WO2019225360A1

WO2019225360A1 - Photomask inspection device and photomask inspection method

Info

Publication number: WO2019225360A1
Application number: PCT/JP2019/018788
Authority: WO
Inventors: 良岸本; 真吾山本; 直人中島
Original assignee: 株式会社Ｓｃｒｅｅｎホールディングス
Priority date: 2018-05-22
Filing date: 2019-05-10
Publication date: 2019-11-28
Also published as: TWI696887B; KR102546388B1; TW202004333A; KR20200141510A; JP2019203942A; JP7023790B2

Abstract

Provided is a photomask inspection device capable of detecting a diffraction pattern more suitable for measurement. The photomask inspection device measures the pattern characteristics of the phase shift portion of a phase shift mask. The photomask inspection device includes a retainer, an irradiation part, a slit mask, a Fourier transformation lens, and a first optical sensor. The retainer retains the phase shift mask. The irradiation part irradiates a region including a transmissive portion and the phase shift portion with light. The slit mask has a slit and is arranged at a position that allows the light that passes through a portion of the transmissive portion in the width direction and the entire phase shift portion in the width direction to pass through the slit. The light passing through the slit is incident on the Fourier transformation lens. The first optical sensor detects the diffraction pattern of the light from the Fourier transformation lens at multiple times.

Description

Photomask inspection apparatus and photomask inspection method

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

In recent years, a phase shift mask has been used to transfer a pattern with high resolution to a substrate such as a semiconductor substrate or a display display substrate. This phase shift mask is formed with a phase shift film that delays the phase of light by a half wavelength.

Patent Document 1 describes a photomask inspection apparatus that measures a phase delay (phase difference) caused by a phase shift film. In this photomask inspection apparatus, light is irradiated onto a photomask through a variable aperture stop, and the light transmitted through the photomask forms an image on a photoelectric converter (sensor) through a Fourier transform lens. Thereby, the photoelectric converter detects a Fourier transform image (diffraction pattern).

The photomask inspection apparatus first irradiates light in a region where no phase difference occurs in the photomask (region only in the transparent portion or region only in the phase member (phase shift film)), and Fourier in the case where no phase difference occurs. The converted image is stored as a reference image. Then, the photomask inspection apparatus irradiates both the transparent portion of the photomask and the phase member with light, and based on the comparison between the Fourier transform image obtained by this irradiation and the reference image, the phase difference due to the phase member is calculated. Calculated.

Japanese Patent Laid-Open No. 4-229863

However, the technique of Patent Document 1 cannot always detect a Fourier transform image (diffraction pattern) suitable for calculating the phase difference. This is because they cannot always be positioned so that the relative position between the variable aperture stop and the photomask is optimal. Since the required accuracy of positioning increases as the pattern width becomes narrower, it is difficult to obtain an optimal Fourier transform image (diffraction pattern) particularly for a photomask having a fine pattern.

Therefore, an object of the present invention is to provide a photomask inspection apparatus and a photomask inspection method that can detect a diffraction pattern more suitable for measurement.

A first aspect of the photomask inspection apparatus includes a light-transmitting part that transmits light, a light-blocking part that blocks light, and a light-transmitting part that is provided between the light-transmitting part and the light-blocking part. A photomask inspection apparatus for measuring a pattern characteristic of a phase shift mask of a phase shift mask in which a phase shift section for shifting a phase with respect to light transmitted through an optical section is formed in a predetermined pattern, wherein the phase shift A holding unit that holds a mask, an irradiation unit that irradiates light to a region including the light transmitting unit and the phase shift unit, a slit, a part in the width direction of the light transmitting unit, and the phase shift unit A slit mask disposed at a position where the light transmitted through the whole in the width direction passes through the slit, a Fourier transform lens into which the light that has passed through the slit is incident, and the Fourier transform lens. And a first optical sensor for detecting the diffraction pattern of light from's at a plurality of timings.

A second aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the first aspect, further comprising a moving mechanism that relatively moves the slit mask and the phase shift mask in plan view, The first optical sensor detects a diffraction pattern at a plurality of timings while the moving mechanism relatively moves the slit mask and the phase shift mask.

A third aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the second aspect, wherein the moving mechanism is configured to move the slit mask and the phase shift along a direction inclined with respect to the width direction. Move relative to the mask.

A fourth aspect of the photomask inspection apparatus is a photomask inspection apparatus according to any one of the first to third aspects, wherein a plurality of diffraction patterns detected by the first optical sensor are at a central position. The diffraction pattern having the smallest light intensity is selected as the selected diffraction pattern, and at least one of the width of the phase shift unit and the phase difference by the phase shift unit is obtained as the pattern characteristic based on the selected diffraction pattern. An arithmetic processing unit is further provided.

A fifth aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the fourth aspect, wherein the arithmetic processing unit is configured to perform the phase shift based on a pitch of intensity of light in the selected diffraction pattern. The width of the part is calculated.

A sixth aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the fourth or fifth aspect, wherein the arithmetic processing unit includes a plurality of peak values or a plurality of light intensity values in the selected diffraction pattern. Based on the difference between the two of the bottom values, the phase difference by the phase shift unit is calculated.

A seventh aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the fourth aspect, wherein the arithmetic processing unit is configured to transmit the intensity distribution of the light transmitted through the light transmitting unit and the phase shift unit, and the phase. A first step of setting a width of the shift unit and a phase difference by the phase shift unit; and a second step of calculating a calculation diffraction pattern using a fast Fourier transform based on the intensity distribution, the width and the phase difference A step, a third step of determining whether the calculated diffraction pattern is similar to the selected diffraction pattern, and a determination in the third step that the calculated diffraction pattern is not similar to the selected diffraction pattern If so, a fourth step is executed in which the second step and the third step are executed by changing the width and the phase difference.

An eighth aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the seventh aspect, wherein the arithmetic processing section transmits each of the phase shift section and the light transmitting section in the first step. The intensity distribution is set so that the intensity of light to be emitted is constant.

A ninth aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the seventh aspect, wherein the arithmetic processing section is a boundary portion between the phase shift section and the light transmitting section in the first step. The intensity distribution is set so that the intensity of light gradually increases from the phase shift portion toward the light transmitting portion.

A tenth aspect of the photomask inspection apparatus is the photomask inspection apparatus according to the seventh aspect, provided between the second optical sensor, the slit mask, and the phase shift mask, and the phase shift mask. An optical element that guides part of the light from the second optical sensor to the second optical sensor, wherein the arithmetic processing unit is configured to calculate the intensity distribution based on the image captured by the second optical sensor in the first step. Set.

An eleventh aspect of the photomask inspection method is provided with a light-transmitting portion that transmits light, a light-shielding portion that blocks light, and provided between the light-transmitting portion and the light-shielding portion. A photomask inspection method for measuring a pattern characteristic of the phase shift portion of a phase shift mask in which a phase shift portion for shifting a phase with respect to light transmitted through the light portion is formed in a predetermined pattern, wherein the irradiation portion is The step of irradiating light to the region including the translucent part and the phase shift part, and the first optical sensor through the slit formed in the slit mask and the Fourier transform lens, the width of the translucent part Detecting a diffraction pattern of light transmitted through a part in the direction and the whole in the width direction of the phase shift unit at a plurality of timings.

According to the first aspect of the photomask inspection apparatus and the eleventh aspect of the photomask inspection method, the relative position between the slit mask and the phase shift mask actually fluctuates slightly. By detecting the diffraction pattern at the timing, a plurality of diffraction patterns corresponding to a plurality of relative positions can be detected. Therefore, it is easier to detect a diffraction pattern suitable for calculating the pattern characteristics of the phase shift unit than when detecting the diffraction pattern only once.

According to the second aspect of the photomask inspection apparatus, since the relative position between the slit mask and the phase shift mask can be controlled by the movement mechanism, the optimum relative position can be included in the movement range. Therefore, the first optical sensor can easily detect a diffraction pattern more suitable for specific calculation of the phase shift unit.

According to the third aspect of the photomask inspection apparatus, the relative velocity component in the width direction can be set low. Therefore, the first optical sensor can easily detect the diffraction pattern at the relative position close to the optimum relative position.

According to the fourth aspect of the photomask inspection apparatus, at least one of the width of the phase shift unit and the phase difference by the phase shift unit can be calculated with high accuracy.

According to the fifth aspect of the photomask inspection apparatus, the width of the phase shift unit can be calculated by a simple calculation.

According to the sixth aspect of the photomask inspection apparatus, the phase difference by the phase shift unit can be calculated with a simple calculation.

According to the seventh aspect of the photomask inspection apparatus, the width of the phase shift unit and the phase difference by the phase shift unit can be calculated with higher accuracy.

