JP2002246429A - Method of evaluating silicon wafer and nitrogen-doped annealed wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of exactly evaluating the density of BMD latently contained in a silicon wafer. SOLUTION: The silicon wafer evaluating method comprises heat treating of a silicon wafer containing oxygen deposits which are smaller than a lower limit of oxygen deposits detectable by a specific measuring instrument, thereby growing all the oxygen deposits smaller than the lower limit size, up to a size detectable by the specific measuring instrument, without producing new oxygen deposits, and measuring the density of the oxygen deposits in the silicon wafer to evaluate it. The nitrogen-doped annealed wafer has a mean signal intensity of 1.5 V or higher, as measured by an OPP and an oxygen deposit density of 1×109 number/cm3 or larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for accurately evaluating the density of oxygen precipitates in a silicon wafer.

[0002]

2. Description of the Related Art As one of the qualities of silicon wafers,
The importance of oxygen precipitate (hereinafter, sometimes referred to as BMD) density as a gettering site for heavy metal impurities during device processing is increasing. In general, the density of oxygen precipitates in a silicon wafer can be determined, for example, by subjecting a wafer to be evaluated to a heat treatment at 800 ° C., 4 hours + 1000 ° C., 16 hours, or the like, to reduce the density of oxygen precipitates originally present in the wafer. After being grown to a size that can be detected without being changed, it is measured by performing an optical method such as an infrared interference method or an infrared scattering method or selective etching, and observing with a microscope.

[0003] However, for example, High Yield Technology, one of the devices using infrared interferometry,
OPP (Optical Precipi)
state Profiler), the detectable BM
Since the lower limit size of D is about 50 nm in diameter, if the size of BMD grown by heat treatment is smaller than that,
It will not be counted as BMD. On the other hand, the lower limit size of the BMD for exhibiting the gettering ability is smaller than that, and it is considered that a sufficient gettering effect can be obtained even at about 20 to 30 nm.

Therefore, in order to strictly evaluate the BMD density for the purpose of evaluating the gettering ability of the wafer to be evaluated, it is necessary to grow all the BMDs latent in the wafer to a detectable size by heat treatment. However, heat treatment is expected to be different if the manufacturing conditions (single crystal pulling conditions, interstitial oxygen concentration, heat treatment conditions, etc.) of the wafer to be evaluated are different. For example, 800 ° C., 4 hours + 1000 ° C., 16 hours Such as typical heat treatment,
It was not clear whether the heat treatment was appropriate for all wafers. Therefore, it is considered that the original BMD density cannot be measured properly depending on the wafer to be evaluated.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has been made by providing a method for accurately estimating the BMD density potentially contained in a silicon wafer. An object of the present invention is to correctly grasp the gettering ability of a target silicon wafer.
Another object of the present invention is to provide a silicon wafer having excellent gettering ability surely before the device process is introduced by measuring the BMD density by the evaluation method.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above object, and the present invention is a method for evaluating a silicon wafer, comprising the steps of: To a silicon wafer containing oxygen precipitates smaller than the lower limit size of, heat treatment for growing oxygen precipitates without generating new oxygen precipitates,
After growing all of the oxygen precipitates smaller than the lower limit size to a size that can be detected by the specific measurement device, the oxygen precipitate density in the silicon wafer is measured by the specific measurement device. This is a silicon wafer evaluation method (claim 1).

As described above, the silicon wafer to be evaluated is subjected to a heat treatment for growing oxygen precipitates without generating new oxygen precipitates, and all the oxygen precipitates smaller than the lower limit size are measured by a specific measuring device. After growing to a detectable size, the oxygen precipitate density in the silicon wafer is measured to determine the potential oxygen content in the silicon wafer, regardless of the silicon wafer manufactured under any manufacturing conditions. Precipitate density can be accurately evaluated.

