JP6142996B2 - Via shape measuring device and via inspection device - Google Patents

Description

  The present invention relates to a via shape measuring device that measures the size or diameter of the bottom surface of a via hole formed in a substrate such as a silicon wafer, and a via inspection device that inspects the bottom surface of a via.

  TSV (Through Silicon Via) technology has been developed as a three-dimensional mounting technology for next-generation silicon. In the TSV technique, a via hole having a diameter of about 5 μm and a depth of about 50 μm is formed by RIE etching before or after forming a wiring layer on a silicon wafer. Subsequently, after an insulating film is formed on the side wall of the via hole, copper is embedded in the via by copper plating to form a columnar electrode. After filling the vias with copper, the back surface of the wafer is back-ground so that the tips of the copper columnar electrodes are exposed, and bump electrodes are formed on the front surface side of the wafer. After the columnar electrodes and bumps are formed, the silicon dies are stacked, and the columnar electrodes penetrating the silicon wafer and the bumps are electrically connected.

  Since the stacked silicon dies are electrically connected by the columnar electrode and the bump, the shape of the tip of the columnar electrode may affect the stability of the contact. Accordingly, there is a demand for the development of an inspection apparatus capable of accurately inspecting the shape of the tip portion of the via formed on the wafer to form the columnar electrode and measuring the diameter of the via bottom. That is, when the diameter of the bottom surface of the via is inaccurate, the diameter of the tip of the columnar electrode is deviated from the reference value, and the electrical connection between the columnar electrode and the bump becomes unstable. In addition, when the bent state of the bottom surface of the via is deviated from a specified value, for example, when the curvature radius of the bottom surface is smaller than the specified value, the tip of the columnar electrode becomes sharp, and similarly the electrical connection between the bumps It becomes unstable. Therefore, it is an urgent task to develop TSV technology to accurately measure the size or diameter of the bottom surface of the via and to inspect the shape of the bottom surface of the via.

  As a method of observing the bottom surface of the via formed on the silicon wafer, a method of performing bright field observation by performing epi-illumination from the surface side of the wafer on which the via is formed can be considered. However, in this method, since the illumination light does not sufficiently enter the inside of the via, the entire via is observed dark and it is difficult to inspect the bottom surface of the via.

  Another possible method is to perform epi-illumination from the back side of the silicon wafer and observe the bottom of the via in bright field. However, with this method, only the central part of the via is observed brightly, and the vicinity of the bottom edge including the side wall part is entirely dark, making it difficult to accurately measure the bottom diameter. It is also known to observe the shape of a via from the back side of a wafer using a confocal laser microscope (see, for example, Patent Document 1).

  Furthermore, it is assumed that the wafer surface is observed using an SEM. However, when the bottom surface is observed using SEM, the yield of secondary electrons generated from the bottom surface is low, and it is difficult to clearly observe the bottom surface of the via.

Furthermore, as an inspection device that detects defects existing inside a silicon wafer, an illumination beam is projected at the Brewster angle toward the back or front surface of the silicon wafer, and the scattered light generated by the defect is collected by an objective lens. The apparatus is known (see, for example, Patent Document 2). In this known inspection apparatus, the illumination beam is projected at an incident angle equal to the Brewster angle, and the scattered light generated by the defect is emitted from the back surface or the front surface of the wafer and collected by the objective lens. Accordingly, since most of the illumination light enters the inside of the silicon, defect detection is performed by dark field illumination, and highly accurate defect detection is performed.
JP 2011-191285 A Japanese Patent No. 5158552

  As described above, measurement of the diameter and curvature of the bottom surface of the via for forming the columnar electrode is extremely important for establishing a stable electrical connection between the columnar electrode and the bump. However, Patent Document 1, which describes a method for observing a via from the back side of a silicon wafer using a confocal laser microscope, refers to the measurement of the depth of the via, but measures the diameter of the bottom of the via. Is not mentioned. Also, there is no mention of inspecting the curvature of the bottom surface of the via. Further, the inspection apparatus described in Patent Document 2 is effective as an inspection apparatus for detecting defects existing inside a wafer because it detects scattered light generated from foreign matter. However, the diameter of the bottom surface of the via cannot be measured, and it is not suitable for measuring the curvature of the bottom surface of the via.

An object of the present invention is to realize a via shape measuring apparatus capable of measuring the size or diameter of the bottom surface of a via formed on a substrate such as a silicon wafer or a glass substrate.
It is another object of the present invention to provide a via inspection apparatus capable of inspecting the shape of the bottom surface of the via and the insulating film and metal material embedded in the via at high speed.

A via shape measuring device according to the present invention is a via shape measuring device that measures the diameter of the bottom surface of a via formed on the surface of a substrate,
A light source device that generates illumination light transparent to the substrate;
An illumination optical system that projects illumination light emitted from the light source device toward the substrate;
An objective lens that is arranged so that the optical axis is orthogonal to the substrate surface, and that collects the reflected light that is reflected by the via and emitted from the back surface of the substrate;
An image sensor that receives reflected light collected by the objective lens;
A signal processing device for determining the diameter of the bottom surface of the via from the image signal output from the image sensor;
The illumination optical system includes a first and a first light incident on the substrate surface at incident angles opposite to each other across the optical axis of the objective lens in a light incident surface including the optical axis of the objective lens and orthogonal to the substrate surface. First and second illumination beam projection means for projecting two illumination beams,
The signal processing apparatus includes: an image forming unit that forms a two-dimensional image of a substrate from an image signal output from the image sensor;
Means for detecting first and second luminance images corresponding to luminance images at or near the edge of the via bottom from the formed two-dimensional image;
Means for obtaining an interval between the detected first and second luminance images.

