Inspection device

Abstract

The purpose of the present invention is to obtain a high-precision reflected image or the like. The inspection apparatus includes: a surface defect detection system including an illumination device including an illumination laser light source device and a reflection observation device including a reflection sensor; and a photoluminescence detection system having a UV irradiation device including an excitation laser light source device and a fluorescence observation device including a fluorescence sensor, the photoluminescence detection system being capable of detecting the photoluminescence while irradiating the object with the illumination laser light source device with the illumination light and irradiating the object with the excitation laser light source device with the excitation light on a common optical path. The measurement light is acquired by the reflection observation device, and the fluorescence is acquired by the fluorescence observation device.

Description

Technical Field

[0001] This invention relates to an inspection apparatus for detecting defects in compound semiconductor substrates, such as silicon carbide substrates, or other semiconductor substrates. Background Technology

[0002] In the manufacturing process of semiconductor devices using SiC substrates, it is crucial to detect defects present in the SiC substrate in order to improve manufacturing yield. As is well known, an illumination beam is projected toward the SiC substrate, and the reflected light and photoluminescence emitted from the SiC substrate are separated and detected to form a reflected image and a photoluminescence image. Defect images are detected based on the reflected image and the photoluminescence image, and the defects are classified (Patent Document 1 and Patent Document 2).

[0003] In the devices of Patent Document 1 and Patent Document 2, reflected images and photoluminescent images are obtained from a single wavelength illumination beam. It is not possible to freely select and construct the sensor and imaging optical system for obtaining the reflected image, and it is not easy to obtain a high-precision reflected image.

[0004] In the devices of Patent Documents 1 and 2, reflected and photoluminescent images are obtained from a single-wavelength ultraviolet illumination beam passing through the slit. However, the intensity of the light passing through the narrow slit is weak, making it difficult to generate sufficient fluorescence for detection and thus difficult to obtain high-precision reflected images. Furthermore, when the wavelength of the illumination light for reflectance measurement is set to ultraviolet light, the low quantum efficiency and low light sensitivity of the image sensor in the ultraviolet region make it difficult to obtain reflected images with excellent S / N ratios.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 5633099

[0008] Patent Document 2: Japanese Patent No. 5713419 Summary of the Invention

[0009] The present invention was made in view of the above-mentioned background technology, and its purpose is to obtain high-precision reflection images at high speed.

[0010] To achieve the above objectives, the inspection apparatus of the present invention comprises: a surface defect detection system having an illumination device including an illumination laser source device and a reflection observation device including a reflection sensor; and a photoluminescence detection system having a UV irradiation device including an excitation laser source device and a fluorescence observation device including a fluorescence sensor, wherein the inspection apparatus irradiates the object with illumination light from the illumination laser source device and excitation light from the excitation laser source device, while acquiring measurement light from the reflection observation device and acquiring fluorescence from the fluorescence observation device.

[0011] In the aforementioned inspection device, an illumination laser source device and an excitation laser source device are prepared separately, thus allowing for free selection of the sensor and optical system used to obtain the reflected image. Sufficient light can be ensured without using a light source that requires light to pass through a slit, thereby enabling the defect detection system to achieve high precision.

[0012] According to a specific aspect of the present invention, the above-described inspection apparatus includes a common optical path type optical system that simultaneously irradiates the illumination laser source device with illumination light and the excitation laser source device with excitation light. In this case, it is possible to simultaneously measure the directly reflected measurement light and the fluorescence caused by excitation, thereby improving the inspection speed.

[0013] According to another aspect of the invention, in the surface defect detection system, the illumination device and the reflection observation device are confocal optical systems. In this case, it is possible to selectively detect only the reflected light from the substrate surface, and thus it is possible to isolate and inspect only the defects on the substrate surface.

[0014] According to another aspect of the present invention, the surface defect detection system is a multi-beam optical system that synthesizes images obtained from multiple line sensors.

[0015] According to another aspect of the invention, the inspection apparatus further comprises an oblique incidence device including an oblique incidence light source device, a dark field observation device including a dark field sensor, and a surface roughness detection system, wherein the oblique incidence device and the surface roughness detection system together with the surface defect detection system and the photoluminescence detection system constitute elements of a shared optical path type optical system.

[0016] According to another aspect of the present invention, the illumination device, the reflection observation device, the UV irradiation device, the fluorescence observation device, the oblique incidence device, and the dark-field observation device are elements of a common optical path type optical system, all having a common objective lens. By having a common objective lens for the surface defect detection system, the photoluminescence detection system, and the surface roughness detection system, the autofocus system can be easily shared among these systems, enabling high-precision measurements.

[0017] According to another aspect of the invention, a photoluminescence detection system illuminates an object using excitation light of multiple wavelengths. In this case, the penetration depth of the excitation light into the substrate depends on the wavelength, thus enabling the inspection of defects of varying depths.

