JP7103314B2 - Carbon concentration evaluation method in silicon single crystal substrate - Google Patents

Description

The present invention relates to a method for simply evaluating the carbon concentration in a silicon single crystal substrate prepared from a silicon single crystal grown by a floating zone melting method (FZ method).

As a substrate for a power semiconductor device, a silicon single crystal substrate made from a silicon single crystal grown by a floating zone melting method is widely used. The silicon single crystal grown by the FZ method has excellent resistivity uniformity in the crystal growth axial direction as compared with the silicon single crystal grown by the Czochralski method (CZ method), and contains almost no oxygen. Since it is not contained, there is an advantage that oxygen-related donors that cause resistivity changes are not generated in the device process.

As a method of doping a dopant in order to control the resistance of a silicon single crystal grown by the FZ method (hereinafter, also referred to as "FZ silicon single crystal"), a gas doping method in which a dopant is doped from an atmospheric gas during crystal growth (hereinafter, also referred to as "FZ silicon single crystal"). The GD method) and the neutron irradiation doping method (NTD method) in which neutrons are irradiated after the silicon single crystal is grown and phosphorus is doped by a nuclear conversion reaction ( ³⁰ Si (n, γ) → ³¹ Si → ³¹ P + β) (NTD method). Non-Patent Document 1). The substrate made from the FZ silicon single crystal is called an FZ silicon single crystal substrate, and the substrate made from the single crystal obtained by the above doping method is a GD-FZ silicon single crystal substrate and an NTD-FZ silicon single crystal, respectively. It is called a board. The NTD-FZ silicon single crystal substrate is used as a substrate for power devices with strict resistivity requirements because the in-plane uniformity of resistivity is superior to that of the GD-FZ silicon single crystal substrate. ..

Further, in the FZ silicon single crystal, nitrogen is often added during crystal growth in order to prevent discharge in the furnace during crystal growth, reduce crystal defects introduced during crystal growth, and improve wafer strength (in order to improve wafer strength). Patent Document 1). The concentration of nitrogen introduced into the grown single crystal is controlled by adjusting the atmospheric gas during crystal growth.

A silicon single crystal substrate widely used as a substrate for a semiconductor device contains carbon as an impurity. Carbon is mixed in the manufacturing process of the silicon single crystal, and may be further mixed in the wafer processing step, the epitaxial growth step, and the device manufacturing step. The carbon in a silicon single crystal is normally present at the silicon lattice position (the carbon present at the lattice position is called the substituted carbon) and is itself electrically inactive. However, when it is ejected to the interstitial position by ion implantation or heat treatment in the device process (carbon existing in the interstitial position is called interstitial carbon), it reacts with other impurities to form a complex and is electrically charged. It becomes active and causes a problem that it adversely affects the device characteristics.

In particular, it has been pointed out that in power devices whose carrier lifetime is controlled by irradiating a silicon substrate with particle beams such as electron beams, protons, and helium ions, a very small amount of carbon of 0.05 ppma or less adversely affects the device characteristics. (Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4). For this reason, it is an important issue to reduce the carbon contained in the silicon substrate as much as possible, and for that purpose, a method for evaluating the carbon concentration with high sensitivity is required.

Examples of the method for measuring the carbon concentration in the silicon crystal include an infrared absorption method, a secondary ion mass spectrometry (SIMS), and a charged particle activation analysis method (Non-Patent Document 5).

In addition, after irradiating the sample with an electron beam, the emission intensity derived from silicon and the emission intensity of defects derived from carbon are obtained by the photoluminescence (PL) method, and these intensities and a calibration curve prepared in advance are used. (Patent Document 2) discloses a method for measuring a carbon concentration using. In this method, a calibration curve is prepared and prepared for each type of raw material of the FZ single crystal, a calibration curve of the same type of raw material as the raw material of the semiconductor sample for measurement is selected, and the selected calibration curve is used. The carbon concentration is obtained from the measured value of the semiconductor sample for measurement by the PL method.

Further, after irradiating the silicon single crystal substrate with a particle beam and then injecting excess carriers, the correlation between the decay curve of the carrier concentration and the carbon concentration is obtained, and the particles are formed on the silicon single crystal substrate to be evaluated from the correlation. A method of evaluating the carbon concentration by measuring the decay curve of the carrier concentration after injecting excess carriers by linear irradiation is disclosed (Patent Document 3).

Further, a method of evaluating the carbon concentration by injecting ions other than carbon and oxygen into the sample and then measuring the concentration of carbon-related defects by the cathode luminescence method or the photoluminescence method (Patent Document 4), or an electron in the sample. A method for evaluating a carbon concentration by measuring the concentration of interstitial silicon clusters by a cathode luminescence method or a photoluminescence method after irradiating a line (Patent Document 5) is disclosed.

On the other hand, as one of the methods for evaluating metal contamination and crystal defects in a silicon single crystal substrate, a method for measuring the carrier recombination lifetime may be used. Non-Patent Document 6 reports that when an FZ silicon wafer is heat-treated at 450 to 700 ° C., the carrier recombination lifetime is reduced. It is speculated that the cause of the reduced carrier recombination lifetime may be a defect associated with vacancies. It is also described that the heat treatment temperature dependence of the carrier recombination lifetime differs between the case where nitrogen is hardly contained and the case where nitrogen is contained. Non-Patent Document 7 suggests that nitrogen is involved in the defects that reduce the recombination lifetime introduced by the heat treatment at 500 ° C. on the FZ silicon wafer.