In this case, the heat treatment temperature and the heat treatment time of the heat treatment for growing the oxygen precipitate without generating the new oxygen precipitate are set according to the lower limit size of the oxygen precipitate which can be detected by the specific measuring device. It is preferable to adjust (claim 2). In this way, all the potential oxygen precipitates in the silicon wafer to be evaluated can be reliably grown to a size that can be detected by the measuring device. In addition, since the heat treatment temperature and the heat treatment time can be adjusted to the minimum, power and time required for evaluation can be minimized.

In this case, an apparatus using an infrared interference method or an infrared scattering method can be used as the specific measuring apparatus. Infrared interferometry is non-destructive,
It has the advantage that it is irrespective of sample contamination, does not require chemical treatment, and has good reproducibility quickly. By moving the focal position in the depth direction of the wafer, the distribution of the oxygen precipitates in the wafer in the depth direction can be evaluated. on the other hand,
The infrared scattering method requires cleavage of the wafer in order to obtain information in the depth direction of the wafer, but otherwise is as simple as the infrared interferometry and has high detection sensitivity.

[0010] In this case, the apparatus using the infrared interference method is an OPP, and when the average signal intensity measured by the OPP becomes 1.5 V or more, the size of the oxygen precipitate can be detected. (Claim 4). When the average signal intensity measured by the OPP is 1.5 V or more, all oxygen precipitates have grown to a size that can be reliably detected, and the measured data accurately evaluates the gettering ability of the wafer. You will know if you are doing it.

In this case, the relationship between the heat treatment temperature and the heat treatment time of the heat treatment for growing the oxygen precipitate without generating a new oxygen precipitate and the oxygen precipitate density measured by a specific measuring device is determined in advance. It is preferable to perform a heat treatment for growing an oxygen precipitate without generating the new oxygen precipitate at a heat treatment temperature and a heat treatment time at which the oxygen precipitate density measured by a specific measuring device reaches a saturation value (claim 5). ).

As described above, the relationship between the heat treatment temperature and the heat treatment time of the heat treatment for growing the oxygen precipitate and the oxygen precipitate density measured by the specific measurement device is previously determined for each type of the measurement device used for the measurement. In addition, if the heat treatment for growing the oxygen precipitate is performed at a heat treatment temperature and a heat treatment time at which the oxygen precipitate density measured by the specific measurement device reaches a saturation value, the minimum heat treatment temperature and heat treatment time Thus, oxygen precipitates potentially contained in the silicon wafer can be reliably grown to a detectable size, and the silicon wafer can be accurately evaluated in a short time.

Alternatively, when the OPP is used as a specific measuring device, the OPP is measured by the heat treatment temperature and the heat treatment time for the heat treatment for growing the oxygen precipitate without generating the new oxygen precipitate in advance. A heat treatment for obtaining an oxygen precipitate without generating a new oxygen precipitate at a heat treatment temperature and a heat treatment time at which the average signal intensity measured by the OPP becomes 1.5 V or more is determined. It is preferable to carry out (claim 6).

As described above, when the average signal intensity measured by the OPP is 1.5 V or more, the density of oxygen precipitates has reached the saturation value, and the oxygen concentration is at the heat treatment temperature and the heat treatment time at which such signal intensity is reached. If the heat treatment for growing the precipitate is performed, all the oxygen precipitates smaller than the lower limit size can be grown to a size that can be reliably detected. Therefore, the gettering ability of the silicon wafer can be accurately and quickly evaluated.

In this case, the heat treatment for growing the oxygen precipitate without generating the new oxygen precipitate is performed at 750 ° C.
It is preferable to carry out at the above temperature (claim 7). This is because if the heat treatment is performed at about 750 ° C. or more, new oxygen precipitates (oxygen precipitate nuclei) are not generated, and the oxygen precipitates can be grown to a detectable size. However, usually, if the heat treatment temperature is 900 ° C. or more, some of the originally existing grown-in precipitates may be dissolved, so that the first heat treatment temperature of the heat treatment for growing the oxygen precipitate is 900 ° C. or more. Is not preferred.