[0018] According to another aspect of the invention, the photoluminescence detection system measures fluorescence from an object in multiple wavelength regions, said multiple wavelength regions including a near-ultraviolet wavelength region and a long-wavelength region with a wavelength longer than said near-ultraviolet wavelength region. Attached Figure Description

[0019] Figure 1 This is a block diagram illustrating the overall structure of the inspection device according to the embodiment.

[0020] Figure 2A The coordinate axes on the platform are shown. Figure 2B This diagram illustrates the relative movement of the objective lens or other components relative to the workpiece.

[0021] Figure 3 This is a diagram illustrating an example of an image acquisition method using a multi-beam approach.

[0022] Figure 4A and Figure 4B This is a diagram illustrating another example of an image acquisition method using multiple beams.

[0023] Figures 5A-5C This diagram illustrates a method for preventing the autofocus system's AF (autofocus) from malfunctioning due to stray light components during surface inspection in a surface defect detection system.

[0024] Figure 6 This diagram illustrates the defect re-inspection process. Detailed Implementation

[0025] Hereinafter, an inspection device and its operation as an embodiment of the present invention will be described with reference to the accompanying drawings.

[0026] Reference Figure 1 The inspection apparatus 100 of this embodiment includes an inspection optical system 2, a stage 4, and a control device 8. A workpiece WO, which is the object of inspection OB by the inspection apparatus 100, is supported on the stage 4. The workpiece WO is, for example, a SiC wafer. In the drawings, XYZ denotes an orthogonal coordinate system. In the optical system, the reference numeral AX denotes the optical axis.

[0027] The inspection optical system 2 includes a surface defect detection system 10 with vertical incident illumination, a first photoluminescence detection system 30 with vertical incident excitation, a second photoluminescence detection system 50 with oblique incident excitation, a surface roughness detection system 70 with oblique incident illumination, a region observation system 91, and an autofocus system 93.

[0028] The surface defect detection system 10 includes an illumination laser source device 11, a beam expander 12, a diffractive optical element (DOE) 13, a first lens system 14, a polarization separation prism (PBS) 15, a second lens system 16, a quarter-wave plate 17, a Nomarski prism 18, and an objective lens 2a as an illumination device 10a. Here, the illumination laser source device 11 outputs laser illumination light I1 with a wavelength of, for example, 445 nm in the visible wavelength region. The laser illumination light I1 has an electric field or polarization plane, for example, in the X direction perpendicular to the paper surface. The beam expander 12 expands the diameter of the laser illumination light I1 beam to, for example, about five times from 1 mm to 5 mm. The diffractive optical element 13 forms multiple beams LB from the laser illumination light I1. The beams LB are collimated. The multiple beams LB are also referred to as multiple beams. The first lens system 14 includes a pair of lenses 14a and 14b that project a pupil onto the object side of the polarization separation prism 15. A polarization-separating prism 15 reflects laser illumination light I1, which has a polarized plane in the X direction perpendicular to the paper plane. A second lens system 16 includes a pair of lenses 16a and 16b, with a projection pupil between its exit side and the objective lens 2a. A central focal point position IF is positioned between the pair of lenses 16a and 16b. A quarter-wave plate 17 makes the laser illumination light I1 circularly polarized. A Nomarski prism 18 enables differential interferometry measurements emphasizing minute irregularities. The objective lens 2a directs the laser illumination light I1 as multiple separate beams LB onto the workpiece WO. A multi-line pattern LP corresponding to the multiple beams LB is projected onto the surface of the workpiece WO. Here, the multiple beams LB are separated from each other about a direction perpendicular to their length direction and projected at equal intervals. In the illumination device 10a, for surface defect inspection, the objective lens 2a serves to direct the laser illumination light I1 perpendicularly onto the workpiece WO.

[0029] In the illumination device 10a, the Normask prism 18 can move back and forth between an operating position on the optical path and a retracted position outside the optical path by means of the drive device M1, allowing for fine-tuning of the configuration on the optical path. The Normask prism 18 separates the polarized light component of the laser illumination light I1 into two components: normal light and abnormal light, and separates the two lights in the transverse X direction to produce a small horizontal distance (shear). The normal light and abnormal light are incident on the workpiece WO at, for example, two points separated in the X direction. The measurement light I2, reflected by the workpiece WO, passes through the Normask prism 18 again and travels in reverse along the same optical path, incident on the multi-linear reflection sensor 23 described later. When there is a height difference between the two points on the workpiece WO where the normal light and abnormal light are incident, the phases of the normal light and abnormal light are misaligned, causing interference when they merge. Therefore, a brightness contrast is generated in the parts of the workpiece WO where there is a gradient distribution, and the unevenness of the surface of the workpiece WO is emphasized.

