JPH05294789A - Method for pulling up silicon crystal - Google Patents

Abstract

(57) [Abstract] [Purpose] To facilitate hydrogen treatment in the absence of silicon melt in the chamber.
We will improve the safety of crystal pulling and reduce costs. [Structure] Hydrogen gas is introduced together with an inert gas into a furnace chamber in which a silicon raw material is absent, high-temperature hydrogen treatment is performed on the furnace member in the chamber, and the hydrogen-treated furnace member is used to perform silicon treatment. By performing the single crystal growth process,
The furnace members are subjected to high temperature hydrogen treatment in the absence of silicon raw material. Alternatively, by performing a single crystal growth process using a silicon raw material containing at least 100 Wppm of hydrogen atoms, most of the hydrogen contained in the silicon raw material is diffused into the chamber at a temperature before the raw material melts. Hydrogen treatment with atoms.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pulling a silicon crystal, and more particularly to a method for pulling a high-purity silicon crystal having a small content of Fe, Cu, Ni and the like.

[0002]

2. Description of the Related Art With the progress of miniaturization and high integration of MOS semiconductor devices, silicon crystal substrates (silicon wafers) having characteristics that harmful crystal defects are not induced in various heat treatment steps in the element manufacturing process have been developed. Increasingly important. In general, metal contamination such as Fe, Cu, and Ni is regarded as a problem as one of the causes of generation of harmful crystal defects such as BMD, OSF, and surface microscopic defects (SMD). On the other hand, in the process of the MOS device, an ultra-clean process in which harmful impurities are less likely to enter is being studied, and accordingly, high purification of the silicon crystal is increasingly required.

Conventionally, the Czochralski method (CZ
Silicon crystal (CZ) by a pulling method known as
As a method for purifying a crystal), a method using a high-purity quartz crucible such as a synthetic quartz crucible and a method using a high-purity silicon raw material such as a zone-refined (floating zone) silicon crystal are known.

However, there is no report that a highly pure crystal was actually obtained. As one of the causes of such a result, the temperature environment in the furnace in the pulled state of the silicon crystal is the silicon raw material melting temperature, that is, about 1420 ° C., which is extremely high. Therefore, metal impurities such as Fe, Cu, and Al are scattered from furnace members such as heaters and heat insulating members made of carbon material, and the inside of the furnace is contaminated.
Generally, Fe, Al, Cu, Ni, etc. are mainly F, respectively.
It is mixed in the carbon material in the form of eO ₃ , AlO ₃ , CuO, NiO, that is, an oxide (hereinafter referred to as metal oxide impurities), and these oxides easily evaporate at a high temperature and the inside of the furnace Will be polluted. Here, the following table shows the analysis results regarding the content of various metal impurities in the heater of the carbon member in use as an example.

[0005]

[Table 1] Therefore, in order to increase the purity of silicon crystals,
It is a very important matter to prevent contamination by the metal impurities contained in the carbon furnace member.

As a method for preventing such contamination from the carbon furnace member, there is a method described in JP-A-2-164788.

According to this method, in the step of melting the silicon raw material, hydrogen gas is introduced into the furnace in addition to an inert gas such as Ar gas, the hydrogen gas reduces the metal oxide impurities by hydrogen, and a carbide is generated. It is made to be stable in a carbon furnace member, its scattering is suppressed, and contamination of the furnace by harmful metal impurities is suppressed.

Further, in this method, hydrogen gas is mixed from the time when the temperature of the silicon raw material reaches 1000 ° C. to immediately before the raw material melts (about 1410 ° C.).

As a result, SiO generated from the silicon melt is prevented from reacting with hydrogen gas to generate H ₂ O and Si. These H ₂ O and Si contaminate the inner wall of the chamber, and drop and adhere to the pulled crystal to deteriorate the crystallinity, that is, polycrystallize. This is an important problem to be solved because it causes a decrease in yield, and as a result, it is intended to prevent it. At the same time, it also aims to realize hydrogen introduction as long as possible.

[0010]

However, in practice, there is a problem that it is very difficult to determine the melt of the raw material, and it is difficult to realize it easily. Actually, hydrogen gas may flow to a locally melted state, and even if it is a small amount, it is the hydrogen gas introduction in the state where silicon melt exists, so the carbon furnace member is contaminated. As a result, the pulled crystal may be polycrystallized.

Since hydrogen gas is a flammable gas, there is a problem in its handling and management method. For example, if there is a leak from the hydrogen gas pipe or its connection, it may cause a large explosion and requires a careful check.

