JP2002287327A - Defect inspection apparatus of phase shift mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect inspection apparatus for a phase shift mask which is capable of surely detecting the defect, more particularly microdefects of the phase shift mask. SOLUTION: This defect inspection apparatus has light releasing means 10 which releases light of a specific wavelength region, a differential interference optical system 11 which changes the light relapsed from this light releasing means 10 to two beams of light and forms a differential interference image from the edge information obtained by synthesis of two beams of the reflected light obtained when the surface of the phase shift mask 6 is irradiated with this light under prescribed conditions, an image resolving system 12 which resolves the differential interference image to two inspection images having different phase differences, two image detectors 13a and 13b which convert the respective images into electronic images and two signal processing circuits 14a and 14b which compare the two inspection images outputted from the respective image detectors 13 and 13b, with two reference images, respectively extract the different edge information for the reference images from the inspection images and detect the defects of the phase shift mask 6.

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 a phase shift mask, and more particularly, to a method for detecting various defects existing in a phase shift mask, in particular, a defect using a differential interference image. The present invention relates to a defect inspection apparatus for a phase shift mask capable of reliably detecting a minute defect by eliminating a blind spot. Note that the “phase shift mask” here includes a light-shielding pattern that defines a plurality of light-transmitting openings on a transparent substrate. A photomask formed with a phase shifter for giving a phase difference (FIG. 3
(a)).

[0002]

2. Description of the Related Art Phase shift masks are, for example, shown in FIGS. 3 (a) and 3 (b).
As shown in FIG. 1, a light-shielding pattern 2 and a light-transmitting opening pattern 3 are formed on a transparent substrate 1 such as glass, and the light-transmitting opening pattern 3 is formed by a shifter portion having a phase shifter.
3a and a non-shifter portion 3b not forming a phase shifter are alternately arranged in the X and Y directions. The non-shifter portion 3b exposes the surface of the transparent substrate 1 as it is, and the shifter portion 3a
λ / {2 (n-1)} (where λ is the exposure wavelength and n is the refractive index of the transparent substrate) is formed as a concave portion having a depth satisfying the relationship;
For example, a phase difference of λ / 2 is given between the light passing through the shifter 3a and the light passing through the non-shifter 3b.

As shown in FIGS. 2 (a) and 2 (b), the defects generated in the phase shift mask are, as shown in FIGS. 2 (a) and 2 (b), a convex defect 4 mainly generated due to a local shortage of etching. In the non-shifter portion 3b, a concave defect 5 mainly caused by local etching is formed.
Is mentioned. Further, when these defects 4 and 5 are roughly classified according to their generation positions, a central convex defect 4a and a central concave defect 5a which are isolated and generated at respective central positions of the shifter portion 3a and the non-shifter portion 3b, and a shifter portion 3a And a peripheral convex defect 4b and a peripheral concave defect 5b generated in contact with the respective peripheral positions of the non-shifter portion 3b.

If the above-mentioned defect exists in the phase shift mask 6, the phase difference between the light transmitted through the shifter 3a and the light transmitted through the non-shifter 3b may deviate from a design value (for example, λ / 2). The resolution decreases with the increase in the shift amount, and the quality of the exposure pattern deteriorates. Therefore, there is a strong demand for developing a means for accurately detecting a defect generated in a phase shift pattern in a manufacturing process of a phase shift mask.

A conventional defect inspection apparatus for a phase shift mask is disclosed in JP-A-5-142754 and JP-A-9-145.
The apparatus described in the former publication uses a comparison between two dies, that is, the interference between transmitted lights of a phase shift mask by a so-called Die to Die method. The apparatus described in (1) uses a comparison between a die and design data, that is, light transmitted through a phase shift mask by a so-called Die to Database method.

However, all of the devices described in the above-mentioned publications use transmitted light, and are suitable for obtaining information in the thickness direction of the phase shift mask. In the case where information on the surface such as the convex defect 4 existing in the non-shifter portion 3b or the concave defect 5 existing in the non-shifter portion 3b is obtained, sufficient detection sensitivity cannot be obtained. Therefore, there is a problem that the apparatus becomes large-scale because it is necessary to prepare a light source having an inspection wavelength equal to the above. In addition, the latter Die
The to Database method also has a problem that the device becomes large because it is necessary to change the wavelength and to create reference data based on the design data in advance for comparison with the detection data.

As a defect inspection apparatus using reflected light instead of using transmitted light as in the above-described apparatus,
Unexamined Japanese Patent Application No. 10-filed by the applicant and already published
No. 177246 discloses a device in which a single die is in a polarization state that is largely shifted in a specific direction (specifically, almost half the size of the phase shifter).
Illuminates the light, synthesizes the interference image obtained by the two reflected lights from the phase shift mask, and compares it with the interference image obtained by another die using the same method to detect defects. can do. Another advantage of the defect inspection apparatus using the reflected light is that information can be obtained through a reciprocating optical path, so that higher sensitivity can be obtained as compared with the transmission method. For example, the wavelength at the time of exposure is 248 nm, and the wavelength at the time of inspecting a defect (inspection wavelength)
Is 488 nm, about twice the sensitivity can be obtained as compared with the transmission system.

