JP3832028B2 - Substrate defect inspection apparatus and defect inspection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a defect inspection apparatus and defect inspection method for a substrate, and in particular, defect inspection for inspecting macroscopic defects such as film thickness unevenness on the substrate surface, dirt, pattern steps formed on the substrate, forgetting exposure, and scratches on the surface. The present invention relates to an apparatus and a defect inspection method.
[0002]
[Prior art]
As a conventional technique 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, and regular reflection light from the substrate surface is obtained. There is a method of inspecting the substrate for defects such as dirt and scratches based on the image information. Japanese Patent Application Laid-Open No. 8-75661 discloses a method for inspecting defects such as scratches, foreign matter, and spots on the substrate by receiving only the diffracted light from the repetitive pattern on the substrate.
[0003]
[Problems to be solved by the invention]
When manufacturing a semiconductor, since the substrate is processed through a number of processes, it is necessary to inspect and manage each process. It was difficult to separate and inspect one layer among a plurality of layers.
[0004]
In a semiconductor wafer, a transparent thin film or the like is coated on a periodic repetitive pattern so that the surface is almost flat or the pitch of the repetitive pattern differs between the surface layer and the layer below it. Things exist.
[0005]
For example, when diffracted light from a sample with a flat surface such as the former is received, information from the repeated pattern of the lower layer is the center, and macroscopic inspection of the thin film on the surface is difficult.
[0006]
In the latter case, it is sufficient if the diffracted light can be received according to the pattern pitch of the layer to be inspected, but the pattern pitch of the transparent thin film on the surface layer is an integral multiple of the pattern pitch of the lower layer. In this case, since it is difficult to receive each diffracted light separately, it is difficult to detect defect information for each process (layer) without error.
[0007]
Accordingly, an object of the present invention is to provide a defect inspection apparatus and a defect inspection method that can inspect various defects for each process (layer) with high reliability.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the substrate defect inspection apparatus according to the first aspect of the present invention has an optical axis of 80 ° to 89 ° with respect to the normal of the surface of the substrate W, as shown in FIGS. An illumination optical system 10 arranged at an angle θi of °; light receiving means 30 for receiving light including information on the surface of the substrate W illuminated by the illumination optical system 10; and predetermined light from the substrate W to selectively receives, a light receiving angle setting means 40 for setting the acceptance angle of the light receiving means 30; and a rotating mechanism 50 for rotating the substrate W about the axis intersecting the substrate W surface, the The light receiving means 30 is configured to receive the light at a plurality of rotation angles by rotating the substrate W by the rotation mechanism 50 .
With this configuration, the optical axis of the illumination optical system is arranged at an angle close to 90 °, ie, 80 ° to 89 ° with respect to the normal line of the substrate surface, so that most of the illumination light is reflected on the surface of the substrate. The information on the surface of the substrate is mainly taken out. Since the light receiving means for receiving light including such information is set to a predetermined light receiving angle by the light receiving angle setting means, predetermined light from the substrate, for example, specularly reflected light directed in a predetermined direction Any one of scattered light and diffracted light can be selectively received. In addition, since a rotation mechanism that rotates the substrate about an axis that intersects the surface of the substrate is provided, it can cope with patterns and scratches in any direction, and the light receiving means rotates the substrate with the rotation mechanism and receives light at a plurality of rotation angles. Because it is configured, it can deal with patterns and scratches in multiple directions. Here, the axis is generally an axis perpendicular to the surface of the substrate.
[0009]
In order to achieve the above object, in the defect inspection apparatus for a substrate according to the second aspect of the present invention, as shown in FIGS. 1 and 2, the light may be specular reflection light or diffracted light.
If comprised in this way, the regular reflection light or diffracted light which goes to the predetermined direction from the board | substrate W can be light-received selectively, and the said light reception angle setting means 40 will receive the regular reflection light or diffracted light from the said board | substrate W. Since the light receiving means 30 is arranged in the direction of receiving light, defects such as thick film unevenness, stains and dirt on the substrate surface can be detected by specular reflection light, or pattern defects on the substrate can be detected by diffracted light.
[0010]
Here, as described in claim 3 , the light reception angle setting means may be configured to set the light reception angle by inclining the illumination optical system and the substrate integrally.
[0011]
If comprised in this way, since an illumination optical system and a board | substrate are inclined integrally, a light reception angle can be set arbitrarily, keeping the incident angle of illumination light constant. Further, the light receiving optical system can be fixedly arranged in the inspection apparatus.