[0030] The surface defect detection system 10 includes an objective lens 2a, a Nomarsky prism 18, a quarter-wave plate 17, a second lens system 16, a polarization separation prism (PBS) 15, a bandpass filter 21, a re-imaging lens 22, and a multi-line reflection sensor 23 as a reflection observation device 10b. The objective lens 2a, Nomarsky prism 18, quarter-wave plate 17, second lens system 16, and polarization separation prism 15 are elements shared with the illumination device 10a. The bandpass filter 21 selectively allows the 445nm wavelength laser illumination light I1 to pass through, preventing the measurement light used for AF (as described later) from incident on the reflection sensor 23. The reflection sensor 23 has multiple line sensors 23a arranged at equal intervals in the Y direction. Each line sensor 23a has a detection surface 23d extending in a direction perpendicular to the scanning direction. Each line sensor 23a detects a pattern, i.e., a multi-line image, of multiple measurement lights I2 corresponding to multiple line beams LB. Here, the multiple line patterns that make up the multiline image are separated from each other about a direction perpendicular to the length direction, and are imaged at equal intervals.

[0031] As described above, the illumination device 10a and the reflection observation device 10b are a confocal optical system, which is capable of having resolution in the depth direction. By setting the illumination device 10a and the reflection observation device 10b as a confocal optical system, it is possible to selectively detect only the reflected light from the substrate surface, and thus it is possible to separate out and inspect only the defects on the substrate surface.

[0032] The first photoluminescence detection system 30 includes an excitation laser source device 31, a beam expander 32, a diffractive optical element 33, a reflector 34, a source lens 35, a dichroic mirror 71, a relay lens system 36, a dichroic mirror 37, a quarter-wave plate 17, and an objective lens 2a as a UV irradiation device 30a. The objective lens 2a and the quarter-wave plate 17 are shared with the illumination device 10a or the reflection observation device 10b of the surface defect detection system 10. The excitation laser source device 31 outputs excitation light E1 in multiple ultraviolet wavelength regions, such as 266 nm and 325 nm. The diffractive optical element 33 diffracts the excitation light E1 uniformly in a two-dimensional direction. That is, the excitation light E1 after passing through the diffractive optical element 33 has a rectangular cross-section.

[0033] The first photoluminescence detection system 30 includes an objective lens 2a, a quarter-wave plate 17, a dichroic mirror 37, a branched semi-transparent mirror 38, a notch filter 39, a pair of fluorescence branched dichroic mirrors 40 and 41, imaging lenses 42, 43, and 44, fluorescence sensors 45, 46, and 47, and a bandpass filter 48 as a fluorescence observation device 30b. The objective lens 2a, quarter-wave plate 17, and dichroic mirror 37 are shared with the UV irradiation device 30a. The first fluorescence sensor 45 detects fluorescence P1 in, for example, the infrared wavelength region above 700 nm. The second fluorescence sensor 46 detects fluorescence P2 in, for example, the visible wavelength region. The third fluorescence sensor 47 detects fluorescence P3 in, for example, the near-ultraviolet wavelength region of 380 nm to 400 nm. The bandpass filter 48 can move between an operating position on the optical path and a retracted position outside the optical path by means of a driving device M2, and can be replaced with other bandpass filters with different transmission wavelengths. Specifically, fluorescence sensors 45, 46, and 47 are TDI (Time Delay Integration) sensors. While the stage is moved in the Y direction, fluorescence sensors 45, 46, and 47 measure fluorescence P1, P2, and P3 with high sensitivity. The TDI sensors have a rectangular detection surface, which is shorter and has fewer pixels in the scanned Y direction, and longer and has more pixels in the unscanned X direction. The TDI sensors capture images while the workpiece WO is moved in the Y direction through scanning. The TDI sensors transfer charge in the Y direction according to the movement speed of the workpiece WO, thus accumulating brightness values, increasing the detected light intensity, and thereby improving sensitivity. Furthermore, the accumulation of brightness values ​​also provides a smoothing effect, thus reducing noise.

[0034] When the workpiece WO is a SiC substrate or wafer, edge-emitting emission occurs even without defects when the workpiece WO is illuminated with excitation light E1. Specifically, SiC wafers fluoresce at wavelengths of 380nm-400nm. When defects are present in the SiC wafer, fluorescence occurs, for example, at a wavelength of 480nm, while fluorescence at wavelengths of 380nm-400nm decreases. There are also reports of fluorescence occurring near wavelengths of 420nm and 450nm when defects or impurities are present in the SiC wafer. Furthermore, there are reports of fluorescence occurring in the infrared region when defects or impurities are present in the SiC wafer.

