JP4884063B2 - Depth measuring device - Google Patents

Description

  The present invention relates to a depth measuring device that measures the depth of a groove or a hole on a substrate using an infrared camera.

  During the manufacturing process of the semiconductor device, various processes are performed on the semiconductor substrate. Among these processes, for example, tens of thousands of holes may be formed on the back surface of the substrate. These holes do not penetrate through the substrate and may be holes with a high aspect ratio that are deep with respect to the diameter of the holes. For example, in the case of a 5 inch or 8 inch silicon wafer, the thickness of the wafer is about 600 μm, the hole diameter provided in the wafer is 25 μm or less, and the hole depth is 200 μm or more, which is 8 times higher. Aspect ratio holes may be drilled. Therefore, it is desired to measure the depth of these high aspect ratio holes in the manufacturing process of the semiconductor substrate.

  Conventionally, the depth of a hole provided on a substrate has been measured using a laser displacement meter. In these methods, first, laser light is irradiated inside the hole, the reflected light is measured, and the distance is measured.

For example, as shown in Patent Document 1, there is a measuring apparatus using a confocal optical system using a light beam such as a blue laser. In this method, a light beam is applied to the substrate surface, and the peak value of the reflected light is obtained. Furthermore, the peak value of the reflected light reflected by the bottom surface of the hole is obtained by moving the position in the optical axis direction. And the depth of the hole formed in the board | substrate can be determined by detecting the relative distance between the objective lens and the board | substrate which generate | occur | produce the peak of the two reflected light.
JP 2003-148925 A

  However, when the conventional laser beam measurement is applied to a hole with a small diameter of 25 μm or less and a high aspect ratio, even if the laser beam is irradiated into the hole, the aspect ratio is high. There was a situation where the depth could not be measured. In addition, the method disclosed in Patent Document 1 has a drawback in that an optical system becomes complicated by using many lenses and mirrors. Further, when measuring a hole with a high aspect ratio, it is necessary to scan the beam at a low speed, which increases the measurement time.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a depth measuring apparatus capable of measuring the depth of a high aspect ratio hole or groove relatively easily and at high speed.

In order to achieve such an object, the invention described in claim 1 of the present invention is a depth measuring device for measuring the depth of a recess formed in a substrate, comprising: an infrared light source that irradiates the substrate with infrared light; In a depth measuring apparatus comprising: an infrared camera that measures an infrared image irradiated on the substrate from the infrared light source; and a position adjusting unit that adjusts the position of the infrared camera, the infrared light is transmitted through the substrate. Then, the position of the infrared camera is adjusted by the position adjusting means, and the configuration of measuring the depth of the concave portion of the substrate by measuring images of transmitted light with the infrared camera at a plurality of positions is adopted.

  Further, as in the second aspect of the invention, the focus position when the image corresponding to the lower surface of the substrate is detected by the infrared camera and the image corresponding to the upper surface of the concave portion (the surface on the back side of the hole). Is measured by the infrared camera, and a value obtained by multiplying the distance difference between the two positions by the refractive index of the substrate is subtracted from the thickness of the substrate. It is also possible to measure the thickness.

It is preferable as defined in claim 3, in focus position on the lower surface of the substrate, the distance position to the shape of the recess from the value of that position looks smallest value multiplied by the refractive index of the substrate By obtaining the above, the depth of the concave portion can also be measured.

  Further, as in the invention described in claim 4, it is preferable to use an illumination lens for converging the infrared rays irradiated from the infrared light source and irradiating the substrate.

Further, as in the invention described in claim 5, when measuring the image of the transmitted light with the infrared camera, the infrared light source is cut with light of other wavelengths so that wavelength sensitivity characteristics are approximately 1100 nm. It is preferable to connect a bandpass filter to be connected.

According to the first aspect of the present invention, by moving the focus position of the infrared camera to each cross-sectional position of the substrate, an image of infrared transmitted light in the cross-section is measured by the infrared camera. That is, since the image is measured at the focus position of the camera of the cross section of the substrate, a relatively clear hole image can be obtained even if the aspect ratio is high. In addition, since the hole diameter in each cross section of the substrate can be measured from the obtained image and the depth of the hole in the wafer can be measured, a high aspect ratio hole can be measured easily and at high speed.

  Moreover, according to the invention of Claim 2 and Claim 3, in addition to the effect of the invention of Claim 1, the depth of a hole can be measured with a simple calculation method.

