Defect inspection device, and defect inspection method

Abstract

The present disclosure presents a defect inspection device in which the optical axis of a detection optical system is inclined with respect to a sample surface, the defect inspection device comprising: a sample stage that supports a sample in order to reduce the effect of image blur on a sensor surface; an illumination optical system that forms a thin-line illumination spot on the surface of the sample; a detection optical system that condenses scattered light of the thin-line illumination spot from the sample surface; and an imaging sensor that has a plurality of pixels and outputs the scattered light intensity of an illumination spot optical image formed on a light-receiving surface by the detection optical system, wherein the optical axis of the detection optical system is inclined with respect to the surface of the sample, the imaging sensor is inclined with respect to the optical axis of the detection optical system such that the major axis of the light-receiving surface coincides with a position conjugate with the thin-line illumination spot, and is disposed rotated with respect to an axis parallel to the long axis of the light-receiving surface of the imaging sensor to reduce the amount of focal point deviation in the optical axis direction caused by the displacement of the sample in the surface height direction.

Description

Defect inspection device and defect inspection method

[0001] The present disclosure relates to a defect inspection apparatus and a defect inspection method.

[0002] In manufacturing lines for semiconductor substrates and thin-film substrates, inspections for defects present on the surfaces of these substrates are carried out to maintain or improve product yields. Optical detection of minute defects requires irradiating the defect with high-power illumination, capturing the light scattered by the defect, and forming an image on the light-receiving surface of a sensor.

[0003] Such defect detection technology is described, for example, in Patent Document 1. In Patent Document 1, a detection optical system is arranged at an angle relative to the sample surface to detect scattered light generated by defects, and an image of a linear illumination spot on the sample surface is formed on a sensor in the detection optical system to perform defect determination. If the height of the sample surface fluctuates during inspection, the sample surface moves out of focus of the detection optical system, resulting in a decrease in the signal intensity detected by the sensor. Patent Document 2 describes a solution to the sample surface height fluctuation problem described in Patent Document 1. The decrease in signal intensity detected by the sensor is suppressed by actively controlling the sensor in the detection optical system in accordance with the sample surface height fluctuation.

[0004] JP 2007-033433 A JP 2022-162881 A

[0005] In the method disclosed in Patent Document 1, fluctuations in the height of the sample surface that occur during inspection have a significant effect on the inspection results. When the height of the sample surface fluctuates, the sample surface moves out of focus of the detection optical system, reducing the image resolution, and the image extends beyond the pixels, reducing the signal output by the sensor.

[0006] Patent Document 2 discloses a solution to this problem. In order to suppress the reduction in image resolution caused by fluctuations in sample surface height during inspection, the amount of sample surface height fluctuation is constantly monitored, and the position of an optical element equipped with an actuator is controlled to correct the amount of fluctuation. However, this requires highly accurate measurement of sample surface height displacement and a dynamic mechanism to compensate for it, which leads to increased implementation difficulty and cost due to the complexity of the system.

[0007] The present disclosure proposes a technique for reducing the effect of image blur on a sensor surface in a defect inspection apparatus in which the optical axis of a detection optical system is tilted with respect to a sample surface.

[0008] In order to solve the above-mentioned problems, the present disclosure proposes, as an example, a defect inspection device for inspecting defects on the surface of a sample, the defect inspection device comprising: a sample stage for supporting the sample; an illumination optical system for forming a thin line illumination spot on the surface of the sample; a detection optical system for collecting scattered light of the thin line illumination spot from the surface of the sample; and an image sensor having a plurality of pixels and outputting the scattered light intensity of the optical image of the illumination spot formed on a light receiving surface by the detection optical system, wherein the optical axis of the detection optical system is inclined with respect to the surface of the sample, and the image sensor is inclined with respect to the optical axis of the detection optical system so that the major axis of the light receiving surface coincides with a position conjugate with the thin line illumination spot, and further, the image sensor is rotated about an axis parallel to the major axis of the light receiving surface of the image sensor so that the amount of focus shift in the optical axis direction caused by displacement of the sample in the surface height direction is small.

[0009] 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.

[0010] According to the technology of the present disclosure, in a defect inspection apparatus in which the illumination optical system and the detection optical system are tilted with respect to the sample surface, it is possible to suppress a decrease in resolution caused by a change in the height of the sample surface.

[0011] 8 is a schematic diagram of an example configuration of a defect inspection apparatus 100 according to the present embodiment. It is a schematic diagram showing the scanning trajectory of the sample 1 by the scanning device ST2 in the defect inspection apparatus shown in FIG. 1. It is a schematic diagram showing another example of the scanning trajectory of the sample. It is a schematic diagram showing an extracted attenuator A2 of the defect inspection apparatus shown in FIG. 1. It is a schematic diagram showing a cross section of the sample 1 cut at the plane of incidence of the illumination light incident on the sample 1. It is a schematic diagram showing a cross section of the sample 1 cut at a plane that is perpendicular to the plane of incidence of the illumination light incident on the sample 1 and includes the normal to the sample surface. It is a schematic diagram showing the configuration of detection optical systems B1, B2, B4-Bn and image sensors C1, C2, C4-Cn. It is a diagram showing an example configuration of the detection optical system B3 into which scattered light emitted from the sample 1 in the normal direction is incident. It is a view taken along the arrow X-X line in FIG. 8. It is a schematic diagram of the three-dimensional arrangement of the sample 1 and the tilted optical system. It is a diagram showing a graph showing an example of the characteristics of an anti-reflection film. It is a diagram showing an example cross-sectional configuration of an image sensor provided in the defect inspection apparatus shown in FIG. 1. 13 is a diagram showing a cross section cut by a plane including the optical axis OA2 and the major axis of the illumination spot BS. FIG. 13 is a diagram showing an arrangement example (arrangement according to a conventional example) when FIG. 13 is viewed from the major axis direction of the image sensors C1.... FIG. 14 is a diagram showing an arrangement example of the light receiving surface of the image sensor according to Example 1. FIG. 15 is a diagram showing the arrangement angle of the illumination optical system and the image sensor of the defect inspection device according to Example 2 of this embodiment. FIG. 16 is a diagram for explaining the arrangement angle of the illumination optical system and the image sensor of the defect inspection device according to Example 3.

[0012] The embodiments and examples of the present disclosure relate to a defect inspection device and a defect inspection method for detecting micro defects on the surface of a semiconductor wafer substrate or the like. The embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the defect inspection device described as an application target is used for, for example, inspecting the surface of a sample (wafer) for defects during a manufacturing process of a semiconductor or the like. The defect inspection device according to each embodiment can quickly detect micro defects and acquire data on the number, position, size, and type of defects.

[0013] <Defect Inspection Apparatus> FIG. 1 is a schematic diagram of a configuration example of a defect inspection apparatus 100 according to this embodiment. The defect inspection apparatus 100 according to this embodiment inspects a sample 1 and detects defects such as foreign particles and dents on the surface of the sample 1 (hereinafter referred to as the sample surface), particularly defects of a type appropriate for the inspection purpose. A representative example of the sample 1 is a disk-shaped semiconductor silicon wafer with a flat surface on which no patterns are formed. The defect inspection apparatus 100 includes a stage ST, an illumination optical system A, detection optical systems B1-Bn (n = 1, 2, ...), image sensors C1-Cn, C3' (n = 1, 2, ...), a signal processing device D, a control device E1, a user interface E2, and a monitor E3. The signal processing device D and the control device E1 may be configured as separate computers, or a single computer may be used for both functions.

[0014] <Stage ST> The stage ST is composed of a sample stage ST1 and a scanning device ST2. The sample stage ST1 is a stage that supports the sample 1. The scanning device ST2 is a device that drives the sample stage ST1 to change the relative position of the sample 1 and the illumination optical system A, and is composed of a translation stage, a rotation stage, and a Z stage. The rotation stage is supported 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, and the rotation stage rotates around an axis that extends vertically. The Z stage functions to adjust the height of the sample surface.

