JP5725501B2 - Inspection device - Google Patents

Description

  The present invention optically detects defects existing in a silicon carbide substrate (SiC substrate) or an epitaxial layer formed on a silicon carbide substrate using an optical device including a differential interference optical system, and detects the detected defects. The present invention relates to a classifying inspection apparatus and defect inspection method.

  A semiconductor device manufacturing method has been developed in which a single crystal layer is formed on a single crystal substrate by an epitaxial growth method, and a device is formed on the formed single crystal layer. In this semiconductor device manufacturing method, a silicon carbide substrate is used as a single crystal substrate, and an epitaxial layer is formed on the silicon carbide substrate by a step flow growth method. Since silicon carbide has superior physical and thermal properties compared to silicon, a method for manufacturing a device using a semiconductor substrate in which an epitaxial layer of silicon carbide is formed on a silicon carbide substrate is high power. This is extremely useful for manufacturing low-loss semiconductor devices.

  In the semiconductor device manufacturing method described above, in order to improve the manufacturing yield and improve the reliability of the device, the defect existing in the silicon carbide substrate and the epitaxial layer is detected, and the type of the detected defect is determined. Classification is extremely important. Conventionally, defect detection by X-ray topography is known as a method for detecting defects present in a silicon carbide substrate (SiC substrate) (see, for example, Patent Document 1). This defect detection method by X-ray topography has an advantage that crystal defects existing in the SiC substrate can be detected nondestructively.

  As a method for optically detecting defects formed on a SiC substrate, a laser scattering type defect inspection apparatus is known (see, for example, Patent Document 2). In this laser scattering type defect inspection apparatus, laser light emitted from a laser diode is incident obliquely on the substrate surface, and scattered light generated on the substrate surface is detected by a photodetector. Defect detection is performed based on the detected scattered light.

As an inspection device for detecting defects in the phase shift mask, a differential interference optical system is arranged in the optical path between the light source and the objective lens, a differential interference image of the phase shift mask is taken, and the defects are detected based on the differential interference image. The inspection apparatus to detect is known (for example, refer patent document 3). In this known inspection apparatus, a differential interference image of a captured phase shift mask is compared with a reference image, and a defect is detected based on the result of the image comparison.
JP 2009-44083 A US Pat. No. 7,201,799 JP 2002-287327 A

  In the defect detection method using X-ray topography described above, crystal defects inside the substrate can be detected, and threading screw dislocations and defects in the basal plane formed in the bulk of the substrate are detected. However, defect inspection by the X-ray topography method not only requires a large apparatus for irradiating X-rays, but also has a drawback that it takes a long time to detect the defect and the inspection cost is expensive.

  Since the laser scattering type defect inspection apparatus detects scattered light generated on the substrate surface, it is possible to detect defects appearing on the substrate surface. However, since undesired scattered light is incident on the photodetector, the defect detection resolution is low and it is difficult to detect fine defects. In particular, the laser scattering type inspection apparatus has low detection sensitivity in the height direction of the sample surface, so that it is difficult to clearly detect minute unevenness defects of several nm to several tens of nm formed on the surface of the SiC substrate. There are drawbacks. That is, lattice defects formed in the bulk of the SiC substrate appear as irregularities of about several nm to several tens of nm on the substrate surface. Accordingly, in the laser scattered light type defect detection, there is a limit in detecting a fine defect existing in the SiC substrate, and there is a limit in the defect type determination.

  Furthermore, since the SiC substrate is transparent in the visible region or the infrared region, the illumination beam passes through the inside of the substrate, is reflected by the back surface of the substrate, and is emitted from the substrate surface. Therefore, in an inspection apparatus that performs area illumination on the substrate surface, it is necessary to remove the influence of reflected light from the back surface of the substrate. As a method for removing the reflected light from the back surface of the substrate, a method using a special spatial filter is assumed, but a problem that the structure of the optical system becomes complicated occurs.

  As a killer defect that becomes a problem when a device is formed in an epitaxial layer formed on a SiC substrate, a micropipe defect is cited. When micropipe defects are formed in the epitaxial layer, there arises a problem that not only the leakage current of the manufactured device increases but also the withstand voltage decreases. Therefore, when manufacturing a device using a SiC substrate, in order to improve the manufacturing yield, it is an urgent issue to detect micropipe defects separately from other defects. In addition, a shape defect having a specific shape such as a carrot defect or a triangle defect is also a fatal killer defect. On the other hand, dislocation defects such as threading screw dislocation defects, edge transition defects, and defects in the basal plane are defects specific to silicon carbide substrates and epitaxial layers, but are not fatal defects in device manufacturing, but killer defects. It is distinguished from. Therefore, if the detected defect can be classified according to the type of the defect, for example, if the part where the killer defect is formed is specified, it becomes possible to obtain extremely useful data for quality control of the manufactured device. . In addition, although dislocation defects are not killer defects, defects that degrade device characteristics occur when the formation density increases. Therefore, if the number of occurrences of dislocation defects is detected for each chip area, useful information for quality control can be obtained.

An object of the present invention is to realize an inspection apparatus and a defect inspection method capable of optically detecting defects existing in a silicon carbide substrate or an epitaxial layer formed on the silicon carbide substrate and classifying the detected defects. .
An object of the present invention is to realize an inspection apparatus capable of outputting defect distribution data indicating the type of defect and the number of defects detected for each chip area where individual devices are to be formed based on the result of defect classification. It is in.
Furthermore, another object of the present invention is to realize an inspection apparatus that has high detection sensitivity and can detect a fine concave or convex defect of about several nanometers and is not affected by reflected light from the back surface of the substrate. It is in.

The inspection apparatus according to the present invention described as a reference is an inspection apparatus that performs defect inspection on a silicon carbide substrate or an epitaxial layer formed on a silicon carbide substrate,
A light source device that generates an illumination beam, a stage that supports a silicon carbide substrate to be inspected and is movable in a first direction and a second direction orthogonal to the first direction, and the illumination beam on the stage An objective lens that projects toward the arranged silicon carbide substrate, and an incident illumination beam that is disposed in an optical path between the light source device and the objective lens, is converted into first and second sub-beams that are coherent with each other. And a differential interference optical system for synthesizing sub-beams reflected on the surface of the silicon carbide substrate or epitaxial layer and emitting an interference beam including phase difference information related to the surface height of the silicon carbide substrate or epitaxial layer; An optical device having an image sensor for receiving an interference beam emitted from the interference optical system, and an output signal from the image sensor, An image forming means for forming a differential interference image on the surface of the plate or the epitaxial layer, a defect detection means for detecting a defect based on the formed differential interference image, and a defect detected based on the differential interference image of the detected defect A signal processing device having defect classification means for classifying is provided.

  Various crystal defects existing in the silicon carbide substrate or the epitaxial layer formed on the silicon carbide appear as minute irregularities of about several nm to several tens of nm on the surface of the substrate or the surface of the epitaxial layer. For example, dislocation defects such as threading screw dislocation defects and defects in the basal plane appear as pit-like defects on the surface of the epitaxial layer. Further, shape defects such as triangle defects and carrot defects appear as concave defects having a relatively large size and a specific shape on the surface of the epitaxial layer. Further, scratches generated in the polishing process are linear concave defects having a depth of about several tens of nanometers. On the other hand, the differential interference optical system can detect unevenness of several nm to several tens of nm on the sample surface as a luminance change. Therefore, in the present invention, crystal defects existing in the silicon carbide substrate and the epitaxial layer formed on the silicon carbide substrate are detected using an optical device including a differential interference optical system.

