JP3422935B2 - Inspection method and apparatus for non-uniformity of translucent substance and method for selecting transparent substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting optical nonuniformity (defects) of a transparent material such as a glass substrate which is a transparent substrate for a photomask or a transparent substrate for an information recording medium, and its method. Non-uniformity of light-transmitting substance, which enables to detect non-uniformity of light-transmitting substance with high sensitivity and high speed by utilizing the property of total reflection on the surface of light-transmitting substance. The present invention relates to a sex inspection method and an apparatus thereof.

[0002]

2. Description of the Related Art In the manufacturing process of semiconductor integrated circuits, photomasks, etc., photolithography is used for forming fine patterns. For example, when manufacturing a semiconductor integrated circuit, a pattern is transferred using a photomask having a pattern formed by a light-shielding film (for example, a chrome film) on a transparent substrate that is highly accurately polished and mirror-finished. There is. An inspection method for a photomask, which can be said to be a master of this pattern, collects light on a minute area of the pattern surface and detects light from the pattern surface, as seen in the surface state inspection device described in Japanese Patent Laid-Open No. 198238/1983. A method of comparing reflected output and transmitted output is known.

[0003]

However, in recent years, with the increase in the density of patterns, not only the inspection of the pattern surface as in the above method but also the fineness of the transparent substrate itself which is highly accurately polished and mirror-finished. Defects are also targets for defect detection. Further, in the above-mentioned method, since light is collected in a minute area of the pattern surface, it is necessary to scan the light by using some means when the inspection area covers a wide range, which is proportional to the area of the inspection area. Therefore, it is difficult to detect minute defects in the transparent substrate because the inspection time is long and the amount of reflected / transmitted light with respect to the pattern itself and the transparent substrate does not change significantly depending on the presence or absence of defects.

Also in a transparent substrate for an information recording medium, an underlayer having good crystallinity and a magnetic layer formed on the surface of the transparent substrate accompanying high density recording, a magnetic head having a low flying height, and the like can be highly accurately prepared. A transparent substrate having a polished surface is required, and minute defects in the transparent substrate itself are also targets for defect detection. However, the existing defect inspection method and device cannot always be said to satisfy the demand for defect detection.

Therefore, in order to solve the above-mentioned problems, the present invention is a method for inspecting a non-uniformity of a light-transmitting substance which can reliably detect the optical non-uniformity of the light-transmitting substance with high accuracy and high speed. And its device.

A further object of the present invention is to provide a method and apparatus for inspecting non-uniformity of a light-transmitting substance, which can immediately extract a desired light-transmitting substance.

[0007]

In order to achieve the above object, the method for inspecting non-uniformity of a light-transmitting substance according to the present invention comprises introducing a laser beam into the light-transmitting substance. A method for inspecting non-uniformity, wherein the translucent material comprises at least one pair of total reflection surfaces facing each other in which laser light introduced into the translucent material repeats total reflection, and a total reflection surface. Is provided so as to oppose the traveling direction of the laser light that travels by repeating total reflection, and the at least one pair of folding surfaces that totally reflect the laser light and return to the total reflection surface is provided. When the optical path in the substance is optically uniform, the laser light that propagates in the light-transmitting substance and is incident on the total reflection surface and the folding surface undergoes total reflection, and at least one set of folded light is used. Propagate and propagate laser light in a repeating fashion between faces The laser light is introduced so that the laser light is spread in the region to be inspected surrounded by the total reflection surface and the folded surface formed by, and in the optical path of the laser light introduced and propagated in the translucent material. When there is a non-uniform portion, the non-uniformity of the translucent material is inspected by detecting light leaking from the total reflection surface and / or the folded surface.

If the translucent material does not have a non-uniform portion such as a scratch on the surface, the laser light introduced into the translucent material repeats total reflection on the surface and the light is confined in the translucent material (laser). Light does not leak to the outside (at the total reflection surface and the folded surface).
However, if the translucent material has a non-uniform portion, the conditions for total reflection are not satisfied, and light leaks from the surface of the translucent material (the total reflection surface and the folded surface described above). That is, if there is a non-uniform portion (defect) such as scratches, cracks, stains due to adhered foreign matter on the surface of the translucent material, if the optical path is uniform, it will become a total reflection surface (total reflection surface and folded surface) Light will leak out. In addition to the unevenness of the surface of the light-transmitting material, defects such as internal scratches, cracks, foreign matters such as bubbles, or striae of glass, which have the same transmittance but differ only in the refractive index Regarding detection of flaws, it is possible to detect if there is a flaw or where the refractive index is different, if it is originally uniform, it will deviate from the optical path (path) that passes and the conditions for total reflection on the surface will not be satisfied, and it will leak to the outside of the translucent material. become.

As described above, in the inspection method of the present invention, the light is substantially confined in the translucent substance by utilizing the geometrical-optical total reflection which is a physical critical phenomenon.
The response to the inspection light in the nonuniform portion and the uniform portion of the translucent material to be inspected is also critical, and the nonuniform portion appears as a leaked light with a dramatic contrast in the background of the dark uniform portion. In other words, the inspection method of the present invention can be called a defect (non-uniformity) inspection method by the light confinement method, in which light inside the container is emitted from pinholes existing in a light-shielding container such as a dark box. As if leaking out, defects such as extremely fine scratches of the translucent material will be observed.

The incident condition of light for confining light (substantially) in the transparent substance by repeating total reflection on the surface of the transparent substance is obtained as follows. In the following, the conditions for confining (substantially) light by multiple total reflection in a transparent material having a rectangular parallelepiped shape such as a transparent substrate will be determined.

Prior to obtaining the conditions for this light confinement, first, as shown in FIG.
The direction of the refracted light when the light is incident from the medium of the above into a medium having a refractive index nt having a light-transmitting property such as glass (note that
In the drawing, the vector is expressed as a normal arrow,
In the document, the vector A is expressed as <A>. ).

As shown in FIG. 27, consider a refracted ray <Lt> when an incident ray <Li> is incident on the boundary surface between the refractive index ni and the refractive index nt. A normal vector which is perpendicular to the boundary surface and faces the incident medium side is defined as <N> (unit vector). The refraction ray vector <Lt> is the vector <N> and <
It exists on a plane defined by Li> and can be represented by a linear combination of <N> and <Li>. That is, it can be expressed as <Lt> = α <Li> + β <N> (1). Here, α and β are coefficients. Further, if the vectors <Li> and <Lt> are also unit vectors in order to simplify the calculation, the following expression is satisfied. <Li> · <Li> = 1, <Lt> · <Lt> = 1 (2)

When the law of refraction (Snell's law) is applied to the refraction at the boundary surface, since the incident angle is θi and the refraction angle is θt, sin θt = (ni / nt) sin θi (3) Further, when θi and θt are represented by vectors, <Li> · <N> = | <Li> | · | <N> | cos (π−θi) = -cosθi (4) <Lt> · <N> = | <Lt> | · | <N> | cos (π−θt) = − cos θt (5).

What is being sought now is the refracted ray vector <Lt>, and if α and β in equation (1) are determined,
<Lt> is determined. Therefore, from the equations (1) to (5), when α and β are represented by ni, nt, and θi, α = ni / nt β = − {1- (ni / nt) ² (1-cos ² θi) } ^1/2 +
(Ni / nt) cos θi, and the direction of the refracted light beam <Lt> with respect to the incident light beam <Li> is determined.

Next, a condition for the refracted light beam thus introduced in a predetermined direction to be trapped in the transparent substance by repeating total reflection on the surface of the rectangular parallelepiped transparent substance is determined.

First, as a first boundary surface of total reflection, xy
Consider a plane. As shown in FIG. 28, the normal vector in the positive direction of the z axis is <Nz> = (0,0,1), and the incident angle θi
And incident vector <L1> (unit vector) = (L1x, L1
When y, L1z) is incident on the xy plane, <L1> · <Nz> = cos (π−θ1) holds. When this is expanded, since L1z = -cos θ1 | <L1> | = 1, under the condition of θ1 ≧ θc, L1x ² + L1y ² + cos ² θ1 = 1 (6) is satisfied.

The incident vector capable of total internal reflection on the xy plane of the first boundary surface may be outside the cone of FIG. 28 formed by rotating the straight line forming the critical angle θc with the z axis around the z axis,
There are infinite number of vectors that satisfy this.

Since the light is reflected on the xy plane, the vector <L2> after reflection becomes <L2> = (L1x, L1y, -L1z) = (L1x, L1y, cos θ1). Furthermore, it is necessary to consider the conditions for this vector <L2> to be totally reflected at the second boundary surface. When the second boundary surface is the xz plane and is incident on the xz plane at the incident angle θ2, <L2> · <Ny> = cos (π−θ2). Here, <Ny> is a unit vector (0, 1, 0) oriented in the positive direction of the y-axis. Expanding the above equation, L1y = −cos θ2 From this equation and the equation (6), it is necessary to satisfy L1x ² = 1−cos ² θ1−cos ² θ2 (7) under the condition of θ1, θ2 ≧ θc. is there.

Since the light is reflected on the xz plane, the vector <L3> after reflection is represented by <L3> = (+ {1-cos ² θ1−cos ² θ2} ^1/2 ,
cos θ2, cos θ1). If this vector <L3> is totally reflected at the third boundary surface, the light confinement is successful. Yz the third boundary surface
If it is a plane and is incident on the yz plane at an incident angle θ3, then <L3> · <Nx> = cos (π−θ3). Note that Nx = (1,0,0). Therefore, the above equation becomes L3x = -cos θ3, and + {1-co
s ² θ1 −cos ² θ2} ^1/2 = −cos θ3, that is, cos ² θ1 + cos ² θ2 + cos ² θ3 = 1 (8) must be satisfied.

At the critical angle θc, sin (π / 2) = (nt
/ Ni) sin θc, so ni = 1.00, nt =
In the case of 1.47, since sin θc = 1 / 1.47, the critical angle θc = 42.9 °.

When θ1 = θ2 = θ3, from equation (8), 3c
os ² θ1 = 1, θ1 = 54 °, and θ1 ≧ 54 °> θc
= 42.9 ° is sufficiently satisfied. The margin with this degree of freedom can be utilized as the degree of freedom that causes the specific reflection surface to perform more total reflection. For substrate glass, <L1> should be selected so as to reduce reflection at the end face.

From the above, the condition for confining light by multiple total reflection is cos ² θ1 + cos ² θ2 + cos ² θ3 = 1 cos θc ≧ cos θ1, cos θ2, cos θ3> 0.

When θc = 42.9 °, cos θc = 0.
Since it is 73, the area that is satisfied by θ1, θ2, and θ3 is cos θ
When 1, cos θ2 and cos θ3 are used as coordinate axes, as shown in FIG. 29, inside a cube with a side of 0.73,
The curved surface 60, which is the surface of a sphere having a radius of 1, is a region that satisfies the total reflection condition.

Although the conditions for total internal reflection of a rectangular parallelepiped light-transmitting substance such as a transparent substrate have been derived in the above, the conditions for the incident angle of light are determined by the same method in a general shape described later. be able to. Also,
The conditions of the incident angle of the light introduced into the translucent material in the embodiments described later are derived based on the above.

In the nonuniformity inspection method of the present invention, the shape of the translucent material is a rectangular (rectangular) flat plate,
Not only a circular or annular flat plate, but also any shape such as a lens having a curved surface with a large curvature, a sphere, a polyhedron, a cylinder, a cylinder, a polygonal prism, etc. The shape of the light-transmitting substance does not matter as long as it is possible to realize a state in which light is confined in the light-transmitting substance by repeating reflections more than the number of times.

