 20 is set in the Y direction. Accordingly, the polygon mirror 20 emits an inspection beam having an elliptical cross section that is periodically deflected and extends in a direction perpendicular to the paper surface.

  The inspection beam emitted from the polygon mirror 20 passes through the fθ lens 19 and enters the Nomarski prism 22 constituting the differential interference optical system via the second objective lens 21. The sharing amount (separation angle) of the Nomarski prism 22 is set to, for example, 0.75 mrd. Thus, by setting the separation angle of the Nomarski prism large, it is possible to capture a bright and dark image resulting from gently changing pits and unevenness as a clear bright and dark image. In addition, it is possible to clearly capture an image of a thin film foreign body whose film thickness changes gently. An ordinary ray and an extraordinary ray are emitted from the Nomarski prism 22, and the ordinary ray and the extraordinary ray intersect at the rear focal point of the objective lens 23 and enter the objective lens 23. The ordinary ray and the extraordinary ray incident on the objective lens 23 are converged and incident on the substrate 1 to be inspected.

  The substrate inspection apparatus according to the present invention is suitable for inspection of various substrates on which a pattern is not formed, such as a synthetic quartz substrate, a substrate having a light shielding film or a halftone film formed on the surface, in addition to a glass substrate. Can be used to inspect for defects.

  The glass substrate 1 is scanned with a focused elliptical beam. The major axis of the elliptical beam extends in the X direction (direction perpendicular to the paper surface), and the polygon mirror 20 periodically deflects the elliptical beam in the Y direction, so that the substrate 1 is two-dimensionally formed by an elliptical light spot. Scanned. At the same time, since the inspection head moves at a constant speed in the X direction, the substrate surface is scanned in a band shape by the beam deflection action by the polygon mirror and the movement of the inspection head in the X direction. As a result, the substrate surface is scanned two-dimensionally at high speed, the throughput is high, and the inspection time for a large glass substrate can be greatly shortened.

  The inspection beam reflected by the surface of the glass substrate 1 is condensed by the objective lens 23 and enters the Nomarski prism 22. In the Nomarski prism 22, the reflected light of the ordinary ray and the reflected light of the extraordinary ray are combined and emitted as a combined interference beam. That is, the components in the direction of the electric field vector of the reflected light from the ordinary ray and the reflected light from the extraordinary ray interfere with each other, and are converted into an interference beam having a luminance corresponding to the phase difference caused by scratches or irregularities on the surface of the glass substrate 1 The Therefore, various defects existing on the surface of the glass substrate can be detected by detecting the luminance change of the interference beam emitted from the Nomarski prism.

  The combined interference beam emitted from the Nomarski prism 22 enters the polygon mirror 20 via the second objective lens 21 and the fθ lens 19 and is descanned. The interference beam reflected by the polygon mirror enters the polarization beam splitter 16 through the dichroic mirror 18 and the imaging lens 17. Then, of the reflected light from the substrate surface, the component whose polarization plane is rotated by 90 ° is reflected by the polarization beam splitter 16. Accordingly, the polarization beam splitter 16 acts as a polarizer that aligns the plane of polarization with respect to the illumination light emitted from the laser light source 11, and acts as an analyzer for the interference light emitted from the Nomarski prism.

  The interference beam emitted from the polarization beam splitter 16 enters the first light detection means 27 through the imaging lens 24 and the two total reflection mirrors 25 and 26. The first light detection means 27 includes five optical fibers 28 to 32, and five photodiodes 33a to 33e (only reference numerals 33a and 33e are shown in the drawing) arranged at the light emitting ends of the respective optical fibers. Have FIG. 2 is a diagram showing the relationship between the light incident surfaces of the five optical fibers and the incident interference beam. In this example, the optical fibers 28 to 32 have an elongated cross section, and these five optical fibers are arranged along the long axis direction of the incident interference beam. Therefore, the elliptical reflected beam from the surface of the glass substrate is received by the five photodiodes 33a to 33b and converted into an electrical signal. Each output signal from the photodiode is amplified by an amplifier and supplied to a signal processing device. Accordingly, five multi-channel detection systems are configured.

