JP4411738B2 - Surface inspection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface inspection apparatus for inspecting defects on a substrate surface in a manufacturing process of a semiconductor circuit element or a liquid crystal display element.
[0002]
[Prior art]
As is well known, in a manufacturing process of a semiconductor circuit element or a liquid crystal display element, a resist circuit pattern is formed through an exposure process of baking a circuit pattern on a photoresist film on a substrate and a developing process of a photosensitive photoresist film. Thereafter, a circuit is formed on the substrate through processing steps such as etching and vapor deposition.
[0003]
In this manufacturing process, if there is a defect in the circuit pattern by the resist, processing is performed according to the defect, resulting in a defective product. Therefore, the defect inspection of the circuit pattern by the resist has been conventionally performed. The defective part is, for example, a part where the cross-sectional shape of the circuit pattern has changed due to defocusing of the exposure machine, a part where the film thickness of the resist has changed, or a part with foreign matter or scratches.
[0004]
At present, the defect inspection in the actual manufacturing process is performed by visual observation. However, in the visual observation, since the inspection standard changes depending on the skill and physical condition of the inspector, a sufficient inspection result cannot be obtained.
Therefore, it has been studied to automate this defect inspection. All of the various types of automatic inspection apparatuses already proposed capture an image (diffraction image) based on diffracted light from a repetitive pattern formed on a substrate, and specify a defect location based on the brightness of the diffraction image. This is because the diffraction efficiency differs between the defective portion and the normal portion on the substrate surface, and thus light and darkness due to pattern abnormality (defect) appears in the diffraction image.
[0005]
[Problems to be solved by the invention]
However, the conventional surface inspection apparatus cannot automatically set the apparatus condition (for example, the tilt angle of the substrate) when capturing the substrate image based on the diffracted light from the repetitive pattern on the substrate to the optimum condition. The optimum condition is a condition in which the traveling direction of the diffracted light generated from the repetitive pattern and the optical axis direction of the light receiving optical system that receives the diffracted light substantially coincide.
[0006]
As is well known, the optimum conditions for the apparatus conditions vary depending on the pitch of the repeated pattern. For this reason, apparatus conditions must be changed according to the pitch of the repetitive pattern formed on the substrate to be inspected. However, in many cases, the design value of the pitch of the repetitive pattern is not informed to the inspector.
Therefore, in the conventional surface inspection apparatus, the diffraction image of the substrate is displayed on the monitor, and the inspector sets the apparatus condition to the optimum condition while looking at the diffraction image on the monitor. It was difficult for the inspector to judge, and there was a problem that the ability and skill of the inspector were required.
[0007]
By the way, if the apparatus conditions are not set to the optimum conditions, an angle shift occurs between the traveling direction of the diffracted light and the optical axis direction of the light receiving optical system. High quality inspection cannot be performed.
The object of the present invention is to automatically set the apparatus conditions to the optimum conditions easily and quickly without requiring the inspector to know the pitch of the repetitive pattern formed on the substrate (the object to be inspected). An object of the present invention is to provide a surface inspection apparatus capable of improving the performance.
[0008]
[Means for Solving the Problems]
The surface inspection apparatus according to the present invention includes an illuminating unit that illuminates a test object, an imaging unit that captures an object image based on diffracted light from the test object, a direction of illumination, and a direction of diffracted light from the test object. Tilting means for tilting the object relative to at least one of the above, a condition control means for setting or changing the tilting state due to tilting when the object image is picked up by the imaging means, and tilting by the condition control means The state of the image is changed little by little, the images captured by the imaging means are captured, the frequency distribution of the density values of the pixels of the image is obtained, and the frequency of the density included in the predetermined range is maximized in the frequency distribution A determination unit that determines the state of inclination as an optimum condition; a detection unit that captures an image of an object image captured by the imaging unit in a state set to the optimum condition and detects a defect of the object to be detected based on the image; Be equipped Those were.
