JP2015072241A - Inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection apparatus capable of detecting defect in a sample and defect on a surface of the sample individually.SOLUTION: The inspection apparatus comprises: an illumination optical system projecting an illumination beam including illumination light in a first wavelength region having transmissivity to a sample and illumination light in a second wavelength region not having transmissivity to the sample; a detection system including a first imaging apparatus 11 imaging a surface reflection image and an internal reflection image of the sample, and a second imaging apparatus 16 receiving surface reflection light formed by the light in the second wavelength region and imaging a surface reflection image of the sample; and a signal processor 13 detecting internal defect of the sample, using the surface reflection image and the internal reflection image formed by the first imaging apparatus and the surface reflection image formed by the second imaging apparatus.

Description

  The present invention relates to an inspection apparatus capable of separately detecting defects or voids existing inside a sample and defects or foreign matters existing on the surface of the sample at the same time.

  In the manufacturing process of a back-illuminated CCD sensor or CMOS sensor, after a device such as a CCD sensor is formed on a device wafer, the back surface of the device wafer is polished so that the thickness of the device wafer becomes about several tens of μm. Polished. Therefore, the device wafer is bonded to the support wafer through the adhesive layer to form a bonded wafer. The bonded wafer is mounted on a polishing apparatus, and backside polishing is performed so that the thickness of the device wafer is about several tens of μm. In this polishing process, it is important to polish so that the thickness of the device wafer becomes a constant thickness, and when the thickness of the device wafer varies, a sensitivity distribution occurs in the manufactured CCD sensor, A defect occurs that degrades the quality of the device. On the other hand, when manufacturing a bonded wafer, air bubbles are often mixed into the adhesive layer. However, if bubbles are formed inside the wafer, the bubbles undergo thermal expansion in the polishing process, causing a problem of local overpolishing. Accordingly, there is a strong demand for the development of an inspection apparatus that can detect bubbles or voids present in the adhesive layer. In addition, if foreign matter adheres to the surface of the support wafer, the pressure contact force against the polishing machine will be distributed, resulting in locally uneven pressure bonding and similarly non-uniform polishing. Therefore, in the bonded wafer, it is desired that not only internal defects but also surface defects can be detected.

  Furthermore, in a silicon wafer, cracks may occur inside the wafer during manufacturing or transportation. Since the crack generated inside the wafer cannot be detected from the outside, when a device is manufactured using the wafer in which the crack exists, a defect that the manufacturing yield decreases occurs. Similarly, there is a demand for detecting cracks formed in the inside of a single crystal silicon wafer or a polycrystalline silicon wafer used as a photoelectric conversion layer of a solar cell panel. Therefore, it is an urgent task to develop an inspection apparatus that can detect defects formed in various wafers.

  As a method for detecting an internal defect of a bonded wafer, it is known to perform transmission illumination on the bonded wafer and detect an internal defect from a transmission image of the bonded wafer (for example, see Patent Document 1). In this known inspection method, a laser beam is projected toward the bonded wafer, a transmission image is formed, and a defect image is detected from the transmission image.

As a method for detecting a defect of a solar battery cell, a method is known in which a transmission image and a reflection image of a cell are separately captured, and a defect is detected from the transmission image and the reflection image (for example, see Patent Document 2). In this known inspection method, a reflective illumination optical system is disposed on the front surface side of the semiconductor wafer constituting the solar battery cell, a transmitted illumination optical system is disposed on the back surface side, and reflected illumination light is projected from the front surface side of the semiconductor wafer. The transmitted illumination light is projected from the back side. Then, visible illumination light is used as reflected illumination light, and infrared illumination light is used as transmitted illumination light. Further, reflected light and transmitted light emitted from the semiconductor wafer are separated by a dichroic mirror.
JP 2011-107144 A JP 2013-53973 A

  In the inspection method disclosed in Patent Document 1, the bonded wafer transmitted illumination light is projected, a transmitted image is captured, and an internal defect image is detected based on the transmitted image. However, in this known inspection method, the image captured by the imaging device includes both the defect image existing on the sample surface and the defect image existing inside the sample. It is technically impossible to detect. Further, there is a drawback that the surface defect and the internal defect of the sample cannot be detected individually. Furthermore, since a laser beam is used as the illumination beam, speckle patterns frequently occur in the illumination beam, and there is a disadvantage that high-precision defect detection cannot be performed. In this case, it is possible to provide a means for removing the speckle pattern, but this causes a problem that the light source device becomes large.

