JP2000347383A - Photomask inspection method and its apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To predict the defect which may be induced by washing after inspection. SOLUTION: The photomask inspection apparatus using a while light interference method of inspecting the photomask formed with shading film patterns of metal on a transparent substrate, in which shading films are covered with metal oxidized films has a Wollaston prism 36 of approximately 1 deg. in a prism angle θ and a data processing section 22 which measures the peak-to-peak distance of the interference fringe images obtained by a solid-state image pickup element of a CCD camera 37, calculates an optical film thickness nd proportional to the peak-to-peak distance and decides a shading film defect position if the optical film thickness nd is off a set range in a position where reference data is within a shading film region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photomask inspection method and apparatus.

[0002]

2. Description of the Related Art In a non-contact type exposure apparatus such as a stepper,
Since a pattern is transferred onto a large number of wafers with one photomask, it is necessary to eliminate defects in the photomask.

In a conventional photomask inspection apparatus, a photomask to be inspected is mounted on an XY stage in which an opening is formed, and light is projected from below the XY stage onto the photomask.
The transmitted light pattern of the photomask is imaged on the image sensor. In the die-to-die comparison method, defects are detected by comparing images of corresponding portions of patterns of two chips by using two optical systems arranged side by side. On the other hand, in the die-to-database comparison method, an image obtained by one optical system is compared with a design pattern to detect a defect.

According to such a photomask inspection apparatus,
Pinholes inside the light-shielding film pattern formed on the photomask, protrusions and recesses at the pattern edge, pattern dropout,
Defective defects such as shorts, disconnections, pattern missizes, and pin dots in openings on the photomask can be detected.

[0005] When the pattern becomes fine, the light transmitted through the opening is diffracted and interferes with the diffracted light from the adjacent opening, so that the resolution of the transmitted light pattern is reduced. In order to reduce the diffracted light, light of a short wavelength such as excimer laser light (UV light) is used, and a phase shift mask is used so that the diffracted lights cancel each other.

When the pattern becomes finer, the defect inspection apparatus also needs to increase the resolution by using short-wavelength light, but the use of short-wavelength light requires a special optical system. When a phase shift mask is used, inspection of a phase shifter, which is a recess having a depth of about 100 nm and formed in a glass substrate, is performed.
The above-mentioned light transmission method is difficult.

Japanese Unexamined Patent Publication No. Hei 10-177246 discloses a technique in which white light from a mercury lamp is vertically incident on a photomask, and interference light between reflected light on a light-shielding film and reflected light on a glass surface of an opening is disclosed. Through a Nomarski prism to separate the light into normal light and abnormal light, obtain two interference optical systems, and detect a defect by a die-to-die method. According to this apparatus, it is possible to detect a defect such as the depth or inclination of the concave portion serving as the phase shifter.

A photomask 10 shown in FIG. 5A has a pattern of a metal film 12 formed on a glass substrate 11, and a metal oxide film 13 is deposited thereon. The metal film 12
It is a film of Cr or Mo. The metal oxide film 13 is a metal oxide film of the metal film 12, and when the metal film 12 is Cr, Cr _x O _y (x: y is arbitrary; for example, x = 1, y =
2), when the metal film 12 is Mo, Mo _x O _y (x: y is arbitrary, for example, x = 1, y = 2). Photomask 1
Numeral 0 indicates that the pellicle is being manufactured, and is washed in a cleaning liquid after the inspection, and a transparent pellicle is stuck on the surface in order to reduce the influence of foreign matter adhesion.

[0009]

However, FIG. 3 (A)
As shown in (1), when the foreign matter 14 adheres to the glass substrate 11 before the metal film 12 is formed, or when the metal oxide film 13 is not formed partially and the metal film 12 is thin, The cleaning removes the foreign matter 14 or removes the metal film 12.
Melts, a pinhole is formed in the metal film 12,
As a result, the photomask 10 may be defective.

Conventionally, such defects caused by cleaning after inspection cannot be predicted.