  The signal processing device processes output signals from the five photodiodes and outputs a video signal of the differential interference image. As described above, the differential interference image outputs a defect image in which a bright image and a dark image corresponding to the concave and convex portions existing on the substrate surface are combined. In addition, in the defect image, the generation order of the bright image and the dark image is reversed according to the unevenness of the substrate surface. Therefore, by performing threshold processing on the video signal in the signal processing apparatus, it is possible to detect convex defects and concave defects present on the substrate surface.

  As a method for detecting a change in luminance of a defect image, output signals during the deflection period of each reflection surface of a polygon mirror are compared with each other to detect the difference, and the difference signal is binarized using two positive and negative thresholds. Processing can be performed, and defect determination can be performed based on the result. For example, if a positive pulse and a negative pulse occur continuously, it is determined as a convex defect, and conversely, if a negative pulse and a positive pulse occur continuously, it is determined as a concave defect. To do.

  Next, detection of scattered light will be described. When a foreign substance exists on the surface of the glass substrate 1, scattered light is generated by the foreign substance. This scattered light travels in a direction opposite to the traveling direction of the inspection beam. Further, if there are bubbles or local refractive index distribution inside the glass substrate, scattered light is also generated from these voids. This scattered light travels in the propagation direction of the inspection beam. Therefore, it is possible to detect a foreign matter defect present on the surface of the glass substrate by detecting the backscattered light generated from the glass substrate 1, and it is possible to detect an internal defect of the substrate by detecting the forward scattered light. . In this example, the back scattered light is detected by the second light detection means 40, and the forward scattered light is detected by the third light detection means 50.

  The second light detection means 40 for detecting the backscattered light is formed of a trumpet-shaped cylindrical body, and a condensing element 41 for condensing the backscattered light generated from the surface of the glass substrate 1 and an objective lens are inserted. A perforated mirror 42 that reflects the reflected light emitted from the condensing element 41, a total reflection mirror 43 that receives the reflected light from the perforated mirror 42, and a scattered light emitted from the total reflection mirror 43. And a first photomultiplier (PMT) 44 for receiving light. When a foreign substance exists on the surface of the glass substrate and the scanning beam is incident on the foreign substance, scattered light reflected on the surface of the foreign substance is generated. This scattered light travels mainly in the direction opposite to the propagation direction of the scanning beam. The backscattered light emitted from the substrate surface is collected by the light collecting element 41, reflected by the reflective inner peripheral surface of the light collecting element, converted into substantially parallel light, and incident on the perforated mirror 42. The aperture mirror 42 has an opening in which the objective lens 23 is inserted at the center, and reflects scattered light traveling toward the periphery of the objective lens toward the total reflection mirror 43. Then, the light is reflected by the total reflection mirror 43, enters the PMT 44, and is converted into an electric signal. An output signal from the PMT 44 is supplied to a signal processing device.

  FIG. 3 is a diagram for explaining the operation of the condensing element 41 that condenses the backscattered light. The condensing element 41 that condenses the scattered light is a reflective member having a shape of a rotating paraboloid, for example, a part of an aluminum paraboloid shaped body cut out by a plane orthogonal to the axis, and pressed and deformed in one direction This is a hollow condensing element that is deformed into an elliptical shape. Therefore, it is formed in a parabolic shape on the inner peripheral surface of the condensing element, and the condensing element 41 also functions as a parabolic mirror. The condensing element 41 has a light incident opening 41a into which forward scattered light emitted from the surface of the substrate 1 enters and an opening diameter larger than the opening diameter of the light incident opening, and the light from which the collected scattered light is emitted. It has an exit opening 41b and a reflective inner peripheral surface 41c located between the light entrance opening 41a and the light exit opening 41b. The light incident opening 41a and the light emitting opening 41b are both elliptical openings. The inner peripheral surface 41c of the light condensing element 41 is formed in a curved surface defined by a paraboloid of revolution when viewed along the first surface including the major axis of the ellipse, and is orthogonal to the first surface. When viewed by cutting the second surface, it is formed into a curved surface defined by an elliptical surface. Note that the focal point of the paraboloid is located outside the apex. The condensing element 41 is disposed so that the focal point of the paraboloid of revolution coincides with the substrate surface. When a foreign substance defect exists on the surface of the substrate 1, forward scattered light traveling at various angles is generated. The forward scattered light is incident on the reflective parabolic surface 41c through the light incident opening of the condensing element 41 that also functions as a parabolic mirror. Since the reflective inner peripheral surface 41c is arranged so that the focal point of the paraboloid coincides with the surface of the substrate, the scattered light traveling at various angles is emitted from the focal point of the paraboloid and is reflective. The light is reflected by the parabolic surface 41c and emitted from the light exit opening 41b as a parallel light flux.

