JPH11190701A - Method and apparatus for inspecting foreign matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect a matter with a high accuracy by sufficiently reducing an inspecting angle while obtaining necessary optical characteristics of an inspecting optical system. SOLUTION: In the case of an inspecting optical system 21 of a substantially uniform reference shape around an optical axis Y for receiving a folded reflected light 2b from a foreign matter 9 of an inspecting point 5a1, the angle θfor disposing the system 21 is set to a small acute angle to interfere with an optical beam 2a emitted to the point 5a1 or the beam 2a and a surface 5b to be inspected, and the matter 9 is inspected by avoiding the beam 2a or the beam 2a and the surface 5a in a deformed shape from the shape 21a of the system 21, thereby achieving its object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign substance for inspecting foreign substances such as dust, hair, metal pieces, glass, chipping, and process products adhered to the surface of a semiconductor wafer, a master of an optical disk, a master of a hard disk, and the like. The present invention relates to an inspection method and an apparatus therefor.

[0002]

2. Description of the Related Art FIG.
A method and apparatus as shown in FIGS. To explain this, after a laser beam b from a laser light source a is collimated by a collimator lens c, it is directed to an inspection point o on a surface e to be inspected by a cylindrical lens d, and is minutely parallel to the surface e to be inspected. Irradiation angle α, for example α =
It is irradiated as an S-polarized laser beam b1 polarized by the polarizer f from the irradiation optical axis x direction set to about 2 ° to form an image in a slit shape, and the reflected light b2 reflected from the inspection point o at that time. Is received on an inspection optical axis y set at an inspection angle θ that forms an acute angle larger than the irradiation angle α, for example, θ = about 30 °, and the S-polarized light in the specific direction transmitted through the analyzer h. P-polarized light components polarized in different directions are detected as foreign matter. FIG. 7 shows the angle relationship between the irradiation optical axis x, the inspection optical axis y, and the surface to be inspected e in a simplified light vector diagram.

An inspection optical system g for this detection is, as shown in FIGS. 6 and 8, equipped with an objective lens j, an analyzer h, and an imaging lens k in one lens barrel m, and receives light. After turning the returning reflected light b2 into parallel light by the collimator lens c, transmitting only the P-polarized component by the analyzer h, and forming the transmitted light on the light receiving surface of the CCD line sensor n by the imaging lens k, A necessary area of the inspection surface e is scanned to perform a foreign substance inspection.

The S-polarized laser beam b1 applied to the inspection point o is reflected under the influence of the surface condition of the inspection point o, and is scattered by the foreign matter p to generate a P-polarized component as shown in FIG. As shown in the figure, forward scattered light b3, side scattered light b4, and back scattered light b5 that is reflected return light b2 received by inspection optical system g are generated. Here, the P-polarized light component generated by light scattering by the foreign matter p is stronger than the P-polarized light component generated by rotation due to reflection from a pattern on a circuit board having a printed wiring pattern. For this reason, the detection signal imaged on the CCD line sensor n and photoelectrically converted can be determined as a foreign substance based on the value of the signal, and can be optically determined with high precision.

[0005]

Recently, there is an increasing demand for detecting finer foreign substances in order to further improve the quality and accuracy of products. But,
The conventional devices shown in FIGS. 6 to 8 cannot respond to this.

The inventors of the present invention have conducted various experiments and have conducted various studies. As a result, the inspection accuracy depends on the inspection angle θ of the inspection optical system g. The characteristic of this dependence is that the light intensity of the P-polarized component of the scattered light from the foreign material p is S (signal), and the P-polarized component of the reflected light from the copper or aluminum wiring pattern on the surface to be inspected e is N (noise). ), Ie, S / N
As a measure of inspection accuracy, as shown in FIG. 9, as the inspection angle θ is smaller, the detection accuracy is increased by an exponential factor, and an S / N of 1 or more is required to detect foreign matter.