When the thickness of a silicon oxide film on a silicon substrate is measured by a film thickness measuring device independent of a photomask using a white light interference method, peaks of interference fringes overlap to measure a distance between the peaks. Because it becomes impossible,
No. 88360 proposes an improved apparatus using white light interferometry for reducing the influence of the overlap and measuring the distance between peaks. However, this device has a complicated optical system and complicated adjustment.

An object of the present invention is to provide a photomask inspection method and apparatus capable of predicting a defect that may be caused by cleaning after inspection in view of the above problems.

It is another object of the present invention to provide a photomask inspection apparatus using a white light interferometry with a simple structure.

[0014]

According to the present invention, there is provided a photomask inspection apparatus for inspecting a photomask in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film. A white light source, an objective lens disposed to face a light-shielding film of a photomask, and light emitted from the white light source incident on the objective lens, and the incident light and the objective lens reflected by the light-shielding film. A half mirror that separates light that re-enters the light, a polarizer that receives the re-incident light, and light that has passed through the polarizer is input,
A polarizing prism that separates the polarized light into ordinary light and extraordinary light whose polarization planes are orthogonal to each other, and an inspection device that passes the ordinary light and the extraordinary light and is arranged so as to form orthogonal Nicols or parallel Nicols with the polarizer. A photon, an electronic camera in which light passing through the analyzer is incident and interference fringes are formed on the solid-state imaging device, and a peak-to-peak distance y of the interference fringe image obtained by the solid-state imaging device is measured. The optical film thickness nd proportional to the peak-to-peak distance y is calculated, and if the optical film thickness is out of the set range at the position where the reference data indicates that the optical film is within the light-shielding film region, it is a light-shielding film defective position. And a data processing device for determining

According to this photomask inspection apparatus, if the optical film thickness in the light-shielding film area is out of the set range, it is determined that the light-shielding film has a defective position. It is possible to know in advance whether there is a risk of new formation, and it is possible to manufacture a highly reliable photomask.

According to the first aspect, according to the configuration further including a storage device in which the design pattern data of the photomask is stored as the reference data, only one optical system is required and the configuration is simplified.

According to a second aspect of the present invention, there is provided a photomask inspection apparatus for inspecting a photomask in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film. And a processing device, wherein the first
And the second measuring device each include a white light source, an objective lens arranged to face the light shielding film of the photomask, and light emitted from the white light source incident on the objective lens, and the incident light and the light shielding A half mirror that separates the light that is reflected by the film and re-enters the objective lens; a polarizer that receives the re-incident light; and a light that passes through the polarizer is input. A polarizing prism that separates the normal light and the extraordinary light that are orthogonal to each other, an analyzer through which the ordinary light and the extraordinary light pass, and an analyzer that is arranged to form orthogonal Nicols or parallel Nicols with the polarizer; and the analyzer. An electronic camera in which light passing therethrough is incident and an interference fringe is formed on a solid-state imaging device, and the data processing device includes an interference camera provided by the solid-state imaging devices of the first and second measurement devices. Distance between peaks y1 and y2 of fringe image
Are measured, and the optical film thicknesses nd1 and nd2, which are respectively proportional to the peak-to-peak distances y1 and y2, are calculated,
If the optical thickness dy1 is outside the set range at a position indicating that the distribution of the optical thickness dy2 is within the light-shielding film region using the optical thickness nd2 as a reference value, the light-shielding film is defective. And a data processing device for determining that there is.

According to this photomask inspection apparatus, no design data is required.

In any one of the first to third aspects, for example, the data processing device determines that a portion where the interference fringe image does not exist is a portion where the metal oxide film does not exist.

According to a third aspect of the present invention, in the photomask inspection apparatus according to the first or second aspect, the polarizing prism has a prism angle of about 1 °.

According to this photomask inspection apparatus, the overlap between the peaks of the interference fringe image can be prevented with a simple configuration without using a complicated optical system as used in JP-A-52-88360. Thus, the distance between peaks can be accurately measured.