[0012]
A defect inspection method for a substrate according to a fourth aspect of the present invention occurs in the illumination step of illuminating the substrate at an incident angle of 80 ° to 89 ° with respect to the surface of the substrate; A first light receiving step for selectively receiving a predetermined light including information on the surface of the substrate ; and rotating the substrate around an axis intersecting the surface of the substrate. A second light receiving step for selectively receiving predetermined light out of light including information on the surface of the substrate from a different direction from the light receiving step ; the first light receiving step and the second light receiving step. And a step of detecting a defect of the substrate based on the information obtained in (1).
[0013]
In this method, since the substrate is illuminated at an angle close to 90 °, that is, 80 ° to 89 ° with respect to the substrate surface, most of the illumination light is reflected by the surface of the substrate, and information on the surface of the substrate is mainly extracted. In the first light receiving step and the second light receiving step, predetermined light of light including information on the surface of the substrate is selectively received, so that a defect corresponding to the selected light is detected under different conditions. Detected.
[0014]
In the above method, as described in claim 5 , the first light receiving step and the second light receiving step selectively receive predetermined diffracted light, scattered light or specularly reflected light generated on the substrate. Is desirable.
[0015]
In this case, if the selected light is specularly reflected light, the information on the film thickness unevenness, stains and dirt on the substrate surface is diffracted light, the pattern information on the substrate is scattered light, and if the light is scattered light, Information on surface scratches and foreign objects is mainly picked up. Then, in the process of detecting defects, defects related to those substrates are detected.
[0016]
In the above method, as described in claim 6 , the defect detecting step includes the information obtained in the first light receiving step and the second light receiving step and the reference information indicating the reference state of the substrate. You may further provide the process of comparing.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
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 of FIG.
[0018]
As shown in FIG. 1, the illumination optical system 10 is fixed relative 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.
[0019]
In the illumination optical system, a light guide 11 that supplies illumination light is arranged with its light exit end face 12 facing the substrate W. 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 such that the emission end face 12 is positioned at the focal position in the light traveling direction of the emission end face 12. In the traveling direction of light from the exit end face 12 arranged and reflected by the cylindrical concave mirror 13, a cylindrical concave mirror 14 having power in a direction perpendicular to the normal line is positioned so that the exit end face 12 is located at the focal position. Is arranged.
[0020]
Here, the illumination optical system 10 is configured so that light from the emission end face 12 reflected by the cylindrical concave mirror 14 is incident on the surface of the substrate W placed on the sample stage 20 at an angle of 80 ° to 89 °. Is arranged. That is, the optical axis of the illumination optical system 10 is arranged on the surface of the substrate W placed on the sample stage 20 so as to have the above-described angle.
[0021]
With this configuration, the light emitted from the exit end face 12 of the light guide 11 is substantially in both the normal direction of the substrate surface, that is, the vertical direction, and the normal direction of the substrate surface, that is, the horizontal direction. The light beam L1 is parallel, and the substrate W is incident on the substrate W at an incident angle close to 90 ° (a grazing 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 for reflection and refraction of light at different boundary surfaces of the medium. Information can be retrieved.
[0022]
Also, the numerical aperture (NA) of the illumination optical system that illuminates the substrate W is perpendicular to the plane direction including the normal of the substrate surface and the optical axis of the illumination optical system 10, in FIG. The shape of the end surface 12 of the light guide 11 is preferably a size proportional to the focal length of each of the cylindrical concave mirror 13 and the cylindrical concave mirror 14 so that the direction of the light guide 11 is equal.
[0023]
On the other hand, a light receiving optical system 30 that receives light from the substrate including information on the surface state of the substrate is provided in the traveling direction 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 specularly reflected light from the substrate W, that is, in this embodiment, the reflection angle on the substrate is the same as the incident angle of 80 ° to 89 °. It is arranged in the direction opposite to the normal at the incident point at an angle. 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 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 be.
[0024]
Accordingly, the parallel light beam L2 specularly reflected by the substrate W is reflected by the concave reflecting mirror 31 and condensed at the entrance pupil position of the imaging lens 32, and the specular reflection image on the surface of the substrate W is converted into a two-dimensional image sensor 33. Tie on top.
[0025]
Here, also from the viewpoint of illumination efficiency, it is desirable that the numerical aperture (NA) of the illumination optical system 10 and the numerical aperture of the light receiving optical system 30 are substantially aligned.