[0015] FIG. 2 is a schematic diagram showing the scanning trajectory of the sample 1 by the scanning device ST2. As will be described later, the illumination spot BS irradiated onto the sample surface by illumination light emitted from the illumination optical system A has an illumination intensity distribution that is long in one direction, as shown in the figure. The major axis direction of the illumination spot BS (the radial direction of the sample stage ST1) is designated S2, and the direction approximately perpendicular to the major axis (the circumferential direction around the rotation axis of the sample stage ST1) is designated S1. As the rotating stage rotates, the sample 1 rotates, and the illumination spot BS scans the sample surface in direction S1. As the translation stage translates, the sample 1 moves horizontally, and the illumination spot BS scans the sample surface in direction S2. As the scanning device ST2 translates and rotates the sample 1, the illumination spot BS moves along a spiral trajectory from the center to the outer edge of the sample 1, as shown in FIG. 2, thereby scanning the entire surface of the sample 1. During one rotation of the sample 1, the illumination spot BS moves in direction S2 by a distance equal to or less than the length of the illumination spot BS in direction S2.

[0016] A scanning device can also be used in which, instead of the rotation stage, another translation stage is provided, whose movement axis extends in a direction intersecting the movement axis of the translation stage in a horizontal plane. In this case, as shown in Figure 3, the illumination spot BS scans the sample surface by overlapping linear trajectories rather than helical trajectories. Specifically, the first translation stage is driven in direction S1 at a constant speed, the second translation stage is driven in direction S2 a predetermined distance (e.g., a distance equal to or less than the length of the illumination spot BS in direction S2), and then the first translation stage is driven in direction S1 again. In this way, the illumination spot BS repeatedly scans linearly in direction S1 and moves in direction S2, thereby scanning the entire surface of the sample 1. Compared to this scanning method, the helical scanning method shown in Figure 2 does not require reciprocating motion and is therefore advantageous for performing sample inspection in a short time.

[0017] 1 is an optical unit including a plurality of optical elements for applying desired illumination light to a sample 1 placed on a sample stage ST1, and forms an illumination spot BS on the sample surface that is long in one direction (direction S2) having a major axis. As shown in FIG. 1, this illumination optical system A includes a laser light source A1, an attenuator A2, an output light adjustment unit A3, a beam expander A4, a polarization control unit A5, a focusing optical unit A6, and reflecting mirrors A7-A9.

[0018] (i) Laser Light Source The laser light source A1 is a unit that emits a laser beam as illumination light. 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 minute defects near the surface of the sample, the laser light source A1 emits a high-power laser beam with an output of 2 W or more in ultraviolet or vacuum ultraviolet light with a short wavelength (e.g., wavelength of 355 nm or less) that does not easily penetrate the interior of the sample 1. In this embodiment, for example, a laser beam with a wavelength of 266 nm is used, but a laser beam with a wavelength of 200-380 nm or near ultraviolet light with a wavelength of 200-380 nm or vacuum ultraviolet light with a wavelength of 10-200 nm can be used depending on the purpose. Furthermore, when the defect inspection device 100 is used to detect defects inside the sample 1, the laser light source A1 emits a visible or infrared laser beam with a long wavelength that easily penetrates the interior of the sample 1.

[0019] (ii) Attenuator FIG. 4 is a schematic diagram illustrating the attenuator A2. The attenuator A2 is a unit that attenuates the light intensity of the illumination light from the laser light source A1. In this embodiment, the attenuator A2 is configured by combining a first polarizing plate A21, a half-wave plate A22, and a second polarizing plate A23. The half-wave plate A22 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 A21, and then the polarization direction is adjusted to the slow axis azimuth angle of the half-wave plate A22 before passing through the second polarizing plate A23. By adjusting the azimuth angle of the half-wave plate A22, the light intensity of the illumination light can be attenuated at any desired rate. If the degree of linear polarization of the illumination light incident on the attenuator A2 is sufficiently high, the first polarizing plate A21 can be omitted. The attenuator A2 is used with a pre-calibrated relationship between the input signal and the attenuation rate. The attenuator A2 is not limited to the configuration shown in Fig. 4, but may also be configured using an ND (Neutral Density) filter with a gradation density distribution. In this case, the attenuation effect can be adjusted by combining multiple ND filters with different densities.

[0020] 1 is a unit that adjusts the angle of the optical axis of the illumination light attenuated by the attenuator A2, and in this embodiment, it is configured to include multiple reflecting mirrors A31 and A32. The reflecting mirrors A31 and A32 sequentially reflect the illumination light, but in this embodiment, the incident / exit surface of the illumination light relative to the reflecting mirror A31 is configured to be perpendicular to the incident / exit surface of the illumination light relative to the reflecting mirror A32.

[0021] Here, the incident and exit planes are planes that include the optical axis that enters the reflecting mirror and the optical axis that exits from the reflecting mirror. For example, if a three-dimensional XYZ Cartesian coordinate system is defined and illumination light is incident on reflecting mirror A31 in the +X direction, the illumination light will be deflected in the +Y direction by reflecting mirror A31 and then in the +Z direction by reflecting mirror A32, although this is different from the schematic diagram shown in Figure 1. In this example, the incident and exit planes of the illumination light for reflecting mirror A31 are the XY plane, and the incident and exit planes for reflecting mirror A32 are the YZ plane.

[0022] The reflecting mirrors A31 and A32 each include a mechanism (not shown) for translating the reflecting mirrors A31 and A32 and a mechanism (not shown) for tilting the reflecting mirrors A31 and A32. The reflecting mirrors A31 and A32, for example, translate in the direction of incidence or emission of the illumination light relative to themselves and tilt around the normal to the incident and emission 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. Note that, although this example illustrates a configuration using two reflecting mirrors A31 and A32, a configuration using three or more reflecting mirrors may also be used.

[0023] (iv) Beam Expander The beam expander A4 is a unit that expands the beam diameter of the incident illumination light and includes multiple lenses A41 and A42. An example of a beam expander A4 is a Galilean type that uses a concave lens as the lens A41 and a convex lens as the lens A42. The beam expander A4 is equipped with a spacing adjustment mechanism (zoom mechanism) for the lenses A41 and A42, and adjusting the spacing between the lenses A41 and A42 changes the expansion ratio of the beam diameter. The beam diameter expansion ratio of the beam expander A4 is, for example, approximately 5-10 times. In this case, if the beam diameter of the illumination light emitted from the laser light source A1 is 1 mm, the beam system of the illumination light is expanded to approximately 5-10 mm. If the illumination light incident on the beam expander A4 is not a parallel beam, adjusting the spacing between the lenses A41 and A42 can collimate the beam (make the beam quasi-parallel) in addition to adjusting the beam diameter. However, the collimation of the light beam may be performed by providing a collimating lens upstream of the beam expander A4, separately from the beam expander A4.

[0024] The beam expander A4 is installed on a translation stage with two or more axes (two degrees of freedom) and is configured so that its position can be adjusted so that its center coincides with the incident illumination light.The beam expander A4 also has a swing angle adjustment function with two or more axes (two degrees of freedom) so that the incident illumination light coincides with the optical axis.

[0025] (v) Polarization Control Unit The polarization control unit A5 is an optical system that controls the polarization state of the illumination light and is composed of a half-wave plate A51 and a quarter-wave plate A52. For example, when performing oblique incidence illumination by inserting a reflecting mirror A7 (described later) into the optical path, using the polarization control unit A5 to polarize the illumination light P increases the amount of scattered light from defects on the sample surface compared to light polarized other than P. If scattered light (called haze) from minute irregularities on the surface of the sample itself interferes with the detection of minute defects, using S-polarized illumination light can reduce the haze compared to light polarized other than S. The polarization control unit A5 can also circularly polarize the illumination light or polarize it at a 45-degree angle, which is intermediate between P and S polarization.

[0026] (vi) Condensing Optical Unit The condensing optical unit A6 is a unit that condenses the illumination light and adjusts the intensity distribution, and is configured to include optical elements such as an aspherical lens, a diffractive optical element, a cylindrical lens array, etc. The optical elements that make up the condensing optical unit A6 are installed perpendicular to the optical axis of the illumination light, as shown in Figure 1.

[0027] (vii) Reflecting Mirror As shown in Figure 1, the reflecting mirror A7 can be moved in parallel in the direction of the arrow by a drive mechanism (not shown) to move in and out of the optical path of the illumination light directed toward the sample 1, thereby switching the incident path of the illumination light with respect to the sample 1. By inserting the reflecting mirror A7 into the optical path, as described above, the illumination light emitted from the polarization control unit A5 is reflected by the reflecting mirror A7 and passes through the focusing optical unit A6 and the reflecting mirror A8 to be incident obliquely on the sample 1. On the other hand, when the reflecting mirror A7 is removed from the optical path, the illumination light emitted from the polarization control unit A5 passes through the reflecting mirror A9, polarizing beam splitter Bi, polarization control unit Bh, reflecting mirror Bk, and detection optical system B3 to be incident perpendicularly on the sample 1.

