Pupil observation method, imaging method, and imaging apparatus

Abstract

To provide a pupil observation method in which an additional optical system does not need to be arranged in the surrounding of an imaging optical system, an imaging method and an imaging device.SOLUTION: There is provided a pupil observation method, which is a pupil observation method in an optical system comprising, an illumination optical system 13 and an imaging optical system 15. The pupil observation method comprises: a step for imaging a first pupil intensity distribution which passed through the illumination optical system 13; a step for installing a pinhole on a pupil on the illumination optical system 13, scanning the pupil on the pinhole, then measuring intensity of emitted light of the imaging optical system 15 for every position of the pinhole as a second pupil intensity distribution; and a step for, on the basis of the first pupil intensity distribution and the second pupil intensity distribution, calculating a third pupil intensity distribution which passed through the imaging optical system 15 and which has higher resolution than that of the second pupil intensity distribution.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pupil observation method, an imaging method, and an imaging device.

Background Art

[0002] An optical device for observing an observation target such as a photomask may have a function of observing a pupil in addition to a function of observing an image plane. Patent Document 1 discloses a technique for measuring a pupil intensity distribution that has passed through an optical system using a Bertrand lens.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0004] When measuring the pupil intensity distribution in an optical device, there is a problem that it is necessary to arrange an additional optical system including a mirror or a lens (for example, a Bertrand lens) around the imaging optical system. In particular, in an EUV (Extreme Ultraviolet) optical system, since there are limitations on the available optical elements and their sizes, it has been difficult to arrange the additional optical system at an appropriate position.

[0005] The present invention has been made to solve such problems, and provides a pupil observation method, an imaging method, and an imaging apparatus that do not require arranging an additional optical system around an imaging optical system.

Means for Solving the Problems

[0006] The pupil observation method according to the present invention is a pupil observation method in an optical system including an illumination optical system and an imaging optical system, imaging a first pupil intensity distribution that has passed through the illumination optical system; installing a pinhole in the pupil of the illumination optical system, scanning the pupil with the pinhole, and measuring, as a second pupil intensity distribution, the intensity of the light emitted from the imaging optical system for each position of the pinhole; calculating a third pupil intensity distribution that has passed through the imaging optical system and has a higher resolution than the second pupil intensity distribution, based on the first pupil intensity distribution and the second pupil intensity distribution; and includes.

[0007] Also, the imaging method according to the present invention is an imaging method for imaging an observation target using an optical system including an illumination optical system and an imaging optical system, imaging a first pupil intensity distribution that has passed through the illumination optical system; installing a pinhole in the pupil of the illumination optical system, scanning the pupil with the pinhole, and measuring, as a second pupil intensity distribution, the intensity of the light emitted from the imaging optical system for each position of the pinhole; calculating a third pupil intensity distribution that has passed through the imaging optical system and has a higher resolution than the second pupil intensity distribution, based on the first pupil intensity distribution and the second pupil intensity distribution; imaging the observation target using the optical system; and includes.

[0008] Also, the imaging apparatus according to the present invention is an optical system including an illumination optical system and an imaging optical system; A first imaging unit that images the first pupil intensity distribution that has passed through the illumination optical system; A pupil control unit that installs a pinhole in the pupil of the illumination optical system and scans the pupil with the pinhole; A second imaging unit that detects the emitted light of the imaging optical system; A measurement unit that measures the intensity of the emitted light for each position of the pinhole as a second pupil intensity distribution; A calculation unit that calculates a third pupil intensity distribution that has passed through the imaging optical system and has a higher resolution than the second pupil intensity distribution based on the first pupil intensity distribution and the second pupil intensity distribution; It is provided with.

Effect of the Invention

[0009] According to the present invention, it is possible to provide a pupil observation method, an imaging method, and an imaging device that do not require arranging an additional optical system around the imaging optical system.

Brief Explanation of Drawings

[0010]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0011] Hereinafter, the specific configuration of this embodiment will be described with reference to the drawings. The following description shows a preferred embodiment of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, those with the same reference numerals indicate substantially the same content.

[0012] (Embodiment 1) FIG. 1 is a schematic configuration diagram showing the configuration of the imaging device 10 according to Embodiment 1. The imaging device 10 includes a light source 11, a pupil control unit 12, an illumination optical system 13, a first imaging unit 14, an imaging optical system 15, a second imaging unit 16, and a processing device 17.

