JP2002012497A - Method for producing silicon single crystal and method for manufacturing epitaxial wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an epitaxial wafer reduced in epitaxial flaw density and excellent in intrinsic gettering effect. SOLUTION: This method for producing a silicon single crystal by CZ method is characterized in that nitrogen is doped in the range of 1×1012-1×1014 atoms/cm3 and the cooling rate at temperatures of 1,150-1,020 deg.C is regulated to more than 2.7 deg.C/min, or further that at temperatures of 1,000-850 deg.C is regulated to below 1.2 deg.C/min. Alternatively, the nitrogen is doped in the range of 5×1013-1×1016 atoms/cm3 and the cooling rate at temperatures of 1,150-800 deg.C is regulated to more than 6.5 deg.C/min. The method for manufacturing an epitaxial wafer comprises growing an epitaxial layer on the surface of the silicon wafer cut out from the silicon single crystal which is produced by the above production method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a silicon single crystal used for a semiconductor integrated circuit device, and a method of manufacturing an epitaxial wafer from the silicon single crystal manufactured by the method. More specifically, when growing an epitaxial layer on a wafer obtained from a nitrogen-doped silicon single crystal, defects such as stacking faults and dislocations (hereinafter referred to as “epitaxial defects”) generated in the epitaxial layer are generated. The present invention relates to a method for manufacturing an epitaxial wafer which exhibits a small and excellent gettering action at the same time.

[0002]

2. Description of the Related Art In recent years, the integration density of silicon semiconductor devices has been rapidly increasing, and the requirements regarding the quality of silicon wafers forming the devices have become strict.
For example, in the so-called "device active region" where devices are formed on a wafer, crystal defects such as dislocations and metallic impurities cause an increase in leakage current and a reduction in carrier lifetime, so they are formed with high integration. As circuits to be implemented become finer, they are more severely restricted.

Conventionally, a wafer cut from a silicon single crystal manufactured by the Czochralski method (hereinafter referred to as “CZ method”) has been used for semiconductor devices. This wafer typically contains 10 ¹⁸ atoms / c
m ³ approximately supersaturated oxygen is contained. This oxygen forms an oxygen precipitate due to the thermal history at the time of device formation, and forms crystal defects such as dislocations and stacking faults. However, during the device manufacturing process, the LOCOS (lo
During the formation by cal oxidation of silicon and the formation of the well diffusion layer, it is maintained at about 1100 ° C for several hours.
so-called DZ layer (denuded zon
e) is formed. Since this DZ layer becomes a device active region, generation of crystal defects was naturally suppressed.

However, with the miniaturization of semiconductor devices, high-energy ion implantation is used for forming wells, and when the device process is performed at a low temperature of 1000 ° C. or less, the above-mentioned oxygen outdiffusion does not sufficiently occur, and the surface of the oxygen is not sufficiently generated. The DZ layer is not sufficiently formed in the vicinity. For this reason, the oxygen of the wafer has been reduced, but it has been difficult to completely suppress the generation of crystal defects.

[0005] Under such circumstances, an epitaxial wafer in which an epitaxial layer substantially free of crystal defects is grown on the wafer has been developed and has been widely used for highly integrated devices. However, even if an epitaxial wafer with high crystal perfection is used, device characteristics will be degraded due to metal impurity contamination of the epitaxial layer in a subsequent device process.

[0006] The contamination by such impurities of the metal element becomes more complicated as the integration becomes higher in density.
The opportunities increase and the impact increases. The elimination of contamination basically consists in making the process environment and the materials used clean, but it is difficult to completely eliminate it in the device process, and a gettering technique is required as a countermeasure. This is a means for capturing the impurity element that has entered due to contamination at a location (sink) outside the device active region and rendering it harmless.