As described above, in order to confine light in the translucent material, the translucent material should have at least one pair of total reflections in which the light introduced into the translucent material repeats total reflection. The surface and the total reflection surface are provided so as to face each other in the traveling direction of the laser light that propagates by repeating total reflection.
It is preferable to provide at least one pair of folding surfaces for totally reflecting the laser light and returning it to the total reflection surface. In particular, the folded surface is important in confining light in the translucent material. The folding surfaces are provided so as to face each other in the light traveling direction, and at least one pair must be provided. This is because light cannot be confined unless the light repeats between the folding surfaces.

When the laser light is introduced, the laser light introduced into the light-transmitting substance is totally reflected by the light propagating in the light-transmitting substance and entering the total reflection surface and the turn-back surface. It is necessary to repeatedly propagate between a set of folding surfaces, and to introduce the laser light so that the laser light reaches the inspection area surrounded by the total reflection surface and the folding surface formed by the propagation. Is. That is, when the optical path in the translucent material is optically uniform, the light introduced into the translucent material propagates while repeatedly undergoing total reflection between the opposed total reflection surfaces, and is reflected by the folding surface (a). After incident and totally reflected, the propagation is repeated in the translucent material, and the folded surface (a)
Other than that, laser light is introduced so that the light that has propagated to the folding surface (a) returns again after being totally reflected by at least one of the folding surfaces (b, c, ...). In this case, the optical path in the transparent material is optically uniform, and if there is no non-uniform portion, total reflection is repeated at the total reflection surface and the return surface, and the total reflection surface and the return surface (the area where the laser light is introduced). Except for), there is no singular point where light leaks, so (substantially) optical confinement is established. When there are one set of folding surfaces, light is confined in one plane with a light-transmitting substance, and when there are more than one pair of folding surfaces, light is trapped in almost the entire area of the light-transmitting substance. Will be done.

In order to confine light (substantially) in the translucent material, there should be substantially no singular point at which the laser light leaks geometrically and optically at the total reflection surface and the folded surface. Laser light may be introduced. "Geometrically"
Therefore, the light introduced by the optical change of the introduced laser light due to the property peculiar to the translucent material, such as Rayleigh scattered light, is not considered here. In addition, "the singular point where the laser light leaks substantially does not exist" is due to the influence of the divergence angle of the laser light itself, and after the total reflection is repeated many times on the total reflection surface and the folded surface, It is considered that a slight amount of laser light does not satisfy the conditions for total reflection and leaks out of the translucent material. Therefore, the effect is taken into consideration to make it “substantially”. The leaked light due to the divergence angle of the laser light itself leaks in the direction along the surface of the translucent material, and therefore is not detected by the detection means and does not affect the detection sensitivity.

In order to confine light in the transparent material, the refractive index of the transparent material with respect to the wavelength λ of the introduced laser light is nt, and the refractive index of the outer medium in contact with the transparent material is Let ni be the angle of light incident on the total reflection surface and the turning surface, and θik (k represents the position where the laser light enters the translucent material and then enters the total reflection surface and the turning surface. The incident positions are sequentially set to k = 1, 2, ...), and θik is a laser beam so that it is equal to or greater than the critical angle θ represented by sin θ = ni / nt on the total reflection surface and the folded surface. Should be introduced.

However, on the surface of the translucent material, for a shape in which it is difficult to confine light by total reflection (for example, a shape having a curved surface with a large curvature), at least 2 provided outside the translucent material. In a set of opposing surfaces (at least one set of total reflection surfaces and at least one set of folding surfaces),
By allowing the light to propagate through the total reflection repeatedly, the non-uniformity can be checked. Specifically, a translucent container having a mirror-finished surface is used, and a translucent substance is contained in a medium (such as a liquid) in the container having a refractive index higher than that of the outer medium of the container. It can be inspected by inserting and introducing a laser beam so as to repeatedly propagate the total internal reflection on the outer surface of the container.

Further, the laser light is geometrically-optically so that all of the laser light is totally reflected at least on the total reflection surface and the folded surface on which the laser light introduced into the translucent material first strikes. By introducing light, light satisfying the conditions of total reflection can be accurately introduced into the translucent substance, which is preferable. Otherwise,
For example, when diffused light propagates in a translucent material in terms of introducing the laser light, the trajectory of the (plural) rays propagating in the translucent material cannot be predicted, so the introduced laser light However, it is difficult to totally reflect almost all the light incident on the total reflection surface and the folded surface, and the optical confinement as in the present invention is not established.

Further, it is preferable that the introduction surface for introducing the laser beam is provided at a position sandwiched by one certain total reflection surface and at least one folding surface. The introduction of the laser light into the translucent substance, it is also possible to introduce from the total reflection surface or folding surface other than the introduction surface, in that case,
As an entrance window for introducing the laser light, an optical member made of a material having substantially the same refractive index as the translucent material must be attached with an adhesive or the like, which is troublesome.
In addition, since the optical member is attached to the total reflection surface or the folded surface, which is the inspection area, the light propagated in the translucent material does not satisfy the total reflection condition and leaks out at the attached position. It is not preferable because it cannot be inspected. In this way, when there is an introduction surface for introducing the laser beam, as a specific introduction method, the introduction is performed only on the introduction surface and on a surface where the angles formed by the introduction surface and the total reflection surface are substantially the same. The light confinement in the present invention is established by introducing the laser light so that the laser light is emitted.

Further, it is preferable that at least the introduction surface of the translucent material for introducing the laser beam is mirror-polished. Laser light is introduced so that light is trapped by repeating total reflection on the total reflection surface and the folded surface, but when the introduction surface is mirror-polished, the introduced laser light is not diffused by the introduction surface, Since the light is propagated as parallel light, all the light incident on the total reflection surface and the folded surface is totally reflected, so that the response of the inspection light in the nonuniform portion and the uniform portion of the translucent material is more critical. And the contrast is improved. Preferably, the entire surface of the transparent material (total reflection surface,
It is desirable that the folded surface and the introduction surface are mirror-polished.

Further, the size of the total reflection surface is L, the width of the introduction surface is d, the refractive index of the transparent material with respect to the wavelength λ of the laser light is nt, and the refractive index of the outer medium in contact with the transparent material is ni,
The beam diameter of the laser light is φ, and the angle of the light that is incident on the total reflection surface and the folding surface is θik (k is the position where the laser light is incident on the total reflection surface and the folding surface after the laser light is introduced into the translucent material. The incident positions are k = 1, 2, ... In particular, the angle of the light that first enters the total reflection surface or the folded surface after the laser light is introduced is θ1), and The number of reflections on the reflecting surface is m, and m is L, d, nt.
If it is expressed by a function of (λ), ni, φ, θ1, then θ
Within the range where all of ik are equal to or greater than the critical angle θ, L, d, nt (λ), ni,
It is preferable to determine at least one of φ and θ1 and introduce the laser light from the introduction surface of the transparent material.

When the light introduced with the laser beam from the introduction surface is repeatedly propagated in the translucent material and the light is again incident on the introduction surface, the light having the critical angle θ or less is incident. Light leaks out. Therefore, when it is desired to cause a larger number of total reflections in the light-transmitting substance (when increasing m), the probability of leaking from the introduction surface may be reduced. Actually, the ray path is obtained by simulation, and the light introduced into the translucent material propagates by repeating total reflection on the total reflection surface and the folded surface, resulting in a large number of reflections before the light leaks on the introduction surface. The width d of such an introduction surface is determined. Specifically, the width d of the introduction surface may be reduced.
The width d of the introduction surface is limited to the beam diameter of the laser beam and the processing of the light-transmitting material, but d is 0.4 mm or less, preferably 0.2 mm or less. However, if it is extremely small (less than 0.1 mm), chipping easily occurs at the interface between the total reflection surface and the introduction surface and at the interface between the folded surface and the introduction surface, which is not preferable.

Further, by selecting the refractive index nt (or the wavelength λ of the laser beam) of the translucent material, m (the number of reflections on the total reflection surface) can be adjusted. Specifically, since the material of the translucent material may be limited depending on the use of the translucent material, it is preferable to select the wavelength λ of the laser light. However, it is preferable that the laser light has a wavelength at which absorption of the light-transmitting substance is small. If the absorption is large, not only the detection sensitivity for nonuniformity is lowered, but also the translucent substance itself may be destroyed, which is not preferable. Further, the wavelength of the laser light also affects the resolution of nonuniformity (such as scratches on the surface). Since the maximum resolution of non-uniformity is the wavelength λ of laser light, if you want to decompose and detect minute defects with a scratch width of 1 μm or less such as a glass substrate for electronic devices as an image, the wavelength of laser light is 1 μm. Below.

Further, in a certain shape of the translucent material (for example, when the total reflection surface and the folding surface are in a vertical relationship), the angle of incidence of laser light on the total reflection surface and the folding surface is Since it has a certain relationship with the angle θ1 at which it first enters the total reflection surface after it is introduced, that angle θ1
By appropriately adjusting, it is possible to adjust m (the number of reflections on the total reflection surface). Actually, θ1 is the light inside the light-transmitting substance after the conditions for the light-transmitting substance (width d of the introducing surface, refractive index nt) and conditions for the laser light (wavelength λ, beam diameter φ) are determined. The laser light is introduced by adjusting θ1 so that the value becomes equal to or more than the reference design value m, which is filled with. However, in general, there are variations in the size (length, etc.) of the total reflection surface due to the difference in processing accuracy in translucent materials. It takes an enormous amount of time to perform inspection after grasping each inspection sample, so it is impractical to change the incident angle of the laser light introduced into the translucent material within the range that causes total internal reflection. The incident light enables high-sensitivity and high-speed detection, and a highly practical inspection method can be realized.

Further, it is preferable that the total reflection surface and the folded surface of the translucent material are orthogonal to each other. With such a configuration, the introduced laser light is likely to be trapped in the translucent material by repeating total reflection on the total reflection surface and the folded surface. The inspection can be performed simultaneously, and high-speed inspection is possible. That is, the incident angle of light is the same in at least one set of total reflection surfaces in which the introduced laser light repeats total reflection,
In addition, the incident angle of light is the same in at least one pair of folding surfaces, and the relationship is constant (when the incident angle of light on the total reflection surface is θ, the incident angle of light on the folding surface is 90 ° −θ.
become. ) Will be propagated.

In addition, in a region to be inspected of a transparent material sandwiched by a set of total reflection surfaces and a set of folding surfaces, the light is filled by the light propagating in the transparent material. After inspecting the non-uniformity in one plane in the inspected area, the non-uniformity of the inspected area is moved by moving the inspected plane relative to the transparent material in the direction in which light fills the inspected area. It is preferable to inspect the sex because the inspection method can be simplified.

Although the general concept of light confinement of the present invention has been described above, in practicing the present invention more concretely, laser light is introduced into the transparent substance to prevent the light-transmissive substance from becoming defective. A method of inspecting for uniformity, wherein the surface of the light-transmissive material comprises at least one set of mutually parallel main surfaces, at least one set of end faces orthogonal to the main surfaces, and the main surface and the end faces. When the optical path in the translucent material is optically uniform, the chamfered portion is sandwiched, and the light that propagates in the translucent material and is incident on the main surface and the end surface is totally reflected. In addition, the laser beam is propagated in a repeating manner between at least one set of end faces, and the laser beam is distributed in the region to be inspected surrounded by the main surface, the end faces and the chamfer formed by the propagation. Laser light is introduced into the translucent material. It is when the inhomogeneities are present in the optical path of the light propagating, checking the non-uniformity of the translucent material from the detecting light leaking from said main surface and / or the end face.

