JP2720269B2 - Method and apparatus for pulling single crystal with controlled convection of melt - 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 and an apparatus for maintaining a melt of a metal, a semiconductor, an oxide or the like in a constant convection state and pulling a single crystal from the melt under a stable condition.

[0002]

2. Description of the Related Art A typical method for growing a single crystal from a melt is the Czochralski method. In the Czochralski method, a crucible 2 arranged inside a closed container 1 as shown in FIG. A heater 4 and a heat insulating material 5 are provided concentrically on the outer periphery of the crucible 2, and the raw material contained in the crucible 2 is intensively heated by the heater 4 to prepare a melt 6. Melt 6 is maintained at a temperature suitable for single crystal growth. The seed crystal 7 is brought into contact with the melt 6 to grow a single crystal 8 that follows the crystal orientation of the seed crystal 7. The seed crystal 7 is rotated by a rotary winding mechanism 1 through a wire 9.
It is suspended from 0 and pulled up while rotating according to the growth of the single crystal 8. The crucible 2 also descends while rotating appropriately via the support 3. The lowering speed and rotation speed of the support 3 and the rotation speed and rising speed of the seed crystal 7 are as follows.
It is controlled according to the growth rate of the single crystal 8 pulled from the melt 6. The obtained single crystal 8 is used as a substrate of a semiconductor device. By the way, with the increase in the degree of integration of semiconductor devices, there is an increasing demand for improving the quality of semiconductor substrates. In order to obtain high quality semiconductor substrates,
It is necessary to suppress dislocations, crystal defects, and the like introduced into the semiconductor single crystal.

[0003]

In the Czochralski method of pulling a single crystal from a high-temperature melt, the state of the melt near the crystal growth interface greatly affects the quality of the obtained single crystal. For example, when a single crystal is pulled up from a melt flowing irregularly in the vicinity of the growth interface, the rate at which minute defects and dislocations are introduced into the single crystal increases. As a result, the quality of the obtained single crystal becomes unstable, and the ratio of the single crystal used as a substrate for a semiconductor device decreases. However, no practical means for accurately and quickly measuring the flow state of the melt has been developed so far. Therefore, controlling the flow pattern of the melt during the pulling operation must rely on the experience of a skilled engineer, and has been a bottleneck in producing high-quality single crystals on an industrial production basis. The present invention has been devised in order to solve such a problem, and detects a load caused by the flow of the melt acting on the probe, and estimates a flow state of the melt from the load to obtain a stable condition. An object of the present invention is to obtain a high-quality single crystal that can be pulled under a single crystal and has no crystal defects or dislocations.

[0004]

According to the convection detecting method of the present invention, in order to achieve the object, a measuring _element whose weight W ₀ in the atmosphere is measured in advance is immersed in a melt, and the weight W is measured.
Calculating a load F from the change in weight W ₁ of the measuring element in the immersion state for ₀ due to the flow of the melt which acts on the measuring element, characterized in that estimating the convection of the melt from該荷load F And When measuring the weight W ₁ of the measuring element at a plurality of measurement points with respect to the vertical and / or horizontal direction of the melt,耐粒shaped body of the melt can be more accurately grasped. Further, when the rotation speed of the crucible, the rotation speed of the single crystal, the output of the heater, and the like are changed in accordance with the variation of the load F so that the load F is maintained within a certain range, the growth of the single crystal pulled from the melt. Conditions are kept constant.

A single crystal pulling apparatus according to the present invention comprises a crucible arranged in a closed container for containing a melt, a support for rotatably supporting the crucible, and a method for heating the melt contained in the crucible to a high temperature. A heater for holding, a rotary winding mechanism for suspending a seed crystal, a measuring element immersed in the melt, a weighing scale for measuring the weight W ₁ of the immersing measuring element, and measurement with the weighing scale The measured weight W ₁ of the measuring _element is compared with the weight W _{0 of the} measuring element in the atmosphere, and a load F due to the flow of the melt acting on the measuring element is calculated. An arithmetic control mechanism for outputting a control signal to the mechanism, wherein the rotation speed of the crucible, the rotation speed of the single crystal, the output of the heater, and the like are changed according to the convection of the melt estimated from the load F. It is characterized by the following.
It is preferable to provide a tracing stylus movable vertically and / or horizontally in the melt so that the load F is detected at a plurality of measurement points. When the load F is detected using a plurality of probes, the flow state of the melt between the probes is also grasped.