  In the solar cell inspection apparatus disclosed in Patent Document 2, a reflection illumination optical system is arranged on one side of a semiconductor wafer to be inspected, and a transmission illumination optical system is arranged on the other side. Since the optical system is used, there is a drawback that the apparatus becomes large. Further, the image captured using the transmission illumination optical system is both an image of a defect existing inside the sample and an image of a defect present on the surface of the sample. Therefore, there has been a fatal defect in which only internal defects existing inside the sample cannot be detected separately from surface defects.

An object of the present invention is to realize an inspection apparatus capable of detecting only defects present in a sample.
Another object of the present invention is to realize an inspection apparatus capable of individually detecting defects existing inside a sample and defects existing on the surface of the sample.

An inspection apparatus according to the present invention is an inspection apparatus for detecting voids or defects existing in a sample to be inspected,
An illumination beam is generated that includes illumination light in a first wavelength range that is transmissive to the sample and illumination light in a second wavelength range that is not transmissive to the sample, and directs the illumination beam toward the sample The illumination optical system
A detection system that receives a reflected beam including surface reflected light emitted from the sample and reflected by the surface of the sample and internally reflected light reflected by a void or a defect inside the sample; and
A signal processing device that receives an output signal output from the detection system and detects voids or defects existing in the sample;
The detection system is formed by a first imaging device that receives the surface reflection light and the internal reflection light and captures a surface reflection image and an internal reflection image of the sample, and light in the second wavelength region. A second imaging device that receives surface reflected light and images a surface reflected image of the sample,
The illumination optical system has an objective lens that projects an illumination beam perpendicularly to a sample disposed on a stage, and the first and second imaging devices transmit reflected light emitted from the sample to the objective lens. Receive light through
The signal processing device includes difference image forming means for forming a difference image between a surface reflection image and an internal reflection image formed by the first imaging device and a surface reflection image formed by the second imaging device. It is characterized by that.

  As a result of various experiments and analyzes by the present inventor, it has been found that bubbles and voids present in the sample can be detected as a reflected image using a reflective illumination optical system. That is, when bubbles exist inside the sample, a refractive index difference is formed between the bubbles and the surrounding medium. Therefore, when illumination light enters the bubble, reflected light is generated due to the difference in refractive index between the bubble and the surrounding medium and the multiple reflection effect inside the bubble. Since this reflected light is condensed by the objective lens when the illumination system is an epi-illumination optical system, an internal reflection image is taken by receiving light by the imaging device via the objective lens.

  On the other hand, since the objective lens collects both the surface reflected light reflected from the surface of the sample and the internally reflected light reflected from the inside of the sample, the imaging device simultaneously captures the surface reflected image in addition to the internally reflected image. . Therefore, when only the internal reflection image information is output, it is necessary to remove the surface reflection image information from the image information output from the imaging device. Therefore, in the present invention, both illumination light in the first wavelength range that passes through the sample and illumination light in the second wavelength range that does not pass through the sample are simultaneously projected as illumination light. In this case, part of the illumination light in the first wavelength region is reflected on the sample surface to become surface reflected light, and the remaining illumination light is transmitted inside the sample and reflected at the interface such as voids or bubbles existing inside. It becomes the internally reflected light. Both the surface reflection light and the internal reflection light are collected by the objective lens to form a surface reflection image and an internal reflection image. On the other hand, since the illumination light in the second wavelength region does not pass through the inside of the sample, it becomes surface reflected light and is condensed by the objective lens to form only the surface reflected image. Accordingly, in the signal processing device, a difference image is formed by subtracting the surface reflection image formed by the illumination light in the second wavelength range from the internal reflection image and surface reflection image formed by the illumination light in the first wavelength range. By doing so, it becomes possible to output only the internal reflection image. As a result, the internal image information and the surface image information of the sample can be output separately only by using a single reflection illumination optical system.