Here, the main surface, the end surface, and the chamfered portion are
It corresponds to the above-mentioned total reflection surface, folded surface, and introduction surface. As a typical shape having the main surface, the end surface, and the chamfered portion, a quadrangular (rectangular) flat plate, a circular plate, an annular flat plate and the like can be mentioned. In this case, the introduced laser light is likely to be (substantially) confined in the translucent substance by repeating total reflection on the main surface and the end face, and in fact, in a wide area of the translucent substance. It is preferable that the inspection can be performed simultaneously and the high-speed inspection can be performed. That is, the incident angle of light on the main surface where the introduced laser light repeats total reflection is the same, and the incident angle of light incident on the end face is also the same. When the incident angle is θ,
Since the incident angle of the light incident on the end face is 90 ° −θ, the light propagates with an angle of incidence on the main surface that first strikes the translucent material and then becomes larger than the critical angle, and The light confinement is substantially established only by setting the incident angle on the end face to be larger than the critical angle. As a specific introduction method, the laser light is introduced so that there is substantially no singular point at which the laser light leaks geometrically and optically on the main surface and the end surface.
Further, the laser light is introduced so that the introduced laser light is emitted only at the chamfered portion.

Further, it is preferable that the translucent material for the above-mentioned nonuniformity inspection method is made of glass. The material of the translucent material is determined by various uses, but in the case of glass, advantages such as being hard, obtaining a very smooth surface by mirror-polishing, good light transmittance, etc. There is.

The above nonuniformity inspection method is more effective when the translucent material is a glass substrate for electronic devices. With the recent increase in pattern density,
Since a glass substrate having a highly polished surface is required, the above-mentioned nonuniformity inspection method is used for inspecting pattern formation such as fine scratches and striae of the substrate and nonuniformity that adversely affects exposure. Is effective.

Further, the above-mentioned nonuniformity inspection method is more effective when the translucent substance is a glass substrate for information recording medium. With the recent trend toward high density recording and low flying height of magnetic heads, a transparent substrate having a highly precisely polished surface is required. This is effective for inspecting non-uniformity that adversely affects recording and low flying of the magnetic head.

The glass substrate for electronic devices, the glass substrate for information recording media, the glass substrate for liquid crystal displays, etc., which have main surfaces parallel to each other and end faces perpendicular to the main surfaces, are introduced. If the generated light is repeatedly totally reflected and confined in the light-transmitting substance, it is possible to inspect a wide range of the light-transmitting substance at the same time, which enables high-speed inspection.

Further, the non-uniformity inspection apparatus for a transparent material according to the present invention is for carrying out the above-mentioned inspection method, in which a laser beam is introduced into the transparent material to detect the non-uniformity of the transparent material. An apparatus for inspecting uniformity, comprising illumination means (irradiation means) for introducing laser light into the transparent substance, and detection means for detecting light leaking from the transparent substance, The translucent material includes an introduction surface for introducing laser light into the translucent material, and at least two sets of surfaces facing each other in which the introduced laser light repeats total reflection, and the illuminating means is illuminating means. When the laser light emitted from is introduced from the introduction surface and the optical path in the transparent substance is optically uniform, the light that propagates in the transparent substance and is incident on the surface is Total internal reflection and at least one set of said surfaces Propagate to repeat, as the laser beam is spread in the inspection region surrounded by said at least two pairs of surfaces are formed by propagating, in which are arranged. With such a configuration, the inspection of the nonuniformity of the light-transmitting substance can be automated, the inspection time can be shortened, and the reliability of the inspection can be improved.

In the above inspection apparatus, it is preferable that the illuminating means is provided with an angle adjusting means for changing the incident angle of the laser light with respect to the light transmitting material. The angle adjusting means not only adjusts the incident angle so that the laser light introduced into the light-transmitting substance repeats total reflection on the surface of the light-transmitting substance and traps the light. It is used when the incident angle is changed within the range where total reflection occurs in order to absorb the dimensional variation due to the difference in the processing accuracy.

A mirror is a typical example of the angle adjusting means. The mirror is arranged between the illuminating means (for example, a laser) and the translucent substance, and adjusts an incident angle with respect to the translucent substance. In addition to the mirror, the illuminating means itself may be provided with an angle adjusting means for changing the angle of the illuminating means with respect to the translucent substance, or the folder for holding the translucent substance may be provided with the angle adjusting means. Further, the incident angle may be adjusted and changed by utilizing the acousto-optic effect of the ultrasonic beam such as an acousto-optic polarizer.

Further, in the above inspection apparatus, it is preferable to provide a moving (scanning) means for moving (scanning) the incident position of the laser light on the transparent substance. This is because it is possible to perform the inspection automatically without leaking the entire region of the transparent material. For example, a lighting device such as a laser and an angle adjusting device such as a mirror are placed on the same table, and a driving device is attached to the table to move the light-transmitting substance along one side one by one or to move the light-transmitting substance. The drive device can be attached to the holding folder and moved.

Further, in the above inspection apparatus, it is preferable that the translucent substance and the detecting means are integrally moved relative to the illuminating means. When the detection area of the detection means is larger than the inspection area, the non-uniformity can be inspected by the relative movement of the translucent substance with respect to the illumination means. Since it is larger than the detection area of the means, the translucent substance and the detection means are integrally moved relative to the illumination means. In the case of relative movement, the illumination means, that is, the illumination optical system such as a laser is fixed, and the translucent substance and / or the detection means is moved by using a driving device, or the translucent substance is used. The detection means may be fixed and / or the illumination optical system such as a laser may be moved.

In the above inspection apparatus, the detecting means is an image pickup camera having an image pickup element (CCD or the like),
It is preferable to have a lens that forms an image of light leaking from the translucent material on the imaging camera, and move the imaging camera and / or the lens relative to the translucent material in a perspective direction. By moving the imaging camera and / or lens relative to the translucent material in the perspective direction, it is possible to focus the imaging camera, and the non-uniformity of the translucent material in the thickness direction (surface scratch, internal Accurate information on striae, bubbles, etc.) can be obtained. For example, the detection means of the imaging camera and the lens are fixed, and the translucent substance, the laser, and the mirror are integrally moved in the perspective direction of the detection means, or conversely, the translucent substance,
The laser and the mirror may be fixed, and the image pickup camera and the detection means of the lens may be moved.

In the above inspection apparatus, it is preferable to provide discrimination means for discriminating presence / absence, type and size of the non-uniformity of the translucent substance based on the information detected by the detecting means.

This is because the presence or absence of non-uniformity existing in the translucent material in advance, the type (scratches or cracks on the surface, striae or foreign matter inside), and the size (area, length, width, depth). For example, the relation (information) of the (image) information of the light leaked from the surface (light intensity, brightness, intensity distribution, depth from the surface, etc.) is accumulated in a computer, etc. , A non-uniform type of translucent material by comparing the (image) information of light detected by inspection with the stored information,
The size can be determined. In this way, by determining the presence / absence of non-uniformity of the translucent substance, the type, and the size,
A desired translucent substance can be extracted. For this reason,
For example, a glass substrate having non-uniformity that affects the pattern formation or the exposure of the transferred material can be removed after the inspection before proceeding to the next step, or can be returned to the re-polishing. You can improve the property.

Further, in the above nonuniformity inspection apparatus, the information on the detected light is obtained by detecting the light detected by the CCD.
The signal-to-noise ratio (10
・ When converted to log ₁₀ (S / N) and processed, the signal-to-noise ratio (10 ・ l) is obtained when the normalized exposure time is 0.025 or more.
It is preferable that og ₁₀ (S / N)) is 4.8 dB or more. Here, the normalized exposure time means (CCD exposure time) / (background signal is (20000/409).
5) CCD maximum exposure time until reaching 100 electrons. (Note that the above-described normalized exposure time can be freely set depending on the measurement conditions and the inspection device.)

When the signal-to-noise ratio is 4.8 dB or more (the signal with respect to the background is 3 times or more of the noise), it is considered to be the level at which image processing can be generally said, and the light-transmitting substance cannot be accurately detected. This is because it is possible to determine the presence / absence, type, and size of uniformity.

Further, in the transparent substrate selection method according to the present invention, the introduction surface for introducing the laser light, the at least one pair of mutually facing main surfaces where the introduced laser light repeats total reflection, and the main surface are separated from each other. A step of preparing a transparent substrate provided with at least one set of end faces provided so as to face each other in the traveling direction of the laser beam that proceeds by repeating total reflection,
When the optical path in the transparent substrate is optically uniform, the light propagating in the transparent substrate and incident on the main surface and the end faces undergo total reflection, and repeat between at least one set of end faces. Such that the laser light is introduced from the introduction surface so that the laser light is distributed in the region to be inspected surrounded by the main surface and the end surface formed by the propagation, and the main surface and / or A step of detecting light leaking from the end face without being totally reflected, information obtained in the detecting step, and presence or absence of non-uniformity existing in a transparent substrate accumulated in advance, information corresponding to type and size And compare
And a step of selecting a transparent substrate.

[0057]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a non-uniformity inspection device for a transparent material according to the present invention.

In FIG. 1, reference numeral 1 is a transparent substrate made of glass such as optical glass which is an object to be inspected. Transparent substrate 1
2 have parallel planes facing each other as shown in FIG. 2, which has a main surface (front surface and back surface) H
And the end face (T face and C face of the chamfered portion). Both surfaces are mirror-polished and then washed. The main surface (front surface and back surface) has a function of repeating total reflection and propagating the laser light introduced into the transparent substrate, and has a function as a total reflection surface. The end faces (T faces) are provided so as to face each other in the traveling direction of light, and the light propagated by repeating total reflection on the main surface is repeated between the facing end faces. Therefore, it has a function as a turnback surface that turns back the light that has been introduced and propagated. Also,
The C surface is a surface sandwiched by the main surface and the end surface (T surface). In general, the surface C is not a target of the region to be inspected because fine scratches on the surface do not pose a problem, and in the present invention, it has a function as an introduction surface for introducing laser light.

Although the main surface (front surface, back surface) as the total reflection surface, the end surface (T surface) as the folded surface, and the C surface that is the introduction surface are all mirror-polished. Especially, mirror polishing of the introduction surface is significant in the light confinement of the present invention. That is, by mirror-polishing the introduction surface, the introduced laser light is not substantially diffused and propagates as substantially parallel light, so that almost all light incident on the main surface and the end surface is totally reflected. However, if the introduction surface is not polished, the light is diffused on the introduction surface, light in multiple directions propagates, and since the respective ray trajectories cannot be predicted, the light confinement of the present invention is Not satisfied. Although the introduction surface was mirror-polished, the laser light to be introduced into the substrate should be mirror-polished if the laser light can be introduced so that all of the laser light is totally reflected at least on the main surface that hits first. Absent. For example, by applying a matching oil or the like having the same refractive index as the substrate in order to form a pseudo mirror surface on the introduction surface of the rough surface,
The optical confinement of the present invention is established.

Further, the transparent substrate 1 is held horizontally by a folder with a minimum of contact portions in order to prevent the total reflection on the surface thereof from being obstructed and to facilitate the inspection of leaked light. FIG. 3 shows an example of a folder of the transparent substrate 1. The folder 20 has a rectangular frame shape for holding the transparent substrate 1, and the bottom of the folder 20 has four corners on the inner peripheral side. The receiving portions 21 for supporting the corners are formed, and the transparent substrate 1 is formed in each receiving portion 21.
A spherical body 22 is provided so as to be in point contact with and support.

Illuminating means for introducing a laser beam for inspecting the nonuniformity from the side surface side of the transparent substrate 1 is provided to the transparent substrate 1. The illuminating means has a laser 2 as a light source that emits illumination light, and mirrors 31 and 32 for illuminating the laser light at a predetermined position and angle on the C surface of the transparent substrate 1. Also, these lasers 2,
The mirrors 31 and 32 are mounted on a table 5 on which a driving device 4 for translating a laser beam in a direction of one side 1a of the transparent substrate 1 is mounted. In this embodiment, since the laser 2 and the mirrors 31, 32 are moved relative to the transparent substrate 1 and the detecting means, the transparent substrate 1 and the detecting means are fixed, and the laser 2 and the mirrors 31, 32 are integrated by the driving device 4. It is structured so that it can be moved to. (It should be noted that a driving device may be attached to the transparent substrate 1 and the detecting means, and the laser 2 and the mirrors 31 and 32 may be fixed so that the transparent substrate 1 and the detecting means can move integrally.) , Laser 2 and mirror 31,
A table (not shown) on which the 32 is mounted is used to focus the CCD when introducing the laser beam to the transparent substrate 1.
In order to detect the non-uniformity in the thickness direction of the, it is possible to move in the XYZ directions. Note that the mirrors 31 and 32 are for fine adjustment of the angle and the like, and the laser light may be directly applied to the substrate 1 from the laser 2 without using the mirrors 31 and 32. Further, an incident angle adjusting means may be provided so that the laser beam introduced into the transparent substrate 1 can be incident with the incident angle varied within a range where total reflection occurs. As the incident angle adjusting means, a mechanism that automatically adjusts the angles of the mirrors 31 and 32 by controlling a computer or the like, or an acousto-optic effect of an ultrasonic beam such as an acousto-optic polarizer is used. Alternatively, the incident angle may be changed.

