JP2008008740A - Method for detecting defect, and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a defect such as foreign matter or deposit on the surface of an inspection object and an internal hollow defect, distinctively with high resolution. <P>SOLUTION: A laser emitted from a laser device 5 is polarized through an analyzer 6 and allowed to enter the inspection object W from an oblique direction, and scattered light SB is imaged by a CCD camera installed on a dark field through an analyzer 8 arranged in a cross Nicol state, and the intensity of the scattered light is determined from acquired image data. The inspection object can be switched into the state where an ultrasonic wave is not applied or into the state where the ultrasonic wave is applied. The scattered light is detected and its intensity is determined in the state where the ultrasonic wave is not applied to the inspection object and in the state where the ultrasonic wave is applied thereto, respectively. It is determined that, when the difference between both intensities of the scattered light exceeds a prescribed threshold, the scattered light is generated from a hollow defect in the inspection object, and that when the difference does not exceeds the threshold, the defect belongs to another kind. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for detecting a defect in an object to be inspected and an apparatus therefor, and more particularly to a method for determining whether or not a defect in an object to be inspected such as a semiconductor wafer is an internal cavity defect and an apparatus therefor.

  In a semiconductor manufacturing process, a defect existing inside a wafer causes deterioration of electrical characteristics and a defect of a semiconductor device as a product. Therefore, when manufacturing a semiconductor device, a defect is inspected for a wafer in a stage before semiconductor manufacturing or a wafer that has been subjected to process processing on the surface after entering the manufacturing process. If a process is performed on a wafer having a defect as it is, it becomes a defective product as a final semiconductor product. Therefore, it is necessary to remove the defect.

  In recent years, as the degree of integration of semiconductor devices increases and the miniaturization of patterns constituting the devices progresses, the size of the defect of the wafer to be detected also becomes smaller, and thus a higher defect detection capability is required. In addition, there are destructive methods and non-destructive methods for detecting defects. In the former case, the defects are exposed to the surface by melting the wafer with an etching solution or physically scraping it, and observed with a microscope or an electron microscope. Is. However, the wafer inspected by this method cannot be used for manufacturing semiconductor devices.

  Non-destructive inspection methods include electrical methods and non-contact inspection methods using light and ultrasonic waves. The electrical inspection method applies an electrical signal to the wafer by attaching an electrode to the wafer or pressing a probe, and detects the presence of a defect in the wafer from a change in the electrical signal. It is difficult to determine the position of the substrate, and contact with an electrode or the like may be necessary, so that it cannot be used for a wafer in a product manufacturing stage.

  Defect detection using ultrasonic waves is a method in which ultrasonic waves are applied to an object to be inspected and ultrasonic waves reflected from the defects are detected by a detector. It can be used to detect defects inside materials that do not transmit light, such as metal, so it is used for inspection inside packages, but it is used to detect wafer defects and foreign matter with high resolution in terms of detection limit and resolution. I will not.

  In the inspection method using light, light scattered by a defect or foreign matter is detected by a dark field or bright field optical system, and the position of the defect is detected simultaneously. A laser transparent to silicon is used to detect defects inside the wafer, and a visible light laser is used to detect defects on the surface or surface layer.

A defect inspection using light and ultrasonic waves is disclosed in the following documents.
Japanese Patent Laid-Open No. 62-177447 JP 2001-208729 A JP 2005-147813 A JP 2002-188999 A JP-A-11-21668 JP 2000-216208 A Japanese Patent Laid-Open No. 10-293101 Japanese Patent Laid-Open No. 10-293102 Japanese Patent No. 3664134

  In Patent Document 1, an electromagnetic ultrasonic wave is transmitted to an object to be inspected, and a laser is directed to the same part as the excitation part of the object to be inspected by the ultrasonic wave. Are described for ultrasonic flaw detection methods for inspection objects such as pipes and steel materials.

  In Patent Document 2, surface acoustic waves are incident on an object to be inspected from an ultrasonic transducer, a laser is irradiated on the surface of the object to be inspected, and the reflected light is received. There is described a defect detection apparatus that detects a frequency difference between emitted light and reflected light, and detects a defect by measuring a vibration speed of an inspection object based on the difference.

