JP2016024042A - Inspection device and autofocusing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection device in which a focus detection position and a focus control position are highly accurately corresponded.SOLUTION: An inspection device according to the present invention comprises: beam formation means (9) that forms an inspection beam to be used for defect detection from a light beam emitted from a light source device (1) and a focus detection beam spatially separated from the inspection beam and to be used for focus detection; and an objective lens (16) that projects the inspection beam and the focus detection beam toward a sample. The inspection beam and the focus detection beam are configured so as to respectively illuminate portions on the sample separated apart in a scanning direction of a stage. In this case, the sample is scanned by the inspection beam after a prescribed time has elapsed since the sample is scanned by the focus detection beam, thereby allowing a focus detection position on the sample and a focus control position thereon to be corresponded.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inspection apparatus equipped with an improved autofocus mechanism and an autofocus method.

An inspection apparatus for projecting an illumination beam emitted from an illumination light source toward a photomask and detecting reflected light or transmitted light emitted from the photomask to perform defect inspection has been widely put into practical use. In this type of inspection apparatus, in order to improve the accuracy of defect detection, it is important to control the focus of an objective lens that collects reflected light and transmitted light emitted from a photomask. For example, when the focus of the objective lens is not well controlled, a blurred sample image is captured, and a defect that the accuracy of defect detection is reduced occurs. Therefore, the inspection apparatus is equipped with an autofocus device so that the focal point of the objective lens is controlled with high accuracy.

As an autofocus device used in a photomask inspection device, an autofocus light source is used in addition to an illumination light source for defect detection, and a light beam emitted from a light source for focus control is projected toward the photomask, and photo An apparatus that receives reflected light from a mask and performs focus detection is known (for example, see Patent Document 1). In this known autofocus device, a beam splitter is disposed in the optical path between the illumination light source for inspection and the objective lens, and the focus detection beam emitted from the light source for focus control passes through the beam splitter to the optical path of the objective lens. Introduced in. And it is projected toward the photomask through the objective lens, is incident on the same position as the illumination position of the inspection beam on the photomask, and the reflected light from the photomask is received by the two-divided photodetector. Focus detection is performed using an output signal from the two-divided photodetector.

As another autofocus method used in the inspection apparatus, the illumination beam emitted from the illumination light source is projected onto the sample via the objective lens, and the reflected light from the sample surface is divided into two via the beam splitter. A method of detecting a defect with one reflected light and performing focus detection with the other reflected light is also known (see, for example, Patent Document 2).

Furthermore, as an autofocus method for a confocal microscope, an illumination beam emitted from an illumination light source is projected onto a sample via an objective lens, and reflected light from the sample is divided into two by a half mirror, and one of the divided reflections is reflected. A method of forming an image signal using light and forming a focus detection signal using the other divided reflected light is also known (see, for example, Patent Document 3). In this known autofocus method, the reflected beam branched for autofocus is further divided into two by another half mirror and received by two photodetectors arranged at the front pin position and the rear pin position, respectively. A focus error signal is formed using output signals from the two photodetectors.
JP 2012-237687 A JP 2012-8431 A JP 2000-162506 A

In the autofocus mechanism that uses a focus detection light source separately from the inspection illumination light source and couples the focus detection beam to the optical path of the objective lens via the beam splitter, various optical elements for autofocus are required. There was a drawback that the manufacturing cost was expensive. In addition, since astigmatism and ghost are likely to occur due to the beam splitter, there is a problem that the accuracy of focus control is lowered.

The method of dividing the reflected light emitted from the sample into two parts, performing defect detection using one of the divided reflected lights, and performing focus detection using the other reflected light is performed by inspecting an optical component constituting the autofocus mechanism with an inspection optical system. There is an advantage that can be shared with other parts. However, in an inspection apparatus that performs focus control using an autofocus mechanism, considerable processing time is required after focus detection is performed until a focus control signal is output to the actuator. In this case, as described in Patent Documents 2 and 3, in the configuration in which the reflected light reflected by the sample is divided into two to perform defect detection and focus detection, the part on which the defect detection is performed on the sample This may cause a situation in which accurate focus control is not performed because the position where focus detection is performed does not match. That is, since a focus control signal for controlling the objective lens is generated after various signal processing is performed on the output signal output from the photodetector for focus detection, the stage moves during the signal processing time, and the actual focus There is a problem in that a portion where detection is performed and a portion where focus control is performed do not match and a focus error occurs. In particular, when the surface of the sample is an inclined surface or when there is a step due to a pattern thin film on the surface of the sample, such as a photomask, the focus control signal cannot respond to the change in height of the sample surface, and the accuracy of focus control is reduced. There was a problem.

An object of the present invention is to provide a focus control mechanism that eliminates the above-described drawbacks, and that the defect detection inspection beam and the focus detection focus detection beam travel along the same optical axis, and does not require a beam splitter. It is to realize an inspection apparatus.
Another object of the present invention is to realize an inspection apparatus in which the focus detection position and the focus control position correspond to each other with high accuracy.

