JPH04349128A - Method for growing crystal - Google Patents

Abstract

PURPOSE:To enhance the quality of a single crystal grown by increasing the concn. of oxygen in a melt layer and increasing the concn. of oxygen taken in the single crystal. CONSTITUTION:A heater 12 is set around a crucible 11, this crucible 11 is filled with starting material for a crystal and powdery or lump SiO2 and the upper parts of them are melted to form a melt layer 17. The thickness of the melt layer 17 is controlled by regulating the position of the heater 12 or the crucible 11 and a single crystal 16 is pulled up from the layer 17 and grown.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing crystals such as silicon single crystals used as semiconductor materials, for example.

0002

2. Description of the Related Art Generally, the Czochralski method (CZ method) is widely used as a method for growing this type of crystal. FIG. 5 is a schematic vertical cross-sectional view showing a crystal growth apparatus used in the conventional CZ method, and 11 indicates a crucible disposed in a chamber. The crucible 11 is composed of an inner layer holding container 11a made of quartz and having a cylindrical shape with a bottom, and an outer layer holding container 11b made of graphite fitted on the outside of the inner layer holding container 11a. A heating type heater 12 is arranged in a concentric cylindrical shape. A heater 12 is installed in the crucible 11.
It is filled with a melt 13 of the raw material melted by
The seed crystal 15 suspended by a pulling shaft 14 made of a pulling rod or wire is immersed in this melt 13, and the seed crystal 15 is pulled upward while rotating, thereby solidifying the melt 13 at the lower end of the seed crystal 15. This causes the single crystal 16 to grow.

When a semiconductor single crystal is grown using this method, impurity elements are often added to the melt 13 before pulling in order to adjust the electrical resistivity and electrical conductivity type of the single crystal 16. However, a phenomenon occurs in which the added impurities segregate in the crystal growth direction of the single crystal 16, and as a result, there is a problem in that the single crystal 16 having uniform electrical characteristics in the crystal growth direction cannot be obtained. This segregation is caused by melt 13
This is because the ratio CS /CL between the impurity concentration CS in the single crystal 16 and the impurity concentration CL in the melt 13 at the growth interface between the single crystal 16 and the single crystal 16, that is, the effective segregation coefficient Ke is not 1. For example, if Ke <1, single crystal 16
As the single crystal 16 grows, the impurity concentration in the melt 13 increases, causing segregation in the single crystal 16.

[0004] A fused layer method is known as a method for suppressing such segregation. FIG. 6 is a schematic longitudinal sectional view of a crystal growth apparatus used in the fused layer method. The fused layer method uses heater 1
2, a solid layer 18 of the raw material for crystallization coexists in the lower part of the crucible 11, and a molten liquid layer 17 of the raw material for crystallization coexists above the solid layer 18, and the impurity concentration in the molten liquid layer 17 is kept constant. In this method, a seed crystal 15 is immersed in a liquid layer 17 and pulled up to grow a single crystal 16. Molten liquid layer 17
As a method for keeping the impurity concentration in a constant value, a constant melt layer thickness method and a melt layer thickness change method have been proposed. In the constant melt layer thickness method, the fixed layer 18 is melted as the single crystal 16 is pulled up to keep the layer thickness of the melt layer 17 constant, and impurities are continuously added to adjust the impurity concentration in the melt layer 17. This is a method of keeping the value constant, and is disclosed in Japanese Patent Publication No. 34-8242, Japanese Utility Model Application Publication No. 61-150862, Japanese Patent Publication No. 62-880, and Japanese Patent Application Publication No. 63-252989. In addition, in the molten layer thickness change method, as the single crystal 16 grows, the crucible 1
This method maintains the impurity concentration in the melt layer 17 constant without adding impurities during pulling of the single crystal 16 by raising and lowering the heater 12 or the heater 12 to change the layer thickness of the melt layer 17. , Japanese Patent Publication No. 61-205691,
JP-A-61-205692, JP-A-61-215
It is disclosed in Publication No. 285 and the like.

In addition to the above-mentioned impurity elements, the single crystal 16 pulled by the CZ method contains 1017 to 1018 atoms.
It contains s·cm−3 of oxygen. Oxygen in the single crystal 16 is essential for increasing the mechanical strength of the wafer or as a gettering source for adsorbing heavy metal contaminants;
Oxygen is supplied by dissolving a part of the inner layer holding container 11a made of quartz into the melt 13 and eluting oxygen. FIG. 7 is a schematic diagram showing the state of oxygen transport by convection of the melt 13. As shown in FIG. 7, the dissolved oxygen is transported throughout the melt 13 by thermal convection a, forced convection b due to the rotation of the single crystal 16, forced convection c due to the rotation of the crucible 11, and Marangoni convection d caused by the difference in surface tension. Ru. At this time, the melt 13
The oxygen concentration in the crucible 11 is controlled by the rotation of the crucible 11 and the single crystal 16.
convection control by rotation of , convection control by applying a magnetic field (Electronic Materials, September 1987, p. 111-115),
This is performed by thermal convection by controlling the heating of the heater 12, oxygen elution amount control, and the like.

