JP2006300553A - Inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device making correct defect inspection even when the inspection surface is tilted greatly. <P>SOLUTION: This device is equipped with: an imaging means 13 for imaging collectively at least a part of a domain of the inspection surface 10A; setting means 11, 16 for setting a tilt angle of the inspection surface with respect to an optical axis 3A of the imaging means 13; and acquisition means 16, 14 for determining a plurality of focal positions to be imaged by the imaging means corresponding to the tilt angle set by the setting means, and for acquiring a plurality of images having different focal positions on the basis of an image signal outputted by imaging the domain by the imaging means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inspection apparatus that performs defect inspection of a surface to be measured.

Using an imaging device such as a camera, with the test surface tilted with respect to the optical axis of the imaging device, collect images of a relatively wide area (for example, the entire area) of the test surface and use this image. An apparatus for performing defect inspection is known (see, for example, Patent Document 1).
JP 2001-289793 A

However, in the above-described inspection apparatus, when the inclination of the surface to be measured becomes large, an out-of-focus portion may appear around the collectively acquired image, and in this case, correct defect inspection cannot be performed. .
An object of the present invention is to provide an inspection apparatus capable of performing a correct defect inspection even when the surface to be measured has a large inclination.

  An inspection apparatus according to the present invention includes an imaging unit that collectively images at least a partial area of a test surface, a setting unit that sets an inclination angle of the test surface with respect to an optical axis of the imaging unit, and the setting unit A plurality of focal positions to be imaged by the imaging means are determined according to the tilt angle set by the imaging means, and a plurality of images having different focal positions are obtained based on imaging signals output by the imaging means by imaging the area. Acquisition means for acquiring.

  In addition, it is preferable that the image forming apparatus further includes a generation unit that cuts out and combines a focused portion from each of the plurality of images acquired by the acquisition unit and generates a composite image related to the region. Furthermore, it is preferable that the acquisition unit acquires an image without switching the focal position when the entire region is included in the focal depth of the imaging unit. Further, when the aperture diameter of the imaging means is larger than a predetermined diameter, the acquisition means reduces the aperture diameter so that the entire area is included in the focal depth of the imaging means, and the focal position It is preferable to acquire an image without switching.

  Furthermore, another inspection apparatus according to the present invention includes an imaging unit that collectively images at least a part of a region of the test surface, and a setting unit that sets an inclination angle of the test surface with respect to the optical axis of the imaging unit. According to the tilt angle set by the setting means, the aperture diameter of the imaging means is adjusted so that the entire area is included within the depth of focus of the imaging means, and the imaging means images the area. Acquisition means for acquiring an image based on an imaging signal to be output.

  According to the present invention, correct defect inspection can be performed even when the inclination of the surface to be inspected is large.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the inspection apparatus 10 of the present embodiment includes a tilt stage 11 on which an object such as a semiconductor wafer or a liquid crystal glass substrate having a test surface 10A is placed, and an illumination unit 12 that illuminates the test surface 10A. And an imaging unit 13 that images the test surface 10A, an image processing unit 14, a display unit 15, and a control unit 16. The control unit 16 controls the tilt stage 11 in accordance with the defect inspection conditions for the test surface 10A to adjust the tilt of the test surface 10A. Further, the control unit 16 controls the imaging unit 13 based on the result of the tilt adjustment of the test surface 10A, and switches the focal position of the imaging unit 13 as necessary.

  Illumination light from the illumination unit 12 is incident on the entire surface of the test surface 10A along the optical axis 2A of the illumination unit 12, and illuminates the entire region of the test surface 10A from an oblique direction. At this time, diffracted light for inspection (for example, first-order diffracted light) is generated in a predetermined direction from the entire surface of the test surface 10A. In order to guide inspection diffracted light along the optical axis 3 </ b> A of the imaging unit 13 and to enter the imaging unit 13, the tilt of the test surface 10 </ b> A is adjusted using the tilt stage 11.

By this tilt adjustment, the tilt angle of the test surface 10A with respect to the optical axis 3A of the imaging unit 13 is set, and at the same time, the tilt angle of the test surface 10A with respect to the optical axis 2A of the illumination unit 12 is also set. Then, diffracted light for inspection can be incident on the imaging unit 13 along the optical axis 3A in accordance with a combination of two inclination angles.
Note that when adjusting the inclination of the test surface 10A, information on the wavelength of the illumination light, information on the pitch of the repetitive pattern on the test surface 10A, and the like are considered. A rotation axis (not shown) when tilting the test surface 10A is perpendicular to the optical axis 3A of the imaging unit 13, and is also perpendicular to the optical axis 2A of the illumination unit 12.

