JPH0340990A - Crucible for single crystal production - Google Patents

Abstract

PURPOSE:To improve the thermal circumstances of Si molten liquid in a single crystal growing part, to restrain the generation of bubbles in the growing part, and to stably pulling the single crystal up by specifying the material and the thickness of each part of the quartz crucible of double structure. CONSTITUTION:This crucible is the crucible for growing Si single crystal in which a partition member 31 is provided in the inner part so as to enclose the crystal concentrically and the partition member 31 has small holes through which the molten liquid of the outside is allowed to move into the inside. In this crucible, the thickness of the crucible bottom part 32 of the part enclosed with the member 31, that is the single crystal growing part, is made larger than 1.3 times the thicker member of the outside part of partition, that is a member 30, and the member 31, and <=2 times the sum of both members. Moreover, the average porosity of the bottom part 32 is not less than the average porosity of the member 31. By this method, the quantity of heat supplied from the side surface of the crucible is larger than that supplied from the bottom part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a quartz crucible used for producing silicon-41 crystals by the Czochralski method.

[Prior Art J The Czochralski method for producing silicon single crystals has been practiced for a long time and is a nearly perfected technology.

As is well known, in this technology, a fresh silicon raw material is placed in a quartz crucible, and a silicon seed crystal is brought into contact with the surface of the melt, and at the same time the silicon seed crystal is rotated and pulled up gradually. As the surface contact surface solidifies, the silicon single crystal grows, thereby obtaining a cylindrical silicon single crystal.

At this time, depending on the purpose, the silicon single crystal may be I) type or N type.
To make a type of semiconductor, an appropriate amount of boron,
Dopants such as antimony and phosphorus are mixed in. The rate at which these dopants are taken into the crystal from the silicon melt (segregation coefficient) is generally less than 1. The concentration of the dopants in a silicon single crystal determines its resistivity, so it is desirable to be constant in the crystal. .

In addition to the doping material intentionally mixed into silicon single crystals as mentioned above, there is also a large amount of oxygen that is unavoidably mixed into the silicon single crystal. Since it greatly affects the characteristics and yield, it is desirable that the thickness be uniform from the top to the bottom of the single crystal.

However, as the pulling of the silicon single crystal progresses, the silicon melt in the crucible decreases, and the above impurity concentration changes. The dopant concentration gradually increases, and as a result, the dopant concentration in the silicon single crystal changes from the top to the bottom of the crystal, and the oxygen concentration in the silicon melt elutes from the quartz crucible into the silicon melt. Since it depends on the amount of oxygen, the concentration of oxygen taken into the crystal changes as the silicon melt decreases.

As mentioned above, the quality of the pulled silicon single crystal varies along the pulling direction. However, products that are actually used as wafers are limited to those having dopant concentration and oxygen concentration within a certain limited range. As a result, the range of products that can be used from pulled silicon single crystals is extremely limited.

Several methods have been proposed to solve these problems, and one of the representative methods considered to be practically possible is one using a double-structured crucible.

That is, in a concentric crucible that is heated from the outer periphery, the melt in the outer crucible and the melt in the inner crucible are separated by a wall but are configured so that they communicate with each other,
A method of simultaneously drawing out the semiconductor crystal from the center and simultaneously supplying the semiconductor material to the outer melt was disclosed in the Japanese Patent Publication 1973-
10184.

FIG. 10 schematically shows an apparatus for producing silicon 41 crystal using a double-structured crucible.
5 is a silicon melt placed in the crucible 22, and 26 is a silicon single crystal pulled up from the surface of the silicon melt in the partition member 23. Note that a hole 24 is formed in the lower part of the partition member 23 for allowing the silicon melt 25 to flow between the outside and inside of the partition member.

FIG. 10 is a schematic diagram when a double crucible is applied to a batch type silicon single crystal production apparatus. A silicon melt having a predetermined dopant concentration is placed inside the partition member 23, and a silicon melt containing no dopant is placed outside of the partition member 23. While pulling up the silicon single crystal 26 from the single crystal growth section, the silicon melt flows from the outside of the partition member toward the single crystal growth section, so that the dopant concentration in the single crystal growth section is always constant. This is what I did.

In addition, in the case shown in Fig. 1θ+b+, the powdered raw material 29 is continuously supplied from the raw material supply pipe 28 to the raw material supply section while pulling the silicon single crystal from the single crystal growth section. The silicon melt 4 is kept constant, and the purpose is to keep the dopant concentration and oxygen concentration constant in the silicon melt in the single crystal growth section.