According to the eighth aspect of the photomask inspection apparatus, the intensity distribution can be easily set.

According to the ninth aspect of the photomask inspection apparatus, the width of the phase shift unit and the phase difference by the phase shift unit can be calculated with higher accuracy.

According to the tenth aspect of the photomask inspection apparatus, the width of the phase shift unit and the phase difference due to the phase shift unit can be calculated with higher accuracy.

It is a perspective view which shows roughly an example of a structure of a photomask inspection apparatus. It is a figure which shows schematically an example of a structure of a photomask inspection apparatus. It is a top view which shows an example of a structure of a slit mask roughly. It is a graph which shows roughly an example of a plurality of diffraction patterns. It is a graph which shows roughly an example of a plurality of diffraction patterns. It is a flowchart which shows an example of operation | movement of a photomask inspection apparatus. It is a flowchart which shows an example of the calculation method of a pattern characteristic. It is a figure for demonstrating an example of the relative moving direction of a slit mask and a phase shift mask. It is a figure which shows an example of a simulation model schematically. It is a graph which shows an example of a calculation diffraction pattern roughly. It is a flowchart which shows an example of the calculation method of a pattern characteristic. It is a figure which shows an example of a simulation model schematically. It is a flowchart which shows an example of operation | movement of a photomask inspection apparatus. It is a flowchart which shows an example of the calculation method of a pattern characteristic.

Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the size and number of each part are exaggerated or simplified as necessary for easy understanding. Moreover, the same code | symbol is attached | subjected about the part which has the same structure and function, and duplication description is abbreviate | omitted in the following description. In the drawings, XYZ orthogonal coordinates are shown as appropriate in order to show the positional relationship of each component. For example, the Z axis is arranged along the vertical direction, and the X axis and the Y axis are arranged along the horizontal direction. In the following description, one side in the Z-axis direction is also referred to as + Z side, and the other side is also referred to as −Z side. The same applies to the X axis and the Y axis.

FIG. 1 is a perspective view schematically showing an example of the configuration of the photomask inspection apparatus 1, and FIG. 2 is a diagram schematically showing an example of the configuration of the photomask inspection apparatus 1. The photomask inspection apparatus 1 is an apparatus for inspecting the phase shift mask 80. Here, first, an example of the phase shift mask 80 to be inspected will be described.

<Phase shift mask>
The phase shift mask 80 is a photomask used in an exposure apparatus (not shown). The exposure apparatus can transfer the pattern to the predetermined substrate by performing an exposure process on the predetermined substrate using the phase shift mask 80. The predetermined substrate is, for example, a semiconductor substrate or a flat panel display substrate.

As illustrated in FIG. 2, the phase shift mask 80 includes a base material 81, a phase shift film 82, and a light shielding film 83. The base material 81 has translucency with respect to light for exposure (for example, ultraviolet rays such as i-line), and is formed of, for example, quartz glass. The base material 81 has a plate-like shape, and has, for example, a rectangular shape in plan view (that is, viewed along the thickness direction). The length of one side of the phase shift mask 80 is set to about several [m], for example.

The phase shift film 82 is formed in a predetermined pattern on one main surface of the substrate 81. Although the phase shift film 82 has translucency with respect to light for exposure, the transmittance is smaller than the transmittance of the substrate 81. The transmittance of the phase shift film 82 is, for example, about several [%] (more specifically, 5 [%]). The phase shift film 82 shifts the phase of the light transmitted through itself by about 180 degrees with respect to the phase of the light transmitted through the light transmitting portion 8a. Such a phase shift film 82 is formed of tantalum oxide or the like, for example.

The light shielding film 83 is formed in a predetermined pattern on the phase shift film 82, for example. The light shielding film 83 is formed in a region inside the outline of the phase shift film 82 in plan view. The light shielding film 83 has a light shielding property for exposure light, and is formed of, for example, chromium or chromium oxide.

Hereinafter, in the phase shift mask 80, a region where the phase shift film 82 is not formed in plan view is referred to as a light transmitting portion 8a, and a region where the light shielding film 83 is formed in plan view is referred to as a light shielding portion 8c. A region between the light portion 8a and the light shielding portion 8c is referred to as a phase shift portion 8b. The light transmitting portion 8a, the phase shift portion 8b, and the light shielding portion 8c are each formed in a predetermined pattern in plan view. The width of the light transmitting portion 8a (width along the X-axis direction in FIG. 2) is set to about 2 to 4 [μm], for example, and the width of the phase shift portion 8b (width along the X-axis direction in FIG. 2) is, for example, 0 It is set to about 3 to 0.5 [μm].

When exposure is performed by the exposure apparatus using the phase shift mask 80, the light transmitted through the light transmitting portion 8a and the light transmitted through the phase shift portion 8b interfere with each other at the boundary portion on the substrate, resulting in interference fringes (dark darkness). ) Is generated. As a result, the contrast of the projected image of the light transmitting portion 8a can be increased. Therefore, the exposure apparatus can transfer the pattern to a predetermined substrate with a higher resolution by using the phase shift mask 80 than when the phase shift mask 80 is not used.

In this phase shift mask 80, the pattern shape of the phase shift portion 8b is directly linked to the transfer capability. For example, when the thickness of the phase shift film 82 in the phase shift unit 8b deviates from the design value, the phase difference due to the phase shift unit 8b deviates from 180 degrees. This reduces the effect of interference, lowers the resolution, and also causes unstable pattern resolution on the transferred substrate, which ultimately reduces manufacturing yield and product quality. It will cause many troubles such as damage. Even if the width of the phase shift unit 8b deviates from the design value, the same trouble occurs. Therefore, in order to determine whether the phase shift mask 80 is good or bad, the pattern characteristics of the phase shift portion 8b formed on the phase shift mask 80 (specifically, the width of the phase shift portion 8b and the phase difference due to the phase shift portion 8b). It is preferable to correctly manage the mask manufacturing process. The phase shift film 82 changes with time due to oxidation, and due to this change, the phase difference due to the phase shift film 82 can also change with time. Therefore, the phase shift mask 80 is preferably inspected periodically.

<Photomask inspection system>
The photomask inspection apparatus 1 measures the pattern characteristics of the phase shift unit 8 b formed on the phase shift mask 80. As illustrated in FIGS. 1 and 2, the photomask inspection apparatus 1 includes an irradiation unit 10, a detection unit 20, a moving mechanism 40, a control unit 50, a lifting mechanism 60, a display unit 70, and a holding unit 90.

The holding unit 90 is a member that holds the phase shift mask 80. The holding unit 90 holds the phase shift mask 80 so that the thickness direction of the phase shift mask 80 is along the Z-axis direction. In the example of FIG. 1, the holding unit 90 holds only the peripheral portion of the phase shift mask 80. Note that the holding unit 90 may support the entire lower surface of the phase shift mask 80 with a translucent member.

The irradiation unit 10 and the detection unit 20 are provided on opposite sides of the phase shift mask 80 in the Z-axis direction. In the example of FIGS. 1 and 2, the irradiation unit 10 is provided on the −Z side with respect to the phase shift mask 80, and the detection unit 20 is provided on the + Z side with respect to the phase shift mask 80.

The irradiation unit 10 irradiates light along the Z-axis direction and causes the light to enter a part of the phase shift mask 80. As the light, for example, light having a wavelength comparable to that of exposure light (for example, i-line) is employed. The irradiation unit 10 includes, for example, a light source 11, a condenser lens 12, a band pass filter 13, a relay lens 14, a pinhole plate 15, a reflection plate 16, and a condenser lens 17.

The light source 11 emits light. The light source 11 is, for example, an ultraviolet irradiator. For example, a mercury lamp can be used as the ultraviolet irradiator. The light irradiation / stop of the light source 11 is controlled by the control unit 50.

The condensing lens 12, the band pass filter 13, the relay lens 14, the pinhole plate 15, the reflecting plate 16, and the condenser lens 17 are arranged in this order between the light source 11 and the phase shift mask 80.

The condensing lens 12 is a convex lens and is disposed so that its focal point is located at the light source 11. The light emitted from the light source 11 becomes collimated light or light having a small divergence angle by the condenser lens 12, and this light is incident on the band pass filter 13. The bandpass filter 13 transmits only light having a predetermined wavelength band (transmission band) among the light. As this wavelength band, a wavelength band of light for exposure (for example, a wavelength band including i-line) can be adopted. The wavelength band of the bandpass filter 13 is set to be narrow, and substantially single wavelength light (so-called monochromatic light) is transmitted through the bandpass filter 13. The light transmitted through the bandpass filter 13 is incident on the relay lens 14.

