Optical inspection device and optical inspection method

Abstract

Disclosed herein is an optical inspection device for inspecting a sample (101), the optical inspection device comprising: an illumination optical system (A) that has a light source, a light beam control mechanism, and a condensing optical unit, and irradiates the surface of a sample with a light beam emitted from the light source through the condensing optical unit; a specular reflection light observation unit (F) that monitors specular reflection light from the surface of the sample; and a control device that controls the illumination optical system on the basis of the specular reflection light. The specular reflection light observation unit has a first imaging element (F4a), a second imaging element (F4b), and a first light splitting element (F3) that splits specular reflection light and causes the light to be incident on each of the first imaging element and the second imaging element. On the basis of information about the position or size of a first light beam (1) received by the first imaging element and information about the position or size of a second light beam (2) received by the second imaging element, the control device independently controls, by means of the light beam control mechanism, at least one among a shift, a tilt, and a light condensing position of the light beam incident on the condensing optical unit.

Description

Optical inspection device and optical inspection method

[0001] The present disclosure relates to an optical inspection device and an optical inspection method.

[0002] In the semiconductor manufacturing process, inspection of semiconductor wafer surfaces for defects is carried out to maintain or improve product yield. As semiconductor processes become more miniaturized, there is a demand for detecting and managing minute defects (a few nanometers or larger) on semiconductor wafers.

[0003] Optical semiconductor inspection equipment detects defects by irradiating a semiconductor wafer with a laser beam and detecting light from defects present on the semiconductor wafer. Optical semiconductor inspection equipment is required to (1) be able to detect minute defects, (2) be able to measure the dimensions of detected defects with high accuracy, (3) be able to measure the positions of detected defects with high accuracy, and (4) be able to inspect a large number of wafers within a certain period of time (high throughput).

[0004] In order to detect smaller defects, it is necessary to increase the amount of light emitted from the defect. Methods for increasing the amount of light include shortening the wavelength of the laser light source, increasing its output, and reducing the laser irradiation area on the wafer. Shortening the wavelength of the laser light source has the effect of increasing the cross-sectional area of ​​the light emitted from the defect and increasing the amount of light emitted from the defect, while increasing the output of the laser light source and reducing the laser irradiation area both have the effect of increasing the amount of light irradiated on the defect and increasing the amount of light emitted from the defect.

[0005] To reduce the laser irradiation area on the wafer, the laser beam is focused on the wafer to form a light spot of several tens to several hundreds of microns. Because the amount of light from a defect is affected by the shape and light intensity of the light spot, stabilizing the shape and light intensity of the light spot is essential for highly accurate measurement of defect dimensions. Furthermore, the position of the defect is estimated from the timing at which the light is received by the detector. In other words, stabilizing the light spot position is essential for highly accurate measurement of defect position.

[0006] Patent Document 1 discloses a technique in which the position of illumination light is measured by beam monitors 22 and 23, and the position or angle of illumination light is adjusted by an output light adjustment unit 4 to return to a predetermined position or angle (see paragraphs 0026-0027 of Patent Document 1). Patent Document 1 also describes that "the height of the sample surface is measured, and if the height is deviated, the deviation is corrected by adjusting the height using the illumination intensity distribution control unit 7 or the Z axis of the stage 103" (see paragraph 0029 of Patent Document 1).

[0007] JP 2012-137350 A

[0008] Although Patent Document 1 describes a technique for correcting illumination light, further development of a technique for stabilizing the quality of a light spot is desired.

[0009] Therefore, the present disclosure provides a technique for stabilizing the light spot irradiated onto a sample in an optical inspection device.

[0010] In order to solve the above problems, the present disclosure provides an optical inspection device that inspects a sample based on light reflected or scattered from the surface of the sample, the optical inspection device comprising: an illumination optical system having a light source, a light beam control mechanism, and a focusing optical unit, and irradiating the surface of the sample with a light beam emitted from the light source through the focusing optical unit; a specular reflection light observation unit that monitors the specular reflection light from the surface of the sample; and a control device that controls the illumination optical system based on the specular reflection light monitored by the specular reflection light observation unit, wherein the specular reflection light observation unit has a first image sensor, a second image sensor, and a first light dividing element that divides the specular reflection light and causes it to enter each of the first image sensor and the second image sensor, and the control device is characterized in that the light beam control mechanism independently controls at least one of the shift, tilt, and focusing position of the light beam incident on the focusing optical unit based on information on the position or size of the first light beam received by the first image sensor and information on the position or size of the second light beam received by the second image sensor.

[0011] Further features related to the present disclosure will become apparent from the description of this specification and the accompanying drawings. Also, aspects of the present disclosure are achieved and realized by the elements and combinations of various elements and the aspects of the following detailed description and the appended claims. The description of this specification is merely exemplary and does not limit the scope or application of the claims of the present disclosure in any way.

[0012] According to the technique of the present disclosure, it is possible to stabilize the light spot irradiated onto the sample in the optical inspection device. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0013] FIG. 1 is a schematic diagram showing an example of the configuration of a defect inspection device according to a first embodiment. FIG. 1 is a schematic diagram showing a scanning trajectory of a sample by a scanning device. FIG. 2 is a schematic diagram showing another example of the scanning trajectory of a sample by a scanning device. FIG. 2 is a schematic diagram showing an example of the configuration of an attenuator. FIG. 3 is a schematic diagram showing an example of the configuration of an illumination light observation unit. FIG. 4 is a schematic diagram showing the positional relationship between the optical axis of illumination light guided to the surface of the sample and the illumination intensity distribution shape. FIG. 3 is a schematic diagram showing an example of the configuration of a specular reflection light observation unit. FIG. 4 is a diagram for explaining the reason for providing an illumination light observation unit. FIG. 5 is a diagram for explaining the reason for providing an illumination light observation unit. FIG. 5 is a diagram for explaining an example of a correction flow of illumination light. FIG. 6 is a diagram for explaining a specular reflection light observation unit. FIG. 6 is a diagram for explaining a specular reflection light observation unit. FIG. 7 is a diagram for explaining a correction flow of light incident on a focusing optical unit. FIG. 7 is a diagram for explaining an example of a correction flow of a beam position during wafer inspection. FIG. 8 is a schematic diagram for explaining the configuration of a defect inspection device according to a second embodiment. FIG. 8 is a diagram for explaining an example of a correction flow of light incident on a focusing optical unit according to the second embodiment.

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, a case will be described in which the technology of the present disclosure is applied to a defect inspection device used in the manufacturing process of semiconductors, etc. Use of the defect inspection device can achieve (1) detection of minute defects, (2) high-precision measurement of detected defects, (3) high-precision measurement of defect positions, and (4) high-throughput inspection.