[Problems to be Solved by the Invention] Based on the above-mentioned conventional technology, when pulling silicon 41 crystal using a double-structured crucible, the thermal environment in the silicon melt is different from that when using a normal single-layered crucible. It would turn out to be exactly the opposite of what it would have been.

In the case of the CZ method using a normal single-layered crucible, the side wall of the crucible is placed closer to the bottom of the crucible.

In other words, the amount of heat input from the side wall of the crucible is greater than the amount of heat input from the bottom of the crucible, and reflecting this, the convection flow of silicon melt in the quartz crucible as shown in Figure 8 is dominant. I'm tired. Under such convection of the silicon melt, there is little variation in the solid-liquid interface between the silicon single crystal and the silicon melt, and stable single crystal growth is achieved.

However, when pulling a silico single crystal using a crucible with a double structure, the amount of heat input to the side of the crucible or the bottom of the single crystal is indirectly input through the raw material supply section, so it is The rate of heat input from the bottom of the crucible becomes larger than when using the crucible. Therefore, the temperature distribution in a crucible with a double structure is reversed when a crucible with a single structure is used, and the maximum temperature of the quartz crucible surrounding the single crystal growth area is located at the bottom of the crucible. The temperature distribution is such that the bottom of the crucible is at a high temperature and the wall surface of the partition member is at a relatively low temperature. Under such a thermal environment with a large proportion of heat input from the bottom, the thermal convection of the silicon melt in the single crystal growth zone is dominated by a flow field as shown in Figure 9, which is completely opposite to Figure 8. 7 Since such a flow field is unstable, the high-temperature silicon melt at the bottom of the crucible is intermittently transported directly to the solid-liquid interface of the silicon single crystal, which causes These thermal fluctuations induce defects in the pulled silicon single crystal, and even cause dislocations.

In addition, pores contained in the quartz crucible are also considered to be a factor that inhibits the stable pulling of silicon single crystals. In other words, the surface of the quartz crucible reacts with the silicon melt and erodes, but at this time, the pores trapped in the quartz crucible pop out into the silicon melt, and the bubbles and quartz fragments generated at this time become silicon monomers. A problem has arisen in that the silicon single crystal becomes dislocated when it reaches the field-liquid boundary of the crystal.

[Purpose of the invention] The present invention has been made to solve the problem described in item h. In a double-structured quartz crucible, by optimizing the material and thickness of each part of the crucible, silicon fusion in the single crystal growth section is improved. A bubble gummy that improves the thermal environment of the liquid and at the same time generates 5Δ inside the single crystal growth area! 5 by suppressing the life
The purpose of this method is to achieve stable pulling of silicon single crystals.

[How to solve the problem J9] The diameter of the bottom of the crucible in the part surrounded by the partition (single crystal growth part) is at least 1.3 times that of the outer part of the partition and the thicker part of the partition. The porosity i contained inside the single crystal growth area should be at least twice the sum of both.
The average value of V is set to be equal to or greater than the average value of s (L) of the porosity of the partition member.Furthermore, the average porosity of the partition member and the inner surface of the bottom of the crucible J in the single crystal growth section is set to 0.2% or less. Constructed from the same quartz material with low porosity.

The amount of heat input into the single crystal growth section is determined by the characteristics and shape of the quartz member surrounding it. The reason why the knob at the bottom of the crucible in the crystal growth bottom is made large is to take advantage of the poor thermal conductivity of quartz to suppress heat input from the bottom of the crucible. In a double structure crucible, when the thickness of each part of the crucible is the same as is conventionally done, the heat flux from the bottom of the crucible is larger than when using a normal -in crucible, and the heat flux from the partition member is large. It becomes too small. This is because the silicon bath on the outside of the partition member becomes an obstacle to the heat flow from the side heating element.

The reason why the thickness of the crucible at the bottom of the inner part is set to be 1.3 times or more than that of the outer part of the partition and the part of the partition member that is closer to the knob is because below this value, the thickness of the crucible is 1.3 times or more than that of the outer part of the partition and the part of the partition member that is closer to the knob. This is because the thermal environment of Tsutsuba cannot be achieved.