The relay lens 14 is a convex lens and condenses incident light in the pinhole 151 of the pinhole plate 15. The pinhole 151 penetrates the pinhole plate 15 in the thickness direction. The pinhole plate 15 is disposed at a position where the pinhole 151 becomes the focal point of the relay lens 14. The light that has passed through the pinhole 151 substantially becomes light emitted from the point light source, and is incident on the reflection surface of the reflection plate 16. The reflecting plate 16 is provided to change the traveling direction of light, and makes the light incident on the condenser lens 17. The condenser lens 17 is a convex lens, and is disposed at a position where the focal point is substantially the pinhole 151. The condenser lens 17 converts the incident light into collimated light or light with a small divergence angle. The NA (numerical aperture) of light from the condenser lens 17 is set to an appropriate value by the condenser lens 17 and the pinhole 151. The irradiation unit 10 irradiates a part of the phase shift mask 80 with this light along the Z-axis direction.

The detection unit 20 detects the light transmitted through the phase shift mask 80 and detects a diffraction pattern by the light. The detection unit 20 includes, for example, an objective lens 21, an imaging lens 22, a prism 23, a slit mask 24, a Fourier transform lens 25, a relay lens 26, and image sensors (optical sensors) 27 and 28.

The objective lens 21, imaging lens 22, prism 23, slit mask 24, Fourier transform lens 25, and image sensor 27 are arranged in this order as they move away from the phase shift mask 80 in the Z-axis direction.

The light transmitted through the part of the phase shift mask 80 is magnified through the objective lens 21 and the imaging lens 22. Part of the light from the imaging lens 22 is reflected by the prism 23 toward the image sensor 28 side. That is, the prism 23 is an optical element that guides part of the light from the phase shift mask 80 to the image sensor 28. This optical element is not limited to the prism 23 but may be a mirror or a half mirror.

The slit mask 24 is disposed at the focal point of the imaging lens 22. Light incident on the slit mask 24 from the imaging lens 22 passes through a slit 24 a formed in the slit mask 24. Since the slit mask 24 blocks light in a region other than the slit 24a and allows light to pass through only the slit 24a, it functions as a field stop for narrowing the field of view. The slit 24a is wide enough to transmit only light from a region including only the phase shift portion 8b and its vicinity.

As illustrated in FIG. 2, the slit mask 24 has a base material 241 and a light shielding film 242. The base material 241 has translucency with respect to light for exposure, and is formed of, for example, quartz glass. The base material 241 has a plate shape, and has, for example, a rectangular shape in plan view. The base material 241 is provided such that its thickness direction is along the Z-axis direction.

The light shielding film 242 is formed on one main surface of the base material 241. The light shielding film 242 has a light shielding property for exposure light, and is formed of, for example, chromium or chromium oxide. The light shielding film 242 is formed to avoid a part of the base material 241 in a plan view. The partial area forms a slit 24a that allows light to pass therethrough. The slit 24a has a long shape in plan view.

FIG. 3 is a plan view schematically showing an example of the configuration of the slit mask 24. In FIG. 3, in order to show an example of the optical positional relationship of the phase shift mask 80 with respect to the slit mask 24, the light transmission part 8a and the phase shift part 8b are also shown with the dashed-two dotted line virtually. That is, the two-dot chain line indicates a projected image in which the light transmitting portion 8 a and the phase shift portion 8 b are projected onto the slit mask 24 via the objective lens 21 and the imaging lens 22. Hereinafter, a projection image obtained by projecting the translucent portion 8a onto the slit mask 24 is referred to as a translucent portion image 80a, and a projection image obtained by projecting the phase shift portion 8b onto the slit mask 24 is referred to as a phase shift portion image 80b.

In the example of FIG. 3, the longitudinal direction of the slit 24a is along the extending direction of the light transmitting portion 8a, and the slit 24a faces the phase shift portion 8b. More specifically, inside the slit 24a, the entire phase direction image 80b in the width direction (here, the X-axis direction) and the translucent image 80a adjacent to the one phase shift image 80b. And a part in the width direction. In other words, the light transmitted through the entire width direction of the phase shift portion 8b and a part of the light transmission portion 8a adjacent to the phase shift portion 8b in the width direction passes through the slit 24a.

Referring to FIG. 2 again, the light passing through slit 24a is imaged on the imaging surface of image sensor 27 via Fourier transform lens 25. The image sensor 27 is arranged such that its imaging surface is located at the focal point of the Fourier transform lens 25.

The image sensor 27 is a CCD image sensor, for example, and generates a captured image IM1 based on light imaged on its imaging surface, and outputs the captured image IM1 to the control unit 50. Since the light forms an image on the image sensor 27 through the Fourier transform lens 25, the captured image IM1 includes a diffraction pattern caused by the light transmitted through the light transmitting portion 8a and the light transmitted through the phase shift portion 8b. . The image sensor 27 is not limited to an image sensor having pixels arranged two-dimensionally, and may be a line sensor having pixels arranged one-dimensionally. In short, the image sensor 27 may be any optical sensor that can convert the luminance distribution of the light intensity pattern (diffraction pattern) formed in the X-axis direction into digital data.

The control unit 50 calculates the pattern characteristics (width and phase difference) of the phase shift unit 8b based on this diffraction pattern. A specific example of the diffraction pattern and a specific example of the calculation method will be described in detail later.

The light from the prism 23 via the relay lens 26 forms an image on the imaging surface of the image sensor 28. The image sensor 28 is arranged so that its imaging surface is located at the focal point of the relay lens 26. The image sensor 28 is a CCD image sensor, for example, and generates a captured image IM2 based on the light imaged on its imaging surface, and outputs the captured image IM2 to the control unit 50. The measurement target region of the phase shift mask 80 appears in the captured image IM2. The control unit 50 may cause the display unit 70 to display the captured image IM2. Thereby, it is possible to visually recognize which region of the phase shift mask 80 the operator is measuring.

The moving mechanism 40 moves the holding unit 90 in the XY plane. As a result, the phase shift mask 80 held by the holding unit 90 also moves in the XY plane. The moving mechanism 40 has, for example, a ball screw mechanism and is controlled by the control unit 50. By moving the phase shift mask 80 in the XY plane, the irradiation unit 10 and the detection unit 20 can be scanned with respect to the phase shift mask 80. Therefore, the pattern characteristics of the phase shift unit 8 b can be measured in a plurality of measurement regions of the phase shift mask 80. The moving mechanism 40 only needs to have a function and a structure for moving the phase shift mask 80 relative to the irradiation unit 10 and the detection unit 20. For example, the irradiation unit 10 and the detection unit 20 are integrated with each other. It may be moved.

The elevating mechanism 60 raises and lowers the holding unit 90 in the Z-axis direction. As a result, the phase shift mask 80 held by the holding unit 90 also moves up and down. The lifting mechanism 60 has, for example, a ball screw mechanism and is controlled by the control unit 50. The lifting mechanism 60 moves the phase shift mask 80 up and down, so that the phase shift mask 80 can be moved to the focal point of the objective lens 21. The raising / lowering mechanism 60 only needs to have a function and a structure for raising and lowering the phase shift mask 80 relative to the detection unit 20. For example, the detection unit 20 may be raised and lowered.

The display unit 70 is a display device such as a liquid crystal display or an organic EL display, and the display content is controlled by the control unit 50. For example, the control unit 50 outputs an image signal including the measurement result to the display unit 70. The display unit 70 displays the measurement result based on the image signal. Further, as described above, the display unit 70 may display the captured image IM2 under the control of the control unit 50.

The prism 23, the slit mask 24, the Fourier transform lens 25, the relay lens 26, and the

image sensors

27 and 28 are built in the optical head 30 of FIG.

Incidentally, since the pattern of the light transmitting portion 8a formed on the phase shift mask 80 is appropriately set depending on the design of the substrate, the extending direction of the light transmitting portion 8a differs depending on the position where the pattern is measured. Therefore, the slit mask 24 may be rotatably provided so that the longitudinal direction of the slit 24a extends along the extending direction of the light transmitting portion 8a at each position on the XY plane.

For example, the optical head 30 may include an upper member 31 and a lower member 32 that are rotatably connected to each other, and the above-described optical element built in the optical head 30 may be built in the upper member 31. The lower member 32 may be fixed to the housing of the photomask inspection apparatus 1 so as not to rotate, and the upper member 31 may be rotatably connected to the lower member 32. According to this, the longitudinal direction of the slit 24a of the slit mask 24 built in the upper member 31 can be adjusted by rotating the upper member 31 in the XY plane. A rotation drive mechanism (for example, a motor) that rotates the upper member 31 relative to the lower member 32 may be provided. This rotation drive mechanism is controlled by the control unit 50.

