JP3332096B2 - Defect inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus for inspecting a defect of a mask used for, for example, a reduction projection exposure of a semiconductor wafer, and more particularly to an inspection apparatus which enlarges and projects an inspection light transmitted or reflected by a mask. Defect inspection method and inspection
And equipment .

[0002]

2. Description of the Related Art A reduction projection exposure method is mainly used for transferring a pattern of an advanced device, but it is essential to stably supply a high quality mask in order to improve the yield. In particular, with the recent miniaturization and large scale of LSIs, inspections for guaranteeing the quality of masks have become increasingly important.

FIG. 4 shows a cross section of a conventionally used exposure mask. Generally, the thickness is 0.09 to 0.
An opaque film such as a chromium film (hereinafter, referred to as a Cr film) is formed in a desired pattern on a 25-inch transparent glass plate. It expresses a desired pattern shape. FIG. 5 shows a cross section of a Levenson-type phase shift mask. This has a structure in which a phase shift film pattern is alternately formed every other region in a region partitioned by a Cr film pattern. The phase shift film is formed with a thickness that shifts the phase of the light transmitted through the mask by approximately a half wavelength. On the projection surface, light that has passed through the phase shift film interferes with light that has passed through the transparent portion in the vicinity. As a result, the transmitted light pattern with sharper edge portions can be obtained as shown in FIG.

A major defect of such an exposure mask is that
There are two points: (1) defective shape of the formed pattern (here, the pattern means both the Cr film and the phase shift film) and (2) foreign matter adhered to the surface of the mask. Since the shape of the Cr film pattern is directly transferred to the wafer at the time of exposure, it is necessary to detect a shape defect of about one third of the pattern line width. Therefore, the current pattern line width is about 1
Since it is μm, it must be inspected to about 0.3 μm.
Even if the foreign matter such as the foreign matter b in FIG. 7A adheres to the Cr film pattern, it may float during the work and move to the transparent part, which may affect the exposure.
Must be detected in the same way as Also, the phase shift film is
As described above, the edge portion of the transmitted light pattern is sharpened depending on the presence or absence of the film, and the function is performed if the edge portion of the phase shift film exists on the Cr film pattern. Therefore, the shape defect of the phase shift film is sufficient if the presence or absence of the pattern edge portion can be confirmed, and the required inspection accuracy is about 1 μm which is almost the same as the pattern line width.

[0005] Inspection of defects such as defective pattern shapes and adhered foreign substances requires a high level of technology, and has a high specific gravity in terms of inspection cost. Therefore, it will be an extremely important technical subject in the future.

[0006] Foreign matter adhering to the Cr film and the transparent portion of the mask (foreign matter a in FIGS. 7A and 8A) shields light transmitted from the back surface of the mask. Therefore, conventionally, defects related to defective shape of the Cr film pattern and foreign matter adhering to the transparent portion have been inspected using the transmitted light image of the mask. As a defect inspection apparatus using a transmitted light image, for example, a "mask inspection apparatus"
(Watanabe et al. “Electronic Materials”, 1988, separate volume, pp. 159-167)
There is a description. As shown in FIG. 3, the defect inspection apparatus (300) includes a stage (310), a light source (320), and a condenser lens system.
(330), an imaging lens system (340), an imaging unit (350), and a calculation unit (360). And the stage section
The mask (10) is placed on (310), the inspection light emitted from the light source (320) is condensed by the condenser lens system (330), and the mask (10) is irradiated from the back side. The image is focused by the imaging lens system (340), the imaging unit (350) captures the projected image and outputs an image signal according to the received light intensity, and the calculation unit (360) detects defects based on the image signal. It is supposed to.

On the other hand, foreign matter (foreign matter b in FIGS. 7 and 11) attached on a low transmittance portion such as a Cr film or a phase shift film does not appear in the transmitted light image. The phase shift film does not appear in the transmitted light image because the edge of the pattern is on the Cr film. Conventionally, masks are used for masking foreign matter adhering to low transmittance portions and pattern shape defects of the phase shift film based on the phenomenon that scattered reflected light is generated when light is applied to portions where the surface shape changes steeply. The inspection was performed by scanning the entire surface with a laser beam and observing the reflected light image.