[0006]

The density of the melt generally decreases as the temperature increases. For example, the Si melt has the temperature dependency shown in FIG. 2, and the Ge melt has the temperature dependency shown in FIG. Further, the melt is maintained at a temperature near the freezing point so that a single crystal grows near the surface, and is maintained at a relatively high temperature below the melt to maintain the entire melt in a liquid phase. The temperature difference of the melt in the vertical direction may exceed 100 ° C., depending on the size of the crucible. Since there is a temperature difference in the vertical direction and the density of the melt varies depending on the temperature, convection as shown in FIG. 4 is generated inside the melt. In a state where a relatively large amount of the melt 6 is stored in the crucible 2,
Since the lower part of the melt 6 has a high temperature, and there is a heat flow from the heater 4 through the side wall of the crucible 2, as shown in FIG. Convection occurs. On the other hand, in a state where the pulling of the single crystal 8 progresses and the amount of the residual melt 6 is reduced, ascending flows and descending flows are generated at a plurality of locations as shown in FIG. The actual convection depends on the aspect ratio (depth / inner diameter ratio) of the crucible 2, the temperature and amount of the melt 6, the output of the heater 4, the conditions for pulling the single crystal 8, and the like. In addition to the above, various patterns are taken.

Changes in the convection pattern affect the quality of the single crystal 8 being pulled. Therefore, in order to obtain a uniform single crystal 8, the single crystal 8
It is necessary to raise. For example, when the melt 6 is convectively flowing as shown in FIG. 4A, the melt 6 is uniformly stirred throughout the entire area of the crucible 2, and the physical property value of the melt 6 near the growth interface is crucible. 2 is stable in a state close to the average value in the entire internal region. Therefore, the number of defect nuclei taken into the solid phase tends to decrease. On the other hand, when convection in which the flow pattern is separated occurs as shown in FIG. 4B, the physical properties of the melt 6 vary depending on the position in the crucible 2, and the physical properties of the melt 6 near the growth interface. Is easily deviated from the average value over the entire area in the crucible 2.
As a result, the number of defect nuclei taken into the solid phase tends to increase.

In the present invention, a measuring element immersed in the melt 6 is used, and the weight change of the measuring element before and after immersion is used.
Detects the flow state. For example, the weight W _{0 in the} atmosphere
The measuring element composed of the weight 11 and the wire 12
And the weight W ₁ of the probe in the immersed state is measured.
Only the buoyancy V acts on the immersed weight 11 when the melt 6 is at rest. In the melt 6 in which convection occurs, a load F caused by the flow of the melt 6 also acts. Therefore, when the surface tension acting on the wire 12 is G, the weight W ₁ of the probe immersed in the melt 6 is expressed by the following equation (1). W ₁ = W ₀ −V−G + F (1) Equation (1) is converted to equation (2), and becomes an equation for calculating the load F. F = W ₁ −W ₀ + V + G (2)

Here, the buoyancy V is calculated in advance from the volume of the weight 11, the density of the melt 6, and the like. Also, the surface tension G
Can also be obtained in advance from temperature dependent data of surface tension, temperature distribution of the melt 6 detected by a thermocouple installed in the melt 6, and the like. Therefore, V + G can be set as the constant term K, and equation (2) is converted to equation (3). F = W ₁ −W ₀ + K = ΔW + K (3) That is, from the weight difference ΔW between the weight W ₀ of the measurement element in the atmosphere and the weight W ₁ of the measurement _element in the immersion state, the melt 6 The load F acting on the probe due to the flow is obtained. Load F
Represents the flow state of the melt 6 at the measurement point where the weight 11 is located. Based on the magnitude of the load F, it is estimated whether an ascending flow or a descending flow occurs at the measurement point, and further, the flow rate of the ascending flow or the descending flow.

As the weight 11 of the tracing stylus, a spherical weight used in the conventional Archimedes method can be used. However, when the flat conical weight 11 is used as shown in FIG. 5, the load F caused by the flow of the melt 6 is received in a large area, so that the measurement accuracy is improved. Also,
As proposed by the present inventors in Japanese Patent Application No. 4-317900, it is also possible to use a tracing stylus with a double weight. The tracing stylus is incorporated in a single crystal pulling apparatus with the equipment configuration shown in FIG. 6, for example. The melt 6 is accommodated in a crucible 2 supported by a support 3 connected to a rotation motor 18 via a rotation shaft 17 so as to be able to rotate and move up and down.
A measuring element in which the weight 11 is suspended by the wire 12 is immersed in the melt 6 from above. The weight W ₁ of the immersed measuring element is measured by the weighing scale 13.