  According to the invention described in claim 4, in addition to the effects of the invention described in claims 1 to 3, the wall surface of the hole is obtained by refracting infrared rays with the illumination lens and irradiating it toward the upper surface of the hole. By reducing the adverse effects of scattered light from the image, a more accurate and clear image can be obtained.

Furthermore, according to the invention described in claim 5, in addition to the effects of the invention described in claims 1 to 4, by attaching a 1100 nm bandpass filter, it is possible to cut light of other wavelengths, The image quality of the image captured by the infrared camera is improved, and the measurement accuracy can be increased.

A depth measurement apparatus according to the present invention is a depth measurement apparatus that measures the depth of a recess formed in a substrate, the infrared light source that irradiates the substrate with infrared light, and the substrate that is irradiated from the infrared light source. In a depth measuring apparatus having an infrared camera for measuring an infrared image and a position adjusting means for adjusting the position of the infrared camera, the infrared light is transmitted through the substrate, and the position adjusting means The depth of the concave portion of the substrate is measured by adjusting the position and measuring images of transmitted light with the infrared camera at a plurality of locations.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a side view showing an embodiment of a depth measuring apparatus according to the present invention. FIG. 2 is a diagram showing holes formed on the wafer (substrate). 2A is a side sectional view of the wafer, and FIG. 2B is an enlarged view of the back surface of the wafer. In the figure, the horizontal direction is the XY direction, and the vertical direction is the Z direction.

  FIG. 1 shows a depth measuring apparatus 1 according to an embodiment of the present invention. In the center of FIG. 1, a wafer (substrate) 2 in which a hole to be measured is formed is disposed. As shown in FIG. 2, the wafer 2 has a hole 2a formed on the back surface thereof. Although the holes 2a are omitted in the drawing, for example, 80,000 holes are formed on one substrate. As shown in FIG. 2B, the hole 2 a does not penetrate the wafer 2, and the diameter of the upper surface of the hole 2 a (the surface on the back side of the hole) is slightly smaller than the diameter of the lower end surface of the wafer 2. Has a tapered shape.

  As shown in FIG. 1, the wafer 2 is fixed to the upper portion of a mounting table 3 in the X direction that can move in the X direction by a chuck 4. The X-direction mounting table 3 is movably mounted on a Y-direction mounting table 5 that is movable in the Y direction. The positions of the mounting table 3 in the X direction and the mounting table 5 in the Y direction are controlled by a high-precision linear scale, and feedback control is performed so that the infrared light hits the position of the hole formed in the wafer. The mounting table 5 in the Y direction is fixed to a plate-like base 6 that spreads in the horizontal direction.

Below the wafer 2, an illumination lens 7 that focuses the light emitted from the light source and irradiates the wafer 2 is disposed. An optical fiber cable 8 is connected to the illumination lens 7. A band pass filter 9 is connected to the tip of the optical fiber cable 8. The bandpass filter 9 cuts light of other wavelengths so that the wavelength sensitivity characteristic of the infrared camera matches approximately 1100 nm. In this example, the band-pass filter 9 is connected. However, as in this example, when the transmitted light is measured, the band-pass filter 9 may not be connected. An infrared light source 10 is arranged on the left of the band pass filter 9 in the figure. The infrared light source 10 emits infrared light having a wavelength of about 1100 nm that is transmitted through the wafer 2. Thus, by matching the wavelength sensitivity characteristic of the infrared camera to 1100 nm that transmits through the silicon wafer, the image quality of the image captured by the infrared camera is improved and the measurement accuracy is increased.

An infrared camera 11 that measures an infrared image is disposed above the wafer 2. At the lower end of the infrared camera 11, an objective lens 12 that has a predetermined depth of focus (range of focus) and detects the enlarged hole of the wafer 2 is disposed. This objective lens 12 can be used for infrared rays and has a shallow focus depth , thereby enabling highly accurate measurement. The side surface of the infrared camera 11 is guided by a highly accurate linear scale 13 as a position adjusting means, and the height position is feedback-controlled. Thus, the focus position can be moved by moving the infrared camera 11 up and down. The linear scale 13 is fixed to an infrared camera fixing base 14 fixed on the base 6.