  FIG. 4 is a diagram for explaining the operation of the light collecting element 41 according to the present invention. FIG. 4A shows a state where scattered light is incident on the reflecting surface of the paraboloid of revolution. The condensing element according to the present invention has a paraboloid shape in which a part of a rotating paraboloid is cut out by two surfaces orthogonal to the optical axis (center axis). When the focal point of the rotating paraboloid is located outside the apex of the paraboloid, scattered light generated from the focal point and traveling at various angles is reflected by the reflective paraboloid and emitted as a parallel beam. . Therefore, when the focal point of the rotating paraboloid is located on the surface of the substrate, the spot-like focal point is located on the surface of the substrate, and the scattered light generated from the foreign matter and traveling in various directions is caused by the parabolic mirror. It is condensed and travels as a parallel light beam. That is, the paraboloid of revolution whose focal point is located outside the apex exerts the action of collecting scattered light. On the other hand, FIG. 4B shows reflection characteristics of an elliptic paraboloid obtained by pressing the rotating paraboloid shown in FIG. 4A in the uniaxial direction so that the cross-sectional shape is deformed to be elliptic. In this case, both the light incident aperture and the light exit aperture are elliptical. In the case of an elliptic paraboloid deformed to have an elliptical cross section, as shown in FIG. 4B, the focal point extending linearly along the optical axis (central axis), that is, the linear focal point is It is formed. FIG. 4C shows a state where the elliptical paraboloid is set so that the substrate surface is positioned on a linear focal point. In this case, the scattered light generated from the linear region on the substrate surface is reflected by the reflecting surface and emitted as a parallel light beam.

  In the present invention, since the surface of the substrate is scanned using an inspection beam having an elliptical cross section, if the rotating paraboloid having the dotted focal point shown in FIG. May not be sufficiently collected. Therefore, in the present invention, an elliptic parabolic mirror having an elliptical cross section as shown in FIG. 4B is used. If a hollow body element having a curved inner surface defined by an elliptic paraboloid mirror is used as a condensing element for collecting scattered light, the scattered light generated from any part of the inspection beam is collected. It becomes possible.

  With reference to FIG. 1, the third light detection means 50 for detecting forward scattered light will be described. A condensing lens 51 with a glass thickness correction mechanism, a mirror 52 with a hole, and a second photomultiplier 53 that receives reflected light from the mirror 52 are disposed on the back side of the glass substrate 1. These optical elements move in synchronization with the inspection head 2 and are mounted on a second inspection head 3 that inspects the substrate surface on the opposite side of the glass substrate 1. When the scanning beam enters a void such as bubbles or local refractive index distribution existing inside the glass substrate, the scanning beam travels with the optical path slightly bent by the void, and is forward scattered light from the back side of the glass substrate. Exit. By detecting the forward scattered light, an internal defect of the glass substrate is detected. In this example, the second photomultiplier 53 receives the scattered light collected by the condenser lens 51 and reflected by the perforated mirror 52. Accordingly, an output signal from the second photomultiplier is supplied to the signal processing device, and a defect detection signal due to an internal defect is generated. It is to be noted that normal transmitted light is emitted to the outside through the opening 52a of the perforated mirror 52 and is prevented from interfering with detection of scattered light.

