JP2000193443A - Method and device for inspecting pattern defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image of high resolution compared with the case that visible light is used as illumination light by projecting high-brightness ultraviolet light(UV light) which is emitted from a laser light source on a sample while reducing its coherence. SOLUTION: While a semiconductor wafer 1 which is an example of a pattern to be inspected is moved at a constant speed when scanning a stage 2, the brightness information of a pattern to be inspected which is formed on the wafer 1 is detected with an image sensor 8. A gradation recognition converter 10 performs logarithmic conversion and exponential/polynominal conversion, etc., and an image wherein illumination light causes thin-film interference for unevenness in brightness is corrected with a thin film formed on the wafer in process. A discharge lamp is excellent as an UV(ultraviolet) light source, with, especially related to a mercury xenon lamp, the bright line in UV region stronger than other discharge lamps. By inserting a diffusion plate on the optical path of an UV laser for rotation and reciprocation, the spatial and time-related coherence is reduced simultaneously. Since a short-wavelength UV or a DUV laser is used with its coherence reduce, the defect of circuit pattern is detected with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting a pattern defect, and more particularly to a pattern defect inspection method suitable for inspecting a pattern defect formed on a semiconductor wafer, a liquid crystal display, a photomask or the like. And its device.

[0002]

2. Description of the Related Art Conventionally, this kind of inspection apparatus is disclosed in
As described in Japanese Patent No. 18326 (Prior Art 1), an image of a pattern to be inspected is detected by an image sensor such as a line sensor while moving the pattern to be inspected, and the detected image signal is delayed by a predetermined time by a surface toughness signal. By comparing the light and shade of the data, inconsistency was recognized as a defect.

Further, as a prior art relating to a defect inspection of a pattern to be inspected, Japanese Patent Application Laid-Open No. 8-320294 (prior art 2) is known. This prior art 2 has a high brightness on an image detected from a pattern to be inspected such as a semiconductor wafer in which a high pattern density region such as a memory mat portion and a low pattern density region such as a peripheral circuit are mixed in a chip. From the frequency distribution, the detected image signal is obtained by A / D conversion so that the brightness or contrast between the high-density region and the low-density region of the pattern to be inspected has a relationship determined by gradation conversion. A gradation conversion is performed on the obtained digital image signal, a function approximation is performed on the gradation-converted image signal and the gradation-changed image signal to be compared, and a difference between these function-approximated curves is integrated. Based on the high-accuracy detection of the positional deviation from this integral value, a technique for inspecting fine defects with high accuracy by comparing the pattern to be inspected in a state where the image signals that have been subjected to both gradation conversions are aligned. Has been described.

[0004] In the case of photomask inspection, there has been an idea of detecting only harmful defects which are affected at the time of exposure by making exposure light and inspection light the same.
There is also disclosed a technique for performing an inspection on a photomask using ultraviolet light (hereinafter, referred to as UV light) as exposure light using the same UV light as the exposure light as a light source. These inventions include techniques for inspecting the appearance of a circuit pattern on a photomask as disclosed in JP-A-8-94338 (Prior Art 3),
No. 78668 (Prior Art 4). Japanese Patent Application Laid-Open No. H10-62258 (Prior Art 5), Japanese Patent Application Laid-Open No. H10-78648 (Prior Art 6), and the like measure the amount of phase shifter in a phase shift mask.

Further, utilizing the fact that the absorption characteristics of the materials used in the process are different between visible light and UV light, a technique for inspecting with visible light and UV light to optically reveal circuit patterns and foreign matter is used. Japanese Patent Application Laid-Open No. 4-165641 (Prior Art 7) and Japanese Patent Application Laid-Open No. 4-282441 (Prior Art 8).

There is an interferometer as a means for optically measuring the outer shape of an object, and an invention in which UV light is applied thereto is disclosed in Japanese Patent Application Laid-Open No. 4-357407 (prior art 9).

[0007]

In recent LSI manufacturing, a circuit pattern formed on a wafer is miniaturized in response to the need for high integration, and the width of the pattern is reduced to 0.2.
The diameter has been reduced to 5 μm or less, and has reached the resolution limit of the imaging optical system. For this reason, an increase in the NA of the imaging optical system, application of the optical super-resolution technology, and enhancement of image processing are being promoted. The above-mentioned prior arts 1 and 2 apply these. However, there is a problem that the increase in NA has reached the physical limit and is weak against a high step pattern. In addition, the optical super-resolution technology and image processing have a non-linear response,
There is a problem that the scope of application is limited.