As a gettering technique, intrinsic gettering (hereinafter simply referred to as "I"), which captures an impurity element by utilizing oxygen precipitates caused by oxygen naturally induced during heat treatment in a device process.
G ”). However, when the wafer is subjected to a high-temperature heat treatment of 1050 ° C. to 1200 ° C. in the epitaxial process, the oxygen precipitation nuclei inherent in the wafer cut out of the silicon single crystal shrink and disappear, and in the subsequent device process, the wafer becomes It becomes difficult to sufficiently induce oxygen precipitation nuclei as a gettering source. Therefore, even if this gettering technique is applied, there arises a problem that a sufficient IG effect on metal impurities cannot be expected over the entire process.

Conventionally, in order to solve such a problem, nitrogen is doped when growing a single crystal by the CZ method, and oxygen precipitation nuclei which are hardly lost even by a high-temperature heat treatment performed in an epitaxial process are formed inside the wafer. A method for producing a silicon single crystal to be formed has been proposed (see, for example, JP-A-11-189493 and JP-A-2000-44389).

According to the proposed manufacturing method, the thermal stability of the oxygen precipitate nuclei in the crystal is increased by doping and growing nitrogen by the CZ method, and the oxygen precipitate nuclei are reduced by the epitaxial process. A silicon single crystal that does not disappear can be obtained. In the case of a wafer cut out of this single crystal, oxygen precipitate nuclei remaining after the epitaxial process form oxygen precipitates from the initial stage of the device process and effectively act as a gettering sink, so The IG effect can be expected from the initial stage.

[0010] However, according to the results of subsequent research, when nitrogen is doped at a high concentration, for example, nitrogen is doped at 1%.
When doped at a concentration of × 10 ¹⁴ atoms / cm ³ or more, thermally stable oxygen precipitate nuclei that are not lost even by high-temperature heat treatment in the epitaxial process are formed inside the wafer and in the vicinity of the wafer surface. Therefore, in the epitaxial process, stacking faults and dislocations are generated in the epitaxial layer starting from the thermally stable oxygen precipitation nuclei formed in the vicinity of the wafer surface, and there is a problem that epitaxial defects are easily induced. There was found. This epitaxial defect causes an increase in device leak current, a deterioration in oxide film breakdown voltage, and the like.

Meanwhile, when doped with nitrogen in a low concentration, for example, when nitrogen is doped at a concentration of 5 × 10 ¹³ atoms / cm ³ or less, although not seen a problem that epitaxial defects, oxygen precipitation nuclei by nitrogen addition Since the effect of increasing the thermal stability of the wafer is low, even high-temperature heat treatment in the epitaxial process causes even the oxygen precipitation nuclei inside the wafer to disappear. Is not formed, and the IG effect is low.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems relating to epitaxial defects accompanying nitrogen doping, and has been made in consideration of an epitaxial wafer formed from a silicon single crystal grown by doping with nitrogen. Even so, the object of the present invention is to provide a method for manufacturing a silicon single crystal and a method for manufacturing an epitaxial wafer, in which the occurrence of epitaxial defects is suppressed and at the same time, oxygen precipitates are sufficiently formed in a high-temperature heat treatment in a device process. I have.

[0013]

Means for Solving the Problems The present inventors have investigated the effect of crystal heat history on the thermal stability of oxygen precipitation nuclei formed in nitrogen-doped single crystals by the CZ method. Using a 6 ″ silicon single crystal, an experiment was performed to change the pulling speed in the middle of the process.

According to a specific experimental method, a straight body is grown up to a length of 500 mm at a pulling speed of 0.7 mm / min, and a length of 500 mm.
At the time of mm, the pulling speed is reduced to 0.2 mm / min or increased to 1.2 mm / min to grow to a length of 550 mm. After that, the pulling speed is returned to 0.7 mm / min again, and the seedling is grown to 850 mm, and then the tail drawing is performed to finish the pulling. At this time, the concentration of nitrogen doped in the single crystal was 1 × 10 ¹³ atoms / cm ³ .

