Defect inspection apparatus

Abstract

The present invention provides a defect inspection apparatus comprising: a stage for holding and moving a sample; an illumination unit for irradiating the sample with light emitted from a light source to form a scanning beam spot on the sample; a detection unit for detecting scattered light from the beam spot and performing photoelectric conversion on the amount of scattered light; and a signal processing unit for processing the photoelectric converted electrical signal. The detection unit includes a first scattered light detection optical system and a second scattered light detection optical system for detecting scattered light from a first illumination region and a second illumination region of the beam spot, respectively. The exposure time of the optical sensor included in the first scattered light detection optical system is longer than the exposure time of the optical sensor included in the second scattered light detection optical system.

Description

Technical Field

[0001] This invention relates to a defect inspection device that inspects the surface of a sample and outputs the location, type, size, etc. of defects. Background Technology

[0002] In production lines for semiconductor substrates, thin-film substrates, etc., defects existing on the surfaces of these substrates are inspected to maintain and improve product yield. In semiconductor substrates, as the formed circuit patterns become smaller, the size of defects affecting product yield also decreases, necessitating increased sensitivity of the inspection equipment. In optical inspection devices, scattered light from defects is detected, and the amount of scattered light is approximately proportional to the sixth power of the defect size. As defect sizes shrink, the amount of detectable reflected light decreases dramatically. Therefore, to detect small defects at high speed and with minimal light intensity, increased detector sensitivity and illumination power density are essential. However, increasing detector sensitivity and illumination power density can lead to saturation of the detection signal for relatively large defects, making it impossible to properly measure the amount of scattered light from defects. In other words, improvements to the illumination and detection systems for detecting fine defects result in a decrease in the upper limit of defect sizes that can be measured without saturation. Generally, the larger the defect size, the greater its impact on product quality. If the detection signal saturates, it becomes difficult to estimate the defect size and classify the defect type. Therefore, in defect inspection, it is required that the signals from both small and relatively large defects be detected as unsaturated. Furthermore, when illuminating foreign objects, they sometimes heat up and burst (particle ablation, Patent Document 1). Increasing the illumination power is effective for detecting small defects, but this increases the heating amount, making foreign objects on the sample surface more prone to bursting. Additionally, it is known that the larger the size of the foreign object, the more likely it is to burst. When a foreign object bursts, the sample surface is contaminated; therefore, it is necessary to have a method to detect foreign objects of a size that are likely to burst before being irradiated with high-power-density illumination and to reduce the power density irradiated onto such foreign objects. In Patent Document 2, for large-diameter foreign objects detected beforehand, an optical modulation element is used to reduce the illumination power.

[0003] In Patent Document 3, when the amount of scattered light is larger than the linear region of the detector and the photoelectric conversion is nonlinear, both fine defects and relatively large defects are detected by correcting its nonlinearity.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2023-544498

[0007] Patent Document 2: Japanese Patent Application Publication No. 2018-71970

[0008] Patent Document 3: International Publication No. 2019 / 159334 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] To detect finer defects, a longer integration time of the detector output is advantageous. This is because a longer integration time results in fewer readouts, thus suppressing the effects of readout noise and other noise. However, if the integration time becomes too long, the detection signal is prone to saturation, reducing the upper limit of the defect size that can be measured without saturation.

[0011] The purpose of this invention is to provide a defect inspection device capable of detecting relatively large defects from small defects with high sensitivity.

[0012] Solution for solving the problem

[0013] To achieve the above objectives, the present invention provides a defect inspection apparatus comprising: a stage for holding and moving a sample; an illumination unit for irradiating the sample with light emitted from a light source to form a scanning beam spot on the sample; a detection unit for detecting scattered light from the beam spot and performing photoelectric conversion on the amount of scattered light; and a signal processing unit for processing the photoelectric converted electrical signal. The detection unit includes a first scattered light detection optical system and a second scattered light detection optical system for detecting scattered light from a first illumination region and a second illumination region in the beam spot, respectively. The exposure time of the optical sensor included in the first scattered light detection optical system is longer than the exposure time of the optical sensor included in the second scattered light detection optical system.

[0014] Invention Effects

[0015] According to the present invention, it is possible to detect defects with high sensitivity, ranging from minute defects to relatively large defects. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the overall structure of the defect inspection device of the present invention.

[0017] Figure 2 This is a diagram illustrating the method of scanning the illumination point on the sample surface.

[0018] Figure 3 This is a diagram showing the configuration and detection direction of the tilt detection unit (first scattered light detection system) of the present invention from above.

[0019] Figure 4This is a side view of the configuration and detection direction of the tilt detection unit (first scattered light detection system) of the present invention.

[0020] Figure 5 This is a schematic diagram illustrating an example configuration of the tilt detection unit (first scattered light detection system) included in the first embodiment of the present invention.

[0021] Figure 6 This is a schematic diagram illustrating an example of the positional relationship between the illumination point and the sensor of the tilt detection unit (first scattered light detection system) included in the first embodiment of the present invention.

[0022] Figure 7 This is a schematic diagram illustrating a configuration example of the vertical detection unit (second scattered light detection system) included in the first embodiment of the present invention.

[0023] Figure 8A This is a diagram showing the illumination points and measurement areas on the sample surface according to the first embodiment of the present invention.

[0024] Figure 8B This is a diagram showing the illumination points and measurement areas on the sample surface according to the second embodiment of the present invention.

[0025] Figure 8C This is a diagram showing the illumination points and measurement areas on the sample surface according to the third embodiment of the present invention.

[0026] Figure 8D This is a diagram showing the illumination points and measurement areas on the sample surface according to the fifth embodiment of the present invention.

[0027] Figure 9 This is an example of the detection signal of the tilt detection unit (first scattered light detection system) provided in the defect inspection device of the present invention.

[0028] Figure 10 It is a graph showing the change in position of the illumination point caused by the displacement in the normal direction of the sample surface.

[0029] Figure 11A This is a diagram illustrating the temporal changes in the relationship between the defect and the position of the illumination point in the second embodiment of the present invention, as well as an example of light intensity adjustment.

[0030] Figure 11B This is a diagram illustrating the temporal changes in the relationship between the location of the defect and the illumination point, as well as an example of light intensity adjustment in the third embodiment of the present invention.

[0031] Figure 11C This is a diagram illustrating the temporal changes in the relationship between the location of the defect and the illumination point, as well as an example of light intensity adjustment, in the sixth embodiment of the present invention.

[0032] Figure 12 This is a diagram illustrating a configuration example of the vertical detection unit (second scattered light detection system) in the third embodiment of the present invention.

[0033] Figure 13 This diagram shows an example of a reflector included in the vertical detection unit (second scattered light detection system) in the third embodiment of the present invention.

[0034] Figure 14 This diagram illustrates the range of defect sizes that can be measured by the advance region detection system and the follow-up region detection system of the tilt detection unit (first scattered light detection system) and the vertical detection unit (second scattered light detection system) in the third embodiment of the present invention.

[0035] Figure 15 This is a diagram illustrating a configuration example of the vertical detection unit (second scattered light detection system) in the fourth embodiment of the present invention.

[0036] Figure 16 This diagram shows an example of the aperture included in the vertical detection unit (second scattered light detection system) in the fourth embodiment of the present invention.

[0037] Figure 17 This is a diagram illustrating a configuration example of the vertical detection unit (second scattered light detection system) in the sixth embodiment of the present invention. Detailed Implementation

[0038] The embodiments of the present invention are described below using the accompanying drawings.

[0039] <First Implementation Method>

[0040] Figure 1 This is a schematic diagram showing the overall structure of the defect inspection apparatus according to the first embodiment of the present invention. The defect inspection apparatus in this diagram includes an illumination unit 101, a stage unit 201 capable of holding a sample, a sample surface displacement detection system 210, a detection unit 301, a signal processing unit 401, a control unit 501, an input unit 601, and a display unit 701. A representative example of the sample 1 inspected by this defect inspection apparatus is a flat, disc-shaped semiconductor silicon wafer without a pattern.

