JP5201443B2 - Surface inspection apparatus and surface inspection method - Google Patents

Description

  The present invention relates to a surface inspection apparatus and a surface inspection method for detecting a defect in a repetitive pattern based on a polarization component of specularly reflected light generated by irradiating a repetitive pattern (line and space pattern) of a test substrate with linearly polarized light. About.

  2. Description of the Related Art Conventionally, an inspection apparatus that uses diffracted light is known as an inspection apparatus for inspecting a defect of a repetitive pattern (line and space pattern) formed on the surface of a wafer. In an apparatus using diffracted light, it is necessary to use light having a short wavelength in order to satisfy the Bragg condition when the pattern pitch is shortened. However, the use of short-wavelength light not only makes the apparatus expensive, but also causes a problem that the resist is exposed when a resist pattern is inspected.

On the other hand, an inspection apparatus using structural birefringence of a repetitive pattern has been proposed. This apparatus irradiates linearly polarized light onto a repetitive pattern and detects light having a component orthogonal to the polarization component for inspection (see, for example, Patent Document 1). According to such an apparatus, when there is a collapse (that is, a defect) in the resist repetitive pattern, the amount of light (light intensity) of the regularly reflected light (polarized light component) to be detected is compared with the case in which the pattern does not collapse. Therefore, it becomes possible to detect a defect in the pattern repeatedly from the amount of specularly reflected light (polarized light component). Thereby, the inspection of the fine repetitive pattern which does not emit diffracted light can be performed without using short wavelength light.
US Patent Application Publication No. 2005 / 0280806A1

  However, such a conventional inspection apparatus can detect a defect (disintegration) of a repeated pattern, but cannot identify the type of the detected defect.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a surface inspection apparatus and a surface inspection method capable of specifying the type of defect.

In order to achieve such an object, in the first embodiment of the present invention, an illumination unit that irradiates a surface of a test substrate having a predetermined repetitive pattern with linearly polarized light, and a surface of the test substrate that is irradiated with the linearly polarized light. Detecting the presence of defects in the repetitive pattern based on the polarization component detected by the detection unit; An inspection unit; and an angle setting unit capable of setting an angle formed by a repeating direction of the repeated pattern and a vibration direction of the linearly polarized light on the surface of the test substrate to be set to a predetermined setting angle, and set by the angle setting unit The illumination unit irradiates the surface of the test substrate with the linearly polarized light at the plurality of set angles, and the detection unit includes the linearly polarized light and the vibration direction of the regular reflected light. Substantially detects the perpendicular polarization component is configured so that the measurement part to identify the type of the defect on the basis of the polarization component detected for each of the plurality of the set angle by the detecting unit, the inspection unit Calculates the light quantity change rate of the polarization component detected by the detection unit for each of the plurality of set angles, and specifies the type of the defect based on the light quantity change rates calculated for the plurality of the set angles. A surface inspection apparatus is provided.

In the second embodiment of the present invention, the illumination step of irradiating the surface of the test substrate having a predetermined repetitive pattern with linearly polarized light, and the specularly reflected light from the surface of the test substrate irradiated with the linearly polarized light, A detection step for detecting a polarization component whose vibration direction is substantially perpendicular to linearly polarized light, an inspection step for inspecting for the presence or absence of defects in the repetitive pattern based on the polarization component detected in the detection step, and An angle setting step for setting an angle formed by a repeating direction and a vibration direction of the linearly polarized light on the surface of the test substrate to a predetermined setting angle, and a plurality of the setting angles set by the angle setting step. Irradiating the surface of the test substrate with the linearly polarized light, and detecting a polarized light component whose vibration direction is substantially perpendicular to the linearly polarized light in the specularly reflected light. Said detected each time on the basis of the polarized light component and a specifying step of specifying a type of the defect, in the identification step, the plurality of the set angle the light amount change rate of the polarized light component detected by the detecting step The surface inspection method is characterized in that the defect type is specified on the basis of the light quantity change rate calculated for each of the plurality of set angles .