[0008]

When the conventional mask shown in FIG. 7A is scanned on the line AA, the chart of the image signal of the transmitted light image is as shown in FIG. 7B. In this case, a portion where an attached foreign matter or defect exists becomes a hill which appears as a deep valley, and a white point becomes a peak in the Cr film portion. As shown in FIG. 7 (c), the image signal chart of the reflected light image has a peak where a sharp change in shape such as an edge portion of the Cr film pattern, a defect, or a deposited foreign matter appears as a peak. (Especially, a high peak is shown for the attached foreign matter.) Usually, the amplification degree of the image signal may be increased in order to further increase the detection sensitivity. In this case, each image signal has a hill or peak level as shown in FIGS. 7 (d) and 7 (e). Is a higher chart. However, in the actual transmitted light image, while the pattern shape of the Cr film is clearly projected, the defect level (white point and black point) of the pattern and the adhered foreign matter have a halfway transmittance, so that the density level is different from that of the periphery. Is small. For this reason, when the image signal of the transmitted light image is amplified, in a transparent portion, while the signal level of the hill increases, the valley indicating the black spot or the adhered foreign substance is buried and cannot be detected. Therefore, the dynamic range of the image signal cannot be widened, and the defect detection accuracy cannot be sufficiently improved.

Further, since the transmittance varies depending on the type of the defect, as described above, it is a reliable inspection method to observe each of the transmitted light image and the reflected light image of the mask. However, observing the transmitted light image and the reflected light image separately or with different devices has many drawbacks such as an increase in the overall inspection time and an increase in the floor space of the device.

In order to solve the above-mentioned difficulties, it is conceivable that the defect inspection using a transmitted light image and the defect inspection using reflected scattered light are simply combined and performed by the same apparatus. In this case, a light source for obtaining a transmitted light image is provided on the back side of the mask, and a light source for a reflected dark field for obtaining a scattered light image is provided on the front side of the mask. May be formed by using the same optical system and the same imaging means to form an image. FIG. 7F is a chart of an image signal on the line AA when the transmitted light image and the reflected light image of the conventional mask are simultaneously taken. This chart has substantially the same shape as the superimposition of the charts of the image signals of the transmitted light image and the reflected light image shown in FIGS. 7B and 7C. It shows a peak at a point. However, the adhered foreign substance a in the transparent portion becomes a valley in the transmitted light image and becomes a peak in the reflected light image, and thus is canceled each other when they are superimposed, so that the difference from the surrounding signal level is reduced, and the S / N of the signal is reduced. The ratio decreases. As a solution in this case, it is conceivable to increase the amount of reflected dark field illumination to increase the scattered light from the attached foreign matter. However, since the light intensity of the scattered light from the pattern edge of the Cr film also increases, it is difficult to distinguish whether the peak in the chart of the image signal is caused by the pattern edge or the attached foreign matter. In the case of a phase shift mask, the number of pattern edge portions further increases, so that the possibility of erroneous determination is further increased.

Accordingly, the present invention provides a defect inspection method and a defect inspection method capable of suitably detecting pattern defects and attached foreign matter on a mask based on image information obtained by imaging a reflected light image from the mask surface .
And equipment .

Further, the present invention provides a defect inspection method capable of suitably detecting a mask pattern defect and an attached foreign matter based on image information obtained by simultaneously capturing a transmitted light image of a mask and a reflected light image from the mask surface. And an apparatus .

[0013]

Means for Solving the Problems The present invention has been made in consideration of the above problems, the rear surface of the test object serving as a mask
First projecting means for projecting inspection light for transmission from
A second method for projecting inspection light for dark field illumination on the surface of the mask
Light emitting means, transmitted light of the mask and the surface of the mask
Image of the scattered reflected light and output as grayscale image information
A single imaging means, and a grayscale change from the grayscale image information.
Edge detection method that extracts edge and obtains edge image information
Step and shading created based on the mask design information
Generates second information by extracting the boundary of shading from image information
Design pattern generating means for performing
For detecting a defect by comparing the information with the second information.
Defect detecting device, comprising: a defect detecting means.
It is a place.