  In the present invention, as a method for measuring the size or diameter of the via formed on the surface of the silicon wafer, an illumination beam traveling from the front surface side where the via is formed toward the back surface side is used. When this illumination beam is incident on the via, it is totally reflected at or near the edge of the via bottom, and is emitted from the wafer as reflected light that travels parallel to the central axis of the via or the optical axis of the objective lens. Therefore, the edge of the bottom surface of the via and the vicinity thereof can be captured as an arcuate luminance image. On the other hand, since the objective lens has a limited collection angle range, when such an illumination beam is incident on a portion other than the edge of the via bottom, it is largely refracted on the back surface of the wafer, and most of the reflected light is reflected by the objective lens. Outgoes far from the light collection range. Therefore, the edge of the via bottom and the vicinity thereof can be clearly detected in the same illumination state as the dark field illumination. Therefore, if illumination is performed from opposite sides across the optical axis of the objective lens, images of opposite edges of the via bottom surface can be formed, so the position of the opposite edge of the via bottom surface is detected using a two-dimensional image. The size or diameter of the via bottom can be measured by measuring the distance between the two edges.

  As a method of forming an illumination beam that proceeds from the front surface side of the wafer toward the back surface side, when a reflective wiring layer is formed on the surface of the silicon wafer via surface, the illumination beam is applied from the back surface side. When projected, the illumination beam is reflected by the wiring layer to form an illumination beam that travels from the front side to the back side. On the other hand, when a wiring layer is not formed on the surface of the wafer, an illumination beam traveling from the front surface side to the back surface side can be formed by projecting the illumination beam onto the wafer surface.

A via inspection device according to the present invention is a via inspection device that inspects the bottom surface of a via formed on the surface of a substrate,
A light source device that generates illumination light transparent to the substrate;
An illumination optical system that projects the illumination light emitted from the light source device toward the back surface of the substrate;
An objective lens that is arranged so that the optical axis is orthogonal to the substrate surface, and that collects the reflected light that is reflected by the via and emitted from the back surface of the substrate;
An image sensor that receives reflected light collected by the objective lens;
A signal processing device that inspects the curved state of the bottom surface of the via and detects the diameter of the bottom surface of the via from the image signal output from the light detection means;
The illumination optical system includes a first and a first light incident on the substrate surface at incident angles opposite to each other across the optical axis of the objective lens in a light incident surface including the optical axis of the objective lens and orthogonal to the substrate surface. First and second illumination beam projection means for projecting two illumination beams,
The signal processing apparatus includes: an image forming unit that forms a two-dimensional image of a substrate from an image signal output from the image sensor;
Means for detecting a first luminance image pair composed of two luminance images corresponding to luminance images at or near the edge of the bottom surface of the via from the formed two-dimensional image;
And means for measuring an interval between two luminance images of the detected first luminance image pair.

  In the via inspection apparatus according to the present invention, a diameter of a via is obtained by detecting a luminance image pair composed of two luminance images and measuring an interval between the two luminance images. By comparing the interval with the reference value, it is possible to determine whether the vias formed on various substrates such as a silicon wafer are good or bad.

According to the present invention, the edge of the bottom surface of the via formed on the substrate or the vicinity thereof is picked up as a luminance image that can be identified from the surroundings. Therefore, the bottom surface of the via is obtained from the luminance image obtained by scanning the substrate using the illumination beam. Can be obtained.
Furthermore, in the present invention, the diameter of the via bottom is obtained by scanning the substrate using two illumination beams facing each other across the optical axis, so that the via inspection can be performed at a high speed.

It is a figure which shows an example of the optical system of the via | veer inspection apparatus by this invention. It is a figure which shows an example of an illumination beam projection part. It is a figure which shows the relationship between the illumination light beam which propagates the inside of a silicon wafer, and the condensing angle of an objective lens. It is a figure for demonstrating the principle of the via | veer shape measuring apparatus by this invention. It is a figure which shows the progress state of the illumination beam which injected into the wafer in detail. It is a figure which shows the two-dimensional image of the via bottom face imaged with an image pick-up element. It is a figure which shows the Example which test | inspects the silicon wafer in which the metal wiring layer is not formed in the wafer surface. It is a figure which shows the Example which improved the angle resolution using the pupil filter. It is a figure which shows an example of the test | inspection algorithm of the test | inspection apparatus by this invention.

  In this example, as a substrate to be inspected, a silicon wafer in which a device and a reflective wiring layer (metal wiring layer) are formed on the surface side and a TSV via hole is formed by etching is used. Then, an illumination beam is projected from the back side of the silicon wafer, and the reflected light reflected by the via, that is, the reflected light reflected by the interface between the inner wall surface of the via and air is collected by the objective lens. The reflected light collected by the objective lens enters the light detection means, measures the diameter of the via bottom based on the image signal output from the light detection means, and inspects the curvature of the via bottom. Of course, when inspecting a silicon wafer on which a metal wiring layer is not formed, the diameter of the bottom surface of the via can be measured by projecting an illumination beam from the surface side where the via hole is formed by etching.