Therefore, the essential approach is to shorten the wavelength used for detection from the conventionally used visible light to the UV light region.

On the other hand, the idea of using the same light source as the exposure light designed for the photomask is effective for the related arts 5 and 6 for measuring the amount of phase shift.
This is because the shift amount is directly linked to the wavelength of the light source. However, when detecting defects by inspecting the appearance of a circuit pattern over the entire surface of an inspection sample or a wide area comparable thereto, it is necessarily appropriate to use the same exposure light (prior art 3, 4). Not necessarily.

This is because the transferability onto the wafer by exposure is not determined only by the wavelength of the light source or the conditions of the optical system. Various factors are complicatedly related, such as exposure amount, resist characteristics, defocus amount, optical characteristics of the base, and development process. Therefore, the prior arts 3 and 4 are suitable for performing a simulation including these complicated conditions and analyzing the transferability of one defect carefully, but a technique for inspecting a large number of circuit patterns in a short time. And different.

In this case, a defect having a possibility to be detected and transferred is as high as possible by a light source focused on defect detection, rather than performing an inspection by using an expensive light source for exposure which is difficult to handle. Thorough detection with sensitivity is a practical solution to this problem.

In this case, to improve the resolution, U
Since V light is used, it is impossible to use visible light for lowering the resolution as in prior arts 7 and 8.

In addition, since it is necessary to perform inspection at high speed,
It is not possible to use a laser beam narrowed down as in the prior art 9. In the region of UV light, high-intensity illumination with a laser is essential because there is no high-intensity discharge lamp.
An interference fringe pattern due to laser interference, so-called speckle, occurs, and overshoot and undershoot occur at the edge of the circuit pattern, so that an image cannot be obtained.

An object of the present invention is to solve the above-mentioned problems and to provide a method and an apparatus for detecting a fine circuit pattern at high speed with high resolution.

[0015]

In order to achieve the above object, according to the present invention, a UV laser light source is used as a light source, and means for suppressing the generation of speckles of the UV laser is provided in an optical path to reduce coherence. The object surface is irradiated with the reduced UV light to detect an image of the object.

As means for suppressing the generation of speckles of the UV laser, more specifically, 1) light from a light source is condensed on one point on a pupil of an objective lens, and the condensed point is detected by a detector. Scan the pupil in time with the accumulation time 2)
The UV light emitted from the laser light source is incident on the bundle of optical fibers whose optical axes have been shifted, and the emitted light is focused on the pupil of the objective lens. 3) Make the optical path length longer than the coherent distance of the laser light source. Means are provided for making the light enter the changed optical fiber group and condensing the emitted light on the pupil of the objective lens, and 4) illuminating the pupil by a combination thereof.

That is, according to the present invention, a pattern defect inspection apparatus includes a laser light source means for emitting an ultraviolet laser,
Coherence reducing means for reducing the coherence of the ultraviolet laser emitted from the laser light source means, irradiation means for irradiating the sample with an ultraviolet laser having reduced coherence by the coherence reducing means, Image detecting means for detecting an image of the sample irradiated with ultraviolet laser by the irradiating means, and defect detecting means for detecting a defect of a pattern formed on the sample based on information on the image of the sample detected by the image detecting means. It is characterized by comprising.

Further, according to the present invention, the pattern defect inspection apparatus includes a laser light source means for emitting an ultraviolet laser, a coherence reducing means for reducing the coherence of the ultraviolet laser emitted from the laser light source means, Objective lens means for irradiating the sample with an ultraviolet laser having passed through the coherence reducing means, image detecting means for detecting an image of the sample irradiated with the ultraviolet laser through the objective lens means, and a comparative image A defect in a pattern formed in the sample by comparing the image signal of the sample output from the image detection unit that has detected the image of the sample with the comparison image signal stored in the storage unit; And a defect detecting means for detecting the defect.

Further, according to the present invention, the pattern defect inspection apparatus includes a laser light source means for emitting an ultraviolet laser, a coherence reducing means for reducing the coherence of the ultraviolet laser emitted from the laser light source means, An objective lens means for irradiating the sample with an ultraviolet laser beam having passed through the coherence reducing means, a table means on which the sample is placed and movable in the XY plane, and an ultraviolet laser beam through the objective lens means. Time delay integration type image sensor means for detecting an image of the irradiated sample; control means for controlling the timing of movement of the table means and imaging of the time delay integration type image sensor means; and storing a comparison image signal. A storage means for comparing an image signal based on the image of the sample detected by the time delay integration type image sensor means with a comparative image signal stored in the storage means, It is characterized in that a defect of the formed pattern was constructed and a defect detection means for detecting.