[0013] In addition to the function of imaging the observation target 20 using an optical system including the illumination optical system 13 and the imaging optical system 15, the imaging device 10 has a function of calculating a third pupil intensity distribution described later. The third pupil intensity distribution is calculated based on a first pupil intensity distribution described later and a second pupil intensity distribution described later.

[0014] The observation target 20 is mounted on a stage (not shown). The observation target 20 is, for example, an EUV (Extreme Ultraviolet) mask. Note that the observation target 20 is not limited to a photomask, and may be other observation targets (for example, a wafer).

[0015] At the time of imaging the observation target 20, the observation target 20 is disposed in the illumination region of the illumination optical system 13 described later. On the other hand, at the time of imaging the first pupil intensity distribution described later, since the first imaging unit 14 described later performs imaging, the observation target 20 may be retracted from the illumination region. Further, at the time of measuring the second pupil intensity distribution described later, in order for the second imaging unit 16 described later to perform the measurement, the illumination light may be reflected using the observation target 20. Specifically, when the observation target 20 is an EUV mask, the illumination light may be reflected using the multilayer of the EUV mask.

[0016] The light source 11 generates illumination light L11. The light source 11 is a lamp light source, an LED (Light Emitting Diode) light source, a laser light source, or the like. The light source 11 may generate EUV light. The illumination light L11 from the light source 11 is incident on the pupil control unit 12.

[0017] During the measurement of the second pupil intensity distribution described later, the pupil control unit 12 installs a pinhole in the pupil of the illumination optical system 13 described later and scans the pupil with the pinhole. For example, the pupil control unit 12 includes an aperture (not shown) through which the illumination light L11 passes, and scans the aperture (not shown) with the pinhole. The aperture (not shown) has a region through which a plurality of lights pass and refers to a plate that realizes an arbitrary pupil distribution, for example, a sigma aperture plate.

[0018] As shown in FIG. 1, the pupil control unit 12 may include a plate 121 having a pinhole 1211. The plate 121 is arranged perpendicular to the traveling direction of the illumination light L11. The pupil control unit 12 scans the pupil 30 with the pinhole 1211 as indicated by the arrow by moving the plate 121.

[0019] Note that the position of the aperture (not shown) is not limited to the inside of the pupil control unit 12 in FIG. 1. The aperture (not shown) may be included inside the illumination optical system 13 described later.

[0020] The illumination optical system 13 is an optical system that guides the illumination light L11 onto a stage (not shown). When the illumination optical system 13 is an EUV optical system, the illumination optical system 13 is a reflection optical system and uses a mirror to guide the illumination light L11 onto the stage (not shown).

[0021] The first imaging unit 14 images the first pupil intensity distribution that has passed through the illumination optical system 13. The first imaging unit 14 is also referred to as the imaging element observation side. As described above, the observation target 20 may be retracted from the imaging region at this time. The first imaging unit 14 is a two-dimensional image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal - Oxide Semiconductor). The first imaging unit 14 outputs the first pupil intensity distribution to a processing device 17 described later.

[0022] The first imaging unit 14 is arranged in front of the observation target 20 with respect to the traveling direction of the emitted light of the illumination optical system 13. In other words, when the illumination optical system 13 is arranged above the observation target 20, the first imaging unit 14 is arranged below the observation target 20 and images the first pupil intensity distribution from below.

[0023] The resolution of the first pupil intensity distribution is higher than that of the second pupil intensity distribution described later. However, since the first pupil intensity distribution is not the pupil intensity distribution that has passed through the imaging optical system 15, imaging the first pupil intensity distribution is not ideal as a pupil observation method for the entire optical system of the imaging device 10.

[0024] The imaging optical system 15 condenses the reflected light L12 reflected by the observation target 20 and emits the emitted light L13. The reflected light L12 passes through the imaging optical system 15 not only during imaging of the observation target 20 but also during measurement of the second pupil intensity distribution described later. The imaging optical system 15 may be an objective lens or a reflective objective mirror.

[0025] The second imaging unit 16 detects the emitted light L13 of the imaging optical system 15 and outputs an electrical signal to the processing device 17. The second imaging unit 16 is a CCD camera, a CMOS image sensor, or the like. The detection result of the second imaging unit 16 is used not only for imaging the observation target 20 but also for measuring the second pupil intensity distribution described later.

[0026] The processing device 17 is a computer including a processor, a memory, and the like. The processing device 17 includes a measurement unit 171 and a calculation unit 172.

