JP2008014714A - Flaw inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flaw inspection method which enables the certain and easy extraction of a defocusing region by photographing the image of an inspection target, especially the regular reflected image thereof. <P>SOLUTION: In the flaw inspection method is constituted so as to inspect the flaw of the inspection target using an imaging system equipped with an irradiator for irradiating the inspection target with illumination light and an imaging device for photographing the image of the inspection target on the basis of at least the light from the inspection target, and includes the step of calculating the incident angle of the irradiator, which satisfies a condition for totally reflecting the illumination light by the surface of the inspection target and the imaging angle of the imaging device, which images a diffracted light at this time, using a flaw-free target and storing the incident angle and the imaging angle along with a reference image and the step of setting the illumination angle of the irradiator to the incident angle and imaging the inspection target at the imaging angle of the imaging device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a defect inspection method.

  For example, in a semiconductor manufacturing process, macro inspection is performed to detect scratches, dust, unevenness, dirt, and the like on the surface of a semiconductor wafer. In this macro inspection, the surface of the semiconductor wafer is irradiated with illumination light, an image of the specularly reflected light, diffracted light, interference light, or the like is picked up by an image pickup device, and the image data is subjected to image processing to thereby damage the surface of the semiconductor wafer. , Dust, unevenness, dirt, and the like are detected (see, for example, Patent Document 1: Japanese Patent Laid-Open No. 9-61365).

In the inspection of a semiconductor wafer as described above, a method of capturing an image by diffracted light from a wafer pattern is generally performed to image defocusing of the semiconductor wafer. However, in the inspection using diffracted light, it is impossible to distinguish between the diffracted light from the surface layer and the diffracted light from the lower layer (underlying layer), so that it takes time and effort to create an imaging recipe. is there.
JP-A-9-61365

  An object of the present invention is to provide a defect inspection method capable of reliably and easily extracting a defocused part by capturing an image of an inspection object, particularly a specular reflection image.

  The invention according to an aspect of the present invention uses an imaging system that includes an irradiation device that illuminates an inspection target and an imaging device that captures an image of the inspection target based on at least light from the inspection target. In the defect inspection method for performing the defect inspection of the inspection object, the incident angle of the irradiation device that satisfies the condition that the illumination light is totally reflected on the surface of the inspection object using the object having no defect, and the diffracted light at that time The imaging angle of the imaging device capable of imaging the image is obtained, the incident angle and the imaging angle are stored together with a reference image, the illumination angle of the irradiation device is set to the incident angle, and the imaging Imaging an inspection object at an imaging angle of the apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, the defect inspection apparatus which can image stably the diffracted light by a surface pattern without being influenced by the diffracted light by a base pattern can be provided. In addition, defocus inspection can be performed without imaging diffracted light, and defect extraction can be performed even when diffracted light does not come out of the wafer surface due to pattern pitch miniaturization.

Embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of a defect inspection apparatus applied to the defect inspection method according to the first embodiment of the present invention. 2 is a cross-sectional view taken along the line 2-2 of FIG.

  As shown in FIG. 1, the defect inspection apparatus includes an illumination unit 30 capable of linear illumination, and an imaging unit 35 provided corresponding to the illumination unit 30 and in which imaging elements are arranged in a line. ing. An inspection object 31 such as a glass substrate or a semiconductor wafer is placed on a mounting table (inspection stage) (not shown) that can move in the direction of arrow X, for example. Then, light emitted from the illumination unit 30 (hereinafter referred to as “incident light” in the present specification. The optical axis of the incident light is referred to as “incident optical axis”) is applied to the inspection object 31, Light that is specularly reflected, diffracted or interfered from the inspection object 31 (hereinafter simply referred to as “reflected light” in the present specification, and the optical axis of the reflected light is referred to as “reflected optical axis”) is input to the imaging unit 35. Based on the image incident and imaged by the imaging unit 35, a defect inspection is performed to determine whether the surface of the inspection object 31 has a defect, the type of defect, and the quality of the inspection object. In this case, the inspection object 31 is scanned by the illumination unit 30 and the imaging unit 35 while moving the inspection object 31 at a constant speed in the X direction. An image of the surface can be acquired.