[0015] [First Embodiment] <Configuration Example of Defect Inspection Apparatus> Fig. 1 is a schematic diagram showing a configuration example of a defect inspection apparatus 100 (optical inspection apparatus) according to a first embodiment. As shown in Fig. 1, an XYZ Cartesian coordinate system is defined in which the vertical direction is the Z axis and the X and Y axes are horizontal directions. The defect inspection apparatus 100 inspects a sample 101 and is configured to detect defects such as film formation abnormalities and foreign matter adhesion on the surface of the sample 101. The defect inspection apparatus 100 employs a rotational scanning method in which the sample 101 is scanned by rotating it in a circumferential direction (θ direction) while moving it in a radial direction (R direction).

[0016] The defect inspection apparatus 100 can also inspect semiconductor silicon wafers (substrates) without patterns formed thereon. Alternatively, the defect inspection apparatus 100 may be an apparatus for inspecting patterned wafers in which dies are arranged in the XY direction (in a matrix) on the surface of a substrate. Fine circuit patterns (microstructures) are densely formed on each die. The unit of exposure used to form these dies is called a shot. If exposure is performed on a die-by-die basis in the manufacturing process of the sample 101, the die and the shot are essentially the same area, but multiple dies may be included in the same shot. If multiple dies are included in the same shot, all dies within the shot may have the same pattern, or the dies included in the same shot may have different patterns.

[0017] The defect inspection apparatus 100 includes a stage ST, an illumination optical system A, multiple detection optical systems B1 to Bn (n=1, 2, ...), sensors C1 to Cn (n=1, 2, ...), a signal processing device D, a memory device DB, a control device E1, an input device E2, a monitor E3, and a specular reflection light observation unit F.

[0018] -Stage- The stage ST has a sample stage ST1 and a scanning device ST2. The sample stage ST1 is a stage that supports the sample 101. The scanning device ST2 is a device that drives the sample stage ST1 to change the relative position of the sample 101 and the illumination optical system A. Although not shown, the scanning device ST2 has a translation stage, a rotation stage, and a Z stage. The rotation stage is mounted on the translation stage via the Z stage, and the sample stage ST1 is supported on the rotation stage. The translation stage translates horizontally together with the rotation stage. The rotation stage rotates (spins) around a rotation axis that extends vertically. The Z stage functions to adjust the height of the surface of the sample 101.

[0019] FIG. 2 is a schematic diagram showing the scanning trajectory of the sample 101 by the scanning device ST2. As will be described later, the light spot BS, which is the incident area of ​​the illumination light emitted from the illumination optical system A on the surface of the sample 101, is a tiny point and has an illumination intensity distribution that is long in one direction as shown in FIG. 2. The long axis direction of the light spot BS is denoted by s2, and the short axis direction perpendicular to the long axis is denoted by s1. The sample 101 rotates with the rotation of the rotary stage, and the light spot BS scans in the s1 direction relative to the surface of the sample 101. The sample 101 moves horizontally with the translation of the translation stage, and the light spot BS scans in the s2 direction relative to the surface of the sample 101. As the scanning device ST2 operates in this manner, the sample 101 translates while rotating, and as shown in FIG. 2, the light spot BS moves in a spiral trajectory from the center of the sample 101 to the outer edge, scanning the entire surface of the sample 101. The light spot BS moves in the s2 direction by a distance equal to or less than the length of the light spot BS in the s2 direction while the sample 101 makes one rotation.

[0020] FIG. 3 is a schematic diagram showing another example of the scanning trajectory of the sample 101 by the scanning device ST2. Scanning devices generally include a second translation stage, whose movement axis extends in a direction intersecting the movement axis of the translation stage in a horizontal plane, instead of the rotational stage. In this case, as shown in FIG. 3, the light spot BS scans the surface of the sample 101 along a linear trajectory rather than a spiral trajectory. Specifically, the first translation stage is driven in translation at a constant speed in the s1 direction, the second translation stage is driven in the s2 direction a predetermined distance (e.g., a distance equal to or less than the length of the light spot BS in the s2 direction), and then the first translation stage is driven in translation again in the s1 direction. This causes the light spot BS to repeatedly linearly scan in the s1 direction and move in the s2 direction to scan the entire surface of the sample 101. Compared to the XY scanning method shown in FIG. 3, the rotational scanning method of this embodiment shown in FIG. 2 does not involve repeated reciprocating acceleration and deceleration, thereby shortening the inspection time of the sample 101.

[0021] - Illumination optical system - Returning to the explanation of Figure 1, the illumination optical system A has a group of optical elements for irradiating desired illumination light onto a sample 101 placed on a sample stage ST1. As shown in Figure 1, the illumination optical system A includes a laser light source A1, an attenuator A2 (light beam control mechanism), an emitted light adjustment unit A3 (light beam control mechanism), a beam shaping unit A4 (light beam control mechanism), a polarization control unit A5 (light beam control mechanism), an illumination light observation unit A6, a focusing optical unit A7, a reflecting mirror A8, a reflecting mirror A9 (light beam control mechanism), a reflecting mirror A10, etc.

[0022] Laser Light Source The laser light source A1 is a unit that emits a laser beam as illumination light. When the defect inspection device 100 is used to detect minute defects near the surface of the sample 101, the laser light source A1 is one that emits a high-power (output of 2 W or more) ultraviolet or vacuum ultraviolet laser beam with a short wavelength (wavelength of 355 nm or less) that does not easily penetrate into the interior of the sample 101. The diameter of the laser beam emitted by the laser light source A1 is typically about 1 mm. When the defect inspection device 100 is used to detect defects inside the sample 101, the laser light source A1 is one that emits a visible or infrared laser beam with a long wavelength that easily penetrates into the interior of the sample 101.

[0023] Attenuator FIG. 4 is a schematic diagram showing an example of the configuration of the attenuator A2. The attenuator A2 is a unit that attenuates the light intensity of the illumination light from the laser light source A1. As an example, the attenuator A2 of this embodiment has a configuration that combines a first polarizing plate A2a, a half-wave plate A2b, and a second polarizing plate A2c. The half-wave plate A2b is configured to be rotatable around the optical axis of the illumination light. The illumination light incident on the attenuator A2 is converted into linearly polarized light by the first polarizing plate A2a, and then the polarization direction is adjusted to the slow axis azimuth angle of the half-wave plate A2b before passing through the second polarizing plate A2c. By adjusting the azimuth angle of the half-wave plate A2b, the light intensity of the illumination light is attenuated at a desired ratio. Although not shown, a mechanism for adjusting the azimuth angle of the half-wave plate A2b is provided, and its drive is controlled by the control device E1. If the degree of linear polarization of the illumination light incident on the attenuator A2 is sufficiently high, the first polarizing plate A2a can be omitted. The attenuator A2 is one in which the relationship between the incident illumination light and the light attenuation rate has been calibrated in advance. The attenuator A2 is not limited to the configuration illustrated in FIG. 4 . For example, the attenuator A2 can also be configured using an ND filter with a gradation density distribution. Alternatively, the attenuator A2 can be configured so that the attenuation effect can be adjusted by combining multiple ND filters with different densities.