Further, in Patent Document 6, in the silicon single crystal (CZ silicon single crystal) pulled up by the Chokralsky method, when the carbon concentration is as low as 1.0 × 10 ¹⁴ atoms / cm ³ or less, the oxygen concentration is increased. Regardless, it is disclosed that the bulk lifetime increases as the carbon concentration decreases. In this case, no heat treatment is performed after the growth of the CZ silicon single crystal.

Japanese Unexamined Patent Publication No. 2017-12203 Japanese Unexamined Patent Publication No. 2019-036661 Japanese Unexamined Patent Publication No. 2019-052083 JP-A-2015-156420 JP-A-2015-1111615 Japanese Unexamined Patent Publication No. 2016-044109

Tatsuo Ito, Masato Toda: Neutron Irradiation Doping of Silicon, Radiation and Industry, No. 64, p. 19 (1994) Sugiyama et al., Silicon Technology No. 87, p. 6 Sugie et al., Silicon Technology No. 148, p. 11 N. Inoue et al. , Physica B 401-402 (2007), p. 477 JEITA EM-3503 "Standard measurement method of substituted carbon atom concentration in silicon crystal by infrared absorption" N. E. Grant et al. , Phys. Status Solidi A. doi: 10.1002 / pssa. 201600360 J. Mullins et al. , J. Apple. Phys. 124,035701 (2018)

However, the above-mentioned conventional infrared absorption method requires a carbon-free reference sample, and in order to measure the carbon concentration with high sensitivity, it is necessary to prepare a thick and highly uniform sample. There was a problem. Further, it is necessary to lengthen the integration time when measuring the absorption spectrum, and there is a problem that the measurement time becomes long.

Further, in the case of SIMS, although the measurement sensitivity has been increased due to recent technological progress, there is a problem that an expensive analyzer and a highly specialized analysis technique are required. Further, in order to measure the carbon concentration with high sensitivity, there is a problem that the measurement time becomes long, for example, it takes a long time to evacuate in order to reduce the disturbance factor from the environment.

In addition, the charged particle activation analysis method has the advantage of being able to measure all carbon regardless of the presence of carbon, but it requires a special device and has low sensitivity, so it can be used as an evaluation method. There was a problem that it was difficult to use in general.

Further, in the techniques of Patent Documents 2 to 5, a large-scale device for irradiating a charged particle beam is required, and when measuring the luminescence intensity, the sample to be measured is cooled to about 30 K or less. There was a problem that it was necessary, laborious and costly. Further, there is a problem that it cannot be applied in the case of an NTD-FZ silicon single crystal substrate irradiated with neutrons to dope phosphorus.

Further, Patent Document 6 shows that the CZ silicon single crystal has a correlation between the bulk lifetime and the carbon concentration even when the heat treatment is not performed. However, the present inventor has conducted diligent research, and as a result of experiments by the present inventor, it has been found that there is no correlation between the carrier recombination lifetime and the carbon concentration in the FZ silicon single crystal when no heat treatment is applied.

The present invention has been made in view of the above-mentioned problems of the prior art, and is a method for easily and quickly evaluating the concentration of carbon contained in a silicon single crystal substrate prepared from a silicon single crystal grown by the FZ method. The purpose is to provide.

In order to achieve the above object, the present invention is a method for evaluating the carbon concentration contained in a silicon single crystal substrate prepared from a silicon single crystal grown by a floating zone melting method.
A first step of preparing a plurality of test silicon single crystal substrates having different carbon concentrations prepared from the silicon single crystal in advance and subjecting the plurality of test silicon single crystal substrates to a predetermined heat treatment.
A second step of measuring the carrier recombination lifetime LT in each of the plurality of test silicon single crystal substrates subjected to the predetermined heat treatment, and
Based on the measured recombination lifetime LT of the carriers of the plurality of test silicon single crystal substrates, the recombination lifetime LT of the carriers in the silicon single crystal substrate or 1 / LT which is the inverse of the recombination lifetime. , The third step of obtaining the correlation with the carbon concentration in the silicon single crystal substrate, and
A fourth method, in which the evaluation silicon single crystal substrate for evaluating the carbon concentration produced from the silicon single crystal is subjected to a heat treatment equivalent to a predetermined heat treatment for the plurality of test silicon single crystals performed in the first step. Process and
A fifth that measures the carrier recombination lifetime LT on the evaluation silicon single crystal substrate that has undergone the same heat treatment to obtain the carrier recombination lifetime LT or 1 / LT of the evaluation silicon single crystal substrate. Process and
The recombined lifetime LT or 1 / LT of the carrier of the obtained evaluation silicon single crystal substrate and the sixth step of evaluating the carbon concentration in the evaluation silicon single crystal substrate based on the correlation. Provided is a method for evaluating a carbon concentration in a silicon single crystal substrate, which comprises the present invention.

When a silicon single crystal substrate made from an FZ silicon single crystal is subjected to a predetermined heat treatment, the carbon contained in the silicon single crystal substrate becomes an electrically active defect (hereinafter, may be referred to as a carbon-related recombination center). Can be made to affect the recombination of carriers. From this, as described above, after the heat treatment of the plurality of test silicon single crystal substrates, the carrier recombination lifetime LT (hereinafter, also referred to as “recombining lifetime” and “LT”) is measured, and LT or 1 By obtaining the correlation between / LT and the carbon concentration in advance and using the correlation, the carbon concentration in the evaluation silicon single crystal substrate to be evaluated can be evaluated easily and quickly. It can be evaluated quickly and at low cost without the need for expensive analyzers and highly specialized analysis techniques as in conventional techniques.

At this time, as the predetermined heat treatment to be performed on the plurality of test silicon single crystal substrates in the first step, the heat treatment is performed at a heat treatment temperature of 600 ° C. or higher and 650 ° C. or lower and a heat treatment time of 4 hours or longer and 16 hours or shorter. Can be applied.

