JPH10339701A - Device and method for checking defect on substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To check various defects on the respective layers of substrate with high reliability. SOLUTION: This device is provided with an optical illumination system 10 with which an optical axis is arranged at an angle θi from 80 deg. to 89 deg. to a normal on the surface of wafer W, light receiving means 30 for receiving light containing information on the surface of wafer W illuminated by the optical illumination system 10, light reception angle setting means 40 for setting the light reception angle of light receiving means 30 in order to selectively receive prescribed light from the wafer W, and rotating mechanism 50 for rotating the wafer W around an axial line crossing the surface of wafer W. Since the optical axis of optical illumination system 10 is arranged at the angle closer to 90 deg. to the normal on the surface of wafer, most of illuminating light is reflected on the surface of wafer W, and the information on the surface of wafer W is mainly extracted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus and a defect inspection method for a substrate, and more particularly to a method of inspecting a substrate for uneven film thickness.
The present invention relates to a defect inspection apparatus and a defect inspection method for inspecting macroscopic defects such as dirt, steps in a pattern formed on a substrate, forgetting exposure, and surface scratches.

[0002]

2. Description of the Related Art As a prior art for automatically inspecting a substrate such as a semiconductor wafer, as disclosed in Japanese Patent Publication No. 6-8789, the incident angle of illumination light with respect to the substrate is made variable, There is a method of photographing specularly reflected light from a camera with a camera and inspecting the substrate for defects such as dirt and scratches based on the image information. Further, Japanese Patent Application Laid-Open No. 8-75661 discloses a method of inspecting a substrate for defects such as scratches, foreign matter, and spots by receiving only the diffracted light from the repetitive pattern on the substrate.

[0003]

When a semiconductor is manufactured, the substrate is processed through a number of processes, so that inspection and management are required for each process. According to this, it has been particularly difficult to separate and inspect one of a plurality of layers formed in layers.

In a semiconductor wafer, a transparent thin film or the like is applied on a periodic repetition pattern, and the surface is almost flat, or the pitch of the repetition pattern between the surface layer and the layer below the same. There are different things.

For example, when diffracted light from a sample having a flat surface such as the former is received, information from a repetitive pattern of the lower layer is mainly used, and macroscopic inspection of a thin film on the surface is difficult.

In the latter case, it is sufficient that the diffracted light can be received in accordance with the pattern pitch of the layer to be inspected. However, the pattern pitch of the transparent thin film on the surface layer is lower than that of the lower layer.
When the pitch is an integral multiple of the pitch, it is difficult to separately receive each of the diffracted lights, and it has been difficult to detect defect information for each process (layer) without error.

Accordingly, an object of the present invention is to provide a defect inspection apparatus and a defect inspection method capable of inspecting various defects in each step (layer) with high reliability.

[0008]

In order to achieve the above object, a defect inspection apparatus for a substrate according to the first aspect of the present invention comprises:
As shown in FIGS. 1 and 2, an illumination optical system 10 whose optical axis is arranged at an angle θi of 80 ° to 89 ° with respect to a normal to the surface of the substrate W; A light receiving means 30 for receiving light including information on the surface of the substrate W; and a light receiving angle setting means 40 for setting a light receiving angle of the light receiving means for selectively receiving predetermined light from the substrate W. And a rotation mechanism 50 for rotating the substrate about an axis crossing the surface of the substrate W.

With this configuration, the optical axis of the illumination optical system is 90 °, ie, 80 ° to 89 ° with respect to the normal to the substrate surface.
, Most of the illumination light is reflected by the surface of the substrate, and mainly information on the surface of the substrate is extracted. Since the light receiving means for receiving the light containing such information is set to a predetermined light receiving angle by the light receiving angle setting means, predetermined light from the substrate, for example, diffracted light traveling in a predetermined direction, Light can be selectively received. Further, since a rotation mechanism for rotating the substrate about an axis intersecting with the surface of the substrate is provided, it is possible to deal with patterns and scratches in any direction. Here, the axis is generally an axis perpendicular to the surface of the substrate.

