JP2005314143A - Method for producing silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method capable of stably forming a shoulder and efficiently pulling a silicon single crystal by adjusting a furnace internal pressure according to the processes of pulling. <P>SOLUTION: The method for producing a silicon single crystal in an Ar gas atmosphere by the CZ process comprises the steps of melting a silicon stock at a furnace internal pressure of 13.3-40.0 kPa (100-300 Torr), acclimatizing a seed crystal to the melt, performing seed-narrowing, forming a shoulder at a furnace internal pressure of 0.67-6.7 kPa (5-50 Torr), and subsequently pulling a straight body part at a furnace internal pressure of 13.3-40.0 kPa (100-300 Torr). Further, the above melting of a silicon stock may include the melting accompanying meltback. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a silicon single crystal by the Czochralski method (hereinafter simply referred to as “CZ method”), and more specifically, by efficiently adjusting the furnace pressure according to the pulling process. The present invention relates to a method for producing a silicon single crystal that can be increased.

  A method of pulling a single crystal by a CZ method is the most widely adopted method for producing a silicon single crystal used for a silicon wafer of a semiconductor material.

  FIG. 1 is a cross-sectional view showing a configuration of an apparatus used for pulling a silicon single crystal by the CZ method. The crucible 2 disposed at the center of the single crystal pulling apparatus 1 has a double structure, and is composed of an inner quartz crucible 2a and an outer graphite crucible 2b. A graphite heater 3 is provided outside the crucible 2, and a silicon melt 4 melted by the heater is accommodated in the crucible 2.

  A pulling wire 5 is used as a single crystal pulling means, and a seed crystal (seed) 6 is attached to the tip thereof. The temperature of the melt 4 is adjusted to such an extent that the seed crystal becomes compatible with the silicon melt, and the lower end of the seed crystal 6 is brought into contact with the surface of the melt 4 and pulled upward to solidify and grow the single crystal 7 at the lower end. .

  Usually, a heat shielding material 8 is installed around the single crystal 7 to block heat radiation from the melt 4 surface and the crucible 2 inner surface, and an argon gas (hereinafter simply referred to as “Ar gas”) as an inert gas in the apparatus. The single crystal 7 is pulled in an Ar gas atmosphere.

  In FIG. 1, Ar gas is injected from the inlet 9 above the single crystal, flows down between the surface of the single crystal 7 and the heat shielding material 8, passes through the surface of the melt 4, and is guided to the outside of the crucible 2. It is discharged from the bottom of the furnace through the exhaust port 10 to the outside of the furnace. At this time, oxides (SiO, SiOx, etc.) evaporated from the surface of the silicon melt 4 are discharged to the outside of the furnace along with the Ar gas.

  When pulling up a single crystal by the CZ method, dislocations remaining in the seed crystal and dislocations generated by thermal stress when the seed crystal is brought into contact with the melt are completely removed. It is necessary not to reach the part (main part). For this reason, a seed squeezing with a diameter of about 5 mm is performed while pulling the seed crystal upward so as to eliminate dislocations from the crystal surface and make the single crystal dislocation-free.

  In this seed squeezing, a seed squeezing part having a desired shape can be formed by controlling the pulling speed and the temperature of the melt. That is, the seed diameter can be reduced by increasing the pulling speed or by increasing the melt temperature, and conversely, the seed diameter can be increased by decreasing the pulling speed and decreasing the melt temperature. it can.

  Next, after the seed squeezing, a shoulder portion is formed in order to secure a straight body portion corresponding to the product diameter. When the shoulder is formed, the crystal diameter is expanded in a conical shape so that the crystal diameter is changed from the seed diameter to the diameter of the straight body while adjusting the pulling speed and the temperature of the melt.

  After the crystal diameter reaches the diameter of the straight body due to the formation of the shoulder portion, the process moves to pulling up the straight body, and the single crystal main body to be a product is grown. And after growing the main-body part of predetermined length, a crystal diameter is reduced, a tail part is formed, and manufacture of a silicon single crystal is complete | finished by cut | disconnecting from a melt.

