JP2720274B2 - Single crystal pulling 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 stably pulling a high-quality Si single crystal from a melt in which introduction of minute defects and dislocations is suppressed.

[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.

[0003] 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 a high-quality semiconductor substrate, it is necessary to suppress dislocations, crystal defects, and the like introduced into the semiconductor single crystal. Further, in order to obtain a semiconductor device substrate with high productivity, it is necessary to pull a large-diameter single crystal.

[0004]

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, in a state where the physical properties are largely fluctuated, clusters, which are aggregates having different microstructures, coexist in the melt. When a single crystal is pulled up from this melt, the probability that micro defects or dislocations reflecting the non-uniformity of the melt structure are introduced into the crystal is increased. As a result, the yield for obtaining a single crystal of constant quality is reduced.

[0005] It is expected that this type of disadvantage will be eliminated by controlling the temperature, which has a significant effect on the melt structure, with high precision. In this regard, in a situation where the influence of temperature fluctuation on the melt structure is not specifically grasped, extremely high accuracy is required. However, excessively high precision requires a great deal of work and time to prepare the melt, and is not a practical solution. The present invention has been devised to solve such a problem, and by estimating the melt state based on the inflection point in the temperature change rate of the melt density, clusters having different microstructures are obtained. It is an object of the present invention to grow a high-quality single crystal at a high yield without introducing micro defects, dislocations, and the like caused by GaN.

[0006]

In order to achieve the object, the single crystal pulling method of the present invention obtains in advance the rate of temperature change of the melt density of a Si melt from which a single crystal is pulled,
The temperature t _{1 at which the} temperature change rate changes from large to small (≒ 1440)
° C.) to maintain the overall Si melt temperature below the temperature t ₁
It is characterized in that a single crystal is pulled from the Si melt maintained below.

[0007]

When a polycrystalline raw material is melted to prepare a Si melt, an irregular microstructure such as crystal anisotropy and interface state of the polycrystalline raw material is taken into the melt in an initial stage of the molten state. I have. In the conventional melt preparation, in order to remove this fine structure, a homogenization heating step of keeping the melt after melting for a predetermined time is adopted. However, in a state where the structure of the melt is not grasped quantitatively, it is necessary to perform the homogenization heating for a sufficient time, and it takes a long time to start pulling. The present inventors have investigated and studied the state of the melt from various viewpoints. In the process, it was found that the change in the melt structure was reflected in the temperature change rate of the melt density.

When the relationship between the temperature and the density of the melt prepared from polycrystalline Si was examined, the relationship shown in FIG. 2 was established between the two. That is, the temperature t ₁ (≒ 14
In the region up to 40 ° C.), the melt density is greatly reduced with the temperature rise. Temperature t ₁ to t ₂ (≒ 1530 ° C)
In the region up to, the rate of increase of the melt density becomes small. Further, in a region exceeding the temperature t _2, the increase rate of the melt density is increased again. The fact that the temperature change rate of the melt density changes in the region 〜 is presumed to be due to the formation of clusters having different microstructures in each of the region 〜.
Alternatively, it is presumed that a cluster having a fine structure different from that of the region is generated in the region, and is mixed with the cluster generated in the region or the region. Therefore, when the Si melt contained in the crucible is at a temperature that extends over a plurality of regions, there is a possibility that heterogeneous clusters may be taken into the Si single crystal being pulled.

For example, while the surface layer of the melt is maintained in a region suitable for pulling a single crystal, when the lower layer of the melt is at the temperature of the region, convection generated in the crucible causes different microstructures. Cluster rises to the liquid level,
It is expected that it will be incorporated into the Si single crystal being pulled. In this regard, in the conventional pulling, the emphasis has been placed on the temperature control in the vicinity of the surface layer of the Si melt, and few examples have been reported in detail regarding maintaining the Si melt at a predetermined temperature or lower including the lower layer. . Under such inference, the present inventors preliminarily set the temperature t for each Si melt for pulling a single crystal.
₁ and t ₂ were obtained, and the entire Si melt was held in a region at a temperature of t ₁ or lower. When a single crystal is pulled up from this Si melt, it is expected that the introduction of minute defects and dislocations due to the incorporation of clusters having different microstructures will be reduced. This was confirmed by the examples described later.

