JP4993691B2 - Wafer backside inspection equipment - Google Patents

Description

  The present invention relates to a wafer back surface inspection apparatus for inspecting defects such as protrusions, dents, deposits, and scratches existing on the back surface of a wafer used for semiconductor manufacturing.

  Needless to say, the defect inspection of the flat portion of the surface of a silicon wafer (hereinafter referred to as “wafer”) used in semiconductor manufacture is inspected with great care in order to reduce the defect rate to zero. On the other hand, since the back surface of the wafer is not the surface on which the semiconductor circuit is formed, the inspection of the back surface of the wafer was not considered very important. In recent years, it has become increasingly clear that minute defects such as protrusions, dents, deposits, and scratches existing on the backside of the wafer have a great influence on the yield in subsequent processes. In other words, if there are protrusions or deposits on the back surface, it affects the pattern accuracy when forming a semiconductor circuit, or as a result of particles or deposits scattering due to fine irregularities or deposits on the backside of the wafer, It has been regarded as a problem that defective products are generated in the subsequent process.

  As an apparatus for inspecting the back surface of a wafer, an apparatus for inspecting a defect on the back surface of a wafer using an area sensor camera is currently known. This device uses the area of the area sensor camera that provides sufficient resolution for the area sensor camera as a unit area, divides the area on the back side of the wafer into the unit areas, and moves the imaging position sequentially. By obtaining a plurality of captured images, the entire surface of the wafer is inspected for defects.

  However, when imaging is performed using an area sensor as described above, it is difficult to provide uniform illumination over the entire area of the unit area, and the captured image can be uneven at the center and the outer end of the imaging area. Therefore, it is difficult to capture an accurate image. In addition, since the image is divided into a plurality of areas and imaged for inspection, there is a problem in terms of accuracy and reproducibility. Furthermore, since the inspection is performed by dividing the image into smaller areas and performing the inspection, the inspection time becomes long, and it is impossible to cope with the increase in the inspection process speed.

  As described above, the wafer back surface inspection apparatus using the area sensor camera needs to inspect the wafer back surface by dividing it into a large number of small areas because of the limitation of resolution of the area sensor. There is a problem that it cannot be obtained under shooting conditions. In addition, since a large number of small areas are imaged, a long inspection time is required, and a mechanism for switching the areas is complicated.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a wafer back surface inspection apparatus that can achieve high inspection accuracy and reproducibility, and can realize a reduction in inspection time by performing inspection at a high speed.

  1st invention is a wafer back surface inspection apparatus which inspects for a defect on the back surface of a wafer, and includes an imaging unit having a line sensor as an imaging device, and an illuminating unit that illuminates an imaging region on the back surface of the wafer so as to provide dark field illumination. And a moving means for moving the wafer in a fixed direction with respect to the imaging means and the illuminating means, and the moving means supports the outer periphery of the wafer by opening the lower surface of the wafer. The wafer back surface inspection apparatus is characterized in that a wafer rotating means for rotating the substantially circular center as a rotation center is provided on the moving means so that the wafer can be rotated while the wafer is placed.

  According to a second invention, in the first invention, the wafer rotating means is mounted on a wafer rotating table on which a wafer is placed and a wafer rotating table on which a ring gear is attached and rotatably supported by the moving means. A wafer back surface inspection apparatus comprising: a drive gear meshing with the ring gear; and a motor attached to an output shaft.

  As described above, the wafer back surface inspection apparatus according to the present invention is an apparatus that inspects the back surface of a wafer using an image pickup unit using a line sensor as an image sensor, and has a significantly higher resolution than an area sensor, and thus has high accuracy. Defects can be implemented. Further, since the entire back surface of the wafer can be imaged at high speed, the inspection time can be shortened. Further, since the wafer is configured to be rotatable while being placed on the moving means, it is possible to detect the defect regardless of the direction of the defect, and to realize a highly accurate wafer back surface inspection apparatus.

  The method and apparatus of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by a present Example.

  FIG. 1 is a front view showing a configuration of a wafer back surface inspection apparatus 1 according to a first embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a side view thereof. It is composed of a table 4, a linear stage 5, and a slide guide 6. Here, the wafer 7 is held on the wafer mounting table 4 with the back surface to be inspected facing down.