Lighting unit 30 is provided with a line illumination portion 32 and the cylindrical lens 33 and illuminates the surface of the test object 31 at an incident angle theta ₁ with respect to the inspection object 31. A light source for illumination is connected to the illumination unit 30 via an optical fiber bundle 32a, and a lamp house having a halogen lamp, a heat ray absorption filter, and a condenser lens inside is used as the illumination light source. ing. The line illumination unit 32 is configured by linearly arranging one or more end faces of the fiber bundle 32a, and a cylindrical lens 33 is disposed at a position spaced parallel to the end face.

When obtaining a specular reflection image, the reflection optical axis of the imaging unit 35 is set to a reflection angle θ ₂ that is the same as the incident angle of the incident optical axis of the illumination unit 30. The imaging unit 35 includes a rod lens array 36 and a linear image sensor 37. The rod lens array 36 forms an image of a linear region of the inspection object 31 illuminated by the illumination unit 30 on the linear image sensor 37.

  In addition, a filter unit 34 is disposed on the reflected optical axis, and allows only light having a specific wavelength among the reflected light from the inspection object 31 to pass therethrough. The filter unit 34 can pass light of a desired wavelength by arbitrarily putting in and out a band pass filter of a plurality of wavelengths on the optical axis.

Note that the incident angle θ ₁ of the illumination unit 30 and the reflection angle θ ₂ of the imaging unit 35 are variable, and can be changed stepwise or continuously for each predetermined angle.

In the defect inspection apparatus configured as described above, the optical system is set so as to image the emitted light with the exit angle θ _{2 on} the wafer surface when the wafer surface is illuminated with the incident angle θ ₁ . Here, when θ ₁ = θ ₂ , so-called regular reflection light is imaged. In this case, FIG. 3 shows luminance change characteristics on the wafer with respect to the imaging angle when the imaging angle and the illumination angle are changed in the range of −90 ° ≦ θ ₁ = θ ₂ ≦ 90 ° and the wafer is imaged. The characteristic shape varies depending on the wafer pattern.

  In FIG. 3, the luminance in the portion to the left of the portion A (imaging angle of about 52 degrees) is a characteristic like a sine wave that vibrates at a period that is an influence of an interference phenomenon with light transmitted through the wafer surface and reflected by the base. Indicates. In this case, the absolute value of the brightness is different due to the influence of the wavelength sensitivity characteristic of the camera and the wavelength component of the illumination light. However, in the portion to the right of part A (that is, when the imaging angle is greater than about 52 degrees), the luminance is substantially equal or higher even if the imaging angle changes. This means that there is no component transmitted through the surface layer of the wafer, and total reflection occurs in the surface layer of the wafer.

  Accordingly, when the wafer surface pattern is illuminated at an angle that causes total reflection and the diffracted light at that time is imaged by the camera, only the diffracted light from the surface pattern can be imaged. In other words, by illuminating the wafer surface pattern at a totally reflecting angle and imaging the diffracted light, it is possible to stably image the diffracted light only on the surface without erroneously imaging the diffracted light of the base. it can. The specific processing flow is as follows.

First, an incident angle θ ₁ that satisfies the condition that the illumination light is totally reflected on the wafer surface at the time of recipe creation and a camera angle θ ₂ that can capture the diffracted light at that time are obtained, and a storage unit (not shown) is set as a setting parameter. Remember it. Further, the non-defective wafer image at that time is stored as reference wafer data.
Next, an illumination angle is set to an angle θ ₁ stored in advance in the recipe, and a camera angle is set to θ ₂ to image a wafer to be inspected.
Then, defect extraction is performed by comparing the imaged wafer image to be inspected with reference wafer data. Determine good / bad of wafer to be inspected.

  As described above, by stably imaging only the diffracted light on the surface due to total reflection, the diffracted light by the underlayer of the wafer is not erroneously imaged.

