JP2002340815A - Pattern inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pattern inspection device capable of suppressing brightness irregularities, while maintaining illumination light to have comparatively high brightness. SOLUTION: An illumination optical system 20A of this pattern inspection device guides incoherent light emitted from an emission face F of an optical fiber array 21 toward a long and narrow illumination region R formed on the surface of a printed circuit board 7 by using nonaxisymmetric image formation elements such as a cylindrical lens 22 or the like. The illumination optical system 20A is constituted so that the illumination system in the longitudinal direction (X direction) of the illumination region R becomes Koehler illumination, and that the illumination system in the short direction (Y direction) of the illumination region R becomes critical illumination. The state of the surface of the printed circuit board 7 illuminated by such illumination light is imaged by using a CCD linear sensor 12 which is long and narrow in the X direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern inspection apparatus which images a pattern (for example, a circuit pattern) provided on the surface of an object to be inspected such as a printed circuit board and detects the presence or absence of a defect.

[0002]

2. Description of the Related Art Conventionally, in inspecting a circuit pattern provided on the surface of an object to be inspected such as a printed circuit board, a pattern inspection apparatus as described in, for example, JP-A-8-122265 is used. .

In this pattern inspection apparatus, a CCD
Using a linear image sensor as an image sensor, and
The following illumination light is used. That is, high-luminance radiation emitted from an ultrahigh-pressure mercury lamp is condensed and made incident on an optical fiber, and light obtained by guiding the incident light to the detection head through the optical fiber is used as illumination light. Then, in this pattern inspection apparatus, by arranging a plurality of emission-side optical fiber wires in a flat shape and arranging them, the emission surface of the optical fiber is formed in an elongated shape like the detection field of view of the CCD linear image sensor, By converging the light on the surface of a printed circuit board to be inspected, an elongated (linear) and high-brightness illumination light is obtained.

[0004]

However, the illumination of the pattern inspection apparatus has the following problems.

[0005] That is, first, this illumination light is constituted as a set of light from a plurality of optical fibers. For example, the luminance distribution of a light beam extracted from an extra-high pressure mercury lamp is such that the luminance at the center is Since the brightness distribution of the bell is higher than the brightness of the illumination light, the brightness of the light emitted from each of the plurality of optical fibers is not uniform. In the illumination area on the surface), luminance unevenness occurs. It can be said that this luminance unevenness is a “macroscopic” luminance unevenness as compared with the luminance unevenness described below. The optical fiber strand has a core portion for transmitting light and a cladding layer outside the core portion. Therefore, luminance unevenness also occurs in each of the lights emitted from the individual optical fibers. This luminance unevenness can be said to be “microscopic” luminance unevenness as compared to the above-described luminance unevenness.

In the above pattern inspection apparatus, in order to obtain high-luminance illumination light, the exit surface of the optical fiber and the surface of the inspection object have an image-forming relationship.
Further, the illumination optical system constituted by a lens or the like has a resolution performance such that illumination light can be narrowed down to an elongated illumination area. Therefore, not only the above-described macroscopic brightness unevenness but also microscopic brightness unevenness occurs on the surface of the inspection object. In a pattern inspection using an image captured using illumination light having such luminance unevenness, there is a problem caused by the luminance unevenness.

[0007] Specifically, since a minute defective portion that should originally appear dark exists in a portion where the illumination high luminance is relatively high due to luminance unevenness, the image is picked up as a bright portion, and the minute defect is overlooked. May be lost. Or, conversely, since a minute defective portion that should originally appear bright is present in a portion where illumination high luminance is relatively low due to luminance unevenness, the image is captured as a dark portion and the minute defect is overlooked. Sometimes. As described above, there is a problem that the detection performance of the pattern defect becomes unstable due to the uneven brightness.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a pattern inspection apparatus that suppresses luminance unevenness while maintaining illumination light at relatively high luminance.

[0009]

In order to achieve the above object, an invention according to claim 1 is a pattern inspection apparatus for inspecting a pattern formed on a surface of an object to be inspected, comprising: an incoherent light emitted from a light source. An illumination optical system for guiding light to an elongated illumination area formed on the surface of the inspection object by using the off-axis symmetric imaging element, and a surface of the inspection object illuminated by the illumination optical system. An imaging unit for imaging, and an inspection unit for performing a pattern inspection based on an image captured by the imaging unit, wherein the illumination optical system is configured such that an illumination method in a longitudinal direction of the illumination area is Koehler illumination. It is configured.

According to a second aspect of the present invention, in the pattern inspection apparatus according to the first aspect of the present invention, the object to be inspected and the imaging means are relatively scanned along a direction intersecting a longitudinal direction of the illumination area. Scanning means for scanning.

According to a third aspect of the present invention, in the pattern inspection apparatus according to the first or second aspect of the present invention, the illumination optical system is configured such that an illumination system in a lateral direction of the illumination area is a critical illumination. Have been.

According to a fourth aspect of the present invention, in the pattern inspection apparatus according to any one of the first to third aspects,
The illumination optical system is configured to be telecentric on the inspection object side.

According to a fifth aspect of the present invention, in the pattern inspection apparatus according to any one of the first to fourth aspects,
The illumination optical system has an elongated emission surface configured as a set of emission points of a plurality of lights.

According to a sixth aspect of the present invention, in the pattern inspection apparatus according to any one of the first to fourth aspects,
The illumination optical system has an emission surface that emits light from the light source to a space, and the emission surface is a focal position closest to the inspection object among object space side focal positions in the illumination optical system. It is provided in.