The weighing scale 13 is preferably arranged movably along the guide rail 14 so that the measuring element can move in the radial direction of the crucible 2. As a result, the weight W ₁ of the measuring element in the immersion state is measured at a plurality of measuring points in the radial direction of the crucible 2. A plurality of tracing styluses and guide rails 14 can be arranged as necessary. In order to control the temperature distribution of the melt 6 with high accuracy, the heater is divided into two upper and lower stages 4a and 4b. The weight W ₁ detected by the weigh scale 13 is input to the arithmetic and control unit 15. The buoyancy V and the surface tension G corresponding to the weight W ₀ and the melt temperature of the tracing stylus in the atmosphere are input to the arithmetic and control unit 15 in advance. Weight W ₁ from weighing scale 13
Is compared with the weight W ₀ by the arithmetic and control unit 15, and the equation (3)
The load F is calculated according to Since the flow state of the melt 6 at the place where the probe is immersed can be determined based on the calculation result, if a change is detected in the flow state, a control signal for suppressing the change is transmitted to the rotary winding mechanism 10 and the heater. 4a,
4b, output to the crucible rotation motor 14 and the like.

When the number of rotations of the crucible 2 increases, the melt 6
On the surface of, a centripetal flow component in which the melt flows toward the center of the crucible 2 becomes strong. Conversely, when the rotation speed of the single crystal 8 is increased, the centrifugal flow component in which the melt flows radially outward on the surface of the melt 6 increases. Therefore, by adjusting the rotation speed of the crucible 2 and / or the single crystal 8,
The flow state on the surface of the melt 6 is adjusted. Further, when the heater output increases, the heat convection inside the melt 6 becomes strong, and the upflow near the wall surface of the crucible 2 and the downflow near the center become strong. Conversely, when the heater output is reduced and the thermal gradient inside the melt 6 is reduced, the upward flow and the downward flow are suppressed.
By controlling the flow state of the melt 6 based on the rotation speed of the crucible 2, the rotation speed of the single crystal 8, the output of the heater 4, and the like, the single crystal 8 is pulled under a constant condition. Therefore, high quality single crystal 8 with improved quality stability
Is obtained. Further, since the pulling conditions are adjusted so as to cancel the influence of the amount of the melt 6 remaining in the crucible 2, the ratio of the melt 6 consumed as the single crystal 8 is also improved, and a good yield is obtained. Be the law. The correlation between the rotation speed of the crucible 2, the rotation speed of the single crystal 8, the output of the heater 4, and the flow state of the melt 6 changes depending on the scale of each facility, the type of the melt, and the like. Yes, it cannot be unconditionally determined.

[0013]

【Example】

Example 1 Growth of Si Single Crystal 40 kg of a polycrystalline Si raw material was placed in a crucible, completely melted by heating with a heater, and then maintained at a temperature of 1430 ° C. After holding the melt for 2 hours, the seed crystals were brought into contact with each other and pulling of the single crystal was started. At this time, the pulling speed was set to 1.0 mm / hour, and a Si single crystal having a diameter of 6 inches was grown. During the pulling, the load F caused by the flow of the melt was continuously measured using the probe shown in FIG. When a change in the load F exceeding a set value was detected, the crystal rotation speed and the heater output were controlled so as to cancel the change. Table 1
Indicates an adjustment amount of the crystal rotation speed and the heater output corresponding to the load variation ΔF at this time.

[Table 1]

The Si single crystal thus obtained while controlling the flow state of the melt has few dislocations and crystal defects,
It could be used as a substrate for a semiconductor device with a yield of 50% or more. On the other hand, the Si single crystal pulled from the melt whose flow state is not controlled has a large amount of dislocations, crystal defects, and the like introduced therein, and the ratio of the Si single crystal used as a substrate for a semiconductor device is 30% or less. .

Example 2 Growth of Ge Single Crystal 3 kg of a polycrystalline raw material of Ge was placed in a crucible, completely melted by heating with a heater, and kept at a temperature of 990 ° C. After holding the melt for 2 hours, the single crystal was pulled up while controlling the flow state of the melt as in Example 1. Table 2 shows the adjustment amounts of the crystal rotation speed and the heater output corresponding to the load fluctuation ΔF at this time.