In this case, the silicon wafer may be a nitrogen-doped CZ silicon wafer. In the case of nitrogen-doped CZ silicon, a stable high-temperature grown-in oxygen precipitate is formed even at as-grown temperature. And heat treatment can be performed efficiently in a short time.

In this case, the silicon wafer is an annealed wafer previously heat-treated at a temperature of 1000 ° C. or more before the heat treatment for growing an oxygen precipitate without generating a new oxygen precipitate. (Claim 9). When evaluating an annealed wafer that has been subjected to a high-temperature heat treatment of 1000 ° C. or more in advance,
Since oxygen precipitates remaining after the high-temperature heat treatment are evaluated, if the temperature does not exceed the high-temperature heat treatment temperature, 1000 from the first stage of the heat treatment for growing the oxygen precipitates.
High-temperature heat treatment at a temperature of not less than ° C. can be performed, and heat treatment can be performed efficiently in a short time.

The present invention also relates to a nitrogen-doped annealed wafer obtained by heat-treating a nitrogen-doped CZ silicon wafer, wherein the average signal intensity measured by OPP is 1.5 V or more, and the oxygen deposition Object density is 1
A nitrogen-doped annealed wafer characterized by being at least 10 ⁹ / cm ³ (claim 10).

Such a nitrogen-doped annealed wafer has oxygen precipitates of a sufficient size and density, and is extremely effective as a wafer exhibiting gettering ability from the beginning of a device process.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to this. The present invention can detect a BMD which can exhibit the gettering ability although its original size is as small as about 20 to 30 nm by a heat treatment of 800 ° C., 4 hours + 1000 ° C., 16 hours which has been generally performed conventionally. This is in view of the fact that the wafer cannot be sufficiently grown to the size and the gettering ability of the wafer cannot be accurately evaluated. That is, the present invention performs a heat treatment to grow oxygen precipitates without generating new oxygen precipitates according to the precipitation behavior of the oxygen precipitates of the silicon wafer, and converts the minute oxygen precipitates smaller than the lower limit of detection to the specific size. After growing to a size detectable by an optical measuring device, the density of oxygen precipitates in the silicon wafer is measured by the specific optical measuring device.

As a result, a conventional heat treatment at 800 ° C. for 4 hours at + 1000 ° C. for 16 hours cannot grow the wafer to a detectable size, thus making it impossible to accurately evaluate the wafer. In addition, by performing an appropriate growth heat treatment, it becomes possible to grow and detect oxygen precipitates potentially existing in the wafer without leakage, thereby enabling accurate evaluation of all wafers.

In this case, the heat treatment temperature and the heat treatment time of the heat treatment for growing the oxygen precipitate are preferably adjusted according to the lower limit size of the oxygen precipitate which can be detected by a specific measuring device. By doing so, the oxygen precipitate can be grown to a detectable size with the minimum heat treatment temperature and heat treatment time.

In the present invention, for example, OPP can be applied to measure the density of the oxygen precipitate grown to a detectable size. Where OPP
Is an application of a Normalski type differential interference microscope. First, a laser beam emitted from a light source is separated into two linearly polarized beams orthogonal to each other at 90 ° phases different from each other by a polarizing prism, and are incident from the wafer mirror side. Let it. At this time 1
When one beam crosses the defect, a phase shift occurs and another
A phase difference occurs between the two beams. Defects are detected by detecting this phase difference with a polarization analyzer after passing through the back surface of the wafer.

This OPP is a non-destructive measurement method, has the advantage that it has no relation to contamination of the sample, does not require chemical treatment, and has good reproducibility quickly. For this reason, the wafer can be extracted during the process, evaluated, and returned to the process. By moving the focal position in the depth direction of the wafer, there is also an advantage that the distribution of oxygen precipitates in the wafer in the depth direction can be evaluated.