According to a seventh aspect of the present invention, in the pattern inspection apparatus according to any one of the first to sixth aspects,
The illumination optical system irradiates the surface of the inspection object with excitation light capable of exciting fluorescence, and the imaging unit captures an image based on the fluorescence excited on the surface of the inspection object.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

<A. First Embodiment><A1.Configuration> FIG. 1 is an external perspective view schematically showing a pattern inspection apparatus 1A according to a first embodiment. This pattern inspection apparatus 1A is an optical inspection apparatus that inspects the presence or absence of a defect in a fine pattern (such as a circuit pattern) formed on the surface of an inspection object such as a printed circuit board 7.

As shown in FIG. 1, the pattern inspection apparatus 1A includes a scanning table 2, a photographing unit 3, an image processing unit 4, a lamp house 5, and an optical fiber 6.
And

The scanning table 2 can be moved in the Y direction by a driving unit having a motor, gears and the like (not shown). On the upper surface of the scanning table 2, a printed circuit board 7, which is an inspection object, is placed and fixed. Therefore, the printed circuit board 7 can be moved in the Y direction (scanning direction) by the scanning table 2.

The pattern inspection apparatus 1A is provided with a plurality (specifically, eight) of photographing units 3 arranged in the X direction. The plurality of photographing units 3 can be integrally moved in the X direction. The X direction is a direction orthogonal to the Y direction which is the scanning direction of the scanning table 2.

As will be described later, since each photographing unit 3 captures an image of an elongated area having the X direction as a longitudinal direction at each moment, the scanning table 2 is scanned with respect to this photographing unit 3 in the Y direction. Thus, a planar image of the surface of the printed circuit board 7 can be captured. Specifically, each photographing unit 3 can obtain an image relating to a photographing area having a predetermined length in the X direction and a scanning distance in the Y direction. Further, since a plurality of such photographing units 3 are arranged in the X direction, one scan in the Y direction can be performed according to the number of photographing units 3.
An image with a larger area can be captured. Further, by slightly moving the plurality of photographing units 3 integrally in the X direction, each photographing unit 3 can be moved to a position in the X direction between the plurality of photographing units 3 before the movement. Therefore, the pattern can be inspected over the entire surface of the printed circuit board 7 by performing the same operation of moving the scanning table 2 in the Y direction after fixing it at that position in the X direction.

The image processing unit 4 is a unit that performs image processing on an image photographed by the photographing unit 3. The image processing unit 4 has a function of comparing the captured image with a reference image (master image) to inspect the presence or absence of a defect in the circuit pattern and the position of the defect. That is, this image processing unit 4
It has a function of performing a pattern inspection based on a captured image. The pattern inspection apparatus 1A further includes a computer (not shown) for controlling the entire apparatus. The input / output unit (keyboard, mouse, display, etc.) of this computer also functions as a man-machine interface of the pattern inspection apparatus 1A.

The lamp house 5 has a light source for emitting incoherent light. As the light source, for example, an ultra-high pressure mercury lamp or the like can be used. The radiation from this ultra-high pressure mercury lamp is incoherent light. By using such incoherent light, coherent noise such as a speckle pattern generated in illumination using coherent light such as laser light can be avoided.

The incoherent light emitted from the lamp house 5 is guided to the photographing unit 3 through the optical fiber 6. The incoherent light guided as described above is used as illumination light at the time of photographing by the photographing unit 3.

FIG. 2 is a perspective view showing the configuration of the photographing unit 3 and the like. As shown in FIG. 2, the imaging unit 3 includes a part of an illumination optical system 20A and an imaging optical system 10.

The photographing unit 3 has an optical fiber array 21, cylindrical lenses 22, 23, 24, an aperture stop 25, a lens 26, and a half mirror 31 as optical elements constituting a part of the illumination optical system 20A. I have. The illumination optical system 20A includes a light source in the lamp house 5, an optical fiber 6, and the like in addition to these optical elements. This illumination optical system 20
A has a function of guiding light emitted from a light source in the lamp house 5 to an elongated (linear) illumination region R formed on the surface of the inspection object (here, the printed circuit board 7). ing.

The optical fiber array 21 is formed by bundling a plurality of optical fibers 6 substantially in parallel with each other, and has an elongated emission surface F for emitting illumination light from the plurality of optical fibers 6. The emission surface F is a surface that emits light from a light source to space.
Here, the emission surface F is configured as a group of a plurality of light emission points, and has a substantially rectangular elongated shape.

FIG. 3 is a sectional view taken along the axial direction of the optical fiber 6, and FIG. 4 is a view showing the exit surface F of the optical fiber array 21.

As shown in FIG. 3, the optical fiber 6 includes a core 6a through which light mainly propagates, and a core 6a.
a and the cladding layer 6b existing around the periphery of a.

As shown in FIG. 4, on the exit surface F of the optical fiber array 21, a plurality of optical fibers 6 are provided in an elongated region having a longitudinal direction in the X direction and a lateral direction in the Z direction. The emission unit openings are arranged. The plurality of optical fibers 6 are adhered and bundled together by an adhesive portion 6c.

The optical fiber array 21
In front of the emission surface F, a rod lens (registered trademark) 21a (FIG. 2) is provided so that the longitudinal direction thereof is along the longitudinal direction of the emission surface F, and the light is emitted from each optical fiber 6. The light is the rod lens 21
Go further through a.

As shown in FIG. 2, the light emitted from the emission surface of the optical fiber array 21 passes through a rod lens 21a, cylindrical lenses 22, 23, 24, an aperture stop 25, and a lens 26. The light is reflected by the mirror 31 and travels downward (-Z direction) to illuminate the elongated illumination region R on the surface of the inspection object. The rod lens 21a and the cylindrical lenses 22, 23, 24 are examples of off-axis symmetric imaging elements. As will be described later, the illumination optical system 20A is configured such that the illumination system in the longitudinal direction (X direction) of the illumination region R is Koehler illumination using these off-axis symmetric imaging elements. Thereby, it is possible to suppress luminance unevenness while maintaining illumination light at relatively high luminance.

