Optical device and method for correcting the optical device

Abstract

The present invention provides an optical device equipped with a gain changing unit that changes a predetermined gain. [Solution] An optical device is provided, comprising: a first detection unit that detects light from an object illuminated by light from a light source and outputs signals corresponding to multiple positions; a second detection unit that detects a portion of the light from the light source and outputs signals corresponding to multiple positions; a signal correction unit that corrects the signals from the first detection unit based on predetermined gains set in advance for each position; and a gain changing unit that changes predetermined gains based on the signals from the second detection unit.

Description

Technical Field

[0001] The present disclosure relates to an optical device and a correction method for an optical device.

Background Art

[0002] Conventionally, there has been a technique for detecting defects present in a sample based on a signal monitoring illumination.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, it is possible to perform more detailed device control based on the output result of the illumination monitor. Therefore, an object of the present disclosure is to provide an optical device including a gain changing unit that changes a predetermined gain.

Means for Solving the Problems

[0005] [[ID=4,2]]The optical device of the present disclosure includes: a first detection unit that detects light from an object illuminated by light from a light source and outputs signals associated with a plurality of positions; a second detection unit that detects a part of the light from the light source and outputs signals associated with a plurality of positions; a signal correction unit that corrects the signals in the first detection unit based on a predetermined gain determined in advance for each position; a gain changing unit that changes the gain to be the predetermined gain based on the signals in the second detection unit, and the gain changing unit If, during a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit changes to an evaluation value different from the first evaluation value, the number of times an evaluation value different from the first evaluation value by more than a first threshold is acquired exceeds a second threshold, the predetermined gain is changed. The signal correction unit is an optical device that corrects the signal in the first detection unit based on a predetermined gain after modification by the gain changing unit.

[0006] The optical apparatus of this disclosure is The system includes a drive unit that changes the relative position between the lighting spot and the object with respect to the stripe of the object, If the evaluation value based on the signals from multiple positions of the second detection unit during illumination of the first stripe changes to a different evaluation value by more than a third threshold greater than the first evaluation value and the first threshold, the drive unit may be controlled to perform illumination of the first stripe again.

[0007] The optical apparatus of this disclosure is The system includes a drive unit that changes the relative position between the lighting spot and the object with respect to the stripe of the object, During a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit while the first stripe is illuminated changes to an evaluation value different from the first evaluation value, if the number of times an evaluation value different from the first evaluation value by more than a first threshold is obtained exceeds a fourth threshold which is greater than the second threshold, The drive unit may be controlled to perform illumination on the first stripe again.

[0008] The optical apparatus of this disclosure is In addition to changing the predetermined gain, adjustments to the optical elements may also be made.

[0009] In the optical apparatus disclosed herein, The object may be critically illuminated by light from the light source.

[0010] In the optical apparatus disclosed herein, The first detection unit and the second detection unit may be in conjugate positions.

[0011] In the optical apparatus disclosed herein, The gain changing unit may change the predetermined gain based on the result of illuminating a specific area of ​​the object.

[0012] The method for controlling the optical apparatus described herein is: A first detection unit detects light from an object illuminated by light from a light source and outputs signals associated with multiple locations. A second detection unit detects a portion of the light from the aforementioned light source and outputs signals corresponding to multiple positions, A signal correction unit corrects the signal from the first detection unit based on a predetermined gain set in advance for each position, A control method for an optical device comprising: a gain changing unit that changes the gain to a predetermined gain based on the signal from the second detection unit, The aforementioned gain changing unit is If, during a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit changes to an evaluation value different from the first evaluation value, the number of times an evaluation value different from the first evaluation value by more than a first threshold is acquired exceeds a second threshold, the predetermined gain is changed. The signal correction unit is a control method for an optical device that corrects the signal at the first detection unit based on a predetermined gain after modification by the gain changing unit.

[0013] The method for controlling the optical apparatus described herein is: The optical device comprises a drive unit that changes the relative position between the illumination spot and the object with respect to the stripe of the object, If, during illumination of the first stripe, the evaluation value based on signals from multiple positions of the second detection unit changes to a different evaluation value by more than a third threshold greater than the first evaluation value and the first threshold, the drive unit may be controlled to perform illumination of the first stripe again.

[0014] The method for controlling the optical apparatus described herein is: The optical device includes a drive unit that changes the relative position between the illumination spot and the object with respect to the stripes of the object. After the evaluation value based on the signals at multiple positions of the second detection unit during the illumination of the first stripe changes to an evaluation value different from the first evaluation value, if the number of times of obtaining an evaluation value exceeding the first threshold exceeds a fourth threshold greater than the second threshold within a predetermined period, The drive unit may be controlled to perform the illumination on the first stripe again.

[0015] The control method of the optical device of the present disclosure is as follows. In addition to changing the predetermined gain, adjustment of the optical element may be performed.

[0016] In the control method of the optical device of the present disclosure, The object may be critically illuminated with light from the light source.