Further, the present invention provides a method for manufacturing a semiconductor device, comprising:
The inspection light for transmission is projected from the surface, and the surface of the mask is exposed.
Inspection light for dark field illumination is projected on the surface and transmitted through the mask.
Single imaging of light and scattered reflected light from the mask surface
Means, and outputs it as grayscale image information.
Edges obtained by extracting the boundaries of shading from light image information
Created based on the image information of the
Extract and generate the boundary of the grayscale change from the grayscale image information
The second information and the edge portion image
Defects characterized by detecting defects by comparing with information
It is a detection method .

When the mask surface is illuminated, strong scattered light is emitted from the pattern edge portions of the opaque film and the phase shift film and from the adhered foreign matter. That is, the reflected light image on the mask surface is an image in which the pattern edge portions of the respective films and the locations of the adhered foreign substances are bright. Therefore, when this captured image is compared with an image of an ideal pattern edge portion generated from the design specification of the mask, a defective pattern shape of the opaque film and the phase shift film and a portion of the adhered foreign matter appear as a mismatched portion between the two images. Thus, a defect can be detected. Further, even if the amplification degree of the image signal is increased, the difference in density level between the pattern defect and the adhered foreign matter in the transparent portion does not become small, so that the detection sensitivity can be sufficiently improved.

In principle, in the reflected light image on the mask surface, the pattern shape defect of each film and all of the adhered foreign matter appear. However, since the defect in the pattern shape of the Cr film directly affects the exposure, it is necessary to inspect the pattern more precisely than the phase shift film and the attached foreign matter. Approximately 1 defect detection accuracy of phase shift film pattern defect and adhering foreign matter
μm, the pattern shape defect of the opaque film
The requirement is strict at 0.3 μm. ). Also, as a real problem,
The reflected light image is used because the reflected light has a lower received light intensity than the transmitted light that can be captured directly, and the reflected light intensity distribution that forms the image draws a gentle Gaussian curve due to the characteristics of the optical system. In this case, the image of the pattern edge portion of the Cr film becomes unclear, and it is difficult to detect the correct shape. on the other hand,
Since the Cr film is light-shielding, the shape of the Cr film pattern is clearly projected on the transmitted light image of the mask. Therefore, the image obtained by simultaneously capturing the transmitted light image and the reflected light image of the mask is C
A sharp peak is shown in the pattern edge portion of the r film and the phase shift film and in the adhered foreign matter, and the boundary between the Cr film and the transparent portion is a sharp grayscale image. Edge image information is generated by extracting a boundary between a light portion and a dark portion divided at a predetermined gray level from the captured image, and this is compared with a gray image showing an ideal edge portion obtained from the design specification of the mask. I do. Since the edge portion image information clearly shows the shape of the Cr film pattern, it is possible to detect defects with higher accuracy.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a defect inspection apparatus (100) according to a first embodiment of the present invention. Inspection equipment (100)
Is a stage (110) and a light source (121) as a light emitting means.
, A condenser lens system (122), a dark-field reflecting mirror (123), a donut mirror (124), and an objective lens system (1
31), an imaging lens system (132), a line sensor (133), and an electric circuit system (140). Hereinafter, first, the configuration of each unit will be described in detail.

The stage (110) is composed of a mask base and XY
θ table (both not shown). The mask base mounts and fixes a mask (10) to be inspected by vacuum suction or the like. The XYθ table is composed of two linear tables which are arranged orthogonally in the in-plane direction of the mask base and are each movable in the longitudinal direction, and one rotary table which is rotatable about an axis orthogonal to the plane. Each table has a linear scale and a rotary table opposed to each other. Each table is driven by receiving a control signal from an arithmetic and control circuit (146), which will be described later, and can detect a current position signal. Has become.

