WO2018016154A1

WO2018016154A1 - Defect inspection device for wide-gap semiconductor substrate

Info

Publication number: WO2018016154A1
Application number: PCT/JP2017/017371
Authority: WO
Inventors: 浩之村田
Original assignee: 東レエンジニアリング株式会社
Priority date: 2016-07-20
Filing date: 2017-05-08
Publication date: 2018-01-25
Also published as: CN109478523A; KR20190031233A; JP2018014377A; TW201812943A; TWI698942B; KR102268931B1; CN109478523B; JP6688184B2

Abstract

Provided is a defect inspection device in which an imaging range of an object to be examined is variable, and which, despite having a simple device configuration, is capable of performing faster and more reliable defect inspection than is conventionally possible, and is also capable of preventing an extension of a defect. Specifically, a defect inspection device for inspecting a defect caused in a wide-gap semiconductor substrate is provided with an excitation light irradiation unit, a fluorescence imaging unit, and a control unit. The fluorescence imaging unit is provided with a plurality of objective lenses having different observation magnification ratios, and with an imaging magnification ratio switching unit which selects one of the plurality of objective lenses to be switched for use as the objective lens. The excitation light irradiation unit is provided with an irradiation magnification ratio modification unit which modifies the irradiation range and energy density of excitation light. In accordance with the observation magnification ratio of the objective lens selected by the imaging magnification ratio switching unit, the control unit modifies the irradiation range and energy density of the excitation light in an illumination magnification ratio modification unit.

Description

Wide gap semiconductor substrate defect inspection system

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

An epitaxial layer formed on a SiC substrate (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 solar power generation, hybrid cars, and electric vehicles. However, since the SiC epitaxial substrate still has many defective crystals, it is necessary to inspect the entire semiconductor substrate for use as a power semiconductor device.

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

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

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

In addition, in a fluorescence microscope for observing a biological specimen, while changing the observation magnification by zoom, by adjusting the size of the field stop of the illumination system (that is, the diameter of the diaphragm) in accordance with the change of the zoom magnification, There has been proposed a technique that prevents the sample from being irradiated with excitation light only in the observation range (that is, prevents the sample from fading) (for example, Patent Document 4).

International Publication WO2014 / 097448 Japanese Patent No. 3917154 JP 2009-44083 A Japanese Patent Laid-Open No. 10-123425

There are a plurality of types of defects that occur in a SiC epitaxial substrate, and the influence on the life and performance of the manufactured device differs depending on the types of defects. Therefore, in order to confirm the effect of improvement by comparing the number and size of defects before and after the improvement of the manufacturing method, or to carry out product inspection before shipping, only specific types of defects can be quickly There was a strong demand to extract it.

However, when imaging the wavelength of the infrared light region by a monochrome camera using the photoluminescence (PL) method as in Patent Document 2, it takes time to acquire an image necessary for inspection, Certainly, the type of defect could not be classified.

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

In the inspection of the SiC epitaxial substrate using the PL method, there is a request to make the imaging magnification of the inspection object variable. However, if the excitation light is excessively irradiated to the inspection object area, the defect may be expanded. There was a desire to minimize the irradiation of excitation light.

However, as in Patent Document 4, in the form in which the aperture diameter of the illumination system is adjusted in accordance with the change in observation magnification, the amount of excitation light is insufficient for imaging at high magnification compared to imaging at low magnification, The imaging time becomes longer. Therefore, there is a problem that the time required for imaging cannot be shortened.