In a photomask inspection method in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film, an optical film thickness of the metal oxide film is measured. According to the photomask inspection method in which the optical film thickness is out of the set range, it is determined that the light-shielding film is in a defective position. According to the photomask inspection method, is there a possibility that a new pinhole is formed in the light-shielding film when the photomask is cleaned after the inspection? This makes it possible to know beforehand whether a photomask with high reliability can be manufactured.

According to a fourth aspect of the present invention, there is provided a photomask inspection method for inspecting a photomask in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film. A white light source, an objective lens arranged opposite to a light-shielding film of a photomask, and light emitted from the white light source being incident on the objective lens. A half mirror that separates the light that re-enters the lens, a polarizer that receives the re-incident light, and light that has passed through the polarizer is incident, and is converted into ordinary light and extraordinary light whose polarization planes are orthogonal to each other. And the refractive indexes for the ordinary light and the extraordinary light are respectively no.
And ne, a polarizing prism having a prism angle θ, the ordinary light and the extraordinary light passed therethrough, an analyzer arranged so as to form orthogonal Nicols or parallel Nicols with the polarizer, and light passing through the analyzer. And an electronic camera in which interference fringes are formed on the solid-state image sensor when light is incident, and the distance y between peaks of the interference fringe image obtained by the solid-state image sensor is measured, and is proportional to the distance y between the peaks. The optical film thickness nd is calculated, and if the optical film thickness is out of the set range at the position where the reference data indicates that the reference data is within the light shielding film region, it is determined that the position is the light shielding film defective position.

[0024]

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

[First Embodiment] In a photomask 10 shown in FIG. 5A, a pattern of a metal film 12 is formed on a glass substrate 11, and a metal oxide film 13 is deposited thereon. The metal film 12 is a film such as Cr or Mo. The metal oxide film 13 is a metal oxide film of the metal film 12. When the metal film 12 is Cr, Cr _x O _y (x: y is arbitrary, for example, x = 1, y = 2), and the metal film 12 When Mo is Mo _x
O _y (x: y is arbitrary; for example, x = 1, y = 2). The photomask 10 is in the process of being manufactured, is washed in a cleaning solution after inspection, and a transparent pellicle is stuck on the surface in order to reduce the influence of foreign matter adhesion.

However, as shown in FIG. 3A, foreign matter 14 adheres to the glass substrate 11 before the metal film 12 is formed, or the metal oxide film 13 is not formed partially and the metal film 12 is not formed. If 12 is thin, by washing
When the foreign matter 14 is removed or the metal film 12 is melted, a pinhole is formed in the metal film 12, and the photomask 10 may be defective. The present inventor has found that when such a defect occurs, the thickness of the metal oxide film 13 deviates from the average value by a predetermined value or more.

The photomask inspection apparatus of the present invention measures the thickness distribution of the metal oxide film 13 and sets the thickness in the light-shielding film region (the region where the light-shielding film should exist in order to form a normal opening pattern). If it is out of the range, it is determined that the position is the light shielding film defective position.

FIG. 1 shows a schematic configuration of a photomask inspection apparatus according to a first embodiment of the present invention using a die pair database method.

The photomask 10 is mounted on an XY stage 20. The stage controller 21 drives the XY stage 20 in response to a control signal from the data processing device 22, and supplies the position of the XY stage 20 to the data processing device 22. An optical system is disposed above the photomask 10, and has a known configuration except that the prism angle θ of the Wollaston prism is small as described later.

The white light emitted from the halogen lamp 30 is converted into substantially parallel light by the condenser lens 31, and a part of the white light is reflected by the half mirror 32, and the lower objective lens 3
3 and converge to the height position of the metal oxide film 13. The light reflected on the upper and lower surfaces of the metal oxide film 13 passes through the objective lens 33 again, becomes substantially parallel light, and a part of the light passes through the half mirror 32.

WU and WL in FIG. 1 respectively indicate the wavefronts of the light reflected at the upper and lower surfaces of the metal oxide film 13 at a certain point in time. The distance between the wavefronts WU and WL is the optical distance of the metal oxide film 13. It is equal to twice the film thickness nd. Where n
And d are the refractive index and thickness of the metal oxide film 13, respectively.

