JPH062637B2 - Single crystal pulling device - Google Patents

Description

The present invention relates to a single crystal pulling apparatus, and more particularly to a single crystal pulling apparatus for semiconductors.

[Conventional technology]

Single crystal pulling device Among others, a silicon single crystal pulling device is a typical one as a semiconductor single crystal pulling device, and other gallium-based, for example, Ga-As-based or Ga-P-based single crystal pulling devices are available. is there. Now, a silicon single crystal pulling apparatus will be described as a representative of them.

That is, a crucible made of quartz glass (usually boron nitride in the case of Ga-As series single crystal) is filled with silicon polycrystal. Since the quartz crucible used in this case is usually thin, its strength may cause the quartz to soften and sometimes break. Therefore, it is inserted into the graphite crucible to reinforce it. Then, the crucible filled with the silicon is rotated or heated as it is by a high frequency induction heating or a resistance type heating element (heater) and heated to about 1500 ° C. to melt the silicon. The seeds of the silicon single crystal supported by the pulling machine above the crucible are immersed in the silicon melt, which is then gradually cooled while being pulled to make another crystal into a single crystal.

Since this single crystal is mainly used for semiconductors, it is required to have extremely high purity, and the quartz glass with which the melt directly contacts is required to have very high purity, but it is used together with this. Each member inside the apparatus is also required to have high purity. And in this lifting device,
As mentioned above, extremely high temperatures, heat resistance and low vapor pressure are required, and most of them are currently carbon materials, usually graphite.

However, due to the extremely high temperature, impurities in the carbon material leached out,
It evaporates and contaminates the silicon melt in the quartz crucible, which in turn lowers the quality of the pulled single crystal and, as a result, significantly lowers the yield.

Moreover, due to recent technological advances, ultra-high-purity single crystals are increasingly required as substrates for highly integrated circuits, and along with this, high-purity graphite members used in pulling equipment are increasingly required. It came to be.

[Problems to be solved by the invention]

The problem to be solved by the present invention is to develop an apparatus that meets the above-mentioned demands required for a conventional single crystal pulling apparatus, and more specifically, it is an extremely high purity single crystal pulling apparatus. We have developed a graphite material that satisfies the various characteristics required for materials such as heat resistance, thermal shock resistance, mechanical characteristics, low vapor pressure, chemical stability, and low outgassing. Is to use.

[Means for solving problems]

This problem is solved by using an extremely high purity graphite material having a total ash content of 5 ppm or less, particularly preferably 1 ppm or less, as a member for a single crystal pulling apparatus.

The present inventor has been continuing research on graphite materials, especially high-purity graphite materials, and in this research, the purity thereof is extremely higher than that of conventional graphite materials, and further, the operational troubles of the conventional method are caused. A solved graphite material and a manufacturing method thereof have been developed and already filed (Japanese Patent Application No. 61-224131). In further subsequent research, it was confirmed that the new high-purity graphite material according to the above-mentioned application is extremely suitable as a member for a single crystal pulling apparatus and can satisfy various characteristics required as a member for this apparatus. The present invention has been completed based on the findings of headings.

[Structure and Action of Invention]

First, the high-purity graphite material used in the present invention will be described.

The graphite material of the present invention has an extremely high purity such that the total ash content (impurity content) is 5 ppm or less, particularly preferably 1 ppm or less. As is apparent from the examples described below, the conventional graphite material or the high purity obtained by the conventional method is used. Its purity is extremely higher than that of chemical graphite materials. The commercially available high-purified graphite material generally has a total ash content of about 20 to 50 ppm, and the graphite material of the present invention is of extremely high purity.

This high-purity graphite material can be manufactured as follows. That is, it is basically manufactured by the method of Japanese Patent Application No. 61-224231. A more detailed description is as follows.