[0035] The second photoluminescence detection system 50 is an oblique-incident optical system, comprising a dual-use laser source device 51, a beam expander 52, a reflector 58, a diffractive optical element 53, a source lens 55, a perforated reflector 59, a relay lens system 36, a dichroic mirror 37, a quarter-wave plate 17, and an objective lens 2a as a UV irradiation device 50a. The relay lens system 36, dichroic mirror 37, quarter-wave plate 17, and objective lens 2a are elements shared with the first photoluminescence detection system 30. The dual-use laser source device 51 outputs excitation light E2, for example, in the ultraviolet wavelength region of 355 nm. The diffractive optical element 53 diffracts the excitation light E2 along the direction of the conical surface. That is, the excitation light E2 after passing through the diffractive optical element 53 has an annular cross-section. By using such an annular cross-section excitation light E2, oblique illumination from all directions is possible, suppressing the directionality of defect detection.

[0036] The second photoluminescence detection system 50 includes an objective lens 2a, a quarter-wave plate 17, a dichroic mirror 37, a branched semi-transparent mirror 38, a notch filter 39, a pair of fluorescence branched dichroic mirrors 40 and 41, imaging lenses 42, 43, and 44, a fluorescence sensor 45, 46, and 47, and a bandpass filter 48 as a fluorescence observation device 50b. The objective lens 2a, quarter-wave plate 17, and dichroic mirror 37 are shared with either the fluorescence observation device 50b or the UV irradiation device 30a.

[0037] The surface roughness detection system 70 is an oblique-incident optical system, comprising a dual-use laser light source device 51, a beam expander 52, a reflector 58, a diffractive optical element 53, a light source lens 55, a perforated reflector 59, a relay lens system 36, a dichroic mirror 37, a quarter-wave plate 17, and an objective lens 2a as a UV irradiation device 70a. The UV irradiation device 70a also functions as the UV irradiation device 50a of the second photoluminescence detection system 50. In this specification, the UV irradiation device 70a is referred to as the oblique-incident device OR, and the dual-use laser light source device 51 is referred to as the oblique-incident light source device OS.

[0038] The surface roughness detection system 70 includes an objective lens 2a, a quarter-wave plate 17, a dichroic mirror 37, a relay lens system 36, a dichroic mirror 71, a bandpass filter 72, an imaging lens 73, and a scattered light sensor 74 as an observation device 70b. The objective lens 2a, quarter-wave plate 17, dichroic mirror 37, and relay lens system 36 are shared with the UV irradiation device 70a. The scattered light sensor 74 directly detects the excitation light E2 scattered on the surface of the workpiece WO, which is obliquely illuminated by the UV irradiation device 50a of the second photoluminescence detection system 50, as the measurement light I3. Specifically, the scattered light sensor 74 is a TDI sensor, which measures the measurement light I3 with high sensitivity while moving the stage in the Y direction. In this specification, the observation device 70b is referred to as the dark-field observation device DR, and the scattered light sensor 74 is referred to as the dark-field sensor DS.

[0039] The area observation system 91 utilizes a portion of the surface defect detection system 10, including a first illumination LED 91a, a polarizing prism 91c, a semi-transparent mirror 91e, a notch filter 91g, an observation dichroic mirror 91i, a bandpass filter 91k, an imaging lens 91m, and a CCD camera 91o. The first illumination LED 91a emits light in a wide bandwidth in the visible wavelength region. Specifically, the first illumination LED 91a is a white LED. By illuminating the first illumination LED 91a, the observation illumination light L2 is guided via the polarizing prism 91c, the semi-transparent mirror 91e, the notch filter 91g, and the observation dichroic mirror 91i to the second lens system 16 and beyond of the surface defect detection system 10. At this time, the observation illumination light L2 incident on the workpiece WO passes through the polarizing prism 91c and the quarter-wave plate 17, becoming circularly polarized, and is incident on the workpiece WO via the objective lens 2a. The observation illumination light L2, reflected by the workpiece WO, travels retrogradely from the objective lens 2a within the surface defect detection system 10. It is then extracted outside the system by the dichroic mirror 91i, reflected by the semi-transparent mirror 91e and the polarization-separating prism 91c, and finally incident on the CCD camera 91o after passing through the imaging lens 91m. The image captured by the CCD camera 91o after illuminating the first illumination LED 91a is equivalent to conventional microscopic observation. At this time, by switching to a bandpass filter 91k with a different transmission wavelength, an observation image of the desired wavelength can be obtained.

[0040] Furthermore, by turning off the first illumination LED 91a of the area observation system 91 and turning on the excitation laser source device 31 of the first photoluminescence detection system 30, direct-incident fluorescence microscopy observation can be performed. Moreover, by turning off the first illumination LED 91a and turning on the combined laser source device 51 of the second photoluminescence detection system 50, oblique-incident fluorescence microscopy observation can be performed.