An inspection apparatus according to the present invention is an inspection apparatus that detects defects existing in a sample placed on a stage,
A light source device for generating an illumination beam;
Beam forming means for forming, from the illumination beam emitted from the light source device, an inspection beam used for defect detection and one or more focus detection beams spatially separated from the inspection beam and used for focus detection;
An objective lens for projecting the inspection beam and the focus detection beam toward the sample;
Imaging means for receiving an inspection beam emitted from the sample and outputting an image signal;
A focus detection system for receiving a focus detection beam emitted from the sample;
A signal processing device that outputs a focus control signal for controlling a relative distance between the sample and the objective lens, using an output signal output from the focus detection system;
The inspection beam and the focus detection beam illuminate different spatially separated portions on the sample, respectively.

In the present invention, a plurality of light beams traveling from the light beam emitted from a single light source while being spatially separated from each other on the same optical axis by a beam forming means such as a diffraction grating or a slit means having a plurality of openings. An illumination beam is formed, one illumination beam is used as an inspection beam for defect detection, and the other illumination beam or beams are used for focus detection. The inspection beam and the focus detection beam illuminate a spatially separated position on the sample. The inspection beam and the focus detection beam emitted from the sample travel in a state of being spatially separated on the same optical axis. Therefore, it is possible to individually detect the inspection beam and the focus detection beam emitted from the sample without using any special separating means such as a beam splitter. As a result, the element constituting the defect detection optical system and the element constituting the focus detection optical system can be shared, and the advantage that the manufacturing cost is reduced is achieved.

Further, as an important advantage, since the inspection beam and the focus detection beam can illuminate different portions on the sample, the focus detection position and the focus control position on the sample can be matched. That is, in the autofocus device, a focus control signal for controlling the objective lens is generated after various signal processing is performed on the output signal output from the focus detection photodetector. Therefore, a time delay caused by signal processing becomes a problem. That is, a focus control signal is output after a considerable time has elapsed due to signal processing after focus detection. On the other hand, since the stage that supports the sample moves during the signal processing time, there is a problem in that the actual focus detection is performed and the region where the focus control is performed does not match, and a focus error occurs. For example, when the sample surface is tilted, the focus control signal does not correspond to the height change of the sample surface due to the time delay caused by the signal processing, and an unclear image is captured, and the accuracy of defect detection decreases. There's a problem. In addition, when there are steps due to various thin films on the sample surface like a photomask, focus control at the time of scanning the surface of the glass substrate using the focus control signal formed when the focus detection beam illuminates the thin film. In some cases, the focus control signal does not correspond to the change in the height of the sample surface, and there is a problem that the accuracy of the focus control is lowered. On the other hand, when the illumination position of the inspection beam and the illumination position of the focus detection beam are separated from each other, the separation direction can be made to correspond to the traveling direction of the stage, and the separation amount can be made to correspond to the signal processing time for generating the focus control signal. For example, the focus detection position and the focus control position can be matched, and the problem of time delay caused by signal processing can be solved.

An inspection apparatus according to the present invention is an inspection apparatus for detecting defects present in a sample arranged on a stage,
A stage that supports the sample to be examined and proceeds in a zigzag manner in a first direction, a second direction opposite to the first direction, and a third direction orthogonal to the first and second directions; ,
A light source device for generating a light beam;
Beam forming means for forming an inspection beam used for defect detection from the light beam emitted from the light source device, and first and second focus detection beams spatially separated from the inspection beam and used for focus detection;
An objective lens that projects the inspection beam and the focus detection beam toward a sample disposed on a stage;
Imaging means for receiving an inspection beam emitted from the sample and outputting an image signal;
First and second focus detection systems that respectively receive the first and second focus detection beams emitted from the sample;
Control means for controlling the relative distance between the sample and the objective lens;
A signal processing device that outputs a focus control signal for controlling a relative distance between the sample and the objective lens by using output signals output from the first and second focus detection systems;
The first and second focus detection beams illuminate portions on the sample that are spatially separated in the first and second traveling directions of the stage across the illumination area of the inspection beam. And

In the present invention, the inspection beam used for defect detection and the focus detection beam used for focus detection are formed so as to be spatially separated from each other from the light beam emitted from the illumination light source, and spatially separated from each other on the sample. Since most of the optical elements for auto-focusing can be shared with the optical elements constituting the defect detection optical system.
Further, since the focus detection beam illuminates a part spatially separated from the inspection beam on the sample, the position where the focus detection is performed and the position where the defect detection is performed on the sample can be associated with high accuracy. It becomes possible, and it becomes possible not to be influenced by the height change of the sample surface, and to perform the focus control with higher accuracy. That is, an autofocus mechanism in which the problem caused by the time delay from the focus detection until the focus control signal is output is solved.