A method for producing a high-purity graphite material in which a carbon material is sequentially fired, graphitized, and highly purified, is a method of performing high-purification by a high-frequency heating means under vacuum or reduced pressure, and a more preferable embodiment is exemplified. For example, That is, (a) in a method for producing a high-purity graphite material in which a carbon material is sequentially fired, graphitized, and then highly purified, graphitization and high purity are performed by a high-frequency heating means under vacuum or reduced pressure in the same apparatus. (B) a manufacturing method in which graphitization and high-purification are partially overlapped and performed in parallel, and (c) in the method for manufacturing a high-purity graphite material, At least one of the purification steps is a method for producing a high-purity graphite material under a pressure of 100 Torr to 1 Torr, and (d) a halogenation reaction and a halogenated product in a high-purification step under vacuum or reduced pressure conditions. A production method in which the withdrawal reaction is carried out simultaneously, and the like. The methods will be described in more detail below.

For convenience of explanation, the present manufacturing method will be described with reference to the drawings showing the apparatus of the present manufacturing method. Incidentally, FIG. 1 is a schematic side sectional view of a vacuum / high frequency heating type high-purity carbon material manufacturing apparatus according to the present manufacturing method.

The first factor that constitutes this manufacturing method is that a high-frequency heating furnace with a small floor area and high energy efficiency is used to heat the raw material.

The second component is the induction heating furnace high-frequency coil (105).
That is, a graphite heater, that is, a susceptor (106) is provided between the heated carbon material (104).

The third factor is the above factor, that is, the high frequency coil.
(105), the susceptor (106), and the heated carbon material (104) are housed in a closed container that can withstand reduced pressure or vacuum.

The heating carbon material (104), the high frequency coil (105), and the susceptor (106) are housed in a vacuum container by the following gas supply pipe (108) and gas discharge pipe (101) in this manufacturing method. ) Is the most important constituent factor, and this makes it possible to efficiently and consistently graphitize and highly purify the heated carbon material (104).

As a fourth constituent factor, the gas supply pipe (10
8), the gas exhaust pipe (101) is provided.

The gas discharge pipe (101) is used when decompressing or vacuuming the inside of the container.
It is also indispensable for exhausting the gas generated during the graphitization process and the purification process. In particular, it is also used for the purpose of drawing out metal halides, metal hydride compounds, etc. evaporated from the graphite material out of the reaction system in the high purity step.

The gas supply pipe (108) is used for the purpose of supplying the halogen-containing gas used in the purification process and / or the H ₂ gas.

These gas supply and discharge pipes can be provided at appropriate places in the vacuum container, and at a plurality of places as necessary.
Considering the flow of gas in the container and the efficiency of contact with the carbon material, it is desirable to provide them on the upper and lower sides or on the symmetrical side of the left and right sides.

FIG. 1 shows an example in which a vertical high-frequency furnace is used and a gas discharge pipe (101) and a supply pipe (108) are provided above and below, respectively. Each tube can be installed on the left and right respectively.

In addition to the above main constituent factors, the following factors can be added as necessary.

That is, as the fifth factor, the heat insulating materials (102) and (103) can be used between the high frequency coil and the susceptor. As the heat insulating material, known materials such as ceramic fiber, carbon fiber and carbon black are used.

As a sixth factor, a water cooling jacket (109) can be provided outside the vacuum container if necessary.

A high-frequency voltage of 250 to 3000 Hz is applied to the high-frequency coil, and power is supplied to the coil installed through the wall of the vacuum container.

Next, a method for producing high-purity graphite of the present production method using the above-mentioned apparatus will be described.

This manufacturing method is basically a method of performing the high-purification step under vacuum or reduced pressure by using a high-frequency heating means, and one desirable mode thereof is to carry out the above-mentioned method using the present apparatus shown in FIG. is there. Further, the present method also includes a method in which the graphitization step and the high-purification step are performed in one furnace, and these steps are sequentially or at least partially performed in parallel. A more detailed description is as follows.

First, N ₂ gas is sent from the gas supply pipe (108) to replace the air inside the container with N ₂ gas, and then the gas exhaust pipe (101) is evacuated or evacuated to make the atmosphere non-oxidizing. To do.