[0028] 5 and 6 are schematic diagrams showing the relationship between the optical axis of illumination light guided obliquely to the sample surface by the illumination optical system A and the illumination intensity distribution shape. Fig. 5 is a schematic representation of a cross section of the sample 1 cut at the plane of incidence of the illumination light incident on the sample 1. Fig. 6 is a schematic representation of a cross section of the sample 1 cut at a plane that is perpendicular to the plane of incidence of the illumination light incident on the sample 1 and includes the normal to the sample surface. The plane of incidence is a plane that includes the optical axis OA1 of the illumination light incident on the sample 1 and the normal to the sample surface. Note that Figs. 5 and 6 only show a portion of the illumination optical system A, and for example, the exit light adjustment unit A3 and the reflecting mirrors A7 and A8 are not shown.

[0029] When the reflecting mirror A7 is inserted into the optical path, the illumination light emitted from the laser light source A1 is focused by the focusing optical unit A6, adjusted to a desired intensity distribution, and reflected by the reflecting mirror A8, obliquely incident on the sample 1. In this way, the illumination optical system A is configured to allow illumination light to be incident on the sample 1 from a direction oblique to the normal to the sample surface. This oblique incidence illumination has its light intensity adjusted by the attenuator A2, its beam diameter adjusted by the beam expander A4, its polarization adjusted by the polarization control unit A5, and its intensity distribution adjusted by the focusing optical unit A6, thereby achieving a uniform illumination intensity distribution within the incident plane. As shown in the illumination intensity distribution (illumination profile) LD1 in FIG. 5 , the illumination spot formed on the sample 1 has a Gaussian light intensity distribution in the direction S2. The beam width L1 in the direction S2, defined at 13.5% of the peak, is, for example, approximately 5 μm to 4 mm.

[0030] In a plane perpendicular to the incident surface and the sample surface, the illumination spot has a light intensity distribution in which the intensity is weaker at the periphery than at the center of the beam, as shown in the illumination intensity distribution (illumination profile) LD2 in Figure 6. Specifically, the intensity distribution resembles a Gaussian distribution reflecting the intensity distribution of the light incident on the focusing optical unit A6, or a first-order Bessel function or sinc function reflecting the aperture shape of the focusing optical unit A6. The length L2 of the illumination intensity distribution in the plane perpendicular to the incident surface and the sample surface is set to be shorter than the beam width L1 shown in Figure 5, for example, approximately 1.0 μm to 10 μm, in order to reduce haze generated from the sample surface. This length L2 of the illumination intensity distribution is the length of the region in the plane perpendicular to the incident surface and the sample surface where the illumination intensity is 13.5% or more of the maximum illumination intensity.

[0031] Furthermore, the angle of incidence of the oblique incidence illumination on the sample 1 (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 A7 and A8. The angle of the reflecting mirror A8 is adjusted by an adjustment mechanism A81. For example, the larger the angle of incidence of the illumination light on the sample 1 (the smaller the illumination elevation angle, which is the angle between the sample surface and the incident optical axis), the weaker the haze that causes noise in the scattered light from minute foreign particles on the sample surface, making it more suitable for detecting minute defects. From the viewpoint of suppressing the effect of haze on the detection of minute defects, it is preferable to set the incident angle of the illumination light, for example, to 75 degrees or more (elevation angle 15 degrees or less). On the other hand, with oblique incidence illumination, the absolute amount of scattered light from minute foreign particles increases as the illumination incident angle decreases. Therefore, from the viewpoint of increasing the amount of scattered light from defects, it is preferable to set the incident angle of the illumination light, for example, to 60 degrees or more and 75 degrees or less (elevation angle 15 degrees or more and 30 degrees or less).

[0032] <Detection Optical System> The detection optical systems B1-Bn (n = 1, 2, ...) are optical units that collect scattered light from the illumination spot BS on the sample surface, and are configured to include multiple optical elements including a collecting lens (objective lens). The "n" in the detection optical system Bn represents the number of detection optical systems. Each objective lens in the detection optical systems B1-Bn is arranged along the hemispherical surface of the upper half of a sphere (celestial sphere) centered on the illumination spot BS on the sample 1. The scattered light incident on the detection optical systems B1-Bn is collected and guided to the corresponding image sensors C1-Cn. In this embodiment, the optical path of the scattered light incident on the detection optical system B3 is branched by a reflecting mirror Bk, and is guided to the image sensor C3 as well as the image sensor C3'.

[0033] <Tilt optical system> Figure 7 is a schematic diagram showing the configuration of the detection optical systems B1, B2, B4-Bn and image sensors C1, C2, C4-Cn. That is, it is a schematic diagram of a detection optical system whose optical axis is tilted with respect to the sample surface. Hereinafter, the detection optical systems B1, B2, B4-Bn and image sensors C1, C2, C4-Cn whose optical axis OA2 is tilted with respect to the sample surface will be abbreviated as "detection optical system B1..." and "image sensor C1...".

[0034] The detection optical systems B1... include a condenser lens (objective lens) Ba, a half-wave plate Bb, a polarizing beam splitter Bc, a half-wave plate Bd, and an imaging lens Be along their optical axis OA2. The scattered illumination light incident on the detection optical systems B1... is guided to the image sensor C1. The detection optical systems B1... also include a beam diffuser Bf in the traveling direction of the light split by the polarizing beam splitter Bc.

[0035] In the detection optical system B1..., the condenser lens Ba condenses the illumination scattered light, and the half-wave plate Bb controls its polarization direction. The half-wave plate Bb can be rotated by an actuator (not shown). The light that passes through the half-wave plate Bb has its optical path split by a polarizing beam splitter Bc according to its polarization. The combination of the half-wave plate Bb and the polarizing beam splitter Bc facilitates separation of optical signals indicating defects in the sample 1 from optical signals that impede defect detection in the sample 1 (roughness scattered light from the sample surface). The light that passes through the polarizing beam splitter Bc is controlled by a half-wave plate Bd to have a polarization direction suitable for detection by the image sensor C1. Meanwhile, the light whose optical path is split by the polarizing beam splitter Bc is attenuated by a beam diffuser Bf to prevent it from becoming stray light.

[0036] The light receiving surface of the image sensor C1 is positioned so that its longitudinal direction coincides with a position conjugate with the illumination spot BS illuminated on the sample surface. The light beam transmitted through the half-wave plate Bd is guided to the image sensor C1 via the imaging lens Be, and an optical image OI of the illumination spot BS is formed on multiple pixels of the image sensor C1. Detection signals of the optical image photoelectrically converted by each pixel of the image sensor C1 are output to a signal processing device D.

[0037] In this way, the detection optical systems B1-Bn collect the scattered light of the illumination spot BS irradiated onto the sample 1 by the illumination optical system A, control the polarization state of the incident scattered light, and form an optical image of the illumination spot BS on the light receiving surface of the corresponding image sensor C1-Cn.

[0038] <Vertical Optical System> Figure 8 shows an example of the configuration of the detection optical system B3, into which scattered light emitted in the normal direction from the sample 1 is incident. Figure 9 is a view taken along the arrows X-X in Figure 8. The detection optical system B3 includes a condenser lens (objective lens) Bi and an imaging lens Bj. The scattered light condensed by the condenser lens Bi is guided to the image sensor C3 by the imaging lens Bj. In this detection optical system B3, a reflecting mirror Bk is disposed at the position of its own pupil between the condenser lens Bi and the imaging lens Bj. During epi-illumination with the reflecting mirror A7 removed from the optical path, illumination light is incident on the sample 1 in the normal direction via the reflecting mirror Bk. In this way, the condenser lens Bi of the detection optical system B3 also serves as a condenser lens that guides epi-illumination to the sample 1.