Here, the light receiving angle setting means may be configured to set the light receiving angle by inclining the illumination optical system and the substrate integrally.

With this configuration, the illumination optical system and the substrate are integrally tilted, so that the light reception angle can be set arbitrarily while the incident angle of the illumination light is kept constant. Further, the light receiving optical system can be fixedly arranged in the inspection apparatus.

A method for inspecting a defect of a substrate according to a third aspect of the present invention includes an illumination step of illuminating the substrate with an incident angle of 80 ° to 89 ° with respect to the surface of the substrate; and the substrate illuminated in the illumination step. A light receiving step of selectively receiving predetermined light out of light including information on the surface of the substrate, which occurs in the step; and a step of detecting a defect of the substrate based on the information obtained in the light receiving step. And

[0013] In this method, the substrate surface is formed at an angle of 80 °
Since the substrate is illuminated at an angle close to 90 ° of 89 °, most of the illuminating light is reflected by the surface of the substrate, and mainly information on the surface of the substrate is extracted. Since a predetermined light of the light including the information on the surface of the substrate is selectively received, a defect corresponding to the selected light is detected.

[0014] In the above method, as set forth in claim 4,
In the light receiving step, it is desirable to selectively receive predetermined diffracted light, scattered light or specular reflected light generated on the substrate.

In this case, if the selected light is specularly reflected light, information on the film thickness unevenness, spots and dirt on the substrate surface is expressed as:
In the case of diffracted light, information on the pattern on the substrate is mainly picked up, and in the case of scattered light, information on surface scratches and foreign substances is mainly picked up. Then, in the step of detecting defects, defects relating to those substrates are detected.

In the above method, the step of detecting the defect may further comprise a step of comparing information obtained in the light receiving step with reference information indicating a reference state of the substrate. May be provided.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing an embodiment of a substrate defect inspection apparatus according to the present invention, and FIG. 2 is a plan view of the apparatus shown in FIG.

As shown in FIG. 1, the illumination optical system 10 is fixed relatively to the substrate stage STG.
It may be mounted on the substrate stage STG. Further, a sample stage 20 having a surface on which the substrate W is placed is provided on the upper surface of the substrate stage STG.

In the illumination optical system, a light guide 11 for supplying illumination light is arranged with its light emitting end face 12 facing the direction of the substrate W. In the light traveling direction of the exit end face 12,
A cylindrical concave mirror 13 having power in a direction parallel to the normal line of the surface of the substrate placed on the sample stage is arranged so that the emission end face 12 is located at the focal position, and the emission reflected by the cylindrical concave mirror 13 In the light traveling direction from the end face 12, a cylindrical concave mirror 14 having power in a direction perpendicular to the normal line is arranged so that the emission end face 12 is located at the focal position.

Here, the light from the exit end face 12 reflected by the cylindrical concave mirror 14 is transmitted to the substrate W placed on the sample stage 20.
The illumination optical system 10 is arranged so as to be incident on the surface at an angle of 80 ° to 89 °. That is, the optical axis of the illumination optical system 10 is disposed on the surface of the substrate W mounted on the sample stage 20 so as to have the above-described angle.

With this configuration, the light emitted from the emission end face 12 of the light guide 11 is directed in the direction normal to the surface of the substrate, ie, in the vertical direction, and in the direction perpendicular to the direction normal to the surface of the substrate, ie, in the horizontal direction. A light beam L1 that is substantially parallel in both directions is incident on the substrate W at an incident angle close to 90 ° (a slight incident angle on the surface of the substrate) to illuminate the surface of the substrate. For this reason, most of the illumination light is reflected on the surface of the substrate by the Fresnel's formula regarding the reflection and refraction of light at different interfaces of the medium. Information can be extracted.

