JP2880092B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single crystal of a semiconductor such as silicon with high yield and high productivity.

[0002]

The production method of the prior art single crystal, (which serial less CZ method) crucible melt <br/> pulling while growing a crystal from the Czochralski method is widely used. This C
When a single crystal is to be obtained by the Z method, for example, a single crystal manufacturing apparatus having a configuration schematically shown in FIG. 1 is used.
Using such a single crystal manufacturing apparatus , first, raw materials are put into a crucible in the figure, and the raw materials are melted by a heater surrounding them.

Then, the seed crystal is dropped from above the melt in the crucible and brought into contact with the surface of the melt . While rotating the seed crystal, it is pulled upward while controlling the pulling speed, thereby producing a single crystal having a predetermined diameter. In this single crystal pulling, the melt flow is controlled for the purpose of preventing polycrystallization and deformation of the crystal, controlling the concentration distribution of dopants and impurities in the crystal, and controlling the temperature conditions near the crystal growth. In addition, the migration of dopants and impurities in the melt has been optimally controlled.

Conventionally, there has been no method for directly examining the flow of a melt, and operating conditions such as a crucible rotation speed, a crystal rotation speed, a relative position between a crucible and a heater, and a heating condition of a heater are adjusted by trial and error to obtain crystal growth. The optimal operating environment has been obtained. As an auxiliary means for determining whether a stable crystal growth environment is realized, there is a method of measuring the temperature of a certain point on the melt surface and using the obtained melt surface temperature fluctuation as an index of the crystal growth environment. Was.

For example, as schematically shown in FIG. 2, a radiation thermometer is mounted above the chamber to measure the temperature at one point on the melt surface. Based on the measurement, the operating conditions were controlled so that the temperature fluctuation was reduced to some extent.

[0006]

However, a lot of time and effort are required to search for the optimum operating conditions by trial and error as described above. In addition, these conditions change with the aging of the carbon member and the like in the pulling furnace. Furthermore, there is a problem in the following point that a guideline for stable crystal growth can be obtained only by measuring the temperature of a certain point on the melt surface using a radiation thermometer.

Conventionally, it has been considered that the temperature distribution of the melt in the crucible is axially symmetric with respect to the rotation axis of the crucible and is stationary. However, according to recent studies by the present inventor, the temperature distribution in the melt may be off-axis depending on operating conditions such as the crucible rotation speed .
In referred revealed that sometimes becomes unsteady.
Due to the unsteady , non- axisymmetric temperature distribution, a low temperature portion and a high temperature portion are formed in the circumferential direction of the melt, and the low temperature portion and the high temperature portion move in the crucible rotation direction. Interface
Temperature fluctuation occurs at a fixed point.

If the temperature of the melt near the crystal growth interface fluctuates greatly, the crystal may be polycrystallized or the impurities incorporated in the crystal may have irregularities. The magnitude of this temperature variation depends on the position of the melt to be measured. That is, it is not possible to know a truly stable crystal growth environment by measuring only one point on the melt surface as in the past.

The temperature gradient in the radial direction on the melt surface is also an important condition to be controlled. If the temperature gradient in the radial direction on the melt surface is extremely small at the time of expanding the shoulder of the crystal, the crystal diameter may suddenly increase and polycrystallization may occur. If the temperature gradient in the radial direction is extremely small during the growth of the straight body of the crystal, the crystal may be greatly deformed, and the yield and productivity of the crystal may be impaired. The temperature gradient in the radial direction on the melt surface could not be observed by the conventional measurement of one point on the melt surface.

Recently, the following three methods have been reported as methods for directly examining the flow of the melt. (1) A method of estimating the flow on the melt surface from the black stripes on the melt surface observed during pulling (Yamagishi, Fusegawa: Journal of the Japanese Society for Crystal Growth VOL17, No3 & 4, 1990). (2) A method in which a tracer is floated on the melt surface and the flow of the melt surface is predicted from the movement of the tracer (Shiraishi: 93rd Spring Special Report, 1st volume, 1a- H-6 ). (3) Put a tracer having almost the same density as the melt into the melt, apply X-rays to the entire melt, and apply X-rays to the melt and the tracer.
A method to follow the movement of the tracer based on the difference in the line transmittance and know the flow of the entire melt (K. Kakimoto, M. Eguchi, H. Watanabe, J
Crystal Growth 88 (1988) 365).

