JP6688184B2 - Wide gap semiconductor substrate defect inspection system - Google Patents

Description

  The present invention relates to an apparatus for inspecting a defect generated in an epitaxial layer formed on a wide gap semiconductor substrate or a material itself forming the wide gap semiconductor substrate.

  A SiC substrate on which an epitaxial layer is formed (a so-called SiC epitaxial substrate) is a wide-gap semiconductor, and is a power semiconductor device that is attracting attention with the spread of photovoltaic power generation, hybrid cars, and electric vehicles. However, since many defect crystals still exist in the SiC epitaxial substrate, it is necessary to perform 100% inspection in order to use it as a power semiconductor device.

  Among them, crystal defects called basal plane dislocations cause expansion of stacking faults that cause deterioration of forward characteristics of pn junction type diodes. Therefore, a manufacturing method has been proposed in which the density of crystal defects including basal plane dislocations is lowered (for example, Patent Document 1).

  And conventionally, the technique of inspecting the crystal defect of the SiC epitaxial substrate by the photoluminescence (PL) method has been proposed (for example, Patent Document 2).

  Alternatively, a technique of nondestructively detecting defects using an X-ray topography method has been proposed (for example, Patent Document 3).

  Further, in a fluorescence microscope for observing a biological sample, while changing the observation magnification by zooming, by adjusting the size of the field diaphragm of the illumination system (that is, the diaphragm diameter) according to the change of the zoom magnification, A technique has been proposed in which excitation light is illuminated only in the observation range to prevent unnecessary light from irradiating the sample (that is, fading of the sample is prevented) (for example, Patent Document 4).

International publication WO2014 / 0977448 Japanese Patent No. 3917154 JP, 2009-44083, A JP-A-10-123425

  There are a plurality of types of defects that occur in a SiC epitaxial substrate, and the types of defects have different effects on the life and performance of manufactured devices. Therefore, in order to check the effect of improvement by comparing the number and size of defects before and after the improvement of the manufacturing method and to perform product inspection before shipping, only the defect of a specific type can be quickly processed. There was a strong desire to extract it into.

  However, in the case where the photoluminescence (PL) method is used to capture the wavelength of the infrared light region by the monochrome camera as in Patent Document 2, not only it takes time to acquire an image necessary for inspection, It was not possible to reliably classify the types of defects.

  On the other hand, when the X-ray topography method is used as in Patent Document 3, it is possible to perform nondestructive inspection, but it takes time to acquire an image necessary for the inspection, and X-rays of higher intensity are used. A large-scale special facility for irradiating the

  Further, in the inspection of the SiC epitaxial substrate using the PL method, there is a demand for making it possible to change the imaging magnification of the inspection target, but there is a possibility that the defect may expand if the inspection region is excessively irradiated with the excitation light. However, there was a demand to minimize the irradiation of excitation light.

  However, in the configuration in which the aperture diameter of the illumination system is adjusted according to the change of the observation magnification as in Patent Document 4, the light amount of the excitation light is insufficient for high-magnification imaging as compared to low-magnification imaging, Imaging time becomes long. Therefore, there is a problem that the time required for imaging cannot be shortened.

  Therefore, the present invention provides a defect inspection apparatus capable of inspecting defects more quickly and more reliably than ever before, and preventing the expansion of defects, while varying the imaging range of the inspection object, despite the simple apparatus configuration. The purpose is to provide.

In order to solve the above problems, one aspect of the present invention is
A defect inspection apparatus for inspecting a defect generated in a wide gap semiconductor substrate,
An excitation light irradiation unit that irradiates the wide gap semiconductor substrate with excitation light,
A fluorescence imaging unit for imaging the photoluminescence light emitted by irradiating the wide-gap semiconductor substrate with the excitation light,
The fluorescence imaging unit includes a plurality of objective lenses having different observation magnifications, and an imaging magnification switching unit that selects and switches any one of the plurality of objective lenses.
The excitation light irradiation unit is provided with an irradiation magnification changing unit that changes the irradiation range and energy density of the excitation light,
Depending on the observation magnification of the selected objective lens in the imaging magnification switching unit, characterized by comprising a control unit for changing the irradiation range and the energy density of the excitation light in the irradiation morphism magnification changing portion, it is a defect inspection apparatus .

