JPH08253388A - Lifting of silicon single crystal - Google Patents

Abstract

PURPOSE: To obtain a silicon single crystal ingot having high reliability and high quality by lifting a silicon single crystal ingot from a fused silicon by CZ method and subsequently subjecting the lifted silicon single crystal ingot to a specific reheating treatment, when the temperature of the ingot is lowered to a prescribed temperature. CONSTITUTION: A fused silicon 7 is held in a crucible 4 in an ingot-lifting device 12, and a silicon single crystal ingot 11 is lifted by Czochralski method. When cooled to a temperature T1 of 20-950 deg.C, the silicon single crystal ingot 11 is reheated to a temperature T2 of 700-1000 deg.C (T2 >T1 ) for 60min or shorter, held at the temperature T2 for 24hrs or shorter, and subsequently gradually cooled. When the silicon single crystal ingot is raised, processed into silicon wafers and then thermally treated, the change in the density of oxide deposits generated in the silicon wafers in dependence on the temperature of the thermal treatment can thereby be prevented. The change in the condition of the thermal treatment in the device process is thus not required for every silicon wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to Czochralski (C
Z) method for growing a silicon single crystal. More specifically, the method of pulling a silicon (Si) single crystal ingot in which the density of oxygen precipitates generated in the silicon wafer after growth is heat-treated and does not depend on the heat treatment temperature, and the as-grown state (hereinafter, as -g
The present invention relates to a method for pulling a silicon single crystal ingot that reduces the flow pattern defect (FPD) density that occurs in a silicon wafer of row n).

[0002]

2. Description of the Related Art As shown in FIG. 10, a silicon single crystal ingot 1 is generally pulled up from a silicon melt 7 held in a quartz crucible 4 supported by a rotating shaft 3 in a lower portion of an ingot pulling apparatus 2. . At the same time, the silicon single crystal ingot 1 is dipped with a seed crystal 9 attached to the tip of the pulling shaft 8 in a silicon melt 7 heated by a heater 6 provided between the heat retaining body 5 and the crucible 4, and the pulling shaft 8 is rotated. While pulling, for example, it is manufactured by pulling up at a speed of 1 mm / min. When the length of the silicon single crystal ingot immediately after the pulling growth is, for example, 30 cm, it has a temperature drop distribution from about 1400 ° C. at the lower end to about 800 ° C. at the upper end.

[0003]

However, since the silicon single crystal ingot pulled up by the CZ method contains supersaturated oxygen, there are a large number of nuclei that form oxygen precipitates, Therefore, in the semiconductor device process, when the wafer manufactured from the silicon single crystal ingot is subjected to various high temperature treatments, oxygen precipitates are formed on the wafer with the nuclei at the center. The density of the oxygen precipitates depends on the heat treatment temperature after the wafer is formed. For example, a plurality of wafers manufactured from a silicon single crystal ingot that has been grown under the above pulling conditions are each dried at 800 ° C. (12 ° C.) in a dry nitrogen (dryN ₂ ) atmosphere.
0 hour hold), 900 ° C (100 hour hold), 1000
When the heat treatment temperature was kept at ℃ (holding for 24 hours), the maximum value of the average density of the three oxygen precipitates (800 ℃
The heat treatment) and the minimum value (heat treatment at 1000 ° C.) differ by about two digits. The formation of oxygen precipitates is caused by dislocations and stacking faults (OSF: oxid
cation induced stacking fault), and these defects lead to serious deterioration of characteristics such as defective oxide film withstand voltage of semiconductor devices and reduction of carrier lifetime, resulting in oxygen precipitation after wafer formation. A method of pulling a silicon single crystal in which the density of the material does not depend on the heat treatment temperature has been desired. Further, among these defects, flow pattern defects (hereinafter referred to as FPD) are known to adversely affect the oxide film breakdown voltage. This FPD is as
-A unique trace (flow pattern) that appears on the wafer surface when a CZ silicon wafer of grown is chemically etched for a long time (30 minutes), which is dissolved by rapid chemical etching or bubbles filled with some gas. Is considered to be something like. Conventionally, after wafer processing to reduce this flow pattern defect, 1100
It was heat treated at ℃. However, the high temperature heat treatment at 1100 ° C. has been desired to be improved from the viewpoint of energy saving.

