JP2009068892A - Inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device capable of grasping decline of inspection accuracy by monitoring the deterioration of a polarization element. <P>SOLUTION: This device is equipped with a detection part (imaging element 35) for detecting the light generated from an inspection object (semiconductor wafer 10) by the light irradiated from a light source; polarization elements 23, 33 arranged in an optical path (an illumination optical system 20; a light-receiving optical system 30) from the light source to the detection part; and a monitor part 50 for monitoring a deterioration degree of the polarization elements 23, 33, based on comparison with a reference polarization element used as a reference for the polarization elements 23, 33. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection apparatus for inspecting a repetitive pattern formed on the surface of, for example, a semiconductor wafer or a liquid crystal substrate.

  As an apparatus for inspecting a repetitive pattern formed on the surface of a semiconductor wafer or liquid crystal substrate, for example, illumination light for inspection is irradiated on the surface of the wafer or substrate, while light generated from the repetitive pattern on the surface of the wafer or substrate is emitted. An apparatus for receiving light and inspecting a defect in a repeated pattern is known.

Among the above inspection apparatuses, an inspection apparatus that uses linearly polarized light as the illumination light for inspection and receives a component related to a change in the polarization state in the repetitive pattern among the light generated from the repetitive pattern and inspects the defect is proposed. (See Patent Document 1). This inspection device can cope with repetitive pattern miniaturization without shortening the wavelength of illumination light. A polarizing element is arranged in the optical path from the light source to the light receiving part through the surface of the wafer or substrate. It is configured.
WO2005 / 040776

  In the above-described apparatus in which the polarizing element is arranged in the optical path, the deterioration of the polarizing element has not been considered as a problem.

  However, when the polarizing element deteriorates, the extinction ratio decreases. That is, light in the vibration direction that is not originally desired to be transmitted is slightly transmitted (leakage light is generated). In the case of inspecting a repetitive pattern in which only a detection output having a low intensity is obtained, this leakage light adversely affects the inspection sensitivity as noise, resulting in a problem that inspection with high accuracy cannot be performed.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an inspection apparatus capable of monitoring deterioration of a polarizing element and grasping a decrease in inspection accuracy.

  The inspection apparatus according to claim 1 of the present invention that achieves the above object is arranged in a detection unit that detects light generated from an object to be inspected by light irradiated from a light source, and an optical path from the light source to the detection unit. And a monitoring unit that monitors the degree of deterioration of the polarizing element based on a comparison between the polarizing element and a reference polarizing element that serves as a reference for the polarizing element.

  In the inspection apparatus according to claim 2 of the present invention, the polarizing element extends from the light source to the inspection object, the first polarizing element is disposed, and the inspection object reaches the detection unit. A second polarizing element disposed in the optical path, wherein the first polarizing element extracts linearly polarized light from the light of the light source, and the second polarizing element vibrates the linearly polarized light from light generated from the inspection object. A polarization component that intersects the surface is extracted.

  According to a third aspect of the present invention, there is provided an inspection apparatus further comprising a display unit that displays a monitor result of the monitor unit.

  According to a fourth aspect of the present invention, the inspection apparatus further includes a monitoring polarizing element and a replacement unit that replaces the monitoring polarizing element in an optical path of the polarizing element.

  The inspection apparatus according to claim 5 of the present invention is characterized in that the monitor unit stores a threshold value regarding the degree of deterioration of the polarizing element, and determines pass / fail of the polarizing element based on the threshold value.

  The inspection apparatus according to claim 6 of the present invention is characterized in that the monitor unit stores the threshold value for each inspection object.

  The inspection apparatus according to claim 7 of the present invention is characterized in that the monitor unit measures the transmittance of the polarizing element and determines the quality of the polarizing element from the transmittance.

  According to the present invention, it is possible to monitor the deterioration of the polarizing element and grasp the decrease in inspection accuracy.

  An embodiment of an inspection apparatus according to the present invention will be described below with reference to FIGS.

  FIG. 1 is a schematic view showing an embodiment of the inspection apparatus of the present invention. The inspection apparatus of this embodiment is an apparatus that is equipped with a PER (Pattern Edge Roughness) optical system shown in FIG. 1 and that automatically inspects the surface of the semiconductor wafer 10 in the manufacturing process of the semiconductor circuit element.