[0041] The signal processing unit 401 and the control unit 501 are computers configured to include, in addition to ROM, RAM, and other memory, a CPU, FPGA, timer, etc. The signal processing unit 401 performs defect inspection and other operations by integrating the output of the detection unit 301, which is based on a time width of a set integration time (exposure time), to obtain a detection signal for any coordinate on the sample surface. As an example, it is conceivable that the signal processing unit 401 is a single computer forming a unit with the main body of the defect inspection apparatus (the illumination unit 101, the stage unit 201, the detection unit 301, and other mechanical parts that perform inspection), but it is also possible for it to be composed of multiple computers connected via a network. In this case, a server can also be used for one of the multiple computers, and the server can also be included in the components of the defect inspection apparatus or the signal processing unit 401. For example, it is possible to configure a computer attached to the main body of the defect inspection apparatus to acquire defect detection signals from the main body, process the detection signals as needed, and send them to a server, where the server performs processing such as defect classification.

[0042] The explosion foreign object detection unit 42, defect judgment unit 43, and other functions of the signal processing unit 401 can be implemented virtually through software or through hardware such as electronic circuits. Furthermore, the signal processing unit 401 and the control unit 501 can be composed of a single computer. Additionally, in Figure 1 The figure shows the explosive foreign object detection unit 42 described in the second embodiment, but the explosive foreign object detection unit 42 is not necessarily required in this embodiment.

[0043] The illumination unit 101 illuminates the sample surface with light emitted from the light source, forming illumination points 20 (beam points) that scan the sample surface. The illumination unit 101 appropriately includes a laser light source 1011, an attenuator 1012, a beam expander 1013, an electro-optic element 1014, a polarization voltage control unit 1015, a polarizer 1016, and an illumination intensity distribution control unit 1017. The laser beam emitted from the laser light source 1011 is adjusted to the desired beam intensity by the attenuator 1012 and to the desired beam diameter by the beam expander 1013, illuminating the surface of the sample 1 (hereinafter referred to as the sample surface).

[0044] The electro-optic element 1014 typically uses a Pockels cell. The electro-optic element 1014 controls the polarization direction of the light input from the beam expander 1013 based on a control voltage input from the polarization voltage control unit 1015. The polarizer 1016 separates the incident light according to the polarization direction. The amount of light incident on the sample surface is controlled by the combination of the electro-optic element 1014 and the polarizer 1016. The polarization voltage control unit 1015 is an example of an amount adjustment unit that adjusts the amount of light irradiated from the laser source 1011 onto the sample surface based on a control signal input from the signal processing unit 401 (or a control signal input from the control unit 501 based on a signal from the signal processing unit 401).

[0045] Depending on the size of the defect to be detected and the magnitude of the scattered light from the minute irregularities of the sample surface (which can be considered noise), the optimal polarization direction and incident angle of the incident light vary. Therefore, although in Figure 1 The description is omitted, but the illumination unit 101 may also be appropriately equipped with an incident light control unit that controls the polarization direction of the light incident on the sample surface or the incident angle of the sample surface.

[0046] As the laser source 1011, to detect minute defects near the sample surface, a high-output laser source is used that oscillates a short-wavelength (below 355nm) ultraviolet or vacuum ultraviolet laser beam with an output of 2W or more, as wavelengths that are difficult to penetrate into the sample. The diameter of the emitted beam is approximately 1mm. To detect defects inside the sample, a wavelength that easily penetrates into the sample is used, employing a visible or infrared laser beam.

[0047] The beam expander 1013 has two or more lens groups, enabling it to enlarge the diameter of the incident parallel beam. For example, a Galilean-type beam expander with a combination of concave and convex lenses can be used. The beam expander 1013 is mounted on a translation stage with two or more axes, allowing for position adjustment to align the predetermined beam position with the center. Furthermore, it has an overall tilt angle adjustment function for the beam expander 1013, ensuring that the optical axis of the beam expander 1013 is aligned with the predetermined beam optical axis. By adjusting the lens spacing, the magnification of the beam diameter can be controlled (zoom mechanism).

[0048] The illumination intensity distribution control unit 1017 is equipped with optical elements such as aspherical lenses, diffractive optical elements, cylindrical lens arrays, and light guides to control the light distribution of illumination on the sample surface.

[0049] When oblique incidence illumination is applied, the height displacement of the sample surface causes displacement of the illumination intensity distribution and defocusing, resulting in disordered illumination intensity distribution. To suppress this, the sample surface displacement detection system 210 measures the height displacement of the sample surface during inspection. If the height deviates from the ideal state, the deviation in illumination intensity distribution is corrected by the Z-axis-based height adjustment of the illumination intensity distribution control unit 1017 or the stage unit 201. Although in Figure 1 The details have been omitted, but the illumination unit 101 may include an illumination light path switching unit 1021 in addition to the optical system that causes the illumination light to be incident obliquely. Figure 7 ) and vertical incident optical system 102 ( Figure 7 This allows the sample to be incident perpendicularly to the sample surface.

[0050] Next, use Figure 2The method of scanning the illumination point 20 formed on the sample surface by the illumination unit 101 and the illumination point 20 on the sample surface is described. As the sample 1, a circular semiconductor silicon wafer is envisioned. The illumination point 20 has an illumination intensity distribution that is longer in one direction. In this embodiment, it is assumed to have an illumination intensity distribution that is longer in the direction of arrow R. Furthermore, the illumination point 20 typically has a two-dimensional Gaussian intensity distribution. The stage unit 201 holds and moves the sample 1, and includes a translation stage, a rotary stage, and a Z-stage for adjusting the height of the sample surface (all not shown). During inspection, the sample is driven to rotate circumferentially by the rotary stage, and the illumination point 20 rotates on the surface of the sample in the direction of arrow θ. Simultaneously, the sample is driven linearly by the straight stage, and the illumination point 20 moves linearly on the surface of the sample in the direction of arrow R. Here, the distance the illumination point 20 moves in the direction of R by the straight stage during the period until it rotates one revolution in the direction of θ by the rotary stage is less than or equal to the length of the longer side of the illumination point 20 in the direction of R. By combining the rotational and linear motions, the stage 201 moves the sample relative to the illumination point 20, which traces a spiral path and scans the entire surface of the sample.

[0051] In addition, although Figure 2 Although not shown in the figure, the stage 201 may also have a linear stage with a moving axis (set as the Y-axis) that is horizontally intersected by the moving axis (set as the X-axis) of the linear stage. In this case, the entire surface of the sample can be scanned by repeating the movement of the illumination point 20 in the X-direction and the movement in the -X-direction while being staggered in the Y-axis direction.

[0052] use Figure 1 as well as Figures 3 to 7 The structure of the detection unit 301 will be described below. The detection unit 301 detects scattered light from the illumination point 20 and performs photoelectric conversion on the amount of scattered light. This detection unit 301 includes a region 202 within the illumination point 20 that serves as a first illumination area (…). Figure 8A The first scattered light detection optical system detects the scattered light from the illumination point 20, and the second illumination area 203 detects the scattered light from the illumination point 20. Figure 8A The second scattered light detection optical system is used to detect the scattered light emitted from the illumination point 20 in a direction inclined relative to the normal of the sample surface. In this embodiment, the first scattered light detection optical system is an imaging optical system, specifically an inclined detection unit 32 that detects light scattered from the illumination point 20 in a direction inclined relative to the normal of the sample surface. The second scattered light detection system is a focusing optical system, specifically a vertical detection unit 303 that detects light scattered from the illumination point 20 in a direction normal to the sample surface. The inclined detection unit 32 includes multiple inclined detection optical systems to detect scattered light from multiple directions emitted from the illumination point 20.