When the pulling speed is reduced in accordance with the change of the pulling speed, the single crystal grown in this manner is gradually cooled from the temperature at the start of the deceleration to a lower temperature side in a temperature range of about 100 ° C. On the other hand, when the pulling speed is increased, the temperature is rapidly cooled from the temperature at the start of deceleration to a lower temperature side in a temperature range of about 100 ° C. After pulling, of the single crystal
A sample is cut out from the part cooled in the temperature range of 1400 to 800 ° C, subjected to a high-temperature heat treatment at 1100 ° C x 16 hours, the number of heat-induced defects is measured, the oxygen precipitate density is measured, and the CZ is pulled up. The thermal stability of the oxygen precipitate formed in was investigated.

FIG. 1 is a diagram showing the relationship between the number of heat treatment-induced defects and the temperature at the start of the pulling rate change in an experiment of changing the pulling rate in the middle of the process by the CZ method. From the results in FIG. 1, it can be seen that by rapidly cooling the temperature range of 1150 ° C. to 1020 ° C., the number of heat treatment induced defects increases and the density of oxygen precipitates increases. Also, it can be seen that the density of oxygen precipitates is stably increased by gradually cooling in the temperature range of 1000 ° C to 850 ° C.

Furthermore, the present inventors investigated the temperature range in which cavities, which are vacancy-type defects formed during the growth of single crystals by nitrogen doping, and the temperature range in which oxygen precipitation nuclei are formed.
Separation quenching experiment by the method was performed. Specifically, after forming a straight body of a single crystal for a predetermined length, the pulling is stopped for a predetermined time, and thereafter, the single crystal is separated from the melt, and the defect density of the single crystal is measured ( If necessary, see JP-A-10-236897).

In the above experiment, the defect formation temperature during crystal growth was
Nitrogen should be 1 × 10 ¹⁴atoms / cm^ThreeConcentration of
To grow a 6 ″ diameter silicon single crystal.
The test conditions were as follows: 5 while raising the straight body at a pulling speed of 1.0 mm / min.
Hr crystal growth stopped, then separated from solid-liquid interface
Later, the single crystal is vertically split in the pulling direction to
The generation density is to be measured. And cavity defects
Is detected by Bio-Rad's defect detector OPP
(Optical Precipitate Profiler)
evaluated.

FIG. 2 is a diagram showing the relationship between the OPP defect density and the temperature at the time of crystal separation in a separation and rapid cooling experiment by the CZ method. From the results in FIG. 2, it can be seen that the temperature range in which cavity defects are easily formed is 1100 ° C. to 1020 ° C. Conventionally,
It was reported that when nitrogen was not added, the temperature range in which cavity defects were formed was 1100 ° C to 1070 ° C (H.Ni
shikawa, T. Tanaka, Y. Yanase, M. Hourai, M. Sanno
and H. Tsuya, Jpn.J. Appl. Phys. Vol36 (1997) p65
95). However, from the above results, it becomes clear that the temperature range of defect formation is expanded to about 50 ° C. lower by doping with nitrogen. That is, it is indicated that the addition of nitrogen suppressed the diffusion of vacancies, and the vacancies had a high degree of supersaturation even at 1070 ° C. or less, and formed cavity defects.

Next, in order to clarify the formation temperature of the oxygen precipitation nucleus, the sample obtained by the cutting and quenching experiment was subjected to an isothermal heat treatment at 1050 ° C. for 4 hours and then etched to measure its density.

FIG. 3 is a diagram showing the relationship between the etch pit density and the temperature at the time of crystal separation in a separation and rapid cooling experiment by the CZ method. From the results in Fig. 3, the temperature at the time of disconnection is
It can be seen that etch pits are observed below 1050 ° C.
In particular, it is remarkable when the temperature at the time of separation is in the range of 1050 ° C to 800 ° C. This indicates that stable oxygen precipitation nuclei are formed in a temperature range of 1050 ° C. or less in the cooling process during crystal growth.

