JPH04317492A - Producing device for silicon single crystal - Google Patents

Abstract

PURPOSE:To reduce flaw generation density in an oxidation inductive laminated layer by forming a heat-insulating cover of a metallic plate made of one kind of metal selected from among Ta, Mo and W incorporating Fe and Cu of the specified amount and below and removing the surface layer thereof at prescribed depth before a furnace is used. CONSTITUTION:Atmospheric gas such as Ar is introduced into a furnace and exhausted from a gas discharging port 12 in the bottom of the furnace to decompress this furnace. Then granular Si is continuously supplied to a dissolving part A of a raw material at the amount equal to the pulling-up amount of single crystal via a supply pipe 15 from a supply chamber 14. The dissolving part A is covered with a heat-insulating cover 10 for inhibiting dissipation of heat the furnace wall. The heat-insulating cover is formed of a metallic plate made of one kind of metal selected from among Ta, Mo and W incorporating <=50ppm Fe and <=10ppm Cu. The surface layer of the heat- insulating cover is removed at >=10mum depth before the furnace is used and thereafter this cover is used. Then Si melt 7 of the dissolving part A is introduced into a single crystal growing part B from the small hole 9 of a partition member 8 made of high- purity quartz. As a result, single crystal is stably pulled up and high-puality Si single crystal 5 is obtained which is small in a flaw density in an oxidation inductive laminated layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is based on the Czochralski method (
The present invention relates to an apparatus for manufacturing large-diameter silicon single crystals by the CZ method (hereinafter referred to as the CZ method), and particularly to a heat-insulating cover.

0002

2. Description of the Related Art Silicon single crystals used in the LSI field are usually manufactured by the CZ method, but in this CZ method, the amount of silicon melt in a crucible decreases as the silicon single crystal grows. Therefore, as the silicon single crystal grows, the dopant concentration in the silicon single crystal increases and the oxygen concentration decreases. That is, the properties of the silicon single crystal change depending on the direction of its growth.

As the density of LSIs increases, the quality required for silicon single crystals becomes stricter year by year, resulting in a problem of lower yields.

As a means to solve this problem, for example, Japanese Patent Publication No. 10184/1984 (page 1, right column, lines 20 to 35) discloses that the inside of a quartz crucible in the CZ method is shaped into a cylindrical shape having small holes for the silicon melt. Alternatively, a method of partitioning with a crucible-shaped quartz partition member and growing silicon single crystals inside the partition member (single crystal growth section) while supplying raw material silicon to the outside of this partition member (raw material melting section) (continuous pulling) law) has been disclosed. A major problem with this method is that it is disclosed in Japanese Patent Application Laid-Open No. 62-241889 (page 2, upper right column, lines 12 to 16).
As pointed out in Section 2), the silicon melt tends to solidify inside the partition member, starting from the partition member.

That is, solidification occurs from the surface of the silicon melt in the single crystal growth area that is in contact with the partition member. This solidification grows toward the center of the crucible where the temperature is lower and inhibits silicon single crystal growth. The reason for this is as follows.

[0006] Quartz glass, which is normally used as a partition member, is easily penetrated by hot wires, and in normal cases, heat is radiated from the part of the upper part of the partition member exposed above the silicon melt surface to the water-cooled furnace wall. Since the silicon melt is large, the heat in the silicon melt is transmitted upward through the partition member and is dissipated from the portion of the partition member exposed on the melting surface. Therefore, the temperature of the melt in the vicinity of the partition member is greatly reduced.

[0007] As described above, the surface of the molten liquid in contact with the partition member is in a state where solidification is extremely likely to occur.

[0008] Recently, it has become possible to produce high-quality granular silicon, and it is thought that it is relatively easy to continuously supply this granular silicon into a silicon melt as raw material silicon in the continuous pulling method. It will be done.

However, if sufficient melting heat is not applied to the granular silicon when the granular silicon is supplied to the surface of the silicon melt, unmelted granular silicon remains. It is not rare for the undissolved particulate silicon to solidify and expand.