  While the imaging range of the inspection target is variable, the defect can be inspected more quickly and more reliably than before, and the expansion of the defect can be prevented, despite the simple device configuration.

It is a schematic diagram showing the whole example composition of the form which embodies the present invention. It is the schematic which shows the principal part of an example of the form which embodies this invention. FIG. 3 is a perspective view schematically showing various defects to be inspected. It is a figure which shows the fluorescence emission characteristic of the board | substrate used as an inspection target, and various defects. It is the image figure which represented typically the monochrome image and color image of various defects imaged by this invention. It is the schematic which shows the whole structure of an example of another form which embodies this invention. It is the schematic which shows the whole structure of an example of another form which embodies this invention.

Embodiments for carrying out the present invention will be described below with reference to the drawings.
In each drawing, the horizontal direction is expressed as the x direction and the y direction, and the direction perpendicular to the xy plane (that is, the gravity direction) is expressed as the z direction.

  FIG. 1 is a schematic diagram showing an overall configuration of an example of a mode for embodying the present invention, and an arrangement of respective parts constituting a defect inspection apparatus 1 is schematically described.

  The defect inspection apparatus 1 according to the present invention inspects a defect generated in the wide gap semiconductor substrate W. Specifically, the defect inspection device 1 includes an excitation light irradiation unit 2, a fluorescence imaging unit 3, a defect inspection unit 4, a control unit 5, and the like. Further, the defect inspection apparatus 1 includes a substrate holding unit 8 and a relative moving unit 9.

  The excitation light irradiating section 2 irradiates the wide gap semiconductor substrate W with the excitation light L1. Specifically, the excitation light irradiation unit 2 includes an excitation light irradiation unit 20, projection lenses 22 and 23, an irradiation magnification changing unit 25, and the like. The excitation light irradiation unit 2 is attached to the device frame 1f via a mounting bracket (not shown) or the like.

  FIG. 2 is a schematic diagram showing a main part of an example of a mode for embodying the present invention. When the distance between the projection lenses 22 and 23 changes, the irradiation range F (for example, F1 to F3) of the excitation light L1 changes. The situation is shown.

  The excitation light irradiation unit 20 is for generating light energy which is a source of the excitation light L1 and includes a light source 21. Specifically, the excitation light irradiation unit 20 can be exemplified by one including a light emitting diode (so-called UV-LED) having an emission wavelength component of around 365 nm as the light source 21.

  The projection lenses 22 and 23 collect the excitation light L1 emitted from the light source 21 and project and irradiate it onto the irradiation range F set on the wide-gap semiconductor substrate W. Specifically, the projection lenses 22 and 23 are composed of one or a plurality of combination lenses including a convex lens and a concave lens.

  The irradiation magnification changing unit 25 changes the irradiation range of the excitation light L1 and the energy density. Specifically, the irradiation magnification changing unit 25 changes the distance between the plurality of lenses 22 and 23 that allows the excitation light L1 to pass therethrough. More specifically, the irradiation magnification changing unit 25 is composed of an electric actuator, and the lens 23 is attached to a slider 26 of the electric actuator. The electric actuator is a mechanism that moves / stops the slider based on a control signal from the control unit 5, and can move / stop the lens 23 to the positions P1 to P3. That is, by moving the lens 23 away from or closer to the lens 22, the irradiation range F and the energy density of the excitation light L1 projected and irradiated onto the surface of the wide-gap semiconductor substrate W are changed. At this time, if the energies of the light emitted from the light source 21 are the same, when the lens 23 is moved at the positions P1 to P3, the excitation light L1 is condensed in a substantially inverse proportion to the area ratio of the irradiation ranges F1 to F3. The degree changes and the energy density changes. For example, if the ratio of the vertical and horizontal dimensions of each irradiation range F1, F2, F3 is approximately 4: 2: 1, the ratio of the energy density of the excitation light L1 in each irradiation range F1, F2, F3 is approximately 1: It will be 4:16.

  The positions P1 to P3 of the slider 26 (that is, the lens 23) are set such that the irradiation range F of the excitation light L1 is the irradiation ranges F1 to F3 suitable for the objective lenses 30a to 30c used in the fluorescence imaging unit 3, respectively. , Preset.

