JP2002005841A - Lighting apparatus for visual inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate visual inspection apparatus which enables observation of a substrate with a high S/N ratio, by selectively irradiating the entire surface of the substrate to be inspected thoroughly with P-polarized light or S-polarized light as the illumination light. SOLUTION: This apparatus is provided with an irradiation means 3 for irradiating the surface of a substrate 1 to be inspected with P-polarized light or S-polarized light as illumination light, a holding means 5 for holding the substrate 1 and a tilting mechanism 7 for rotating the holding means 5 within a plane vertical to the substrate 1, including the axis of the illumination light. The irradiation means 3 is provided with a light source 9 for emitting the illumination light, a Fresnel lens 11 for focusing the illumination light emitted from the light source 9 and a first polarizing plate 13, with which the illumination light guided via the Fresnel lens 11 is selectively given optical characteristics of the P-polarized light or the S-polarized light to light the surface of the substrate. The holding means 5 is provided with a second polarizing means 19 to extinguishing the illumination light transmitted through the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate appearance inspection apparatus for inspecting the appearance of a substrate such as a wafer or a liquid crystal glass plate.

[0002]

2. Description of the Related Art Conventionally, in this type of apparatus, the surface of a substrate to be inspected is irradiated with illumination light for observation, and the optical change of the light reflected from the surface of the substrate is visually observed, whereby the appearance of the surface of the substrate is observed. Has been inspected. When foreign matter such as dust and scratches is present on the surface of the substrate to be inspected, scattered light is generated from the foreign matter, and a difference in intensity is generated between the reflected light reflected from the substrate surface. The observer detects such a difference in intensity and visually observes foreign substances present on the substrate surface.

[0003]

However, in the conventional apparatus, the polarization observation has not been performed. However, when a polarizing plate is interposed in the illumination optical path, the amount of light that can reach the substrate surface is reduced by about 30%. As a result, the light intensity of scattered light generated from foreign substances such as dust and scratches is also reduced. This is because there is a problem that visual observation becomes difficult.

In a conventional apparatus, a substrate to be inspected is controlled by a substrate holder so as to rotate and swing at an arbitrary angle with respect to an illumination optical axis. For this reason, even when the polarized light having the P-polarized component is radiated through the polarizing plate, the substrate to be inspected rotates and swings to change the angle of the polarized light with respect to the optical axis. There is a problem in that illumination combined with P-polarized light and S-polarized light is performed, and the interposition of a polarizing plate becomes meaningless.

Furthermore, in the case of polarized illumination, there is a problem that it is difficult to perform stable visual observation of the appearance of the substrate because the reflectance of the substrate surface greatly changes in accordance with the irradiation angle.

Conventionally, scattered light generated from foreign substances such as dust and scratches present on the surface of a substrate (background light refers to reflected light that is directly reflected from the substrate surface or the like excluding scattered light). The emphasis was on making it stand out.

For this reason, conventionally, as a countermeasure for increasing the amount of scattered light generated from a foreign substance, attention has been focused only on increasing the amount of illumination light applied to a substrate to be inspected. No consideration was given to improving the ratio to light (that is, the S / N ratio). At best, the surface of the substrate holder was painted black to suppress the generation of background light.

In recent years, a device for visually observing the appearance of the substrate surface by rotating the substrate to be inspected by a predetermined angle with respect to the optical axis of the illumination light (see Japanese Patent Application No. 3-266307), and A device for selectively illuminating the entire substrate surface with illumination light having different optical characteristics and observing the appearance of the substrate surface has been developed (see Japanese Patent Application No. 4-31922).

In these apparatuses, it is required to irradiate the entire surface of the substrate to be inspected with illumination light to observe a substrate surface having a high S / N ratio, but it has not been put to practical use yet.

The present invention has been made in order to meet such a demand, and an object of the present invention is to selectively irradiate P-polarized or S-polarized illumination light without unevenness on the entire surface of a substrate to be inspected, thereby achieving S / N ratio.
An object of the present invention is to provide a board appearance inspection apparatus capable of performing a board observation with a high ratio.

