JPH04338192A - Device for producing silicon single crystal - Google Patents

Abstract

PURPOSE:To prevent contamination of silicon single crystal based on impurity of heavy metal by providing a cylindrical partition made of quartz to the space between a heat shielding body made of metal and single crystal being grown in a device equipped with the metal heat shielding body wherein silicon single crystal having a large caliber is produced by a CZ process. CONSTITUTION:A partition member 2 made of quartz is provided to the inside of a crucible 1 made of the same. Moreover a heat shielding body 8 made of metal is provided which covers both the partition member 2 and the dissolving part of a raw material. Silicon melt 5 is thermally insulated to prevent generation of coagulation. Furthermore a cylindrical partition 10 made of quartz is provided to the space between this heat shielding body 8 and single crystal 11 being grown. Single crystal 11 is prevented from being contaminated by impurities based on heavy metal constituting the heat shielding body 8. Silicon for a raw material is continuously supplied to the outside of the partition member 2 from a feeder 3 and melted. This melt is introduced to the inside of the partition member 2 via a small hole 6 provided thereto. Single crystal 11 is grown by a Czochralski process. Thereby silicon single crystal having a large caliber is grown and density of generating a laminate flaw inducing oxidation is reduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is based on the Czochralski method (
This invention relates to an apparatus for manufacturing large-diameter silicon single crystals using the CZ method (hereinafter referred to as the CZ method).

0002

2. Description of the Related Art Conventionally, silicon single crystals used in the LSI field are usually manufactured by the CZ method. For example, Japanese Patent Publication No. 40-10184 (page 1, left column, lines 20 to 35)
In this CZ method, a cylindrical quartz partition with a circulation hole for the silicon melt is installed inside the quartz crucible containing the silicon melt to partition the silicon melt inside and outside, and the partition A method is disclosed in which silicon single crystals are continuously grown inside a partition while supplying raw material silicon to the outside.

[0003] Japanese Patent Application Laid-Open No. 62-241889 (
As pointed out in the lower left column of page 2, lines 2 to 6), in this method, the silicon melt tends to solidify starting from the partition member inside the partition, which inhibits the growth of silicon single crystals. This problem becomes more apparent as the diameter of the silicon single crystal increases from 6 to 10 inches.

In order to solve this problem, a method of covering the partition member with a heat insulating cover (thermal shield) to prevent the occurrence of solidification is proposed, for example, in JP-A-1-153589. It is disclosed that the upper part is covered with a heat insulating cover, and the heat insulating cover suppresses the dissipation of heat to the horizontal furnace wall, etc. above the crucible, and keeps the silicon melt around the partition member and the raw material melting part warm. There is.

Various materials such as graphite and metals can be considered for the heat shield, but the inventors have found that graphite, which is commonly used as a material for the furnace components of silicon single crystal production equipment, has a high radiation Since the ratio is large, the heat retention effect is not necessarily sufficient. On the other hand, metals with low emissivity can effectively block upward dissipation of heat, so they have a large heat retention effect and are well suited to the purpose of use as a heat shield.

[0006] By constructing this heat shielding body with a metal plate, even when pulling a large diameter silicon single crystal at high speed, there is no solidification from the partition member or unmelted raw material remains in the raw material melting section. , stable single crystal pulling operation becomes possible.

However, the heat shield is used in a high temperature environment inside a single crystal pulling furnace, and it is necessary to use a high melting point metal such as tantalum, molybdenum, or tungsten. In particular, tantalum is an extremely malleable metal and is easy to work with in various ways, making it easy to use.

[0008]

[Problems to be Solved by the Invention] As described above, by covering the partition member with a high-purity heat shielding material made of one selected from tantalum plate, molybdenum plate, or tungsten plate, silicon from the partition member can be removed. It is possible to prevent the solidification of the melt and the undissolved supply of raw materials in the raw material melting section, making it possible to stably grow silicon single crystals using the continuous pulling method.

However, silicon single crystals grown using carbon with high heat retention properties or high melting point metals such as tantalum and molybdenum as heat shields suffer from oxidation-induced stacking faults when processed into silicon wafers. (hereinafter OS
It was found that the generation density of OSF (OSF) tends to increase, and is particularly noticeable (OSF density of about 103 pieces/cm2) when metals such as tantalum and molybdenum are used as the material for the heat shield.