  In order to establish a good electrical connection between the columnar electrode and the bump, it is necessary to form a normal bottom-shaped via, and the bottom diameter is measured as a parameter for inspecting the bottom of the via. As a result, the quality of the via formed in the wafer can be determined, and the diameter of the bottom or tip of the via can be measured and compared with a reference value to perform defect inspection on the via. As a comparison inspection with a reference value, for example, an image of the bottom edge of a via can be taken, and a defective via and its address can be detected by die-to-die comparison inspection. The present invention is also applicable to the case where a glass substrate is used as a sample to be inspected, the diameter of the bottom surface of a via or trench formed in the glass substrate is measured, and the curvature of the bottom surface is inspected.

  FIG. 1 is a diagram showing an example of an optical system of a via inspection apparatus according to the present invention, and FIG. 2 is a plan view of the configuration of an illumination beam projection unit of the via inspection apparatus shown in FIG. 1 viewed from the optical axis direction of the objective lens. It is. A silicon wafer 1 to be inspected is placed on a stage 2. An XY stage that can move in a first direction (X direction) and a second direction (Y direction) orthogonal to the first direction is used as the stage 2, and supports the wafer 1 and constitutes a scanning system. The stage 2 is moved in a zigzag manner in the X direction and the Y direction by a drive signal supplied from the signal processing device 3, and the entire back surface of the silicon wafer 1 to be inspected is scanned by an illumination beam. A position sensor 4 is connected to the stage 2 to detect the position of the moving stage in the X direction and the Y direction, and the position information is supplied to the signal processing device 3. The signal processing device 3 specifies the address of the via in which the abnormality is recognized using the input position information.

  An illumination beam in an optically transparent wavelength region is projected from the illumination beam projection unit 5 toward the silicon wafer 1 placed on the stage. In this example, two polarization preserving fibers 10a and 10b are used as means for projecting an illumination beam. An illumination beam is projected from these polarization plane preserving fibers to form an illumination area on the silicon wafer 1. In this example, the polarization-maintaining fibers 10a and 10b project P-polarized illumination light onto the silicon wafer at an incident angle substantially equal to the Brewster angle (74 °). Accordingly, the reflectance at the surface of the silicon wafer 1 becomes substantially zero, and most of the projected illumination light enters the inside of the silicon wafer. Note that a GIN lens or rod lens that functions as a collimator lens is attached to the tip of the polarization-maintaining fiber, and a parallel illumination beam is emitted from the polarization-maintaining fiber.

  Since the metal wiring layer is formed on the surface of the silicon wafer 1 (the side directly facing the stage 2), the illumination beam is transmitted through the back surface of the wafer 1 and reflected at the interface with the wiring layer on the front surface side. The vias formed on the surface of the wafer are illuminated. Then, the light is reflected at the interface between the inner wall of the via and air near the edge of the bottom surface of the via, passes through the back surface of the wafer 1, and is collected by the objective lens (objective optical system) 6. The illumination light incident on the bottom surface of the via is partly reflected by Fresnel at the interface between the inner wall of the bottom surface and the air, passes through the back surface of the wafer, and enters the objective lens 6. The objective lens 6 is arranged so that its optical axis is orthogonal to the surface of the silicon wafer 1.

  The reflected light condensed by the objective lens 6 enters the image sensor 8 through the imaging lens 7. In this example, a line CCD sensor is used as the image sensor. As an image sensor other than the line sensor, a TDI sensor, a two-dimensional CCD sensor, or a CMOS sensor can be used. The image signal output from the image sensor 8 is supplied to the signal processing device 3, and the signal processing device 3 forms a two-dimensional image of the entire surface of the silicon wafer. Then, a two-dimensional image of the via is formed based on the reflected light reflected by the via from the formed two-dimensional image, the diameter of the via bottom is measured from the via two-dimensional image, and the curvature of the via bottom is inspected. The

  Next, an illumination beam projection method will be described. FIG. 2 is a plan view of the illumination beam projection unit 5 viewed along the optical axis direction of the objective lens. The illumination beam projection unit 5 will be described with reference to FIGS. 1 and 2. The illumination beam projection unit supports the two polarization-maintaining fibers 10a and 10b that project the illumination beam toward the back surface (the surface on which the device and the wiring layer are not formed) of the silicon wafer 1, and these polarization-maintaining fibers. And a holding plate 12 for fixing the polarization preserving fibers 10 a and 10 b to the support plate 11. The two polarization-maintaining fibers are maintained in a state in which the coating is removed on the distal end side thereof. The support plate 11 is formed with two V-grooves facing each other across the illumination area, and a polarization-preserving fiber is disposed in these V-grooves and fixed with an adhesive. Further, the holding plate 12 is attached with an adhesive in a state where the polarization-maintaining fiber is disposed in each V-groove, and the two polarization-maintaining fibers are fixed.