  According to the present invention, it is possible to specify the type of defect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the surface inspection apparatus 1 of the present embodiment includes a stage 20 that supports a semiconductor wafer 10 (hereinafter referred to as a wafer 10) that is a substrate to be tested, an illumination system 30, and a light receiving system 40. It is prepared for. In addition, the surface inspection apparatus 1 includes an image processing unit 50 that performs image processing of an image captured by the light receiving system 40, and a monitor 55 that displays an image captured by the light receiving system 40 and an image processing result by the image processing unit 50. It has. The surface inspection apparatus 1 is an apparatus that automatically inspects the surface of a wafer 10 in a manufacturing process of a semiconductor circuit element. After exposure / development of the uppermost resist film, the wafer 10 is carried from a wafer cassette (not shown) or a developing device by a conveyance system (not shown), and is sucked and held on the stage 20.

  A plurality of chip regions are arranged on the surface of the wafer 10, and in each chip region, as shown in FIG. 2, a plurality of line portions 2A and a space portion 2B located between the adjacent line portions 2A. A repetitive pattern 12 (line and space pattern) is formed. The repetitive pattern 12 is a resist pattern (for example, a wiring pattern) in which a plurality of line portions 2A are arranged at a constant repetitive pitch P along the short direction. The arrangement direction of the line portions 2A is referred to as “repetitive direction of the repeated pattern 12”.

  Here, the design value of the line width of the line portion 2A in the repetitive pattern 12 is set to ½ of the pitch P. That is, the repetitive pattern 12 has a concavo-convex shape in which the line portions 2A and the space portions 2B are alternately arranged along the repetitive direction, and when the repetitive pattern 12 is formed according to the design value with an appropriate exposure focus, The line width of 2A and the line width of the space portion 2B are equal, and the volume ratio between the line portion 2A and the space portion 2B is approximately 1: 1. Such a shape is also called an ideal shape.

  In the present embodiment, it is assumed that the pitch P of the repeating pattern 12 is sufficiently small compared to the wavelength of illumination light (linearly polarized light described later) with respect to the repeating pattern 12. For this reason, diffracted light is not generated from the repetitive pattern 12, and the defect inspection of the repetitive pattern 12 cannot be performed by diffracted light.

  The stage 20 of the surface inspection apparatus 1 supports the wafer 10 on the upper surface and fixes and holds the wafer 10 by, for example, vacuum suction. Further, the stage 20 is rotatable about the normal A1 at the center of the upper surface as a central axis. By this rotation mechanism, the repeating direction of the repeating pattern 12 on the wafer 10 can be rotated within the surface of the wafer 10. The stage 20 has a horizontal upper surface, and can always keep the wafer 10 in a horizontal state.

  In the present embodiment, in order to maximize the sensitivity of defect inspection of the repeated pattern 12, the repeating direction of the repeated pattern 12 on the wafer 10 is set to illumination light (linearly polarized light L) on the surface of the wafer 10 as shown in FIG. Inclination is set at an angle of 45 degrees with respect to the vibration direction. The angle is not limited to 45 degrees, and can be set in an arbitrary angle direction such as 22.5 degrees or 67.5 degrees.

  As shown in FIG. 1, the illumination system 30 includes an illumination device 31, a first polarizing plate 32, and a first concave reflecting mirror 33. The illumination device 31 includes a light source such as a mercury lamp (not shown) and a wavelength selection filter, and can emit light having a specific wavelength. The 1st polarizing plate 32 makes the light inject | emitted from the illuminating device 31 into the linearly polarized light L (refer FIG. 3) according to the direction of a transmission axis. The first concave reflecting mirror 33 converts the light from the first polarizing plate 32 reflected by the first concave reflecting mirror 33 into a parallel light beam and irradiates the wafer 10 as the test substrate. That is, the illumination system 30 is an optical system telecentric with respect to the wafer 10 side.

  In the illumination system 30, the light from the illumination device 31 becomes p-polarized linearly polarized light L via the first polarizing plate 32 and the first concave reflecting mirror 33 and enters the entire surface of the wafer 10. At this time, the incident angle of the linearly polarized light L at each point of the wafer 10 is the same because of the parallel light flux, and corresponds to the angle θ formed by the optical axis and the normal line A1.