[0026]
If there is an abnormal level difference due to resist coating unevenness on the surface of the substrate W or partial exposure abnormality, etc., the reflectivity will reflect such an abnormality, which is different from that of a normal substrate. Thus, an abnormality can be detected.
[0027]
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).
[0028]
sinθd−sinθi = mλ / p (1)
When the incident angle is close to 90 °, sin θi in equation (1) is almost equal to 1. Therefore, if sin θi = 1 is set, equation (1) is
sinθd = mλ / p + 1 (2)
It becomes.
[0029]
When receiving diffracted light, the light receiving angle determined by the equation (1) must be set according to the pitch information of the pattern, but by rotating the entire light receiving optical system 30a around the center of the substrate W, By adjusting the light reception angle and setting the emission angle from the substrate surface to the diffraction angle θd obtained by the equation (1) as shown by the broken line in FIG. 1, an image by the diffracted light L3 can be obtained. it can.
[0030]
Here, if the pattern level difference and the ratio of unevenness (duty ratio) are different from the normal pattern, the diffraction efficiency will be different and the brightness of the diffraction pattern will be different from that of the normal pattern. By comparing, abnormality can be inspected.
[0031]
The point that the incident angle of the illumination system is set to about 90 ° to increase the surface reflectance and efficiently receive the diffracted light from the surface is the same as in the case of receiving regular reflection light. As another method for changing the light receiving angle, the entire stage STG may be tilted 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 perpendicular to the optical axis of the illumination optical system 10.
[0032]
When receiving scattered light, it is desirable to set the light receiving optical system 30 in such a direction that the diffracted light from the pattern does not directly enter the two-dimensional image sensor 33. Although detection of scattered light is effective for detecting foreign matter and scratches on the substrate W, scattered light from the scratches is strongly emitted in a direction perpendicular to the scratches, and therefore the direction in which the scattered light should be received differs depending on the direction of the scratches. . Therefore, the sample stage 20 on which the substrate W is placed has a structure that can rotate 360 °. The sample stage 20 is rotated by a rotation mechanism 50 (see FIG. 1) provided on the substrate stage STG, which has a rotation axis parallel to the upper surface of the sample stage 20 on which the substrate W is placed, and thus the normal line of the surface of the substrate W. Is done. The rotation mechanism 50 may be mounted on the substrate stage STG.
[0033]
In this way, the substrate W is inspected in two directions of at least 0 ° and 45 ° around the normal. This is the same as the above-described two methods in that the abnormality is inspected by comparing the image at each rotation angle with the image of the normal pattern.
[0034]
As described above, an optimum observation direction can be set by selecting an arbitrary light receiving angle and rotating the substrate surface around the normal to observe the surface of the substrate from different directions. In addition, it is possible to inspect a defect on the substrate based on a plurality of pieces of image information obtained under different conditions.
[0035]
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 by the reflected light. It is.
[0036]
Next, an embodiment of a defect inspection method for a substrate according to the present invention will be described with reference to FIGS. FIG. 3 shows a flow of inspection performed by selectively starting diffracted light after the start of inspection, and FIG. 4 shows a flow of inspection performed by selectively receiving specularly reflected light. FIG. 5 shows a flow from an inspection performed by selectively receiving scattered light to a determination of whether the substrate is good or defective and the completion of the defect inspection method.
[0037]
First, as shown in FIG. 3, in the present embodiment, information on the pattern formed on the substrate is read (step SP1). It is determined whether the pattern is a periodic pattern (step SP2). If the pattern is not a periodic pattern, an inspection performed by receiving diffracted light is unnecessary, and an inspection that receives specularly reflected light (FIG. 4, FIG. 4). You may bypass to process SP8) (X1).
[0038]
In the case of a periodic pattern, for example, a line and space pattern, the rotation angle around the normal line on 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).
[0039]
Further, the diffraction angle with respect to the pattern pitch is calculated according to the formula (1) or the formula (2) (step SP4). The light receiving angle is set to the diffraction angle θd obtained by the calculation (step SP5). Of course, step 3 may be after step 5.
[0040]
Illumination light is irradiated at an incident angle close to 90 ° on the surface of the substrate whose direction and inclination are set as described above (step 6). Then, information on the surface of the substrate is taken in and diffracted light generated from the substrate is received. Here, the light receiving angle may be further adjusted to the most appropriate angle while receiving the diffracted light.
[0041]
The captured image is compared with a reference image prepared in advance that gives a substrate-free state (step 8). The substrate is placed in a defective product tray (X3, FIG. 5, step 28).
[0042]
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).