  The image pickup means 2 is an image pickup means using a linear sensor array as an image pickup device, and is arranged so as to pick up the back surface of the wafer 7 from directly below the wafer as shown in FIGS. The linear sensor array used in the present embodiment employs an element having a particularly high resolution, and is configured to detect even a minute scratch or defect.

  The linear sensor array has a scanning function by arranging pixels in a straight line. To obtain a two-dimensional image, the linear sensor array is moved in the scanning direction of the linear sensor array, that is, in a direction orthogonal to the linear direction in which the pixels are arranged. It is necessary to let In FIG. 1, the scanning direction of the linear sensor array itself mounted on the image pickup means is a direction perpendicular to the paper surface, and the linear stage 5 moves the wafer 7 to be inspected in the direction of the arrow A to make it two-dimensional. Get an image.

  Since the linear sensor array has an imaging range, in order to capture an image exceeding the imaging range, the linear sensor array is divided into several regions as shown in FIG. 5, and the imaging unit 2 and the illumination unit 3 are arranged respectively. To do. In FIG. 5, the imaging means 2 and the illumination means 3 are arranged in three areas, a left area, a center area, and a right area, and the captured image of the entire back surface of the wafer 7 is obtained.

  As shown in FIG. 6, the illumination unit 3 includes a linear light guide 31 and a cylindrical lens 32. A metal haloid lamp (not shown) is connected to the line-shaped light guide 31, and diffused illumination light is emitted from the line-shaped light guide 21. The cylindrical lens 32 is a lens having a cylindrical shape divided into two. As shown in FIG. 6, the cylindrical lens 32 is disposed between the linear light guide 21 and the wafer 7 and diffused from the linear light guide 21. The light is converged to illuminate the back surface of the wafer to be inspected at a wide angle of incidence with illumination light that illuminates the back surface of the wafer.

  Since the diffused light is emitted from the line-shaped light guide 21, the diffused light enters the imaging position of the imaging means 2 in the line direction of the line-shaped light guide 21. On the other hand, when the cylindrical lens 32 is not disposed between the linear light guide 21 and the wafer 7, the light beam incident on the imaging position of the imaging means 2 becomes illumination light with an extremely narrow incident angle with respect to the moving direction of the wafer 7. Limited. As a result, there arises a problem that light that is reflected on the defect and incident on the imaging means 2 is limited.

  Therefore, as shown in FIG. 6, the diffused light emitted from the line-shaped light guide 31 is converged so that the illumination light is incident at a wide angle in the wafer movement direction as well, between the line-shaped light guide 31 and the wafer 7. The lens 32 is disposed. At this time, the aperture of the cylindrical lens 32 is selected so that the illumination light converged by the cylindrical lens 32 illuminates the imaging position of the imaging means 2 at a wide angle, and its installation position is adjusted. The light source used for the line-shaped light guide 31 is suitable for blue light because the contrast becomes high.

  The illumination means 3 is configured to be able to adjust the irradiation angle with respect to the wafer 7. As shown in FIG. 1, the guide hole 34 provided in the illumination means mounting base 33 is formed to be a part of an arc centering on the irradiation position of the illumination means 3 of the wafer 7. Is rotatable around the irradiation position of the illumination means 3 of the wafer 7. Depending on the state of defects or scratches formed on the back surface of the wafer 7, the contrast due to dark field illumination may be poor, and an image having a high contrast can be obtained by setting the illumination angle of the illumination means 3 to the wafer 7 to an appropriate angle. Can be obtained.

  As shown in FIGS. 1 and 2, the wafer mounting table 4 is formed to be movable in the arrow A direction by a linear stage 5 and a slide guide 6. The linear stage 5 is guided by a precisely machined rail and a linear guide bearing combined therewith, and has a drive unit that can be precisely positioned, and moves the wafer mounting table 4 at a constant speed. The slide guide 6 includes a slide bush 61 and a slide shaft 62, and supports the load of the wafer mounting table 4 and realizes its smooth movement. That is, the moving means of the present embodiment is composed of the wafer mounting table 4, the linear stage 5, and the slide guide 6.