[0010] This is because the solid granular silicon floats on the surface of the melt due to the density difference, and since the solid granular silicon has a higher thermal emissivity than the silicon melt, heat is easily removed. It is. In particular, when granular silicon adheres to and aggregates on the partition member at the surface of the silicon melt in the raw material melting zone, as in the case of solidification in the single crystal growth zone described above,
Since heat is rapidly removed through the partition member, coagulation is likely to occur and spread. In the future, if the amount of raw material silicon to be supplied increases as the diameter of silicon single crystals increases and the pulling speed increases, this phenomenon will become more likely to occur.

[0011] Furthermore, this problem does not essentially change even if the raw material silicon to be supplied is in a form other than granules.

[0012] Japanese Patent Laid-Open No. 1-153589 proposes a method for preventing the occurrence of coagulation from the partition member and for preventing unmelted raw silicon from being supplied. This publication states that the area above the partition member and the raw material melting area is covered with a heat insulating cover, and the heat insulating cover prevents heat from dissipating to the water-cooled furnace wall above the crucible. It is disclosed that the molten liquid is kept warm.

[0013] Also, even in a conventional CZ method silicon single crystal manufacturing apparatus in which there is no partition member etc., the pulling speed can be increased by using a cover with a shape different from that in the above case. .

[0014] Various materials such as graphite and metal can be considered for the heat-insulating cover, but according to the inventors' study, graphite, which is commonly used as a material for the internal components of silicon single crystal furnaces, has a high emissivity. Therefore, the heat retention effect is not 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 intended use of the heat insulation cover.

By constructing this heat-insulating cover 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 lifting operation becomes possible.

[0016] However, the heat insulating cover 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.

[0017]

[Problem to be Solved by the Invention] As described above, by covering the partition member with a heat insulating cover made of a high purity tantalum plate, molybdenum plate, or tungsten plate, it is possible to prevent melt from the partition member. It is possible to prevent the solidification of the raw material and the undissolved supply of the raw material in the raw material melting section, and it has become possible to stably grow silicon single crystals using the continuous pulling method.

However, single crystals grown using this metal plate heat-insulating cover tend to have a high density of oxidation-induced stacking faults (hereinafter referred to as OSF) of about 103/cm2, resulting in poor crystal quality. It turns out there is a problem.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a silicon single crystal manufacturing apparatus that does not have an OSF or has a very low OSF density.

[0020]

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 includes a quartz crucible containing a silicon melt, an electric resistance heating element that heats the quartz crucible from the side, and a device that divides 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 insulating cover that covers the partition member and the raw material melting section, a pressure reducing device for reducing the pressure inside the furnace that houses each of the components, and the raw material. In a silicon single crystal production apparatus having a raw material supply device that continuously supplies raw silicon to a melting part, the heat insulating cover is a metal plate of one type selected from tantalum, molybdenum, or tungsten containing 50 ppm or less of Fe and 10 ppm or less of Cu. The surface layer of the metal plate is pre-coated to a depth of 10 μm before use.
This silicon single crystal production apparatus is characterized in that it consists of a metal plate from which m or more of the metal plate has been removed.

[0022]

[Operation] Next, the circumstances leading to the present invention will be described.

[0023] First, the present inventors conducted the following study as to the cause of the large number of OSFs in a silicon single crystal grown by a continuous pulling method using a heat insulating cover made of a metal plate.

The cause of OSF in single crystals was first thought to be the influence of the thermal history of the crystal due to the presence of a heat insulating cover, so in order to change the thermal history of the crystal, a heat insulating cover in the single crystal pulling furnace was Single crystals were grown by changing the structure and shape of the hot zone in various ways. However, in neither case could the density of OSF generation be reduced.

Next, impurity contamination of the single crystal is considered to be the cause of OSF. The source of contamination was considered to be heavy metal impurity elements contained in the quartz crucible and quartz partition members used during crystal growth, which were mixed into the silicon melt due to quartz dissolution.
Although single crystals were grown with different amounts of impurities contained, the OSF density did not change.