[0041] The autofocus system 93 uses a part of the surface defect detection system 10 and includes a second illumination LED 93a, a bandpass filter 93r, a stripe pattern mask 93s, a polarizing prism 93c, an imaging lens 93m, a semi-transparent mirror 91e, a dichroic mirror 91i for observation, a semi-transparent mirror 93j, a first CCD sensor 93p, and a second CCD sensor 93q. The second illumination LED 93a emits light in a wide bandwidth in the visible wavelength region. Specifically, the second illumination LED 93a is a white LED. The bandpass filter 93r can be switched to a filter with desired transmission wavelength characteristics by means of a turntable assembling multiple bandpass filters, enabling the wavelength of the monitoring AF light L3, i.e., the illumination wavelength for AF, to correspond to the wavelength observed or measured. The stripe pattern mask 93s is used to project a stripe pattern onto the surface of the workpiece WO. If the stripe pattern projected onto the surface of the workpiece WO is clear, it indicates that the focus is on.

[0042] The striped pattern on the workpiece WO is projected onto the first CCD sensor 93p and the second CCD sensor 93q by the objective lens 2a, the second lens system 16, and the imaging lens 93m. The CCD sensors 93p and 93q are image sensors, and their operation is controlled by the AF control circuit 7b. The AF control circuit 7b can determine whether the objective lens 2a is in a focusing state, a forward focusing state, or a backward focusing state based on the contrast of the images detected by the CCD sensors 93p and 93q, and can output this focusing or offset state to the control device 8. Furthermore, the first CCD sensor 93p is configured to be offset forward relative to the focusing state, and the second CCD sensor 93q is configured to be offset backward relative to the focusing state. Thus, a focusing state can be achieved by moving the objective lens 2a vertically in the Z direction using the lens stage 5, and stopping the movement of the objective lens 2a at a position where the contrast of the pattern detected by the first CCD sensor 93p matches the contrast of the pattern detected by the second CCD sensor 93q.

[0043] The autofocus system 93 can adjust its focus state not only on the surface of the workpiece WO, but can also shift it in the depth direction of the workpiece WO. For example, in the measurement of fluorescence P1, P2, and P3, the focus can be aligned with the interior of the workpiece WO. For example, by shifting the objective lens 2a to a position that applies a shift to the detection results of the CCD sensors 93p and 93q, which are image sensors, the focus can be aligned with the interior of the workpiece WO.

[0044] A drive circuit 6a is provided along with the surface defect detection system 10. The drive circuit 6a operates under the control of the control device 8, illuminates the workpiece WO with a perpendicular incident illumination through the illumination laser light source device 11, and saves the detection results of the reflection sensor 23.

[0045] Accompanying the first photoluminescence detection system 30 are a light source driving circuit 6b and a sensor driving circuit 6c. The light source driving circuit 6b operates under the control of the control device 8, using the excitation laser light source device 31 to provide perpendicular-incident light excitation to the workpiece WO. The sensor driving circuit 6c operates under the control of the control device 8, storing the detection results of the fluorescence sensors 45, 46, and 47.

[0046] A light source driving circuit 6d is provided along with the second photoluminescence detection system 50. The light source driving circuit 6d operates under the control of the control device 8, and provides oblique-incidence light excitation to the workpiece WO through the combined laser light source device 51. In addition, the fluorescence generated by the oblique-incidence light excitation is detected by fluorescence sensors 45, 46, and 47, and the sensor driving circuit 6c stores the detection results of fluorescence sensors 45, 46, and 47.

[0047] A sensor drive circuit 6e is provided along with the surface roughness detection system 70. The sensor drive circuit 6e operates under the control of the control device 8, and detects the scattered light from the workpiece WO being illuminated by the oblique incidence type via the scattered light sensor 74. In addition, the oblique incidence type illumination is performed by a dual-purpose laser light source device 51 driven by the light source drive circuit 6d.

[0048] A camera drive circuit 7a is provided along with the area observation system 91. The camera drive circuit 7a operates under the control of the control device 8, emitting illumination light through the first illumination LED 91a while acquiring and recording the area image of the workpiece WO through the CCD camera 91o.

[0049] An AF control circuit 7b is provided along with the autofocus system 93. The AF control circuit 7b operates under the control of the control device 8, emitting AF light from the second illumination LED 93a while judging the contrast status of the image acquired by the CCD sensors 93p and 93q.

[0050] Objective lens 2a is supported by lens stage 5 and can move vertically in the Z direction. The movement of lens stage 5 is controlled by lens drive device 5a. Under the control of control device 8, lens stage 5 causes objective lens 2a to move slightly in the Z direction, thereby adjusting the focus state of the image detected by reflection sensor 23.

[0051] The stage 4 can support the workpiece WO and move it in the XY and Z directions, and can rotate it around the X, Y, and Z axes. The movement of the stage 4 is controlled by the stage controller 4a. Under the control of the control device 8, the stage 4 can precisely move the workpiece WO to a predetermined position and can move the workpiece WO along a specified path at a desired speed.