Further, according to the present invention, a pattern defect inspection apparatus includes an ultraviolet laser light source, a coherence reducing means for lowering the coherence of an ultraviolet laser emitted from the ultraviolet laser light source, A projection means for projecting an ultraviolet laser beam having passed through the reduction means onto a pupil of the objective lens; and an ultraviolet laser projected on the pupil of the objective lens by the projection means, substantially in the detection field of the object through the objective lens. Illumination means, an image detection means for detecting an image of the object almost uniformly illuminated by the illumination means, and image data obtained from the image of the object detected by the image detection means are stored in advance. And a detecting means for detecting a defect on the object by comparing the image data.

The present invention also provides a laser light source having a wavelength of 4
A laser shorter than 00 nm is emitted, the emitted laser is irradiated on the sample through the coherence reducing means, an image of the sample irradiated with the laser is detected, and an information base on the detected image of the sample is detected. And detecting a defect of a pattern formed on the sample.

Further, according to the present invention, an ultraviolet laser is emitted from a laser light source, and the emitted ultraviolet laser is irradiated onto a sample via a coherence reducing means and an objective lens. The obtained image of the sample is detected through the objective lens, and the image signal of the sample image obtained through the detection through the objective lens is compared with the comparison image signal stored in the storage means to form the image on the sample. A pattern defect inspection method characterized by detecting a defect of a detected pattern.

Further, according to the present invention, an ultraviolet laser is emitted from a laser light source, and is mounted on a table which moves in a plane via a means for reducing coherence of the emitted ultraviolet laser and an objective lens. The image of the sample illuminated on the sample and irradiated with the ultraviolet laser through the objective lens is detected in synchronization with the movement of the table by a time-delay-integration type image sensor. A pattern defect inspection method characterized in that an image signal based on a detected image of a sample is compared with a comparative image signal stored in advance to detect a defect of a pattern formed on the sample.

Further, according to the present invention, an ultraviolet laser emitted from a laser light source is scanned on a pupil of an objective lens, and the ultraviolet laser scanned on the pupil is irradiated on a sample via an objective lens. Detecting the image of the sample irradiated by the laser with a storage type detector, and detecting the pattern defect formed on the sample using the image signal of the sample obtained by detecting with the storage type detector. Is a pattern defect inspection method characterized by the following.

Further, according to the present invention, the coherency of the coherent light emitted from the light source is reduced in the middle of the optical path, and the light having the reduced coherency is irradiated on the sample via the objective lens, thereby reducing the coherency. An image of the sample irradiated with light is detected by an accumulation type detector via an objective lens, and an image signal obtained from the image of the sample detected by the accumulation type detector is compared with a previously stored comparative image signal. This is a pattern defect inspection method characterized by detecting a defect of a pattern formed on a sample by comparing.

Further, according to the present invention, an ultraviolet laser is emitted from a laser light source, and the emitted ultraviolet laser is irradiated onto a semiconductor wafer on which a circuit pattern is formed via a coherence reducing means and an objective lens. A comparative image in which an image of a circuit pattern of a semiconductor wafer irradiated with an ultraviolet laser is detected by a solid-state imaging device via an objective lens, and an image signal based on the image of the circuit pattern detected by the solid-state imaging device is stored in advance. This is a pattern defect inspection method characterized by detecting a defect smaller than 0.2 μm on a semiconductor wafer by comparing with a signal.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method and an apparatus for inspecting a defect of a pattern to be inspected according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of an apparatus according to the present invention. Reference numeral 2 denotes an X, Y, Z, θ (rotation) stage on which a semiconductor wafer 1 as an example of a pattern to be inspected is placed. Reference numeral 7 denotes an objective lens. An illumination light source (UV laser) 3 illuminates the semiconductor wafer 1, which is an example of the pattern to be inspected. Reference numeral 5 denotes a polarizing beam splitter, which is configured to reflect illumination light from an illumination light source 7 and perform, for example, bright field illumination on the semiconductor wafer 1 through an objective lens 7. Reference numeral 6 denotes a quarter-wave plate, which forms a high-efficiency half mirror in combination with the polarization beam splitter 5. Reference numeral 4 denotes a scanning mechanism for scanning a laser beam from a light source on a pupil of the objective lens 7. Reference numeral 8 denotes an image sensor, which outputs a grayscale image signal corresponding to the brightness (shade) of light reflected from the semiconductor wafer 1, which is an example of a pattern to be inspected. Reference numeral 9 denotes an A / D converter, which converts a grayscale image signal obtained from the image sensor 8 into a digital image signal.