[0009]
As described above, the determination unit determines the optimum condition of the tilt state by tilting , and the condition control unit automatically sets the tilt state to the optimum condition to capture the object image. Based on the image obtained from the imaging unit at this time Since the detection means detects the defect of the object to be inspected, a stable inspection result that does not depend on the ability or skill of the inspector can be obtained. In addition, since the optimum condition is determined based on the frequency distribution of the pixel values of the image obtained from the imaging means, it is possible to easily and quickly automatically set the inclination state .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings .
[0011]
As shown in FIG. 1, the surface inspection apparatus 10 according to the present embodiment includes an inspection stage 12 on which a wafer 11 that is an object to be inspected is placed, an illumination optical system 13 that illuminates the wafer 11 on the inspection stage 12, and illumination. A light receiving optical system 14 that receives diffracted light from the wafer 11 illuminated by the optical system 13 and an image processing device 15 are included.
Among these, the inspection stage 12 can be tilted within a predetermined angle range about an axis along the X direction (direction perpendicular to the paper surface) (angle adjusting means). Here, the direction parallel to the reference normal line (normal line 11a in the horizontal state) of the inspection stage 12 (wafer 11) is taken as the Z direction. A direction orthogonal to the X direction and the Z direction is defined as a Y direction.
[0012]
The illumination optical system 13 (illumination means) is a decentered optical system composed of a light source 21 and a concave reflecting mirror 22. The light source 21 emits a light beam L1 (wavelength λ is constant) in a visible range (0.4 μm to 0.7 μm). The exit surface of the light source 21 is located on the focal plane of the concave reflecting mirror 22. The concave reflecting mirror 22 is a reflecting mirror whose inner surface is a reflecting surface, and is disposed obliquely above the inspection stage 12. That is, the axis (optical axis O1) passing through the center of the concave reflecting mirror 22 and the center of the inspection stage 12 is arranged to be inclined by a predetermined angle (incident angle θi) with respect to the normal line 11a. Here, a surface (incident surface) including the optical axis O1 and the normal line 11a of the inspection stage 12 (wafer 11) is parallel to the YZ plane.
[0013]
In the above illumination optical system 13, the light beam L <b> 1 emitted from the light source 21 is reflected by the concave reflecting mirror 22, and then becomes a substantially parallel light beam (illumination light L <b> 2) and is irradiated onto the wafer 11 on the inspection stage 12. The illumination light L2 is a light beam in which the center line of the light beam reaching an arbitrary point on the wafer 11 is substantially parallel to the optical axis O1. With this illumination light L2, the entire surface of the wafer 11 is illuminated at a predetermined angle (incident angle θi).
[0014]
Here, the orientation of the wafer 11 in the XY plane is determined based on the orientation flat and the notch by an alignment mechanism and a transport mechanism (not shown), and the linear direction of the repetitive pattern formed on the surface is the optical axis O1. On the other hand, it is placed so as to be substantially orthogonal.
[0015]
For this reason, the illumination light L2 is incident on the repetitive pattern of the wafer 11 from the direction of 90 degrees. Then, from the repeated pattern of the wafer 11, diffracted light L3 is generated in various directions within the incident surface (YZ surface).
Here, the diffraction condition can be expressed by the following equation (1) using the wavelength λ and the incident angle θi of the illumination light L2, the diffraction angle φk and the diffraction order k of the diffracted light L3, and the pitch p of the repetitive pattern. .
[0016]
p (sinθi−sinφk) = kλ (1)
In the equation (1), the incident angle θi is defined as a positive angle direction on the incident side with reference to the normal line 11a of the wafer 11, and a negative angle direction on the reflection side. With respect to the diffraction angle φk, the angle direction seen on the incident side with reference to the normal line 11a of the wafer 11 is minus, and the angle direction seen on the reflection side is plus. With respect to the diffraction order k, the angle direction expected on the incident side with respect to the 0th-order diffracted light (regular reflection light) with k = 0 is positive, and the angular direction expected on the reflection side is negative.
