JP2009246106A - Stencil mask defect inspecting method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that although a dummy pattern image is formed in advance based upon design data so as to make a comparison with the shape of an actual opening and automatic inspection is carried out, a desired pattern image generated from the design data by using technique for image processing can not be practically used for the inspection since the desired pattern image does not have completely matching corner states, contrast, etc., with respect to the shape of an opening of an actually manufactured stencil mask and may cause misdetection. <P>SOLUTION: Disclosed is the stencil mask defect inspecting method and device which irradiates the stencil mask obliquely with linear parallel light and measures the shape of the opening 8 using a non-reflection image of an image obtained by imaging surface reflected light, so as to inspect a defect of the opening 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a defect inspection method and apparatus for a stencil mask used in semiconductor manufacturing.

  On the stencil mask, many fine patterns of several μm or 1 μm or less and openings such as holes are formed so that the charged particle beam can pass through. The charged particle beam passes through and is reduced or projected at the same magnification on the wafer.

  In the process of manufacturing a stencil mask that requires such a fine pattern, the defect inspection of the shape of the opening is performed, and the cause analysis of the detected defect of the shape of the opening is performed to improve the process.

  Through the above, the reliability of the stencil mask is improved, and it is possible to contribute to semiconductor manufacturing with higher precision and higher density. The present invention provides a method and apparatus for inspecting a stencil mask defect for detecting defects in the shape of the opening of the stencil mask.

  In recent years, miniaturization of semiconductor devices has progressed, and for example, in an exposure process, an exposure apparatus using a charged particle beam capable of forming a finer pattern is used. Although the stencil mask is mounted and used in such an apparatus, miniaturization is progressing also in the length of the opening parts, such as various patterns and holes formed on the stencil mask, for the reason described above.

  When such a defect in the shape of the opening of the stencil mask exists, a defective pattern is transferred to the wafer in semiconductor manufacturing, and a normal circuit cannot be formed, resulting in a decrease in yield.

  For this reason, in the manufacture of stencil masks, inspection of defects in the shape of the opening is performed, and quality assurance of the stencil mask is performed for semiconductor device manufacturers.

  Conventionally, as a method for inspecting the shape of the opening of the stencil mask, a visual inspection using a microscope is performed. For example, a visual inspection using a dark field function with good edge observation of a pattern is performed.

  According to this method, a defect in the shape of the opening of the stencil mask can be inspected relatively easily over a wide range. However, when detecting a defect having a minute opening shape, it is necessary to increase the magnification of the microscope. In this case, there is a problem that the visual field for visual inspection becomes narrow and takes a very long time.

  In addition, as a problem of visual inspection using a microscope, there is a concern that a defect in the shape of the opening may be overlooked due to manual inspection, a decrease in the ability of the operator, or a variation in detection performance by a person.

  Regardless of visual inspection, microscope image processing using laser or white light and automatic inspection methods to detect feature points by devising an optical system have been devised, but defects in the shape of the opening of the stencil mask Therefore, it is difficult to extract only defects in the shape of the opening of the stencil mask, and to distinguish the normal shape from the shape of the opening.

  In a method called a pattern comparison method, an inspection is usually performed because there is no pattern as a reference for comparison because a pattern group of openings of the same stencil mask is not repeatedly formed in the stencil mask. Is impossible.

  In addition, in an inspection apparatus called a design data comparison method, a pseudo pattern image is generated in advance based on design data in order to perform comparison with an actual opening shape, and automatic inspection is performed. However, even if a desired pattern image is generated from design data by using image processing techniques, the corner shape, contrast, etc. do not completely match the shape of the opening of the actually produced stencil mask. Therefore, it was a cause of false detection and could not be usefully used for inspection.

The patent literature is as follows.
JP 2006-170932 A

  As described above, in the conventional inspection method for a stencil mask, it takes a very long time to visually detect a minute opening shape defect on the stencil mask, and an automatic method such as laser, microscope, or design data comparison. In the inspection, there are problems such as false detection or inability to compare with a reference pattern to be compared, and it has been difficult to actually use.