Conventionally, in crystals without addition of nitrogen, formation of oxygen precipitation nuclei is observed only when the temperature at the time of separation is 900 ° C.
Although the temperature range was described as follows, it can be seen from the above results that the temperature range in which oxygen precipitation nuclei were formed was increased by adding nitrogen. This is because the residual vacancies increase due to the effect of nitrogen addition, the free energy for forming oxygen precipitation nuclei decreases, and it becomes possible to form oxygen precipitation nuclei in a higher temperature range than before.

The present invention has been completed on the basis of the findings obtained by the above-described pulling speed change experiment and the separation quenching experiment by the CZ method. In particular, epitaxial defects are generated according to the concentration of nitrogen to be doped. The present inventors have found that there is an appropriate cooling rate for producing a single crystal having an excellent oxygen precipitate density, and have completed the present invention.

In the method of manufacturing a silicon single crystal according to the first aspect, nitrogen is preferably 1 × 10 ¹² atoms / cm ³ or less by a CZ method.
A method for producing a silicon single crystal doped in a range of 1 × 10 ¹⁴ atoms / cm ³ , wherein a cooling rate is set to 2.7 ° C./min or more in a temperature range where the single crystal is 1150 ° C. to 1020 ° C. (Hereinafter, referred to as “first method”).

In the first method, the range of the concentration of nitrogen to be doped is limited to 1 × 10 ¹² atoms / cm ³ to 1 × 10 ¹⁴ atoms / cm ^{3 because the} concentration of nitrogen is lower than 1 × 10 ¹² atoms / cm ^3. Is low, the thermal stability effect of the oxygen precipitate nuclei is low, so that the oxygen precipitate nuclei inside the wafer are extinguished by the high-temperature heat treatment in the epitaxial step, and 1 × 10 ¹⁴ atoms / c
If concentrations than m ³ is high, in the thermal stability effect of oxygen precipitation nuclei is too high, high thermal stability oxygen precipitate nuclei present in the vicinity of the wafer surface even when subjected to high temperature heat treatment of the epitaxial step Does not disappear and an epitaxial defect is generated.

The reason why the temperature range for cooling is limited to 1150 ° C. to 1020 ° C. is that, as is apparent from the result of FIG. This is because the density of the object can be increased. Furthermore, what sets the cooling rate to be rapid cooling of 2.7 ° C./min or more is the cooling rate secured in the pulling rate change test described above, and it has been confirmed that a sufficient cooling effect is exhibited.

That is, in the first method, by setting the range of the nitrogen concentration to a relatively low concentration of 1 × 10 ¹² atoms / cm ³ to 1 × 10 ¹⁴ atoms / cm ³ , thermally stable oxygen deposition Suppress nucleation while keeping the single crystal quenched in the temperature range of 1150 ° C to 1020 ° C to prevent agglomeration of vacancies captured at the solid-liquid interface and keep the concentration of residual vacancies high Thus, the formation of oxygen precipitation nuclei is started at a higher temperature, thereby achieving the growth of oxygen precipitation nuclei. Thereby, generation of epitaxial defects can be prevented, and oxygen precipitates can be sufficiently formed even in heat treatment after epitaxial growth.

According to a second aspect of the present invention, there is provided a method of manufacturing a silicon single crystal, wherein nitrogen is set to 1 × 10 ¹² atoms / cm ³ or less by a CZ method.
A method for producing a silicon single crystal doped in the range of 1 × 10 ¹⁴ atoms / cm ³ , wherein the single crystal has a cooling rate of 2.7 ° C./min or more in a temperature range of 1150 ° C. to 1020 ° C.
The cooling rate in the temperature range of 00 ° C. to 850 ° C. is 1.2 ° C./min or less (hereinafter, referred to as “second method”).

The second method is as follows, except that the cooling rate in the temperature range of 1000 ° C. to 850 ° C. is set to 1.2 ° C./min or less.
It is the same as the first method. Here, the slow cooling in the temperature range of 1000 ° C. to 850 ° C. is, as is apparent from the results of FIG. 1, that the slow cooling in this temperature range also promotes the growth of oxygen precipitation nuclei. This makes it possible to form oxygen precipitation nuclei having a relatively large size.