An object of the present invention is to provide a method for pulling a silicon single crystal ingot which suppresses a change in the density of oxygen precipitates appearing in the silicon wafer during heat treatment in a semiconductor device process due to the heat treatment temperature.
Another object of the present invention is to provide a method for pulling a silicon single crystal that reduces the FPD density generated in an as-grown silicon wafer.

[0005]

As shown in FIG. 9, the present invention is an improvement of a method for pulling a silicon single crystal ingot 11 from a silicon melt 7 held in a crucible 4 in a pulling device 12. The characteristic first structure is that the silicon single crystal ingot 11 has a temperature of 20 to 950 ° C. as shown in FIG.
The temperature was raised to a temperature T ₂ of the 700 to 1000 ° C. followed by longer be 60 minutes at the time of the drop to the temperature T ₁ (T _2>
T ₁ ), holding at this temperature T _{2 for} at least 24 hours, and then slowly cooling it to obtain a silicon wafer after growth and subjecting it to a heat treatment, the change in the density of oxygen precipitates generated in this silicon wafer due to the above heat treatment temperature. To suppress.

Further, the characteristic second structure is that the silicon single crystal ingot 11 is 700 to 1000 as shown in FIG.
Long at the time when lowered to a temperature T ₃ of ℃ at this temperature T ₃ also hold 24 hours, the density of the subsequent slow cooling oxygen precipitates generated in the silicon wafer when heat-treated in the growing after the silicon wafer by It is to suppress the change due to the heat treatment temperature.

Further, the characteristic third structure is that the silicon single crystal ingot 11 is 700 to 1000 as shown in FIG.
And ° C. long followed at the time of the drop to a temperature T ₄ of the temperature was lowered to a temperature T ₅ also further 500 to 900 ° C. for 30 minutes (T ₅ <
T ₄ ), holding at this temperature T _{5 for} at least 24 hours, and then slowly cooling it to obtain a silicon wafer after growth and subjecting it to a heat treatment. To suppress.

Further, the characteristic fourth structure is, as shown in FIG. 4, when the silicon single crystal ingot 11 is lowered to a temperature T _{6 of} 20 to 950 ° C., the temperature is kept at 950 to 1050 ° C. for 60 minutes at the maximum. to a temperature T ₇ raised (T ₇ ≧
T ₆ ), this temperature T ₇ is held for at least 24 hours, and then slowly cooled to reduce the FPD density generated in the as-grown silicon wafer.

The present invention will be described in detail below. As a means for raising the once lowered temperature of the silicon single crystal ingot of the present invention, as shown in FIG. 9, the periphery of the silicon single crystal ingot 11 being pulled is heated by the auxiliary heater 10 or the silicon immediately after being pulled up is grown. There is a method of heating a single crystal ingot with an auxiliary heater. When the temperature is lowered to room temperature, the ingot may be reheated in the pulling device, or the ingot may be taken out of the device and heated by another heater. Also, as a means for holding the temperature of the ingot once lowered, it is wrapped with a heat insulating material without slowing down the pulling rate, or the pulling rate after growing is increased,
There is a method of raising the temperature to a predetermined temperature T ₃ . As a method of further rapidly lowering the once lowered temperature T ₄ of the ingot, there is a method of increasing the pulling rate after growth to raise it to a region of a predetermined temperature T ₅ (T ₅ <T ₄ ). The predetermined temperature range is created by heating the temperature to T ₃ or T ₅ with an auxiliary heater. The method for measuring the temperature of the silicon single crystal ingot of the present invention is not particularly limited as long as the object of the present invention is achieved, and in this method, for example, a method based on temperature measurement data of a thermocouple attached to the ingot, Alternatively, there is a method of measuring the temperature of the silicon single crystal ingot which is being pulled up by a non-contact type infrared temperature sensor.

The pulling speed of the present invention is 0.6 to 2.0 mm.
/ Minute range. If it is less than 0.6 mm / min, the productivity is inferior, and if it exceeds 2.0 mm / min, there is a problem that it is difficult to grow a single crystal. Further, when the temperature of the silicon single crystal ingot reaches the temperature T ₁ , the temperature rises to the temperature T ₂ in 60 minutes at the longest because T _{3 in} the case shown in FIG. 2 exceeds 60 minutes.
Since it can be substituted by a method such as = T _1, it is not necessary to raise the temperature particularly for a long time. For the same reason, the temperature of the silicon single crystal ingot is lowered to the temperature T ₅ at the time when it reaches the temperature T ₄ for at most 30 minutes. Further, when the temperature of the silicon single crystal ingot reaches the temperature T ₆ , the temperature rises to the temperature T ₇ in 60 minutes even if it is longer than 60 minutes because the effect does not change. Therefore, it is particularly necessary to raise the temperature in a long time. Absent.