A preferred embodiment of the inspection apparatus according to the present invention includes a device wafer on which various devices are formed as the sample to be inspected, and a support wafer constituted by a silicon wafer bonded to the device wafer via an adhesive layer. And a bonded wafer containing
The first wavelength range is set to an infrared wavelength that is transmissive to silicon, and the second wavelength range is set to a visible range that is not transmissive to silicon,
The inspection apparatus detects a void or a defect present in the adhesive layer as an internal reflection image.

  In the case of a bonded wafer in which a device wafer and a support wafer are bonded via an adhesive layer, bubbles and voids are easily formed in the adhesive layer, and the refractive index difference between the bubbles and voids and the surrounding medium is large. Therefore, these defects can be detected as an internal reflection image having a luminance different from that of the surrounding medium.

  In the present invention, since the surface reflection image and the internal reflection image of the sample are captured using the reflection illumination optical system, defects and voids existing inside the sample are removed from the surface defect using a single illumination optical system. And can be detected separately. Furthermore, since the illumination light in the wavelength range that passes through the sample and the illumination light in the wavelength range that does not pass through the sample are projected at the same time, it is possible to individually output the internal defect information and the surface defect information of the sample. .

It is a figure which shows the whole structure of the test | inspection apparatus by this invention. It is a figure which shows an example of a bonded wafer. It is a diagram which shows the state which the illumination light approached into the inside of a sample. It is a figure which shows an example of a signal processing apparatus. It is a figure explaining the effect | action of a difference image formation means. It is a figure which shows the modification of the test | inspection apparatus by this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

  FIG. 1 is a diagram showing the overall configuration of an inspection apparatus according to the present invention. In this example, a bonded wafer is used as a sample to be inspected. The bonded wafer includes a device wafer on which various devices are formed, and a support wafer that is formed of a silicon substrate and is bonded to the device wafer via an adhesive layer. In this example, an illumination beam is projected from the support wafer side, and bubbles, voids, and defects existing in the adhesive layer are detected. Of course, the inspection apparatus according to the present invention can detect not only bonded wafers but also defects and voids existing inside a single silicon wafer or a bonded wafer in which two silicon wafers are directly bonded. Furthermore, defects and voids existing inside the semiconductor wafer constituting the semiconductor cell of the solar battery can also be detected.

  In this example, the halogen lamp 1 is used as an illumination light source included in the illumination optical system. A silicon wafer has a property of transmitting light having a wavelength in the infrared region and not transmitting light having a wavelength in the visible region shorter than the infrared region. On the other hand, the halogen lamp 1 emits an illumination beam including both wavelength light in the infrared region (first wavelength region) and wavelength light in the visible region (second wavelength region). Therefore, part of the illumination light is reflected by the surface of the silicon wafer (sample), and the remaining illumination light enters the silicon wafer. The illumination beam emitted from the halogen lamp 1 enters the optical fiber 2 and is emitted from the light exit end. The illumination beam emitted from the optical fiber 2 enters the beam splitter 5 via the first and second relay lenses 3 and 4. The beam splitter 5 is composed of a half mirror and functions to separate the illumination beam from the illumination light source toward the sample and the reflected beam emitted from the sample.

  The illumination beam emitted from the beam splitter 5 is projected onto the sample 7 to be inspected via the objective lens 6. The optical axis of the objective lens 6 is arranged so as to be orthogonal to the sample surface. Therefore, the illumination optical system constituted by the optical elements arranged in the optical path from the illumination light source 1 to the objective lens 6 forms an epi-illumination optical system.

  The bonded wafer, which is the sample 7 to be inspected, is arranged on the stage 8 so that the support wafer faces the objective lens. The stage 8 is constituted by an XY stage and moves in a zigzag shape. Therefore, the entire surface of the sample (bonded wafer) 7 is scanned by the zigzag relative movement of the stage 8.