However, in the apparatus described in Japanese Patent Application Laid-Open No. Hei 10-177246, in order to minimize the occurrence of a pseudo defect when the phase shifter is formed by a concave portion, the lateral shift amount of the two lights is set to be large. However, the present applicant has further studied and found that when a plurality of small defects having a smaller plane size exist at close positions, signals obtained from these small defects overlap. It was found that sufficient surface resolution could not be obtained, and it was difficult to specify a defective address. Further, if a defect has a specific phase amount, the signal levels of the inspection image and the reference image match, and the defect may not be detected as a defect.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a defect inspection apparatus for a phase shift mask, and more particularly, a method for detecting various defects existing in a phase shift mask, particularly, a defect using a differential interference image. An object of the present invention is to provide a defect inspection apparatus for a phase shift mask that can reliably detect a minute defect by eliminating a blind spot in the method.

[0010]

In order to achieve the above object, a defect inspection apparatus for a phase shift mask according to the present invention comprises a light-shielding pattern defining a plurality of light-transmitting openings on a transparent substrate. A defect inspection apparatus for a phase shift mask formed by forming a phase shifter that gives a phase difference between exposure lights passing therethrough in one of the openings,
A light emitting means for emitting light in a specific wavelength range, and the light emitted from the light emitting means is changed into two lights in a polarized state, and these lights are specified relative to each other on the surface of the phase shift mask. A differential interference optical system for irradiating with a slight lateral shift in the direction and forming a differential interference image from edge information representing the surface shape of the phase shift mask obtained by combining two reflected lights from the phase shift mask surface; An image decomposition system that decomposes the differential interference image into first and second inspection images that are two differential interference images having different phase differences;
A first image detector for converting the first inspection image into an electronic image, and a first inspection image output from the first image detector, which is associated with the first inspection image by another means. A first signal for comparing the obtained first reference image and extracting first edge information, which is different edge information for the first reference image, from the first inspection image to detect a defect of the phase shift mask; A processing circuit, a second image detector for converting the second inspection image into an electronic image, and a second inspection image output from the second image detector corresponding to the second inspection image. A second edge information, which is different edge information for the second reference image, is extracted from the second inspection image by comparing with a second reference image obtained by another means, and a defect of the phase shift mask is detected. Having a second signal processing circuit A.

The light emitting means includes a mercury lamp as a light source, a condensing lens for condensing light emitted from the mercury lamp, and a light transmitted through the condensing lens. Or a laser oscillator serving as a light source, and an acousto-optic device that vibrates laser light emitted from the laser oscillator in the main scanning direction. When,
It is preferable to adopt a configuration having a relay lens.

The differential interference optical system includes a polarizer for selectively transmitting only specific light out of the light emitted from the light emitting means, and a polarizer for reflecting substantially half of the light transmitted through the polarizer. It is possible to provide a configuration including a half mirror, a Nomarski prism that changes light into two by transmitting light reflected by the first half mirror, and an objective lens that focuses light transmitted through the Nomarski prism. preferable.

The image resolving system includes a second half mirror for decomposing the differential interference image formed by the differential interference optical system into first and second inspection images as transmitted light and reflected light, respectively, and the second half mirror and the first half mirror. Alternatively, it is preferable to provide a configuration having a phase plate that is disposed between the second image detector and the phase difference between the incident lights.

The image detector is a linear image sensor in which a plurality of light receiving elements are arranged in a line in a direction corresponding to the main scanning direction, or a two-dimensional imaging in which a plurality of light receiving elements are arranged in a two-dimensional array. Preferably it is a device.

It is preferable to irradiate the two lights in the polarized state on the surface of the phase shift mask while being shifted laterally by 45 ° with respect to each other. It is more preferable to irradiate the surface of the phase shift mask with a lateral shift within a range smaller than half the dimension of the phase shifter.

Further, the detection of the defect is performed by the first and second steps.
An inspection image optical system for obtaining an inspection image and a reference image optical system for obtaining the first and second reference images are provided above the same phase shift mask, and both image optical systems have the same configuration. It is preferable to detect a defect using these, or to detect a defect using the same image optical system for both the first and second inspection images and the first and second reference images.

In addition, as means for scanning two light beams to be irradiated on the surface of the phase shift mask, the phase shift mask is mounted on an xy stage movable in a main scanning direction and a direction orthogonal to the main scanning direction. And moving the xy stage.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings. FIG. 1 schematically shows an example of the configuration of a phase shift mask defect inspection apparatus according to the present invention, and FIG. 2 shows the surface of a phase shift mask having a convex defect 4 and a concave defect 5. FIG. 3 shows the surface shape of a phase shift mask having no defect. FIG. 2 (a) and FIG. 3 (a) are diagrammatic plan views, and FIG. Is a cross-sectional view taken along the line II-II in FIG.
(b) is a sectional view taken along line III-III in (a) of FIG.

The phase shift mask 6 is provided on the transparent substrate 1.
A light-shielding pattern 2 and a plurality of light-transmitting aperture patterns 3 defined by the light-shielding pattern 2 are provided.