  Next, the autofocus mechanism will be described. In this example, a focus error signal is generated by an optical lever method. A laser light source 61 that generates a light beam having a wavelength of 670 nm is used as a light source that generates a focus detection beam for autofocus. The focus detection beam emitted from the laser light source 61 passes through the beam splitter 62, is reflected by the total reflection mirror 63, enters the dichroic mirror 18, and enters the optical path of the inspection beam. Then, the light passes through the dichroic mirror 18 and enters the polygon mirror 20 through the fθ lens 19. The focus detection beam reflected by the polygon mirror passes through the fθ lens 19 again and enters the objective lens 23 through the second objective lens 21 and the Nomarski prism 22. The focus detection beam is focused by the objective lens 23 and focused on the surface of the substrate 1. The focus detection beam emitted from the objective lens is incident on the surface of the substrate 1 at an oblique angle. The focus detection beam reflected by the substrate surface again passes through the objective lens 23 and travels in the reverse optical path as return light. That is, the light enters the polygon mirror 20 through the Nomarski prism 22, the second objective lens 21, and the fθ lens 19, and is descanned. Further, the light is reflected by the polygon mirror, passes through the fθ lens 19 and the dichroic mirror 18, and is reflected by the total reflection mirror 63. Further, the light is reflected by the beam splitter 62 and enters the beam displacement element 65 through the imaging lens 64. The beam displacement element 65 is constituted by a rotatable parallel plane plate, for example. By rotating the plane-parallel plate around the optical axis, the incident beam is translated so as to be displaced from the optical axis in the rotational direction. For example, in the example shown in FIG. 1, by rotating the plane parallel plate 65 around the optical axis within the paper surface, the incident focus detection beam is translated in a direction away from or closer to the optical axis. To do. After the position of the focus detection beam in the optical axis direction is adjusted by the beam displacement element 65, the focus detection beam enters the photodetector 66 to form a focus detection spot. The photodetector 66 has two light receiving regions 66b and 66c divided by a dividing line 66a. In this example, the dividing line 66a extends in a direction orthogonal to the paper. By adjusting the beam displacement element 65, the focus detection spot is positioned on the dividing line 65a and set to the in-focus state.

  FIG. 5 is a diagram showing the principle of focus control by the optical lever system. In FIG. 5, the upper stage is a diagram showing the relationship between the substrate surface and the focus detection beam, and the lower stage is a diagram showing the state of the focal spot formed on the photodetector. FIG. 5B shows a state where the focus detection beam is focused on the surface of the substrate 1. When the focus detection beam is focused on the surface of the substrate, the focus detection spot formed on the photodetector 66 is located on the dividing line 66a, and the two light receiving areas 66b and 66c have the same amount of light. Is incident. FIG. 5A shows a state in which the substrate 1 is displaced in the direction away from the objective lens in the optical axis direction, or the inspection head is displaced in the direction away from the substrate. In this case, since the focus detection beam is reflected at a point displaced from the optical axis, the focus detection spot formed on the photodetector 66 is displaced in a direction orthogonal to the dividing line 66a (in this example, the focus spot). Is displaced to the right of the drawing). FIG. 5C shows a state where the substrate is displaced in the direction approaching the objective lens or the inspection head is displaced in the direction approaching the substrate. When the substrate is displaced toward the objective lens in the optical axis direction, the focus detection beam is reflected on the surface of the substrate at a point displaced to the opposite side from the optical axis, so that the focal spot formed on the photodetector 66 is , It is displaced in the opposite direction to the direction orthogonal to the dividing line 66a. As described above, when the substrate is displaced in the optical axis direction (Z-axis direction) of the objective lens, the amount of light incident on the two light receiving regions 66b and 66c of the photodetector 66 changes. A focus control signal for driving the inspection head in the optical axis direction can be formed based on the output signal.