  In this example, the illumination optical system performs area illumination, and the illumination beam illuminates a relatively large circular area on the sample surface. The silicon wafer on which the illumination beam is incident is transparent to the illumination light in the infrared region, which is the first wavelength region, and not transparent to the illumination light in the visible region, which is the second wavelength region. . Therefore, a part of the illumination light in the first wavelength band is reflected on the surface of the support wafer to become surface reflected light, and the remaining illumination light enters the support wafer and is reflected by voids and defects existing inside. It becomes the internally reflected light. In other words, since there is a difference in refractive index between the material constituting the defect or void and the surrounding material, the illumination light incident on the interface is reflected by the difference in refractive index and forms internally reflected light with a brightness different from that of the surroundings. To do. For example, if bubbles exist in the adhesive layer of the bonded wafer, the refractive index of the bubbles and the refractive index of the adhesive are significantly different, so some of the illumination light is reflected at the interface between the bubbles and the adhesive, Form reflected light.

  Illumination light in the second wavelength range, which is the visible range, is not transmissive to the silicon wafer, and is reflected by the surface of the support wafer to form surface reflected light. These surface reflected light and internal reflected light in the first wavelength range and surface reflected light in the second wavelength range are emitted from the sample as reflected beams and are collected by the objective lens 6.

  The reflected beam collected by the objective lens passes through the beam splitter 5 and enters the half mirror 9. The reflected beam reflected by the half mirror 9 enters the first imaging device 11 through the imaging lens 10. The first imaging device is composed of a CCD sensor or InGaAs sensor having sensitivity to infrared light. Surface reflected light and internal reflected light in the first wavelength range and surface reflected light in the second wavelength range are incident on the first imaging device. Accordingly, the first imaging device 11 captures the surface reflection image and the internal reflection image of the sample. The image signal output from the first imaging device is amplified by the amplifier 12 and supplied to the signal processing device 13.

  The reflected beam that has passed through the half mirror 9 enters the infrared cut filter 14, the reflected light in the infrared region is removed, and only the reflected light in the visible region that is the second wavelength region is transmitted. The reflected light in the second wavelength band emitted from the infrared cut filter 14 enters the second imaging device 16 through the imaging lens 15. The second imaging device is constituted by a CCD sensor or a CMOS sensor having sensitivity to visible light. Since the light incident on the second image pickup device 16 is only the reflected light reflected from the sample surface, the second image pickup device picks up the surface reflection image of the sample. The image signal output from the second imaging device is amplified by the amplifier 17 and supplied to the signal processing device 13. In addition, when using the sensor which does not have a sensitivity with respect to the light of an infrared region as a 2nd imaging device, the infrared cut filter 14 can be abbreviate | omitted.

  FIG. 2 shows a structure of a bonded wafer as an example of a sample to be inspected as a cross-sectional view. The bonded wafer includes a device wafer 20 having a device layer 20a in which devices such as a CCD sensor and a CMOS sensor are formed in layers, an adhesive layer 21 made of an adhesive such as polyimide, and a silicon wafer. And a support wafer 22 constituted by Since the device layer 20a of the device wafer 20 mainly includes a reflective wiring layer having a fine line width, it acts as a reflection layer as a whole with respect to the incident illumination beam. In this example, the device layer 20 a is bonded so as to directly face the support wafer 22 through the adhesive layer 21. For example, the thickness of the device wafer and the support wafer is set to 775 μm, and the thickness of the adhesive layer is set to several tens of μm.

On the surface 22 a of the support wafer 22, there may be a surface defect 23 due to foreign matter adhesion or the like. In addition, bubbles are mixed in the adhesive layer 21 when bonded, and these bubbles 24 form voids. If air bubbles are present in the adhesive layer, when the back surface of the device wafer 20 is polished to a thickness of about several tens of μm in a subsequent polishing step, the air bubbles expand, and swelling occurs in a portion where the air bubbles exist. For this reason, a local excessive polishing portion is formed in the polishing process, and a problem occurs that a thickness distribution is formed on the device wafer. When a thickness distribution occurs on a device wafer, a luminance distribution occurs in the captured image in a back-illuminated CMOS sensor or the like in which a light receiving surface is formed on the back side of the device wafer, and the quality of the captured image is reduced. Deteriorating defects occur. Furthermore, there is a risk that the device wafer will be cracked when excessively polished. Accordingly, there is a strong demand to detect voids present in the adhesive layer separately from other defects.