[0039] On the other hand, the reflecting mirror Bk also plays a role in branching the optical path of a portion of the scattered light incident from the illumination spot BS by oblique incidence illumination or epi-illumination into the detection optical system B3. As mentioned above, the illumination spot BS has a linear intensity distribution that is long in the direction S2. As shown in FIG. 9 , the reflecting mirror Bk is longer than the illumination spot BS in the minor axis direction (direction S1) of the linear illumination spot BS as viewed from the image sensor C3, but shorter than the illumination spot BS in the major axis direction (direction S2) of the illumination spot BS. As a result, scattered light that enters the detection optical system B3 from the sample 1 and does not interfere with the reflecting mirror Bk enters the image sensor C3 via the imaging lens Bj, while scattered light that interferes with the reflecting mirror Bk is reflected by the reflecting mirror Bk.

[0040] Scattered light from the sample 1 enters the detection optical system B3 and is reflected by the reflecting mirror Bk, and is guided to the image sensor C3' via the polarization control unit Bl, the polarizing beam splitter Bm, and the imaging lens Bo. Like the polarization control unit A5, the polarization control unit Bl includes a quarter-wave plate Bl1 and a half-wave plate Bl2, and can adjust the polarization of the scattered illumination light incident from the reflecting mirror Bk to any desired polarization. During oblique incidence illumination, the polarization of the scattered illumination light incident on the polarizing beam splitter Bm is controlled to linear polarization by the quarter-wave plate Bl1 of the polarization control unit Bl, so that the scattered illumination light reflected by the reflecting mirror Bk passes through the polarizing beam splitter Bm and enters the imaging lens Bo. Furthermore, under epi-illumination conditions in which the reflecting mirror A7 is removed from the optical path, the polarization of the illumination light can be controlled by the polarization control unit Bl so that the illumination light traveling toward the sample 1 enters the detection optical system B3 with any desired polarization direction (e.g., circular polarization).

[0041] <Image Sensor> The image sensors C1-Cn are lines with light-receiving surfaces in which multiple pixels are arranged in a line (array), and each corresponds to a detection optical system B1-Bn. These image sensors C1-Cn use CMOS (Complementary Metal-Oxide-Semiconductor) sensors or CCD (Charge Coupled Device) sensors. The image sensors C1-Cn perform photoelectric conversion of the optical image of the illumination spot BS formed on the light-receiving surface by the corresponding detection optical system, perform predetermined sampling, convert the analog electrical signal into digital data, and output it to the signal processing device D as a data set of scattered light intensity of the optical image.

[0042] In this embodiment, the light-receiving surfaces of the image sensors C1-Cn are tilted with respect to the optical axis OA2 in accordance with the tilt of the optical axis OA2 of the corresponding detection optical system with respect to the sample surface (described below), and the major axes of the light-receiving surfaces are aligned at a position conjugate with the illumination spot BS irradiated on the sample surface. This excludes image sensor C3, which faces the illumination spot BS in the normal direction to the sample surface. The light-receiving surface of image sensor C3 is perpendicular to the optical axis OA2 of the detection optical system B3. Image sensors C1-Cn are each positioned so that the major axis of their light-receiving surfaces (the center line extending in the longitudinal direction) is parallel to the major axis of the optical image OI ( FIG. 7 ) of the illumination spot BS, and the entire illumination spot BS fits within the one-dimensional light-receiving surface formed by an array of pixels.

[0043] As mentioned above, a portion of the scattered light collected by the detection optical system B3 is guided to the image sensor C3' in addition to the image sensor C3. The image sensor C3' may be a two-dimensional CCD image sensor, a CMOS image sensor, or a PSD (position-sensitive detector). The image sensor C3' also photoelectrically converts the optical image collected by the detection optical system B3, performs predetermined sampling, and converts the electrical signal into digital data by analog-to-digital conversion, which is then output to the signal processing device D.

[0044] <Signal Processing Device> The signal processing device D shown in FIG. 1 is a computer that processes detection signals input from the image sensors C1-Cn and C3', and is configured to include a CPU, FPGA, timer, etc. in addition to ROM, RAM, and other memories. While the signal processing device D is assumed to be configured as a single computer that forms a unit with the main body of the defect inspection device 100 (stage, illumination optical system, detection optical system, sensor, etc.), it may also be configured as multiple computers. In this case, a server may be used as one of the multiple computers. This is an example in which a server is included as a component of the defect inspection device 100. For example, a configuration is possible in which a computer attached to the main body of the device acquires defect detection signals from the main body of the device, processes the detection data as needed, and transmits it to a server, where defect detection, classification, and other processing are performed by the server.

[0045] The signal processing device D includes an illumination spot position analysis circuit D1, a memory D2, a signal integration circuit D3, and a defect detection circuit D4. The illumination spot position analysis circuit D1, the signal integration circuit D3, and the defect detection circuit D4 are, for example, programs.

[0046] The illumination spot position analysis circuit D1 analyzes the position of the illumination spot BS based on the digital data input from the imaging sensors C1-Cn, C3'. The memory D2 stores the digital data input from the imaging sensors C1-Cn, C3' and the position data calculated by the illumination spot position analysis circuit D1, and accumulates them as scattered light data. The signal integration circuit D3 integrates multiple scattered light data output from the same sensor at different positions of the illumination spot BS based on the scattered light data accumulated in the memory D2, and integrates scattered light data similarly integrated for different sensors. The defect detection circuit D4 extracts high-frequency, high-brightness areas on the sample surface as defects based on the scattered light data after integration. Each circuit of the signal processing device D can be configured, for example, with an FPGA. Furthermore, at least some of the functions of these circuits (especially downstream processing) can be executed by a server.

[0047] To further explain the processing performed by the signal combining circuit D3, the signal combining circuit D3 adds up the scattered light intensities of data obtained by scanning the linear illumination spot BS of the sample 1 in the longitudinal direction at the same coordinates on the sample surface. In other words, when the sample 1 is spirally scanned, if coordinates on the sample surface are expressed in the rθ coordinate system, the scattered light intensities at the same coordinates are added up for scattered light data with the same θ coordinate but different r coordinates. In the rθ coordinate system, the r coordinate is the radial coordinate on the sample surface, and the θ coordinate is the azimuthal coordinate on the sample surface, which is a different concept from the elevation angle θ in FIG. 10 . Even for scattered light data output from the same sensor, the imaging positions of scattered light from the same coordinates (i.e., pixels receiving scattered light from the same coordinates) will be shifted by the amount of movement of the sample stage ST1 during one rotation of the sample 1. Therefore, the correspondence between the pixels from which signals to be added as scattered light intensities at the same coordinates are calculated based on the amount of movement of the sample stage ST1.

[0048] <Control Device> The control device E1 is a computer that controls the defect inspection device 100, and like the signal processing device D, it is configured to include a CPU, FPGA, timer, etc. in addition to ROM, RAM, and other memories. The control device E1 is connected to the user interface E2, monitor E3, and signal processing device D by wire or wirelessly. The functions of the signal processing device D may be incorporated into the control device E1, so that the control device E1 also serves as the signal processing device D. The user interface E2 is a device through which the user inputs various operations, and various input devices such as a keyboard, mouse, touch panel, etc. may be used as appropriate.

[0049] The control device E1 receives inputs of the encoders of the rotation stage and translation stage, and inspection conditions input from the user interface E2 in response to operator operation. The inspection conditions include, for example, the type, size, shape, and material of the sample 1, illumination conditions, and detection conditions. The control device E1 also outputs signals commanding the operation of the stage ST in response to height fluctuations in the sample 1 and inspection conditions, and outputs coordinate data of the illumination spot BS synchronized with defect detection signals to the signal processing device D. The control device E1 also displays and outputs defect inspection results obtained by the signal processing device D on the monitor E3. Although not shown, the control device E1 may also be connected to a defect review-scanning electron microscope (DR-SEM), which is an electron microscope used for defect inspection. In this case, the control device E1 can receive defect inspection result data from the DR-SEM and transmit it to the signal processing device D.

[0050] <Various Settings> Figure 10 shows a schematic diagram of the three-dimensional arrangement of the sample 1 and tilting optical system. The optical axis OA2 of each of the detection optical systems B1 is tilted at an angle θ with respect to the normal (normal direction s3) of the sample 1. The projection of the optical axis OA2 on the sample surface is tilted at an angle φ with respect to the major axis direction unit vector S2 of the illumination spot BS.

[0051] When the optical axis OA2 of the detection optical systems B1 is tilted at an angle θ with respect to the normal to the sample 1 and the projection of the optical axis OA2 on the sample surface is tilted at an angle φ with respect to the major axis of the illumination spot BS, the unit vector d of the optical axis OA2 in three-dimensional space is expressed by the following equation (1): d = (sin θ sin φ, sin θ cos φ, cos θ) (1) The angle α formed by this vector d and the unit vector s2 of the major axis of the illumination spot BS can be calculated using equation (2).