As described above, by performing the heat treatment at a heat treatment temperature of 600 ° C. or higher and 650 ° C. or lower and a heat treatment time of 4 hours or more and 16 hours or less, the carbon contained in the silicon single crystal substrate is more effectively electrically activated. Since it is possible to form various defects and affect the recombination of carriers, the carbon concentration can be evaluated more reliably and quickly.

By setting the heat treatment temperature to 600 ° C. or higher, the carrier recombination center formed during crystal growth can be more effectively eliminated in the GD-FZ silicon single crystal substrate. Further, in the NTD-FZ silicon single crystal substrate, the carrier recombination center formed during crystal growth and subsequent neutron irradiation can be more effectively eliminated. As a result, by setting the heat treatment temperature to 600 ° C. or higher and the heat treatment time to 4 hours or longer, the carrier recombination lifetime can be made more strongly dependent on the carbon concentration regardless of the dopant doping method. By later obtaining and using the above correlation, it is possible to more reliably evaluate the carbon concentration in the silicon single crystal substrate.
Further, by setting the heat treatment temperature to 650 ° C. or lower and the heat treatment time to 4 hours or more, it is possible to more effectively avoid the carrier recombination lifetime from being strongly dependent on the nitrogen concentration regardless of the dopant doping method. Since the carrier recombination lifetime can be made more strongly dependent on the carbon concentration, it is possible to more reliably evaluate the carbon concentration in the silicon single crystal by obtaining and using the above correlation after the heat treatment. can.
The upper limit of the heat treatment time is not particularly limited, but by setting it to 16 hours or less, it is possible to prevent the heat treatment time from becoming long and inefficient.

Further, in the second step and the fifth step, the microwave photoconductive attenuation method can be used as a method for measuring the recombination lifetime LT of the carrier.

As described above, by using the microwave photoconducting attenuation method (Microwave Photoconductive Decay measurement: μ-PCD method), the carrier recombination lifetime can be measured easily and quickly.

As described above, according to the method for evaluating the carbon concentration in a silicon single crystal of the present invention, after the FZ silicon single crystal substrate is heat-treated, the carrier recombination lifetime is measured, and the carrier recombination lifetime is measured. Since the correlation between carbon concentration and carbon concentration is obtained in advance and the carbon concentration is evaluated based on the correlation, a conventional technique that requires an expensive analyzer, highly specialized analysis technology, or takes time for measurement. Compared with, the carbon concentration can be evaluated easily and quickly.

It is a figure which shows the flow of the carbon concentration evaluation method in the silicon single crystal substrate of this invention. It is a figure which shows the relationship between the recombination lifetime (LT) of a carrier measured in an experimental example, and a carbon concentration. The heat treatment time is 16 hours, and the heat treatment temperature is 600 ° C. for (a), 625 ° C. for (b), and 650 ° C. for (c). It is a figure which shows the relationship between the reciprocal (1 / LT) of the carrier recombination lifetime measured in the experimental example, and carbon concentration. The heat treatment time is 16 hours, and the heat treatment temperature is 600 ° C. for (a), 625 ° C. for (b), and 650 ° C. for (c). It is a figure which shows the relationship between the recombination lifetime (LT) of a carrier measured in an experimental example, and a carbon concentration. The heat treatment temperature is 650 ° C., and the heat treatment time is 4 hours for (a), 8 hours for (b), and 16 hours for (c). It is a figure which shows the relationship between the reciprocal (1 / LT) of the carrier recombination lifetime measured in the experimental example, and carbon concentration. The heat treatment temperature is 650 ° C., and the heat treatment time is 4 hours for (a), 8 hours for (b), and 16 hours for (c). It is a figure which shows the relationship between the recombination lifetime (LT) of a carrier measured in an experimental example, and a carbon concentration. This is the case when no heat treatment is applied. It is a figure which shows the relationship between the reciprocal (1 / LT) of the carrier recombination lifetime measured in the experimental example, and carbon concentration. This is the case when no heat treatment is applied.

Hereinafter, the present invention will be described in detail with reference to the drawings as an example of embodiments, but the present invention is not limited thereto.
As described above, the conventional technique has a problem that an expensive analyzer, a specialized analysis technique, and a time required for measurement are required.
Therefore, the present inventor has made extensive studies on a method capable of evaluating the carbon concentration more easily and quickly in the FZ silicon single crystal substrate. After subjecting the silicon single crystal substrate to a predetermined heat treatment, the carrier recombination life When the time LT was measured, it was found that there was a correlation between LT or 1 / LT and the carbon concentration.

Further, a predetermined heat treatment and carrier recombination lifetime LT are measured on a plurality of test FZ silicon single crystal substrates having different carbon concentrations, and the LT or 1 / LT and the carbon concentration in the substrate are measured. On the other hand, the FZ silicon single crystal substrate for evaluation, which is the actual evaluation target, is subjected to the same heat treatment and LT measurement, and the obtained LT or 1 / LT and its carbon based on the above correlation are obtained. By evaluating the concentration, it was found that the carbon concentration can be evaluated more easily, faster and at lower cost than the conventional evaluation method, and the carbon concentration evaluation method in the silicon single crystal substrate of the present invention was completed.

Hereinafter, the method for evaluating the carbon concentration in the silicon single crystal substrate of the present invention will be described in more detail with reference to FIG.
First, the entire process will be described. As shown in FIG. 1, it consists of the first to third steps (S1 to S3), and uses a test silicon single crystal substrate (carbon concentration is known and each is different), and FZ silicon. Preliminary tests for determining the correlation between the carrier recombination lifetime LT in a single crystal substrate or 1 / LT, which is the inverse of the LT, and the carbon concentration in the FZ silicon single crystal substrate, and the fourth to sixth steps ( It consists of S4 to S6), and consists of this test for evaluating the carbon concentration in the evaluation silicon single crystal substrate (carbon concentration is unknown) to be evaluated. For both the preliminary test and the main test, an FZ silicon single crystal substrate made from an FZ silicon single crystal is used.