  The V-groove formed in the support plate 11 is inclined so that the illumination beam is incident on the sample surface at an incident angle substantially equal to the Brewster angle of the sample. For example, when inspecting a via formed in a silicon wafer, when using near-infrared wavelength light (for example, 1300 nm wavelength light), the Brewster angle of the silicon material is about 74 °. The polarization preserving fiber is supported so that the illumination beam emitted from the light emitting ends of the fibers 10a and 10b is incident on the surface of the silicon wafer 1 at an incident angle of 74 °. Since the Brewster angle varies depending on the optical characteristics of the sample, the support plate has an inclination angle so that it can be illuminated with an incident angle equal to the corresponding Brewster angle depending on the optical characteristics of the sample to be inspected. It is desirable to prepare. In this example, the illumination beam is projected at an incident angle equal to the Brewster angle. However, it is also possible to project the illumination beam at an incident angle other than the Brewster angle.

  The two polarization plane preserving fibers 10a and 10b are arranged so as to face each other in a light incident plane that includes the optical axis of the objective lens 6 and is orthogonal to the surface of the silicon wafer. That is, the two polarization preserving fibers 10a and 10b project an illumination beam at an incident angle substantially equal to the Brewster angle (74 °) to illuminate the illumination area. Therefore, the illumination area formed on the silicon wafer is illuminated at the Brewster angle from two opposite directions.

  FIG. 3 shows the relationship between the illumination light beam propagating inside the silicon wafer and the focusing angle of the objective lens. In this example, an objective lens having a magnification of 50 times and a numerical aperture of 0.6 will be described as an objective lens. The refractive index of the silicon wafer is 3.5 and the thickness is 775 μm (in the case of φ300 mm wafer). The silicon wafer of this example has a metal reflective layer formed on the back surface. When an illumination beam having a wavelength of 1300 nm is projected onto a silicon wafer, the Brewster angle is approximately 74 °. When the illumination beam is projected onto the silicon wafer at an incident angle equal to the Brewster angle, it is refracted at the surface of the silicon wafer and propagates inside the wafer at a refraction angle of 16 °.

  According to the calculation, the condensing angle of the objective lens with NA = 0.6 is about 37 °. When the illumination beam is incident on the surface of the silicon wafer at this angle, the refraction angle at the wafer surface is about 10 °. Therefore, if the reflected beam that is totally reflected or Fresnel reflected at the interface between the inner wall of the via and the air inside the via propagates within the wafer within an angle range of ± 10 ° with respect to the optical axis of the objective lens, The reflected reflected beam is collected by the objective lens, and light rays propagating through the wafer at other angles are not collected by the objective lens and do not contribute to the formation of a two-dimensional image.

  FIG. 4 shows the principle of the via shape measuring apparatus according to the present invention. The silicon wafer 20 has a front surface 20a and a back surface 20b, and vias 21 are formed on the front surface 20a. It should be noted that the dimension of the silicon wafer in the depth direction is shown in a reduced scale. The via 21 is formed by RIE etching and is a pore having a circular cross section. The via has a side wall 21a and a bottom surface 21b. Further, the central axis of the via is indicated by L, and the central axis L is orthogonal to the front surface 20a and the rear surface 20b of the wafer and parallel to the optical axis of the objective lens. Due to the characteristics of RIE etching, the bottom surface 21b is formed as a continuous curved surface. In the bottom surface 21b of the via, a portion (edge portion) connected to the side wall is parallel to the central axis L, and a central portion of the bottom surface 21b is orthogonal to the central axis L. That is, the bottom surface of the via is a curved surface that continuously changes from an angle of 0 ° to an angle of 90 ° with respect to the central axis L.

  In this example, the illumination beam is projected onto the wafer surface 20a at an incident angle equal to the Brewster angle. The illumination beam is a parallel light beam. The illumination beam is refracted at a refraction angle of 16 ° at the surface 20a of the wafer and enters the inside of the wafer. Here, after being refracted, the light beam b1 is incident on the back surface 20b of the wafer by grazing the via, refracted at a refraction angle of 74 °, and emitted to the outside. Since this illumination light beam b1 is significantly deviated from the focusing range of the objective lens, it is not collected by the objective lens.

  Next, the light beam b3 is incident on the via sidewall 21b, totally reflected, and incident on the back surface 20b of the wafer. Then, the light is refracted at a refraction angle of 74 ° and emitted to the outside. Since this illumination light b3 is also significantly deviated from the range of the collection angle of the objective lens, it is not collected by the objective lens.

  Next, the illumination light beam that enters the edge of the bottom surface of the via or the vicinity thereof will be described. The light beam b2 is refracted at a refraction angle of 16 [deg.] On the surface 20a of the wafer, enters the inside of the wafer, and enters near the boundary between the side wall and the bottom surface, which is the edge of the via. In this case, when the incident portion forms an inclination angle of 8 ° with respect to the via central axis L, the illumination light beam b2 is totally reflected at the corresponding portion and becomes a reflected light beam parallel to the via central axis L, and the back surface 20b of the wafer. And exits as it is. Since this reflected light ray is within the range of the collection angle of the objective lens, it is collected by the objective lens. That is, since the vicinity of the edge of the bottom surface of the via is a curved surface slightly inclined with respect to the center axis L, the illumination light incident on the edge or the vicinity thereof is totally reflected at the interface between the inner wall of the via and the air, Since the light is incident on the back surface 20b of the wafer in a state substantially parallel to or nearly parallel to the axis, it is condensed by the objective lens and forms an image of the bottom edge. Therefore, the distance between the edges of the bottom surface of the via is measured by projecting an illumination beam from the opposite side across the via and measuring the distance D1 between the light beams collected by the objective lens. Here, the part forming an angle of 8 ° with respect to the central axis of the via on the bottom surface of the via is located in the vicinity of the intersection between the bottom surface and the side wall, and thus can be regarded as the position of the edge of the bottom surface.