Above the transparent substrate 1, the transparent substrate 1
Detection means is provided for detecting laser light leaking from the device. The detection means is provided with a lens system (imaging optical system) 7 for forming an image of the leaked light from the CCD 6 and the transparent substrate 1 on the CCD 6. The photosensor for detecting the light leaked from the transparent substrate 1 is not limited to the CCD, but a photomultiplier or the like may be used. Further, when using visible laser light as the illumination light, it is possible to visually detect the leaked light from the substrate 1 and omit the detection means.
When a CCD is used as the detection means, there are a full-frame system equipped with a mechanical shutter function and an interline system that does not require a mechanical shutter, but an interline system CCD is preferable in consideration of durability. Further, it is preferable that the CCD has a fan for forced heat dissipation and an electronic cooling function in order to reduce noise.

Further, the CCD 6 is connected to an image processing device 12 including a computer for processing the detected image through an A / D converter 11 for converting the detected analog signal into a digital signal. .

The image processing device 12 analyzes the image signal from the CCD 6 and displays the shape pattern of leaked light due to non-uniformity, the amount of light, the intensity distribution, etc., and the transparent substrate 1.
Presence or absence of non-uniformity, type (scratches or cracks on the surface, internal striae or foreign matter, etc.), size (area, length, width, depth,
It has a discriminating unit for discriminating a region). In addition, in the storage unit of the image processing apparatus 12, information on leaked light (shape pattern of leaked light, amount of light, luminance, intensity distribution, surface, corresponding to types and sizes of nonuniformity existing on the transparent substrate, respectively) Depth, etc.), a measurement value (basic data) obtained by measurement in advance is input.

Next, a specific inspection method performed by using the inspection apparatus of FIG. 1 will be described. As an inspection target, 152.4 ×
The size of 152.4 × 6.35mm and the width of C side is 0.4.
The mm glass substrate for a photomask (glass substrate) was inspected. As shown in FIG. 2, from the C surface of the glass substrate, the angle of incidence θi on the main surface that first strikes after entering the glass substrate is larger than the critical angle θc, and the angle of incidence on the end face of the glass substrate ( 90 ° -θ) is the critical angle θc
The laser light was irradiated so as to be larger than that. Since the refractive index of the glass substrate is 1.47 and the critical angle θc is about 42.9 °, the incident angle θi is set to 44.1 °. That is, in this method of introduction, laser light is introduced so that there is no singular point (geometrically) at which laser light leaks out on the main surface and end face of the glass substrate, and only on the C plane. The feature is that the laser light is introduced so that the introduced laser light is emitted. The laser is He-
Using Ne laser, beam diameter 0.5mm, beam divergence angle 1mrad, laser power 0.5m
A laser beam with W and a wavelength of 543 nm was irradiated.

Since the main surface which is the total reflection surface and the end surface which is the folded surface are all in a vertical (orthogonal) relationship in the substrate used this time, the incident angle of light incident on the main surface is the same. In addition, the incident angles of the light incident on the end faces are the same, and they have a constant relationship (when the incident angle of the light on the main surface is θi, the incident angle of the light incident on the end face is 90 °).
−θi. ) Will be propagated. Therefore, light confinement is established only by setting the incident angle θi on the main surface and the incident angle 90 ° −θi on the end face, which first strikes after entering the glass substrate, to be larger than the critical angle θc. In the case of a typical shape (for example, a shape in which the main surface and the end surface are not in a vertical relationship), it becomes a little complicated. Here, the refractive index of the glass substrate with respect to the wavelength λ of the introduced laser light is nt, the refractive index ni of the outer medium (air) in contact with the glass substrate is 1, and the angle of incidence on the main surface and the end face of the glass substrate is θik. (K represents a position where the laser light is introduced into the glass substrate and then is incident on the main surface and the end face, and the incident positions are k = 1, 2, ... In order), and θik is all s.
Optical confinement will not be realized unless it is introduced so that it becomes equal to or larger than the critical angle θ represented by inθ = ni / nt. As described above, it is advantageous for optical confinement that the main surface and the end surface are in a vertical relationship.

The laser light incident on the transparent substrate (glass substrate) 1 by the illuminating means is, as shown in FIG.
The total reflection is repeated on the main surface and the end surface of the substrate 1, and the substrate 1 is almost confined in the substrate 1. The substantially confined state means that the introduced laser light propagates in the transparent substrate and is incident on the chamfered portion which is the introduction surface, that is, as long as it is incident on the main surface and the end surface, the transparent substrate is Means to repeat the total reflection and continue to propagate. Therefore, the laser light incident in the Y direction is emitted from the substrate 1
Is spread in a Y-direction cross section (a region to be inspected) in a Y direction, and the light is completely scanned by propagation due to total reflection.

As described above, the laser light introduced into the glass substrate is repeatedly totally reflected on the main surface and the end face of the glass substrate and is almost confined in the glass substrate. If the glass surface has scratches due to mixing or the like, the conditions for total reflection are not satisfied, and light leaks from the scratched portions. In addition, even for defects that have the same transmittance but differ only in the refractive index, which is characteristic of glass striae, etc., the original orbit (optical path) is deviated at the point where the refractive index is different, and total reflection does not occur on the main surface or end face. It will leak out of the substrate 1.
This leaked light is detected by the detection means.

It is to be noted that, by irradiating the light having the one cross-section shape, a one-line inspection can be performed when viewed from the main surface side of the substrate 1, and this inspection process is performed by driving the table 5 in the direction of one side 1a of the substrate 1. By moving in (X direction),
The non-uniformity of the entire area of the substrate 1 can be inspected. That is, this is
In a region of the substrate to be inspected, which is sandwiched between a main surface that is a set of total reflection surfaces of the substrate and an end surface that is a set of folded surfaces, the light is filled by propagating the light in the substrate. A method for inspecting non-uniformity by performing non-uniformity (defect) inspection on a plane in the inspection area and then moving the inspection plane relative to the substrate in a direction in which light fills the inspection area. Is.

The results detected by this inspection apparatus are shown in FIGS. FIG. 4 is an image of a scratch on the glass substrate surface detected by the CCD 6. FIG. 5 shows information of light detected by the CCD on one side in the width direction of the scratch,
The image is processed by a computer through an A / D converter (analog-digital converter). The CCD used at this time was an interline CCD (without mechanical shutter) equipped with an electronic cooling function, and the number of elements was 1
300 × 1030, detection area 8.71 × 6.90m
m, CCD saturation amount of 20,000 electrons is used, and the measurement conditions are CCD exposure time of 200 msec.
And

The X axis of FIG. 5 shows the coordinate in the width direction of the scratch, and Y
The axis shows the detected light intensity. The unit of the X-axis scale is pixel, and in this inspection system, it is × 50 (50 times)
Since an objective lens of x and an imaging lens of x 0.45 (0.45x) are used, 1 pixel is 6.7 [μm] /
(50 × 0.45), that is, approximately 0.3 μm (6.7 μm represents the size of one pixel of the CCD). The light intensity is decomposed into 12 bits (4096: 1), and the scale is (20000/4095) Y (Y:
Scale) Electron. As is clear from FIG. 5, the intensity of the light leaked from the scratch has a peak value of (2000
(0/4095) × 4095 = 20,000 electrons, which exceeded the allowable value of the CCD, and the intensity of light in the area other than the scratch was 0. In this way, the image detected by the detection means has a line-shaped non-uniform portion such as a scratch on the pitch-dark background.
Since it looks like dots, it is possible to clearly discriminate non-uniform portions such as scratches from the obtained image. here,
Considering the propagation by total internal reflection in the glass substrate, the light in the substrate continues to propagate in the glass substrate without any elements that weaken the light during the propagation, except for very small absorption in a uniform area. . As a result, almost all of the applied light is concentrated on the nonuniform portion, and the nonuniform portion appears sharply with a very clear contrast.
Therefore, minute scratches can be detected with high sensitivity. On the other hand, FIG.
4 is an image obtained by observing a scratch similar to that in FIG. 4 with an optical microscope (reflection / bright field), and FIG. 7 is the image subjected to the same image processing as in FIG. As can be seen from FIGS. 6 and 7, the scratch signal is buried in the surrounding background signal,
This method could not detect the scratch. still,
When the scratches in FIGS. 4 and 6 were observed with an atomic force microscope (AFM), it was confirmed that the scratches had a width of 0.13 μm and a depth of 0.0013 μm.

In the above embodiment, the transparent substrate 1
When it is desired to confirm the incident angle θi of the laser light with respect to the light emitted from the optical member 8, if a wedge-shaped optical member 8 is installed on the surface of the substrate through a matching oil, as shown in FIG. Refraction angle γ and optical member 8
The incident angle θi can be obtained from the apex angle and the like. Also,
If an optical member such as the optical member 8 is used as an entrance window for introducing the inspection light into the substrate, the chamfered portion (C surface) of the substrate
Light can also be introduced from other sources.

Next, in order to clarify the difference between the case where the non-uniformity is detected by the conventional optical microscope under the normal illumination and the case where the non-uniformity is detected by the inspection method of the present invention, an arbitrary scratch is observed. Then, FIG. 8 shows the relationship between the signal noise ratio and the normalized exposure time when image processing similar to the above is performed. Here, the normalized exposure time means (CCD exposure time) / (background signal is (20000/409).
5) CCD maximum exposure time to reach 100 electrons), and the signal to noise ratio is 10 log
_{It was set to 10} (S / N). As is clear from FIG. 8, in the conventional inspection method using normal illumination, 3 dB is the highest even if the normalized exposure time is lengthened, whereas in the inspection method of the present invention, the signal-noise ratio is 30 dB. The result exceeded. In the inspection method of the present invention, the maximum signal-to-noise ratio remains at 36 dB, but due to the limitation of the saturation amount of the CCD camera, a very high S / N ratio exceeding 36 dB is actually obtained. Seem. (It should be noted that the negative signal-noise ratio in normal lighting is considered to be the result of the scratch signal being buried in noise.)
Therefore, the inspection method of the present invention far exceeds the generally accepted image processable level of 4.8 dB (the signal with respect to the background is more than 3 times the noise), and the non-uniformity of the light-transmitting material is caused. It can be said that the presence / absence, type, and size can be accurately determined.

Further, although the incident angle θi is set to 44.1 ° in the above embodiment, the optimum incident angle for repeating more total reflection can be easily selected by the following simulation. The results of simulating how light propagates in the transparent substrate will be described below.

First, as shown in FIG. 9, the calculation result when light is propagated along one side (y-axis direction) of the transparent substrate 1 will be described. In this simulation, the size of the transparent substrate 1 is 152.4 × 152.4 × 6.35 mm, which is the same as that of the photomask glass substrate of the above-described embodiment, and the width of the C plane is 0.4 mm. The refractive index of the transparent substrate 1 was 1.47 for quartz glass, and the refractive index around the transparent substrate 1 was 1.00 for air. In addition, a vector (unit vector) indicating the direction of a light ray incident on the chamfered C surface (which makes an angle of 45 ° with respect to the main surface and the T surface) of the transparent substrate 1 is (0.0000000, 0.6864532, -0.7271740).
). The simulation result is shown in FIG.