[0024] Emitted Light Adjustment Unit Returning to the explanation of FIG. 1 , the emitted light adjustment unit A3 adjusts the position and angle of the optical axis of the illumination light attenuated by the attenuator A2. The emitted light adjustment unit A3 of this embodiment has multiple reflecting mirrors A3a and A3b. The reflecting mirrors A3a and A3b sequentially reflect the illumination light. In this embodiment, the incident and exit surfaces of the illumination light relative to the reflecting mirror A3a are configured to be perpendicular to the incident and exit surfaces of the illumination light relative to the reflecting mirror A3b. The incident and exit surfaces are surfaces that include the optical axis of the light incident on the reflecting mirror A3a and the optical axis of the light emitted from the reflecting mirror. When the illumination light is configured to be incident on the reflecting mirror A3a in the +X direction, which is different from the schematic diagram of FIG. 1 , for example, the illumination light travels in the +Y direction by the reflecting mirror A3a and then changes its direction of travel to the +Z direction by the reflecting mirror A3b. In this example, the incident and exit planes of illumination light relative to the reflecting mirror A3a are set to the XY plane, and the incident and exit planes of illumination light relative to the reflecting mirror A3b are set to the YZ plane.

[0025] Although not shown, the reflecting mirrors A3a and A3b are provided with mechanisms for translating and tilting the reflecting mirrors A3a and A3b, respectively (four-axis configuration). As such translational movement mechanisms (shift mechanisms) and tilt mechanisms, the emitted light adjustment unit A3 includes stages on which the reflecting mirrors A3a and A3b are mounted, and motors or actuators for driving the stages. The driving of these translational movement mechanisms and tilt mechanisms is controlled by the control device E1. With this configuration, the reflecting mirrors A3a and A3b, for example, translate in the incident or exit direction of the illumination light relative to themselves and tilt around the normal to the incident and exit surfaces. This allows, for example, the offset amount and angle in the XZ plane and the offset amount and angle in the YZ plane of the optical axis of the illumination light emitted from the emitted light adjustment unit A3 in the +Z direction to be independently adjusted. While a configuration using two reflecting mirrors A3a and A3b has been illustrated, a configuration using three or more reflecting mirrors may also be used.

[0026] Beam Shaping Unit The beam shaping unit A4 is a unit that arbitrarily enlarges or reduces the size of the incident illumination light. The beam shaping unit A4 is configured by, for example, a beam expander, a cylindrical lens, an anamorphic prism, or a combination thereof.

[0027] An example of a beam expander is a Galilean type using concave and convex lenses. Although not shown, the beam expander is provided with a lens spacing adjustment mechanism (zoom mechanism), and adjusting the lens spacing changes the expansion ratio of the beam diameter. The zoom mechanism includes, for example, rails on which the lenses are mounted and a motor that drives the rails. The drive of the zoom mechanism motor is controlled by a control device E1. The expansion ratio of the beam diameter by the beam expander is, for example, approximately 5 to 10 times. In this case, if the beam diameter of the illumination light emitted from the laser light source A1 is 1 mm, the beam diameter of the illumination light is expanded to approximately 5 to 10 mm. If the illumination light incident on the beam expander is not a parallel beam, collimation (quasi-parallelization of the beam) along with the beam diameter can be achieved by adjusting the lens spacing. However, the collimation of the beam may also be achieved using a collimating lens installed upstream of the beam expander separately from the beam expander.

[0028] The beam expander is installed on a translation stage with two or more axes (two degrees of freedom), which allows its position to be adjusted so that its center coincides with the incident illumination light.The beam expander also has a tilt angle adjustment function with two or more axes (two degrees of freedom) so that the incident illumination light coincides with its optical axis.The translation stage of the beam expander is controlled by a control device E1.

[0029] When using cylindrical lenses, one example is to use two cylindrical lenses with different focusing distances. A cylindrical lens has the effect of focusing light only along one axis perpendicular to the optical axis. Therefore, by using two cylindrical lenses with different focusing distances, it is possible to change the size only in any axis direction perpendicular to the incident optical axis, thereby forming an elliptical illumination light shape. Similarly to cylindrical lenses, anamorphic prisms can also change the size only in any axis direction perpendicular to the incident optical axis. By combining these lenses, it is possible to form any shape of illumination light.

[0030] Polarization Control Unit The polarization control unit A5 is an optical system that controls the polarization state of the illumination light. The polarization control unit A5 has a half-wave plate A5a and a quarter-wave plate A5b. For example, by using the polarization control unit A5 to polarize the illumination light as P-polarized light, the amount of scattered light from defects on the surface of the sample 101 can be increased compared to light polarized other than P-polarized light. If scattered light (called haze) from minute irregularities on the surface of the sample 101 interferes with the detection of minute defects, using S-polarized light to polarize the illumination light can reduce the haze compared to light polarized other than S-polarized light. The polarization control unit A5 can also circularly polarize the illumination light or polarize it at 45 degrees, which is intermediate between P-polarized and S-polarized light.

[0031] Illumination Light Observation Unit Figure 5 is a schematic diagram showing an example configuration of the illumination light observation unit A6. The illumination light observation unit A6 has a beam sampler A6a, a half mirror A6b, and two image sensors A6c and A6d (a third image sensor and a fourth image sensor). The illumination light emitted from the polarization control unit A5 is sampled by the beam sampler A6a, and the sampled light is split by the half mirror A6b. The split light each travels a different optical path length and is captured by the image sensors A6c and A6d.

[0032] The beam sampler A6a is used to guide (sample) a given amount of light to the illumination light observation unit A6. The beam sampler may be an optical element having a function of splitting light, such as a beam splitter, a polarizing beam splitter, or a pellicle beam splitter. The sampled light is split into two by a half mirror. The half mirror may be any optical element having a function of splitting light, such as a beam splitter, a polarizing beam splitter, or a pellicle beam splitter.