[0017] In the control method of the optical device of the present disclosure, The first detection unit and the second detection unit may be at conjugate positions.

[0018] In the control method of the optical device of the present disclosure, The gain change unit may change the predetermined gain based on the result of illuminating a specific region of the object.

Advantages of the Invention

[0019] According to the present disclosure, an optical device including a gain change unit that changes a predetermined gain is provided.

Brief Description of the Drawings

[0020] [Figure 1] It is a diagram showing the optical system of the optical device according to the embodiment. [Figure 2] It is a diagram showing an example of correction by the gain according to the embodiment. [Figure 3] It is a block diagram showing the configuration of the optical device according to the embodiment. [Figure 4] This figure shows the correction scan profile according to the embodiment. [Figure 5] This is flowchart 1 of the control method for the optical device according to the embodiment. [Figure 6] This is flowchart 2 of the control method for the optical device according to the embodiment. [Figure 7] This figure shows the optical system of an optical device according to a modified example. [Modes for carrying out the invention]

[0021] Embodiment Embodiments of the present invention will be described below with reference to the drawings. However, the invention claimed is not limited to the following embodiments. Furthermore, not all of the configurations described in the embodiments are necessarily essential for solving the problem. For clarity of explanation, the following descriptions and drawings have been omitted and simplified as appropriate. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations have been omitted where necessary.

[0022] (Description of the optical device according to the embodiment) Figure 1 is a diagram showing the optical system of the optical device according to the embodiment. Figure 2 is a diagram showing an example of correction by gain according to the embodiment. Figure 3 is a block diagram showing the configuration of the optical device according to the embodiment. Figure 4 is a diagram showing the correction scan profile according to the embodiment. The optical device according to the embodiment will be described with reference to Figures 1 to 4. The optical device is a device for inspecting defects, etc., on an object to be inspected.

[0023] As shown in Figure 1, the optical device according to this embodiment comprises an illumination optical system 10, a detection optical system 20, a monitor unit 30, and a processing unit 40. The illumination optical system 10 comprises a light source 11, an ellipsoidal mirror 12, an ellipsoidal mirror 13, and a recessed mirror 14. The detection optical system 20 comprises a perforated concave mirror 21, a convex mirror 22, and a first detector 23. The perforated concave mirror 21 and the convex mirror 22 constitute a Schwarzschild magnification optical system. The monitor unit 30 comprises a cut mirror 31, a concave mirror 32, and a second detector 33. The object to be inspected is, for example, an EUV mask 50. However, the object to be inspected is not limited to an EUV mask 50.

[0024] The light source 11 generates illumination light L11. The illumination light L11 contains, for example, EUV light of 13.5 nm, which is the same as the exposure wavelength of the EUV mask 50 to be inspected. The illumination light L11 generated from the light source 11 is reflected by the ellipsoidal mirror 12. The illumination light L11 reflected by the ellipsoidal mirror 12 travels while being focused and is concentrated at the focal point IF1. The focal point IF1 is located in a position conjugate to the upper surface 51 of the EUV mask 50.

[0025] The illumination light L11, after passing through the focal point IF1, spreads out as it travels and enters a reflecting mirror such as the ellipsoidal mirror 13. The illumination light L11 that enters the ellipsoidal mirror 13 is reflected by the ellipsoidal mirror 13, and as it travels, it is focused and enters the recessed mirror 14. In other words, the ellipsoidal mirror 13 causes the illumination light L11 to enter the recessed mirror 14 as focused light. The recessed mirror 14 is positioned directly above the EUV mask 50. The illumination light L11 that enters the recessed mirror 14 and is reflected enters the EUV mask 50. That is, the recessed mirror 14 causes the illumination light L11 to enter the EUV mask 50.

[0026] The ellipsoidal mirror 13 focuses the illumination light L11 onto the EUV mask 50. The illumination optical system 10 is positioned so that when the illumination light L11 illuminates the EUV mask 50, the image of the light source 11 is projected onto the upper surface 51 of the EUV mask 50. Therefore, the illumination optical system 10 provides critical illumination. In this way, the illumination optical system 10 illuminates the object to be inspected using critical illumination provided by the illumination light L11 generated by the light source 11.

[0027] The EUV mask 50 is placed on the stage 52. Here, the plane parallel to the top surface 51 of the EUV mask 50 is defined as the XY plane, and the direction perpendicular to the XY plane is defined as the Z direction. The illumination light L11 is incident on the EUV mask 50 from a direction inclined from the Z direction. That is, the illumination light L11 is incident at an oblique angle to illuminate the EUV mask 50.

[0028] Stage 52 is an XYZ driven stage. By moving Stage 52 in the XY direction, a desired area of ​​the EUV mask 50 can be illuminated. Furthermore, by moving Stage 52 in the Z direction, focus adjustment can be performed.

[0029] Illumination light L11 from light source 11 illuminates the inspection area of ​​the EUV mask 50. The inspection area illuminated by illumination light L11 is, for example, 0.5 mm square. Reflected light L12, which is incident from a direction inclined with respect to the Z direction and reflected by the EUV mask 50, is incident on the perforated concave mirror 21. A hole 21a is provided in the center of the perforated concave mirror 21.