  When a silicon single crystal is manufactured using the above-described CZ method, various dopants are added to the silicon melt in order to adjust the polarity of the single crystal and its resistivity. As typical dopants, boron is generally used for p-type and phosphorus is used for n-type, and arsenic, antimony, red phosphorus, etc. are used for n-type low-resistance single crystal growth.

  As described above, oxides (SiO, SiOx, etc.) evaporate from the surface of the silicon melt during the process of manufacturing a silicon single crystal. Foreign matter may adhere to the growing silicon single crystal and cause dislocations in the pulled single crystal. In particular, n-type dopants such as arsenic and antimony have high volatility, and easily combine with oxygen in the melt to evaporate from the surface of the melt as a complex oxide. As the amount of evaporation increases, dislocations are likely to occur in the single crystal.

  If there is dislocation in the silicon single crystal during pulling, it will be difficult to continue growing the silicon single crystal thereafter. For this reason, in the case where dislocations occur in the silicon single crystal at a relatively early stage, an operation of once immersing the dislocated silicon single crystal in the melt, adjusting the liquid temperature, and re-dissolving it, The so-called meltback may be performed, and the pulling may be performed again through dissolution, seed squeezing and shoulder formation.

  In such a case, since it takes a long time to grow a single crystal, the dope amount (concentration) in the raw material melt decreases as the amount of complex oxide evaporated from the surface of the melt decreases, and the desired specific resistance No single crystal can be obtained. In particular, when growing an n-type low-resistance silicon single crystal doped with high concentrations of arsenic, antimony, etc., it is necessary to add a new doping agent to the silicon melt in order to maintain a predetermined specific resistance. Sometimes it becomes.

  In the production of a silicon single crystal by the CZ method, the pressure in the furnace affects the amount of oxide evaporation, the bubbles present in the silicon melt, and also the bubbles in the quartz crucible. It is an important operating condition along with gas supply conditions. For this reason, various proposals have heretofore been made regarding the conditions of the furnace pressure in the production of a silicon single crystal by the CZ method.

  For example, in Patent Document 1, a silicon raw material is melted at a furnace pressure of 6.5 to 40.0 kPa (65 to 400 mbar), and a single crystal is pulled from the silicon melt in a furnace of 9.5 kPa (95 mbar) or less. A method for producing a single crystal under pressure has been proposed.

  According to the manufacturing method of Patent Document 1, by performing high-pressure melting and low-pressure pulling at an appropriate furnace pressure, the problem of pinholes generated in high-pressure operation (high-pressure melting and high-pressure pulling) is eliminated, and low-pressure operation ( It is said that dislocations caused by evaporated SiO, which is a problem in low-pressure melting and low-pressure pulling, can be effectively suppressed.

  Further, Patent Document 2 discloses a silicon single material in which a polycrystalline silicon raw material is melted at a furnace pressure of 0.5 to 6.0 kPa (5 to 60 mbar) and pulled up at a furnace pressure of 10.0 kPa (100 mbar) or more. Crystal pulling methods have been proposed.

  In the manufacturing method of Patent Document 2, the pressure adjustment differs from the furnace pressure condition adopted in Patent Document 1. However, according to the proposed operating conditions, the occurrence of single crystal pinholes is suppressed and initial operation troubles are prevented. It is disclosed that the carbon concentration in the single crystal can be reduced.

  Further, in Patent Document 3, from the melting of silicon to the transition from shoulder growth to straight body growth, that is, the initial stage of pulling is set to a furnace pressure of 0.67 to 1.33 kPa (5 to 10 Torr), and thereafter A method of producing a single crystal by pulling up at a furnace pressure of 3.33 to 5.32 kPa (25 to 40 Torr) has been proposed.