The control unit 50 can control the photomask inspection apparatus 1 as a whole. For example, as described above, the control unit 50 controls the irradiation by the irradiation unit 10, the movement by the movement mechanism 40, the elevation by the elevation mechanism 60, and the rotation of the optical head 30. The control unit 50 also functions as an arithmetic processing unit that calculates the pattern characteristics of the phase shift unit 8b based on the captured image IM1 generated by the image sensor 27.

The control unit 50 is an electronic circuit device, and may include, for example, an arithmetic processing unit and a storage medium. The arithmetic processing device may be an arithmetic processing device such as a CPU (Central Processor Unit). The storage unit may include a non-temporary storage medium (for example, ROM (Read Only Memory) or a hard disk) and a temporary storage medium (for example, RAM (Random Access Memory)). For example, the non-temporary storage medium may store a program that defines the processing executed by the control unit 50. When the processing device executes this program, the control unit 50 can execute the processing defined in the program. Of course, part or all of the processing executed by the control unit 50 may be executed by hardware.

<Measurement method based on diffraction pattern>
FIG. 4 is a graph schematically showing an example of the plurality of diffraction patterns DP1 to DP5. In FIG. 4, the vertical axis indicates the intensity of light, and the horizontal axis indicates the position in the X-axis direction. Therefore, it can be said that the diffraction pattern is a luminance profile.

The diffraction patterns DP1 to DP5 are diffraction patterns obtained when the relative positions of the slit 24a and the phase shift mask 80 in plan view are changed. Here, a distance d (see FIG. 3) is introduced as a parameter indicating the relative position. In the example of FIG. 3, the translucent part image 80a and the phase shift part image 80b are located inside the slit 24a in plan view. Specifically, inside the slit 24a, the translucent image 80a is positioned on the −X side, and the phase shift image 80b is positioned on the + X side. The distance d is the distance from the −X side end of the slit 24a to the boundary between the translucent part image 80a and the phase shift part image 80b. The greater this distance d, the greater the proportion of the translucent part image 80a in the slit 24a. That is, most of the light transmitted through the slit 24a is occupied by the light from the light transmitting portion 8a.

The diffraction patterns DP1 to DP5 are diffraction patterns obtained when the distance d is changed. The distance d corresponding to the diffraction patterns DP1 to DP5 is shorter as the number at the end of the code of the diffraction pattern is smaller. That is, the diffraction pattern DP1 is a diffraction pattern corresponding to the shortest distance d, and the diffraction pattern DP5 is a diffraction pattern corresponding to the longest distance d.

Note that the range of change of the distance d is set as follows. That is, the change range is set so that the whole of the phase shift portion image 80b in the width direction is included in the slit 24a. That is, the change range of the distance d is set so that a part of the phase shift portion image 80b does not protrude from the slit 24a in the width direction. In other words, the width of the slit 24a (the width along the X-axis direction) is set so that the entire phase shift portion image 80b in the width direction is included in the slit 24a when the distance d is changed within the change range. Is done.

As illustrated in FIG. 4, the diffraction patterns DP <b> 1 and DP <b> 2 have an upwardly convex shape (that is, a single mountain shape). This is because when the distance d is short, the light from the translucent part 8a is shielded by the slit 24a, so that only the light from the phase shift part 8b passes through the slit 24a. Therefore, the diffraction pattern becomes a diffraction pattern with a simple rectangular opening, and has such a distribution shape. Further, in the diffraction patterns DP1 and DP2, the peak value of the light intensity is relatively small. This is because the aperture is small and the transmittance of the phase shift portion 8b is low.

In the illustration of FIG. 4, the diffraction patterns DP3 to DP5 have a two-peak shape having two peaks. This is due to the fact that not only the light from the phase shift unit 8b but also the light from the light transmission unit 8a sufficiently passes through the slit 24a and the phase thereof is shifted by approximately 180 degrees as the distance d increases. This is because an interference pattern is generated. In the example of FIG. 4, a double peak shape is shown, but when the horizontal axis region is made wider, new peaks appear on both sides (see also FIG. 5).

Hereinafter, the position where the light intensity takes the bottom value between the highest peak value and the next highest peak value is referred to as the center position x0.

The peak values of the diffraction patterns DP3 to DP5 and the bottom value at the center position x0 increase as the distance d increases. This is because in the light passing through the slit 24a, the light increases from the light transmitting portion 8a having a high transmittance.

In the diffraction pattern DP3, the light intensity (bottom value) at the center position x0 is zero. This means that the complex amplitude of the light beam that passes through the light transmitting portion 8a and the slit 24a in this order is equal to the complex amplitude of the light beam that passes through the phase shift portion 8b and the slit 24a in this order. That is, when both complex amplitudes are equal to each other, the light is weakened by the same amount at the center position x0, so that the light intensity (bottom value) becomes zero.

When the complex amplitudes match each other, the following formula is established.

ws ′ = w ′ · √t (1)
Here, referring also to FIG. 3, ws ′ indicates the width (that is, distance d) of the region located inside the slit 24 a in the translucent portion image 80 a, and w ′ indicates the width of the phase shift portion image 80 b. And t indicates the transmittance of the phase shift unit 8b.

In consideration of the magnification α by the objective lens 21 and the imaging lens 22, the actual width w (= w ′ / α) of the phase shift portion 8b and the width ws (= ws) of the light transmitting portion 8a corresponding to the slit 24a. '/ Α) is introduced, equation (2) is derived from equation (1).

ws = w · √t (2)
For example, when the width w of the phase shift portion 8b is 0.4 [μm] and the transmittance t of the phase shift portion 8b is 0.05 (= 5 [%]), the light transmitting portion 8a corresponding to the slit 24a. The width ws is 0.089 [μm]. That is, if the slit mask 24 can be positioned with respect to the phase shift mask 80 so that the width ws becomes 0.089 [μm], the image sensor 27 can generate the captured image IM1 including the diffraction pattern DP3. That is, the diffraction pattern DP3 can be detected.

By the way, the strong and weak pitch (for example, the distance between the peak positions of the light intensity) Δdx in the diffraction pattern DP3 is the distance (pitch) Δx between the centers of the translucent part image 80a and the phase shift part image 80b inside the slit 24a. '(See also Fig. 3). Specifically, the pitch Δdx is theoretically proportional to the center-to-center distance Δx ′. The proportionality coefficient β1 can be obtained in advance by simulation or experiment. Therefore, if the pitch Δdx is obtained from the diffraction pattern DP3, the center-to-center distance Δx ′ can be obtained based on the pitch Δdx.

Further, this center-to-center distance Δx ′ geometrically satisfies the following relational expression (see also FIG. 3).

w ′ + ws ′ = 2 · Δx ′ (3)
Since the expression (3) is a parameter for each translucent portion image 80a and phase shift portion image 80b in the slit mask 24, these are converted into parameters for the translucent portion 8a and the phase shift portion 8b. Specifically, substituting w = w ′ / α, ws = ws ′ / α and Δx = Δx ′ / α into Equation (3), the following equation can be derived.

w + ws = 2 · Δx (4)
The following equations can be derived from equations (2) and (4).

w = 2 · Δx / (1 + √t) (5)
Assuming that the transmittance t of the phase shift unit 8b is substantially equal to the design value of the film or the transmittance t ^ of the adjacent test pattern, if the center-to-center distance Δx (= Δx ′ / α) can be obtained, the equation Can be used to calculate the width w of the phase shift unit 8b.

Also, the phase difference θ by the phase shift unit 8b can be obtained based on the diffraction pattern. FIG. 5 is a graph schematically showing an example of the plurality of diffraction patterns DP3, DP31 to DP34. The diffraction patterns DP3, DP31 to DP34 are diffraction patterns obtained when the phase difference θ is changed in a state where the formula (2) is satisfied. Since equation (2) holds, the bottom value at the center position x0 is zero in any of the diffraction patterns DP3 and DP31 to DP34. The diffraction pattern DP3 shows a diffraction pattern when the phase difference θ is 180 degrees, and the diffraction patterns DP31 to DP34 have a phase difference θ of 144 (= 360 × 0.4) degrees and 162 (= 360 × 0. The diffraction patterns at 45), 198 (= 360 × 0.55) and 216 (= 360 × 0.6) are shown.