However, the tracer was put into the melt and melted.
Crystal growth is impossible with the method of knowing the liquid flow. Also,
The method of knowing the melt flow from the black stripe pattern on the melt surface
The relationship between the state and the melt flow is not yet clear. Thus, there are problems with these methods for use in actual single crystal manufacturing sites.

An object of the present invention is to obtain an optimum pulling environment for crystal growth by quickly and in detail grasping a two-dimensional temperature distribution on a melt surface and its time variation before pulling a single crystal. And

[0013]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have observed the melt surface two-dimensionally, and have grasped the time variation of the melt surface temperature in a stable manner. The present inventors have found a method for pulling a single crystal, and have completed the present invention.

[0014] Namely, the present invention is pulled up after contacting the seed crystal with the melt, in the single crystal manufacturing method for manufacturing a single crystal by pulling a seed crystal, a single crystal
That the seed crystal is pulled from in contact with the melting solution before
A method for producing a single crystal, characterized in that an optimum crystal growth environment is grasped by measuring a two-dimensional temperature distribution on the surface of the melt and its time variation beforehand.

The present invention also relates to a single crystal manufacturing method for manufacturing a single crystal by bringing a seed crystal into contact with a melt of a crystal member melted by a heater in a rotating crucible and then pulling the seed crystal. In the method, the single crystal is drawn.
Before raising , the crystal growth environment of the single crystal is grasped by measuring the two-dimensional temperature distribution on the melt surface of the crystal member and its time variation, and the rotation speed of the crucible, By adjusting the rotation speed of the single crystal, the relative position of the crucible and the heater, and the heating conditions of the heater, the crystal growth of the single crystal is controlled so that the temperature distribution on the melt surface of the crystal member becomes axially symmetric. A single crystal production method characterized by controlling an environment.

The present invention also relates to a single crystal manufacturing method for producing a single crystal by bringing a seed crystal into contact with a melt of a crystal member melted by a heater in a rotating crucible and then pulling the seed crystal. In the method, the single crystal is drawn.
Before raising , the crystal growth environment of the single crystal is grasped by measuring the two-dimensional temperature distribution on the melt surface of the crystal member and its time variation, and the rotation speed of the crucible, By adjusting the rotation speed of the single crystal, the relative position between the crucible and the heater, and the heating conditions of the heater, at least the temperature distribution near the crystal growth interface can be made closer to axial symmetry or the time variation of the temperature can be reduced. A method for producing a single crystal, characterized by controlling a crystal growth environment of the single crystal.

[0017]

According to the present invention, an operation guide for obtaining an optimum environment for crystal growth by grasping the crystal growth environment in detail by measuring the melt surface temperature two-dimensionally from above the single crystal pulling melt. Can be easily created.

In pulling a single crystal, radiant energy corresponding to the temperature is emitted from the surface of the melt. The relationship between radiant energy Q and temperature T is as follows if no other reflections are superimposed.

Q = εσT ⁴ where ε is the emissivity of the melt,
σ represents the Stefan-Boltzmann constant, and T represents the melt surface temperature. By measuring this radiant energy two-dimensionally from above and converting it to a temperature according to the above conversion formula or a conversion formula modified to suit the actual system, the melt surface temperature is known in a non-contact manner be able to.

By observing these continuously, the time variation of the melt surface temperature can be known two-dimensionally. By changing operating conditions such as a crucible rotation speed, a crystal rotation speed, a relative position between the crucible and the heater, and a heating condition of the heater, the melt surface temperature distribution and the temperature fluctuation can be changed. Accordingly, these melt surface temperature data serve as an operation guide for obtaining an optimum operating environment for crystal growth. The method described above has the advantage that, even if the members in the furnace change over time, the operating conditions can be optimally corrected by always observing the surface temperature of the melt, so that an operation taking into account the change over time is possible. .