  The imaging unit 13 is a camera, for example, and captures the diffracted light for inspection from the test surface 10A in a state where the test surface 10A is tilted with respect to the optical axis 3A (the state after the tilt adjustment). The entire surface of the inspection surface 10A is imaged collectively. The field of view of the imaging unit 13 corresponds to the entire area of the test surface 10A. The imaging unit 13 is provided with an imaging lens that forms a diffracted image of the entire surface of the test surface 10A based on the diffracted light for inspection, and an image sensor disposed on the surface on which the diffracted image is formed.

  The imaging unit 13 outputs an imaging signal to the image processing unit 14 when imaging the entire area of the test surface 10A. The image processing unit 14 collects images of the entire area of the test surface 10A based on the imaging signal from the imaging unit 13 and displays the images on the display unit 15 as necessary. For example, when the test surface 10A is circular and the imaging direction by the imaging unit 13 is oblique, the image of the test surface 10A based on the imaging signal from the imaging unit 13 is elliptical. Therefore, it is preferable to generate a circular image 5A (FIG. 1) by performing a correction process that converts the elliptical shape into a circular shape.

  Here, as shown in FIG. 2A, when the tilt angle Θ of the test surface 10A is small and the entire area of the test surface 10A is included within the focal depth of the imaging unit 13, the batch acquisition is performed as described above. The image 5A (FIG. 1) of the measured surface 10A is in focus throughout the entire area. Therefore, correct defect inspection can be performed using the image 5A. FIG. 2A shows a case where the focal position of the imaging unit 13 is located on the rotation axis including the center of the test surface 10A.

  However, as shown in FIG. 2B, when the inclination angle Θ of the test surface 10A is large and the periphery of the test surface 10A deviates from the depth of focus of the imaging unit 13, an image 5A (10A) of the test surface 10A acquired collectively. The image is out of focus in the vicinity of FIG. In this case, even if the image 5A is used, correct defect inspection cannot be performed. FIG. 2B also shows the case where the focal position of the imaging unit 13 is located on the rotation axis including the center of the surface to be inspected 10A.

  Therefore, in the inspection apparatus 10 of the present embodiment, an image acquisition process for the entire area of the test surface 10A is performed according to the procedure of the flowchart shown in FIG. When the tilt adjustment (step S1) of the test surface 10A is completed, it is determined whether or not the tilt angle Θ set thereby is less than a predetermined value ΘA (step S2). As shown in FIG. 4A, the predetermined value ΘA is a length L obtained by projecting the diameter Φ in the direction perpendicular to the rotation axis of the test surface 10A in the direction of the optical axis 3A. The inclination angle ΘA is equal.

  When the tilt angle Θ set by the tilt adjustment is less than the predetermined value ΘA (step S2 is YES, the state of FIG. 2A), that is, the entire area of the test surface 10A is included in the depth of focus of the imaging unit 13. In this case, the control unit 16 performs the process of step S3 in FIG. In step S3, the entire area of the surface to be inspected 10A is imaged as it is, with the focus position of the imaging unit 13 being set to the center of the surface to be inspected 10A. As a result, an in-focus image can be acquired over the entire area, and a correct defect inspection can be performed by analyzing the image.

  On the other hand, when the inclination angle Θ set by the inclination adjustment is equal to or larger than the predetermined value ΘA (step S2 is NO, the state of FIG. 2B), that is, the periphery of the test surface 10A is out of the focal depth of the imaging unit 13. In the case where it is detected, the control unit 16 proceeds to the process of step S4. In step S4, it is determined whether the inclination angle Θ is less than a predetermined value ΘB. As shown in FIG. 4B, the predetermined value ΘB is a length L obtained by projecting the diameter Φ in the direction perpendicular to the rotation axis of the test surface 10A in the direction of the optical axis 3A. The inclination angle ΘB is equal to twice.

  When the inclination angle Θ set by the inclination adjustment is not less than the predetermined value ΘA and less than the predetermined value ΘB (step S4 is YES), the control unit 16 performs the process of step S5. In step S5, the test surface 10A is divided into two areas (1) and (2) shown in FIG. 5A, and the focus position of the imaging unit 13 is set near the center of one area (1) ( In FIG. 5B, the entire area of the test surface 10A is imaged collectively. Further, the entire area of the test surface 10A is collectively imaged in a state where the focus position of the imaging unit 13 is set near the center of the other region (2) (FIG. 5C).