It is a figure which shows an example of the test | inspection apparatus by this invention. It is a figure which shows the progress state of a stage. It is a figure which shows the illumination area of the test | inspection beam and focus detection beam which are formed on a sample. It is a figure which shows an example of a signal processing apparatus. It is a figure which shows the modification of the test | inspection apparatus by this invention. It is a figure which shows the illumination area of the test | inspection beam and focus detection beam which are formed on a sample. It is a figure explaining the effect at the time of setting a focus detection beam aslant to an inspection beam. It is a figure which shows the Example applied to the test | inspection of a wafer edge.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a diagram showing an example of an inspection apparatus according to the present invention. In the present invention, a photomask or various semiconductor substrates can be used as a sample to be inspected for defects. Various substrates such as a silicon substrate, a silicon carbide substrate, and a silicon carbide substrate on which an epitaxial layer is formed can be used as the semiconductor substrate. As the illumination light source, a lamp light source and a laser light source that generates illumination light in the visible region or ultraviolet region can be used. Furthermore, the present invention can also be applied to a focus control mechanism in an inspection apparatus that projects illumination light obliquely on the sample surface and collects reflected light or scattered light emitted from the sample by an objective lens. Furthermore, the present invention can be applied not only as an inspection apparatus but also to a microscope that captures a sample image.

In this example, a semiconductor substrate is used as a sample to be inspected, a laser light source is used as an illumination light source, an inspection beam for defect inspection and a focus detection beam for focus control are generated from a laser beam emitted from the laser light source, and autofocusing is performed. Defect inspection is performed while operating the mechanism. A laser diode is used as the illumination light source 1. The laser beam emitted from the laser diode enters the acoustooptic device 3 through the collimator lens 2. The acousto-optic device 3 periodically deflects the incident laser beam in a first direction (X direction orthogonal to the paper surface) at high speed. The deflection frequency can be set to 60 kHz, for example. The light beam emitted from the acoustooptic device 3 enters the diffraction grating 8 through the relay lens 4, the total reflection mirror 5, the relay lens 6 and the total reflection mirror 7. The relay lenses 4 and 6 function as a relay optical system that expands the beam diameter of the illumination beam incident on the diffraction grating 8. Accordingly, the light beam whose diameter is enlarged and periodically vibrates in the first direction is incident on the diffraction grating 8.

The diffraction grating 8 is set so that the grating line is parallel to the deflection surface (vibration surface) of the light beam emitted from the acoustooptic device, and is diffracted in a direction perpendicular to the deflection surface of the light beam emitted from the acoustooptic device. Demonstrate the effect. Accordingly, the 0th-order diffracted light and the higher-order diffracted light are generated on both sides of the deflecting surface of the incident illumination beam from the diffraction grating 8. These 0th order light and higher order diffracted light propagate on the same optical axis in a state of being spatially separated from each other. In addition, since an illumination beam periodically deflected at high speed is incident on the diffraction grating, zero-order light and high-order diffracted light periodically deflected at high speed are emitted from the diffraction grating. In addition, as for the mutual separation distance and beam intensity of the 0th-order light and the higher-order diffracted light, desired diffracted light can be emitted by appropriately designing the grating pitch of the diffraction grating.

The diffraction grating 8 functions as a beam forming element or beam splitting element that forms a plurality of illumination beams from the incident light beam, and generates an inspection beam and two focus detection beams from the incident light beam. The inspection beam is used for detecting a defect present in the sample, and the two focus detection beams are used for focus detection for autofocus. The inspection beam and the two focus detection beams are spatially separated in a direction orthogonal to the first direction (Y direction parallel to the paper surface), the inspection beam is located in the center, and the focus detection beams are respectively located on both sides thereof. To position. That is, in this example, the 0th order light is used as the inspection beam, and the + side and − side high order diffracted light is used as the focus detection beam. Accordingly, the diffraction grating 8 emits three beams that are spatially separated from each other in the direction orthogonal to the deflection direction of the acoustooptic element and periodically vibrate along the deflection direction of the acoustooptic element. In this example, the 0th order light and one higher order diffracted light are generated on the + side and the − side, respectively. Of course, a plurality of higher order diffracted lights are generated together with the 0th order light, and a plurality of higher order diffracted lights are focused It can also be used as a detection beam.

The inspection beam and the two focus detection beams that vibrate at high speed travel in a state of being spatially separated from each other on the same optical axis. These three beams are reflected by the polarization beam splitter 10, enter the total reflection mirror 12 through the lens 11. These three beams are reflected by the total reflection mirror 12 and enter the objective lens 16 through the first and second relay lenses 13 and 14 and the quarter-wave plate 15.

The inspection beam and the two focus detection beams are focused by the objective lens 16 and are incident on the semiconductor substrate 17. An actuator 18 is connected to the objective lens 16. The actuator 18 is driven by a drive signal generated from the focus control signal output from the signal processing device, and moves the objective lens 16 along the optical axis direction according to the detected focus error. The relative distance between the sample and the objective lens is controlled by the relative movement of the objective lens in the optical axis direction, and focus control is performed. The focus control can also be performed by moving the stage supporting the photomask in the optical axis direction of the objective lens.