[0052] The above-mentioned optical elements (including light source and sensor, hereinafter the same) constituting the illumination device 10a and reflection observation device 10b of the surface defect detection system 10, (2) the optical elements constituting the UV irradiation device 30a and fluorescence observation device 30b of the first photoluminescence detection system 30, (3) the optical elements constituting the UV irradiation device 50a and fluorescence observation device 50b of the second photoluminescence detection system 50, (4) the optical elements constituting the UV irradiation device 70a and observation device 70b of the surface roughness detection system 70, (5) the optical elements constituting the area observation system 91, and (6) the optical elements constituting the autofocus system 93 together constitute a common optical path type optical system 102. In the common optical path type optical system 102, in particular, the objective lens 2a is used for all of the surface defect detection system 10, the first photoluminescence detection system 30, the second photoluminescence detection system 50, the surface roughness detection system 70, the area observation system 91, and the autofocus system 93. The shared optical path optical system 102, which simultaneously illuminates the illumination light I1 and the excitation light E1, can simultaneously measure the directly reflected measurement light I2 and the excitation-based fluorescence P1, P2, and P3, thereby improving inspection speed. Furthermore, since the objective lens 2a is shared in the surface defect detection system 10, the photoluminescence detection systems 30 and 50, and the surface roughness detection system 70, it is easy to share the autofocus system 93 with respect to these systems, enabling high-precision measurements.

[0053] The control device 8 is a computer, which has arithmetic processing device, storage device, communication device, etc., and performs actions according to the program or the operator's instructions.

[0054] Figure 2A The coordinate axes on stage 4 are shown. Figure 2B This diagram illustrates the relative movement of the objective lens 2a and other components relative to the stage 4 and the workpiece WO. In this case, the Y direction is the main scanning direction, and the X direction is the sub-scanning direction. The inspection area IR is directly below the objective lens 2a. The objective lens 2a or the inspection area IR moves in stages along the trajectory TR. A multi-line pattern LP is projected in the inspection area IR. The trajectory TR includes the main scan trajectory TR1 (shown as a solid line) and the sub-scan trajectory TR2 (shown as a dashed line). As a result, the inspection area IR moves in a manner that covers the entire surface Wa of the workpiece WO.

[0055] Figure 3This diagram illustrates an example of a multi-beam image acquisition method using multiple wire bundles (LBs). In the diagram, four blocks represent the elapsed time of one frame (T = 0, 1, 2, 3), and the patterns (A, B, C, D) within each block represent imaginary patterns formed on the workpiece (WO). Arrow V indicates the stage 4 or the workpiece (see reference). Figure 2B The arrow V' represents the relative movement of the beam bundles. In this case, assuming P / W0 = 2 and n = 2 (the number of beams is 5), the beam bundle LB moves W0 × 5 in one step. Here, P represents the beam spacing, W0 represents the beam size, and n represents any positive number. In the illustrated example, the detection results of the 5 beam bundles LB need to be rearranged in memory in the order of 3 → 1 → 4 → 2 → 5. Although the detection results of the first and last two beam bundles LB at the beginning and end of the scan are useless, the pattern on the workpiece WO can be continuously acquired and reconstructed while the workpiece WO moves at a constant speed. For example, it can be done as follows... Figure 4A As shown, with P / W0 = 2 and n = 3 (7 beams), the beam LB moves W0 × 7 in one step. In this case, the detection results of the 7 beam LBs are rearranged in memory in the order of 4th → 1st → 5th → 2nd → 6th → 3rd → 7th. Furthermore, P / W0 is not limited to 2 and can be 3 or more. Specifically, for example, it can be as follows... Figure 4B As shown, with P / W0 = 3 and n = 2 (7 beams), the beam LB moves W0 × 7 in one step. In this case, the detection results of the 7 beam LBs are rearranged in memory in the order of 5th → 3rd → 1st → 6th → 4th → 2nd → 7th. Based on the above, it is clear that the second multi-beam or beam group is arranged after the (n+1)th beam LB in the first multi-beam. Typically, the number of beams N in a multi-beam is given as N = n × (P / W0) + 1, and the stage speed v is given as v = W0 × N / T.