[0017]
The diffracted light L3 is generated in directions of various diffraction angles φk that satisfy the above formula (1) with respect to the wavelength λ of the illumination light L2. However, any diffracted light L3 is included in the incident surface (YZ plane).
On the other hand, the light receiving optical system 14 is a decentered optical system including a concave reflecting mirror 23, a diaphragm 24, an imaging lens 25, and a CCD image sensor 26.
[0018]
The concave reflecting mirror 23 is a reflecting mirror similar to the concave reflecting mirror 22 described above, and is disposed obliquely above the inspection stage 12. In other words, the axis (optical axis O2) passing through the center of the concave reflecting mirror 23 and the center of the inspection stage 12 is arranged to be inclined by a predetermined angle (light receiving angle θd) with respect to the normal line 11a. Here, the optical axis O2 is always included in the incident plane (YZ plane).
[0019]
The diaphragm 24 is disposed on the focal plane of the concave reflecting mirror 23 located on the side of the inspection stage 12. The position of the diaphragm 24 is in the vicinity of the pupil of the light receiving optical system 14 and is conjugate with the exit surface of the light source 21 described above. The size of the diaphragm 24 is slightly larger than the diameter of the image of the light source 21 (light source image) formed on the pupil plane of the light receiving optical system 14.
The imaging lens 25 is disposed on an axis (optical axis O3) passing through the center of the diaphragm 24 and the center of the concave reflecting mirror 23. The imaging surface of the CCD imaging device 26 (imaging means) is located at the focal plane of the imaging lens 25.
[0020]
In the above-described light receiving optical system 14, the diffracted light L3 generated from the wafer 11 is reflected by the concave reflecting mirror 23 and then converges to reach the diaphragm 24 (the pupil of the light receiving optical system 14). Then, the diffracted light L3 that has passed through the diaphragm 24 is condensed on the imaging surface of the CCD imaging device 26 by the imaging lens 25. On the imaging surface of the CCD imaging device 26, an image of the wafer 11 (wafer image 11A shown in FIG. 2) is formed by the diffracted light L3.
[0021]
Here, in the wafer image 11 </ b> A, a large number of bright image portions 11 </ b> B corresponding to regions where the repeated pattern is formed on the wafer 11 and dark image portions 11 </ b> C corresponding to street lines on the wafer 11 appear. The CCD image pickup device 26 picks up a wafer image 11A (object image) and outputs an image signal to the image processing device 15.
By the way, in the surface inspection apparatus 10 of this embodiment, the illumination optical system 13 and the light receiving optical system 14 are fixed. Therefore, the incident angle θi and the light receiving angle θd can be adjusted by tilting the inspection stage 12 (wafer 11) by a predetermined angle (tilt angle φ) around the axis along the X direction. However, the sum of the incident angle θi and the light receiving angle θd is always constant (for example, 40 degrees).
[0022]
In the surface inspection apparatus 10, if the diffracted light L3 generated from the wafer 11 can be guided along the optical axis O2 of the light receiving optical system 14 (the diffraction angle φk in the equation (1) is made to coincide with the light receiving angle θd), the CCD A good wafer image 11A can be picked up by the image pickup element 26.
Whether the wafer image 11A picked up by the CCD image pickup device 26 is good depends on the apparatus conditions (tilt angle φ of the wafer 11) when the wafer image 11A is picked up. That is, if the tilt angle φ is set to the optimum condition (optimum tilt angle φs), a good wafer image 11A can be obtained. Incidentally, the optimum tilt angle φs differs depending on the pitch p of the repetitive pattern formed on the wafer 11.
[0023]
Next, the image processing device 15 will be described. Inside the image processing apparatus 15, a control unit 16, a condition determination unit 17 that determines the optimum tilt angle φs of the wafer 11, and a defect detection unit 18 that detects defects of the wafer 11 are provided.