The semiconductor substrate 17 is disposed on the stage 19. The stage 19 is constituted by an XY stage, and proceeds in a zigzag manner by a drive signal supplied from the signal processing device. FIG. 2 diagrammatically shows the progress of the stage. The stage 19 proceeds in a zigzag manner along the scanning line, and the entire surface of the semiconductor substrate 17 is scanned by the inspection beam. In FIG. 2, the scanning line of the stage is indicated by a one-dot chain line. The stage proceeds in the first scanning direction along the first scanning line after the start of the inspection, and then the distance corresponding to the beam width of the inspection beam in the third scanning direction orthogonal to the first direction. Just move. Subsequently, the process proceeds in the second scanning direction opposite to the first scanning direction along the second scanning line. Subsequently, it moves by a distance corresponding to the beam width of the inspection beam in the third direction, and then proceeds in the first scanning direction along the third scanning line. In this way, the entire surface of the semiconductor substrate 17 is scanned with the inspection beam. Note that a position sensor 20 is connected to the stage 19 to detect the position of the stage in the first and second directions and output the position information to the signal processing device. Note that the scanning line information indicating the position in the third direction is generated in the signal processing device. Therefore, the signal processing apparatus can specify the address of the detected defect using the position information output from the position sensor 20 and the scanning line information.

FIG. 3 diagrammatically shows the illumination area formed on the semiconductor substrate 17 by the inspection beam and the focus detection beam. In FIG. 3, the field of view of the objective lens is denoted by reference numeral 21. On the semiconductor substrate, a first illumination area 22 is formed by an inspection beam, and the second and second focus detection beams are moved back and forth along the direction of the stage of the first illumination area 17 by the first and second focus detection beams. Third illumination areas 23a and 23b are formed. Since the inspection beam and the bifocal detection beam are periodically deflected at high speed in the first direction, a substantially linear illumination area is formed by these three beams. In the present invention, the illumination position of the inspection beam and the illumination position of the focus detection beam are spatially separated on the sample. That is, the focus detection beam illuminates a position different from the illumination position of the inspection beam. The extending direction of the linear first illumination area formed by the inspection beam is set to be orthogonal to the first and second scanning directions of the stage. Further, the separation distance between the first illumination area 22 and the second and third illumination areas 23a and 23b is determined during the signal processing from when the focus detection beam is detected until the focus control signal is formed. Correspond to the distance traveled.

As described above, a considerable processing time is required until the focus detection beam is received by the light receiving element and is subjected to signal processing to form a focus control signal. Therefore, when the inspection beam and the focus detection beam illuminate the same part on the sample, the stage moves by a distance corresponding to the processing time for forming the focus control signal, causing a problem that the focus control is delayed. To do. That is, a considerable shift occurs between the position where the focus detection is actually performed and the position where the inspection beam is illuminated. In order to solve such a problem, in the present invention, the illumination position of the inspection beam and the illumination position of the focus detection beam are separated by a distance that the stage moves during signal processing. Thus, by separating the illumination position of the inspection beam and the illumination position of the focus detection beam, the position where the focus is detected on the sample (focus detection position) and the illumination position of the inspection beam (inspection position) are matched. It becomes possible.

Furthermore, in this example, in view of the stage moving in a zigzag manner in the first scanning direction and the second scanning direction opposite to the first scanning direction, the second and Third illumination areas 23a and 23b are formed. That is, referring to FIG. 3, when the stage moves in the first scanning direction, the sample is scanned by the inspection beam after a predetermined time has elapsed after being scanned by the first focus detection beam. Therefore, by performing focus control using the focus control signal formed based on the first focus detection beam, the focus detection position and the illumination position of the inspection beam can be matched. Further, when the stage moves in the second scanning direction opposite to the first scanning direction, focus control can be performed using a focus control signal formed from the second focus detection beam. In this way, by performing scanning with the two focus detection beams so as to move back and forth along the moving direction of the stage with the inspection beam interposed therebetween, focus control corresponding to stage scanning that proceeds in a zigzag manner can be performed. In this case, the focus detection signal can be selected using the number of the scanning stripe of the stage progression. For example, when scanning an odd-numbered scan stripe, the focus detection signal detected by the first focus detection beam is used. The focus control signal can be generated by using the focus detection signal detected by the second focus detection beam when the even-numbered scanning stripe (scanning line) is scanned.

Referring to FIG. 1, the inspection beam and the two focus detection beams incident on the photomask are reflected by the surface of the photomask and collected by the objective lens 16. These three reflected beams propagate on the same optical path in a spatially separated state. The three reflected beams emitted from the objective lens propagate in the optical path in the opposite directions, and enter the total reflection mirror 12 through the quarter-wave plate 15, the second and first relay lenses 14 and 13. Further, the light is reflected by the total reflection mirror 12 and enters the polarizing beam splitter 10 through the lens 11 that acts as an imaging lens. Since the inspection beam and the focus detection beam have passed through the quarter-wave plate 15 twice, they pass through the polarization beam splitter 10.

The inspection beam emitted from the polarization beam splitter 10 is imaged on the image sensor 24. A line sensor or a TDI sensor can be used as the image sensor, and in this example, a line sensor is used. The line sensor reads the electric charge at a reading speed corresponding to the moving speed of the stage and outputs it as an image signal to the signal processing device 25. The first and second focus detection beams emitted from the polarization beam splitter are reflected by total reflection mirrors 26 and 27, respectively, and enter the first and second focus detection systems 28 and 29, respectively. In the present invention, since the inspection beam and the two focus detection beams are spatially separated from each other, an advantage that an optical means for separating the inspection beam and the focus detection beam emitted from the sample is unnecessary is achieved. Therefore, the inspection beam and the focus detection beam emitted from the sample can be individually incident on the photodetector only by arranging the total reflection mirror in the optical path.