The cooling rate in a limited temperature range is 1.2 ° C.
The reason why the slow cooling is set to be not more than / min is based on the above-mentioned pulling rate change test, and is because sufficient growth of oxygen precipitation nuclei can be achieved.

According to a third aspect of the present invention, there is provided a method of manufacturing a silicon single crystal, wherein nitrogen is 5 × 10 ¹³ atoms / cm ³ or less by a CZ method.
A method for producing a silicon single crystal doped in the range of 1 × 10 ¹⁶ atoms / cm ³ , wherein the single crystal has a cooling rate of 6.5 ° C./min or more in a temperature range of 1150 ° C. to 800 ° C. (Hereinafter, referred to as “third method”).

As described above, it is effective to set the nitrogen concentration low from the viewpoint of preventing the generation of epitaxial defects. However, when the nitrogen concentration is increased, the oxygen precipitation nuclei inside the wafer are thermally reduced. Therefore, it is effective to use the heat treatment since high temperature heat treatment suppresses its disappearance and contributes to increase in oxygen precipitate density.

Therefore, the present inventor believes that even if the thermally stable oxygen precipitation nuclei are not large in size, the oxygen precipitation nuclei near the wafer surface will disappear by the high-temperature heat treatment of epitaxial growth. Invented a method.

In the third method, first, the range of the concentration of nitrogen to be doped is set to a relatively high concentration of 5 × 10 ¹³ atoms / cm ³ to 1 × 10 ¹⁶ atoms / cm ³ , so that a thermally stable oxygen is added. The formation of precipitation nuclei is aimed at. By rapidly cooling the temperature range of 1150 ° C. to 800 ° C. at 6.5 ° C./min or more, a temperature range in which cavity defects are formed (see FIG. 2) and a temperature range in which oxygen precipitate nuclei grow (see FIG. 3) 1150)
By cooling as quickly as possible in the temperature range of ℃ to 800 ℃, the formation of cavity defects and the growth of thermally stable oxygen precipitate nuclei, which are presumed to be the cause of epitaxial defects, are suppressed.

The upper limit of the nitrogen concentration to be doped in the third method is set to 1 × 10 ¹⁶ atoms / cm ³ or less. If the upper limit is exceeded, dislocation of the single crystal due to generation of a crystal axis breakage occurs during single crystal growth. However, the product yield is greatly reduced. Also, the cooling rate is defined as rapid cooling at 6.5 ° C./min or more. If the cooling rate is lower than this, the effect of suppressing the condensation of vacancies is small due to the high concentration of nitrogen to be doped. This is because a large oxygen precipitation nucleus having a thermally stable large size is formed because the effect of suppressing is low.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an epitaxial wafer, wherein an epitaxial layer is grown on a surface of a silicon wafer cut from a silicon single crystal obtained by the first to third methods. And

It is possible to produce an epitaxial wafer which exhibits an excellent IG effect and has few epitaxial defects. In other words, a high quality epitaxial wafer having no defect in the device active region can be manufactured.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the oxygen concentration in a single crystal to be grown is set to 4 × 10 ¹⁷ atoms / cm ³ (ASTM'79 ) Is desirable. As described above, a silicon single crystal manufactured by the CZ method usually contains 10 ¹⁸ atoms / cm ³
Although the degree of supersaturated oxygen is contained, if the contained oxygen concentration is insufficient, the wafer strength is significantly reduced,
This is because a sufficient IG effect cannot be exhibited.

The doping method employed in the present invention may be any method as long as it can dope a required concentration of nitrogen. For example, mixing of a nitride in a raw material or a melt, and addition of nitrogen Floating zone method (FZ method)
Of silicon crystal and wafer with silicon nitride film formed on the surface by mixing, raw material growth, single crystal growth while flowing nitrogen or nitrogen compound gas into furnace, nitrogen to polycrystalline silicon at high temperature before melting Blowing of a nitrogen compound gas, use of a crucible made of nitride and the like can be mentioned.