On the other hand, the imaging optical system 10 includes a photographing lens 11
And a CCD linear sensor 12 and a half mirror 31. In this embodiment, the imaging optical system 1
0 does not have the filter 15 (indicated by a two-dot chain line in the figure).

The photographing lens 11 is constituted by one or a plurality of lenses. The CCD linear sensor 12
It has a structure in which a plurality of CCD cells are arranged linearly, and the arrangement of the plurality of linear CCD cells is arranged so as to be parallel to the longitudinal direction (X direction) of the elongated illumination region R. Have been. The half mirror 31 is shared by the imaging optical system 10 and the illumination optical system 20A.

When illumination light is applied to the surface of the printed circuit board 7 by the illumination optical system 20A, the illumination light is reflected by the surface of the printed circuit board 7 and reflected upward (+ Z
Direction). The reflected light is reflected by the half mirror 31
This time, the light passes through the lens and travels further upward, and the photographing lens 1
1 and proceed to the CCD linear sensor 12.

When the reflected light from the illumination area R is received by the CCD linear sensor 12, the received light is converted into an electric signal by photoelectric conversion, and A / D (analog / digital) conversion is performed. By each C
The pixel value of the pixel corresponding to the CD cell is determined.

Here, the surface of the printed circuit board 7 and the CCD linear sensor 12 have a conjugate relationship with respect to the photographing lens 11. In other words, the surface of the printed circuit board 7 and the CCD linear sensor 12 have an imaging relationship with respect to the photographing lens 11. Therefore, CCD linear sensor 1
2 can clearly capture the situation of the surface of the printed circuit board 7. As described above, the CCD linear sensor 12 functions as an imaging unit that images the surface of the inspection object illuminated by the illumination optical system.

As described above, with the movement of the scanning table 2 in the Y direction, the photographing unit 3 and the printed circuit board 7 on the scanning table 2 move relatively in the Y direction. By performing a photographing operation in accordance with the relative movement between the printed board 7 and the photographing unit 3, the surface of the printed circuit board 7 can be scanned by the photographing unit 3.

<A2. Illumination principle> FIG.
FIG. 6 is a top view when A is viewed from above (Z direction), and FIG. 6 is a side view when the illumination optical system 20A is viewed from the side (X direction).
The illumination using the illumination optical system 20A on the surface of the inspection object will be described with reference to FIGS. 5 and 6, apart from the illumination region R,
The position of the virtual illumination area R0 is shown. The illumination area R0 is an illumination area when the half mirror 31 does not exist, and is optically the same as the illumination area R. In the following description, it is appropriately used for convenience.

In this embodiment, the rod lens 21a and the cylindrical lens 2 which are off-axis symmetric imaging elements are used.
2, 23, and 24 will be used to exemplify a case where the illumination systems in the longitudinal direction and the lateral direction of the illumination region R are different from each other. Specifically, the illumination region R
The illumination optical system 20A is configured such that the illumination method in the longitudinal direction of the illumination region is Koehler illumination, and the illumination method in the short direction of the illumination region R is critical illumination (critical illumination).
Is exemplified.

<Illumination in the Longitudinal Direction of the Illumination Region R> First, with reference to the top view of FIG. 5, the fact that the illumination system in the longitudinal direction of the illumination region R is Koehler illumination will be described.

In the XY plane, three lenses, that is, the cylindrical lens 22, the cylindrical lens 24, and the lens 26 have an optical function of refracting light.

The exit surface F of the optical fiber array 21 is located at the front focal position of the cylindrical lens 22, and the front focal position of the cylindrical lens 24 is located at the rear focal position of the cylindrical lens 22 (see FIG. 7). . Here, this cylindrical lens 2
A cylindrical lens 23 exists at a position near the rear focal point of the lens 2. Further, an aperture stop 25 exists at the rear focal position of the cylindrical lens 24. Therefore, the exit surface F of the optical fiber array 21 and the aperture stop 25 have a conjugate relationship (that is, an imaging relationship).

The aperture stop 25 is located at the front focal position of the lens 26, and the surface of the printed circuit board 7 is located at the rear focal position of the lens 26. Therefore, when viewed from the surface of the printed circuit board 7 through the lens 26, the aperture stop 25 appears to be located at infinity.

Further, the optical path in the XY plane will be described in more detail. Here, light emitted from the central position P2 in the X direction of the optical fiber array 21 will be described. FIG. 7 is a view similar to FIG.
5 differs from FIG. 5 in that an optical path for light emitted from the position P2 is indicated by oblique lines.

The light emitted from the emission surface F of the optical fiber array 21 passes through the rod lens 21 a having no optical function of refracting the light in the XY plane and travels to the cylindrical lens 22. Since the cylindrical lens 22 has an optical function of refracting light in the XY plane, the light is refracted by the cylindrical lens 22, is collimated, and travels as parallel light. Then, the parallel light reaches the position of the cylindrical lens 23.

The cylindrical lens 23 does not have an optical function of refracting light in the XY plane, and the light proceeds as it is without being refracted by the cylindrical lens 23 and reaches the cylindrical lens 24.

The cylindrical lens 24 has an optical function of refracting light in the XY plane. The light is refracted by the cylindrical lens 24 and forms an image on the aperture stop 25.

Therefore, the image of the light source emitted from the exit surface of the optical fiber array 21
It can be seen that the image is projected at the position of No. 5.

Thereafter, the light imaged at the aperture stop 25 further travels to the lens 26.