  Furthermore, as a result of analysis of differential interference images of various crystal defects existing in the silicon carbide substrate or epitaxial layer by the present inventor, differential interference images of various crystal defects existing in the silicon carbide substrate or epitaxial layer are obtained for each crystal defect. It was found that the image was taken as a defect image having a specific shape or luminance distribution. That is, various dislocation defects such as a screw dislocation defect and a defect in the basal plane appear as pit shapes on the surface of the substrate or the epitaxial layer, and the differential interference image is a combination of the high luminance image portion and the low luminance image portion. It is captured as a unique light and dark image. Further, a differential interference image of a shape defect such as a triangle defect or a carrot defect formed in the epitaxial layer is taken as a large-sized low-luminance image having a specific shape such as a triangle. Further, the micropipe defect is a hollow hole and is captured as a dot-like low luminance image. Further, the bump defect is also captured as a specific differential interference image. Therefore, dislocation defects, shape defects and micropipe defects can be distinguished from other defects based on their differential interference images. Based on such an analysis result, in the present invention, the defect is detected based on the captured differential interference image and the detected defect is classified based on the captured differential interference image. If the detected defect is classified, information on the cause of the defect can be obtained, and useful quality control information on the formation of the silicon carbide substrate and the epitaxial layer can be obtained. In defect classification, it is necessary that at least shape defects and dislocation defects having a specific shape can be distinguished from other defects.

  In a preferred embodiment of the inspection apparatus according to the present invention, the signal processing apparatus further outputs means for outputting map information obtained by dividing the silicon carbide substrate to be inspected into a plurality of chip areas on which individual devices are to be formed, and Defect distribution data output means for outputting defect distribution data indicating the type of detected defect or the type and number of detected defects for each chip area using the classification result of the defect classification means and the map information. It is characterized by having.

  As described above, when a silicon carbide substrate or an epitaxial layer is inspected using an inspection apparatus including a differential interference optical system, the type of defect can be determined from the differential interference image of the detected defect. Therefore, in the present invention, using the map information obtained by dividing the silicon carbide substrate to be inspected into a plurality of chip areas where individual devices are to be formed, the type of defect detected using the classification result of the defect classification means And / or defect distribution data indicating the number of each chip area. If the defect distribution data is obtained, quality control data for each chip area of the silicon carbide substrate can be obtained, so that the device manufacturing yield can be considerably improved.

  Another preferred embodiment of the inspection apparatus according to the present invention is characterized in that the defect distribution data output means outputs defect distribution data including data indicating the presence or absence of killer defects and the number of detected dislocation defects.

  In the present invention, it is possible to classify the detected crystal defect into a killer defect that is a fatal defect for manufacturing a device and other defects by using the differential interference image of the defect. That is, shape defects such as triangle defects and micropipe defects are killer defects that are fatal to the manufacture of the device. If a device is formed at a site where these killer defects exist, the device may be defective. It is expensive. On the other hand, dislocation defects such as screw dislocation defects and defects in the basal plane are crystal defects peculiar to silicon carbide substrates, but are not fatal defects in device manufacturing, and there are a few dislocation defects. Even if a device is formed, the device operates normally. On the other hand, if there are a large number of dislocation defects in one chip area, the characteristics of the device may be deteriorated. Therefore, in the present invention, defect distribution data including data indicating the presence / absence of killer defects and the number of dislocation defects is output for each chip area.

An inspection apparatus according to the present invention is an inspection apparatus that detects crystal defects that appear on the surface of a silicon carbide substrate or the surface of an epitaxial layer formed on the silicon carbide substrate, and classifies the detected crystal defects .
A light source device that generates an illumination beam having an opaque wavelength in the ultraviolet region with respect to the silicon carbide substrate, and supports the silicon carbide substrate to be inspected and moves in the first direction and the second direction orthogonal to the first direction. A possible stage, an objective lens that projects the illumination beam toward a silicon carbide substrate disposed on the stage, a differential interference optical system disposed in an optical path between the light source device and the objective lens, and the carbonization An imaging device that receives reflected light reflected by the surface of the silicon substrate or the surface of the epitaxial layer via the objective lens and the differential interference optical system, and captures a reflected image of the surface of the silicon carbide substrate or the surface of the epitaxial layer. image forming the output signal receives, differential interference image by the reflected light emitted from the surface of the silicon carbide substrate or epitaxial layer from the optical device, and the imaging device having And forming means, and defect detecting means for performing defect detection on the basis of the formed differential interference image, the signal processing apparatus and a defect classification means for classifying the defects based on the differential interference image of the detected defect comprises,
The defect classifying unit identifies a defect image having a large specific shape, classifies the defect image as a shape defect including a carrot defect, identifies a point-like low-luminance defect image, And second classification means for classifying as follows.

  The silicon carbide substrate is transparent to wavelength light in the visible region and infrared region. Therefore, when a silicon carbide substrate is scanned with an illumination beam having a wavelength in the visible region or infrared region using a scanning device that performs area illumination, reflected light that enters the substrate and is reflected by the back surface of the substrate is collected by the objective lens. And enters the light detection means. When such reflected light is incident on the light detection means, the detection sensitivity is greatly reduced. Therefore, in the present invention, a light source device that generates an illumination beam having a wavelength in the ultraviolet region is used in order to remove the influence of reflected light from the back surface of the silicon carbide substrate. Since the wavelength light in the ultraviolet region is opaque with respect to silicon carbide, no reflected light is generated from the back surface of the substrate, and a problem that the detection sensitivity is lowered is prevented. It is desirable to use ultraviolet light having a wavelength shorter than 350 nm as wavelength light in the ultraviolet region.

A defect inspection method according to the present invention is a defect inspection method for detecting defects present in a silicon carbide substrate or an epitaxial layer formed on a silicon carbide substrate, and classifying the detected defects.
Using an optical device including a differential interference optical system, scanning the surface of the silicon carbide substrate or epitaxial layer with an illumination beam to form a differential interference image of the surface of the silicon carbide substrate or epitaxial layer;
A defect detection step of detecting defects based on the imaged differential interference image;
A defect classification step of classifying the detected defect based on the differential interference image of the detected defect.

  Since the inspection apparatus according to the present invention captures a differential interference image of the surface of the silicon carbide substrate or the epitaxial layer, a luminance image of minute irregularities of about several nanometers to several tens of nanometers formed on the surface of the substrate or the epitaxial layer. Can be imaged. Therefore, it is possible to detect various defects such as dislocation defects and shape defects, which are crystal defects peculiar to the silicon carbide substrate. Furthermore, since the differential interference images of dislocation defects, micropipe defects, and shape defects have different shapes and luminance distributions for each defect, it is possible to classify the defects based on the differential interference images. Furthermore, since the detected defects are classified according to their types, the silicon carbide substrate is divided into chip areas in which devices are to be formed, and detected for each chip area using the classification results of the defect classification means. It becomes possible to output defect distribution data indicating the type and / or number of defects.