Further, there is also a problem that, in the above-mentioned temperature state, a low temperature portion such as a heat retaining member of the carbon furnace member is not sufficiently effective in preventing pollution.

Furthermore, if a higher purity carbon material is used, it is possible to obtain a higher purity silicon crystal, but such a carbon material is extremely expensive and a large amount of silicon crystal is used. This results in higher costs. Further, even if a high-purity carbon material is used, the high-purity carbon material is contaminated by repeated use, and in this case, a high-purity crystal cannot be obtained in the end.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to make it possible to easily realize hydrogen treatment in the absence of silicon melt in the chamber. Therefore, it is another object of the present invention to provide a method for pulling a silicon crystal that enables pulling a crystal with high purity.

Another object of the present invention is to improve safety and reduce cost at the same time.

[0016]

According to a first aspect of the present invention, there is provided a method for pulling a silicon crystal, wherein hydrogen gas is introduced together with an inert gas into a furnace chamber in which a silicon raw material is absent, and hydrogen gas is introduced into a furnace member inside the chamber. On the other hand, after high-temperature hydrogen is applied, the silicon single crystal is grown using the hydrogen-treated furnace member.

In the high temperature hydrogen process, the inside of the chamber is set to 1
It is desirable to raise the temperature to 400 ° C. or higher.

Further, the furnace used in the high temperature hydrogen process can be a hydrogen treatment furnace different from the one used in the single crystal growth process or the same furnace used in the single crystal growth process. is there.

Further, the method for pulling a silicon crystal according to the present invention of claim 5 is characterized in that a silicon raw material containing at least 100 Wppm of hydrogen atoms is used.

The single crystal growth described in claim 5 and the high temperature hydrogen treatment described in claim 1 can be used in combination.

[0021]

According to the present invention as set forth in claim 1, since the furnace member is subjected to high-temperature hydrogen treatment in the absence of silicon raw material,
The hydrogen treatment in the state where the silicon melt is absent in the chamber can be easily realized without the need for the melt determination.

According to the present invention of claim 5, most of the hydrogen atoms contained in the silicon raw material are released into the chamber at a temperature before the raw material is melted, so that the silicon melt is formed in the chamber. Hydrogen treatment in the absence can be easily realized without the need for melt determination.

Further, according to the present invention, hydrogen pipe management and the like are unnecessary, and the safety is high.

Further, the high-purity carbon furnace member can be made to last for a long time, and it is not necessary to increase the cost of the raw material due to the low hydrogen requirement, and it is possible to produce a high-purity single crystal with a cheaper raw material. It is possible to significantly reduce the cost.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 illustrates a pulling method according to a first embodiment of the present invention.

The feature of the present invention resides in that the high temperature hydrogen treatment step shown in FIG. 1 (a) is performed before the pulling step shown in FIG. 1 (b). The configuration of the furnace and the like and the well-known single crystal growth process that have appeared will be described.

In FIG. 1, reference numeral 1 denotes a furnace body having a pulling chamber inside, and the furnace body 1 is generally composed of a main body cylindrical portion 2 and a crystal extracting cylindrical portion 3.

A carbon crucible 4 is arranged in the center of the main body cylindrical portion 2, and 5 is a supporting shaft thereof. Carbon crucible 4
Is fixed to the upper end of the support shaft 5, a quartz crucible 6 is placed inside the crystal pulling step, and raw materials are stored in the quartz crucible 6. The support shaft 5 is configured to move up and down and rotate, whereby the quartz crucible 6 is moved up and down and rotated. A heater 7 is installed outside the carbon crucible 4, and the heat of the heater 7 melts the raw material in the quartz crucible 6. 8 and 9 are heaters 7
Electrode. A heat insulation cylinder 10 is installed between the heater 7 and the main body cylinder portion 2 to improve the efficiency of heat use of the heater 7.

The crystal take-out cylinder portion 3 is connected to the upper end of the main body cylinder portion 2 and extends in the vertical direction, and the wire winding device 11 is attached to the upper end portion thereof. Reference numeral 12 is a wire pulled out from the wire winding device 11.
A seed chuck 13 for supporting a seed crystal is provided at the lower end of 2.
Is installed.

Reference numeral 14 is a gas inlet, and 15 is a gas outlet. The gas introduction part 14 is connected to the upper end of the crystal take-out cylinder part 3, and the gas discharge part 15 is connected to the bottom part of the main body cylinder part 2.