The lens 26 has an optical function of refracting light in the XY plane. The light is refracted by the lens 26 and collimated, and further proceeds as parallel light to reach the surface of the printed circuit board 7. I do.

FIG. 8 shows this optical path, that is, the aperture stop 25.
FIG. 4 is an enlarged view showing an optical path until the light imaged in the vicinity of the center of FIG. In FIG. 8, in order to schematically show the principle, the shapes and the like of the aperture stop 25 and the lens 26 are not shown, and only their positions are shown. In FIGS. 7 and 8 and the like, the illumination region R is the illumination region R for ease of illustration.
It is shown as being at position 0.

As described above, the image of the light emitted from the emission surface F of the optical fiber array 21 is projected on the position of the aperture stop 25, and
Exist at the rear focal position of the lens 26. That is, an image of light emitted from the emission surface F of the optical fiber array 21 is projected on the rear focal position of the lens 26. Therefore, it is understood that the illumination system of the illumination optical system 20A is Koehler illumination in the XY plane, that is, the illumination system in the longitudinal direction of the illumination region R is Koehler illumination.

The illumination principle will be described with reference to FIGS. 9 and 10. FIG. 9 is a view similar to FIGS. 5 and 7, except that the optical path for the light emitted from the position P1 is indicated by oblique lines.
Is different.

As shown in FIG. 9, the light emitted from the position P1 on the plus side (+ X side) of the emission surface of the optical fiber array 21 in the X direction from the position P2 (+ X side) is opened by the illumination optical system 20A. The stop 25 forms an image at the position Q1. Similarly, although not shown, the light emitted from the position P3 on the minus side (−X side) of the position P2 in the X direction of the emission surface of the optical fiber array 21 is similarly emitted by the illumination optical system 20A.
An image is formed at a position Q3 in the aperture stop 25. As described above, the light emitted from the optical fiber array 21 forms an image at the position of the aperture stop 25.

FIG. 10 is an enlarged view showing the optical path after that of the light imaged at the aperture stop 25 in this way. FIG. 10 is a view similar to FIG. 8 described above. However, in FIG. 8, only the optical path of the light emitted from the point Q2 is shown, while in FIG. 10, the points Q1, Q2, Q
The optical path of the light emitted from No. 3 is also shown.

As shown in FIG. 8, the light beams L21, L22 and L23 emitted from the point Q2 are collimated by being refracted by the lens 26 and irradiated on the illumination region R. That is, the light emitted from the point Q2 is
The illumination area R extends in the X direction of the illumination area R on the surface.
To reach.

Similarly, as shown in FIG. 10, the light rays L11, L12, L13 emitted from the point Q1 are collimated by being refracted by the lens 26 and illuminate the entire illumination area R. That is, the light emitted from the point Q1 reaches the illumination region R in a state where the light is spread in the X direction of the illumination region R on the surface of the printed circuit board 7.

Similarly, the light ray L3 emitted from the point Q3
The light beams L1, L32, and L33 are collimated by being refracted by the lens 26, and are irradiated on the entire illumination region R. That is, the light emitted from the point Q3 reaches the illumination area R in a state where the light is spread in the X direction of the illumination area R on the surface of the printed circuit board 7.

Further, according to the Koehler illumination, three points a, b, and c in the X direction on the illumination area R are different from each other.
In both cases, light of the same degree arrives. Hereinafter, this will be described.

First, for point a, points Q1, Q2, Q
Light rays (indicated by dashed lines) emitted in a predetermined direction from all points including 3 arrive. For example, ray L from point Q1
11, light ray L21 from point Q2, light ray L3 from point Q3
1 reach point a. This state is shown as a hatched portion in FIG. Note that FIG. 11 is a view similar to FIG. 9 and the like, except that the state in which light rays emitted from the points P1, P2, and P3 at a predetermined angle reach the point a is indicated by hatching. 9 is different from FIG.

Similarly, for the point b, the points Q1, Q2,
Light rays (indicated by broken lines) emitted in a predetermined direction (in this case, -Y direction) from all points including Q3 arrive. For example, ray L12 from point Q1, ray L2 from point Q2
2. The light beam L32 from the point Q3 reaches the point b.

Further, for the point c, the points Q1, Q2,
Light rays (indicated by a two-dot chain line) emitted in a predetermined direction from all points including Q3 arrive. For example, light ray L13 from point Q1, light ray L23 from point Q2, light ray L from point Q3
33 reach point c.

As described above, all the lights from the plurality of point light sources reach all the points in the illumination area R. For this reason, even when the luminances of the emitted lights at the points P1, P2, and P3 are different from each other, the points a, b, and
The luminance at c is almost the same. For example, even when the luminance A1 of the emitted light at the point P1, the luminance A2 of the emitted light at the point P2, and the luminance A3 of the emitted light at the point P3 are different from each other, the points a, b, and c respectively have , Since light from any of the points P1, P2, and P3 arrives,
The ratio of the luminance at each of the points a, b, and c is the ratio of the total value of the luminance from each point, ((A1 + A2 + A3) :( A1
+ A2 + A3): (A1 + A2 + A3)), that is, (1: 1: 1). As described above, the uneven brightness can be eliminated.

As described above, the light emitted from points P1, P2, and P3 (which can also be expressed as light from points Q1, Q2, and Q3)
In any case, the light reaches the illumination region R in a state where the illumination region R spreads in the X direction on the surface of the printed circuit board 7, so that it is possible to realize uniform illumination by suppressing luminance unevenness.

Also, for example, by appropriately changing the focal length and the like of each lens of the illumination optical system 20A, the incident angle θ of the incident light beam L11 at the point a of the illumination area R can be appropriately set. is there. That is, the numerical aperture N
A can be set appropriately. For example, even when there are many fine irregularities on the surface of a printed circuit board, setting the numerical aperture NA to an appropriate size can reduce the shading of the image of the fine irregularities and shoot. It is possible.