  In Patent Document 3, a surface of an object to be measured is irradiated with a pulse laser to generate an elastic wave, and a laser for a continuous wave signal is irradiated on the surface of the object to be measured coaxially with the pulse laser. A material nondestructive inspection method and apparatus for detecting an internal defect of an object to be measured by detecting a change in a frequency component by entering reflected light affected by a scattering surface and an elastic wave into a laser interferometer is described. .

  In Patent Document 4, a laser is irradiated on an inspection object such as a semiconductor wafer, reflected and scattered light from the inspection object is detected in a plurality of directions, and the directivity of the reflected and scattered light is detected by comparing the detection results. Describes that a defect such as a flaw in an object to be inspected and a foreign object are distinguished from each other.

  In Patent Document 5, a laser is incident on a sample to be inspected, and the scattered light and emitted light are divided into a plurality of different wavelength bands to form an image on an imaging device, and the content of the defect is identified from the obtained plurality of images. Describes defect inspection methods.

  Patent Document 6 irradiates two pulsed lasers with different incident angles and shifted oscillation timings on the surface of a semiconductor wafer or the like, and one of the lasers scatters both particles and pits. An inspection method is described in which the other laser is set so that the scattered light from the pits is reduced, and the particle or pit is discriminated from the detection result of both scattered lights.

  In Patent Documents 7 and 8, the wavelength λ1 at which the reflectance R becomes a maximum value and the wavelength λ2 at which the reflectance R becomes a minimum value when the wavelength of the laser incident on the test object is changed are obtained, and the wavelengths λ1, λ2 are obtained. By detecting optical information when each laser is incident on the object to be detected, a defect detection method for distinguishing between defects near the surface of the object to be detected and defects on the surface, and in that case, It is described that a scattered image of a defect is observed as a whole with a microscope in which a laser is incident obliquely on an object to be examined and arranged above.

  In Patent Document 9, a laser beam is irradiated on a wafer surface to scan, and light reflected or scattered on the wafer surface is received by a plurality of light receiving systems having different light receiving angles (high angle and low angle) with respect to incident light. A method for inspecting the surface of a semiconductor wafer in which a difference in standard particle conversion size based on a ratio of received light intensity in a plurality of light receiving systems is obtained to determine the form and type of a defect is described.

  In Patent Documents 1 and 2, internal cavity defects cannot be detected with high resolution. In Patent Document 3, the presence or absence of an internal defect is detected, but the influence of the scattering surface of the material surface due to ultrasonic waves is detected by signal light, which is suitable for nondestructive inspection of concrete structures. It is not suitable for detecting internal defects such as high resolution.

  In Patent Documents 4 and 5, the content of the defect is identified from the relationship between the directivity of reflected / scattered light and the wavelength band, but it is not suitable for accurately detecting the internal defect. Further, in Patent Document 6, since the two pulse lasers are irradiated at different timings, the configuration and the control mechanism become complicated, and even if surface defects such as particles and pits can be detected, internal cavity defects It is not suitable for detecting.

In Patent Documents 7 and 8, surface defects and internal defects are distinguished and detected based on the difference in wavelength, but it cannot be determined whether or not the defects are internal cavity defects.
In Patent Document 9, the type and form of the defect on the wafer surface are determined from the combination of numerical values of the standard particle equivalent size of the scatterer based on the scattered light intensity ratio at different light receiving angles. It cannot be determined.

  As described above, the internal cavity defect can be detected with high resolution in the inspection of the defect of the inspection object such as the semiconductor wafer in the conventional electrical inspection or the inspection of the defect using light or ultrasonic wave. I couldn't. In the case of an object to be inspected such as a semiconductor wafer, the removal method differs depending on the type of defect, so it is necessary not only to have a defect on the wafer but also to determine the type of defect along with it. There has been a need for a detection method and a detection apparatus that can detect defects such as foreign matters and precipitates on the body surface and internal cavity defects with high resolution.