Among these, the control unit 16 tilts the inspection stage 12 (wafer 11) about the axis along the X direction, thereby setting the apparatus condition (tilt angle φ) when the CCD image sensor 26 captures the wafer image 11A. Or change (condition control means). Specifically, when the optimum tilt angle φs of the wafer 11 is determined, the tilt angle φ of the wafer 11 is changed every predetermined angle (for example, 0.1 degree). Further, when the defect of the wafer 11 is detected, the tilt angle φ of the wafer 11 is set to the optimum tilt angle φs.
[0024]
Further, the control unit 16 converts the image of the wafer 11 obtained from the CCD image pickup device 26 into a digital image of predetermined bits (for example, 8 bits). This digital image is output to the condition determination unit 17 when the optimum tilt angle φs of the wafer 11 is determined, and to the defect detection unit 18 when a defect of the wafer 11 is detected.
When the optimum tilt angle φs of the wafer 11 is determined, the control unit 16 configured as described above captures the image of the wafer 11 while changing the tilt angle φ, and sequentially determines the conditions of the digital images when the tilt angle φ is different. To the unit 17.
[0025]
In determining the optimum tilt angle φs of the wafer 11, the condition determination unit 17 (determination unit) sequentially takes in digital images of the wafer 11 from the control unit 16, and all the pixels (512 × 512 pixels) for each digital image. The density value of each pixel is examined, the number of pixels is counted for each density value, and a frequency distribution of the density values of the pixels is created.
The frequency distribution of density values is obtained by determining the frequency (number of pixels) at which each density value pixel appears in one digital image. Incidentally, a graph showing the frequency distribution of density values is called a density histogram. When the digital image is 8 bits, the pixel density value is 256 steps (0 to 255).
[0026]
Further, the condition determination unit 17 does not have a distribution of density values equal to or higher than a predetermined density in the frequency distribution of density values corresponding to each digital image, and the total number of pixels included in a predetermined good range (target pixel) Count).
The creation of the frequency distribution and the counting of the number of pixels of interest are performed on a plurality of digital images having different tilt angles φ of the wafer 11. Then, the condition determining unit 17 compares the number of pixels of interest in digital images having different tilt angles φ (see FIG. 3), and the tilt angle φ of the digital image in which the number of pixels of interest has an extreme value Np (maximum value) is optimally tilted. The angle φs is determined.
[0027]
Information regarding the determined optimum tilt angle φs is output from the condition determination unit 17 to the control unit 16. The control unit 16 automatically sets the tilt angle φ of the wafer 11 to the optimum tilt angle φs determined by the condition determination unit 17 when the wafer 11 is inspected for defects.
The defect detection unit 18 (detection means) captures a digital image of the wafer 11 from the control unit 16 when performing defect detection on the wafer 11 and performs image processing. In addition, the defect detection unit 18 monitors the light quantity of the image and determines the wafer based on the brightness of the image. Eleven defect locations are identified.
[0028]
When the defect detection unit 18 detects a defect on the wafer 11, a good wafer image 11A is taken with the tilt angle φ of the wafer 11 set to the optimum tilt angle φs, so that a highly reliable inspection result can be obtained. In addition, since the optimum tilt angle φs is determined by the condition determining unit 17 and the tilt angle φ is automatically set to the optimum tilt angle φs by the control unit 16, a stable inspection result regardless of the ability or skill of the inspector can be obtained. You can also. Furthermore, since the frequency distribution of density values of each pixel constituting the digital image is created and the optimum tilt angle φs is determined, the apparatus conditions can be easily and quickly set automatically.
[0029]
In the above-described embodiment, the example in which the condition determining unit 17 creates the frequency distribution by examining the density values of all the pixels of each digital image has been described. However, a part included in an appropriate partial region in the image The frequency distribution may be created by examining the density values of the pixels. As a partial region of the image used for creating the frequency distribution, for example, a bright image portion 11B (FIG. 2) corresponding to a region on the wafer 11 where the repeated pattern is formed can be considered. Further, since each bright image portion 11B corresponds to each other, density values may be integrated between corresponding pixels, and a frequency distribution may be created based on the integrated value.
