JP2509477B2 - Crystal growth method and crystal growth apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applied to a crystal growth technique by a pulling method, particularly a semiconductor single crystal pulling technique,
A technology to control the temperature distribution in the radial direction of the surface temperature of the material melt filled in the crucible by placing a temperature control plate on the surface of the melt to improve the pulling speed of the single crystal and the quality of the obtained crystal. Regarding

[0002]

2. Description of the Related Art Conventionally, in a semiconductor single crystal pulling technique, in particular, in a silicon single crystal pulling technique by the Czochralski (CZ) method, there has been an improvement in productivity and influence of thermal history on the crystal during pulling. For control, a kind of inverted conical heat radiation plate such as disclosed in Japanese Patent Publication No. 57-40119 and Japanese Patent Publication No. 231040 is provided around the pulled crystal. There is technology. These cut off or reflect the heat from the heater for heating and the radiant heat from the melt surface that reach through the crucible, thereby increasing the cooling rate of the pulled crystal.

[0003]

However, in these techniques, the surface of the melt is partially overheated by the heat radiated by the heat radiating plate, and the temperature distribution of the entire melt is not normal. In some cases, the crystal characteristics were adversely affected. Also, to further increase the pulling speed,
It is also desired in terms of productivity.

Further, conventionally, in the CZ method, regarding the temperature distribution state of the melt surface, it is well known that the operator who actually pulls up the pattern changes even during pulling of one single crystal. Usually this pattern is
As it progresses from the top side (beginning of pulling) of the single crystal to the tail side (end of pulling), it changes from X to Z in Fig. 4, but when it becomes a state like Z, it becomes difficult to pull up the single crystal. , There are times when we give up on the way.

The higher the speed of pulling the single crystal, the more the pattern of the temperature distribution becomes Y and Z. This is to accelerate the solidification of silicon,
Although it is necessary to lower the heating value of the heater, the amount of silicon solidification heat (430 cal / g) generated per unit time increases, so the temperature on the inner wall of the crucible has to be reduced. . In the CZ method, although the temperature of the melt in the radial direction of the crucible must be controlled, there is no effective technique therefor, and thus this has not been performed in the past. When the pattern changed from Y to Z, it was common to slow down the pulling speed or increase the electric power to the heater to escape the failure of pulling. This has a very bad influence on the quality and productivity of the pulled single crystal.

[0006]

In order to solve the problems of the prior art, the present invention provides a new pulling technique that enables control of the temperature distribution of the melt in the radial direction. The material melt melted by a heater as an external heating means surrounding the crucible is melted,
In the technique of growing a crystal by immersing a seed crystal and gradually pulling it up, it is above the melt surface,
By providing a temperature control plate in the region surrounding the pulling crystal, the temperature distribution of the melt surface during the pulling of the crystal, at the same time to the lowest at the solid-liquid interface under the pulling crystal, at the same time,
The present invention is characterized by a method and apparatus for always maintaining the height gradually increasing toward the inner wall surface of the crucible.

Further, when the temperature control plate is moved so that the distance from the melt surface can be varied according to the pulling state during pulling of the crystal, the temperature distribution on the melt surface can be easily controlled to the above-mentioned state. Become.

Further, the temperature control plate has a holding portion along the crystal pulling region, and an umbrella-shaped portion provided at the lower end portion thereof which extends downward in the outward direction or horizontally and reaches the vicinity of the inner wall surface of the crucible. .

Here, if the inclination of the umbrella-shaped portion of the temperature control plate is set to 15 ° or less with respect to the horizontal plane, the temperature distribution on the surface of the melt will be good.

[0010]

In the present invention, as described above, the temperature distribution of the surface of the material melt heated and melted by the heater from the portion just below the crystal to the portion in contact with the inner wall of the crucible is changed at any point during the pulling. It is intended to realize high-speed pulling of a crystal having good quality by controlling so that the portion directly below the crystal has the lowest temperature and the temperature becomes higher toward the outside. The reason why the present invention uses such an action is I
In order to obtain an excellent-quality large-diameter silicon single crystal for C, for example, in the CZ method, the most important thing is to pull the crystal around the position A (FIG. 4) at which the crystal solidifies from the melt. It is in the so-called longitudinal temperature distribution state that determines the temperature history of the obtained silicon single crystal, and in the so-called lateral temperature distribution state of the melt surface toward the inner wall of the crucible that influences the solidification state from the melt. Is.

The former is a high temperature state (1350 ° C.) immediately after solidification is completed.
From the above), the medium temperature state (13
(00-900 ℃), and further transition to a low temperature state (900-450 ℃) above, precipitation of solute oxygen in the single crystal, or formation of donors, and the dramatic disappearance of various crystal defects. It is presumed that it affects the occurrence of the

On the other hand, the latter influences whether the crystal can be pulled up without any trouble regardless of the physical phenomenon in the single crystal. In principle, the suitable temperature of the silicon melt is considered to be only the temperature of the melt just below the silicon single crystal, but when it is industrially manufactured, the temperature of the entire melt in the crucible, especially the temperature distribution of its surface, Control is important.

