JP2017062157A - Epitaxial wafer surface inspection device and epitaxial wafer surface inspection method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer surface inspection device capable of detecting the presence or absence of an epitaxial scratch on an epitaxial wafer surface.SOLUTION: An epitaxial wafer surface inspection device 100 of the present invention includes: an optical system 30 including a first spot illumination 21 installed at an angle θof 60 degrees or more and 80 degrees or less with respect to a surface of an epitaxial wafer 1, a second spot illumination 22 installed at an angle θof 60 degrees or more and 80 degrees or less with respect to the surface, and an imaging part 10 installed perpendicular to the surface; and a scanning part 40 scanning the optical system 30 parallel to the surface. On a plane parallel to the surface, the first spot illumination 21 and the second spot illumination 22 are located at positions forming a separation angle of 85 degrees or more and 95 degrees or less around the imaging part 10.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an epitaxial wafer surface inspection apparatus and an epitaxial wafer surface inspection method using the same, and more particularly to an epitaxial wafer surface inspection apparatus capable of inspecting for the presence of scratch-like defects that may exist on the epitaxial wafer surface.

  As a substrate used in the manufacturing process of a semiconductor device, a wafer made of a semiconductor such as a silicon wafer is widely used. As such a wafer, a polished wafer (PW wafer) obtained by slicing a single crystal ingot and mirror polishing, an epitaxial wafer in which an epitaxial layer is formed on the surface of the PW wafer, and the like are known. For example, epitaxial wafers are used as device substrates for various semiconductor devices such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), DRAMs (Dynamic Random Access Memory), power transistors, and back-illuminated solid-state imaging devices. . In this specification, the description of “epitaxial wafer surface” refers to the surface of the epitaxial wafer on the side where the epitaxial layer is formed.

  In order to improve yield and reliability in the manufacturing process of semiconductor devices, a defect inspection technique on the front and back surfaces of a wafer that is a substrate of a semiconductor device is becoming extremely important. Defects existing on the front and back surfaces of the wafer are diverse, such as crystal defects such as pits and COPs, polishing unevenness and scratches caused by processing, and adhesion of particles as foreign matter.

  Conventionally, the front and back surfaces of a wafer after mirror polishing of the finished surface are scanned with laser light using an LPD (Light Point Defect) inspection device (laser surface inspection machine), and particles existing on the front and back surfaces are scanned. Wafer inspection for detecting scattered light caused by scratches or the like has been performed. In addition, in order to determine the presence or absence of a defect that is difficult to discriminate with the LPD inspection apparatus, an appearance inspection that visually determines the front and back surfaces of the wafer is also used. Since the appearance inspection is a sensory inspection, variations in the determination by the inspector are unavoidable, and it takes time for the inspector to learn. Therefore, establishment of an objective inspection method and an automatic inspection method is required.

  Thus, as one of the wafer inspection methods, the present applicants previously proposed a method for appropriately evaluating a wafer without relying on visual inspection, in particular regarding defects on the back side of the front and back surfaces of the wafer in Patent Document 1. Yes. That is, a map processing step of continuously capturing part images on the back side of the wafer along the circumferential direction of the wafer, synthesizing the captured part images to create an entire image on the back side of the wafer, and differential processing the entire image A differential processing step of creating a differential processing image of the wafer back surface, and detecting and evaluating polishing unevenness, cloudiness, scratches, and particles based on the whole image or the differential processing image. Is the method.

The optical system 50 for creating the whole image will be described with reference to FIGS. Note that FIG. 1B is a diagram in which the main part is extracted from FIG. 1A in order to illustrate the irradiation light L ₁ and the reflected light (scattered light) L ₂ irradiated by the ring fiber illumination 51. is there. The optical system 50 includes a ring fiber illumination 51, a lens barrel 52, a telecentric lens 53, and a light receiving unit 54 including a CCD camera. The light source of the ring fiber illumination 51 is an ultra high pressure mercury lamp. When the irradiation light L ₁ irradiated by the ring fiber illumination 51 is incident on the wafer 1 at an angle θ ₀ (for example, 20 °) with respect to the wafer surface and collides with a defect D existing on the surface of the wafer 1, the scattered light L _2. Occurs. The light receiving unit 54 receives vertical scattered light out of the scattered light L ₂ and images it, and captures and records an image having brightness information of the scattered light together with position information of the optical system 50.