[0030]
In the above-described embodiment, the condition determination unit 17 determines the tilt angle φ of the digital image in which the number of pixels of interest in the frequency distribution has the extreme value Np as the optimum tilt angle φs (FIG. 3). The tilt angle φ of the digital image that has a predetermined number other than the extreme value may be determined as the optimum tilt angle φs.
Further, in the above-described embodiment, the condition determination unit 17 counts the number of target pixels from the frequency distribution of density values corresponding to each digital image, and determines the optimum tilt angle φs by comparing the number of target pixels. Not limited to. Since a bright image portion 11B and a dark image portion 11C appear in the wafer image 11A (FIG. 2), the frequency distribution of density values corresponding to each digital image has two peaks corresponding to the image portions 11B and 11C. It becomes a shape to include. Thus, for example, determine the contrast corresponding to a difference between the density value from the two peaks of the frequency distribution of the density value, Ru can also determine the optimal conditions by comparing the contrast. In this case, it is preferable to determine the tilt angle φ of the digital image that maximizes the contrast as the optimum tilt angle φs.
[0031]
In the above-described embodiment, the condition determination unit 17 determines the optimum condition based on the frequency distribution of the pixel density values. However, the condition determination unit 17 determines the frequency distribution of pixel values other than the density values (for example, the hue value and the saturation value). An optimum condition can also be determined based on this.
Furthermore, in the above-described embodiment, the apparatus in which the illumination optical system 13 and the light receiving optical system 14 are fixed has been described as an example. However, the illumination optical system 13 and the light receiving optical system 14 can be rotated around an axis along the X direction. It can also be configured. In this case, even if the wafer 11 (inspection stage 12) is fixed, by rotating at least one of the illumination optical system 13 and the light receiving optical system 14, apparatus conditions (at least one of the incident angle θi and the light receiving angle θd) are rotated. ) Can be adjusted.
[0032]
In the above-described embodiment, the apparatus configuration in which the wavelength λ of the illumination light L2 is constant has been described as an example. However, for example, a configuration in which the wavelength λ of the illumination light L2 is variable as in the surface inspection apparatus 40 illustrated in FIG. but the present invention is Ru can be applied. 4, the same components as those in FIG. 1 are denoted by the same reference numerals.
In the surface inspection apparatus 40, the light beam from the white light source 41 is irradiated to the wafer 11 through the spectroscopic element 42, the pinhole 43, and the illumination lens 44 (illumination light L2). The spectroscopic element 42 is configured by a prism, for example, and rotates about an axis along the X direction (direction perpendicular to the paper surface). The light beam from the white light source 41 is split by passing through the spectroscopic element 42, and only the light beam having a predetermined wavelength λ corresponding to the rotation angle of the spectroscopic element 42 is guided to the pinhole 43. Since the pinhole 43 is disposed on the focal plane of the illumination lens 44, the substantially parallel illumination light L2 is irradiated onto the wafer 11 at a predetermined angle.
[0033]
Then, the diffracted light L3 from the wafer 11 is condensed on the image pickup surface of the CCD image pickup device 26 via the light receiving lens 45 and the aperture stop 46. The aperture stop 46 is disposed in the vicinity of the pupil position of the light receiving lens 45.
In the surface inspection apparatus 40 configured in this way, the control unit 16 adjusts the wavelength of the illumination light L2 by rotating the spectroscopic element 42 around an axis along the X direction (direction perpendicular to the paper surface), An apparatus condition for capturing an image of the wafer 11 with the CCD image sensor 26 is set or changed.
[0034]
That is, when determining the optimum condition of the apparatus condition, the control unit 16 captures an image of the wafer 11 while changing the wavelength λ of the illumination light L2, and the condition determining unit selects a digital image when the apparatus condition (wavelength λ) is different. 17 to output.
