JP2000311925A - Appearance inspection device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To detect a defective portion such as uneven resist coating on a semiconductor substrate. A light source that irradiates a semiconductor substrate with light, a conversion unit that converts reflected light from the surface of the semiconductor substrate into image information, and an emphasis that emphasizes defect information of the semiconductor substrate included in the converted image information Means, in advance, non-defective reference information storage means for storing non-defective reference information of various positions on the semiconductor substrate and various regions, setting means for setting a measurement position and a measurement area on the semiconductor substrate, Integrating means for integrating the emphasized image information of the measured position and measurement area, and comparing the integration result with the non-defective reference information of the same position and the same area as the integration result to determine whether the semiconductor substrate is good or bad. A determination unit for determining a defect; and a control unit for controlling a series of processes to be repeated so that the measurement position and the measurement region of the setting unit are variously changed and the semiconductor substrate is covered. Have.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visual inspection apparatus for inspecting the appearance of a semiconductor substrate (wafer), and more particularly to a visual inspection apparatus for a patterned wafer for detecting a defective portion such as uneven resist coating.

[0002]

2. Description of the Related Art Defects of a wafer with a pattern include fine pattern defects having a size of sub-μm to several μm, foreign matters, or film thicknesses over the entire wafer or the entire chip, depending on the size and appearance of the defect. Includes pale abnormalities such as unevenness, shallow scratches, and spots.

[0003] In particular, for macroscopic light defects, conventionally, a wafer is illuminated from an arbitrary angle and visually inspected, and in addition to Japanese Patent Application Laid-Open Nos. 8-247958 and 9-1.
Japanese Patent Application Laid-Open No. 72044 discloses a method of measuring a luminance value of scattered light when illumination is applied.

According to the means disclosed in Japanese Patent Application Laid-Open No. 8-247958, the chip is divided into areas with uniform luminance distribution (inspection window), and the average luminance value, upper limit value, and lower limit value in the inspection window are determined for non-defective wafers. Calculate the value.
Similarly, regarding the defective sample, a lower limit is set for a defect having a high luminance value, and an upper limit value is set for a defect having a low luminance value. After sufficiently acquiring such data statistically, an upper limit threshold and a lower limit threshold for separating good / defective products are determined. This threshold is, for the same type of wafer,
It is applied uniformly, and is applied uniformly regardless of the position in the wafer.

Further, according to the means disclosed in Japanese Patent Application Laid-Open No. 9-172444, reflected light / scattered light from a minute area is captured by a slit or pinhole camera, and the upper limit and lower limit of the non-defective luminance value are set for each wafer type. Set the inspection area to 2 according to the tilt angle and rotation angle of the wafer holding stage.
Measurement / inspection is performed by dividing into dimension matrix areas.

[0006]

As one of the above-mentioned light defects, there is a resist coating defect caused by surface foreign matter. Usually, the resist coating uses a spin coating method in which a resist solution is injected into the center of a rotating wafer and the resist is diffused toward the outer periphery of the wafer using centrifugal force to form a uniform film thickness. FIG. 12 shows a coating state as viewed from the upper surface of the wafer. In FIG. 12, the resist diffuses in the direction of the white arrow in the figure.

FIG. 13 shows the above spin coating method.
FIG. 5 is a cross-sectional view of a flow of a resist when a foreign substance is present on a wafer surface as viewed from a lateral direction. If foreign matter or precipitates are present on the wafer surface during resist coating, the resist solution spreads over these. After getting over foreign substances and precipitates, the amount of surface adhesion changes, and a phenomenon occurs in which the film thickness is locally different from other parts. As a result, abnormalities in resist coating occur not only in places where foreign matter and precipitates are present but also in the radial direction of rotation.

[0008] When viewed from above, the defect appears as a radial defect directed outward from the position where the foreign matter is located, as shown in FIG. This defect is observed as a change in the luminance of reflected light with respect to illumination because the reflectance varies depending on the film thickness and the size of the step of the film.

However, even in the case of a non-defective resist coating in which both the average film thickness and the film thickness variation are within the standard, the degree of scattering differs due to the surface condition of the film, differences in film components, changes over time in illumination, and the like. There are cases. As a result, an offset is applied to the luminance level, such as overall bright or dark, and a state where the luminance values are not the same even though the wafers are the same type of normal wafer occurs.

[0010] On the other hand, the linear resist coating defect is measured as a minute defect having a small change in luminance.
In some cases, the defect is included in the upper limit value and the lower limit value of the luminance of the non-defective product, and the determination becomes impossible. For example, even if a resist application failure occurs on a wafer having a high luminance value and the luminance value in the defective portion is locally reduced, it is within the non-defective range and does not always exceed the lower limit of the non-defective range.