The lower limit of the temperature T ₁ is 20 ° C. is 20
Or that less than ° C. takes a long time for cooling, or requires special cooling device, it is because not change the effect of the above invention, to the upper limit of the temperature T ₁ of the 950 ° C., the temperature T ₂
This is because the lower limit of is too high. The reason why the lower limit of the temperature T ₂ is 700 ° C. is that it takes a very long time to obtain the effect at a temperature lower than this, and the upper limit of the temperature T ₂ is set to 1
The reason why the temperature is set to 000 ° C. is that the density of precipitates is remarkably lowered at a temperature higher than this. This temperature T ₁ is 6
The range of 00 to 950 ° C. is preferable, and the temperature T ₂ is 70.
The range of 0-950 degreeC is preferable. Further, it is necessary to achieve the holding time of the temperature T ₂ of at most 24 hours in order to achieve the object of the present invention, and the preferable holding time is 700 to 8
It is 6 to 24 hours at 50 ° C, and 10 hours at the longest at 850 to 950 ° C. The reason why the lower limit of the temperature T ₃ is 700 ° C. is that it takes a long time to obtain the effect at a temperature lower than this, and the upper limit of the temperature T ₃ is 1000 ° C.
This is because the precipitate density is remarkably reduced at a temperature higher than this. The temperature T ₃ is preferably in the range of 700 to 950 ° C. Further, the holding time of the temperature T ₃ is at most 24 hours in order to achieve the object of the present invention, and the preferable holding time is 700 to 850 ° C., 6 to 24 hours, and 85.
It is 10 hours at the longest at 0 to 950 ° C.

[0012] to the lower limit of the temperature T ₄ to 700 ° C. is, T ₅
The reason is that the upper limit of the temperature T ₄ becomes too low, and the upper limit of the temperature T ₄ is set to 1000 ° C. because the precipitate density is remarkably reduced at the temperature higher than this. The lower limit of the temperature T ₅ is set to 500 ° C. because it takes a long time to obtain the effect at a temperature lower than this, and the upper limit of the temperature T ₅ is set to 90 ° C.
The reason for setting the temperature to 0 ° C. is that the lower limit value of the temperature T ₄ becomes too high. The temperature T ₄ is preferably in the range of 700 to 900 ° C., and the temperature T ₅ is preferably in the range of 600 to 800 ° C.. Further, the holding time of the temperature T ₅ is at most 24 hours in order to achieve the object of the present invention, and the preferable holding time is at most 24 hours. The lower limit of temperature T ₆ is 20 ° C
The reason for this is that if the temperature is lower than 20 ° C., it takes a long time to lower the temperature, or a special cooling device is required, and the effect of the present invention does not change, and the upper limit of the temperature T ₆ is set to 950 ° C. This is because the effect of the present invention cannot be obtained unless the temperature T ₆ is lower than the temperature T ₇ . The lower limit of temperature T ₇ is 950 ° C
This is because the effect is small at a temperature lower than this, and the upper limit of the temperature T ₇ is set to 1050 ° C. because the effect is not improved at a temperature higher than this. This temperature T ₆
Is preferably in the range of 700 to 950 ° C, and the temperature T ₇ is preferably in the range of 950 to 1000 ° C. Further, the holding time of the temperature T ₇ is set to be at most 24 hours in order to achieve the object of the present invention, and the preferable holding time is at most 6 hours. In this specification, slow cooling refers to natural cooling or furnace cooling.