  As a result, the following two images can be acquired in order. The first image is an image acquired in the state shown in FIG. 5B, and the portion corresponding to the region (1) of the test surface 10A is in focus, but the region of the test surface 10A (2 The part corresponding to) is out of focus. The second image is an image acquired in the state of FIG. 5C. Contrary to the above, the portion corresponding to the region (1) is out of focus, but corresponds to the region (2). The part is in focus.

  The two images having different focal positions obtained in this way are subjected to the image composition processing in step S7 in the image processing unit. The image processing unit 14 cuts out the in-focus portion from each of the two images and combines them, that is, the portion corresponding to the region (1) of the image acquired in the state of FIG. 5 (b) and FIG. 5 (c). A portion corresponding to the region (2) of the image acquired in the state is combined to generate one composite image relating to the entire area of the test surface 10A.

  As described above, in the inspection apparatus 10 of the present embodiment, even when the inclination angle Θ set by the inclination adjustment is large and is greater than or equal to the predetermined value ΘA and less than the predetermined value ΘB, the focus position of the imaging unit 13 is switched in two stages. Thus (see FIG. 5), two images with different focal positions are acquired in order, and finally combined to generate a combined image in focus throughout the entire area. Therefore, a correct defect inspection can be performed by analyzing this composite image.

  When the inclination angle Θ set by the inclination adjustment is equal to or larger than the predetermined value ΘB (step S4 is NO), the control unit 16 performs the process of step S6. In step S6, the test surface 10A is divided into the three regions (1) to (3) shown in FIG. 6, and the test surfaces are sequentially arranged in the state where the focus positions are aligned with these regions (1) to (3). The entire area of 10A is imaged collectively to obtain three images with different focal positions. Thereafter, the image processing unit 14 performs the same image composition process (step S7) as described above, and generates one composite image relating to the entire area of the test surface 10A.

  As described above, in the inspection apparatus 10 of the present embodiment, even when the inclination angle Θ set by the inclination adjustment is large and is equal to or larger than the predetermined value ΘB, the focus position of the imaging unit 13 is switched in three stages (see FIG. 6). ), Sequentially acquiring three images with different focal positions, and combining them at the end, it is possible to generate a combined image in focus throughout the entire area. Therefore, a correct defect inspection can be performed by analyzing this composite image, and the inspection quality is improved.

  Furthermore, in the inspection apparatus 10 according to the present embodiment, when the inclination angle Θ of the test surface 10A is equal to or larger than the predetermined value ΘA, the present invention is not limited to the case where the in-focus portion is cut out from each of the plurality of images and combined. A correct defect inspection can be performed without performing image synthesis processing. When the images are not combined, the defect inspection may be performed in order using the focused portion in each of the plurality of images (without using the non-focused portion). However, generating a single composite image that is in focus throughout the entire area by image composition simplifies the work at the time of inspection, enabling efficient defect inspection and improving throughput.

  Further, in the inspection apparatus 10 of the present embodiment, when the inclination angle Θ of the test surface 10A is small and less than the predetermined value ΘA (FIG. 2A), the focus position of the imaging unit 13 is not switched. An image is acquired at only one focal position. For this reason, it is possible to suppress the situation in which the throughput is reduced due to the acquisition of a plurality of images to a minimum. Therefore, correct defect inspection can be efficiently performed regardless of the inclination angle Θ of the test surface 10A.

Furthermore, in the inspection apparatus 10 of the present embodiment, the field of view of the imaging unit 13 corresponds to the entire area of the test surface 10A, and images of the entire area of the test surface 10A are acquired at a time. it can.
(Modification)
In the above-described embodiment, the example in which the depth of focus of the imaging unit 13 is not changed has been described. However, the present invention is not limited to this. The aperture diameter of the imaging unit 13 may be variable, and the depth of focus of the imaging unit 13 may be changed according to the aperture diameter. The depth of focus is inversely proportional to the square of the aperture diameter. When changing the depth of focus, when combining the switching of the focus position, it is preferable to perform the following processing.