[0030] The reflected light L12 reflected by the perforated concave mirror 21 is incident on the convex mirror 22. The convex mirror 22 reflects the reflected light L12 incident from the perforated concave mirror 21 toward the hole 21a of the perforated concave mirror 21. The reflected light L12 that has passed through the hole 21a is detected by the first detector 23. The first detector 23 is a detector that includes a TDI (Time Delay Integration) sensor and acquires image data of the EUV mask 50 that is to be inspected. The first detector 23 includes a plurality of image sensors arranged in a line in one direction. Linear image data captured by the plurality of image sensors arranged in a line is called one-dimensional image data, or one frame. The first detector 23 acquires multiple one-dimensional image data by scanning in a direction orthogonal to one direction. The image sensor is, for example, a CCD (Charge Coupled Device). However, the image sensor is not limited to a CCD.

[0031] In this manner, the detection optical system 20 collects the reflected light L12 from the object to be inspected, which is illuminated by the illumination light L11, and detects the collected reflected light L12 with the first detector 23 to acquire image data of the EUV mask 50. The image data is, for example, one-dimensional image data.

[0032] The reflected light L12 contains information such as defects in the EUV mask 50. The specularly reflected light of the illumination light L11 incident on the EUV mask 50 from a direction tilted with respect to the Z direction is detected by the detection optical system 20. If a defect exists in the EUV mask 50, the defect is observed as a dark image. This observation method is called bright-field observation. Multiple one-dimensional image data of the EUV mask 50 acquired by the first detector 23 are output to the processing unit 40 and processed into two-dimensional image data.

[0033] As shown in Figure 1, the cut mirror 31 of the monitor unit 30 is positioned between the ellipsoidal mirror 13 and the recessed mirror 14, and extracts a portion of the illumination light L11 between the ellipsoidal mirror 13 and the recessed mirror 14. The cut mirror 31 reflects a small portion of the beam of illumination light L11. This portion of the beam is, for example, the upper part of the beam.

[0034] In the cross-sectional area of ​​the illumination light L11 perpendicular to the optical axis 15 at the position where the cut mirror 31 is placed, the cross-sectional area of ​​a portion reflected by the cut mirror 31 is smaller than the cross-sectional area of ​​the illumination light L11 other than that portion.

[0035] For example, if the cross-sectional area of ​​the illumination light L11 perpendicular to the optical axis 15 at the position where the cut mirror 31 is placed is 100, then some of the cross-sectional areas are approximately 1. The extraction angle of the illumination light L11 extracted from the light source 11 in the direction perpendicular to the optical axis 15 is, for example, ±7°. The range used as illumination light L11 for the EUV mask 50 is, for example, ±6°. For use in the monitor unit 30, the upper part of the illumination light L11 beam, for example, in the range of 1°, is extracted by the cut mirror 31. Even if only a small portion of the upper part of the beam is extracted in this way, the amount of light from the illumination light L11 on the EUV mask 50 does not decrease significantly. Therefore, a decrease in the accuracy of the object being inspected can be suppressed.

[0036] The cut mirror 31 is positioned, for example, near the pupil in the illumination optical system 10. By extracting the illumination light L11 with the cut mirror 31 at a position near the pupil in the illumination optical system 10, a good correlation can be obtained between the image data acquired by the first detector 23 and the image data acquired by the second detector 33. Even if the numerical aperture (NA) for the first detector 23 and the NA for the second detector 33 are different, and the point spreading function (PSF) is different, the difference in NA does not affect this embodiment because the plasma size is sufficiently large compared to the PSF size.

[0037] The illumination light L11 reflected by the cut mirror 31 travels while being narrowed, and converges at the focal point. After that, the illumination light L11 spreads out and enters the concave mirror 32.

[0038] The concave mirror 32 and several other mirrors (not shown) magnify the illumination light L11 extracted by the cut mirror 31. The image data acquired by the second detector 33 can also be magnified to a high degree. For example, a magnification of 500x can be achieved using multiple mirrors.

[0039] In this embodiment, the magnification of the luminance distribution image data acquired by the monitor unit 30 is the same as the magnification of the image data of the object to be inspected acquired by the detection optical system 20. However, the magnification of the luminance distribution image data acquired by the monitor unit 30 may be lower than the magnification of the image data of the object to be inspected acquired by the detection optical system 20. The solid angle required for extraction is the square of the ratio of the magnifications. For example, if the magnification of the first detector 23 is 20 times and the magnification of the second detector 33 is 2 times, the solid angle required for extraction by the cut mirror 31 is 1 / 100 of the solid angle of extraction from the light source 11. Converted in terms of NA, it is 1 / 10.