  In order to solve the above problems, the present invention proposes an optical automatic inspection method and apparatus that can perform stencil mask defect inspection and does not rely on visual inspection, and accurately perform defects in the shape of the opening. Provide a method that can

  According to a first aspect of the present invention, a defect in the opening is inspected by irradiating the stencil mask with linear parallel light from an oblique direction and measuring the shape of the opening with a non-reflective image in the captured image obtained by imaging the surface reflected light. A stencil mask defect inspection method is provided.

  According to a second aspect of the present invention, there is provided the stencil mask defect inspection method according to the first aspect, wherein the imaging is to capture an image formed by enlarging the surface reflected light.

  According to a third aspect of the present invention, there is provided the stencil mask defect inspection method according to the first or second aspect, wherein a defect is formed when the width of the non-reflective image exceeds a specified value.

  The stencil mask defect inspection method according to any one of claims 1 to 3, wherein an optical system that irradiates linear parallel light and images surface reflected light is scanned while relatively moving sequentially. I will provide a.

  In the above description, when there is no defect in the shape of the opening of the stencil mask, the length of the non-reflective image width of the captured image by the surface reflected light is the same as the design value. On the other hand, when there is a defect in the shape of the opening of the stencil mask, the length of the non-reflective image width of the captured image by the surface reflected light deviates from the design value.

  Therefore, in order to determine the presence or absence of a defect in the shape of the opening, the entire image of the stencil mask in which the opening is provided is scanned, and the captured image obtained by the surface reflection light obtained from the area in which the opening is provided. What is necessary is just to compare whether the length of the intermittent part of the non-reflective image is not deviated from the design value.

  A stage having a stencil mask mounted thereon and movable in the X and Y directions, a linear parallel light irradiation device that irradiates linear parallel light from an oblique direction with respect to the stencil mask, and an optical system that images surface reflected light. Image processing means for processing a captured image, defect determination means for performing defect determination based on a processed image subjected to image processing by the image processing means, and output means for outputting defect determination information determined by the defect determination means A stencil mask defect inspection apparatus according to the stencil mask defect inspection method according to claim 4 is provided.

  The optical system in the above is configured such that, for example, a slit or a cylindrical lens and a condenser lens such as an objective lens are combined to make the laser linear, and the stencil mask surface is focused on the surface from obliquely above. Is achieved. The surface can be irradiated with linear parallel light with a width of about several μm.

  In the optical system in the above, if the laser is irradiated from directly above rather than obliquely with respect to the stencil mask surface, the reflected light from the mask surface returns to directly above, and the observation optical system is usually provided directly above, An optical system that separates all of these becomes necessary and becomes complicated. For this reason, it is desirable to use an optical system that irradiates a laser from obliquely above.

  In the optical system described above, the sheet beam irradiated obliquely from above the stencil mask is condensed on the surface and reflected to the opposite side. However, the image captured by the reflected surface light is the magnification and imaging of the imaging optical system. An arbitrary magnification can be obtained depending on the size of the element.

  During the inspection, when linear parallel light such as a sheet beam by a laser scans the surface of the stencil mask, if there is no defect in the opening, one non-reflective image is obtained in the captured image by the surface reflected light. . In other words, if an XY stage equipped with a stencil mask is adjusted so that the focal length is kept equal without mechanical distortion with respect to an optical system that irradiates linear parallel light such as a laser sheet beam, a non-reflective image Will appear as a single continuous line at a certain position at a height L on the captured image.

  On the other hand, when the sheet beam scans the opening on the stencil mask, it is considered that there is an intermittent portion in the non-reflected image of the captured image by the surface reflected light.

  This is because the opening of the stencil mask penetrates through the charged particle beam so that the sheet beam passes through without being reflected when the opening exists at the irradiation site. Accordingly, the linear parallel light is reflected only from a region where the aperture is not open, that is, the charged particle beam shielding portion, and the surface reflected light is imaged onto the image sensor.

  As a result, the non-reflective image of the captured image by the surface reflected light does not form a continuous straight line at the opening, but becomes a non-reflective image of the captured image by the surface reflected light having an intermittent portion corresponding to the pattern width in the middle.