In order to adjust the conditions of the heat treatment for growing the oxygen precipitates, the present inventors conducted the following experiments on the relationship between the heat treatment temperature and the heat treatment time and the oxygen precipitate density measured by a specific measuring device. Was done. (Experiment 1) A plurality of 200 mm diameter nitrogen-doped annealed wafers with different initial interstitial oxygen concentrations produced by the CZ method were prepared. Wafer manufacturing conditions and wafer specifications are as follows. (200 mm wafer) p-type, crystal orientation <100>, resistivity about 10 Ωcm, nitrogen concentration 5 × 10 ¹³ / cm ³ , initial interstitial oxygen concentration 11, ^13, 15 ppma (JEI
DA: Japan Electronics Industry Promotion Association standard), annealing conditions:
Ar 100% atmosphere, 1200 ° C, 1 hour

These wafers were heated at 1000 ° C. for 4 hours.
Heat treatment for ~ 24 hours was performed in a nitrogen atmosphere containing 2% oxygen. The oxygen precipitate density of these wafers was measured using an OPP (Hi
gh Yield Technology) and a BMD analyzer MO which is an apparatus using an infrared scattering method.
-401 (manufactured by Mitsui Kinzoku Mining). BMD
With the analyzer MO-401, the measurement was performed using the LST (infrared scattering tomography) method. Where LST
The method is a type of light scattering method, in which the size and distribution of oxygen precipitates are measured by irradiating infrared rays from the surface or cleavage plane of the wafer and observing the light scattered by the oxygen precipitates from the cleavage plane or surface. How to The experimental results are shown in FIGS. Incidentally, the oxygen precipitate density was also measured for those not subjected to the heat treatment at 1000 ° C.

FIG. 1 shows that in the case of the OPP measurement, the heat treatment time at 1000 ° C. for each of the wafers having an initial interstitial oxygen concentration (Oi) of 15, 13, and 11 ppma is about 1 hour.
It can be seen that the detected BMD density increases until 5 hours, about 16 hours, and about 24 hours. However, when the heat treatment time is longer than that, the detected value of the BMD density reaches the saturation value, and it is found that the detected value does not increase any more.

FIG. 2 shows that in the case of LST measurement, BMD
The time at which the density was saturated was about 0 hour (only for Ar annealing), about 4 hours, and about 8 hours at 1000 ° C. for wafers having initial interstitial oxygen concentrations (Oi) of 15, 13, and 11 ppma, respectively. Until this is the case, it can be seen that the detected BMD density increases. However, when the heat treatment time is longer, the detected value of the BMD density reaches the saturation value as in the case of the OPP measurement, and it is found that the detected value does not increase any more.

From the above results, when the value detected by each measurement method reaches the saturation value, all the oxygen precipitates in the wafer have grown to a detectable size, and even if the heat treatment is continued further. It is expected that the oxygen precipitate density will not change.

Therefore, the relationship between the heat treatment temperature and the heat treatment time of the heat treatment for growing the oxygen precipitate and the oxygen precipitate density measured by a specific measurement device is determined in advance for each measurement device, and the measured oxygen precipitate is determined. If heat treatment is performed to grow oxygen precipitates at the heat treatment temperature and heat treatment time at which the material density reaches the saturation value, the size of oxygen precipitates that are potentially present in the wafer can be detected with the minimum heat treatment temperature and heat treatment time. In addition to the growth, the gettering ability can be accurately known from the oxygen precipitate density.

The difference between the OPP measurement and the LST measurement regarding the heat treatment time at which the BMD density reaches the saturation value is due to the difference in detection sensitivity, and it can be said that the LST measurement has a higher size-related detection sensitivity. The saturation density indicates the measured potential BMD density of the nitrogen-doped annealed wafer, and the difference between the saturation density OPP and LST is considered to be a measurement error.