<Illumination in Shorter Direction of Illumination Region R> Next, referring to the side view of FIG. 6, the illumination method in the shorter direction of the illumination region R is critical illumination (critical illumination).
Will be described.

The light emitted from the emission surface F of the optical fiber array 21 passes through the rod lens 21a and the cylindrical lens 22, and travels to the cylindrical lens 23.

The rod lens 21a has an optical function of refracting light in the YZ plane. The rod lens 21a efficiently takes in light emitted from the emission surface F of the optical fiber array 21 at a large angle, and captures the light. It is refracted and corrected to a relatively small exit angle. By arranging such a rod lens 21a close to the emission surface F of the optical fiber array 21, light emitted from the optical fiber array 21 at a large angle can be efficiently taken in and the light quantity loss can be suppressed. It is. The light emitted from the emission surface F is a rod lens 21a.
After being refracted and corrected to a smaller exit angle, the light goes to the cylindrical lens 22.

Further, the cylindrical lens 22 does not have an optical function (or optical power) for refracting light in the YZ plane, and the light travels without being refracted by the cylindrical lens 22. Reaches the cylindrical lens 23.

The cylindrical lens 23 has an optical function of refracting light in the YZ plane. The light is refracted by the cylindrical lens 23, collimated, and travels as parallel light.

The cylindrical lens 24 has no optical function of refracting light in the YZ plane, and the light proceeds without being refracted by the cylindrical lens 22. This light further travels and passes through the aperture stop 25 before reaching the lens 26.

The lens 26 has an optical function of refracting light in the YZ plane.
The refracted light is reflected by the half mirror 31, changes its traveling direction downward, travels, and forms an image in the illumination region R of the printed circuit board 7.

As described above, since the position of the exit surface F of the optical fiber array 21 and the position of the surface to be illuminated (the surface of the printed circuit board 7) have an image forming relationship in the YZ plane, the illumination of the illumination optical system 20A is performed. The method is a critical illumination (critical illumination) in the YZ plane. That is, it is understood that the illumination method in the short direction of the illumination region R is critical illumination.

As described above, since the illumination system of the illumination optical system 20A performs the critical illumination in the YZ plane, the illumination light can be efficiently focused on the illumination region R.

As described above, according to the pattern inspection apparatus 1A of this embodiment, since the illumination system in the longitudinal direction of the illumination region R is Koehler illumination, illumination light having a uniform luminance distribution and good uniformity is obtained. be able to. Therefore, it is possible to suppress luminance unevenness in illumination for pattern inspection. Furthermore, since the illumination method in the short direction of the illumination region R is critical illumination, high-luminance illumination light can be obtained by performing efficient light collection. In this way, by effectively using the illumination light without waste, it is possible to reduce the number of lamps used and the rated output of the lamps. Along with this, it is also possible to reduce the power consumption of the entire pattern inspection apparatus 1A.

As shown in FIG. 8, the light further traveling from the aperture stop 25 is refracted by the lens 26,
In the image space of No. 6, the principal ray travels parallel to the axis. In this case, when viewed through the lens 26 from the surface of the printed circuit board 7, the aperture stop 25 appears to be located at infinity. That is, the illumination optical system 20A is a telecentric system configured to be telecentric on the inspection object (printed board 7) side. As a result, even if there is significant unevenness on the printed circuit board to be photographed, the size of the photographed image does not change. Therefore, a photographed image of the same size can be obtained regardless of the unevenness of the surface of the printed circuit board 7, so that the pattern comparison inspection can be performed more accurately.

Further, in the above embodiment, since illumination is performed using the light source that emits incoherent light, coherent noise such as a speckle pattern generated in illumination using coherent light such as laser light. Does not occur at all. As described above, in the illumination optical system 20A, the incident angle θ of the incident light beam L11 at the point a of the illumination region R is appropriately changed by appropriately changing the focal length and the like of each lens of the illumination optical system 20A. Can be set to That is, the numerical aperture NA
Can be appropriately set. As described above, by appropriately setting the numerical aperture NA, the printed circuit board 7 is formed.
Even when there are surface irregularities, the influence of scattering and the like due to the irregularities is suppressed, the S / N ratio is increased, and pattern defects and scratches on the surface of the printed circuit board 7 are detected more appropriately. You can do things.

FIG. 12 is a side view showing a state in the vicinity of the emission surface F of the optical fiber array 21.
Rod lens 21a is optical fiber array 2
1 is arranged in close proximity to the emission surface F. In this state, the output light from the output surface F from the optical fiber array 21 forms a virtual image at the position of the point E. This point E exists at the front focal position of the cylindrical lens 23.

By using such a rod lens 21a, it is possible to efficiently take in the light emitted from the optical fiber array 21 and suppress the light quantity loss.

On the other hand, the rod lens 21a is not limited to the case where it is arranged at a position as shown in FIG. For example, it may be arranged at a position as shown in FIG. In FIG. 13, the front focal position of the rod lens 21 a is
And the rear focal position of the rod lens 21 a is located at the front focal position of the cylindrical lens 23.
Therefore, the illumination system of the illumination optical system 20A is Koehler illumination even in the YZ plane. That is, the illumination system in the short direction of the illumination region R is also Koehler illumination.

However, in this case, Y of the illumination optical system 20A
Since the illumination system in the Z plane is Koehler illumination, the light collection efficiency is reduced as compared with the case of critical illumination. In particular, when it is desired to improve the light collection efficiency, it is preferable that the illumination system in the YZ plane of the illumination optical system 20A be a critical illumination as in the above embodiment.