JP 2010-103275 A

  Here, the present inventors examined that the technique described in Patent Document 1 is applied to the inspection of the defect state on the epitaxial wafer surface. Then, although the technique of patent document 1 can detect the various defects which exist in the epitaxial wafer surface, it exists in the epitaxial wafer surface called "epitaxial scratch" (refer FIG.2 (A) mentioned later). A scratch-like defect could not be detected. Since this epitaxial scratch is a defect detected in the conventional visual inspection, the technique described in Patent Document 1 is not sufficient to ensure that the epitaxial wafer is a good product. Must be used together. However, as described above, since the appearance inspection requires determination by an inspector, establishment of a technique capable of objectively inspecting the epitaxial wafer surface is required.

  Accordingly, an object of the present invention is to provide an epitaxial wafer surface inspection apparatus capable of detecting the presence or absence of epitaxial scratches on the surface of the epitaxial wafer and an epitaxial wafer surface inspection method using the same.

In order to achieve the above object, the present inventors have intensively studied. The epitaxial scratch is a scratch-like defect D existing on the surface of the epitaxial wafer, as schematically shown in FIG. FIG. 2B is a cross-sectional view taken along the line II in FIG. The present inventors have examined the defect D in detail. As a result, when an epitaxial layer E is grown on the surface of the substrate S when there is a scratch-like defect D ′ on the surface of the base substrate S, the epitaxial scratch is obtained. It was found that D was formed. Although it may depend on the crystal orientation, the epitaxial scratch D is gently raised starting from the scratch-like defect D ′ formed locally. Therefore, the present inventor believes that an epitaxial scratch D cannot be detected by a conventional inspection apparatus using ring fiber illumination that irradiates at an angle θ ₀ that is relatively horizontal even though it can be sensed by visual observation. Thought. Therefore, the idea was to use spot illumination that illuminates the surface of the epitaxial wafer at an angle that is relatively perpendicular to the conventional ring fiber illumination. By using this spot illumination, the present inventors have found that the scattered light from the defect D ′ can be received and, as a result, the epitaxial scratch D can be detected, and the present invention has been completed. This invention is based on said knowledge and examination, The summary structure is as follows.

  The epitaxial wafer surface inspection apparatus of the present invention includes a first spot illumination installed at an angle of 60 degrees or more and 80 degrees or less with respect to the surface of the epitaxial wafer, and 60 degrees or more and 80 degrees or less with respect to the surface. An optical system including a second spot illumination installed at an angle; and an imaging unit installed perpendicular to the surface; and a scanning unit that scans the optical system in parallel with the surface. The separation angle between the first spot illumination and the second spot illumination centering on the photographing unit is 85 degrees or more and 95 degrees or less on a plane parallel to the surface.

  Here, it is preferable that the first and second spot illuminations have an ultrahigh pressure mercury lamp light source.

  The first and second spot illuminations are preferably installed at the same angle with respect to the epitaxial wafer surface.

  Further, the epitaxial wafer surface inspection method of the present invention uses the above-described epitaxial wafer surface inspection apparatus to continuously take a part image of the surface while scanning the optical system with the scanning unit, and And a detection step of detecting a pattern image peculiar to a scratch-like defect present on the surface from the whole image.

  In this case, it is preferable to further include an image processing step of performing image processing on the whole image prior to the detection step, and in the detection step, the detection is performed based on the whole image processed.

  According to the present invention, it is possible to provide an epitaxial wafer surface inspection apparatus capable of detecting the presence or absence of epitaxial scratches on the epitaxial wafer surface and an epitaxial wafer surface inspection method using the same because spot illumination that is appropriately installed is used. it can.

Is a schematic diagram illustrating the optical system used in the prior art, (A) is a schematic view showing an entire optical system, (B) is a schematic diagram showing the incident light L ₁ and the scattered light L _2. It is a schematic diagram of the epitaxial wafer surface in which the epitaxial scratch was formed, (A) is a top view, (B) is II sectional drawing of (A). It is a schematic diagram of the epitaxial wafer surface inspection apparatus according to one Embodiment of this invention, (A) is a perspective view, (B) is a schematic cross section, (C) is a schematic plan view. (A) is the whole image which shows the epitaxial scratch in an Example, (B) is what image-processed the whole image of (A).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a schematic view of an epitaxial wafer surface inspection apparatus 100 according to an embodiment of the present invention, in which (A) is a perspective view of the epitaxial wafer surface inspection apparatus 100, and (B) is a schematic cross section of (A). (C) is a schematic plan view of (A). In each drawing, only the main part of the epitaxial wafer surface inspection apparatus 100 is shown for convenience of explanation.