[0033] The split light beams travel different optical path lengths and are captured by the image sensors A6c and A6d. More specifically, when the optical path length from the half mirror A6b to the image sensor A6c is L1 and the optical path length from the half mirror A6b to the image sensor A6d is L2, the relationship L1<L2 is established. The reason for providing the illumination light observation unit A6 will be described later. The image sensors A6c and A6d have the function of capturing one-dimensional or two-dimensional images of light. One example is a high-speed, high-sensitivity camera equipped with a solid-state image sensor such as a CCD, CMOS, or SPAD (Single Photon Avalanche Diode). The captured image data from the image sensors A6c and A6d is input to the signal processing device D.

[0034] Regarding oblique incidence illumination: Figure 6 is a schematic diagram showing the positional relationship between the optical axis of illumination light guided to the surface of sample 101 by illumination optical system A and the illumination intensity distribution shape. Figure 6 shows a schematic cross section of sample 101 cut at the plane of incidence of illumination light incident on sample 101. The plane of incidence is a plane that includes the optical axis OA of the illumination light incident on sample 101 and the normal to the surface of sample 101. Note that Figure 6 shows only a portion of illumination optical system A, and for example, the output light adjustment unit A3, reflecting mirrors A8 to A10, and illumination light observation unit A6 are not shown.

[0035] The illumination light emitted from the laser light source A1 is focused by the focusing optical unit A7, reflected by the reflecting mirror A10, and obliquely incident on the sample 101. In this way, the illumination optical system A is configured to direct illumination light obliquely onto the surface of the sample 101. The light intensity of this oblique incidence illumination is adjusted by the attenuator A2, the illumination light shape is adjusted by the beam shaping unit A4, and the polarization is adjusted by the polarization control unit A5, thereby controlling the illumination intensity distribution within the incident plane. As shown in the illumination intensity distribution LD1 (illumination profile) in Figure 6, the light spot formed on the sample 101 has a Gaussian light intensity distribution in the s2 direction, and the length of the beam width l1, defined at 13.5% of the peak, is, for example, approximately 25 μm to 4 mm.

[0036] Furthermore, the angle of incidence of the oblique incidence illumination on the sample 101 (the tilt angle of the incident optical axis relative to the normal to the sample surface) is adjusted to an angle suitable for detecting minute defects by adjusting the positions and angles of the reflecting mirrors A9 and A10. The reflecting mirror A9 has two reflecting mirrors A9a and A9b and a mechanism (not shown) for adjusting these angles (a four-axis configuration). The angle of the reflecting mirror A10 is adjusted by the adjustment mechanism A10a. For example, the larger the angle of incidence of the illumination light on the sample 101 (the smaller the illumination elevation angle between the sample surface and the incident optical axis), the weaker the scattered light (haze) from minute irregularities and patterns on the sample surface, which becomes noise in the scattered light from minute defects on the sample surface. From the viewpoint of suppressing the effect of haze on the detection of minute defects, the incident angle of the illumination light can be set, for example, to 75 degrees or more (elevation angle 15 degrees or less). On the other hand, with oblique incidence illumination, the smaller the illumination incidence angle, the greater the absolute amount of scattered light from minute foreign particles. Therefore, from the perspective of increasing the amount of scattered light from defects, the incidence angle of the illumination light can be set to, for example, 60 degrees or more and 75 degrees or less (elevation angle 15 degrees or more and 30 degrees or less).

[0037] --Detection optical system-- Returning to the explanation of Figure 1, the detection optical systems B1 to Bn (n = 1, 2, ...) are units that collect illumination scattered light from the sample surface. The detection optical systems B1 to Bn have multiple optical elements including a collecting lens (objective lens). The "n" in the detection optical system Bn represents the number of detection optical systems. Three detection optical systems B1 to B3 are shown in Figure 1. However, the number of detection optical systems B1 to Bn is not limited to a specific number, and may be one or more.

[0038] -Sensors- Sensors C1 to Cn (n = 1, 2, ...) are sensors that convert the illumination scattered light collected by the corresponding detection optical systems B1 to Bn into electrical signals and output detection signals. Sensors C1, C2, C3, ... correspond to the detection optical systems B1, B2, B3, ..., respectively. These sensors C1 to Cn can be single-pixel point sensors such as photomultiplier tubes and SiPM (silicon photomultiplier tubes), which perform photoelectric conversion of weak signals with high gain. In addition, sensors with multiple pixels arranged one-dimensionally or two-dimensionally, such as CCD sensors or CMOS sensors, can also be used for sensors C1 to Cn. The detection signals output from sensors C1 to Cn are input to signal processing device D as needed.

[0039] -Control Device- The control device E1 is a computer that controls the defect inspection device 100. The control device E1 has a storage device including at least one of ROM, RAM, HDD, or SSD, an arithmetic processing device such as a CPU, GPU, or FPGA, a timer, etc. The control device E1 is connected to the input device E2, the monitor E3, and the signal processing device D by wire or wirelessly. The input device E2 is a device through which a user inputs settings such as inspection conditions into the control device E1. As the input device E2, various input devices such as a keyboard, a mouse, or a touch panel can be appropriately adopted.

[0040] The control device E1 receives inputs such as the output of the encoders of the rotation stage and translation stage (the rθ coordinate of the light spot BS on the sample 101) and inspection conditions entered by the user via the input device E2. The inspection conditions include the type, size, shape, or material of the sample 101, the illumination conditions of the illumination optical system A, and the detection conditions of the detection optical system B and sensor C. Other inspection conditions include, for example, the sensitivity settings of each sensor C1 to Cn, the gain values ​​and thresholds used for defect determination, and the determination area settings (such as the central angle α). When scanning the sample 101 using a rotational scanning method, differences arise in the detection channels depending on the θ coordinate on the sample, as described below. Gain values, threshold values, and the like can be set according to the θ coordinate or intra-die coordinates, taking this θ coordinate dependency into account. The detection channel typically refers to the output signal of the sensors C1 to Cn, but it can also include a subset of the output signals of these sensors C1 to Cn, or a signal obtained by weighting and adding the output signals or subsets of the sensors C1 to Cn. When the gain value and threshold value are set according to the θ coordinate or the coordinate within the die, the gain value and threshold value for each detection channel change with the rotation period of the sample 101 .

[0041] The control device E1 also outputs command signals to command the operation of the stage ST, the illumination optical system A, etc. in accordance with the inspection conditions, and outputs coordinate data of the light spot BS synchronized with the defect detection signal to the signal processing device D. The control device E1 also displays an inspection condition setting screen, inspection data (inspection image, etc.) of the sample 101, etc. on the monitor E3. As inspection data, in addition to the final inspection result obtained by integrating the signals from each of the sensors C1 to Cn, individual inspection results from these sensors C1 to Cn can also be displayed. The inspection condition setting screen can display a setting section for setting the above-mentioned gain value, threshold value, etc. in accordance with the θ coordinate for each detection channel.