The epitaxial wafer manufactured according to the present invention is doped with nitrogen by the first to third methods, slices a silicon single crystal having a controlled thermal history, polishes the surface, and forms an epitaxial layer after cleaning. . When growing an epitaxial layer, apply any method for forming an epitaxial layer without crystal defects, such as a thermal decomposition method of a vapor phase growth method, on the wafer surface obtained by cutting out the single crystal described above. Can be.

[0041]

EXAMPLES In order to confirm the effects of the first to third methods of the present invention, confirmation tests were performed based on the following Examples 1 to 3. However, the content of the present invention is not limited to these examples.

FIG. 4 is a view for explaining a schematic configuration of an apparatus for producing a silicon single crystal by the CZ method used in the embodiment.
A crucible 1 is arranged at the center of the apparatus, and is composed of a quartz container 1a and a graphite container 1b fitted to the outside thereof.
A heater 2 is disposed concentrically around the outer periphery of the crucible 1, and a melt 3 melted by the heater is accommodated in the crucible 1. Above the crucible 1, a pulling shaft 4 is provided with a seed crystal 5 attached thereto, and is rotatably and vertically movable so that the single crystal 6 can be grown from the lower end of the seed crystal 5.
The heat shield material 7 surrounds the single crystal 6 to be grown.
Is arranged.

In the second method, in addition to the first method, 1000 ° C.
It is to be cooled slowly in the temperature range of ~ 850 ° C. There are various methods for implementing the second method using the manufacturing apparatus shown in FIG. For example, it becomes possible by optimizing the heat shield material 7. As shown in FIG. 5, the heat radiation from the heater 2 is increased by partially thinning the heat insulating material of the heat shield material 7, and the silicon single crystal is gradually cooled in a temperature range of 1000 ° C. to 850 ° C. can do. (Example 1) In Example 1, in order to confirm the effect of the first method, using the manufacturing apparatus shown in FIG.
p-type (100) silicon single crystal (initial oxygen concentration: 1 × 10
¹⁸ atoms / cm ³ (ASTM'79)). 115 when pulled up
For cooling in the temperature range of 0 ° C to 1020 ° C, the pulling speed is 0.7mm /
A single crystal was manufactured by controlling the concentration in the range of min to 2.0 mm / min and changing the concentration of nitrogen to be doped. Table 1 shows the nitrogen concentration and the cooling rate at this time.

A wafer was cut out from the manufactured single crystal, and after polishing and cleaning the surface, an epitaxial layer was grown at a deposition temperature of 1150 ° C., and the epitaxial defect density was measured by a commercially available surface defect measuring device. Next, these wafers are heat-treated at 1000 ° C for 16 hours, the wafers are cleaved, selective etching is performed for 5 minutes with a light etching solution, and the etching pit density is counted with an optical microscope to form the wafers. The heat treatment induced defect density was measured. Table 1 shows the measurement results.

[0045]

[Table 1] Sample 1 was quenched at a cooling rate of 2.5 ° C./min or more in a temperature range of 1150 ° C. to 1020 ° C., and the nitrogen concentration was 1.3 × 10 ¹⁴ ato.
Due to the high concentration of doping at ms / cm ³ , the heat-induced defects were observed at a high density of 8.7 × 10 ⁴ / cm ² . This is because the thermal stability of the oxygen precipitation nuclei was significantly improved by the addition of a high concentration of nitrogen. At the same time, the density of epitaxial defects was also significantly increased. Therefore, when the nitrogen concentration is 1
It can be seen that doping exceeding × 10 ¹⁴ atoms / cm ³ is not desirable because it increases epitaxial defects in the first method.

Samples 2 and 5 have a nitrogen concentration of 1 × 10 ¹⁴ at.
oms / cm ³ or less, 1150 ℃ ～ 1020 ℃
Since the cooling rate in the temperature range was 2.5 ° C./min or less, which was out of the specified range, the heat treatment-induced defect was as low as 6.5 × 10 ³ / cm ² or less. Further, the density of epitaxial defects was also low.

