JP5007620B2 - Method for detecting crystal defects in a silicon single crystal wafer - Google Patents

Description

  The present invention relates to a method for detecting crystal defects existing near the surface of a semiconductor substrate.

  Silicon single crystal wafers used as substrates for semiconductor integrated circuit elements are mainly manufactured by the Czochralski method (CZ method). At this time, the surface of the quartz crucible in contact with the silicon melt is melted, and oxygen is dissolved in the silicon melt and is taken into the growing crystal. The oxygen atoms aggregate during crystal growth and cooling and become oxygen precipitation nuclei. Therefore, when a silicon single crystal wafer collected from the grown crystal is subjected to a heat treatment in a device process or the like, the nucleus grows in the wafer bulk portion to form BMD (Bulk Micro Defect).

As a method for detecting the BMD, there are a selective etching method, an infrared laser tomography method (LST), a SIRM method, an OPP (Optical Precipitate Profiler) method, and the like.
Among these measurement methods, selective etching and LST methods are examples of evaluation methods that can evaluate the BMD distribution in the depth direction.

Of these methods, a method of combining angle polishing and selective etching has been often used. It was possible to obtain the distribution in the depth direction of BMD by increasing the accuracy in the depth direction by performing angle polishing. Therefore, it was used to examine the DZ width of a DZIG (Denuded Zone Intrinsic Gettering) wafer. In addition, BMD depth distribution after IC device process could be analyzed.
However, this method is difficult to measure even if BMD is generated because the size of the BMD does not increase in the case of low temperature heat treatment performed in the current IC for leading edge.

The 90-degree scattering infrared laser tomography method is known to be able to measure BMD with high sensitivity, but it is also known that measurement near the wafer surface is difficult. This is because the intensity of the scattered light from the incident surface (wafer surface) of the laser light is larger than the scattered light due to the defect, so that the scattered light due to the defect could not be detected.
However, the infrared laser tomography method has a sensitivity that can sufficiently measure even a small BMD produced by low-temperature heat treatment. Therefore, although the sensitivity is good with respect to the BMD formed in the wafer bulk portion instead of the surface of the wafer, it was not possible to evaluate the BMD having a small wafer surface.

  However, even a small BMD is known to cause a device failure when it exists on the wafer surface. This is because the vicinity of the surface is close to the device active layer, so that it is easily affected by BMD near the surface and is likely to cause a wafer defect.

As described above, an apparatus capable of measuring BMD near the surface is not sensitive to BMD measurement formed by low-temperature heat treatment, and the intensity of scattered light on the surface is too strong in a sensitive apparatus, so measurement near the surface Can not do.
However, when performing fine processing at the current level, the influence of small BMD existing near the surface can no longer be ignored. Therefore, it is very important to measure the minute BMD near the surface. is there.

  In order to solve such problems, an appropriate inclination is provided on the side surface of the test sample mounting table, and a defect detection light beam is incident from this inclined surface. At that time, the reflected light travels along the surface layer of the test sample. A method for evaluating the BMD in the surface layer using the method is disclosed (see Patent Document 1). Further, a method is disclosed in which the back surface of a silicon wafer is mirror-polished obliquely and light having energy smaller than the energy corresponding to the forbidden band width of the semiconductor is incident from the obliquely-polished surface (see Patent Document 2). .

  In addition, laser light with energy less than the band gap and laser light with energy greater than the band gap are incident, the carrier is excited by the laser light greater than the band gap, and the energy less than the band gap is absorbed by the carrier. A method of detecting defects only near the surface by reducing the depth of incidence of light is disclosed (see Patent Document 3). However, although these methods can measure BMD from the wafer surface to a certain depth, they can only evaluate to a certain depth, and thus cannot measure a deep region of the wafer. Moreover, since the sensitivity is still insufficient, it is not suitable for measuring a small BMD near the surface.

JP-A-6-140488 JP-A-6-201594 JP-A-9-246337

  The present invention has been made in view of the above problems, and has high measurement sensitivity capable of measuring even a minute defect such as a small BMD formed in the vicinity of a wafer surface after a low-temperature process which is an advanced device process. An object is to provide a method for detecting a crystal defect.