It is a figure which shows an example of the optical apparatus by this invention. It is a figure which shows an example of the signal processing apparatus by this invention. It is a figure which shows the defect classification method by this invention. It is a figure which shows an example of a defect distribution data output device. It is a figure which shows an example of map information. It is a figure which shows the modification of the optical apparatus by this invention. It is a figure which shows another modification of the optical apparatus by this invention.

FIG. 1 is a diagram showing an example of an optical device according to the present invention. In this example, a confocal scanning device having a differential interference optical system is used as the optical device, and the entire surface of the silicon carbide substrate is scanned by the confocal scanning device to capture a differential interference image on the entire surface of the substrate. Various image processing is performed on the obtained differential interference image to detect the defect and its coordinates (address). In addition, using the address information of the detected defect, the differential interference image of the defect can be reviewed and the detected defect can be classified. Furthermore, since the scanning can be performed in the Z-axis direction (optical axis direction) as a characteristic of the confocal scanning device, the inspection device according to the present invention not only captures the differential interference image of the silicon carbide substrate, but also detects the detected defect. The three-dimensional shape information of the defect can be acquired from the confocal image, and the cross-sectional shape information (surface contour information) of the detected defect can also be acquired. Therefore, when determining the defect type, the differential interference image of the defect, the three-dimensional shape, and the cross-sectional shape can be used, and the defect type can be determined by coordinate comparison of the defect coordinates.

  Referring to FIG. 1, a mercury lamp is used as the illumination light source 1. Various illumination light sources other than mercury lamps such as a xenon lamp and a laser light source can also be used. The illumination beam emitted from the illumination light source 1 is incident on an optical fiber bundle 2 in which a plurality of optical fibers are stacked in a circle, propagates through the optical fiber, and is emitted as a divergent beam having a substantially circular cross section. Incident. The filter 3 emits green wavelength light (e-line: wavelength 546 nm) from the incident light beam. The light beam emitted from the filter is converted into a parallel beam by the converging lens 4 and enters the slit 5. The slit 5 is disposed at the pupil position of the converging lens 4 and has an elongated opening extending in a first direction (a direction orthogonal to the paper surface). Here, the first direction is referred to as the X direction. The width of the opening of the slit 5 is set to 10 to 20 μm, for example. Therefore, an elongated line-shaped light beam extending in the first direction is emitted from the slit 5. The linear light beam emitted from the slit 5 enters the polarizer 6 and is converted into polarized light having a single vibration surface. This line-shaped polarized beam is reflected by the half mirror 7 functioning as a beam splitter, and enters the vibrating mirror 9 through the relay lens 8.

  A drive circuit 10 is connected to the vibration mirror 9, and the drive circuit 10 drives the vibration mirror based on a control signal supplied from the signal processing device 11. The oscillating mirror 9 deflects the incident linear light beam in a second direction (Y direction) orthogonal to the first direction. The signal processing device 11 has position information in the Y direction of the light beam based on the angle information of the vibrating mirror. Note that other scanning devices such as a polygon mirror may be used instead of the vibrating mirror. Further, when scanning by moving the stage, the vibrating mirror is not always necessary. The line-shaped light beam emitted from the vibrating mirror 9 enters the differential interference optical system 14 via the relay lenses 12 and 13. In this example, a Nomarski prism is used as the differential interference optical system. The linear polarized beam incident on the Nomarski prism 14 is converted into two sub beams whose vibration planes are orthogonal to each other. A phase difference of (2m + 1) π / 2 is given between these two sub-beams, where m is a natural number. Therefore, it is possible to detect a defect having a height change of several nm formed on the surface of the SiC substrate as a luminance image. Further, the shearing amount of the Nomarski prism is set to 2 μm, for example. The Nomarski prism 14 is detachably disposed in the optical path, and is inserted in the optical path when capturing a confocal differential interference image of the SiC substrate. In other cases, for example, when capturing a three-dimensional image of the sample and When the surface contour image of the sample is taken, it is removed from the optical path.

  The two sub beams emitted from the Nomarski prism 14 enter the objective lens 15. The objective lens 15 focuses the incident two line-shaped sub-beams and projects them toward the silicon carbide substrate 17 to be observed arranged on the stage 16. Accordingly, the surface of the SiC substrate 17 is scanned in the second direction (Y direction) perpendicular to each other by two line-shaped sub-beams extending in the first direction (X direction). As a substrate to be inspected, both a SiC substrate on which no epitaxial layer is formed and a SiC substrate on which an epitaxial layer is formed are used.

  The stage 16 is configured by an XY stage that can move in the X direction and the Y direction. The position information of the stage is detected by the position sensor 18, and the position information of the stage is supplied to the signal processing device 11. When a defect is detected by scanning the entire surface of the SiC substrate 17, the entire surface of the SiC substrate can be scanned by moving the stage 16 in a zigzag manner in the Y direction and the X direction while maintaining the oscillating mirror 9 in a stationary state. . Alternatively, the stage 16 can be continuously moved in the first direction, and combined with scanning in the second direction by the oscillating mirror 9, the entire surface of the SiC substrate can be inspected. Also, when reviewing using the address of the detected defect, the stage is moved in the X and Y directions based on the coordinate information of the defect so that the defect is positioned in the field of view, and the vibrating mirror is scanned in the second direction. Thus, a differential interference image in the vicinity of the defect can be taken.

  A motor 19 and a motor drive circuit 20 are connected to the objective lens 15, and can be moved along the optical axis direction by a drive control signal supplied from the signal processing device 11. The position of the objective lens in the optical axis direction is detected by the position sensor 21 and supplied to the signal processing device 11. Here, the motor 19 changes the relative distance in the optical axis direction between the objective lens and the SiC substrate on the stage, that is, the relative distance between the focal point of the light beam that scans the substrate surface and the substrate surface. Functions as a means. The objective lens can move in the optical axis direction with a resolution of 10 nm.

  Due to the characteristics of the confocal scanning device, the oscillating mirror 9 is driven while moving the objective lens 15 in the optical axis direction, and a two-dimensional confocal image of the surface of the SiC substrate is taken a plurality of times, and the maximum luminance value is obtained for each pixel. By detecting the generated position in the optical axis direction, it is possible to acquire three-dimensional shape information (three-dimensional shape image) of the SiC substrate surface. Further, based on the acquired three-dimensional shape information, two-dimensional shape information (cross-sectional shape information) indicating the SiC substrate surface as a cross section can be acquired. Therefore, like micropipe defects formed in the epitaxial layer, hollow hole defects can be detected separately from other defects by acquiring surface contour shape information including three-dimensional shape information or cross-sectional shape information. Is possible. When capturing a two-dimensional confocal image, the Nomarski prism 14 is imaged off the optical path.