[0013]

In general, many precipitation nuclei are formed in the cooling process after crystal growth. When these precipitation nuclei are heat-treated at a certain temperature, stable precipitation nuclei grow at that temperature and unstable precipitation nuclei disappear. When a crystal is grown by a usual method, precipitation nuclei of various degrees of stability exist, and the precipitation nuclei that are stable at low temperatures have a higher density. Therefore, when the wafer is heat-treated, a denser precipitate is usually generated at lower temperatures. In the case of FIG. 1, the two-step heat treatment is performed at the temperature T ₁ and the temperature T ₂ during the crystal cooling. Therefore stables at temperatures T ₁ of the precipitation nuclei formed when cooled to a temperature T ₁ is slightly grows, the more stable precipitation nuclei at a high temperature. Further temperature T
By raising the temperature to ₂ and holding it, the stable precipitation nuclei and those not stable at temperature T ₂ are separated. Since the formation of precipitation nuclei in the course of cooling after holding at temperature T ₂ is small, while retaining at temperature T _2, that is, while the precipitation nuclei are stabilized, for example, the precipitation nuclei such as point defects It can be inferred that the amount of the formation nuclei during the cooling was suppressed because the elements to be formed reached the equilibrium concentration or were reduced by being consumed, and the generation amount of the precipitation nuclei during cooling was suppressed. Therefore, only the precipitation nuclei separated and stabilized by the temperatures T ₁ and T ₂ and the respective holding times are formed, and a crystal in which the density of the generated precipitation nuclei does not depend on the heat treatment temperature can be produced.

In the case of FIG. 2, the two-step heat treatment of FIG. In the case of FIG.
In the case where crystals are normally produced, the precipitation nuclei formed during the cooling from the temperature T ₄ to the temperature T ₅ are rapidly cooled to reduce and hold the same idea as in the case of FIG. In the case of FIG. 4, several possibilities are suggested from the experimental results. When FPD is already formed at the time of cooling to the temperature T ₆ during pulling of the crystal, the FPD at this time is at a temperature T ₇ rather than the FPD existing in the crystal once cooled to room temperature. Low thermal stability,
In other words, it becomes more stable as the temperature decreases. Alternatively, the amount of FPD reduction varies depending on the difference in shape during heat treatment, that is, the influence of the crystal surface during heat treatment. Temperature T ₆
Then, if the FPD has not been formed yet, FP
It is considered that the concentration of the elements forming D, such as vacancies and interstitial silicon atoms, reaches an equilibrium state during the heat treatment at about 1000 ° C., and FPD is hardly formed at this concentration.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. <Example 1> First, in order to examine the temperature distribution of each part in the pulling direction (length direction) of the silicon single crystal ingot being pulled, a diameter of 5 inches after the growth was completed by the ingot pulling device 2 shown in FIG. A silicon single crystal ingot with a length of 800 mm and a depth of 400 m parallel to its central axis.
m holes were made, and a plurality of thermocouples were mounted in the holes at equal intervals. The ingot to which this thermocouple was attached was set in the same pulling device 2, and the ingot was heated while holding the silicon melt by the heater 6 under the heating conditions for normal pulling. Then, the temperature was measured with a thermocouple while gradually melting the silicon single crystal ingot. As a result, the bottom (0 mm) of the ingot being pulled up to the top (8 mm)
The temperature distribution in the pulling direction up to 00 mm) was grasped.

Next, as shown in FIG. 9, an auxiliary heater 10 was provided at a position in the pulling device 2 shown in FIG. 10 where the ingot being pulled reaches 900 ° C. 9, the same components as those shown in FIG. 10 are designated by the same reference numerals. In this example, the auxiliary heater 10 was installed by selecting its heat quantity and length L so that the ingot being pulled could be held at 1000 ° C. for 6 hours. At this time, the time required to raise the temperature from 900 ° C. to 1000 ° C. was 10 minutes. Using the pulling device 12 shown in FIG.
The silicon single crystal ingot 11 was pulled up and grown at a constant speed of mm / min. The thermal history of this ingot is shown by the one-dot chain line in FIG. The grown ingot 11 was taken out from the apparatus 12 and sliced perpendicularly to the pulling direction of the ingot to obtain a plurality of silicon wafers. These were dried in an atmosphere of dry nitrogen (dryN ₂ ) at 800 ° C. for 120 hours and 90
Each sample was heat treated at 0 ° C. for 100 hours to obtain samples A ₁ and A ₂ .