The first and second focus detection systems 28 and 29 are focus detection systems having the same structure, and output signals of two photodetectors arranged so as to receive the focus detection beams in the front pin state and the rear pin state, respectively. A focus error signal is formed by forming the difference. The focus detection beam incident on the first focus detection system 28 is divided into two by the beam splitter 30. One of the divided beams is incident on the first photodetector 31 through the slit, and the other beam is incident on the second photodetector 32 through the slit. The first photodetector is disposed behind the focal point of the focus detection beam, and the second photodetector is disposed in front of the focal point. These first and second photodetectors can be composed of, for example, a photomultiplier. The luminance signals output from the first and second photodetectors are output to the signal processing device 25 via an amplifier.

The second focus detection beam incident on the second focus detection system 29 is incident on the beam splitter 33 and divided into two. One of the divided beams is incident on a third photodetector 34 disposed behind the focusing point via a slit, and the other beam is disposed on the front side of the focusing point via a slit. 35 is incident. The luminance signals output from the third and fourth photodetectors are output to the signal processing device 25 through an amplifier.

FIG. 4 is a diagram showing an example of a signal processing apparatus. An image signal output from the image sensor 24 is supplied to the A / D converter 40, converted into a digital signal, and supplied to the defect detection means 41. The defect detection means 41 detects a defect by die-to-die comparison, for example. That is, the brightness value of the input image signal is compared with a reference brightness value to detect a defect. For example, when a foreign substance exists on the semiconductor substrate to be inspected, scattered light is generated by the foreign substance, and the luminance value of the image signal input to the image sensor is reduced from the reference luminance value. Therefore, a defect and a defect image can be detected by comparing the luminance value of the input image signal with the reference value. The detected defect is supplied to the defect information forming means 42. The position information output from the position sensor 20 is supplied to the defect information forming unit 42 via the A / D converter 43. Further, scanning line information indicating the sequence number of the scanned scanning line is also input to the defect information forming means. The position information supplied from the position sensor indicates, for example, the position in the X direction on the sample, and the scanning line information indicates the position in the Y direction orthogonal to the X direction. Therefore, the address of the defect is specified using the position information and the scanning line information supplied from the position sensor. The defect information forming means 42 pairs the detected defect identification information and the address information and outputs them as defect information. The output defect information can be stored, for example, in a defect memory and used for various processes. For example, a defect image of a desired defect can be reviewed. It is also possible to calculate the number of defects detected for each chip formed on the semiconductor substrate.

The luminance signals output from the first and second photodetectors 31 and 32 constituting the first focus detection system 28 are converted into digital signals by the A / D converters 44 and 45, and the first focus error is detected. The signal is supplied to the signal forming means 46. The luminance signals output from the third and fourth photodetectors 34 and 35 constituting the second focus detection system 29 are converted into digital signals by the A / D converters 47 and 48, and the second The focus error signal forming means 49 is supplied. The first and second focus error signal forming means perform the following arithmetic processing to form first and second focus error signals S1 and S2 indicating the amount of displacement of the focus point of the inspection beam with respect to the sample surface.
S1 = (P1-P2) / (P1 + P2)
S2 = (P3-P4) / (P3 + P4)
Here, P1 to P4 indicate the intensities of the luminance signals output from the first to fourth photodetectors.

The obtained focus error signals S1 and S2 are supplied to the selection means 50. Scan line information indicating the sequence number of the scan stripe (scan line) scanned by the stage is also input to the selection means 50. The selection means 50 determines whether the sequence number of the input scanning stripe is even or odd, and selects one of the input focus error signals according to whether it is odd or even. For example, when the stage scans along an odd-numbered scanning line, the first focus error signal S1 generated using the focus detection signal output from the first focus error detection system 28 is selected, and the scanning stripe is formed. In the case of an even number, the second focus error signal S2 generated using the focus detection signal output from the second focus error detection system 29 is selected. The selected focus error signal is supplied to the focus control signal generation means 51. The focus control signal forming unit generates a focus control signal for controlling the actuator from the input focus error signal, and supplies the focus control signal to the actuator 18. Since the actuator is supplied with a drive signal corresponding to the focus error, an autofocus mechanism is configured, and the focal point of the inspection beam can always be positioned on the sample surface.

Note that the selection means 50 can be arranged between the four photodetectors and the focus error signal forming means. In this case, a single focus error signal forming unit is provided after the selection unit, and one of the signals output from the first focus detection system or the second focus detection system according to the sequence number of the scanning stripe of the stage. The output signal is supplied to the focus error signal forming means. Further, the selection means 50 can be provided at the subsequent stage of the focus control signal forming means 51. In this case, two series of focus control signal forming means are provided, and the selection means selects one of the focus control signals and supplies it to the actuator 18.

FIG. 5 shows a modification of the inspection apparatus according to the present invention. In this example, a lamp light source is used as an illumination light source, and a defect present in the photomask is detected using a TDI sensor as an image sensor. In addition, the same code | symbol is attached | subjected to the component same as the component used in FIG. 1, and the description is abbreviate | omitted.