As the light source (121), for example, a high-pressure mercury lamp that emits inspection light of e-line to g-line is used, and the light source (121) is installed in a direction substantially orthogonal to an optical axis of an optical system constituting an image pickup means described later. I have. The condenser lens system (122) collects the inspection light emitted from the light source (121). The dark-field reflecting mirror (123) is a so-called semi-transmissive mirror, which reflects the converged inspection light and deflects it in the direction of the mask (10) mounted and fixed. The donut mirror (124) has an annular shape in which a hollow cone whose inner periphery forms a mirror surface is cut in two planes orthogonal to the axis thereof, and the apex of the cone is a mask (10).
And the axis thereof is disposed so as to substantially coincide with the optical axis of the deflected inspection light. Then, as the light emitting means,
The inspection light emitted from the light source (121) and condensed by the condenser lens system (122) is deflected by the dark field reflecting mirror (123) downward in FIG. 1 and further by the donut mirror (124). Is refracted, and the mask (1
0) The inspection point on the surface is illuminated by epi-illumination. The inspection light is masked by driving the XYθ table.
(10) The entire surface is scanned.

The objective lens system (131) is disposed substantially vertically above the mask (10), and refracts reflected light from the surface of the mask (10) to convert it into substantially parallel light. . The imaging lens system (132) is disposed in the traveling direction of the parallel light and at a position where its focal point is formed on the line sensor (133). The line sensor (133) is, for example, a linearly arranged photosensor that outputs an electric signal corresponding to the received light intensity. Each photosensor is synchronized with the scanning of the inspection light accompanying the driving of the XYθ table. The sensor outputs an analog image signal.

The electric circuit system (140) includes an amplifier circuit (141),
Analog / Digital (hereinafter A / D) conversion circuit
(142), image memory (143), and design pattern generation circuit
(144), defect detection circuit (145), and operation control circuit (146)
It is composed of The amplification circuit (141) amplifies the analog image signal output from the line sensor (133),
The A / D conversion circuit (142) performs A / D conversion of the amplified analog image signal into a digital image signal having, for example, 1024 gradations. The image memory (143) receives the digital image signal and stores it as two-dimensional and shaded image information (hereinafter, referred to as a sensor pattern). The design pattern generation circuit (144)
By sequentially reading design data relating to the mask pattern from an external or built-in memory, a reflected light image of the mask ideally created in accordance with the design specifications will actually be obtained through the imaging means (that is, the optical system). Each pixel corresponds to the output from the element of the line sensor (133) one-to-one according to the characteristics of the line sensor (133) and the response characteristics of the line sensor (133)
A two-dimensional gray image is generated and stored as a design pattern. Defect detection circuit (145)
Is designed to faithfully compare a sensor pattern and a design pattern for each pixel and detect a mismatched portion between the two as a defect. The arithmetic control circuit (146) is composed of a central processing unit (Central Processing Unit: CPU) and various hardware circuits, and is electrically connected to each of the above units, so as to control the operation of the entire apparatus. ing.

The operation control circuit (146) is provided with an input section (151) such as a console and a display section (152) such as a CRT display and a printer, so that an instruction can be inputted from outside and the operation result can be obtained. It can output. Next, the operation of the present embodiment will be described together with the operation of the defect inspection apparatus (100).

First, the mask (10) to be inspected is placed on the stage (110), and the XYθ table is driven to set it at a predetermined position. Next, the light source (121) is turned on to start the inspection.

The inspection light for dark-field illumination emitted from the light source (121) is condensed by the condenser lens system (122) and is reflected by the dark-field reflecting mirror (1).
At 23), the light is deflected in the direction of the mask (10). Donut mirror (1
24) irradiates the inspection point on the mask (10) by reflecting a part of the inspection light. On the surface of the mask (10), the film (Cr
Includes both films and phase shift films. ) Strongly scattered light is emitted at the point where the surface shape changes sharply, such as the pattern edge portion or the attached foreign matter.

The scattered and reflected light from the surface of the mask (10) is condensed by the objective lens system (131) to become substantially parallel light, passes through the dark field reflecting mirror (123), and passes through the imaging lens system (132). ) To form an image on the line sensor (133). In this reflected light image, the pattern edge portion of the film and the location of the adhered foreign matter are bright,
Other flat portions become dark and shaded images. And
The line sensor (133) captures the reflected light image and outputs an analog image signal in synchronization with the driving of the XYθ table.

An amplifier circuit (141) amplifies the analog image signal, and an A / D converter circuit (142) A / D converts the analog image signal into a digital image signal. The image memory (143) receives a digital image signal and stores it as a sensor pattern.