  In the production method of Patent Document 3, the pressure in the furnace is lowered at the initial stage of pulling, and the SiO that evaporates from the free surface of the melt is reduced by lowering the rotation speed of the crucible. In addition, the amount of oxygen in the silicon melt is reduced, In addition, the amount of oxygen dissolved from the quartz crucible is controlled by adjusting the rotation of the crucible in the latter half of the pulling, and the decrease in oxygen concentration on the tail side of the single crystal can be prevented.

  As described above, when an n-type low-resistance silicon single crystal is produced by the CZ method, when the arsenic, antimony, or red phosphorus is doped and pulled, the oxides are often evaporated, Condensation and dropping at, foreign matter may enter the crystal interface and cause dislocation. In this case, it may be necessary to perform meltback according to the pulling condition and add a dopant to the silicon melt.

However, since the manufacturing method proposed in Patent Documents 1 to 3 is not intended to manufacture the above-described n-type low resistance crystal doped with arsenic, antimony, or red phosphorus, It cannot suppress that dope oxide evaporates from the surface of a melt. For this reason, in the pulling process, it becomes unstable particularly in the formation of the shoulder, and the single crystal is easily dislocated due to the foreign matter caused by the oxide, and the frequency of meltback increases.
Therefore, Patent Document 4 is a method for producing a silicon single crystal having a specific resistance of 0.01 to 0.03 Ωcm by doping antimony, and the furnace pressure is set to 5.33 to 13.3 kPa (40 to 100 Torr). It has been proposed to suppress the evaporation of antimony while supplying Ar gas and discharging silicon oxide (SiO).

  According to the manufacturing method proposed in Patent Document 4, since the furnace pressure is 5.33 to 13.3 kPa (40 to 100 Torr), the difference between the furnace pressure and the vapor pressure of antimony in the melt is reduced. The amount of antimony evaporated from the melt can be greatly reduced.

  However, in this manufacturing method, it is necessary to discharge silicon oxide (SiO) in a state where the pressure in the furnace is kept high. For example, the supply amount of Ar gas is as large as about 50 to 200 liters / minute. become. For this reason, the heat burden on the exhaust gas becomes large, the exhaust gas cooling device needs to be enlarged, and the Ar gas flow rate increases, resulting in an unstable state such as vibration of the surface of the melt. Easy to be. For this reason, in the formation of the shoulder portion in the initial stage of pulling, the crystal may be disturbed, and troubles such as dislocation may occur.

Japanese Patent No. 3360626

JP-A-5-9097 JP-A-8-133886 Japanese Patent No. 2575360

  As described above, as a conventional method for producing a silicon single crystal, a single crystal in which pinholes generated in the pulling process and dislocation caused by SiO evaporated from the surface of the melt is suppressed or the oxygen concentration distribution is uniform. In order to raise the temperature, a method of adjusting the pressure in the furnace is disclosed (Patent Documents 1 to 3). Furthermore, when manufacturing an n-type low-resistance silicon single crystal using antimony, a method of suppressing the evaporation of antimony while supplying Ar gas and discharging silicon oxide (SiO) with the furnace pressure slightly increased Has been proposed (Patent Document 4). However, either method has a problem that dislocations are likely to occur in the single crystal in forming the shoulder portion of the silicon single crystal in the initial stage of pulling.

  In the process of forming the shoulder portion of the silicon single crystal, the crystal growth state in the shoulder formation is very unstable because the operation of sharply expanding the crystal diameter is performed by adjusting the pulling speed and the like. The oxide that evaporates from the melt surface is easily taken in, and the flow of Ar gas that flows on the melt surface changes due to the change in the shape of the single crystal. There is a problem that it is easy to dislocation. In particular, there is a problem that dislocations become conspicuous in the shoulder growth of an n-type low-resistance silicon single crystal in which the complex oxide of the dopant is rapidly evaporated.

