JP2008039465A - Visual examination system and visual examination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a visual examination system capable of detecting large abnormalities that are not received in a visual field without overlooking the same, and to provide a visual examination method. <P>SOLUTION: The visual examination system has acquiring means (S1 and S2) for setting the partial region of the surface of matter in the visual field, to acquire the image thereof and a deciding means (S4) for deciding the existence of the abnormalities of protruding from the visual field on the surface of the matter. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an appearance inspection apparatus and an appearance inspection method used for observing an object surface.

In order to detect an abnormality such as a defect by observing the surface of an object such as a semiconductor wafer, an apparatus that acquires and processes an image of a partial region of the surface is known (see, for example, Patent Document 1). At the time of processing, the acquired image of the partial area and the reference image are compared, and an abnormality detection process such as a defect is performed within a single field of view corresponding to the partial area image.
JP 2001-118896 A

However, since the above apparatus performs an abnormality detection process within a single visual field, there is a problem that even if there is a large abnormality (for example, a cluster defect) that does not fit in the visual field, this is missed.
An object of the present invention is to provide an appearance inspection apparatus and an appearance inspection method capable of detecting without overlooking a large abnormality that does not fit in the visual field.

The appearance inspection apparatus according to the present invention includes an acquisition unit configured to set a partial area of the surface of the object in the field of view and acquire an image of the partial area, and a size that protrudes from the field of view on the surface based on the image. Determination means for determining whether or not there is an abnormality.
Further, in the above appearance inspection apparatus, when it is determined that there is an abnormality, the acquisition unit relatively moves the object and the visual field to reset the protruding portion of the abnormality in the visual field. The image of the area including the protruding portion is further acquired.

Further, in the above appearance inspection apparatus, when the acquisition unit determines that there is an abnormality, the acquisition unit moves the object and the field of view relative to each other by the size of the field of view and includes the protruding portion. The image of is acquired.
The appearance inspection apparatus may further include a generating unit configured to combine the image of the partial region acquired by the acquiring unit and the image of the region including the protruding portion to generate a composite image related to the abnormality. It is a thing.

According to the appearance inspection method of the present invention, a partial region of the surface of an object is set in a visual field, an image of the partial region is acquired, and an abnormality of a size that protrudes from the visual field on the surface is based on the image. It is to determine the presence or absence.
Further, in the above appearance inspection method, when there is the abnormality, the object and the visual field are relatively moved to reset the abnormal protruding part in the visual field, and an image of the region including the protruding part is obtained. To get more.

In the appearance inspection method described above, when there is an abnormality, the object and the field of view are relatively moved by the size of the field of view, and an image of an area including the protruding portion is acquired.
In the appearance inspection method, the image of the partial region and the image of the region including the protruding portion are synthesized to generate a composite image related to the abnormality.

  According to the present invention, it is possible to detect without missing a large abnormality that does not fit in the field of view.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the appearance inspection apparatus 10 of the present embodiment includes a stage 12 that supports a wafer 11, a transfer control mechanism unit 13 connected to the stage 12, and an optical microscope unit that is disposed above the stage 12. (14, 15) and a computer 16 are provided. The appearance inspection apparatus 10 is used for observing, for example, a circuit pattern formed on the surface 1A of the wafer 11 in a semiconductor element manufacturing process.

The stage 12 moves the wafer 11 in the XY directions based on a control signal from the transfer control mechanism unit 13 when observing the wafer 11. The optical microscope section (14, 15) includes an objective lens 14, a CCD camera 15, and an illumination system (not shown). The field of view of the optical microscope section (14, 15) corresponds to a partial region of the surface 1A of the wafer 11.
Control signals from the computer 16 are output to the optical microscope section (14, 15) at an appropriate timing. Based on this control signal, the optical microscope section (14, 15) acquires an enlarged image (hereinafter referred to as “microscope image”) of a partial region of the surface 1 A of the wafer 11 and outputs it to the computer 16.

  In the computer 16, the microscope image of the wafer 11 acquired by the optical microscope unit (14, 15) is processed, and a circuit pattern defect or foreign matter on the surface 1 A of the wafer 11 is automatically detected. What is detected includes scratches and pseudo defects in addition to defects and foreign matter. In this case, these are collectively referred to as “abnormal”. Further, the computer 16 appropriately displays a microscope image of the wafer 11 on the monitor 6A so that the operator can observe it.