[0011]

In order to achieve the above object, a board appearance inspection apparatus according to the present invention comprises a light source which emits illumination light for illuminating a substrate to be inspected, and a light source which emits light from the light source. First polarizing means for selectively converting the illumination light into p-polarized light or s-polarized light, and holding the inspection target substrate in an optical path of the illumination light polarized through the first polarizing means A table, a second polarizing means for transmitting only scattered light generated from a foreign substance existing on the surface of the substrate to be inspected in the case of S-polarized illumination, and the substrate to be inspected including the illumination optical axis; And a tilt mechanism for rotating in a plane perpendicular to the plane.

The illumination light emitted from the light source is selectively converted into P-polarized light or S-polarized light through the first polarizing means.
Irradiation is performed on the substrate to be inspected held on the holding table. P, S
Each polarized light has different characteristics with respect to the reflection on the glass surface and the scattered light of the foreign matter. By using this characteristic, the P-polarized illumination increases the S / N ratio between the scattered light and the background light. Extracts only the scattered light of the foreign matter by the second polarizing means.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a board appearance inspection apparatus according to one embodiment of the present invention will be described with reference to FIGS. It is assumed that a substrate to be inspected made of glass is set in the apparatus of this embodiment.

First, the characteristics of the observation illumination light of P-polarized light and S-polarized light will be described with reference to FIGS.

FIG. 2A shows a substrate 1 to be inspected in air.
The relationship between the incident angle (θ) and the reflectance (r) when a P-polarized or S-polarized illumination light is applied to a smooth glass surface (refractive index n = 1.5) is shown.

Here, as shown in FIGS. 2 (b) and 3 (a), the substrate 1 to be inspected is tilted while irradiating the substrate 1 with P-polarized illumination light, and the angle with respect to the illumination optical axis. When the angle formed by the reflection angle (θ1) and the refraction angle (θ2) becomes 90 °, the reflectance becomes 0 (zero), and tan θ = n (n = 1.5) (1) ) There is a relationship. The incident angle (θ) at this time is called a Brewster angle (θB).

FIG. 4 shows the distribution of scattered light when the P and S polarized light strikes foreign matter C such as dust and scratches.

As described above, the illumination light has a Brewster angle (θ
When the light enters the surface of the substrate 1 to be inspected in B), only the scattered light generated from the foreign matter C such as dust and scratches existing on the surface of the substrate 1 reaches the observer's eyes D, and the other illumination light Then, the light passes through the substrate surface and is absorbed by the substrate 1 to be inspected. For this reason,
On the observer's eyes D, only the image of the foreign matter C existing on the substrate surface is projected.

However, as shown in FIG. 3A and FIG. 4, the Brewster angle (θ B) is actually an incident angle of about 55 ° when calculated using equation (1). For this reason,
From the scattering distribution of FIG. 4 and the position of the eyes D of the observer, the scattered light generated from the foreign matter C is difficult for the observer to see.

On the other hand, as shown in FIGS.
In the case of an angle (θ3) smaller than the Brewster angle (θB), even if there is room light and background light, the distribution of scattered light generated from the foreign matter C becomes stronger toward the observer, and the glass surface is reflected. Is smaller than the natural light illumination, the contrast of the foreign matter C increases.

As the background light, the back surface reflected light E reflected from the back surface of the substrate 1 to be inspected also contributes to this, but as shown in FIG. The back surface reflectivity with respect to the incident angle (θ) of the illumination
The characteristics are the same as the characteristics shown in FIG.

Next, when the S-polarized illumination light is applied to the substrate 1 to be inspected, as shown in FIGS. 2A and 2B, while the incident angle (θ) is small, it is not different from the P-polarized light. When the incident angle (θ) exceeds 15 °, the reflectance (r) increases as compared with the P-polarized light. 4, the scattering intensity of the scattered light generated from the foreign matter C existing on the substrate surface also increases.