[0040] The illumination light L11 that enters the concave mirror 32 and is reflected by the concave mirror 32 is detected by the second detector 33. The second detector 33 is a detector that includes a TDI (Time Delay Integration) sensor and acquires image data of the brightness distribution of the illumination light L11. The second detector 33 includes multiple image sensors arranged in a line in one direction. The linear image data captured by the multiple image sensors arranged in a line is called one-dimensional image data, or one frame, as with the first detector 23. The second detector 33 acquires multiple one-dimensional image data by scanning in a direction orthogonal to one direction. The one-dimensional image data acquired by the second detector 33 shows the power fluctuation and brightness distribution of the illumination light L11. The image sensor is, for example, a CCD (Charge Coupled Device). However, the image sensor is not limited to a CCD.

[0041] For example, the optical system is arranged so that the image of the light source 11 of the illumination light L11 is formed on the second detector 33. As a result, the monitor unit 30 acquires image data (hereinafter sometimes referred to as "image data of power fluctuations and brightness distribution" or "monitor image") that can identify the power fluctuations and brightness distribution of the illumination light L11 detected by illuminating the second detector 33 with a portion of the illumination light L11 using critical illumination. Therefore, the brightness distribution and power fluctuations can be corrected with high accuracy. The first detector 23 and the second detector 33 are conjugate. In this manner, the monitor unit 30 focuses a portion of the illumination light L11, detects the focused illumination light L11 with the second detector 33, and acquires image data of the power fluctuation and brightness distribution of the illumination light L11. The image data of the power fluctuation and brightness distribution of the illumination light L11 acquired by the second detector 33 is output to the processing unit 40.

[0042] The processing unit 40 is connected to the detection optical system 20 and the monitor unit 30 by signal lines or wirelessly. The processing unit 40 receives image data of the object to be inspected from the first detector 23 in the detection optical system 20. The processing unit 40 also receives image data of the power fluctuation and brightness distribution of the illumination light L11 from the second detector 33 in the monitor unit 30.

[0043] The processing unit 40 corrects the image data of the EUV mask 50 acquired by the detection optical system 20 based on the power fluctuation and brightness distribution image data acquired by the monitor unit 30. At the same time, the processing unit 40 inspects the EUV mask 50 from the corrected image data of the EUV mask 50. Since the inspection of the object to be inspected is performed from the corrected image data of the object to be inspected, the optical device 1 can be described as an optical device 1 equipped with a correction device.

[0044] The processing unit 40 performs shading correction to correct the brightness distribution of the illumination light L11 detected by the first detector 23.

[0045] Based on Figure 2, the outline of shading correction will be explained. Assume that the original luminance profile detected by the first detector 23 has an upward-convex shape. In contrast, the processing unit 40 (signal correction unit) performs shading correction by applying a gain that has a downward-convex shape to the profile. As a result, the shaded-corrected profile becomes flat. By using a flat profile, for example, defect inspection of an object based on the difference between the luminance of a certain pixel and the luminance of surrounding pixels can be performed with greater accuracy.

[0046] Here, the gain is a predetermined gain that is set to have a specific shape in advance, taking into account the characteristics of the first detector 23 and the illumination light L11. Note that the shape of the predetermined gain shown in Figure 2 is just one example, and the shape of the predetermined gain may be any shape (for example, a flatter shape) as long as the Profile after correction by shading correction is made to an arbitrary shape.

[0047] Incidentally, in inspections using critical illumination, the state of the light source (bright spot) has a significant impact on fluctuations in the luminance distribution at the first detector 23. For example, if the light source (bright spot) moves in a plane component perpendicular to the optical axis, the position (vertex position) of the luminance profile at the first detector 23 that is convex upward will fluctuate in the left-right direction.

[0048] Patent Document 1 proposes a solution to these problems, namely an apparatus and method for shading correction that takes into account fluctuations in the luminance distribution at the first detector 23. The processing unit 40 in this embodiment performs shading correction that takes into account fluctuations in the luminance distribution at the first detector 23 using a similar method.

[0049] In other words, the processing unit 40 determines how to apply a predetermined gain to the luminance profile acquired by the first detector 23 based on the luminance profile acquired by the second detector 33. For example, based on the result of determining that the vertex position of the luminance profile acquired by the second detector 33 has moved by +x1 in the +X direction relative to the vertex position of the reference luminance profile, the processing unit 40 performs shading correction on the first detector 23 based on a gain obtained by moving the predetermined gain by +x1 in the X direction. Alternatively, as another example, based on the result of determining that the intensity of the vertex position of the luminance profile acquired by the second detector 33 is ΔI greater than the intensity of the vertex position of the reference luminance profile, the processing unit 40 performs shading correction on the first detector 23 based on a gain obtained by decreasing the predetermined gain by -ΔI. In this explanation, the vertex position of the luminance profile of the second detector 33 was used as the comparison point, but any point may be used as the comparison point. Furthermore, the movement of the predetermined gain in the X-axis direction or in the intensity direction may be applied to the entire predetermined gain, or it may be applied to a part of the predetermined gain, such as the field of view position (position on the X-axis) where fluctuations are particularly large.