  A wafer turntable 41 is rotatably supported on the wafer mounting table 4, and as shown in FIG. 4, the wafer 7 to be inspected is opened on its lower surface which is the inspection surface, and the edge of the wafer turntable 41 is opened. It is held in a horizontal posture by being supported by the part. In this embodiment, a method of placing the wafer 7 on the edge portion of the wafer turntable 41 is employed in order to avoid damaging the wafer 7 due to a gripping device or the like.

The wafer turntable 41 is provided with a ring gear 42 provided with a knife-edge guide, and is rotatably held by a ring gear holding bearing 43. The ring gear 42 meshes with a drive gear attached to the output shaft of the motor 44, and the wafer turntable 41 rotates by driving the motor 44. As a result, the wafer 7 held on the wafer mounting table 4 rotates around the center position of the circle. The wafer turntable 41 is configured to be able to rotate and position the wafer to an arbitrary position. In particular, the wafer turntable 41 is configured to be able to position the wafer 7 in at least two directions orthogonal to each other. Has been.

  In the above description, the embodiment in which the wafer is moved has been described. However, the present invention is not limited to this. For example, the wafer turntable is fixed, and the wafer can be rotated on the wafer turntable. In addition, the entire wafer may be scanned by configuring the imaging unit and the illumination unit so as to be movable.

  Next, the function of the wafer back surface inspection apparatus of this embodiment and the process of performing the inspection will be described. The wafer 7 is transferred by a transfer device (not shown), and the wafer 7 is transferred to the wafer rotating table 5 of the wafer mounting table 4. The wafer holding method according to the present embodiment has a structure in which the wafer 7 is supported not by a gripping device or the like but by a tapered portion provided at the edge of the wafer 7 or an edge that does not affect the back surface inspection.

  The wafer 7 is moved at a constant speed in a fixed direction by the linear stage 5, and the back surface (lower surface) of the wafer 7 is imaged by the three imaging devices 2. Since the image pickup device mounted on the image pickup means 2 is a linear sensor array 21 in which pixels are arranged in a line, scanning is performed in the main scanning direction in which the image pickup devices are arranged, and at the same time, the linear sensor array in the sub-scanning direction. By repeating scanning while moving in the movement direction, that is, in the direction of arrow A, a two-dimensional image is obtained.

  Since the imaging range of the linear sensor array of the imaging means 2 is limited, for example, a 300 mm wafer is divided into three imaging ranges as shown in FIG. Take an image. In order for the holder part indicating the pixels of the linear sensor array 21 to interfere with the adjacent holder part, the positions are shifted as shown in FIG.

  The illumination light emitted from the linear light guide 31 of the illumination means 3 is refracted by the cylindrical lens 32 and illuminates the imaging position of the wafer 7. Here, the line direction of the linear light guide 31 is arranged so as to coincide with the main scanning direction of the linear sensor array 21, and the main scanning direction of the linear sensor array 21 is almost affected by refraction by the cylindrical lens. The back surface of the wafer is illuminated as diffuse light.

  On the other hand, in the sub-scanning direction of the linear sensor array 21, that is, the moving direction of the wafer, the illumination light that has passed through the cylindrical lens 22 is refracted. In particular, the light that has entered the outermost portion of the cylindrical lens is refracted greatly, and the wafer is refracted. 7 with a large incident angle. As a result, at the imaging position of the wafer 7, the illumination light is incident with a large incident angle from any direction.

  The illumination unit 3 is arranged with respect to the imaging unit 2 so as to be dark field illumination. When there is a defect such as a protrusion, a dent, a deposit, or a scratch at the imaging position of the wafer 7, the illumination is incident at a wide angle. Of the illumination light from the means 7, the reflected light reflected by the defect is observed as a shining point in the imaging means 3. That is, if there is a defect on the wafer surface, it can be recognized as a bright spot with high contrast.

  After the first imaging is completed by moving the wafer 7 on the linear stage 5, the motor 44 is driven to rotate the wafer turntable 41, and a position different from the direction placed at the time of the first imaging. For example, the wafer 7 is rotated to a position rotated by 90 ° from the direction in which it was placed at the time of the first imaging. Next, the linear stage 5 is driven again, and the second imaging is performed to obtain images of the wafer 7 in two different directions.