  As described above, when the edge of a via is illuminated using an illumination beam that travels from the front side to the back side of the wafer, the illumination beam incident on the position deviated from the edge deviates from the focusing range of the objective lens. Only the illumination beam incident on or near the edge is collected by the objective lens. Therefore, by illuminating the edge of the via bottom from opposite directions across the via, a two-dimensional image of the edge is captured, and the diameter of the via bottom is measured by measuring the distance between the two edge images. be able to.

  FIG. 5 shows in more detail the progress of the illumination beam when illuminating from the backside of the wafer. For the sake of clarity, the dimension in the depth direction of the silicon wafer is shown in a reduced scale. In this example, a silicon wafer 30 having a metal wiring layer 31 formed on the surface is used as an inspection target, and a via 32 formed on the silicon wafer 30 is inspected. The via 32 has a side wall portion 32a and a bottom surface 32b having a circular cross section. Since the via 32 is formed by RIE etching, the side wall is orthogonal to the surface of the wafer, and the bottom surface 32b is convexly extended from 0 ° (edge portion) to 90 ° (central portion of the via) with respect to the optical axis. A curved surface is formed.

  In the drawing, the first illumination beam BL is projected at the Brewster angle (74 °) from the left side with the via 32 interposed therebetween, and the second illumination beam BR is projected at the Brewster angle from the right side. These illumination beams BL and BR are parallel light beams in which the whole beam is parallel. The silicon wafer 30 placed on the stage moves relative to the direction orthogonal to the paper surface by moving the stage, and the illumination beam is in a stationary state. Accordingly, the silicon wafer 30 is scanned two-dimensionally by two illumination beams incident at an incident angle equal to the Brewster angles in opposite directions. For the sake of clarity, the first illumination beam BL will be described using the illumination rays b1 to b7. However, the second illumination beam BR has the opposite incident direction, and the others are the first. The detailed description is omitted because it is the same as the illumination beam BL.

  The illumination beam b1 is incident on the back surface of the silicon wafer 30 at a Brewster angle, refracted at a refraction angle of 16 °, and travels. Then, the light is reflected by the metal wiring layer 31 formed on the front surface side of the silicon wafer, refracted on the back surface of the wafer, and emitted from the wafer at an emission angle of 74 °. Since this illumination light beam b1 greatly exceeds the range of the condensing angle of the objective lens, it is not collected by the objective lens.

  Similarly, the illumination light beam b2 is refracted on the back surface of the silicon wafer, reflected by the metal wiring layer, and emitted to the outside of the wafer. Since this illumination beam also exceeds the focusing range of the objective lens, it is not collected by the objective lens.

  The illumination light beam b3 is refracted at a refraction angle of 16 ° on the back surface of the wafer, reflected by the wiring layer 21, and incident near the edge of the bottom surface of the via. In this case, when the illumination light beam is incident on the via, the illumination light beam is totally reflected at the interface between the inner wall of the via and air due to the relationship between the refractive indexes of silicon and air. At this time, when the bottom surface of the via forms an angle of 8 ° with respect to the optical axis of the objective lens, the illumination beam b3 incident near the edge is totally reflected near the edge of the bottom surface of the via and reflected parallel to the optical axis. A light beam is emitted from the wafer. This reflected light beam is condensed by the objective lens to form a luminance image.

  The illumination beam b4 is reflected by the wiring layer 31 and enters the via sidewall 22a. This light beam is reflected by the side wall of the via, reflected by the wiring layer 21 again, travels inside the wafer, and is emitted from the back surface at an emission angle of 74 °. This light beam also significantly exceeds the focusing range of the objective lens and is not collected by the objective lens.

  The illumination light beam b5 is refracted on the back surface of the wafer and then enters the bottom surface 32b of the via. Part of this illumination light beam is reflected by Fresnel at the interface between the via bottom and air. In this case, when the incident bottom surface portion is a curved surface having an angle of 82 ° with respect to the central axis L of the via, the reflected light reflected by Fresnel is parallel to the optical axis of the objective lens and is emitted from the wafer as it is. It is condensed by the objective lens. Therefore, a luminance image is formed when the bottom surface is incident on a portion that forms an angle of 82 ° with respect to the central axis and the vicinity thereof.

  Furthermore, the illumination light beam b6 is incident on the bottom surface 22b of the via, a part of which is Fresnel-reflected in the opposite direction and is emitted from the back surface. Since this reflected light also exceeds the range of the collection angle of the objective lens, it is not collected by the objective lens.

  Further, the illumination light beam b7 is refracted on the back surface of the wafer, enters the opposite wiring layer via the via, is reflected by the wiring layer, and exits from the back surface of the wafer. This light beam is not condensed by the objective lens.

  As described above, when the via formed in the wafer and the vicinity thereof are illuminated by the illumination beam of the parallel luminous flux, only the reflected light generated from the portions that form an angle of 8 ° and 82 ° with respect to the optical axis of the bottom surface of the via. The light is condensed by the objective lens and forms a luminance image. As described with reference to FIG. 3, since the objective lens has a range with respect to the condensing angle, reflected light from portions having angles of 8 ± α ° and 82 ± α ° also forms a luminance image.