The present invention was made in view of the above circumstances, and uses a metal heat shield to maintain a high growth rate while preventing contamination by heavy metal impurities.
It is an object of the present invention to provide a silicon single crystal manufacturing apparatus in which there is no OSF generation density or the OSF generation density is extremely low.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and achieve the above-mentioned objects.

The present invention provides a self-rotating quartz crucible containing molten silicon, an electric resistance heating element that heats the quartz crucible from the side, and a quartz crucible that supplies the molten silicon to a single crystal growth section and a raw material melting section. a quartz partition member that is divided into two parts and has small holes through which the silicon melt can flow; a heat shield that covers the quartz partition member and the raw material melting section; In a silicon single crystal production apparatus having a pressure reduction device and a raw material supply device that continuously supplies raw silicon to the raw material melting section, a cylindrical quartz partition wall is provided in a space between the heat shield and the growing single crystal. 1 is a silicon single crystal manufacturing apparatus characterized in that:

Furthermore, the optimum value of the diameter of the cylindrical quartz partition wall is determined by the inner and outer diameters, where the diameter of the silicon single crystal is X (mm) and the minimum inner diameter of the heat shield is Y (mm). The above-mentioned silicon single crystal manufacturing apparatus is characterized in that each of the crystals is X+10 (mm) or more and Y-20 (mm) or less.

[0014]

[Operation] The present inventors have found the following reason for the large number of OSFs in silicon wafers obtained from silicon single crystals grown by the continuous pulling method using a heat shield made of a metal plate such as tantalum. We considered this.

First, the OSF generation density was investigated when a silicon single crystal was grown using heat shields of the same shape but different materials. The results are shown in FIG.

FIG. 6 shows the OSF generation density for each distance from the center of the processed silicon wafer from the grown silicon single crystal by changing the material of the heat insulating cover as a heat shield to Mo, Ta, and C. This is a graph.

As is clear from FIG. 6, the OSF generation density is higher when a heat shield made of molybdenum or tantalum is used than when a heat shield made of carbon is used.

[0018] Since the emissivity of metal and carbon is different,
The heat retention ability differs, and the heat history that the crystal receives also changes.

In order to examine whether the difference in the OSF generation density was influenced by thermal history, the shape of the heat shield was designed as shown in FIG. 7. ,
An example in which the angle at which the cooling surface of the crystal is viewed is increased to promote cooling of the crystal. (b) is an example in which the heat shield is placed close to the crystal to strengthen the heat retention of the crystal. (c) is the body of the heat shield. As shown in the example in which heating from the sides of the crystal is promoted, single crystals were grown by changing the shape and the thermal history received by the silicon single crystal in various ways, and the OSF generation density was measured. As long as a metal material was used for the shield, no significant change was observed in the OSF generation density.

On the other hand, when comparing the amounts of heavy metal impurities such as iron and copper contained in metals and carbon, it is found that impurities in metals are generally more than one order of magnitude higher than impurities in carbon. For example, in the case of iron, 50p in molybdenum
pm, 30 ppm in tantalum, 2 ppm in carbon
, for copper, 5 ppm in molybdenum and 1 in tantalum.
0ppm, 1ppm in carbon, total amount of impurities, more than 290ppm in molybdenum, 250ppm in tantalum
pm or more and 20 ppm or less in carbon, and the amount of impurities in the material corresponds to the size of the OSF generation density.

Furthermore, almost no OSF was detected in a silicon wafer obtained from a single crystal grown by the CZ method in an atmosphere free of impurities without using a heat shield.

As a result of the above study, the O
The main cause of the frequent occurrence of SF is thought to be as follows, in addition to the thermal history experienced by the silicon single crystal.

That is, the heat shield is maintained in a high-temperature environment directly above the silicon melt, and therefore heavy metal impurities such as iron and copper, which are contained in the constituent members of the heat shield and evaporate from the heat shield, are removed. This is because molecules adhere to the surface of the growing silicon single crystal through vapor phase diffusion, and penetrate from the surface into the interior through solid phase diffusion, resulting in heavy metal contamination of the single crystal.

According to this idea, it has been found that using carbon for the heat shield is advantageous for growing single crystals with low OSF density within the silicon wafer surface, and as shown in FIG.
The results also support this.