Further, the present inventors conducted the following experiment when measuring using OPP. (Experiment 2) A nitrogen-doped annealed wafer having a diameter of 200 mm produced by the CZ method under the same conditions as the wafer used in (Experiment 1), and a 150-mm diameter nitrogen-produced wafer also produced by the CZ method and having micro-BMD introduced by low-temperature heat treatment A wafer (non-doped with nitrogen) was prepared. Manufacturing conditions and wafer specifications for a 150 mm wafer are as follows. (150 mm wafer) p-type, crystal orientation <100>, resistivity about 10 Ωcm, initial interstitial oxygen concentration 15, 16, 19 ppma (JEI
DA standard) annealing _conditions: N 2 100% atmosphere, 700 ° C., 4 hours

By subjecting these samples to heat treatment at 1000 ° C. for 4 to 24 hours in a nitrogen atmosphere containing 2% oxygen, the BMD size was changed to
Its density and size were measured by P. Further, with respect to the nitrogen-doped annealed wafers, those without the heat treatment at 1000 ° C. were also measured. The measurement mode is Z scan, the measurement position is 30 to 90 μm deep from the wafer surface, the center of the wafer, R / 2 (a position closer to the outer circumference by １ ／ of the radius from the center), and the edge 10 mm (from the outermost circumference of the wafer). The relationship between the average signal intensity of the scattered light and the BMD density was measured at three points (positions inside 10 mm). FIG. 3 shows the measurement results.

From FIG. 3, it can be seen that the BMD density increases with the signal strength and is about 1.5 V regardless of the final saturation value.
From the above, it can be seen that there is almost no change. This tendency did not depend on the type of wafer or the initial oxygen concentration. From this result, in the measured wafers, there are those in which most of the oxygen precipitates have grown to a detectable size or more, and those that contain oxygen precipitates below the lower detection limit, and the measured BMD density is constant. Those reaching the saturation value are considered to be those in which most of the oxygen precipitates have grown beyond the detectable size. If the average signal intensity is about 1.5 V or more, it is estimated that most BMDs grow to a detectable size, and the original BMD density of the wafer to be measured can be measured. In contrast, the average signal strength is about 1.
When the voltage is lower than 5 V, it is considered that the measured value of the BMD density indicates only the density of the oxygen precipitate having a size exceeding the lower limit of detection because the BMD has not reached a sufficient size.

Therefore, the relationship between the heat treatment temperature and the heat treatment time of the heat treatment for growing the oxygen precipitate and the average signal intensity measured by the OPP is determined in advance, and the measured average signal intensity becomes 1.5 V or more. When the heat treatment is performed at the heat treatment temperature and the heat treatment time, the oxygen precipitate potentially existing in the wafer can be grown to a detectable size with the minimum heat treatment temperature and the heat treatment time.

In the present invention, the heat treatment that does not generate new oxygen precipitates is determined by the heat treatment temperature, and varies depending on the interstitial oxygen concentration in the silicon wafer, the conditions for pulling the single crystal, and the like. Generally, if the heat treatment is performed at 750 ° C. or higher, no new oxygen precipitates (oxygen precipitate nuclei) are generated.

On the other hand, in the case of an unheated as-grown wafer other than the heat treatment for eliminating the oxygen donor, if the initial heat treatment temperature is 900 ° C. or higher, g as originally existed.
Since some of the row-in precipitates may be dissolved, it is not preferable to set the temperature of the first heat treatment of the heat treatment for growing the oxygen precipitate to 900 ° C. or higher.

On the other hand, when an annealed wafer previously subjected to a high-temperature heat treatment at 1000 ° C. or more is evaluated, oxygen precipitates remaining after the high-temperature heat treatment are to be evaluated. If there is no temperature, there is no problem even if high-temperature heat treatment is performed in the first stage of heat treatment for growing oxygen precipitates.