In the general CZ method in which the heater is used to heat from the outer periphery, heat is always radiated by conduction, radiation or convection from a heated object such as a graphite crucible, a quartz crucible and a silicon melt. As a result, the desirable lateral temperature distribution is as shown in FIG. 3, but of course the electric power to the heater is controlled so that the temperature just below the crystal in FIG. Freezing temperature of (1420
Normally, automatic control is performed so that the temperature is maintained at (° C).
This includes the so-called "optical type", in which the diameter of the silicon single crystal is optically measured and used for control, and the so-called "weight type" in which the variation in the diameter of the silicon single crystal is sensed by weight and used for control. , "Whichever method is used,
It is general that a means for simultaneously controlling the heat generation amount of the heater heating the melt and the pulling rate of the single crystal is incorporated in the control system. However, in order to obtain a good quality crystal, it is not good to give the pulling rate a large proportion of the control, and therefore it is desirable to increase the proportion of the temperature control to the silicon melt.

That is, when the technique according to the present invention shown in FIGS. 1 to 3 is adopted, the umbrella-shaped portions 9, 9 ', 9 "of the temperature control plates 7, 7', 7" are radiated on the surface of the melt. In addition to suppressing the above, the holding portions 8, 8 ′, 8 ″ around the crystal allow heat to escape upward by conduction and accelerate the cooling rate of the solid-liquid interface,
It is considered that the radial temperature distribution state of the melt surface maintains the ideal pattern of X in FIG. 4 and does not fall into the Y or Z state in any situation during pulling.
Therefore, if the temperature control plate is made movable so as to follow the fluctuation of the melt surface level, this action and effect are further stabilized.

[0015]

[Comparative Example] In the single crystal growth apparatus by the CZ method shown in FIG. 5, a quartz crucible (16 inches) 2 was placed in a graphite crucible 1 and placed in a preset cylindrical graphite heater (inner diameter 16 inches) 3. It was installed and 45 kg of the raw material silicon nugget was loaded into the quartz crucible. The inside of the apparatus was evacuated, the atmosphere was replaced with argon gas, the raw material was heated and melted by the graphite heater 3 to form a melt, and then a seed crystal 4 of 5 mm × 5 mm was dipped in the surface of the melt to be familiar. The production of the single crystal 5 was started by gradually pulling up the seed crystal, and the single crystal 5 was grown to have a diameter of 6 inches. Thereafter, the calorific value of the graphite heater was adjusted so that the pulling speed was 1.3 mm / min, and the growth was further continued. Single crystal growth length is 400m
When approaching m 2, a part of the silicon melt began to solidify from a part of the inner wall 6 of the crucible into an island shape. The island gradually increased in size, extended toward the center of the crucible, and at the crystal length of 480 mm, there was a danger of contact between the crystal and the island, so we abandoned pulling.

[0016]

EXAMPLE 1 The same apparatus as in Comparative Example was used to completely melt the raw material silicon, and then the temperature control plate 7 was loaded in the pulling apparatus as shown in FIG. The temperature control plate 7 has a cylindrical holding portion 8 and an umbrella-shaped portion 9, and the holding portion 8 surrounds the periphery of the single crystal to be pulled. Further, a supporting portion 14 for supporting the temperature control plate is provided at an intermediate height of the holding portion 8 and is fixed to an upper portion of a heat insulating cylinder 15 of the single crystal growth apparatus. Further, the outer edge 10 of the umbrella-shaped portion 9 reaches near the boundary surface between the inner wall of the quartz crucible and the melt. The inner diameter of the holding part is 229 mmφ, the angle α formed by the horizontal plane of the umbrella-shaped part is 5 °, and the shortest distance from the melt surface is 25
mm, and the distance between the outer edge 10 and the quartz crucible 2 is 25 mm. The umbrella-shaped portion 9 keeps the temperature of the melt surface warm, and the holding portion conducts heat at the solid-liquid interface by conduction.

The same operation as in the comparative example was performed, and the pulling speed was 1.3 mm / min. Then, the pulling of a single crystal having a diameter of 6 inches was started. Even when the crystal length was 400 mm, solidified islands did not appear from the inner wall of the crucible, the same pulling rate was maintained until the end, and finally a 640 mm long silicon single crystal was obtained.

When the umbrella-shaped portion is slightly inclined as in this embodiment, the circumferential contact area between the inner wall surface of the crucible and the melt surface can be more effectively kept warm than the solid-liquid interface.
It was found that even if the inclination was set more than 15 ° from the horizontal plane, the effect was not particularly remarkable.