  FIG. 6 is a diagram showing an example of an autofocus mechanism according to the present invention. Output signals from the two light receiving regions 66b and 66c are amplified by the amplifiers 67a and 67b, respectively, and supplied to the subtracting means 68 and the adding means 69, respectively. The subtracting unit 68 detects the difference between the output signals from the two light receiving areas to form a difference signal. This difference signal is a signal corresponding to a signal error, and its sign indicates whether it is a front pin state or a rear pin state. Further, the adding means 69 adds the two output signals to form an added signal. The difference signal and the addition signal are supplied to the dividing means 70, and the difference signal is divided by the addition signal to form a normalized focus error signal. The normalized focus error signal is used as a focus control signal for driving the inspection head in the optical axis direction. The focus control signal output from the dividing means 70 is amplified to a predetermined level by the power amplifier 71 and supplied to a driving device that displaces the inspection head in the optical axis direction. In this example, the driving device is constituted by a motor 72 and a ball screw 73. The inspection head is driven in the direction of the optical axis in accordance with the detected focus error. Therefore, the inspection head is controlled to be always focused on the substrate surface. In this example, the light incident on the optical fiber located at the center and the two optical fibers located at both ends is used. However, the optical fiber located at the center and one light arranged at one end are used. It is also possible to generate a focus detection signal using the optical output of the fiber.

  Next, the focus setting for autofocus will be described. When a substrate surface without a pattern is imaged, such as a glass substrate, a quartz substrate, or a substrate with a halftone film or a light-shielding film formed on a glass substrate, the video signal does not contain a bright / dark luminance pattern. It is extremely difficult to set the focus. On the other hand, the inspection apparatus according to the present invention converts a laser beam generated from an inspection light source into a beam having an elliptical section using a cylindrical lens, and scans the surface of the substrate with the elliptical beam. Here, the cylindrical lens is a kind of astigmatism element, and the shape of the spot formed on the light detection means changes according to the focus state of the inspection beam with respect to the substrate surface. In this example, the focus detection apparatus is configured using the characteristic characteristic of the inspection beam.

  7A to 7C show spot shapes of the inspection beam formed on the light detection means in accordance with the focus state of the inspection beam with respect to the substrate surface. The inspection beam (interference beam) reflected by the substrate surface is incident on the five optical fibers 28 to 32 to form a light spot 80. FIG. 7A shows the shape of the spot 80a at the time of focusing when the inspection beam is focused on the surface of the substrate. At the time of focusing, an elliptical spot having a long axis coinciding with the arrangement direction of the five optical fibers is formed. Accordingly, the amount of inspection light incident on each optical fiber is the same. FIG. 7B shows the shape of the spot 80b at the near focus where the focus of the inspection beam is displaced to the objective lens side with respect to the substrate surface. At the near focus, the major axis and the minor axis of the ellipse are inverted, and a vertically long elliptical spot is formed. Therefore, at the near focus, the amount of inspection light incident on the optical fibers located at both ends decreases, and the amount of inspection light incident on the optical fiber located at the center increases. Furthermore, the shape of the spot 80c formed at the time of far focus is shown in FIG. 7C. At the time of far focus, the major axis and minor axis of the ellipse are not reversed, and an enlarged elliptical spot is formed on the five optical fibers. In this case, the amount of inspection light incident on each optical fiber is substantially the same. As described above, in the present invention, the shape of the spot formed by the inspection beam formed on the light detection means changes according to the focus state of the inspection beam with respect to the substrate surface. In view of this characteristic, the present invention realizes a focus detection device that represents the focus state of the inspection beam based on the output signal from the light detection means.

  FIG. 8 is a diagram showing an example of a focus detection apparatus according to the present invention. Output signals from the five photodiodes 33a to 33e are amplified by the amplifiers 81a to 81e, respectively. Output signals from the photodiodes 33a and 33e coupled to the optical fibers located at both ends in the arrangement direction of the optical fibers are supplied to the adding means 83 constituting the focus detection device 82. The output signal from the photodiode 33c coupled to the optical fiber located at the center is supplied to the double multiplier 84. The output signal from the adder 83 and the output signal from the multiplier 84 are supplied to the subtractor 85 to form a difference signal between the output signal of the multiplier 84 and the output signal of the adder 83. This difference signal forms a focus detection signal indicative of the focus state of the inspection beam with respect to the substrate surface.

  FIG. 9 is a graph showing the relationship between the position of the inspection head in the optical axis direction and the focus detection signal. At the time of far focus, the amount of light incident on the five photodiodes is the same, so the focus detection signal is almost zero. From this state, the inspection head approaches the in-focus position, and the focus detection signal is zero even in the in-focus position. On the other hand, when the focus position shifts to the near focus state, the output signal of the photodiode 33c coupled to the optical fiber located at the center starts increasing, and the output signal of the photodiode coupled to the optical fibers at both ends decreases. To start. As a result, the focus detection signal rapidly increases with the in-focus position of the inspection head as a boundary. Therefore, the starting point where the focus detection signal increases is the in-focus position, that is, the best focus position.