[0056] Figures 5A-5C This diagram illustrates a method for preventing the autofocus system 93 from malfunctioning due to stray light components generated in various optical elements during surface inspection using the surface defect detection system 10. Figure 5A This diagram illustrates the function of the Normask prism 18, which separates the polarized component of the laser illumination light I1 into two components: normal light and abnormal light. The normal and abnormal light are incident on the workpiece WO at two points, for example, separated in the Y direction. The measurement light I2, reflected by the workpiece WO, again travels in reverse along the same optical path through the Normask prism 18. At this point, regarding the protrusion Wb, tilted surfaces SL+ and SL- exist on one and the other slope. Figure 5BThis diagram illustrates the effect of tilting SL+ and SL- on brightness contrast. With the background phase (i.e. delay) of the Nomaski prism 18 set to 90 degrees, the brightness contrast increases with tilting SL+, thus becoming brighter, and decreases with tilting SL-, thus becoming darker. Therefore, it is possible to distinguish between the two types of tilting SL+ and SL-. Figure 5C This is a conceptual diagram illustrating the detection intensity of the laser illumination light I1 when the surface defect detection system 10 performs differential interferometry measurement on the surface of workpiece WO, and the detection intensity of the AF light by the autofocus system 93. The horizontal axis represents the delay β of the Normask prism 18. In a specific example, the illumination wavelength of the laser illumination light I1 is λ. DIC =445nm, the wavelength of the AF light is λ AF ~560nm. In differential interferometry, it is desirable for the laser illumination light I1 to be detected in a state like a black circle (●) (maximum tilt state). This maximizes the slope of the change in light intensity, resulting in the highest sensitivity and facilitating the determination of the protrusion Wb, i.e., the unevenness of the defect shape. On the other hand, it is desirable for the AF light to be detected in a state like a white circle (○) (minimum tilt state). In this case, the AF light directed towards the workpiece WO is incident on the Nomaski prism 18, for example, as right-handed circularly polarized light, and the AF light reflected from the workpiece WO exits the Nomaski prism 18, for example, as left-handed circularly polarized light, in a perpendicular state. Thus, the AF light and stray light in its wavelength region are blocked by the polarization separation prism 93c, preventing detection by the first CCD sensor 93p and the second CCD sensor 93q of the autofocus system 93. In particular, when the workpiece WO is a SiC wafer, the SiC wafer is nearly transparent (reflectivity approximately 10%) in the visible wavelength region, resulting in low reflected light intensity. It is important to improve the optical S / N ratio by removing stray light components generated in all optical elements. That is, by setting the delay β of the Normask prism 18 at the target location where the laser illumination light I1 is at its maximum tilt state (shown by the black circle) and the AF light is at its minimum state (shown by the white circle), it is possible to suppress the influence of stray light on the AF operation during differential interferometry. The following relationship holds regarding the delay β.

[0057]

[0058] β: Delay, x: Prism position, β0: Initial phase at x = 0

[0059] λ: wavelength, n o (n e ): The refractive index of normal light (abnormal light), θ w wedge angle

[0060] At the wavelength λ of AF light AF The illumination wavelength λ of laser illumination light I1DIC When the value is an integer multiple of 4, it is easy to adjust the target area so that the laser illumination light I1 is at its maximum tilt (as shown by the black circle) and the AF light is at its minimum tilt (as shown by the white circle). The wavelength of the AF light can be adjusted by adjusting the transmission characteristics based on the switching of the bandpass filter 93r. Regarding the delay β, as described above, it can be adjusted by shifting the position of the Nomaski prism 18.

[0061] Figure 6 This diagram illustrates the defect re-inspection process. The re-inspection is performed after the overall inspection of the workpiece WO. During the overall inspection of the workpiece WO, the surface defect detection system 10, the first photoluminescence detection system 30, the second photoluminescence detection system 50, and the surface roughness detection system 70 operate simultaneously and in parallel. For the entire workpiece WO, they simultaneously detect surface defect information under perpendicular incident illumination, fluorescence distribution information under perpendicular incident excitation, fluorescence distribution information under oblique incident excitation, and surface roughness information under oblique incident illumination. Furthermore, during the re-inspection, the system can move to areas with defects or other anomalies for individual observation of these areas.

[0062] First, under the control of the control device 8, the stage 4 is moved so that the objective lens 2a is positioned opposite the defect or abnormal position of the workpiece WO (step S11). Next, under the control of the control device 8, the autofocus system 93 is activated to perform AF (step S12). The control device 8 determines the type of defect or abnormality at that position (step S13).

[0063] In the case of a surface defect or anomaly, the excitation laser source device 31 is turned off (step S14), and the first illumination LED 91a of the area observation system 91 is turned on (step S15). The control device 8 determines whether observation by the area observation system 91 is possible (step S16). If observation by the area observation system 91 is possible ("Yes" in step S16), an area image of the workpiece WO is acquired using the CCD camera 91o of the area observation system 91 (step S17). If observation by the area observation system 91 is not possible ("No" in step S16), a relative scan of the workpiece WO is performed in the vicinity of the abnormal area, and surface defect information is acquired using the surface defect detection system 10 (step S18). Thus, a defect image of the abnormal area can be acquired and displayed to the operator.