[0006]

In the molten layer method as described above, since the solid layer 18 is present at the bottom of the crucible 11, the contact area between the crucible 11 and the molten liquid layer 17 is smaller than in the CZ method. There was a problem in that the concentration of oxygen taken into the pulled single crystal 16 was low. Therefore, compared to the single crystal 16 grown by the CZ method, the mechanical strength is weaker, and contaminants such as heavy metals are not removed from the device active region of the wafer, which deteriorates the characteristics of the devices formed on the wafer. This was a contributing factor. The present invention was made in view of the above circumstances, and it is possible to grow a single crystal by mixing powdered or lumpy SiO2 when filling a crucible with crystal raw materials and growing the crystal by the molten layer method. An object of the present invention is to provide a crystal growth method that can increase the concentration of oxygen taken in and improve the quality of a single crystal.

[0007]

[Means for Solving the Problems] A crystal growth method according to the present invention includes filling a crucible with a heater around the crucible, and melting the upper part of the crystal raw material to form a molten liquid layer. , in a crystal growth method in which a crystal is grown by pulling up from the melt layer while controlling the layer thickness of the melt layer by adjusting the position of the heater or the crucible, the crucible is filled with a crystal raw material; It is sometimes characterized by mixing powdered or lumpy SiO2.

[0008]

[Operation] Oxygen is normally taken into the single crystal from the melt layer through the following processes (1) to (3). (1) Oxygen is eluted due to dissolution of quartz at the interface between the melt and the quartz crucible (SiO2 → Si+2O). (2) Oxygen moves within the melt layer due to convection. (3) At the interface between the melt layer and the atmosphere (melt layer surface), oxygen evaporates as SiO (Si+O→SiO
↑), or incorporated into the single crystal at the interface (growth interface) between the melt layer and the single crystal (O(in Melt)
→O(inCrystal)). In the present invention, in the molten layer method, oxygen is supplied not only from the process (1) in the molten layer but also from the solid layer, so that the oxygen concentration in the molten layer increases. Therefore, the oxygen concentration in the pulled single crystal increases.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to drawings showing embodiments thereof. FIG. 1 is a schematic longitudinal sectional view of a crystal growth apparatus according to the present invention, and numeral 21 in the figure is a chamber. The chamber 21 is a substantially cylindrical vacuum container;
A crucible 11 is disposed approximately at the center of the crucible 1 . Crucible 1
1 is composed of an inner layer holding container 11a made of quartz and having a cylindrical shape with a bottom, and an outer layer holding container 11b made of graphite and having a cylindrical shape with a bottom fitted on the outside of the inner layer holding container 11a. A shaft 22 for rotating and raising and lowering the crucible 11 is installed on the lower surface of the outer layer holding container 11b, and a heater 12, such as a resistance heating type, is arranged on the outer periphery of the crucible 11 so as to be movable up and down. Further, a heat retaining cylinder 23 is provided around the outside of the heater 12. A molten liquid layer 17 and a solid layer 18 are formed in the crucible 11 by adjusting the relative vertical positions of the crucible 11 and the heater 12.
can be formed by relatively adjusting their respective thicknesses.

On the other hand, above the crucible 11, a pulling shaft 14 is vertically installed so as to be able to rotate and move up and down, passing through a small, approximately cylindrical pull chamber 24 that is connected to the upper part of the chamber 21. A seed crystal 15 is attached to the lower end of the shaft 14. After the lower end of the seed crystal 15 is immersed in the molten liquid layer 17, by rotating and raising it, the single crystal 1
6 is made to grow.

When growing a single crystal using the apparatus configured as described above, first, bulk or granular polycrystalline silicon and powder or lump Si are placed in the crucible 11 as solid raw materials.
O2 is filled in the required amount determined by back calculation from the volume of the single crystal 16 to be pulled. It is preferable for SiO2 to be in powder form because it is easier to mix uniformly into the raw silicon and the oxygen distribution in the axial direction of the single crystal 16 becomes uniform. Furthermore, when granular SiO2 with a diameter of about 10 to 50 mm is mixed, the granules do not melt and float to the growth interface of the single crystal 16, increasing the frequency of polycrystallization of the single crystal 16. It is better not to use it. Bulk SiO2 having a diameter of 50 mm or more can be used. lumpy SiO2
If a rod-shaped object is used as a crucible and placed in a position parallel to the axis of the crucible 11, the amount of SiO2 dissolved will be constant, and the unmelted SiO2 will become a single crystal 16.
This prevents the single crystal 16 from floating to the growth interface and becoming polycrystalline. FIG. 2 is a schematic diagram showing a case where the crucible 11 is filled with polycrystalline silicon and powdered SiO2, and FIG. 3 is a schematic diagram showing a case where the crucible 11 is filled with polycrystalline silicon and bulk SiO2.