As shown in FIG. 2A, the light transmitting aperture pattern 3 has a shifter portion 3a having a phase shifter and a non-shifter portion 3b having no phase shifter alternately arranged in the X and Y directions. The non-shifter portion 3b exposes the surface of the transparent substrate 1 as it is, and the shifter portion 3a has d = λ / ｛2 (n−
1) Under the design, a phase shifter is formed as a concave portion having a depth satisfying the relationship of｝, and a phase difference of λ / 2 occurs between light passing through the shifter portion 3a and light passing through the non-shifter portion 3b. It was formed. 2A and 3A, the shifter 3a
The shifter 3a is hatched in order to distinguish between the shifter 3b and the non-shifter 3b.

The defect inspection apparatus 7 shown in FIG. 1 includes an inspection image optical system 8 for obtaining an inspection image and a reference image optical system 9 for obtaining a reference image. And the reference image from the reference image optical system 9 to perform a defect inspection. In FIG. 1, the inspection image optical system 8 and the reference image optical system 9 are image optical systems having the same configuration, and these image optical systems are configured to image adjacent chips or dies in the same phase shift mask. I do.

In the case of FIG. 1, the optical system shown on the right is the inspection image optical system 8, and the optical system shown on the left is the reference optical system 9.
It is. These optical systems 8 and 9 include a light emitting means 10, a differential interference optical system 11, an image resolving system 12, and a first
And second image detectors 13a and 13b, and first and second signal processing circuits 14a and 14b.

As shown in FIG. 1, for example, the light emitting means 10 includes a mercury lamp 15 as a light source, a condenser lens 16 for condensing light emitted from the mercury lamp 15, and a condenser lens 16 Light of a specific wavelength range among transmitted light, for example, i
And a band-pass filter 17 for selectively transmitting only light having a specific wavelength of 365 nm in the case of a g-line and 436 nm in the case of a g-line. Alternatively, as shown in FIG. A laser oscillator 18, an acousto-optic device 19 for vibrating a laser beam emitted from the laser oscillator 18, for example, an 488 nm Ar laser beam in the main scanning direction, and a relay lens 20.
However, it is not particularly limited to these configurations, and other light emitting means may be used as long as light in a specific wavelength range can be emitted. In the latter case, the acousto-optic element 19 is used as a means for scanning the laser beam in the main scanning direction. However, the phase shift mask 6 can be moved in the main scanning direction and in a direction orthogonal thereto.
If the xy stage is placed on the -y stage and the xy stage is also moved in the main scanning direction, the arrangement of the acousto-optic element 19 can be omitted.

The differential interference optical system 11 converts the light emitted from the light emitting means 10 into a light having a specific vibration surface, for example, by transmitting the light through a polarizer 21 shown in FIG. The light is made incident on a mirror 22, and about half of the incident light is reflected by the first half mirror 22 and is reflected by a Nomarski prism.
23, and the remaining light quantity is absorbed after passing through the first half mirror 22. The Nomarski prism 23 changes the two lights in a polarized state and places these lights on the surface of the phase shift mask 6 in a specific direction (preferably
Irradiation is performed by slightly shifting (preferably within a range smaller than の of the opening size of the shift portion 3a in which the phase shifter is formed) a horizontal shift in the direction of 45 °. A differential interference image is formed from edge information indicating the surface shape of the phase shift mask 6 obtained by combining two reflected lights from the surface of the mask 6 (see FIG. 5).

The amount of the lateral shift depends on the mask design rule, the allowable defect size, etc., but is preferably at least ４ and less than の of the opening size of the shift portion 3a. In the case of the 130 nm rule in the device, it is more preferable to set it to 150 to 300 nm.

FIG. 4 shows an image obtained by projecting two images obtained by irradiating two lights laterally displaced in the direction of 45 ° on the surface of the phase shift mask 6 onto an image detector. FIG. 5 shows an example of a differential interference image obtained from this projection image. Note that the “edge information” here refers to information such as contours of the shifter portion 3a and the non-shifter portion 3b, which are light transmitting apertures, and contours of convex defects and concave defects. As shown in FIG. 5, this is information having a certain line width corresponding to the horizontal shift amount.

As shown in FIG. 1, the image resolving system 12 decomposes the differential interference image formed by the differential interference optical system 11 into first and second inspection images as transmitted light and reflected light, respectively.
The half mirror 24 is disposed between the second half mirror 24 and the first or second image detector 13a, 13b (in FIG. 1, between the second half mirror 24 and the second image detector 13b). In addition, it is preferable to adopt a configuration having a phase plate 25 that causes a phase difference in incident light, but it is not limited to this configuration.

The image detectors 13a and 13b are for converting the differential interference image into an electronic image, and are two-dimensional imaging devices 26a and 26a in which a plurality of light receiving elements are arranged in a two-dimensional array.
26b (FIG. 1) or a linear image sensor in which a plurality of light receiving elements are arranged in a line in a direction corresponding to the main scanning direction
26c, 26d (FIG. 13).

The signal processing circuits 14a and 14b output inspection images 27 which are output images of the first and second image detectors 13a and 13b, respectively.
a, 27b are compared with reference images 28a, 28b obtained by another means.
a, 29b are the reference images 28a,
The defect of the phase shift mask 6 can be detected by extracting only the different edge information for 28b. It is preferable that the inspection images 27a, 27b and the reference images 28a, 28b are amplified by image signal amplifiers 31a, 31b as shown in FIG. 1 and then compared by comparison circuits 29a, 29b.