[0027] The measurement unit 171 receives the detection result by the second imaging unit 16 and measures the intensity of the emitted light L13 for each position of the pinhole 1211 as the second pupil intensity distribution. The intensity of the emitted light L13 may be detected as an integrated value of the signal intensity in the second imaging unit 16. The measurement unit 171 outputs the measurement result of the second pupil intensity distribution to the calculation unit 172 described later.

[0028] The second pupil intensity distribution is the pupil intensity distribution that has passed through the imaging optical system 15, but has lower resolution than the first pupil intensity distribution. This is because if the size of the pinhole 1211 is reduced to increase the resolution, the signal intensity at the second imaging unit 16 decreases, resulting in a decline in measurement accuracy. Therefore, the measurement of the second pupil intensity distribution is not ideal as a pupil observation method for the optical system of the imaging device 10.

[0029] The calculation unit 172 calculates a third pupil intensity distribution based on the first pupil intensity distribution and the second pupil intensity distribution. The third pupil intensity distribution is the pupil intensity distribution that has passed through the imaging optical system 15 and has higher resolution than the second pupil intensity distribution. By calculating the third pupil intensity distribution, the pupil of the optical system of the imaging device 10 can be observed more appropriately.

[0030] Specifically, the calculation unit 172 can calculate the third pupil intensity distribution based on the product of the first pupil intensity distribution and the second pupil intensity distribution. The calculation unit 172 may normalize the first pupil intensity distribution or the second pupil intensity distribution and then calculate the product of the two.

[0031] In addition to the function of calculating the third pupil intensity distribution, the imaging device 10 has a function of imaging the observation target 20. According to the imaging device 10, the state of the pupil of the optical system can be observed using the third pupil intensity distribution, and it can be determined whether the imaging of the observation target 20 is being performed appropriately.

[0032] The imaging device 10 calculates a third pupil intensity distribution based on the first pupil intensity distribution and the second pupil intensity distribution described above. Therefore, the imaging device 10 can appropriately observe the pupil without arranging an additional optical system around the imaging optical system 15. In other words, according to the imaging device 10, the pupil that has passed through the imaging optical system can be observed while minimizing the installation space of the optical system.

[0033] Next, with reference to FIG. 2, the case where the optical system is an EUV optical system will be described in detail. FIG. 2 is a schematic diagram showing the configuration of the imaging device 10a. The imaging device 10a is a specific example of the imaging device 10 described above. The observation target 20 is an EUV mask and includes a multilayer that reflects illumination light. A pellicle may be attached to the EUV mask.

[0034] The imaging device 10a includes a light source 11, a pupil control unit 12, a reflective optical system 131, a bending mirror 132, a first imaging unit 14, an imaging optical system 15, a second imaging unit 16, and a processing device 17. In FIG. 2, a three-dimensional orthogonal coordinate system of XYZ is shown for clarity of explanation. Note that the Z direction is the vertical direction and is parallel to the thickness direction of the observation target 20. Therefore, the Z direction becomes the height direction.

[0035] Hereinafter, the description will focus on the differences from FIG. 1. The light source 11 is an EUV source that generates EUV light. The pupil control unit 12 includes a plate 121 having a pinhole 1211, as shown above the pupil control unit 12 in FIG. 2. Also, the pupil control unit 12 includes a sigma aperture plate 122 on which a pattern is formed, as shown below the pupil control unit 12 in FIG. 2. The plate 121 and the sigma aperture plate 122 are arranged perpendicular to the Y axis. The pupil control unit 12 scans the pupil 30 of the illumination light L11 by moving the plate 121 within the XZ plane when measuring the second pupil intensity distribution.

[0036] The reflective optical system 131 and the bending mirror 132 constitute the illumination optical system 13 described above. The reflective optical system 131 and the bending mirror 132 guide the illumination light L11 onto the stage where the observation target is arranged.

[0037] The first imaging unit 14 is located on the negative Z-axis side of the observation target 20 and images the first pupil intensity distribution. The image shown below the first imaging unit 14 in FIG. 2 shows the first pupil intensity distribution P1. The light intensity is represented by a gray scale. The first pupil intensity distribution P1 includes the pattern formed on the sigma aperture plate 122, as indicated by the white arrow.