While scanning the stage 2 to move the semiconductor wafer 1 as an example of the pattern to be inspected at a constant speed, the brightness information of the pattern to be inspected formed on the semiconductor wafer 1 by the image sensor 8 (shading image signal ) Is detected.

Reference numeral 10 denotes a gradation converter, and an A / D converter 9
For digital image signals output from
It performs gradation conversion as described in JP-A-320294. That is, the flooring converter 10 performs logarithmic conversion, exponential conversion, polynomial conversion, and the like, and corrects an image in which illumination light causes thin-film interference by a thin film formed on a semiconductor wafer by a process, thereby causing uneven brightness. Things. The gradation converter 10 is configured to output, for example, an 8-bit digital signal. Reference numeral 11 denotes a delay memory for storing and delaying the output image signal from the gradation converter 10 for one cell or a plurality of cells constituting a repeated semiconductor wafer, or for one chip or one shot.

Reference numeral 12 denotes a comparator, which outputs a gradation-converted image signal output from the gradation converter 10 and the delay memory 1
This is to detect a defect by comparing with the delayed image signal obtained from Step 1.

The comparator 12 compares an image delayed by an amount corresponding to the cell pitch or the like output from the delay memory 11 with a detected image, and obtains array data on the semiconductor wafer 1 obtained based on design information. Input means 1 composed of a keyboard, a disk, etc.
By inputting in step 5, the CPU 13 creates defect inspection data based on the coordinates of the input arrangement data on the semiconductor wafer 1 and stores the result of the comparison by the comparator in the storage device 14. The defect inspection data can be displayed on a display device such as a display as needed, or can be output to an output device.

The details of the comparator are described in JP-A-61-212708.
For example, an image alignment circuit, a difference image detection circuit of an aligned image, a mismatch detection circuit for binarizing a difference image, a binarized output It is composed of a feature extraction circuit for renting out the area, length (projection length), coordinates, and the like.

Next, the light source 3 will be described. As described above, it is necessary to shorten the wavelength in order to increase the resolution. However, in the wavelength region of UV light (ultraviolet light) or DUV (far ultraviolet light) where the effect is most obtained, the wavelength is increased. It is difficult to obtain illuminance illumination. Discharge lamps are excellent UV light sources, and mercury xenon lamps are particularly
The bright line in the region is stronger than other discharge lamps.

FIG. 2 shows an example of the radiation intensity with respect to the wavelength of the mercury xenon lamp. Compared to the conventional wide wavelength range of visible light, the emission line in the DUV region is 1 to 3 of the total output light.
It is only 2% (about 30% in the visible region). Also,
The efficiency with which light emitted from a discharge lamp, which emits light in a non-directional manner, can be guided onto the sample is extremely low even with a carefully designed optical system.After all, illumination with a discharge lamp in the UV region requires a sufficient amount of light. It is very difficult to secure.

Even if a high-output discharge lamp is used to improve the illuminance (brightness) on the sample, the size of the luminescent spot is only larger than that of a low-output discharge lamp. However, this does not improve the luminance (light power per unit area).

Accordingly, UV or DUV (hereinafter, referred to as a central wavelength below 400 nm, preferably shorter than 300 nm).
It is considered that it is suitable to use a laser as a light source in order to perform effective and high-luminance illumination in a region (together, referred to as UV). The present invention provides means for solving the problem when illuminating a sample using the UV laser as a light source.

FIG. 3 shows the illumination state of the objective lens pupil and the visual field on the sample when illuminated with ordinary white light. A in the figure
S indicates a pupil and FS indicates a visual field. At the pupil position, the image of the light source forms an image 31, and at the position of the visual field, the entire visual field is almost uniformly illuminated.
2

Next, FIG. 4 shows a case where illumination is performed by a laser light source. In this case, the light source image 41 at the pupil position becomes a point.
The circuit pattern illuminated 42 in the visual field on the sample becomes, for example, an image having a detected waveform as shown in d) in the case of a cross-sectional pattern as shown in FIG.

As described above, when the circuit pattern is illuminated with the laser beam and an image of the circuit pattern is obtained, overshoot, undershoot, or speckle occurs at the edge portion due to the σ of the illumination. Because it is small. This means that the field of view on the sample below the objective lens is not illuminated from various angles. On the other hand, with normal white light illumination, illumination with a certain size is performed on the pupil, and the field of view on the sample is illuminated from a direction having an angle range equivalent to the NA (numerical aperture) of the objective lens. It is carried out.