  FIG. 3 is a diagram illustrating a state when the illumination beam is incident on the bonded wafer. In FIG. 3, the left side shows a state when infrared illumination light is incident, and the right side shows a state when visible illumination light is incident. First, the state of illumination light in the infrared region will be described. Since the silicon wafer is transparent to infrared light, when infrared illumination light is incident on the support wafer 22, about 30% of the illumination light is reflected on the surface of the support wafer, and the remaining 70% is illuminated. The light passes through the support wafer 22.

  The reflected light reflected from the surface of the support wafer is collected by the objective lens to form a surface reflection image. On the other hand, in many cases, foreign matter or the like adheres to the surface of the support wafer 22 to form the surface defect 23. In this case, when the illumination light is incident on the surface defect 23, the incident illumination light is scattered, and thus the reflected light whose luminance is lower than that of the reflected light from the normal part is collected by the objective lens. Therefore, the surface defect is captured as a low-brightness surface reflection image in most cases, except for foreign matters having a high reflectance such as metal.

  The illumination light incident on the support wafer 22 travels inside the support wafer and enters the interface between the support wafer 22 and the adhesive layer 21. Part of the illumination light is reflected at the interface, and the remaining illumination light passes through the interface and enters the adhesive layer. The illumination light transmitted through the adhesive layer is incident on the device layer 20a of the device wafer 20 located on the lower side. Since the device layer acts as a reflective layer, the illumination light is reflected by the device layer 20a, passes through the adhesive layer 21 and the support wafer 22, and is collected by the objective lens.

  If bubbles 24 are present in the adhesive layer 21, the refractive index of the bubbles and the refractive index of the adhesive are significantly different, so that part of the illumination light is reflected at the interface between the adhesive and the bubbles (voids). Forms internally reflected light. Furthermore, the illumination light transmitted through the inside of the bubble is also reflected at the lower interface between the bubble and the adhesive. These internally reflected lights again pass through the adhesive layer and the support wafer, and are collected by the objective lens to form an internally reflected image. At this time, a phase difference is formed between the reflected light reflected from the upper interface of the bubble and the reflected light reflected from the lower interface according to the size of the bubble. When the formed phase difference is π or an odd multiple thereof, a low luminance image is obtained due to the interference action, and when it is an integral multiple of 2π, a bright image is obtained. Therefore, the void image formed by the internally reflected light becomes a bright image or a dark image according to the size of the bubbles. In addition, when the bubble size is large, a continuous phase difference is formed, so that an image of bright and dark interference fringes is taken. Therefore, since the reflection image of internal defects such as voids is captured as a dark or bright image, the form of the image may be similar to the surface reflection image.

  Next, the state when the illumination light in the visible range is incident on the support wafer will be described. As shown in the right side of FIG. 3, the visible range illumination light does not pass through the silicon wafer, so that most of the visible range illumination light is reflected by the surface of the support wafer 22. On the other hand, when the surface defect 23 exists on the surface of the support wafer 22, the illumination light incident on the surface defect is scattered, and the intensity of the reflected light collected by the objective lens decreases. Therefore, the surface defect is detected as a low-brightness surface reflection image. In addition, when the surface defect is a metallic foreign matter, it is detected as a high luminance image. These low-brightness and high-brightness surface reflection images are substantially the same as the surface reflection image captured by illumination light in the visible range as the image form.