When the wafer to be evaluated is a nitrogen-doped CZ silicon wafer, a stable grown-in oxygen precipitate is formed at a high temperature even if the wafer is as-grown. A high-temperature heat treatment at 1000 ° C. or higher can be performed at the first stage of the heat treatment for growing the object.

As a method of using the evaluation method of the present invention, as-
Regardless of the grown wafer or the annealed wafer, the wafer to be shipped to the wafer user is evaluated by the evaluation method of the present invention to obtain the density of oxygen precipitates, and the heat treatment conditions applied to this wafer (for generating new oxygen precipitates) It can be provided to the wafer user together with the data of (no heat treatment). In this case, the wafer user predicts that a gettering effect determined by at least the oxygen precipitate density can be obtained by, for example, designing a device process by a heat treatment at or below the heat treatment temperature. Because you can do it.

[0041]

EXAMPLES Hereinafter, specific examples and comparative examples of the present invention will be described.
However, the present invention is not limited to these.
is not. (Example 1) Diameter 200 mm, crystal orientation <100>, resistance
Silicon wafer doped with nitrogen having a resistivity of about 10 Ωcm
Was produced as an evaluation sample. Nitrogen concentration of wafer is 5 ×
10 ¹³Pieces / cm. Also, the interstitial acid of the wafer
The elemental concentration was 11 ppma (JEIDA). This way
Heat treatment at 1200 ° C. for 1 hour
After the treatment, oxygen precipitates in the wafer were evaluated.

Here, according to FIGS. 1 and 3 obtained in advance, for the wafer under the same conditions as the above-mentioned wafer, the heat treatment at which the size of the oxygen precipitate grows to a size all detectable by the above-mentioned OPP is performed at 1000 ° C. This is a heat treatment for 24 hours. Therefore, the wafer to be evaluated was subjected to a heat treatment for growing oxygen precipitates at 1000 ° C. for 24 hours in a nitrogen atmosphere containing 2% oxygen. The oxygen precipitate density of the wafer after the heat treatment was measured by OPP.
The measurement result was 4 × 10 ⁹ pieces / cm ³ . At this time, the average signal intensity was 1.5 V or more, and the oxygen precipitate had grown sufficiently, and it was found that the obtained precipitate density was an accurate measurement value.

(Comparative Example 1) A silicon wafer under the same conditions as in Example 1 was manufactured, and N was used as a conventional general heat treatment.
800 ° C. ₂ gas atmosphere, after the heat treatment of 4 hours, 1000 ° C. The _{O 2} gas atmosphere, subjected to a heat treatment of 16 hours. Thereafter, the oxygen precipitate density of the wafer was measured by the same OPP used in the examples. The measurement result is 1 × 10
^{The value was 9} / cm ³ , which was lower than the numerical value of the example, although the wafer under the same conditions was measured by the same measuring device.

From the above results, according to the method of the present invention,
It can be seen that all the oxygen precipitates potentially present in the wafer can be grown to a detectable size and measured, and that accurate evaluation of the wafer is possible. On the other hand, according to the conventional method, depending on the manufacturing conditions of the wafer, it is not possible to make all the minute oxygen precipitates in the wafer a detectable size, so the measured value is only for the oxygen precipitates whose size exceeds the lower limit of detection. Will show the value of
It turns out that accurate evaluation may not be possible.

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

For example, in the above description, the case where the OPP is mainly used as the measuring device has been described, but the present invention is not limited to this, and optical methods such as the LST method and optical methods are used. The present invention can also be applied to a case where a measuring device that does not use a device is used.

[0047]

As described above, according to the present invention, there is provided an evaluation method capable of accurately evaluating the density of oxygen precipitates potentially contained in a silicon wafer regardless of the wafer manufacturing conditions. . Therefore, the gettering ability of the silicon wafer to be evaluated can be correctly grasped. Further, by specifying a wafer by this evaluation method, it is possible to provide a silicon wafer having excellent gettering ability even before the device process is introduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a heat treatment time of a heat treatment for growing an oxygen precipitate and an oxygen precipitate density measured by OPP.