The fluorescence imaging unit 3 images the photoluminescence light L2 emitted by the excitation light L1 being applied to the wide gap semiconductor substrate W.
Specifically, the fluorescence imaging unit 3 includes a lens unit 30, an imaging magnification switching unit 31, a fluorescence filter unit 32, an imaging camera 33 and the like. The fluorescence imaging unit 3 is attached to the device frame 1f via a mounting bracket (not shown) or the like.

  The lens unit 30 projects and forms an image of a plane of a portion of the wide gap semiconductor substrate W to be inspected on the image sensor 34 of the imaging camera 33. Specifically, the lens unit 30 includes a plurality of objective lenses having different observation magnifications. More specifically, the lens unit 30 is provided with an objective lens 30a having a magnification of 5 times, an objective lens 30b having a magnification of 10 times, and an objective lens 30c having a magnification of 20 times.

  The imaging magnification switching unit 31 selects and switches any one of the plurality of objective lenses 30a to 30c included in the lens unit 30. Specifically, the imaging magnification switching unit 31 is composed of an electric actuator mechanism, and the objective lenses 30a to 30c are attached to the electric actuator mechanism. More specifically, the electric actuator mechanism is a mechanism that slides and stands still based on a control signal from the control unit 5, and selectively switches which magnification of the objective lens to use.

  The fluorescence filter unit 32 absorbs or reflects the wavelength component of the excitation light L1 and attenuates it, while passing the photoluminescence light L2 emitted from the site to be inspected. Specifically, the fluorescence filter unit 32 is composed of a bandpass filter arranged between the lens unit 30 and the imaging camera 33. More specifically, the bandpass filter includes wavelength components (light in the ultraviolet region in the above case, particularly light having a wavelength of 385 nm or less) included in the excitation light L1 and light in the infrared region (eg, 800 nm or more). Is absorbed or reflected to be attenuated, and ultraviolet light or visible light having a wavelength longer than 385 nm contained in the photoluminescence light L2 is transmitted.

  The imaging camera 33 captures the photoluminescence light L2 that has passed through the fluorescence filter unit 32 and outputs a video signal (analog signal) or video data (digital signal) to the outside. The image pickup camera 33 includes an image sensor 34.

  The image sensor 34 processes the received light energy in time series and sequentially converts it into an electric signal. Specifically, the image sensor 45 can be exemplified by an area sensor in which a large number of light receiving elements are two-dimensionally arranged, and more specifically, a monochrome camera or a color camera including a CCD image sensor, a CMOS image sensor, or the like. It is configured.

  The defect inspection unit 4 performs an inspection based on the image captured by the fluorescence image capturing unit 3. Specifically, the defect inspection unit 4 is composed of a computer (hardware) having an image processing function and its execution program (software).

  More specifically, when the video signal (analog signal) or video data (digital signal) output from the image pickup camera 33 is input, the defect inspection unit 4 receives image grayscale information (for example, a luminance value. A color image). If so, the defect candidates are extracted based on color information such as hue, brightness, and saturation), and the defect types are determined, the defect types are subdivided, and the defect count and Output of position information and so on (so-called defect inspection) are performed.

[Defect type]
FIG. 3 is a perspective view schematically showing types of defects to be inspected.
Here, as types of defects that have occurred in the wide-gap semiconductor substrate W, various types of defects that have occurred inside the SiC epitaxial layer W2 formed on the SiC substrate W1 are illustrated. Further, the base surface B of the epitaxial layer W2 is shown by a broken line. Further, in the figure, the growth direction of defects is shown as a direction along the base surface B that makes a predetermined angle with the x direction.

  Representative examples of defects to be inspected in the present invention include basal plane dislocations E1 inherent in the SiC epitaxial layer and stacking faults E2 inherent in the SiC epitaxial layer. The stacking fault E2 is simply called a "stacking fault", but can be further subdivided into defect types such as 1SSF to 4SSF. Note that 1SSF is also referred to as a single shockley stacking fault. Similarly, 2SSF is a Double Shockley Stacking Fault, 3SSF is a Triple Shockley Stacking Fault, and 4SSF is a Quadruple Shockley Stacking Fault. Also known as Stacking Fault).