  As described above, since there are cases where the reflected image due to defects or voids present in the sample and the reflected image due to defects present on the surface of the sample are common in the form of the luminance image, there are no defects present within the sample. In the case of detecting only voids, a measure for discriminating between the internal reflection image and the surface reflection image is required. In the present invention, the signal processing device 13 distinguishes between the internal reflection image and the surface reflection image. FIG. 4 is a diagram illustrating an example of an algorithm executed by the signal processing device. In this example, the signal processing apparatus uses software processing by a computer. The image signal output from the first imaging device 11 is converted into a digital signal by the A / D converter 30a and stored in the first image memory 31a. Since the first imaging device receives reflected light in the infrared region, the first image memory 31a stores the surface reflection image and the internal reflection image. The image signal output from the second imaging device 16 is also converted into a digital signal by the A / D converter 30b and stored in the second image memory 31b. Since the second imaging device 16 receives reflected light in the visible range, only the surface reflection image of the sample is stored in the second image memory 31b.

  The image information stored in the first and second image memories is supplied to the gain / offset adjusting means 32a and 32b, respectively. The gain / offset adjusting means adjusts the luminance levels of the images output from the two imaging devices so as to match each other. That is, the luminance level of the surface reflection image formed by the illumination light in the infrared region and the luminance level of the surface reflection image formed by the illumination light in the visible region coincide with each other, and the luminance levels of the background coincide with each other. Thus, the gain and offset amount of the image signal are adjusted.

  The two pieces of image information adjusted for gain and offset are supplied to the difference image forming unit 33. The difference image forming unit 33 forms a difference between the image information output from the first image memory 31a and the image information output from the second image memory 31b. The image information output from the first image memory includes a surface reflection image and an internal reflection image, and the image information output from the second image memory is a surface reflection image. Therefore, the difference image forming unit 33 outputs only the image information from which the surface reflection image is removed, that is, the internal reflection image. This state is shown diagrammatically in FIG. 5A shows images stored in the first and second memories 31a and 31b, FIG. 5B shows an image subjected to gain / offset adjustment processing, and FIG. 5C shows difference image formation. The processed image is shown.

  The image information output from the difference image forming unit is supplied to the void detection unit 34, where a void is detected from the internal reflection image information, and internal defect information is output. The void detection means determines whether the internal reflection image detected in consideration of the characteristics of the internal reflection image, for example, interference fringe characteristics, is an image due to a void or an image due to other defects. Can do. Also, the internal defect information can be output or stored as a pair of the position information of the stage output from the position sensor connected to the stage, the void detected using the pixel information of the imaging device, and its address.

  The surface image information stored in the second image memory 31b is supplied to the defect detection means 35, and a defect is detected from the surface image of the sample. As a defect detection method, an image signal is compared with a threshold value of a predetermined luminance value, and if the comparison result exceeds a predetermined threshold value, it can be determined that the defect is a defect. Therefore, surface defect information is output using the surface image information output from the second image memory. The surface defect information is output as a pair of defect type and its address. When the internal defect information and the surface defect information are information indicating an address of a defect or a void, the internal defect information and the surface defect information are accessed by accessing the first and second memories 31a and 31b from the internal defect information and the surface defect information, respectively. It is also possible to output images and surface defect images.

  FIG. 6 is a view showing a modification of the inspection apparatus according to the present invention. In addition, the same code | symbol is attached | subjected and demonstrated to the component same as the component used in FIG. In this example, two superluminescent light emitting diodes (high brightness light emitting diodes: SLED or SLD) are used as illumination light sources. The first SLED 40 emits infrared light having a center wavelength of 1300 nm, and the second SLED 41 emits visible light having a center wavelength of 800 nm. The SLED generates illumination light having a relatively broad wavelength band as compared with a laser, and can generate a light beam that is incoherent in time, has a short coherent length, and has no speckle pattern. Therefore, there is an advantage that an illumination area having a uniform luminance distribution can be formed. On the other hand, since the laser light source generates a temporally coherent light beam, an infinite number of speckle patterns are formed in the emitted laser beam. For this reason, in order to form an illumination area with a uniform luminance distribution, an optical device that reduces the speckle pattern is necessary, and the structure of the illumination optical system is complicated. In consideration of the above-described characteristics of SLED, it is preferable to use a super luminescent light emitting diode as an illumination light source.