As illustrated in FIG. 5, the waveforms of the diffraction patterns DP3, DP31 to DP34 are different depending on the phase difference θ. In other words, the phase difference θ can be obtained based on the detected waveform of the diffraction pattern. For example, the center position x0 varies according to the phase difference θ. Specifically, the center position x0 moves to the + X side as the phase difference θ increases. Therefore, the center position x0 when the phase difference θ is 180 degrees is set as a reference position in advance, and the relationship between the difference between each center position x0 and the reference position and the phase difference θ is determined by simulation or experiment, for example. Set in advance. If the difference between the center position x0 of the detected diffraction pattern and the reference position is obtained, the phase difference θ can be obtained based on the obtained difference and the above relationship.

Further, since each peak value and each bottom value in the diffraction pattern take a value corresponding to the phase difference θ, the phase difference θ may be obtained based on each peak value or each bottom value instead of the center position x0. For example, in the region on the + X side from the center position x0, each peak value decreases as the phase difference θ increases, and each bottom value decreases as the phase difference θ increases. On the other hand, in the region on the −X side from the center position x0, each peak value increases as the phase difference θ increases, and each bottom value increases as the phase difference θ increases.

Hereinafter, the peak value closest to the center position x0 in the + X side region is referred to as a primary peak value, and the peak value closest to the center position x0 in the −X side region is referred to as a −1st order peak value. .

Here, as an example of a parameter for calculating the phase difference θ, a peak difference Δp obtained by subtracting the primary peak value from the negative primary peak value is employed. FIG. 5 shows the peak difference Δp for the diffraction pattern DP34 as an example. This peak difference Δp increases as the phase difference θ increases. For example, the peak difference Δp in the diffraction pattern DP3 is zero, the peak difference Δp in the diffraction patterns DP31 and DP32 has a negative value, and the peak difference Δp in the diffraction pattern DP31 is smaller than the peak difference Δp in the diffraction pattern DP32. Further, the peak difference Δp in the diffraction patterns DP33 and DP34 has a positive value, and the peak difference Δp in the diffraction pattern DP34 is larger than the peak difference Δp in the diffraction pattern DP33. The relationship between the peak difference Δp and the phase difference θ can be set in advance by, for example, simulation or experiment. Therefore, if the peak difference Δp of the detected diffraction pattern is obtained, the phase difference θ can be calculated based on the peak difference Δp.

Note that it is not always necessary to adopt the peak difference Δp between the first-order peak value and the −1st-order peak value, and the difference between any two of the plurality of peak values may be employed. However, since the fluctuation amount of the peak difference Δp between the peak values of the primary and −1st order with respect to the phase difference θ is larger than the difference between the other two, the phase difference θ can be obtained with high accuracy.

Also, the bottom value may be adopted instead of the peak value. Specifically, a difference between a plurality of bottom values may be adopted. However, since the fluctuation amount of the difference between the bottom values with respect to the phase difference θ is smaller than the peak difference Δp, it is desirable to employ the peak difference Δp from the viewpoint of improving accuracy.

As described above, based on the waveform of the diffraction pattern (for example, the diffraction patterns DP3, DP31 to DP34, etc.) when the bottom value at the center position x0 is zero, the width w of the phase shift unit 8b and the position by the phase shift unit 8b. The phase difference θ can be calculated.

However, in order to detect this diffraction pattern, at the position where the width ws becomes an optimum value or in the vicinity thereof, the interference pattern due to the two light beams respectively transmitted through the light transmitting portion 8a and the phase shift portion 8b appears remarkably. It is necessary to position the slit mask 24 with respect to the phase shift mask 80. The required accuracy of this positioning is higher as the width ws is smaller. For example, when the width ws is 0.089 [μm], an accuracy of about several to several tens [nm] is required. The width ws also depends on the width w of the phase shift portion 8b (Equation (2)), and it can be said that the phase shift mask 80 having a finer pattern width has a higher required positioning accuracy.

Now, under the above condition (transmittance t = 0.05), as can be understood by those skilled in the art from the equation (5), the calculated width w of the phase shift unit 8b has the slit mask 24 and the phase shift. A calculation error (measurement error) approximately 0.8 times as large as an error in positioning with the mask 80 (several to several tens [nm]) occurs. That is, a maximum calculation error of about 16 [nm] may occur. By the way, in a pattern with particularly high required line width accuracy, the entire line width including the phase shift portion 8b is directly controlled by the resist process and is strictly controlled. Therefore, a measurement accuracy of about 5 to 10 [nm] is required. Is done. However, the required accuracy of the individual width w of the phase shift unit 8b is not as high as the entire line width, and the above positioning accuracy (several to several tens [nm]) is sufficient for practical use.

Therefore, in the photomask inspection apparatus 1, the image sensor 27 repeatedly detects diffraction patterns at different timings while changing the relative position between the slit mask 24 and the phase shift mask 80 with the passage of time. Thereby, the diffraction pattern corresponding to the optimal relative position or its vicinity is detected. Hereinafter, a specific example of the operation of the photomask inspection apparatus 1 will be described.

<Example of operation of photomask inspection apparatus>
FIG. 6 is a flowchart showing an example of the operation of the photomask inspection apparatus 1. Here, it is assumed that the control unit 50 initially irradiates the irradiation unit 10 with light.

First, in step S1, the control unit 50 controls the moving mechanism 40 to perform rough alignment with the phase shift mask 80 on the XY plane. Specifically, the moving mechanism 40 moves the phase shift mask 80 in the XY plane so that the irradiation unit 10 and the detection unit 20 face the measurement target region of the phase shift mask 80 in the Z-axis direction. This measurement target region includes both the translucent part 8a and the phase shift part 8b. This alignment is not an alignment with such an accuracy that a diffraction pattern with a bottom value of zero at the center position x0 can always be detected, but a coarse alignment. Further, the control unit 50 controls the rotation driving mechanism of the optical head 30 to rotate the optical head 30 so that the longitudinal direction of the slit 24a is along the extending direction of the light transmitting unit 8a in the measurement target region.

Next, in step S2, the control unit 50 controls the elevating mechanism 60 to perform autofocus processing. Specifically, the elevating mechanism 60 adjusts the position of the phase shift mask 80 in the Z-axis direction so that the distance between the objective lens 21 and the phase shift mask 80 becomes the focal length.

Next, in step S <b> 3, the image sensor 27 captures the diffraction pattern at a plurality of timings while the slit mask 24 and the phase shift mask 80 are relatively finely moved, and outputs the captured image IM <b> 1 to the control unit 50. To do. In other words, the image sensor 27 detects the diffraction pattern at a plurality of timings while changing the relative position of the slit mask 24 and the phase shift mask 80 in plan view with time. More specifically, the control unit 50 controls the moving mechanism 40 to move the phase shift mask 80 relative to the slit mask 24 along the width direction of the slit 24a (here, the X-axis direction). In FIG. 3, the moving direction D1 of the phase shift mask 80 is schematically indicated by a block arrow.

Note that this movement range includes the optimum relative position where the width ws becomes the optimum value (for example, 0.089 [μm]) or the vicinity thereof with a high probability. Therefore, in step S3, there is a timing at which the relative position between the slit mask 24 and the phase shift mask 80 is optimal or in the vicinity thereof. Therefore, any one of the plurality of captured images IM1 generated by the image sensor 27 includes a diffraction pattern corresponding to a relative position close to the optimum relative position.

Note that the relative speed between the phase shift mask 80 and the slit mask 24 during imaging (relative speed in step S3) is preferably low, and is set lower than the relative speed in step S1, for example. According to this, it is easy to detect the diffraction pattern corresponding to the relative position close to the optimum relative position.

Next, in step S4, the control unit 50 selects a diffraction pattern used for measurement from a plurality of diffraction patterns respectively included in the plurality of captured images IM1. Hereinafter, the selected diffraction pattern is also referred to as a selective diffraction pattern SP1. More specifically, the control unit 50 selects the diffraction pattern having the smallest light intensity (bottom value) at the center position x0 as the selected diffraction pattern SP1.

Next, in step S5, the control unit 50 calculates the pattern characteristics (width w and phase difference θ) of the phase shift unit 8b based on the selected diffraction pattern SP1. FIG. 7 is a flowchart showing a specific example of a pattern characteristic calculation method of the phase shift unit 8b.

In step S51, the control unit 50 obtains the pitch Δdx of the intensity of light in the selected diffraction pattern SP1. For example, in the selected diffraction pattern SP1, the control unit 50 uses the difference between the position when the light intensity takes the first-order peak value and the position when the light intensity takes the −1st-order peak value as the pitch Δdx. calculate.

Next, in step S52, the control unit 50 calculates the width w of the phase shift unit 8b based on the pitch Δdx calculated in step S51. More specifically, the control unit 50 obtains the center-to-center distance Δx based on the pitch Δdx calculated in step S51, and sets the width w of the phase shift unit 8b based on the center-to-center distance Δx and Expression (4). calculate. The relationship between the pitch Δdx and the center-to-center distance Δx is preset by, for example, simulation or experiment, and is stored in, for example, a storage medium of the control unit 50.