On the other hand, the design pattern generating circuit (144) first makes the low transmittance portions such as the Cr film and the phase shift film dark and the transparent portions based on the design data stored in the external or built-in memory. To generate a two-dimensional gray image in which is brightly drawn. Next, from the two-dimensional grayscale image, the boundary between the bright part and the dark part divided at a predetermined grayscale level (ie,
Only a pattern edge portion of a Cr film or a phase shift film) is extracted, and an image in which only this boundary line is brightly generated is generated. The grayscale image showing only the pattern edge portion brightly is an image in which a reflected light image of the mask (10) ideally created according to the design specifications will be actually obtained through the above-mentioned imaging means, and each pixel is The output signal from each element of the line sensor (133) has a one-to-one correspondence. Then, the design pattern generation circuit (144) stores and holds the two-dimensional grayscale image as a design pattern. As a method of extracting a boundary between a light portion and a dark portion divided at a predetermined gray level from the gray image (extracting only the pattern edge portion from the image of the mask (10) pattern), a method of differentiating the gray image is used. And morphological methods.
In the former case, the brightness of the image changes sharply at the boundary between the low transmittance portion such as the Cr film and the transparent portion, and the differential value increases. Therefore, if the absolute value of the differential value is represented by the gray level, the pattern edge portion appears bright. Because. In the latter morphology method, an image obtained by reducing one or several pixels around the pattern of a bright portion in an image and an image before the reduction are subtracted. In this case, the pattern of the bright portion after the degeneration is completely coincident with the bright portion before the degeneration and is canceled, but the surrounding pixels removed by the degeneration are not canceled because they do not match with the same pixel after the degeneration. Remains. Therefore, if the non-coincidence part is represented by the gray level, an image in which only the edge of the light part is extracted can be generated (see FIG. 9).

The defect detection circuit (145) includes an image memory (143)
From above, the above-mentioned sensor pattern is transferred to the design pattern generation circuit (1
44), the above design patterns are read out, and the two patterns are faithfully compared for each pixel to detect a mismatched portion between the two. However, where the pattern shape of the mask (10) conforms to the design specifications and no foreign matter adheres to the surface, the gray level of the corresponding pixel on the sensor pattern matches that of the design pattern, and if there is a defect, The shading levels of the two do not match. Therefore, the defect detection circuit (145)
If the unmatched portion exceeds a predetermined threshold, it is determined that a defect exists, and a defect detection signal is sent to the arithmetic processing circuit (146). The arithmetic processing circuit (146) receives the defect detection signal,
The result is displayed externally through a T display or a printer (152).

The defect detection circuit (145) first detects a pixel whose signal value of the edge portion exceeds a predetermined threshold value from the sensor pattern, and then determines whether an edge exists at a corresponding position of the design pattern. If the two do not match, it may be determined that a defect exists, and a defect detection signal may be output.

FIG. 2 shows the configuration of a defect inspection apparatus (200) according to a second embodiment of the present invention. Inspection equipment (200)
Is a stage section (210) and a light source as first light emitting means.
(221), condenser lens system (222), and second light projecting means (230)
And an objective lens system (241), an imaging lens system (242), a line sensor (243), and an electric circuit system (250) as imaging means. Hereinafter, first, the configuration of each unit will be described in detail. The stage (210), the second light projecting means, and the imaging means are provided in the stage (11) in the defect inspection apparatus (100).
0), since the configuration is substantially the same as each of the light projecting means and the imaging means, the description will be simplified. As the light source (221), for example, a high-pressure mercury lamp that emits inspection light of e-line to g-line is used, and a mask (1) is used.
0) It is disposed substantially vertically below the back side. Condensing lens system
The reference numeral (222) is provided between the light source (221) and the mask (10), and focuses the inspection light. And the first
As the light projecting means, the mask (10) is illuminated from the back side to obtain light transmitted through the mask (10).

The second light projecting means (230) comprises a light source, a condenser lens system, a dark field reflecting mirror, and a donut mirror (both not shown). Each part has substantially the same configuration as the light projecting means (120) in the first embodiment, and the second light projecting means (230) has an irradiation point of the inspection light from the first light projecting means. The position substantially the same as that of the mask (10) is illuminated with incident light from the surface of the mask (10) with substantially the same optical axis as the light transmitted through the mask (10). Each inspection light from the first and second light projecting means (230) scans the entire surface of the mask (10) by driving an XYθ table built in the stage section (210). .