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

In order to solve the above problems, an aspect of the present invention is as follows.
A defect inspection apparatus for inspecting defects generated in a wide gap semiconductor substrate,
An excitation light irradiation unit for irradiating excitation light toward the wide gap semiconductor substrate;
A fluorescence imaging unit that images photoluminescence emitted by irradiating the wide gap semiconductor substrate with excitation light;
The fluorescence imaging unit includes a plurality of objective lenses having different observation magnifications, and includes an imaging magnification switching unit that selects and switches any one of the plurality of objective lenses.
The excitation light irradiation unit includes an irradiation magnification change unit that changes the irradiation range and energy density of excitation light,
A defect inspection apparatus comprising: a control unit that changes an irradiation range and energy density of excitation light in an illumination magnification changing unit according to an observation magnification of an objective lens selected in an imaging magnification switching unit.

つつ While changing the imaging range of the inspection target, it is possible to inspect defects more quickly and reliably than before, despite the simple device configuration, and to prevent the expansion of defects.

It is the schematic which shows the whole structure of an example of the form which embodies this invention. It is the schematic which shows the principal part of an example of the form which embodies this invention. It is the perspective view which represented typically the various defects used as inspection object. It is a figure which shows the fluorescence emission characteristic of the board | substrate used as a test object, and various defects. It is the image figure which represented typically the black-and-white 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.

Hereinafter, modes for carrying out the present invention will be described with reference to the drawings.
In each figure, 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 the overall configuration of an example of a form embodying the present invention, in which the arrangement of each part constituting the defect inspection apparatus 1 is schematically described.

The defect inspection apparatus 1 according to the present invention inspects defects generated in the wide gap semiconductor substrate W. Specifically, the defect inspection apparatus 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 irradiation part 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).

FIG. 2 is a schematic diagram showing a main part of an example 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 generates light energy that is the source of the excitation light L1, and includes a light source 21. Specifically, the excitation light irradiation unit 20 can be exemplified by a light source having a light emitting diode (so-called UV-LED) having an emission wavelength component of around 365 nm as the light source 21.

Projection lenses

22 and 23 condense the excitation light L1 emitted from the light source 21, and project and irradiate the irradiation range F set on the wide gap semiconductor substrate W. Specifically, the

projection lenses

22 and 23 are composed of one or more combination lenses including a plurality of convex lenses and concave lenses.

The irradiation magnification changing unit 25 changes the irradiation range and energy density of the excitation light L1. Specifically, the irradiation magnification changing unit 25 changes the distance between the plurality of

lenses

22 and 23 that allow the excitation light L1 to pass therethrough. More specifically, the irradiation magnification changing unit 25 is configured by an electric actuator, and a lens 23 is attached to a slider 26 of the electric actuator. The electric actuator is a mechanism that moves and stops the slider based on a control signal from the control unit 5, and can move and stop the lens 23 to 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 L <b> 1 projected onto the surface of the wide gap semiconductor substrate W are changed. At this time, if the energy of the light emitted from the light source 21 is the same, when the lens 23 is moved at the positions P1 to P3, the excitation light L1 is condensed almost in 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 the irradiation ranges F1, F2, and F3 is approximately 4: 2: 1, the ratio of the energy density of the excitation light L1 in the irradiation ranges F1, F2, and F3 is approximately 1: 4:16.

Note that the positions P1 to P3 of the slider 26 (that is, the lens 23) are 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. , Set in advance.

The fluorescence imaging unit 3 images the photoluminescence light L2 emitted by irradiating the wide gap semiconductor substrate W with the excitation light L1.
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).

The lens unit 30 projects and forms a planar image of a portion to be inspected on the wide gap semiconductor substrate W 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 includes an objective lens 30a having an observation 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 one of the plurality of objective lenses 30a to 30c provided in the lens unit 30. Specifically, the imaging magnification switching unit 31 includes 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 stops based on a control signal from the controller 5, and selectively switches which magnification objective lens is used.