The present invention has been made to solve the above-described problems, and the defect detection method according to the present invention penetrates into the inspected body in a state where no ultrasonic wave is applied and a state where an ultrasonic wave is applied. Detection means installed in a dark field via an analyzer arranged in crossed Nicols by irradiating a laser beam of a wavelength that can be polarized by a polarizer and then irradiating a position on the surface of the object to be inspected. A method for detecting defects in an object to be inspected by
Irradiating a laser in an oblique direction with a predetermined angle at a position on the surface of the object to be inspected without applying ultrasonic waves to the object to be inspected, and detecting the scattered light to obtain an intensity;
The laser is obliquely formed at the same predetermined angle at the same position on the surface of the object to be inspected as the laser is incident with the ultrasonic wave being applied to the object to be inspected and the ultrasonic wave not being applied. To detect the scattered light and obtain the intensity,
Both scatterings are obtained by calculating the difference between the intensity of scattered light obtained without applying ultrasonic waves to the object to be inspected and the intensity of scattered light obtained with ultrasonic waves applied to the object to be inspected. When the difference in light intensity exceeds a predetermined threshold, the scattered light is due to a cavity defect in the inspected body, and when it does not exceed the threshold, it is determined that it is another type of defect,
It consists of
The object to be inspected may be a silicon wafer used for semiconductor manufacturing, and an internal cavity defect may be detected using infrared light.

Further, an apparatus for inspecting a defect according to the present invention includes a support part of an inspection object, an ultrasonic generator for applying ultrasonic waves to the inspection object, and the inspection object supported by the support part. A laser device for irradiating a body with a laser via a polarizer, a drive unit for relatively moving the object to be inspected and the laser device, and a crossed Nicols laser scattered light emitted to the object to be inspected The scattered light detecting means arranged in the dark field so as to receive light through the analyzer arranged in the and the arithmetic processing for calculating the scattered light intensity from the scattered light data received by the scattered light detecting means And a control unit, wherein the control unit switches between the state in which the ultrasonic wave is not applied to the object to be inspected and the state in which the ultrasonic wave is applied, and the operation processing unit does not apply the ultrasonic wave. The difference between the intensity of scattered light and the intensity of scattered light when an ultrasonic wave is applied is obtained, and control is performed to determine whether the scattered light is due to a cavity defect inside the object to be inspected. It is a thing.
The laser apparatus may include an infrared laser for inspecting a defect inside the object to be inspected and a visible light laser for inspecting a surface layer of the object to be inspected.

  In the present invention, when irradiated with a polarized laser with ultrasonic waves applied to the object to be inspected, strong scattered light that does not preserve the polarization state is generated in the internal cavity defect, and the polarization state is generated in the other defects. Can be used to distinguish whether a defect is a cavity defect inside the object to be inspected, a foreign object on the surface, a precipitate, or the like, and detect the defect in the object to be inspected with high resolution. .

  A method for detecting a wafer defect according to the present invention will be described. In the present invention, the surface of an object to be inspected such as a wafer is irradiated with a laser, and the scattered light is measured and analyzed to detect defects. In particular, a laser having a wavelength that can penetrate into the object to be inspected is irradiated. Thus, the cavity defect in the inspected body is detected.

  In the case of detecting an internal defect with respect to a silicon wafer as an object to be inspected, an infrared laser that can penetrate to a required depth in the silicon wafer is used as the laser. A laser beam polarized by a polarizer (polarizer) is irradiated to the wafer surface obliquely with respect to the wafer surface, and the scattered light from the wafer is detected by light detection means arranged in a dark field. At that time, an analyzer (analyzer) is arranged in front of the light detection means so as to be crossed Nicols, and a change in the polarization state is detected. Also, a means for applying an ultrasonic wave to the inspection location of the wafer is provided, and the scattered light is detected between the case where the ultrasonic wave is not applied to the wafer and the case where the ultrasonic wave is applied to the same inspection location. The difference in the scattered intensity distribution is detected.