  The linear scale 5, the infrared light source 10, the infrared camera 11, the linear scale 13, and the like are connected to a control device 15 shown in the lower part of the figure. An example of the control device 15 is a personal computer. The control device 15 controls the linear scale 5 so that the infrared rays from the light source are irradiated to the holes formed in the wafer 2. Further, the infrared light source 10 is controlled to irradiate infrared light from the light source, and the image of the hole diameter is measured while improving the contrast of the image detected by the infrared camera 11 or performing noise removal processing. Further, the control device 15 controls the linear scale 13 to control the height position of the infrared camera 11 so that the depth of the hole can be measured.

Next, a depth measuring method using the depth measuring apparatus according to the present invention will be described.
FIG. 3 is a diagram illustrating the principle of the depth measurement method. FIG. 4 is a diagram showing an image detected by the infrared camera. FIGS. 4A to 4D show images detected when the infrared camera is focused on the cross-sections A to D of FIG.

  A cross section of the wafer 2 described with reference to FIGS. 1 and 2 is shown below FIG. The wafer 2 has a tapered hole 2a. As the wafer 2, for example, a 5-inch or 8-inch silicon wafer can be used. The thickness of the silicon wafer is about 600 μm, the hole diameter provided in the wafer is 25 μm or less, and the hole depth is 200 μm or more. The shape of the hole is not limited to this, and for example, a hole having a hole diameter of 50 μm or less and a depth of about 650 μm can be measured.

Infrared light 20 emitted from an infrared light source is irradiated from below the wafer 2. Since the silicon wafer has a characteristic of transmitting infrared light having a wavelength of 1100 nm , the infrared light 20 passes through the wafer 2 from the bottom to the top in the portion where the hole 2a is not formed. However, in the portion where the hole 2a is formed, it hits the upper surface of the hole 2a and does not penetrate upward from there. This is because carbon, oxide, or the like is attached to the inner surface of the hole 2a so that the infrared ray 20 from the attached portion is not incident, that is, the infrared ray 20 is not transmitted . In this example, the infrared rays emitted from the infrared light source are applied to the wafer 2 without passing through the illumination lens 7 (see FIG. 1).

  Above the wafer 2, the objective lens 12 and the infrared camera 11 described in FIG. At the time of measurement, the objective lens 12 and the infrared camera 11 are moved up and down, and the image is measured by adjusting the focus position of the infrared camera 11 to each cross section.

  The depth measuring method using the depth measuring apparatus of the present invention will be described with reference to FIG. First, as shown in FIG. 3, infrared rays 20 are applied to the holes 2 a formed in the wafer 2. Then, a difference in contrast between the light transmitted through the wafer 2 and the light blocked by the carbon on the inner surface of the hole 2a is photographed as an image by the infrared camera 11. This photographing can be performed over a plurality of locations while changing the focus position. In this example, as shown in FIG. 3, the focus positions are aligned at four locations A to D. In this example, the infrared camera images are taken at four locations on the wafer 2, but the present invention is not limited to this, and the depth of the holes can be determined more accurately by measuring at more locations. Can be measured.

  In this photographing, first, the focus of the infrared camera 11 is set on the upper surface of the wafer 2 and the focus position of the infrared camera 11 at that time is stored. In this example, the position A in FIG. 3 is the upper surface of the wafer 2, and the image at that time is FIG. From there, the focus position of the infrared camera 11 is gradually lowered to search for a focus position where the shape of the hole 2a is best seen. Since the hole 2a is tapered, the position where the diameter of the hole 2a is the smallest and clearly visible is the upper surface of the hole 2a. In this example, the position B in FIG. 3 corresponds, and the image at that time is FIG. 4B.

When the infrared camera 11 is moved vertically downward from this position and the focus position is lowered, the hole 2a is tapered, so that the image of the hole diameter gradually increases. In this example, the position of C in FIG. 3 is the midpoint of the hole 2a, and the image at that time is FIG. 4C. Further, when the focus position is lowered, the focal point of the bottom surface of the wafer 2 is eventually reached. In this example, the position of D in FIG. 3 is at the lower surface of the wafer 2, an image at that time is shown in FIG 4 (d).

The image shown in FIG. 4 is subjected to image processing by the control device 15 shown in FIG. 1, and the focus position (position D in FIG. 3) when the image corresponding to the lower surface of the wafer 2 is detected and the upper surface of the hole 2a. The focus position (position B in FIG. 3) when the image corresponding to is detected by the linear scale 13 is measured. Then, the depth obtained by multiplying the distance difference between the two positions by the refractive index of the wafer from the thickness of the wafer 2 is the depth of the hole 2a . Further, the focus position is aligned with the lower surface of the wafer 2 while viewing the image of the infrared camera 11 (position D in FIG. 3), and from the position value to the position where the hole 2a appears to be the smallest (position B in FIG. 3). A value obtained by multiplying the distance by the refractive index of the wafer 2 can be used as the hole depth. If there is a thin film of another material on the upper surface of the wafer 2 or the like, it is necessary to consider its refractive index.