<B. Second Embodiment> Next, a pattern inspection apparatus 1B according to a second embodiment of the present invention will be described. The pattern inspection apparatus 1B according to the second embodiment includes:
It has a configuration similar to that of the pattern inspection apparatus 1A according to the first embodiment, but differs from the first embodiment in the configuration of the illumination optical system. The following description focuses on the differences. Parts having the same configuration as the first embodiment are denoted by the same reference numerals.

FIG. 14 is a schematic perspective view showing a schematic configuration of a part of the illumination optical system 20B.

The illumination optical system 20 B has an optical fiber array 21, an aperture stop 41, a cylindrical lens 42, a lens 43, and a half mirror 31.
These have a function of guiding light emitted from a light source in the lamp house 5 to an elongated illumination region R formed on the surface of the inspection object (here, the printed circuit board 7). In order to suppress aberration, the cylindrical lens 42 is preferably formed as a non-cylindrical surface, and the lens 43 is preferably formed as an aspheric surface.

FIG. 15 is a top view of the illumination optical system 20B viewed from above (Z direction), and FIG.
FIG. 2 is a side view as viewed from the side (X direction). The illumination using the illumination optical system 20B on the surface of the inspection object will be described with reference to FIGS.

The second embodiment exemplifies a case in which the cylindrical lens 42, which is an off-axis symmetric imaging element, uses different illumination systems in the longitudinal and lateral directions of the illumination region R. I do.
Specifically, the illumination system in the longitudinal direction of the illumination region R is configured to be Koehler illumination, and the illumination system in the lateral direction of the illumination region R is configured to be critical illumination.

The illumination optical system 20B according to the second embodiment includes:
When the illumination system in the longitudinal direction of the illumination area is Koehler illumination, the emission surface F of the optical fiber array 21 is provided at the focal position closest to the inspection object among the object space side focal positions in the illumination optical system. In this point, it is significantly different from the first embodiment.

First, with reference to the top view of FIG. 15, it will be described that the illumination system in the longitudinal direction of the illumination region R is Koehler illumination.

In the XY plane, only the lens 43 has an optical function (optical power) of refracting light.

The exit surface F of the optical fiber array 21 is located at the front focal position of the lens 43, and the surface of the printed circuit board 7 is located at the rear focal position of the lens 43. Therefore, the illumination system of the illumination optical system 20A is XY
It can be seen that Koehler illumination is provided in the plane, that is, the illumination system in the longitudinal direction of the illumination region R is Koehler illumination.

Next, referring to the side view of FIG.
The fact that the illumination method in the short direction of the illumination region R is critical illumination will be described.

In the YZ plane, an optical action (optical power) for refracting light is applied to the cylindrical lens 4.
2 and the lens 43.

The exit surface F of the optical fiber array 21 is located at the front focal position of the cylindrical lens 42, and the printed circuit board 7 is located at the rear focal position of the lens 43.
Surface.

The light emitted from the emission surface F of the optical fiber array 21 is stopped down by the aperture stop 41,
The light is refracted by the cylindrical lens 42 and collimated. After that, the parallel light is refracted by the lens 43 and forms an image on the surface of the printed circuit board 7.

Therefore, it can be understood that the illumination system of the illumination optical system 20B is a critical illumination in the YZ plane, that is, the illumination system in the lateral direction of the illumination region R is the critical illumination.

The illumination optical system 20B according to the second embodiment
The same effect as in the first embodiment can also be obtained by the pattern inspection apparatus 1B using. In the illumination optical system 20B of the second embodiment, when the illumination system in the longitudinal direction of the illumination area is set to Koehler illumination, the front focal position (in other words, the object space focal position) of the illumination optical system 20B is changed. Since the exit surface F of the optical fiber array 21 is provided at the focal position closest to the object to be inspected, that is, at the focal position on the object space side of the lens 43, the number of lenses can be reduced to achieve a simple configuration. It is possible. Here, the “object-space-side focal position” refers to a focal position on the opposite side to the image-space-side focal position of the imaging element (for example, the lens 43) or the imaging element group (in other words, opposite to the inspection object). Side focal position).

On the other hand, in the illumination optical system 20A (see FIG. 7) of the first embodiment, the illumination optical system 20A
Of the front focal position Q2 of the lens 26, the front focal position (not shown) of the cylindrical lens 24, and the front focal position P2 of the cylindrical lens 22, the focal position Q2 closest to the inspection object.
(In this case, the exit surface F exists at a front focal position P2 of the cylindrical lens 22, that is, a focal position P2 furthest from the inspection object).
A larger number of lenses are required than the illumination optical system 20B of the second embodiment.

<C. Third Embodiment> Next, a pattern inspection apparatus 1C according to a third embodiment of the present invention will be described. The pattern inspection apparatus 1C according to the third embodiment includes:
It is a further modified example of the pattern inspection apparatus 1B according to the second embodiment. The configuration of the illumination optical system is further different from the second embodiment. The following description focuses on the differences.
Parts having the same configuration as the first embodiment are denoted by the same reference numerals.

FIG. 17 is a schematic perspective view showing a schematic configuration of a part of the illumination optical system 20C.

The illumination optical system 20C comprises an optical fiber array 21, a lens 51, an aperture stop 52, cylindrical lenses 53 and 54, a lens 55, and a half mirror 3.
And 1. The illumination optical system 20C has a function of guiding light emitted from a light source in the lamp house 5 to an elongated illumination region R formed on the surface of the inspection object (the printed circuit board 7 in this case). ing.