Next, a voltage is gradually applied to the induction coil (105) to heat the susceptor (106), and the radiant heat of the heated carbon material (104).
To 800 to 1000 ° C. for usually 1 to 10 hours, preferably 3
After keeping it for ~ 5 hours, gradually raise the temperature to 2450 ~ 2
5 to 24 hours, preferably 7-1 while adjusting to 500 ° C
Hold for 5 hours.

Since the inside of the container is maintained at about 1 to 100 Torrp, preferably about 10 to 40 Torr from the time when heating is started, it is convenient to discharge the degassing gas that slightly volatilizes at this stage.

At a stage where graphitization has progressed to a certain extent, a halogen gas such as dichlorodifluoromethane is supplied from the gas supply pipe (108) in a depressurized state (the flow rate is increased or decreased depending on the amount of the heated carbon material to be filled in the container. 3-8 at 1-7 NTP / kg
Supply about time.

The halogen gas used for high purification is necessary to increase the vapor pressure by using impurities contained in the carbon material, particularly metal impurities, as a halogen salt to increase the vapor pressure, and evaporate and volatilize this to increase the purity of the carbon material that is the base material. However, as the halogen, any of those which have been conventionally used can be used. For example, not only chlorine and chlorine compounds but also fluorine and fluorine compounds can be used. Furthermore, chlorine or fluorine gas can be used together. Good. It is also possible to use a compound containing fluorine and chlorine in the same molecule, such as monochlorotrifluoromethane, trichloromonofluoromethane, dichlorodifluoroethane, trichloromonofluoroethane and the like.

Regarding the type of impurities, for example, sulfur content, H ₂ has a high refining effect, so especially for low sulfur grade products, after stopping the supply of dichlorodifluoromethane, continue to supply H ₂ gas. You can also do it.

When the high-purification operation is completed, the temperature in the furnace is further increased and the temperature is maintained at 3000 ° C. for about 10 to 30 hours to complete the process.

During the process of cooling the furnace, the pressure inside the vessel is strongly reduced to 10 ^{-2 to} 10 ^-4 Torr at about 2000 ° C, and the high-purity carbon material with less outgas can be obtained by cooling.

Stop energizing, fill the container with N ₂ gas, replace it, and return to normal pressure and room temperature.

Although the above method shows a method of performing graphitization and high purity in one furnace, it goes without saying that only high purity may be performed by the above method in this method.

It is desirable to maintain the pressure in the container in the range of 100 Torr to 1 Torr when performing the purification or the graphitization with this method. The pressure in the container is set to be halide, chlorinated and / or fluorinated impurities, or residual N ₂ upon substitution.
Sum of vapor pressure (partial pressure) of various compounds such as gas (total pressure)
If the pressure is higher than 100 Torr, the depressurizing effect will be low, and therefore the time required for high purification will be long, the quality will be the same as the conventional atmospheric pressure method, and if it does not reach 1 Torr. The absolute amount of halogen supply becomes small, the purification of deep carbon material becomes insufficient, and a large amount of pump power is required to remove the generated gas, which is not a good idea. Incidentally, 100 to 1 Torr, particularly preferably 50 to 5 Torr
The product with the best rr can be obtained.

As one applied aspect of the practice of the present invention, during high-purity operation,
To increase / decrease the pressure in the reaction vessel in a pulse,
Diffusion of halogen gas to the deep layer of carbon material, replacement, and elimination and replacement of halogenated products from the deep layer are complete,
More effective.

In addition to the above-mentioned high purity, the graphite material of the present invention is preferably isotropic. In this case, the isotropic property means that all physical properties exhibit almost the same properties in each direction, and that, for example, they exhibit substantially the same behavior both electrically and in a heat body. . When the graphite material of the present invention is used in a pulling apparatus, this isotropy is different in required items such as electrical resistance, coefficient of thermal expansion, and mechanical strength depending on the type and site of the member. All of the carbonaceous materials satisfy these requirements, and particularly as a constituent material of the device according to the present invention, a highly isotropic material having an anisotropic ratio of 1.10 or less, particularly 1.03 to 1.07 or less. preferable. In this case, the anisotropic ratio means that physical, mechanical, electrical and chemical properties of each material are x, y and z.
The ratio of the maximum value to the minimum value is 1.10 for each axis and each direction.
Hereinafter, it is preferably 1.07 to 1.03 or less.