[0050] As shown in Figure 3, the optical device 1 according to this embodiment includes a first detection unit 301, a second detection unit 302, and a processing unit 40 including a signal correction unit 303 and a gain changing unit 304.

[0051] The first detection unit 301 corresponds to the first detector TDI1. The first detection unit 301 detects light from an object illuminated by a light source. The first detection unit 301 outputs the light signal associated with multiple positions. Multiple positions refer to the association of detection units arranged in one dimension with the detector.

[0052] The second detection unit 302 corresponds to the second detector TDI2. The second detection unit 302 detects a portion of the light from the light source. The second detection unit 302 outputs the light signal associated with multiple positions. Multiple positions refer to the association of detection units arranged in one dimension with the detector.

[0053] The signal correction unit 303 corrects the signal from the first detection unit 301 based on a predetermined gain set in advance for each position. The signal correction unit 303 corrects the signal from the first detection unit 301 based on a predetermined gain. For example, the corrected signal will be the value shown as the Profile with Shading in Figure 2. Correcting based on a predetermined gain may include, as described above, correcting the predetermined gain for at least some of the field of view positions with a gain obtained by moving the predetermined gain in the X-axis direction, or correcting the predetermined gain with a gain obtained by moving the predetermined gain in the Intensity direction.

[0054] Furthermore, if the predetermined gain has been changed by the gain changing unit as described later, the signal correction unit 303 corrects the signal at the first detection unit 301 based on the changed predetermined gain.

[0055] (Control during fluctuations) The processing unit 40 performs variable control to address state changes that cannot be fully handled by the signal correction based on a predetermined gain by the signal correction unit 303, as described above, that is, to enable finer device control. Variable control includes, as described later, rewriting the gain to a predetermined gain by the gain change unit 304, rescanning via drive control of the stage 52, or other optical adjustments.

[0056] The gain changing unit 304 changes a predetermined gain based on the signal from the second detection unit 302, that is, based on the evaluation result for the evaluation image described below. Changing the predetermined gain is an example of control during fluctuations.

[0057] The processing unit 40 performs a rescan based on the signal from the second detection unit 302, that is, based on the evaluation results for the evaluation image described below. Rescan is an example of control during fluctuations. The processing unit 40 may perform optical adjustments in place of, or in addition to, changing a predetermined gain or performing a rescan, based on the signal from the second detection unit 302, that is, based on the evaluation results for the evaluation image described below. The processing unit 40 may perform a rescan or optical adjustments in addition to changing a predetermined gain.

[0058] (Image for evaluation) The evaluation images will be explained based on Figure 4. The left side of Figure 4 shows a portion of the monitor image acquired based on the signal from the second detection unit 302 when an inspection image of a certain stripe is acquired. Here, a stripe is a virtually set area on the object to be inspected, and may mean an image area of ​​the object to be inspected obtained based on the signal from the first detection unit 301 by relatively moving the object to be inspected from one end to the other in the Y-axis direction while keeping the position in the X-axis direction constant, with the direction in which the sensors are arranged in a line as the X-axis direction. Furthermore, an inspection image of a certain stripe may mean an image of the object to be inspected obtained based on the first detection unit 301 when the object to be inspected is relatively moved in the Y-axis direction for any one of the multiple stripes that exist on the object to be inspected.

[0059] With the second detection unit 302 configured as described above, when an inspection image of a certain stripe is acquired, a monitor image is acquired based on the signal from the second detection unit 302. As an example, in the monitor image shown in the left diagram of Figure 4, the vertical direction corresponds to the time (or scan position if the second detection unit 302 is TDI), and the horizontal direction corresponds to the direction in which the sensors are arranged in a line.

[0060] An image obtained by extracting at least a portion of the monitor image is called an evaluation image, and an example is shown in the right-hand figure of Figure 4. An evaluation image is an image used to evaluate whether a predetermined level of power fluctuation or brightness distribution fluctuation has occurred, based on the signal from the second detection unit 302 acquired at a certain time, or based on the average or sum of signals from the second detection unit 302 acquired at multiple consecutive time points.

[0061] As an example, the evaluation image may be obtained by dividing the output of the line-arranged sensors of the second detection unit 302 for each control time into 10 sections (f1 to f10) and arranging them in order of control time (t1 to t10), as shown in the right-hand figure of Figure 4. The values ​​of each section f1 to f10 may be the sum of the outputs of four sensors belonging to each section, for example, if 40 sensors are arranged in a line. Alternatively, instead of arranging the signals for each control time in order of time, the evaluation image may be obtained by extracting signals at a certain period from multiple control times and arranging them in order of time, or by averaging the output of the second detection unit 302 for each control time over multiple consecutive control times (for example, four consecutive control times) and arranging them in order of control time. The right-hand figure of Figure 4 illustrates an evaluation image obtained by arranging the output of the second detection unit 302 for every three control times indicated by the diagonal lines in the monitor image of the left-hand figure of Figure 4, corresponding to f1 to f10, for 10 control times.