A mercury xenon lamp is used as the illumination light source, and illumination light having a wavelength of 313 nm is emitted from the illumination light emitted from the mercury xenon lamp through a filter (not shown). The illumination beam emitted from the mercury xenon lamp 60 propagates through the optical fiber 61 and is emitted as a divergent beam having a substantially circular cross section. The illumination beam emitted from the optical fiber 61 passes through the focusing lens 9 and enters a beam forming unit that forms a plurality of beams. In this example, a field stop (slit means) 62 disposed at the imaging position is used as the beam forming means. The field stop 62 has three slit-shaped openings 62a to 62c. The slit-shaped first opening 62a located at the center extends in the first direction (a direction orthogonal to the paper surface) and forms an inspection beam used for defect inspection, and has a relatively wide opening width. Have. The slit-like second and third openings 62b and 62c located on both sides form an oblique angle with respect to the first direction and form a focus detection beam for autofocus. Therefore, the line-shaped beam emitted from the central first opening 62a constitutes an inspection beam for defect inspection, and the two line-shaped beams emitted from the second and third openings 62b and 62c, respectively, Form first and second focus detection beams. These three beams travel on the same optical axis while being spatially separated from each other. The inspection beam and the two focus detection beams are reflected by the polarization beam splitter 10 and enter the total reflection mirror 12 through the lens 11. These three beams are reflected by the total reflection mirror 12 and enter the objective lens 16 through the first and second relay lenses 13 and 14 and the quarter-wave plate 15.

The inspection beam and the two focus detection beams are focused by the objective lens 16 and incident on the photomask 63 to illuminate spatially separated portions on the photomask. FIG. 6 shows an illumination area formed on the photomask by the inspection beam and the two focus detection beams. In FIG. 6, the code | symbol 21 shows the visual field of an objective lens. A first line-shaped illumination area 64 by the inspection beam is formed at the center of the field of view of the objective lens, and second and third illumination areas 65a and 65b are formed by the focus detection beam in a direction orthogonal to the advancing direction of the stage. Is done.

In this example, with respect to the first illumination area 64 formed by the inspection beam, the second and third illumination areas 65a and 65b formed by the focus detection beam form an angle, that is, an angle other than parallel. To extend. For example, when inspecting a photomask, a large number of rectangular patterns whose edges extend in the X and Y directions are formed on the photomask. In this case, when the extension direction of the edge portion of the pattern coincides with the extension direction of the focus detection beam, diffracted light or scattered light is generated by the diffraction action at the edge portion of the mask pattern, and the focus detection signal fluctuates. There is a problem that accurate focus control is not performed. On the other hand, if the focus detection beam scans on the edge of the mask pattern when it is set to be oblique rather than parallel to the inspection beam as in the present invention, the line-shaped focus detection beam Since only a part is positioned on the edge portion and the other beam portions are scanned at positions deviating from the edge, the problem caused by the diffraction effect that occurs when scanning the pattern edge is eliminated.

FIG. 7 is a diagram for explaining the effect when the focus detection beam is set obliquely with respect to the inspection beam. FIG. 7A shows a state in which the second and third illumination areas formed by the focus detection beam are set parallel to the first illumination area formed by the inspection beam, and FIG. Indicates a state in which the second and third illumination areas are set obliquely to the first illumination area (the crossing angle is approximately 10 °). Reference numeral 21 denotes a field of view of the objective lens, and a pattern formed on the photomask is indicated by a broken line. A large number of rectangular patterns whose pattern edges extend in the X and Y directions are formed on the photomask. On the other hand, in the defect inspection of a photomask, generally, the defect inspection is performed by setting the extending direction of the inspection beam parallel to the edge direction of the pattern. That is, the inspection is performed by setting the extending direction of the pattern edge to be orthogonal to the moving direction of the stage. In this case, when the extension direction of the edge portion of the pattern coincides with the extension direction of the focus detection beam, diffracted light or scattered light is generated by the diffraction action at the edge portion of the mask pattern, and the focus detection signal fluctuates. There is a problem that accurate focus control is not performed. Under such circumstances, as shown in FIG. 7A, when the focus detection beam is set parallel to the inspection beam, almost the entire focus detection beam scans the pattern edge at the same time, and an erroneous focus error signal is generated. There is a risk of being formed. On the other hand, as shown in FIG. 7B, if the focus detection beam is set obliquely with respect to the inspection beam, even if a part of the focus detection beam scans the pattern edge, most of the other Since the part other than the pattern edge is scanned, the occurrence of a defect due to the pattern edge is prevented. The angle formed by the focus detection beam with respect to the inspection beam is preferably in the range of 5 to 30 °, and can be set to 10 °, for example.

The inspection beam and the focus detection beam emitted from the photomask are collected by the objective lens and travel on the same optical axis while being spatially separated from each other. Then, the inspection beam enters the TDI sensor 66, and defect inspection is performed based on the output signal. The two focus detection beams are incident on the first and second focus detection systems 28 and 29, respectively, and focus control is performed using the output signals.