Next, a specific example of the observation operation of the wafer 11 in the appearance inspection apparatus 10 will be described.
The observation recipe is stored in advance in the computer 16, and the computer 16 executes an observation operation according to the recipe. An example of the procedure is shown in the flowchart of FIG.
When the wafer 11 to be observed is placed on the stage 12, the computer 16 first (step S 1) sends information on the observation position registered in the recipe on the surface 1 A of the wafer 11 to the transfer control mechanism unit 13. Output.

  Therefore, the transfer control mechanism unit 13 performs transfer control (XY direction) of the stage 12 based on the observation position information from the computer 16, and sets the observation position specified by the recipe on the surface 1 </ b> A of the wafer 11 to the optical microscope. Set in the field of view (14, 15). At this time, a partial region including the observation position of the surface 1A (hereinafter referred to as “observation region”) is set in the field of view, and an enlarged image of the observation region is formed on the imaging surface of the CCD camera 15 via the objective lens 14. .

Next (step S2), the computer 16 controls the CCD camera 15. Then, a microscope image (see, for example, FIG. 3A) based on an enlarged image of the observation area on the surface 1A of the wafer 11 is acquired from the CCD camera 15. In addition, the computer 16 displays the microscope image on the monitor 6A.
Next (step S3), the computer 16 processes a microscope image (for example, FIG. 3A) and detects an abnormality of the surface 1A of the wafer 11. This abnormality detection process is performed using abnormality detection software installed in the computer 16.

For example, an image of a good sample prepared in advance (for example, FIG. 3B) is used as a reference image, and after the image alignment between the reference image and the above-described microscope image, two images (FIG. 3A) , (b)). That is, a difference intensity is obtained between corresponding pixels of two images, and a difference image (for example, FIG. 3C) is generated from the distribution.
When some circuit pattern is included in the observation area of the surface 1A of the wafer 11, an actual image of the circuit pattern appears in the microscope image (FIG. 3A), and the circuit pattern appears in the reference image (FIG. 3B). The image of a non-defective product is included. For this reason, in the difference image between them (FIG. 3C), not the image of the circuit pattern itself, but a portion (abnormality 20 such as a defect in the circuit pattern) that is different from the non-defective product appears in the actual image.

Then, in order to automatically detect the presence / absence of the abnormality 20 from the difference image (FIG. 3C), a size comparison between each pixel value (difference intensity) of the difference image and a predetermined threshold value is performed. As a result of the comparison, if there is a pixel value portion larger than the threshold value in the difference image, this is determined as abnormality 20. Judge other parts as normal.
In addition, when the abnormality 20 detected in the difference image includes a plurality of types of abnormality 21 and 22 (FIGS. 3D and 3E) having different pixel values, the threshold value is set for the above-described size comparison. Accordingly, these can be detected separately from each other.

  If the above-described abnormality detection process (step S3) is performed, the presence / absence of the abnormality 20 (or abnormality 21, 22) on the surface 1A of the wafer 11 is determined in the field of view corresponding to the microscope image (FIG. 3A). Judgment can be made. However, the above abnormalities are not always within a single visual field. It is quite possible that a large anomaly associated with (or not associated with) anomalies 20-22 detected within the field of view has spread beyond the field of view.

Therefore, in the present embodiment, in order to detect without missing a large abnormality that does not fit in the field of view (hereinafter referred to as a cluster defect as appropriate), the processing after the next step S4 is performed.
In step S4, it is determined whether or not there is an abnormality in the size of the surface 1A that protrudes from the visual field. This determination is made, for example, when the pixel value larger than the threshold used in step S3 is included in each pixel on the four sides of the difference image (FIG. 3C) obtained from the microscope image (FIG. 3A). It may be performed depending on whether or not there is.

When there is no pixel value larger than the threshold value among the pixels on the four sides of the difference image (FIG. 3C), there is no abnormality in the size that protrudes from the visual field on the surface 1A of the wafer 11 (that is, all abnormalities are present). 2 (step S4 is No), the processing of steps S5 to S9 is omitted, and the processing of FIG.
On the other hand, if there is a pixel value larger than the threshold value among the pixels on the four sides of the difference image (FIG. 3C), it is determined that there is an abnormality in the size that protrudes from the field of view on the surface 1A (step S4). Is Yes), the process proceeds to step S5.

In the example of FIG. 3C, since the upper side and the left side of the four sides of the difference image include pixel values (hatched portions) larger than the threshold value, the abnormality 20 is the current visual field (see FIG. 4A). It is thought that it protrudes from the upper side and the left side. In FIG. 4A, the prediction of the protruding portion is illustrated by a dotted line.
In step S5, the stage 12 is controlled in accordance with any one of the protruding directions of the abnormality 20, and the wafer 11 is moved minutely by the size of the visual field in the movement direction with respect to the visual field of the optical microscope section (14, 15). Then, the region 31 (FIG. 4B) including the protruding portion of the abnormality 20 is reset in the field of view as a new observation region. At this time, by setting the minute movement amount of the wafer 11 to the size of the visual field (δ), the region 31 including the protruding portion adjacent to the original observation region 30 can be set in the visual field.