However, the cooling efficiency of the crystal becomes low due to the difference in emissivity, and when a carbon heat shield is used,
Compared to the case of metals, the growth rate of silicon single crystals is about half, 0.6 to 0.7 mm/min, which is slow, resulting in poor productivity. Therefore, it became necessary to devise a method to prevent heavy metal contamination while maintaining a high growth rate by using a metal heat shield, and the present invention was created.

In the present invention, a cylindrical quartz partition wall is placed between the heat shield and the silicon single crystal in order to prevent heavy metal impurity molecules evaporated from the heat shield from adhering to the silicon single crystal. This is what I did. Providing this quartz partition wall,
The first effect is that even if heavy metal impurity molecules evaporate from the heat shield and diffuse into the single crystal in a vapor phase, they are blocked by the quartz partition wall and can prevent contamination of the single crystal. Most of the heavy metal impurity molecules thus diffused adhere to the quartz surface, and the number of molecules that reach the silicon single crystal is drastically reduced.

The second effect is that since quartz, which has extremely good thermal conductivity and is almost thermally transparent, is used as the material for the partition walls, the thermal environment, which greatly influences the growth conditions of silicon single crystals, can be changed before and after installing the partition walls. One advantage is that silicon single crystals can be grown under almost the same growth conditions as before installation, as shown in the examples described later, without making any major changes.

In view of the fact that changes in the thermal environment greatly affect the stable growth of single crystals and crystal quality, the feature of not causing changes in the thermal environment is extremely advantageous in implementing the present invention. be.

In addition, in the Examples described later, the relationship between the diameter of the quartz partition wall and the OSF generation density at the edge of the wafer made from the obtained silicon single crystal was determined.
When pulling a 6-inch diameter single crystal, we found that the OSF generation density gradually increases when the outer diameter of the quartz partition wall exceeds 200 mm, and the minimum value of the quartz partition wall diameter exceeds 200 mm. It has been found that the temperature is determined at the lower limit of a range that does not cause contact with the silicon single crystal that is shaken during the growth of the silicon single crystal.

Furthermore, it has been found that when the difference between the outer diameter of the quartz partition wall and the minimum inner diameter of the heat shield becomes 20 mm or less, the OSF generation density increases.

From these findings, the diameter of the silicon single crystal 11 is X (mm), and the minimum inner diameter of the heat shield 8 is Y (mm).
It has been found that the optimum diameter of the quartz partition wall 10 is preferably such that the inner diameter is X+10 (mm) or more and the outer diameter is Y-20 (mm) or less.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view schematically showing a silicon single crystal manufacturing apparatus used in an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a 20-inch diameter quartz crucible holding a silicon melt 5, which is supported by a graphite crucible 4, which is rotated by a motor at a normal speed of 10 rpm on a pedestal 15. Ru.

2 is a quartz partition member with a diameter of 16 inches arranged concentrically with the quartz crucible 1;
Inside, the silicon melt 5 is divided into a single crystal growth section and a raw material melting section.

Reference numeral 3 denotes a silicon raw material supply device, through which granular polysilicon is supplied to the raw material melting section outside the quartz partition member 2. The silicon melt 5 in the raw material melting section passes through the melt flow hole 6 and flows into the crystal growth section inside the quartz partition member 2 .

7 is a contact surface between the partition and the melt surface, and in the present invention, the silicon melt is prevented from solidifying from the contact surface 7 and the granular silicon raw material is promoted to dissolve in the raw material melting section. For this purpose, a heat shield 8 (thermal cover) made of molybdenum or tantalum and having a thickness of 0.2 mm is installed.

Reference numeral 9 denotes an electric resistance heating element surrounding the graphite crucible 4, and 10 denotes a cylindrical partition wall made of high-purity quartz proposed in the present invention, which is provided between the heat shield 8 and the silicon single crystal. In this example, the outer diameter is 180 mm and the height is 1.
A cylinder with a diameter of 85 mm and a thickness of 5 mm was used.

Reference numeral 11 indicates a silicon single crystal, and in this example, the purpose is to grow a silicon single crystal with a diameter of 6 inches. Further, the diameter of this silicon single crystal is controlled by detecting the weight change accompanying the diameter change from time to time by a crystal weight sensor installed outside the figure.