  First, in order to grow a silicon single crystal having a predetermined low resistivity, it is necessary to reduce evaporation of the dopant that evaporates from the surface of the melt. In order to suppress the evaporation of the oxide, the evaporation of the dopant from the melt surface can be suppressed by maintaining the furnace pressure high during the pulling process. However, if the pressure in the furnace is kept high, the flow rate of Ar gas flowing on the surface of the melt is reduced, and the effect of discharging the evaporated material evaporating from the melt surface to the outside of the furnace is reduced. It becomes easy to fall as a foreign object in the vicinity of the growing interface.

  For this reason, if the flow rate of Ar gas supplied into the furnace is increased while maintaining a high pressure in the furnace, the flow rate of Ar gas flowing on the surface of the melt can be increased, and the evaporate evaporated from the surface of the melt can be removed from the outside of the furnace. The effect of discharging can be enhanced. However, since the total flow rate of Ar gas flowing on the surface of the melt becomes excessive, the surface of the melt vibrates, or the surface temperature of the melt decreases and the melt surface freezes. It is impossible to increase the Ar gas flow rate by increasing the Ar gas supply amount.

  On the other hand, if the pressure in the furnace is kept low, it is possible to enhance the effect of discharging the evaporated material evaporating from the melt surface to the outside of the furnace, but the evaporation of the dopant from the melt surface cannot be suppressed, and the predetermined Therefore, it becomes impossible to grow an n-type silicon single crystal having a low resistivity. In addition, if the pressure in the furnace is low, the expansion of bubbles remaining in the quartz crucible is promoted and the surface of the quartz crucible is easily peeled off, so that the peeled foreign matter is taken into the single crystal and causes dislocation. There is.

  As described above, the effect of adjusting the pressure in the furnace has advantages and disadvantages depending on the pressure condition, and the conventionally proposed methods for adjusting the pressure in the furnace suppress the occurrence of single crystal dislocations in shoulder formation. It was difficult to pull up dislocation-free single crystals having a predetermined resistivity.

  The present invention has been made in view of the above-described conventional problems. Even when an n-type low-resistance silicon single crystal is manufactured by the CZ method, the silicon single-crystal having a desired low resistivity is obtained. An object of the present invention is to provide a method for producing a silicon single crystal, in which a crystal is obtained and the yield of dislocation-free silicon single crystal can be improved by reducing the occurrence of dislocations in shoulder formation as much as possible. Yes.

  In order to solve the above-mentioned problems, the present inventor has made detailed studies on the behavior of the melt and the single crystal in the shoulder formation performed in the initial pulling stage.

  FIG. 2 is a partially enlarged view schematically showing a process of seed drawing, shoulder formation, and straight body pulling performed in an initial pulling stage. In FIG. 2 (a), the seed crystal 6 is lowered and its tip is brought into contact with the surface of the melt 4 so as to be sufficiently blended with the melt. By sufficiently acclimatizing, the temperature difference between the seed crystal 6 and the melt 4 can be reduced, the thermal stress resulting from the temperature difference can be reduced, and the number of dislocations introduced can be reduced.

  In FIG. 2 (b), the seed squeezing with a diameter of about 5 mm is performed while solidifying the melt 4 at the tip of the seed crystal 6 by pulling it up at a high speed. Next, in FIG. 2C, the pulling speed of the seed crystal 6 is decreased, and the diameter of the seed constriction part 7a is grown to the diameter of the straight body part to form the shoulder part 7b. Furthermore, in FIG.2 (d), it has changed to the raising of a main-body part through the transition process to the straight body part 7c following formation of the shoulder part 7b.

  In the process of forming the shoulder portion shown in FIG. 2 (c), if the temperature distribution of the melt 4 is rapidly changed, it becomes difficult to control the diameter of the single crystal, and the crystal is rapidly deformed or further has dislocations. Will be triggered. Further, in the transition process to the straight body part following the shoulder formation shown in FIG. 2D, the Ar gas flow is likely to fluctuate with the change of the crystal shape, and the solid-liquid interface shape changes. It becomes easy to receive.