  FIG. 4 is a diagram showing the fluorescence emission characteristics of the substrate to be inspected and various defects, in which the horizontal axis shows the wavelength and the vertical axis shows an example of the fluorescence emission intensity.

  The photoluminescence light L2 emitted from the wide-gap semiconductor substrate W has a wavelength component (mainly 385 to 395 nm) due to band edge emission and emission of an impurity level (when there is no “basal plane dislocation” or “stacking fault”). A wavelength component (mainly 450 to 700 nm) due to so-called DA pair emission) is included.

  On the other hand, if the wide-gap semiconductor substrate W has “basal plane dislocations”, the photoluminescence light L2 emitted from the basal plane dislocation sites is mainly light having a wavelength of 610 nm or more, particularly light having a wavelength of about 750 nm. It

  On the other hand, if the wide-gap semiconductor substrate W has a "stacking fault", from the stacking fault site, according to the defect type of the stacking fault, the wavelength is around 420 nm for 1SSF, around 500 nm for 2SSF, and around 480 nm for 3SSF. In the case of 4SSF, photoluminescence light having a wavelength near 460 nm is mainly emitted. In addition to the above, stacking faults that emit photoluminescence light having a wavelength of 600 nm or less have been confirmed.

[Extraction of defects]
FIG. 5 is an image diagram schematically showing a monochrome image and a color image of various defects imaged by the present invention. FIG. 5 exemplifies grayscale image images of various defects when the image captured by the image capturing camera 33 is a monochrome image and how the various defects appear when the image is a color image. Further, for comparison, a grayscale image of various defects in an image (photoluminescence light in the infrared region) imaged by the conventional technique is also shown. For the convenience of substituting black and white for color images, the difference in color information can be expressed by combining the visual expression of the captured photoluminescence light and the main wavelength component while appropriately changing the type of hatching. There is.

  In the defect inspection unit 4 according to the present invention, image processing is performed on the acquired image to extract regions or parts of grayscale information or color information different from the background image as defect candidates, and according to a predetermined determination standard. A series of program processing for performing defect inspection is executed.

Control unit 5, in response to observation magnification of the selected objective lens in the imaging magnification switching unit 30, and changes the irradiation range F and the energy density of the excitation light L1 in magnification changing section 2 5 morphism irradiation.

  The control unit 5 is connected to the irradiation magnification changing unit 25 and the imaging magnification switching unit 31, respectively, and switches the objective lenses 30a to 30c to be used by sliding / resting the electric actuator, and changes the positions P1 to P3 of the slider 26. Can be changed. Therefore, the control unit 5 selects which of the plurality of objective lenses 30a to 30c is to be used, and the lens 22 and the lens 22 so that the irradiation ranges F1 to F3 of the excitation light L1 are suitable for the magnification of the objective lens. The distance to the lens 23 can be changed. That is, the irradiation range F and the energy density of the excitation light L1 can be changed in association with the observation magnification of the objective lenses 30a to 30c to be used.

  Further, the control unit 5 is also connected to each device provided in the defect inspection apparatus 1, such as the substrate holding mechanism of the substrate holding unit 8 and the relative moving unit 9, and can collectively control each device. . Specifically, the control unit 5 includes hardware such as a computer CP and a programmable logic controller (also referred to as a sequencer) and its execution program (software), and an operator via an operation panel and switches (not shown). Each device is controlled based on the operation, the various setting data, and the execution program.

  The substrate holding unit 8 holds the wide-gap semiconductor substrate W to be inspected in a predetermined posture. Specifically, the substrate holding unit 8 may be, for example, one that holds the wide gap semiconductor substrate W by a substrate holding mechanism such as a negative pressure suction plate, an electrostatic suction plate, or a grip chuck mechanism, so that the upper surface is horizontal. It is arranged.

  The relative movement unit 9 moves the substrate holding unit 8 relative to the excitation light irradiation unit 2 and the fluorescence imaging unit 3. Specifically, the relative movement unit 9 moves along the rails 91X and 91Y attached to the device frame 1f in the X direction and the Y direction at a predetermined speed or at a predetermined position on the rail. The sliders 92X and 92Y that are stationary are provided. The substrate holding portion 8 is attached on the slider 92Y.