  The two reflected beams reflected from the surface of the SiC substrate are collected by the objective lens 15 and enter the differential interference optical system 14. The two reflected sub-beams are synthesized by the differential interference optical system 14 to form an interference beam including the height change of the SiC substrate surface as phase difference information. For example, when a concave or convex defect of about several nanometers exists on the surface of the SiC substrate, one of the two sub beams incident on the SiC substrate surface scans on the defect, and the other sub beam is normal. Since the surface portion is scanned, a phase difference corresponding to the height of the defect is introduced between the two sub beams. As a result, the interference beam emitted from the differential interference optical system 14 includes, as phase difference information, an unevenness change of about several nm that appears on the surface of the SiC substrate due to crystal defects.

  The interference beam emitted from the Nomarski prism 14 propagates in the opposite direction along the original optical path, enters the vibrating mirror 9 through the relay lenses 13 and 12, and is descanned by the vibrating mirror. The interference beam emitted from the vibration mirror 9 passes through the lens 8 acting as an imaging lens, passes through the half mirror 7, and enters the analyzer 22. The analyzer 22 is arranged in a relationship of orthogonal Nicols with respect to the polarizer 6. Accordingly, light other than the polarized light synthesized in the Nomarski prism 14 is blocked, and only light constituting the differential interference image is transmitted through the analyzer 21.

  The line-shaped interference beam that has passed through the analyzer 22 enters a linear image sensor 24 that functions as an imaging device via a positioner 23. The linear image sensor 24 has a plurality of light receiving elements arranged in a direction corresponding to the first direction, and receives the incident line-shaped interference beam. Each light receiving element of the linear image sensor converts phase difference information included in the interference beam into luminance information. Therefore, the unevenness of about several nm formed on the surface of the SiC substrate or the surface of the epitaxial layer is displayed as a luminance image. The light receiving element array arranged in the linear shape of the linear image sensor is almost equivalent to a light receiving element array in which a pin hole is disposed on the front surface of each light receiving element because the entrance opening is limited by the frame. Therefore, the confocal optical system having the differential interference optical system is configured by receiving the reflected light from the SiC substrate surface by the linear image sensor.

  The electric charge accumulated in each light receiving element of the linear image sensor is sequentially read out by a read control signal supplied from the signal processing device 11 and output as a one-dimensional image signal on the surface of the SiC substrate. The one-dimensional image signal output from the linear image sensor is amplified by the amplifier 25 and supplied to the signal processing device 11 through the camera link. The signal processing device 11 includes an image processing board, and generates a two-dimensional image of the SiC substrate surface using the received one-dimensional image signal, position information of the vibrating mirror, position information of the stage, and the like. In addition, the generated two-dimensional image is subjected to various image processes including a filtering process, a binarization process, and a threshold comparison process to detect a defect and acquire its coordinates.

  The SiC substrate is transparent in the visible light wavelength range. For this reason, when the surface of the SiC substrate is scanned with a light beam, the incident light beam is transmitted through the inside of the SiC substrate, and the reflected light reflected from the back surface of the SiC substrate is incident on the detector, resulting in a decrease in resolution. . For this reason, both the case where the SiC substrate is imaged by the differential interference microscope and the case where the defect is detected by the laser scattering method have a drawback that the resolution is low and the accuracy of the defect detection is lowered. In contrast, the confocal inspection apparatus according to the present invention has a configuration that is substantially equivalent to a pinhole disposed on the front surface of the linear image sensor. Out of the optical path, it does not enter the light receiving element of the linear image sensor, but only the reflected light reflected by the surface of the SiC substrate enters the linear image sensor. As a result, by using the inspection apparatus according to the present invention, it is possible to capture a confocal differential interference image having a higher resolution than the differential interference image obtained by the differential interference microscope, and to perform defect detection with higher detection accuracy. Is possible.

  The differential interference optical system detects minute irregularities of about several nanometers formed on the sample surface as a phase difference, so that SiC substrates are caused by crystal defects existing on the substrate such as edge dislocation defects and dislocations in the basal plane. When pits (concave portions) having a depth of several nanometers are formed on the surface, it is possible to detect a pit image as a luminance image. Furthermore, with respect to protrusion defects and concave defects, upward and downward slopes are detected as low-intensity images or high-intensity images on the differential interference image, so the brightness change between the brightness and darkness displayed in the captured differential interference image It is possible to determine whether the defect is a concave defect or a convex defect. Therefore, it is possible to easily determine whether the defect is a pit defect or a bump defect based on the captured bright and dark differential interference image.

  Since the optical apparatus shown in FIG. 1 constitutes a confocal scanning apparatus having a differential interference optical system, a confocal differential interference image on the surface of the SiC substrate can be taken, and further, three-dimensional contour shape information on the surface of the SiC substrate and It is also possible to acquire surface contour shape information indicating the contour of the SiC substrate surface as a cross-sectional image. That is, as a characteristic of the confocal optical system, when the focal point of the scanning beam is located on the sample surface, reflected light having the maximum luminance is incident on the linear image sensor, and linearly as the focal point of the scanning beam is displaced from the sample surface. The amount of reflected beam incident on the image sensor is reduced. Therefore, while moving the objective lens along the optical axis direction, that is, moving the focusing point of the line-shaped scanning beam along the optical axis direction, scanning with the vibrating mirror captures a plurality of two-dimensional confocal images. Then, by detecting the position in the optical axis direction of the objective lens that generates the maximum luminance signal of the linear image sensor for each pixel, three-dimensional shape information indicating the contour of the SiC substrate surface is acquired. Further, from the acquired three-dimensional shape information, it is also possible to acquire surface contour information that indicates a surface contour that shows a SiC substrate cut by an arbitrary surface as a cross section. Therefore, by capturing a three-dimensional image of the detected defect, the shape of the defect can be displayed in three dimensions, and information useful for determining the type of defect can be obtained.

Next, it will be described in what form the defect formed in the SiC substrate and the epitaxial layer is captured in the differential interference image captured by the inspection apparatus according to the present invention.
[Shape defects]
Shape defects such as a triangle defect, a carrot defect, and a comet defect are concave defects having a large size, and are defects having a specific shape such as a triangular shape or a carrot shape. Therefore, a low-intensity image having a specific shape is captured as a differential interference image.
[Micropipe defects]
Micropipes are defects in the form of hollow holes. Therefore, when the scanning beam scans over the micropipe defect, the reflected light from the bottom surface of the hole does not enter the linear image sensor or only a small amount of reflected light, so that it is detected as a dot-like low luminance image. .
[Edge dislocation defects]
Edge dislocation defects appear as pit structures on the surface of the SiC substrate or epitaxial layer. Therefore, it has a structural form having two downward and upward inclined surfaces, and in the differential interference image, it is detected as a specific bright and dark luminance image in which the low luminance image portion and the high luminance image portion are combined.
[Spiral dislocation defects]
Similar to the edge dislocation defect, the screw dislocation appears as a pit structure on the surface of the SiC substrate and the epitaxial layer, and is detected as a bright and dark luminance image.
[Flaws in the basal plane]
The defects in the basal plane appear as pit structures on the surface of the SiC substrate and the surface of the epitaxial layer. Therefore, the differential interference image is detected as a bright and dark luminance image.
[bump]
The bump is a protrusion-like defect and has an upward slope and a downward slope, and is thus detected as a bright and dark luminance image. However, the generation order of the high luminance image portion and the low luminance image portion is opposite to the pit defect (dislocation defect) along the scanning direction. Therefore, the high-definition image portion and the low-luminance image portion are identified from the dislocation defect by the difference in generation order.
[Step bunching]
When the epitaxial layer is formed by the step flow growth method, step bunching may occur. This step bunching is a step defect extending in a direction orthogonal to the orientation flat provided on the silicon carbide substrate. The differential interference image of step bunching is taken as a line-like low-intensity image extending in a direction orthogonal to the orientation flat of the substrate. Therefore, the line-like low-luminance image extending in the direction orthogonal to the orientation flat of the substrate is classified as step bunching.
[Foreign matter adhesion]
When a foreign object adheres to the surface, a foreign object with high reflectivity such as metal is detected as a dot-like high-intensity image, and when a foreign object with low reflectivity adheres, it is detected as a dot-like dark low-intensity image .
[scratch]
Scratches may be formed during the polishing process of the substrate. Since this scratch has a linear concave structure, it is detected as a linear bright and dark luminance image on the confocal differential interference image.