[0043]
If the information about the pattern formed on the substrate is known in advance as the characteristics of each substrate, the reading step SP1 and the periodic pattern determination step SP2 are omitted, and the direct X1 or less described below will be omitted. The present inspection method may be started from the regular reflection light receiving step or the irregular reflection light receiving step.
[0044]
With reference to FIG. 4, the inspection process performed by receiving regular reflection light will be described. First, the light receiving angle is set to be the same as the incident angle of the illumination light (step SP11). Next, the illumination light is irradiated at an incident angle close to 90 ° on the surface of the substrate with the inclination (the light receiving angle) set (step 12). Then, the information on the surface of the substrate is taken in and the regular reflection light reflected from the substrate is received, and the regular reflection image is taken in. Here, the light receiving angle may be further adjusted to the most appropriate angle while receiving the reflected light.
[0045]
The captured regular reflection image is compared with a reference image prepared in advance that gives a substrate state without defects (step 14). Such a substrate is placed in a defective product tray (X3, FIG. 5, step 28). If it is determined in step 14 that the image is the same as the reference image, the process proceeds to the next step (X2, FIG. 5, step SP21).
[0046]
With reference to FIG. 5, an inspection process performed by receiving irregularly reflected light will be described. First, the light receiving optical system is set to a light receiving angle suitable for receiving irregularly reflected light with respect to the substrate. Diffuse reflected light is emitted in almost any direction, unlike the case of regular reflection or diffracted light. For example, if it is set in a direction that avoids regular reflected light, or a direction that avoids the directions of primary and secondary diffracted light, Efficient observation with irregularly reflected light is possible.
[0047]
Illumination light is irradiated at an incident angle close to 90 ° on the surface of the substrate thus set in direction and inclination (step 22). Then, the scattered light generated from the substrate is received by taking in information on the substrate surface. Here, the light receiving angle may be further adjusted to the most appropriate angle while receiving scattered light again.
[0048]
The captured image is compared with a reference image prepared in advance that gives a substrate-free state (step 24). The substrate is placed in a defective product tray (X3, step 28). Then, it is determined whether or not a substrate to be inspected still remains (step SP29).
[0049]
If it is determined in step 24 that the image is the same as the reference image, it is next determined whether to observe from another angle around the normal of the substrate surface. If the image is observed from another angle, the substrate is rotated here. Then (step SP26), the process returns to step SP21, and the inspection performed by receiving scattered light at that position is repeated.
[0050]
If it is determined in step 25 that there is no need to further rotate and observe the substrate, the substrate is placed in a non-defective tray (step SP27). Then, it is determined whether or not there is still a substrate to be inspected (process SP29).
[0051]
If there are still substrates to be inspected, the next substrate is placed on the inspection table (step SP30), and it is determined whether the substrate is the same type as the previously inspected substrate. Returning to 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, so the process returns to step SP2.
[0052]
If it is determined in step 29 that all the substrates have been inspected, the inspection ends (END).
[0053]
As described above, the case where the process is performed in the order of the diffracted light receiving process for receiving the periodic pattern, the regular reflected light receiving process, and the irregularly reflected light receiving process has been described. However, the order is not limited to this, for example, regular reflection or irregular reflection. The order of diffracted light may be used. In the case of a substrate having no periodic pattern, the diffracted light reception inspection may be omitted, but in general, the regular reflection process and the irregular reflection process are not omitted.
[0054]
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.
[0055]
As described above, when a transparent thin film or the like is applied on a repetitive pattern having periodicity and the surface state of a sample with a substantially flat surface is inspected, the foreign matter is detected by detecting scattered light from the foreign matter. Can be detected. Further, the film thickness unevenness on the surface can be detected because the regular reflection image on the surface has uneven brightness.
[0056]
Here, in order to increase the reflectance of the surface as much as possible and prevent the illumination light from reaching the lower layer, the incident angle of the illumination system is set to 80 ° to 89 ° and as close to 90 ° as possible. Desirably, the angle is 87 ° to 89 °. For example, in one embodiment, the incident angle is 88 °. In this case, most of the illumination light (90% or more) is reflected on the surface. FIG. 1 shows the case where the incident angle is 88 °, but FIG. 1A shows the periphery 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.