Hereinafter, each step will be described in detail. First, a plurality of test silicon single crystal substrates having different carbon concentrations are prepared in advance, and the plurality of test silicon single crystal substrates are heat-treated (first step, S1 in FIG. 1). A plurality of test silicon single crystal substrates having different carbon concentrations can be prepared by preparing a test silicon single crystal substrate from a plurality of silicon single crystals grown by the FZ method having different carbon concentrations in advance. At this time, a silicon single crystal substrate made from a silicon single crystal grown by the FZ method, which is an evaluation target, can also be prepared at the same time (evaluation silicon single crystal substrate). The method for preparing these silicon single crystal substrates is not particularly limited in the present invention. For example, it can be prepared by cutting a wafer from the silicon single crystal in question and performing a chemical etching process to remove the cutting damage. Next, a predetermined heat treatment is performed on the plurality of prepared silicon single crystal substrates for testing.

At this time, regarding the above-mentioned predetermined heat treatment, it is particularly desirable that the heat treatment temperature is 600 ° C. or higher and 650 ° C. or lower, and the heat treatment time is 4 hours or longer and 16 hours or lower. The atmosphere of the heat treatment is not particularly limited. For example, it can be oxygen, nitrogen, argon, or a mixed gas thereof.

By heat-treating the silicon single crystal substrate in this way, the carbon contained in the silicon single crystal substrate can form electrically active defects and affect the carrier recombination. Although details will be described later, the effect can be more effectively exerted by performing the heat treatment at the heat treatment temperature and the heat treatment time in the above range. Therefore, as in the subsequent step, the carbon concentration in the silicon single crystal can be easily evaluated by measuring the carrier recombination lifetime LT after the heat treatment and obtaining the correlation between the LT or 1 / LT and the carbon concentration. Can be done more reliably.
In particular, by setting the heat treatment time to 16 hours or less, it is possible to prevent inefficiency due to a long heat treatment.

Next, the carrier recombination lifetime LT is measured in each of the heat-treated test silicon single crystal substrates (second step, S2 in FIG. 1).
The carrier recombination lifetime is affected by surface recombination on the surface of the silicon single crystal substrate as well as the recombination centers generated on the silicon single crystal substrate. When the surface recombination of the silicon single crystal substrate becomes a problem in the measurement of the carrier recombination lifetime, a treatment for suppressing the surface recombination is performed. Thermal oxidation treatment (oxide pacification) and electrolytic solution treatment (chemical pacification) are generally used as treatments for suppressing this surface recombination.

In the present invention, it is more preferable to avoid performing the heat treatment in addition to the heat treatment in the first step. If the atmosphere of the heat treatment in the first step is oxygen or a mixed gas containing oxygen, a thermal oxide film can be formed on the surface of the silicon single crystal substrate, but the heat treatment temperature is low, so that a sufficient passivation effect can be obtained. May not be obtained. From this, as a treatment for suppressing surface recombination, in the present invention, it is more preferable to perform chemical passivation after removing the surface oxide film and the like formed in the first step.

The microwave photoconductive attenuation method (μ-PCD method) can be used to measure the carrier recombination lifetime. The measurement conditions in the μ-PCD method may be generally used conditions, and are described in, for example, the document “JEIDA-53-1997“ Method for measuring recombination lifetime by reflected microwave photoconductive attenuation method of silicon wafer ””. It can be measured according to the conditions and the like. A commercially available measuring device can be used. As described above, by using the μ-PCD method, the carrier recombination lifetime can be measured extremely easily and quickly.

Next, based on the carrier recombination lifetime LT of the plurality of test silicon single crystal substrates measured in the second step, the carrier recombination lifetime LT of the FZ silicon single crystal substrate or the recombination life The correlation between 1 / LT, which is the inverse of the time, and the carbon concentration in the FZ silicon single crystal substrate is obtained (third step, S3 in FIG. 1). The LT after heat treatment depends on the carbon concentration in the silicon single crystal substrate, and the higher the carbon concentration, the lower the LT and the higher 1 / LT. Therefore, by obtaining the LT or 1 / LT after the heat treatment, carbon is obtained. The concentration can be evaluated.

Next, the carbon concentration in the evaluation silicon single crystal substrate is evaluated using the correlation obtained in advance as described above. Specifically, the carbon concentration is evaluated by the following fourth to sixth steps.
The evaluation silicon single crystal substrate for which the carbon concentration is evaluated is subjected to the same heat treatment as the heat treatment for the plurality of test silicon single crystal substrates performed in the first step (fourth step, S4 in FIG. 1). ). This heat treatment can be performed separately from the heat treatment for the test silicon single crystal substrate, but it can also be performed at the same time.

Next, the recombination lifetime LT of the carrier of the evaluation silicon single crystal substrate is measured to obtain the LT or 1 / LT value of the evaluation silicon single crystal substrate (fifth step, S5 in FIG. 1). ..
Further, the carbon concentration in the evaluation silicon single crystal substrate is evaluated based on the LT or 1 / LT value thus obtained and the correlation obtained in the third step (sixth step, S6) in FIG.

In this way, after the evaluation silicon single crystal substrate to be evaluated is heat-treated, the carrier recombination lifetime is measured, and the LT or 1 / LT and the carbon concentration obtained in advance using the test silicon single crystal substrate are obtained. By using the correlation of, the carbon concentration contained in the evaluation silicon single crystal substrate can be evaluated easily and quickly.