Furthermore, although a single crystal was grown by the CZ method using a heat-insulating cover made of a metal plate without using a quartz partition member or supplying raw silicon, the OSF density was still high.

Therefore, the present inventors conducted various studies and found that silicon single crystal OSF grown using a heat insulating cover
The reason for this is that heavy metal impurities such as Fe and Cu, which are contained in trace amounts in the metal plate of the thermal cover, have a concentration of 0.01 to 0.
It is exposed to a high-temperature environment directly above the silicon melt under a reduced pressure of 0.5 atmospheres, evaporates, attaches to the surface of the growing silicon single crystal through vapor phase diffusion, and then penetrates into the interior from the surface through solid phase diffusion. It was discovered that this was due to metal contamination of the single crystal.

Furthermore, the entire metal plate of the heat insulating cover is as follows:
Even if the amount of heavy metal impurities is extremely small, the surface layer contains
It was also found that heavy metal impurities were present, which were quite concentrated. Although it is not clear how many metal impurities are included in the single crystal, OSFs will occur frequently.
Even levels around 1010 atoms/cm3 or less can cause OSF.

Commercially available high-purity tantalum plates used as thermal covers usually contain heavy metal impurities such as Fe, Cu, and Ni.
m or less, Cu is said to be less than 10 ppm, and as a result of the analysis conducted by the present inventors, the inside of the metal plate contains 10 ppm or less of Fe.
The surface layer of the metal plate contains 100 ppm of Fe, although the Cu content is very small, 1 ppm.
It was found that heavy metal impurities were concentrated, such as 10 ppm or more for Cu.

These heavy metal impurities are exposed to a high-temperature environment directly above the silicon melt under reduced pressure, evaporate, adhere to the surface of the growing silicon single crystal by vapor phase diffusion, and then adhere to the surface of the growing silicon single crystal by solid phase diffusion. It is thought that it penetrates into the interior.

[0031] Tantalum itself, which is a constituent material of the thermal cover, has a high melting point and is difficult to evaporate, and its diffusion rate in silicon is extremely low, so it hardly penetrates into the single crystal. It is considered that there is no possibility of it being a causative contaminant.

On the other hand, Fe, Cu, etc. have a diffusion coefficient in silicon of 10-4 to 10-6 in the crystal growth temperature range.
Since it has a large velocity of cm2/s, it easily diffuses from the surface of the single crystal toward the interior of the crystal, and becomes a cause of OSF as a contaminant.

The OSF concentration distribution in the radial direction in a silicon single crystal produced by using a commercially available tantalum plate as it is as a heat-insulating cover shows the concentration profile and pattern of metals such as Fe and Cu when the metals are solid-diffused. The fact that they agree extremely well supports the validity of the above-mentioned study by the present inventors.

[0034] The present invention removes the heavy metal impurity concentration layer on the surface layer of the metal plate, thereby suppressing the evaporation of heavy metal impurity elements such as Fe and Cu from the metal plate. This reduces the amount of heavy metal impurities that enter.

This will be explained in FIG. 2 in the embodiment described later.
The explanation will be based on.

A metal plate such as a tantalum plate has a concentration distribution of heavy metal impurities in the surface layer as shown by the curve in FIG. Before using such a metal plate as a thermal cover,
The surface layer is removed by 10 μm or more, preferably 20 μm or more, thereby removing the heavy metal impurity concentrated layer.

[0037] Hereinafter, an explanation will be given using a tantalum plate as an example of the metal plate and Fe as the heavy metal impurity. There is an Fe-enriched layer with a maximum depth of 20 μm on the surface layer of the tantalum plate. Before using this plate as a heat insulating cover, its surface layer is removed by means such as acid etching.

However, if the depth of the removed surface layer was less than 10 μm, the Fe-enriched layer would not be completely removed, so the depth was limited to 10 μm or more.