Example 2 Up to a single crystal growth length of 300 mm, the shortest distance from the melt surface of the temperature control plate 7 (set to H) was set to 100 mm, and then at 400 mm, H = 50 mm and 600 mm. By the way,
Except for the point that Z was gradually changed so that H = 25 mm,
The silicon single crystal was pulled up in the same manner as in Example 1 except for other conditions. The pulling speed was constant at 1.3 mm / min., And no island was generated until the end. Finally, a 642 mm long silicon single crystal was obtained.

As shown in FIG. 2, the temperature control plate 7'is provided with a shaft 11 fixed to the upper end of the holder 8'on the inner wall 12 of the chamber of the pulling device, and a driving source (not shown) from outside the chamber. ), It moves up and down in conjunction with the rotating gear 13.

Example 3 The same procedure as in Example 1 was carried out, but the shape of the temperature control plate 7 "was changed to that shown in FIG. 3. The shape of the temperature control plate used in this example was an umbrella-shaped portion 9". Is set horizontally, and the holding portion 8 "has a thickness. The surface of the melt is kept at a high temperature by the reflection heat-retaining action of the umbrella-shaped portion 9", and the vicinity of the solid-liquid interface is reversed. The heat is effectively dissipated by the conductive action of the thick holding portion 8 "and is maintained at a low temperature. Since the heating source is outside the crucible, the ideal temperature of the melt surface rising from the center of the crucible to the outside A gradient pattern is formed.

The same effect can be seen in this embodiment as well.
A silicon single crystal having a crystal length of 644 mm and a diameter of 6 inches could be obtained.

The physical properties of the single crystals obtained in Examples 1 to 3 were examined, but no significant difference from those produced by the conventional method was observed.

In each of the embodiments, graphite was used as the material of the temperature control plate, but of course, other than this, a metal material such as molybdenum may be used. Alternatively, a multi-layer structure may be used.

[0025]

According to the present invention, the temperature distribution pattern of the melt surface in the radial direction of the crucible is gradually increased from the solid-liquid interface portion toward the inner wall surface of the crucible at any stage from the start to the end of pulling. It can be maintained so as to rise, so that even if the pulling speed of the single crystal is increased, the melt temperature on the crucible side does not decrease. Therefore, the crystal can be pulled up at such a rate that solidification islands have been formed on the melt to make the pulling impossible, and thus the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a single crystal growth apparatus showing an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a single crystal growth apparatus showing a different embodiment of the present invention.

FIG. 3 is a vertical sectional view of a single crystal growth apparatus showing still another embodiment of the present invention.

FIG. 4 is a schematic diagram showing a temperature distribution state on the melt surface.

FIG. 5 is a vertical sectional view of a conventional single crystal growth apparatus.

[Explanation of symbols]

 1 Graphite crucible 2 Quartz crucible 3 Graphite heater 4 Seed crystal 5 Single crystal 6 Crucible inner wall 7, 7 ', 7 "Temperature control plate 8, 8', 8" Holding part 9, 9 ', 9 "Umbrella part 10 Outer edge 11 Shaft 12 Chamber inner wall 13 Gear 14 Bearing 15 Heat insulation tube

Claims (6)

(57) [Claims] 1. A method of growing a crystal by immersing a seed crystal in a material melt, which is filled in a container and made into a molten state by an external heating means, and gradually pulls it up By providing a temperature control plate in the region surrounding the crystal pulling region above the region, the temperature distribution on the melt surface is the lowest at the solid-liquid interface under the pulling crystal during the crystal pulling, and is gradually higher toward the inner wall surface of the container. A method for growing a crystal characterized by maintaining. 2. The temperature distribution on the surface of the melt is kept at the lowest level at the solid-liquid interface under the pulling crystal during pulling the crystal by changing the position of the temperature control plate according to the displacement of the melt surface during pulling the crystal. The crystal growth method according to claim 1, wherein the crystal growth method maintains the temperature gradually higher toward the inner wall surface of the container. 3. A method of growing a crystal by immersing a seed crystal in a material melt filled in a container and made into a molten state by an external heating means and gradually pulling it up A crystal growth apparatus characterized in that a temperature control plate is provided in a region surrounding a crystal pulling region above the region. 4. The temperature control plate has a holding portion along the crystal pulling region, and an umbrella-like portion provided at a lower end portion of the holding portion that opens downward downward or horizontally and reaches the vicinity of the inner wall surface of the container. The crystal growth apparatus according to claim 3. 5. The crystal growth apparatus according to claim 4, wherein the inclination of the umbrella-shaped portion of the temperature control plate is 15 ° or less with respect to the horizontal plane. 6. The crystal growth apparatus according to claim 3, wherein the temperature control plate is vertically movable.