The temperature t _{1 at} which the temperature change rate of the melt density changes,
To determine t ₂ , it is assumed that the melt density is accurately measured. In this regard, it is preferable to measure the melt density using a liquid density measuring element developed by the present inventors (see Japanese Patent Application No. 4-317900). This liquid density probe is
It has the advantage that the melt density can be measured with high accuracy without being affected by surface tension. In fact, when the melt density was measured using this liquid density gauge, the inflection point shown in FIG. 2 was first clearly observed in the rate of temperature change of the melt density.

In the present invention, temperatures t ₁ and t _{2 at} which the rate of temperature change of the melt density changes are first determined for the melt raw material from which the single crystal is pulled. Then, as shown in FIG. 3, the melt raw material whose temperatures t ₁ and t ₂ are known is accommodated in the crucible 2,
While measuring the temperature of the melt 6 with the thermometers 11u and 11d,
A melt 6 is prepared. Temperature information of the melt 6 detected by the thermometers 11u and 11d is input to the control mechanism 12. The control mechanism 12 calculates a required heating current based on the input value, and outputs a control signal to each of the upper heater 4u and the lower heater 4d. When the temperatures of the melt 6 measured by the thermometers 11 u and 11 d are both lower than or equal to the temperature t ₁ , the seed crystal 7 is brought into contact with the liquid surface of the melt 6 and the pulling of the single crystal 8 is started. The pulled single crystal 8 does not take in defects caused by clusters, and is a product having a uniform crystal orientation.

[0012]

EXAMPLE The density of a melt prepared by dissolving polycrystalline Si had the relationship shown in FIG. 2 with temperature. That is, from the melting point (about 1420 ° C.) to the temperature t ₁ (≒ 1440)
The temperature change rate of the melt density in the region up to (° C.) is clearly different from the temperature change rate in the region above the temperature t ₁ . This difference suggests that heterogeneous clusters are generated in the region.

[0013] thermometer 11u, while the temperature both in the temperature t ₁ following melt 6 measured by 11d, it began pulling of the single crystal 8. At this time, the temperature fluctuation range of the melt 6 was 15 ° C. or less. The obtained single crystal is
As shown in Table 1, it was of high quality with few defects such as dislocations. Note that in Table 1, the temperature was partially changed to the temperature t.
A single crystal pulled from the melt 6 at a temperature higher than ₁ by about 20 ° C. at the maximum is shown as a comparative example. The temperature fluctuation was 60 ° C. at the maximum, and was obtained by processing the detection values by the thermometers 11 u and 11 d by the control mechanism 12.

[0014]

[Table 1]

[0015]

As described above, in the present invention, the temperature change rate of the melt density of the Si melt is determined in advance, and the temperature of the entire Si melt is reduced to a temperature t ₁ or less at which the temperature change rate changes. Is maintained, and the single crystal is pulled up from the Si melt in this state. As a result, there is no introduction of micro defects or dislocations presumed to be caused by the incorporation of clusters having different microstructures dispersed in the melt, and a high quality product can be obtained under stable conditions.

[Brief description of the drawings]

Fig. 1 Single crystal pulling by Czochralski method

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

FIG. 3 is a drawing device employed in the present invention.

[Explanation of symbols]

1: Closed container 2: Crucible 3: Support 4,
4u, 4d: heater 5: heat insulating material 6: melt 7: seed crystal 8: single crystal 9: wire 10: rotary winding mechanism 11u,
11d: thermometer 12: control mechanism

 ────────────────────────────────────────────────── ─── 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 Akira Nagashima 4-13-12 Kitamachi, Kichijoji, Musashino-shi, Tokyo (72) Inventor Shigeyuki Kimura 3-712 Takezono, Tsukuba-shi, Ibaraki (56) References JP-A-2-97475 (JP, A) JP-A-3 60491 (JP, A) JP-A-4-317494 (JP, A)

Claims (1)

(57) [Claims] 1. A temperature change rate of a melt density of a Si melt from which a single crystal is pulled is obtained in advance, and the temperature of the Si melt is lowered to a temperature not higher than a temperature t ₁ (≒ 1440 ° C.) at which the temperature change rate changes from large to small. A single crystal pulling method comprising pulling a single crystal from a Si melt maintained at the temperature t ₁ or lower while maintaining the whole.