  In the defect inspection method using dark field illumination using the linear sensor array as an imaging means, when the moving direction of the wafer 7 to be inspected and the direction of the flaw are substantially the same, the contrast is lowered and the flaw is observed. The phenomenon of difficulty occurs. Even if the illumination light is made uniform using the cylindrical lens 32, the direction of the defect is still observed. Therefore, in order to improve the inspection accuracy, the wafer turntable 41 is arranged in a different direction, for example, a direction rotated by 90 ° from the first imaging posture, and the whole wafer 7 is imaged again, thereby taking two different directions. Obtain an inspection image. By obtaining scan images in two different directions on the wafer 7 in this manner, it is possible to observe defects such as directional scratches.

  As shown in FIG. 1, the illumination means 3 is configured so that the incident angle of the illumination light with respect to the wafer 7 can be adjusted. Depending on the type of scratch, the illumination means 3 can be set to an angle convenient for observation. Can do.

  In the wafer back surface inspection apparatus according to the present embodiment, the imaging unit 2 is disposed directly below the wafer 7 and the illumination unit 3 is disposed obliquely with respect to the wafer 7. However, the present invention is not limited to this, and the regular reflection of the illumination unit 3 is performed. What is necessary is just to implement | achieve dark field illumination by arrange | positioning in the position where light does not inject into an imaging means directly. For example, the illumination unit may be disposed directly below the wafer, and the imaging unit may be disposed obliquely with respect to the wafer.

  In this embodiment, the entire surface of the wafer is covered with three image pickup means. However, the present invention is not limited to this. By increasing the resolution by arranging a large number of image pickup means in a single line, higher definition can be achieved. It is possible to obtain an inspection image.

  Furthermore, the wafer back surface inspection apparatus according to the present embodiment is configured such that the wafer back surface is disposed downward and the imaging means and the illumination means are disposed below the wafer to perform inspection work. There is no need to flip it upside down.

  The wafer backside inspection apparatus of the present invention is an apparatus for inspecting the backside of a wafer using an imaging means using a line sensor as an image sensor, and has a remarkably high resolution compared to an area sensor. Can be implemented at high speed. Further, since the wafer can be rotated while being placed on the moving means, the defect can be detected regardless of the direction of the defect, so that a highly accurate wafer back surface inspection apparatus is realized.

  As described above, the wafer backside inspection apparatus according to the present invention can realize high-precision inspection, so that the occurrence of defects in the post-process can be reduced and high-speed inspection work can be performed to ensure high productivity. This can greatly contribute to the industry.

  It is a front view which shows the structure of the wafer back surface inspection apparatus of a present Example in a partial cross section.   It is a top view which shows the structure of the wafer back surface inspection apparatus of a present Example.   It is a side view which shows the structure of the wafer back surface inspection apparatus of a present Example.   It is sectional drawing which shows the structure of a wafer mounting base.   It is explanatory drawing which shows the inspection area | region of the wafer back surface of a present Example with a bottom view.   It is explanatory drawing explaining the structure and function of an illumination means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wafer back surface inspection apparatus 2 Imaging means 3 Illumination means 4 Wafer mounting base 5 Linear stage 6 Slide guide 7 Wafer 31 Line-shaped light guide 32 Cylindrical lens 33 Illumination means mounting base 34 Guide hole 41 Wafer rotation base 42 Ring gear 43 Ring gear holding Bearing 44 Motor 61 Slide bush 62 Slide shaft

Claims (2)

A wafer back surface inspection apparatus for inspecting a wafer back surface defect,
Imaging means comprising a line sensor as an imaging element;
Illuminating means for illuminating the imaging region on the back surface of the wafer so as to be dark field illumination;
A moving means on which a wafer is placed and moves the wafer in a fixed direction relative to the imaging means and the illumination means ;
With
The moving means is provided with wafer rotating means on the moving means for supporting the outer periphery of the wafer with the lower surface of the wafer in an open state and rotating the substantially circular center of the wafer as a rotation center, and the wafer is rotated while the wafer is placed. Made possible,
A wafer back surface inspection apparatus characterized by the above.   The wafer back surface inspection apparatus according to claim 1,
  The wafer rotating means is
  A wafer turntable on which a wafer is placed, wherein a ring gear is attached and rotatably held by the moving means;
  A motor provided on the moving means, and a drive gear that meshes with the ring gear is attached to the output shaft;
A wafer backside inspection apparatus characterized by comprising:

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