However, the thermal environment of the CZ method (-heavy crucible) cannot be completely achieved by only considering the thickness of the crucible of 5 or more. Even if the bottom is made thicker, if the material is a material that conducts heat well, The effect of this will be greatly reduced. The amount of heat that enters and exits through quartz is determined by thermal conductivity and by transmission as radiant heat.1 The thermal conductivity of quartz is about several kcal/W・h・K, and the more opaque the quartz glass is, the higher the thermal conductivity becomes. Sex gets worse. Furthermore, the transmittance of heat as radiant heat is more strongly dependent on the transparency of the quartz glass, and the higher the porosity of the quartz, the greater the proportion of radiant heat that is scattered, and the lower the transmittance. By making the bottom thicker, thermal conductivity can be worsened, but if it is transparent to radiant heat, the effect of suppressing the amount of heat transferred is small. The reason for setting the height to be equal to or higher than that of the component is to take the above points into consideration.

However, when the bottom of the crucible is made of quartz with high porosity, when the quartz is heated, the internal pores expand, and as the quartz surface melts.

It is said that bubbles and quartz fragments are released into the silicon melt, causing dislocations in the silicon single crystal. The reason why the inner surface of the bottom of the crucible in the single crystal growth section is made of quartz with low porosity is to avoid this phenomenon.

In addition, the thickness of the bottom of the single crystal growth section should be less than twice the thickness of the partition member and the members outside the partition member combined. This is because the amount of heat input cannot be secured.

Single crystal a makes the porosity of the partition member 0.2% or less.
This is to promote heat input to the bottom from the sides and ensure the required amount of heat input as a whole. That is, if the partition member is made of quartz with high porosity, the amount of heat passing through it will be reduced, so the thickness of the bottom of the crucible must be increased accordingly.

This is because it becomes impossible to secure the necessary amount of heat input to the single crystal part.

[Function] A partition is installed inside to surround the crystal in concentric circles,
And the silicon single crystal i! is provided with a small hole in the partition so that the melt on the outside of the partition can move inward. ? In the method of pulling silicon single crystals using a synthetic quartz crucible, by optimizing each part of the quartz crucible,
The thermal environment within the single crystal growth section is improved, and thermal convection of the silicon melt is stabilized.

In addition, the heat transmittance of quartz parts practically depends on the porosity of the quartz, and the lower it is, the higher the heat transmittance becomes, so the porosity of the partition member should be lower than the porosity of the bottom of the crucible. From Kotobanko, the crucible side compared to the bottom of the crucible [? II
The amount of heat input from I (partition member) can be increased.

Furthermore, by making the surface of the quartz member surrounding the single crystal growth region low in porosity, it is possible to prevent the generation of air bubbles.

[Example] FIG. 1 is a cross-sectional view schematically showing an example of the present invention. In FIG. 1, 30 is a side wall of a quartz crucible, 31 is a partition member, and 32 is a crucible bottom of a single crystal growth section.

The partition member 31 is made of low-porosity quartz with an average porosity of 0.2% or less, and 30 and 32 have an average porosity of 0.5%.
Composed of ~1.5% regular opaque quartz. The thickness of each part of the crucible is, for example, 10 m for the crucible side wall 30, IOM for the partition member 31, and 2(+n) for the bottom of the crucible.

FIG. 4 is a sectional view of the entire apparatus used for pulling silicon single crystals using the quartz crucible as described above.

A quartz crucible 1 is set in a graphite crucible 2, and the graphite crucible 2 is supported by a pedestal 3'' so that it can move up and down and rotate. 4 is the silicon raw material placed in the melting pot, and the silicon t that is grown into a columnar shape.
IT crystal 5 is raised. Reference numeral 6 denotes a heater that takes and chews the graphite crucible 2, and 7 denotes a hot zone insulating material surrounding this heater 6, which is basically the same as a single crystal pulling apparatus using the ordinary Czochralski method.

In such an apparatus, if a double-structured quartz crucible as shown in Figure 1 is used, the amount of heat input from the bottom of the single crystal growth section is suppressed, and in comparison, the amount of heat input from the side part (partition member) is suppressed. It is now possible to increase the convection of the silicon melt, making it possible to obtain stable convection of the silicon melt.

The experimental results of the researchers to confirm the effect of the embodiment shown in FIG. 1 are shown in FIGS. 5 and 6.
w, the thickness of the bottom of the crucible when the average porosity of the partition member is 0.2% and the uniform porosity of the bottom of the crucible is 085%, F, (dislo-cation f
ree) rate relationship.

As is clear from Fig. 5, when the thickness of the bottom of the crucible is less than 13 layers, there is no effect of suppressing heat input from the bottom of the crucible, so stable pulling of silicon single crystals cannot be achieved;
It has been found that when the temperature is higher than am, the heat input from the bottom of the crucible is suppressed too much, causing a problem in the step of heating and melting the raw material silicon.