FIG. 3 is a schematic diagram showing the flow of the melt during the CZ pulling. The feature of the melt flow in the CZ pulling is that the melt heated on the crucible side wall rises along the crucible side wall and changes the direction of the flow in the direction of the crucible center axis near the free surface.
Then, after sinking near the central axis, it changes its direction at the crucible bottom and flows toward the crucible side wall. FIG. 3
A flow (meridional flow) in the vertical cross section of (a) is formed. Usually, the crucible is rotated in pulling up the CZ. Thereby, the flow induced by the crucible rotation overlaps the above flow. A fluid that is density-stratified (a state in which there is a density difference in the fluid) and is rotating is called a rotationally-stratified fluid, a typical example of which is the Earth's atmosphere. Liquid flow and the flow of the Earth's atmosphere are very similar.

The following facts have been found from the temperature measurement experiments and numerical simulations of the present inventor using such a rotating stratified fluid.

When the rotation of the rotating stratified fluid is low, the flow is substantially axisymmetric and the melt surface temperature distribution is also substantially axisymmetric (FIG. 3A). However, as the crucible rotation speed is increased, a horizontal vortex is generated on the free surface of the melt, and the flow transitions non- axisymmetrically . As a result, the temperature distribution on the melt surface becomes non-axially symmetric (FIG. 3B) .

The axisymmetric temperature distribution moves in the crucible rotation direction at a speed dependent on the crucible rotation speed. By focusing on one point on the circumference of a certain diameter of the melt surface due to the rotation of the non- axisymmetric temperature distribution, the low temperature melt and the high temperature melt are periodically or unsteady. In order to come to that point, a temperature fluctuation occurs at that point based on the temperature difference between the low temperature and high temperature melts. The magnitude and cycle of this temperature change differ depending on the radial position of interest , and a radial position having the maximum temperature change amplitude exists on the melt surface.

Further, the radial position having the maximum temperature fluctuation amplitude changes depending on operating conditions such as the crucible rotation speed. As the crucible rotation is further increased, the flow in the vertical section and the temperature distribution in the horizontal section are as shown in FIG. In this state, even in the same non- axisymmetric temperature distribution, a region with small temperature fluctuation is formed near the central axis. That is, the largest part of the temperature fluctuation moves closer to the crucible side wall than in FIG.

For the above reasons, it can be understood that an accurate melt temperature environment cannot be obtained by measuring the temperature of only one point on the melt surface.

The temperature gradient in the radial direction on the melt surface also changes depending on operating conditions such as the crucible rotation speed.

In the present invention, the two-dimensional distribution of radiant energy emitted from the surface of the melt is observed with an imaging device such as a CCD camera, converted into an electric signal, and converted into a temperature, whereby the surface of the melt is converted to a temperature. Two-dimensional temperature distribution is obtained. While displaying this two-dimensional temperature distribution on the display, change the operating conditions such as the crucible rotation speed, crystal rotation speed, crucible position, heater heating conditions, etc. during operation to obtain the optimal state for crystal pulling. .

[0029]

The present invention will be described below in more detail with reference to examples. As shown in FIG. 4, the surface temperature distribution of the melt without any crystals was measured two-dimensionally from the upper part of the chamber above the melt by a CCD camera. In FIG. 5, 4 in an 18-inch crucible
FIG. 4 is a schematic diagram of a surface temperature distribution when the melt surface is observed from above by the above method after 5 kg of polycrystalline silicon is melted. Note that the dotted line in the figure indicates a position corresponding to a 6-inch crystal. FIG. 5A shows a temperature distribution at a crucible rotation speed of 2 rpm. FIG. 5B shows a temperature distribution at a crucible rotation speed of 8 rpm.

The temperature distribution on the melt surface is a crucible rotation speed 2r.
At pm, a non- axisymmetric transition had already occurred, which was rotating in the crucible rotation direction. The largest point of this non-axial symmetry is the edge of the crystal just 6 inches from the center of the crucible.
It was present in a position corresponding to (Figure 5 (a)).