The pulling apparatus of the present invention will be described below with reference to FIG. However, FIG. 2 is a drawing showing a part of the device of the present invention, and for convenience of explanation, this is schematically shown separately in FIG. 4 of (a) to (d). Fig. 2 (a) mainly shows the part centering on the crucible, Fig. 2 (b) mainly shows the part centering on the side, and Fig. 2 (c) shows the part centering on the lower part of the crucible, Further, FIG. 4D is a schematic cross-sectional explanatory view showing a portion centering on the upper portion and the lower portion. In the figure, (1) is a graphite crucible, (2) is a graphite heater, (3) is a heat insulating tube,
(4) is a heat insulating material, (5) is a cushioning material, (6) is a spacer, (7) is a crucible tray, (8) is a support for crucible replacement, and (9) is a crucible tray retainer cover, ( 10) is a fastener for fixing the electrode (heater) and the clamp,
(11) is a vapor leakage prevention ring, (12) is an electrode (heater), (13) is an electrode clamp, (14) is a liquid leakage tray, and (15) is an upper lid. Further, (16) indicates a crucible made of quartz or boron nitride, and (17) indicates silicon.

In the apparatus of the present invention, at least one of the members (1) to (15) is made of the high purity graphite material, and preferably, the members (1) to (3) are both the high purity graphite. It consists of materials.

The graphite crucible (1) is used to protect and reinforce the quartz or boron nitride crucible inside, and its shape and size are not particularly different from those of the conventional one. The heater (2) is of a resistance type in FIG. The heat insulating tube (3) is used for reflecting the radiant heat from the heater (2) and for protecting the heat insulating material (4), and the thickness thereof is usually 3 to 12 and preferably about 5 to 8 mm. . Usually, the heat insulating tube (3) is provided with a slight space between it and the graphite crucible (2), and is installed with or without a space with the heat insulating material (4). It is particularly preferable that these members (1) to (3) have high purity and areotropic. By being isotropic, damage resistance is improved, processing is facilitated, and thermal expansion is isotropic, and particularly the heater (2) has uniform electric characteristics. The heat insulating material (4) is used for heat insulation and is provided between the heater (2) and the outer wall to exhibit heat insulating and heat retaining effects.

Insulation (4) is used for insulation, heater (2)
It is installed between the outer wall and the outer wall, and exerts heat insulation and heat retention effects.

In the device of the present invention, the cushioning material (5) is located between the quartz crucible (16) and the graphite crucible (1), exerts a cushioning action between them, and is used to protect both crucibles. It also has the function of adjusting the position (height) of the crucible. A corrugated sheet or a flat sheet is used as the cushioning material (5). These heat insulating materials and cushioning materials do not necessarily have to be isotropic, and graphite felt, expanded graphite compacts, hollow balloon graphite spheres or compacts thereof, and graphite materials coated with a graphite jacket material good. The spacer (6) is located between the graphite crucible (1) and the crucible tray (7) and is used as a heat insulating function, a position adjusting member, and a cushioning member. As the material used, a graphite graphite compact, a hollow graphite sphere solidified with resin or pitch and carbonized, and a laminated structure of these and a flat plate-like isotropic carbon material are used. It is also necessary that the total ash content be 5 ppm or less. The crucible tray is used to set the crucible at a predetermined position, and isotropic graphite material is preferably used.
At this time, a graphite material reinforced with carbon fibers (hereinafter referred to as a composite material) may be used.

The crucible pan support (8) is used for supporting the crucible pan (7) and may be separate from or integral with the crucible pan. The support (8) may be a composite material as the graphite material, and isotropic material is preferably used.

The cover (9) is used for the purpose of protecting the support (8) from silicon vapor, is preferably isotropic as well, and a composite material may be used.