<Embodiment 2> As shown in FIG. 9, an auxiliary heater 10 is provided at a position where the ingot being pulled in the pulling device 2 shown in FIG. 10 reaches 700 ° C., and the ingot being pulled by the auxiliary heater 10 is 900. A silicon single crystal ingot 11 was pulled up and grown in the same manner as in Example 1 except that the temperature could be maintained at 6 ° C. for 6 hours. 700 at this time
The time required to raise the temperature from ℃ to 900 ℃ is 20
It was a minute. The thermal history of this ingot is shown by the broken line in FIG. A plurality of silicon wafers were obtained from this ingot 11 in the same manner as in Example 1. Dry nitrogen (dryN)
₂ ) In the atmosphere, at 800 ℃ for 120 hours and at 900 ℃ for 10 hours.
Samples B ₁ , B ₂ and B ₃ were obtained by heat treatment at 0 ° C. and 1000 ° C. for 24 hours, respectively.

<Embodiment 3> As shown in FIG. 9, an auxiliary heater 10 capable of setting a temperature of 900 ° C. is provided in the upper part of the pulling device 12. When the growth was completed, the heater 6 of the device 12 was turned off to cool the entire device to room temperature. Next, when the ingot reaches room temperature, the ingot is pulled up above the auxiliary heater 10 and then the auxiliary heater 10 is turned on to set the atmosphere inside the auxiliary heater 10 to 2
The temperature was set to 900 ° C. At this time, the temperature of the crystal is raised to 200 ° C. After that, the ingot was lowered to the auxiliary heater 10 and kept in this state for 6 hours. 200 at this time
The time required to raise the temperature from ℃ to 900 ℃ is 40
It was a minute. The thermal history of this ingot is shown by the solid line in FIG. A plurality of silicon wafers were obtained from this ingot 11 in the same manner as in Example 1. Dry nitrogen (dryN)
₂ ) In the atmosphere, at 800 ℃ for 120 hours and at 900 ℃ for 10 hours.
Samples C ₁ , C ₂ and C ₃ were obtained by heat treatment at 0 ° C. and 1000 ° C. for 24 hours respectively.

<Embodiment 4> An auxiliary heater (not shown) was provided at a position where the ingot being pulled reaches 700 ° C. in the pulling device 2 shown in FIG. This auxiliary heater was installed by selecting its heat quantity and length so that the ingot being pulled could be kept at 700 ° C. for 24 hours. Using this apparatus, a silicon single crystal ingot was pulled up and grown in the same manner as in Example 1. The thermal history of this ingot is shown by the solid line in FIG.
A plurality of silicon wafers were obtained from this ingot in the same manner as in Example 1. These were heat-treated in a dry nitrogen (dryN ₂ ) atmosphere at 800 ° C. for 120 hours and 900 ° C. for 100 hours to obtain samples D ₁ and D ₂ .

<Embodiment 5> As shown in FIG. 9, an auxiliary heater capable of setting a temperature of 700 ° C. is provided in the upper portion of the pulling device 2. The top of the ingot being pulled is 900 ° C
When it reached the position reaching, the growth was terminated and the ingot was pulled up to the atmosphere of 700 ° C. by the auxiliary heater.
This auxiliary heater is used to pull the ingot under pulling at 700 ℃.
The heat quantity and length were selected and installed so that it could be held for a long time. At this time, the time required to lower the temperature from 900 ° C. to 700 ° C. was 10 minutes. The thermal history of this ingot is shown by the solid line in FIG. A plurality of silicon wafers were obtained from this ingot in the same manner as in Example 1. These were heat-treated at 800 ° C. for 120 hours and 900 ° C. for 100 hours in a dry nitrogen (dryN ₂ ) atmosphere to obtain samples E ₁ and E ₂ .

Comparative Example 1 A silicon single crystal ingot was pulled and grown in the same manner as in Example 1 by using the pulling apparatus 2 shown in FIG. 10 in which the auxiliary heater was removed from the pulling apparatus 2 in FIG. A plurality of silicon wafers were obtained from this ingot 1 in the same manner as in Example 1. These were dried in an atmosphere of dry nitrogen (dryN ₂ ) at 800 ° C. for 120 hours and 90
Samples F ₁ , F ₂ and F ₃ were obtained by heat treatment at 0 ° C. for 100 hours and 1000 ° C. for 24 hours.