  In view of the characteristics of the focus detection signal described above, in the present invention, prior to the inspection, the focus detection signal is detected while the inspection head is displaced in the optical axis direction, and the output of the focus detection signal starts increasing from zero. The position of the head in the optical axis direction is detected and set as the best focus position. Then, the beam displacement element 65 of the autofocus mechanism is adjusted so that the output intensities of the two light receiving regions 66b and 66c of the photodetector 66 are equal to each other. In the state set in this way, the autofocus mechanism is operated to output a focus control signal. Then, a drive signal is supplied to the motor 72 shown in FIG. 6, and focus control is performed so that the inspection beam during inspection is focused on the surface of the substrate.

  Next, the drive system for the inspection head will be described. FIG. 10 is a diagrammatic plan view showing an inspection head driving apparatus. A vibration isolator is prepared, and a base (not shown) is placed thereon. A substrate 1 to be inspected is fixedly arranged in a vertical shape on a base. Stone pillars 90a and 90b are arranged on both sides of the substrate 1, respectively. Y-axis drive ball screws 91a and 91b for moving the inspection head in the Y-axis direction are arranged on the stone pillars 90a and 90b, respectively. The stone pillar is provided with two Y-axis guide rails 92a, 92b and 92c, 92d, respectively. Support frames 93a and 93b are connected to the ball screws 91a and 91b and the Y-axis guide rail, respectively. Further, two linear motors 94a and 94b for driving in the X direction are provided so as to face each other with the substrate surface of the substrate 1 interposed therebetween, and X-axis guide rails 95a and 95b are provided. The first inspection head 2 is mounted on the linear motor 94a and the X-axis guide rail 95a, and the second inspection head 3 is mounted on the linear motor 94b and the X-axis guide rail 95b. The linear motors 94a and 94b and the X-axis guide rails 95a and 95b are connected to the support frames 93a and 93b. Further, the first and second inspection heads 2 and 3 are connected to a ball screw 73 and a motor 72 constituting a driving device for displacing the inspection head in the optical axis direction of the objective lens.

  The two inspection heads 2 and 3 are driven in the same direction in synchronization with each other in the X direction by linear motors 94a and 94b. In addition, by driving the shaft drive ball screws 91a and 91b, the two support frames move in synchronization with the Y-axis direction, and the movement of the two support frames in the Y-axis direction causes the rear motor, the X-axis guide rail, and the inspection. The head is driven in the Y-axis direction. In this example, it is assumed that zigzag driving is performed, and the first and second inspection heads are moved at a predetermined speed in the X direction by a linear motor, reach the end on the opposite side of the X direction, and then have a predetermined pitch in the Y direction. And move further in the direction opposite to the X direction by the linear motor. The entire surface of the glass substrate is scanned with the inspection beam by the movement by the driving device and the scanning by the polygon mirror.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiments, the Nomarski prism is used as the differential interference optical system, but various differential interference optical elements such as Walston prisms and lotion prisms may be used. In the above-described embodiment, the defect inspection is performed on five channels using five photodiodes. However, the number of channels is not limited to five, and an appropriate number of channels can be set according to the purpose and the like. .

  Further, in the above-described embodiments, the defect inspection of the glass substrate has been described. However, the present invention is also applicable to the inspection of a quartz substrate and a substrate in which a halftone film or a light shielding film is formed on the surface of the glass substrate. In addition to the glass substrate, it can also be applied to defect inspection of a pellicle used for protecting a photomask. Since the pellicle is a thin transparent film and not a rigid body, it has a characteristic of being easily deformed during inspection. For this reason, if a defect is inspected using a confocal optical system, the pellicle is locally displaced during the inspection, and the reflected light from the pellicle does not properly enter the light detection means, so that an effective defect inspection is performed. I can't. On the other hand, the inspection optical system of the present invention is a non-confocal optical system, and even if the pellicle surface is displaced or deformed during the inspection, the reflected light from the pellicle is incident on the light detection means, so an accurate defect Inspection can be performed. Therefore, the concept of a substrate includes a pellicle.