  The same applies to the illumination beam BR facing in the opposite direction, and only the reflected light generated from the portions having angles of 8 ° and 82 ° with respect to the central axis L of the via is condensed by the objective lens to form a luminance image. .

  Here, the portion where the via bottom has an inclination angle of 8 ° with respect to the central axis is in the vicinity of the edge of the bottom, and therefore the portion having the inclination angle of 8 ° can be regarded as the edge of the bottom.

  FIG. 6 shows a two-dimensional image (luminance image) of the via bottom imaged by the image sensor 8 by illuminating the silicon wafer with an illumination beam. A first luminance image pair composed of the reflection images 40R and 40L of the inclined surface that forms an angle of 8 ° with respect to the central axis of the via bottom surface 32b is captured. A second luminance image pair is captured. Since the via 32 is a circular hole, the reflected images 40R and 40L and 41R and 41L are arc-shaped luminance images. Here, the distance D1 between the luminance images 40R and 40L of the first luminance image pair corresponds to the distance between the edges of the via bottom, that is, the diameter. Accordingly, the diameter of the via bottom is obtained by detecting an arcuate luminance image from the formed two-dimensional image using an image processing technique and measuring the interval between the two arcuate luminance images. By comparing the obtained interval between the two luminance images with a reference value, it is inspected whether the via bottom is formed as prescribed, and a defect can be determined if it is deviated from the reference value.

  A distance D2 between the two images 41R and 41L at the site where the inclination angle is 82 ° corresponds to the curvature of the via bottom. That is, when the curvature of the bottom surface is sharp, the interval between the two luminance images 41R and 41L of the second luminance image pair is shortened. Therefore, by measuring the distance D2 between the reflection images 41R and 41L at the part where the inclination angle is 82 °, it is possible to determine whether the via bottom is formed in the reference shape or the reference curvature, and the distance is the reference value. If it is shorter, it can be determined as a defect.

  Next, a case where there is no reflective wiring layer on the wafer surface where vias are formed will be described. In this case, as described with reference to FIG. 4, the illumination beam is projected from the front surface side where the via of the silicon wafer is formed, reflected by the via, and reflected light emitted from the back surface of the wafer is detected, and two-dimensional By forming an image (luminance image), the via diameter can be measured.

  Further, FIG. 7 shows another embodiment for inspecting a silicon wafer in which a metal wiring layer is not formed on the wafer surface. In FIG. 7, the same components as those used in FIG. In this example, rotatable half-wave plates 50a and 50b are respectively disposed on the emission sides of the two polarization-maintaining fibers 10a and 10b. The illumination beam emitted from the light source can be switched between P-polarized light and S-polarized light by rotating and adjusting the half-wave plates 50a and 50b. Therefore, when inspecting a silicon wafer on which a metal wiring layer is formed, the half-wave plate is adjusted to project P-polarized light, and when inspecting a silicon wafer on which a metal wiring layer is not formed, S-polarized light is applied. Adjust to emit. The S-polarized illumination beam passes through the back surface of the silicon wafer 1, propagates inside the wafer, and is reflected by Fresnel on the front surface of the wafer. Therefore, by using the illumination beam reflected by Fresnel on the front surface, the via can be illuminated by the illumination beam traveling from the front surface side toward the back surface.

  FIG. 8 shows an embodiment in which the angular resolution is improved by using a pupil filter. In this example, the pupil filter 50 is disposed at a position conjugate to the pupil via the pupil position of the objective lens or the relay lens. The pupil filter selectively allows only the reflected light traveling in a specific angle range out of the reflected light reflected by the vias of the substrate. Therefore, by using the pupil filter, it is possible to observe with a high angular resolution when the curvature changes gently like the bottom surface of the via, which is useful for determining the quality of the bottom surface.

  The pupil filter 50 includes a light blocking unit 50a that blocks incident light and a light transmission unit 50b that transmits incident light. The upper part of FIGS. 8A to 8C shows three types of pupil filters. The pupil filter shown in FIG. 8A is effective in detecting and inspecting a portion where the edge portion is inclined by 3 ° with respect to the optical axis and the bottom surface is inclined by 77 °. The pupil filter shown in FIG. 8B is effective in detecting and inspecting a portion where the edge portion is inclined by 8 ° with respect to the optical axis and the bottom surface is inclined by 82 °. Further, the pupil filter shown in FIG. 8C is effective in detecting a portion where the edge portion is inclined by 13 ° and the bottom surface is inclined by 88 ° with respect to the optical axis.

  Next, the algorithm of the inspection apparatus will be described. FIG. 9 is a diagram illustrating an example of an inspection algorithm in the signal processing device. An image signal output from the image sensor 8 is amplified by an amplifier 60, converted into a digital signal by an A / D converter 61, and supplied to the signal processing device 8. Further, the position information of the silicon wafer output from the position sensor 4 is also supplied to the signal processing apparatus and used as position information.