  The inspection apparatus according to the present embodiment includes an inspection stage 11 on which a semiconductor wafer 10 as an inspection object is placed, an illumination optical system 20 that irradiates light (linearly polarized light) to the semiconductor wafer 10, and an illumination optical system 20. A light receiving optical system 30 that receives a polarized light component (a polarized light component that intersects (orthogonal) linearly polarized light) caused by structural birefringence generated on the surface of the semiconductor wafer 10 by irradiation of the inspection light, and an output of the light receiving optical system 30 Are equipped with an image processing device 40, a monitor unit 50, a display unit 60 for displaying the monitoring result on the monitor unit 50, and an alignment system 70.

  After exposure / development of the uppermost resist film, the semiconductor wafer 10 is conveyed from a wafer cassette (not shown) or a developing device by a conveyance system (not shown) and is attracted to the inspection stage 11.

  The illumination optical system 20 includes a light source 21, an exit lens 22, a first polarizing element 23, a polarization compensation plate 24, and an illumination-side concave mirror 25.

  As the light source 21, a halogen lamp, a metal halide lamp, a mercury lamp, or the like is used. The light from the light source 21 passes through a wavelength selection filter (not shown), an ND filter for light amount adjustment, etc., and only a part of the wavelength of light is extracted as illumination light and enters the exit lens 22. Illumination light emitted from the exit lens 22 is converted into substantially parallel light by a spherical concave reflecting mirror 25 to illuminate the semiconductor wafer 10 placed on the stage 11.

  The polarization element 23 and the polarization compensation plate 24 are disposed in the optical path between the exit lens 22 and the concave reflecting mirror 25. The illumination light emitted from the exit lens 22 is converted into linearly polarized light L1 by the polarizing element 23. The linearly polarized light L1 is collimated by the concave reflecting mirror 25 via the polarization compensator 24, and the collimated light of the linearly polarized light L1 illuminates the semiconductor wafer 10.

  In order to improve the throughput, it is extremely advantageous to collect images of the entire wafer surface of the semiconductor wafer 10 at one time. Therefore, in this embodiment, as described above, the light flux from the light source 21 is expanded, The concave mirror 25 is collimated to illuminate the entire surface of the semiconductor wafer 10.

  The linearly polarized light L 1 incident on the semiconductor wafer 10 is reflected by the surface of the semiconductor wafer 10 and enters the light receiving optical system 30. The light receiving optical system 30 includes an imaging side concave mirror 31, a polarization compensation plate 32, a second polarizing element 33, and an objective lens 34. The polarization compensator 32 and the polarizing element 33 are disposed in the optical path between the imaging side concave mirror 31 and the objective lens 34.

  The first polarizing element 23 and the second polarizing element 33 are arranged in a crossed Nicols relationship. The condensed light beam reflected by the imaging side concave mirror 31 passes through the polarization compensation plate 32 and the polarization element 33 arranged in a crossed Nicol relationship with the polarization compensation plate 24 and the polarization element 23, and then forms an image (not shown) with the objective lens 34. The lens forms an image on the imaging surface of the imaging element 35 disposed at a position conjugate with the surface of the semiconductor wafer 10 to form an image of the surface of the semiconductor wafer 10.

  As shown in FIG. 2, a plurality of chip regions 10a are arranged in the XY direction on the surface of the semiconductor wafer 10, and a repeated pattern 10b is formed in each chip region 10a. The arrangement direction (X direction) of the line portion of the repetitive pattern 10b is referred to as “repetitive direction of the repetitive pattern 10b”.

  In the present embodiment, it is assumed that the pitch of the repeating pattern 10b is sufficiently small compared to the wavelength of illumination light for the repeating pattern 10b. The principle of defect inspection in the present embodiment is described in Japanese Patent Application No. 2003-366255 filed by the applicant of the present application. Therefore, the description of the principle is omitted here.