In the apparatus thus constructed, the quartz crucible 6 is installed in the carbon crucible 4, the granular silicon raw material is put in the quartz crucible 6, and Ar gas as an inert gas is supplied from the gas introduction section 14 every minute. It is introduced at 90 liters, and at the same time, the chamber is brought into a decompressed state of about 15 Torr by forcibly exhausting from the gas exhaust unit 15 with an exhaust pump, and the temperature of the heater 7 is raised to about 1600 ° C. As a result, the silicon raw material begins to melt when it reaches about 1420 ° C., and eventually the entire raw material melts to become silicon melt Si ^(l) . Soshitara, lowering the seed chuck 13, a seed crystal Si held in this ^(S) immersed in the silicon melt Si ^(l), a seed chuck 13 while rotating the quartz crucible 6 into the silicon melt Si ^(l) By relatively gradually raising it, a columnar single crystal Si ^{(C )} having the same crystal orientation as that of the seed crystal Si ^(S) is obtained. Finally, the seed chuck 13 is pulled up to the uppermost part of the crystal taking-out cylinder portion 3, the crystal is cooled to near room temperature, and taken out to the outside.

In the pulling process of the present invention, as described above, the high temperature hydrogen treatment of the furnace member is performed before such a single crystal growth treatment.

That is, as shown in FIG. 1 (a), carbon furnace members such as the carbon crucible 4, the heater 7 and the heat retaining member 10 are subjected to high temperature hydrogen treatment in the absence of raw materials in the chamber. This is because Ar gas containing several% of H ₂ gas was introduced into the chamber from the gas introduction unit 14 at a rate of about 100 liters per minute, and at the same time, the pressure inside the chamber was reduced to about 15 Torr by the exhaust pump through the gas discharge unit 15. Then, the heater 7 is energized, and the heater 7 is heated to about 1600 ° C. and held for about 2 hours. As a result, metal oxide impurities are reduced by hydrogen to the carbon furnace member, and the carbon furnace member is singularized, so that the carbon furnace member is in a stable state where it is not deposited.

By performing single crystal growth as described above after such high temperature hydrogen treatment, metal impurities are not precipitated from the carbon furnace member during the treatment, and high purity single crystal pulling is possible. Becomes

In the following, a cleaning treatment (cleaning with a choline / H ₂ O ₂ / H ₂ O solution → dilute HF treatment → cleaning → drying) was carried out in a chamber subjected to high-temperature hydrogen treatment as described above 5 ″. Arrange the mirror wafer Si ^(W) as shown in FIG.
Flowing r gas at 100 liters / minute, the chamber is set to about 15
With the pressure reduced to Torr, energize the heater and set the heater temperature to about 1
After keeping the temperature at 600 ° C. for 2 hours, the power of the heater 7 was turned off, the chamber was cooled to room temperature, the above-mentioned wafer Si ^(W) was taken out, and the metal impurities attached to this wafer Si ^(W) were analyzed and evaluated. The result is shown. Here, the wafer surface was vapor-decomposed and atomic absorption spectrometry was used. Further, a chamber not subjected to the high temperature hydrogen treatment was also analyzed and evaluated under the same conditions. The results are shown in the table below.

[0037]

[Table 2] The table shows the degree of contamination when the high temperature hydrogen treatment was not performed as "1", and shows the relative comparison value when the high temperature hydrogen treatment was performed.

As is clear from this table, in the chamber subjected to the high temperature hydrogen treatment in the method of the present invention, the metal impurity contamination is significantly reduced as compared with the chamber not subjected to the treatment. By the way, the numerical values shown in the table are of the same order as those in the quartz crucible.

In the high temperature hydrogen treatment according to the present invention, the temperature of the heater 7 is set to 1000 ° C., 1200 ° C., 14 ° C.
As a result of testing Fe as a representative example, the effect of reducing metal contamination when held for 2 hours at 00 ° C. and 1600 ° C. was obtained, and the data shown in FIG. 3 were obtained.
In addition, in FIG. 3, the Fe value is “1” when the Fe value is 1600 ° C.
Is the relative comparison value.

Further, in the high temperature hydrogen treatment according to the present invention, the temperature of the heater 7 is set to 1600 ° C. and the holding time is set to 30.
As a result of testing Fe as a typical example, the effect of reducing metal contamination at 1 minute, 2 hours, 3 hours, and 4 hours is shown.
The data shown in FIG. 4 were obtained. Fe here
The value is a relative comparison value in which the value when the holding time is 2 hours is "1".

As can be seen from the above, in the high-temperature hydrogen treatment according to the present invention, good results can be obtained by keeping the temperature of the heater 7 at 1400 ° C. or higher and holding it for 2 hours.