[0053] use Figure 3 as well as Figure 4The configuration of the tilt detection optical system relative to illumination point 20 is described. For example... Figure 3 As shown, in this embodiment, the tilt detection unit 32 includes a plurality of (four in this example) tilt detection optical systems 302a-302d. Figure 3 This is a top view of the configuration of the tilt detection optical systems 302a-302d. The angle between the direction of travel of the oblique incident illumination when viewed from a direction perpendicular to the sample surface and the detection directions of the tilt detection optical systems 302a-302d is defined as the detection azimuth angle. Each detection direction of the tilt detection optical systems 302a-302d is the direction in which each optical axis (the center line of each detection opening) of the tilt detection optical systems 302a-302d extends. The tilt detection unit 32 includes a tilt detection optical system 302a located in front of the illumination incident direction, a tilt detection optical system 302b located behind, and tilt detection optical systems 302c and 302d located symmetrically with respect to them about the illumination incident surface. For example, the tilt detection optical system 302a is configured with a detection azimuth angle of 0 degrees or more and 90 degrees or less, and the tilt detection optical system 302b is configured with a detection azimuth angle of 90 degrees or more and 180 degrees or less. The illumination incident surface is the surface that includes the optical axis of the illumination section 101 and is orthogonal to the sample surface at the illumination point 20.

[0054] Figure 4 A side view showing the configuration of tilt detection optical systems 302a and 302b. Figure 4 Illustrations of the tilt detection optical systems 302c and 302d are omitted. The angles formed by each detection direction of the tilt detection optical systems 302a-302d relative to the normal to the sample surface are defined as the detection zenith angle. (Not limited to...) Figure 3 as well as Figure 4 The example shown can also be modified by changing the number and position of the tilt detection optical system.

[0055] Figure 5 Examples of specific structural diagrams for tilt detection optical systems 302a-302d are shown below. Each of the tilt detection optical systems 302a-302d has an optical axis 3029. Figure 5 The R direction and θ direction shown are related to Figure 2The R direction and θ direction correspond. In the tilt detection optical system 302a-302d, the scattered light generated from the illumination point 20 is focused by the objective lens 3021, and the polarization direction is controlled by the polarization control filter 3022. As the polarization control filter 3022, for example, a half-wave plate can be used, and the rotation angle of the half-wave plate can be controlled by a drive mechanism such as a motor. In order to efficiently detect the scattered light, the detection NA of the objective lens 3021 is preferably 0.3 or more. The objective lens 3021, which is positioned close to the sample surface, has its lower end cut off as needed to avoid interference with the sample surface. The scattered light whose polarization direction is controlled by the polarization control filter 3022 is incident on the imaging lens 3023, and the intermediate image of the illumination point 20 is imaged at the position of the aperture 3024. The opening diameter of the aperture 3024 is set to allow only the light from the area of ​​the image of the illumination point 20 detected by the sensor (optical sensor) 3028 to pass through. Aperture 3024 allows only the central portion of the illumination intensity distribution with strong light in the R direction to pass through, while blocking the weaker light regions at the beam ends. Furthermore, the aperture diameter of aperture 3024 in the θ direction is the same size as the image of illumination point 20 formed by aperture 3024, suppressing interference such as air scattering caused when illumination passes through air. The intermediate image formed at the location of aperture 3024 is converged again by condenser lens 3025 and incident on polarization beam splitter 3026, where it is split according to the polarization direction controlled by polarization control filter 3022. The beams split by polarization beam splitter 3026 are respectively incident on imaging lenses 3027-1 and 3027-2, forming images on the light-receiving surfaces of sensors 3028-1 and 3028-2, which serve as photoelectric conversion units, thus forming images of illumination point 20 on each light-receiving surface. Cylindrical lenses 3027-1 and 3027-2 can also be used for imaging in only one direction.

[0056] Figure 6 This indicates the relationship between sensor 3028 and illumination point 20. Figure 6The optical path branches of the polarization beam splitter 3026 are omitted. As described above, the linear illumination point 20 is imaged onto multiple sensors 3028 by the tilt detection optical systems 302a-302d, forming an optical image 21 of the illumination point 20 on the light-receiving surfaces of the multiple sensors 3028. The sensors 3028 are either line sensors or TDI (Time-Delay-Integration) sensors. As a type of sensor, for example, CMOS (Complementary Metal-Oxide-Semiconductor) sensors, CCD (Charge Coupled Device) sensors, SiPM (Silicon Photomultipliers) sensors, PMT (Photo multiplier Tube) sensors, or APD (Avalanche Photo Diode) sensors can be used. Typically, a line sensor is configured such that the normal direction of its light-receiving surface is aligned with the optical axis of the detection optical system, but in this embodiment, the array-shaped light-receiving portion 30281 (light-receiving surface) of the sensor 3028 is tilted relative to the optical axis 3029 of each tilt detection optical system 302a-302d. The light-receiving part 30281 is configured such that its array direction is parallel to the long side direction of the optical image 21. Although in Figure 5 The illustration is omitted, but a pair of cylindrical lenses 30210 and 30211 are arranged between the objective lens 3021 and the imaging lens 3023. These cylindrical lenses 30210 and 30211 constitute a cylindrical lens beam expander, so that the expansion of the optical image 21 formed by the illumination point 20 in the short side direction γ is smaller than the expansion of the optical image 22 in the long side direction σ.

[0057] Sensor 3028 captures an optical image 21 and outputs it as an electrical signal. Sensor 3028 has a light-receiving portion 30281 and an anti-reflection film at a position one-dimensionally conjugate to the illumination point 20 illuminating the surface of sample 1. The light-receiving portion 30281 is conjugate to the sample surface in the long-side direction σ, but not in the short-side direction γ. However, the short-side direction γ corresponds to the short-side direction of the illumination point 20, therefore the image height of the optical image 21 is low, and almost no focus shift occurs. Therefore, by increasing the imaging magnification of the optical image 21 in the short-side direction γ, the deviation of the incident angle towards the light-receiving portion 30281 can be reduced.

[0058] use Figure 7The structure of the vertical detection unit 303 and its relationship with the vertical incident optical system 102 will be explained. In the vertical detection unit 303, a condensing relay lens system 3031, including multiple lenses, focuses the scattered light generated from the illumination point 20 in a direction (e.g., the normal direction) toward a small detection zenith angle. The intermediate image of the illumination point 20 formed by the condensing relay lens system 3031 is magnified or reduced by a magnification adjustment lens system 3032 at a desired magnification, and imaged at the position of the aperture 3033 to form an intermediate image 23. This intermediate image 23 is then focused again by the condensing lens 3034 and guided to the sensor (optical sensor) 3035, which serves as the photoelectric conversion unit of the vertical detection unit.

[0059] Although Figure 1 The middle is omitted, but as Figure 7 As shown, the illumination unit 101 may also include a perpendicular incident optical system 102 that directs light along the normal direction of the sample surface. In this embodiment, the illumination unit 101 has an illumination path switching unit 1021 that switches the light path at a predetermined position, thus forming a structure capable of switching between oblique incident illumination and perpendicular illumination. The illumination path switching unit 1021 is composed of multiple mirrors, etc., arranged in the illumination path. Furthermore, as... Figure 7 As shown, the vertical detection unit 303 and the vertical incident optical system 102 share some optical elements, forming an illumination point 20 on the sample surface in the same manner as oblique incident illumination. The illumination relay system of the vertical incident optical system 102 includes a lens 1022 and a reflector 1023, and shares a lens on the side closest to the sample surface in the condenser relay lens system 3031 with the vertical detection unit 303. The illumination light passing through the lens 1022 is reflected by the reflector 1023, becoming the same optical axis as the condenser relay lens system 3031 and illuminating the sample surface. The reflector 1023 is movable and is inserted into the optical path only during vertical illumination.