[Table 2]

The obtained Ge single crystal had few dislocations and crystal defects, and could be used as a semiconductor device substrate with a yield of 6% or more. On the other hand, the Ge single crystal pulled from the melt whose flow state was not controlled had a large amount of dislocations, crystal defects, and the like introduced therein, and the proportion used as a substrate for a semiconductor device was 10% or less. In the above embodiment, a case where a single crystal is pulled from a melt of Si and Ge has been described as an example. However, the present invention is not limited to this, and is similarly applied to single crystal pulling using other melts. For example, S
i-Ge mixed melt, GaAs, ZnSe, ZnTe, S
Compound melts such as iS and GeS, metallic melts such as Fe, Ni and Cu, and organic melts such as anthracene are also available.
Similarly, a high-quality single crystal can be obtained by measuring the load F and controlling the pulling conditions so as to reduce the load fluctuation.

[0017]

As described above, in the present invention, the flow state of the melt is estimated from the load F acting on the probe, and the pulling condition is controlled so that the flow state is constant. Therefore, the single crystal is pulled under a constant condition, and a single crystal with excellent quality stability is obtained. Further, even if the amount of the melt remaining in the crucible decreases, the flow condition is maintained constant by controlling the heater output, the crucible rotation speed, the crystal rotation speed, etc., so that the melt consumed as a single crystal Ratio also increases.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating pulling of a single crystal by a conventional Czochralski method.

FIG. 2 is a graph showing the temperature dependence of the Si melt density.

FIG. 3 is a graph showing the temperature dependence of the Ge melt density.

FIG. 4 is a diagram illustrating convection of a melt.

FIG. 5 shows an example of a probe.

FIG. 6 is a diagram illustrating pulling of a single crystal according to the present invention.

[Explanation of symbols]

1: Closed container 2: Crucible 3: Support 4:
Heater 5: Insulation material 6: Melt 7: Seed crystal 8: Single crystal 9: Wire 10: Rotary winding mechanism 11: Bob 12: Wire 13: Weight scale 14: Guide rail 15: Operation control device 17: Rotating shaft 18 ： Rotary motor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Eiji Tokizaki 1-15-4 Tokodai, Tsukuba City, Ibaraki Prefecture Sky Heights B-202 (72) Inventor Kazutaka Terashima 206-3 Nakano, Ebina City, Kanagawa Prefecture (72) Inventor Shigeyuki Kimura 3-712 Takezono, Tsukuba City, Ibaraki Prefecture (56) References JP-A-50-26776 (JP, A) JP-A-2-97475 (JP, A) JP-A-3-60491 (JP, A)

Claims (5)

(57) [Claims] 1. A measuring _element whose weight W ₀ is previously measured in an atmosphere is immersed in a melt, and a change in the weight W ₁ of the measuring _{element in} the immersion state with respect to the weight W _{0 is applied} to the measuring element. A method for detecting a convection of a melt for pulling a single crystal, wherein a load F due to the flow of the melt acting on the melt is calculated, and a convection state of the melt is estimated from the load F. 2. A method for detecting a convection of a melt for pulling a single crystal, wherein the weight W _{1 according to} claim ₁ is measured at a plurality of measurement points in a vertical direction and / or a horizontal direction of the melt. 3. The rotation speed of a crucible, the rotation speed of a single crystal, the output of a heater, and the like are changed according to the change in the load F so that the load F according to claim 1 is maintained within a certain range. Single crystal pulling method. 4. A crucible arranged in a closed container for containing a melt, a support rotatably supporting the crucible, a heater for keeping the melt contained in the crucible at a high temperature,
A rotating winding mechanism suspended seed crystal, a measuring element which is immersed in the melt, a weighing scale for measuring the weight W ₁ of the submerged the measuring element, the measuring element measured by the weight meter the weight W ₁ as compared with the weight W ₀ of the measuring element in the atmosphere,
A calculation control mechanism for calculating a load F due to the flow of the melt acting on the measuring element and outputting a control signal to the support and the rotary winding mechanism; and The rotation speed of the crucible according to convection,
A single crystal pulling apparatus, wherein a rotation speed of the single crystal, an output of the heater, and the like are changed. 5. The measuring element according to claim 4, wherein the load F is detected at a plurality of measuring points in the vertical direction and / or in the melt.
Alternatively, a single crystal pulling apparatus provided so as to be movable in a horizontal direction.