JPH09235191A - Growth of single crystal and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for raising a single crystal little in crystal defects by inhibiting the generation of depressions in an area around the raised crystal to prevent the production of polycrystals without locally heating an interface between the solid and the liquid, and to provide a device therefor. SOLUTION: This method for raising a single crystal comprises lifting the single crystal from the melted liquid of a raw material by a liquid-sealed czochralski method. Therein, the improvement comprises immersing the tip of a cylinder having a larger inner diameter than the target diameter of the straight body portion of the raised crystal in a liquid sealing agent, rotating a crucible and the raised crystal mutually in reverse directions to prevent the generation of depressions on the interface between the solid and the liquid and simultaneously lifting the raised crystal with a lifting shaft. And the device is used for the method.

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 growing an oxide single crystal, a compound semiconductor single crystal, etc. by a liquid sealed Czochralski method.

[0002]

2. Description of the Related Art Generally, a single crystal bulk of GaAs or the like grows by the Czochralski method (CZ method) or the liquid-encapsulated Czochralski method (LEC method), but polycrystals are partially generated during the growth. There was a problem. FIG. 6 shows a conventional LE
It is a conceptual diagram of the apparatus which implements C method. In this device, a crucible 5 provided with a susceptor 4 is supported by a lower shaft 3 in the center of a high-pressure chamber 1, a raw material melt 6 and a liquid sealant 7 are contained in the crucible 5, and the crucible 5 is held by an upper shaft 2. The seed crystal 8 thus obtained is immersed in the raw material melt 6 to pull up the single crystal 9. A heater 10 is arranged around the raw material melt 6, a heater 11 is arranged around the single crystal 9, and a heat insulating material 12 is arranged inside the high-pressure chamber 1.

The cause of the above polycrystallization is, as shown in FIG. 7, that the shape of the solid-liquid interface between the grown crystal and the raw material melt is dented in the peripheral portion of the grown crystal and propagates perpendicularly to the solid-liquid interface. It is considered that dislocations accumulate in the peripheral portion and become polycrystalline. Therefore, in order to prevent this kind of polycrystallization, it is necessary to prevent depression of the solid-liquid interface peripheral portion of the grown crystal.

As a method for preventing depression of the solid-liquid interface by the LEC method, the power of the heater installed near the solid-liquid interface is increased as much as possible to locally heat the side surface of the grown crystal to dissipate heat from the crystal to the side. A method to suppress it has been proposed [HITACHI CAB
LE REVIEW No. 9 (1990) 55].

[0005]

However, the above method has the following problems. In order to locally heat the side surface of the crystal, it is necessary to shorten the heater length to some extent and apply a large amount of power. As a result, the current density flowing through the heater becomes very large, and the life of the heater becomes very short.

Since the heater is heated through the susceptor for supporting the crucible, which is made of carbon or the like, the heat is conducted in the susceptor so that the heat is uniformly distributed in the vertical direction. Therefore, essentially no local heating is possible. Further, since the liquid sealant B ₂ O ₃ hardly transmits radiant heat, it is impossible to effectively heat the vicinity of the most important growth interface.

Since not only the peripheral portion of the crystal but also the entire side surface of the crystal is heated to suppress the heat radiation to the side, the solid-liquid interface is largely convexed to the melt side, so that the crystal grows. Large residual strain remains in the formed crystal, and the in-plane uniformity of the characteristics of the wafer cut from the crystal deteriorates.

The liquid-encapsulated Czochralski method is usually used to grow a single crystal containing a volatile element, but the grown crystal pulled from the liquid encapsulant is a crystal in which the volatile element evaporates from its surface. Has the problem of being damaged,
The surface temperature of the liquid sealant could not be raised so high. As a result, the temperature gradient in the growth axis direction cannot be made too small (the temperature gradient in the growth of GaAs single crystal is usually about 100 ° C./cm), and large thermal stress is generated in the grown crystal, resulting in crystal defects (dislocations). ), And only crystals with a high residual strain were obtained.