(Epitaxial wafer surface inspection equipment)
As shown in FIG. 3A, an epitaxial wafer surface inspection apparatus 100 according to an embodiment of the present invention is installed at an angle θ ₁ of 60 degrees or more and 80 degrees or less with respect to the surface of the epitaxial wafer 1. Spot illumination 21, a second spot illumination 22 installed at an angle θ ₂ of 60 degrees or more and 80 degrees or less with respect to the surface, and an imaging unit 10 installed perpendicular to the surface. The epitaxial wafer surface inspection apparatus 100 includes a scanning unit 40 that scans the optical system 30 in parallel with the surface. Here, in a plane parallel to the surface, the separation angle θ ₃ between the first spot illumination 21 and the second spot illumination 22 with respect to the imaging unit 10 is 85 degrees or more and 95 degrees or less. 2A and 2B, the epitaxial wafer 1 is obtained by epitaxially growing the epitaxial layer E on the surface of the substrate S, and the surface of the epitaxial wafer 1 is epitaxial. It means the surface on the side where the layer E is formed. Hereinafter, details of each component will be described in order.

  The configuration of the imaging unit 10 is not particularly limited as long as scattered light from the surface of the epitaxial wafer 1 can be received and imaged. For example, the imaging unit 10 can be configured by a lens barrel 12, a lens 13, and a light receiving unit 14. As the lens barrel 12, the lens 13, and the light receiving unit 14, commonly used ones can be used. For example, a telecentric lens can be used as the lens 13, and a CCD camera can be used as the light receiving unit 14. The photographing unit 10 may be considered to be obtained by removing the ring fiber illumination 51 from the optical system 50 described in FIG.

Next, as shown in FIGS. 3A and 3B, the first spot illumination 21 is installed at an angle θ ₁ of 60 degrees or more and 80 degrees or less with respect to the surface of the epitaxial wafer 1. Similarly, the second spot illumination 22 is installed at an angle θ ₂ of 60 degrees or more and 80 degrees or less with respect to the surface of the epitaxial wafer 1. The angle θ ₁ and the angle θ ₂ may be different from each other, but are preferably installed at the same angle or substantially the same angle. Irradiance unevenness at the irradiated portion of the epitaxial wafer 1 can be reduced, and detection sensitivity can be leveled. Further, each of the angle θ ₁ and the angle θ ₂ is more preferably 65 degrees or more and 75 degrees or less, and particularly preferably 68 degrees or more and 72 degrees or less. As an example, each of the angle θ ₁ and the angle θ ₂ can be set to 70 degrees. By setting the incident angle of each spot illumination within such an angle range, light can enter deeper than the epitaxial layer of the epitaxial wafer 1 and deeper than the surface of the silicon wafer substrate serving as the base substrate. Therefore, changes in the growth plane orientation array other than the steps on the surface side of the epitaxial silicon wafer 1 can be more easily captured. If the angle θ ₁ exceeds 80 degrees, the first spot illumination 21 may interfere with the installation position of the imaging unit 10. When the angle θ ₁ is less than 60 degrees, the scattered light intensity from the defect D ′ formed on the substrate S of the epitaxial wafer 1 is reduced as described above with reference to FIGS. As a result, the epitaxial scratch D cannot be detected. The reason why the angle θ ₂ is in the above range is the same reason.

Further, as shown in FIG. 3C, the separation angle θ ₃ between the first spot illumination 21 and the second spot illumination 22 around the imaging unit 10 is a plane parallel to the surface of the epitaxial wafer 1. It is set to 85 degrees or more and 95 degrees or less. Here, the separation angle θ ₃ is preferably approximately 90 degrees, and more preferably 90 degrees. Note that FIG. 3B corresponds to a cross-sectional view taken along the line II-II in FIG. 3C, but only a main portion is described for clarification of a positional relationship of each component.

The reason why the separation angle θ _{3 is set} to the above-mentioned angle is that the epitaxial scratch D often has a crystal orientation dependency, and the first spot illumination 21 and the second spot illumination 22 are installed at this position, and at least 2 This is because the surface of the epitaxial wafer 1 is irradiated from the direction. By doing so, it is possible to reliably receive the scattered light from the epitaxial scratch D (as a result, the defect D ′ of the substrate S) regardless of the crystal orientation dependency. In addition to the first and second spot illuminations 21 and 22, spot illumination may be further provided to irradiate the surface of the epitaxial wafer 1 from three or more directions.