The objective lens system (241) condenses the transmitted light of the mask (10) and the scattered reflection inspection light from the surface of the mask (10) and converts them into substantially parallel light. The imaging lens system (242) refracts the substantially parallel light to form the transmitted light image and the reflected light image of the mask (10) on the imaging surface of the line sensor (243). The line sensor (243)
These projection images are taken and an analog image signal is output in synchronization with scanning of inspection light.

The electric circuit system (250) includes an amplifier circuit (251) and
An A / D conversion circuit (252), an image memory (253), an edge detection circuit (254), a design pattern generation circuit (255),
It comprises a defect detection circuit (256) and an operation control circuit (257). The amplification circuit (251) amplifies the analog image signal, and the A / D conversion circuit (252) A / D converts the amplified analog image signal into a digital image signal. The image memory (253) stores and holds the digital image signal as two-dimensionally shaded image information (hereinafter referred to as a sensor pattern). An edge part detection circuit (254) extracts only a boundary between a light part and a dark part divided by a predetermined shading level from the sensor pattern, and expresses only this boundary line brightly (hereinafter referred to as a second sensor). Pattern). The design pattern generation circuit (255) sequentially reads design data relating to the pattern of the mask (10) from an external or built-in memory, and a mask ideally created in accordance with the design specifications is actually obtained through the above-described imaging means. (Ie, the characteristics of the optical system and the line sensor (24
3) According to the response characteristics of each pixel, each pixel is a line sensor (243)
(One-to-one correspondence with the output of each element) is generated and stored as a design pattern. The defect detection circuit (256) faithfully compares the sensor pattern and the design pattern for each pixel, and detects a mismatched portion between the two as a defect. The arithmetic and control circuit (257) includes a central processing unit (Central Processin
g Unit: CPU) and various hardware circuits, and are electrically connected to the above-described units, so as to control the operation of the entire apparatus. Next, the operation of the present embodiment will be described together with the operation of the defect inspection apparatus (200).

First, the mask (10) to be inspected is placed on the stage (210), and the XYθ table is driven to set it at a predetermined position. Next, the first and second light emitting means (2
30) Start the inspection by operating.

The inspection light emitted from the light source (221) is condensed by the condenser lens system (222) and irradiates the mask (10) from the back side. On the other hand, the inspection light emitted from the second light emitting means (230) irradiates the surface of the mask (10) so as to converge in an annular shape by the same operation as the light emitting means in the first embodiment. Thus, the inspection light from the light source (221) is transmitted light, a part of which is shielded by the Cr film, and the second light projecting means (23)
The inspection light from 0) for dark field illumination generates strong scattered reflected light when illuminating a pattern edge portion on the surface of the mask (10) or a place where the shape change such as a stuck foreign matter is sharp.

The transmitted light and the scattered reflected light are both condensed by the objective lens system (241), become substantially parallel light, travel on substantially the same optical axis, and are line-formed by the imaging lens system (242). A projected image is formed on the imaging surface of the sensor (243). This projected image is almost the same as an image obtained by superimposing the transmitted light image and the reflected light image of the mask (10), the transparent portion is bright, the low transmittance portion such as the Cr film is dark, and the Cr film / phase The light and shade image has a bright peak at the pattern edge portion of the shift film and at the place where the foreign matter is attached. The line sensor (243) captures the projected image and outputs an analog image signal in synchronization with the scanning of the mask (10) by driving the XYθ table. For example, FIG.
An image signal obtained by scanning the phase shift mask shown in FIG. 8A is composed of an image signal obtained by capturing only a transmitted light image (see FIG. 8B) and an image signal obtained by obtaining only a scattered reflected light image (see FIG. 8C). )) Is approximately the same as the superimposition of FIG.
The chart is as shown in Here, it is assumed that the image of the adhered foreign matter in the scattered reflected light image becomes brighter by a at the density level compared to the surroundings, the image of the attached foreign matter in the transmitted light image becomes darker by b at the density level compared to the surroundings, and Is the noise level of c, b> nc and b> nc (where n represents an S / N ratio and is usually an integer of 2 or more). Adjust the light intensity of the light source for transmission and the light source for transmission (221). (At this time, the light intensity of the light source for dark field illumination is experimentally about 10 times stronger than the light source for transmission (221). .)