[0042] 1, a DR-SEM (Defect Review-Scanning Electron Microscope), which is an electron microscope for defect inspection, may be connected to the control device E1 via a LAN or other means. In this case, it is also possible for the control device E1 to receive data on the defect inspection results from the DR-SEM and transmit the data to the signal processing device D.

[0043] -Signal Processing Device- The signal processing device D is a computer that processes the detection signals input from the sensors C1 to Cn. Like the control device E1, the signal processing device D has a storage device including at least one of ROM, RAM, HDD, or SSD, and an arithmetic processing device such as a CPU, GPU, or FPGA. The signal processing device D can be configured as a single computer that forms a unit with the main body of the defect inspection device 100 (stage ST, illumination optical system A, specular reflection light observation unit F, detection optical systems B1 to Bn, sensors C1 to Cn, etc.). The signal processing device D can also be configured as multiple computers connected to the defect inspection device 100 via a network. For example, a configuration can be adopted in which a computer attached to the main body of the defect inspection device 100 acquires defect detection signals from the device main body, processes the detection data as necessary, and transmits it to a server, where defect detection, classification, and other processing are performed.

[0044] -Specular Reflection Light Observation Unit- Figure 7 is a schematic diagram showing an example configuration of the specular reflection light observation unit F. The specular reflection light observation unit F has a collimator lens F1, an attenuator F2, a half mirror F3, two image sensors F4a and F4b (first and second image sensors), and a condenser lens F5. Light focused on the surface of the sample 101 by the illumination optical system A is reflected from the surface of the sample 101 and enters the specular reflection light observation unit F. The light reflected and diverged from the surface of the sample 101 is collimated by the collimator lens F1. This collimated light then passes through the attenuator F2 and is split into two (light 1 and light 2) by the half mirror F3. The split light 1 (first light beam) is imaged by the image sensor F4a as a parallel light. Meanwhile, the split light 2 (second light beam) is focused by the condenser lens F5 and imaged by the image sensor F4b.

[0045] The collimating lens F1 is used to convert the specularly reflected light diverging from the sample 101 into parallel light and guide it to the image sensors F4a and F4b. Instead of a collimating lens, an optical element capable of generating parallel light, such as a cylindrical lens or a parabolic mirror, may be used. The amount of transmitted parallel light is adjusted by the attenuator F2. This is to adjust the brightness when capturing images with the image sensors F4a and F4b. In an optical inspection device, the amount of light incident on the surface of the sample 101 varies depending on the size of the defect to be inspected. Therefore, the amount of light transmitted through the attenuator F2 is appropriately adjusted taking into account the amount of light incident on the surface of the sample 101 and the dynamic range of the image sensor. Since the attenuator F2 needs to have variable transmittance depending on the amount of light incident on the surface of the sample 101, an ND filter with gradation may be used in addition to the attenuator.

[0046] The half mirror F3 is used to split the specularly reflected light into two light beams that are incident on the image pickup elements F4a and F4b, respectively. Here, the half mirror F3 may be any optical element that has a function of splitting light, such as a beam splitter, a polarizing beam splitter, or a pellicle beam splitter.

[0047] The image sensors F4a and F4b have the function of capturing one-dimensional or two-dimensional images of light. Examples include high-speed, high-sensitivity cameras equipped with solid-state image sensors such as CCDs, CMOSs, and SPADs (Single Photon Avalanche Diodes). While the present embodiment has been described with reference to a camera having two image sensors, the number of image sensors may be more than two.

[0048] <Reason for Providing an Illumination Light Observation Unit> Figures 8A and 8B are diagrams for explaining the reason for providing an illumination light observation unit A6. As described above, illumination light sampled from the illumination optical system A by the beam sampler A6a is split by the half mirror A6b. At this time, the light that has passed through the short optical path (optical path length L1) is imaged by the image sensor A6c, and the light that has passed through the long optical path (optical path length L2) is imaged by the image sensor A6d. Figure 8A shows a reference state in which the optical axis and beam size are adjusted according to the adjustment specifications. In this reference state, the luminance distribution when imaged by the image sensor A6c is Im1, and the luminance distribution when imaged by the image sensor A6d is Im2. At this time, the beam position (near point beam position) of the luminance distribution Im1 is X1, and the beam size is d1. The beam position (far point beam position) of the luminance distribution Im2 is X2, and the beam size is d2.

[0049] 8B shows a state in which at least one of the optical axis and the beam size has changed from the reference state. In this state, the luminance distribution when imaged by the image sensor A6c is Im3, and the luminance distribution when imaged by the image sensor A6d is Im4. In this case, the beam position (near point beam position) of the luminance distribution Im3 is X3, and the beam size is d3. The beam position (far point beam position) of the luminance distribution Im4 is X4, and the beam size is d4. Note that although the luminance distribution will be described as one-dimensional, it can be considered equally well in two dimensions.

[0050] In this case, the amount of optical axis tilt T in the changed state with respect to the reference state is calculated as T = arctan(((X4 - X3) - (X2 - X1)) / (L2 - L1)). The amount of optical axis shift S in the changed state with respect to the reference state is calculated as S = (X4 - X2) - L2 sin(T) = (X3 - X1) - L1 sin(T). The amount of change θ in the divergence angle of the beam in the changed state with respect to the reference state is calculated as θ = arctan(((d4 - d3) - (d2 - d1)) / (2 * (L2 - L1))). The amount of change M in the magnification of the beam in the changed state with respect to the reference state is calculated as M = (d4 - d2) / 2 - L2 sin(θ) = (d3 - d1) / 2 - L1 sin(θ). Furthermore, since the sum of the luminance of the image obtained by the image sensor A6c or A6d is proportional to the power of the illumination light, if the sum of the luminance of the luminance distribution Im1 is IS1 and the sum of the luminance of Im3 is IS2, the amount of change W in the beam power from the reference state to the changed state can be calculated as W = IS2 / IS1. These calculations can be performed by the signal processing device D.

[0051] In this way, by providing the illumination light observation unit A6, it is possible to obtain the amount of optical axis shift, amount of tilt, amount of change in divergence angle, amount of change in magnification, and amount of change in power from the reference state of the illumination optical system A. Using this information, it is possible to correct the illumination light.