[0039] Tantalum plates often contain impurities such as molybdenum and tungsten, but these high-melting metal elements with melting points exceeding 2000°C are difficult to evaporate and are difficult to evaporate in silicon. Since the diffusion rate of tantalum is extremely low, even if it is contained as an impurity in the tantalum plate, it is unlikely to become a contaminant for the silicon single crystal.

[0040] In order to remove the concentrated layer on the surface layer of the metal plate, not only the above-mentioned acid etching method but also the method for removing the heavy metal impurity concentrated layer can be used for the OSF reduction effect as long as the conditions of the present invention are met. You don't have to.

[0041]

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 vertical sectional view schematically showing a silicon single crystal manufacturing apparatus used in an example of the present invention.

In FIG. 1, reference numeral 1 denotes a quartz crucible having a diameter of 20 inches, which is supported by a graphite crucible 2, which is supported on a pedestal 4 by a rotatable mechanism.

Reference numeral 3 denotes an electric resistance heating element surrounding the graphite crucible, 5 a silicon single crystal, and 6 a heat insulating material surrounding the quartz resistance heating element 3, all of which are housed in the chamber 11.

Reference numeral 7 denotes a silicon melt (molten amount: 25 kg) placed in the quartz crucible 1, from which a silicon single crystal 5 is pulled.

In this example, the silicon single crystal is P-doped (N-type), has a resistance value of 10 ohm cm, a diameter of 6 inches, and an average pulling rate of 1.2 mm/min.

Atmospheric gas (argon gas) is introduced into the furnace from a gas inlet (not shown) provided above the pulling chamber 13, and is discharged from the exhaust port 12 at the bottom of the furnace by the pressure reducing device 16. The pressure inside the furnace is 0.02 atmospheres.

[0048] The above is no different from an ordinary silicon single crystal manufacturing apparatus using the Czochralski method.

Reference numeral 8 denotes a partition member made of high-purity quartz and having a diameter of 16 inches and installed in the crucible 1 so that its axis is aligned with the crucible 1. This partition member 8 has a small hole 9 with a diameter of 3 mm, and the silicon melt in the raw material melting section A (outside the partition member 8) passes through this small hole 9 in the single crystal growth section B (the partition member 8 more inward).

The upper edge of this partition member 8 is exposed above the level of the silicon melt, and the lower edge is either fused to the quartz crucible 1 in advance or melted in the initial stage. They are fused together by the heat generated when making a silicon melt.

In the raw material melting section A, granular silicon is continuously introduced into the raw material supply pipe 15 from a storage hopper (not shown) in the raw material supply chamber 14 via a cutting device (not shown). Supplied. The supply amount is approximately 55 g/min, which is equal to the single crystal pulling amount from single crystal growth section B.
constant.

Further, in order to keep the concentration of the silicon melt constant, a dopant is also suitably supplied through the same raw material supply pipe 15 at the same time as the granular silicon.

In the present invention, although not shown, a control means for reliably controlling the temperature of the raw material melting section A and the single crystal growth section B, a single crystal pulling and rotation means, a crucible rotation means, and an atmospheric gas supply means are provided. Of course, be prepared.

Next, 10 is a heat insulating cover, which has a thickness of 0.
Constructed of 2mm high purity tantalum plate.

The concentration distribution profile of the heavy metal impurity element (Fe) in the surface layer of this tantalum plate was investigated, and the results were as shown in FIG.

FIG. 2 is a graph showing the Fe concentration (ppm) on the vertical axis and the depth (μm) from the metal plate surface on the horizontal axis.

As shown in FIG. 2, a depth of 2 from the surface of the metal plate
It can be seen that the Fe concentration increases rapidly within 0 μm. That is, heavy metal impurities (Fe) form a concentrated layer on the surface layer of the heat insulating cover.

Therefore, in this embodiment, hydrofluoric acid (HF) and nitric acid (HN
Etched for 20 minutes in a mixture of O3) and pure water,
A high purity tantalum plate whose surface layer had been removed to a depth of 30 μm was used.