  On the surface of the inspection stage 11, the semiconductor wafer 10 on which the above-described repetitive pattern 10b is formed is placed and fixedly held by vacuum suction or the like. The inspection stage 11 is configured to be rotatable around a predetermined rotation axis orthogonal to the stage surface by a stage rotation mechanism (not shown). By this stage rotation mechanism, the angle formed by the longitudinal direction (Y direction) of the repeated pattern formed on the surface of the semiconductor wafer 10 with respect to the linearly polarized vibrating surface of the light beam L1 that illuminates the semiconductor wafer 10 is set to an arbitrary angle. Can do.

  Between the illumination-side concave mirror 25 and the imaging-side concave mirror 31, an alignment system 70 for detecting the orientation of the repetitive pattern 10b formed on the surface of the semiconductor wafer 10 placed on the inspection stage 11 is disposed. A longitudinal angle Y of the repetitive pattern 10b with respect to the illumination optical system 20 and the light receiving optical system 30 is detected by a stage rotation mechanism by detecting a preset angle of the linearly polarized vibrating surface of the light beam L1 and the longitudinal direction Y of the repetitive pattern 10b. Can be adjusted.

  The alignment system 70 illuminates the outer edge of the semiconductor wafer 10 when the inspection stage 11 is rotating, detects the position in the rotation direction of an external reference (for example, a notch) provided on the outer edge, and at a predetermined position. The inspection stage 11 is stopped. As a result, the repetitive direction (X direction in FIG. 2) of the repetitive pattern 10b of the semiconductor wafer 10 can be set to be inclined at an angle of 45 degrees with respect to an illumination light incident surface 3A (see FIG. 3) described later. it can.

  In the present embodiment, the linearly polarized light beam L1 is P-polarized light. As shown in FIG. 4A, a plane including the traveling direction of the linearly polarized light L1 and the vibration direction of the vector (vibrating surface of the linearly polarized light L1) is included in the incident surface (3A) of the linearly polarized light L1. The vibration plane of the linearly polarized light L <b> 1 is defined by the transmission axis of the polarizing element 23 disposed in front of the illumination side concave mirror 25.

  Since the linearly polarized light L1 incident on the semiconductor wafer 10 is P-polarized light (FIG. 4A), the repetitive direction (X direction) of the repetitive pattern 10b of the semiconductor wafer 10 is incident on the linearly polarized light L1 as shown in FIG. When the angle is set to 45 degrees with respect to the surface (3A), the direction of the vibrating surface of the linearly polarized light L1 on the surface of the semiconductor wafer 10 (the V direction in FIG. 5) and the repeating direction of the repeating pattern 10b (the X direction) Is also set to 45 degrees.

  In other words, the linearly polarized light L1 has a repeating pattern 10b in a state where the direction of the vibration surface (V direction in FIG. 5) on the surface of the semiconductor wafer 10 is inclined by 45 degrees with respect to the repeating direction (X direction) of the repeating pattern 10b. Is repeatedly incident on the pattern 10b.

  Such an angle state between the linearly polarized light L1 and the repeated pattern 10b is uniform over the entire surface of the semiconductor wafer 10 1. Even if 45 degrees is replaced with any one of 135 degrees, 225 degrees, and 315 degrees, the angle state between the linearly polarized light L1 and the repeated pattern 10b is the same. The reason why the angle formed by the direction of the vibration surface (V direction) and the repeat direction (X direction) in FIG. 5 is set to 45 degrees is to maximize the sensitivity of the defect inspection of the repeat pattern 10b.

  When the repeating pattern 10b is illuminated using the linearly polarized light L1, the elliptically polarized light L2 is generated in the regular reflection direction from the repeating pattern 10b (FIGS. 1 and 4B). In this case, the traveling direction of the elliptically polarized light L2 coincides with the regular reflection direction. The regular reflection direction is a direction inclined by an angle equal to the incident angle of the linearly polarized light L1 with respect to the normal line 1A (FIG. 3) of the inspection stage 11. As described above, since the pitch of the repeated pattern 10b is sufficiently smaller than the illumination wavelength, no diffracted light is generated from the repeated pattern 10b.