[0052] α=arccos(sinθ・cosφ)... (2)

[0053] In this case, when the height of the sample surface is at the reference position, the optical image OI of the illumination spot BS fits on the light-receiving surface of the image sensor C1 without correcting the optical system or sensor position. If the length of the major axis of the illumination spot BS is 2L, a difference Δz, shown in equation (3), occurs in the working distance (the distance between the sample 1 and the detection optical system B1, etc.) between the center of the field of view on the sample surface and a point a distance x away from the center of the field of view in the direction of the major axis vector s2.

[0054] Δz=x(sinθ・cosφ), |x|<L... (3)

[0055] Furthermore, the imaging magnification M in the direction perpendicular to the optical axis OA2 is determined by the condenser lens Ba and the imaging lens Be. When this imaging magnification M is used, the positions of the optical images OI at the center of the field of view and at a point on the sample surface that is a distance x away from the center of the field of view in the direction of the major axis vector s2 differ by ΔZ, as expressed by equation (4), along the optical axis OA2.

[0056] ΔZ = M ２ x (sinθ・cosφ), |x|<L... (4)

[0057] Generally, a line sensor is positioned so that its light-receiving surface is perpendicular to the center line (optical axis) of the light beam emitted by the imaging lens. In contrast, in this embodiment, as shown in FIG. 7 , the light-receiving surfaces of the image sensors C1... are tilted with respect to the optical axis OA2, and an optical image without defocusing is detected regardless of the difference in working distance Δz that occurs within the field of view of the detection optical system B1..., which is an inclined optical system. The unit vector v2 of the major axis (center line extending in the longitudinal direction) of the light-receiving surface is set so that it is included in the same plane as the vector s2 of the major axis of the illumination spot BS and the unit vector d of the optical axis OA2, and the angle β with respect to the vector d satisfies Equation (5).

[0058] tanα=M・tanβ... (5)

[0059] As the imaging magnification M increases, the angle β between vectors d and v2 decreases according to equation (5), and the angle of incidence of reflected light on image sensor C1 increases. When the imaging magnification is increased to M=2, the scattered light enters image sensor C1 at an angle of incidence approaching 90 degrees at most. However, since the absorptance of the anti-reflection coating Ca (FIG. 11) of image sensor C1 depends on the angle of incidence of the light rays and decreases at angles of incidence approaching 90 degrees, the imaging magnification M is set to 2 or less.

[0060] Here, with regard to the scattered light beam incident on the condenser lens Ba, particularly if a lens with a large numerical aperture is used as the condenser lens Ba, the scattered light will be incident on the image sensor C1 from a wide range of directions. If the range of incident angles of light on the image sensor C1 is wide, the characteristics of the anti-reflection coating Ca (Figure 11) will reduce the light absorption rate of the image sensor C1, which is disadvantageous in terms of inspection sensitivity. The spread of the light beam incident on the image sensor C1 is calculated by multiplying the spread of the light beam exiting the imaging lens Be by the reciprocal of the imaging magnification M. By setting the imaging magnification M to 1 or greater, the range of incident angles of light on the image sensor C1 can be narrowed, thereby suppressing the reduction in the absorption rate of the anti-reflection coating Ca. Furthermore, if the imaging magnification M is 1 or greater, the optical image OI is enlarged, thereby reducing the area on the sample surface corresponding to each pixel of the image sensor C1. As a result, noise caused by haze is reduced, improving inspection sensitivity. For this reason, the imaging magnification M is set to 1 or more, and the angle β is smaller than the angle α. Typically, when the imaging magnification M is set to about 1.3, the angle β becomes smaller than the angle α by 5 degrees or more.

[0061] A cross-sectional view of the image sensor C1 is shown in Figure 12. The image sensor C1 is configured by laminating, in order from the side where scattered light is incident, an anti-reflection film Ca, a photodiode Cb, and wiring Cc. A photodiode Cb is provided for each pixel, and photoelectric conversion is performed by the photodiode Cb at each pixel. The wiring Cc transmits the electrical signal output from each pixel independently for each pixel.

[0062] The incident light beams LA to LC shown in the example represent trajectories of light incident on the image sensor C1 from different directions in the same light beam. The incident light beam LA is light incident on a trajectory that coincides with the optical axis OA2 shown in FIG. 7. The incident light beams LB and LC are light incident at angles oblique to the optical axis OA2. Even the same light beam, like the incident light beams LA to LC, includes light incident on the light receiving surface from various angles, and the anti-reflection coating Ca must suppress the surface reflection of such light. The anti-reflection coating Ca can be made of, for example, hafnium oxide (HfO ２ In order to prevent a decrease in the amount of light received by the image sensor C1, it is necessary to consider that the anti-reflection coating Ca exhibits a high absorptance for incident light LA-LC and the like.

[0063] Here, the solid curve in Figure 11 represents the absorptance characteristics of S-polarized light. The dashed curve represents the absorptance characteristics of P-polarized light. As the graph shows, the absorptance of P-polarized light decreases as the angle of incidence increases, reaching approximately 50% at an angle of incidence of approximately 60 degrees. The absorptance of S-polarized light increases as the angle of incidence increases within a range of approximately 0 to 70 degrees, and an absorptance of 70% or more is maintained within a range of approximately 0 to 80 degrees.

[0064] For this reason, the rotation angle of each half-wave plate Bd (FIG. 7) of the detection optical systems B1 is controlled so that S-polarized light is incident on the image sensor C1. Taking into account that the light-receiving surface of the image sensor C1 is tilted with respect to the optical axis OA2 of the detection optical systems B1, it is desirable to tilt the normal to the light-receiving surface of the image sensor C1 with respect to the optical axis OA2 of the detection optical systems B1 by, for example, an angle between 10 degrees and 80 degrees. This allows the anti-reflection coating Ca to perform effectively and prevents a decrease in the amount of received light.

[0065] 12, a sensor having a structure in which the photodiode Cb is located on the light incident side of the wiring Cc is known as a BSI (Back Side Illumination) sensor. In this embodiment, scattered light is incident on the light receiving surface of the image sensor C1 from a direction oblique to the normal to the light receiving surface. However, in a BSI sensor, the light is not blocked by the wiring Cc, so the amount of light received by each pixel can be ensured. In this respect, a BSI sensor is advantageous over an FSI (Front Side Illumination) sensor, in which the wiring is located on the light incident side of the photodiode and obliquely incident light is absorbed by the wiring, reducing the amount of incident light per pixel.

[0066] <Effect of sample height fluctuations on inspection> Ideally, the sample 1 shown in Figure 10 should not fluctuate in height in the normal direction s3 during inspection. However, particularly in the case of an rθ stage, the sample rotates at high speed during inspection, and stage vibrations and misalignment of the rotation axis can cause height fluctuations of the sample surface of approximately several tens of micrometers at high frequencies of several tens to several hundreds of Hz. This height fluctuation occurs at a maximum frequency equal to the rotation frequency of the sample. If a fluctuation in the height of the illumination spot BS occurs, the position of the optical image OI formed on the light-receiving surfaces of the image sensors C1 to -Cn (excluding image sensor C3) will shift.

[0067] In order to increase the capture rate of scattered light in the detection optical systems B1..., it is desirable to use a lens with a large numerical aperture for the condenser lens Ba. However, if other conditions are the same, the greater the numerical aperture, the shallower the focal depth of the detection optical systems B1.... This focal depth is calculated using the numerical aperture NA and the wavelength λ, as follows: λ / (2NA ２ For example, when λ=266 μm and NA=0.55, the depth of focus is 0.4 μm.

[0068] On the other hand, fluctuations in the height of the sample surface displace the focal position of the detection optical system B1, blurring the optical image OI and reducing the signal output by the image sensor C1. Consider the case where the illumination spot BS is displaced by Δs3 in the s3 direction due to fluctuations in the height of the sample surface that occur during inspection. Figure 13 is an explanatory diagram of focus deviation due to fluctuations in the height of the illumination spot BS. For simplicity, optical elements other than the condenser lens Ba and imaging lens Be of the detection optical system B1 are not shown. Figure 13 shows a cross section cut along a plane containing the optical axis OA2 and the major axis of the illumination spot BS.