[0052] 9 is a diagram illustrating an example of a flow of correcting illumination light. In step S11, the control device E1 determines whether the total luminance is within a prescribed range (adjustment specifications). If the answer is No, the process proceeds to step S12. If the answer is Yes, the process proceeds to step S13. In step S12, the control device E1 controls the attenuator A2 based on information on the beam power change amount W obtained from the signal processing device D, and corrects the power of the illumination light.

[0053] In step S13, the control device E1 determines whether the beam position is within a specified range (adjustment specifications). If the answer is No, the process proceeds to step S14. If the answer is Yes, the process proceeds to step S15. In step S14, the control device E1 controls the emitted light adjustment unit A3 based on the optical axis tilt amount T to correct the tilt amount of the illumination light. The control device E1 also controls the emitted light adjustment unit A3 based on the optical axis shift amount S to correct the shift amount of the illumination light. This corrects the basic optical axis of the illumination light. Alternatively, the tilt amount and shift amount of the emitted light adjustment unit A3 can be adjusted based on the optical axis shift amount at the near point beam position and the optical axis tilt amount at the far point beam position.

[0054] In step S15, the control device E1 determines whether the beam size is within the specified range (adjustment specifications). If the answer is No, the process proceeds to step S16. If the answer is Yes, the process proceeds to step S17. In step S16, the control device E1 controls the lens spacing adjustment mechanism of the beam shaping unit A4 (beam expander) based on the magnification change amount M to correct the beam size of the illumination light.

[0055] In step S17, the control device E1 determines whether the beam size ratio (divergence angle change amount) is within the specified range (adjustment specifications). If the answer is No, the process proceeds to step S18. If the answer is Yes, the illumination light adjustment process ends. In step S18, the control device E1 controls the beam shaping unit A4 (beam expander) based on the divergence angle change amount θ to correct the divergence angle (collimation) of the illumination light. Since correcting the divergence angle also changes the size of the illumination light, it is necessary to correct the size of the illumination light again after correcting the divergence angle. Therefore, after performing step S18, the process of step S16 is performed again.

[0056] If the predetermined adjustment specifications are not achieved even after the above-described series of corrections are performed, the control device E1 determines that the device status is abnormal and outputs an error to the monitor E3. This makes it possible to prompt the user of the defect inspection device 100 to perform maintenance on the device. Note that the timing of performing the power adjustments in steps S11 and S12 can be changed as desired within the flow of FIG. 9.

[0057] In this way, by providing the illumination light observation unit A6, the optical axis shift, tilt, size, divergence angle, and power of the illumination light can be efficiently corrected, contributing to stabilization of the illumination light. In particular, the correction of shift and tilt aligns the optical axis of the illumination light entering the beam shaping unit A4 with the optical axis of the expander, etc., thereby achieving the effect of suppressing aberrations.

[0058] <Reason for Providing a Specular Reflection Observation Unit> The reason for providing the specular reflection observation unit F will be explained. As described above, light transmitted through the focusing optical unit A7 is reflected by the surface of the sample 101 and enters the specular reflection observation unit F. The focusing optical unit A7 includes a lens, a parabolic mirror, a cylindrical lens, and a drive mechanism for these. In an optical inspection device, a light spot of several tens to several hundreds of micrometers is formed on the surface of the sample 101, so the shape and position of the light spot have a significant impact on the inspection results. When the axis of the focusing optical unit A7 does not coincide with the incident optical axis of the illumination light, aberration occurs, which changes the shape and position of the light spot. Furthermore, when the illumination light enters an optical element and transmits or reflects, processing errors and adjustment errors in the optical element itself cause an increase in wavefront aberration that is not intended in the design. Increasing wavefront aberration deteriorates the focusing performance of the illumination light, resulting in an increase in the size and deformation of the light spot. Therefore, in this embodiment, the specular reflection observation unit F is used to stabilize the light focused on the surface of the sample 101. In addition, the reasons for performing correction using the specular reflection light observation unit F separately from correction of the illumination optical system A using the illumination light observation unit A6 are (1) to align the optical axis of the light incident on the focusing optical unit A7 with the axis of the focusing optical unit A7 and suppress aberrations, and (2) to correct thermal expansion of the optical system and its holding parts due to internal thermal fluctuations, or optical axis fluctuations after the illumination light observation unit A6 due to mechanical vibrations.

[0059] 10A to 10C are diagrams for explaining the specular reflection light observation unit F. The specular reflection light observation unit F has an imaging optical system. For example, the focal length of the focusing optical unit A7 is assumed to be f1. The focal length of the collimating lens F1 is assumed to be f2. The focal length of the focusing lens F5 is assumed to be f3. In this case, the distance from the focusing optical unit A7 to the collimating lens F1 is assumed to be f1+f2. The distance from the collimating lens F1 to the focusing lens F5 is assumed to be f2+f3. The distance from the focusing lens F5 to the image sensor F4b is assumed to be f3. However, the distance between the lenses varies slightly depending on the refractive index of the optical elements inside the specular reflection light observation unit F, such as the attenuator F2. Furthermore, the distance from the collimating lens F1 to the image sensor F4a may be any value.

[0060] 10A shows a case where the optical axis OA of the light incident on the condenser lens F5 is shifted. In this case, the position of the image on the image sensor F4b (the condensed beam position) remains unchanged, while only the position of the image on the image sensor F4a (the parallel beam position) changes. Therefore, the signal processing device D calculates the shift amount of the light before it enters the condenser lens F5 based on the position of the image on the image sensor F4a.

[0061] 10B shows a case where the optical axis OA of the light incident on the condenser lens F5 is tilted. In this case, the position of the image on the image sensor F4a and the position of the image on the image sensor F4b change, so the amount of tilt is calculated.

[0062] 10C shows a case where the focusing optical unit A7 is displaced in the optical axis direction. In this case, the focusing point is displaced from the surface of the sample 101, and the size of the image on the image sensor F4a (short-axis beam size) and the size of the image on the image sensor F4b (long-axis beam size) change, and the amount of focus position displacement is calculated based on this.

[0063] In this way, by providing the specular reflection light observation unit F, it is possible to obtain the amount of optical axis shift, amount of optical axis tilt, and amount of light focusing position deviation of the light before it enters the focusing optical unit A7. By using this information, it is possible to correct the light that enters the focusing optical unit A7.

[0064] 11 is a diagram illustrating an example of a correction flow for light incident on the focusing optical unit A7. In step S21, the control device E1 determines whether the beam position is within a specified range (adjustment specifications). If the answer is No, the process proceeds to step S22. If the answer is Yes, the process proceeds to step S23. In step S22, the control device E1 controls the reflecting mirror A9 based on the tilt amount acquired from the signal processing device D to correct the tilt. The control device E1 also controls the reflecting mirror A9 based on the shift amount to correct the shift.