For coherent (having coherence) light such as laser light, σ (proportional to the size of the light source on the pupil) is zero. This is because the image on the pupil becomes a point because the light source image of the coherent light is a point. Of course, as shown in FIG. 5, the light beam 51 expanded by another lens system can be projected on the pupil. However, since the laser has coherence, all light is eventually emitted from the position of σ = 0. The same result 52 is obtained, and this does not solve the problem. Therefore, means for reducing the coherence of the laser light is required. To reduce coherence, either temporal coherence or spatial coherence may be reduced. Therefore, in the present invention, an image of the light source is formed on the pupil of the objective lens of the inspection apparatus, for example, first illuminating the position 61 in FIG. It is proposed to scan as, and illuminate 65 on the visual field. During this time, images of speckle, overshoot, and undershoot are obtained at each position, but since the obtained times are different from each other, there is no interference with each other. Thus, when they are added on the detector, we end up with the same image as with an incoherent light source. For the addition on the detector, the detector is suitably a storage type detector such as a CCD image sensor.

The scanning in this case may be a spiral scan 66 or a television-like (raster) scan 67 as shown in FIGS. B) and c), or may be another scan. However, it goes without saying that scanning must be performed within the accumulation time of the detector. Therefore,
Scanning may be performed in synchronization with the operation of the detector.

In this way, in FIG. 6, it is possible to obtain an image of the illumination 65 with respect to the entire field of view such as a) FS in FIG.

Although not shown, a secondary light source composed of a plurality of point light sources is formed by inserting a fly-eye lens into the optical path of the UV laser light emitted from the laser light source. The same effect can be obtained by forming an image of the secondary light source consisting of the following on the pupil of the objective lens and changing the position of the image of the secondary light source with time on the pupil of the objective lens. it can.

Here, the detector is a storage-type detector, and a one-dimensional sensor (for example, a solid-state imaging device such as a CCD image sensor) which is advantageous for scanning an inspection sample at high speed over a narrow field of view like a microscope. Consider using). FIG.
As shown in (1), even if the one-dimensional sensor 71 illuminates the entire field of view, only the region 72 contributes to the detection, and the region 73 occupying most of the light power does not contribute to the detection. . In order to improve the illuminance, it is preferable to perform linear illumination on the one-dimensional sensor 71 as shown in an area 82 as shown in FIG. (A two-dimensional image is obtained by scanning the CCD image sensor in the direction perpendicular to the direction in which the sensor array of the CCD image sensor is arranged in the field of view.) In that case, on the pupil, as shown in FIG. (Longitudinal direction of 91 shown by a thick solid line in the figure) is illuminated, so that the field of view on the sample has a CCD image sensor 7
Lighting 92 conforming to the shape of 1 can be performed. Also,
Scanning on the pupil is performed in the X direction. At this time, the scanning cycle Ts is equal to the accumulation time T of the CCD image sensor.
Perform shorter than i. As a result, the images can be added. The problem is that, in this scanning, the illumination in the Y direction cannot be scanned because the illumination spreads from the beginning in the Y direction on the pupil. For this reason, overshoot / undershoot generated in the Y direction of the CCD image sensor in the visual field cannot be reduced. Conversely, when scanning in the Y direction on the pupil, Y
When the length in the direction is shortened, the width in the Y direction in the visual field increases, and the illuminance decreases.

To solve this problem, in the present invention, as shown in FIG. 10, among CCD image sensors, a TDI image sensor (Time Delay Integration image sensor): a plurality of one-dimensional image sensors are two-dimensionally integrated. The output of each one-dimensional image sensor is delayed by a predetermined time, and then added to the output of an adjacent one-dimensional image sensor that has imaged the same position of the target, thereby increasing the amount of detected light. (TDI image sensor). For a TDI image sensor,
Since N stages (several tens to 100 stages) of CCD image sensors are arranged in the field of view, the illumination light is effectively used for detection even if the width of the illuminated area in the field of view is increased N times.

Therefore, the length of the condensed light 102 on the pupil in the Y direction can be reduced to about 1 / N of that in the case of the CCD image sensor, so that the light can be scanned on the pupil in both the X and Y directions. Become. As a result, the X ·
Overshoots and undershoots occurring in both Y directions can be reduced, and a good detected image can be obtained.

The scanning period Ts on the pupil may be shorter than N times the accumulation time of one stage of the TDI image sensor. However, in consideration of the illuminance distribution generated in the visual field, it is preferable that Ts is shorter than 1/2 of N times Ti, for more uniform detection.