  The illumination beam emitted from the first SLED 40 and the illumination beam emitted from the second SLED 41 are incident on the half mirror 42 functioning as a beam combining element, and include a single illumination light including infrared illumination light and visible illumination light. Converted into an illumination beam. Instead of the half mirror, a dichroic mirror that reflects infrared light and transmits visible light can also be used. This illumination beam enters the beam splitter 5 via the first and second relay lenses 3 and 4. Further, the illumination beam is projected toward the sample 7 through the objective lens 6. The reflected beam including the reflected light reflected on the surface and inside of the sample 7 enters the dichroic mirror 43 through the objective lens 6 and the beam splitter 5. The dichroic mirror 43 reflects reflected light in the infrared region and transmits reflected light in the visible region. The reflected light in the visible range passes through the dichroic mirror and enters the second imaging device 16 through the imaging lens 10. The second imaging device 16 is a linear CCD or linear CMOS sensor.

  The reflected light in the infrared region reflected by the dichroic mirror 43 enters the first imaging device 44 through the imaging lens 15. In this example, the first imaging device is composed of two InGaAs line sensors 44a and 44b that are spaced apart and parallel to each other in a direction corresponding to the moving direction of the stage. Since the InGaAs sensor has an advantage of having high sensitivity in the infrared region, it is suitable for capturing an internal reflection image. On the other hand, the InGaAs line sensor has a drawback that the number of defective pixels is large. Therefore, when imaging is performed with only one InGaAs line sensor, there is a risk that an incomplete image is formed due to defective pixels. Therefore, in this example, two InGaAs line sensors are used that are spaced apart from each other in the moving direction of the stage, that is, the scanning direction of the illumination beam and arranged in parallel with each other. Since the two InGaAs line sensors are spaced apart from each other in the scanning direction, for example, the same time as the second InGaAs line sensor 44b after a predetermined time has elapsed after the reflected light is incident on the first InGaAs line sensor 44a. Reflected light enters. Therefore, the same image signal is output from the two InGaAs line sensors.

In this example, image signals output from each pixel of two InGaAs line sensors are used in a complementary manner. That is, for example, a defective pixel is obtained in advance for the first InGaAs line sensor, and the image signal output from the corresponding pixel of the second InGaAs line sensor is used without using the image signal output from the pixel. In this way, by using the image signals output from the two InGaAs line sensors in a complementary manner, the advantage of having high sensitivity in the infrared region of the InGaAs sensor can be utilized while eliminating the defect of many defective pixels. it can. Of course, if an InGaAs line sensor with few defective pixels is available, a single InGaAs line sensor can be used. In addition, defect-free pixel InGaAs sensors are likely to require sorting and are expensive.

Furthermore, as another modified example, an SLED having a center wavelength of 1300 nm is used for internal observation, and visible light having a wavelength of 380 to 780 nm is used for surface observation, and these illumination lights are projected toward the sample through separate optical paths. . In this case, reflected light of 1300 nm is imaged by an InGaAs sensor, and reflected light in the visible range is imaged by a CCD sensor or a CMOS sensor.

Each imaging device can use a line sensor or a two-dimensional sensor. When a two-dimensional sensor is used, the stage is moved by a step-and-repeat method, and when a line sensor is used, the reflected light is scanned along one axis of the stage. The entire surface is scanned by moving the scan width along another axis.

  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 embodiments, a bonded wafer in which a device wafer and a support wafer are bonded via an adhesive layer has been described. However, an internal inspection of a bonded wafer in which two silicon wafers are directly bonded is performed. It is also possible. Further, the present invention can be applied not only to a silicon substrate but also to the case of individually detecting internal defects existing inside various semiconductor wafers such as GaAs substrates and SiC substrates and surface defects existing on the surface. it can.

  Further, in the above-described embodiment, the entire surface of the sample is scanned by the XY movement of the stage. However, the stage can be moved by a step-and-repeat method. In this case, it is also possible to perform a two-dimensional scan by arranging a galvanometer mirror in the optical path of the reflected beam emitted from the sample.