FIG. 6 shows different edge information for the first or second reference image 28a or 28b from the first or second inspection image 27a or 27b in each comparison circuit 29a or 29b. This shows an example of an image when only the second edge information 30a or 30b is extracted.

FIGS. 7 (a) to 7 (d) show examples of a reference image of the shifter section 3a and typical inspection images of each defect. FIGS. 8 (a) to 8 (d) show 4 shows an example of a reference image of the non-shifter portion 3b and a typical inspection image of each defect. Fig. 7
When extracting a defect extraction image as shown in FIG. 6 from the reference image of the shifter section 3a and the inspection image in (a) to (d), the signal intensity of each defect portion in the inspection image is two edge information components. The signal intensity of each edge information component is represented by I _i (i is 1-1a to 1-3a and 1-1b to 1-3b in FIG. 7), and the signal intensity of a portion corresponding to the reference image is represented by I _i . _Is I _refi (i is 1 in FIG. 7), and R is the signal strength of each edge information component of the defect portion in the defect extraction image, and R = I _i −I _refi can be defined. Further, the case of the non-shifter portion 3b shown in FIGS. 8A to 8D can be similarly defined.

At this time, FIG. 9 shows the signal intensity of each edge information component of the defect portion in the defect extraction image plotted against the defect phase amount (°). FIG. 9 shows the first embodiment of the present invention. It shows an example when a defect signal is obtained by an image detector.

From the results shown in FIG.
Signal strength I of the obtained two edge information_1-1aAnd I
_1-1bAnd two edge information obtained from the central concave defect
Signal strength I _2-1aAnd I_2-1bAnd the same defect rank
In the case of phase amount, one edge information signal from the central convex defect
Strength I_1-1aOf edge information from the central concave defect
Signal strength I_2-1bAre the same (ie, FIG. 9
It is confirmed that each waveform shown in
means. ), Signal of other edge information from central convex defect
Signal strength I_1-1bAnd other edge information from the central concave defect
Signal strength I_2-1aIt turns out that becomes the same.

In the case of the left peripheral convex defect, the right peripheral convex defect, the left peripheral concave defect, and the right peripheral concave defect, the signal intensity of one edge information component of the two edge information components is respectively included. I _1-2a , I _1-3b , I _2-2a and I
_2-3b are the signal intensities I _1-2a and I
_2-3b with is the same as the signal strength I _1-1a and I _2-1b central defect, the signal intensity I _1-3b and I _2-2a is central defect signal intensity I _1-1b and I _{2 -1a} , but
It can be seen that the signal intensities I _1-2b , I _1-3a , I _2-2b and I _2-3a of the other edge components all have different waveforms from the other signal intensities.

Further, based on these results, the edge information components of the defect intersect (coincide) at the position of the phase amount where R = 0.
In this case, it means that the defect detection signal cannot be detected with respect to the type and phase amount of the defect. That is, in the case of FIG. 9, when the defect phase amount is 90 °, the signal intensities I _1-1a and I _1-1b of the edge component of the central convex defect and the signal intensity I _2- of the edge component of the central concave defect _1a and I _2-1b are both zero, and both edge information components of the central convex defect and the central concave defect are the same as the signal intensities I _ref1 and I _{ref2 of} the portions corresponding to the respective reference images. This is because it is not possible to detect.

FIGS. 10 (a) and 10 (b) show a reference image when the central convex defect cannot be detected by the first image detector when the central convex defect present in the shifter portion 3a exists. 9 shows an example of an inspection image. In this case, it can be seen that the reference image and the inspection image are the same.

FIG. 11 is a graph in which the signal strength of each edge information component of a defect portion in the defect extraction image obtained by the second image detector of the present invention is plotted against the defect phase amount (°). FIG. 11 shows a case where a phase difference of 90 ° is given between the normal light and the abnormal light by the function of the phase plate.

FIGS. 12A and 12B show an example of a reference image and an inspection image in the case where a central convex defect exists in the shifter portion 3a. It can be seen that the central convex defect that could not be detected by the image detector was detected. In addition, a similar test was performed for the central concave defect, and it was confirmed that the defect was detected in the same manner as the central convex defect.

From the above, the central convex defect having a specific defect phase amount (90 ° in the above case) cannot be detected from the edge information obtained from the first image detector, but has a specific phase difference. By providing the information, the edge can be detected by the edge information obtained from the second image detector. Therefore, in the present invention, since the two image detectors are simultaneously operated to detect a defect, one image is detected. The dead zone of the detector can be compensated for by the other image detector. As a result, the defect inspection apparatus of the present invention can reliably detect even a minute defect having any amount of phase by a single inspection. This makes it possible to detect a defect of a phase shift mask, in particular, a defect using a differential interference image, thereby eliminating a blind spot and reliably detecting a minute defect.

FIG. 1 shows a case in which the inspection images 27a, 27b and the reference images 28a, 28b are obtained by using different image optical systems 8, 9, but as shown in FIG. image
Both 27a, 27b and reference images 28a, 28b can be obtained using the same image optical system 8.