[0065] In step S23, the control device E1 determines whether the beam size is within a specified range (adjustment specifications). If the answer is No, the process proceeds to step S24. If the answer is Yes, the correction process ends. In step S24, the control device E1 controls at least one of the parabolic mirror or the cylindrical lens of the focusing optical unit A7 (at least one of the drive mechanisms for these) based on the amount of focus position deviation, and corrects the focus position.

[0066] In this way, by providing the specular reflection light observation unit F, it is possible to correct the tilt, shift, and focusing position deviation of the light incident on the focusing optical unit A7. As a result, this contributes to stabilizing the light spot formed on the surface of the sample 101. Furthermore, the specular reflection light observation unit F has the advantage of being able to observe the specular reflection light during the inspection of the silicon wafer, allowing correction during the inspection.

[0067] FIG. 12 is a diagram illustrating an example of a flow of beam position correction during wafer inspection. Wafer inspection is performed, for example, after the above-described correction of the basic optical axis of the illumination light and correction of the light incident on the focusing optical unit A7. After wafer inspection begins, in step S31, the control device E1 determines whether the beam position is within a specified (adjustment specification) range. If the answer is No, the process proceeds to step S32. If the answer is Yes, the correction process ends. In step S32, the control device E1 controls the reflecting mirror A9 based on the focused beam position acquired from the signal processing device D to correct the tilt. Note that while only tilt correction during inspection has been illustrated, shift correction or correction of the focused position deviation amount can also be performed in addition to or instead of the above.

[0068] Summary of First Embodiment As described above, the defect inspection apparatus 100 according to the first embodiment includes an illumination optical system A that irradiates the surface of the sample 101 with illumination light (light beam) emitted from a laser light source A1 through a focusing optical unit A7, a specular reflection light observation unit F that monitors light specularly reflected from the surface of the sample 101, and a control device E1 that controls the illumination optical system A based on the monitored specular reflection light. The illumination optical system A includes a laser light source A1, an attenuator A2 (light beam control mechanism), an emitted light adjustment unit A3 (light beam control mechanism), a beam shaping unit A4 (light beam control mechanism), a polarization control unit A5 (light beam control mechanism), a reflecting mirror A9 (light beam control mechanism), and a focusing optical unit A7. The specular reflection light observation unit F includes an image sensor F4a (first image sensor), an image sensor F4b (second image sensor), and a half mirror F3 (first light dividing element) that divides the specular reflection light into a first light beam and a second light beam and causes the first and second light beams to enter the image sensors F4a and F4b, respectively. The control device E1 independently controls at least one of the shift, tilt, and focusing position of the light beam incident on the focusing optical unit A7 using the reflecting mirror A9 or the focusing optical unit A7 (light beam control mechanism) based on information on the position or size (parallel beam position, short-axis beam size) of light 1 (first light beam) received by the image sensor F4a and information on the position or size (focused beam position, long-axis beam size) of light 2 (second light beam) received by the image sensor F4b.

[0069] This stabilizes the quality of the position, size, intensity, and other aspects of the light spot formed on the surface of the sample 101. As a result, the defect detection sensitivity and coordinate accuracy of the detected defects of the defect inspection device 100 can be stabilized. For example, as in Patent Document 1, when observing a light spot using an observation optical system installed perpendicular to the wafer surface, the laser light of the light spot needs to be scattered perpendicular to the wafer surface. Since silicon wafers used in semiconductor manufacturing processes scatter only a small amount of light perpendicular to the wafer surface, a separate wafer with a specially designed material and surface roughness must be used for observation. In contrast, the defect inspection device 100 of this embodiment uses specularly reflected light, eliminating the need to prepare a separate wafer for observing the light spot and the need to transport such a separate wafer. Therefore, the inspection throughput is not reduced. Furthermore, the ability to correct the beam during inspection of the sample 101 also contributes to improved throughput.

[0070] Second Embodiment Aberrations that change the shape or position of the light spot on the surface of the sample 101 occur when the axis of the focusing optical unit A7 does not coincide with the incident optical axis of the illumination light, when the surface shape of the optical element is spherical, etc. In the second embodiment, a configuration will be described in which a control mechanism for "wavefront aberration (deviation of the actual wavefront from the ideal wavefront)" that comprehensively handles such aberrations is incorporated into the defect inspection apparatus 100.

[0071] The wavefront refers to the phase distribution of light and is a characteristic of the illumination light itself. When illumination light enters an optical element and passes through or is reflected, an increase in wavefront aberration that was not intended in the design occurs due to processing errors or adjustment errors in the optical element itself. The expansion or deformation of the light spot size occurs as a result of the deterioration of the focusing performance of the illumination light due to the increase in wavefront aberration as a disturbance. Wavefront aberration is an element that cannot be fully controlled by correcting the tilt, shift, and focusing position deviation amount in the first embodiment. As will be described later, the inclusion of a wavefront aberration control mechanism enables even more flexible adjustment of the light spot.

[0072] FIG. 13 is a schematic diagram showing the configuration of an illumination optical system A and a specular reflection light observation unit F of a defect inspection apparatus according to a second embodiment. The wavefront aberration control mechanism according to this embodiment includes a wavefront control element G1 and a wavefront observation element G2. The wavefront control element G1 is an element for changing and controlling the wavefront of illumination light, and may be, for example, a deformable optical element. The deformable element's incident surface is deformed by an actuator. By changing the wavefront of light through deformation to reduce wavefront aberration, the focusing performance of the illumination light can be stabilized. Deformable elements are broadly classified into transmissive and reflective types. A transmissive deformable element may be a lens or a phase plate, which simplifies the optical path, but has the drawback of being difficult to improve durability against light intensity. Low durability prevents an increase in the amount of light irradiated onto defects on the surface of the sample 101, making it unsuitable for a defect inspection apparatus. On the other hand, a reflective deformable element is a mirror, and although the footprint of the optical path is enlarged, it can be expected to be durable and tends to have a wider wavefront control range than a transmissive element. Therefore, it is desirable to use a reflective deformable element (deformable mirror) as the wave-front control element G1. Examples of actuators for the deformable mirror include stacked piezoelectric elements, bimorph piezoelectric elements, MEMS, and voice coil motors, and any of these may be used. Furthermore, the wave-front control element G1 is included in the illumination optical system A on the optical path, and may be placed anywhere as long as appropriate control is possible. Based on the first embodiment, the wave-front control element G1 can be installed downstream of the beam shaping unit A4, for example, as shown in FIG. 13 . Because it is a reflective element, simple reflecting mirrors G1a and G1b are provided before and after the wave-front control element G1, which causes the optical path to become non-linear.