However, the light intensity of the background light reflected from the holding plate surface also increases. As a result, the background of the visual field becomes bright, the contrast of the foreign matter C decreases, and the observer's eyes D
Unnecessary intense light begins to reach the camera.

In consideration of the characteristics of the P-polarized light and the S-polarized light, the use of the P-polarized light as the illumination light for observation makes the scattering generated from the foreign matter C such as dust and scratches present on the surface of the substrate 1 to be inspected. It is advantageous over S-polarized light in that it can make light stand out from other light. However, P-polarized light is disadvantageous in that the scattering intensity of scattered light is weaker than in the case of S-polarized light.

Therefore, the board appearance inspection apparatus of this embodiment is
The scattered light generated from the foreign matter C such as dust and scratches present on the surface of the substrate 1 to be inspected is distinguished from other light, and the foreign matter C
In order to improve the detection capability of the substrate, it is configured such that the substrate observation can be performed by utilizing the mutual advantages of the P-polarized light and the S-polarized light.

FIG. 1 schematically shows the configuration of a board appearance inspection apparatus according to this embodiment.

As shown in FIG. 1, the apparatus for inspecting the appearance of a substrate according to the present embodiment holds irradiation means 3 for irradiating P-polarized or S-polarized illumination light to the surface of a substrate 1 to be inspected, and holds the substrate 1 to be inspected. A holding means 5 and an inclination mechanism 7 for rotating the holding means 5 in a plane including the illumination optical axis and perpendicular to the substrate 1 to be inspected are provided.

The irradiating means 3 includes a light source 9 for emitting illumination light.
A Fresnel lens 11 for converging the illumination light emitted from the light source 9, and a predetermined optical characteristic given to the illumination light guided through the Fresnel lens 11 so as to be applied to the surface of the substrate 1 to be inspected. And a first polarizing plate 13 for illumination. The first polarizing plate 13 has a function of appropriately and selectively giving optical characteristics of P-polarized light or S-polarized light to received illumination light.

The holding means 3 comprises: a holding table 15 having a holding surface 15a wider than the substrate 1 to be inspected;
And a plurality of suction holding portions 17 protruding from the holding surface 15a. When the substrate to be inspected 1 is placed on the holding table 15, the substrate to be inspected 1 is sucked and held by the plurality of sucking and holding sections 17 that are in contact with the back surface thereof. As a result, the test substrate 1 is fixed on the holding table 15.

The tilting mechanism 7 is attached to one end of the holding base 15 and has a function of swinging the other end of the holding base 15 in the direction of arrow A in FIG.
By driving the tilting mechanism 7 to swing the holding table 15, the substrate 1 to be inspected fixed on the holding table 15 is at a predetermined angle (specifically, 0 ° to 0 °) with respect to the illumination optical axis B. (A range of 40 degrees).

Further, the board appearance inspection apparatus of this embodiment has a second polarizing plate 19 on the holding surface 15 a of the holding table 15. The second polarizing plate 19 is configured to be adjustable so as to be in a crossed Nicols state with respect to the polarization direction of the illumination light transmitted through the substrate 1 to be inspected.

Further, the board appearance inspection apparatus of the present embodiment includes a third polarizing plate 21 in front of the observer's eyes D. Third
The polarizing plate 21 is configured to be adjustable so that the polarization direction of the reflected light reflected from the front surface and the back surface of the inspection target substrate 1 becomes crossed Nicols.

Hereinafter, the operation of the board appearance inspection apparatus of this embodiment will be described with reference to FIG.

First, when inspecting the appearance of the substrate using the P-polarized illumination light, as shown in FIG. 1, the illumination light emitted from the light source 9 includes the Fresnel lens 11 and the first polarizing plate 1.
The light is converted into P-polarized light via 3 and irradiates the surface of the substrate 1 to be inspected.

At this time, the tilt mechanism 7 is driven to change the tilt of the holding table 15 in the direction of arrow A in the figure, thereby changing the tilt angle of the substrate 1 to be inspected with respect to the illumination optical axis B.