[0011]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving the above-mentioned problems, and the invention according to claim 1 comprises a light source for irradiating light to a semiconductor substrate to be inspected. Converting means for converting the reflected light from the surface of the semiconductor substrate into image information; emphasizing means for emphasizing defect information of the semiconductor substrate included in the image information converted by the converting means; Position, non-defective reference information storage means for storing non-defective reference information of various regions, setting means for setting a measurement position and a measurement area on the semiconductor substrate, and a measurement position and a measurement area set by the setting means. Integrating means for integrating the image information enhanced by the enhancing means; comparing the integration result of the integrating means with the non-defective reference information in the same position and in the same area as the integration result; A determination unit for determining whether the substrate is good or defective; and a control unit for controlling a series of processes to be repeated so as to cover the semiconductor substrate by changing a measurement position and a measurement region of the setting unit in various ways. A visual inspection apparatus characterized in that:

The invention according to claim 2 is characterized in that the measurement region is represented by a region surrounded by a concentric circle having two different radii (R1, R2) and two straight lines having an intersection angle θ. An appearance inspection apparatus according to claim 1.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of the appearance inspection apparatus of the present invention. The appearance inspection apparatus of the present invention will be described with reference to FIG.
As shown in FIG. 1, a wafer 2 to be inspected is placed on an XY stage 1 and is movable in a horizontal direction.

The light of the light source 4 is projected on the surface of the wafer 2 and
The scattered light reflected on the wafer surface forms an image on the imaging surface of the camera 5 by the lens 3 to obtain an image of the wafer surface. The formed pattern image is converted into a digital signal by the A / D converter 7 and stored in the image data storage unit 8 as image data.

The image data stored in the image data storage section 8 is emphasized by a defect emphasizing section 9 at a defective portion and sent to an integration processing section 10. The integration processing unit 10 calculates the sum of pixel values (area value) for the inside of the calculation area set by the measurement area setting unit 11. Here, the calculation region is set by changing its size and position, and the calculation of the area value is performed each time.

At the time of generating reference data using a good wafer,
The result of the calculation performed by the integration processing unit 10 is a non-defective reference data storage unit 1.
3 is stored. In the case of a wafer inspection, the calculation result of the integration processing unit 10 and the data of the non-defective reference data storage unit 13 are compared by the determination processing unit 12 to determine good or bad.

The control relating to the above processing is performed by the overall control unit 6.
It is performed by

Next, the processing of the defect emphasizing section 9 will be described in detail.

The linear resist coating defects targeted in the present invention are minute as described above, and the change in the luminance level of the scattered light is small. In the defective portion, the scattered luminance value is smaller (darker) or larger (brighter) than the surroundings due to a film step or the like.

For example, when the luminance value of a defective portion which looks dark is represented by a luminance value distribution on a line traversing a coating defective portion as an image density after A / D conversion, as shown in FIG. It has an extremely low luminance value.

As an example of a method of enhancing such a local density change, a differentiation process shown in Expression 1 or Expression 2 is used.

{(Ad) ² + (bc) ² } ... Equation 1 | A + 2B + CG-2H-I | + | A + 2D + GC-2F-I | ... Equation 2 where a, b , C, d represent the gray levels of the pixels of the digital image shown in FIG. 3 (A), and A, B, C, D, E,
F, G, H, and I represent the gray levels of the pixels of the digital image shown in FIG.

FIG. 4 shows the result of differentiating the defective portion shown in FIG. 2. The density level of the defective portion is increased, and the defect is emphasized.

For example, when this is performed on the wafer image of FIG. 5, only a defective portion becomes an image (emphasized image) which is emphasized as compared with a normal portion as shown in FIG. Numerous methods other than the above two methods have been proposed as the differential processing method, and an optimum method can be selected according to the image state. Therefore, means other than the above two methods may be used in the defect emphasizing section 9. In some cases, the density value of the defective portion is higher than that of the normal portion, but the result is the same when the differential processing is performed.

At the stage where the processing in the defect emphasizing section 9 is completed, a minute change in density due to a video signal, a noise component of a camera, a pattern, and the like is simultaneously emphasized. Normally, since the contrast of the defective portion is low, if a portion where the density of the emphasized image is equal to or higher than the reference value is uniformly determined to be defective, erroneous detection is performed on portions other than these defective portions as shown in FIG.