Note that 12 is a lifting chamber, 13 is a main chamber upper lid, 14 is a main chamber body, 1
6 is an upper heat insulating cylinder, 17 is a side heat insulating cylinder, 18 is an exhaust hole, and atmospheric gas (argon gas) is drawn into the pulling chamber 1.
2. The gas is introduced into the furnace through the gas inlet (not shown) provided above and discharged through the exhaust hole 18 at the bottom of the furnace, and the pressure inside the furnace during single crystal growth is adjusted to 0.01 to 0.03 atm. be done.

FIG. 2 schematically shows details of the heat shield 8. The heat shield 8 is made up of a cylindrical portion 21 and a flat plate portion 23 having an opening 22, as shown in FIG.

By providing this opening 22, the gas flow state within the silicon single crystal manufacturing apparatus is optimized.
This is useful for preventing the formation of dislocations in the silicon single crystal 11.

Using the silicon single crystal manufacturing apparatus shown in FIG. 1, using the continuous pulling method and setting the crystal growth environment as described above, a silicon single crystal was grown and manufactured. A silicon single crystal with a diameter of 6 inches or more of 80 cm or more could be grown with a probability of about 90% or more. This probability is completely comparable to that before the quartz partition wall 10 was installed.

Silicon wafers were manufactured from the silicon single crystals obtained, and for quality evaluation, they were heat-treated at 1100° C. for 30 to 120 minutes in a humid O 2 atmosphere, and then the OSF generation density was measured.

Comparing the growth conditions before and after installing the quartz partition wall 10, the power input to the electric resistance heating element 9 during growth of the constant diameter section was 84.5 to 85.5 kW before installation, and 85.5 kw after installation. There is almost no change from 5 to 85.7kw, and the crystal growth rate at that time is also 1.0.
~1.2 mm/min, and there was no change before and after installation.

Further, FIG. 3 shows changes in the in-plane distribution of OSF generation density when silicon single crystals grown before and after using the quartz partition wall 10 are processed into wafers. The results are shown in FIG.

As shown in FIG. 3, the OSF density is 100 in the case of the present invention, and 101 to 103 in the conventional case.
It was found that the OSF generation density of wafers obtained from silicon single crystals grown before and after the installation of the quartz partition walls 10 was considerably reduced, and the effect of installing the quartz partition walls 10 was clear.

The heavy metal impurity molecules evaporated from the heat shield 8 are adsorbed onto the surface of the quartz partition wall 10, forming a highly concentrated impurity layer on the very surface layer of the quartz partition wall 10.

Quartz partition wall 1 before and after growing silicon single crystal
The surface layer of No. 0 was cleaned with hydrofluoric acid, and the concentrations of iron and copper in the cleaning solution were compared and investigated. The results are shown in FIG. When cleaning the surface layer with hydrofluoric acid, the relative ratio of impurities clearly increases after growth.

FIG. 4 shows the relative ratios of the contents of iron and copper after growth, depending on the growth time, assuming that the content of impurities iron and copper in the cleaning solution for the quartz partition wall 10 before growth is 1, respectively. This is a graph.

As shown in FIG. 4, the iron and copper impurities in the cleaning solution increase monotonically as the growth time increases, and when the growth time exceeds about 100 hours, the amount of impurities in the cleaning solution becomes saturated. This seems to be because the amount of impurities that could be adsorbed to the quartz partition wall 10 was exceeded by keeping the quartz partition wall 10 in an impurity atmosphere for a long time.

After the crystal growth, the impurity layer on the surface of the quartz partition wall 10 was washed away with hydrofluoric acid, so that the quartz partition wall 10 was restored to a clean surface and could be reused.

It has been found that there is an appropriate value for the diameter of the quartz partition wall 10 in order to obtain the above effects.

That is, when growing a 6-inch diameter silicon single crystal using a heat shield with a minimum inner diameter of 220 mm, the O
The influence of the outer diameter of the quartz partition wall 10 on the SF generation density was investigated, and the results are shown in FIG.

FIG. 5 is a graph showing the relationship between the tube diameter of the quartz partition wall 10 and the OSF generation density at the edge of the wafer.

As shown in FIG. 5, the OSF generation density gradually increases when the outer diameter of the quartz partition wall 10 exceeds 200 mm.