  The image signal input by the position sensor is supplied to the two-dimensional image forming means 62 to form a two-dimensional image of the silicon wafer. In this example, a defect is detected by die-to-die comparison inspection. For example, when a via is not formed at a predetermined position, or when the diameter of the via deviates from a reference value, and when an arc-shaped luminance image is not formed at a predetermined position, a defective via is detected by image comparison inspection. Can be detected. The two-dimensional image information of one die is supplied to the image memory 63. Subsequently, a two-dimensional image of the next die is formed and sequentially supplied to the comparison means 64. The comparison unit 64 compares two input image signals and detects a difference in luminance value. The detected difference value is supplied to the threshold comparing means 65. The threshold value comparison means 65 determines whether or not the input difference value exceeds a preset threshold value. If the difference value exceeds the threshold value, the threshold value comparison means 65 determines that the defect is a defect and generates a defect detection signal including the address of the defect.

  The two-dimensional image information output from the two-dimensional image forming unit 62 is also supplied to the luminance image detecting unit 65. The luminance image detecting unit 66 detects two luminance image pairs. In other words, the brightness image of the edge of the via and its vicinity and the brightness image of the bottom surface of the via are arc-shaped brightness images, and therefore, four arc-shaped brightness images are detected using an image processing technique. Then, two arcuate luminance images having an outer symmetrical shape are detected as a first luminance image pair, and two arcuate luminance images having an inner symmetrical shape are detected as a second luminance image pair. The two detected luminance image pairs are supplied to the interval detection means 67, and the interval between the luminance images of the first and second arc-shaped luminance image pairs is detected. The interval between the luminance images can be determined by detecting the distance between two symmetrical luminance images in the scanning direction of the illumination beam, that is, the direction orthogonal to the moving direction of the stage. The detected interval between the luminance images of the first and second luminance image pairs is output as via diameter information and bottom surface curvature information.

  Further, the interval information between the two detected luminance images is supplied to the threshold comparing means 68. The threshold comparison means determines whether or not the interval between the two input luminance image means is within a predetermined interval range. When the threshold is exceeded and below the threshold, it is determined as a defective via and is output as via defect information. . That is, if the detected via diameter is out of the predetermined range, it is determined as a defective via. If the distance between the bottom luminance image pairs is out of the predetermined range, the curvature of the bottom surface is out of the predetermined range. It is determined that it is a defective via.

  In the via inspection, all the vias formed on the silicon wafer may be inspected, or a sampling inspection for inspecting only vias at predetermined positions may be performed.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the illumination optical system is configured to project the illumination beam at an incident angle equal to the Brewster angle. However, the incident angle of the illumination beam is not limited to the Brewster angle, and other than the Brewster angle. The incident angle can be set.

  Furthermore, in the above-described embodiment, the polarization plane preserving fiber is used as the illumination beam projecting means. However, it is also possible to project the light beam emitted from the light source device toward the substrate surface as a parallel light beam using a lens system. is there.

  Furthermore, it is also possible to place a galvanometer mirror in the optical path between the objective lens and the line sensor and take a two-dimensional image at a specified position.

  Furthermore, in the above-described embodiments, a silicon wafer is used as a sample to be inspected. However, the present invention can also be applied to the case where the diameter and size of the bottom surfaces of vias and trenches formed on a glass substrate are measured.

DESCRIPTION OF SYMBOLS 1,20,30 Silicon wafer 2 Stage 3 Signal processing apparatus 4 Position sensor 5 Illumination beam projection part 6 Objective lens 7 Imaging lens 8 Image pick-up element 10a, 10b Polarization plane preservation | save fiber
11 Support plate 12 Presser plate 21, 32 Via 31 Wiring layer

Claims (14)

A via shape measuring device that measures the size or diameter of the bottom surface of a via formed on the surface of a substrate,
A light source device that generates illumination light transparent to the substrate;
An illumination optical system that projects illumination light emitted from the light source device toward the substrate;
An objective optical system that is arranged so that the optical axis is orthogonal to the substrate surface, collects the reflected light reflected by the via and emitted from the back surface of the substrate;
An image sensor that receives reflected light collected by the objective lens;
A signal processing device for obtaining the size of the bottom surface of the via from the image signal output from the image sensor;
The illumination optical system includes a first and a first light incident on the substrate surface at incident angles opposite to each other across the optical axis of the objective lens in a light incident surface including the optical axis of the objective lens and orthogonal to the substrate surface. First and second illumination beam projection means for projecting two illumination beams,
The signal processing device detects, from the image signal output from the image sensor, first and second luminance images corresponding to luminance images at or near the edge of the via bottom surface;
A via shape measuring apparatus comprising: means for obtaining an interval between the detected first and second luminance images. 2. The via shape measuring apparatus according to claim 1, wherein the first and second luminance images are formed by reflected light that is totally reflected at or near an edge of a bottom surface of the via and emitted from a back surface of the substrate. Via shape measuring device characterized by the above.