  Next, the defect inspection method will be described. As a characteristic of the SiC substrate, when a dislocation defect exists in the SiC substrate, the dislocation defect existing on the surface of the SiC substrate propagates into the epitaxial layer when an epitaxial layer is formed thereafter. For example, if basal plane dislocations are formed on the SiC substrate before the epitaxial layer is formed, the basal plane dislocations become edge dislocation defects in the epitaxial layer when the epitaxial layer is formed on the SiC substrate. Or, it becomes a dislocation defect in the basal plane. In addition, defects having specific shapes such as carrot defects and half-moon defects formed in the epitaxial layer are often formed due to screw dislocations in the SiC substrate. In view of the characteristics of these SiC substrates, the following two methods can be used as the defect inspection method according to the present invention. In the first inspection method, the entire surface of the SiC substrate is scanned before forming the epitaxial layer, a differential interference image over the entire surface of the SiC substrate is acquired, and defects and their coordinates are detected from the differential interference image. Thereafter, an epitaxial layer is formed on the SiC substrate. Then, scanning is performed on the entire surface of the epitaxial layer after the epitaxial layer is formed, and a differential interference image is captured on the entire surface of the epitaxial layer. Then, defect detection is performed on the SiC substrate after the epitaxial layer is formed. In this method, since differential interference images before and after the formation of the epitaxial layer are obtained, it is possible to compare defect images before and after the formation of the epitaxial layer. It is also possible to detect defects formed during the growth of the epitaxial layer.

  The second inspection method uses the inspection apparatus according to the present invention shown in FIG. 1 to capture a confocal differential interference image over the entire surface of the SiC substrate before the epitaxial layer is formed, and to obtain the acquired confocal differential interference image. Image processing is performed for the defect and its address (coordinate information) is acquired. Next, an epitaxial layer is formed on the SiC substrate after inspection. Subsequently, the SiC substrate on which the epitaxial layer is formed is mounted again on the inspection apparatus, and the portion designated by the defect address detected by the previous defect inspection is positioned in the visual field of the inspection apparatus on the surface of the epitaxial layer. Then, a differential interference image on the surface of the epitaxial layer is taken. Then, with respect to the differential interference image of the defects on the surface of the epitaxial layer, the defects are classified from the viewpoint of the shape, size, and luminance distribution of the defects. According to this inspection method, since the confocal differential interference image is not captured on the entire surface of the substrate after the epitaxial layer is formed, but only a part is captured on the substrate, there is an advantage that the inspection time is shortened.

  FIG. 2 is a diagram illustrating an example of the signal processing device 11 that performs defect detection and defect classification. In this example, the entire surface of the SiC substrate before the epitaxial layer is formed is scanned to detect defects, and the entire SiC substrate after the epitaxial layer is formed is detected to detect defects. Perform defect classification. Of course, it is possible to classify defects detected by performing defect inspection on the silicon carbide substrate before the epitaxial layer is formed, or detecting defect detected by performing defect inspection on the silicon carbide substrate after the epitaxial layer is formed. It is also possible to classify the generated defects.

  The one-dimensional image signal output from the linear image sensor 24 and amplified by the amplifier 25 is converted into a digital signal by the A / D converter 30 and supplied to the signal processing device 11. A stage position signal (digital signal) indicating the position of the stage 16 that supports the substrate is also supplied to the signal processing device 11. Further, an objective lens position signal (digital signal) output from the position sensor 21 indicating the position of the objective lens in the optical axis direction is also supplied to the signal processing device 11. In this example, the signal processing apparatus 11 is configured by software executed by a computer, and various means operate under the control of the control means 31. The signal lines from the control means 31 are not shown in the drawing because the drawings are crossed.

  The one-dimensional image signal input to the signal processing device 11 is sent to the two-dimensional image generation means 32 to form a two-dimensional image, that is, a two-dimensional differential interference image. The two-dimensional image signal is supplied to the first image memory 33, and the differential interference image on the surface of the SiC substrate before the epitaxial layer is formed is accumulated in the first image memory 33. The two-dimensional image signal formed by the two-dimensional image generation unit 32 is supplied to the defect detection unit 34. The defect detection means 34 is also supplied with a stage position signal and position information of each light receiving element of the linear image sensor. The defect detection means 34 includes filtering means, binarization means, and threshold value comparison means, and performs image processing on the input two-dimensional image to detect defects. At the same time, the coordinates (address information) of the detected defect are also acquired using the stage position signal and the position information of each light receiving element of the linear image sensor. When a defect is detected, the identification number of the detected defect and its coordinate information are stored in the first defect memory 35 as a pair.

  When observing a defect formed on the SiC substrate, a differential interference image of a defect desired to be reviewed can be observed under the control of the control means 31. In this case, the control means executes the following processing. That is, the first defect memory 35 is accessed, and a defect address specified by the defect identification number input via the keyboard is acquired. Subsequently, the first image memory 33 is accessed, an image of a predetermined size at the acquired address is taken out, output as a defect image of the SiC substrate, and can be displayed on the monitor. Further, when classifying defects on the SiC substrate, the defect image is extracted from the first image memory using the defect coordinate information stored in the defect memory under the control of the control means 31. It supplies to the classification means 36. Then, the defect classification means 36 determines the type of defect.

  After the defect inspection of the SiC substrate is completed, the SiC substrate is sent to an epitaxial layer growth apparatus, and an epitaxial layer (single crystal layer) is formed on the SiC substrate.

  The substrate on which the epitaxial layer is formed is mounted again on the inspection apparatus that has performed the defect inspection, and the above-described defect inspection is performed, and defect detection and defect coordinate acquisition are performed on the surface of the epitaxial layer. That is, a two-dimensional differential interference image on the surface of the epitaxial layer is generated by the two-dimensional image generation means 32, and the generated two-dimensional image is stored in the second image memory 37. Further, the generated differential interference image is sent to the defect detection means 34 to detect defects formed on the surface of the epitaxial layer, and the coordinates of the detected defects are stored in the second defect memory 38 together with the identification number. Therefore, the second defect memory 38 stores the defect identification number and its address as a pair.