  Also, if the sheet beam scans a portion where there is a defect in the opening on the stencil mask, the non-reflective portion of the non-reflected image of the captured image by the surface reflected light is larger than the length of the normal intermittent portion depending on the size of the defect. Or small.

  According to a sixth aspect of the present invention, there is provided the stencil mask defect inspection apparatus according to the fifth aspect, wherein the defect size and area are calculated from the scanning time when the defect is determined.

According to the present invention, it is possible to inspect defects in the shape of the opening of the stencil mask, and it is possible to analyze the cause and correct the detected defects. As a result, the quality and reliability of the stencil mask are improved. In addition, since it is possible to automatically perform defect inspection of the shape of the opening of the stencil mask, there is no risk of manual adhesion of foreign matters and defects that were problematic during visual inspection, contributing to improved yield. .

  FIG. 1 shows a conceptual plan view of a stencil mask to be inspected. Basically, a silicon wafer or the like is used as the substrate 1, and an opening 2 made of a fine pattern through which a charged particle beam passes is formed.

  FIG. 2 is a conceptual diagram of the defect inspection of the shape of the opening according to the present invention. The laser 3 is shaped into a sheet beam 4 that is linear parallel light on the incident side, and is incident on the substrate surface obliquely from above. The apparatus is mechanically adjusted in advance so that the stencil mask 1 to be inspected is set at the focal position 7 and the non-reflected image 5 of the captured image by the surface reflected light is obtained.

  In the above, the sheet beam 4 is reflected by the surface of the stencil mask 1, and the non-reflected image 5 of the picked-up image by the surface reflected light which is the reflected light is incident on the inspection camera 6 which is an installed image pickup device. At this time, the focal point of the optical system on the reflection side is also adjusted to the focal position 7 on the stencil mask of the sheet beam.

  FIG. 3 is a detailed perspective view of the defect inspection of the shape of the opening using the surface reflection by the defect inspection of FIG. 2, and is a conceptual perspective view when viewed obliquely from above. Since the opening 8 of the stencil mask is a through-hole, when there is no defect, the non-reflected image 9 that is not reflected from the surface of the captured image 5 on the reflection side is the same width as the width of the opening 8 irradiated with the sheet beam. It becomes.

  FIG. 4 is a conceptual diagram in the case where the defect 11 having the shape of the opening exists. The width of the non-reflective image 9 is large or small corresponding to the width 12 of the opening.

  FIG. 5 is a conceptual diagram of a non-reflective image of a captured image by surface reflected light when no opening is present in the stencil mask in the case described above. Since the XY stage on which the stencil mask is mounted is adjusted so that there is no mechanical distortion and the focal length on the incident side is kept constant on the wafer, the non-reflected image 5 of the captured image by the surface reflection light obtained is It will always be a straight line without interruption in the same place.

  FIG. 6 is a conceptual diagram of a non-reflected image of a captured image by surface reflected light when an opening exists in the stencil mask. In this case, since there is no non-reflected image 5 of the captured image due to the surface reflected light and all the surface reflected light from the opening 8 is imaged, the non-reflected image 5 is the portion where the surface reflected light having the intermittent portion 9 is imaged. Become.

  FIG. 7 is a conceptual diagram of a non-reflective image of a captured image by surface reflected light when a defect exists in the shape of the opening of the stencil mask. In this case, since the non-reflected image 5 of the captured image by the surface reflected light has the defect 11 having the shape of the opening, the width of the surface reflected light imaged, that is, the width of the intermittent portion 9 of the non-reflected image is This is a width obtained by adding the width 12 of the defect portion to the width 10 of the opening portion.

  Therefore, the width of the interrupted part of the non-reflected image of the captured image by the surface reflected light of all patterns is obtained from the design data in advance, and the width of the interrupted part is monitored during the inspection, and the pattern defect is detected when it exceeds the set level And output an alarm.

FIG. 8 is a conceptual diagram of an inspection apparatus according to the present invention. It is assumed that the stencil mask 1 is mounted on the XY stage 14 and the stencil mask alignment operation with respect to the apparatus is completed.

  The optical system 16 includes a laser that is a linear parallel light irradiation device on the incident side and a camera that is an imaging device on the reflection side, and XY so that the formed sheet beam scans the entire surface of the stencil mask 11. The stage 14 moves.