(Second Embodiment)
Since the configuration of the defect inspection apparatus according to the second embodiment is the same as that of the first embodiment, illustration and description thereof are omitted.
As described above, when the optical system is set for regular reflection imaging, and the imaging angle and illumination angle are changed by the same angle with respect to the wafer in this state, the characteristics shown in FIG. 3 are obtained. However, it is known that the normal pattern portion and the defocus portion show different luminance change characteristics when the imaging angle is changed, as shown in FIG. 4, for example. In FIG. 4, a solid line indicates a change in luminance in the normal pattern, and a broken line indicates a change in luminance in the defocus pattern.

  In the defect inspection by the conventional reference wafer comparison method, the defect is basically extracted by the luminance difference between one captured image and one reference image. If this luminance difference is small, other parts are extracted. There is a high possibility that the defect will be overlooked by being buried in the pseudo defect. However, by giving each pixel of the captured image also characteristic information as shown in FIG. 4, the feature of the pixel can be emphasized. For this reason, it becomes possible to extract a defective part stably by imaging regular reflection light, without imaging diffracted light. The specific processing flow of the second embodiment is as follows.

  First, when the recipe is created with the optical system in the state for specular reflection imaging, the luminance change characteristics in each pixel when the imaging angle and illumination angle are changed by the same angle with respect to the wafer are obtained, and each pixel unit is obtained. The luminance change characteristic is stored. Here, the characteristic (that is, the change in luminance with respect to the imaging angle) differs between the defective part and the normal part.

  At the time of defect extraction, the difference between the defective part and the normal part is detected by comparing the reference image and the captured image with not only the luminance comparison but also the difference in the shape of the luminance change characteristic. As a result, the defocused part can be extracted by imaging the specularly reflected light.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements.

  In addition, for example, even if some structural requirements are deleted from all the structural requirements shown in each embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the effect of the invention Can be obtained as an invention.

It is a figure which shows schematic structure of the defect inspection apparatus applied to the defect inspection method which concerns on the 1st Embodiment of this invention. It is 2-2 sectional drawing of FIG. It is a figure which shows the luminance change characteristic on a wafer with respect to the imaging angle when the imaging angle and the illumination angle are changed in the range of −90 ° ≦ θ ₁ = θ ₂ ≦ 90 ° to image the wafer. It is a figure which shows the example from which the change characteristic of a brightness | luminance when changing an imaging angle is different.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 ... Illumination part 31 ... Test object 32 ... Line illumination part 32a ... Optical fiber bundle 33 ... Cylindrical lens 34 ... Filter part 35 ... Imaging part 36 ... Rod lens array 37 ... Linear image sensor

Claims (4)

Defect inspection of the inspection object using an imaging system including an irradiation device that illuminates the inspection object and an imaging device that captures an image of the inspection object based on at least light from the inspection object In the defect inspection method to be performed,
Using an object having no defect, the incident angle of the irradiation device that satisfies the condition that the illumination light is totally reflected on the surface of the inspection object, and the imaging angle of the imaging device capable of imaging the diffracted light at that time Determining and storing the incident angle and the imaging angle together with a reference image;
And setting the illumination angle of the irradiation device to the incident angle, and imaging the inspection object at the imaging angle of the imaging device. Defect inspection of the inspection object using an imaging system including an irradiation device that illuminates the inspection object and an imaging device that captures an image of the inspection object based on at least light from the inspection object In the defect inspection method to be performed,
Capturing a reference image while changing an incident angle of the irradiation device and an imaging angle of the imaging device using an object having no defect, and obtaining a first luminance change characteristic for each pixel;
Capturing an inspection image of the inspection object under the same conditions as the object having no defect to obtain a second luminance change characteristic for each pixel;
Comparing the first luminance characteristic with the second luminance characteristic, a defect inspection method comprising: The defect inspection method according to claim 2, further comprising a step of comparing luminance for each pixel. 4. The defect inspection method according to claim 2 or 3, wherein the incident angle and the imaging angle are set to the same angle.

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