  The sliders 92X and 92Y are connected to the control unit 5 via an amplifier unit for control and the like, and are moved on the rails 91X and 91Y at a predetermined speed based on a control signal from the control unit 5 or the rails. It can be stationary at a predetermined position above. More specifically, the so-called step-and-repeat method in which image acquisition (that is, imaging) for inspection is performed in a stationary state, and after moving to the next imaging position, the imaging state is again stationary for image acquisition. The image is acquired at.

  Due to such a configuration, the defect inspection apparatus 1 according to the present invention makes the imaging range of the inspection object of the wide gap semiconductor substrate W variable, and is quicker and more reliable than the conventional one in spite of the simple apparatus configuration. The defect can be inspected, and the defect can be prevented from expanding.

In the above description, the configuration including the irradiation magnification changing unit 25 is illustrated as an embodiment of the excitation light irradiating unit 2, and the irradiation magnification changing unit 25 changes the distance between the lenses of the projection lenses 22 and 23 to generate the excitation light. The form which changes the irradiation range F (for example, F1-F3) and energy density of L1 was illustrated. With such a configuration, it is possible to change the magnification in multiple steps while configuring the excitation light irradiation unit 2 with the minimum number of lenses. Further, by using the projection lenses 22 and 23, it is possible to sharply set the light amount difference between the inside and outside of the irradiation ranges F1 to F3 of the excitation light L1, and even if the irradiation range is changed, energy loss is prevented and irradiation is performed. The energy density within the range F1 to F3 can be changed.
[Another form]
However, in embodying the present invention, the present invention is not limited to the above-described form, and a plurality of projection lenses having different projection magnifications are provided as the excitation light irradiation unit, and the irradiation magnification changing unit includes a projection lens that allows the excitation light L1 to pass. The mode may be switched.

  FIG. 6 is a schematic diagram showing a main part of an example of another embodiment embodying the present invention, and an embodiment including an excitation light irradiation unit 2B instead of the excitation light irradiation unit 2 is illustrated.

  The excitation light irradiation unit 2B includes an excitation light irradiation unit 20, an irradiation magnification changing unit 25B, projection lenses 28a to 28c, and the like. The excitation light irradiation unit 20 constituting the excitation light irradiation unit 2B and the irradiation magnification changing unit 25B are attached to the device frame 1f via a mounting bracket (not shown) or the like.

  The excitation light irradiation unit 20 has the same configuration as that included in the excitation light irradiation unit 2 described above, and thus detailed description thereof will be omitted.

  The irradiation magnification changing unit 25B is composed of a turret type lens holder and a rotary actuator. The rotary actuator rotates and keeps the turret type lens holder at a predetermined angle based on a control signal from the controller 5. Projection lenses 28a to 28c having different projection magnifications are attached to the turret type lens holder.

  The projection lenses 28a to 28c collect the excitation light L1 emitted from the light source 21 of the excitation light irradiation unit 20 and project / irradiate the excitation light L1 on the irradiation range F set on the wide gap semiconductor substrate W. Specifically, the projection lenses 28a to 28c project the light emitted from the light source 21 to the irradiation ranges F1 to F3 at a predetermined projection magnification, and each includes one or a plurality of convex lenses or concave lenses. It is composed of a combination lens and the like.

  Since the excitation light irradiation unit 2B has such a configuration, the projection lenses 28a to 28c to be used are switched based on the control signal from the control unit 5 and projected onto the surface of the wide gap semiconductor substrate W. The irradiation range F (for example, F1 to F3) and the energy density of the excitation light L1 can be changed. Then, the projection lenses 28a to 28c are optimized and designed to the irradiation ranges F1 to F3 of the excitation light L1, respectively, so that the difference between the light amounts inside and outside the irradiation ranges F1 to F3 of the excitation light L1 is set steeply. It is preferable that the energy density in the irradiation ranges F1 to F3 can be changed while preventing energy loss even if the irradiation range is changed.

  The irradiation magnification changing unit according to the present invention is not limited to the above-described configuration (that is, the irradiation magnification changing units 25 and 25B) described with reference to FIG. 1 and FIG. The present invention can be embodied.

  FIG. 7 is a schematic diagram showing a main part of an example of still another mode for embodying the present invention, and a mode including an excitation light irradiation unit 2C in place of the above-described excitation light irradiation units 2 and 25B is illustrated. ing.