The numerical aperture (NA) of the illumination optical system for illuminating the substrate W is different from the plane direction including the normal of the substrate surface and the optical axis of the illumination optical system 10, ie, the paper plane direction in FIG. The shape of the end face 12 of the light guide 11 may be a dimension proportional to the focal length of each of the cylindrical concave mirror 13 and the cylindrical concave mirror 14 so that the end face 12 is equal in the direction perpendicular to the direction.

On the other hand, a light receiving optical system 30 for receiving light from the substrate including information on the surface condition of the substrate is provided in the direction of travel of the light from the substrate. In FIG. 1, the light receiving optical system 30 has a direction in which the concave reflecting mirror 31 receives the specularly reflected light from the substrate W, that is, in this embodiment, the reflection angle on the substrate is 8
It is arranged at the same angle as the incident angle of 0 ° to 89 ° and in the direction opposite to the normal at the incident point. Further, in the traveling direction of the reflected light from the concave reflecting mirror 31, the imaging lens 32 and the two-dimensional image sensor 33 are arranged in this order, and the surface of the substrate W and the surface of the two-dimensional image sensor 33 are substantially conjugated. It is arranged to become.

Accordingly, the parallel light beam L2 specularly reflected by the substrate W is reflected by the concave reflecting mirror 31, and the image forming lens 32
And a regular reflection image of the surface of the substrate W is formed on the two-dimensional image sensor 33.

Here, from the viewpoint of illumination efficiency, the illumination optical system 1
It is desirable that the numerical aperture (NA) of 0 and the numerical aperture of the light receiving optical system 30 be substantially the same.

If there is an abnormal step due to uneven resist coating on the surface of the substrate W or partial exposure abnormality, the reflectivity reflects such an abnormality, and is different from that of a normal substrate. An abnormality can be detected by comparing.

Next, consider the case of receiving diffracted light. If there is a periodic repetitive pattern on the test substrate W, diffracted light is generated according to the pitch. As shown in FIG. 1, the diffraction angle θd with respect to the incident angle θi satisfies the following relationship when the pattern pitch and wavelength are p and λ, respectively, and the diffraction order is m (integer).

Sin θd−sin θi = mλ / p (1) When the incident angle is close to 90 °, sin θi in equation (1)
Is approximately equal to 1, so if we put sinθi = 1,
Equation (1) becomes sin θd = mλ / p + 1 (2)

In order to receive the diffracted light, the light receiving angle must be set to a value determined by the equation (1) according to the pattern pitch information, but the entire light receiving optical system 30a is rotated around the center of the substrate W. The light receiving angle is adjusted by setting the angle of incidence, and as shown by the broken line in FIG. 1, the emission angle from the substrate surface is set to the diffraction angle θd obtained by Expression (1).
An image using the diffracted light L3 can be obtained.

Here, if the ratio of the pattern step and the unevenness (duty ratio) is different from the normal pattern, the diffraction efficiency is different and the brightness of the diffraction image is different from that of the normal pattern. Are different from each other, the abnormality can be inspected by comparison.

As in the case of regular reflection light reception, the surface reflectance is increased by setting the incident angle of the illumination system to around 90 °, and the diffracted light from the surface is efficiently received. As another method of changing the light receiving angle, the entire stage STG may be inclined while the relative positional relationship between the illumination optical system 10 and the substrate W is kept constant. For this purpose, the substrate stage STG is provided with a light receiving angle setting means 40. The rotation axis is substantially in a plane including the surface of the substrate W, and is oriented in a direction orthogonal to the optical axis of the illumination optical system 10.

When receiving scattered light, it is desirable to set the light receiving optical system 30 in a direction in which diffracted light from the pattern does not directly enter the two-dimensional image sensor 33. The detection of scattered light is effective for detecting foreign matter and scratches on the substrate W,
Since the scattered light due to the flaw is strongly emitted in a direction perpendicular to the flaw, the direction in which the scattered light should be received differs depending on the direction of the flaw. Therefore, the sample stage 20 on which the substrate W is placed is 360
゜ The structure can be rotated. The sample stage 20 is rotated by a rotation mechanism 50 (see FIG. 1) provided on the substrate stage STG and having an upper surface on which the substrate W of the sample stage 20 is mounted and having a rotation axis parallel to the normal line of the surface of the substrate W. Is done.
The rotation mechanism 50 may be mounted on the substrate stage STG.