[0060] use Figure 8A The relationship between region 202 on the sample surface measured by the tilt detection unit 32 and region 203 on the sample surface measured by the vertical detection unit 303 in this embodiment will be explained. These regions 202 and 203 can be set, for example, by the size and shape of the openings of apertures 3024 and 3033. Region 202 measured by the tilt detection unit 32 is the region on the sample surface where the light-receiving portion 30281 of the sensor 3028 included in the tilt detection unit 32 is projected. Region 203 measured by the vertical detection unit 303 is the region on the sample surface where the outline of the light-receiving surface of the sensor 3035 included in the vertical detection unit 303 is projected. Region 202 measured by the tilt detection unit 32 is the central portion of the long side direction R of the illumination point 20, and this region is determined by the aperture 3024 included in the tilt detection unit 32.

[0061] In this embodiment, the region 203 measured by the vertical detection unit 303 is determined by the aperture 3033 included by the vertical detection unit 303 in such a way that it includes the entire region 202 measured by the tilt detection unit 32. Therefore, the vertical detection unit 303 detects scattered light from the region 203, which includes the region 202 measured by the tilt detection unit 32. Figure 8A As shown, the aperture 3033 included in the vertical detection unit 303 only allows the central portion of the illumination intensity distribution of the illumination point 20, which has a high light intensity in the R direction, to pass through, and blocks the two ends of the beam with low light intensity. In addition, the opening diameter of the aperture 3033 in the θ direction is the same size as the image of the illumination point 20 imaged by the aperture 3033, suppressing interference such as air scattering caused when the illumination passes through the air.

[0062] Regarding minute defects on the sample surface, the amount of scattered light from the illumination point 20 towards the tilt detection optical system 302a-302d (i.e., oblique scattering) is greater than the amount of scattered light scattered towards the vertical detection unit 303. Therefore, the detection sensitivity of the tilt detection unit 32 is higher than that of the vertical detection unit 303. To further improve the sensitivity for minute defects, the integration time of the outputs of each sensor 3028 included in the tilt detection unit 32 is set to be longer than the integration time of the output of the sensor 3035 in the vertical detection unit 303. This suppresses the decrease in S / N caused by readout noise, etc. On the other hand, by extending the integration time, the amount of light integrated in a single exposure increases, thus the detection signal from relatively large defects is prone to saturation. If the detection signal saturates, it becomes difficult to estimate the size of the defect and classify the defect type. The size and type of the defect are important for estimating the impact of the defect on the final semiconductor device product.

[0063] To address this issue, in this embodiment, the following differences are provided between the sensor 3035 of the vertical detection unit 303 and the sensor 3028 of the tilt detection unit 32.

[0064] First, in this embodiment, a laser with higher power than the laser typically used in the inspection of sample 1 is used to detect scattered light from minute defects. In high-output lasers, pulsed lasers are more advantageous than continuous-wave lasers due to the nonlinearity of the wavelength conversion element. Therefore, in this embodiment, a QCW (Quasi Continuous Wave) pulse with an oscillation frequency in the range of several MHz to tens of MHz is used to start the laser as the laser source 1011. The control unit 501 inputs the laser oscillation synchronization signal to the sensor 3035 of the vertical detection unit 303. The sensor 3035 then samples the input signal in sync with it and performs A / D conversion. By synchronizing with the laser oscillation, it is less susceptible to noise such as dark current. For example, when the rotation speed of the stage 201 is constant at an angular velocity, the movement speed of the field of view on the sample surface varies between the inner and outer peripheries of the sample surface. The emission time of each pulse is typically in the picosecond range, so the movement of the field of view during the emission time of one pulse can be ignored. Therefore, even when the rotational speed of the rotary table is constant at an angular velocity, by synchronizing the sampling of sensor 3035 with the oscillation timing of the pulsed oscillating laser, the influence of changes in the movement speed of the field of view on the sample surface can be suppressed. In contrast, sensor 3028 of tilt detection unit 32 focuses on detecting minute amounts of light and is configured to sample multiple pulses by a single integration, that is, integration of the signal at a single coordinate.

[0065] In this embodiment, the integration time of the output of sensor 3035 in vertical detection unit 303 is set to be shorter than the integration time of the output of sensor 3028 in tilt detection unit 32. That is, the exposure time of sensor 3028, which is part of the first scattered light detection optical system, is longer than the exposure time of sensor 3035, which is part of the vertical detection unit 303, which is part of the second scattered light detection optical system. By setting the integration time of the output of vertical detection unit 303 to be shorter than that of tilt detection unit 32, the defect size that can be detected due to signal desaturation in vertical detection unit 303 can be increased compared to tilt detection optical system 302. As for the type of sensor 3035 in vertical detection unit 303, similar to sensor 3028, a CMOS sensor, CCD sensor, SiPM sensor, PMT sensor, or APD sensor can be used. However, when synchronizing sampling with an oscillation frequency of tens of MHz, it is difficult to make small charges move with the oscillation frequency in CMOS sensors and CCD sensors.

[0066] The signal processing unit 401 includes a function to determine the size of the defect based on the detection signals from the sensor 3035 and the sensor 3028. Figure 1The defect determination unit 43 (shown) calculates defect information by appropriately integrating the detection signals from the vertical detection unit 303 and the tilt detection unit 32. For relatively small defects where the detection signal of the sensor 3028 is not saturated in all tilt detection optical systems 302a-302d, the defect information is calculated using only the signal from the tilt detection unit 32 because the detection signal of the vertical detection unit 303 is small. For relatively large defects where the detection signal of the sensor 3028 is saturated in at least one of the tilt detection optical systems 302a-302d, the defect information is calculated using the detection signals from both the vertical detection unit 303 and the tilt detection unit 32.

[0067] Specifically, the estimation of the defect size for larger defects is explained. Typically, defect size estimation is performed by comparing the ratio of the power density of the light illuminating the defect to the measured amount of scattered light with a sensitivity curve obtained through calibration or simulation using standard particles. However, since the vertical detection unit 303 is a focused detection system, although the amount of scattered light is calculated based on the detection signal from the vertical detection unit 303, the spatial location information of the defect is not determined. The illumination power density distribution is not uniform but Gaussian; therefore, to determine the power density illuminating the defect, the defect's location information is required.

[0068] use Figure 9 An example of the detection signal from the tilt detection unit 32 and an inference of the defect location information are explained. Figure 9 The horizontal axis represents the R direction, and the horizontal axis values ​​of the detection signals (curves) of each pixel of the sensor 3028, which acts as a line sensor, correspond to their positions on the sample surface. The vertical axis represents the amount of scattered light measured at each pixel. Figure 9 In the example, due to the large defect size, the pixels detecting scattered light from near the defect location become saturated, making it impossible to directly obtain the amount of scattered light from the detection signal of the tilt detection unit 32. However, the location of the defect can be inferred, for example, from the saturated pixels, as its centroid position. Figure 9 In the example, three pixels near the defect location are saturated. It is assumed that the center of these three pixels coincides with the actual defect location due to an error of an order of magnitude in the pixel size along the R direction. To more accurately infer the location information, for example by detecting light and using the signals from the unsaturated surrounding pixels, an improvement in the accuracy of defect location inference can be expected.

[0069] As described above, the vertical detection unit 303 has a short sensor integration time, making it difficult for the detection signal to saturate, thus enabling the measurement of scattered light even from relatively large defects. However, the defect location is unknown based on the signal from the vertical detection unit 303, making accurate size calculation difficult. However, as described above, the defect location can be inferred from the detection signal from the tilt detection unit 32. Therefore, the power density irradiated on the defect can be calculated using the power density distribution of the illumination light obtained beforehand through optical simulation, or the power density distribution of the illumination light measured by a power density distribution measurement optical system (not shown), as will be described later.