  For this reason, in the process of forming the shoulder and the subsequent transition to the straight body, it is important to grow a single crystal in an environment where there is no evaporant as much as possible around the solid-liquid interface. It is necessary to ensure a sufficient Ar gas flow rate for discharging the evaporated oxide. However, if the operation of increasing the Ar gas flow rate by increasing the Ar gas supply amount, the surface of the melt vibrates, the surface temperature of the melt decreases, the surface of the melt freezes, and the single crystal is pulled up itself. Therefore, it is necessary to avoid increasing the amount of Ar gas supplied.

  Therefore, in the process of forming the shoulder portion and the subsequent transition process to the straight body portion, it is effective to increase the oxide discharge effect by increasing the Ar flow rate in the furnace and maintaining the furnace pressure at a low pressure. Become. Here, since the pressure in the furnace is maintained at a low pressure, the expansion of bubbles remaining in the quartz crucible is promoted, and there is a concern that surface separation of the quartz crucible may be induced. The time required for the subsequent transition process to the straight body portion is much shorter than the other raw material melt formation time and the straight body portion formation time, and there is no risk of contamination due to bubble growth in the quartz crucible.

  On the other hand, in order to obtain a silicon single crystal having a predetermined resistivity, it is necessary to reduce the amount of oxide generated in the dopant evaporated from the melt surface. In addition, in order to obtain a silicon single crystal without dislocation, it is necessary to consider suppressing expansion of bubbles remaining in the quartz crucible. For this reason, it is effective to suppress the evaporation of residual dopant and to suppress the expansion of residual bubbles by maintaining the furnace pressure at a high level in the melting of the silicon raw material, the seed squeezing, and the pulling up after the straight body part. Become.

  As described above, the present inventors made it the most important issue to suppress the occurrence of dislocations in the shoulder formation of a single crystal, and in the shoulder formation, the occurrence of dislocations was suppressed by maintaining the furnace pressure at a low pressure. In the processes other than the shoulder formation, it was concluded that it is effective to suppress the evaporation of the dopant itself by maintaining the furnace pressure at a high level.

  The present invention has been completed based on the above examination results, and has the gist of the following method (1) for producing a single crystal.

  (1) In a method for producing a silicon single crystal in an Ar gas atmosphere by the CZ method, the silicon raw material is melted at a furnace pressure of 13.3 to 40.0 kPa (100 to 300 Torr), and the seed crystal is adapted to reduce the seed squeezing. And then forming a shoulder at an in-furnace pressure of 0.67 to 6.7 kPa (5 to 50 Torr), followed by an in-furnace pressure of 13.3 to 40.0 kPa (100 to 300 Torr). This is a method for producing a silicon single crystal characterized by performing pulling.

  (2) In the method for producing a silicon single crystal according to (1), the silicon raw material can be melted with meltback.

  In the present invention, “manufacturing a silicon single crystal in an Ar gas atmosphere” means that the pressure in the pulling furnace of the apparatus configuration shown in FIG. 1 is adjusted to a reduced pressure, and Ar gas is used as an inert gas. It means that the atmosphere in the furnace is constituted by continuing to supply at a flow rate.

  According to the present invention, the process of “shoulder formation” while maintaining the furnace pressure at a low pressure is a process of forming the shoulder shown in FIG. And a subsequent process of completing the growth up to the diameter of the straight body part and transitioning to the straight body part. Specific switching and adjustment of the pressure in the furnace is performed at the initial stage of `` shoulder formation '' that has little effect on the pulling operation, and at the same time when the transition to the straight body portion is stable and the straight body portion is lifted stably, for example, the straight body It can be set as the time of moving to a part and raising 50 mm.

  According to the method for producing a silicon single crystal of the present invention, the shoulder portion can be stably formed, the single crystal can be produced with a high yield, and the deterioration of the quartz crucible is alleviated. The manufacturing cost can be significantly reduced.