Now, when the relationship between the inspection angle θ and the S / N value is viewed in the case of the foreign matter p having the same size in the conventional inspection optical system g, when the inspection angle θ is 15 °, FIG. As shown in a), the entire backscattered light b5 from the foreign matter p enters the opening n of the inspection optical system g, the amount of received P-polarized light component becomes maximum, and the S value becomes maximum. In the case of 30 °, only a part of the back scattered light b5 enters the opening n as shown in FIG. 10B, and the amount of the P-polarized light component received in the back scattered light b5 from the foreign matter p is greatly reduced. , S values decrease. Therefore, when the inspection angle θ is large, the ratio of the N value is large, and the inspection accuracy is low. In addition, when the foreign substance p to be inspected is small, for example, about 0.5 μm or less, the amount of the backscattered light b5 from the foreign substance p becomes very small, and the amount of the P-polarized component that can be received by the inspection optical system g becomes very small. Therefore, if the inspection angle θ is large, the inspection accuracy is greatly reduced,
Can't respond to recent demands. Therefore, the inspection angle θ is 1
It is desired that the angle be set as small as about 5 °.

[0008] However, the inspection optical system g is conventionally known as shown in FIGS.
As shown in (1), a lens having a uniform shape around the inspection optical axis y, that is, a circular reference shape is used, and the lens barrel m has a cylindrical shape. Also, backscattered light b from minute foreign matter p
In order to sufficiently detect the P-polarized component of No. 5, the inspection optical system g
Requires a numerical aperture NA of at least about 0.3. Accordingly, from the equation of NA = sin θa, the opening angle θa required for the objective lens j of the inspection optical system g is set to about θa = 17.5 °, and the opening diameter is about 50 mm.

The inspection optical system g is arranged so that the lens barrel m avoids the laser beam b and the surface to be inspected e for the foreign substance inspection.

In order to prevent the laser beam b from being shaken by the lens barrel m in consideration of all fluctuation factors in the actual machine, a margin angle θ between the tip of the lens barrel m and the laser beam b is set.
m is required, and specifically, is set to about 2 ° to 5 °. Further, between the opening angle θa and the margin angle θm, the backscattered light b5 is received by the lens barrel m.
There is also a dead angle θk of about °. Therefore, the inspection angle θ is θ = α + θm + θk + θa. Even if the minimum angle is set, θ = 2 ° + 2 ° + 5 ° + 17.5 ° = 26.5 °, and it is difficult to fall below 25 °. For this reason, conventionally, sufficient inspection accuracy has not been obtained for minute foreign substances of about 0.5 μm or less.

An object of the present invention is to provide a high-precision inspection of foreign objects by sufficiently reducing the inspection angle while sufficiently securing necessary optical characteristics of an inspection optical system based on such knowledge. It is an object of the present invention to provide a method and an apparatus therefor.

[0012]

In order to achieve the above object, a foreign matter inspection method according to the present invention is directed to an inspection point on a surface to be inspected, a small irradiation angle almost parallel to the surface to be inspected. A light beam polarized in a specific direction is irradiated from the irradiation optical axis, and the reflected light from the inspection point at that time is reflected on the inspection optical axis at an inspection angle larger than the irradiation angle with the surface to be inspected. In order to detect a polarized component polarized in a direction different from the specific direction as a foreign object, the inspection angle is set to a substantially uniform reference shape around an optical axis for receiving the reflected light. In the case of an optical system, a light beam or a light beam to irradiate the inspection point is set at a small acute angle so as to interfere with the light beam and the surface to be inspected, and the light beam or the light beam is deformed from the reference shape of the inspection optical system. , Light beam and inspection surface Only with it is characterized by the detection of the foreign substance.