Next, in step S53, the control unit 50 obtains the peak difference Δp of the selected diffraction pattern SP1. For example, in the selected diffraction pattern SP1, the control unit 50 calculates a value obtained by subtracting the first-order peak value from the −1st-order peak value as the peak difference Δp.

Next, in step S54, the control unit 50 calculates the phase difference θ by the phase shift unit 8b based on the peak difference Δp calculated in step S53. Note that the relationship between the peak difference Δp and the phase difference θ is preset by, for example, simulation or experiment, and is stored in, for example, a storage medium of the control unit 50. The control unit 50 obtains the phase difference θ by the phase shift unit 8b based on the peak difference Δp calculated in step S53 and the relationship.

The series of calculations may be performed based on one selected diffraction pattern SP1, or may be performed based on a plurality of diffraction patterns near the position where the relative position is optimal. As a specific example, among the detected M (M is 3 or more) diffraction patterns, the upper N (N is 2 or more and less than M) diffraction patterns having a small bottom value at the center position x0 are selectively diffracted. It may be selected as the pattern SP1. Alternatively, N diffraction patterns whose bottom value at the center position is equal to or less than a predetermined reference value may be selected as the selected diffraction pattern SP1. According to this, it is possible to use N diffraction patterns in which the effect of interference appears relatively strongly. Then, pattern characteristics may be obtained statistically from the results of the selected N selected diffraction patterns SP1. For example, an average or regression analysis can be adopted as the statistics. As a specific example, one selected diffraction pattern SP1 may be averaged to calculate one diffraction pattern, and the pattern characteristics of the phase shift unit 8b may be obtained based on the diffraction pattern as described above.

Next, in step S6, the control unit 50 causes the display unit 70 to display the calculated pattern characteristics (width w and phase difference θ) of the phase shift unit 8b. Thereby, the worker can judge the quality of the phase shift part 8b of the phase shift mask 80. Note that the control unit 50 may determine whether or not the calculated pattern characteristic of the phase shift unit 8b is within a preset good range and display the determination result on the display unit 70. According to this, the worker can quickly know the quality of the phase shift unit 8b.

Note that the processing in steps S1 to S6 may be repeatedly executed while sequentially changing the measurement target region. Thereby, the entire surface of the phase shift mask 80 can be inspected.

As described above, according to the photomask inspection apparatus 1, the diffraction pattern is detected at a plurality of timings while changing the relative positions of the slit mask 24 and the phase shift mask 80 in plan view. Therefore, the detected plurality of diffraction patterns include a diffraction pattern corresponding to a relative position close to the optimum relative position. Therefore, the pattern characteristics of the phase shift unit 8b can be calculated based on a more suitable diffraction pattern.

By the way, in Patent Document 1, a reference image (reference diffraction pattern) detected when light is irradiated to a region having no phase difference is used. When this reference diffraction pattern is used, it is necessary to measure the diffraction pattern in the measurement target region at a time different from the measurement time of the reference diffraction pattern. Since each measurement time is different, a difference (for example, an optical axis shift or the like) may occur in the state of the optical system at each measurement time due to heat generated in the apparatus during that period. That is, the optical conditions at both measurement times may be different from each other. Thus, if the optical conditions are different, a measurement error occurs in the pattern characteristics of the phase shift unit 8b. On the other hand, in the photomask inspection apparatus 1, it is not necessary to use such a reference diffraction pattern. Therefore, the occurrence of the measurement error can be avoided, and the pattern characteristics of the phase shift unit 8b can be calculated with high accuracy.

In the above example, the control unit 50 selects the diffraction pattern with the smallest light intensity at the center position x0 among the plurality of diffraction patterns as the selected diffraction pattern SP1. According to this, the diffraction pattern corresponding to the relative position closest to the optimum position can be selected. Therefore, the pattern characteristics of the phase shift unit 8b can be calculated with higher accuracy than when other diffraction patterns are used.

In the above example, the width w of the phase shift unit 8b is calculated based on the strong and weak pitches in the selected diffraction pattern SP1. According to this, the width w of the phase shift unit 8b can be calculated by a simple process.

In the above-described example, the phase difference θ by the phase shift unit 8b is calculated based on the peak value difference in the selected diffraction pattern SP1. Accordingly, the phase difference θ by the phase shift unit 8b can be calculated with a simple process.

In the above example, the width w and the phase difference θ are calculated by analyzing the diffraction pattern of the light transmitted through one slit 24a. Therefore, compared to the case where the pattern characteristics of the phase shift part are calculated based on the interference of light transmitted through the slits using two slits, the distance between the translucent parts 8a (distance between patterns) is smaller. It is easy to apply to a narrow phase shift mask 80. That is, the photomask inspection apparatus 1 can also be applied to a phase shift mask 80 for a line and space pattern or a hole pattern array with a narrow interval.

<Presence or absence of movement mechanism control>
In the above example, the image sensor 27 generates the captured image IM1 at a plurality of timings while the moving mechanism 40 moves the phase shift mask 80 relative to the slit mask 24 (step S3). However, the movement by the moving mechanism 40 is not always necessary. The amount of fine movement required in the present embodiment is constantly generated due to bending of the device structural material (for example, the moving mechanism 40). Alternatively, since residual vibration occurs during the period until the apparatus after the relative movement of the phase shift mask 80 with respect to the slit mask 24 is settled, the diffraction pattern may be detected during this period. That is, a plurality of diffraction patterns respectively corresponding to a plurality of relative positions may be detected using this residual vibration.

In short, regardless of whether or not the relative position between the slit mask 24 and the phase shift mask 80 varies under controllable conditions, the image sensor 27 can operate at a plurality of timings while the relative position varies over time. The diffraction pattern may be detected sequentially. That is, in step S3, the image sensor 27 may sequentially generate captured images IM1 at a plurality of timings and detect a plurality of diffraction patterns in a state where the moving mechanism 40 is not performing a moving operation.

Also by this, it is possible to detect a plurality of diffraction patterns respectively corresponding to a plurality of relative positions. That is, as compared with the case where the diffraction pattern is detected only once, the image sensor 27 can easily detect a diffraction pattern more suitable for calculating the pattern characteristics of the phase shift unit 8b. Then, by selecting a diffraction pattern more suitable for measurement from a plurality of diffraction patterns, the pattern characteristics of the phase shift unit 8b can be calculated with higher accuracy.

On the other hand, when there is no control by the moving mechanism 40, the fluctuation range of the relative position depends on the surrounding environment and the like, and it is not known whether the optimum relative position is included in the fluctuation range. On the other hand, when the movement mechanism 40 moves the phase shift mask 80 relative to the slit mask 24, the phase shift mask 80 is slit so that the optimum relative position is included in the movement range. It can be moved relative to the mask 24. Therefore, a plurality of detected diffraction patterns can include a diffraction pattern closer to the optimum relative position, and as a result, the pattern characteristics of the phase shift unit 8b can be calculated with higher accuracy.

<Moving direction>
As described above, the positioning accuracy between the slit mask 24 and the phase shift mask 80 may be required to be several tens [nm] or less. Therefore, in order to appropriately detect the diffraction pattern at a timing when the relative position between the slit mask 24 and the phase shift mask 80 is within the accuracy, it is desirable that the relative speed between the phase shift mask 80 and the slit mask 24 is low.

Therefore, the moving mechanism 40 may move the phase shift mask 80 relative to the slit mask 24 along a direction inclined with respect to the width direction of the slit 24a (in other words, the width direction of the phase shift portion 8b). FIG. 8 is a diagram for explaining the moving direction D1 of the phase shift mask 80 with respect to the slit mask 24. FIG. In FIG. 8, the moving direction D1 is schematically indicated by a block arrow. The moving direction D1 intersects the width direction of the slit 24a within a range of about 30 to 60 degrees, for example. If the phase shift mask 80 is moved relative to the slit mask 24 along the moving direction D1, the relative velocity component along the width direction of the slit 24a can be reduced. According to this, it is easy to detect a diffraction pattern corresponding to a more optimal relative position.