[0069] If a vector e is orthogonal to the vector d in a plane including the vectors d and s3, then the vector can be expressed as in the following equation (6).

[0070] e=-s3 / sinθ+d / tanθ... (6)

[0071] When the illumination spot BS moves in the direction of s3 by Δs3, the focal position of the optical image OI moves in the direction of the vector d by M ２A variation of M·Δs3·sin θ occurs in the direction of vector e. That is, if the displacement vector of the focus position of the optical image OI is Δv, it can be expressed as in the following equation (7).

[0072] Δv=M ２ ・Δs3・cosθ・d+M・Δs3・sinθ・e ... (7) Comparative Example

[0073] 14 shows an example of arrangement (arrangement according to a conventional example) when viewed from the long axis direction of the image sensor C1 in FIG. 13. From FIG. 14, the amount of displacement Δf of the focus position of the detection optical system B1 with respect to the optical axis OA2 can be expressed by equation (8).

[0074] Δf=(l3・Δv) / (d・l3)... (8)

[0075] Furthermore, if the angle between the normal vector l3 of the image sensor surface and the displacement vector Δv of the in-focus position of the optical image OI is a, and the angle between the detection optical axis vector d and the normal vector l3 of the image sensor surface is b, then equation (8) can be expressed as equation (9).

[0076] Δf=|Δv|・cosa / cosb... (9)

[0077] In an oblique imaging system in which the object plane is tilted with respect to the optical axis OA2, the light receiving surfaces of the image sensors C1... are arranged so that they are conjugate with the optical image OI. That is, the short axis direction vectors l1 and v1, the long axis direction vectors l2 and v2, and the normal direction vector l3 are arranged so that v3 is conjugate with each other.

[0078] In this arrangement, for example, when M = 1 and θ = 55 degrees, a = 0 degrees and b = 55 degrees in equation (9). If we consider a case where the height fluctuation of the illumination spot BS is Δs3 = 1 μm, equations (7) and (9) result in Δf = 1.7 μm, which exceeds the depth of focus (out of focus) shown above. When the focus position shifts in this way and the light-receiving surface of the image sensor C1 moves out of the depth of focus, the optical image OI becomes blurry and enlarged. The optical image OI no longer fits within the pixels of the image sensor, reducing the signal output by the pixels and resulting in a deterioration in inspection sensitivity.

[0079] To suppress the effects of sample surface height fluctuations on inspection, a mechanism that controls the height of the sample stage in response to the sample surface height fluctuations is effective. However, it is difficult to suppress large fluctuations by driving a heavy sample stage to follow the sample surface height fluctuations that occur at the same frequency as the high-speed rotation of the sample 1, which can be up to several thousand RPM. In order to facilitate the design of a mechanism for suppressing sample surface height fluctuations through active control, it is desirable to be able to reduce the effects of sample surface height fluctuations on inspection. Below, we consider how to achieve this by changing the installation angle of the image sensors C1...

[0080] In Example 1, in order to reduce the degradation of resolution due to sample surface height fluctuations (displacement of surface height in the s3 direction), a detection optical system configuration is proposed in which the imaging plane of the image sensor is positioned at a position rotated by a predetermined angle from a position conjugate with the optical image OI when there is no sample surface height fluctuation. The imaging plane of the image sensor rotated by the predetermined angle (the angle defined by angles a and b in Equation (9)) intersects with the image plane (plane conjugate with the illumination spot BS) at the focal position of the optical image OI affected by sample surface height fluctuations.

[0081] <Image Sensor Placement> As described above, in the major axis direction of the illumination spot BS, an optical image OI is detected without defocusing, regardless of the difference in working distance ΔZ that occurs within the field of view of the detection optical system. In other words, the image sensors C1... are placed so that the major axis vector l2 of the light-receiving surface of the image sensor coincides with the major axis vector v2 of the optical image OI. However, there is a degree of freedom for the other axes. Consider rotating the installation angle about an axis parallel to the major axis direction l2 of the light-receiving surface of the image sensor.

[0082] FIG. 15 is a diagram showing an example of the arrangement of the light-receiving surface of the image sensor according to the first embodiment. For example, as shown in FIG. 15, consider an arrangement in which the short-axis vector l1 of the light-receiving surface of the image sensor is perpendicular to the optical axis OA2 of the detection optical system B1. In this case, under the conditions of imaging magnification M=1 in the direction perpendicular to the optical axis OA2 and θ=55 degrees, a=47 degrees and b=33 degrees in equation (9). In this case, from equations (7) and (9), if the illumination spot BS fluctuates by Δs3=1 μm due to fluctuations in the height of the sample surface, Δf=0.82 μm is calculated. In other words, it can be seen that the impact of fluctuations in the height of the sample surface on inspection sensitivity can be reduced compared to before the installation angle of the image sensor was changed.

[0083] The feature of Example 1 is that angles a and b are adjusted so that the displacement Δf of the focal position in the above formula (9) is small, and the image sensor is rotated and fixed. Angles a and b that make Δf zero are the optimal rotation angles, but they may be affected by in-plane displacement of the sample 1 (displacement in the plane direction defined by s1 and s2). A configuration for reducing the influence of in-plane displacement of the sample will be described later in Example 2.

[0084] This measure changes the angle of light incident on the image sensor surface. As mentioned above, in order to effectively utilize the performance of the anti-reflection coating Ca on the light-receiving surface of the image sensor, it is necessary to consider that the angle of incidence on the image sensor surface must be between 10 degrees and 80 degrees.

[0085] <Advantages of Example 1> (i) In Example 1, for detection optical systems B1... whose optical axes OA2 are inclined with respect to the sample surface, the effect of shifting of the focal position of the detection optical systems B1... from the light-receiving surface of the image sensor in the detection optical axis direction d, which occurs due to fluctuations in the height of the illumination spot BS in the normal direction s3 of the sample surface, is reduced. In this way, it is possible to suppress a decrease in the signal-to-noise ratio during inspection caused by fluctuations in the height of the illumination spot BS.

[0086] (ii) In particular, in Example 1, the installation angle of the image sensor during measurement is simply adjusted in advance. Therefore, no additional active control is required. This has the advantage of simplifying the device configuration and contributing to stabilization during operation.

[0087] The second embodiment proposes a configuration example in which an image sensor is arranged so as to reduce the influence of height fluctuations on the sample surface, and also reduces the influence of displacement within the sample surface.

[0088] 16 is a diagram showing the arrangement angles of the illumination optical system and the image sensor of a defect inspection apparatus according to Example 2 of this embodiment. This embodiment is similar to the first embodiment except for the differences from the first embodiment described in FIG.

[0089] Example 2 differs from Example 1 in that the installation angle of the image sensor is rotated 90 degrees from the initial position around the major axis direction vector l2 of the image sensor light receiving surface, so as to suppress the effect of height fluctuations on the sample surface, and a beam position stabilization mechanism is introduced into the illumination optical system A. In this positioning, scattered light is incident on the image sensors C1... at a large angle of incidence. As described above, by setting the imaging magnification M to 1 or more, the range of angles of incidence on the image sensors C1... can be narrowed, and a decrease in the light absorption rate by the anti-reflection coating Ca can be suppressed.

[0090] 16, in equation (9), a = 90 degrees (the angle between a = l3 and Δv), and the influence of height variations on the sample surface can be ignored, but there is a possibility that a large displacement of the focal position relative to the light-receiving surface of the image sensor will occur due to displacement of the illumination spot BS in the short-axis direction vector. Note that when a = 90 degrees, Δf = 0 in equation (9), and therefore the influence of height variations on the sample surface is zero. However, from the perspective of reducing the influence of height variations on the sample surface, the angle a does not necessarily have to be 90 degrees, and the rotation angle shown in Example 1 (an angle that can reduce height variations on the sample surface) may also be used.

[0091] Random fluctuations in the emission angle of the laser light source and vibrations of optical elements caused by rotating the sample at high speed during inspection cause fluctuations in the minor axis direction s1 and major axis direction s2 of the illumination spot BS at frequencies of up to several tens to several hundreds of Hz. Due to the arrangement of the light receiving surface of the image sensor, displacement in the major axis direction s2 does not affect the inspection sensitivity.

[0092] Here, the influence that the fluctuation of the minor axis direction vector s1 of the illumination spot BS has on the inspection will be described. If the angle formed by the vector s1 and the vector d is γ, γ can be expressed by the following equation (10).