  The excitation light irradiation unit 2C includes an excitation light irradiation unit (not shown), a diffusion plate 24, projection lenses 22 and 23, an irradiation magnification changing unit 25, and the like. The excitation light irradiation unit can be exemplified by a configuration in which a light source such as a lamp light source is guided by a light guide, and the excitation light L1 is emitted from the light guide emission unit 29. The excitation light L1 emitted from the light guide emission unit 29 is arranged so as to be emitted to the diffusion plate 24. The diffuser plate 24 improves the illuminance uniformity in the plane irradiated with the excitation light L1. The projection lenses 22 and 23 are arranged at positions facing the light guide emission section 29 with the diffusion plate 24 interposed therebetween.

  The projection lenses 22 and 23 project and irradiate the surface of the wide-gap semiconductor substrate W with the excitation light L1 that has been irradiated onto and passed through the diffusion plate 24. The projection lenses 22 and 23, the diffuser plate 24, and the irradiation magnification changing unit 25B, which form the excitation light irradiation unit 2C, are attached to the device frame 1f via mounting brackets (not shown) or the like. Further, a light guide emission unit 29 is attached on the slider 26 of the irradiation magnification changing unit 25. The projection lenses 22 and 23 included in the excitation light irradiation unit 2C and the irradiation magnification changing unit 25 have substantially the same configurations as those included in the excitation light irradiation unit 2 described above, and thus detailed description will be given. Omit it.

  Since the excitation light irradiation unit 2C has such a configuration, the slider 26 (that is, the light guide emission unit 29) of the irradiation magnification changing unit 25 is moved to the positions P1 to P3 based on the control signal from the control unit 5. By moving and stopping, the irradiation range F and the energy density of the excitation light L1 projected and irradiated onto the surface of the wide gap semiconductor substrate W are changed. The positions P1 to P3 of the slider 26 are set in advance so that the irradiation range F of the excitation light L1 becomes the irradiation ranges F1 to F3 suitable for the objective lenses 30a to 30c used in the fluorescence imaging unit 3, respectively. .

  Since the excitation light irradiation unit 2C has such a configuration, the positions P1 to P3 of the light guide emission unit 29 are switched based on the control signal from the control unit 5 and projected onto the surface of the wide gap semiconductor substrate W. The irradiation range F (for example, F1 to F3) and the energy density of the excitation light L1 to be irradiated can be changed. In this case, although the light amount difference between the inside and outside of the irradiation range F1 to F3 of the excitation light L1 is not steep like the excitation light irradiation units 2 and 2B described above, the surface of the wide gap semiconductor substrate W has a relatively simple device configuration. It is preferable because the irradiation range F (for example, F1 to F3) and the energy density of the excitation light L1 that is irradiated onto the can be changed.

Further, the irradiation magnification changing unit according to the present invention is not limited to such a configuration, and is provided with the excitation light irradiation unit 20 and the projection lens 22, and is configured to irradiate the excitation light L1 with a constant spread angle. The unit 20 and the projection lens 22 may be integrated with each other or moved away from the wide gap semiconductor substrate W.

  Even with such a configuration, the irradiation magnification changing unit can change the irradiation range F (for example, F1 to F3) and the energy density of the excitation light L1 projected and irradiated onto the surface of the wide-gap semiconductor substrate W. The present invention can be embodied.

[Substrate to be inspected, type of defect]
In the above description, one type of wide-gap semiconductor substrate W to be inspected is one in which an epitaxial layer is grown on a SiC substrate, and a defect generated inside the epitaxial layer and at the interface with the SiC substrate is inspected. The morphology is shown.

  However, the wide gap semiconductor is not limited to the SiC substrate and may be a substrate made of a semiconductor such as GaN. Then, the wavelength of the excitation light L1 to be irradiated may be set appropriately according to the material of the substrate to be inspected. Then, depending on the material of the substrate to be inspected, the wavelength L1 of the excitation light, and the characteristics of the photoluminescence light L2 with respect to the defect type, the density information and the color information for classifying the defect types may be set appropriately.