<Another Example of Calculation Method of Pattern Characteristic of Phase Shift Unit 8b>
Next, another example of the method for calculating the pattern characteristics of the phase shift unit 8b based on the selected diffraction pattern SP1 will be described. First, the outline will be described. The control unit 50 sets respective initial values as values of the unknown width w and the phase difference θ, and calculates a diffraction pattern (hereinafter referred to as a calculation diffraction pattern) using the initial values. Then, the control unit 50 determines whether or not the calculated diffraction pattern is similar to the selected diffraction pattern SP1. In other words, the control unit 50 determines whether or not the difference between the calculated diffraction pattern and the selected diffraction pattern SP1 is large. When it is determined that they are not similar, that is, the difference is large, the control unit 50 changes the value of the width w and the value of the phase difference θ and calculates the calculated diffraction pattern again. The controller 50 repeatedly executes the above operation until the calculated diffraction pattern is similar to the selected diffraction pattern, that is, until the difference becomes smaller than the reference value. The value of the width w and the value of the phase difference θ when the arithmetic circuit pattern is similar to the selected diffraction pattern indicate measured values.

<Simulation model>
FIG. 9 is a diagram schematically showing an example of a simulation model M1 for calculating a calculation diffraction pattern. The simulation model M1 shows the light intensity distribution in the region corresponding to the slit 24a in the phase shift mask 80. The intensity of light in the light transmitting portion 8a, the phase shift portion 8b, and the light shielding portion 8c is set in advance based on the respective transmittances (for example, pattern design values). In the simulation model M1 of FIG. 9, the light intensity in each of the light transmitting portion 8a, the phase shift portion 8b, and the light shielding portion 8c is set to be constant. Therefore, the light intensity steeply rises at the boundary between the light transmitting portion 8a and the phase shift portion 8b. Similarly, the light intensity sharply increases at the boundary between the phase shift portion 8b and the light shielding portion 8c. Standing up. In this simulation model M1, the widths w and ws satisfy Expression (2), and the width w is an unknown number. In the simulation model M1, the phase difference θ in the phase shift unit 8b is also an unknown number.

<Calculated diffraction pattern>
The control unit 50 calculates a diffraction pattern corresponding to the simulation model M1 using a known simulator. It is obvious that this calculation can be easily performed by a fast Fourier transform. FIG. 10 is a graph schematically showing the calculated diffraction patterns AP1 to AP4. The calculated diffraction patterns AP1 to AP4 are calculated diffraction patterns obtained when the phase difference θ is changed. Specifically, the calculated diffraction patterns AP1 to AP4 have phase differences of 180 degrees, 208.8 degrees (= 360 × 0.58), 216 degrees (= 360 × 0.6), and 223.2 degrees (= 360), respectively. This is an arithmetic circuit pattern when × 0.62). In the example of FIG. 10, an example of the selective diffraction pattern SP1 is also shown for reference. In the example of FIG. 10, the selected diffraction pattern SP1 is similar to the calculated diffraction pattern AP3.

<Operation of control unit>
FIG. 11 is a flowchart illustrating an example of the operation of the control unit 50. This flow corresponds to a specific example of step S5 in FIG. First, in step S501, the control unit 50 sets the value of the width w of the phase shift unit 8b and the value of the phase difference θ by the phase shift unit 8b to respective initial values. The initial value may be set in advance, for example.

Next, in step S502, the control unit 50 calculates a calculation diffraction pattern based on the values of the width w and the phase difference θ. Specifically, the control unit 50 calculates a calculation diffraction pattern by applying a simulator using fast Fourier transform to the simulation model M1.

Next, in step S503, the control unit 50 determines whether or not the calculated diffraction pattern calculated in step S502 is similar to the selected diffraction pattern SP1. For example, the control unit 50 generates difference information indicating a difference between the calculated diffraction pattern and the selected diffraction pattern SP1, and determines whether the difference is smaller than a reference value. Although the difference information need not be particularly limited, for example, the sum of absolute values of the differences in light intensity at each position of the calculated diffraction pattern and the selected diffraction pattern SP1 can be employed. The smaller the sum, the smaller the difference. Alternatively, as the difference information, for example, a first difference between the pitch Δdx in the calculated diffraction pattern and the pitch Δdx in the selected diffraction pattern SP1, and a second difference between the peak difference Δp in the calculated diffraction pattern and the peak difference Δp in the selected diffraction pattern SP1. Differences may be employed. The smaller the difference, the smaller the difference between the calculated diffraction pattern and the selected diffraction pattern SP1.

When it is determined that the calculated diffraction pattern is not similar to the selected diffraction pattern SP1, in step S504, the control unit 50 changes at least one of the value of the width w and the phase difference θ, and updates the simulation model M1. To do. Next, the control unit 50 executes Step S503. That is, when the calculated diffraction pattern is not similar to the selected diffraction pattern SP1, it is considered that at least one of the width w and the phase difference θ is still separated from the measured value. Then, the calculated diffraction pattern is calculated again (step S503), and it is determined whether or not the calculated calculated diffraction pattern is similar to the selected diffraction pattern SP1 (step S504). By repeating steps S502 to S504, the calculated diffraction pattern will eventually be similar to the selected diffraction pattern SP1.

When it is determined in step S503 that the calculated diffraction pattern is similar to the selected diffraction pattern SP1, in step S6, the control unit 50 uses the latest width w and the phase difference θ as the measured values, and displays the display unit 70. To display.

As described above, the operation diffraction pattern similar to the selected diffraction pattern SP1 is calculated using the fast Fourier transform on the simulation model M1. According to this, the width w of the phase shift unit 8b and the phase difference θ by the phase shift unit 8b can be obtained with higher accuracy.

Moreover, in the simulation model M1, the light intensity of each of the light transmitting portion 8a and the phase shift portion 8b is set to be constant. Therefore, setting of the intensity distribution is simple and the calculation process can be simplified.

<Method for Determining Width of Phase Shift Section and Phase Difference by Phase Shift Section>
In order to efficiently calculate a calculation diffraction pattern similar to the selected diffraction pattern SP1, the control unit 50 may determine the values of the width w and the phase difference θ based on the difference information in step S504. That is, the control unit 50 may determine the values of the width w and the phase difference θ so that the difference between the calculated diffraction pattern and the selected diffraction pattern SP1 is reduced. For example, consider the case where the first difference and the second difference are adopted as the difference information. In this case, the control unit 50 changes the value of the width w so that the first difference becomes small, and changes the value of the phase difference θ so that the second difference becomes small.

More specifically, when the pitch Δdx in the calculated diffraction pattern is larger than the pitch Δdx in the selected diffraction pattern, the control unit 50 increases the width w to reduce the pitch Δdx in the next calculated diffraction pattern. Change to a smaller value. When the peak difference Δp in the calculated diffraction pattern is larger than the peak difference Δp in the selected diffraction pattern, the control unit 50 reduces the phase difference θ to reduce the peak difference Δp in the next calculated diffraction calculation pattern. Change to a value.

According to this, the calculation diffraction pattern calculated next can be brought close to the selected diffraction pattern SP1. Therefore, a calculation diffraction pattern similar to the selected diffraction pattern SP1 can be calculated earlier.

<Another example of simulation model>
In the simulation model M1, the light intensity is set to be constant in each of the light transmitting portion 8a and the phase shift portion 8b. However, in practice, at the boundary between the light transmitting portion 8a and the phase shift portion 8b, it is considered that the light intensity gradually increases with an inclination from the phase shift portion 8b toward the light transmitting portion 8a. It is done. The same applies to the boundary portion between the light shielding portion 8c and the phase shift portion 8b. Therefore, such a simulation model may be utilized.

FIG. 12 is a diagram schematically showing an example of the simulation model M2. In the simulation model M2, the light intensity increases at the boundary between the light shielding unit 8c and the phase shift unit 8b as it goes from the light shielding unit 8c to the phase shift unit 8b, and the inclination thereof is on the phase shift unit 8b side. It is steep enough. Similarly, the light intensity increases at the boundary between the phase shift unit 8b and the translucent unit 8a as it goes from the phase shift unit 8b to the translucent unit 8a. It is steep. Such light intensity distribution may be preset, for example. As the width of the phase shift unit 8b in this case, the width from the position where the light intensity becomes a preset first predetermined value to the position where the preset second predetermined value can be adopted. .

If the simulation model M2 is adopted, the control unit 50 can calculate the calculation diffraction pattern more in accordance with the actual situation, and calculates the width w of the phase shift unit 8b and the phase difference θ by the phase shift unit 8b with higher accuracy. can do.

The simulation model M2 may be set in advance. Alternatively, the control unit 50 uses a predetermined image simulator based on the pattern design values of the phase shift mask 80 (transmittance of the light transmitting unit 8a, transmittance of the phase shift unit 8b, width w of the phase shift unit 8b, etc.). Then, a simulation model M2 (light intensity distribution) may be generated.