  The image processing unit 17 monitors a non-reflective image other than the surface reflected light of the captured image by the surface reflected light under inspection. Here, the width of the design pattern is set, and a signal is output to the computer 18 when there is a change in the width of the intermittent portion of the non-reflected image of the captured image due to the surface reflected light.

  The computer 18 records the current coordinates from the stage controller 15 when the above signal is input.

  Further, in the detected defect of the shape of the opening, the size of the defect can be obtained, and FIG. 9 is a conceptual scanning diagram of the method.

  When there is a defect in the shape of the opening 8, it can be seen that the non-reflective image interrupted portion 7 that is not imaged as surface reflected light of the irradiated laser passes from the defect start portion 18 to the defect end portion 19. In this case, the width of the intermittent portion 9 of the non-reflected image 5 of the captured image by the surface reflected light changes every moment. If the time passing through the defective portion is t, the area of the pattern defect 11 is the intermittent portion 9. Can be obtained by integrating the dimensional variation 12 of the above with time t. Therefore, it is desirable to record the incidental information of the detected defect.

  When the inspection is completed as described above, the computer outputs a defect map of the shape of the opening of the stencil mask to the display unit of the inspection apparatus based on the recorded coordinates.

  The coordinates of the pattern defect in the output defect map are relative to the center of the stencil mask or the alignment mark or a specific position, so if it is a microscope or device with an automatic stage, it can be observed and analyzed again. It is.

  For example, it is possible to transfer the recorded detection coordinates of the defect in the shape of the opening to the microscope apparatus, classify the detected defect by performing a detailed inspection by an operator, and the like.

It is a conceptual top view of the stencil mask used as a test object. It is a conceptual side view of the defect inspection system of the shape of an opening part. It is a conceptual perspective view of the defect inspection method of the stencil mask by this invention. It is a conceptual perspective view of the defect inspection method of the stencil mask by this invention when there exists a defect of the shape of an opening part. It is the image imaged when there is no opening. It is the image imaged when an opening part exists. It is the image imaged of the opening part of the part in which the shape defect existed. It is a conceptual block diagram of a stencil mask defect inspection apparatus. It is a conceptual diagram of the scanning for calculating | requiring the magnitude | size of the defect of the shape of an opening part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stencil mask 2 Opening part 3 Laser 4 Sheet beam 5 Non-reflective image 6 Camera for imaging 7 Focus position 8 Opening part 9 Intermittent part of non-reflective image 10 Width of opening part on picked-up image 11 Defect in shape of opening part 12 Opening 13 XY stage 14 Stage controller 15 Cutting optical system 16 Image processing unit 17 Computer 18 Start point of dimensional variation of non-reflected image of image taken by surface reflected light 19 Non-reflected image taken by surface reflected light End point of image dimension variation

Claims (6)

  A stencil mask defect inspection method for inspecting a defect in an opening by irradiating a stencil mask with linear parallel light from an oblique direction and measuring the shape of the opening with a non-reflective image in a captured image obtained by imaging surface reflection light .   The stencil mask defect inspection method according to claim 1, wherein the imaging is to capture an image formed by enlarging surface reflection light.   3. The stencil mask defect inspection method according to claim 1, wherein a defect is formed when the width of the non-reflective image exceeds a specified value.   4. The stencil mask defect inspection method according to claim 1, wherein scanning is performed by sequentially moving an optical system that irradiates linear parallel light and picks up surface reflected light.   A stage mounted with a stencil mask and movable in the X and Y directions, a linear parallel light irradiation device that irradiates linear parallel light from an oblique direction with respect to the stencil mask, an optical system that images surface reflected light, and a captured image captured 5. An image processing means for processing a defect, a defect determination means for performing defect determination based on a processed image subjected to image processing by the image processing means, and an output means capable of outputting defect determination information determined by the defect determination means. Stencil mask defect inspection apparatus by the stencil mask defect inspection method.   6. The stencil mask defect inspection apparatus according to claim 5, wherein the defect size and area are calculated from the scanning time when the defect is determined.