  The imaging-side concave mirror 31 is a reflecting mirror similar to the illumination-side concave mirror 25 of the illumination optical system 20 described above, reflects the elliptically polarized light L2 and guides it toward the objective lens 34, and cooperates with the objective lens 34 and the imaging lens. Then, the light is condensed on the image pickup surface of the image pickup device 35.

  A polarizing element 33 is disposed between the objective lens 34 and the imaging side concave mirror 31. The direction of the transmission axis of the polarizing element 33 is set so as to be orthogonal to the transmission axis of the polarizing element 23 of the illumination optical system 20 described above (in a crossed Nicols state). Therefore, only the polarization component corresponding to the polarization component L3 in FIG. 4C of the elliptically polarized light L2 can be extracted and guided to the imaging device 35 by the polarization element 33. As a result, a reflection image of the semiconductor wafer 10 is formed on the imaging surface of the imaging element 35 with a polarization component corresponding to the polarization component L3 in FIG.

  The image pickup device 35 is, for example, a CCD image pickup device or the like, and photoelectrically converts a reflected image of the semiconductor wafer 10 formed on the image pickup surface and outputs an image signal to the image processing device 40. The brightness of the reflected image of the semiconductor wafer 10 is substantially proportional to the light intensity of the polarized component (the magnitude of the polarized component L3 in FIG. 4C), and the reflected image of the semiconductor wafer 10 is brightest because of the repeated pattern 10b. Is the ideal shape. Note that the brightness and darkness of the reflected image of the semiconductor wafer 10 appears for each shot region 10a.

  The image processing device 40 captures a reflected image of the semiconductor wafer 10 based on the image signal output from the image sensor 35. In the image processing apparatus 40, a reflected image of a non-defective wafer is stored in advance for comparison. A non-defective wafer is one in which the repetitive pattern 10b is formed on the entire surface in an ideal shape. It is considered that the luminance information of the reflected image of the non-defective wafer shows the highest luminance value.

  Therefore, when the image processing apparatus 40 captures the reflection image of the semiconductor wafer 10 that is the inspection object, the image processing apparatus 40 compares the luminance information with the luminance information of the reflection image of the non-defective wafer. Then, the defect of the repeated pattern 10b is detected based on the amount of decrease in the luminance value in the dark part of the reflected image of the semiconductor wafer 10. For example, if the amount of decrease in luminance value is larger than a predetermined threshold (allowable value), it is determined as “defect”, and if it is smaller than the threshold, it is determined as “normal”.

  The polarization compensation plate 24 disposed in the optical path of the illumination optical system 20 and the polarization compensation plate 32 disposed in the light receiving optical system 30 are generated due to the exit lens 22, the illumination-side concave mirror 25, and the imaging-side concave mirror 31. This eliminates disturbance of the polarization plane.

  As described above, in the inspection apparatus of the present embodiment, the linearly polarized light L1 is used, and the vibration surface direction (V direction) in FIG. 5 is repeatedly inclined with respect to the repetition direction (X direction) of the repeated pattern 10b. In order to illuminate the pattern 10b and to detect defects in the repeated pattern 10b based on the magnitude of the polarization component L3 in FIG. 4C among the elliptically polarized light L2 generated in the regular reflection direction, it is compared with the illumination wavelength. Even if the pitch of the repeated pattern 10b is sufficiently small, the defect inspection can be surely performed. In other words, the linearly polarized light L1, which is the illumination light, can be reliably repetitively miniaturized without shortening the wavelength.

  The polarizing element 23 disposed in the optical path of the illumination optical system 20 and the polarizing element 33 disposed in the optical path of the light receiving optical system 30 may be deteriorated by light passing through these optical paths due to long-term use or the like. When the polarizing elements 23 and 33 deteriorate, the extinction ratio decreases. That is, light in a vibration direction that is not originally desired to be transmitted is transmitted (leakage light is generated). This leaked light may adversely affect the inspection sensitivity as noise.

  Therefore, in the inspection apparatus of this embodiment, the monitor unit 50 monitors the degree of deterioration of the polarizing elements 23 and 33. For example, when the polarizing element 23 deteriorates, the light that has passed through the polarizing element 33 arranged in the crossed Nicol state is received by the imaging element 35 as leakage light. The received light including leakage light is photoelectrically converted and input to the image processing apparatus 40 as an image signal. The image processing apparatus 40 acquires a reflected image of the semiconductor wafer 10 from the input image signal. The image brightness of the reflected image increases when there is a large amount of leakage light.