On the other hand, since Samples 3, 4, 6, and 7 were all quenched at a temperature of 1150 ° C. to 1020 ° C. at a rate of 2.7 ° C./min or more, the density of the heat-induced defects was increased, and The density could be reduced. By performing cooling as specified in the present invention, the aggregation of vacancies taken in at the solid-liquid interface can be suppressed, and the growth of oxygen precipitation nuclei can be promoted by increasing the residual vacancy concentration. Example 2 In Example 2, in order to confirm the effect of the second method, the same 8-inch p-type (Example) as in Example 1 was used by using a single crystal manufacturing apparatus using a heat shield material shown in FIG. 100)
Was produced. 1150 ℃ ~ 10 when pulled up
The cooling rate in the temperature range of 20 ° C is 2.7 ° C / min or more, and the cooling rate in the temperature range of 1000 ° C to 850 ° C is 1.2 ° C / min.
The pulling speed was controlled at 1.3 mm / min so as to be as follows. Further, a single crystal was manufactured by changing the concentration of nitrogen to be doped. Table 2 shows the nitrogen concentration and the cooling rate at this time.

A wafer was cut out of the manufactured single crystal, and after polishing and cleaning the surface, an epitaxial layer was grown under the conditions of a deposition temperature of 1150 ° C., and the epitaxial defect density was measured in the same manner as in Example 1. The density of the heat-induced defects formed therein was measured. Table 2 shows the measurement results.

[0049]

[Table 2] Samples 8 to 11 all satisfy the cooling conditions of the first method, so that the results show that the epitaxial defect density is low and the heat treatment induced defect density is relatively high.

Samples 8 and 9 further have a cooling rate of 1.2 ° C./min in a temperature range of 1000 ° C. to 850 ° C. specified in the second method.
Since the following slow cooling conditions are satisfied, the density of the heat treatment-induced defect is as high as 1.2 × 10 ⁴ / cm ² or more even in Sample 8 having a low nitrogen concentration while the density of the epitaxial defect remains low. I have.

Samples 10 and 11 are results obtained when the cooling conditions of the second method are not satisfied. However, except that the cooling rates in the temperature range of 1000 ° C. to 850 ° C. are different, samples 9 and 11 have the same conditions. Comparison of Sample 11 shows that Sample 9 satisfying the slow cooling condition of the second method has about twice the heat treatment induced defect density.

As in Samples 8 and 9, 1150 ° C to 1020 ° C
By rapidly cooling and passing through the temperature range of above, the aggregation of vacancies taken in at the solid-liquid interface is suppressed, the concentration of residual vacancies is increased, and the formation of oxygen precipitation nuclei is started from a higher temperature side,
The growth of oxygen precipitation nuclei is promoted . 1000 ℃ ~ 850 ℃
By gradually cooling the temperature range, oxygen precipitation nuclei can be further grown. Example 3 In Example 3, in order to confirm the effect of the third method, a 6-inch, p-type (100) silicon single crystal (initial oxygen concentration: 1.2 × 10 ¹⁸ atoms / cm ³ (ASTM'79 )). A single crystal was manufactured by controlling the cooling rate in the temperature range of 1150 ° C. to 800 ° C. during the pulling by changing the pulling rate under two conditions of 1.2 mm / min or 1.9 mm / min. The concentration of nitrogen doped into the single crystal was as high as 5 × 10 ¹⁴ atoms / cm ³ . Table 3 shows the conditions at this time.

A wafer was cut from the manufactured single crystal, and after polishing and cleaning the surface, an epitaxial layer was grown under the conditions of a deposition temperature of 1150 ° C., and the epitaxial defect density was measured in the same manner as in Example 1. The density of the heat-induced defects formed therein was measured. Table 3 shows the measurement results.