As the fastening tool (10), a composite material is preferably used because it is used to fasten the electrode (heater) and the clamp (13).

The vapor leak prevention ring (11) is not always necessary,
Has a function to prevent the vapor in the crucible from moving to the upper part,
The graphite material is preferably isotropic.

In the device of the present invention, at least one of the above members is made of an ultra-high purity graphite material, and preferably isotropic or a composite material, and as a result, a high-purity single crystal can be obtained. It can be done.

In order to show that the graphite material of the present invention has an ultrahigh purity, Table 1 shows the amount of impurities in the ultrahigh purity graphite material produced by the apparatus and method according to the present invention and the conventional method. The amount of impurities in the commercially available high-purity product obtained in step 1 and the amount of impurities in the ordinary graphite material not subjected to the high-purity treatment are shown in comparison.

However, the samples A, B, and C are as follows.

Sample A: Product according to the method of the invention. As the raw graphite material, sample C was used in a high-purification container at an internal pressure of 20 to 25 Torr and at 900 ° C. for 4 hours.
HR, manufactured at 2450 to 2500 ° C for 10 HR, zochlorodifluoromethane 3NTR / kg for high purification, and 3000 ℃ for 20 HR.

Sample B: Sample C that has been subjected to atmospheric pressure high-purification treatment by a known method.

Sample C: Commercial product (isotropic graphite material with apparent density of 1.80, before purification), manufactured by Toyo Tanso Co., Ltd.

The analysis method was based on emission spectroscopy and atomic absorption spectrometry. The unit of the number is ppm, and the (-) mark represents "not detected".

It should be noted that in any of the materials of the present invention, it is necessary that the total ash content is 5 ppm or less.

Incidentally, the total ash content of the samples A, B, and C was 1 ppm, 10 ppm, and 410 ppm, respectively, measured according to Japanese Industrial Standard (JIS) R7223-1979, and therefore the sample A is within the scope of the present invention. , Samples B and C are outside the scope of the invention.

As shown in the analysis values in Table 1, the graphite material applied to the apparatus of the present invention has a total ash content of 1 ppm or less, substantially 0 ppm ( Although it is almost undetectable), some contamination is unavoidable during handling in the work process such as packaging, transportation, and installation in the pulling device after it is taken out. A carbon material is used.

In the present invention, the use of a high-purity graphite material having a total ash content of 5 ppm or less improves the properties of the graphite member such as the outgassing property, which affects the quality of the pulled single crystal, as described above. There is. From the viewpoint of making this point clearer, the outgassing properties of the samples A, B and C were measured.

The measuring method is as follows.
m) was put in, the gas was evacuated by a vacuum pump, the cock of the quartz tube was closed, and the sample was heated for 20 minutes. The gas generated using a cock was introduced into a mass spectrometer, and pressure measurement and qualitative / quantitative analysis were performed. Results are shown in FIG.

Outgassing of Sample A with a total ash content of 1 ppm is 10 ppm total ash content
The characteristics are different from those of (Sample B) and 410 ppm (Sample C), and especially in the temperature range of about 900 ° C to 1100 ° C, Sample A shows almost no change in the outgas amount and shows flattening. B (total ash content 10 ppm) and sample C (total ash content 410 ppm) showed an increase in outgas amount, and the outgas amount of sample B and sample C at a temperature of 1100 ° C were about 3.8 times that of A, respectively. About 13 times more.

Similarly, when the outgassing property of the total ash content of 5 ppm was also examined, it was not much different from the characteristics of the sample A having the total ash content of 1 ppm, and the flattening between about 900 ° C. and 1100 ° C. observed at the total ash content of 1 ppm was 5 ppm total ash content. Also seen in the one.