The fluorescent filter unit 32 allows the photoluminescence light L2 emitted from the region to be inspected to pass through while absorbing or reflecting the wavelength component of the excitation light L1 and attenuating it. Specifically, the fluorescence filter unit 32 is configured by a band-pass filter disposed between the lens unit 30 and the imaging camera 33. More specifically, the band-pass filter includes a wavelength component (in the above case, light in the ultraviolet region, particularly light having a wavelength of 385 nm or less) and light in the infrared region (for example, 800 nm or more) included in the excitation light L1. Is absorbed or reflected to attenuate, and ultraviolet light or visible light having a wavelength longer than 385 nm contained in the photoluminescence light L2 is allowed to pass through.

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

The image sensor 34 processes received light energy in time series and sequentially converts it into an electrical 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. More specifically, the image sensor 45 is 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 inspection based on the image captured by the fluorescence imaging unit 3. Specifically, the defect inspection unit 4 includes a computer (hardware) having an image processing function and an execution program (software) thereof.

More specifically, when the video signal (analog signal) or the video data (digital signal) output from the imaging camera 33 is input, the defect inspection unit 4 is configured to display image density information (for example, luminance value, color image). (Including color information such as hue, brightness, saturation, etc.), defect candidates are extracted to determine what kind of defect it is, classify the defect type, count defects, Output position information (so-called defect inspection).

[Defect types]
FIG. 3 is a perspective view schematically showing the types of defects to be inspected.
Here, as the types of defects generated in the wide gap semiconductor substrate W, various defects generated in the SiC epitaxial layer W2 formed on the SiC substrate W1 are illustrated. Further, the basal plane B of the epitaxial layer W2 is indicated by a broken line. In the drawing, the growth direction of the defect is shown as a direction along the basal plane B that forms a predetermined angle with the x direction.

As defects to be inspected in the present invention, basal plane dislocations E1 inherent in the SiC epitaxial layer and stacking faults E2 inherent in the SiC epitaxial layer are typically exemplified. The stacking fault E2 is simply referred to as “stacking fault”, but can be further subdivided into defect types such as 1SSF to 4SSF. Note that 1SSF is also referred to as Single Shockley Stacking Fault. Similarly, 2SSF is Double Shockley Stacking Fault, 3SSF is Triple Shockley Stacking Fault, 4SSF is Quadruple Shockley Stacking Fault Also called Stacking Fault).

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

When there is neither “basal plane dislocation” nor “stacking defect”, 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 impurity levels ( A wavelength component (mainly 450 to 700 nm) due to so-called DA pair emission is included.

On the other hand, if there is “basal plane dislocation” in the wide gap semiconductor substrate W, the photoluminescence light L2 emitted from the basal plane dislocation site mainly emits light having a wavelength of 610 nm or more, particularly light having a wavelength of about 750 nm. The

On the other hand, if there is a “stacking fault” in the wide gap semiconductor substrate W, from the stacking fault portion, depending on the type of stacking fault, the wavelength is about 420 nm for 1SSF, the wavelength is about 500 nm for 2SSF, the wavelength is about 480 nm for 3SSF, In the case of 4SSF, photoluminescence light having a wavelength of about 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.

[Defect extraction]
FIG. 5 is an image diagram schematically showing black and white images and color images of various defects picked up by the present invention. FIG. 5 illustrates a gray image image of various defects when the image captured by the imaging camera 33 is a black and white image, and how the various defects appear when the image is a color image. Further, for comparison, grayscale image images of various defects in an image captured by the prior art (imaging photoluminescence light in the infrared region) are also shown. In addition, for the convenience of performing a black and white substitute explanation for a color image, the difference in color information is expressed by combining the visual expression of the captured photoluminescence light and the main wavelength component while appropriately changing the type of hatching. Yes.

In the defect inspection unit 4 according to the present invention, image processing is performed on the acquired image, and a region or part of light / dark information or color information different from the background image is extracted as a defect candidate, and in accordance with a predetermined criterion. A series of program processing for performing defect inspection is executed.

The control unit 5 changes the irradiation range F and the energy density of the excitation light L1 in the illumination magnification changing unit 20 according to the observation magnification of the objective lens selected by the imaging magnification switching unit 30.