  A general light source can be used as the first spot illumination 21 and the second spot illumination 22, and the surface of the epitaxial wafer 1 is irradiated to sufficiently obtain the scattered light intensity resulting from the epitaxial scratch D. If it is a thing, it will not restrict | limit in particular. It is preferable that the 1st spot illumination 21 and the 2nd spot illumination 22 have an ultrahigh pressure mercury lamp light source with high illumination intensity.

  The optical system 30 includes the imaging unit 10, the first spot illumination 21, and the second spot illumination 22, and irradiates the surface of the epitaxial wafer 1 with the first spot illumination 21 and the second spot illumination 22. The scattered light is received and a part image of the surface of the epitaxial wafer 1 is acquired. The optical system 30 may include a holding unit (not shown) that holds these positional relationships and an adjustment unit (not shown) that adjusts the positional relationship.

  The scanning unit 40 scans the optical system 30 in parallel with the surface of the epitaxial wafer 1 while maintaining the positional relationship among the imaging unit 10, the first spot illumination 21, and the second spot illumination 22 in the optical system 30. The scanning unit 40 may scan the optical system 30 in the circumferential direction, or may scan vertically and horizontally. In addition, the epitaxial wafer surface inspection apparatus 100 may include a plurality of (for example, three) optical systems 30, and the scanning unit 40 may scan the respective optical systems 30 in the circumferential direction. The scanning unit 40 can be composed of an arm connected to the optical system 30, a drive stepping motor for driving the arm, a servo motor, and the like.

  By using the epitaxial wafer surface inspection apparatus 100 described above, since the imaging unit 10 can receive and image the scattered light caused by the epitaxial scratch D, the epitaxial scratch D, which could not be sensed without visual observation in the past, can be detected. It can be detected.

  The epitaxial wafer 1 is preferably an epitaxial silicon wafer obtained by epitaxially growing a silicon epitaxial layer on the surface of a mirror-finished silicon wafer. The thickness of the epitaxial layer is not particularly limited. For example, if the thickness is 1 μm or more and 15 μm or less, the epitaxial wafer surface inspection apparatus 100 can be used to reliably check the presence or absence of epitaxial scratches. In addition, it is preferable that the surface orientation of the main surface of this silicon wafer is a (100) plane. This is because the above-described epitaxial scratch D becomes particularly problematic using FIG.

(Epitaxial wafer surface inspection method)
Next, an embodiment of an epitaxial wafer surface inspection method using the above-described epitaxial wafer surface inspection apparatus 100 will be described. The present embodiment is obtained by acquiring an entire image of the surface of the epitaxial wafer 1 by continuously capturing part images of the surface of the epitaxial wafer 1 while scanning the optical system 30 by the scanning unit 40. And a detection step of detecting a scratch-like defect pattern existing on the surface of the epitaxial wafer 1 from the entire image.

  That is, in the acquisition step, first, when the optical system 30 is located at a predetermined position, a part image of the surface of the epitaxial wafer 1 is taken. Next, the scanning unit 40 scans the optical system 30 at a position different from the predetermined position, and takes a part image on the surface of the epitaxial wafer 1. For example, the surface of the epitaxial wafer 1 is divided into about 100 to 200, and this photographing and scanning are repeated for each of the divisions, and the part images on the surface of the epitaxial wafer 1 are continuously photographed to synthesize the part images. An entire image of the surface of the wafer 1 is acquired. An example of the obtained whole image is FIG. 4A described later in the embodiment.

  Next, a detection step of detecting a scratch-like defect pattern present on the surface of the epitaxial wafer 1 is performed from the entire image acquired in the above acquisition step. Here, the epitaxial scratch D has a defect pattern unique to this defect. Therefore, conditions are set using the defect pattern length, the aspect ratio, the elliptical flatness ratio, etc., which are peculiar to the epitaxial scratch D, and a defect pattern that meets these conditions is detected from the entire image. In the entire image obtained using the epitaxial wafer surface inspection apparatus 100, if there is a scratch-like defect pattern that meets the above conditions, it can be evaluated that the epitaxial scratch D exists, and if there is no scratch-like defect pattern, It can be evaluated that the epitaxial scratch D does not exist.