[0062] For the sake of explanation, the evaluation image is said to be generated from a portion of the monitor image, but it is not limited to this, and the evaluation image may be generated directly from the second detection unit 302. Also, since it may be data containing information that can be used for image generation, although it is referred to as an evaluation image above, the evaluation image does not have to be displayed on a display unit or the like in a way that the user can recognize it as an image. In that case, the evaluation image may be appropriately referred to as evaluation data.

[0063] (Evaluation value used to determine whether or not control is necessary during fluctuations) The processing unit 40 uses the intensity value and uniformity calculated based on the aforementioned evaluation image as evaluation values ​​used to determine whether or not control is necessary during fluctuations. As an example of an evaluation value, the intensity value can be calculated using the following formula, for example. (Average - Shading Target) / Shading Target For example, at time t1, the average is (103+100+98+98+99+102+104+106+104+106) / 10 = 102. If the shading target is 100, the intensity value at time t1 will be 0.02.

[0064] Uniformity, as an example of an evaluation metric, can be calculated using the following formula, for example. (Maximum value - Minimum value) / (Maximum value + Minimum value) For example, at time t1, the maximum value is 106 and the minimum value is 98, so the uniformity at time t1 is 8 / 204 = 0.039216.

[0065] (Determination of whether control is necessary during fluctuations) (Part 1: Gain rewriting process) The processing unit 40 (gain changing unit 304) performs the following gain rewrite when it determines that fluctuations in the evaluation value within a relatively small range have occurred multiple times within a predetermined period.

[0066] In other words, the gain changing unit changes a predetermined gain during a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit 302 has changed to an evaluation value different from the first evaluation value, if the difference from the first evaluation value exceeds a first threshold and the number of times a different evaluation value is acquired exceeds a second threshold. Changing the predetermined gain includes making the value of the gain to be the predetermined gain for each field of view position (position on the X axis) different from the value before the change, and / or making the shape of the gain to be the predetermined gain different from the shape before the change. The predetermined period may, for example, be the period during which the same stripe in which it was detected that the evaluation value had changed to an evaluation value different from the first evaluation value is being inspected. The first evaluation value is a reference value, and may be, for example, 0.0 for intensity and 0.0 for uniformity. Note that "different from the first evaluation value exceeding a predetermined threshold" may mean that the absolute value of the difference between the first evaluation value and the acquired evaluation value exceeds a predetermined threshold.

[0067] The processing unit 40 (gain changing unit 304) changes the gain to a predetermined gain, and the signal correction unit 303 corrects the signal based on the changed predetermined gain as described above. This allows the signal correction unit 303 to appropriately handle state changes that cannot be adequately addressed by correcting the signal based on the predetermined gain before the change (including correcting for at least some of the field of view positions of the predetermined gain before the change with a gain obtained by moving the predetermined gain before the change in the X-axis direction, and / or correcting with a gain obtained by moving the predetermined gain before the change in the Intensity direction).

[0068] (Part 2: Rescan process) If the processing unit 40 determines that a fluctuation in the evaluation value has occurred within a relatively large range of values, it performs a rescan process. Rescan is a process in which the drive unit is controlled as described later to reacquire the inspection image from the beginning for the stripe that is the target of the inspection image acquisition.

[0069] In other words, when the processing unit 40 determines that the evaluation value based on the signals from multiple positions of the second detection unit 302 differs from the first evaluation value by more than a third threshold when acquiring an inspection image of a predetermined stripe, it drives the stage 52 to reacquire the inspection image of the predetermined stripe.

[0070] The first evaluation value is a reference value, and may be, for example, 0.0 for intensity and 0.0 for uniformity. The same value used for determining the rescan process may be used as the reference value for determining the rescan process as the reference value used for determining the gain rewrite process described above. Alternatively, a value different from the reference value (first evaluation value) used for determining the gain rewrite process described above (second evaluation value) may be used as the reference value for determining the rescan process. Note that a difference from the first evaluation value exceeding a predetermined threshold means that the absolute value of the difference between the first evaluation value and the acquired evaluation value exceeds the predetermined threshold. The third threshold (threshold for the absolute value of the difference from the first evaluation value used for determining the rescan process) is greater than the first threshold (threshold for the absolute value of the difference from the first evaluation value used to determine the gain change) described above. In this case, the same value used for determining the rescan process may be used as the reference value for determining the rescan process as the reference value used for determining the gain rewrite process described above.

[0071] Furthermore, the processing unit 40 may drive the stage 52 to perform illumination of the first stripe again if, during a predetermined period after the evaluation value based on multiple positions of the second detection unit 302 during illumination of a predetermined stripe changes to an evaluation value different from the first evaluation value, the number of times an evaluation value different from the first evaluation value exceeds the fourth threshold. The second threshold and the fourth threshold are predetermined numbers, and may be different numbers, with the fourth threshold being greater than the second threshold.