[0073] The wavefront observation element G2 is also called a wavefront sensor. It is operated in conjunction with the wavefront control element G1 to observe the wavefront of the illumination light and store the data in the signal processing device D. The signal processing device D calculates the target wavefront for stabilizing the light spot based on the data acquired from the wavefront observation element G2. Any type of element, such as a Shack-Hartmann sensor, a wavefront curvature sensor, or a pyramid sensor, can be used as the wavefront sensor. Many elements are in the form of a general camera with a wavefront measurement mechanism added, and therefore also function as a simple image capture element for the illumination light. Any solid-state image sensor, such as a CCD, CMOS, or SPAD, can be used for this wavefront sensor. Ideally, the wavefront sensor should be able to observe the wavefront of the illumination light immediately before it is focused. Therefore, it should be installed as downstream in the optical path as possible. Based on the first embodiment, as shown in FIG. 13, the image capture element F4a, onto which the split light 1 (parallel light) is incident, can be replaced with the wavefront observation element G2 (wavefront sensor) in the specular reflection light observation unit F. This is because, as mentioned above, the wavefront sensor can also be used as an imaging element.

[0074] The wavefront of the specularly reflected light is constantly observed by the wavefront observation element G2. That is, the specularly reflected light observation unit F obtains the wavefront aberration of the light in addition to the optical axis shift amount, optical axis tilt amount, and focusing position deviation amount of the light before it enters the focusing optical unit A7. When this information is used to correct the illumination light, a step of controlling the wavefront is added to the correction flow.

[0075] 14 is a diagram illustrating an example of a correction flow for light incident on the focusing optical unit A7 according to the second embodiment. As shown in FIG. 14, the correction flow is basically the same as that shown in FIG. 11. However, it differs from FIG. 11 in that the collimated beam position used in correcting the beam position in step S22 is acquired not from the imaging device F4a but from the wavefront observing element G2 (imaging device). Furthermore, in correcting the focusing position in step S24, the wavefront control element G1 (deformable mirror) is controlled based on information about the wavefront of the illumination light (beam) additionally acquired from the wavefront observing element G2 (imaging device).

[0076] In this way, by providing a wavefront aberration control mechanism (wavefront control element G1 and wavefront observation element G2), it is possible to correct illumination light that cannot be handled by the first embodiment, and improve the light-collecting performance. As a result, it is possible to further stabilize the size and shape of the light spot on the surface of the sample 101.

[0077] [Modifications] The present disclosure is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present disclosure, and it is not necessary to include all of the described configurations. Furthermore, a part of one embodiment can be replaced with a configuration of another embodiment. Furthermore, a configuration of another embodiment can be added to a configuration of one embodiment. Furthermore, a part of the configuration of each embodiment can be added to, deleted from, or substituted for a part of the configuration of another embodiment.

[0078] 100... Defect inspection apparatus 101... Sample A... Illumination optical system B1 to B3... Detection optical system C1 to C3... Sensor D... Signal processing device E1... Control device

Claims

1. An optical inspection apparatus for inspecting a sample based on light reflected or scattered from the surface of the sample, comprising a light source, a light beam control mechanism, and a condenser optical unit, an illumination optical system that irradiates the surface of the sample with a light beam emitted from the light source through the condenser optical unit, a specular reflection light observation unit that monitors specular reflection light from the surface of the sample, and a control device that controls the illumination optical system based on the specular reflection light monitored by the specular reflection light observation unit, wherein the specular reflection light observation unit includes a first imaging element, a second imaging element, and a first light splitting element that splits and incident the specular reflection light on each of the first imaging element and the second imaging element, and the control device is based on information on the position or size of a first light beam received by the first imaging element and information on the position or size of a second light beam received by the second imaging element, and independently controls at least one of a shift, a tilt, or a focusing position of the light beam incident on the condenser optical unit by the light beam control mechanism.

2. The optical inspection apparatus according to claim 1, wherein the illumination optical system further includes a wavefront control element.

3. The optical inspection apparatus according to claim 2, wherein the second imaging element includes a wavefront sensor.

4. The optical inspection apparatus according to claim 2, wherein the light beam control mechanism includes a size control mechanism configured to be able to adjust the size of the light beam emitted from the light source, and the wavefront control element is disposed immediately after the size control mechanism.

5. The optical inspection apparatus according to claim 1, wherein the specular reflection light observation unit further includes a condenser element provided between the second imaging element and the light splitting element.

6. The optical inspection apparatus according to claim 1, wherein the condenser optical unit and the specular reflection light observation unit constitute an imaging optical system.

7. The illumination optical system further includes an illumination light observation unit having a third imaging element and a fourth imaging element for monitoring the light beam, and a second light splitting element for splitting and incidentally irradiating the light beam to each of the third imaging element and the fourth imaging element. The third imaging element is installed at a distance closer to the light source than the fourth imaging element. The control device independently controls at least one of the shift, tilt, intensity, size, or divergence angle of the light beam incident on the condenser optical unit by the light beam control mechanism based on the information on the intensity, position, or size of the third light beam received by the third imaging element and the information on the intensity, position, or size of the fourth light beam received by the fourth imaging element. The optical inspection apparatus according to claim 1.

8. The optical inspection apparatus according to claim 1, wherein the light beam control mechanism includes at least one of an intensity control mechanism, a position control mechanism, an angle control mechanism, or a size control mechanism of the light beam.

9. An optical inspection method performed by an optical inspection apparatus for inspecting a sample based on light reflected or scattered from the surface of the sample. The optical inspection apparatus includes a light source, a light beam control mechanism, and a condenser optical unit, and an illumination optical system for irradiating the surface of the sample with the light beam emitted from the light source through the condenser optical unit, and a control device for controlling the illumination optical system. The illumination optical system includes an illumination light observation unit having a first imaging element and a second imaging element for monitoring the light beam, and a light splitting element for splitting and incidentally irradiating the light beam to each of the first imaging element and the second imaging element. The first imaging element is installed at a distance closer to the light source than the second imaging element. The optical inspection method includes obtaining, by the control device, the information on the intensity, position, or size of the first light beam received by the first imaging element and the information on the intensity, position, or size of the second light beam received by the second imaging element, and controlling, by the control device, the light beam control mechanism based on the obtained information to independently control at least one of the shift, tilt, intensity, size, or divergence angle of the light beam incident on the condenser optical unit. An optical inspection method including the above.

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