Further, the minimum value of the diameter of the cylindrical quartz partition wall 10 is determined at the lower limit of the range that does not cause contact with the silicon single crystal shaken during the growth of the silicon single crystal. If the inner diameter of the partition wall 10 was 165 mm or more, stable crystal growth was possible without contacting the silicon single crystal.

Further, when the diameter of the silicon single crystal was varied to 5 inches or more, the OSF generation density increased when the difference between the outer diameter of the quartz partition wall 10 and the minimum inner diameter of the heat shield became 20 mm or less. understood.

This result shows that the quartz partition wall 10 is
If the surface temperature of the quartz partition wall 10 increases, the adsorption ability of heavy metal impurity molecules to the surface of the partition wall 10 decreases, and the heavy metal impurity molecules that could not be completely adsorbed or were desorbed again become gaseous. This is thought to be due to the phase diffusion, which caused some substances to adhere to and contaminate the silicon single crystal.

From these results, the diameter of the silicon single crystal 11 is X (mm), and the minimum inner diameter of the heat shield 8 is Y (mm).
It has been found that the optimum diameter of the quartz partition wall 10 is preferably such that the inner diameter is X+10 (mm) or more and the outer diameter is Y-20 (mm) or less.

[0061]

Effects of the Invention The silicon single crystal production apparatus according to the present invention can stably produce large diameter crystals without changing the growth conditions before and after installation by installing a quartz partition wall between a heat shield and a silicon single crystal. This has the effect of being able to grow silicon single crystals and significantly reducing the OSF generation density compared to before installation.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view schematically showing an embodiment of a silicon single crystal manufacturing apparatus according to the present invention;

FIG. 2 is a schematic diagram of a heat shield used in an example of the present invention;

[Fig. 3] O
A graph showing changes in the in-plane distribution of SF generation density,

[Figure 4
] A graph showing the relationship between the content of iron and copper contained in the cleaning solution and crystal growth time when cleaning the surface layer of a quartz partition wall in an example of the present invention,

FIG. 5: O of the wafer edge portion in the embodiment of the present invention.
A graph showing the influence of the outer diameter of the quartz partition wall on the SF generation density,

FIG. 6 is a graph comparing the in-plane distribution of OSF generation density when single crystals grown using molybdenum, tantalum, and carbon heat shields are processed into wafers,

FIG. 7 is an explanatory diagram showing an example of a metal heat shield whose shape is changed in order to change the thermal history of a single crystal. However, (a) is an example in which the cooling of the crystal is accelerated, (b) is an example in which the heat retention of the crystal is strengthened, and (c) is an example in which the body of the heat shield is eliminated and heating from the side of the crystal is promoted.

[Explanation of symbols]

1. Quartz crucible, 2 Quartz partition member, 3. Silicon raw material supply device, 4 Graphite crucible, 5. Silicon melt, 6 Melt flow hole, 7 Contact surface between partition and melt, 8. Heat shield, 9 Electric resistance heating element, 10 Quartz bulkhead, 11 Silicon single crystal, 12 Pulling chamber, 13　Main chamber top lid, 14 Main chamber body, 15 Pedestal, 16 Upper heat insulation tube, 17　Side heat insulation tube, 18 Exhaust hole.

Claims (2)

[Claims] Claim 1: A rotating quartz crucible containing a silicon melt, an electric resistance heating element that heats the quartz crucible from the side, and dividing the silicon melt into a single crystal growth section and a raw material melting section within the quartz crucible. and a quartz partition member having small holes through which the silicon melt can flow; a heat shield covering the quartz partition member and the raw material melting section; In the silicon single crystal production apparatus, which has a pressure reduction device and a raw material supply device that continuously supplies raw silicon to the raw material melting section, a cylindrical quartz is provided in a space between the heat shield and the growing single crystal. A silicon single crystal production device characterized by providing a silicon partition wall. 2. The optimum value of the diameter of the cylindrical quartz partition wall is defined as the inner diameter and outer diameter, where the diameter of the silicon single crystal is X (mm) and the minimum inner diameter of the heat shield is Y (mm). 2. The silicon single crystal manufacturing apparatus according to claim 1, wherein each of the diameters is set to be not less than X+10 (mm) and not more than Y-20 (mm).