  In parallel with the defect inspection for the epitaxial layer or after the defect inspection is completed, defect classification is performed on the detected defect. When the defect detection means 34 detects a defect, an identification number is assigned, and the identification number and the defect address are stored in the defect memory as a pair. At the same time, the image memory 37 is accessed, and an image of a predetermined size at the position specified by the defect address information is supplied to the defect classification means 36 together with the identification number and the defect address, and the defect classification is performed based on the differential interference image of the defect. Done.

  FIG. 3 is a diagram showing an example of a defect classification method according to the present invention. In step 1, defect classification 1 based on the shape and size of the defect image is executed. As defects formed in the epitaxial layer, defects having specific shapes such as carrot defects, triangle defects, comet defects, and half-moon defects are killer defects that are fatal to the manufacture of devices. When these killer defects are captured as differential interference images, they are detected as low-luminance images having a relatively large size and a specific shape, and are clearly distinguished from other defects. Therefore, in this example, first, a large-sized low-luminance image having a specific shape is extracted based on the shape and size of the defect image, and is classified as a shape defect. Then, the classified shape defects are classified into carrot defects, triangle defects, comet defects and the like based on the shape of the luminance image (step 1).

  Subsequently, defect classification 2 based on the shape and size of the defect image is executed for the defect image not identified in step 1 (step 2). In this classification step, micropipe defects are classified. Micropipe defects are killer defects that are fatal to device manufacturing. Since the micropipe defect is a hollow hole, when scanning with an illumination beam, reflected light from the epitaxial layer is not generated, or reflected light having a luminance considerably lower than a specified value is generated. Therefore, the differential interference image due to the micropipe defect is a point-like low-brightness image. Therefore, in step 2, the defect image detected as a point-like low-luminance image is classified as a micropipe defect.

  Subsequently, the defect images not classified in steps 1 and 2 are classified based on the luminance distribution of the defect image (step 3). Dislocation defects such as threading screw dislocation defects, defects in the basal plane, and edge transition defects are defects that do not correspond to killer defects that are fatal to the manufacture of the device. These dislocation defects appear as pits on the surface of the epitaxial layer. Since the pit has a downward slope and an upward slope along the scanning direction of the illumination beam, the pit is captured as a bright and dark image in which the high-luminance image portion and the low-luminance image portion are combined. Therefore, the defect image having the brightness distribution of light and dark is classified as a dislocation defect (step 3).

  Subsequently, bump defects that are convex defects are classified (step 4). Bump defects are also detected as bright and dark luminance distribution images. However, the generation order of the high luminance image portion and the low luminance image portion is opposite to the pits along the scanning direction. Therefore, a bright and dark image in which the generation order of the high luminance image portion and the low luminance image portion is opposite can be classified as a bump defect.

  Subsequently, step bunching is detected for the defect image not identified in steps 1 to 4 (step 5). Step bunching is a characteristic step defect when an epitaxial layer is formed by a step flow growth method. This step bunching is detected as a line-like low-brightness image extending in a direction orthogonal to the orientation flat formed on the substrate. Therefore, the line-like low-brightness image extending in the direction orthogonal to the orientation flat is classified as step bunching (step 5).

  A defect caused by scratch is identified for the defect image not identified in steps 1 to 5 (step 6). Scratches are defects generated in the polishing process, and are linear concave defects. Therefore, the linear bright and dark image is classified as a scratch.

  For the defect image not identified in steps 1 to 6, a defect due to foreign matter adhesion is identified (step 7). A defect image resulting from the adhesion of a foreign substance such as a highly reflective metal is captured as a high-luminance point image. Therefore, the high-luminance point image is classified as a defect due to foreign matter adhesion (step 7).

  The defect images not identified in steps 1 to 7 are classified as other defects other than the above-described seven types of defects (step 8).

  The defect classification method described above can also be applied to the defect classification on the SiC substrate surface before the epitaxial layer is formed. In SiC substrates, there are no shape defects such as carrot defects, triangle defects, and comet defects, and step bunching. However, defects such as micropipe defects, dislocation defects, and scratches are identified by the defect classification described above.

  It is not necessary to classify all the seven defects described above, and it is possible to classify only the defects necessary for manufacturing the device. For example, a triangle defect is a killer defect that is fatal to the manufacture of a device. Thus, it is possible to identify only killer defects and treat the remaining defects as other defects. Alternatively, when the number of dislocation defects is small, there is no problem in manufacturing the device, but when a large number of dislocation defects are formed, the reliability of the device may be deteriorated. Therefore, in the defect classification step, it is possible to execute a process in which shape defects and dislocation defects are identified and other defects are not identified. That is, the type of defect classified in the defect classification process can be set as appropriate based on the purpose and design concept of the inspection apparatus.

  With reference to FIG. 2, the processing content of the defect classification means 36 of the inspection apparatus according to the present invention will be described. In parallel with the defect detection process or after the defect detection process is completed, defect classification is performed. The defect classification means 36 of this example has the 1st-8th classification means 40-47 as an example, and determines whether the inputted defect image is a defect image formed due to what kind of defect. First, the defect image is supplied to the first classification means 40. The first classification means 40 classifies the input image based on the shape and size. That is, the first classifying unit 40 has shape information serving as a reference for a specific image such as a carrot defect or a comet defect, and determines whether the received defect image is similar to a specific shape. By this shape determination, a defect image having a relatively large size and a specific shape is identified and classified as a shape defect such as a triangle defect, a carrot defect, or a comet defect.

  A defect image that has not been determined as a shape defect by the first classifying means 40 is supplied to the second classifying means 41. The second classification unit 41 determines whether or not the input defect image is a dot-like low-luminance image having a size of about several μm to several tens of μm. When the determination result corresponds to a dot-like low luminance image, it is determined that the defect is a micropipe defect.

  A defect image that has not been identified as a micropipe defect is supplied to the third classification means 42. The third classification means 42 identifies dislocation defects. The third classifying unit determines whether the input defect image is a bright and dark image obtained by combining the high-luminance image portion and the low-luminance image portion, and determines the generation order of the high-luminance image portion and the low-luminance image portion. To do. As a determination result, when the input defect image is a bright and dark image and the generation order of the bright and dark image portions is a predetermined order, it is determined that the input defect image is a defect image due to a dislocation defect.

  A defect image that has not been determined to be a dislocation defect is supplied to the fourth classification unit 43. The fourth classification means identifies bump defects. The fourth classification means determines whether or not the input defect image is a bright and dark image in which the high-luminance image portion and the low-luminance image portion are combined and determines the generation order of the high-luminance image portion and the low-luminance image portion. To do. As a determination result, when the input defect image is a bright and dark image and the generation order of the bright and dark image portions is a predetermined order, it is determined that the input defect image is a defect image due to a bump defect.

  If it is not determined that the defect is a bump defect, the defect image is supplied to the fifth classification unit 44, and it is determined whether or not the defect image is a defect image by step bunching. The defect image by step bunching is a linear low-brightness image extending in a direction orthogonal to the orientation flat formed on the substrate. Therefore, if the input defect image is a low-luminance image extending in a direction orthogonal to the orientation flat, the fifth classification unit 44 identifies the defect image as a defect image by step bunching.