In FIG. 10, the incident angle is the incident angle with respect to the surface (main surface) which the light beam first strikes after entering the substrate 1, and the incident angle was changed in increments of 0.05. The z-coordinate at the time of emission represents the z-coordinate when the light beam is emitted from the transparent substrate 1 and the lower surface of the substrate 1 is set to z = 0.

FIG. 11 is a graph showing the number of times of surface reflection at each incident angle in FIG. As can be seen from FIG.
It is preferable to select an incident angle that increases the number of surface reflections in accordance with the shape of the transparent substrate and the like. Alternatively, the incident angle of the light to be introduced may be changed.

Further, FIG. 12 shows how light propagates in the substrate at an incident angle of 43.35 °. 12
In each of (1), (2), and (3), the number of surface reflections is 50.
This is the state at the time of 250 times, 661 times (at the time of injection).
In this simulation, for the sake of simplification of calculation, the propagation is limited to the region within the cross section of one plane (yz plane), but as shown in FIG. You can see that it propagates. As in this simulation, when introducing light parallel to one side (y direction) of the transparent substrate, in order to make the illumination light strike the entire area of the transparent substrate, use a mirror or the like to The light may be scanned along the (x direction), or the light spread like a slit in the x direction may be introduced from the C surface.

Next, C in the simulation of FIG.
Figure 1 shows the simulation results when the width of the surface and the refractive index of the glass substrate (corresponding to the wavelength of the laser beam) were changed.
3, FIG. 14 and FIG. In this simulation, the glass substrate has a refractive index of 1.46 (corresponding to a laser beam wavelength of 543 nm), and the C plane has a width of 0.2 mm.
(FIG. 13), 0.4 mm (FIG. 14), 0.8 mm (FIG. 1)
The conditions were the same as those of the simulation performed in FIG. 9 except that the conditions were changed to 5).

As can be seen from FIGS. 13 to 15, it can be seen that the number of surface reflections decreases as the width of the C plane increases. This is because when the laser light introduced from the C plane propagates through the transparent substrate and enters the C plane again,
Since the light incident on the surface is incident at an angle smaller than the critical angle θ and leaks without being totally reflected, the light propagated in the transparent substrate becomes C by increasing the width of the C surface.
This is because the probability of incidence on the surface has increased.
Therefore, in order to increase the number of surface reflections within the transparent substrate, the width of the C surface may be reduced. Glass substrate for photomask used this time (152.4 × 152.4 × 6.3
In the case of 5 mm), if the number of surface reflections is about 300, the transparent substrate will be sufficiently filled with light, so that the width of the C surface is preferably 0.4 mm or less.

Further, comparing FIGS. 11 and 14 in which the widths of the C planes are both 0.4 mm, the refractive index of the transparent substrate (or the wavelength of the laser light (the refractive index of the transparent substrate is the wavelength of the laser light is The critical angle for satisfying the total internal reflection condition is also changed by changing (1)), and the number of surface reflections can be adjusted. The greater the difference between the refractive index of the transparent substrate and the outer medium (eg, air) of the transparent substrate, the greater the degree of freedom of the critical angle for satisfying the condition of total internal reflection. Accordingly, the number of surface reflections also increases. However, in reality, the material of the transparent substrate may be limited depending on the application,
Normally, by selecting the wavelength of the laser light appropriately,
The number of surface reflections can be adjusted. However, the wavelength of the laser light is preferably a wavelength having a small absorption with respect to the transparent substrate, and it also affects the resolution of the nonuniformity. Therefore, the wavelength of the laser light is selected in consideration of the above points.

FIG. 16 shows a locus of light rays when a light ray in a more general direction is introduced into the transparent substrate instead of a light ray parallel to one side as in the above simulation. In this simulation, a vector indicating the direction of the ray that strikes the C surface of the transparent substrate 1 is (0.6924, 0.3823, -0.6117).
Other conditions are the above simulation (Fig. 9)
Same as. As shown in the figure, the introduced light ray is repeatedly totally reflected in the transparent substrate 1, is substantially confined in the substrate, and propagates throughout the substrate. Therefore, the entire area of the transparent substrate, which is the inspection area, can be inspected at a high speed and in a batch without performing any scanning of the illumination light.

Considering the simplification of the inspection method, the three-dimensional direction vector (x, y, z) of the incident light is set so that the introduced light may cover the entire area of the translucent material. Therefore, rather than introducing light from a certain point on the substrate, one surface having a light-transmitting substance is determined as in the above embodiment, and the incident angle that satisfies the total reflection condition is determined within the surface and the light is introduced. After that, it is preferable to move the incident position of light according to the shape of the translucent material because the inspection method can be further simplified. This is particularly effective in the case of a substrate in which translucent materials have surfaces facing each other.

In the above embodiment, the laser light is introduced from one side 1a of the transparent substrate 1, but the invention is not limited to this, and the light may be introduced from the side 1b or the side 1a.
The inspection may be performed by introducing light from two directions of a and the side 1b. It is preferable to introduce light from two directions, the side 1a and the side 1b, to inspect, which is effective for detecting a directional defect or the like and enables more highly accurate inspection.

As described above, according to the present invention, which is characteristic of scratches on glass, it can be detected because it emits light in a specific irradiation direction, but it cannot be detected because it does not emit light depending on the irradiation direction. It is extremely effective for the detection of defects that have it. By repeating geometric optical total reflection, light is almost confined inside the object to be inspected, which is made of a light-transmitting substance. Although it will be out of the orbit of the object and leak to the outside of the object to be inspected, even if the only non-uniform portion is a defect having directivity to light, the non-uniform portion will change in the process of repeating total reflection. This is because it will be illuminated from different directions. On the other hand, in the conventional method, since light is focused in order to increase the contrast and light is irradiated from one direction, it is almost impossible to detect a defect having directionality even for a defect having a relatively large size.

Further, regarding the detection of defects having the same transmittance but different refractive index, which are characteristic of glass striae, etc., the original orbit is deviated at the point where the refractive index is different and the defect is leaked to the outside of the object to be inspected. Therefore, it becomes detectable. However, the conventional method for detecting the reflected light output and the transmitted light amount of the collected light cannot be detected in principle.

By using the inspection method of the above-described embodiment, the glass substrate having a defect can be quickly and appropriately removed, and the productivity of the glass substrate can be improved. It is to be noted that a glass substrate for a photomask which falls within the range of specifications can be obtained by subjecting a glass substrate having a defect such as a scratch on the surface to precise mirror polishing and cleaning treatment again.

The above-described inspection method is used, for example, in an inspection process after the manufacturing process of a glass substrate which is a transparent substrate for a photomask. However, the size (length) of the glass substrate depends on the processing accuracy. Etc.) (usually the tolerance of the transparent substrate for photomask is the length:
± 0.4 mm, thickness: about ± 0.1 mm). For this reason,
If the inspection is performed after grasping the size of each glass substrate having variations and obtaining the optimum total reflection condition of each glass substrate, it takes a huge amount of time and is not practical. Because, if you take an inspection method that measures the exact dimensions of the glass substrate and grasps the incident conditions that cause more total reflection, then let the laser light enter,
This is because an additional time is required before the inspection, which is {(glass substrate dimension measurement time) + (simulation time)} × (number of inspection sheets).

In this case, the laser light introduced into the glass substrate is totally reflected by the main surface (front surface, back surface) and the end faces (other than the C face), and the light is repeated within at least one pair of end faces. Even if there are variations in the dimensions of the glass substrate, it is possible to detect the optical non-uniformity of the glass substrate with high sensitivity and high speed by varying the incident angle with, and it is a highly practical non-uniformity inspection method. And equipment.

That is, when the optical path in the transparent material is optically uniform, the incident angle is changed within the range where total reflection can occur on the surface of the transparent material, and light is introduced into the transparent material. By doing so, even if there are variations in the dimensions of the translucent material and there are some differences in the optimum total reflection conditions for each translucent material, instead of introducing incident light in a fixed direction, the incident angle Since different light is introduced and propagates in various paths while being totally reflected, the light can reach every corner of the translucent material without leaking.

As means for changing the incident angle with respect to the substrate, as with the angle adjusting means of FIG.
A mechanism that can be connected to a computer to control the angle automatically is installed, an angle adjustment mechanism is installed in the folder that holds the laser itself or the substrate, and the acousto-optic effect of the ultrasonic beam such as an acousto-optic polarizer is used. Then, the incident angle may be changed. The incident angle with respect to the substrate is, for example, the glass substrate for photomask (152.4 × 152.4 ×) made of the above-mentioned quartz glass.
6.35 mm), the incident angle θi of the laser light is 4
It is advisable to change continuously within the range of 5.0 ° to 44.0 °.

Further, the introduction of the laser light into the transparent substance is performed based on the information of the transparent substance, which is effective especially when a plurality of (transparent) transparent substances are inspected. Inspection is possible.

Here, the information on the light-transmitting substance means the relative positional relationship between the light-transmitting substance and the illuminating means, the surface state of the light-transmitting substance (whether it is mirror-finished, etc.). The information on the relative positional relationship between the translucent substance and the illuminating means is necessary for the light from the illuminating means to be appropriately introduced into a predetermined position of the translucent substance, and the surface state of the translucent substance. As for the information, if the surface is not a mirror surface, it becomes difficult to detect the non-uniformity of the light-transmitting material, so such substrates are excluded in advance (return to the previous step (polishing, etc.) if necessary). It can be used in some cases.

By providing the position detecting means for detecting the relative positional relationship between the light-transmitting substance and the illuminating means, and providing the transmitting means for transmitting the information obtained by the position detecting means to the illuminating means, a plurality of means are provided. Efficient inspection is possible when inspecting (sheets). Here, the position detecting means is
For example, it refers to a distance measuring device using laser light (such as a laser scanning measuring system or a laser interferometric measuring device), and the transmitting means captures data from the position detecting means,
A computer that feeds back to an illuminating unit, an angle adjusting unit, a moving unit that moves the incident position of the introduced light, and the like. In addition, for observing the surface state of the translucent material, for example, T for removing the inspection object which is not mirror-finished
Devices such as a V camera and a CCD image sensor image sensor may be provided.

In the above embodiment, the presence or absence of non-uniformity of the translucent material based on the information of the light detected by the detecting means,
It is preferable to provide a discriminating means for discriminating the type and the size.

This is based on the presence or absence of non-uniformity existing in the light-transmitting substance in advance, the type (scratches or cracks on the surface, striae or foreign matter inside), and the size (area, length, width, depth). Information such as the amount of light leaked from the surface (luminance, brightness, intensity distribution, depth from the surface, etc.) is stored in a computer, etc. By comparing the detected light information with the stored information, it is possible to determine the presence / absence, type, and size of the non-uniformity of the translucent material. By thus determining the presence / absence, type, and size of the non-uniformity of the translucent substance, the desired translucent substance can be immediately extracted. For this reason,
For example, a glass substrate having non-uniformity that affects the pattern formation or the exposure of the transferred material can be removed after the inspection before proceeding to the next step, or can be returned to the re-polishing. You can improve the property.

This discrimination method will be concretely described by using the inspection apparatus of FIG. The light leaked from the substrate 1 is reflected by the lens system 7
Is imaged on the CCD 6 surface of the CCD camera. As described above, the shutter of the CCD camera is kept open while scanning the one-line laser irradiation area over the entire main surface of the substrate 1, and the image data of the entire main surface of the substrate 1 is accumulated. The image data captured by the CCD camera is A /
The signal is converted into a digital signal by the D converter 11, is input to the image processing device 12, is stored in the storage unit, and is subjected to image analysis by the determination unit. The discriminating unit compares the image data of the light detected by the inspection with the basic data of the image information previously input to the storage unit, so that the transparent substrate 1
The presence / absence of non-uniformity, type, and size are determined. Further, the movement amount of the table 5 and the like (information on the irradiation position of the substrate 1) is inputted to the image processing device 12 from a laser interferometer (not shown) or the like, and the image data of the CCD camera and the position data of the substrate 1 are input. From this, it is possible to find at what position (x, y) of the substrate 1 there is a non-uniform portion of what kind and size.