[0072] Stage 52 is a drive unit that moves in the XYZ directions. Stage 52 changes the relative position between the illumination spot, which is the focal point, and the object. For example, if one stripe is obtained along the Y axis, the stage is driven in the Y axis direction in order to illuminate the same stripe with the illumination spot.

[0073] In addition to changing the predetermined gain, the processing unit 40 may also adjust the optical elements. The adjustment of the optical elements may be automatic or manual, but adjustment within the range that can be done automatically is preferred.

[0074] The gain changing unit 304 may determine the predetermined gain after modification based on the result of illuminating a specific area of ​​the object. For example, the gain changing unit 304 may determine the predetermined gain after modification based on the result of illuminating a defect-free reference area of ​​the object.

[0075] The above configuration provides an optical device or the like that includes a gain changing unit for changing a predetermined gain.

[0076] (Description of the correction method for the optical device according to the embodiment) Figure 5 is flowchart 1 of the control method for the optical device according to the embodiment. Figure 6 is flowchart 2 of the control method for the optical device according to the embodiment. The control method for the optical device according to the embodiment will be explained with reference to Figures 5 and 6.

[0077] As shown in Figure 5, first, the object to be inspected is illuminated using critical illumination (step S501). Next, image data of the object to be inspected is acquired (step S502). Image data of the object to be inspected is acquired by the first detector TDI1. Next, monitor image data is acquired (step S503). Monitor image data is acquired by the second detector TDI2. Next, it is determined whether control during fluctuation is necessary (step S504).

[0078] If control during fluctuations is required (if the answer to step S504 is YES), the predetermined gain is rewritten, or a rescan is performed, or optical adjustment is carried out. The rewriting of the predetermined gain or rescan will be described later with reference to Figure 6. If the predetermined gain is rewritten, the process proceeds to step S505. If a rescan is performed, the process ends.

[0079] If control during fluctuations is not required (if NO in step S504), the image data to be inspected is corrected based on a predetermined gain (step S505). Next, it is determined whether or not the stripe scan is complete (step S506). If the stripe scan is complete (if YES in step S506), the counter is reset and the process ends (step S507). The counter will be described later. If the stripe scan is not complete, the process returns to step S501.

[0080] The control during fluctuations will be explained based on Figure 6. When determining whether it is necessary to perform at least one of the various control methods during fluctuations, for example, an evaluation value (S1) is calculated from the monitor image data at each time point (step S601). The evaluation value is calculated from the image data of the second detector TDI2. Next, it is determined whether the difference between the evaluation value S1 and the first evaluation value exceeds the third threshold (step S602). It is determined whether the difference between the evaluation value S1 and the first evaluation value exceeds the third threshold and changes significantly. If it exceeds the third threshold (if YES in step S602), a rescan is performed (step S603).

[0081] If the difference between evaluation value S1 and the first evaluation value does not exceed the third threshold (if NO in step S602), the evaluation value (S2) is calculated from the averaged image of monitor image data from multiple consecutive time points (step S604). Next, it is determined whether the difference between evaluation value S2 and the first evaluation value exceeds the first threshold (step S605). If the difference between evaluation value S2 and the first evaluation value does not exceed the first threshold (if NO in step S5605), the process proceeds to step S505 without performing fluctuation control. If the difference between evaluation value S2 and the first evaluation value exceeds the first threshold (if YES in step S605), the counter is incremented (step S606). It is determined whether the counter exceeds the threshold number of counts (step S607). If the counter exceeds the threshold number of counts (if YES in step S607), the predetermined gain is rewritten and the process proceeds to step S505 (step S608). If the counter does not exceed the threshold number of times (in the case of NO in step S607), the process proceeds to step S505 without performing the variable control.

[0082] The above configuration provides a control method for an optical device equipped with a gain changing unit that changes a predetermined gain. In S603, a rescan is performed, but if certain conditions are met, a gain rewrite may also be performed. The predetermined conditions may include, for example, when multiple rescans are performed on the same stripe, or when a rescan is performed again when the elapsed time since the last rescan is less than a predetermined amount. This prevents repeated rescans.

[0083] (Application of control methods to modified optical devices) Figure 7 shows a modified optical device. Light emitted from the light source 100 is shone onto the object 116 and detected by the first detection unit 124. A portion of the light emitted from the light source is also shone onto the second detection unit 106 and detected. The light detected by the second detection unit 106 is used to correct the light detected by the first detection unit.

[0084] The control method of this disclosure is also applicable to such optical systems. That is, fluctuation control is performed based on the light detected by the second detection unit 106. Fluctuation control may include gain rewriting, rescanning, and optical adjustment. The control subsystem 110 and the computer subsystem 126 include processing units (signal correction unit, gain change unit).

[0085] Then, during a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit 106 changes to an evaluation value different from the first evaluation value, if the number of acquisitions of evaluation values ​​that differ from the first evaluation value by more than a first threshold exceeds a second threshold, the predetermined gain is changed (predetermined gain rewriting process). The signal correction unit corrects the signal at the first detection unit based on the predetermined gain changed by the gain change unit.