[0054]

[Table 3] In Samples 12 and 14, the cooling rate in the temperature range of 1150 ° C. to 800 ° C. was 4.1 ° C./min, which was different from the condition specified in the third method. Therefore, the sample having a nitrogen concentration of 5 × 10 ¹⁴ atoms / cm ³ was used. In FIG. 12, the density of the heat treatment-induced defects was observed to be 4.8 × 10 ⁵ / cm ² or more, but the density of the epitaxial defects was also extremely high.

On the other hand, since the samples 13 and 15 were cooled under the conditions specified in the third method, the nitrogen concentration was 5 × 10 ¹⁴ atom
Sample 13 of s / cm ³ , the density of heat-induced defects was 2.0 × 1
0 ⁵ / cm ² or more, and at the same time, the density of epitaxial defects is sufficiently low, and a high-quality epitaxial wafer having no defects in the device active region can be obtained.

[0056]

According to the method for producing a silicon single crystal and an epitaxial wafer of the present invention, even if the wafer is produced from a silicon single crystal produced by doping with nitrogen, the density of epitaxial defects can be reduced. At the same time, a silicon single crystal for a semiconductor device exhibiting excellent IG capability can be obtained. That is, by using a wafer cut from this silicon single crystal, a high-quality epitaxial wafer having no defect in the device active region can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of heat treatment-induced defects and the temperature at the start of pulling rate change in an experiment of changing the pulling rate in the middle of the process by the CZ method.

FIG. 2 is a diagram showing the relationship between the OPP defect density and the temperature at the time of crystal separation in a separation rapid cooling experiment by the CZ method.

FIG. 3 is a diagram showing a relationship between an etch pit density and a temperature at the time of crystal separation in a separation rapid cooling experiment by a CZ method.

FIG. 4 is a diagram illustrating a schematic configuration of an apparatus for manufacturing a silicon single crystal by a CZ method used in an example.

FIG. 5 is a view showing an example of the shape of an optimized heat shield material.

[Explanation of symbols]

 1: Crucible, 1a: Quartz container 1b: Graphite container, 2: Heater 3: Melt, 4: Pulling shaft 5: Seed crystal, 6: Single crystal 7: Heat shield material

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Eiichi Asayama 2201 Kamioda, Ehoku-cho, Kishima-gun, Saga Prefecture F-term (reference) 4G077 AA02 AA03 BA04 CF10 DB01 EA02 EB01 ED04 HA06 HA12 5F053 AA12 AA25 AA49 DD01 FF04 GG01 KK10 RR03 RR20

Claims (4)

[Claims] 1. The method according to claim 1, wherein the nitrogen content is 1 × 10 by the Czochralski method.
^A method for producing a silicon single crystal doped in the range of ¹² atoms / cm ³ to 1 × 10 ¹⁴ atoms / cm ³ , wherein the single crystal is
2.7 ℃ / min cooling rate in the temperature range of 50 ℃ ～ 1020 ℃
A method for producing a silicon single crystal, characterized by the above. 2. The method according to claim 1, wherein the nitrogen content is 1 × 10 by the Czochralski method.
^A method for producing a silicon single crystal doped in the range of ¹² atoms / cm ³ to 1 × 10 ¹⁴ atoms / cm ³ , wherein the single crystal is
2.7 ℃ / min cooling rate in the temperature range of 50 ℃ ～ 1020 ℃
A method for producing a silicon single crystal, wherein the cooling rate in a temperature range of 1000 ° C. to 850 ° C. is 1.2 ° C./min or less. 3. The method according to claim 1, wherein said Czochralski method comprises 5 × 10 5 nitrogen.
^A method for producing a silicon single crystal doped in the range of ¹³ atoms / cm ³ to 1 × 10 ¹⁶ atoms / cm ³ , wherein the single crystal is 11
6.5 ℃ / min cooling rate in the temperature range of 50 ℃ ~ 800 ℃
A method for producing a silicon single crystal, characterized by the above. 4. An epitaxial wafer characterized by growing an epitaxial layer on a surface of a silicon wafer cut from a silicon single crystal produced by the method according to claim 1. Production method.