When the irradiation area of the substrate 1 has a non-uniform portion, the non-uniform portion (and the periphery thereof) appears to shine like dots, and when this is magnified with an optical microscope, an image as shown in FIG. 17 is observed. (Note that the image in FIG. 17 is the image in which the brightness and darkness of the actually observed image are reversed). The linear image 41 as shown in FIG. 17A is due to a scratch on the surface of the substrate 1, and its typical size is 30 μm in length, 0.2 μm in width, and 0. The size is about 002 μm (the size of such fine scratches was measured by an atomic force microscope). Also, many collected images 42 as shown in FIG. 17B are due to striae inside the substrate 1 or foreign matter such as gas, and their typical size is about 1 mm in diameter. is there. In this way, the pattern and size of the image differ depending on the non-uniformity existing on the substrate 1,
The type of non-uniformity can be determined. Further, since the image 42 due to striae and the like looks more vague than the image 41 due to scratches, it can be discriminated also from the brightness and intensity distribution of the image.

The size of the non-uniform portion can be determined from the amount of detected light. Furthermore, whether the non-uniformity exists on the surface of the substrate 1 (scratches, cracks, etc.) or inside the substrate 1 (stripe, foreign matter, etc.) is focused on the bright spot portion of the substrate 1 with an optical microscope. It can be determined from the in-focus location (depth). In order to achieve high-speed processing, the non-uniformity inspection is performed by first inspecting the surface of the substrate 1 for the presence of bright spot-like leaked light, and then only for the substrate 1 in which leaked light is detected. Further, it is preferable to inspect by further enlarging the spots that shine like bright spots with an optical microscope.

In order to determine this non-uniformity, if light is introduced into the substrate 1 from different incident positions and different directions (two directions), even if there is directional non-uniformity (defect), leakage light This is preferable because it is possible to accurately determine the presence / absence, type, and size of the nonuniformity, since the reliable information can be obtained.
As a method of introducing the light, as shown in FIG. 18, the laser light L1 is applied in the direction of the side 1a of the transparent substrate 1 (X direction).
The laser light L2 may be simultaneously introduced in the direction of b (Y direction), or the laser light of different directions may be introduced into the substrate 1 one by one (X, Y directions, etc.) for inspection.

Further, as shown in FIG. 19, when the laser light L is introduced from the corner portion of the transparent substrate 1 by using the laser 13 and the mirrors 14 and 15 to inspect for non-uniformity, Similarly, the imaging optical system 16, C
The type and size of the nonuniformity can be discriminated by the CD camera 17 and the image processing device 18.

Further, in the above embodiment, the example in which the laser light is introduced into the substrate 1 only in one direction of the y direction and the inspection is performed, but in the case where the laser light is introduced into the substrate 1 from different incident positions and different directions Further, the laser beams L1 and L2 do not necessarily have to be at different incident positions, and, for example, as shown in FIG. However, the effect of the present invention that the directional nonuniformity can be reliably detected is achieved.

Further, in the above embodiment, the laser beam is introduced into the transparent substrate from the chamfered portion which is the C surface, but it is also possible to introduce it from the surface other than the chamfered portion. In that case, an optical member made of a material having substantially the same refractive index as the transparent substrate may be attached as an entrance window for introducing the laser light with an adhesive or the like. However, in order to simplify the inspection method, repeat more total reflection in the transparent substrate, and inspect the nonuniformity over the entire area, it is preferable to introduce the laser light from the chamfered portion, which is the C surface. This is because, when an optical member having an entrance window for introducing laser light is attached, light propagates in the transparent substrate does not satisfy the condition of total reflection, so that light leaks out.
The chamfered portion is preferably mirror-finished, and the smaller the width of the chamfered portion is, the better.
It is preferably m or less, more preferably 0.2 mm or less. However, if it is extremely small (less than 0.1 mm), chipping may occur during mirror polishing, which is not preferable.

Next, a method of selecting transparent substrates which can be used for various purposes by using the inspection method and the inspection apparatus of the present invention will be described with reference to the drawings. FIG. 21 is a diagram showing an inspection process flowchart for selecting a transparent substrate.

A specific selection method performed by using the inspection apparatus of FIG. 1 will be described with reference to the inspection process flowchart of FIG.

Determination / Alignment of Inspection Area As the transparent substrate 1 to be inspected, 152.4 × 152.4 × 6.
A glass substrate (glass substrate) for a photomask having a size of 35 mm and having a C-plane width of 0.4 mm and made of quartz glass was prepared.

The glass substrate is conveyed by a conveying means (not shown) until it is pressed against a stage guide pin (not shown) fixed at a reference position of the inspection device, and the glass substrate is positioned (step 1). At this time, the origin and coordinates in the glass substrate are determined.

Next, the inspection area is specified based on the previously determined coordinates. Since this inspection area and the measurement visual field of the CCD do not necessarily match, if they do not match, the measurement area is divided (A1, A2, A) corresponding to the CCD visual field.
3, B1, B2, B3, ...) (FIG. 22) (step 2). At this time, the measurement areas A1, A2, A3, B1, B2, B3, ...
The measurement fields of view are the same. The CCD used for measurement is
Interline CCD (without mechanical shutter) equipped with electronic cooling function, 1300 x 1035 elements,
A detection area of 8.71 × 6.90 mm was used, and the measurement visual field was measured at a measurement magnification of 0.7.

Next, the incident position and the incident angle of the laser light are adjusted so that the laser light propagates in the inspection area (step 3). As for the incident position and the incident angle of the laser beam, the information of the glass substrate is obtained by the position detecting means (not shown) which detects the relative positional relationship between the transparent substrate and the laser, and the laser beam is accurately applied to the glass substrate having different dimensions. Adjust the mirror and table to introduce the laser light so that the light can be introduced. As for the incident angle, since the refractive index of the glass substrate is 1.46 and the critical angle θc is about 43.2 °, the incident angle θi
Was set to 45.0 °.

Next, when the laser light is introduced into the glass substrate, the incident angle of the laser light is varied within the range where the total reflection is repeatedly propagated (step 4). This is because, in the process of inspecting a plurality of glass substrates, even if each of the glass substrates varies in size due to the difference in processing accuracy, the light beam propagating in the glass substrate is changed by changing the incident angle of light. Since the locus is also slightly shifted, it is performed to absorb the variation in the processing accuracy of the glass substrate and inspect the glass substrate for non-uniformity, but also to align the CCD image in the next step. It is a thing.
The means for changing the incident angle is one that is equipped with a mechanism that automatically adjusts the angle of the mirror by controlling a computer or the like, or uses the acousto-optic effect of an ultrasonic beam such as an acousto-optic polarizer. The angle may be changed. The variation of the incident angle was such that the incident angle θi was continuously changed in the range of 45.0 ° to 44.0 ° which satisfies the total reflection.

Next, in order to accurately discriminate the light leaking from the transparent substrate, that is, the nonuniformity, the CCD image is focused (step 5). Focusing is performed by moving the glass substrate, the laser, and the mirror integrally in the z-axis direction (lens and CCD direction). The glass substrate, the mirror and the laser may be fixed, and the lens and the CCD may be integrally moved in the z-axis direction.

Inspection of Non-uniformity in Inspection Area As shown in a partially enlarged view in FIG. 22, laser light L parallel to the y-axis direction passes through coordinates (A1X1, A1Y1) with one divided measurement area A1. Laser light L is introduced from the chamfered surface, which is the introduction surface, so as to propagate, and the incident angle is changed within the range where the total reflection is repeatedly propagated in the glass substrate (45.0 ° to 44.0 °). Inspect for non-uniformity. Then, the laser beam L is moved in the x-axis direction by the same scanning, and the nonuniformity is inspected until it passes through the coordinates (A1XX, A1Y1) at the end of the measurement area A1, and the nonuniformity in the measurement area A1. Is completed (step 6). The exposure of the CCD is performed from the start to the end of the nonuniformity inspection of the measurement area A1. In addition, the inspection of the non-uniformity in the measurement area A1 is performed by injecting the laser light so that the laser light passing through (A1X1, A1Y1) and parallel to the x-axis direction is propagated, and moving the laser light in the y-axis direction. Good. Further, the laser beams in the two directions orthogonal to each other may be introduced in combination. In this way, when light in a plurality of different directions is introduced into the glass substrate when viewed from the main surface side, the light is irradiated into the glass substrate from a plurality of directions, and directional nonuniformity ( Even if there is a defect, it can be reliably detected.

In the image processing step 6, the information (analog signal) of the light leaked from the glass substrate detected by the CCD is converted into a digital signal by the A / D converter for image processing by the information storage means such as a computer. To do. The information of the light converted into the digital signal is accumulated by the information accumulating means such as a computer and the intensity of the light as shown in FIG.
It is decomposed into bits (4096: 1) and image processing is performed (step 7). The Y axis in FIG. 23 represents the intensity of light,
One scale is (20,000 / 4095) · Y (Y: scale) electrons.

[0114] result of the image processing in an allowed determination step 7 of heterogeneity, inhomogeneities present in the glass substrate, it is determined that scratches on the substrate surface, has been in advance flaw tolerance design value (20000/4095) In contrast to × 200 electrons (background is (20,000 / 40
95) × 100 electrons or less), the glass substrate was determined to be defective because it exceeds the allowable design value (step 8).

In this embodiment, since a scratch exceeding the allowable range is found on the substrate surface in the inspection area A1, the non-uniformity inspection of the next inspection area A2 is not performed and the substrate is re-polished and cleaned. However, if no non-uniformity is found in the inspection area A1, the previously divided inspection areas A2, A3, B1, B2, ... And the steps 6 to 8 (in some cases, steps 2 to 8) ) Is repeated. Then, when it is determined that all the inspection regions are equal to or less than the allowable design value of nonuniformity, the glass substrate for photomask is selected as a good product.

By using the screening method of the above-mentioned embodiment, the glass substrate having a defect can be eliminated quickly and appropriately, and the productivity of the glass substrate can be improved. It should be noted that the glass substrate for a photomask which falls within the range of specifications can be obtained by subjecting the glass substrate having a defect to precision mirror polishing and cleaning treatment again.

FIG. 24 shows a second embodiment in which the transparent substrate selecting method of the present invention is applied to a magnetic disk glass substrate. It should be noted that the description of the steps which are the same as those in the first embodiment applied to the photomask glass substrate is omitted.

As the transparent substrate 1 to be inspected, both main surfaces (H), inner peripheral end surface (T1 surface) and outer peripheral end surface (T2 surface),
The chamfered surface (C surface) is mirror-polished and has a diameter of 95 mm (3.
5 inch) φ, thickness 0.8 mm, circular hole in the center (diameter 2
A disk-shaped magnetic disk glass substrate (glass substrate) made of quartz glass of 0 mmφ) was prepared.

As shown in FIG. 24, the inspection area is A1, A from the inner peripheral side to the outer peripheral side of a certain area on the main surface of the transparent substrate.
The measurement area is divided into 2, A3, ... And non-uniformity is inspected for each divided measurement area.