Hereinafter, as the heat treatment conditions in the present invention, it is preferable that the heat treatment temperature is 600 ° C. or higher and 650 ° C. or lower and the heat treatment time is 4 hours or longer (16 hours or shorter).
As described above, when the FZ silicon single crystal substrate is heat-treated, particularly the heat treatment at the heat treatment temperature and the heat treatment time within the above range, as in the evaluation method of the present invention, the silicon single crystal substrate is more effectively contained. The carbon can be made to form electrically active defects and affect the recombination of carriers, and thus the carbon concentration in the silicon single crystal substrate can be easily evaluated more reliably. can.

Assuming that there is only one type of defect acting as the carrier recombination center, LT is proportional to the reciprocal of the recombination center density, so 1 / LT is the relative density of the recombination center. From this, when carbon is involved in the recombination center of the carrier, a correlation with the carbon concentration can be obtained for both LT and 1 / LT. Therefore, when obtaining the correlation with the carbon concentration, either LT or 1 / LT may be used. The changes in the absolute values of LT and 1 / LT with respect to the change in carbon concentration are larger in LT when the carbon concentration is low, and larger in 1 / LT when the carbon concentration is high.

As described above, especially when the FZ silicon single crystal substrate is heat-treated under the above conditions, the LT depends on the carbon concentration of the silicon single crystal substrate, and the higher the carbon concentration, the lower the LT and 1 / LT. The reason for the increase is considered as follows.

In the silicon single crystal growth step, intrinsic point defects (pores and interstitial silicon) are generated in the silicon single crystal, but when nitrogen is added under the standard FZ silicon single crystal growth conditions, the pores become predominant. Become. During the cooling process during crystal growth, nitrogen and vacancies react to form a nitrogen and vacancies complex (hereinafter referred to as nitrogen-related complex), which can contribute to the formation of nitrogen-related complex after cooling. Nitrogen and vacancies that were not present remain. When heat treatment is performed after growing a silicon single crystal, in addition to the nitrogen-related complex formed during the cooling process during the growth of the silicon single crystal, the remaining nitrogen reacts with the vacancies to form a nitrogen-related complex. .. This nitrogen-related complex acts as a carrier recombination center, and the higher the nitrogen concentration, the higher the density of the nitrogen-related complex. Therefore, the higher the nitrogen concentration, the higher the 1 / LT (relative density of the recombination center). , LT becomes low. The present inventor has found that LT or 1 / LT becomes dependent on the nitrogen concentration under heat treatment conditions different from the above heat treatment conditions in the present invention.

Further, when a silicon single crystal is irradiated with neutrons, intrinsic point defects are excessively generated in the silicon single crystal. Excessively generated vacancies and interstitial silicon are unstable by themselves, so they may recombine, cluster vacancies or interstitial silicon, or light element impurities (dopants) contained in a silicon single crystal. , Oxygen, carbon, nitrogen, etc.) to form a complex (hereinafter referred to as irradiation defect). The clusters of vacancies and interstitial silicon and the complex of vacancies and interstitial silicon and light element impurities act as the recombination center of carriers, and the higher the neutron irradiation dose, the higher the density of irradiation defects. The higher the irradiation amount, the higher the 1 / LT (relative density of the recombination center) and the lower the LT.

Since these nitrogen-related complexes formed during the growth of silicon single crystals and irradiation defects formed during neutron irradiation are thermally unstable, they disappear by heat treatment at least 600 ° C. or higher. Further, the nitrogen-related composite formed by the heat treatment after growing the silicon single crystal is formed in a short time when the heat treatment temperature is at least 700 ° C., but at the same time, nitrogen and pores are removed from the silicon single crystal substrate. Since it diffuses in a direction, the density of the nitrogen-related complex starts to increase and decrease after a certain heat treatment time. On the other hand, when the heat treatment temperature is 600 ° C. or higher and 650 ° C. or lower, carbon contained in the silicon single crystal forms electrically active defects and affects the recombination of carriers.

As a result, when the heat treatment is performed at a heat treatment temperature of 600 ° C. or higher and 650 ° C. or lower and a heat treatment time of 4 hours or longer, silicon is more reliably and extremely effectively with respect to the carrier recombination lifetime. It is considered that the influence of nitrogen-related complexes formed during single crystal growth or heat treatment and irradiation defects formed by neutron irradiation can be reduced, and the influence of carbon-related recombination centers can be increased.

In the present invention, the above-mentioned method for evaluating the carbon concentration in a silicon single crystal substrate and the particularly preferable heat treatment conditions (heat treatment temperature is 600 ° C. or higher and 650 ° C. or lower and heat treatment time is 4 hours or longer) are described in the above findings and the following. Based on the findings obtained by experiments such as.
<Experimental example>
A plurality of FZ silicon single crystal substrates having different carbon concentrations were prepared as FZ silicon single crystal substrates prepared from silicon single crystals grown by the FZ method. At this time, the dopant is phosphorus, and as a method for doping phosphorus, a gas doping method (GD method) in which phosphorus is doped from the atmospheric gas at the time of crystal growth and a nuclear conversion reaction ( ³⁰ ) in which neutrons are irradiated after the silicon single crystal is grown. The neutron irradiation doping method (NTD method) in which phosphorus is doped with Si (n, γ) → ³¹ Si → ³¹ P + β) was used. The dopant concentration, oxygen concentration, carbon concentration, nitrogen concentration, diameter, and crystal plane orientation of the plurality of FZ silicon single crystal substrates are as follows.