From the substrate 1 to be inspected, scattered light generated from foreign substances C such as dust and scratches present on the substrate surface, reflected light directly reflected from the substrate surface, and back-surface reflected light E reflected from the back surface of the substrate (see FIG. 2 (b)).

The illumination light transmitted through the substrate 1 to be inspected is
The second polarizing plate 19 provided on the holding table 15 is irradiated. At this time, the second crossed Nicols with respect to the polarization direction of the illumination light (in such a case, the second crossed Nicols with respect to the P polarized light).
Is adjusted. As a result, the illumination light transmitted through the inspection target substrate 1 is canceled by the second polarizing plate 19, and
Generation of background light from the holding surface 15a of the holding table 15 is prevented.

In the apparatus for inspecting the appearance of a substrate according to the present embodiment, a third polarizing plate 21 is disposed in front of the eyes D of the observer, and the third polarizing plate 21 is reflected from the substrate 1 to be inspected. Adjustment is made in crossed Nicols with respect to the polarization direction (P-polarized light) of light (reflected light from both the front and back surfaces of the substrate). As a result, the reflected light reflected from the front surface and the back surface of the inspection target substrate 1 is shielded by the third polarizing plate 21, and the observer's eyes D
Only the scattered light generated from the foreign matter C present on the surface of the substrate 1 to be inspected is projected.

Accordingly, in the case of the P-polarized light, the front and back surfaces of the substrate 1 to be inspected and the holding surface 15a of the holding table 15 are useless for observation.
Can be shielded from reflected light reflected from the light source, so that scattered light generated from foreign matter C such as dust and scratches can be made more gentle to the eyes D of the observer. As a result, the ability to detect foreign matter C present on the surface of the substrate 1 to be inspected can be improved.

Further, even when the focused light illumination is used as the P-polarized light and the eye D is positioned near the focal point of the reflected light,
Since the reflected light does not directly enter the eyes, it is possible to observe a substrate having a high S / N ratio without causing the eyes D to be blurred.

In the case where the P-polarized illumination light is used, the holding table is set so that the incident angle (θ) of the illumination light applied to the inspection target substrate 1 is within a certain range (about 15 ° to 40 °). 1
By controlling 5, the ratio of the light intensity of the scattered light to the light reflected from the glass surface can be increased, and thus the third polarizing plate 21 is not necessarily required.

Next, when inspecting the appearance of the substrate using S-polarized illumination light, as shown in FIG. 1, the illumination light emitted from the light source 9 includes the Fresnel lens 11 and the first polarizing plate 1.
The light is converted into S-polarized light through 3 and is irradiated on the surface of the substrate 1 to be inspected.

At this time, the tilting mechanism 7 is driven to change the tilt of the holding table 15 in the direction of arrow A in the drawing, thereby changing the tilt angle of the substrate 1 to be inspected with respect to the illumination optical axis B.

From the substrate 1 to be inspected, scattered light generated from foreign substances C such as dust and scratches present on the substrate surface, reflected light directly reflected from the substrate surface, and back-surface reflected light E reflected from the back surface of the substrate (see FIG. 2 (b)).

When the S-polarized illumination light is used, the light intensity of the scattered light generated from the foreign matter C such as dust and scratches present on the substrate surface increases as compared with the case where the P-polarized illumination light is used. The light intensity of each of the reflected light and the back surface reflected light E also increases.

The illumination light transmitted through the substrate 1 to be inspected is
The second polarizing plate 19 provided on the holding table 15 is irradiated. At this time, the second crossed Nicols with respect to the polarization direction of the illumination light (in such a case, the second crossed Nicols with respect to the S polarized light).
Is adjusted. As a result, the illumination light transmitted through the inspection target substrate 1 is canceled by the second polarizing plate 19, and
Generation of background light from the holding surface 15a of the holding table 15 is prevented.