FIG. 2 is a diagram showing a relationship between a heat treatment time of a heat treatment for growing an oxygen precipitate and an oxygen precipitate density measured by a measuring device using an LST method.

FIG. 3 is a diagram showing a relationship between an average signal intensity measured by an OPP and a BMD density at that time.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/322 H01L 21/322 Y F-term (Reference) 2G051 AA51 AB02 BA10 BA11 CB02 CC07 EC03 2G059 AA05 BB16 CC07 CC20 EE01 EE02 EE05 EE09 GG01 GG04 HH01 JJ12 JJ19 MM03 4G077 AA02 AB01 BA04 GA01 GA06 4M106 AA01 BA08 CB03 CB19 DH13

Claims (10)

[Claims] 1. A method for evaluating a silicon wafer, comprising:
A silicon wafer containing an oxygen precipitate smaller than the lower limit size of the oxygen precipitate that can be detected by a specific measuring device, a heat treatment for growing the oxygen precipitate without generating a new oxygen precipitate is added to the silicon wafer, After growing all of the smaller oxygen precipitates to a size that can be detected by the specific measuring device, the density of oxygen precipitates in the silicon wafer is measured by the specific measuring device. Evaluation method. 2. A heat treatment temperature and a heat treatment time of a heat treatment for growing an oxygen precipitate without generating the new oxygen precipitate according to a lower limit size of the oxygen precipitate which can be detected by the specific measuring device. The method for evaluating a silicon wafer according to claim 1, wherein: 3. The method for evaluating a silicon wafer according to claim 1, wherein an apparatus using an infrared interference method or an infrared scattering method is used as the specific measurement apparatus. 4. An apparatus using the infrared interference method is an OPP, and an average signal intensity measured by the OPP is 1.5.
4. The method for evaluating a silicon wafer according to claim 3, wherein when the voltage is equal to or higher than V, it is determined that all the oxygen precipitates have grown to a detectable size. 5. A relation between a heat treatment temperature and a heat treatment time of a heat treatment for growing an oxygen precipitate without generating the new oxygen precipitate in advance and an oxygen precipitate density measured by the specific measuring device is determined. A heat treatment for growing an oxygen precipitate without generating the new oxygen precipitate at a heat treatment temperature and a heat treatment time at which the oxygen precipitate density measured by the specific measuring device reaches a saturation value. The method for evaluating a silicon wafer according to any one of claims 1 to 4. 6. A relation between a heat treatment temperature and a heat treatment time of a heat treatment for growing an oxygen precipitate without generating a new oxygen precipitate and an average signal intensity measured by the OPP is determined in advance, and the relation is measured by the OPP. The heat treatment for growing an oxygen precipitate without generating the new oxygen precipitate is performed at a heat treatment temperature and a heat treatment time at which the average signal intensity becomes 1.5 V or more. Evaluation method of silicon wafer described in (1). 7. The method according to claim 1, wherein the heat treatment for growing the oxygen precipitates without generating new oxygen precipitates is performed at a temperature of 750 ° C. or more. Evaluation method of the evaluated silicon wafer. 8. The method for evaluating a silicon wafer according to claim 1, wherein the silicon wafer is a CZ silicon wafer doped with nitrogen. 9. The silicon wafer is an annealed wafer previously heat-treated at a temperature of 1000 ° C. or more before a heat treatment for growing an oxygen precipitate without generating a new oxygen precipitate. The method for evaluating a silicon wafer according to claim 1. 10. A nitrogen-doped annealed wafer obtained by heat-treating a nitrogen-doped CZ silicon wafer, wherein the average signal intensity measured by OPP is 1.
A nitrogen-doped annealed wafer having a voltage of 5 V or more and an oxygen precipitate density of 1 × 10 ⁹ / cm ³ or more.