<Comparative Test 1 and Evaluation> Observation of Occurrence of Oxygen Precipitates Samples A ₁ and A _{2 of} Example 1 and Sample B of Example 2
_{1 to} B ₃ , Samples C _{1 to} C ₃ of Example 3, Samples D ₁ and D _{2 of} Example 4, and Samples E ₁ and E _{2 of} Example 5,
Each surface of Samples F _{1 to} F ₃ of Comparative Example 1 was treated with an etching solution having selectivity for oxygen precipitates, and then observed with an optical microscope. The results of Examples 1 to 5 are shown in FIG. 5, and the results of Comparative Example 1 are shown in FIG. As is clear from FIGS. 5 and 6, the density of oxygen precipitates of the sample of Comparative Example 1 decreases as the heat treatment temperature increases, whereas the density of oxygen precipitates of the samples of Examples 1 to 5 decreases. It was almost constant regardless of the temperature. Specifically, the densities of oxygen precipitates in the samples F ₁ and F _{3 of} Comparative Example 1 varied from the order of 10 ⁷ / cm ^{3 to} the order of 10 ⁹ / cm ³ and differed by about two orders of magnitude. Samples A ₁ and A ₂ of 10 ⁷ / c
m ³ and the samples B _{1 to} B ₃ of Example 2 were on the order of 10 ⁸ / cm ³ . The samples C _{1 to} C ₃ of Example ₃ and the samples E ₁ and E ₂ of Example 5 were 10 ⁹
/ Cm ^3, of the samples D ₁ and D of Example 4.
₂ was on the order of 10 ¹⁰ / cm ³ .

<Embodiment 6> An auxiliary heater 10 was provided in the pulling device 2 shown in FIG. 10 at a position where the ingot being pulled reaches 700 ° C. as shown in FIG. In this example, the auxiliary heater 10 was installed by selecting its heat quantity and length L so that the ingot being pulled could be held at 980 ° C. for 6 hours.
At this time, the time required to raise the temperature from 700 ° C. to 980 ° C. was 30 minutes. A silicon single crystal ingot 11 was pulled and grown in the same manner as in Example 1 using the pulling apparatus 12 shown in FIG. The thermal history of this ingot is shown by the solid line in FIG. Ingot 11 after training
Was taken out from the device 12 and sliced perpendicularly to the pulling direction of the ingot to obtain a silicon wafer. This wafer was used as sample G.

Example 7 An auxiliary heater 10 was provided as shown in FIG. 9 at a position where the ingot being pulled in the pulling device 2 shown in FIG. 10 reached 700 ° C. In this example, the amount of heat and the length L of the auxiliary heater 10 were selected and set so that the ingot being pulled up could be held at 1000 ° C. for 6 hours. At this time, the time required to raise the temperature from 700 ° C. to 1000 ° C. was 30 minutes. Thereafter, the silicon single crystal ingot 11 is pulled up and grown in the same manner as in Example 6,
A silicon wafer was obtained by slicing perpendicularly to the pulling direction of the ingot. This wafer was designated as sample H.

<Comparative Example 2> An auxiliary heater 10 was provided as shown in FIG. 9 at a position where the ingot being pulled in the pulling device 2 in FIG. 10 reached 700 ° C. In this example, the amount of heat and the length L of the auxiliary heater 10 are selected and set so that the ingot being pulled up can be held at 700 ° C. for 6 hours.
Thereafter, as in Example 6, the silicon single crystal ingot 11
Was pulled up and grown, and a silicon wafer of Sample I was obtained from the ingot.

Comparative Example 3 An auxiliary heater 10 was provided as shown in FIG. 9 at a position where the ingot being pulled inside the pulling device 2 shown in FIG. 10 reached 700 ° C. In this example, the heat amount and length L of the auxiliary heater 10 are selected and set so that the ingot being pulled up can be held at 900 ° C. for 6 hours.
At this time, the time required to raise the temperature from 700 ° C. to 900 ° C. was 20 minutes. Thereafter, a silicon single crystal ingot 11 was pulled up and grown in the same manner as in Example 6, and a silicon wafer of Sample J was obtained from the ingot.