The control unit 5 is connected to the irradiation magnification changing unit 25 and the imaging magnification switching unit 31, and switches the objective lenses 30 a to 30 c to be used by sliding and stopping the electric actuator, and sets the positions P 1 to P 3 of the slider 26. Can be changed. Therefore, the control unit 5 selects which one of the plurality of objective lenses 30a to 30c is to be used, and the lens 22 so that the irradiation range F1 to F3 of the excitation light L1 suitable for the magnification of the objective lens is obtained. The distance to the lens 23 can be changed. That is, the irradiation range F and energy density of the excitation light L1 can be changed in conjunction with the observation magnification of the objective lenses 30a to 30c to be used.

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 movement unit 9, and can control the devices in an integrated manner. . Specifically, the control unit 5 includes hardware such as a computer CP and a programmable logic controller (also referred to as a sequencer) and an execution program (software) thereof, and is an operator via an operation panel and switches (not shown). Control of each device is performed based on the operation according to the above, 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 can be exemplified by a unit that holds the wide gap semiconductor substrate W by a substrate holding mechanism such as a negative pressure adsorption plate, an electrostatic adsorption plate, or a gripping chuck mechanism, and the upper surface is horizontal. Has been placed.

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 is attached to the device frame 1f and extends in the X direction or the Y direction, and moves on the rails at a predetermined speed or at a predetermined position on the rails. The sliders 92X, 92Y and the like that are stationary are provided. A substrate holding unit 8 is attached on the slider 92Y.

The sliders 92X and 92Y are connected to the control unit 5 via a control amplifier unit or the like, and move on the rails 91X and 91Y at a predetermined speed based on a control signal from the control unit 5 or the rails 92X and 92Y. It can be stopped at a predetermined position above. More specifically, a 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 device is in a stationary state for image acquisition again. The image acquisition is performed.

Due to such a configuration, the defect inspection apparatus 1 according to the present invention makes the imaging range of the inspection target of the wide gap semiconductor substrate W variable and is quicker and more reliable than the conventional apparatus despite a simple apparatus configuration. In addition, it is possible to inspect defects and prevent the expansion of defects.

In addition, in the above, the structure provided with the irradiation magnification change part 25 is illustrated as embodiment of the excitation light irradiation part 2, and the irradiation magnification change part 25 changes excitation light by changing the distance between the lenses of the

projection lenses

22 and 23. An example of changing the irradiation range F (for example, F1 to F3) and the energy density of L1 is illustrated. Such a configuration is preferable because 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, the difference in the amount of light inside and outside the irradiation ranges F1 to F3 of the excitation light L1 can be set steeply, and irradiation can be performed while preventing energy loss even if the irradiation range is changed. The energy density in the range F1 to F3 can be changed.
[Another form]
However, in realizing the present invention, the present invention is not limited to the above-described form, and the excitation light irradiation unit includes a plurality of projection lenses having different projection magnifications, and the irradiation magnification change unit includes a projection lens that allows the excitation light L1 to pass therethrough. It may be a form of switching.

FIG. 6 is a schematic view 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 apparatus frame 1f via attachment brackets (not shown).

Since the excitation light irradiation unit 20 has the same configuration as that provided in the excitation light irradiation unit 2 described above, detailed description thereof is omitted.

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

The projection lenses 28a to 28c are for condensing the excitation light L1 emitted from the light source 21 of the excitation light irradiation unit 20, and projecting and irradiating 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 more convex lenses or concave lenses. It consists of a combination lens.

Since the excitation light irradiation unit 2B has such a configuration, the projection lenses 28a to 28c to be used are switched based on a 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 energy density of the excitation light L1 can be changed. The projection lenses 28a to 28c are designed to be optimized for the irradiation ranges F1 to F3 of the excitation light L1, respectively, so that the light quantity difference between the inside and outside of the irradiation ranges F1 to F3 of the excitation light L1 can be set sharply. This is preferable because 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 form (that is, the irradiation

magnification changing parts

25 and 25B) described with reference to FIG. 1 and FIG. The present invention can be embodied.