The amplifying circuit (251) amplifies the analog image signal, and A / D converts the A / D conversion circuit (252) into a digital image signal. The image memory (253) receives the digital image signal and stores it as a sensor pattern.

The edge detection circuit (254) is provided in the image memory.
(253) A sensor pattern is read out, and a boundary between a light portion and a dark portion divided at a predetermined shading level is extracted from the sensor pattern, and a second sensor pattern expressing only this boundary line bright is generated. In the second sensor pattern, a portion where the shape change is sharp, such as a pattern edge portion of the Cr film / phase shift film and a portion where a foreign substance is attached, appears brightly on the surface of the mask (10). For example, when the image signal shown in FIG. 8 (d) is processed by the edge detection circuit (254), a chart of the image signal as shown in FIG. 8 (e) is obtained.

On the other hand, based on design data stored in an external or built-in memory, the design pattern generation circuit (255) first darkens and transmits a low transmittance portion such as a Cr film or a phase shift film. Create a two-dimensional gray image in which the part is drawn brightly. Next, a boundary between a light part and a dark part (that is, a pattern edge portion of a Cr film or a phase shift film) divided at a predetermined gradation level is extracted from the two-dimensional gradation image, and a gradation image showing only this boundary line brightly. Generate This grayscale image is obtained by actually imaging a mask ideally created in accordance with the design specifications through the above-described imaging means, and extracting the boundary of the grayscale change by the edge detection circuit (254). Corresponds one-to-one. Then, the design pattern generation circuit (255) stores and holds the generated grayscale image as a design pattern.

As in the first embodiment, the extraction of the boundary of the shading change performed by the edge detection circuit (254) and the design pattern generation circuit (255) is performed by differentiating the original image, or This is performed using a morphology method.

The defect detection circuit (256) faithfully compares the second sensor pattern and the design pattern for each pixel and detects a mismatch between the two. At a normal place where the pattern shape of the mask (10) is as designed and there is no foreign matter adhering to the surface, the gray level of the corresponding pixel on the second sensor pattern matches that of the design pattern, and conversely there is a defect. In this case, the shading levels of the two do not match. Defect detection circuit (256)
When the mismatch portion exceeds a predetermined threshold value, it determines that a defect exists and sends a defect detection signal to the arithmetic processing circuit (257). For example, when the image signal obtained by actually capturing the image shown in FIG. 8D and the ideal image signal shown in FIG. 8E are subjected to a subtraction process, the peak relating to the adhering foreign matter does not exist on the design pattern. Therefore, as shown in FIG. 8 (f), that part is extracted as a mismatched part and determined to be a defect. Then, the arithmetic processing circuit (2
57) inputs the defect detection signal and outputs the inspection result to the outside via a CRT display or a printer (262).

It should be noted that the detection of a defect is not limited to the one performed by comparing the signal values of the edge portions in the sensor pattern. For example, if the original two-dimensional grayscale image obtained from the imaging means is compared with the design pattern, a thin C
A translucent defect remaining without removing the r film can be detected.

The structure of the present invention is not limited to the above embodiment, but can be modified without changing the gist of the invention. For example, in the above embodiment, the defect is detected by comparing the projected image of the mask obtained by imaging with the design pattern. However, the defect may be compared with another chip pattern in the mask or between the masks. Further, in the above embodiment, in order to speed up the arithmetic processing, the data is temporarily stored in the image memory built in the electric circuit system, and the arithmetic processing is performed after collecting the data. However, the output signal of the line sensor is sequentially processed. It may be. In the second embodiment, the wavelengths of the light source for transmitted illumination and the light source for reflected dark field are not particularly limited. However, since detection sensitivity is better when short-wavelength light is used, if one wants to strictly inspect the pattern of the Cr film, one method is to use short-wavelength component inspection light as transmitted illumination.