In order to solve the above problems, in the present invention, an infrared laser beam is incident, and scattered light scattered by the crystal defect is detected, thereby detecting and evaluating the crystal defect near the surface. in the detection method, a silicon single crystal wafer used for measurement, and the silicon single crystal wafer was prepared another silicon single crystal wafer, and cleaving the silicon single crystal wafer of two said, two silicon single that the cleavage The crystal wafer is overlapped so that the cleavage planes coincide with each other , and a liquid having a refractive index equivalent to the refractive index of the silicon single crystal wafer is interposed between the two overlapped silicon single crystal wafers. perpendicular or direction to the opposite major surface a wafer and the surface in which superposition of the silicon single crystal wafer prepared separately from for the measurement It is incident, provides a method for detecting crystal defects and detecting crystal defects of a silicon single crystal wafer for measurement by Rukoto measuring the advanced scattered light to the cleavage plane direction (claim 1).

  In this way, a wafer different from the measurement wafer is prepared, the two wafers to be measured are overlapped and the gap between them is filled with a liquid having a refractive index equivalent to that of a silicon single crystal wafer. By interposing it, the refractive index change plane that causes the incident laser light to scatter is quasi-disappeared, so that it is possible to scatter the laser light that should be generated on the surface near the area to be measured. This makes it possible to detect scattered light scattered by defects existing in the region to be measured (near the surface of the wafer for measurement) and to detect crystal defects in the vicinity of the wafer surface. it can.

In addition, it is preferable to use silicone oil as the liquid interposed between the two silicon single crystal wafers.
In this way, the surface tension is low, so it easily spreads on the wafer surface, has good light transmission over a wide wavelength range, is chemically stable, and has a refractive index equivalent to that of a silicon single crystal wafer. By interposing a certain silicone oil between two silicon single crystal wafers, it is possible to prevent scattering of infrared laser light on the surface of the wafer for measurement. Therefore, it is possible to detect with high sensitivity the laser beam scattered by the crystal defects existing in the vicinity of the measurement wafer surface.

A dummy wafer is preferably used as the silicon single crystal wafer on the side on which the infrared laser beam is incident.
As described above, by using the dummy wafer, it can be repeatedly used for the measurement. Therefore, it is not necessary to prepare a silicon single crystal wafer for each measurement, and the cost can be reduced.

As described above, in the crystal defect detection method of the present invention, in addition to the silicon single crystal wafer for measurement, another silicon single crystal wafer is prepared, the surfaces to be measured are overlapped, and silicon is placed in the gap. A liquid having a refractive index equivalent to that of a single crystal wafer is filled and interposed in the gap. As a result, the refractive index change surface that causes the incident laser light to scatter is quasi-disappeared, so that it can be handled optically as a single wafer, apparently showing the area to be measured as a single sheet. By making it exist in the bulk of the wafer, it is possible to suppress the scattering of the laser light that should be generated on the wafer surface near the region to be measured. For this reason, it becomes possible to detect with high sensitivity the scattered light that is scattered by defects existing in the region to be measured (near the wafer surface for measurement), and to detect crystal defects near the wafer surface. Can do.
The 90 degree scattering type LST is a highly sensitive measurement for BMD, but has the disadvantage that the surface cannot be measured. Since scattering can be suppressed, the advantage of high sensitivity can be measured, and the surface BMD can be measured. From this, it became possible to accurately evaluate the surface BMD after the low-temperature process, which is a leading-edge device process that was difficult with various conventional measurement methods, by a simple method.

Hereinafter, the present invention will be described more specifically.
As described above, development of a method for detecting a crystal defect with high measurement sensitivity that can measure even a minute defect such as a small BMD formed near the wafer surface after a low-temperature process, which is an advanced device process, is awaited. It was.

  Therefore, the present inventors use a method that does not cause scattering on the wafer surface when a laser beam is incident in the 90-degree-scattering LST method that has high sensitivity to crystal defects. We intensively studied whether or not minute surface crystal defects could be detected.

  First, the inventors paid attention to a phenomenon in which scattering does not occur on the sample surface by covering the sample surface where scattering occurs with a material having the same refractive index as that of the sample.

Therefore, since the substance having the same refractive index as that of the silicon single crystal wafer is a silicon single crystal wafer, a dummy silicon single crystal wafer for suppressing scattering that is not a measurement sample is superposed on the measurement surface side of the measurement sample and measurement is performed. It was.
However, in this method, laser light is scattered when it escapes from the sample and enters the dummy silicon, and the scattered light passes through the gap between the wafers and interferes with the scattered light from the surface crystal defects, It was very difficult to detect the scattered light at the defect.