Therefore, the condition determination unit 17 can determine the optimum condition (optimum wavelength λs) of the apparatus condition (wavelength λ) as in the case of the surface inspection apparatus 10 described above. Information on the determined optimum wavelength λs is output from the condition determining unit 17 to the control unit 16, and the wavelength λ of the illumination light L2 is automatically set to the optimum wavelength λs when the defect detection unit 18 inspects the defect of the wafer 11.
[0035]
As described above, when the defect detection unit 18 detects a defect on the wafer 11, a good wafer image 11A is captured in a state where the wavelength λ of the illumination light L2 is set to the optimum wavelength λs. can get. Further, since the optimum wavelength λφs is determined by the condition determining unit 17 and the wavelength λ is automatically set to the optimum wavelength λφs by the control unit 16, it is possible to obtain a stable inspection result regardless of the ability or skill of the inspector.
[0036]
【The invention's effect】
As described above, according to the surface inspection apparatus of the present invention, to determine the optimum conditions for the state of tilt by tilting the determining means, since the condition control means for setting the optimum state of the inclined, the object to be detected Even if the inspector does not know the pitch of the formed repetitive pattern, automatic setting of optimum conditions can be performed easily and quickly. In addition, an object image is captured in a state automatically set to the optimum condition, and the detection means detects a defect of the object to be detected based on the image obtained from the imaging means at this time, so it does not depend on the ability or skill of the inspector. A stable inspection result can be obtained, and the reliability of the inspection result can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a surface inspection apparatus 10;
FIG. 2 is a diagram showing an example of a wafer image 11A by diffracted light.
FIG. 3 is a graph showing the relationship between the number of pixels of interest in the frequency distribution and the tilt angle φ.
4 is a diagram showing a configuration of a surface inspection apparatus 40. FIG.
【The invention's effect】
DESCRIPTION OF SYMBOLS 10, 40 Surface inspection apparatus 11 Wafer 12 Inspection stage 13 Illumination optical system 14 Light reception optical system 15 Image processing apparatus 16 Control part 17 Condition determination part 18 Defect detection part 21, 41 Light source 22, 23 Concave reflector 24 Diaphragm 25 Imaging lens 26 CCD image sensor 42 Spectroscopic element 43 Pinhole 44 Illumination lens 45 Light receiving lens 46 Aperture stop

Claims (4)

Illuminating means for illuminating the test object;
Imaging means for imaging an object image based on diffracted light from the test object;
Tilt means for tilting the object relative to at least one of the direction of illumination and the direction of diffracted light from the object;
Condition control means for setting or changing the state of tilt due to tilting when the object image is captured by the image capturing means;
The condition control means changes the inclination state in small increments, captures images captured by the imaging means, obtains a frequency distribution of density values of pixels of the image, and includes the frequency distribution within a predetermined range. Determining means for determining, as an optimum condition, the state of the slope at which the frequency of the concentration is maximized;
Before SL captures an image of the object image captured by the imaging means in a state set to the optimum condition, characterized by comprising a detecting means for detecting a defect of the object to be inspected on the basis of the image Surface inspection device. The surface inspection apparatus according to claim 1 ,
The surface inspection apparatus, wherein the determining means determines the optimum condition based on a concentration difference between at least two peaks appearing in the frequency distribution. In the surface inspection apparatus according to claim 1 or 2 ,
The optical system included in the illumination unit and the imaging unit is fixed to the device,
The tilt means tilts the test object about an axis perpendicular to the optical axis of the optical system,
The surface inspection apparatus, wherein the condition control means sets or changes the state of the inclination according to an inclination angle of the object to be examined. In the surface inspection apparatus according to any one of claims 1 to 3 ,
A wavelength adjusting means for adjusting the wavelength of the illumination light emitted from the illumination means to the object to be examined;
The condition control means adjusts the wavelength condition by said wavelength adjusting means, equipment condition setting or surface inspection apparatus characterized by making changes.

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