In such a configuration, when the inspection optical system has a substantially uniform reference shape around the inspection optical axis as in the related art, on the side facing the light beam irradiated to the inspection point on the surface to be inspected, The inspection angle is set to a state where the light beam or the light beam and the surface to be inspected interfere with each other, and the inspection angle on the surface to be inspected is reduced by an amount smaller than the inspection angle in the case of the conventional arrangement that does not interfere with the reference shape. It can be brought closer to the optical path side of reflected light reflected from a certain foreign matter, and the inspection optical system avoids the light beam, or the light beam and the surface to be inspected by a deformation shape from its reference shape, so that the inspection optical system can be moved to an inspection point. There is no such a case that the light beam irradiated for the purpose is shaken by the inspection optical system, and the deformed shape is the side of the reference shape of the inspection optical system opposite to the light beam of the opening. The light beam or the portion not interfering with the light beam and the surface to be inspected is obtained as a shape cut off at least on the objective lens side as in the foreign matter inspection device of the present invention, and has a small numerical aperture without interference in the reference shape. As in the case of setting, since the light receiving area of the reflected light reflected from the foreign matter does not become extremely small, while ensuring the necessary optical characteristics of the inspection optical system together with the foreign matter inspection device of the present invention, Since the inspection angle can be reduced, the amount of reflected reflected light from the foreign matter can be increased comprehensively, and small foreign matter can be inspected with high accuracy.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A representative embodiment of a foreign matter inspection method and apparatus according to the present invention will be described below with reference to FIGS.

In this embodiment, as shown in FIGS. 1 and 2,
For example, an irradiation optical system 11 that irradiates an inspection point 5a1 on a surface 5a to be inspected such as a circuit board 5 having a circuit pattern formed on a surface thereof using a laser beam 2 from a laser light source 1 as a light beam. . However, the present invention is not limited to this, and various types of straight light can be used. The irradiation optical system 11 emits the laser beam 2 toward the inspection point 5a1 from the direction of the irradiation optical axis X set to a minute irradiation angle α almost parallel to the inspection surface 5a, for example, α = about 2 °. The laser light 2 is collimated by a collimator lens 3 and then collimated by a cylindrical lens 4.
An image is formed in a slit shape on the upper inspection point 5a1. Inspection point 5
The laser beam 2 irradiated to a1 is an S-polarized laser beam 2a polarized by the polarizer 6.

When the inspection point 5a1 is irradiated with the laser light 2a, the reflected light from the foreign matter 9 is a forward scattered light 2b1, a side scattered light 2b2, and a back scattered light 2b as shown in FIG. Light 2b3 and the like are scattered and reflected in various directions. The back scattered light 2b3 is reflected by the inspection optical system 21 as the reflected light 2b to form an image on the CCD line sensor 8, and the inspection of the foreign substance 9 is performed based on the electric signal photoelectrically converted by the CCD line sensor 8 at that time. Do. In this case, the relationship among the irradiation angle α of the laser beam 2a, the inspection angle θ at which the reflected reflected light 2b is received, and the surface 5a to be inspected is simply shown in a vector diagram in FIG.

For such light reception, the inspection optical system 21
Is arranged so as to receive light on the inspection optical axis Y forming an acute inspection angle θ larger than the irradiation angle α with the surface 5a to be inspected, as in the related art. In the present embodiment, the inspection angle θ is set smaller than before, for example, 15 °. The inspection optical system 21 includes an objective lens 12, which is a collimator lens, an analyzer 13, and an imaging lens 14, provided in one lens barrel 15, and the backscattered light 2b3 received as the reflected light 2b is reflected by the objective lens 12. After being converted into parallel light, only the P-polarized light component is transmitted by the analyzer 13, and the transmitted P-polarized laser light 2 c is transmitted by the imaging lens 14 to the CCD.
An image is formed on the light receiving surface of the line sensor 8. The output of the CCD line sensor 8 scans the required area of the surface 5a to be inspected through the analyzer 13 to detect, as a foreign substance, a P-polarized component polarized in a direction different from the S-polarized light in the specific direction. Do it. In the illustrated embodiment, the objective lens 12 has a two-element configuration including lenses 12a and 12b.
One or three or more sheets may be used, and the specific configuration is not particularly limited. Further, various photoelectric conversion elements such as a photodiode can be used in place of the CCD line sensor 8, and various forms having a light receiving surface corresponding to the inspection visual field can be employed instead of the line sensor.