Therefore, a liquid having the same refractive index as that of the silicon single crystal wafer is poured into the gap between the two silicon single crystal wafers. Then, optically, the interface (refractive index changing surface) that existed between the wafers disappeared, and two wafers can be observed like a single wafer, so it became a single piece. It was possible to position the vicinity of the surface of the wafer to be measured at the center of the wafer.
The present inventors have found that this method can measure the sample surface without impairing the effectiveness of the high sensitivity of the apparatus, and completed the present invention.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
First, the infrared laser tomography method will be briefly described below.
For example, as a silicon single crystal wafer used for measurement, a wafer whose center is cleaved is used. This silicon single crystal wafer is placed on the stage of an infrared scattering tomography apparatus, and the main surface of the wafer is irradiated with infrared laser light. If there are crystal defects inside the wafer, incident laser light will be scattered, so the number, size, and position of crystal defects can be evaluated by detecting the scattered light with a detector placed in the direction of the cleavage plane. Is.

An example of the details of the crystal defect detection method of the present invention is shown below, but the present invention is not limited to these.
First, a silicon single crystal wafer for measuring crystal defects and a silicon single crystal wafer are prepared separately.

Here, a wafer prepared separately from the measurement wafer can be a dummy wafer. As will be described in detail later, this dummy wafer is used for incidence of laser light.
By using a dummy wafer as a separate wafer from the measurement wafer, the dummy can be used repeatedly for measurement, eliminating the need to prepare a silicon single crystal wafer for each measurement and reducing costs. Can be achieved.

  Next, after scratching with a diamond pen or the like so as to pass through the center of the wafer, each of the prepared two wafers was cleaved into two.

  Thereafter, the cleaved silicon single crystal wafer for measurement was mounted on an infrared scattering tomography apparatus, and then the wafer was stacked so that the cleavage planes coincided, and another wafer for measurement was mounted.

Next, a liquid having a refractive index equivalent to that of the silicon single crystal wafer was filled in the gap between the two previously mounted silicon single crystal wafers.
As a result, the refractive index change surface, which is the main cause of the scattering of the laser light incident on the wafer, is quasi-disappeared so that it can be handled optically as a single wafer. In other words, by making the area near the surface of the measurement wafer that you want to measure appear to exist in the bulk of the wafer that has been artificially merged, Scattering of the generated laser light can be suppressed. This makes it possible to accurately detect scattered light scattered by defects existing in the region to be measured (near the surface of the measurement wafer), and to detect crystal defects in the vicinity of the wafer surface. it can.

  Here, the refractive index equivalent to the refractive index (1.46) of the silicon single crystal wafer is 1.46 ± 0.1, and a liquid having a refractive index in this range is used as a gap between the two silicon single crystal wafers. By interposing, in the case of air (refractive index ≈ 1.00), the refractive index difference is remarkably eliminated and it can be optically handled as a single wafer. Of course, it is needless to say that the smaller the difference in refractive index between the intervening liquid and the silicon single crystal, the better.

Here, silicone oil can be used as a liquid having a refractive index equivalent to that of a silicon single crystal wafer.
Two pieces of silicone oil with low surface tension, easy to spread on the wafer surface, good light transmission over a wide wavelength range, chemically stable, and refractive index equivalent to silicon single crystal wafer By interposing between the single crystal wafers, the familiarity between the liquid and the wafer surface can be increased, and since the refractive index is equivalent, it can be regarded as an optically single silicon single crystal wafer. Can do.
In addition, the refractive index of the silicone oil interposed in the gap between the silicon single crystals may be any value that approximates the refractive index (1.46) of the silicon single crystal wafer, and does not limit the type of silicone oil. Absent. As long as the silicone oil has a refractive index close to 1.46, other characteristics (viscosity, specific gravity, thermal conductivity, etc.) may be different.

Thereafter, infrared laser light was incident on the inside of the wafer from a direction perpendicular to the main surface of the dummy wafer so as to be parallel to the cleavage plane (perpendicular to the main surface).
Of the laser light scattered inside the crystal of the silicon single crystal wafer for measurement, by measuring the scattered light traveling in the cleavage plane direction with a detector, it is possible to measure crystal defects existing inside the wafer. .

  Here, as a method of recognizing the surface position of the measurement wafer in the image obtained by measuring the measurement results of the measurement wafer when two silicon wafers are stacked, (1) a thin line appears in the image, so measure it Recognize the wafer surface for measurement, (2) Before the dummy wafer is overlaid, confirm the position of the wafer surface in advance, and when the dummy wafer is mounted and filled with silicone oil, the measurement wafer is not displaced. Etc. are considered. Then, the surface position of the measurement wafer can be clarified by these methods, and thereby the crystal defects existing on the wafer surface to be measured can be accurately detected, and the evaluation can be performed.