Thus, the substrate W is inspected in at least two directions of 0 ° and 45 ° around the normal line. It is the same as the above-mentioned two systems in that an abnormality is inspected by comparing an image at each rotation angle with an image of a normal pattern.

As described above, the optimum observation direction can be obtained by selecting a configuration in which an arbitrary light receiving angle can be selected and a configuration in which the substrate surface can be observed from different directions by rotating around the normal line of the substrate surface. Can be set, and a defect inspection on a substrate can be performed based on a plurality of pieces of image information obtained under different conditions.

As shown in FIG. 2, the reason why the reflection direction of the concave reflecting mirror 31 is shifted from the center of the substrate W is to prevent the reflected light from being affected by the diffracted light when detecting the reflected light. In order to

Next, an embodiment of a method for inspecting a defect of a substrate according to the present invention will be described with reference to FIGS. FIG.
Shows the flow of an inspection performed by starting the inspection and selectively receiving diffracted light, FIG. 4 shows a flow of an inspection performed by selectively receiving specularly reflected light, and FIG. Inspection performed by selectively receiving scattered light and discrimination between good and bad of the board,
The flow until the defect inspection method is completed is shown.

First, as shown in FIG. 3, in this embodiment, information on a pattern formed on a substrate is read (step SP1). It is determined whether or not the pattern is a periodic pattern (step SP2). If the pattern is not a periodic pattern, the inspection performed by receiving the diffracted light is unnecessary. It may be bypassed to step SP8) (X1).

In the case of a periodic pattern, for example, a line and space pattern, the rotation angle around the normal to the surface of the substrate is set so that the direction of the line is orthogonal to the direction in which the illumination light is incident (step SP3). ).

The diffraction angle with respect to the pattern pitch is
The calculation is performed according to equation (1) or equation (2) (step SP4). The light receiving angle is set to the calculated diffraction angle θd (step SP5). Of course, step 3 may be performed after step 5 here.

The surface of the substrate whose direction and inclination are set as described above is irradiated with illumination light at an incident angle close to 90 ° (step 6). Then, information on the surface of the substrate is captured to receive the diffracted light generated from the substrate. Here, the light receiving angle may be further adjusted to the most appropriate angle while receiving the diffracted light.

The captured image is compared with a reference image which provides a state of a defect-free substrate prepared in advance (Step 8). Such a substrate is placed in a defective tray (X3, FIG. 5, step 28).

If it is determined in step 8 that the image is the same as the reference image, the process proceeds to the next step (X1, FIG. 4, step SP11).

If the information on the pattern formed on the substrate is known in advance as the characteristic of each substrate, the reading step SP1 and the step SP2 of determining whether the pattern is a periodic pattern are omitted, and the following description will be omitted. The present inspection method may be started from the regular reflection light receiving step of X1 or less or the irregular reflection light receiving step.

Referring to FIG. 4, an inspection process performed by receiving specularly reflected light will be described. First, the light receiving angle is set to be equal to the incident angle of the illumination light (step SP11). Next, illumination light is applied to the surface of the substrate whose inclination (the light receiving angle) is set at an incident angle close to 90 ° (step 12). And it takes in the information on the substrate surface and receives the specularly reflected light reflected from the substrate,
Capture a regular reflection image. Here, the light receiving angle may be further adjusted to the most appropriate angle while receiving the reflected light.

The captured specular reflection image is compared with a reference image prepared in advance, which gives a state of a defect-free substrate (step 14), and if not the same as an acceptable level, it is determined to be unnecessary. Then, such a substrate is placed in a defective product tray (X3, FIG. 5, step 28). If it is determined in step 14 that it is the same as the reference image, the process proceeds to the next step (X2, FIG. 5, step SP21).