Above the half mirror 32, a polarizer 34
And the analyzer 35 are arranged so as to form parallel Nicols or orthogonal Nicols. A Wollaston prism 36 having a prism angle θ is arranged between the polarizer 34 and the analyzer 35. The Wollaston prism 36 separates the incident linearly polarized light into ordinary light and extraordinary light whose polarization planes are orthogonal to each other.

When the wavefronts WU and WL advance and pass through the Wollaston prism 36, the wavefronts WU1 and WL1 of the ordinary light and the wavefronts WU2 and WU of the extraordinary light are separated by this separation.
L2, and interference fringes of both lights are formed. The interference fringes are magnified and imaged by the CCD camera 37, and the image signals are digitized and supplied to the data processing device 22.

The light intensity on a line passing through the optical axis on the imaging surface of the CCD camera 37 is as shown in FIG. 2 in the case of the above-mentioned parallel Nicols, and a large peak appears at the center and peaks appear on both sides. In the case of orthogonal Nicols, the peak position is the same as in the case of parallel Nicols. However, in the case of parallel Nicols, the peak is positive, whereas in the case of orthogonal Nicols, the peak is negative. The center peak corresponds to the wavefront intersections P1 and P2 in FIG. 1, and the peaks on both sides correspond to the wavefront intersections P3 and P4 in FIG. As shown in FIG. 1, consider a Y axis passing through the optical axis and perpendicular to the optical axis. The origin O of the Y axis is on the optical axis. The position y of the intersection P4 on the Y axis is the distance y between the peaks in FIG. 2, and the following equation is established.

Nd = (y / m) (ne−no) tan θ (1) where ne and no are the refractive indexes of the Wollaston prism 36 for extraordinary rays and ordinary rays, respectively, and m is CCD.
This is the magnification of the camera 37.

Since the optical film thickness nd is as small as, for example, about 150 °, y becomes small, and the center peak shown in FIG. 2 and the peaks on both sides thereof overlap, and the measurement peak position becomes unclear. Therefore, the overlap is prevented by reducing the prism angle θ to increase y. For this purpose, as a result of an experiment, it was found that the prism angle θ was about 3 ° or less, and preferably about 1 °.

The optical system of the photomask inspection apparatus according to the first embodiment is characterized in that the Wollaston prism 36 having such a prism angle θ is used. Thus, there is no need to use a complicated optical system as used in the above-mentioned JP-A-52-88360.

The data processing device 22 includes an XY stage 2
The optical thickness nd of the metal oxide film 13 on the optical axis is calculated based on the above equation (1) in correspondence with the current position of 0. However, when a peak cannot be detected, nd = 0. Thus, the distribution of the optical film thickness nd as shown in FIG. 3B is obtained with respect to the photomask 10 as shown in FIG. On the other hand, the photomask 1 is stored in the storage device 38.
0 layout data is stored. The data processing device 22 refers to this data and determines whether or not the position of the XY stage 20, that is, the position on the photomask 10 that intersects with the optical axis is within the light-shielding film region. If it is within the light-shielding film region, it is determined whether or not the optical film thickness nd is a value between the upper limit UL1 and the lower limit LL1 in FIG. For example, UL1 = 1.3nd0, LL1 = 0.7nd
0, where nd0 is the average value of the normal thickness of the metal oxide film 13 and is obtained in advance by measurement.

Since the above-described interference does not occur at the opening of the photomask 10, a peak as shown in FIG. 2 does not occur. Therefore, when this peak is equal to or less than the set value, it is determined that the area is an opening, and the opening pattern is obtained. Storage device 38
It is determined whether or not the obtained opening pattern is normal with reference to the data of (1).

According to the first embodiment, if the optical film thickness nd is out of the set range in the light-shielding film area, the position of the light-shielding film is determined to be defective. It is possible to know in advance whether there is a possibility that a new pinhole will be formed, and a highly reliable photomask can be manufactured.