In general, when such minute density changes such as noises and patterns are emphasized, the grayscale values are dispersed at a low value and appear uniformly on the entire surface of the wafer. On the other hand, the defective portion appears in a special shape due to the cause. For example, in the case of poor resist coating, a radial line is formed from the center. Here, means for increasing the detection sensitivity of the defective portion by using such a feature is employed. The means will be described below.

As shown in FIG. 7, an area represented by an overlap between a rectangular area passing through the center of the wafer and an annular area surrounded by two concentric circles is set as a measurement area on the wafer. For example, the hatched portion in FIG.
A region surrounded by two concentric circles, and a region surrounded by a rectangular region having a width w and having an intersection angle θ.

FIG. 8 shows the positional relationship between the measurement area and the defective part.

FIG. 8A shows a case where an emphasized defect exists in the measurement area, and the area value becomes large.

FIG. 8B shows a case where no defect exists in the measurement area. Generally, the value of the area is sufficiently smaller than that of FIG. 8A.

FIG. 8 (C) shows a case where an emphasized defect is partially present in the measurement area, and the area value in the area is an intermediate value between FIGS. 8 (A) and 8 (B). I take the.

FIG. 8D shows a case where the measurement area is larger than the defective area. Since a defective portion and an unnecessary emphasized portion other than the defective portion are included, the value becomes larger than the value of FIG.

In general, when there is no defect, for the same reason as in FIG. 8B, the area value is proportional to the size of the area area. 8A, the value of the area per unit area is larger than that of the area without the defect. That is, the detection sensitivity is the highest in the area value in the measurement region where the size (width, length) matches the defective portion.

Here, since the size and position of the defective region are unknown, the size (width, length) of the measurement region is changed and the position is also changed, and the area component value is obtained over the entire wafer. Then, the value is compared with the area value for each size (width, length) of each measurement region when there is no defect. According to such a method, when the resist application defect and the measurement region match in both size and position, the detection sensitivity of the defective portion can be increased relatively to a noise component that is not a defective portion or a minute change in the pattern. .

Next, a method of registering an inspection standard and a method of performing an inspection will be described with reference to FIGS. 9, 10 and 11. FIG.

FIG. 9 is a flowchart of a non-defective reference data registration process performed using a non-defective wafer.

First, in the image input in the process 100, an image in which the above-mentioned defect is emphasized is created in the process 101. Next, the measurement area size and position are initialized in processing 102, 103, and 104, the measurement area A is set on the enhanced image in processing 105, and the area value G (A) in the measurement area A of the enhanced image is set in processing 106. ). The result is
In step 7, the area value G (A) is classified for each measurement area A having the same set value of L, and stored in the non-defective reference data storage unit 13 as non-defective reference data.

In process 108, it is determined whether L satisfies the termination condition (whether the size exceeds the wafer size). If not, the size is increased by a certain amount (process 1).
12) Return to processing 105 again. If the area L exceeds the wafer size, the process is terminated.

For example, A (0), A (1), A (2),.
(N), assuming that the measurement area A (i) is an area as shown in FIG. 10A, the measurement area A (i + 1) is an area whose size is larger than A (i) by L1. Where A
The size in _{(i) L A (i)} , when the A (i + 1) the size in the L _{A (i + 1),} the _{L A (i + 1) =} L A (i) + L1.

In steps 109 and 113 and steps 110 and 114, the position of the area is changed by a fixed amount, and the same processing is repeated.

As described above, when the processing 110 satisfies the termination condition, the non-defective reference data is obtained for the entire area on the wafer whose size and position have been changed, and the processing 111 ends.

Processing 102, 103, 104, 10
5,108,109,110,112,113,114
Is performed by the measurement area setting unit 11, and the processing 106 and 107 are performed by the determination processing unit 12.

Further, in order to increase the reliability of the non-defective reference data, the above process is repeated even when the process is performed on a plurality of non-defective wafers.

FIG. 11 is a flowchart at the time of wafer inspection.

First, in the image input in the process 200, an image in which a defect is emphasized in the process 201 is created.
Next, the measurement area size and position are initialized in processes 202, 203, and 204, and the measurement region A on the emphasized image is set in process 205. Measurement area A of the emphasized image in process 206
Of the area G (A) is obtained. Processing 20
In 7, the non-defective reference data stored in the non-defective reference data storage unit 13 is compared with non-defective reference data having the same L. If it is smaller than all the applicable non-defective standard data, it is determined to be within the non-defective standard, and the process is continued. On the other hand, if there is a value larger than or equal to the relevant non-defective reference data, it is determined to be defective.