Dopant concentration: 6.0 × 10 ¹³ to 8.7 × 10 ¹³ atoms / cm ³ ,
Oxygen concentration: <0.1 ppma (when prepared from FZ silicon single crystal grown using polysilicon as a silicon raw material),
0.1 to 0.4 ppma (when prepared from FZ silicon single crystal grown using single crystal silicon grown by the Czochralski method (CZ method) as a silicon raw material),
Carbon concentration: 4 × 10 ^14-5 × 10 ¹⁵ atoms / cm ³ ,
Nitrogen concentration: 4 × 10 ^14-3 × 10 ¹⁵ atoms / cm ³ ,
Diameter: 200 mm,
Crystal plane orientation: (100).

The oxygen concentration was measured by the infrared absorption method (using the conversion factor specified by JEIDA), and the carbon concentration and the nitrogen concentration were measured by the secondary ion mass spectrometry (SIMS). The phosphorus concentration was determined using the Irvine curve from the resistivity measured by the four-probe method.

A silicon single crystal substrate having an oxygen concentration of less than 0.1 ppma is produced from a silicon single crystal grown by the FZ method using a normal polycrystalline silicon ingot as a raw material (referred to as pure Poly-FZ). Further, the silicon single crystal substrate having an oxygen concentration of 0.1 to 0.4 ppma is produced from a silicon single crystal grown by the FZ method using a silicon single crystal ingot grown by the CZ method as a raw material (). (Called CZ-FZ). At this time, when the silicon single crystal ingot grown by the CZ method is used as a raw material, the oxygen concentration varies in the range of 0.1 to 0.4 ppma depending on the difference in the oxygen concentration contained in the raw material and the single crystal growing conditions.

Next, the prepared silicon single crystal substrate was heat-treated. At this time, the heat treatment time was set to 16 hours, and the heat treatment temperature was shaken in the range of 600 to 650 ° C. Separately from this, the heat treatment temperature was set to 650 ° C., and the heat treatment time was shaken in the range of 4 to 16 hours. Under all heat treatment conditions, the heat treatment atmosphere was oxygen.

Next, the surface oxide film of the heat-treated silicon single crystal substrate was removed with an aqueous solution of hydrofluoric acid, and then a chemical passivation treatment was performed using an iodine-ethanol solution. Then, the carrier recombination lifetime LT was measured by the μ-PCD method. At this time, about 1600 points were measured at intervals of about 4 mm in the in-plane of the wafer having a diameter of 200 mm, excluding the region from the outer circumference to about 10 mm, and the average value was taken as the LT value. Moreover, 1 / LT was obtained from the measured LT.

Next, the correlation between LT or 1 / LT and the carbon concentration was investigated. The relationship between LT or 1 / LT and the carbon concentration is shown in FIGS. 2 to 5. The difference in the marks in each figure indicates the difference between the silicon raw material (pure Poly raw material, CZ raw material) and the phosphorus doping method (GD method, NTD method). In the case of the / GD method, Δ is the CZ raw material / GD method, □ is the pure Poly raw material / NTD method, and ◇ is the CZ raw material / NTD method.

FIG. 2 shows the relationship between LT and carbon concentration when the FZ silicon single crystal substrate is heat-treated at different temperatures. The heat treatment time is 16 hours, and the heat treatment temperature is 600 ° C. for (a), 625 ° C. for (b), and 650 ° C. for (c). At any heat treatment temperature, LT strongly depends on the carbon concentration, and the lower the carbon concentration, the higher the LT. Further, since there is almost no difference between the phosphorus doping method and the silicon raw material, it can be seen that the correlation between LT and the carbon concentration does not depend on the phosphorus doping method or the silicon raw material. Further, although not shown, since there is almost no difference depending on the nitrogen concentration, it can be seen that the correlation between LT and the carbon concentration does not depend on the nitrogen concentration. From this, it can be seen that the carbon concentration can be evaluated by measuring the LT after performing a predetermined heat treatment.

FIG. 3 shows the relationship between 1 / LT and the carbon concentration when the FZ silicon single crystal substrate is heat-treated at different temperatures. The heat treatment time is 16 hours, and the heat treatment temperature is 600 ° C. for (a), 625 ° C. for (b), and 650 ° C. for (c). At any heat treatment temperature, 1 / LT strongly depends on the carbon concentration, and the lower the carbon concentration, the lower the 1 / LT. Further, since there is almost no difference between the phosphorus doping method and the silicon raw material, it can be seen that the correlation between 1 / LT and the carbon concentration does not depend on the phosphorus doping method or the silicon raw material. Further, although not shown, since there is almost no difference depending on the nitrogen concentration, it can be seen that the correlation between 1 / LT and the carbon concentration does not depend on the nitrogen concentration. From this, it can be seen that the carbon concentration can be evaluated by measuring the carrier recombination lifetime (LT) after performing a predetermined heat treatment and determining 1 / LT.

FIG. 4 shows the relationship between LT and carbon concentration when the FZ silicon single crystal substrate is heat-treated for different times. The heat treatment temperature is 650 ° C., and the heat treatment time is 4 hours for (a), 8 hours for (b), and 16 hours for (c). In any of the heat treatment times, LT strongly depends on the carbon concentration, and the lower the carbon concentration, the higher the LT. Further, since there is almost no difference between the phosphorus doping method and the silicon raw material, it can be seen that the correlation between LT and the carbon concentration does not depend on the phosphorus doping method or the silicon raw material. Further, although not shown, since there is almost no difference depending on the nitrogen concentration, it can be seen that the correlation between LT and the carbon concentration does not depend on the nitrogen concentration. From this, it can be seen that the carbon concentration can be evaluated by measuring the carrier recombination lifetime (LT) after performing a predetermined heat treatment.