In order to perform uniform illumination on the visual field, it is preferable that the light from the laser light source is not focused directly on the pupil, but is focused through a fly-eye or an integrator.

Next, means for reducing spatial coherence will be described. In order to reduce the spatial coherence, light having an optical path difference longer than the coherence length of the laser may be obtained. More specifically, as shown in FIG. Is incident on the optical fiber 111 or the glass rod bundled with the length changed, the output light becomes incoherent (no coherence) light. By arranging these on the pupil, an image without overshoot, undershoot, and speckle can be obtained.

In this method, the shorter the coherence length of the laser light source, the better. For this purpose, as shown in FIG. 11A), the oscillation wavelength band Δλ1 is narrow, and a single longitudinal mode (oscillation spectrum) is obtained. It is more suitable to use a material having a plurality of longitudinal modes and a wide Δλ2 as shown in FIG.

As another device for reducing the spatial coherence, the lateral mode (spatial distribution, light intensity I with respect to space) of the emitted light changes when the optical fiber is incident on the optical fiber with the optical axis shifted. Some use the phenomenon.
Usually, such a mode change is considered to be a disadvantageous phenomenon for industrial use, and it is general to endeavor to reduce the change in the transverse mode. As shown in FIG. 12, various optical axes are deliberately shifted to be incident on the fiber 121, and emitted light a), b) c), d), e)...
As a result, the obtained emitted lights are incoherent with each other, and are arranged on the pupil.

FIG. 13 shows a state in which the light emitted from the laser light source 3 is separated by the polarizing beam splitter 131 into two lights 133/134 having polarization planes orthogonal to each other. 132 is a mirror for changing the direction.

Since light having polarization planes perpendicular to each other has no coherence, light having no coherence can be obtained with a very simple configuration. Although only two lights can be obtained by this method, by combining this with the method already described, light having no coherence can be easily obtained.

Further, since the light sources independent of each other have no coherence, as shown in FIG.
., Each point of the pupil of the objective lens 7 may be illuminated as it is.

If the above-described method using the polarizing beam splitter is combined with this, as shown in FIG.
The effect of doubling the laser light source can be obtained. If the number of beams is the same, the number of laser light sources can be reduced to half by using a polarizing beam splitter, and the cost can be reduced.

As described above, there have been described a plurality of means for reducing the coherence of the UV laser, illuminating a plurality of points on the pupil with the UV laser having the reduced coherence, and condensing the image with the objective lens to obtain an image. May be combined with each other, or a reduction method equivalent to these methods may be used.

Although not shown, a diffusion plate is inserted in the middle of the optical path of the UV laser, and the diffusion plate is rotated or reciprocated, thereby simultaneously reducing the spatial coherence and the temporal coherence of the UV laser. It can also be done. Further, this diffusion plate may be used in combination with the above-described other means for reducing coherence.

According to the present invention, a UV laser or a DUV laser having a short wavelength can be used with reduced coherence, so that a defect in a circuit pattern having a pattern width smaller than 0.2 μm can be sufficiently corrected. Can be detected.

[0059]

According to the present invention, high-intensity UV light emitted from a laser light source can be illuminated on a sample with reduced coherence, so that it can be compared with a conventional case where visible light is used as illumination light. As a result, a high-resolution image can be obtained, and a defect can be detected with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a defect inspection apparatus for a pattern to be inspected according to the present invention.

FIG. 2 is a diagram illustrating an emission spectrum of discharge tube illumination.

FIG. 3 is a diagram showing an illumination state on a pupil and a visual field of a detection objective lens by discharge tube illumination.

FIG. 4 is a diagram showing illumination conditions on a pupil and a visual field of a detection objective lens by laser illumination, a pattern on a visual field, and a detection signal therefrom.

FIG. 5 is a diagram showing an illumination state on a pupil and a field of view of a detection objective lens by laser illumination spread on a pupil.

FIG. 6 is a diagram showing an illumination state on a pupil and a field of view of a detection objective lens by laser illumination according to the present invention.

FIG. 7 is a diagram showing a relationship between a CCD image sensor detector and an illumination area in a visual field according to the present invention.

FIG. 8 is a diagram showing a relationship between a CCD image sensor detector and an illumination area in a visual field according to the present invention.

FIG. 9 is a diagram showing a CCD image sensor detector on a pupil and a field of view of a detection objective lens by laser illumination according to the present invention and an illumination state.