It is preferable to use an xy stage 32 movable in the main scanning direction and in a direction perpendicular to the main scanning direction as a means for scanning the irradiation light on the surface of the phase shift mask.

[0042]

Next, an embodiment of a defect detecting apparatus for a phase shift mask according to the present invention will be described in detail.

Embodiment 1 The defect inspection apparatus of Embodiment 1 has a configuration as shown in FIG. In other words, the inspection image optical system 8 and the reference image optical system 9 having the same configuration are provided, and each of the image optical systems 8 and 9 uses the mercury lamp 15 as a light source for generating illumination light and is emitted from the mercury lamp 15. The light beam enters the band-pass filter 17 and the polarizer 21 through the condenser lens 16 and, for example, i
Only radiation having a specific vibration surface at a specific wavelength such as a line, a g-line, or another wavelength (e-line or the like) is selectively transmitted. still,
In this embodiment, the wavelength (inspection wavelength) of light to be selectively transmitted is 365 nm.

Next, the selectively transmitted light is incident on the first half mirror 22, and the light amount of about half is reduced by the first half mirror 22.
And the remaining light quantity is absorbed after passing through the first half mirror 22. The light reflected by the first half mirror 22 is made incident on the Nomarski prism 23 constituting the image optical systems 8 and 9 together with the objective lens 33. Nomarski Pris 23
Set so that the angle of the wedge is 45 ° with respect to the polarization direction. Accordingly, two mutually coherent illumination lights (illumination light by normal light and illumination light by extraordinary light) which are shifted from the Nomarski prism 23 in the horizontal direction by 45 ° are emitted, and these illumination lights enter the objective lens 33. The objective lens 33
The rear focal point is arranged so as to coincide with the intersection of the normal light and the abnormal light of the Nomarski prism 23.

Accordingly, two illumination lights parallel to each other and slightly displaced in the horizontal direction are emitted from the objective lens 33, and are perpendicularly incident on the phase shift mask 6 to be inspected for defects arranged on the xy stage 32. I do. As a result, the phase shift mask 6
Will be illuminated by two illumination lights that are coherent and shifted from each other.

The two reflected lights from the phase shift mask 6 are combined by the Nomarski prism 23 via the objective lens 33. Further, the light combined by the Nomarski prism 23 is transmitted by the first half mirror 22 with only about half the amount of light and enters the second half mirror 24,
In the second half mirror 24, as in the case of the first half mirror 22, about half of the light is transmitted and the remaining light is reflected.

The light transmitted through the second half mirror 24 is subjected to interference by the analyzer 34a extracting a polarized light component selected from the normal light and the extraordinary light.
Through the two-dimensional imaging device 26a as the first image detector 13a
Incident on. On the other hand, the light reflected by the second half mirror 24 gives a specific phase difference between the normal light and the abnormal light by the phase plate 25. Further, interference is generated by extracting a polarized light component selected from the normal light and the abnormal light by the analyzer 34b, and enters the two-dimensional imaging device 26b as the second image detector 13b via the imaging lens 35b. .

The combined image combined by the Nomarski prism 23 is projected on each of the first and second image detectors 13a and 13b. Since the two images to be combined are images formed by mutually coherent illumination light, the combined image is an interference image. Therefore, the output signals of the first and second image detectors 13a and 13b are based on the intensity determined by the amplitude and the phase information of the reflected light, and the interference image obtained by the first image detector 13a and
The interference image obtained by the second image detector 13b is a result of providing a different phase difference between the normal light and the abnormal light, so that the two interference images are different.

Thereafter, the respective two-dimensional imaging devices 26a, 26
b are sequentially read out and supplied to comparison circuits 29a and 29b via respective image signal amplifiers 31a and 31b. Also,
The reference image signal from the reference image optical system 9 is also supplied to comparison circuits 29a and 29b via an image signal amplifier. And a comparison circuit
At 29a and 29b, the inspection image signal is compared with the reference image signal to output a defect detection signal.

The Nomarski prism 23 is set so that the angle of the wedge is 45 ° with respect to the polarization direction.
The two images are combined with a lateral shift of 45 °. The amount of the lateral shift can be freely set by the declination angle between the normal ray and the extraordinary ray by the Nomarski prism 23 and the focal length of the objective lens 33.
Can be arbitrarily set according to the planar size of the defect to be detected. As a result,
The composite image shown in FIG. 4 is projected onto the two-dimensional imaging devices 26a and 26b.

Since the composite image is a composite image composed of two images formed by mutually coherent illumination light, the image signals output from the two-dimensional imaging devices 26a and 26b include not only the amplitude but also the phase information. The resulting interference image signal is included. Such image interference is generally referred to as differential interference because interference occurs in the laterally shifted direction in accordance with the change in the phase of the reflected light from the phase shift mask 6, and is obtained. The image is a differential interference image in the same direction.