[Second Embodiment] FIG. 4 shows a schematic configuration of a photomask inspection apparatus according to a second embodiment of the present invention using a die-to-die method.

A plurality of identical die patterns (all patterns in the die) are formed on the photomask 10. Optical systems 40A and 40B disposed above photomask 10
Are the same as those in the optical system shown in FIG. 1, and the distance between the optical axes is adjusted to be equal to the distance between the die patterns on the photomask 10.

CCD camera 3 of optical systems 40A and 40B
The image data output from 7A and 37B, respectively,
The data is supplied to the data processing device 22C. Data processing device 2
2C is the optical film thickness nd1 and nd of the metal oxide film 13 at the optical axis position of the optical systems 40A and 40B as described above.
2 is calculated. Assuming that the distribution of the optical film thickness nd2 is normal, it is determined from the distribution whether or not the optical film thickness nd2 is within the light-shielding film region, and the optical film thickness nd1 is set within the determined light-shielding film region as described above. If it is outside, it is determined as a light shielding film defective position. Similarly, assuming that the distribution of the optical film thickness nd1 is normal, it is determined from the distribution whether or not the optical film thickness nd1 is within the light shielding film region, and the optical film thickness nd2 is outside the set range within the determined light shielding film region. If so, it is determined that the light-shielding film is defective.

For example, the optical film thicknesses nd1 and nd of the metal oxide film 13 having the patterns shown in FIG. 3A and FIG.
2 were measured in parallel by the optical systems 40A and 40B, respectively, and when the distributions of the optical film thicknesses nd1 and nd2 as shown in FIGS. 3B and 5B were obtained, (nd2-n
The distribution of d1) is as shown in FIG. FIG. 5 (C)
AA1 and AA2 are light-shielding film regions determined from the distribution of the optical film thickness nd2.
If 2-nd1> UL2 or nd2-nd1 <LL2, that portion is determined to be a light-shielding film defect. The upper limit UL2 and the lower limit LL2 are, for example, UL2 = 0.3nd0 and LL2 =
−0.3nd0.

If the above-mentioned peak is not more than the set value, it is determined that the aperture is an aperture, and the aperture pattern determined based on the output image data of the CCD camera 37A is used as a reference pattern, which is used as the output image data of the CCD camera 37B. Based on the determined opening pattern, the quality is determined.
Similarly, the aperture pattern determined based on the output image data of the CCD camera 37B is used as a reference pattern, and
The quality is determined by comparing the aperture pattern determined based on the output image data of the CCD camera 37A with the aperture pattern.

According to the second embodiment, the same effects as those of the first embodiment can be obtained.

The image data may be stored in a storage device, and the quality may be determined by processing the data later. In this case, the optical film thickness nd0 may be an average value of measured values of the metal oxide film on the photomask 10 to be inspected.

The Wollaston prism 36 may be a polarizing prism that separates incident linearly polarized light into ordinary light and extraordinary light whose polarization planes are orthogonal to each other, and may be a lotion prism or a Sinalmon prism.

Further, the method of the present invention is not limited to the photomask inspection apparatus having the above-described configuration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a photomask inspection apparatus according to a first embodiment of the present invention using a die pair database method.

FIG. 2 is a diagram showing a light intensity distribution on a line passing through an optical axis on an imaging surface of a CCD camera 37;

FIG. 3A is an explanatory cross-sectional view of the photomask 10, and FIG.
Is a diagram showing the distribution of the optical film thickness nd measured for this cross section.

FIG. 4 is a diagram showing a schematic configuration of a photomask inspection apparatus according to a second embodiment of the present invention using a die-to-die method.