  If the defect image is not identified by the fifth classification means, the defect image is supplied to the sixth classification means 45. The sixth classification means identifies a defect image due to scratches. A scratch is a linear polishing mark and a linear concave defect. Therefore, the defect image due to scratch is captured as a linear bright and dark image. When the input defect image is a linear bright and dark image, the sixth classification unit 45 determines that the defect image is a scratch defect.

  The defect image that has not been identified by the sixth classification means is supplied to the seventh classification means 46. The seventh classification means identifies foreign matter adhesion defects. When a foreign object having a high reflectance such as metal adheres, it is captured as a dot-like high-intensity image. Therefore, the seventh classifying unit determines that the defect image is a defect due to foreign matter adhesion when the input defect image is a dot-like high luminance image.

  The defect images that have not been identified by the first to seventh classification means 40 to 46 are classified as defect images caused by other defects by the eighth classification means.

  It is not necessary to have all the classification means 40 to 47, and it can be set as appropriate according to the purpose of the defect inspection. For example, it is possible to have only means for classifying shape defects and means for classifying dislocation defects, and other defects can be treated as other defects. Alternatively, it is possible to provide means for classifying micropipe defects in addition to shape defects and dislocation defects. Further, it is possible to provide a classification means for classifying only killer defects.

  As a result of the defect classification, the defect classification means 36 outputs defect classification information. The defect classification information includes the identification number, type, and address of the detected defect for each defect. Then, the defect classification information is supplied to a subsequent defect distribution data output device.

  FIG. 4 is a diagram illustrating a defect distribution data output device that forms a distribution state of detected defects on a substrate. The inspection apparatus according to the present invention can detect defects and classify the detected defects based on the differential interference image. Therefore, it is possible to grasp the distribution state of various defects on the silicon carbide substrate by using the detected defect type and defect address information. That is, it is possible to output the defect distribution state in the inspected substrate using the defect classification information output from the defect classification means. The defect classification information output from the defect classification unit 36 is supplied to the defect distribution data forming unit 50. A mapping means 51 is connected to the defect distribution data forming means 50. The mapping unit 51 forms map information obtained by mapping a plurality of chip areas 17-i where devices are to be formed, and supplies the map information to the defect distribution data forming unit 50. FIG. 5 is a diagram showing an example of map information in which a plurality of chip areas 17-i where devices are to be formed are mapped on the silicon carbide substrate 17.

  The defect classification information includes the identification number of each defect, its type, and its coordinate information. The map information includes coordinate information and arrangement information of each chip area where a device is to be formed. The defect distribution data forming means 50 uses the defect classification information and the map information, creates information indicating the type and number of defects included in each chip area 17-i for each chip area, and outputs it as defect distribution data. To do. The content of the defect distribution data can be set according to the purpose of the defect inspection, for example, can be information that displays only the type of detected defect, or the type of detected defect and its defect type. Information indicating the number can also be used.

  The defect distribution data can include killer defect information. For example, a shape defect such as a triangle defect or a carrot defect is a killer defect, and there is a risk that an inoperable device is formed when the device is formed in the chip area. Therefore, the defect distribution data forming means 50 can provide an indication that a killer defect exists for a chip area where a killer defect such as a shape defect exists. In addition, dislocation defects and step bunching are not killer defects, but if the frequency of occurrence (number) increases, the reliability of the formed device may decrease. Therefore, the number of dislocation defects is displayed for each chip area. Then, based on the defect distribution data, a chip area including a killer defect and a chip area where a dislocation defect exceeding a predetermined number is determined as a defective chip area, and devices formed in the defective chip area can be excluded. If such defect distribution data is output, a defective chip area can be specified, so that it is possible to obtain useful quality control data for improving the device manufacturing yield. The type of defect included in the killer defect can be determined in accordance with the purpose of the defect inspection, for example, only the shape defect can be a killer defect, or the shape defect and the micropipe defect can be regarded as a killer defect. It is also possible to do.

  An optical device that scans the surface of an SiC substrate or an epitaxial layer using a plurality of scanning beams arranged along a first direction will be described. In addition, the same code | symbol is attached | subjected and demonstrated to the component same as the component used in FIG. A laser light source 60 is used as an illumination light source. The wavelength of the laser beam emitted from the laser light source can be a wavelength in the infrared region, visible region, or ultraviolet region. The laser beam emitted from the laser light source 60 enters the diffraction grating 61 and is converted into a plurality of light beams (multi-beams) arranged along the first direction. The multi-beam enters the polarization beam splitter 64 through the first and second relay lenses 62 and 63, passes through the polarization beam splitter 64, and enters the oscillating mirror 9. The oscillating mirror 9 is used when reviewing the detected defect, and is maintained stationary when the defect detection process is performed. The oscillating mirror deflects a plurality of incident light beams along a second direction orthogonal to the first direction. The plurality of light beams reflected by the oscillating mirror 9 enter the Nomarski prism 14 via the third and fourth relay lenses 65 and 66 and the quarter wavelength plate 67. Each light beam incident on the Nomarski prism 14 is converted into two sub beams whose vibration surfaces are orthogonal to each other. A phase difference of (2m + 1) π / 2 is given between these two sub-beams, where m is a natural number.

  The two sub beams emitted from the Nomarski prism 14 enter the objective lens 15. The objective lens 15 focuses the incident sub-beam and projects it toward the silicon carbide substrate 17 to be observed arranged on the stage 16. Accordingly, the surface of the SiC substrate 17 is scanned in the second direction orthogonal to the arrangement direction of the light beams by the two rows of sub-beams arranged along the first direction. The stage 16 that supports the silicon carbide substrate 17 is configured by a stage that can move in the X and Y directions. When the defect detection process is performed, the entire surface of silicon carbide substrate 17 is scanned by the sub beam by moving the stage. When reviewing the detected defect, the stage 16 is kept stationary, the defect area is scanned by the scanning of the vibration mirror 9, and the defect image is displayed on the monitor. The position of the stage 16 is detected by a position sensor (not shown) and supplied to the signal processing device 11.

  The sub beam reflected by the surface of the SiC substrate 17 is condensed by the objective lens 15 and enters the Nomarski prism 14. In the Nomarski prism, the reflected beams related to each other are synthesized to generate a plurality of interference beams including a change in the height of the SiC substrate surface as a phase difference. The plurality of interference beams are incident on the oscillating mirror 9 through the quarter-wave plate 67 and the fourth and third relay lenses 66 and 65. Then, it is descanned by the vibrating mirror and enters the polarization beam splitter 64. Since a plurality of incident interference beams pass through the quarter wavelength plate twice, they are reflected by the polarization plane of the polarization beam splitter and enter the linear image sensor 69 through the imaging lens 68. The linear image sensor 69 includes a one-dimensional line sensor in which a plurality of photodiodes are arranged in a line in a direction corresponding to the first direction. Each interference beam then enters the corresponding photodiode. The electric charge accumulated in each photodiode is sequentially read by a drive signal supplied from the signal processing device 11 and supplied to the signal processing device 11 as a one-dimensional image signal. In the signal processing apparatus, defect detection and classification of the detected defect are performed based on FIGS.