[0057]
In addition, for samples where the surface layer and lower layer have different repeated pattern pitches, diffracted light must be received in accordance with the pattern pitch of the layer to be inspected. Even when the light cannot be separated well (when the pitch is an integral multiple), the incident angle of the illumination system is also set to 80 ° to 89 ° and as close to 90 ° as possible. Furthermore, it is desirable to set it as 87 degrees-89 degrees. For example, in the preferred embodiment, the incident angle is 88 °. By doing in this way, the surface reflectance of a board | substrate can be improved and the diffracted light from the surface can be received efficiently.
[0058]
Thus, by selecting an optimum detection mode according to the sample, it is possible to perform a highly reliable inspection for various defects in each process.
[0059]
The illumination optical system 10 and the light receiving optical system 30 are preferably telecentric optical systems. If comprised in this way, illumination is performed with the same incident angle over the whole surface of a to-be-inspected board | substrate, and it can observe with the same light receiving angle. Therefore, it is not necessary to change the inclination of the substrate little by little, as is often done by visual inspection to inspect defects on the substrate surface.
[0060]
Further, the illumination optical system 10 may be composed of two groups of optical elements having different powers in the orthogonal direction, and the dimensional shape of the aperture stop may be inversely proportional to the power.
[0061]
As described above, according to the present invention, an optimal detection mode can be selected from reflected light, diffracted light, and scattered light according to the sample substrate, and reliability against various defects in various processes can be selected. High inspection is possible.
[0062]
Moreover, since the apparatus is configured to obtain surface image information, it is desirable to perform these inspections at the end of each process.
[0063]
These methods can be applied not only to detection of semiconductor wafers but also to detection of defects and foreign matters on large substrates for liquid crystals.
[0064]
【The invention's effect】
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 on the surface of the substrate, and the surface defect which is the first layer is detected. It becomes possible to do. In addition, since predetermined light is selectively received from the surface of the substrate, for example, any of the specularly reflected light, scattered light, and diffracted light can be selected and received, and it is suitable for detection with those lights. Makes it possible to detect defects. In this way, various defects for 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 apparatus of the present invention.
FIG. 2 is a plan view of the apparatus of FIG.
FIG. 3 is a flowchart showing a portion of a method performed by receiving diffracted light in the embodiment of the defect detection method of the present invention.
FIG. 4 is a flowchart showing a portion of a method performed by receiving regular reflection light in the embodiment of the defect detection method of the present invention.
FIG. 5 is a flowchart showing a portion of a method performed by receiving scattered light in the embodiment of the defect detection method of the present invention.
[Explanation of symbols]
10 Illumination optical system 11 Light guide (optical fiber)
12 exit end face 13 cylindrical concave mirror 14 cylindrical concave mirror 20 sample stage 30 light receiving optical system 31 concave reflecting mirror 32 imaging lens 33 two-dimensional image sensor 40 light receiving angle setting means 50 rotating mechanism θi incident angle θd diffraction angle W substrate STG substrate stage L1 incident Light L2 Reflected light L3 Diffracted light

Claims (6)

A substrate defect inspection apparatus;
An illumination optical system disposed with an optical axis at an angle of 80 ° to 89 ° with respect to the normal of the surface of the substrate;
Light receiving means for receiving light including information on the surface of the substrate illuminated by the illumination optical system;
A 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 that rotates the substrate about an axis that intersects the surface of the substrate;
The light receiving means is configured to receive the light at a plurality of rotation angles by rotating the substrate by the rotation mechanism ;
Substrate inspection system. The light is specularly reflected light or diffracted light ;
The defect inspection apparatus for a substrate according to claim 1 . The substrate according to claim 1 or 2 , wherein the light reception angle setting means is configured to set the light reception angle by integrally tilting the illumination optical system and the substrate. Defect inspection equipment. An illuminating step of illuminating the substrate with an incident angle of 80 ° to 89 ° with respect to the surface of the substrate;
A first light receiving step for selectively receiving predetermined light of light including information on the surface of the substrate generated in the substrate illuminated in the illumination step;
The substrate is rotated about an axis intersecting the surface of the substrate, and predetermined light is selectively received from light including information on the surface of the substrate from a direction different from that of the first light receiving step. A second light receiving step ;
A step of detecting a defect of the substrate based on information obtained in the first light receiving step and the second light receiving step ;
Substrate defect inspection method. The first light receiving step and said second receiving step, characterized by selectively receiving a predetermined diffracted light, scattered light or specular light produced by said substrate; according to claim 4, Substrate defect inspection method. The step of detecting the defect further comprises a step of comparing information obtained in the first light receiving step and the second light receiving step with reference information indicating a reference state of the substrate; 6. The substrate defect inspection method according to claim 4 or 5 .

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