In view of the above, the present invention solves the above problems and suppresses the depression of the solid-liquid interface peripheral portion of the grown crystal to prevent polycrystallization without relying on local heating of the solid-liquid interface. An object of the present invention is to provide a method for growing a single crystal with few crystal defects and an apparatus for the same.

[0010]

The present invention has succeeded in solving the above-mentioned problems by employing the following constitutions. (1) In a single crystal growth method of pulling a crystal from a raw material melt by the liquid-encapsulated Czochralski method, the tip of a cylindrical body having an inner diameter larger than the target diameter of the straight body part of the growing crystal is placed in the liquid sealant. A method for growing a single crystal, which comprises immersing and pulling a grown crystal with a pulling shaft while preventing depression of a solid-liquid interface.

(2) The method for growing a single crystal according to the above (1), wherein the rotation of the cylindrical body is stopped to pull up the grown crystal.

(3) The grown crystal is pulled while rotating the cylindrical body integrally with the pulling shaft.
(1) The method for growing a single crystal as described above.

(4) The method for growing a single crystal according to the above (1), wherein the growing crystal is pulled while rotating the cylindrical body at a rotation speed different from that of the pulling shaft and the crucible.

(5) Instead of the cylindrical body, a cylindrical body having the same cross-sectional shape as the crystal habit of the grown crystal, or a cylindrical body having an oval cross-section in the crystal growth for cutting the wafer in a direction not perpendicular to the growth axis The method for growing a single crystal according to any one of the above (1) to (4), characterized in that

(6) The method for growing a single crystal according to any one of the above (1) to (5), characterized in that the cylindrical body is heated.

(7) One of the above (1) to (6), characterized in that the upper end of the cylinder is closed and the vapor pressure of the volatile element forming the grown crystal is applied to the cylinder. The method for growing a single crystal according to.

(8) The inner diameter of the cylindrical body is 5 to 30 mm, preferably 5 to 20 mm from the target diameter of the straight body of the growing crystal.
A large one is used, the distance from the melt surface to the tip of the cylindrical body is 30 mm or less, preferably 10 mm or less, and the rotation speed of the crucible is 5 rpm or more, preferably 10 to 30 r.
pm, the grown crystal has a relative rotation speed with the cylindrical body of 0 to 5 rp
m, preferably 0 to 3 rpm, and the relative rotational speed of the cylindrical body with the crucible is 5 rpm or more, preferably 10 to 30
By rotating at rpm, the single crystal is pulled up while preventing depression of the solid-liquid interface (1) ~
The method for growing a single crystal according to any one of (7).

(9) Liquid sealing In a single crystal growing apparatus for pulling a crystal from a raw material melt by the Czochralski method, a cylindrical body having an inner diameter larger than the target diameter of the straight body portion of the growing crystal is liquid-sealed at its tip. Means for supporting so as to be immersed in the stopping agent, means for supporting the crucible containing the raw material melt so as to be rotatable up and down by the lower shaft, and means for supporting the seed crystal at the lower end of the upper shaft so as to be rotatable up and down, An apparatus for growing a single crystal, comprising means for adjusting the number of rotations and the ascending / descending speed of the vertical shaft and the cylindrical body in response to the change in the shape.

(10) The apparatus for growing a single crystal according to (9) above, wherein the cylindrical body is rotatably supported integrally with the pulling shaft.

(11) The apparatus for growing a single crystal according to (9) above, wherein the cylindrical body is rotatably supported independently of the vertical axis.

(12) The apparatus for growing a single crystal according to the above (9), characterized in that the cylindrical body is fixed to a stationary portion of the growth apparatus.

(13) Instead of the cylinder, a cylinder having the same cross-sectional shape as the crystal habit of the growing crystal, or a cylinder having an elliptical cross-section when growing a crystal for cutting a wafer in a direction not perpendicular to the growth axis. The apparatus for growing a single crystal according to any one of the above (9) to (12), characterized in that

(14) The apparatus for growing a single crystal according to any one of the above (9) to (13), characterized in that a heating means for the cylindrical body is additionally provided.