Referring to FIG. 5, an inspection process performed by receiving diffusely reflected light will be described. First, the light receiving optical system is set at a light receiving angle suitable for receiving diffusely reflected light with respect to the substrate.
Diffusely reflected light is emitted in almost every direction, unlike the case of regular reflection or diffracted light. For example, if the direction is set so as to avoid specularly reflected light or to avoid the direction of primary and secondary diffracted light, Observation with diffused light can be performed efficiently.

The surface of the substrate whose direction and inclination are set as described above is irradiated with illumination light at an incident angle close to 90 ° (step 22). Then, information on the substrate surface is taken in and scattered light generated from the substrate is received. Here, the light receiving angle may be further adjusted to the most appropriate angle while receiving the scattered light again.

The captured image is compared with a reference image prepared in advance, which gives the state of a defect-free substrate (step 24), and if the images are not the same as acceptable, it is determined to be defective. Such a substrate is placed in a defective tray (X3, step 28). Then, it is determined whether or not the substrate to be inspected still remains (step SP29).

If it is determined in step 24 that the image is the same as the reference image, it is next determined whether or not to observe from another angle around the normal to the substrate surface. The substrate is rotated (step SP26), the process returns to step SP21, and the inspection performed by receiving scattered light at that position is repeated.

If it is determined in step 25 that the substrate does not need to be further rotated for observation, the substrate is placed in a non-defective tray (step SP27). Then, it is determined whether or not the substrate to be inspected still remains (step SP29).

If the substrate to be inspected still remains,
The next substrate is placed on the inspection table (step SP30), and it is determined whether the substrate is the same type of substrate as the substrate previously inspected. If not, the process returns to step SP1 (X4).
The process is repeated from reading the pattern information. If they are the same type, it is not necessary to read the pattern information.
Return to P2.

If it is determined in step 29 that all the substrates have been inspected, the inspection is terminated (END).

The case where the steps of receiving the diffracted light for receiving the periodic pattern, the step of receiving the regular reflected light, and the step of receiving the irregularly reflected light are described above. However, the order is not limited to this. The order of reflection, irregular reflection, and diffracted light may be used.
In the case of a substrate having no periodic pattern, the diffracted light receiving inspection may be omitted, but the specular reflection step and the irregular reflection step are generally not omitted.

As described above, the defect can be determined by comparing the state of the substrate having no defect, that is, the reference state, with the state of the substrate to be inspected.

As described above, when inspecting the surface condition of a sample having a substantially flat surface with a transparent thin film applied on a periodic repeating pattern, scattered light from a foreign substance is detected. Thus, foreign matter can be detected. Further, the unevenness of the film thickness on the surface can be detected because the regular reflection image on the surface becomes uneven in brightness.

Here, the reflectance of the surface is increased as much as possible,
In order to prevent the illumination light from reaching the lower layer, the incident angle of the illumination system is set to 80 ° to 89 °, and is set as close to 90 ° as possible. Desirably, it is 87 ° to 89 °. For example, in one embodiment, the incident angle is 88 °. In this case, most (90% or more) of the illumination light is reflected on the surface. FIG. 1 shows a case where the incident angle is 88 °, but FIG. 1A shows the vicinity of the sample when the incident angle is 80 ° so that the relationship between the incident illumination light and the regular reflection light can be easily understood. Is partially shown.

In a sample in which the pitch of the repetitive pattern of the surface layer and the lower layer is different, the pattern of the layer to be inspected is
Although the diffracted light must be received in accordance with the pitch of the light source, if the diffracted light from the surface layer and the lower layer cannot be separated well (when the pitch is an integral multiple), the angle of incidence of the illumination system is still 80 ° or more. 89 ° and as close as possible to 90 °. Further, the angle is desirably set to 87 ° to 89 °. For example, in a preferred embodiment, the incident angle is 88 °. This makes it possible to increase the surface reflectance of the substrate and efficiently receive the diffracted light from the surface.