[0070] By combining the detection signals from the vertical detection unit 303 and the tilt detection unit 32, the defect location and the amount of scattered light, as well as the illumination power density irradiating the defect, can be measured, and the size of the defect can be calculated with high precision in the signal processing unit 401.

[0071] When calculating the illumination power density irradiating the defect, the illumination power density distribution on the sample surface is used as described above. During inspection, the sample rotates at high speed, so the position of the sample surface can vibrate and change in the normal direction of the sample surface at the μm level. Due to this change, the illumination becomes blurred, and the illumination power density distribution may change. Additionally, in the case of oblique incidence illumination, such as... Figure 10 As shown, the illumination point 20 shifts in the R direction due to the displacement of the sample surface in the normal direction, thereby changing the illumination power density distribution. Due to these factors, the estimation of the power density irradiated to the defect becomes inaccurate, thus increasing the error in the calculation of the defect size. To address this issue, a sample surface displacement detection system 210 is used to measure the displacement of the sample surface in the normal direction during inspection. The displacement of the sample surface measured by the sample surface displacement detection system 210 is input to the defect determination unit 43. In the defect determination unit 43, pre-stored data (e.g., table data) regarding the change in illumination power density distribution at each position in the normal direction of the sample surface is used to calculate the power density irradiated to the defect based on the position of the sample surface in the normal direction. This reduces the measurement error of the defect size caused by the displacement of the sample surface in the normal direction.

[0072] According to the present invention, the vertical detection unit 303, which is the second scattered light detection optical system, has a shorter exposure time than the tilt detection unit 32, which is the first scattered light detection optical system. Therefore, the detection signal is less likely to saturate compared to the tilt detection unit 32, and the amount of scattered light can be measured even for relatively large defects. In this way, by using multiple detection optical systems with different exposure times, the dynamic range is expanded, and defects ranging from small to relatively large can be detected with high sensitivity.

[0073] Furthermore, in this embodiment, the integration time of the output of the sensor 3035 included in the vertical detection unit 303 is set to be relatively short, but the sensor that relatively shortens the integration time does not necessarily have to be sensor 3035. For example, for a portion (at least one) of the multiple tilt detection optical systems 302a-302d of the tilt detection unit 32, the integration time of sensor 3028 may also be set to be shorter than that of the other detection optical systems. That is, a portion of the tilt detection optical systems can be used instead of the vertical detection unit 303.

[0074] <Second Implementation Method>

[0075] In this embodiment, the case where region 203 (second illumination region) on the sample surface measured by the vertical detection unit 303 includes a region located in the positive R direction relative to region 202 (first illumination region) measured by the tilt detection unit 32 will be described. Region 203 only needs to be at least partially located in the positive R direction relative to region 202, and regions 202 and 203 may also partially overlap. That is, region 203 (second illumination region) includes a prior region that was scanned on the sample earlier than region 202 (first illumination region) in time.

[0076] The aperture 3033 included in the vertical detection unit 303 allows light from the portion of the intermediate image 23 in which the light intensity is low at the beam end that is blocked by the aperture 3024 in the tilt detection unit 32 to reach the light source. Figure 2 The region on the positive R side passes through. Figure 8B The relationship between regions 202 and 203 in this embodiment is illustrated. For example... Figure 2 As described, illumination point 20 scans the entire sample surface in a spiral motion from the center of the sample outwards. That is, region 203 is the region on the sample surface where a certain coordinate is illuminated with weak light before region 202. Each coordinate on the sample surface is first illuminated with weak light when crossing region 203, and then illuminated with stronger light when crossing region 202 in the next cycle. In this embodiment, regions 202 and 203 do not partially overlap.

[0077] Therefore, as will be described later, it is possible to detect defects such as foreign objects that may burst (hereinafter sometimes referred to as bursting foreign objects) before irradiating them with high-power-density illumination, thus preventing bursting. The detection of bursting foreign objects must be performed in real-time during defect inspection as the sample 1 rotates dozens of times within one second, thus requiring high-speed processing. In this regard, the vertical detection unit 303 is a focused detection system, therefore the output is a single signal, suitable for high-speed processing.

[0078] The signal processing unit 401 includes a burst foreign object detection unit 42 that detects burst foreign objects based on the detection signal from the sensor 3035 of the vertical detection unit 303. The burst foreign object detection unit 42 extracts burst foreign objects by comparing the detection signal acquired by the sensor 3035 with a predetermined threshold set after high-pass filtering. In the burst foreign object detection unit 42, for example, foreign objects whose defects detected by the vertical detection unit 303 exceed the predetermined threshold are presumed to be burst foreign objects as particles of a predetermined size or larger. The light intensity adjustment unit (polarization voltage control unit 1015) adjusts the power density of the illumination light irradiating the burst foreign object in region 202 as described below when the vertical detection unit 303 detects a burst foreign object of a predetermined size (light intensity) or larger in region 203 as a particle. In this case, the signal processing unit 401 can also be configured to change the aforementioned threshold based on the measurement result of the sample surface displacement input from the sample surface displacement detection system 210. By adjusting the threshold according to the displacement of the sample surface, it is possible to address changes in the illumination power density distribution caused by displacement in the normal direction of the sample surface.

[0079] use Figure 11A The situation regarding the explosive foreign object extracted by the explosive foreign object detection unit 42 is explained. Figure 11A (1) shows an example of the change in illumination power density irradiated to the defect during inspection. The horizontal axis is the R direction, and the illumination power density distribution (Gaussian) along the long side is recorded. In addition, the defect positions at times t1, t2, and t3 relative to the illumination power density distribution are indicated by dashed lines. The radius vector movement distance 204 is the distance that the illumination point 20 is moved by the R-stage during the period when the sample is rotated once by the rotary table, and it varies depending on the inspection mode. The defect signal with coordinate X that is in region 203 at time t1 and detected by the vertical detection unit 303 is input to the explosive foreign object detection unit 42 to determine whether it is an explosive foreign object. If it is determined to be an explosive foreign object, the control unit 501 stores the defect position (coordinate X) and controls the amount of light when detecting coordinate X in region 202. Figure 11A(2) An example is shown of the time variation of the power density irradiated onto the sample surface by the polarization voltage control unit 1015 and the electro-optic element 1014. If it is determined that the signal at coordinate X detected in region 203 at time t1 is a bursting foreign object, the control unit 501 controls the polarization voltage control unit 1015 and the electro-optic element 1014 to reduce the illumination power density at the timing (times t2, t3) when the illumination point 20 irradiates the defect location (coordinate X) one week later. The illumination power density is reduced to a preset value based on the defect size inferred from the detection signal at time t1 to prevent bursting. The illumination power density of the light irradiating the bursting foreign object can be a constant value, for example, using data (table data) that predefines the relationship between the size of the bursting foreign object (signal intensity detected in region 203) and the illumination power density, determined based on the signal intensity detected in region 203.

[0080] The size estimation of the explosive foreign object in this embodiment will be explained. As described in the first embodiment, the amount of scattered light can be obtained from the detection signal of the vertical detection unit 303. Figure 11A In example (1), the power density P(t1) irradiated by the explosive foreign object at time t1 can be calculated as follows, using the position information of the explosive foreign object inferred from the saturated detection signal output from the tilt detection unit 32 at time t (t1 < t).

[0081] P(t1)=Pr(x(t)-Rp*N)

[0082] Here, Pr is the illumination power density distribution in the R direction, x(t) is the position of the bursting foreign object inferred from the saturated detection signal measured by the tilt detection unit 32 at time t, Rp is the radius vector movement distance 204, and N is the number of times (rotations) the sample 1 is rotated through the θ stage from time t1 to time t. Pr can be the illumination power density distribution obtained from optical simulation, or it can be the illumination power density distribution measured by a point monitoring optical system (not shown). In addition, Pr is set to the power density distribution that takes into account the amount of light source power reduction to prevent the bursting of the foreign object, input from the bursting foreign object detection unit 42 or the control unit 501. Furthermore, it can also be the illumination power density distribution that takes into account the change caused by the sample surface displacement at time t1, based on the measurement results of the sample surface displacement detection system 210.