  Furthermore, although the polygon mirror is used as the beam deflecting element in the above-described embodiment, various scanners such as a vibrating mirror can be used.

  Furthermore, in the above-described embodiment, the inspection heads are arranged on both sides of the substrate and inspected from both sides of the substrate. However, one inspection head is provided so as to face one substrate surface of the substrate. It is also possible to inspect only one side of the substrate.

1 is a diagram showing an overall configuration of a substrate inspection apparatus according to the present invention. It is a figure which shows the shape of the interference beam which injects into a 1st photon detection means. It is a figure which shows the advancing state of the scattered light radiate | emitted from the substrate surface. It is a figure for demonstrating the effect | action of the condensing element by this invention. It is a figure for demonstrating the focus state of an optical lever system. It is a figure which shows an example of an auto-focus mechanism. It is a figure which shows the state of the light spot formed on five optical fibers. It is a figure which shows an example of the focus inspection apparatus by this invention. It is a graph which shows the change of the focus detection signal with respect to a position in the optical axis direction of an inspection head. It is a figure which shows the drive system of the board | substrate inspection apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2, 3 Inspection head 11 Laser light source 12 Faraday isolator 13 Collimator lens 14 Right angle prism 15 Cylindrical lens 16 Polarizing beam splitter 17 Imaging lens 18 Dichroic mirror 19 fθ lens 20 Polygon mirror 21 Second objective lens 22 Differential interference optics System 23 Objective lens 24 Imaging lens 25, 26 Total reflection mirror 27 First light detection means 28-32 Optical fibers 33a-33e Photodiode 40 Second light detection means 41 Condensing element 44, 53 PMT
50 Third light detection means

Claims (12)