FIG. 10 is a diagram showing a TDI image sensor detector on a pupil and a field of view of a detection objective lens by laser illumination according to the present invention and an illumination state.

FIG. 11 is a diagram illustrating a device for reducing spatial coherence of laser illumination according to the present invention.

FIG. 12 is a diagram illustrating a device for reducing spatial coherence of laser illumination according to the present invention.

FIG. 13 is a diagram illustrating a device for reducing spatial coherence of laser illumination according to the present invention.

FIG. 14 is a diagram illustrating a device for reducing spatial coherence of laser illumination according to the present invention.

FIG. 15 is a diagram illustrating a device for reducing spatial coherence of laser illumination according to the present invention.

[Explanation of symbols]

1 ... inspection sample, 2 ... stage, 3 ... laser light source, 4 ...
Coherence reduction optical system, 7: objective lens, 8: detector, 19: signal processing circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko Nakata 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd. F-term (Reference) in Hitachi, Ltd. Production Research Laboratory 2F065 AA49 CC18 CC19 DD03 DD11 GG04 GG22 HH17 JJ00 JJ03 JJ26 LL03 LL10 LL36 LL37 MM16 PP12 QQ03 QQ11 QQ14 QQ24 QQ25 QQ27

Claims (21)

[Claims] 1. A laser light source means for emitting an ultraviolet laser, a coherence reducing means for reducing the coherence of an ultraviolet laser emitted from the laser light source means, and a coherence reducing means for coherence. Irradiating means for irradiating the sample with an ultraviolet laser with reduced intensity, image detecting means for detecting an image of the sample irradiated with the ultraviolet laser by the irradiating means, and an image of the sample detected by the image detecting means A defect detecting means for detecting a defect in a pattern formed on the sample based on information on the pattern. 2. The pattern defect inspection apparatus according to claim 1, wherein said coherence reducing means is means for reducing at least temporal coherence of said laser light source means. 3. The pattern defect inspection apparatus according to claim 2, wherein said coherence reducing means includes means for scanning a light spot converged on a pupil of an irradiation lens. 4. A laser light source means for emitting an ultraviolet laser, a coherence reducing means for reducing the coherence of the ultraviolet laser emitted from the laser light source means, and said laser light passing through said coherence reducing means. Objective lens means for irradiating the sample with an ultraviolet laser, image detection means for detecting an image of the sample irradiated with the ultraviolet laser through the objective lens means, and storage means for storing a comparison image signal, A defect for detecting a defect in a pattern formed on the sample by comparing an image signal of the sample output from the image detection unit that has detected the image of the sample with a comparison image signal stored in the storage unit; A pattern defect inspection apparatus comprising: a detection unit. 5. A laser light source means for emitting an ultraviolet laser, a coherence reducing means for reducing the coherence of an ultraviolet laser emitted from the laser light source means, and said laser light passing through said coherence reducing means. An objective lens means for irradiating the sample with an ultraviolet laser; a table means on which the sample is placed and movable in an XY plane; and an object lens means for irradiating the sample with the ultraviolet laser through the objective lens means. A time delay integration type image sensor means for detecting an image, a control means for controlling timing of movement of the table means and imaging of the time delay integration type image sensor means, and a storage means for storing a comparison image signal Comparing the image signal based on the image of the sample detected by the time delay integration type image sensor means with the comparison image signal stored in the storage means, Pattern defect inspection apparatus characterized by comprising a defect detection means for detecting defects made patterns. 6. The pattern defect inspection apparatus according to claim 4, wherein said coherence reducing means scans said ultraviolet laser on a pupil of said objective lens means. 7. The coherence reducing means has an optical path section composed of a plurality of optical fibers or glass rods having different lengths, and emits ultraviolet laser emitted from the laser light source section to a plurality of optical path sections. The pattern defect inspection apparatus according to claim 4, wherein the light is incident from one end of the optical fiber or the glass rod and is emitted from the other end toward the objective lens. 8. The coherence reducing means has an optical path section comprising a plurality of optical fibers or glass rods, and emits ultraviolet laser emitted from the laser light source means to the plurality of optical fibers or glass rods in the optical path section. The pattern defect inspection apparatus according to claim 4, wherein the light is incident on one end of the lens from an oblique direction and is emitted from the other end toward the objective lens. 9. An ultraviolet laser light source, a coherence reducing means for lowering the coherence of the ultraviolet laser emitted from the ultraviolet laser light source, and an ultraviolet laser passing through the coherence reducing means. Projecting means for projecting onto the pupil of the objective lens, illuminating means for illuminating the ultraviolet laser projected by the projecting means onto the pupil of the objective lens almost uniformly in the detection field of the object through the objective lens; Image detecting means for detecting an image of the object almost uniformly illuminated by the illuminating means, and comparing image data obtained from the image of the object detected by the image detecting means with previously stored image data And a detecting means for detecting a defect on the object. 