  FIG. 7 shows another modification of the optical apparatus mounted on the inspection apparatus according to the present invention. In this example, area illumination that illuminates a relatively wide area is used. In addition, the same code | symbol is attached | subjected and demonstrated to the component same as the member used in FIG. In this example, a laser light source 70 that emits an ultraviolet laser beam is used as the light source device. The SiC substrate is transparent to light in the visible and infrared wavelengths. For this reason, the reflected light from the back surface of the substrate is incident on the light detection means, resulting in a problem that the sensitivity of defect detection is lowered. Therefore, in this example, a laser light source 70 that emits illumination light having a wavelength in the ultraviolet region is used as the illumination light source. Since the wavelength light in the ultraviolet region is opaque with respect to the SiC substrate, generation of undesired reflected light from the back surface of the SiC substrate is prevented. Note that it is desirable to use light having a wavelength of 350 nm or less as illumination light in the ultraviolet region. The laser beam emitted from the laser light source 70 enters the converging lens 4 through the optical fiber 2 and is converted into an expanded parallel beam. This parallel beam passes through the polarizer 6 and is converted into a polarized beam having a substantially circular cross section. The polarized beam is reflected by the half mirror 7 functioning as a beam splitter, and enters the vibrating mirror 9 via the relay lens 8.

  The laser beam reflected by the oscillating mirror 9 enters the Nomarski prism 14 via the relay lenses 12 and 13. The Nomarski prism 14 is connected to a motor 71 for setting the shearing direction. The shearing direction of the motor 71 is controlled by a drive signal from the signal processing device 11 and can be set, for example, in a direction orthogonal to the orientation flat of the silicon carbide substrate to be inspected. Two sub beams are emitted from the Nomarski prism 14 and enter the objective lens 15. The objective lens 15 projects the two sub beams toward the silicon carbide substrate 17 disposed on the stage 16. Therefore, area illumination is performed on the surface of silicon carbide substrate 17 by a circular illumination beam.

  The stage 16 is configured by an XY stage that can move in the X direction and the orthogonal Y direction. As the stage 16 moves in a zigzag shape in the X and Y directions, it is scanned two-dimensionally by a circular illumination beam. The reflected beam from the surface of the silicon carbide substrate or the epitaxial layer formed thereon is condensed by the objective lens 15 and enters the Nomarski prism 14. The interference beam emitted from the Nomarski prism passes through the relay lenses 13 and 12 and enters the vibrating mirror 9. The interference beam emitted from the vibration mirror 9 passes through the lens 8 acting as an imaging lens, passes through the half mirror 7, and enters the analyzer 22.

  The interference beam that has passed through the analyzer 22 enters the line sensor 72 that functions as an image sensor through the positioner 23. The one-dimensional image signal output from the line sensor 72 is supplied to the signal processing device 11 through the amplifier 25. In the signal processing device 11, a differential interference image is formed, and defect detection and defect classification are performed based on the formed differential interference image. Note that a TDI sensor may be used as an image sensor instead of the line sensor. When a TDI sensor is used as the image sensor, the charge transfer speed of the TDI sensor and the moving speed of the stage are made to correspond.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the relative distance between the focal point of the scanning beam and the substrate surface is changed by moving the objective lens in the optical axis direction, but the objective lens is fixed and the SiC substrate is supported. It is also possible to change the relative distance between the focal point of the scanning beam and the substrate surface by moving the stage in the optical axis direction.

  Furthermore, in the above-described embodiments, the confocal scanning device using a line-shaped scanning beam and the confocal scanning device that scans the sample surface with multiple beams have been described as the confocal scanning device. It is also possible to use a confocal scanning device that scans the substrate surface.

  Further, in the above-described embodiments, the Nomarski prism is used as the differential interference optical system, but other differential interference optical systems such as a lotion prism and a Walston prism can be used.

DESCRIPTION OF SYMBOLS 1 Illumination light source 2 Optical fiber 3 Filter 4 Focusing lens 5 Slit 6 Polarizer 7 Half mirror 8, 12, 13 Relay lens
9 oscillating mirror 10 drive circuit 11 signal processing device 14 Nomarski prism 15 objective lens 16 stage 17 SiC substrate 18 position sensor 19 motor 20 drive circuit 21 position sensor 22 analyzer 23 positioner 24 linear image sensor 25 amplifier 30 A / D converter 31 Control means 32 Two-dimensional image generation means 33 First image memory 34 Defect detection means 35 First defect memory 36 Defect classification means 37 Second image memory 38 Second defect memory

Claims (6)

An inspection apparatus that detects crystal defects that appear on the surface of a silicon carbide substrate or the surface of an epitaxial layer formed on the silicon carbide substrate, and classifies the detected crystal defects ,
A light source device that generates an illumination beam having an opaque wavelength in the ultraviolet region with respect to the silicon carbide substrate, and supports the silicon carbide substrate to be inspected and moves in the first direction and the second direction orthogonal to the first direction. A possible stage, an objective lens that projects the illumination beam toward a silicon carbide substrate disposed on the stage, a differential interference optical system disposed in an optical path between the light source device and the objective lens, and the carbonization An imaging device that receives reflected light reflected by the surface of the silicon substrate or the surface of the epitaxial layer via the objective lens and the differential interference optical system, and captures a reflected image of the surface of the silicon carbide substrate or the surface of the epitaxial layer. image forming the output signal receives, differential interference image by the reflected light emitted from the surface of the silicon carbide substrate or epitaxial layer from the optical device, and the imaging device having And forming means, and defect detecting means for performing defect detection on the basis of the formed differential interference image, the signal processing apparatus and a defect classification means for classifying the defects based on the differential interference image of the detected defect comprises,
The defect classifying unit identifies a defect image having a large specific shape, classifies the defect image as a shape defect including a carrot defect, identifies a point-like low-luminance defect image, And a second classifying means for classifying as follows. 2. The inspection apparatus according to claim 1, wherein the defect classification means further includes third classification means for identifying a defect image in which a high-luminance image portion and a low-luminance image portion are combined and classifying the defect image as a dislocation defect. An inspection apparatus comprising: 3. The inspection apparatus according to claim 1, wherein the defect classification unit further identifies a linear low-luminance image extending in a direction orthogonal to an orientation flat formed on the silicon carbide substrate, as step bunching. An inspection apparatus comprising fourth classification means for classifying.   The inspection apparatus according to claim 1, wherein a line sensor or a TDI sensor is used as the imaging element.   The inspection apparatus according to claim 2, wherein the light source device generates a linear illumination beam extending in one direction or a plurality of illumination beams arranged in a line, and the imaging elements are arranged in a line. An inspection apparatus comprising: a linear image sensor having a plurality of light receiving elements, wherein the optical device is configured as a confocal optical device. 6. The inspection apparatus according to claim 1, wherein the signal processing device further includes an image memory for storing a differential interference image formed by the image forming unit, and a detected defect. An inspection apparatus having an address memory for storing an address and outputting a differential interference image of a detected defect as defect image information.

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