FIG. 5A is an explanatory cross-sectional view of the photomask 10, and FIG.
3 is a diagram showing the distribution of the optical film thickness nd measured for this cross section, and FIG. 3C is a diagram showing the optical film thickness nd of FIG.
It is a diagram which shows the difference with the optical film thickness nd of (B).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Photomask 11 Glass substrate 12 Metal film 13 Metal oxide film 14 Foreign material 15 Missing portion of metal oxide film 20 XY stage 21 Stage controller 22, 22C Data processing device 30 Halogen lamp 31 Condenser lens 32 Half mirror 33 Objective lens 34 Polarizer 35 Analyzer 36 Wollaston prism 37, 37A, 37B CCD camera 38 Storage device 40A, 40B Optical system

Claims (4)

[Claims] 1. A photomask inspection apparatus for inspecting a photomask in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film, comprising: a white light source; An arranged objective lens, and a half mirror that causes light emitted from the white light source to enter the objective lens, and separates the incident light and light reflected by the light-shielding film and re-entering the objective lens. A polarizer into which the re-incident light is incident; a polarizing prism into which light transmitted through the polarizer is incident and separating it into ordinary light and extraordinary light whose polarization planes are orthogonal to each other; And an analyzer arranged so as to form orthogonal Nicols or parallel Nicols with the polarizer, and an electronic camera in which light passing through the analyzer is incident and interference fringes are imaged on a solid-state imaging device. And the solid-state imaging device Peak distance y of the resulting interference fringe image
Is measured, and the optical film thickness nd is proportional to the distance y between the peaks.
A data processing device that calculates the reference data and determines that the optical film thickness is out of the set range at a position indicating that the reference data is within the light-shielding film region and that the optical film is a defective light-shielding film position. Characteristic photomask inspection equipment. 2. A photomask inspection apparatus for inspecting a photomask in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film, comprising: a first and a second measuring device; a data processing device; Wherein each of the first and second measuring devices comprises: a white light source; an objective lens arranged to face a light-shielding film of a photomask; and light emitted from the white light source incident on the objective lens. A half mirror that separates the incident light from the light reflected by the light-shielding film and re-entering the objective lens; a polarizer to which the re-incident light is incident; and a light transmitted through the polarizer, and A polarizing prism that separates this into ordinary light and extraordinary light whose polarization planes are orthogonal to each other, and an inspection device that passes the ordinary light and the extraordinary light and is arranged so as to form orthogonal Nicols or parallel Nicols with the polarizer. A photon and the analyzer An electronic camera that receives the incident light and forms an interference fringe on the solid-state imaging device; and the data processing device includes an interference fringe obtained by the solid-state imaging device of the first and second measurement devices. The inter-peak distances y1 and y2 of the image are measured, respectively, and the optical film thicknesses nd1 and nd2 are calculated in proportion to the inter-peak distances y1 and y2, respectively, and the optical film thickness nd2 is used as a reference value for the optical film. Thickness dy
And a data processing device for determining that the optical film thickness dy1 is outside the set range at a position indicating that the distribution of 2 is within the light-shielding film region is a light-shielding film defective position. Photomask inspection equipment. 3. The polarizing prism according to claim 1, wherein the prism angle is approximately one.
The photomask inspection apparatus according to claim 1 or 2, wherein ゜. 4. A photomask inspection method for inspecting a photomask in which a metal light-shielding film pattern is formed on a transparent substrate and the light-shielding film is covered with a metal oxide film, wherein a measuring device is prepared. A light source, an objective lens arranged to face the light-shielding film of the photomask, and light emitted from the white light source being incident on the objective lens. The incident light and the light reflected by the light-shielding film are reflected by the objective lens. A half mirror for separating incident light; a polarizer to which the re-incident light is incident; and light transmitted through the polarizer, which is separated into ordinary light and extraordinary light whose polarization planes are orthogonal to each other. A polarizing prism that passes through the ordinary light and the extraordinary light, and an analyzer that is arranged so as to form orthogonal Nicols or parallel Nicols with the polarizer. Is imaged on the solid-state image sensor. That it has an electronic camera, the distance between peaks y of the resulting interference fringe image in the solid-state image pickup element
Is measured, and the optical film thickness nd is proportional to the distance y between the peaks.
A photomask inspection method, wherein, if the optical film thickness is out of the set range at a position where the reference data indicates that the reference data is within the light-shielding film region, it is determined that the position is a light-shielding film defective position.