<Another example of simulation model>
Referring to FIG. 2, the photomask inspection apparatus 1 includes an image sensor 28. The image sensor 28 images a measurement target region of the phase shift mask 80, and generates a captured image IM2. Therefore, the control unit 50 may set the light intensity distribution of the simulation model based on the captured image IM2. As a specific example, the pixel value of each pixel in the measurement target region included in the captured image IM2 may be employed in the light intensity distribution of the simulation model. According to this, it is possible to set a simulation model that is more realistic.

Since the intensity distribution of the light transmitted through the light transmitting portion 8a and the phase shift portion 8b is almost the same in the vicinity of the measurement target region and its extension, the light transmission portion 8a and the phase shift portion 8b in the vicinity of the measurement target region. The pixel value of each pixel may be adopted. For example, when it is difficult to specify the measurement target region in the captured image IM2 due to a shift of the optical system or the like, or the measurement target region is not included in the captured image IM2, and a region in the vicinity thereof is included. In some cases, a pixel value in a nearby region may be employed. As a more specific example, the pixel value of each pixel of the light transmitting portion 8a and the phase shift portion 8b located on the extension of the measurement target region may be adopted as the light intensity distribution of the simulation model.

<Operation of photomask inspection apparatus>
FIG. 13 is a flowchart showing an example of the operation of the photomask inspection apparatus 1. First, in step S11, the controller 50 controls the moving mechanism 40 to perform step movement. This step movement indicates movement to a position suitable for the image sensor 28 to image the measurement target area (or an area in the vicinity thereof). Next, in step S12, as in step S2, the control unit 50 controls the lifting mechanism 60 to perform autofocus processing.

Next, in step S13, the image sensor 28 generates the captured image IM2, and outputs the captured image IM2 to the control unit 50.

Next, in step S14, the control unit 50 stores in the storage medium an image corresponding to the measurement target region (or an image in the vicinity thereof) in the captured image IM2. For example, a preset region of the captured image IM2 is extracted as a measurement target region (or a nearby region), and the image is stored in a storage medium.

Next, in step S15, similarly to step S1, the control unit 50 controls the moving mechanism 40 to move the phase shift mask 80 with respect to the slit mask 24 so that the slit 24a faces the measurement target region. Then, alignment in the XY plane is performed.

In step S16, as in step S3, the image sensor 27 generates the captured image IM1 at a plurality of timings with the slit mask 24 and the phase shift mask 80 relatively finely moved, and the captured image IM1. Is output to the control unit 50.

Next, in step S17, as in step S4, the control unit 50 selects a diffraction pattern (selected diffraction pattern SP1) from a plurality of diffraction patterns.

Next, in step S18, the control unit 50 calculates the pattern characteristics of the phase shift unit 8b based on the selected diffraction pattern SP1. FIG. 14 is a flowchart showing a specific example of this calculation method. First, in step S511, the control unit 50 sets the light intensity distribution of the simulation model based on the captured image IM2. As a more specific example, each pixel value of the image stored in step S14 is adopted as the light intensity distribution of the simulation model. The phase difference θ may be set constant at each position of the phase shift unit 8b, or may be set at the same inclination as the light intensity distribution at each boundary.

Next, the control unit 50 executes steps S512 to S515. Steps S512 to S515 are the same as steps S501 to S504, respectively, and repeated description is avoided.

When it is determined in step S514 that the calculated diffraction pattern is similar to the selected diffraction pattern SP1, in step S19, as in step S6, the control unit 50 displays the latest width w and phase difference θ on the display unit 70 as measured values. Display.

According to this, since the light intensity distribution of the simulation model is set based on the captured image IM2, it is possible to calculate the calculation diffraction pattern in accordance with the actual situation, and the width w and the phase difference θ with higher accuracy. Can be calculated.

As described above, the photomask inspection apparatus and the photomask inspection method have been described in detail, but the above description is illustrative in all aspects, and the present disclosure is not limited thereto. The various modifications described above can be applied in combination as long as they do not contradict each other. And it is understood that many modifications which are not illustrated may be assumed without departing from the scope of this disclosure.

DESCRIPTION OF SYMBOLS 1 Photomask inspection apparatus 8a Light transmission part 8b Phase shift part 8c Light-shielding part 10 Irradiation part 24 Slit mask 24a Slit 25 Fourier transform lens 27 1st optical sensor (image sensor)
28 Second optical sensor (image sensor)
40 moving mechanism 50 arithmetic processing unit (control unit)
80 Phase shift mask

Claims

A light transmitting part that transmits light, a light blocking part that blocks light, and a phase between the light transmitted through the light transmitting part and provided between the light transmitting part and the light blocking part. A phase shift mask in which a phase shift portion to be shifted is formed in a predetermined pattern, a photomask inspection apparatus for measuring pattern characteristics of the phase shift portion,
A holding unit for holding the phase shift mask;
An irradiating unit that irradiates light to a region including the translucent unit and the phase shift unit;
A slit mask that has a slit and is arranged at a position where light that has passed through a part of the translucent part in the width direction and the whole of the phase shift part in the width direction passes through the slit;
A Fourier transform lens into which light that has passed through the slit is incident;
A photomask inspection apparatus comprising: a first optical sensor that detects a diffraction pattern of light from the Fourier transform lens at a plurality of timings.
The photomask inspection apparatus according to claim 1,
A moving mechanism that relatively moves the slit mask and the phase shift mask in plan view;
The first optical sensor detects a diffraction pattern at a plurality of timings while the moving mechanism relatively moves the slit mask and the phase shift mask.
The photomask inspection apparatus according to claim 2,
The photomask inspection apparatus, wherein the moving mechanism moves the slit mask and the phase shift mask relative to each other along a direction inclined with respect to the width direction.
The photomask inspection apparatus according to any one of claims 1 to 3,
A diffraction pattern having the smallest light intensity at a central position among the plurality of diffraction patterns detected by the first optical sensor is selected as a selected diffraction pattern, and the width of the phase shift unit and the width are selected based on the selected diffraction pattern. A photomask inspection apparatus further comprising an arithmetic processing unit that obtains at least one of the phase differences by the phase shift unit as the pattern characteristics.
The photomask inspection apparatus according to claim 4,
The said arithmetic processing part is a photomask inspection apparatus which calculates the width | variety of the said phase shift part based on the pitch of the intensity of the light in the said selective diffraction pattern.
The photomask inspection apparatus according to claim 4 or 5, wherein
The said arithmetic processing part is a photomask inspection apparatus which calculates the phase difference by the said phase shift part based on the difference of two among the some peak value or the some bottom value of the light intensity in the said selected diffraction pattern.
The photomask inspection apparatus according to claim 4,
The arithmetic processing unit includes:
A first step of setting an intensity distribution of light transmitted through the light transmitting part and the phase shift part, a width of the phase shift part, and a phase difference by the phase shift part;
A second step of calculating an operational diffraction pattern using a fast Fourier transform based on the intensity distribution, the width, and the phase difference;
A third step of determining whether the computed diffraction pattern is similar to the selected diffraction pattern;
In the third step, when it is determined that the calculated diffraction pattern is not similar to the selected diffraction pattern, the width and the phase difference are changed, and the second step and the third step are executed. A photomask inspection apparatus that executes the process.
The photomask inspection apparatus according to claim 7,
The said arithmetic processing part is a photomask inspection apparatus which sets the said intensity distribution so that the intensity | strength of the light which permeate | transmits each of the said phase shift part and the said light transmission part may become fixed in the said 1st process.
The photomask inspection apparatus according to claim 7,
In the first step, the arithmetic processing unit gradually increases the light intensity at the boundary between the phase shift unit and the translucent unit from the phase shift unit toward the translucent unit. A photomask inspection apparatus for setting the intensity distribution as described above.
The photomask inspection apparatus according to claim 7,
A second optical sensor;
An optical element that is provided between the slit mask and the phase shift mask and guides a part of light from the phase shift mask to the second optical sensor;
The said arithmetic processing part is a photomask inspection apparatus which sets the said intensity distribution based on the image imaged by the said 2nd optical sensor in the said 1st process.
A light transmitting part that transmits light, a light blocking part that blocks light, and a phase between the light transmitted through the light transmitting part and provided between the light transmitting part and the light blocking part. A phase shift mask in which a phase shift portion to be shifted is formed in a predetermined pattern, a photomask inspection method for measuring pattern characteristics of the phase shift portion,
A step of irradiating light to a region where the irradiating unit includes the translucent unit and the phase shift unit;
A diffraction pattern of light transmitted by the first optical sensor through a slit formed in the slit mask and a part in the width direction of the light transmitting part and the whole in the width direction of the phase shift part via a Fourier transform lens. And a step of detecting at a plurality of timings.