  Further, when an n-type low resistance silicon single crystal is manufactured by doping arsenic, antimony, red phosphorus or the like, the shoulder is stably formed, and the silicon melt and the dopant are used throughout the pulling process. It is possible to efficiently produce a silicon single crystal having a desired low resistivity by suppressing the evaporation of oxides caused by this reaction. In addition, since the evaporation amount of the dopant can be suppressed, the frequency of additional doping can be reduced, and at the same time as the productivity is improved, the introduction of the dopant can be reduced and the manufacturing cost can be reduced.

  In the manufacturing method of the present invention, in an Ar gas atmosphere, a silicon raw material is melted at a furnace pressure of 13.3 to 40.0 kPa (100 to 300 Torr), a seed crystal is applied, and then seed squeezing is performed, followed by 0.67. The shoulder is formed at a furnace pressure of ˜6.7 kPa (5 to 50 Torr), and then the straight body is pulled up at a pressure of 13.3 to 40.0 kPa (100 to 300 Torr). It is said.

  Here, the Ar gas atmosphere can be configured by continuing to supply Ar gas into the furnace at a constant flow rate, and varies depending on the pulling device and the crystal to be grown, for example, 20 to 400 liters / minute. A flow rate can be employed.

  In the manufacturing method of the present invention, it is desirable that the target silicon single crystal is an n-type low resistance crystal doped with arsenic, antimony, or red phosphorus. Usually, in order to reduce the specific resistance of the crystal, the amount of dope added to the raw material melt is increased, and the concentration of the dopant contained in the crystal is increased. However, when arsenic, antimony, or red phosphorus is used as a dopant, increasing the amount of addition increases the oxide of the dopant that evaporates from the surface of the melt, and grows a low-resistance crystal. Can be difficult.

  Therefore, to suppress the evaporation of the oxide of the dopant, it is effective to keep the furnace pressure high. Therefore, in the manufacturing method of the present invention, not only pulling up the straight body part that becomes the main body of the single crystal, but also melting of the silicon raw material, subsequent liquid temperature stabilization, and seed squeezing process, and further remelting with meltback During this process, the furnace pressure is kept high.

  In order to increase the pressure in the furnace, it is necessary to maintain it at 13.3 to 40.0 kPa (100 to 300 Torr). The upper limit of the furnace pressure was set to 40.0 kPa. If the pressure is increased beyond this, the Ar gas flow becomes too slow, and the purge effect is reduced. This is because of concern. On the other hand, the lower limit of the furnace pressure is set to 13.3 kPa, and if the pressure is lower than this, evaporation of the dopant from the melt surface is promoted too much, and it is difficult to obtain a predetermined resistivity quantitatively. This is because dislocation of the single crystal due to the oxide occurs due to an increase in the evaporation amount of the oxide. Furthermore, a desirable furnace pressure is 13.3 to 26.6 kPa.

  Further, by maintaining the furnace pressure high, the expansion of bubbles remaining in the quartz crucible is eliminated, and the surface of the quartz crucible is prevented from being peeled, so that the shoulder can be stably formed. As a result, the life of the quartz crucible can be further extended, the yield rate of the single crystal to be pulled up can be improved, and an efficient silicon single crystal can be produced.

  On the other hand, by maintaining the furnace pressure high while keeping the Ar gas flow rate constant, the Ar gas flow rate is slowed down, so the action of the Ar gas to discharge the evaporated material from the melt (purge effect) is reduced. Will do. For this reason, dislocations are more likely to occur in the process of forming the shoulder, which is likely to be unstable, as compared with raw material melting, seed drawing, and pulling up the straight body.

  As described above, if the flow rate is increased in order to ensure the flow rate of Ar gas in the furnace, the flow rate of Ar gas flowing on the surface of the melt becomes excessive, and the formation of the shoulder becomes more unstable. Therefore, in order to form the shoulder portion stably, it is necessary to eliminate fluctuations in Ar gas supply conditions while ensuring the Ar gas flow rate.