As described above, the optimum detection mode according to the sample is
By selecting a code, a highly reliable inspection for various defects in each process can be performed.

The illumination optical system 10 and the light receiving optical system 30
Is preferably a telecentric optical system. With this configuration, illumination is performed at the same incident angle over the entire surface of the substrate to be inspected, and observation can be performed at the same light receiving angle. Therefore, it is not necessary to change the inclination of the substrate little by little in order to inspect the surface of the substrate for defects, as is often done by visual inspection.

Further, the illumination optical system 10 may be composed of two groups of optical elements having different powers in orthogonal directions to each other, and the dimensional shape of the aperture stop may be inversely proportional to the power.

As described above, according to the present invention, an optimum detection mode can be selected from among reflected light, diffracted light, and scattered light in accordance with a sample substrate, and various types of defects in various processes can be selected. And highly reliable inspection can be performed.

Since the apparatus is configured to obtain surface image information, it is desirable to perform these inspections each time the process is completed.

These methods can be applied not only to the detection of defects and foreign substances in large substrates for liquid crystals but also to semiconductor wafers.

[0064]

As described above, according to the present invention, since the illumination light is incident on the substrate at an angle of 80 ° to 89 °, most of the light is reflected by the surface of the substrate, and the first layer is formed. Surface defects can be detected. Also, since predetermined light is selectively received from the surface of the substrate, for example, specular reflection light, scattered light, or any one of diffracted lights can be selected and received,
It makes it possible to detect defects suitable for detection with these lights. In this way, various defects in each layer of the substrate can be inspected with high reliability.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment of a defect detection device of the present invention.

FIG. 2 is a plan view of the apparatus of FIG.

FIG. 3 is a flowchart showing a part of a method for detecting and receiving diffracted light in an embodiment of the defect detection method of the present invention.

FIG. 4 is a flowchart showing a part of a method of receiving and receiving specularly reflected light in an embodiment of the defect detection method of the present invention.

FIG. 5 is a flowchart showing a part of a method of receiving scattered light in the embodiment of the defect detection method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Illumination optical system 11 Light guide (optical fiber) 12 Emission end face 13 Cylindrical concave mirror 14 Cylindrical concave mirror 20 Sample stage 30 Reception optical system 31 Concave reflection mirror 32 Imaging lens 33 Two-dimensional image sensor 40 Reception angle setting means 50 Rotation mechanism θi Incident angle θd Diffraction angle W Substrate STG Substrate stage L1 Incident light L2 Reflected light L3 Diffracted light

Claims (5)

[Claims] 1. An apparatus for inspecting defects of a substrate, comprising: an illumination optical system having an optical axis disposed at an angle of 80 ° to 89 ° with respect to a normal to the surface of the substrate; Light receiving means for receiving light including information on the surface of the substrate; light receiving angle setting means for setting a light receiving angle of the light receiving means for selectively receiving predetermined light from the substrate; A rotation mechanism for rotating the substrate about an axis intersecting the surface of the substrate;
Inspection device for substrate. 2. The light receiving angle setting unit according to claim 1, wherein the light receiving angle setting means is configured to set the light receiving angle by inclining the illumination optical system and the substrate integrally.
Inspection device for substrate. 3. An illumination step of illuminating the substrate at an angle of incidence of 80 ° to 89 ° with respect to the surface of the substrate; including information about the surface of the substrate that occurs at the substrate illuminated in the illumination step. A light receiving step of selectively receiving a predetermined light out of the light; and a step of detecting a defect of the substrate based on information obtained in the light receiving step; Inspection methods. 4. The method according to claim 3, wherein the light receiving step selectively receives predetermined diffracted light, scattered light or specularly reflected light generated in the substrate. . 5. The method according to claim 3, wherein the step of detecting the defect further includes a step of comparing information obtained in the light receiving step with reference information indicating a reference state of the substrate. Item 5. A method of inspecting a substrate for defects according to Item 4.