In the illumination optical system 20C of the third embodiment, when the illumination system in the longitudinal direction of the illumination area is Koehler illumination, the focal point closest to the inspection object among the object space side focal positions in the illumination optical system. The optical fiber array 21 is located at a position (specifically, a focus position on the object space side for an imaging element group including the lens 51, the cylindrical lens 53, and the lens 55 of the illumination optical system).
This is common to the second embodiment in that the light exit surface F is provided.

However, in the third embodiment, a cylindrical lens 5 having a cylindrical surface instead of a non-cylindrical surface is used.
3, 54 and a lens 51 having a spherical surface instead of an aspherical surface.
An example will be described in which aberration is suppressed by appropriately combining 55 and 55. That is, by appropriately combining and using a plurality of lenses, it is possible to suppress aberration without using an aspheric lens or a non-cylindrical cylindrical lens.

FIG. 18 is a top view of the illumination optical system 20C as viewed from above (Z direction), and FIG.
FIG. 2 is a side view as viewed from the side (X direction). The illumination using the illumination optical system 20C on the surface of the inspection object will be described with reference to FIGS.

In the third embodiment, the use of the cylindrical lenses 53 and 54, which are non-axially symmetric imaging elements, makes it possible to use different illumination systems in the longitudinal direction and the lateral direction of the illumination region R. Is exemplified. Specifically, the illumination system in the longitudinal direction of the illumination region R is configured to be Koehler illumination, and the illumination region R
Is configured so that the illumination system in the short side direction becomes critical illumination.

As can be seen from FIGS. 18 and 19, the cylindrical lens 54 has the same function as the lens 42 of the second embodiment, and the lens 55 has the same function as the lens 43 of the second embodiment. have. And
In the third embodiment, in order to correct aberrations,
It further has a lens 51 and a cylindrical lens 53.

Here, in the XY plane, the lens 5
When the surface of the printed circuit board 7 is located at the rear focal position of the optical element 5 and the optical element groups 51, 53, and 55 are viewed as one optical element, the front focal position of the optical element group (in other words, Since the exit surface F of the optical fiber array 21 is disposed at the focal position on the optical element group opposite to the object to be inspected, it can be understood that the illumination system in the longitudinal direction of the illumination region R is Koehler illumination. .

Also, in the YZ plane, the lens 51
The output surface F of the optical fiber array 21 and the surface of the printed circuit board 7 are formed so as to have an image-forming relationship by the optical action of the illumination optical system 20C including the illumination optical system 20C. It turns out that the lighting system is a critical lighting.

The illumination optical system 20C according to the third embodiment
The same effect as in the second embodiment can also be obtained by the pattern inspection apparatus 1C using. Further, in the illumination optical system 20C of the third embodiment, since aberration is corrected by using a plurality of lenses, aberration can be suppressed without using aspherical and non-cylindrical lenses.

<D. Others> In the above embodiment,
Although a cylindrical lens or a rod lens is used as an off-axis symmetric imaging element, the present invention is not limited to this, and a toric lens having different curvatures in two directions orthogonal to each other, and a Fresnel lens having image forming properties in one direction The above-described illumination optical system 20 may be configured using a refractive index dispersion lens, a cylindrical surface mirror, and the like.

Further, in the above-described embodiment, the case where the pattern inspection is performed using the photographed image of the normal reflected light from the illumination region R has been described, but the present invention is not limited to this, and The present invention can also be applied to a pattern inspection apparatus that performs a pattern inspection using a captured image.
This is based on the fact that when a specific wavelength is applied to a printed circuit board or the like, the base material (insulating layer) generates fluorescence different from the wavelength of the irradiation light, but the pattern (metal conductor) does not generate fluorescence. , By detecting the generated fluorescence,
A pattern inspection is performed.

Specifically, in the lamp house 5,
A filter (not shown) that selectively transmits light having a wavelength capable of exciting fluorescence (g-line, h-line, i-line, etc.) is provided, and the printed circuit board 7 is irradiated. Then, the fluorescence is excited on the surface of the printed circuit board 7 in response to the irradiation of the excitation light. Further, a filter 15 for selectively transmitting the excited fluorescence (indicated by a two-dot chain line in FIG. 2)
Is provided between the printed circuit board 7 and the CCD linear sensor 12. While this filter 15 does not transmit the reflected light of the irradiation light applied to the printed circuit board 7,
The filter has a wavelength selectivity that allows the fluorescence excited on the surface of the printed circuit board 7 to pass through in response to the irradiation light. The half mirror 31 may have the same wavelength selectivity as the filter 15.

Then, the fluorescent light selectively transmitted by the filter 15 out of the light from the printed circuit board 7 is received by the CCD linear sensor 12, and an image based on the fluorescent light is created. It is also possible to perform a pattern inspection using the image obtained by the fluorescence detection thus obtained.

In particular, in an apparatus that performs fluorescence detection, illumination of extremely high luminance is required due to the extremely low brightness of fluorescence with respect to illumination light (excitation light). By applying, the merit of using the illumination light efficiently is further increased. In other words, the merits such as the above-described power consumption reduction are further enhanced.

[0115]

As described above, according to the first aspect of the present invention, the illumination optical system is configured so that the illumination system in the longitudinal direction of the illumination area is Koehler illumination. It is possible to make the luminance of the illumination light uniform in the longitudinal direction and suppress luminance unevenness.

According to the second aspect of the present invention, the apparatus further comprises scanning means for relatively scanning the object to be inspected and the image pickup means along a direction intersecting with the longitudinal direction of the illumination area. While intensively illuminating the illumination area with
An image having a two-dimensional spread can be captured.

According to the third aspect of the present invention, the illumination optical system is configured so that the illumination method in the short direction of the illumination area is critical illumination, so that the illumination efficiency is short in the short direction of the illumination area. Can be further improved.