  In this embodiment, since the linearly polarized light L incident on the wafer 10 is p-polarized light, the repeating direction of the repeated pattern 12 is the incident surface of the linearly polarized light L (linearly polarized light on the surface of the wafer 10) as shown in FIG. When the angle is set to 45 degrees with respect to the L traveling direction), the angle formed by the vibration direction of the linearly polarized light L on the surface of the wafer 10 and the repeating direction of the repeating pattern 12 is also set to 45 degrees. In other words, the linearly polarized light L changes into the repeated pattern 12 so as to cross the repeated pattern 12 diagonally with the vibration direction of the linearly polarized light L on the surface of the wafer 10 inclined by 45 degrees with respect to the repeated direction of the repeated pattern 12. It will be incident.

  As shown in FIG. 1, the light receiving system 40 includes a second concave reflecting mirror 41, a second polarizing plate 42, and an imaging device 43, and the optical axis passes through the center of the stage 20. It arrange | positions so that only angle (theta) may incline with respect to normal line A1. Therefore, the specularly reflected light from the repeated pattern 12 travels along the optical axis of the light receiving system 40. The second concave reflecting mirror 41 is the same reflecting mirror as the first concave reflecting mirror 33, reflects regular reflection light from the repeated pattern 12 and condenses it on the imaging surface of the imaging device 43.

  However, a second polarizing plate 42 is disposed between the second concave reflecting mirror 41 and the imaging device 43. The direction of the transmission axis of the second polarizing plate 42 is set so as to be orthogonal to the transmission axis of the first polarizing plate 32 of the illumination system 30 described above (crossed Nicol state). Therefore, the second polarizing plate 42 extracts a polarization component (for example, an s-polarized component) whose vibration direction is substantially perpendicular to the linearly polarized light L from the regular reflection light from the repetitive pattern 12 and guides it to the imaging device 43. be able to. As a result, a reflected image of the wafer 10 is formed on the imaging surface of the imaging device 43 by the polarization component of the regular reflection light from the repetitive pattern 12 that is substantially perpendicular to the linearly polarized light L and the vibration direction.

  The imaging device 43 is configured by, for example, a CCD imaging device and the like, photoelectrically converts a reflected image of the wafer 10 formed on the imaging surface, and outputs an image signal to the image processing unit 50. The brightness of the reflected image of the wafer 10 is substantially proportional to the amount of light (light intensity) of the polarization component detected by the imaging device 43 and changes according to the shape of the repeated pattern 12. The reflected image of the wafer 10 becomes brightest when the repeated pattern 12 has an ideal shape (when the pattern does not collapse). The brightness of the reflected image of the wafer 10 appears for each shot area.

  The image processing unit 50 captures a reflected image of the wafer 10 based on the image signal output from the imaging device 43. Note that the image processing apparatus 50 stores a reflection image of a non-defective wafer in advance for comparison. A non-defective wafer is one in which the repetitive pattern 12 is formed on the entire surface in an ideal shape. Therefore, it is considered that the amount of light (light intensity) appearing as the signal intensity in the reflected image of the non-defective wafer shows the highest value.

  Therefore, when the image processing unit 50 captures the reflected image of the wafer 10 as the test substrate, the image processing unit 50 compares the light amount (signal intensity) with the light amount (signal intensity) of the reflected image of the non-defective wafer. Then, the defect of the repetitive pattern 12 is detected based on the amount of decrease in the amount of light in the dark portion in the reflected image of the wafer 10. For example, if the light amount change 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”. Then, the light quantity comparison result by the image processing unit 50 and the reflected image of the wafer 10 at that time are output and displayed on the monitor 55.

  In addition, as described above, the image processing unit 50 may be configured to store the reflection data of the non-defective wafer in advance, or to previously store the array data of the shot area of the wafer 10 and the light amount threshold value. . In this case, since the position of each shot area in the captured reflection image of the wafer 10 is known based on the array data of the shot area, the light quantity of each shot area is obtained. Then, a pattern defect is detected by comparing the amount of light with a stored threshold value. A shot area whose light amount is smaller than the threshold value may be determined as a “defect”.

  A surface inspection method using the surface inspection apparatus 1 having such a configuration will be described below with reference to the flowchart shown in FIG. First, in step S101, the surface of the wafer 10 that is the substrate to be tested is irradiated with linearly polarized light L. At this time, the light emitted from the illumination device 31 is converted into p-polarized linearly polarized light L by the first polarizing plate 32 and becomes a parallel light beam by the first concave reflecting mirror 33 on the surface of the wafer 10. Irradiated.