Next, an inspection apparatus for inspecting the edge of the semiconductor wafer will be described. In a semiconductor device manufacturing process, various material layers are deposited on a wafer, and an etching process, an impurity implantation process, and a cleaning process are performed. On the other hand, if the cleaning process is insufficient, there is a problem of contamination due to the remaining foreign matter. Therefore, it is necessary to inspect the edge of the wafer after the cleaning process. FIG. 8 diagrammatically shows a wafer edge inspection system. 8A is a schematic side view, FIG. 8B is a schematic plan view, and FIG. 8C shows an illumination area formed on the wafer. Referring to FIG. 8A, the vacuum holding means 71 is connected to the motor 70, and the wafer 72 to be inspected is held by the holding means 71. The wafer 72 is rotated by the rotation of the motor, and an inspection beam and a focus detection beam are projected from the objective lens 73 of the inspection apparatus toward the edge 72a of the rotating wafer. In FIG. 8B, the inspection beam is indicated by a solid line, and the focus detection beam is indicated by a broken line. When viewed in the direction of rotation of the wafer, the edge of the wafer is scanned with the focus detection beam L1, and after a predetermined time has elapsed, it is scanned with the inspection beam L2. That is, as shown in FIG. 8C, an illumination area S1 of the focus detection beam is formed along the rotation direction on the edge of the wafer, and an illumination area S2 of the inspection beam is formed at a predetermined interval. In the inspection of the edge of the semiconductor wafer, there is a high possibility that the distance between the objective lens of the inspection apparatus and the surface of the edge will fluctuate due to center deflection or the like. Therefore, by using the inspection apparatus of the present invention, the edge inspection can be performed while maintaining a good focus state. In the wafer inspection, since the wafer rotates in one direction, focus control can be performed by providing only one focus detection beam.

The present invention is not limited to the above-described embodiments, and various changes and modifications are possible. For example, in the above-described embodiments, the inspection apparatus that detects a defect present in the sample has been described. However, the present invention can also be used as a microscope that captures an image of the sample. In this case, the inspection beam is used as an imaging beam for imaging a sample image, and the remaining illumination beam is used as a focus detection beam.

Further, in the above-described embodiment, a single focus detection beam is provided on each side of the microscope. However, a plurality of focus detection beams are formed on both sides of the inspection beam, and a plurality of focus detection beams are formed. It is also possible to form a focus detection signal using a beam. In this case, an average value of a plurality of focus detection signals can be calculated to generate a focus error signal.

Further, a laser light source may be used as the illumination light source, and the laser beam emitted from the laser light source may be passed through a diffusion means having a lens array and a rod-shaped homogenizer, and the laser beam from which the speckle pattern has been removed may be used as the illumination beam. Is possible. In this case, a laser beam having a large cross-sectional area without a speckle pattern can be obtained, so that the inspection beam and the focus detection beam can be generated using the slit means.

DESCRIPTION OF SYMBOLS 1 Illumination light source 2 Collimator lens 3 Acoustooptic element 4, 6 Relay lens
5,7 Total reflection mirror 8 Diffraction grating 9 Converging lens 10 Polarizing beam splitter 11 Lens 12 Total reflection mirror 13, 14 Relay lens 15 1/4 wavelength plate 16 Objective lens 17 Semiconductor substrate
DESCRIPTION OF SYMBOLS 18 Actuator 19 Stage 20 Position sensor 24 Image pick-up element 25 Signal processor 26, 27 Total reflection mirror 28 1st focus detection system 29 2nd focus detection system 30, 33 Beam splitter 31, 32, 34, 35 Photo detector

Claims (15)