  In the case of a cavity defect inside the crystal, it is known that scattered light due to the defect inside the crystal preserves the polarization direction of the incident light when no ultrasonic wave is applied to the wafer. For this reason, in the two-dimensional photodetection device, the scattered light is hardly transmitted by the analyzer arranged in the crossed Nicols on the front side. However, in a state where ultrasonic waves are applied to the wafer, strong scattered light is generated in the two-dimensional photodetection device, and this scattered light changes its polarization state, so that it passes through an analyzer arranged in crossed Nicols. In this way, the intensity of scattered light from the detected wafer differs between the state in which no ultrasonic wave is applied and the state in which it is applied, but this changes the polarization state of the scattered light in the state in which the ultrasonic wave is applied. It is because.

  Considering further that the polarization state of scattered light differs depending on whether or not ultrasonic waves are applied to the wafer, since the elastic modulus of the cavities and silicon differs greatly in the cavity defect (COP) inside the crystal, When applied, an elastic strain is generated in the vicinity. The cavity defect inside the crystal is generally octahedral, and stress is concentrated particularly near the corner of the cavity. Due to the strain field in the crystal structure near the local cavity, the scattered light is normally scattered by the scattered light. In the case of a cavity defect inside the crystal, the polarization state of the scattered light changes with respect to the incident light due to the action of ultrasonic waves. Occurs. Therefore, with respect to the scattered light due to the cavity defects inside the crystal, the intensity of the scattered light that passes through the analyzer disposed in crossed Nicol with the ultrasonic wave applied is increased.

  On the other hand, in the case of foreign matters on the surface of the wafer, it is known that the polarization state changes during scattering, unlike internal cavity defects. However, in the case of foreign matter on the surface, since the surroundings are vacuum or gas, the photoelastic effect when the ultrasonic wave is applied is weak, and the polarization state is not particularly changed by applying the ultrasonic wave.

  As described above, when the difference in intensity of the scattered light between the state where no ultrasonic wave is applied and the state where the ultrasonic wave is applied is large enough to exceed a certain threshold, the scattered light is due to a cavity defect inside the crystal. In addition, if the intensity of scattered light transmitted through an analyzer placed in crossed Nicols does not change between when the ultrasonic wave is not applied and when it is applied, this scattered light is considered to be due to surface foreign matter or precipitates. .

FIG. 1 shows a cross view of laser light scattered on a wafer of laser light polarized by a polarizer with respect to cavity defects inside the crystal and precipitates on the surface when the frequency of ultrasonic waves applied to quartz (SiO ₂ ) is changed. It shows how the intensity detected via an analyzer located in Nicol changes. The intensity of the scattered light due to the precipitate does not change greatly depending on the frequency of the ultrasonic wave, but the intensity of the scattered light due to the internal cavity defect has a high peak when the frequency of the ultrasonic wave is close to 90 kHz.

  In the present invention, as described above, whether or not the polarization direction of the scattered light changes due to the photoelastic effect when ultrasonic waves are applied to the wafer is detected, and the scattered light is due to a cavity defect inside the crystal. Or a method of discriminating whether it is due to foreign matter or precipitates on the surface.

  Scattered light is not generated at a position where there is no defect when the laser beam is irradiated on the wafer surface, and therefore the scattered light is not detected by the two-dimensional light detection means arranged in the dark field. Scattered light is detected by a two-dimensional light detection means at a place where there is a defect, and the scattered light is detected as an image in which bright spots due to scattered light on a black background are unevenly distributed as shown in FIG. The intensity of each spot in the image is measured and the integrated intensity value is calculated to obtain the scattered light intensity that characterizes the defect. At the same time, the scattered light intensity is obtained, that is, the data of the position where the defect exists is acquired and stored in the storage means.

  In this way, the operation of storing the intensity of the scattered light and the position where the defect exists by irradiating the surface of the wafer with the laser and storing the data in the storage means is performed in a state where the ultrasonic wave is not applied to the wafer and the wafer. Each is performed for the state in which the sound wave is applied. After that, compare the scattered light intensity at the same position on the wafer with no ultrasonic wave applied and the scattered light intensity when an ultrasonic wave is applied to find the difference, and whether the difference exceeds a certain threshold Determine whether or not. The threshold value is appropriately set to, for example, a value of 50% with respect to the peak value in the ultrasonic frequency-scattering intensity cavity defect graph shown in FIG. When such a threshold value is exceeded, it is determined that there is an internal cavity defect at that position, and when the threshold value is not exceeded, it is assumed that the defect is other than that.