  For this reason, in the manufacturing method of the present invention, the pressure in the furnace is maintained in order to keep the Ar gas flow rate constant and at the same time secure the Ar gas flow rate in the process of forming the shoulder portion that tends to be unstable and the transition process to the straight body portion. Must be maintained at a low pressure.

  When the furnace pressure is set to a low pressure, it is necessary to maintain the pressure within the range of 0.67 to 6.7 kPa (5 to 50 Torr). The upper limit of the pressure in the furnace is set to 6.7 kPa. If the pressure exceeds this value, the flow rate of Ar gas becomes too slow, and the oxide evaporated from the surface of the melt is not sufficiently discharged. This is because dislocation occurs in the single crystal during formation. On the other hand, the reason why the lower limit of the furnace pressure is 0.67 kPa is because it is based on the equipment specifications of the pulling apparatus to which the present invention can be applied. Furthermore, a desirable range when the furnace pressure is low is 2.66 to 5.32 kPa.

  The production method of the present invention can be applied regardless of whether the polarity of the silicon single crystal is p-type or n-type, but is particularly highly doped with arsenic, antimony, or red phosphorus, which tends to cause dislocations in shoulder formation. This is effective for manufacturing an n-type low-resistance silicon single crystal. Specifically, by the four-deep-needle measurement method, the dopant was doped at a high concentration so that the resistivity was less than 2.7 mΩcm for arsenic, less than 18 mΩcm for antimony, and 1.5 m and less than Ωcm for red phosphorus. This is effective for the production of silicon single crystals.

Below, the effect by the manufacturing method of the silicon single crystal of this invention is demonstrated based on specific Example 1 and 2. FIG.
Example 1
Using the pulling apparatus shown in FIG. 1, arsenic was doped and a silicon single crystal having a diameter of 6 inches was pulled. At the time of pulling, the silicon raw material melt was doped with arsenic, then seeded with a seed crystal to squeeze the seed, grow the shoulder, and then lift the straight body. The effects of the furnace pressure when the crystal length of the straight body portion reached 800 mm on the good crystal index, initial trouble occurrence frequency, and specific resistance were investigated. The survey results are shown in Table 1.

The crystal non-defective index shown here is a numerical value serving as a yield index, which is obtained by dividing the crystal weight of a product per operation by the raw material weight, and as described later, “conventional example (base condition)” “1” was relatively compared, and 1.10 or higher was regarded as a non-defective product.
On the other hand, the occurrence frequency of the initial trouble is the number of times that single crystal disorder (dislocation) occurred during one operation, and similarly, the value in the “conventional example (base condition)” is relatively compared as 1, 1.02 or less was regarded as a good product. Furthermore, the specific resistance is a measured value at a portion where the pulling up of the straight body portion (0 mm position of the straight body portion) is started.

  The pressure in the furnace is adjusted by the "melting" process of melting the silicon raw material, the "seed squeezing" process in which the seed crystal is blended to perform seed squeezing, the shoulder growth and the subsequent transition to the straight body part (straight body part 50 mm The process was divided into the “shoulder part formation” process including the “lower shoulder part” process and the “straight body part” process from pulling up the straight body part (after 50 mm of the straight body part) to the end. If there was a meltback, it was included in the “seed squeezing” process.

  From the results shown in Table 1, Example 1 of the present invention obtained by the production method of the present invention has a crystal quality index improved by about 0.1 points in comparison with the “conventional example” and the occurrence of initial trouble. The frequency was 1.01, almost unchanged. Furthermore, in Example 1 of the present invention, the specific resistance is improved by about 0.19 mΩcm, and by maintaining the furnace pressure at a high pressure except for the “shoulder formation” process, evaporation of the arsenic-doped oxide is suppressed. It depends.

  In the present invention example 2, the pressure in the furnace was increased in the “melting” process, the “seed squeezing” process, and the “straight trunk part” process as compared with the above-described invention example 1, but the same in the “shoulder formation” process. Maintained at a low pressure. For this reason, the initial trouble is not much different from that of the “conventional example”, but the crystal good product index and the specific resistance are greatly improved as compared with the conventional example.