An inspection apparatus for detecting defects present in a sample placed on a stage,
A light source device for generating a light beam;
A beam forming means for forming, from a light beam emitted from the light source device, an inspection beam used for defect detection and one or more focus detection beams spatially separated from the inspection beam and used for focus detection;
An objective lens for projecting the inspection beam and the focus detection beam toward the sample;
Imaging means for receiving an inspection beam emitted from the sample and outputting an image signal;
A focus detection system for receiving a focus detection beam emitted from the sample;
A signal processing device that outputs a focus control signal for controlling a relative distance between the sample and the objective lens, using an output signal output from the focus detection system;
The inspection beam and the focus detection beam illuminate different spatially separated portions on the sample, respectively. The inspection apparatus according to claim 1, wherein the inspection beam and the focus detection beam illuminate portions separated from each other in the scanning direction of the stage on the sample,
2. The inspection apparatus according to claim 1, wherein the sample is scanned with the inspection beam after a predetermined time has elapsed after being scanned with the focus detection beam. In the inspection apparatus according to claim 1 or 2, a laser light source is used as the light source device,
The beam forming means includes an acoustooptic element that periodically deflects a light beam emitted from the light source device in a direction orthogonal to the scanning direction of the stage, a light beam emitted from the acoustooptic element, an inspection beam, and an inspection beam. An inspection apparatus comprising: a diffraction grating that generates one or a plurality of focus detection beams spaced apart in a direction orthogonal to the deflection direction of the acoustooptic device. 4. The inspection apparatus according to claim 1, wherein the diffraction grating generates at least two focus detection beams that are in succession in the scanning direction of the stage with the inspection beam interposed therebetween. . In the inspection apparatus according to claim 1 or 2, a lamp light source or a laser light source is used as the light source device,
The beam forming means includes a slit means having a slit-shaped first opening and a second opening spaced from the first opening, and extends from the first opening in a direction perpendicular to the scanning direction of the stage. An inspection apparatus in which a line-shaped inspection beam is emitted and a focus detection beam is emitted from the second opening. 6. The inspection apparatus according to claim 5, wherein the beam forming means includes a slit-shaped first opening and second and third openings facing each other across the first opening,
A line-shaped inspection beam is emitted from the first opening, and a line-shaped scanning focus detection beam is emitted from the second and third openings, respectively.
An inspection apparatus characterized in that on the sample, the two focus detection beams illuminate portions spatially separated in the advancing direction of the stage across an illumination area illuminated by the inspection beam. The inspection apparatus according to claim 5 or 6, wherein the second and third openings are formed in a strip shape so that a line-shaped focus detection beam is emitted,
2. The inspection apparatus according to claim 1, wherein the line-shaped focus detection beam forms a line-shaped illumination area having an oblique angle with respect to the line-shaped illumination area by the inspection beam on the sample. An inspection apparatus for detecting defects present in a sample arranged on a stage,
A stage that supports the sample to be examined and proceeds in a zigzag manner in a first direction, a second direction opposite to the first direction, and a third direction orthogonal to the first and second directions; ,
A light source device for generating a light beam;
Beam forming means for forming an inspection beam used for defect detection from the light beam emitted from the light source device, and first and second focus detection beams spatially separated from the inspection beam and used for focus detection;
An objective lens that projects the inspection beam and the focus detection beam toward a sample disposed on a stage;
Imaging means for receiving an inspection beam emitted from the sample and outputting an image signal;
First and second focus detection systems that respectively receive the first and second focus detection beams emitted from the sample;
Control means for controlling the relative distance between the sample and the objective lens;
A signal processing device that outputs a focus control signal for controlling a relative distance between the sample and the objective lens by using output signals output from the first and second focus detection systems;
The first and second focus detection beams illuminate portions on the sample that are spatially separated in the first and second traveling directions of the stage across the illumination area of the inspection beam. Inspection equipment. 9. The inspection apparatus according to claim 8, wherein when the stage advances in the first direction, the sample is scanned with the inspection beam after a predetermined time has elapsed after being scanned with the first focus detection beam, and the stage is in the second direction. When traveling in the direction, the sample is scanned by the inspection beam after a predetermined time after being scanned by the second focus detection beam,
When the stage proceeds in the first direction, the signal processing device forms a focus control signal using an output signal output from the first focus detection system, and a second direction opposite to the first direction. A defect inspection apparatus, wherein a focus control signal is formed using an output signal output from the second focus detection system when traveling in a direction. The inspection apparatus according to claim 9, wherein the stage proceeds in a zigzag manner along a scanning line that is sequentially defined along the third direction,
The signal processing device outputs either an output signal output from the first focus detection system or an output signal output from the second focus detection system based on the number of the scanning line scanned by the stage. An inspection apparatus that generates a focus control signal using the inspection apparatus. 11. The defect inspection apparatus according to claim 10, wherein the signal processing device generates a focus error signal from output signals of the first and second focus detection systems, and a focus control signal from the generated focus error signal. Having means for generating,
When the scanning line number of the stage is an odd number, the focus control is performed by the focus control signal generated using the output signal from the first focus detection system, and when the scanning line number of the stage is an even number, the second is performed. An inspection apparatus in which focus control is performed by a focus control signal generated using an output signal from a focus detection system. 12. The inspection apparatus according to claim 1, wherein the sample is a photomask, a semiconductor substrate, a semiconductor substrate on which an epitaxial layer is formed, a silicon carbide substrate, or silicon carbide on which an epitaxial layer is formed. An inspection apparatus using a substrate. An autofocus method for controlling a relative distance between a sample placed on a stage and an objective lens,
Forming a plurality of illumination beams spatially separated from the light beam emitted from the light source;
Projecting the plurality of illumination beams toward the sample to form a plurality of spatially separated illumination areas on the sample;
Of the plurality of illumination beams, one illumination beam is used as an inspection beam or an imaging beam, and the remaining illumination beam is used as a focus detection beam.
Detecting a focus detection beam emitted from the sample to generate a focus error signal, and generating a focus control signal from the generated focus error signal;
An autofocus method comprising: a focus control step of controlling a relative distance between a focusing point of an inspection beam or an imaging beam and a sample using the focus control signal. The autofocus method according to claim 13, wherein the inspection beam and the focus detection beam illuminate portions separated from each other in the scanning direction of the stage on the sample,
An autofocus method, wherein the sample is scanned with an inspection beam after a predetermined time has elapsed after being scanned with a focus detection beam. 15. The autofocus method according to claim 14, wherein the stage that supports the sample includes a first direction, a second direction opposite to the first direction, and a third direction orthogonal to the first and second directions. Progress in a zigzag shape along the direction of
In the beam forming step, first and second focus detection beams spaced apart from each other with the inspection beam formed are formed,
When the stage travels in the first direction, the sample is scanned by the inspection beam after a predetermined time has elapsed after being scanned by the first focus detection beam, and when the stage travels in the second direction, the sample is second An autofocus method comprising: scanning with an inspection beam after elapse of a predetermined time after scanning with a focus detection beam.

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