[0093] γ=arccos(sinθ・sinφ)... (10)

[0094] If a vector g is orthogonal to the vector d in a plane including the vector d and the vector s1, when the illumination spot BS moves by Δs1 in the minor axis direction s1, the focal position of the optical image OI moves by M in the direction of the vector d. ２ A variation of M·Δs1·sin γ occurs in the direction of vector g. That is, the displacement vector Δv′ of the in-focus position of the optical image OI can be expressed by the following equation (11).

[0095] Δv′=M ２ ・Δs1・cosγ・d+M・Δs1・sinγ・g ... (11)

[0096] The displacement Δf′ of the focal position of the detection optical systems B1, . . . with respect to the optical axis direction OA2 can be expressed as in equation (12) by considering it in the same way as equation (8).

[0097] Δf'=(l3・Δv') / (d・l3)... (12)

[0098] Moreover, equation (12) can be written as equation (13) below.

[0099] Δf'=|Δv'|・cosc / cosb... (13)

[0100] Here, c represents the angle formed by the normal vector l3 of the image sensor surface and the displacement vector Δv′ of the in-focus position of the optical image OI.

[0101] 16 where a = 90 degrees, vector l3 and Δv' are parallel, and equation (13) takes a finite value. By substituting Δs1 = 1 μm, c = 0 degrees, and b = 52.5 degrees, Δf' = 1.6 μm is obtained, which shows that the movement of the illumination spot BS in the minor axis direction s1 has a non-negligible effect on the inspection sensitivity.

[0102] To suppress fluctuations in the minor axis direction s1 of the illumination spot BS, a beam position stabilization mechanism is introduced. This beam position stabilization mechanism can be configured, for example, with a position sensing detector A10 that detects the beam position, two actuator-equipped mirrors A11 that correct the beam position, and a control device A12 that generates control signals for the actuator-equipped mirrors based on signals from the position sensing detector.

[0103] The position sensing detector A10 can be, for example, a PSD or a four-segment photodiode. While the position sensing detector A10 is arranged in the illumination optical system using the beam sampler A13 in FIG. 16, the position sensing detector A10 may also be arranged to observe specularly reflected light from the sample surface (A10 detects specularly reflected light with the same reflection angle as the incident angle of the laser light). The actuator-equipped mirror A11 can be a voice coil type or a piezo type. The control device A12 can be, for example, a PID control circuit.

[0104] If the beam position fluctuates during measurement, the output signal of the position sensing detector A10 changes. The control device A12 acquires the amount of change in the output signal of the position sensing detector A10 and operates the actuator-equipped mirror A11 to correct the amount of change. This makes it possible to suppress fluctuations in the minor axis direction s1 of the illumination spot BS. In other words, it is possible to suppress a decrease in sensitivity during inspection.

[0105] According to the second embodiment, the direction of movement of the illumination spot BS, which affects the inspection sensitivity by changing the installation angle of the image sensor, can be limited to the minor axis direction s1, and the movement can be corrected by the beam position stabilization mechanism. Note that the beam position stabilization mechanism can also be applied to the configuration of the first embodiment.

[0106] Example 3 proposes a configuration in which the installation angle of the image sensor can be changed for each sample. Fig. 17 is a diagram for explaining the arrangement angle of the illumination optical system and the image sensor of a defect inspection apparatus according to Example 3. Except for the differences from Example 1 shown in Fig. 15, Example 3 has the same configuration as Example 1.

[0107] <Configuration example for optimizing the installation angle of the image sensor for each sample> Example 3 differs from Example 1 in that the image sensors C1... are mounted on an electric single-axis rotation stage F with the long axis direction 12 of the image sensors C1... as the rotation axis, and the angle of the image sensors C1... with respect to the optical axis OA2 can be changed as desired, and in that a displacement measurement unit G (e.g., a laser displacement meter or the like: measurement height displacement Δh) is provided that measures the surface shape of the sample 1, such as warpage and distortion, before the start of inspection.

[0108] In the third embodiment, the installation angles of the image sensors C1... are optimized in advance so as to obtain the highest inspection sensitivity for each inspection condition. In a defect inspection device, measurement conditions are changed depending on the inspection purpose. In the case of an rθ stage, in inspections requiring high throughput, the scanning device ST2 is rotated at a high frequency of several tens to hundreds of Hz. In addition, when inspecting for minute foreign particles or defects, the scanning device ST2 is rotated at a relatively low speed of several to several tens of Hz. Therefore, the height of the sample surface and the magnitude of fluctuation in the minor axis direction s1 of the illumination spot BS that may occur vary depending on the inspection purpose.

[0109] In an inspection in which the scanning device ST2 is rotated at high speed, fluctuations in the illumination spot BS that occur during the inspection also occur at high frequencies, and therefore large fluctuations are expected. In this case, the image sensors C1... are rotated in advance before the inspection using the motorized single-axis rotation stage F so as to reduce the effects of fluctuations. At this time, it is advisable to select the installation angle of the image sensors C1... so as to reduce the effects of fluctuations in the direction in which fluctuations are particularly large, between the height of the sample surface and the minor axis direction s1 of the illumination spot BS.

[0110] On the other hand, in an inspection in which the scanning device ST2 is rotated at a low speed, it is expected that fluctuations in the illumination spot BS that occur during the inspection will be smaller than in an inspection in which the scanning device ST2 is rotated at a high speed. In this case, to improve the inspection sensitivity, the image sensors C1... are rotated in advance before the inspection using the electric single-axis rotation stage F so that the angle at which the anti-reflection coating Ca on the light-receiving surface of the image sensor C1... can be most effectively utilized. In other words, the light-receiving surface of the image sensor C1... is installed so that it is perpendicular to the optical axis OA2.

[0111] Furthermore, the sample 1 is not perfectly flat and has inherent warping and distortion. It is assumed that the illumination spot BS will vary in magnitude in the s3 direction during inspection depending on the surface shape of the sample 1.

[0112] Therefore, before starting inspection, it is advisable to measure the surface shape of the sample 1 in advance using the displacement measurement unit G and determine the installation angles (angles a and b) of the image sensor C1, etc., taking into account the magnitude of the displacement (Δh) of the illumination spot BS in the s3 direction, which varies for each sample. In other words, if the sample 1 has significant warping or distortion (large Δh), the installation angle of the image sensor is selected so that the influence of the displacement in the s3 direction is minimized. If the warping or distortion is small (small Δh), the installation angle is selected so that the performance of the anti-reflection coating Ca on the image sensor's light-receiving surface can be effectively demonstrated (the values ​​of angles a and b are determined so that the configuration is resistant to in-plane displacement of the sample). Alternatively, a table specifying the installation angles (angles a and b) corresponding to the measured displacement (Δh) in the s3 direction can be prepared in advance, and the installation angles (angles a and b) can be obtained from the table when the displacement (Δh) is obtained for the sample being measured, and the image sensor can be positioned accordingly.

[0113] The information on the surface shape of the sample 1 is not limited to the results of measurement by the displacement measuring unit G, but may also be obtained by including results of measurements made in advance outside the defect inspection apparatus 100 in the sample ID and using these results.

[0114] <Effects of Example 3> According to Example 3, apart from the effects of Example 1, the installation angle of the image sensor C1... can be optimally set regardless of the measurement conditions, and the performance of the anti-reflection film Ca can be effectively exhibited, thereby suppressing a decrease in the amount of received light. others

[0115] The embodiments of the present disclosure are not limited to the examples described above and can be modified as appropriate. Not all of the elements included in the examples described above are necessarily required, and some components (excluding required elements) can be omitted as appropriate. Furthermore, some of the components of one embodiment can be replaced with components of another embodiment as appropriate, or components of another embodiment can be added to one embodiment.