  Next (step S6), the same control as in step S2 is performed, and a microscope image of the region 31 including the protruding portion of the abnormality 20 is acquired. Next (step S7), the same processing as step S3 is performed, and after generating a difference image (FIG. 4C) from the microscope image of the region 31 including the protruding portion, the abnormality 23 is automatically detected from the difference image. Judgment is made. At this time, it is preferable to use the same threshold as in step S3.

Further, in the next step S8, it is determined whether or not there is a pixel value larger than the threshold value in each pixel on the side that is not adjacent to the past observation region among the four sides of the difference image (FIG. 4C). Judgment is made to determine whether or not there is a new protruding direction.
In the example of FIG. 4C, the right side of the four sides of the difference image is adjacent to the past observation region 30, and among the other upper side, left side, and lower side, each pixel on the upper side is larger than the threshold value. Contains the value (hatched part). For this reason, it is considered that the abnormality 23 detected from the difference image (FIG. 4C) protrudes further upward from the current visual field (see FIG. 4D).

  When there is a new protruding direction as described above (Yes in step S8), the process returns to step S5. And the process of step S5-S7 is repeated. As a result, for example, as shown in FIG. 5A, in addition to the difference images of the original observation region 30 and the adjacent region 31 including the protruding portion, the difference images of the regions 32 to 35 including the protruding portion are obtained in order. be able to. In the difference image of the region 35, there are pixel values larger than the threshold value on the right side and the lower side, but since both are adjacent to the region observed in the past, the image acquisition is completed.

If it is determined in step S8 that there is no new protruding direction (No in step S8), the process proceeds to the next step S9, and the difference image of the original observation region 30 and the difference images of the protruding portions 31 to 35 are combined. Then, a composite image related to one large abnormality 24 (FIG. 5B) is generated. The process of FIG. 2 is terminated.
If there is another observation position designated by the recipe in the surface 1A of the wafer 11, the process of FIG. 2 may be repeated. Although it depends on the manufacturing process of the wafer 11, the sampling inspection is usually performed at 5 (or 9) locations on the surface 1 </ b> A of the wafer 11.

Thus, according to the appearance inspection apparatus 10 of the present embodiment, based on the microscopic image of the partial region (the observation region 30 in FIG. 5A) including the observation position specified by the recipe, the surface 1A is viewed from the field of view. Since it is determined whether or not there is an abnormality with a size that protrudes, even if there is a large abnormality 24 (for example, a cluster defect) that does not fit in the field of view, it can be detected without missing it.
Furthermore, according to the appearance inspection apparatus 10 of the present embodiment, when there is a large abnormality 24, the protruding portion of the large abnormality 24 is sequentially arranged while keeping the size of the field of view constant without changing the magnification of the objective lens 14. Set in the field of view and acquire a microscope image. For this reason, the whole image can be reliably detected regardless of the size of the abnormality 24 on the surface 1A. Further, the size and shape of the abnormality 24 can be accurately calculated based on the moving amount and moving direction of the stage 12.

  Note that the present invention is not limited to the above example, and when a large abnormality 24 is discovered, the magnification of the objective lens 14 may be reduced to widen the field of view, and the entire image of the abnormality 24 may be detected. However, since there is a limit to the reduction in magnification, the entire image may not be detected depending on the size of the abnormality 24. In addition, since a magnification error occurs due to the magnification change, the size or shape of the abnormality 24 may not be detected accurately. Therefore, as in the above example, it is desirable to detect a whole image of the abnormality 24 by acquiring a plurality of microscope images without changing the magnification of the objective lens 14.

  Further, in the appearance inspection apparatus 10 according to the present embodiment, when the stage 12 is finely moved in the abnormal protrusion direction, the minute movement amount is set to the size of the visual field (δ), so that the surface 1A of the wafer 11 is adjacent. A plurality of regions (the observation region 30 and the protruding portions 31 to 35 in FIG. 5A) can be set in order in the field of view. For this reason, the entire image of the large abnormality 24 can be detected continuously and efficiently without a gap. However, the minute movement amount may be set smaller or larger than the visual field size (δ).