After filling polycrystalline silicon and SiO2, they are melted from above by a heater 12 to form a molten liquid layer 17, so that the molten liquid layer 17 and the solid layer 18 coexist. By controlling the positions of the heater 12 and the crucible 11, the thickness of the melt layer 17 is set to a predetermined thickness, and phosphorus is introduced as an impurity to diffuse the phosphorus. Then, the lower end of the seed crystal 15 is immersed in the melt layer 17 and pulled up while rotating the pulling shaft 14, thereby growing the single crystal 16 at the lower end. At this time, along with the dissolution of quartz at the interface between the molten liquid layer 17 and the crucible 11 (SiO2 → Si+2O), the solid layer 18
Since more oxygen is supplied, the oxygen concentration in the melt layer 17 is increased, and it is possible to grow the single crystal 16 having an oxygen concentration necessary as a gettering source.

[0013] Specific numerical values will be listed and explained below. Using the above-mentioned apparatus, the crucible 11 was filled with approximately 60 kg of polycrystalline silicon in the form of lumps or granules and approximately 10 kg of SiO2 in the form of powder or lumps, and the crucible 11 had a diameter of 6 cm and a length of approximately 50 cm.
The silicon single crystal 16 was pulled up and the oxygen concentration at the center at a crystal length of 20 cm was measured. At this time, the oxygen concentration in the single crystal grown by the conventional method was also measured in the same manner. As a result, the oxygen concentration in a single crystal grown by the conventional method is approximately 1015 to 1016 atoms.
cm-3, whereas the oxygen concentration in the single crystal grown by the method of the present invention was approximately 1017 to 1019 atoms.
It was s·cm-3. Therefore, it was found that the method of the present invention is effective in increasing the oxygen concentration in single crystals.

FIG. 4 shows powdered Si mixed into raw material silicon.
It is a graph showing the relationship between the amount of O2 and the oxygen concentration in a single crystal. The amount of SiO2 is 2.5 kg, 5 kg, 7
．． 5 kg and 10 kg were added, each with a crystal length of 20 kg.
The oxygen concentration in the center at the cm position was measured. As a result, it was found that the oxygen concentration in the single crystal could be controlled by changing the amount of SiO2 added, although there were variations in the distribution due to the dependence on the mixing method of SiO2.

[0015]

As described above, in the present invention, when filling a crucible with raw materials for crystallization, powdered SiO2 is uniformly mixed in, or lumpy SiO2 with a diameter of 50 mm or more is erected parallel to the axis of the crucible. Since the crystal is grown by the molten layer method, the oxygen concentration in the molten liquid layer can be increased, the oxygen concentration taken into the single crystal can be uniformly increased, and the quality of the single crystal can be improved. In addition, it becomes possible to manufacture high-quality devices with a high yield. Further, the present invention has excellent effects such as being able to control the oxygen concentration in the single crystal by changing the amount of SiO2 added.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view of a crystal growth apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a crucible filled with polycrystalline silicon and powdered SiO2.

FIG. 3 is a schematic diagram showing a crucible filled with polycrystalline silicon and bulk SiO2.

FIG. 4 is a graph showing the relationship between the amount of powdered SiO2 mixed into raw silicon and the oxygen concentration in the single crystal.

FIG. 5 is a schematic vertical cross-sectional view showing a crystal growth apparatus used in the conventional CZ method.

FIG. 6 is a schematic vertical cross-sectional view of a crystal growth apparatus used in the fused layer method.

FIG. 7 is a schematic diagram showing the state of oxygen transport by convection of the melt.

[Explanation of symbols]

11 Crucible 12 Heater 14 Pulling shaft 15 Seed crystal 16 Single crystal 17 Molten liquid layer 18 Solid layer 21 Chamber 23　Heat insulation cylinder

Claims (1)

[Claims] 1. A crucible with a heater installed around it is filled with a raw material for crystallization, an upper part of the raw material for crystallization is melted to form a molten liquid layer, and the position of the heater or the crucible is adjusted to In a crystal growth method in which a crystal is grown by pulling up a crystal from a melt layer while controlling the layer thickness of the melt layer, powdery or bulk Si is
A crystal growth method characterized by mixing O2.