(15) A cylindrical body having a closed upper end is used as the cylindrical body, and a reservoir containing a volatile element constituting a growing crystal is provided, and the reservoir is connected to the cylindrical body in a ventilable manner,
The vapor pressure of the volatile element in the cylinder can be adjusted by adjusting the heater output of the reservoir.
(9) The single crystal growth apparatus as described in any one of (13).

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have found that natural convection of a raw material melt and rotation of a grown crystal when a single crystal is grown while rotating a crucible for growing a crystal by a conventional liquid sealed Czochralski method. When the forced convection accompanied by the flow was investigated, the flows of the raw material melt and the liquid sealant were due to the convection due to the vertical temperature gradient in the crucible (natural convection), the convection due to the rotation of the crucible, and the rotation of the grown crystal. Convection affects each other. The liquid sealant is closer to the rotation speed of the crucible as it is closer to the crucible, and is closer to the rotation speed of the growth crystal as it is closer to the growing crystal, but the crucible has a larger contact surface with the liquid sealant. Also, it is greatly affected by the rotation of the crucible. As a result, in the raw material melt, the rotation of the crucible and the rotation of the liquid sealant, which is strongly influenced by the rotation, have a greater effect than the rotation of the growing crystal, and thus the raw material melt rises near the crucible side wall as shown by the arrow in FIG. After that, natural convection that flows toward the grown crystal becomes dominant, and forced convection due to the rotation of the grown crystal is restricted below the solid-liquid interface, and the melt temperature near the outer periphery of the solid-liquid interface rises, causing solidification. It seems that the peripheral part of the liquid interface becomes concave.

Therefore, the present inventors have noticed that a liquid sealant such as B ₂ O ₃ has a large viscosity, and in the present invention,
As shown in FIG. 1, by immersing the lower end of the cylindrical body arranged around the grown crystal in the liquid sealant and fixing the cylindrical body to the immovable member of the growth apparatus or rotating integrally with the grown crystal,
By rotating independently of the growing crystal and crucible, and mitigating the degree to which the liquid sealant is affected by the rotation of the crucible, natural convection of the raw material melt in the vicinity of the solid-liquid interface is suppressed, and by the rotation of the growing crystal. It is intended to expand the range of forced convection near the solid-liquid interface, and as a result, prevent depression at the peripheral portion of the solid-liquid interface.

That is, in the present invention, the influence of the rotation of the crucible on the rotation of the liquid sealant is suppressed in order to weaken the natural convection near the surface of the raw material melt and expand the range of the forced convection due to the grown crystal. So that the inner diameter of the cylindrical body relative to the diameter of the straight body portion of the grown crystal (5 to 30 mm larger than the diameter of the straight body portion), the depth of the liquid sealant at the time of growing the straight body portion, the liquid sealing of the cylindrical body It is desirable to select the depth of immersion in the stopper and the direction and speed of rotation of the cylinder relative to the rotation of the crucible and the growing crystal.

Further, in the present invention, by heating the cylindrical body, it is possible to promote the heat retention of the liquid sealant and / or the pulling crystal in the cylindrical body, and suppress the heat radiation from the grown crystal to the side. Therefore, it is possible to enhance the effect of preventing depression at the peripheral portion of the solid-liquid interface.

Further, in the present invention, a cylindrical body having a closed upper end is used, which is connected to a reservoir for accommodating a volatile element constituting a growing crystal so as to be ventilated, and an output of a heater arranged around the reservoir is provided. By adjusting the vapor pressure of the volatile element in the cylindrical body, it is possible to prevent the escape of the volatile element from the growing crystal, high quality single crystal even if the temperature gradient of the solid-liquid interface is gentle. Can be obtained. It should be noted that an airtight container covering the entire crucible can be provided with an opening / closing mechanism to supply volatile element vapor, but in the present invention, it is possible to supply the volatile element vapor with a relatively simple structure in which the reservoir is attached to a cylindrical body. Adjustable.