In the present embodiment, the inspection optical system 21 is set to have the same optical characteristics as in the above-described conventional example, and the aperture angle θa satisfies the numerical aperture NA = 0.3.
Since the aperture diameter is about 50 mm when a is set to 17.5 °, the inspection light θ indicated by the imaginary line 21a in FIG. In the reference shape, which is a cylinder substantially uniform around the axis Y, the inspection angle is set so as to interfere with the laser beam 2a and the surface 5a to be inspected on the side facing the laser beam 2a irradiated to the inspection point 5a1. While θ is set to 15 °, the inspection optical system 21 is shown by a solid line in FIG.
(B), the foreign substance 9 is detected in a deformed shape from the reference shape as shown in FIG. 2 while avoiding the laser beam 2a and the inspection surface 5a.

In an actual apparatus, it is easy to form a deformed shape from the reference shape by cutting the inspection optical system 21 of the reference shape to the minimum necessary. The solid line in FIG. 1 (b), at least on the side of the objective lens 12 as shown in FIG.
The cutting may be performed at the position of the cutting angle θb with respect to the inspection optical axis Y in consideration of only the margin angle θm with the laser beam 2a.
In other words, the objective lens 12 is exposed from the lens barrel 15 by the resection and directly faces the surface 5a to be inspected.
Does not occur and can be omitted. There are various cutting methods such as cutting off and grinding. Needless to say, it is of course possible to assemble the necessary shape formed from the beginning.

Here, the ablation angle θb is as follows: θb = θ− (α + θm), and the irradiation angle α is set to 2 ° and the margin angle θm is set to 2 ° as in the past, and the ablation angle θb is about 11 °.

Accordingly, the inspection angle θ becomes θ = θb + α + θm, and when α = 2 ° and θm = 2 °, θb =
Since it is 11 °, θ = 2 ° + 2 ° + 11 ° = 15 °, which satisfies the above-described installation condition of the present embodiment.

As described above, when the inspection optical system 21 has a substantially uniform reference shape around the inspection optical axis Y as in the related art, the laser beams 2 and 2a that irradiate the inspection point 5a1 on the surface 5a to be inspected are On the opposite side, the inspection angle θ is set in a state of interfering with the laser beams 2 and 2a and the surface 5a to be inspected, so that the inspection angle θ is smaller than the inspection angle θ in the conventional arrangement that does not interfere with the reference shape. As shown in FIG. 5A, the reflected light 2b from the foreign material 9 at the inspection point 5a1 on the inspection surface 5a can be brought closer to the optical path side.

The inspection optical system 21 changes the shape of the laser beam 2, 2a and the surface
By avoiding a, the laser beam 2, 2a irradiated toward the inspection point 5a1 is not shaken by the inspection optical system 21.

Further, the deformed shape of the inspection optical system 21 is such that a part of the opening 21b on the side facing the laser beams 2 and 2a in the reference shape has the laser beams 2 and 2a as shown in FIG. 5B, which is obtained as a shape that is cut off by the amount not to interfere with the surface 5a to be inspected and has a small numerical aperture without interference in the reference shape, as in the case of the virtual opening 21c shown by a virtual line in FIG. In addition, most portions can be received without the light receiving area of the reflected reflected light 2b from the foreign material 9 becoming extremely small, and about 10% of the portion where the light intensity of the backscattered light 2b3 as the reflected reflected light 2b is strong. Thus, in the present embodiment, the inspection angle θ can be reduced while sufficiently securing the necessary optical characteristics of the inspection optical system 21. Return And overall increase the amount of received reflected light 2b, it is possible to 0.5μm even less small particles 9 to improve the SN ratio to inspect with high accuracy.

FIG. 9 shows that the inspection angle θ of the inspection optical system 21 is slightly smaller than the conventional lower limit of 25 °.
As described above, the inspection optical system 21 is effective at an exponential multiple, so that the inspection optical system 21 is installed at an inspection angle θ such that it interferes with at least the laser beam 2a in the reference shape, and the inspection optical system 21 is deformed from the reference shape. It is effective to avoid the laser beam 2a, and it is within the scope of the present invention.

Further, the object of the present invention can be achieved even by cutting off at a plane W parallel to the inspection optical axis Y, as shown by a dashed line in FIG. 1B. In short, various specific configurations can be adopted without changing the gist of the present invention.