  Further, the defect inspection apparatus 1 according to the present invention inspects not only defects generated in the epitaxial layer formed on the surface of the wide gap semiconductor substrate W but also defects generated in the material itself forming the wide gap semiconductor substrate W. Can also be applied to.

  Further, the defects to be inspected are not limited to the above-exemplified defects, but may be dislocation defects such as micropipes, threading screw dislocations, threading edge dislocations, and other types of defects. Then, the wavelength of the excitation light L1 and the wavelength of the photoluminescence light L2 that passes through the fluorescence filter unit 20 (that is, the filtering wavelength of the fluorescence filter unit 20) can be set appropriately according to the types of defects to be detected. good.

[Modification of excitation light / fluorescence filter]
In the above description, the excitation light irradiation unit 20 of the excitation light irradiation unit 2 includes a UV-LED as a light source, irradiates light having a wavelength of about 365 nm as the excitation light L1, and the photoluminescence light L2 has a wavelength of 385 to 800 nm (that is, light). , Ultraviolet light close to the visible light region or light in the visible light region).

  However, the wavelength component of the excitation light L1 may be appropriately determined according to the substrate to be inspected and the type of defect. Similarly, the wavelength band of the photoluminescence light L2 to be imaged for the defect inspection (that is, filtering) is determined depending on the substrate to be inspected, the type of the defect, and the excitation light L1. It may be appropriately determined according to the wavelength of.

  Specifically, if various defects to be inspected are generated in the SiC epitaxial layer grown on the SiC substrate, light of 375 nm or less (so-called ultraviolet light) is irradiated as the excitation light L1, and the GaN substrate is irradiated. If it is generated in the GaN epitaxial layer grown above, deep ultraviolet light of 365 nm or less is irradiated as the excitation light L1.

  For example, since various defects to be inspected are generated in the GaN epitaxial layer grown on the GaN substrate, the excitation light L1 is deep ultraviolet light having a wavelength of around 300 nm, and the photoluminescence light L2 is visible at 350 to 400 nm. For ultraviolet light close to the light range, a fluorescence observation filter having a characteristic of attenuating 350 nm or less and passing 350 nm or more is used.

  Further, the light source 21 provided in the excitation light irradiation unit 20 is not limited to the UV-LED, but may be a configuration using a laser oscillator, a laser diode, a xenon lamp, or the like. For example, when a laser oscillator or a laser diode is used, the so-called UV laser, which is a combination of a YAG laser or a YVO4 laser and THG, is used to irradiate the excitation light L1 having a predetermined wavelength. On the other hand, when a white light source such as a xenon lamp, a metal halide lamp, a mercury xenon lamp, or a mercury lamp is used, a UV transmissive filter or a dichroic that passes the wavelength component of the excitation light L1 and absorbs or reflects other wavelength components. A mirror or the like is used to irradiate the excitation light L1 having a predetermined wavelength. As the light source 21, a method such as a point light source or a surface light source can be appropriately selected, and the focal length and the location of the projection lens may be set according to the method of the light source.

  Further, the fluorescence filter unit 32 is not limited to the above-described configuration, and may be configured by a coating film provided on the surfaces of the objective lenses 30a to 30c and the image sensor 35.

[Modification of imaging magnification switching unit]
In the above description, as the imaging magnification switching unit 31, an electric actuator mechanism that slides / rests based on a control signal from the control unit 5 has been illustrated. However, the imaging magnification switching unit 31 may be configured to switch the objective lenses 30a to 30c by another method, or may be configured by an electric revolver mechanism that rotates / stops based on a control signal from the control unit 5. .

[Modification of control unit]
In embodying the present invention, in the case where the image acquisition is performed by the step-and-repeat method as described above, the excitation light L1 is not emitted during the movement to the next image pickup position (so-called extinguished light). ) It is preferable to keep the state.

  Specifically, the illumination light irradiation unit 20 and the control unit 5 are connected to each other, and ON / OFF of the current for emitting the illumination light by remote operation or opening / closing of the shutter is controlled to switch ON / OFF of the excitation light L1. The configuration is With such a configuration, the control unit 5 irradiates the excitation light L1 at the time of imaging with the imaging camera 33, and does not irradiate the excitation light L1 while moving to the next imaging position (so-called off). The state can be switched to another state, and unnecessary excitation light L1 is not emitted during the movement of the wide-gap semiconductor substrate W (that is, at the time of non-inspection), so that the defect expansion prevention effect can be enhanced.