[0083] Regarding other structures and functions, this embodiment is the same as the previously described embodiment.

[0084] In this embodiment, the same effects as in the previously described embodiment can be obtained. Furthermore, bursting foreign objects can be detected in region 202, which scans the sample surface prior to region 202 in time. Additionally, by reducing the illumination power density directed at the detected bursting foreign objects, the bursting of defects can be effectively suppressed.

[0085] <Third Implementation Method>

[0086] In this embodiment, the vertical detection unit 303 is described as including multiple detection systems (preliminary area detection system 312 and subsequent area detection system 311) that detect different areas on the sample surface respectively. Figure 8C The relationship between regions 202 and 203 in this embodiment is illustrated. For example... Figure 2 As described, illumination point 20 scans the entire sample surface in a spiral motion from the center of the sample outwards. That is, region 203 reaches a certain coordinate on the sample surface before region 202. However, unlike the second embodiment, in this embodiment, a portion of region 203 overlaps with region 202. The portion of region 203 that does not overlap with region 202 is the preceding region 2031, and the portion of region 203 that overlaps with region 202 is the following region 2032. The following region 2032 is the region that is scanned on the sample in time after the preceding region 2031. In this embodiment, the following region 2032 includes the entirety of region 202, but a portion of region 202 (e.g., the end in the -R direction) may also deviate from the following region 2032.

[0087] use Figure 12 The structure of the vertical detection unit 303 in this embodiment will be described. In the vertical detection unit 303 of this embodiment, an aperture 3041 is provided at the position of the intermediate image of the illumination point 20 formed by the focusing relay lens system 3031. The aperture 3041 blocks light from the unmeasured area in the illumination point 20 to prevent stray light. In the first and second embodiments, at the position where the aperture 3033 is provided, in this embodiment, a light path branching mirror 3040 is provided to branch the light path to the subsequent area detection system 311 and the preceding area detection system 312.

[0088] use Figure 13 The optical path branch mirror 3040 will be described. Positioned at the intermediate image 23, the optical path branch mirror 3040 includes a light-shielding portion 30401, a reflecting portion 30402, and a transmitting portion 30403. The transmitting portion 30403 can be made of a material with high transmittance at the light source wavelength, or it can be a structure where only this portion is removed, allowing light reaching that region to pass directly (i.e., without an opening in the structure). The reflecting portion 30402 allows light from passing through the rear region 2032 of region 203 (… Figure 8C The light reflected from the preceding region 2031 (located in the positive R direction within region 203) is guided towards the rearward region detection system 311. The transmission unit 30403 directs the light from the preceding region 2031 (located in the positive R direction within region 203) to the rearward region detection system 311. Figure 9The light from C) passes through and is directed to the advance area detection system 312. The light-shielding part 30401 blocks the light from the end of the beam in the negative R direction. The light-shielding part 30401 has the effect of preventing unnecessary reduction of laser power in the detection of explosive foreign objects in this embodiment.

[0089] return Figure 12 Continuing with the description of the vertical detection unit 303, scattered light from the preliminary region 2031 reaches the preliminary region detection system 312 through the optical path branch mirror 3040. The intermediate image 23 passing through the optical path branch mirror 3040 is focused by the condenser lens 3034. In this embodiment, a SiPM sensor is used as the sensor (optical sensor) 3042, which is the photoelectric conversion unit of the preliminary region detection system 312. While SiPM sensors can achieve high current amplification, they have the characteristic that a non-sensing region exists on the light-receiving surface, and photons incident on this region will not be detected. In this embodiment, the intermediate image 23 focused by the condenser lens 3034 is guided to the sensor 3042 by the microlens array 3036, reducing the number of photons incident on the non-sensing region and improving detection efficiency.

[0090] On the other hand, the scattered light from the rearward region 2032 is reflected by the optical path branch mirror 3040 and guided to the rearward region detection system 311. The intermediate image 23 reflected by the optical path branch mirror 3040 is focused by the condenser lens 3037 and detected by the photoelectric conversion unit, i.e., the sensor (optical sensor) 3039, of the rearward region detection system 311. The ND filter 3038 that allows the light incident on the sensor 3039 to pass through is configured to switch between multiple ND filters with different optical concentrations, thereby adjusting the photon collection efficiency of the rearward region detection system 311 within a predetermined range.

[0091] Next, the calculation of the defect size in this embodiment will be explained. In this embodiment, the signals from the three detection systems—the preceding region detection system 312, the following region detection system 311, and the tilt detection unit 32—are combined to calculate the defect size. The preceding region 2031 is the part with low power density at the end of the illumination point 20, and therefore the amount of scattered light is also small. That is, the preceding region detection system 312 can detect the largest range of defect sizes. Both the following region detection system 311 and the tilt detection unit 32 detect scattered light from the region 202 with high illumination power density, but due to the aforementioned difference in integration time, the tilt detection unit 32 can detect a smaller defect size.

[0092] The minimum defect size that can be measured by the advance area detection system 312 depends on the power density distribution within the advance area 2031. From the viewpoint of inspection throughput, it is preferable to set the area 202 as large as possible to expand the range that can be inspected in one cycle. In this embodiment, the power density of the illumination point 20 has a two-dimensional Gaussian distribution, and the area 202 is set to a range where the illumination power density is 1 / e2 or more of the peak value. In this case, the illumination power density within the advance area 2031 is at most 13.5% of the peak value within the area 202. Depending on the size of the radius shift spacing 204, even defects saturated in the tilt detection section 32 may not be detectable by the advance area detection system 312. The follow-up area detection system 311 adjusts the photon collection efficiency through the ND filter 3038 to detect defects of sizes that are saturated in the tilt detection section 32 but have low light intensity and are difficult to detect in the advance area detection system 312. That is, the photon collection efficiency of the follow-up area detection system 311 is set to be lower than that of the advance area detection system 312.

[0093] Figure 14 This represents the relationship between the defect sizes that can be measured by the three detection systems: the preliminary area detection system 312, the subsequent area detection system 311, and the tilt detection unit 32. The horizontal axis represents the defect size, indicating the range of defect sizes where sufficient scattered light can be detected in each detection system and the detection signal is not saturated. Measurement ranges 1301, 1302, and 1303 are the ranges of defect sizes that can be measured by the tilt detection unit 32, the subsequent area detection system 311, and the preliminary area detection system 312, respectively. For defects of saturated sizes by the tilt detection unit 32, the defect size is calculated in the same manner as in the first and second embodiments. That is, the defect determination unit 43 calculates the amount of scattered light based on the detection signal from the subsequent area detection system 311 or the preliminary area detection system 312. In addition, the defect determination unit 43 calculates the defect position based on the saturated detection signal from the tilt detection unit 32 and calculates the illumination power density irradiated to the defect based on the illumination curve. The defect size is calculated based on the illumination power density and the amount of scattered light thus calculated.

[0094] use Figure 11B and Figure 14 The detection of explosive foreign objects in this embodiment will be explained. Figure 14 In this context, defect size 1304 is the lower limit of the defect size that could potentially burst under maximum power density illumination within the illumination point 20. That is, defects larger than defect size 1304 are bursting foreign objects, requiring adjustment of the illumination power. In this embodiment, the illumination power density within the preliminary region 2031 is low, such as... Figure 14As shown, it is difficult to detect defects close to the size of defect 1304 by the preliminary area detection system 312, so a two-stage explosion foreign object detection is performed using the subsequent area detection system 311.