FIG. 5 shows the relationship between 1 / LT and the carbon concentration when the FZ silicon single crystal substrate is heat-treated for different times. The heat treatment temperature is 650 ° C., and the heat treatment time is 4 hours for (a), 8 hours for (b), and 16 hours for (c). In any of the heat treatment times, 1 / LT strongly depends on the carbon concentration, and the lower the carbon concentration, the lower the 1 / LT. Further, since there is almost no difference between the phosphorus doping method and the silicon raw material, it can be seen that the correlation between 1 / LT and the carbon concentration does not depend on the phosphorus doping method or the silicon raw material. Further, although not shown, since there is almost no difference depending on the nitrogen concentration, it can be seen that the correlation between 1 / LT and the carbon concentration does not depend on the nitrogen concentration. From this, it can be seen that the carbon concentration can be evaluated by measuring the carrier recombination lifetime (LT) after performing a predetermined heat treatment and determining 1 / LT.

Further, the carrier recombination lifetime LT was measured by the same procedure except that the prepared silicon single crystal substrate was not heat-treated, and 1 / LT was obtained from the measured LT.

FIG. 6 shows the relationship between LT and carbon concentration when the FZ silicon single crystal substrate is not heat-treated. In FIG. 6, in the case of the NTD-FZ silicon single crystal substrate, the recombination lifetime was extremely short due to the damage of neutron irradiation, which was about 0.1 μsec. As described above, when the FZ silicon single crystal substrate is not heat-treated, the LT does not depend on the carbon concentration. Therefore, it can be seen that the carbon concentration cannot be evaluated by measuring the carrier recombination lifetime (LT). ..

FIG. 7 shows the relationship between 1 / LT and the carbon concentration when the FZ silicon single crystal substrate is not heat-treated. As described above, when the FZ silicon single crystal substrate is not heat-treated, 1 / LT does not depend on the carbon concentration. Therefore, it is possible to measure the carrier recombination lifetime (LT) and obtain 1 / LT. It turns out that the carbon concentration cannot be evaluated.

In the experimental example shown in FIG. 2-3, the heat treatment time was set to 16 hours, but even when the heat treatment time was set to 4 hours and 8 hours in the same experiment, the relationship between LT and 1 / LT and the carbon concentration was set. In, the same tendency (correlation) as in FIG. 2-3 was observed.
Further, in the experimental example of FIG. 4-5, the heat treatment temperature was set to 650 ° C., but even when the heat treatment temperature was set to 600 ° C. and 625 ° C. in the same experiment, the relationship between LT and 1 / LT and the carbon concentration was set. In, the same tendency as in FIG. 4-5 was observed.
Furthermore, when the same experiment was conducted in the range where the heat treatment temperature and the heat treatment time were 600 ° C. or higher and 650 ° C. or lower, respectively, slightly out of the range of 4 hours or more and 16 hours, the same tendency as in FIG. 2-5 was observed. Was done.
In any case, when heat treatment is performed, the carbon concentration can be evaluated based on the obtained correlation, and when the heat treatment time and heat treatment temperature are within the range of 600 ° C. or higher and 650 ° C. or lower, 4 hours or longer and 16 hours, The carbon concentration could be evaluated with high accuracy.

As described above, by measuring the carrier recombination lifetime LT after heat-treating the FZ silicon single crystal substrate, a correlation between LT (or 1 / LT) and the carbon concentration is obtained, and the correlation is obtained. It can be seen that the carbon concentration in the silicon single crystal substrate can be evaluated easily and quickly by using the relationship. In particular, it is extremely preferable to perform the heat treatment at a heat treatment temperature of 600 ° C. or higher and 650 ° C. or lower and a heat treatment time of 4 hours or longer and 16 hours or shorter because a clearer correlation can be obtained more reliably.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
(Example)
The carbon concentration in the FZ silicon single crystal substrate was evaluated by the carbon concentration evaluation method of the present invention as shown in FIG.
(Preliminary test)
First, a plurality of test silicon single crystal substrates having different carbon concentrations were heat-treated (S1 in FIG. 1). The plurality of test silicon single crystal substrates are FZ silicon single crystal substrates prepared from silicon single crystals grown by the FZ method, and the dopant concentration, oxygen concentration, carbon concentration, nitrogen concentration, diameter, and crystal plane orientation are It is the same as the above-mentioned experimental example.
At this time, the heat treatment temperature was 650 ° C., the time was 16 hours, and the atmosphere was oxygen.

Next, the surface oxide film of the heat-treated test silicon single crystal substrate was removed with an aqueous hydrofluoric acid solution, and then a chemical passivation treatment was performed using an iodine-ethanol solution. Then, the carrier recombination lifetime LT was measured by the μ-PCD method (S2 in FIG. 1). At this time, about 1600 points were measured at intervals of about 4 mm in the in-plane of the wafer having a diameter of 200 mm, excluding the region from the outer circumference to about 10 mm, and the average value was taken as the LT value. Moreover, 1 / LT was obtained from the measured LT.
In the evaluation method of the present invention, it is sufficient to obtain and use either LT or 1 / LT, but in order to show the effectiveness in each case, both values are obtained here, and both are obtained as follows. The carbon concentration was evaluated by showing the correlation with the carbon concentration in the case of.

Next, the correlation between LT and 1 / LT and the carbon concentration was acquired (S3 in FIG. 1). As a result, the correlations shown in FIGS. 2 (c) and 3 (c) were obtained.