Using such a silicon single crystal manufacturing apparatus, silicon wafers were manufactured from silicon single crystals manufactured by the continuous pulling method, and were heated at 800° C. for 3 hours and then at 1000° C. for 15 hours for quality evaluation. After heat treatment was performed in a dry O2 atmosphere, the OSF density was measured and found to be 2 to 9 pieces/cm2.

[0060] Also, by changing the etching time of the tantalum plate of the heat insulating cover 10 and using the tantalum plate having a different surface layer removed depth t, a silicon single crystal is grown in the same manner as above, and a silicon wafer is manufactured. Then, for quality evaluation, the same heat treatment as above was performed, and the OSF density was measured. The results are shown in FIG.

FIG. 3 shows the removed depth t of the surface layer of the heat insulation cover metal (tantalum) plate and the silicon single crystal OS.
It is a graph figure showing the relationship with F density.

The OSF density shown here is an average value within the silicon wafer surface.

As shown in FIG. 3, when the depth t from the surface of the metal plate removed by etching was less than 10 μm, 3×10 1 to 10 3 OSFs/cm 2 were present. On the other hand, when the depth t from the surface of the metal plate removed is 10 μm or more, the OSF density is 30 pieces/cm2 or less, and the depth t from the surface of the metal plate is
is 20 μm or more, the OSF density is 10 pieces/cm
2 or less.

Note that the heavy metal impurity concentrated layer on the surface of the metal plate can also be removed by heat treating the tantalum metal plate used at high temperature in a vacuum. An example of effective heat treatment conditions in this case is to perform the treatment at 1500° C. for 1 hour under a degree of vacuum of 2×10 −5 torr or more.

[0065]

[Effects of the Invention] The silicon single crystal production apparatus of the present invention having the above-described configuration can increase the amount of single crystal pulled without causing solidification from the partition member on the silicon melt surface or producing undissolved raw material silicon to be supplied. It has become possible to stably produce high-quality, large-diameter silicon single crystals with a diameter of 6 to 10 inches and an OSF generation density of 30 pieces/cm2 or less while supplying raw material silicon in an amount commensurate with the above.

[0066] Furthermore, even in the production of silicon single crystals using the ordinary CZ method, the silicon single crystal production apparatus of the present invention can increase the pulling speed and produce high-quality products with an OSF generation density of 30 pieces/cm2 or less. - Large diameter silicon single crystals can be produced stably.

[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 graph schematically showing the concentration distribution profile of a heavy metal impurity element (Fe) in the surface layer of the metal plate of the heat insulation cover.

FIG. 3 is a graph showing the relationship between the removed depth t of the surface layer of the metal (tantalum) plate of the heat insulation cover and the OSF density (in-plane average value) of a silicon single crystal.

[Explanation of symbols]

1. Quartz crucible, 2 Graphite crucible, 3. Electric resistance heating element, 4 Pedestal, 5. Silicon single crystal, 6 Insulation material, 7. Silicon melt, 8 Partition member, 9 Small hole, 10　Heat cover, 11 Furnace chamber 12 Atmosphere gas outlet, 13. Pulling chamber, 14 Raw material supply chamber, 15 Raw material supply pipe, 16　Pressure reduction device, A raw material melting section, B. Single crystal growth department.

Claims (1)

[Claims] [Claim 1] A quartz crucible containing a silicon melt, an electric resistance heating element that heats the quartz crucible from the side,
A quartz partition member that divides the silicon melt into a single crystal growth zone and a raw material melting zone in a quartz crucible and has a small hole through which the silicon melt can flow, and a heat-retaining cover that covers the partition member and the raw material melting zone; In the silicon single crystal production apparatus, which has a pressure reducing device for reducing the pressure inside the furnace accommodating each of the components, and a raw material supply device that continuously supplies raw silicon to the raw material melting section, the heat insulating cover is made of 50p of Fe.
pm or less, consisting of one type of metal plate selected from tantalum, molybdenum, or tungsten with a Cu content of 10 ppm or less, and characterized in that it consists of a metal plate from which the surface layer of the metal plate has been removed to a depth of 10 μm or more before use. Silicon single crystal production equipment.