In the differential interference image obtained in this manner, the signal intensity of the contour where the surface shape of the phase shift mask 6 changes is changed by the light-shielding pattern 2, the shifter 3a and the non-shifter 3b.
Thus, an image changed with respect to the signal intensity at is obtained. This image is obtained not only for the contours of the shifter portion 3a and the non-shifter portion 3b in the phase shift mask 6, but also for the defect existing at the center of the shifter portion 3a and the non-shifter portion 3b, Can also be obtained for the contours of defects existing in

These signal intensities change in accordance with the phase difference between the normal ray and the extraordinary ray, and the Nomarski prism
By adjusting the position of 23, it can be changed freely.By adjusting this appropriately, it is possible to adjust the intensity of the signal generated according to the contour of the defect and the contour of the shifter 3a and the non-shifter 3b. And the resulting signal strength.

The two inspection images 27a and 27b obtained by the inspection image optical system 8 and the two reference images 28a and 28b obtained by the reference image optical system 9 are compared by comparison circuits 29a and 29b, respectively. As shown in FIG. 6, the inspection images 27a, 27
b, different edge information 30a for the reference images 28a and 28b,
Only 30b is extracted and these are output as images, and since these images can extract only the outline of the defective portion, the addresses for specifying the defect positions,
A signal corresponding to the size of the defect and the depth direction of the defect is obtained, whereby the defect of the phase shift mask can be detected.

Embodiment 2 The defect inspection apparatus according to the second embodiment is a defect inspection apparatus having a higher resolution than the apparatus according to the first embodiment.
It has a configuration as shown in FIG. That is, the inspection image 27a,
27b and the reference images 28a and 28b are both obtained by using the same image optical system, and the wavelength is set as a light source for generating illumination light.
A laser oscillator 18 for generating an Ar laser beam having a wavelength of 488 nm is used. The laser beam emitted from the laser oscillator 18 is made incident on an acousto-optic element 19 via an expander and a collimator lens (not shown), and Vibration is performed at high speed in the scanning direction (x direction).

This laser beam enters the first half mirror 22 via the relay lens 20, and the light amount of about half thereof is reduced to the first half mirror.
The light is reflected by the half mirror 22 and enters the Nomarski prism 23 constituting the differential interference optical system. The laser light becomes two beam lights slightly shifted laterally by the Nomarski prism 23, and these two beam lights are focused on the objective lens 33 together with the Nomarski prism 23 and arranged on the xy stage 32. The light vertically enters the phase shift mask 6 to be inspected for defects. As a result, the phase shift mask 6
Is two-dimensionally scanned by two minute spots formed by two focused light beams slightly displaced from each other.

The two reflected lights from the phase shift mask 6 are combined by the Nomarski prism 23 via the objective lens 33. Further, the light combined by the Nomarski prism 23 is transmitted by the first half mirror 22 with only about half the amount of light and enters the second half mirror 24,
As in the case of the first half mirror 22, about half of the light is transmitted and the remaining light is reflected.

The light transmitted through the second half mirror 24 is subjected to interference by the analyzer 34a extracting a polarized light component selected from the normal light and the extraordinary light.
Then, the light enters the linear image sensor 26c, which is the first image detector 13a. On the other hand, the light reflected by the second half mirror 24 gives a specific phase difference between the normal light and the abnormal light by the phase plate 25. Further, interference is generated by extracting a polarized light component selected from normal light and abnormal light by the analyzer 34b, and the second image detector 13 passes through the imaging lens 35b.
b is incident on the linear image sensor 26d.

Each of the linear image sensors 26c and 26d has a plurality of light receiving elements arranged on a line in a direction corresponding to the main scanning direction. Therefore, the reflected beam from the phase shift mask 6 scans the linear image sensors 26c and 26d at high speed. Since the light receiving elements of the linear image sensors 26c and 26d form a confocal optical system having a masked minute light incident surface, it is possible to capture a high-resolution differential interference image with flare light removed. it can.

As shown in FIG. 14, the output signals from the linear image sensors 26c and 26d are read out line by line and supplied to the image signal amplifiers 31a and 31b, respectively. The signal is supplied to delay circuits 36a and 36b.
Is supplied to the comparison circuits 29a and 29b via the comparators 29a and 29b.
Supplied to 29b.

The delay amounts of the delay circuits 36a and 36b can be freely set in consideration of the periodicity of the pattern to be inspected.
A defect detection signal is generated based on a difference between the two signal waveforms by comparing the image signal supplied via 36.

The drive control of the defect inspection apparatus is performed by a synchronization signal supplied from a synchronization signal generation circuit 37. An AO synchronization signal is supplied from the synchronization signal generation circuit 37 to the AO driver 38, and the AO driver 38 controls the driving of the acousto-optic element 19. In addition, the stage drive circuit
A synchronizing signal is supplied to 39, and the xy stage 32 is moved in the x and y directions by a driving mechanism (not shown). Further, a synchronizing signal is supplied from the synchronizing signal generating circuit 37 to the CCD driver 40 to read out the electric charges accumulated in each light receiving element of each linear image sensor 26c, 26d line by line. Further, the synchronization signal is supplied from the synchronization signal generation circuit 37 to the defect coordinate storage circuit 41, and the defect detection signal is also supplied to specify the address where the defect is present and store the address.

Therefore, the defect inspection apparatus according to the second embodiment can accurately detect the address at which a defect exists by employing such a configuration.

The present invention is not limited to the above-described embodiment, and various changes and modifications are possible. For example, as the reference image information, the entire image signal of the phase shift mask 6 to be inspected is stored in a memory, and the image signal obtained in the inspection process is compared with the image signal stored in the memory to detect the presence of a defect. Can also be detected.