  There is a difference in penetration depth from the surface when irradiated by the wavelength of the laser, and the wavelength of the laser is selected depending on the depth of observation from the surface of the wafer. In the case of a visible light laser, it is about several microns from the surface, whereas in the case of an infrared light laser, it extends to the entire inside of the wafer, so that it is suitable for detection of cavity defects inside the wafer. In addition, in the case of a wafer during the device manufacturing process, a metal pattern or the like is formed inside, and when an infrared laser reaching the inside of the wafer is irradiated, strong scattering occurs from the internal metal part, and defects can be detected. Since it becomes difficult, it is preferable that only a surface layer defect caused by a visible light laser be detected.

FIG. 3 shows a flow of a process for detecting a defect of a wafer as an object to be inspected. The object to be inspected is the same as that other than the wafer. In the case of a silicon wafer before the device manufacturing process, a silicon oxide film coated on the surface or a pattern is formed in the manufacturing process. It may be the case. As the laser to be irradiated, visible light is used when inspecting defects on the surface layer of the wafer, and infrared light is used when inspecting defects inside the wafer. In the case where a wiring pattern or the like is formed inside the wafer, when an infrared laser penetrating the inside of the wafer is irradiated, strong scattered light is generated and it becomes difficult to inspect the defect. .
1 shows the case of quartz (SiO ₂ ), the peak position of the internal cavity defect differs depending on the material of the object to be inspected. As the ultrasonic wave to be applied, it is necessary to apply an ultrasonic wave having a frequency at which the scattered light has a peak due to an internal cavity defect to the material to be inspected.

[Defect detection equipment]
A description will be given with reference to FIG. 4 showing one embodiment of an apparatus for detecting defects of a wafer as an object to be inspected according to the present invention. In FIG. 4, reference numeral 1 denotes a pedestal unit, which includes a drive source 3 and a drive mechanism for driving the stage 2 on which the wafer W is placed. In the stage 2, a hole 2 a is formed in the lower part of the wafer, and the ultrasonic generator 4 is provided so as to be close to the lower side of the placed wafer W. The stage 2 is driven by a driving source 3 so as to scan the wafer W two-dimensionally in a horizontal plane via a driving mechanism (not shown).

  The laser device 5 is disposed above the surface of the wafer W, and the laser LB emitted from the laser device 5 irradiates the surface of the wafer W in an oblique direction via a polarizer (polarizer) 6 disposed on the front side. It is like that. The scattered light SB on the surface of the wafer W is imaged by a CCD camera 7 as a two-dimensional light detection means arranged in a dark field through an analyzer (analyzer) 8 arranged in front of the cross Nicol.

  The drive source 3, the ultrasonic generator 4, the laser device 5, and the CCD camera 7 are controlled in response to control signals supplied from the control unit 10. Image data of scattered light picked up by the CCD camera 7 is supplied to the image acquisition unit 11, and data indicating the wafer position by an encoder or the like provided in the drive source 3 is supplied to the image acquisition unit, and laser irradiation is performed. Thus, the image data and the position of the wafer W when the scattered light is imaged are associated with each other. Reference numeral 12 denotes a storage unit that stores and holds the image data of the scattered light and the position of the wafer W that are associated with each other. Reference numeral 13 denotes an integrated intensity value of the scattered light spot from the image data held in the storage unit. An arithmetic circuit unit that calculates and determines a difference in the integrated intensity value of the scattered light spot among a plurality of image data, and determines whether or not the difference is larger than a threshold value. Reference numeral 14 denotes a display unit that displays the results of calculation and discrimination by the arithmetic circuit unit 13.

  The control unit 10 supplies control signals to the drive source 3, the ultrasonic generator 4, the laser device 5, and the CCD camera 7 to control their operations, and signals indicating the position of the wafer from the drive source 3, CCD The operation of the image acquisition unit 11, the storage unit 12, the arithmetic circuit unit, and the display unit 14 that receive the image signal of scattered light from the camera 7 is controlled as a whole. These may be configured as hardware, but can also be configured using a general-purpose personal computer and software for processing image data.