[0095] For defects of a size that can be detected by the advance area detection system 312, and Figure 11A The second embodiment described herein also performs the detection of explosive foreign objects. The handling of explosive foreign objects that are difficult to detect in the preliminary area detection system 312 and are larger than the defect size 1304 is as follows: Figure 11B As shown. In Figure 11B In (1), at time t1, the explosive foreign object is located in the preceding region 2031, but its size is small, so the preceding region detection system 312 cannot detect it. At time t2, which corresponds to the next cycle, the explosive foreign object enters the following region 2032 and region 202. The explosive foreign object described here is small. Therefore, the illumination area where the explosive foreign object exists at time t2 is a low region in the following region 2032 and region 202 before the power density reaches its peak, so the explosive foreign object will not explode at time t2. However, at time t3, which corresponds to the next cycle, the explosive foreign object is irradiated with a high power density, so the explosive foreign object may explode.

[0096] In this embodiment, a ruptured foreign object not detected by the preceding area detection system 312 at time t1 is detected by the following area detection system 311 at time t2. The detection signal in the tilt detection unit 32 is saturated, but the following area detection system 311 is not saturated and can detect the ruptured foreign object. The detection signal from the following area detection system 311 is input to the ruptured foreign object detection unit 42 to determine whether it is a ruptured foreign object. If it is determined to be a ruptured foreign object, the control unit 501 stores the position of the ruptured foreign object and controls the amount of light illuminating the ruptured foreign object in the next revolution.

[0097] like Figure 11B (2) As shown, the control unit 501 controls the polarization voltage control unit 1015 and the electro-optic element 1014 to reduce the illumination power density at the moment when the illumination point 20 illuminates the location of the stored explosive foreign object after the next cycle (time t3). The illumination power density is reduced to a preset value based on the size of the explosive foreign object inferred from the detection signal at time t2, so that the explosive foreign object does not explode.

[0098] That is, in this embodiment, when the preceding region detection system 312 detects particles of a size greater than or equal to a first threshold in the preceding region 2031, the polarization voltage control unit 1015 adjusts the power density of the illumination light irradiating the explosive foreign object (particle of a size greater than or equal to the first threshold) in the following region 2032 and region 202 according to the control signal from the signal processing unit 401 input via the control unit 501, following the same principle as in the second embodiment. Furthermore, when the preceding region detection system 311 detects explosive foreign objects of a size greater than or equal to a second threshold (particles smaller than particles of a size greater than or equal to the first threshold) in the following region 2032, the polarization voltage control unit 1015 adjusts the power density of the illumination light irradiating the particles of a size greater than or equal to the second threshold in region 202 according to the control signal from the signal processing unit 401 input via the control unit 501. The power density of the illumination light irradiating the explosive foreign object detected by the advance area detection system 312 and the power density of the illumination light irradiating the explosive foreign object detected by the follow-up area detection system 311 can be set to the same value if they are set to constant values, but for example, the latter can be set to be higher than the former. Alternatively, the power density of the illumination light irradiating the explosive foreign object can be varied according to the size (light intensity) of the explosive foreign object. Furthermore, the signal processing unit 401 can be configured to change at least one of the first threshold and the second threshold based on the measurement result of the sample surface displacement input from the sample surface displacement detection system 210. By changing these thresholds according to the displacement of the sample surface, changes in the illumination power density distribution caused by displacement in the normal direction of the sample surface can be addressed.

[0099] Furthermore, in this embodiment, if the position of the explosive foreign object in region 202 moves in the negative R direction after time t3, the subsequent region detection system 311 cannot detect the scattered light from the explosive foreign object through the light-shielding part 30401 of the optical path branch reflector 3040. Therefore, during subsequent orbiting, when the explosive foreign object crosses region 202, no laser power reduction control is performed. This prevents unnecessary reduction in laser power and avoids a decrease in sensitivity to small foreign objects.

[0100] In this embodiment, the other structures and functions are the same as in the described embodiment, and the same effects can be obtained. Furthermore, according to this embodiment, explosive foreign objects that are difficult to detect in the preceding region 2031 can be detected in the following region 2032, improving the effect of suppressing the explosion of explosive foreign objects. Relatedly, by setting the photon collection efficiency of the following region detection system 311 to be lower than that of the preceding region detection system 312, defects of a size that are saturated in the tilt detection section 32 but difficult to detect in the preceding region detection system 312 due to low light intensity can be easily detected by the following region detection system 311. Through the effect of the light-shielding portion 30401 of the optical path branch reflector 3040, excessive reduction of laser power can be prevented, and reduced sensitivity to small foreign objects can be prevented.

[0101] <Fourth Implementation Method>

[0102] In this embodiment, the vertical incident optical system 102 and the vertical detection unit 303 have different structural components. Figure 15 An example of the structure of the vertical detection unit 303 and the vertical incident optical system 102 in this embodiment is shown. Figure 15 In the middle, to and Figure 7 or Figure 12 Same or corresponding element labels and Figure 7 or Figure 12 Same symbols, but explanations omitted.

[0103] Figure 15 The vertically incident optical system 102 and the vertical detection unit 303 shown branch the optical axis through a semi-reflective mirror 1024. In this structure, when using vertically incident light to inspect the sample 1, the illumination light reflected orthogonally from the sample surface is focused by the focusing relay lens system 3031, thus the orthogonally reflected light becomes noise and hinders the detection of the tiny scattered light from the defect. Therefore, in Figure 15 In one example, the vertical detection unit 303 has an additional spatial filter (light intensity adjustment aperture) 3043 at the position of the pupil surface to block the light reflected from the mirror.

[0104] use Figure 16 The spatial filter 3043 will be described. Figure 16 In this context, X and Y are orthogonal coordinates in the pupil plane, respectively, and are perpendicular to the optical coordinate system. Figure 2The θ and R directions correspond to each other. The illumination light is concentrated on the sample surface into a thin line with the θ direction as the shorter side, so the positively reflected light of the illumination is greatly extended in the X direction corresponding to the θ direction on the pupil surface. The light-shielding part 30431 of the spatial filter 3043 is a rod, which blocks a rectangular area that is long in the X direction on the pupil surface. In addition, the light-shielding part 30431 is configured to switch between rods of different thicknesses, which can change the width of the light-shielding part 30431 in the Y direction. As a result, the photon collection efficiency of the vertical detection unit 303 can be adjusted during vertical illumination.

[0105] In this embodiment, the other structures, functions, and effects are the same as in the previously described embodiments.

[0106] <Fifth Implementation Method>

[0107] In this embodiment, the case where the illumination point 20 is set as multiple points and the regions 202 and 203 are set as different illumination points will be described in the second embodiment. For example, by assembling optical elements such as a beam splitter in the illumination unit 101, multiple parallel beams are formed based on the emitted light from the laser source 1011, thereby forming multiple illumination points. The power density of the multiple illumination points can vary, for example, depending on the beam splitting ratio of the beam splitter. The method of forming multiple illumination points is not limited to this example, and appropriate design changes such as using multiple light sources can be made.

[0108] Figure 8D The relationship between regions 202 and 203 and the illumination point in this embodiment is shown. In this embodiment, the illumination unit 101 illuminates the sample surface with a secondary illumination point 20b, which has a relatively low power density, in addition to the main illumination point 20a, which has the highest power density. Region 202 is configured to include the main illumination point 20a, and region 203 is configured to include the secondary illumination point 20b. In the second embodiment ( Figure 8B In this embodiment, region 203 is the beam end of illumination point 20, therefore the intensity of scattered light is low, and the detection sensitivity for smaller-sized foreign objects in the burst foreign object may be reduced. In this embodiment, a secondary illumination point 20b is formed separately from the main illumination point 20a for use in region 203, therefore, by appropriately setting the regional power density of the secondary illumination point 20b, the detection sensitivity for defects in region 203 can be improved.

[0109] In this embodiment, the other structures, functions, and effects are the same as in the previously described embodiments.