According to the fourth aspect of the present invention, since the illumination optical system is configured to be telecentric on the inspection object side, even if the distance between the illumination optical system and the inspection object changes. Can be kept unchanged.

According to the fifth aspect of the present invention, even when the illumination optical system has an elongated emission surface configured as a set of a plurality of emission points of light, a plurality of point light sources can be disposed between the plurality of point light sources. Luminance unevenness can be suppressed.

According to the sixth aspect of the present invention, the exit surface is provided at the focal position closest to the inspection object among the object space side focal positions in the illumination optical system, so that the number of lenses is reduced. And a simple configuration.

According to the invention described in claim 7, the illumination optical system irradiates the surface of the inspection object with excitation light capable of exciting fluorescence, and the imaging means performs excitation on the surface of the inspection object. Since an image based on the obtained fluorescence is captured, a pattern inspection using the fluorescence can be performed. In fluorescence detection that requires illumination light of higher luminance, illumination light of high luminance can be efficiently obtained while suppressing luminance unevenness. Therefore, power consumption can be further reduced.

[Brief description of the drawings]

FIG. 1 is an external perspective view schematically showing a pattern inspection apparatus 1A according to a first embodiment.

FIG. 2 is a perspective view showing a configuration and the like of a photographing unit 3;

FIG. 3 is a cross-sectional view of the optical fiber 6 along the axial direction.

FIG. 4 is an emission surface F of the optical fiber array 21;
FIG.

FIG. 5 is a top view of the illumination optical system 20A viewed from above (Z direction).

FIG. 6 is a side view of the illumination optical system 20A viewed from the side (X direction).

FIG. 7 is a top view of the illumination optical system 20A viewed from above (Z direction).

FIG. 8 is a diagram showing an optical path from an aperture stop 25 to a printed circuit board 7;

FIG. 9 is a top view of the illumination optical system 20A viewed from above (Z direction).

FIG. 10 is a diagram showing an optical path from an aperture stop 25 to a printed circuit board 7;

FIG. 11 is a top view of the illumination optical system 20A viewed from above (Z direction).

FIG. 12 is a side view showing a state near an emission surface F of the optical fiber array 21.

FIG. 13 is a side view showing a state near an emission surface F of an optical fiber array 21 according to a modification.

FIG. 14 is a schematic perspective view illustrating a schematic configuration of an illumination optical system 20B according to a second embodiment.

FIG. 15 is a top view of the illumination optical system 20B viewed from above (Z direction).

FIG. 16 is a side view of the illumination optical system 20B viewed from the side (X direction).

FIG. 17 is a schematic perspective view illustrating a schematic configuration of an illumination optical system 20C according to a third embodiment.

FIG. 18 is a top view of the illumination optical system 20C viewed from above (Z direction).

FIG. 19 is a side view of the illumination optical system 20C viewed from the side (X direction).

[Explanation of symbols]

Reference Signs List 1A, 1B, 1C Pattern inspection apparatus 2 Scanning table 3 Imaging unit 4 Image processing unit 5 Lamp house 6 Optical fiber 7 Printed circuit board 10 Imaging optical system 12 CCD linear sensor 20, 20A, 20B, 20C Illumination optical system 21 Optical fiber array 21a Rod lens 22, 23, 24, 42, 53, 54 Cylindrical lens 25, 41, 52 Aperture stop 26, 43, 51, 55 Lens 31 Half mirror F Outgoing surface R Illumination area

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Atsushi Tamada 4-chome Tenjin Kitamachi 1-chome, Horikawa-dori-Terauchi, Kamigyo-ku, Kyoto F-term (reference) 2F065 AA56 BB02 CC01 DD04 FF04 GG03 GG14 HH05 JJ05 JJ25 LL03 LL08 LL22 LL30 LL59 2G051 AA65 AB07 AB20 AC21 BA01 BB09 BB17 CA03 CA07

Claims (7)

[Claims] 1. A pattern inspection apparatus for inspecting a pattern formed on a surface of an object to be inspected, wherein incoherent light emitted from a light source is irradiated onto a surface of the object by using an off-axis symmetric imaging element. An illumination optical system for guiding an elongated illumination area formed in the imaging optical system; an imaging unit for imaging the surface of the inspection object illuminated by the illumination optical system; and a pattern based on the image captured by the imaging unit. Inspection means for performing an inspection, wherein the illumination optical system is configured such that an illumination method in a longitudinal direction of the illumination area is Koehler illumination. 2. The pattern inspection apparatus according to claim 1, further comprising: a scanning unit that relatively scans the inspection object and the imaging unit along a direction that intersects a longitudinal direction of the illumination area. A pattern inspection apparatus, comprising: 3. The pattern inspection apparatus according to claim 1, wherein the illumination optical system is configured such that an illumination system in a lateral direction of the illumination area is a critical illumination. Pattern inspection equipment. 4. The pattern inspection apparatus according to claim 1, wherein the illumination optical system is configured to be telecentric on the inspection object side. Inspection equipment. 5. The pattern inspection apparatus according to claim 1, wherein the illumination optical system has an elongated emission surface configured as a set of emission points of a plurality of lights. Characteristic pattern inspection equipment. 6. The pattern inspection apparatus according to claim 1, wherein the illumination optical system has an emission surface that emits light from the light source to a space, and the emission surface. Is provided at a focal position closest to the inspection object among the object space side focal positions in the illumination optical system. 7. The pattern inspection apparatus according to claim 1, wherein the illumination optical system irradiates a surface of the inspection object with excitation light capable of exciting fluorescence. The pattern inspection apparatus according to claim 1, wherein the imaging unit captures an image based on fluorescence excited on a surface of the inspection object.