A substrate inspection apparatus that simultaneously inspects a large substrate fixedly arranged vertically so that the substrate surface extends in the vertical direction from both sides thereof,
First and second inspection heads arranged so as to face each other with the substrate to be inspected therebetween;
A first driving device that moves the first and second inspection heads in synchronization with the first direction in the vertical plane, and a second drive that moves the first and second inspection heads in synchronization with the second direction orthogonal to the first direction. Equipment,
A signal processing device that performs defect detection based on output signals output from the first and second inspection heads,
The first and second inspection heads include an inspection beam generator that generates an inspection beam, an objective lens that projects the inspection beam onto the substrate surface, and an optical path between the inspection beam generator and the objective lens. A differential interference optical system disposed on the substrate, first light detection means for receiving an interference beam reflected by the substrate surface and synthesized by the differential interference optical system via the objective lens, the inspection beam generating device, and the objective lens , A beam deflecting device that periodically deflects the inspection beam in the second direction, a second light detecting means for detecting backscattered light reflected by the substrate surface, and the substrate passing therethrough And a third light detecting means for detecting the forward scattered light ,
The third light detection means of the first inspection head is mounted on the second inspection head, the third light detection means of the second inspection head is mounted on the first inspection head,
Surfaces on both sides of the substrate are simultaneously two-dimensionally scanned by movement of the first and second inspection heads in the first direction and beam scanning in the second direction orthogonal to the first direction by the beam deflecting means,
The signal processing device mainly detects uneven defects present on the substrate surface based on an output signal from the first light detection means, and mainly detects a defect on the substrate surface based on an output signal from the second light detection means. A substrate inspection apparatus for detecting an existing foreign substance defect and detecting an internal defect mainly present in the substrate based on an output signal from the third light detection means .   2. The substrate inspection apparatus according to claim 1, wherein the inspection beam generation device generates an inspection beam having an elliptical cross section whose major axis extends in the first direction on the substrate surface, and the rotation of the beam deflection device. The axis is set to be parallel to the major axis of the incident inspection beam, and the substrate surface is periodically scanned in the second direction by an elliptical inspection beam whose major axis extends in the first direction. A substrate inspection apparatus.   3. The substrate inspection apparatus according to claim 2, wherein the first light detection means includes a plurality of optical fibers having light incident surfaces arranged along one direction, and light reception optically coupled to each of the optical fibers. A substrate inspection apparatus characterized in that the arrangement direction of the light incident surface of the optical fiber coincides with the major axis of the incident interference beam. 4. The substrate inspection apparatus according to claim 1, wherein the second light detecting unit receives a back-scattered light and a condensing element that collects the back-scattered light emitted from the substrate surface. 5. A photomultiplier, and a mirror optical system that causes the backscattered light emitted from the light collecting element to enter the photomultiplier,
The condensing element includes a light incident opening through which backscattered light emitted from the substrate surface is incident, a light emitting opening from which the backscattered light is emitted, having a larger opening diameter than the light incident opening, and light. A substrate inspection apparatus comprising a hollow body having a reflective inner peripheral surface formed between an entrance opening and a light exit opening. The substrate inspection apparatus according to claim 4, wherein the light incident opening and the light emitting opening of the hollow body are formed in an elliptical shape,
The reflective inner peripheral surface is formed in a curved surface defined by a paraboloid of revolution when viewed along a first surface that includes the major axis of the ellipse, and is a second orthogonal to the first surface. When viewed by cutting the surface, it is formed into a curved surface defined by an elliptical surface,
The substrate inspection apparatus, wherein the backscattered light incident on the reflective inner peripheral surface is emitted substantially parallel to the optical axis.   6. The substrate inspection apparatus according to claim 1, wherein the third light detection means includes a condenser lens that receives forward scattered light emitted from the substrate, and a hole in which a hole is formed. And a photomultiplier for receiving forward scattered light emitted from the mirror with a hole.   7. The substrate inspection apparatus according to claim 1, wherein a glass substrate, a quartz substrate, a substrate having a halftone film or a light-shielding film formed on a surface, or a pellicle is used as the substrate. A board inspection apparatus characterized by the above. 8. The substrate inspection apparatus according to claim 1, wherein the first and second inspection heads include an autofocus mechanism that focuses the inspection heads on the substrate surface, and these A substrate inspection apparatus, wherein a driving device for displacing the inspection head in the optical axis direction of the objective lens is mounted . 9. The substrate inspection apparatus according to claim 8, wherein the autofocus mechanism includes a light source that generates a focus detection beam having a wavelength different from the wavelength of the inspection beam, and first and second adjacent to each other across a dividing line. A photodetector having two light receiving areas and receiving a focus detection beam reflected by the substrate; and a signal processing means for outputting a focus control signal based on output signals from the two light receiving areas. The focus detection beam emitted from the light source is coupled to the optical path of the inspection beam via an optical element disposed between the inspection beam generator and the objective lens, and the focus detection beam reflected by the substrate is The substrate inspection apparatus is separated from an optical path of an inspection beam through the optical element . 10. The substrate inspection apparatus according to claim 9, wherein a beam adjustment for displacing a focus detection beam reflected by the substrate in a direction orthogonal to a dividing line of the photodetector in an optical path between the optical element and the photodetector. A board inspection apparatus characterized in that means is arranged . 11. The substrate inspection apparatus according to claim 10, wherein, prior to defect inspection, the inspection head is continuously displaced along the optical axis direction of the objective lens, and the inspection head is optimized based on an output signal from the focus detection apparatus. The focus position of the autofocus mechanism is set to the detected best focus position by adjusting the beam adjusting means and the beam adjusting means is adjusted, and defect inspection is performed in the focus state. Substrate inspection device. 4. The substrate inspection apparatus according to claim 3, wherein the first and second inspection heads include an autofocus mechanism that focuses the inspection heads on the substrate surface, and the inspection heads are light beams of the objective lens. A driving device for axial displacement is mounted on each,
The autofocus mechanism includes an output signal from a light receiving element coupled to an optical fiber located in the center of the arrangement direction of the optical fibers and an output signal from a light receiving element coupled to the optical fiber arranged at an end. A substrate inspection apparatus comprising: a focus detection unit that detects a focus state of the inspection head based on the focus detection signal output from the focus detection unit.