  The monitor unit 50 acquires luminance information in the reflected image from the image processing device 40, and monitors the luminance information to monitor the degree of deterioration of the polarizing elements 23 and 33. As described above, the brightness of the reflected image of the semiconductor wafer 10 received by the image sensor 35 (the magnitude of the polarization component L3 in FIG. 4C) differs depending on the repetitive pattern 10b. When inspecting the semiconductor wafer 10 having the repetitive pattern 10b that generates light having a large polarization component L3 in FIG. 4C, the noise component due to leakage light can be inspected even if ignored. In this case, the monitor unit 50 sends a monitoring result that can be inspected to the display unit 60, and the display unit 60 displays this. However, when inspecting the semiconductor wafer 10 having the repeated pattern 10b that generates light with a small polarization component L3, a noise component due to leakage light cannot be ignored. In this case, the monitor unit 50 sends an uninspectable monitoring result to the display unit 60, and the display unit 60 displays the result.

  FIG. 6 is a flowchart showing a procedure for determining whether or not inspection is possible on the monitor unit 50.

  In step S 1, the polarizing element 23 in the illumination optical system 20 is replaced with a non-degraded reference polarizing plate 80 that is a monitoring polarizing element, and a reflected image of the semiconductor wafer 10 that is the object to be inspected is acquired. Measure. The reference polarizing plate 80 is used only when determining the degree of deterioration of the polarizing element 23 and is not normally used at the time of inspection, but can be used instead of the polarizing element 23. The polarizing element 23 and the reference polarizing plate 80 enter the optical path of the illumination optical system 20 by the switching unit 81 and exit from the optical path.

  In step S2, image luminance measurement data is acquired, and a luminance value A is obtained from the measurement data.

  In step S3, the allowable noise value B of the semiconductor wafer 10 is calculated from the allowable S / N ratio. The magnitude of the allowable noise value B varies depending on the type of the repeated pattern 10b of the semiconductor wafer 10. In the case of the repetitive pattern 10b that generates light having a large polarization component L3 in FIG. 4C, the allowable noise value B is large, and in the case of the repetitive pattern 10b that generates only light having a small polarization component L3 in FIG. Then, the allowable noise value B is small.

  In step S4, the polarizing element 23 is returned into the optical path of the illumination optical system 20, the semiconductor wafer 10 is replaced with the reference substrate, the reference substrate is illuminated with the linearly polarized light L1 generated by the polarizing element 23, and the reflected image is acquired. To do. The reference substrate is, for example, a semiconductor wafer or a liquid crystal glass substrate on which a circuit is not baked (without a repeated pattern). The acquired reflected image is a crossed Nicos image, and the image is originally dark. However, this image changes brightly when there is light leakage.

  In step S5, the in-plane average luminance value is acquired from the reflection image of the reference substrate. This in-plane average luminance value indicates a noise luminance value C unique to the inspection apparatus.

  In step S6, the noise luminance value C and the allowable noise value B are compared. When the noise luminance value C unique to the inspection apparatus is larger than the allowable noise value B, it is determined that the polarization element 23 has deteriorated and leakage light has occurred, and the process proceeds to step S7. Is displayed (prompt judgment of replacement of polarizing plate). If the noise luminance value C unique to the inspection apparatus is smaller than the allowable noise value B, it is determined that the polarization element 23 has not deteriorated and there is little leakage light, and the process proceeds to step S8. Show that it is possible.

  When there is a display indicating that inspection is possible on the display unit 60, the inspection apparatus starts the surface inspection of the semiconductor wafer 10, captures the reflected image of the semiconductor wafer 10 that is the object to be inspected, and obtains the luminance information as a non-defective product. Compared with the luminance information of the reflected image of the wafer, the defect of the repeated pattern 10b is detected based on the amount of decrease in the luminance value of the dark portion of the reflected image of the semiconductor wafer 10.