Then, as in the flowchart of the registration process, it is determined in step 208 whether L satisfies the termination condition. If L is not satisfied, the size is increased (step 213), and the process returns to step 205 again.

In steps 209 and 214 and steps 210 and 215, the position of the area is changed, and the same processing is repeated.

As described above, when the processing 210 satisfies the termination condition, the entire area on the wafer whose size and position are changed is within the non-defective product standard, so it is determined to be non-defective and the process ends.

Processing 202, 203, 204, 20
5,208,209,210,213,214,215
Is performed by the measurement area setting unit 11, and the processing 206 and 207 are performed by the determination processing unit 12.

Further, the settings of R1, θ1, L0, and L1 used in the process of changing the measurement area can be changed according to the required inspection accuracy and speed.
The range of L, R, and θ is, for example, 0 ≦ θ ≦ 2 when the size of a defect to be detected in the R direction is 10 mm or more for a wafer having a diameter of 8 inches (203.2 mm).
π, 0 ≦ R ≦ (101.6-L) mm, 10 mm ≦ L ≦
101.6 mm, and L0 may be 10 mm or less.

In the above processing, a CCD camera is used as an image input means, but an image pickup means using another photoelectric conversion element may be used.

[0053]

According to the first and second aspects of the present invention, fine and light linear resist coating defects radially generated in the radial direction of rotation can be prevented from being reflected by the reflection efficiency of the entire semiconductor substrate. Detects with high sensitivity and high reliability without being affected by the offset of the luminance level caused by the influence or the fluctuation of the overall level due to the aging of the light source, and by suppressing the influence of noise and patterns. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of a visual inspection device of the present invention.

FIG. 2 is a diagram showing an example of image density around a defective coating.

FIG. 3 is a diagram illustrating neighboring pixels in a differentiation process.

FIG. 4 is a diagram illustrating an example of a defect emphasized image density around a coating defect.

FIG. 5 is a view for explaining an image state of a wafer having a resist coating failure.

FIG. 6 is a diagram illustrating an image of a wafer having a resist coating failure after an emphasis process.

FIG. 7 is a diagram illustrating a method for setting a measurement area.

FIG. 8 is a diagram illustrating a relationship between a measurement area position and a defective position.

FIG. 9 is an operation flowchart when non-defective reference data is registered.

FIG. 10 is a diagram illustrating setting of a measurement area.

FIG. 11 is an operation flowchart at the time of inspection.

FIG. 12 is a diagram illustrating a resist coating method.

FIG. 13 is a view for explaining a state of occurrence of resist coating failure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 XY stage 2 Wafer 3 Lens 4 Light source 5 CCD camera 6 Overall control unit 7 A / D conversion means 8 Image data storage unit 9 Defect enhancement unit 10 Area calculation unit 11 Measurement area setting unit 12 Judgment processing unit 13 Good quality reference data storage Unit 21 image input unit 22 image processing unit

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H01L 21/30 564C F-term (Reference) 2F065 AA49 BB03 CC19 CC31 FF42 HH12 JJ03 JJ09 JJ26 PP12 QQ03 QQ13 QQ14 QQ24 QQ25 RR01 RR09 2G05 A1 AB01 AB02 AB20 CA04 DA07 EA08 EA09 EA11 EA14 EB01 EB09 EC01 ED01 ED05 ED09 ED14 4M106 AA01 BA04 CA39 DB04 DB07 DB30 DJ04 DJ11 DJ12 DJ13 DJ18 DJ19 DJ21 5F046 JA04 JA21 JA22

Claims (2)

[Claims] A light source for irradiating a semiconductor substrate, which is an object to be inspected, with light; a conversion unit for converting reflected light from the surface of the semiconductor substrate into image information; and the image information converted by the conversion unit. ,
Emphasizing means for emphasizing defect information of the semiconductor substrate; previously, various positions on the semiconductor substrate, a non-defective reference information storage means for storing non-defective reference information of various regions, and a measurement position and a measurement area on the semiconductor substrate. Setting means for setting; integrating means for integrating the image information of the measurement position and the measurement area set by the setting means emphasized by the emphasizing means; integration results of the integrating means; ,
A determination means for comparing the non-defective reference information of the same area to determine whether the semiconductor substrate is good or defective; and a method for changing the measurement position and the measurement area of the setting means in various ways to cover the semiconductor substrate. And a control means for performing control so as to repeat the above processing. 2. The method according to claim 1, wherein the measurement area is defined by two different radii (R).
The visual inspection device according to claim 1, wherein the visual inspection device is represented by a region surrounded by a concentric circle of (1, R2) and two straight lines having an intersection angle θ.