<Comparative Example 4> An auxiliary heater 10 was provided in the upper portion of the pulling device 2 shown in FIG. 10 as shown in FIG. In this example, the auxiliary heater 10 was installed by selecting its heat quantity and length L so that the ingot could be held at 900 ° C. for 6 hours. When the growth was completed, the heater 6 of the device 12 was turned off to cool the entire device to room temperature. Next, when the ingot reaches room temperature, the ingot is heated by the auxiliary heater 10
After pulling up to a higher position, the auxiliary heater 10 was turned on, and the atmosphere inside the auxiliary heater 10 was raised to 900 ° C. in 2 hours. At this time, the temperature of the crystal is raised to 200 ° C. After this, the ingot was lowered to the auxiliary heater 10, and the ingot was held in this state for 6 hours. At this time, the time required to raise the temperature from 200 ° C. to 900 ° C. was 40 minutes. Thereafter, a silicon single crystal ingot 11 was pulled up and grown in the same manner as in Example 6, and a silicon wafer of Sample K was obtained from the ingot.

Comparative Example 5 A silicon single crystal ingot was pulled and grown in the same manner as in Example 1 by using the pulling apparatus 2 shown in FIG. 10 which is the same as the pulling apparatus 2 of FIG. 9 except that the auxiliary heater is not provided. . A silicon wafer of Sample M was obtained from this ingot 1.

<Example 8> A silicon wafer of Sample N was obtained by pulling up and growing the ingot in the same manner as in Example 6 except that the holding time by the auxiliary heater was set to 24 hours.

<Example 9> A silicon wafer of Sample O was obtained by pulling up and growing the ingot in the same manner as in Example 7 except that the holding time by the auxiliary heater was set to 24 hours.

<Comparative Example 6> A silicon wafer of Sample P was obtained by pulling up and growing the ingot in the same manner as in Comparative Example 2 except that the holding time by the auxiliary heater was changed to 24 hours.

<Comparative Example 7> A silicon wafer of Sample Q was obtained by pulling up and growing the ingot in the same manner as in Comparative Example 3 except that the holding time by the auxiliary heater was set to 24 hours.

<Comparative Test 2 and Evaluation> Observation of FPD Density Generation First, a chemical etching solution (Secco etchant) containing potassium dichromate, hydrofluoric acid and water was prepared, and the sample surface was perpendicular to this liquid surface. So that samples G, H, N and O of Examples 6 to 9 and samples I of Comparative Examples 2 to 7,
Each of J, K, M, P, and Q was lowered, and in that state, they were immersed in an etching solution for 30 minutes. A sample was taken out from the etching solution and the FPD density was examined with an optical microscope. As a result, the density of the peculiar flow pattern changed with the heat history during the pulling of the ingot. 6 while raising the temperature during pulling
FIG. 7 shows the FPD densities of Samples G and H of Examples 6 and 7 and Samples I, J, K, and M of Comparative Examples 2 to 5, which were held for a time. FIG. 8 shows the FPD densities of Samples N and O of Examples 8 and 9 and Samples M, P and Q of Comparative Examples 5 to 7 which were heated for 24 hours during pulling. As is clear from FIGS. 7 and 8, Comparative Examples 2 to 7 showed no significant difference in FPD density as compared with Comparative Example 5 (denoted by Ref. In the figure) which does not use an auxiliary heater. Examples 6-9
In comparison with Comparative Example 5, the FPD density variation was small and the FPD density decreased by about one digit. Specifically, FPD
Has an average density of about 7 × 10 ⁵ / cm ³ to about 1 in Comparative Examples 2 to 7.
While it was 5 × 10 ⁵ / cm ³ , in Examples 6 to 9, it was about 1 × 10 ⁵ / cm ³ to about 2 × 10 ⁵ / cm ³ .

[0034]

As described above, according to the method for pulling a silicon single crystal of the present invention, the density of oxygen precipitates that appear in a silicon wafer when heat-treated in the semiconductor device process after pulling depends on the heat-treatment temperature. However, the change in the density of oxygen precipitates due to the heat treatment temperature is suppressed. As a result,
Since it is not necessary to change the heat treatment conditions in the device process for each silicon wafer, a highly reliable and high quality silicon single crystal ingot can be obtained. Further, according to another method of pulling a silicon single crystal of the present invention, the FPD density generated in an as-grown silicon wafer can be reduced, and the conventional high temperature heat treatment process up to 1100 ° C. can be omitted to save energy consumption. Has the advantage of being less

[Brief description of drawings]

FIG. 1 is a temperature distribution diagram during pulling up of a silicon single crystal ingot according to Examples 1 to 3 of the present invention.