Figure 6 shows the case where the thickness of the partition member and the outer part of the partition is 1 Onv, the thickness of the bottom of the crucible is 13 mm, and the average porosity of the crucible IfF is 0.5% and 0.2%. It shows the relationship between the porosity, F, and ratio of the partition member. As is clear from this figure, if the porosity of the partition member becomes larger than the average porosity of the bottom of the crucible or exceeds 0.2%, stable pulling of silicon single crystals may be impaired. Understood.

2nd Ij! In Example J, the inner and outer surfaces of the single crystal growth section are made of high-porosity quartz, and the inner surface is made of low-porosity quartz. The results of an experiment to confirm the effect of the embodiment shown in FIG. 2 are shown in FIG. 7. In FIG. The porosity of 0.2%,
This figure shows the relationship between the porosity of the inner surface of the bottom of the crucible and 1), F, when the porosity of the outside of the crucible bottom is 1.2%.

From this figure, it was found that by setting the porosity of the inner surface of the bottom of the crucible to 0.2% or less, more stable silicon single crystal pulling could be achieved.

Welding of a double-structured crucible as shown in Figure 2 is carried out as part of the crucible manufacturing process inside the shell, but it is also possible to weld the quartz parts of each part using the amount of heat input when melting the silicon raw material. It is. The embodiment shown in FIG. 3 uses two crucibles, a large-diameter crucible 35 with high porosity and a small-diameter crucible with low porosity, and the outer bottom surface of the small-diameter crucible and the inner bottom surface of the large-diameter crucible are As a result, a double-structured crucible is constructed to obtain substantially the same effect as the embodiment shown in FIG. 2.

[Effects of the Invention] As is clear from the above explanation, this Komei is a silicon single crystal manufacturing method using a double-structured crucible, in which the amount of heat input from the 01 plane in the single crystal growth section is supplied from the bottom. By making it larger than that, stable thermal convection of the silicon melt is obtained, and generation of bubbles from the quartz is prevented, stable pulling of the silicon single crystal can be achieved, and the effect of implementation is large.

[Brief explanation of drawings]

Figures 1, 2, and 3 are cross-sectional views schematically showing examples of the present invention, and Figure 4 schematically shows an example of a silicon single crystal pulling apparatus used in carrying out the present invention. 5, 6, and 7 are diagrams showing the experimental results of the embodiment of the present invention, and FIGS. 8 and 9 are diagrams showing the case using a single structure crucible and the conventional double structure respectively. FIG. 10 is an explanatory diagram showing an example of a silicon single crystal production method using a double-structured crucible. 1: Crucible, 2: Graphite crucible, 3: Silicon raw material, 4:
Silicon melt, 5. Silicon single crystal, 6. Heater, 8
゛Chamber, ll: Partition member. (inner crucible), 12: small hole, 30: crucible side wall, 3
1: Partition member, 32: Crucible bottom, 35: Large-diameter crucible, 36: Small-diameter crucible Applicant: Shomoto Steel Tube Co., Ltd. 1 Figure 0: Average porosity of crucible bottom = 0 .5% mouth: Average porosity of the bottom of the crucible = 0.2% Figure 7 Porosity of the inner surface of the bottom of the crucible (%) Section

Claims (4)

[Claims] (1) Quartz for silicon single crystal growth in which a partition is installed inside to surround the crystal concentrically, and a small hole is opened in the partition so that the melt on the outside of the partition can move inward. In a crucible, the thickness of the bottom of the crucible in the part surrounded by the partition (single crystal growth part) is thicker than 1.3 times the outer part of the partition and the thicker part of the partition, and 1. A quartz crucible for growing silicon single crystals, wherein the average porosity of the bottom of the crucible in the crystal growth section is greater than or equal to the average porosity of the partition. (2) A quartz crucible for single crystal growth according to claim (1), characterized in that the bottom of the crucible of the single crystal growth section consists of an inner layer with low porosity and an outer layer with high porosity. . (3) The quartz crucible for single crystal growth according to claim (2), characterized in that the inner layer of the crucible bottom of the single crystal growth section and the partition member are made of the same quartz member. (4) In claim (3), the layer inside the crucible bottom of the single crystal growth section and the partition member have a porosity of 0.2.
A quartz crucible for growing single crystals, characterized in that it is composed of a low porosity crucible of less than %.