The flattening of the outgas amount between about 900 ° C. and 1100 ° C. observed in Sample A does not show this flattening when the total ash content exceeds 5 ppm, and the outgas amount starts to increase.
This gas is diffused and taken into the melt, which affects the purity in the single crystal. Compared with a graphite material whose total ash content is 5 ppm or less and a material whose total ash content exceeds 5 ppm, a silicon single crystal pull-up shows that there are significant differences in the results in terms of ensuring the quality of the single crystal and preventing crystal defects. I understood.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an example of an apparatus for producing a high-purity graphite material used in the present invention, and FIG. 2 is a schematic view of an example of the apparatus of the present invention. is there. FIG. 3 is a curve diagram showing the results of measuring the outgassing properties of sample A (total ash content 1 ppm) within the scope of the present invention and samples B and C (10 ppm and 410 ppm) outside the scope of the present invention. (1) …… Graphite crucible (2) …… Graphite heater (3) …… Insulation cylinder (4) …… Insulation material (5) …… Buffer material (6) …… Spacer (7) …… Crucible saucer (8) ) …… Support for crucible saucer (9) …… Support for crucible saucer (10) …… Fastener for fixing electrode (heater) and clamp (11) …… Steam leakage prevention ring (12) Electrode heater (13) Electrode heater clamp (14) Liquid leakage saucer (15) Top lid (16) …… Quartz or boron nitride crucible (17) …… Silicone (101)… … Gas exhaust pipe (102)… Heat insulation material (103)… Heat insulation material (104)… Carbon material to be heated (105)… High frequency coil (106)… Susceptor (107)… Saucepan (108)… … Gas supply pipe (109) …… Jacket (301) …… Outgas curve of total ash content 1ppm) （302） …… Total ash content 10 ppm) outgas curve (303) ... total ash content 410ppm) outgas curve

Claims (15)

[Claims] 1. A single crystal pulling apparatus, wherein at least one of a graphite crucible, a graphite heater and a graphite heat insulating tube is made of a high purity graphite material having a total ash content of 5 ppm or less. . 2. A total ash content of at least a part of the material constituting the heat insulating material used between the graphite heater and the outer wall of the reaction chamber is 5.
The single crystal pulling apparatus according to claim 1, which is made of a high-purity graphite material of ppm or less. 3. The single crystal pulling apparatus according to claim 1, wherein the cushioning material used between the inner crucible and the graphite crucible is a high-purity graphite material having a total ash content of 5 ppm or less. 4. The single crystal pulling apparatus according to claim 1, wherein the spacer used between the graphite crucible and the graphite crucible tray is a high-purity graphite material having a total ash content of 5 ppm or less. 5. The apparatus for pulling a single crystal according to claim 1, wherein the graphite crucible tray located immediately below the graphite crucible is made of a high-purity graphite material having a total ash content of 5 ppm or less. 6. The single crystal pulling apparatus according to claim 1, wherein the support of the crucible tray is a high-purity graphite material having a total ash content of 5 ppm or less. 7. The support cover of the crucible tray has a total ash content of 5 ppm.
The single crystal pulling apparatus according to claim 1, which is made of the following high-purity graphite material. 8. The apparatus for pulling a single crystal according to claim 1, wherein the liquid-leaking tray located under the crucible tray is a high-purity graphite material having a total ash content of 5 ppm or less. 9. The total ash content of the electrode clamp (connecting rod) is 5 ppm.
The single crystal pulling apparatus according to claim 1, which is made of the following high-purity graphite material. 10. The apparatus for pulling a single crystal according to claim 1, wherein the fastening tool for fastening the electrode and the clamp is made of a high-purity graphite material having a total ash content of 5 ppm or less. . 11. The single crystal pulling apparatus according to claim 1, wherein the vapor leakage prevention ring is made of a high-purity graphite material having a total ash content of 5 ppm or less. 12. The single crystal pulling apparatus according to claim 1, wherein the single crystal is a semiconductor single crystal. 13. A single crystal pulling apparatus according to any one of claims 1 to 11, wherein the high-purity graphite material is isotropic. 14. The apparatus for pulling a single crystal according to claim 1, wherein the isotropic range is an anisotropic ratio of 1.1 or less. 15. The single crystal pulling apparatus according to any one of claims 1 to 11, wherein the anisotropic ratio is in the range of 1.03 to 1.10.