FIG. 7 is a schematic view showing the main part of an example of still another embodiment that embodies the present invention, and an embodiment including an excitation light irradiation unit 2C instead of the excitation

light irradiation units

2 and 25B described above is illustrated. ing.

The excitation light irradiation unit 2C includes an excitation light irradiation unit (not shown), a diffusion plate 24,

projection lenses

22, 23, an irradiation magnification changing unit 25, and the like. The excitation light irradiation unit may be configured to guide a lamp light source or the like with a light guide, and the excitation light L1 is emitted from the light guide emitting unit 29. Further, the excitation light L <b> 1 irradiated from the light guide emitting unit 29 is arranged to be irradiated to the diffusion plate 24. The diffusion plate 24 improves the illuminance uniformity within the surface irradiated with the excitation light L1.

Projection lenses

22 and 23 are arranged at positions facing the light guide emitting portion 29 with the diffusion plate 24 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 and passed through the diffusion plate 24. The

projection lenses

22 and 23, the diffusing plate 24, and the irradiation magnification changing unit 25B constituting the excitation light irradiating unit 2C are attached to the apparatus frame 1f via mounting brackets (not shown). Further, a light guide emitting unit 29 is attached on the slider 26 of the irradiation magnification changing unit 25. The

projection lenses

22 and 23 provided in the excitation light irradiation unit 2C and the irradiation magnification changing unit 25 have substantially the same configuration as those provided in the excitation light irradiation unit 2 described above. Omit.

Since the excitation light irradiating unit 2C has such a form, the slider 26 (that is, the light guide emitting unit 29) of the irradiation magnification changing unit 25 is moved to positions P1 to P3 based on a control signal from the control unit 5. By moving and stationary, 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 is the irradiation ranges F1 to F3 suitable for the objective lenses 30a to 30c used in the fluorescence imaging unit 3. .

Since the excitation light irradiation unit 2C has such a configuration, the positions P1 to P3 of the light guide emitting unit 29 are switched based on a 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) of the irradiated excitation light L1 and the energy density can be changed. In this case, unlike the above-described excitation

light irradiation units

2 and 2B, the light amount difference between the inside and outside of the irradiation range F1 to F3 of the excitation light L1 is not steep, but the surface of the wide gap semiconductor substrate W with a relatively simple device configuration. This is preferable because the irradiation range F (for example, F1 to F3) and the energy density of the excitation light L1 irradiated to the laser beam can be changed.

In addition, the irradiation magnification changing unit according to the present invention is not limited to such a configuration, and includes an excitation light irradiation unit 20 and a projection lens 22, and is configured to irradiate the excitation light L1 with a constant divergence angle. The unit 20 and the projection lens 22 may be integrally formed with or away from the wide gap semiconductor substrate W.

Even in such a form, 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, as an example of the type of wide gap semiconductor substrate W to be inspected, an epitaxial layer grown on a SiC substrate is exemplified, and defects occurring inside the epitaxial layer and at the interface with the SiC substrate are inspected. The form to do was 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. And according to the material of the board | substrate used as test object, what is necessary is just to set the wavelength of the excitation light L1 to irradiate suitably. Then, according to 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, shading information and color information for classifying the defect type may be set as appropriate.

In addition, 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 constituting the wide gap semiconductor substrate W. It can also be applied to.

Further, the defect to be inspected is not limited to the defect exemplified above, but may be a dislocation defect such as a micropipe, a threading screw dislocation, a threading edge dislocation, or another type of defect. If the wavelength of the excitation light L1 and the wavelength of the photoluminescence light L2 that passes through the fluorescent filter unit 20 (that is, the filtering wavelength of the fluorescent filter unit 20) are appropriately set according to the type of defect 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 around 365 nm as the excitation light L1, and the photoluminescence light L2 is light having a wavelength of 385 to 800 nm (that is, , An example of a configuration that is ultraviolet light or visible 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, what wavelength band of the photoluminescence light L2 to be imaged for defect inspection passes (that is, filtering) depends on the substrate to be inspected, the type of defect, and the excitation light L1. What is necessary is just to determine suitably according to a wavelength.