  The inspection apparatus of the present invention is not limited to the one shown in the above embodiment. For example, a threshold value for the degree of deterioration of the polarizing elements 23 and 33 may be stored in the monitor unit 50 in advance. This threshold value is set for each repeated pattern 10b formed on the semiconductor wafer 10. This is because the magnitude of the polarization component L3 in FIG. 4C generated by the repeated pattern 10b is different. In this way, inspection efficiency can be improved.

  Further, in this embodiment, the deterioration of the polarizing element 23 is determined by comparing the noise luminance C obtained from the reflected image of the reference substrate and the allowable noise luminance B, but the reference substrate is received by using the reference polarizing plate 80. The deterioration may be determined by comparing the average luminance with the average luminance received using the polarizing element 23.

  Further, the degree of deterioration of the polarizing elements 23 and 33 may be obtained by measuring the transmittance of polarized light instead of measuring the image luminance. This is because, when polarized light that is not transmitted through the polarizing elements 23 and 33 is transmitted through the polarizing elements 23 and 33, the transmitted light can be regarded as leakage light of the polarizing elements 23 and 33.

  Moreover, although the case where the deterioration degree of the polarizing element 23 is monitored is shown in the above embodiment, this is because the polarizing element 23 has a larger amount of light irradiation than the polarizing element 33 and is not easily deteriorated. This is because, for example, the degree of deterioration of the polarizing element 33 can be estimated by monitoring the degree of deterioration. However, it goes without saying that the polarizing element 33 may be monitored separately from the polarizing element 23.

It is the schematic which shows one Embodiment of the test | inspection apparatus of this invention. It is an external view of the surface of the semiconductor wafer inspected with the inspection apparatus of FIG. It is a figure explaining the inclination state of the entrance plane (3A) of linearly polarized light L1, and the repeating direction (X direction) of a repeating pattern. It is a figure explaining the vibration direction of linearly polarized light L1 and elliptically polarized light L2. It is a figure explaining the inclination state of the direction (V direction) of the vibration surface of the linearly polarized light L1, and the repeating direction of a repeating pattern. It is a flowchart of the judgment procedure in a monitor part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor wafer 11 Inspection stage 20 Illumination optical system 21 Light source 22 Output lens 23 Polarization element 25 Illumination side concave mirror 30 Light reception optical system 31 Imaging side concave mirror 33 Polarization element 34 Objective lens 35 Imaging element 40 Image processing apparatus 50 Monitor part 60 Display part

Claims (7)

A detection unit for detecting light generated from the object to be inspected by light emitted from the light source;
A polarizing element disposed in an optical path from the light source to the detection unit;
A monitor unit that monitors the degree of deterioration of the polarizing element based on a comparison with a reference polarizing element that serves as a reference for the polarizing element;
An inspection apparatus comprising: The inspection apparatus according to claim 1,
The polarizing element includes a first polarizing element disposed in an optical path from the light source to the inspection object, and a second polarizing element disposed in an optical path from the inspection object to the detection unit. ,
The first polarizing element extracts linearly polarized light from the light of the light source;
2. The inspection apparatus according to claim 1, wherein the second polarizing element extracts a polarization component intersecting with the vibration plane of the linearly polarized light from light generated from the inspection object. The inspection apparatus according to claim 1 or 2,
An inspection apparatus further comprising a display unit for displaying a monitoring result in the monitor unit. The inspection apparatus according to any one of claims 1 to 3,
A polarizing element for monitoring;
A replacement unit for replacing the polarizing element for monitoring in the optical path of the polarizing element;
An inspection apparatus further comprising: The inspection apparatus according to any one of claims 1 to 4,
The said monitoring part memorize | stores the threshold value about the deterioration degree of the said polarizing element, and determines the quality of the said polarizing element based on this threshold value. The inspection apparatus according to claim 5, wherein
The said monitoring part memorize | stores the said threshold value for every said to-be-inspected object, The inspection apparatus characterized by the above-mentioned. The inspection apparatus according to any one of claims 1 to 6,
The monitor unit measures the transmittance of the polarizing element, and determines the quality of the polarizing element from the transmittance.

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