[0045]

As described above in detail, according to the defect inspection apparatus of the present invention, the pattern defect and the adhering foreign matter of the mask can be suitably determined based on the image information obtained by imaging the reflected light image from the mask surface. Can be detected. Further, according to the defect inspection apparatus of the present invention, it is possible to suitably detect a pattern defect and an attached foreign matter on the mask based on image information obtained by simultaneously capturing a transmitted light image of the mask and a reflected light image from the mask surface. can do. In addition, the simple structure reduces the cost of the apparatus and shortens the inspection time. In semiconductor manufacturing, etc., the yield at the time of reduced projection exposure has dramatically improved,
As a result, a great industrial effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a defect inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a defect inspection apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional defect inspection apparatus.

FIG. 4 is a diagram showing a cross section of a conventional exposure mask.

FIG. 5 is a diagram showing a cross section of a Levenson-type phase shift mask.

FIG. 6 is a diagram illustrating the operation of a Levenson-type phase shift mask.

7A is a diagram showing the surface of a conventional mask and a defect on the surface, FIG. 7B is a diagram showing a chart of an image signal of a transmitted light image obtained by scanning the mask on line AA, and FIG. c) is the mask A
-A diagram showing a chart of an image signal of a reflected light image taken by scanning on the A line, (d) is a diagram showing a chart of an amplified image signal of the transmitted light image, (e) is an amplified image of the reflected light image FIG. 7F is a diagram showing a signal chart, and FIG. 7F is a diagram showing an image signal chart obtained by simultaneously taking a transmitted light image and a reflected light image on the line AA.

8A is a diagram showing a cross section of a Levenson-type phase shift mask having a defect on the surface, FIG. 8B is a diagram showing a chart of an image signal obtained by capturing a transmitted light image, and FIG. A diagram showing a chart of an image signal obtained by taking an image, (d) is a diagram showing a chart of an image signal obtained by simultaneously taking the transmitted light image and the reflected light image, (e) is processed by the edge part detection circuit FIG. 7F is a diagram illustrating a chart of an image signal, and FIG. 7F is a diagram illustrating a chart of an image signal obtained by performing a subtraction process on the image signal after the edge portion detection and the image signal based on the design data.

FIG. 9 is a diagram showing a method of extracting a pattern edge by a morphology method.

[Explanation of symbols]

10 mask, 110 stage part, 121 light source, 122 condensing lens system, 123 dark field reflecting mirror, 124 donut mirror, 131 objective lens system, 132 imaging lens system, 133
... Line sensor, 141 ... Amplification circuit, 142 ... A / D conversion circuit, 143 ... Image memory, 144 ... Design pattern generation circuit,
145: Defect detection circuit, 221: Light source, 222: Condensing lens system, 254: Edge detection circuit.

(56) References JP-A-4-318550 (JP, A) JP-A-62-181723 (JP, A) JP-A-63-268245 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01N 21/84-21/958

Claims (4)

(57) [Claims] 1. A first light projecting means for projecting inspection light for transmission from the back side of a mask to be inspected, and a second light projecting means for projecting inspection light for dark field illumination on a surface of the mask. Means, a single imaging means for imaging transmitted light of the mask and scattered reflected light from the surface of the mask and outputting it as gray image information, and extracting a boundary of gray change from the gray image information to obtain an edge. Edge part detecting means for obtaining partial image information; design pattern generating means for generating second information obtained by extracting a boundary of shading change from shading image information created based on the mask design information; A defect detection device comprising: a defect detection unit configured to detect a defect by comparing image information with the second information. 2. An inspection light for transmission is projected from a back surface of a mask to be inspected, and an inspection light for dark field illumination is projected on a surface of the mask. The scattered and reflected light is imaged by a single imaging means and output as grayscale image information, and edge portion image information obtained by extracting a boundary of grayscale change from the grayscale image information and the mask design information are used. A second information generated by extracting a boundary of a grayscale change from the grayscale image information generated in the above step, and comparing the second information with the edge image information to detect a defect. Detection method. 3. A method for differentiating the grayscale image information output from the imaging unit or processing the grayscale image information output from the imaging unit using a homology method to determine the boundary of the grayscale change. 3. The method according to claim 2, wherein the defect is extracted. 4. The defect detection method according to claim 2, wherein said mask is a phase shift mask.