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

For example, since various defects to be inspected are generated in a GaN epitaxial layer grown on a GaN substrate, the wavelength of the excitation light L1 is deep ultraviolet light near 300 nm, and the photoluminescence light L2 is visible in the range of 350 to 400 nm. In the case of ultraviolet light close to the light region, 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, and may be configured 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 pumping light L1 having a predetermined wavelength is irradiated using a so-called UV laser in which a YAG laser, a YVO4 laser, and THG are combined. 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 transmission filter or dichroic that passes the wavelength component of the excitation light L1 and absorbs or reflects the other wavelength components. It is configured to irradiate the excitation light L1 having a predetermined wavelength using a mirror or the like. The light source 21 can be appropriately selected from a point light source, a surface light source, and the like, and the projection lens focal length and location may be set in accordance with the light source method.

Further, the fluorescent filter section 32 is not limited to the above-described configuration, and may be configured by a coating film applied to 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, the electric actuator mechanism that slides and stops based on the control signal from the control unit 5 is exemplified. However, the imaging magnification switching unit 31 may be configured to switch the objective lenses 30a to 30c by other methods, or may be configured by an electric revolver mechanism that rotates and stops based on a control signal from the control unit 5. .

[Modification of control unit]
In the embodiment of 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 irradiated while moving to the next imaging position (so-called light-off). ) State is preferable.

Specifically, the illumination light irradiation unit 20 and the controller 5 are connected, and the ON / OFF control of the excitation light L1 is controlled by turning on / off the current for emitting the illumination light by remote operation and opening / closing the shutter. The configuration is as follows. If it is such a structure, the control part 5 will irradiate the excitation light L1 at the time of the imaging with the imaging camera 33, and will not irradiate the excitation light L1 while moving to the next imaging position (so-called light extinction). It is possible to switch to the state, and unnecessary irradiation of the excitation light L1 is not performed during the movement of the wide gap semiconductor substrate W (that is, at the time of non-inspection), so that the defect expansion preventing effect can be enhanced.

However, the ON / OFF switching control of the excitation light L1 is not an essential function. When the energy density is low such as observation at a low magnification, or when the movement to the next place is compared with the time required for the inspection time. The excitation light L1 may be constantly irradiated as long as it does not significantly affect the extension of the defect, such as when the time during which the excitation light L1 is irradiated is short.

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

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

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 placed is set in the X direction with respect to the excitation light irradiation unit 2 and the fluorescence imaging unit 3 attached to the apparatus frame 1f. A mode of moving in the Y direction is illustrated. However, the relative movement unit 9 is not limited to such a configuration, and may have the following form.
(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 apparatus 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 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 Fluorescent filter unit 33 Imaging camera 34 Image sensor L1 Excitation light L2 Photoluminescence light W Wide gap semiconductor Substrate (subject to inspection)
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

A defect inspection apparatus for inspecting defects generated in a wide gap semiconductor substrate,
An excitation light irradiation unit for irradiating excitation light toward the wide gap semiconductor substrate;
A fluorescence imaging unit that images 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 includes an imaging magnification switching unit that selects and switches any one of the plurality of objective lenses.
The excitation light irradiation unit includes an irradiation magnification changing unit that changes an irradiation range and energy density of the excitation light,
A defect inspection apparatus comprising: a control unit that changes an irradiation range and energy density of the excitation light in the illumination magnification changing unit according to an observation magnification of the objective lens selected in the imaging magnification switching unit .
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 passes the excitation light.
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.