[0064] In the event of an internal defect or anomaly, the excitation laser source device 31 is activated (step S24), and the first illumination LED 91a of the area observation system 91 is deactivated (step S25). The control device 8 selects the bandpass filter 48 and fluorescence sensors 45, 46, and 47 for the desired wavelength region according to operator instructions or program specifications (step S26). Then, the control device 8 activates the first photoluminescence detection system 30, etc., to acquire a fluorescence image of the workpiece WO (step S27).

[0065] When defects or anomalies exist on the surface and inside, the control device 8 synthesizes these images and displays them on a display (not shown) provided on the control device 8 (step S28). Coloring, region classification, and three-dimensional display are also possible when synthesizing images.

[0066] The inspection apparatus 100 described above includes: a surface defect detection system 10, which has an illumination device 10a including an illumination laser source device 11 and a reflection observation device 10b including a reflection sensor 23; and a photoluminescence detection system 30, which has a UV irradiation device 50a including an excitation laser source device 31 and a fluorescence observation device 50b including fluorescence sensors 45, 46, and 47. The inspection apparatus 100 irradiates the object OB with illumination light I1 from the illumination laser source device 11 and excitation light E1 from the excitation laser source device 31, while acquiring measurement light I2 from the reflection observation device 10b and acquiring fluorescence P1, P2, and P3 from the fluorescence observation device 50b.

[0067] In the inspection device 100 described above, an illumination laser source device 11 and an excitation laser source device 31 are respectively prepared, so the sensor and optical system used to obtain the reflected image can be freely selected, and the surface defect detection system 10 can be made highly accurate.

[0068] Furthermore, in the aforementioned inspection apparatus 100, the photoluminescence detection systems 30 and 50 illuminate the object using excitation light E1 of multiple wavelengths. In this case, since the penetration depth of the excitation light E1 into the substrate, which is the object OB or the workpiece WO, depends on the wavelength, it is possible to inspect defects of different depths in the substrate.

[0069] This invention is not limited to the embodiments described above and can be implemented in various ways without departing from its spirit. Those skilled in the art can appropriately apply various modifications or alterations to the structure and details of the invention within the scope of the technical concept set forth in the claims. For example, the workpiece WO, which is the object of inspection, is not limited to SiC wafers, but can also be other compound semiconductor substrates such as Ga2O3 or GaN, or Si wafers.

[0070] In the above embodiment, fluorescence P1 is detected by the first fluorescence sensor 45 in the infrared wavelength region above 700 nm, fluorescence P2 is detected by the second fluorescence sensor 46 in the visible wavelength region, and fluorescence P3 is detected by the third fluorescence sensor 47 in the near-ultraviolet wavelength region of 380 nm-400 nm. However, it is also possible to use two fluorescence sensors to measure fluorescence in two wavelength regions. In this case, for example, the first fluorescence sensor 45 or the second fluorescence sensor 46 can be omitted.

[0071] In addition, this application claims priority based on Japanese Patent Application No. 2023-063355, filed on April 10, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. An inspection device comprising: A surface defect detection system comprising an illumination device including an illumination laser source and a reflection observation device including a reflection sensor; and A photoluminescence detection system comprising a UV irradiation device including an excitation laser source and a fluorescence observation device including a fluorescence sensor. The inspection device simultaneously illuminates the object with illumination light from the illumination laser source device and excitation light from the excitation laser source device, while acquiring measurement light from the reflection observation device and fluorescence from the fluorescence observation device.

2. The inspection device according to claim 1, wherein, The inspection device includes a common optical path type optical system, which performs illumination of the illumination laser source device and excitation of the excitation laser source device in parallel.

3. The inspection device according to claim 1, wherein, In the surface defect detection system, the illumination device and the reflection observation device are confocal optical systems.

4. The inspection device according to claim 1, wherein, The surface defect detection system is a multi-beam optical system that synthesizes images obtained from multiple line sensors.

5. The inspection device according to claim 1, wherein, The inspection device also includes an oblique incidence device containing an oblique incidence light source, a dark field observation device containing a dark field sensor, and a surface roughness detection system. The oblique incidence device and the surface roughness detection system together with the surface defect detection system and the photoluminescence detection system constitute the elements of a shared optical path type optical system.

6. The inspection device according to claim 5, wherein, The illumination device, the reflection observation device, the UV irradiation device, the fluorescence observation device, the oblique incidence device, and the dark-field observation device, as part of the shared optical path type optical system, share a common objective lens.

7. The inspection device according to claim 1, wherein, The photoluminescence detection system uses excitation light of multiple wavelengths to illuminate the object.

8. The inspection device according to claim 1, wherein, The photoluminescence detection system measures fluorescence from the object in multiple wavelength regions, including a near-ultraviolet wavelength region and a long-wavelength region with wavelengths longer than the near-ultraviolet wavelength region.

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