  Only when the aperture diameter of the imaging unit 13 is larger than a predetermined diameter (for example, a diameter that can ensure a predetermined brightness) and the inclination angle Θ is equal to or greater than the predetermined value ΘA, the depth of focus within the imaging unit 13 is reduced. The aperture diameter is reduced so that the entire surface 10A is included, and an image is acquired without switching the focal position. By performing such a process giving priority to the adjustment of the aperture diameter, it is possible to further suppress the situation in which the throughput is reduced, and it is possible to efficiently perform a correct defect inspection regardless of the inclination angle Θ.

  Further, the focus position of the imaging unit 13 is fixed (for example, the focus position is aligned with the center of the test surface 10A), and within the focal depth of the imaging unit 13 according to the tilt angle Θ set by tilt adjustment. The aperture diameter of the imaging unit 13 may be adjusted so that the entire area of the test surface 10A is included, so that one image is always acquired. In this case, the entire inspection surface 10A is always included in the focal depth regardless of the inclination angle Θ, so that correct defect inspection can be performed even when the inclination angle Θ is large.

  Furthermore, in the above-described embodiment, an example in which the entire area of the test surface 10A is collectively imaged has been described, but the present invention is not limited to this. The present invention can also be applied to a case where a part of the surface to be inspected 10A is collectively imaged. In this case, it is preferable that a plurality of imaging units are provided in the inspection apparatus, and each imaging unit divides and captures different areas of the test surface 10A, and combines them to obtain an image of the entire area of the test surface 10A.

  In the above-described embodiment, the example in which the defect inspection is performed based on the diffracted light (for example, the first-order diffracted light) from the test surface 10A has been described, but the present invention is not limited to this. In addition, even when performing defect inspection based on inspection light such as specularly reflected light (corresponding to 0th-order diffracted light) from the surface to be detected 10A, scattered light, polarized light, etc., the surface to be tested with respect to the optical axis of the imaging unit If the image is acquired with the tilted, the same effect can be obtained by applying the present invention. The inclination angle of the test surface with respect to the optical axis of the imaging unit for specularly reflected light and polarized light is set so that the inclination angle of the test surface with respect to the optical axis of the illumination unit is equal.

It is the schematic which shows the whole structure of the test | inspection apparatus 10 of this embodiment. It is a figure explaining the case where 10 A of test surfaces are contained in the focal depth of the imaging part 13, and the case where the periphery of 10 A of test surfaces remove | deviate from the depth of focus (b). 4 is a flowchart for explaining image acquisition processing in the inspection apparatus 10; It is a figure explaining predetermined values ΘA and ΘB of the inclination angle Θ of the test surface 10A. It is a figure explaining the area | region division (a) in case inclination | tilt angle (THETA) is more than predetermined value (THETA) A and less than predetermined value (THETA) B, and the switching (b) and (c) of a focus position. It is a figure explaining the area | region division | segmentation in case inclination-angle (THETA) is more than predetermined value (THETA) B.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inspection apparatus 10A Test surface 11 Tilt stage 12 Illumination part 13 Imaging part 2A, 3A Optical axis 14 Image processing part 16 Control part

Claims (5)

Imaging means for collectively imaging at least a partial area of the surface to be examined;
Setting means for setting an inclination angle of the test surface with respect to the optical axis of the imaging means;
A plurality of focal positions to be imaged by the imaging means are determined according to the tilt angle set by the setting means, and a plurality of different focal positions are determined based on imaging signals that the imaging means images and outputs the area. An inspection apparatus comprising: an acquisition means for acquiring an image of the above. The inspection apparatus according to claim 1,
An inspection apparatus, further comprising: generating means for cutting out and synthesizing in-focus portions from each of the plurality of images acquired by the acquiring means to generate a composite image related to the region. The inspection apparatus according to claim 1 or 2,
The said acquisition means acquires an image, without switching the said focus position, when all of the said area | region is contained in the focal depth of the said imaging means. The inspection apparatus characterized by the above-mentioned. The inspection apparatus according to claim 3,
When the aperture diameter of the imaging means is larger than a predetermined diameter, the acquisition means reduces the aperture diameter so that the entire area is included within the focal depth of the imaging means, and switches the focus position. An inspection apparatus characterized in that an image is acquired without performing the above. Imaging means for collectively imaging at least a partial area of the surface to be examined;
Setting means for setting an inclination angle of the test surface with respect to the optical axis of the imaging means;
According to the tilt angle set by the setting means, the aperture diameter of the imaging means is adjusted so that the entire area is included within the depth of focus of the imaging means, and the imaging means images the area. An inspection apparatus comprising: an acquisition unit that acquires an image based on an imaging signal to be output.

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