1 Halogen lamp 2 Optical fiber 3, 4 Relay lens
5 Beam splitter 6 Objective lens 7 Sample 8 Stage 9 Half mirror 10, 15 Imaging lens 11 First imaging device 12, 17 amplifier
13 Signal Processing Device 14 Infrared Cut Filter 16 Second Imaging Device 20 Device Wafer 21 Adhesive Layer 22 Support Wafer 23 Surface Defect 24 Void 30a, 30b A / D Converter 31a, 31b Image Memory 32a, 32b Gain / Offset Adjustment Means 33 Difference image forming means 34 Void detecting means 35 Defect detecting means 40 First SLED
41 Second SLED
42 half mirror

Claims (9)

An inspection device for detecting voids or defects existing in a sample to be inspected,
An illumination beam is generated that includes illumination light in a first wavelength range that is transmissive to the sample and illumination light in a second wavelength range that is not transmissive to the sample, and directs the illumination beam toward the sample The illumination optical system
A detection system for receiving a reflected beam including surface reflected light reflected by the surface of the sample and internally reflected light reflected by voids or defects inside the sample; and
A signal processing device that receives an output signal output from the detection system and detects voids or defects existing in the sample;
The detection system is formed by a first imaging device that receives the surface reflection light and the internal reflection light and captures a surface reflection image and an internal reflection image of the sample, and light in the second wavelength region. A second imaging device that receives surface reflected light and images a surface reflected image of the sample,
The illumination optical system has an objective lens that projects an illumination beam perpendicularly to a sample disposed on a stage, and the first and second imaging devices transmit reflected light emitted from the sample to the objective lens. Receive light through
The signal processing device includes difference image forming means for forming a difference image between a surface reflection image and an internal reflection image formed by the first imaging device and a surface reflection image formed by the second imaging device. Inspection apparatus characterized by that.   2. The inspection apparatus according to claim 1, wherein the signal processing device outputs internal image information of a sample based on an output from the difference image forming unit, and based on an output from the second imaging device. An inspection apparatus that outputs surface image information. The inspection apparatus according to claim 1 or 2, wherein the sample to be inspected is a device wafer on which various devices are formed, and a support that is bonded to the device wafer via an adhesive layer and is constituted by a silicon wafer. A bonded wafer including a wafer is used,
The first wavelength range is set to an infrared wavelength that is transmissive to silicon, and the second wavelength range is set to a visible range that is not transmissive to silicon,
The inspection apparatus detects a void or a defect present in the adhesive layer as an internal reflection image.   The inspection apparatus according to claim 3, wherein the bonded wafer is arranged on a stage so that the support wafer faces the objective lens, and the illumination beam is projected toward the support wafer. Inspection equipment.   5. The inspection apparatus according to claim 3, wherein the illumination optical system includes a halogen lamp that generates an illumination beam including illumination light having an infrared wavelength and illumination light having a visible wavelength as a light source. Inspection equipment.   5. The inspection apparatus according to claim 3, wherein the illumination optical system includes, as a light source, a first SLED that generates illumination light having an infrared wavelength, and a second SLED that generates illumination light having a visible wavelength. An inspection apparatus comprising: an SLED; and beam combining means for combining the illumination light emitted from the first and second SLEDs to form a single illumination beam.   7. The inspection apparatus according to claim 1, wherein the detection system transmits light in the first wavelength range and reflects light in the second wavelength range or the first wavelength range. Select a dichroic mirror that reflects light in the wavelength range and transmits light in the second wavelength range, or a beam splitting element that splits the reflected beam emitted from the sample into two beams and light in the first wavelength range An inspection apparatus comprising an optical filter that cuts automatically.   8. The inspection apparatus according to claim 3, wherein the first imaging device includes an InGaAs sensor having sensitivity to wavelength light in an infrared region, and the second imaging device is visible. A wafer inspection apparatus comprising a CCD sensor or a CMOS sensor having sensitivity to light in the wavelength range. 9. The inspection apparatus according to claim 8, wherein the InGaAs sensor includes two InGaAs line sensors arranged in parallel to each other, and the output signals output from the pixels of the two InGaAs line sensors are used in a complementary manner. Inspection equipment.

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