  3. The via shape measuring apparatus according to claim 1, wherein the light source device emits linearly polarized illumination light, and the first and second illumination beam projecting units are P-polarized first and second illuminations. A via shape measuring apparatus which projects a beam toward a front surface of the substrate or a back surface facing the front surface at an incident angle substantially equal to a Brewster angle.   The via shape measurement apparatus according to claim 3, wherein the illumination optical system includes two polarization-maintaining fibers optically connected to the light source device, and the polarization-maintaining fibers are formed of silicon wafer vias. A via shape measuring apparatus that projects P-polarized first and second illumination beams at an incident angle substantially equal to a Brewster angle toward a formed front surface or a back surface facing the front surface.   5. The via shape measuring apparatus according to claim 4, wherein an optical element acting as a collimator lens is fixed to a tip of the polarization plane preserving fiber, and a substantially entire P-polarized illumination beam has a Brewster angle and the surface of the silicon wafer. Alternatively, the via shape measuring device is projected on the back surface. In the via shape measuring apparatus according to any one of claims 1 to 5, a silicon wafer in which a reflective wiring layer is formed on a surface on which a via is formed is used as the substrate.
The first and second illumination beams are projected onto the back surface of the silicon wafer at an incident angle substantially equal to the Brewster angle,
The objective lens is a reflected beam that is transmitted through the back surface of the silicon wafer, reflected by a wiring layer formed on the surface of the wafer, further totally reflected at or near the bottom edge of the via, and emitted from the back surface of the silicon wafer. A via shape measuring device characterized by condensing the light. In the via shape measuring apparatus according to any one of claims 1 to 5, a silicon wafer in which a wiring layer is not formed on a surface on which a via is formed is used as the substrate.
The first and second illumination beams are projected at an incident angle approximately equal to the Brewster angle toward the surface of the silicon wafer where the vias are formed,
The said objective lens permeate | transmits the surface of a silicon wafer, and also totally reflects in the edge of the bottom face of a via | veer, or its vicinity, and condenses the reflected beam radiate | emitted from the back surface of a silicon wafer, The via | veer shape measuring apparatus characterized by the above-mentioned.   8. The via shape measurement apparatus according to claim 1, wherein a pupil filter is disposed at a pupil position of the objective lens, and reflected light in a predetermined angle range out of reflected light emitted from the back surface of the substrate. A via shape measuring apparatus characterized in that only the light is incident on the image sensor. A via inspection device for inspecting the bottom surface of a via formed on the surface of a substrate,
A light source device that generates illumination light transparent to the substrate;
An illumination optical system that projects the illumination light emitted from the light source device toward the back surface of the substrate;
An objective lens that is arranged so that the optical axis is orthogonal to the substrate surface, and that collects the reflected light that is reflected by the via and emitted from the back surface of the substrate;
An image sensor that receives reflected light collected by the objective lens;
A signal processing device that inspects the curved state of the bottom surface of the via and detects the diameter of the bottom surface of the via from the image signal output from the light detection means;
The illumination optical system includes a first and a first light incident on the substrate surface at incident angles opposite to each other across the optical axis of the objective lens in a light incident surface including the optical axis of the objective lens and orthogonal to the substrate surface. First and second illumination beam projection means for projecting two illumination beams,
The signal processing apparatus includes: an image forming unit that forms a two-dimensional image of a substrate from an image signal output from the image sensor;
Means for detecting a first luminance image pair composed of two luminance images corresponding to luminance images at or near the edge of the bottom surface of the via from the formed two-dimensional image;
A via inspection device comprising: means for measuring an interval between two luminance images of the detected first luminance image pair. In the via inspection apparatus according to claim 9, a silicon wafer in which a reflective wiring layer is formed on a surface on which a via is formed is used as the substrate.
The first and second illumination beams are projected toward the back surface of the silicon wafer;
The signal processing device further includes two luminance images formed from the two-dimensional image formed by the image forming unit at an interval shorter than the interval between the two luminance images of the first luminance image pair. Means for detecting a second luminance image pair and means for measuring an interval between the detected luminance images of the second luminance image pair, and between the detected luminance images of the first and second image pairs A via inspection device that performs pass / fail determination of vias based on the interval information. The via inspection apparatus according to claim 10, wherein the first and second illumination beams are projected toward the back surface of the silicon wafer at an incident angle substantially equal to a Brewster angle,
The objective lens passes through the back surface of the silicon wafer, is reflected by the wiring layer formed on the surface of the wafer, is further totally reflected at or near the bottom edge of the via, and is reflected from the back surface of the silicon wafer. And a via inspection apparatus that collects reflected light that passes through the back surface of the silicon wafer and is reflected by the bottom surface of the via. 12. The via inspection apparatus according to claim 11, wherein the first luminance image pair passes through the back surface of the substrate, is reflected by a wiring layer formed on the surface of the substrate, and is at or near the edge of the bottom surface of the via. And is formed by reflected light emitted from the back surface of the wafer,
2. The via inspection apparatus according to claim 1, wherein the second luminance image pair is formed by reflected light that passes through the back surface of the substrate, is reflected by the bottom surface of the via, and is emitted from the back surface of the wafer. In the via inspection apparatus according to claim 9, a silicon wafer in which a reflective wiring layer is not formed on a surface on which a via is formed is used as the substrate.
The first and second illumination beams are projected at an incident angle substantially equal to the Brewster angle toward the surface of the wafer in which vias are formed,
The objective lens collects reflected light that passes through the surface of the silicon wafer and is totally reflected at or near the edge of the bottom surface of the via. 14. The via inspection apparatus according to claim 9, wherein the substrate is disposed on a stage that moves in a zigzag manner in a main scanning direction and a sub-scanning direction orthogonal to the main scanning direction. A via inspection apparatus, wherein a direction is set to be orthogonal to the light incident surface.

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