[0110] <Sixth Implementation Method>

[0111] In this embodiment, the case where the vertical detection unit 303 in the third embodiment includes imaging detection but does not include focusing detection will be described. Figure 17An example of the vertical detection unit 303 in this embodiment is shown. In the vertical detection unit 303 of this embodiment, the intermediate image 23 is imaged onto the sensor 3039 of the rear area detection system 311 by a condenser lens 3037 and an imaging lens 3044. The sensor 3039 of the rear area detection system 311 is a line sensor, just like the sensor 3028 of the tilt detection unit 32. The sensor 3042 of the leading area detection system 312 is the same as in the previously described embodiment.

[0112] In this embodiment, since the defect location information is obtained from the detection signal of the rear area detection system 311 of the vertical detection unit 303, when the tilt detection unit 32 calculates the size of the saturated defect, it is not necessary to combine it with the location information obtained from the detection signal of the tilt detection unit 32, which simplifies the calculation process of the defect size.

[0113] Furthermore, compared to the third embodiment, it has the effect of suppressing unnecessary power reduction and sensitivity reduction. (Using...) Figure 11C This needs to be explained. Figure 11C In example (1), the downstream area detection system 311 measures light intensity at time t4 that is approximately the same as the light intensity measured at time t2. In this case, if the downstream area detection system 311 is a focused detection system, the defect location information cannot be obtained from the burst foreign object detection unit 42, and it is unknown where the detected defect is located within region 202. Therefore, it is difficult to determine whether the power density irradiated to the defect increases or decreases relatively in the next cycle based on the amount of scattered light measured at time t4. Therefore, if the third embodiment is applied... Figure 11C In the case of a previous scenario, the measured light intensity at time t4 would be used to reduce the light intensity at time t5. However, in reality, at time t5, the power density of the illumination reaching the defect is reduced compared to time t4. Therefore, light intensity adjustment at time t5 is unnecessary and may even reduce the detection sensitivity of small defects.

[0114] In contrast, in this embodiment, by setting the rear area detection system 311 as an imaging detection system, the location information of the defect can be used in determining whether light intensity adjustment is needed in the explosive foreign object detection unit 42. In this case, the power density of the illumination at time t5 can be measured in real time relative to the actual illumination. Figure 11C In the example, the defect detected at time t4 is reduced, thus suppressing the unnecessary power reduction and sensitivity reduction mentioned above.

[0115] In this embodiment, the other structures, functions, and effects are the same as in the previously described embodiments.

[0116] <Variation Example>

[0117] This invention is not limited to the embodiments described above and can include various modifications. For example, the embodiments described above are detailed embodiments for the purpose of easily understanding and illustrating the invention, and are not limited to having all the structures described. A part of the structure of a certain embodiment can be replaced with the structure of another embodiment, and the structure of another embodiment can be added to the structure of a certain embodiment. In addition, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0118] The aforementioned structures, functions, processes, and processing units can be partially or entirely implemented using hardware such as integrated circuits. The aforementioned structures and functions can also be implemented in software by a processor interpreting and executing programs that implement each function. The programs, tables, files, and other information that implement each function can be stored on various storage media. Examples of various storage media include memory, hard disks, SSDs (Solid State Drives), flash memory cards, and DVDs (Digital Versatile Disks).

[0119] In various embodiments, the input and output lines of the signal represent the input and output lines that are considered necessary for the specification, but may not represent all input and output lines in the actual product. In fact, it can be considered that almost all the structures are interconnected.

[0120] Symbol Explanation

[0121] 20—Illumination point (beam point), 20a—Main illumination point (beam point), 20b—Secondary illumination point (beam point), 32—Tilt detection unit (first scattered light detection optical system), 101—Illumination unit, 201—Stage unit, 202—Region (first illumination region), 203—Region (second illumination region), 210—Sample surface displacement detection system, 301—Detection unit, 303—Vertical detection unit (second scattered light detection optical system), 311—Backward region detection system, 312—Forward region detection system, 401—Signal processing unit, 1011—Laser source (light source), 1015—Polarization voltage control unit (light intensity adjustment unit), 2031—Forward region, 2032—Backward region, 3028—Sensor (optical sensor), 3035—Sensor (optical sensor), 3039—Sensor (optical sensor), 3042—Sensor (optical sensor), 3043—Spatial filter.

Claims

1. A defect inspection device, characterized in that, have: The stage section holds the sample and moves it; The illumination section illuminates the sample with light emitted from the light source, forming a beam of light that scans on the sample. The detection unit detects the scattered light from the beam point and performs photoelectric conversion on the amount of scattered light; as well as The signal processing unit processes the electrical signal converted from photoelectric signal. The detection unit includes a first scattered light detection optical system and a second scattered light detection optical system that respectively detect scattered light from a first illumination region and a second illumination region in the beam point. The exposure time of the optical sensor included in the first scattered light detection optical system is longer than that of the optical sensor included in the second scattered light detection optical system.

2. The defect inspection device according to claim 1, characterized in that, The second illumination area includes a prior area that is scanned on the sample in time prior to the first illumination area.

3. The defect inspection device according to claim 2, characterized in that, The second scattered light detection optical system includes: a prior region detection system that detects scattered light from the prior region; and a subsequent region detection system that detects scattered light from the subsequent region, the subsequent region being scanned on the sample after the prior region in time.

4. The defect inspection device according to claim 3, characterized in that, The photon collection efficiency of the subsequent region detection system is set to be lower than that of the preceding region detection system.

5. The defect inspection device according to claim 3, characterized in that, It includes a light intensity adjustment unit that adjusts the light intensity from the light source.

6. The defect inspection device according to claim 5, characterized in that, When the second scattered light detection optical system detects particles of a size greater than or equal to a threshold in the second illumination area, the light intensity adjustment unit adjusts the power density of the first illumination area irradiated with the particles of the size greater than or equal to the threshold.

7. The defect inspection device according to claim 5, characterized in that, If the preceding region detection system detects particles with a size greater than or equal to a first threshold within the preceding region, the light intensity adjustment unit adjusts the power density of the following region and the first illumination region irradiated with the particles having a size greater than or equal to the first threshold. If a particle with a size of a second threshold or higher is detected in the rear area by the rear area detection system, the light intensity adjustment unit adjusts the power density of the first illumination area irradiated to the particle with a size of a second threshold or higher.

8. The defect inspection device according to claim 6, characterized in that, The beam points are multiple points, and the first illumination area and the second illumination area are areas with different beam points.

9. The defect inspection device according to claim 1, characterized in that, The first scattered light detection optical system is configured at an angle relative to the sample surface. The light-receiving surface of the optical sensor included in the first scattered light detection optical system is tilted relative to the optical axis in a manner conjugate with respect to the sample surface.

10. The defect inspection device according to claim 1, characterized in that, The light source is a pulsed oscillating laser.

11. The defect inspection device according to claim 10, characterized in that, The optical sensor included in the second scattered light detection optical system samples the light synchronously with the oscillation timing of the pulsed oscillating laser.

12. The defect inspection device according to claim 1, characterized in that, The first scattered light detection optical system is an imaging optical system. The second scattered light detection optical system is a focusing optical system.

13. The defect inspection device according to claim 1, characterized in that, The signal processing unit uses the defect location information obtained from the first scattered light detection optical system and the scattered light quantity signal obtained from the second scattered light detection optical system to calculate the size of the defect.

14. The defect inspection device according to claim 1, characterized in that, The second scattered light detection optical system includes a spatial filter that blocks the illumination light reflected orthogonally from the sample surface.

15. The defect inspection device according to claim 6, characterized in that, This includes a sample surface displacement detection system, which measures the displacement of the sample surface. The signal processing unit changes the threshold based on the measurement result of the sample surface displacement input from the sample surface displacement detection system.

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