  On the other hand, in the conventional crystal defect detection method, an infrared laser beam is directly incident on the surface of the measurement wafer cleaved at the center, and scattered light scattered by defects existing inside the crystal is placed on the cleavage plane. Detection is performed by a detector. In this method, since scattered light generated on the surface of the wafer for measurement is also detected, it is impossible to distinguish between scattered light scattered by crystal defects existing near the surface and scattered light scattered on the surface. Since the intensity of the scattered light on the surface is much stronger, the scattered light at the crystal defect could not be detected.

FIG. 1 shows how the incident laser light is scattered on the surface of the measurement sample according to the present invention and the prior art. FIG. 1A is a conceptual diagram showing the state of scattering of incident laser light on the surface of a measurement sample in the crystal defect detection method of the present invention, and FIG.
As shown in FIG. 1A, in the crystal defect detection method of the present invention, a measurement wafer is scattered in the surface of the dummy wafer 2 on which the infrared laser beam is incident, but is in the vicinity of the region to be measured. Since the silicone oil 3 is present on the surface of 1, no laser light scattering occurs, and scattering occurs only at crystal defects. As a result, the crystal defect 4 near the surface can be detected.
On the other hand, in the conventional crystal defect detection method shown in FIG. 1B, when the scattered light is detected by the detector, the intensity of the scattered light scattered on the wafer surface is too strong. Appears blurry. For this reason, crystal defects cannot be detected.

FIG. 2 shows an example of a cross-sectional view of the wafer surface measured by the present invention and the prior art.
FIG. 2A shows an image obtained by detecting scattered light in the vicinity of the surface of a silicon single crystal wafer measured using the crystal defect detection method of the present invention with a detector.
FIG. 2B is an image when the conventional crystal defect detection method is used.

Thus, as a result of actual measurement, as shown in FIG. 2A, according to the crystal defect detection method of the present invention, incident laser light is scattered on the surface of the wafer to be measured. Therefore, it was found that scattered light scattered by a small crystal defect existing in the vicinity can be detected as it is.
On the other hand, in the conventional method for detecting a crystal defect shown in FIG. 2B, the intensity of scattered light scattered on the surface of the wafer for measurement is very strong. Light could not be detected, and only scattered light scattered by crystal defects in the wafer bulk could be detected.

FIG. 3 shows an example of the density distribution in the depth direction of the BMD on the surface of the silicon single crystal wafer measured by the present invention and the prior art.
As shown in FIG. 3, in the conventional crystal defect detection method, the presence of crystal defects could not be evaluated by scattered light on the surface at a certain distance from the wafer surface. According to the method, it can be confirmed that there is no crystal defect on the wafer surface, and the BMD density distribution in the wafer evaluated from the measurement results is almost the same, and the detection accuracy of the present invention is high. I understand.

  As described above, according to the crystal defect detection method of the present invention, since laser light scattering does not occur on the surface of the measurement wafer, by using a device having high measurement sensitivity, it is possible to detect minute defects existing near the surface. Scattered scattered light can be detected. That is, minute crystal defects can be detected.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

It is a conceptual diagram which shows the mode of scattering of the incident laser beam in the wafer surface in this invention and a prior art. It is a figure which shows an example of the cross-sectional observation figure of the wafer surface measured by this invention and the prior art. It is a figure which shows an example of the density distribution with respect to the depth direction of BMD of the silicon single crystal wafer surface measured by this invention and the prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Measuring wafer, 2 ... Dummy wafer, 3 ... Silicone oil, 4 ... Crystal defect.

Claims (3)

A silicon single crystal wafer used for measurement in the method of detecting crystal defects by infrared scattering tomography, which detects and evaluates crystal defects in the vicinity of the surface by detecting the scattered light scattered by crystal defects by entering an infrared laser beam When, the said silicon single crystal wafer was prepared another silicon single crystal wafer, and cleaving the silicon single crystal wafer of two said overlaid as a cleavage plane of the two silicon single crystal wafers were the cleavage matches In addition, a liquid having a refractive index equivalent to the refractive index of the silicon single crystal wafer is interposed between the two stacked silicon single crystal wafers, and the infrared laser beam is prepared separately from the measurement wafer. the silicon and superimposed planes of the single crystal wafer is incident from a direction perpendicular to the opposite major surface, diffusing proceeded to the cleavage plane direction Detection methods of crystal defects and detecting crystal defects of a silicon single crystal wafer for measurement by Rukoto measuring the light.   2. The method for detecting a crystal defect according to claim 1, wherein silicone oil is used as a liquid interposed between the two silicon single crystal wafers.   3. The method for detecting a crystal defect according to claim 1, wherein a dummy wafer is used as the silicon single crystal wafer on which the infrared laser beam is incident.

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