[0027]

According to the foreign matter inspection method and apparatus of the present invention, the required optical characteristics of the inspection optical system can be sufficiently ensured.
Since the inspection angle can be reduced, the amount of reflected reflected light from the foreign matter can be increased comprehensively, and small foreign matter can be inspected with high accuracy.

[Brief description of the drawings]

FIG. 1 shows a main part of an inspection optical system side of a foreign matter inspection apparatus according to an embodiment of the present invention, in which (a) is a cross-sectional view showing a light receiving state, and (b) is an objective lens side of the inspection optical system. FIG.

FIG. 2 is a perspective view showing the entire foreign matter inspection apparatus of FIG. 1;

FIG. 3 is a vector explanatory diagram of the device of FIG. 2;

FIG. 4 is an explanatory diagram of scattered light reflected from a foreign substance in a foreign substance inspection state in the apparatus shown in FIGS. 1 and 2;

FIGS. 5A and 5B are explanatory diagrams illustrating a relationship between an opening of an inspection optical system of the apparatus in FIGS. 1 and 2 and an incident state of backscattered light from a foreign substance, wherein FIG. 5A illustrates a virtual incident state and FIG. 2 shows actual incident states in the embodiment.

FIG. 6 is a perspective view showing an entire conventional foreign matter inspection device.

FIG. 7 is a vector explanatory diagram of the device of FIG. 6;

8 is a cross-sectional view showing a main part of the apparatus of FIG. 6 on the inspection optical system side in a light receiving state.

9 shows the relationship between the inspection angle of the inspection optical system of the apparatus shown in FIG. 6 with respect to the surface to be inspected and the S / N values of the foreign matter signal S and the noise signal D detected through the inspection optical system. It is a graph shown.

10A and 10B are explanatory diagrams of an incident state of backscattered light from an opening of an inspection optical system and a foreign substance of the apparatus of FIG. 6, in which FIG. 10A shows an ideal incident state and FIG. Is shown.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 laser light 2a S-polarized laser light 2b, 2b3 folded reflected light 2c P-polarized laser light 5a surface to be inspected 6 polarizer 8 CCD line sensor 9 foreign matter 11 irradiation optical system 12 objective lens 13 analyzer 14 imaging Lens 15 Lens barrel 21 Inspection optical system 21a Reference form diagram 21b Aperture α Irradiation angle θ Inspection angle θa Aperture angle θb Cutting angle X Irradiation optical axis Y Inspection optical axis W, Z Cutting surface

Claims (3)

[Claims] 1. A light beam polarized in a specific direction from an irradiation optical axis having a minute irradiation angle almost parallel to an inspection surface is irradiated toward an inspection point on the inspection surface, and The reflected light from the inspection point at that time is received on the inspection optical axis forming an inspection angle larger than the irradiation angle with the surface to be inspected, and the polarized component polarized in a direction different from the specific direction is contaminated. In the case of an inspection optical system having a substantially uniform reference shape around an optical axis for receiving the reflected light, a light beam or a light beam or a light beam applied to the inspection point is detected. It is set at a small acute angle so as to interfere with the inspection surface, and in the deformed shape from the reference shape of the inspection optical system, the light beam or the light beam and the detection of the foreign matter while avoiding the surface to be inspected. Foreign matter inspection method 2. A light beam polarized in a specific direction is emitted from an irradiation optical system on an irradiation optical axis having a minute irradiation angle almost parallel to the inspection surface toward an inspection point on the inspection surface. Then, the reflected light reflected from the inspection point at that time is received by the inspection optical system on the inspection optical axis forming an inspection angle larger than the irradiation angle with the surface to be inspected, and polarized in a direction different from the specific direction. In a foreign matter inspection device that detects a polarized component as a foreign matter, the inspection optical system, from a substantially uniform reference shape around the optical axis, cut off the side facing the light beam to be irradiated and the surface to be inspected, A foreign matter inspection device, which is disposed close to a light beam. 3. The foreign matter inspection apparatus according to claim 2, wherein the inspection optical system is cut off on the objective lens side in a plane substantially along the surface to be inspected.