The non-uniformity inspection is performed by using the disk-shaped glass substrate 1
The laser light L is introduced from the outer peripheral end face toward the center (O) direction of the disk, and the radial direction (r
(Direction) to confine light within one plane (repeated total reflection on both main surfaces of the transparent substrate so that light repeats on inner and outer end faces), and drive device for rotating the disk (not shown)
The disk is rotated by to move the laser light L in the circumferential direction (θ direction) of the disk. Specifically, with reference to FIG. 25, the laser 25, so that the laser beam L parallel to the r direction propagates through the coordinates (A1r1, A1θ1) of the measurement area A1 divided as shown in FIG. Mirror 2
Laser light L is introduced into the chamfered surface (C surface) which is the introduction surface by 6, 27, and within the range (45.0 ° to 44.0 °) in which the total reflection is repeatedly propagated in the disk-shaped glass substrate 1. Change the angle of incidence and check for non-uniformity. Then, the disk-shaped glass substrate 1 is rotated, and the same scanning is performed with the laser light θ.
When the inspection of the nonuniformity of the measurement region A1 passing through (A1r1, A1θX) is completed, the inspection of the nonuniformity in the measurement region A1 is completed. In the non-uniformity inspection, the laser light may be introduced from the inner peripheral end surface of the disk, or may be incident from both the inner peripheral surface and the outer peripheral end surface.

Similar to the first embodiment, image processing and non-uniformity allowance determination were performed. As a result, the inspection area
In A1, no defect beyond the allowable range was found, so
The inspection areas were changed to the inspection areas A2, A3, B1, B2, ... And the same nonuniformity inspection as the inspection area A1 was performed. The entire area of the disk-shaped glass substrate was inspected for non-uniformity, but no defect exceeding the allowable range was found, so it was judged as a good product.

As in the case of the first embodiment, when a defect exceeding the allowable range is found in a certain inspection area, it is judged as a defect and the next inspection area is not inspected for non-uniformity.
It is also possible to move to the re-polishing and cleaning steps of the substrate.

Further, in the above-described inspection method and selection method, as unnecessary light that lowers the contrast of light leaking from the nonuniformity (defects) of the translucent substance, a microscopic characteristic peculiar to the translucent substance is used. There is Rayleigh scattered light and the like that is scattered due to density fluctuations. In order to reduce such unnecessary light, at least two lights having different wavelengths are introduced into the translucent material, or light leaking a specific polarization is introduced to detect nonuniformity. It is possible to improve the contrast and to detect with higher sensitivity and accuracy. In addition,
In the case of introducing at least two lights having different wavelengths, the Rayleigh scattered light is light of a color in which lights having different wavelengths are mixed, so that the mixed light between the translucent substance and the detection means is It can be removed by using a (color) filter that absorbs or reflects the wavelength range. Also,
In the case of introducing the latter light that leaks a specific polarized light, it becomes a light with a unique polarization characteristic and polarization state due to Rayleigh scattering.
By utilizing the difference between the polarization characteristics of light leaked due to non-uniformity, a polarization filter, between the translucent substance and the detection means,
By placing a polarizing element such as a polarizing plate or a polarizing prism, Rayleigh scattered light can be effectively removed.

In addition, as unnecessary light that reduces the contrast of the light leaked from the non-uniformity (defects) of the translucent material, the light that could not be completely introduced into the translucent material is reflected on the surface of the translucent material. There is stray light that is reflected and enters a detection system that detects the nonuniform detection light. To reduce this stray light,
The introduced light is condensed and reduced by an optical system such as a lens according to the size of the introduction surface of the transparent material on which the laser light is incident, and the condensed laser light is transmitted from the introduction surface. The introduction surface has a concave cross section so that the light is introduced into the inside as substantially parallel light. As a result, stray light can be reduced, the contrast of nonuniform detection light can be increased, and high-sensitivity and high-precision detection can be achieved.

As another factor that lowers the contrast of light leaked from the non-uniformity (defects) of the translucent material, as shown in FIG. 26 (the same figure (1) is a perspective view, (2) is It is a side cross-sectional view), the translucent material is a rectangular flat plate having a main surface, an end surface, and a chamfered surface, and the laser light L is introduced from the introduction surface (the chamfered surface (C surface)) to cause nonuniformity. When inspecting, light may leak from the chamfered surface other than the introduction surface and become stray light. In this case, the light guide body 5 in which a plurality of optical fibers arranged in the surface direction of the chamfered surface are bundled between the chamfered surfaces other than the chamfered surface that introduces light, which opposes the light traveling direction.
By connecting with 0, the light leaked from the chamfered surface can be introduced again into the translucent material, so stray light can be reduced and the introduced laser light can be more effectively concentrated in the non-uniform portion. , The contrast is increased, and it becomes possible to detect with high sensitivity and high speed.

In the embodiment of the inspection method and the first and second embodiments of the selection method, the transparent substrate made of glass is used as the translucent material having the mirror-finished surface. However, any material such as an optical plastic such as an acrylic resin or an optical crystal such as a crystal can be used as long as the inspection light can be transmitted.

In the embodiment of the inspection method and the first and second embodiments of the selection method, an example in which the entire transparent substrate has a mirror-finished surface is given.
However, the present invention is not limited to this, and may be a transparent substrate having a surface that is not partially or entirely mirror-finished. For example, in the case of a glass substrate that is a glass substrate for a photomask, the end faces other than the main surface on which a pattern is not formed may not be mirror-polished, and in the case of a glass substrate for a magnetic disk, a film such as a magnetic layer is formed. This is the case when the inner and outer edges of the main surface are not mirror-finished.In that case, the surface is mirror-finished by applying a liquid such as matching oil to the surface that is not mirror-finished. Since it becomes a surface (free surface of liquid, pseudo mirror surface), it is possible to inspect a non-uniform portion by the inspection method and inspection apparatus of the present invention. In particular, it is effective when it is desired to inspect only the non-uniform portion (stria, bubbles, foreign matters, etc.) existing inside the translucent material at the stage where mirror finishing is not performed.

The liquid to be applied for forming the pseudo mirror surface may be a matching oil or an encapsulant used for optical parts, or a glass scratch-shielding agent. The liquid applied to the surface of the translucent substance may remain in a liquid state after being applied, or may be in a solidified state such as a jelly or a hard film. Further, as a method for applying the liquid, as long as it can be applied smoothly to the surface of the light-transmitting substance, such as brush application (applying a liquid such as a brush or sponge with liquid), spray application, spin coating, etc., Any method may be used. In that case, it is appropriately selected according to the liquid to be used and the coating surface.

Further, when the translucent substance and the liquid have substantially the same refractive index, the applied mirror-like liquid surface has
Optically, the surface of the light-transmitting substance is substantially formed, and the light introduced into the light-transmitting substance can be totally reflected and returned to the inside. Specifically, since quartz glass (refractive index 1.46) is often used for the transparent substrate, the refractive index is close,
Liquids that are easy to handle include Canadian balsam (refractive index 1.52), enteran new (trade name, refractive index 1.4.
9), diiodomethane (methylene iodide, refractive index 1.7)
4), cedar oil (refractive index 1.52), liquid paraffin (refractive index 1.48), aquatex (trade name, refractive index 1.4), glycerin (refractive index 1.46) and the like.

For water-insoluble substances such as Canadian balsam and enteran new, the refractive index and viscosity can be adjusted by adding an organic solvent such as xylene, and water-soluble substances such as glycerin and aquatex are added. The refractive index and viscosity can be adjusted by adding water. Further, examples of the glass scratch-shielding agent include emulsion compositions containing polyorganosiloxane and polydiorganosiloxane as main components described in JP-B-6-4496.

The inspection when the entire surface of the transparent substrate is not mirror-finished includes, for example, the case where only the nonuniformity (stripe, bubbles, foreign matter, etc.) inside the transparent substrate is inspected. In this case, if there is a non-uniform portion inside, it becomes a fatal defect. For example, in the case of a phase shift mask glass substrate, defective products can be excluded by inspecting at the stage before mirror finishing. Therefore, the manufacturing cost is low.

The shape of the translucent material is not limited to a quadrangular (rectangular) or circular substrate, but may be a block shape, a sphere, a cylinder, a cylinder, a polygonal cylinder or a curved surface. In particular,
When the transparent material is a substrate having surfaces facing each other, particularly at least two substrates having parallel flat surfaces facing each other (for example, a quadrangle (rectangle) or a disc), the introduced light is totally reflected. By repeating the above steps, the state of being easily confined in the substrate can be obtained, and in fact, a wide area of the translucent material can be inspected at the same time, and high-speed inspection becomes possible. Further, the substrate can be applied to inspection of various substrates such as glass substrates for electronic devices (for photomasks (phase shift masks)), glass substrates for liquid crystal displays, glass substrates for information recording (magnetic discs, optical discs, etc.). . Since the information recording glass substrate is disk-shaped, when actually inspecting, laser light is made incident from a polished outer or inner peripheral end face (for example, a chamfered portion).
When inspection of both sides of the substrate is required, detection means may be provided above and below the substrate to inspect both sides of the substrate at once.

In the above embodiment, the gas laser (He-Ne laser) is used as the laser.
Not limited to this, a laser in the visible range such as a semiconductor laser, or an excimer laser in the ultraviolet range or Nd-YA in the infrared range as long as it absorbs little light-transmitting substance.
G laser, CO2 laser, etc. can be used as a light source for inspection. In particular, it is preferable to use a laser in the ultraviolet range (for example, a harmonic of an excimer laser or a YAG laser) because foreign substances and the like adhering to the substrate surface can be expected to be removed by the action of evaporation or evaporation.

Further, in the above embodiment, an example in which the angle adjusting means for changing the incident angle with respect to the substrate is attached to the mirror between the laser and the substrate has been described, but the incident angle of the laser beam with respect to the substrate is changed. If you can
Any configuration may be used, and the laser itself may be provided with the angle adjusting means, or the folder supporting the substrate may be provided with the angle adjusting means. The laser light may be guided using an optical fiber instead of the mirror as in the above embodiment. At that time, even if the emitting end of the optical fiber is moved along each side of the substrate using a guide or the like, or the incident angle is changed by applying vibration or the like to the emitting end of the optical fiber. Good.

[0135]

As described in detail above, according to the present invention,
Since the laser light is confined in the translucent material by utilizing the physical critical phenomenon of total internal reflection, the response to the inspection light in the non-uniform part and the uniform part of the translucent material is also critical. The non-uniformity appears with a very clear contrast, and the non-uniformity such as fine scratches can be detected with high sensitivity and with high accuracy and high speed. Furthermore, it is possible to detect not only unevenness of the surface of the light-transmitting material but also internal defects such as scratches and striae.

Further, by determining the presence / absence, type and size of the non-uniformity of the translucent substance based on the information of the light leaked from the surface of the translucent substance, the desired translucent substance can be immediately obtained. It can be extracted and the productivity of the translucent substance can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a non-uniformity inspection device for a light-transmitting substance according to the present invention.

FIG. 2 is an enlarged side view of a part of the transparent substrate of FIG.

FIG. 3 is a perspective view showing an example of a folder that holds a transparent substrate.

4 is an image of a scratch on the surface of the glass substrate detected by the inspection apparatus of FIG.

5 is a diagram showing a light intensity distribution in the width direction of a scratch, which is obtained by image processing from the light information of the image of FIG.

FIG. 6 is an image when the scratch of FIG. 4 is observed with an optical microscope (reflection / bright field).

7 is a diagram showing a light intensity distribution in the width direction of a scratch, which is obtained by image processing from the light information of the image of FIG.

FIG. 8 is a graph comparing the detection sensitivities of the method of the present invention and the conventional method, and is a graph showing the relationship between the signal noise ratio and the normalized exposure time.

FIG. 9 is a perspective view for explaining a simulation for obtaining a ray trace in a transparent substrate when a laser beam is introduced into the transparent substrate along one side thereof.

10 is a diagram showing an example of a result of the simulation of FIG.

11 is a graph showing the relationship between the incident angle on the transparent substrate in FIG. 10 and the number of surface reflections.

FIG. 12 is a ray trace diagram showing how the light propagates in the transparent substrate, obtained by the simulation of FIG.

13 is a graph showing the relationship between the incident angle on the transparent substrate and the number of surface reflections in another example of the simulation shown in FIG.

FIG. 14 is a graph showing the relationship between the incident angle on the transparent substrate and the number of surface reflections in another example of the simulation shown in FIG.