Further, in the case of FIG. 4, attention is paid to the periodicity of the pattern to be inspected of the phase shift mask 6, and a case is shown in which the pattern is laterally shifted by 45 ° with respect to the periodic change direction (x, y directions). However, depending on the pattern shape and the periodic direction of the phase shift mask 6 to be inspected, or the pattern of the defect, the apparatus may be configured to be shifted laterally in a direction different from 45 °.

Further, in the above-described embodiment, the differential interference image obtained by the second image detector is 90% smaller than the differential interference image obtained by the first image detector by the function of the phase plate.
Although a case where a phase difference of 90 ° is given is shown, a case where a phase difference other than 90 ° may be given may be used. In addition, the device configuration of the present invention can be obtained from the first and second image detectors. In addition to the edge information, a device configuration including third and subsequent image detectors that can obtain images by giving different phase differences may be used.

Further, in each of the above-described embodiments, the Nomarski prism 23 is used as an optical element constituting the image optical systems 8 and 9. However, two light beams such as a Wollaston prism and a lotion prism are generated. Optical elements can also be used.

In addition, in the above-described embodiment, the defect inspection of the phase shift mask 6 having the phase shifter giving the phase difference of λ / 2 has been described, but λ / 6, λ / 3, 2λ /
Needless to say, the present invention can be applied to defect inspection of a phase shift mask in which a phase shifter giving a desired phase difference such as 3 is formed.

[0069]

As described above, according to the present invention,
Using the image optical system having the above-described configuration, edge information representing the surface shape of the phase shift mask obtained by synthesizing two reflected lights slightly shifted laterally from the surface of the phase shift mask is obtained, and two types of inspection images are obtained. By extracting only different edge information for each reference image from the reference image, even if there is a minute defect in the shifter portion and the non-shifter portion that cannot be detected by the conventional defect inspection device, A remarkable effect that the contour can be reliably detected as a change in signal strength can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of a defect inspection apparatus (first embodiment) for a phase shift mask according to the present invention.

FIGS. 2A and 2B show a configuration of a phase shift mask having a defect in a shifter portion and a non-shifter portion, wherein FIG. 2A is a plan view and FIG. 2B is a cross-sectional view taken along line II-II of FIG.

3A and 3B show a configuration of a phase shift mask having no defect in a shifter portion and a non-shifter portion, wherein FIG. 3A is a plan view and FIG. 3B is a cross-sectional view taken along line III-III of FIG. .

FIG. 4 is a diagram showing an example of an image synthesized by two reflected lights.

FIG. 5 is a diagram showing an example of a differential interference image of a phase shift mask projected on an image detector.

FIG. 6 is a diagram showing signal processing for detecting a defect from the inspection image and the reference image projected on the image detector.

FIG. 7 is a diagram illustrating an example of a reference image of a shifter section 3a and an inspection image when various convex defects exist.

FIG. 8 is a diagram showing an example of a reference image of a non-shifter portion 3b and an inspection image when various concave defects exist.

FIG. 9 is a diagram in which a defect signal intensity R of an edge information component of each defect obtained by a first image detector is plotted with respect to a defect phase amount.

FIG. 10 is a diagram showing an example of a reference image and an inspection image obtained by a first image detector in a shifter section 3a having a central convex defect.

FIG. 11 is a diagram in which a defect signal intensity R of an edge information component of each defect obtained by a first image detector is plotted with respect to a defect phase amount.

FIG. 12 is a diagram showing an example of a reference image and an inspection image obtained by a second image detector in a shifter section 3a having a central convex defect.

FIG. 13 is a diagram illustrating an example of a schematic configuration of a defect inspection apparatus for a phase shift mask according to a second embodiment.

FIG. 14 is a diagram illustrating an example of a schematic configuration of a defect inspection apparatus for a phase shift mask according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light-shielding pattern 3 Light transmission opening pattern 3a Shifter part 3b Non-shifter part 4 Convex defect 4a Central convex defect 4b Peripheral convex defect 5 Concave defect 5a Central concave defect 5b Peripheral concave defect 6 Phase shift mask 7 Defect inspection Apparatus 8 Inspection image optical system 9 Reference image optical system 10 Light emitting means 11 Differential interference optical system 12 Image decomposition system 13a First image detector 13b Second image detector 14a First signal processing circuit 14b Second signal processing circuit 15 Mercury Lamp 16 Condenser lens 17 Band pass filter 18 Laser oscillator 19 Acousto-optic element 20 Relay lens 21 Polarizer 22 First half mirror 23 Nomarski prism 24 Second half mirror 25 Phase plate 26a, 26b Two-dimensional imaging device 26c, 26d Linear image Sensor 27a First inspection image 27b Second inspection image 28a First reference image 28b Second reference image 29a First comparison circuit 29b Second comparison circuit 30a, 30b Defect edge information 31a , 31b Image signal amplifier 32 xy stage 33 Objective lens 34a, 34b Analyzer 35a, 35b Imaging lens 36a, 36b Delay circuit 37 Synchronous signal generation circuit 38 AO driver 39 XY stage drive circuit 40 CCD driver 41 Defect Coordinate storage circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 21/956 G06T 1/00 305A 5L096 G06T 1/00 305 7/00 300E 7/00 300 H01L 21/66 J H01L 21/027 G01B 11/24 F 21/66 H01L 21/30 502P F-term (reference) 2F065 AA03 AA12 AA49 AA56 CC00 CC18 DD03 FF49 FF52 GG04 GG12 GG22 HH04 HH13 JJ02 JJ03 JJ09 LL33 LL33 LL65 MM16 NN05 PP12 QQ00 QQ11 QQ13 QQ25 QQ31 RR02 2G051 AA56 AB06 BA10 CA04 DA07 EA14 EB01 ED04 ED11 2H095 BB03 BD04 BD12 BD17 BD20 4M106 AA09 BA04 BA05 CA38 DB02 DB08 DB12 DB13 DB03 5BA03 GA03 JA03