  In addition, it is preferable to further have an image processing step of performing image processing on the acquired whole image prior to the above-described detection step. And in the above-mentioned detection process, it is preferable to detect a scratch-like defect pattern based on the whole image subjected to image processing. In the image processing step, for example, if a differential processing image is acquired from the entire image, the influence of noise and the like can be suppressed, and defects existing on the surface of the epitaxial wafer 1 can be detected more clearly. Note that FIG. 4B, which will be described later, is obtained by subjecting the entire image of FIG. 4A to differentiation processing and thinning processing. If a scratch-like defect pattern is detected based on the entire image that has been subjected to image processing, the detection accuracy of the epitaxial scratch D can be further increased.

  As mentioned above, although embodiment of this invention was described, these show the example of typical embodiment, Comprising: This invention is not limited to these embodiment, In the range of the summary of invention. Various changes can be made. Similarly, the following examples do not limit the present invention in any way.

In order to confirm that an epitaxial scratch can be detected using the epitaxial wafer surface inspection apparatus 100 according to an embodiment of the present invention, the following experiment was performed.
First, a silicon wafer after finishing polishing having a diameter of 300 mm and a thickness of 775 μm (so-called polished wafer (also called a PW wafer)) is prepared, and a silicon epitaxial layer having a thickness of 2 μm is epitaxially grown to prepare an epitaxial silicon wafer. did. Visual inspection was performed on the surface of the epitaxial wafer in advance, and it was confirmed that the epitaxial silicon wafer had an epitaxial scratch.

When the epitaxial wafer surface inspection apparatus 100 is used to scan each of the three optical systems 30 in the circumferential direction of the wafer and synthesize the part images obtained from the respective optical systems 30, an overall image shown in FIG. It was. Note that an ultra-high pressure mercury lamp light source was used for the first spot illumination 21 and the second spot illumination. θ ₁ and θ ₂ were 70 degrees, and θ ₃ was 90 degrees.

  It can be confirmed from FIG. 4A that an arc-shaped pattern (that is, a scratch-shaped pattern) is formed by continuous dot-like defects at the center of the wafer. If the whole image is differentiated and thinned, an image shown in FIG. 4B is obtained, and an arc-shaped pattern can be confirmed in the same manner. These arc-shaped patterns were confirmed to have the same size, shape and position as the epitaxial scratches confirmed by the visual inspection conducted in advance. Therefore, it was confirmed that the presence or absence of the epitaxial scratch can be reliably inspected by the inspection apparatus and the inspection method according to the embodiment of the present invention.

  Further, even when an epitaxial silicon wafer having a silicon epitaxial layer with a thickness in the range of 2 μm to 8 μm was inspected for the presence or absence of epitaxial scratches using this epitaxial wafer surface inspection apparatus 100, the same as in the above-described embodiment. It was confirmed that the inspection was possible.

  ADVANTAGE OF THE INVENTION According to this invention, the epitaxial wafer surface inspection apparatus which can test | inspect the presence or absence of the epitaxial scratch in the epitaxial wafer surface, and the epitaxial wafer surface inspection method using the same can be provided.

1 Epitaxial wafer (wafer)
DESCRIPTION OF SYMBOLS 10 Image | photographing part 21 1st spot illumination 22 2nd spot illumination 30 Optical system 40 Scanning part D Epitaxial scratch

Claims (5)

A first spot illumination installed at an angle of 60 degrees to 80 degrees with respect to the surface of the epitaxial wafer, and a second spot illumination installed at an angle of 60 degrees to 80 degrees with respect to the surface And an optical system comprising a photographing unit installed perpendicular to the surface,
A scanning unit that scans the optical system in parallel with the surface,
Epitaxial wafer surface inspection characterized in that a separation angle between the first spot illumination and the second spot illumination is 85 degrees or more and 95 degrees or less on a plane parallel to the surface, with the imaging unit as a center. apparatus.   The epitaxial wafer surface inspection apparatus according to claim 1, wherein the first and second spot illuminations have an ultrahigh pressure mercury lamp light source.   The epitaxial wafer surface inspection apparatus according to claim 1 or 2, wherein the first and second spot illuminations are installed at the same angle with respect to the epitaxial wafer surface. Using the epitaxial wafer surface inspection apparatus according to any one of claims 1 to 3, the part image of the surface is continuously photographed while the optical system is scanned by the scanning unit. An acquisition process for acquiring the entire image;
An epitaxial wafer surface inspection method comprising: a detection step of detecting a scratch-like defect pattern existing on the surface from the whole image. Prior to the detection step, further comprising an image processing step of image processing the entire image,
The epitaxial wafer surface inspection method according to claim 4, wherein in the detection step, the detection is performed based on the entire image subjected to the image processing.