  However, this ON / OFF switching control of the excitation light L1 is not an indispensable function, and it is necessary to move to the next place when the energy density is low such as observation at a low magnification or when the inspection time is required. The excitation light L1 may be constantly irradiated as long as the irradiation of the excitation light L1 is short and the extent of the defect expansion is not so affected.

[Modification of relative moving unit / imaging camera]
In the above description, the example in which the image acquisition is performed by the step-and-repeat method is illustrated as an example of the relative movement unit 9. However, in embodying the present invention, the image acquisition is not limited to such a method and the image acquisition is performed by the scanning method. It may be performed.

Specifically, the following forms can be exemplified.
(1) The excitation light L1 is strobe-emitted using an imaging camera equipped with an area sensor.
(2) Using the imaging camera equipped with the line sensor and the TDI sensor, the excitation light L1 is constantly emitted. At this time, the line sensor and the TDI sensor are arranged so that the longitudinal direction of the line sensor and the TDI sensor intersects with the scanning direction of the relative moving unit 9 (desirably, orthogonally).

Further, in the above description, as an example of the relative movement unit 9, the substrate holding unit 8 on which the wide gap semiconductor substrate W is mounted is set in the X direction and the excitation light irradiation unit 2 and the fluorescence imaging unit 3 attached to the device frame 1f. The form of moving in the Y direction has been illustrated. However, the relative moving unit 9 is not limited to such a configuration and may have the following forms.
(1) The excitation light irradiation unit 2 and the fluorescence imaging unit 3 are moved in the X direction or the Y direction, and the substrate holding unit 8 is moved in the Y direction or the X direction.
(2) The excitation light irradiation unit 2 and the fluorescence imaging unit 3 are moved in the X direction and the Y direction, and the substrate holding unit 8 is fixed to the device frame 1f.

DESCRIPTION OF SYMBOLS 1 Defect inspection apparatus 2 Excitation light irradiation part 3 Fluorescence imaging part 4 Defect inspection part 5 Control part 8 Substrate holding part 9 Relative movement part 20 Excitation light irradiation unit 21 Light source 22 Projection lens 23 Projection lens 24 Diffuser plate 25 Irradiation magnification change part 26 Slider 27 Irradiation magnification changing unit 28a to 28b Projection lens 29 Light guide emitting unit 30 Lens unit 30a to 30c Objective lens 31 Imaging magnification switching unit 32 Fluorescence filter unit 33 Imaging camera 34 Image sensor L1 Excitation light L2 Photoluminescence light W Wide gap semiconductor Board (inspection target)
W1 substrate (SiC, GaN, etc.)
W2 Epitaxial layer E1 Basal plane dislocation E2 Stacking fault F Irradiation range F1 Irradiation range (for 5x objective lens)
F2 irradiation range (for 10x objective lens)
F3 irradiation range (for 20x objective lens)

Claims (3)

A defect inspection apparatus for inspecting a defect generated in a wide gap semiconductor substrate,
An excitation light irradiation unit that irradiates excitation light toward the wide gap semiconductor substrate,
A fluorescence imaging unit for imaging the photoluminescence light emitted by irradiating the wide-gap semiconductor substrate with the excitation light,
The fluorescence imaging unit includes a plurality of objective lenses having different observation magnifications, and an imaging magnification switching unit that selects and switches any one of the plurality of objective lenses,
The excitation light irradiation unit is provided with an irradiation magnification changing unit that changes the irradiation range and energy density of the excitation light,
Depending on the observation magnification of the selected objective lens in the imaging magnification switching unit, characterized by comprising a control unit for changing the irradiation range and the energy density of the excitation light in the irradiation morphism magnification changing unit, a defect inspection apparatus. The excitation light irradiation unit includes a plurality of projection lenses having different projection magnifications,
The defect inspection apparatus according to claim 1, wherein the irradiation magnification changing unit switches a projection lens that allows the excitation light to pass therethrough. The excitation light irradiation unit includes a plurality of lenses that pass the excitation light,
The defect inspection apparatus according to claim 1, wherein the irradiation magnification changing unit changes a distance between the plurality of lenses.

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