In addition, a silicon crystal is actually pulled up by the method of the present invention, a mirror wafer is processed from this, and dr
750 ° C x 3 hours + 1000 ° C x 18 in yO ₂ atmosphere
When heat treatment was performed under the condition of time and the crystal defect OSF was evaluated, a very good result of 1 / cm ² or less, which was 20 to 30 / cm ² of a normal commercial wafer, was obtained.

The high temperature hydrogen treatment conditions and the single crystal growth conditions at that time are as follows. First, the high-temperature hydrogen treatment condition is that the temperature of the heater 7 is about 1600 ° C., the high-temperature holding time is 2 hours, and the hydrogen gas / Ar gas is (15 liters / minute).
/ (100 liters / minute). The single crystal growth conditions are as follows: the raw material charge is 35 kg, the quartz crucible 6 is 16 ″, and the Ar gas is 100 liters / minute.
rr In a reduced pressure state, the pulled crystal is an N type of 5 ″ and has a crystal orientation of <100>.

As described above, according to this embodiment, since the furnace member is subjected to the high temperature hydrogen treatment in the absence of the silicon raw material, the hydrogen treatment in the absence of the silicon melt in the chamber is judged as the melt. It will be easy to implement without the need.

Even if the furnace used in the high-temperature hydrogen treatment step is a hydrogen treatment furnace for a carbon furnace member different from the one used in the single crystal growth treatment step, it is the same furnace used in the single crystal growth treatment step. Even if it is feasible. According to the former, the operation rate of crystal pulling is not lowered, and according to the latter, it is possible to save the trouble of re-installing the carbon furnace member from the hydrogen treatment furnace to the single crystal treatment furnace after the high temperature hydrogen treatment. ..

Next, FIGS. 5 and 6 illustrate a method for pulling a silicon crystal according to a second embodiment of the present invention.

The pulling method of the present invention is characterized in that a silicon raw material containing 100 Wppm or more of hydrogen is used as a silicon raw material for single crystal growth.

As shown in FIGS. 5A and 6, after the raw material Si ^(M) is charged in the quartz crucible 6, single crystal growth is performed under normal conditions. That is, the Ar gas is flown into the chamber and the heater 7
Energize to raise the temperature. Then, when the temperature of the heater 7 reaches about several hundreds of degrees Celsius, hydrogen is released from the raw material Si ^(M) . Due to this hydrogen, the metal oxide impurities in the carbon furnace member are reduced and become singular and stable, so that the carbon furnace member is less likely to be scattered. When the raw material Si ^(M) begins to melt at about 1420 ° C., most (99%) of the hydrogen contained in the raw material Si ^(M) is diffused, so even locally, the silicon melt Si ^(L) In the state in which is present, the hydrogen treatment is no longer complete. Then, as shown in FIG. 5 (b), after all the raw materials are converted to silicon melt Si ^(L) ,
The seed crystal Si ^(S) is dipped in silicon melt Si ^(L) , and the single crystal Si ^(C) is pulled up as shown in FIG. 5 (c).

Here, actually, a granular raw material Si ^(M) containing hydrogen well exceeding 100 Wppm was charged in a 16-inch quartz crucible 6 by about 35 kg, and Ar gas was flowed in the chamber at about 90 liters / minute. Then, the pressure was reduced to about 15 Torr, the heater 7 was heated to melt the raw material Si ^(M) , and then about 30 kg of an N type crystal enclosure <100>, 6 ″ ^φ silicon single crystal was pulled up.

Further, in order to evaluate the metal contamination in the furnace during the crystal pulling, the 5 ″ mirror wafer Si ^(W) pre-cleaned as described above was placed in the chamber as shown in FIG. The metal impurities adhering to the mirror wafer Si ^(W) were decomposed in the gas phase, and measured and evaluated by the atomic absorption spectrometry (AAS method). However, the above-mentioned metal contamination was also performed on the Siemens silicon raw material which is widely used in the market. As a result, the data shown in the following table were obtained.

[0051]

[Table 3] This table shows "1" for hydrogen-free Siemens raw material
Is a relative comparison value representing the degree of reduction of metal contamination by the method of the present invention.

According to this table, it can be seen that the contamination of metal impurities is significantly reduced when the hydrogen-containing raw material is used, as compared with the case where the hydrogen-free raw material is used.

FIG. 8 shows the relationship between the hydrogen concentration of the silicon raw material and Fe, which is a typical example of metal contamination, and in this case as well, a relative comparison value with "1" for the hydrogen-free Siemens raw material. It shows with.

As is clear from this figure, when the hydrogen concentration in the raw material is 100 Wppm or more, metal contamination is significantly reduced.