  Further, in the appearance inspection apparatus 10 according to the present embodiment, finally, the difference image of the original observation region 30 and the difference images of the protruding portions 31 to 35 are combined to relate to a large abnormality 24 (for example, a cluster defect). Since a composite image is generated, an effect substantially equivalent to the expansion of the visual field can be obtained. Further, by displaying this composite image on, for example, the monitor 6A, the entire image of the abnormality 24 can be grasped at a glance.

  Further, in the appearance inspection apparatus 10 of the present embodiment, when the large abnormality 24 includes a plurality of types of abnormality 25 and 26 (FIG. 5C) having different pixel values, these are determined according to the difference in the pixel values. Can also be detected separately from each other. The cause of the large abnormality 25 (small abnormality 26) can also be specified from the magnitude relationship or positional relationship of the abnormality 25, 26. For example, the small abnormality 26 is a foreign matter, and the large abnormality 25 is film thickness unevenness caused by a spin coater.

(Modification)
In the above-described embodiment, when the abnormal protruding portion of the surface 1A of the wafer 11 is reset within the visual field, the stage 12 is controlled to slightly move the wafer 11, but the present invention is not limited to this. In addition, the wafer 11 may be fixed and the field of view of the optical microscope unit (14, 15) may be moved minutely, or both the wafer 11 and the field of view may be moved. That is, if the wafer 11 and the visual field are relatively moved, the same effect can be obtained.

  Further, in the above-described embodiment, when there is a large abnormality 24, the protruding direction of the abnormality 24 is determined from the pixel values of the four sides of the difference image and moved slightly in the new protruding direction. It is not limited. Regardless of the protruding direction of the abnormality 24, the minute movement may be repeated around the observation region 30 specified by the recipe. However, as in the present embodiment, it is preferable to make a minute movement according to the protruding direction of the large abnormality 24, and the throughput is improved.

Further, in the above-described embodiment, the appearance inspection apparatus 10 using the wafer 11 as an inspection object has been described as an example, but the present invention is not limited to this. For example, the present invention can be applied to an inspection apparatus that uses a liquid crystal substrate as a test object, or an inspection apparatus that observes an electronic component mounted on the substrate as a test object.
When the same pattern is repeatedly arranged, such as the surface 1A of the wafer 11, if the amount of minute movement is the same as the die pitch, only one reference image is required, and the recipe creation time can be shortened. At this time, if the field of view is the same size as the die, a plurality of continuous microscope images can be acquired (the reference image is also the same size as the die). However, the plurality of microscopic images may be discontinuous.

1 is a schematic diagram illustrating a configuration of an appearance inspection apparatus 10. FIG. 3 is a flowchart showing a procedure of an observation operation for a wafer 11. It is a figure explaining a microscope image, a reference image, and a difference image. It is a figure explaining the protrusion direction and minute movement of an abnormality. It is a figure explaining repetition of a minute movement, and the big abnormality 24. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Appearance inspection apparatus; 11 Wafer; 12 Stages; 13 Transfer control mechanism part;
14 objective lens; 15 CCD camera; 16 computer

Claims (8)

An acquisition means for setting a partial area of the surface of the object in the field of view and acquiring an image of the partial area;
An appearance inspection apparatus comprising: a determination unit configured to determine whether there is an abnormality of a size protruding from the visual field on the surface based on the image. The appearance inspection apparatus according to claim 1,
When the acquisition unit determines that there is an abnormality, the object and the visual field are relatively moved to reset the abnormal protruding part into the visual field, and an image of the region including the protruding part is obtained. A visual inspection apparatus characterized by further acquiring The appearance inspection apparatus according to claim 2,
The acquisition means, when it is determined that there is an abnormality, relatively moves the object and the field of view by the size of the field of view, and acquires an image of a region including the protruding portion. Appearance inspection device. In the visual inspection apparatus according to claim 2 or 3,
An appearance inspection apparatus further comprising a generating unit that combines the image of the partial region acquired by the acquiring unit and the image of the region including the protruding portion to generate a composite image related to the abnormality. . Set a partial area of the surface of the object in the field of view to obtain an image of the partial area,
An appearance inspection method, wherein the presence or absence of an abnormality of a size that protrudes from the visual field on the surface is determined based on the image. The appearance inspection method according to claim 5,
When the abnormality is present, the object and the visual field are relatively moved to reset the abnormal protruding portion in the visual field, and an image of a region including the protruding portion is further acquired. Appearance inspection method. The appearance inspection method according to claim 6,
When there is an abnormality, the object and the visual field are relatively moved by the size of the visual field, and an image of an area including the protruding portion is acquired. In the appearance inspection method according to claim 6 or 7,
A visual inspection method comprising: synthesizing an image of the partial area and an image of an area including the protruding portion to generate a composite image related to the abnormality.

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