[0038] The imaging optical system 15 condenses the reflected light L12 reflected by the observation target 20 and makes it incident on the second imaging unit 16. The second imaging unit 16 is, for example, a CCD sensor. Based on the position of the pinhole 1211 in the pupil control unit 12 and the detection result in the second imaging unit 16, the second pupil intensity distribution is measured. The image shown above the imaging optical system 15 in FIG. 2 shows the second pupil intensity distribution P2. The second pupil intensity distribution P2 is an image with lower resolution than the first pupil intensity distribution P1. As indicated by the white arrow, the second pupil intensity distribution P2 is measured by scanning in the pupil control unit 12.

[0039] The processing device 17 calculates the product of the first pupil intensity distribution and the normalized second pupil intensity distribution as the third pupil intensity distribution using the following formulas (1) and (2). The image shown above the processing device 17 in FIG. 2 shows the third pupil intensity distribution P3. The dotted area corresponds to the pupil.

Number

Number

[0040] Next, with reference to FIG. 3, the flow of the pupil observation method according to the embodiment will be described. FIG. 3 is a flowchart illustrating the flow of the pupil observation method according to the embodiment. Steps S201 to S204 indicate steps of measuring the second pupil intensity distribution, step S101 indicates a step of measuring the first pupil intensity distribution, and step S301 indicates a step of calculating the third pupil intensity distribution. The order of steps S201 to S204 and step S101 may be reversed. The observation target 20 is an EUV mask and is assumed to have a multilayer.

[0041] In step S201, the stage on which the observation target 20 is mounted is moved, and the illumination light L11 is reflected by the multilayer. Note that the illumination light L11 may be reflected using a mirror or the like.

[0042] In step S202, the sigma aperture plate 122 is scanned with the pinhole 1211. At this time, as shown in step S203, the number of photons incident on the second imaging unit 16 is counted.

[0043] In step S204, the second pupil intensity distribution is determined. The second pupil intensity distribution is used to calibrate the first pupil intensity distribution and calculate the third pupil intensity distribution.

[0044] In step S101, the first pupil intensity distribution is imaged using the first imaging unit 14. As described above, the first pupil intensity distribution represents the pupil intensity distribution that does not pass through the imaging optical system. Before step S101, the observation target 20 may be retracted from the illumination area.

[0045] In step S301, the third pupil intensity distribution is calculated based on the first pupil intensity distribution and the second pupil intensity distribution. The third pupil intensity distribution is the intensity distribution of the pupil that has passed through the imaging optical system and has a higher resolution than the second pupil intensity distribution.

[0046] Finally, the effects of the pupil observation method according to the embodiment will be described. In an imaging device, in order to measure the pupil intensity distribution of the entire optical system, it is ideal to measure the pupil intensity distribution in front of the imaging element. However, when obtaining a high-magnification magnified image, it has been difficult to directly observe the pupil due to the physical position of the pupil being close to the components of the imaging optical system and the small size of the pupil. Also, although it is possible to arrange lenses and mirrors in the optical system to project the pupil intensity distribution onto the imaging element, it has been physically difficult to arrange the additional optical system at an appropriate position.

[0047] According to the pupil observation method according to the embodiment, the pupil intensity distribution of the entire optical system can be appropriately calculated based on the first pupil intensity distribution with high resolution and the second pupil intensity distribution with low resolution. In particular, even in an EUV optical system where a transmissive lens cannot be used, the pupil of the entire optical system can be appropriately observed.

[0048] As described above, the embodiments of the present invention have been described, but the present invention includes appropriate modifications that do not impair its object and advantages, and furthermore, is not limited by the above embodiments.

Explanation of Reference Numerals

[0049] 10, 10a Imaging device 11 Light source 12 Pupil control unit 121 Plate 1211 Pinhole 122 Sigma aperture plate 13 Illumination optical system 131 Reflection optical system 132 Bending mirror 14 First imaging unit 15 Imaging optical system 16 Second imaging unit 17 Processing device 171 Measurement unit 172 Calculation unit 20 Object to be observed 30 Pupil L11 Illumination light L12 Reflected light L13 Emitted light P1 First pupil intensity distribution P2 Second pupil intensity distribution P3 Third pupil intensity distribution

Claims

1. A pupil observation method in an optical system including an illumination optical system and an imaging optical system, comprising: imaging a first pupil intensity distribution that has passed through an aperture plate disposed at the pupil of the illumination optical system; installing a pinhole at the pupil of the illumination optical system, scanning the aperture plate with the pinhole, and measuring, as a second pupil intensity distribution, the intensity of the light emitted from the imaging optical system for each position of the pinhole; calculating a third pupil intensity distribution that has passed through the imaging optical system and has a higher resolution than the second pupil intensity distribution, based on the product of the intensities corresponding to common positions on the pupil plane in the first pupil intensity distribution and the second pupil intensity distribution; A pupil observation method including the above steps.