  In FIG. 4, only one laser device 5 is shown. In particular, when inspecting for cavity defects inside the wafer, an infrared laser device may be used. However, when also inspecting the surface layer of the wafer, a visible light laser is additionally provided and selectively used. To be able to. In addition, although the wafer is mounted on a stage that is driven and controlled on the base unit 1, scanning may be performed by moving the laser device while the wafer is fixed. it can. In this case, the drive source 3 and the drive mechanism are provided on the drive unit side of the laser device.

  The present invention distinguishes and detects surface foreign matter, precipitates, and internal cavity defects when inspecting the presence or absence of defects in an inspection object including a semiconductor wafer, and evaluates the quality of the inspection object and removes defects. It can be used to determine how.

Scattered light intensity detected through an analyzer in which the scattered light of the laser polarized by the polarizer was placed in crossed Nicols when the frequency of the ultrasonic wave applied to the crystal was changed. It is a graph which shows the change of. It is a figure which shows roughly the condition of the scattered light by the to-be-inspected object detected by the two-dimensional light detection means. It is a flowchart which shows the process of detecting the defect by this invention. It is a figure which shows one form of the apparatus for test | inspecting the defect by this invention.

Explanation of symbols

1 stand 2 stage 3 drive source 4 ultrasonic generator 5 laser device 6 polarizer 7 CCD camera 8 analyzer 10 control unit 11 image acquisition unit 12 storage unit 13 arithmetic circuit unit 14 display unit W wafer LB laser SB scattered light

Claims (4)

In a state where no ultrasonic wave is applied and in a state where an ultrasonic wave is applied, a laser beam having a wavelength that can penetrate into the inspected body is polarized by a polarizer and irradiated to a position on the surface of the inspected object. A method for detecting a defect of an object to be inspected by detecting the intensity of scattered light with a detecting means installed in a dark field via an analyzer arranged in crossed Nicols,
Irradiating a laser in an oblique direction with a predetermined angle at a position on the surface of the object to be inspected without applying ultrasonic waves to the object to be inspected, and detecting the scattered light to obtain an intensity;
The laser is obliquely formed at the same predetermined angle at the same position on the surface of the object to be inspected as the laser is incident with the ultrasonic wave being applied to the object to be inspected and the ultrasonic wave not being applied. To detect the scattered light and obtain the intensity,
Both scatterings are obtained by calculating the difference between the intensity of scattered light obtained without applying ultrasonic waves to the object to be inspected and the intensity of scattered light obtained with ultrasonic waves applied to the object to be inspected. When the difference in light intensity exceeds a predetermined threshold, the scattered light is due to a cavity defect in the inspected body, and when it does not exceed the threshold, it is determined that it is another type of defect,
A method for detecting a defect characterized by comprising:   The method for detecting a defect according to claim 1, wherein the object to be inspected is a silicon wafer used for semiconductor manufacture, and an internal cavity defect is detected using infrared light.   A support part of the object to be inspected, an ultrasonic generator for applying an ultrasonic wave to the object to be inspected, a laser apparatus for irradiating the object to be inspected supported by the support part via a polarizer, and A dark field so as to receive a drive unit for relatively moving the object to be inspected and the laser device, and the scattered light of the laser irradiated to the object to be inspected via an analyzer arranged in crossed Nicols. The control unit comprises: a scattered light detection unit disposed in the control unit; an arithmetic processing unit that performs a calculation process for obtaining scattered light intensity from scattered light data received by the scattered light detection unit; and a control unit. Switches between the state in which the ultrasonic wave is not applied to the object to be inspected and the state in which the ultrasonic wave is applied, and the scattered light intensity when the ultrasonic wave is not applied and the scattered light intensity when the ultrasonic wave is applied in the arithmetic processing unit Determining a difference, a device for the scattered light to detect a defect, characterized in that to perform the control so as to determine whether or not due to void defects of the test subject unit thereby.   The laser apparatus includes an infrared laser for inspecting a defect inside the object to be inspected and a visible light laser for inspecting a surface layer of the object to be inspected. An apparatus for detecting a defect according to claim 3.

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