FIG. 15 is a graph showing the relationship between the incident angle on the transparent substrate and the number of surface reflections in another example of the simulation of FIG. 9.

FIG. 16 is a ray trace diagram showing a result of simulating light propagation when laser light is introduced into a transparent substrate.

FIG. 17 is a diagram showing an image of a scratch or the like on a transparent substrate observed by the nonuniformity inspection of the present invention.

FIG. 18 is a perspective view showing a state where laser light is introduced into a transparent substrate from two directions.

FIG. 19 is a schematic configuration diagram showing an embodiment in which laser light is introduced from a corner portion of a transparent substrate.

FIG. 20 is a perspective view showing an embodiment in which laser light is introduced into a plurality of different directions from the same incident position on a transparent substrate.

FIG. 21 is a flowchart showing an embodiment of an inspection process for selecting a non-defective product / defective product of a transparent substrate.

FIG. 22 is a view for explaining the first embodiment in which the transparent substrate selection method of the present invention is applied to a photomask glass substrate.

FIG. 23 is a diagram showing a light intensity distribution in a width direction of a scratch obtained by image processing from optical information of an image of a scratch on the surface of a glass substrate detected by the inspection of the first embodiment of FIG. 22.

FIG. 24 is a diagram for explaining a second embodiment in which the transparent substrate selecting method of the present invention is applied to a magnetic disk glass substrate.

FIG. 25 is a diagram for explaining the inspection method of the second embodiment of FIG. 24.

FIG. 26 is a diagram showing another embodiment of the non-uniformity inspection of the present invention.

FIG. 27 is a diagram showing refraction of light on a boundary surface having a different refractive index.

FIG. 28 is a diagram used to determine a total reflection condition on the surface of a translucent material.

FIG. 29 is a diagram showing a region satisfying a total reflection condition in which light is confined by multiple total reflection in a rectangular parallelepiped light-transmitting substance.

[Explanation of symbols]

1 transparent substrate 2 laser 6 CCD 7 lens system 11 A / D converter 12 Image processing device 31, 32 Mirror L laser light H main surface

─────────────────────────────────────────────────── ─── Continuation of front page (31) Priority claim number Japanese Patent Application No. 9-360331 (32) Priority date December 26, 1997 (December 26, 1997) (33) Priority claim country Japan (JP) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 21/84-21/958 G01M 11/00-11/08 G03F 1/00-1/16

Claims (26)

(57) [Claims] 1. A method for inspecting the non-uniformity of a light-transmitting substance by introducing laser light into the light-transmitting substance, wherein the light-transmitting substance is the laser light introduced into the light-transmitting substance. At least one set of total reflection surfaces facing each other that repeats reflection, and provided between the total reflection surfaces so as to face each other in the traveling direction of the laser light that proceeds by repeating total reflection, and totally reflects the laser light. At least one pair of folding surfaces for returning to the total reflection surface, and when the optical path in the transparent material is optically uniform, propagates through the transparent material and the total reflection surface and the folding surface. The laser light incident on the surface is totally reflected, and the laser light is propagated so as to repeat between at least one pair of folding surfaces, and the total reflection surface and the folding surface formed by propagating the laser light. Laser light is emitted in the enclosed inspection area. Introducing laser beam to span, when the introduced the transparent substance in inhomogeneities in the optical path of the laser light propagating exists, the total reflection surface and /
Alternatively, the method for inspecting non-uniformity of a translucent substance is characterized in that the non-uniformity of the translucent substance is inspected by detecting light leaking from the folding surface. 2. The laser beam according to claim 1, wherein the total reflection surface and the folded surface introduce the laser light so that there is substantially no singular point where the laser light leaks geometrically. Non-uniformity inspection method for light-sensitive substances. 3. The refractive index of the translucent material with respect to the wavelength λ of the introduced laser light is nt, and the refractive index of the outer medium in contact with the translucent material is ni, and the light is incident on the total reflection surface and the turning surface. The angle of the light is θik (k is the position where the laser light is introduced into the translucent material and then is incident on the total reflection surface and the folding surface, and the incident positions are k = 1, 2, ... .) Is the critical angle θ expressed by sin θ = ni / nt on the total reflection surface and the folded surface.
The method for inspecting nonuniformity of a translucent material according to claim 1, wherein the laser light is introduced as described above. 4. The laser light introduced geometrically optics into the light-transmitting substance is introduced so that all of the laser light is totally reflected at least at the first total reflection surface or the turn-back surface. The method for inspecting nonuniformity of a translucent material according to any one of claims 1 to 3, wherein: 5. An introduction surface for introducing a laser beam is provided at a position sandwiched between one total reflection surface and at least one folding surface. The method for inspecting non-uniformity of a light-transmitting substance as described in 1 above. 6. The laser light is introduced so that the introduced laser light is emitted only on a surface having substantially the same angle between the introduction surface and the total reflection surface. Non-uniformity inspection method for translucent materials. 7. The method for inspecting nonuniformity of a light-transmitting substance according to claim 5, wherein at least the introduction surface is mirror-polished. 8. The size of the total reflection surface is L, the width of the introduction surface is d, the refractive index of the light transmissive material with respect to the wavelength λ of the laser light is nt, and the outer medium in contact with the light transmissive material is The refractive index is ni, the beam diameter of the laser light is φ, and the angle of the light the laser light is incident on the total reflection surface and the folding surface is θik (k is after the laser light is introduced into the translucent material. It represents the position of incidence on the total reflection surface and the folded surface,
The incident positions are sequentially set to k = 1, 2, .... In particular, the angle of light that first enters the total reflection surface or the folded surface after the laser light is introduced is θ1. ), The number of times the laser light is reflected by the total reflection surface is m, and m is L, d, nt
If it is expressed by a function of (λ), ni, φ, θ1, then θ
Within the range where all of ik are equal to or greater than the critical angle θ, L, d, nt (λ), ni,
8. The method for inspecting non-uniformity of a light-transmitting substance according to claim 5, wherein at least one of φ and θ1 is determined and laser light is introduced from the introduction surface. . 9. The method for inspecting nonuniformity of a translucent material according to claim 1, wherein the total reflection surface and the folded surface are orthogonal to each other. 10. In a region to be inspected for a transparent material, which is sandwiched by the set of total reflection surfaces and the set of folding surfaces, the laser light propagates in the transparent material to generate light. After inspecting for non-uniformity in one plane in the filled inspection area, the inspection plane is relatively moved with respect to the translucent material in a direction in which light fills the inspection area. 10. The non-uniformity inspection method for a transparent substance according to claim 1, wherein the non-uniformity of the inspection area is inspected. 11. A method for inspecting a non-uniformity of a light-transmitting substance by introducing laser light into the light-transmitting substance, wherein the surface of the light-transmitting substance is at least one pair of mutually parallel main surfaces. , Having at least one set of end surfaces orthogonal to the main surface, and a chamfered portion sandwiched by the main surface and the end surface, when the optical path in the translucent substance is optically uniform, It is formed by causing laser light propagating in a light-transmissive material to be incident on the main surface and the end surface by total reflection and propagating in a repeating manner between at least one set of end surfaces. Introducing laser light so that the laser light is spread in the inspected region surrounded by the main surface, the end face and the chamfered portion, and a non-uniform portion is present in the optical path of the laser light that is introduced and propagates in the translucent material. When present, said major surface and / or Nonuniformity inspection method translucent material, characterized in that the detecting light leaking from the serial end face and adapted to inspect the ununiformity of the light-transmitting material. 12. The laser light is introduced so that there is substantially no singular point at which the laser light leaks geometrically and optically on the main surface and the end surface.
A method for inspecting non-uniformity of a light-transmitting substance as described above. 13. The method for inspecting nonuniformity of a translucent material according to claim 11, wherein the laser light is introduced so that the laser light introduced only from the chamfered portion is emitted. 14. The refractive index of the transparent material with respect to the wavelength λ of the introduced laser light is nt, and the refractive index of the outer medium in contact with the transparent material is ni, so that the laser light enters the transparent material. When the angle of the light incident on the main surface that first strikes is θ1, θ1 is the sin on the main surface.
It is necessary to introduce the laser light from the introduction surface such that θ = ni / nt is equal to or greater than the critical angle θ and (90 ° −θ1) is equal to or greater than the critical angle θ represented by the above formula at the end face. The method for inspecting nonuniformity of a translucent material according to claim 11, which is characterized in that. 15. The non-uniformity inspection method for a light-transmitting substance according to claim 11, wherein at least the chamfered portion is mirror-polished. 16. The method for inspecting nonuniformity of a transparent material according to claim 15, wherein the entire surface of the transparent material is mirror-polished. 17. In a region to be inspected of a transparent material sandwiched by the set of main surfaces and the set of end faces, light is filled by propagating laser light in the transparent material. After inspecting the non-uniformity on one plane in the inspection area, the inspection area is moved relative to the transparent material in a direction in which light fills the inspection area. The non-uniformity inspection method for a light-transmitting substance according to claim 11, wherein the non-uniformity inspection is performed. 18. The non-uniformity inspection method for a transparent substance according to claim 1, wherein the transparent substance is made of glass. 19. The non-uniformity inspection method for a transparent material according to claim 18, wherein the transparent material is a glass substrate for an electronic device or a glass substrate for an information recording medium. 20. An apparatus for inspecting non-uniformity of a light-transmitting substance by introducing laser light into the light-transmitting substance, comprising: illumination means for introducing the laser light into the light-transmitting substance; Detecting means for detecting light leaking from the volatile substance,
Wherein the translucent material has an introduction surface for introducing laser light into the translucent material, and at least two pairs of surfaces of the introduced laser light that are opposed to each other and repeat total reflection. The means is that the laser light emitted from the illumination means is
While being introduced from the introduction surface, when the optical path in the translucent substance is optically uniform, the light propagating in the translucent substance and incident on the surface is totally reflected, and Arranged so that the laser beam is propagated in a repeating manner on at least one set of the surfaces, and the laser light is distributed in an area to be inspected surrounded by the at least two sets of surfaces formed by the propagation. An apparatus for inspecting nonuniformity of a translucent material, characterized by: 21. The non-uniformity inspection apparatus for a transparent material according to claim 20, wherein the illuminating means is provided with an angle adjusting means for changing an incident angle of light with respect to the transparent material. 22. The non-uniformity inspection device for a transparent material according to claim 20, further comprising moving means for moving a light incident position on the transparent material. 23. The non-uniformity of the translucent material according to claim 20, wherein the translucent material and the detection means are integrally moved relative to the illumination means. Sex testing equipment. 24. The detecting means has an image pickup camera having an image pickup element, and a lens for forming an image of light leaking from a light-transmitting substance on the image pickup camera, and the light is transmitted through the image pickup camera and / or the lens. 24. The non-uniformity inspection device for a light-transmitting substance according to claim 20, wherein the device is moved relative to the transparent substance in a perspective direction. 25. A discriminating means for discriminating presence / absence, type, and size of non-uniformity of a light-transmitting substance based on information detected by said detecting means. The non-uniformity inspection device for a light-transmitting material according to one item. 26. An introduction surface for introducing laser light, at least one pair of mutually facing main surfaces where the introduced laser light repeats total reflection, and progress of the laser light for repeating total reflection between the main surfaces. A step of preparing a transparent substrate provided with at least one set of end faces provided so as to face each other in the direction, and when the optical path in the transparent substrate is optically uniform, it propagates in the transparent substrate The laser light incident on the surface and the end faces is totally reflected and is propagated repeatedly between the at least one set of end faces, and the main surface formed by the propagation and the end face surrounded by the end faces are formed. A step of introducing laser light from the introduction surface so that the laser light is distributed in the inspection region; a step of detecting light leaking from the main surface and / or the end surface without being totally reflected; And a step of selecting a transparent substrate by comparing the information obtained in 1. with the information corresponding to the presence, type, and size of non-uniformity existing in the transparent substrate in advance. Transparent substrate sorting method.