Claims (12)

[Claims] 1. A light-shielding pattern that defines a plurality of light-transmitting openings on a transparent substrate, and a phase shifter that gives a phase difference between exposure light passing through these light-transmitting openings in one of the adjacent light-transmitting openings. A defect inspection apparatus for a phase shift mask, comprising: a light emitting unit that emits light in a specific wavelength range; and a light emitting unit that emits light emitted from the light emitting unit in a polarization state.
And irradiates the light onto the surface of the phase shift mask with a slight lateral shift with respect to each other in a specific direction, and obtains a phase obtained by combining two reflected lights from the phase shift mask surface. A differential interference optical system that forms a differential interference image from edge information representing the surface shape of the shift mask; and converting the differential interference image into first and second inspection images that are two differential interference images having different phase differences. An image decomposition system for decomposing, a first image detector for converting the first inspection image into an electronic image, and a first inspection image output from the first image detector as the first inspection image. A first edge information, which is different edge information with respect to the first reference image, is extracted from the first inspection image by comparing with a first reference image obtained by another means in correspondence with the first reference image. Detect A first signal processing circuit, a second image detector for converting the second inspection image into an electronic image, and a second inspection image output from the second image detector. A phase shift mask for extracting second edge information, which is different edge information with respect to the second reference image, from the second inspection image by comparing with a second reference image obtained by another means corresponding to the image; A second signal processing circuit for detecting a defect of the phase shift mask. 2. The light emitting means includes: a mercury lamp as a light source; a condenser lens for condensing light emitted from the mercury lamp; and a specific wavelength band of light transmitted through the condenser lens. The defect inspection apparatus for a phase shift mask according to claim 1, further comprising a bandpass filter that selectively transmits light. 3. The light emitting device according to claim 1, wherein the light emitting unit includes a laser oscillator as a light source, an acousto-optic device that vibrates laser light emitted from the laser oscillator in a main scanning direction, and a relay lens. Defect inspection device for phase shift mask. 4. A differential interference optical system, comprising: a polarizer for selectively transmitting only specific polarized light out of the light emitted from the light emitting means; and reflecting substantially only half of the light transmitted through the polarizer. 2. A first half mirror for making light, a Nomarski prism that changes light into two by transmitting light reflected by the first half mirror, and an objective lens that focuses light transmitted through the Nomarski prism. 4. The defect inspection apparatus for a phase shift mask according to 2 or 3. 5. An image decomposition system, comprising: a second half mirror for decomposing a differential interference image formed by a differential interference optical system into first and second inspection images as transmitted light and reflected light, respectively.
The phase shift according to any one of claims 1 to 4, further comprising: a phase plate disposed between the second half mirror and the first or second image detector to cause a phase difference between incident lights. Mask defect inspection equipment. 6. The phase shift mask according to claim 1, wherein the image detector is a linear image sensor in which a plurality of light receiving elements are arranged in a line in a direction corresponding to a main scanning direction. Defect inspection equipment. 7. The image detector includes a plurality of light receiving elements.
2. A two-dimensional imaging device arranged in a two-dimensional array.
6. The defect inspection apparatus for a phase shift mask according to any one of claims 1 to 5. 8. The phase shift according to claim 1, wherein the two lights in the polarization state are irradiated on the surface of the phase shift mask while being shifted laterally by 45 ° with respect to each other. Mask defect inspection equipment. 9. The two lights in the polarization state are separated from each other on the surface of the phase shift mask by に 対 し of the dimension of the phase shifter.
The defect inspection apparatus for a phase shift mask according to any one of claims 1 to 8, wherein the irradiation is performed while being shifted laterally within a range of smaller dimensions. 10. An inspection image optical system for obtaining the first and second inspection images and a reference image optical system for obtaining the first and second reference images are provided above the same phase shift mask. The defect inspection apparatus for a phase shift mask according to claim 1, wherein both image optical systems have the same configuration, and a defect is detected using both image optical systems. 11. The first and second inspection images and the first and second inspection images.
The defect inspection apparatus for a phase shift mask according to any one of claims 1 to 10, wherein a defect is detected for both the second reference image and the second reference image using the same image optical system. 12. The defect of the phase shift mask according to claim 1, wherein the phase shift mask is mounted on an xy stage movable in a main scanning direction and a direction orthogonal to the main scanning direction. Inspection equipment.