2. The aperture plate has a pattern formed thereon, and the step of imaging the first pupil intensity distribution includes imaging, as the first pupil intensity distribution, an image including the pattern formed on the aperture plate. The pupil observation method according to claim 1.

3. The optical system is an EUV (Extreme Ultraviolet) optical system. The pupil observation method according to any one of claims 1 or 2.

4. The step of calculating the third pupil intensity distribution includes calculating the third pupil intensity distribution based on the product of the intensities corresponding to common positions on the pupil plane in the first pupil intensity distribution and the normalized second pupil intensity distribution. The pupil observation method according to any one of claims 1 to 3.

5. The step of imaging the first pupil intensity distribution includes imaging the first pupil intensity distribution using a first imaging unit disposed behind an observation target onto which the light emitted from the illumination optical system is incident from the front. The pupil observation method according to any one of claims 1 to 4.

6. The step of measuring the second pupil intensity distribution includes reflecting the light emitted from the illumination optical system using the observation target and measuring the second pupil intensity distribution. The pupil observation method according to claim 5.

7. An imaging method for imaging an observation target using an optical system including an illumination optical system and an imaging optical system, comprising: imaging a first pupil intensity distribution that has passed through an aperture plate disposed at the pupil of the illumination optical system; installing a pinhole at the pupil of the illumination optical system, scanning the aperture plate with the pinhole, and measuring, as a second pupil intensity distribution, the intensity of the light emitted from the imaging optical system for each position of the pinhole; A step of calculating a third pupil intensity distribution that has a higher resolution than the second pupil intensity distribution, based on the product of the intensities corresponding to a common position on the pupil plane in the first pupil intensity distribution and the second pupil intensity distribution, and that has passed through the imaging optical system; A step of imaging the observation target using the optical system; An imaging method including the above.

8. The aperture plate has a pattern formed thereon, The step of imaging the first pupil intensity distribution includes imaging, as the first pupil intensity distribution, an image including the pattern formed on the aperture plate. The imaging method according to claim 7.

9. An optical system including an illumination optical system and an imaging optical system, A first imaging unit that images a first pupil intensity distribution that has passed through an aperture plate disposed at the pupil of the illumination optical system; A pupil control unit that installs a pinhole at the pupil of the illumination optical system and scans the aperture plate with the pinhole; A second imaging unit that detects the emitted light of the imaging optical system; A measurement unit that measures, as a second pupil intensity distribution, the intensity of the emitted light for each position of the pinhole; A calculation unit that calculates a third pupil intensity distribution that has a higher resolution than the second pupil intensity distribution, based on the product of the intensities corresponding to a common position on the pupil plane in the first pupil intensity distribution and the second pupil intensity distribution, and that has passed through the imaging optical system; An imaging apparatus including the above.

10. The aperture plate has a pattern formed thereon, The first imaging unit images, as the first pupil intensity distribution, an image including the pattern formed on the aperture plate. The imaging apparatus according to claim 9.

11. A pupil observation method in an optical system including an illumination optical system and an imaging optical system, the method including: A step of imaging a first pupil intensity distribution that has passed through an aperture plate disposed at the pupil of the illumination optical system; A step of installing a pinhole at the pupil of the illumination optical system, scanning the aperture plate with the pinhole, and measuring, as a second pupil intensity distribution, the intensity of the emitted light of the imaging optical system for each position of the pinhole; A step of calculating a third pupil intensity distribution that has a higher resolution than the second pupil intensity distribution, based on the first pupil intensity distribution and the second pupil intensity distribution, and that has passed through the imaging optical system; Including the above, The step of calculating the third pupil intensity distribution calculates the third pupil intensity distribution using the following formula: 【Number 1】 P1(x, y) represents the first pupil intensity distribution, PID(x, y) represents the normalized second pupil intensity distribution, P3(x, y) represents the third pupil intensity distribution, and (x, y) represents the position on the pupil plane corresponding to the position (x, y) of the pinhole. Pupil observation method.

Images