10. A laser having a wavelength shorter than 400 nm is emitted from a laser light source, and the emitted laser is irradiated onto a sample via a coherence reducing means, and an image of the sample irradiated with the laser is detected. And detecting a defect of a pattern formed on the sample based on the detected information on the image of the sample. 11. An ultraviolet laser is emitted from a laser light source, and the emitted ultraviolet laser is irradiated onto a sample via a coherence reducing means and an objective lens, and the sample irradiated with the ultraviolet laser is emitted. Is formed on the sample by detecting the image of the sample through the objective lens, and comparing the image signal of the image of the sample obtained by detection through the objective lens with a comparison image signal stored in a storage unit. A pattern defect inspection method characterized by detecting a defect of a detected pattern. 12. A laser light source emits an ultraviolet laser, and irradiates a sample mounted on a table moving in a plane via a means for reducing the coherence of the emitted ultraviolet laser and an objective lens. Then, an image of the sample irradiated with the ultraviolet laser through the objective lens is detected in synchronization with the movement of the table by a time delay integration type image sensor, and detected by the time delay integration type image sensor means. A pattern defect inspection method, wherein an image signal based on the detected image of the sample is compared with a comparative image signal stored in advance to detect a defect in a pattern formed on the sample. 13. The apparatus according to claim 10, wherein the ultraviolet laser radiated to the sample via the coherence reducing means has a spatially reduced coherence. The described pattern defect inspection method. 14. The coherence reducing means includes a plurality of optical fibers or glass rods having different lengths, and the ultraviolet laser is used to control the plurality of optical fibers or glass rods having different lengths. 14. The pattern defect inspection method according to claim 13, wherein the ultraviolet laser reduces the spatial coherence by passing through. 15. The coherence reducing means has a plurality of optical fibers or glass rods, and the ultraviolet laser is obliquely incident on the plurality of optical fibers or glass rods of the coherence reducing means. 14. The pattern defect inspection method according to claim 13, wherein the ultraviolet laser is spatially reduced in coherence by passing through an optical fiber or a glass rod. 16. The apparatus according to claim 10, wherein the ultraviolet laser irradiating said sample via said coherence reducing means is detected on said sample with reduced coherence temporally. 13. The pattern defect inspection method according to any one of claims 12 to 12. 17. The method according to claim 17, wherein the position of a speckle formed on the sample is changed in a time shorter than the detection time by an ultraviolet laser irradiated to the sample via the coherence reducing means. 17. The method of claim 16, wherein the temporal coherence of an ultraviolet laser is reduced.
The described pattern defect inspection method. 18. An ultraviolet laser emitted from a laser light source is scanned on a pupil of an objective lens, and the ultraviolet laser scanned on the pupil is irradiated on a sample through the objective lens, and the ultraviolet laser is irradiated. Detecting the irradiated image of the sample with a storage-type detector, and detecting a defect in a pattern formed on the sample using an image signal of the sample obtained by detection with the storage-type detector. A pattern defect inspection method characterized by the following. 19. The pattern defect inspection method according to claim 18, wherein a cycle of scanning the ultraviolet laser on the pupil of the objective lens is shorter than an accumulation time of the accumulation type detector. 20. A method for reducing the coherency of coherent light emitted from a light source in the middle of an optical path, irradiating the light with reduced coherency onto a sample via an objective lens,
An image of the sample irradiated with the light with reduced coherency is detected by a storage-type detector via the objective lens, and an image signal obtained from the image of the sample detected by the storage-type detector is obtained. A pattern defect inspection method, wherein a defect of a pattern formed on the sample is detected by comparing with a comparative image signal stored in advance. 21. An ultraviolet laser is emitted from a laser light source, and the emitted ultraviolet laser is irradiated onto a semiconductor wafer on which a circuit pattern is formed via a coherence reducing means and an objective lens, and the ultraviolet laser is emitted. The solid-state imaging device detects an image of the circuit pattern of the semiconductor wafer illuminated by the solid-state imaging device through the objective lens, and an image signal based on the circuit pattern image detected by the solid-state imaging device is stored in advance. A pattern defect inspection method, wherein a defect smaller than 0.2 μm on the semiconductor wafer is detected by comparing with an image signal.