  The specularly reflected light reflected by the surface of the wafer 10 is collected by the second concave reflecting mirror 41 and is polarized by the second polarizing plate 42 with a polarization component (for example, substantially perpendicular to the linearly polarized light L of the specularly reflected light). , S-polarized components) are extracted and guided onto the imaging surface of the imaging device 43. Therefore, in the next step S <b> 102, the polarization component guided onto the imaging surface of the imaging device 43 is detected by the imaging device 43. At this time, the imaging device 43 photoelectrically converts the reflected image of the wafer 10 by the polarization component of the specularly reflected light that is substantially perpendicular to the linearly polarized light L formed on the imaging surface, and performs image processing on the image signal. To the unit 50.

  Then, in the next step S103, the presence or absence of defects in the repetitive pattern 12 is inspected based on the polarization component detected in the previous step. At this time, the image processing unit 50 compares the light amount (signal intensity) of the image of the wafer 10 input from the imaging device 43 with the light amount (signal intensity) of the image of the non-defective wafer, and sets a preset threshold value for the change in light amount. When it exceeds, it is determined that there is a defect.

  When the image processing unit 50 determines that the repeated pattern 12 is defective, the stage 20 is rotated so that the repeated direction of the repeated pattern 12 is (45 degrees) with respect to the vibration direction of the linearly polarized light L on the surface of the wafer 10. To) is set to tilt at an angle of 67.5 degrees. Next, at the set angle of 67.5 degrees, similarly to steps S101 and S102, the surface of the wafer 10 is irradiated with the linearly polarized light L, and the linearly polarized light L and the vibration direction of the regular reflected light from the wafer 10 are changed. Detects a substantially perpendicular polarization component. Then, the type of a certain defect is specified based on the light amount of the polarization component detected at the set angles of 45 degrees and 67.5 degrees.

  The inventor of the present application, as shown in FIG. 5, in the repetitive pattern 12 ′ including a defect having an inclination dependency inclined in one direction within the surface of the wafer 10 with respect to the extending direction of the line portion, It has been discovered that when a polarization component is detected at a plurality of setting angles and a light amount change rate (contrast) of the polarization component is calculated, a contrast difference occurs at a plurality of setting angles. For example, as shown in FIGS. 6A and 6B, when the detected light quantity distribution (light intensity distribution) of the polarization component is converted into a contrast distribution, the setting angle of 67.5 degrees is 45 degrees. It was found that the contrast is relatively higher than the case. In the present embodiment, the light amount change rate (contrast) is defined as a value obtained by dividing the maximum light amount, that is, the difference between the detected light amount and the light amount in the case of a non-defective wafer. Further, the inclination angle of the repetitive pattern 12 ′ as shown in FIG. 5 is defined as an asymmetric angle α.

  Therefore, the image processing unit 50 calculates the contrast of the light amount described above from the light amount of the polarization component detected at the setting angles of 45 degrees and 67.5 degrees, and uses the contrast difference shown in FIG. Specifically, the contrast difference between the contrast at the setting angle of 67.5 degrees and the contrast at the setting angle of 45 degrees is calculated, and the asymmetric angle α is calculated backward from the calculated contrast difference from the graph of FIG. Thus, the inclination angle (asymmetric angle α) of the repetitive pattern 12 ′ including defects having inclination dependency is calculated. As a result, the inclination angle (asymmetric angle α) of the repetitive pattern 12 ′ including a defect having an inclination dependency that inclines in one direction within the surface of the wafer 10 can be obtained. If no contrast difference occurs, the repetitive pattern has other types of defects. Thus, according to the surface inspection apparatus 1 of the present embodiment, it is possible to specify the type of defect detected by the repeated pattern.

  At this time, as described above, by specifying the defect type based on the light amount change rate (contrast) detected for each of the plurality of setting angles, the defect type can be specified relatively easily.

  As described above, the type of the defect to be identified is a defect having an inclination dependency in which at least a part of the repetitive pattern 12 is inclined to one side within the surface of the wafer 10. It is effective to specify.

  As shown in FIG. 7 (and FIG. 8), when the repetitive pattern 12 ″ (12 ′ ″) is broken symmetrically (that is, when the defect has no inclination dependency), the above-described implementation is performed. It is known that the contrast difference described in the form does not occur.