Further, a 6 ″ mirror wafer which was pulled up using a silicon raw material containing about 200 Wppm of hydrogen was prepared, and the temperature was set at 780 ° C. × 3 hours + 1000 in a dryO ₂ atmosphere.
Heat-treated at ° C. × 16 hours, was evaluated the occurrence of crystal defects OSF, 3 Ke / cm ² with respect OSF20~30 Ke / cm ² of commercially available Siemens material conventionally used methods
The results were very good as below.

As described above, according to the present embodiment, most of the hydrogen atoms contained in the silicon raw material are diffused into the chamber at the temperature before the raw material is melted, so that the silicon melt is generated in the chamber. Hydrogen treatment in the absence can be easily realized without the need for melt determination.

Further, according to this embodiment, hydrogen pipe management and the like are unnecessary, and the safety is high.

Further, it is possible to prolong the life of the high-purity carbon furnace member, and to increase the cost of the raw material due to the low hydrogen requirement, and it is possible to produce a single crystal of higher purity at a lower cost, which is remarkable. Cost reduction can be achieved.

The embodiments of the present invention have been described above.
It is also possible to use the method of the first embodiment and the method of the second embodiment in combination.

That is, after the high temperature hydrogen treatment step of the first embodiment, single crystal growth is performed using a hydrogen-containing raw material. As a result, a greater effect of reducing metal contamination can be expected.

[0061]

As described above, according to the present invention as set forth in claim 1, since the furnace member is subjected to the high temperature hydrogen treatment in the absence of the silicon raw material, the silicon melt in the chamber is absent. The effect that the hydrogen treatment can be easily realized without the need for the melt judgment is provided.

According to the fifth aspect of the present invention, most of the hydrogen atoms contained in the silicon raw material are diffused into the chamber at the temperature before the raw material is melted, so that the silicon atoms in the chamber are diffused. This makes it possible to easily realize the hydrogen treatment in the absence of the melt without the need for the melt judgment.

Furthermore, the present invention eliminates the need for hydrogen pipe management and the like, and is highly safe.

Furthermore, the high-purity carbon furnace member can be made to last for a long time, and it is not necessary to increase the cost of the raw material due to the low hydrogen requirement, and it is possible to produce a high-purity single crystal with a cheaper raw material. Therefore, significant cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a process explanatory view illustrating a silicon crystal pulling method according to a first embodiment of the present invention.

FIG. 2 is an explanatory view of a metal contamination evaluation method for the furnace chamber in the first embodiment.

FIG. 3 is a graph showing the temperature dependence of Fe contamination.

FIG. 4 is a graph showing the dependency of Fe contamination on high temperature holding time.

FIG. 5 is a process explanatory view illustrating a method for pulling up a silicon crystal according to a second embodiment of the present invention.

6 is an explanatory view of the setting state in the furnace before the pulling method shown in FIG. 5 is started.

FIG. 7 is an explanatory diagram of a metal contamination evaluation method for the furnace chamber in the second embodiment.

FIG. 8 is a graph showing the dependence of Fe contamination on the raw material hydrogen concentration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace body 2 Main body cylinder part 3 Crystal extraction cylinder part 4 Carbon crucible 6 Quartz crucible 7 Carbon heater 10 Carbon heat insulation cylinder 11 Wire winding device 12 Wire 13 Seed chuck 14 Gas introduction part 15 Gas discharge part

Claims (6)

[Claims] 1. A hydrogen gas is introduced together with an inert gas into an in-furnace chamber in which a silicon raw material is absent, high-temperature hydrogen treatment is performed on the in-chamber member, and the hydrogen-treated furnace member is used. A method of pulling a silicon crystal, which comprises growing a silicon single crystal by means of a method of pulling. 2. The inside of the chamber is set to 1 in the high temperature hydrogen treatment process.
The method for pulling a silicon crystal according to claim 1, wherein the temperature is raised to 400 ° C. or higher. 3. The silicon according to claim 1, wherein the furnace used in the high temperature hydrogen treatment step is a hydrogen treatment furnace different from the one used in the single crystal growth treatment step. Crystal pulling method. 4. The method for pulling a silicon crystal according to claim 1, wherein the furnace used in the high temperature hydrogen treatment step is the same furnace used in the single crystal growth treatment step. .. 5. A method for pulling a silicon crystal, which comprises a single crystal growth step using a silicon raw material containing at least 100 wppm of hydrogen atoms. 6. The method for pulling a silicon crystal according to claim 5, which comprises the high-temperature hydrogen treatment step according to claim 1 before performing single crystal growth.