Next, a method for irradiating the wafer with infrared rays collected by the illumination lens will be described.
FIG. 5 is a diagram illustrating a method of irradiating a wafer by collecting infrared rays with an illumination lens. In FIG. 5, the wafer 2 in which the holes 2a are formed is arranged. The hole 2a has a tapered shape with a large diameter on the lower surface side.

  An illumination lens 7 (see FIG. 1) is disposed on the lower surface of the wafer 2. Infrared rays applied to the lower surface of the illumination lens 7 are refracted by the lens and incident obliquely toward the upper surface of the hole 2a. By the way, when parallel light illumination is applied to the wafer 2, irregular reflection occurs in the vicinity of the hole 2a, and a shadow like a hole is formed not on the upper surface of the hole 2a, and an image of this shadow is measured. There is a possibility that an error occurs in the depth of the hole and the accuracy of depth measurement is lowered. Therefore, as shown in this example, the irradiating lens 7 refracts infrared rays and irradiates the light toward the upper surface of the hole 2a, thereby reducing the adverse effects caused by irregular reflection around the hole 2a, and a more accurate and clear image. Can be obtained.

The embodiment of the present invention has been described above , but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The depth measurement apparatus according to the present invention can be applied to a depth measurement apparatus that can measure the depths of holes and grooves having a high aspect ratio formed on substrates of various sizes, which are used in manufacturing processes of semiconductor substrates. .

It is a side view which shows one Embodiment of the depth measuring apparatus which concerns on this invention. It is a figure which shows the hole formed on the wafer (board | substrate). 2A is a side sectional view of the wafer, and FIG. 2B is an enlarged view of the back surface of the wafer. It is a figure which shows the principle of the depth measuring method. It is a figure which shows the image detected with the infrared camera. FIGS. 4A to 4D show images detected when the infrared camera is focused on the cross-sections A to D of FIG. It is a figure which shows the method of condensing infrared rays with the lens for illumination, and irradiating a wafer.

DESCRIPTION OF SYMBOLS 1 ... Depth measuring apparatus 2 ... Wafer 2a ... hole 3 ... X direction mounting table 4 ... Chuck 5 ... Y direction mounting table 6 ... Base 7 ... Illumination Lens 8 ... Optical fiber cable 9 ... Band pass filter 10. Infrared light source 11. Infrared camera 12. Objective lens 13. Linear scale 14. Fixing base 15. Control device 20. Infrared

Claims (5)

A depth measuring device that measures the depth of a recess formed in a substrate,
An infrared light source for irradiating the substrate with infrared light;
An infrared camera for measuring an infrared image irradiated on the substrate from the infrared light source;
Position adjusting means for adjusting the position of the infrared camera;
In a depth measuring device having
The infrared ray is transmitted through the substrate, the position of the infrared camera is adjusted by the position adjusting means, and the depth of the concave portion of the substrate is measured by measuring images of transmitted light with the infrared camera at a plurality of locations. A depth measuring device characterized by measuring.   A focus position when an image corresponding to the lower surface of the substrate is detected by the infrared camera, and a focus position when an image corresponding to the upper surface of the recess (the surface on the back side of the hole) is detected by the infrared camera; The depth of the concave portion is measured by calculating a value obtained by subtracting a value obtained by multiplying the distance difference between the two positions by the refractive index of the substrate from the thickness of the substrate. Depth measuring device as described.   The focus position is aligned with the lower surface of the substrate, and the depth of the recess is measured by obtaining a value obtained by multiplying the distance from the position value to the position where the shape of the recess appears to be the smallest by the refractive index of the substrate. The depth measuring apparatus according to claim 1.   4. The depth measuring apparatus according to claim 1, wherein an illumination lens for converging the infrared rays irradiated from the infrared light source and irradiating the substrate is used. When measuring the transmitted light image with the infrared camera, the infrared light source is connected to a band-pass filter that cuts light of other wavelengths so that wavelength sensitivity characteristics are approximately 1100 nm. Item 5. The depth measuring device according to any one of Items 1 to 4.

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