  In the above-described embodiment, the polarization component is detected at the setting angles of 45 degrees and 67.5 degrees. However, the present invention is not limited to this. For example, the polarization component is further detected at the setting angle of 22.5 degrees. Detection may be performed, and the polarization component may be detected for a plurality of arbitrary set angles.

  In the above-described embodiment, the example in which the linearly polarized light L is p-polarized light has been described. However, the present invention is not limited to this. For example, s-polarized light may be used instead of p-polarized light. At this time, the polarization component detected by the imaging device 43 is, for example, a p-polarized component.

  In the above-described embodiment, the linearly polarized light L is generated using the illumination light from the illumination device 31 and the first polarizing plate 32. However, the present invention is not limited to this. If the laser which supplies is used as a light source, the first polarizing plate 32 is not necessary.

It is a figure showing the whole surface inspection device composition concerning the present invention. It is the schematic of a repeating pattern. It is a figure explaining the inclination state of the entrance plane of a linearly polarized light and the repeating direction of a repeating pattern. It is a flowchart of the surface inspection using a surface inspection apparatus. It is the schematic of the repeating pattern containing the defect which has inclination dependence. (A) is a graph which shows the relationship between the light quantity of a polarization component, and an asymmetric angle, (b) is a graph which shows the relationship between the contrast and the asymmetric angle of light quantity. It is the schematic of the repeating pattern containing the defect which does not have inclination dependence. It is the schematic which shows another example of the repeating pattern containing the defect which does not have inclination dependence.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface inspection apparatus 10 Wafer (substrate to be tested) 12 Repeat pattern 20 Stage (angle setting part) 30 Illumination system (illumination part)
40 Light receiving system (detection unit) 50 Image processing unit (inspection unit)
L Linearly polarized light

Claims (4)

An illumination unit that irradiates the surface of the test substrate having a predetermined repeating pattern with linearly polarized light;
A detection unit for detecting a polarization component whose vibration direction is substantially perpendicular to the linearly polarized light among specularly reflected light from the surface of the test substrate irradiated with the linearly polarized light;
Based on the polarization component detected by the detection unit, an inspection unit that inspects the presence or absence of defects in the repetitive pattern;
An angle setting unit capable of setting an angle formed by the repeating direction of the repeating pattern and the vibration direction of the linearly polarized light on the surface of the test substrate to a predetermined setting angle;
At the plurality of set angles set by the angle setting unit, the illumination unit irradiates the surface of the substrate with the linearly polarized light, and the detection unit includes the linearly polarized light and the vibration direction of the regular reflected light. Is configured such that the inspection unit identifies the type of the defect based on the polarization component detected for each of the plurality of setting angles by the detection unit .
The inspection unit calculates a light amount change rate of the polarization component detected by the detection unit for each of the plurality of set angles, and based on the light amount change rate calculated for each of the plurality of set angles, A surface inspection device characterized by identifying the type . The surface inspection apparatus according to claim 1 , wherein the type of the defect is a defect having an inclination dependency in which at least a part of the repetitive pattern is inclined in one direction within the surface of the test substrate. An illumination step of irradiating the surface of the test substrate having a predetermined repeating pattern with linearly polarized light;
A detection step of detecting a polarization component whose vibration direction is substantially perpendicular to the linearly polarized light out of specularly reflected light from the surface of the test substrate irradiated with the linearly polarized light;
Based on the polarization component detected in the detection step, an inspection step for inspecting the presence or absence of defects in the repetitive pattern;
An angle setting step of setting an angle formed by the repeating direction of the repeating pattern and the vibration direction of the linearly polarized light on the surface of the test substrate to a predetermined setting angle;
At the plurality of set angles set by the angle setting step, the surface of the substrate to be tested is irradiated with the linearly polarized light, and the polarized light component whose vibration direction is substantially perpendicular to the linearly polarized light is detected from the regular reflected light. And a specifying step of specifying the type of the defect based on the polarization component detected for each of the plurality of the set angles ,
In the specifying step, a light amount change rate of the polarization component detected in the detection step is calculated for each of the plurality of set angles, and the defect is determined based on the light amount change rates calculated for the plurality of set angles. A surface inspection method characterized by identifying the type . The surface inspection method according to claim 3 , wherein the type of the defect is a defect having an inclination dependency in which at least a part of the repetitive pattern is inclined in one direction within the surface of the test substrate.

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