[0086] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of Symbols]

[0087] 1 Optical device, 10 Illumination optical system, 11 Light source, 12 Ellipsoidal mirror, 13 Ellipsoidal mirror, 14 Recessed mirror, 20 Detection optical system, 21 Perforated concave mirror, 22 Convex mirror, 23 First detector, 30 Monitor unit, 31 Cut mirror, 32 Concave mirror, 33 Second detector, 40 Processing unit, 50 EUV mask, 51 Top surface, 52 Stage, L11 Illumination light, L12 Reflected light, 301 First detection unit, 302 Second detection unit, 303 Signal correction unit, 304 Gain change unit

Claims

1. A first detection unit detects light from an object illuminated by light from a light source and outputs signals associated with multiple locations. A second detection unit detects a portion of the light from the aforementioned light source and outputs signals corresponding to multiple positions, A signal correction unit corrects the signals from the first detection unit based on a predetermined gain set in advance for each position, The system includes a gain changing unit that changes the gain to a predetermined gain based on the signal from the second detection unit, The aforementioned gain changing unit is During a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit changes to an evaluation value different from the first evaluation value, if the number of times an evaluation value different from the first evaluation value by more than a first threshold is acquired exceeds a second threshold, the predetermined gain is changed. The signal correction unit is an optical device that corrects the signal in the first detection unit based on a predetermined gain after modification by the gain changing unit.

2. The system includes a drive unit that changes the relative position between the lighting spot and the object with respect to the stripe of the object, The optical apparatus according to claim 1, wherein when the evaluation value based on signals from multiple positions of the second detection unit during illumination of the first stripe changes to a different evaluation value by more than a third threshold greater than the first evaluation value and the first threshold, the drive unit is controlled to perform illumination of the first stripe again.

3. The system includes a drive unit that changes the relative position between the lighting spot and the object with respect to the stripe of the object, During a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit while the first stripe is illuminated changes to an evaluation value different from the first evaluation value, if the number of times an evaluation value different from the first evaluation value by more than a first threshold is obtained exceeds a fourth threshold which is greater than the second threshold, The optical apparatus according to claim 1, wherein the drive unit is controlled to perform illumination on the first stripe again.

4. The optical apparatus according to any one of claims 1 to 3, wherein, in addition to changing the predetermined gain, the optical elements are adjusted.

5. The optical apparatus according to any one of claims 1 to 3, wherein the object is critically illuminated by light from the light source.

6. The optical apparatus according to any one of claims 1 to 3, wherein the first detection unit and the second detection unit are in a conjugate position.

7. The optical apparatus according to any one of claims 1 to 3, wherein the gain changing unit performs the change of the predetermined gain based on the result of illuminating a specific area of ​​the object.

8. A first detection unit detects light from an object illuminated by light from a light source and outputs signals associated with multiple locations. A second detection unit detects a portion of the light from the aforementioned light source and outputs signals corresponding to multiple positions, A signal correction unit corrects the signals from the first detection unit based on a predetermined gain set in advance for each position, A control method for an optical device comprising: a gain changing unit that changes the gain to a predetermined gain based on the signal from the second detection unit, The aforementioned gain changing unit is During a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit changes to an evaluation value different from the first evaluation value, if the number of times an evaluation value different from the first evaluation value by more than a first threshold is acquired exceeds a second threshold, the predetermined gain is changed. A control method for an optical device, wherein the signal correction unit corrects the signal in the first detection unit based on a predetermined gain after modification by the gain modification unit.

9. The optical device comprises a drive unit that changes the relative position between the illumination spot and the object with respect to the stripe of the object, A control method for an optical device according to claim 8, wherein when the evaluation value based on signals from multiple positions of the second detection unit during illumination of the first stripe changes to a different evaluation value by more than a third threshold greater than the first evaluation value and the first threshold, the drive unit is controlled to perform illumination of the first stripe again.

10. The optical device comprises a drive unit that changes the relative position between the illumination spot and the object with respect to the stripe of the object, During a predetermined period after the evaluation value based on the signals from multiple positions of the second detection unit while the first stripe is illuminated has changed to an evaluation value different from the first evaluation value, if the number of times the evaluation value that exceeds the first evaluation value and the first threshold is obtained exceeds a fourth threshold which is greater than the second threshold, A control method for an optical apparatus according to claim 8, comprising controlling the drive unit to perform illumination on the first stripe again.

11. A control method for an optical apparatus according to any one of claims 8 to 10, wherein in addition to changing the predetermined gain, the optical elements are adjusted.

12. A method for controlling an optical apparatus according to any one of claims 8 to 10, wherein the object is critically illuminated by light from the light source.

13. A control method for an optical apparatus according to any one of claims 8 to 10, wherein the first detection unit and the second detection unit are in a conjugate position.

14. The control method for an optical apparatus according to any one of claims 8 to 10, wherein the gain changing unit performs the change of the predetermined gain based on the result of illuminating a specific area of ​​the object.

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