[0116] 1 Sample 100 Defect inspection device A Illumination optical system B1-Bn Detection optical system Be, Bj, Bg Imaging lens (some optical elements) BS Illumination spot C1-Cn Imaging sensor D Signal processing device (computer) A12, E1 Control device (computer) F Motorized one-axis rotation stage G Displacement measurement unit l1 Minor axis vector of the light-receiving surface of the imaging sensor l2 Major axis vector of the light-receiving surface of the imaging sensor l3 Normal vector of the light-receiving surface of the imaging sensor M Imaging magnification OA2 Optical axis of the detection optical system OI Optical image of the illumination spot ST1 Sample stage s1 Short vector of the illumination spot s2 Long vector of the illumination spot s3 Normal vector of the illumination spot v1 Minor axis vector of the optical image v2 Long axis vector of the optical image v3 Normal vector of the optical image α Inclination angle of the optical axis of the detection optical system with respect to the longitudinal direction of the illumination spot β γ: Inclination angle of the light receiving surface of the image sensor with respect to the optical axis of the detection optical system γ: Inclination angle of the optical axis of the detection optical system with respect to the short side direction of the illumination spot Δs3: Amount of height fluctuation Δv3: Displacement amount of the focus position of the optical image due to height fluctuation

Claims

1. A defect inspection device for inspecting defects on the surface of a sample, comprising: a sample stage for supporting the sample; an illumination optical system for forming a thin line illumination spot on the surface of the sample; a detection optical system for collecting scattered light from the thin line illumination spot from the surface of the sample; and an image sensor having a plurality of pixels for outputting the scattered light intensity of the optical image of the illumination spot formed on a light-receiving surface by the detection optical system, wherein the optical axis of the detection optical system is inclined with respect to the surface of the sample, and the image sensor is inclined with respect to the optical axis of the detection optical system so that the major axis of the light-receiving surface coincides with a position conjugate with the thin line illumination spot, and further, the image sensor is rotated about an axis parallel to the major axis of the light-receiving surface of the image sensor so that the amount of shift in the light-focus point in the optical axis direction caused by displacement of the sample in the surface height direction is small.

2. A defect inspection device according to claim 1, wherein the imaging sensor is positioned so that a portion thereof intersects with the image plane of the optical image of the illumination spot formed at a position conjugate with the thin line illumination spot.

3. A defect inspection device as set forth in claim 1, wherein, when the angle between the displacement vector Δv of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction and the normal vector of the light-receiving surface is a and the angle between the vector of the optical axis of the detection optical system and the normal vector of the light-receiving surface is b, the amount of displacement Δf of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction with respect to the optical axis direction of the detection optical system is expressed as Δf = |Δv| cosa / cosb, and the angles a and b are determined so that the amount of displacement Δf is small, and the imaging sensor is positioned in accordance with the determined angles a and b.

4. A defect inspection device according to claim 3, wherein the angle a is 47 degrees and the angle b is 33 degrees.

5. A defect inspection device according to claim 1, further comprising a beam position stabilization mechanism for correcting positional fluctuations within the surface of the sample of the thin line illumination spot formed on the surface of the sample.

6. A defect inspection device according to claim 5, wherein the beam position stabilization mechanism comprises: a light position detector that detects the position of the illumination light irradiated onto the sample; an actuator-equipped mirror that reflects the illumination light emitted from the light source; and a control device that controls the orientation of the actuator-equipped mirror based on the position of the illumination light detected by the light position detector, thereby changing the direction of the illumination light.

7. A defect inspection device as defined in claim 5, wherein the angle between the displacement vector Δv of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction and the normal vector of the light-receiving surface is a, and the angle between the vector of the optical axis of the detection optical system and the normal vector of the light-receiving surface is b, the amount of displacement Δf of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction with respect to the optical axis direction of the detection optical system is expressed as Δf = |Δv| cosa / cosb, and the angles a and b are determined so that the amount of displacement Δf is small, and the imaging sensor is positioned in accordance with the determined angles a and b.

8. A defect inspection device according to claim 7, wherein the angle a is 90 degrees.

9. A defect inspection device according to claim 1, further comprising: a rotation stage that rotates the image sensor around an axis perpendicular to the optical axis of the detection optical system; a height displacement measurement unit that measures displacement in the surface height direction of the sample; and a control device that rotates the rotation stage based on the displacement in the surface height direction of the sample measured by the height displacement measurement unit, thereby enabling inspection of the defect in accordance with the displacement in the surface height direction of the sample.

10. A defect inspection device according to claim 9, wherein the angle between the displacement vector Δv and the normal vector of the light-receiving surface is a, and the angle between the vector of the optical axis of the detection optical system and the normal vector of the light-receiving surface is b, the amount of displacement Δf of the focal position of the illumination spot optical image in the optical axis direction of the detection optical system due to the displacement of the sample in the surface height direction is expressed as Δf = |Δv| cosa / cosb, and the control device sets the angles a and b according to the magnitude of the measured displacement Δh of the sample in the surface height direction, and rotates the rotation stage in accordance with the determined angles a and b so as to reduce the amount of displacement Δf.

11. A defect inspection method for inspecting defects on the surface of a sample, comprising: using an illumination optical system to irradiate illumination light onto the surface of the sample placed on a sample stage and form a thin line illumination spot on the surface of the sample; using a detection optical system whose optical axis is inclined with respect to the surface of the sample to collect scattered light of the thin line illumination spot from the surface of the sample; and using an image sensor having a plurality of pixels to output the scattered light intensity of the optical image of the illumination spot formed on a light receiving surface by the detection optical system, wherein the image sensor is inclined with respect to the optical axis of the detection optical system so that the major axis of the light receiving surface coincides with a position conjugate with the thin line illumination spot, and further, is rotated about an axis parallel to the major axis of the light receiving surface of the image sensor so that the amount of focus shift in the optical axis direction caused by displacement of the sample in the surface height direction is small.

12. A defect inspection method according to claim 11, wherein the imaging sensor is positioned so that a portion thereof intersects with the image plane of the optical image of the illumination spot which is formed at a position conjugate with the thin line illumination spot.

13. A defect inspection method as set forth in claim 11, wherein, when the angle between the displacement vector Δv of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction and the normal vector of the light-receiving surface is a and the angle between the vector of the optical axis of the detection optical system and the normal vector of the light-receiving surface is b, the amount of displacement Δf of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction with respect to the optical axis direction of the detection optical system is expressed as Δf = |Δv| cosa / cosb, and the angles a and b are determined so that the amount of displacement Δf is small, and the image sensor is positioned in accordance with the determined angles a and b.

14. A defect inspection method according to claim 13, wherein the angle a is 47 degrees and the angle b is 33 degrees.

15. A defect inspection method according to claim 11, further comprising correcting positional fluctuations within the surface of the sample of the thin line illumination spot formed on the surface of the sample using a beam position stabilization mechanism.

16. A defect inspection method as set forth in claim 15, wherein correcting the positional fluctuation of the thin line illumination spot formed on the surface of the sample using the beam position stabilization mechanism includes: detecting the position of the illumination light irradiated onto the sample using an optical position detector; and changing the direction of the illumination light by using a control device to control the orientation of an actuator-equipped mirror that reflects the illumination light emitted from a light source based on the position of the illumination light detected by the optical position detector.

17. A defect inspection method as defined in claim 15, wherein, when the angle between the displacement vector Δv of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction and the normal vector of the light-receiving surface is a and the angle between the vector of the optical axis of the detection optical system and the normal vector of the light-receiving surface is b, the amount of displacement Δf of the focal position of the optical image of the illumination spot due to the displacement of the sample in the surface height direction with respect to the optical axis direction of the detection optical system is expressed as Δf = |Δv| cosa / cosb, and the angles a and b are determined so that the amount of displacement Δf is small, and the imaging sensor is positioned in accordance with the determined angles a and b.

18. A defect inspection method according to claim 17, wherein the angle a is 90 degrees.

19. A defect inspection method according to claim 11, further comprising: using a height displacement measurement unit to measure the displacement of the sample in the surface height direction; and using a control device to rotate a rotation stage that rotates the image sensor around an axis perpendicular to the optical axis of the detection optical system, based on the measured displacement of the sample in the surface height direction, thereby enabling inspection of the defect in accordance with the displacement of the sample in the surface height direction.

20. A defect inspection method as defined in claim 19, wherein, when the angle between the displacement vector Δv and the normal vector of the light-receiving surface is a and the angle between the vector of the optical axis of the detection optical system and the normal vector of the light-receiving surface is b, the amount of displacement Δf of the focal position of the illumination spot optical image in the optical axis direction of the detection optical system due to the displacement of the sample in the surface height direction is expressed as Δf = |Δv| cosa / cosb, and the control device is used to set the angles a and b according to the magnitude of the measured displacement Δh of the sample in the surface height direction, and rotate the rotation stage in accordance with the determined angles a and b so as to reduce the amount of displacement Δf.

Images