(Main test)
Next, a phosphorus-doped GD-FZ silicon single crystal substrate by the gas doping method and a phosphorus-doped NTD-FZ silicon single crystal substrate by the neutron irradiation doping method were prepared from separately grown FZ silicon single crystal ingots. A silicon single crystal substrate for evaluation whose carbon concentration was unknown was heat-treated. The dopant concentration of the GD-FZ silicon single crystal substrate is 6.2 × 10 ¹³ atoms / cm ³ , the oxygen concentration is 0.2 ppma (JEIDA), the nitrogen concentration is 1.5 × 10 ¹⁵ atoms / cm ³ , and the diameter is 200 mm. The crystal plane orientation is (100). The dopant concentration of the NTD-FZ silicon single crystal substrate is 6.5 × 10 ¹³ atoms / cm ³ , the oxygen concentration is 0.4 ppma (JEIDA), the nitrogen concentration is 3.5 × 10 ¹⁵ atoms / cm ³ , and the diameter is 200 mm. The crystal plane orientation is (100). At this time, the heat treatment conditions were the same as in the preliminary test, the heat treatment temperature was 650 ° C., the time was 16 hours, and the atmosphere was oxygen (S4 in FIG. 1).

Next, the surface oxide film of the heat-treated evaluation silicon single crystal substrate was removed with an aqueous hydrofluoric acid solution, and then a chemical passivation treatment was performed using an iodine-ethanol solution. Then, the carrier recombination lifetime LT was measured by the μ-PCD method. At this time, about 1600 points were measured at intervals of about 4 mm in the in-plane of the wafer having a diameter of 200 mm, excluding the region from the outer circumference to about 10 mm, and the average value was taken as the LT value. Moreover, 1 / LT was obtained from the measured LT. As a result, the LT of the GD-FZ silicon single crystal substrate was 296.7 μsec, and the 1 / LT was 0.003 μsec ^-1 . The LT of the NTD-FZ silicon single crystal substrate was 93.1 μsec, and the 1 / LT was 0.011 μsec ^-1 (S5 in FIG. 1).

Next, the carbon concentration in the evaluation silicon single crystal substrate was evaluated based on the correlations shown in FIGS. 2 (c) and 3 (c) (S6 in FIG. 1). As a result, the carbon concentration in the GD-FZ silicon single crystal substrate was found to be about 5 × 10 ¹⁴ atoms / cm ³ , and the carbon concentration in the NTD-FZ silicon single crystal substrate was found to be about 3 × 10 ¹⁵ atoms / cm ³ .

(Comparison example)
Another silicon single crystal substrate was prepared from an adjacent position of the silicon single crystal ingot on which the evaluation silicon single crystal substrate of the example was prepared, and the carbon concentration of the silicon single crystal substrate was measured by SIMS. SIMS analysis was outsourced to an analysis contractor with specialized skills.
As a result, the carbon concentration in the GD-FZ silicon single crystal substrate was 4.8 × 10 ¹⁴ atoms / cm ³ , and the carbon concentration in the NTD-FZ silicon single crystal substrate was 3.1 × 10 ¹⁵ atoms / cm ³ . rice field. However, it took more than a week to obtain the measurement result, and the analysis cost was high.

As described above, while the conventional technique requires a long time for measurement and is costly, in the present invention, the recombination lifetime of carriers after heat treatment can be measured by a simple method, so that carbon can be easily and quickly measured. The concentration can be evaluated. Moreover, the carbon concentration can be obtained with the same measurement accuracy as the conventional technique.

The present invention is not limited to the above embodiment. The above embodiment is an example, and any one having substantially the same structure as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. It is included in the technical scope of the invention.

Claims (3)

It is a method for evaluating the carbon concentration contained in a silicon single crystal substrate prepared from a silicon single crystal grown by the floating zone melting method.
A first step of preparing a plurality of test silicon single crystal substrates having different carbon concentrations prepared from the silicon single crystal in advance and subjecting the plurality of test silicon single crystal substrates to a predetermined heat treatment.
A second step of measuring the carrier recombination lifetime LT in each of the plurality of test silicon single crystal substrates subjected to the predetermined heat treatment, and
Based on the measured recombination lifetime LT of the carriers of the plurality of test silicon single crystal substrates, the recombination lifetime LT of the carriers in the silicon single crystal substrate or 1 / LT which is the inverse of the recombination lifetime. , The third step of obtaining the correlation with the carbon concentration in the silicon single crystal substrate, and
A fourth method, in which the evaluation silicon single crystal substrate for evaluating the carbon concentration produced from the silicon single crystal is subjected to a heat treatment equivalent to a predetermined heat treatment for the plurality of test silicon single crystals performed in the first step. Process and
A fifth that measures the carrier recombination lifetime LT on the evaluation silicon single crystal substrate that has undergone the same heat treatment to obtain the carrier recombination lifetime LT or 1 / LT of the evaluation silicon single crystal substrate. Process and
The recombined lifetime LT or 1 / LT of the carrier of the obtained evaluation silicon single crystal substrate and the sixth step of evaluating the carbon concentration in the evaluation silicon single crystal substrate based on the correlation. A method for evaluating a carbon concentration in a silicon single crystal substrate, which comprises. In the first step, as a predetermined heat treatment to be applied to the plurality of test silicon single crystal substrates, a heat treatment having a heat treatment temperature of 600 ° C. or higher and 650 ° C. or lower and a heat treatment time of 4 hours or more and 16 hours or less is performed. The method for evaluating a carbon concentration in a silicon single crystal substrate according to claim 1. The silicon single crystal according to claim 1 or 2, wherein a microwave photoconductive attenuation method is used as a method for measuring the recombination lifetime LT of the carriers in the second step and the fifth step. A method for evaluating the carbon concentration in a crystal substrate.

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