In the apparatus for inspecting the appearance of a board according to the present embodiment, a third polarizing plate 21 is disposed in front of the eyes D of the observer, and the third polarizing plate 21 is reflected from the substrate 1 to be inspected. The cross direction is adjusted with respect to the polarization direction (S-polarized light) of light (reflected light from both the front and back surfaces of the substrate). As a result, the reflected light reflected from the front surface and the back surface of the inspection target substrate 1 is shielded by the third polarizing plate 21, and the observer's eyes D
Only the P component scattered light having a strong light intensity generated from the foreign matter C existing on the surface of the substrate 1 to be inspected is projected.
In such a case, foreign matter C such as dust and scratches appears in the observer's eyes D as if it were floating in a dark field of view. As a result, foreign matter C existing on the surface of the substrate 1
Observation of a substrate having a high N ratio can be performed.

As described above, the board appearance inspection apparatus of this embodiment selectively irradiates the P-polarized or S-polarized illumination light without unevenness on the entire surface of the board to be inspected, thereby observing a board having a high S / N ratio. It can be performed.

[0049]

Since the apparatus for inspecting the appearance of a substrate according to the present invention includes the second polarizing means for transmitting only the scattered light generated from the foreign matter present on the surface of the substrate to be inspected, the entire surface of the substrate to be inspected is provided. A substrate having a high S / N ratio can be observed by selectively irradiating P-polarized or S-polarized illumination light without unevenness.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a board appearance inspection apparatus according to one embodiment of the present invention.

FIG. 2A is a diagram showing a relationship between an incident angle (θ) and a reflectance (r) when irradiating P or S-polarized illumination light on a smooth glass surface of a substrate to be inspected in air. And (b) is a diagram showing a light guide path of illumination light applied to the substrate to be inspected.

3 (a) and 3 (b) show dirt and scratches when the substrate to be inspected is tilted while irradiating the substrate with the P-polarized illumination light to change the angle with respect to the illumination optical axis. Foreign matter C such as
FIG. 4 is a diagram showing a state of generation of scattered light generated from the light source.

FIG. 4 is a diagram showing the scattering intensity of scattered light generated when P-polarized light and S-polarized light are irradiated on a foreign substance such as dust and scratches.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inspection board | substrate, 3 ... Irradiation means, 5 ... Holding means, 7 ... Inclination mechanism, 9 ... Light source, 11 ... Fresnel lens, 13 ... First
Polarizing plate, 19 ... second polarizing plate.

Claims (6)

[Claims] 1. An illumination device used for an appearance inspection device that irradiates a surface of a substrate to be inspected to inspect for defects and the like, comprising: a light source that irradiates illumination light to the substrate to be inspected; An illumination device for visual inspection, comprising: a Fresnel lens disposed in an optical path; and a polarizing plate for illumination light, which imparts polarization characteristics to illumination light of the light source. 2. The illumination device for visual inspection according to claim 1, wherein the Fresnel lens focuses illumination light from the light source and irradiates the focused light onto the substrate to be inspected. 3. A transmission light polarizing plate having cross Yucol optical characteristics with respect to a polarization direction of transmitted light transmitted through the substrate to be inspected, is disposed in a transmission optical path of the substrate to be inspected. The lighting device for visual inspection according to 1. 4. A reflected light polarizing plate having optical characteristics of crossed Nicols with respect to a polarization direction of reflected light reflected by the substrate to be inspected, is disposed in a reflection optical path of the substrate to be inspected. Item 2. An illumination device for visual inspection according to Item 1. 5. A lighting device used in a visual inspection device that irradiates a surface of a substrate to be inspected to inspect for defects and the like, wherein a light source irradiates illumination light to the substrate to be inspected, and an illumination optical path of the light source A Fresnel lens disposed therein; a polarizing plate for illumination light that selectively provides P-polarized or S-polarized optical characteristics to the illumination light of the light source; and a transmission optical path transmitted through the substrate to be inspected. And a polarizing plate for transmitted light that can be adjusted so as to be crossed with respect to the polarization direction of the transmitted light. 6. A reflected light polarizing plate which can be adjusted so as to be in a crossed Nicols state with respect to the polarization direction of the reflected light, is further disposed in a reflected light path reflected by the substrate to be inspected. Item 6. An illumination device for visual inspection according to Item 5.