FIG. 2 is a temperature distribution diagram during pulling up of a silicon single crystal ingot of Example 4 of the present invention.

FIG. 3 is a temperature distribution diagram during pulling up of a silicon single crystal ingot of Example 5 of the present invention.

FIG. 4 is a temperature distribution diagram during pulling up of a silicon single crystal ingot of Example 6 of the present invention.

FIG. 5 is a diagram showing changes in the density of oxygen precipitates according to the heat treatment temperature of the silicon wafers that were heat-treated after being grown in Examples 1 to 5;

FIG. 6 is a diagram showing changes in the density of oxygen precipitates according to the heat treatment temperature of this silicon wafer that has been heat-treated as a grown silicon wafer in Comparative Example 1.

FIG. 7 is a diagram showing FPD densities of as-grown silicon wafers of Examples 6 and 7 and Comparative Examples 2 to 5.

FIG. 8 shows FPD densities of as-grown silicon wafers of Examples 8 and 9 and Comparative Examples 5 to 7.

FIG. 9 is a configuration diagram of a pulling device having an auxiliary heater used for growing a silicon single crystal ingot.

FIG. 10 was used to grow a silicon single crystal ingot,
The block diagram of the pulling apparatus which does not have an auxiliary heater.

[Explanation of symbols]

 1,11 Silicon single crystal ingot 2,12 Ingot pulling device 4 Quartz crucible 6 Heater 7 Silicon melt 10 Auxiliary heater

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Sakamoto, 1-297 Kitabukuro-cho, Omiya-shi, Saitama, Central Research Laboratory, Mitsubishi Materials Corporation (72) Hideo Tanaka 1-297, Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Central Research Institute Co., Ltd. (72) Inventor Hisa Furuya 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Central Research Laboratories

Claims (4)

[Claims] 1. A silicon single crystal ingot (11) formed from a silicon melt (7) held in a crucible (4) in a pulling device (12).
In the method of pulling up, the silicon single crystal ingot (11) is cooled to a temperature T _{1 of} 20 to 950 ° C. and then 70 minutes at a maximum at 60 minutes.
The temperature is raised to a temperature T _{2 of 0} to 1000 ° C. (T ₂ > T ₁ ), kept at this temperature T _{2 for} at least 24 hours, and then slowly cooled to obtain a silicon wafer after growth, A method for pulling a silicon single crystal, which suppresses a change in the density of oxygen precipitates generated in a silicon wafer due to the heat treatment temperature. 2. A silicon single crystal ingot (11) formed from a silicon melt (7) held in a crucible (4) in a pulling device (12).
In pulling Ru way, be longer at this temperature T ₃ when the silicon single crystal ingot (11) has fallen to a temperature T ₃ of 700 to 1000 ° C. 24
A method for pulling a silicon single crystal characterized by suppressing a change due to the heat treatment temperature in a density of oxygen precipitates generated in a silicon wafer after being grown by being held for a time and then gradually cooled to be a silicon wafer after growth. . 3. A silicon single crystal ingot (11) formed from a silicon melt (7) held in a crucible (4) in a pulling device (12).
In the method of pulling up, the silicon single crystal ingot (11) is further lowered to a temperature T _{5 of} 500 to 900 ° C. for at least 30 minutes at the time when the temperature falls to a temperature T _{4 of} 700 to 1000 ° C. (T ₅ <
T ₄ ), holding at this temperature T _{5 for} at least 24 hours, and then slowly cooling it to obtain a silicon wafer after growth and subjecting it to a heat treatment, a change in the density of oxygen precipitates generated in this silicon wafer due to the heat treatment temperature A method for pulling a silicon single crystal, characterized by suppressing. 4. A silicon single crystal ingot (11) formed from a silicon melt (7) held in a crucible (4) in a pulling device (12).
In the method of pulling up, the silicon single crystal ingot (11) is cooled to a temperature T _{6 of} 20 to 950 ° C. and then 95 minutes at a maximum for 60 minutes.
The temperature is raised to a temperature T _{7 of 0} to 1050 ° C. (T ₇ ≧ T ₆ ), kept at this temperature T _{7 for} at least 24 hours, and then gradually cooled, whereby the silicon wafer in the as-grown state is produced. A method for pulling a silicon single crystal, which comprises reducing a flow pattern defect density.