Further, the temperature gradient in the radial direction of the melt surface also has the minimum value at the position where the temperature fluctuation is greatest. As a result of pulling up the 6-inch crystal in this state, almost all the crystals were polycrystallized in the process of expanding the shoulder of the crystal. On the other hand, FIG.
Although the temperature distribution on the melt surface shows an asymmetric axis even in the state of (b), the portion where the temperature fluctuation on the melt surface is the largest and the portion where the temperature gradient in the radial direction is the smallest are increased by increasing the crucible rotation speed. Moved out of the radial position of the 6-inch crystal, and the crystal was pulled as a single crystal without polycrystallization or deformation.

[0032]

As described above, the single connection according to claim 1 is provided.
In crystal manufacturing method, Runode can grasp the optimum temperature environment of reliably melt surface from one point measurement of the conventional melt surface temperature to know the crystal growth environment, optimal temperature conditions for crystal growth It can be used as an operation guide.

In the method for producing a single crystal according to the present invention ,
By adjusting the rotation speed of the crucible, the rotation speed of the single crystal , the relative position between the crucible and the heater, and the heating conditions of the heater, the temperature distribution on the melt surface can be made axially symmetric.
Therefore, a high-quality single crystal can be manufactured. Accordingly
High success rate of single crystal pulling
Can be of high quality.

In the method for producing a single crystal according to the third aspect , the rotation speed of the crucible, the rotation speed of the single crystal , the relative position between the crucible and the heater, and the heating conditions of the heater are adjusted at least in the vicinity of the crystal growth interface. Temperature distribution close to the axis target
Or reduce the temperature fluctuation over time
The success rate of single crystal pulling of single crystal is high,
In addition, a high-quality single crystal can be manufactured.

[Brief description of the drawings]

FIG. 1 is a drawing schematically showing a CZ furnace.

FIG. 2 is a drawing showing one-point measurement of a melt surface by a radiation thermometer.

FIG. 3 shows a typical flow of a melt in CZ pulling;
It is a figure showing the crucible rotation dependence of a temperature distribution.

FIG. 4 is a drawing showing two-dimensional temperature measurement of the melt surface by an imaging device such as a CCD camera.

FIG. 5: CC at crucible rotation at 2 rpm and 8 rpm
It is the figure which represented typically the temperature distribution of the melt surface observed by the D camera.

[Explanation of symbols]

 a: Crystal b: Melt c: Crucible d: Crucible support e: Crucible holder f: Crucible shaft g: Heater h: Heat insulation material i: Furnace wall

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C30B 15/20-15/28 C30B 28/00-35/00

Claims (3)

(57) [Claims] In a single crystal production method for producing a single crystal by bringing a seed crystal into contact with a melt and then pulling the seed crystal, a two-dimensional surface of the melt is formed before the single crystal is pulled. A method for producing a single crystal, characterized in that an optimum crystal growth environment is ascertained by measuring a temperature distribution and a time variation thereof. Wherein In the rotating crucible, after contacting a seed crystal to the crystal member melt melted by a heater, in the single crystal manufacturing method for manufacturing a single crystal by pulling a seed crystal, the Before pulling up the single crystal, the crystal growth environment of the single crystal is grasped by measuring the two-dimensional temperature distribution on the melt surface of the crystal member and its time variation, and based on this, the rotation speed of the crucible is determined. By adjusting the rotation speed of the single crystal, the relative position between the crucible and the heater, and the heating conditions of the heater, the temperature distribution of the single crystal is adjusted so that the temperature distribution on the melt surface of the crystal member becomes axially symmetric. A method for producing a single crystal, comprising controlling a crystal growth environment. 3. In the rotating crucible, after contacting a seed crystal to the crystal member melt melted by a heater, in the single crystal manufacturing method for manufacturing a single crystal by pulling a seed crystal, the Before pulling up the single crystal, the crystal growth environment of the single crystal is grasped by measuring the two-dimensional temperature distribution on the melt surface of the crystal member and its time variation, and based on this, the rotation speed of the crucible is determined. By adjusting the rotation speed of the single crystal, the relative position between the crucible and the heater, and the heating conditions of the heater, at least the temperature distribution near the crystal growth interface is made close to the axial symmetry or the time variation of the temperature is reduced. Controlling the crystal growth environment of the single crystal so as to obtain a single crystal.