In Comparative Example 3, pulling was performed while maintaining the furnace pressure at a high pressure in the “seed squeezing” process, the “shoulder formation” process, and the “straight trunk part” process. For this reason, the specific resistance was sufficiently low as compared with the “conventional example”, but it was frequently generated at about twice the frequency of occurrence of the initial trouble, and good results were not obtained.
(Example 2)
As in Example 1, using the pulling apparatus shown in FIG. 1, a silicon single crystal having a diameter of 8 inches was pulled by doping boron. Therefore, after doping boron into the silicon raw material melt, the seed crystal was blended to perform seed squeezing to form a shoulder portion, and then the straight body portion was pulled up. The effect of the pressure in the furnace when the crystal length of the straight body portion reached 1400 mm on the good crystal index, initial trouble occurrence frequency, and specific resistance was investigated. The survey results are shown in Table 2.

  At this time, the crystal non-defective index and the initial trouble occurrence frequency were the same as in the case of Example 1. However, when boron is doped, it is difficult to predict the change in the specific resistance by adjusting the furnace pressure, so the specific resistance is measured. Did not.

  From the results shown in Table 2, the initial trouble occurrence frequency was the same as that of the “conventional example” by adjusting the pressure in the furnace defined in the present invention to both of the present invention examples 1 and 2, but the non-defective product remained as the crystal good product index. The rate improved by 0.11 to 0.13 points.

  In Comparative Example 3, pulling was performed while maintaining the furnace pressure at a high pressure in the “seed squeezing” process, the “shoulder formation” process, and the “straight trunk part” process. For this reason, compared with the “conventional example”, the initial trouble frequency increased and the number of meltbacks increased.

  According to the method for producing a silicon single crystal of the present invention, the shoulder portion can be stably formed, the single crystal can be produced with a high yield, and the deterioration of the quartz crucible is alleviated. The reduction in manufacturing cost becomes significant.

  Further, when an n-type low resistance silicon single crystal is manufactured by doping arsenic, antimony, red phosphorus or the like, the shoulder is stably formed, and the silicon melt and the dopant are used throughout the pulling process. It is possible to suppress the evaporation of the oxide generated by this reaction and to efficiently produce a low resistance crystal.

  In addition, since the evaporation amount of the dopant can be suppressed, the frequency of additional doping can be reduced, and at the same time as the productivity is improved, the introduction of the dopant can be reduced and the manufacturing cost can be reduced. Therefore, the method for producing a silicon single crystal of the present invention can be widely applied to the production of silicon wafers used for semiconductor substrates.

It is sectional drawing which shows the structure of the apparatus used for pulling of the silicon single crystal by CZ method. It is the elements on larger scale which showed typically the process of seed drawing-shoulder formation-straight body part raising performed at the initial stage of raising.

Explanation of symbols

1: single crystal pulling device, 2: crucible 2a: quartz crucible, 2b: graphite crucible 3: heater, 4: melt 5: pulling wire, 6: seed crystal (seed)
7: Single crystal, 7a: Seed throttling part 7b: Shoulder part, 7c: Straight trunk part (main body part)
8: heat shielding material, 9: inlet 10: outlet

Claims (2)

  In a method for producing a silicon single crystal in an argon (Ar) gas atmosphere by the Czochralski method, a silicon raw material is melted at a furnace pressure of 13.3 to 40.0 kPa (100 to 300 Torr), and the seed crystal is adapted to be seeded. After carrying out throttling and then forming a shoulder at an in-furnace pressure of 0.67 to 6.7 kPa (5 to 50 Torr), a straight cylinder is subsequently applied at an in-furnace pressure of 13.3 to 40.0 kPa (100 to 300 Torr). A method for producing a silicon single crystal, wherein the part is pulled up. The method for producing a silicon single crystal according to claim 1, wherein the silicon raw material is melted with meltback.

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