The shape of the cylinder used in the present invention is generally circular in cross section, but in the growth of a crystal having a strong crystal habit, the same shape as the crystal habit or the substrate is cut out in a direction not perpendicular to the growth axis. In growing such a crystal, it is preferable to use a cylinder having an elliptical cross section.

The method of installing the cylindrical body is independent of the rotation of the crucible and the pull-up shaft and fixed and held by the immovable member of the apparatus, the method of rotating integrally with the pull-up shaft,
Also, there is a method of rotating the pulling shaft and the crucible independently of the rotation.

The method of independently fixing and holding is to fix the upper end of the cylindrical body to a stationary member such as a heat insulating material in the chamber, as shown in FIG. In order to keep the immersion depth of the cylinder constant, it is necessary to match the decreasing speed of the melt depth with the ascending speed of the lower shaft.

The method of rotating integrally with the pulling shaft is shown in FIG.
As shown in, the upper end of the cylinder is supported by the upper shaft, and it is necessary to provide a moving mechanism for lowering the cylinder as the growing crystal is pulled up. When the cylinder is rotated together with the crystal, the effect of forced convection by the cylinder is greatest.

The method of rotating the pulling shaft and the crucible independently of each other is to rotatably support the cylindrical body independently of the crucible and the growing crystal. By doing so, desired convection can be obtained. The cylindrical body of the present invention can be made of carbon, pBN, quartz or the like.

[0035]

【Example】

Example 1 A GaAs single crystal was grown by the LEC method using the growth apparatus shown in FIG. 3 in which a cylindrical body was fixed to a heat insulating material. The target diameter of the straight body part of the grown crystal was 110 mm, the inner diameter of the cylinder was 120 mm, and the thickness of the cylinder was 1 mm. The cylinder made of pBN was used. 800 g of ₂ O ₃ was added, and the thickness of the liquid sealant B ₂ O ₃ during the growth of the straight body was about 23 mm.
Then, the number of revolutions of the crucible at the time of growing the straight body portion was 10 rpm, the number of revolutions of the seed crystal was 2 rpm, and the pulling rate was 5 mm / H. The tip of the cylindrical body was located 5 mm above the raw material melt.

The obtained crystal was a single crystal having a length of 210 mm and an average diameter of 108 mm. In order to investigate the shape of the solid-liquid interface of the single crystal, it was sliced along the growth axis, HF with a concentration of 50%, CrO ₃ 100 g, and water 520 cc.
When a wafer is immersed in an etching solution consisting of, and etched for 10 minutes while irradiating with light, and crystal growth fringes are observed, it is almost horizontal at the solid-liquid interface periphery as shown in FIG.
It can be seen that the depression in the peripheral portion was substantially suppressed. Further, when a (100) wafer was cut out from the obtained crystal and etched with molten KOH to examine the in-plane distribution of dislocation density, it was as shown by the ● mark in FIG. 11, and the average dislocation density was 58800 cm ^{−. Was 2} .

Example 2 A GaAs single crystal was grown in the same manner as in Example 1 except that the cylindrical body was rotated at the same rotation speed as the grown crystal as shown in FIG. The upper shaft with a non-circular cross section was set through a hole of the same shape as the upper shaft cross-section opened in the upper part of the cylinder so that the rotation of the upper shaft could be transmitted to the cylinder. Further, the cylindrical body was supported by a heat insulating material so as not to move up and down. The positional relationship between the tip of the cylinder and the surface of the raw material melt was kept constant by raising the lower axis at the same rate as the rate of decrease in the depth of the raw material melt accompanying the growth of crystals. The obtained crystal was a single crystal having a length of 200 mm and an average diameter of 110 mm. When the growth stripes were observed in the same manner as in Example 1, as shown in FIG. 9, a tendency of convexity was recognized in the peripheral portion of the solid-liquid interface.

Comparative Example 1 A GaAs single crystal was grown in the same manner as in Example 1 except that the cylindrical body was omitted. The obtained crystal had a length of 200 mm and a maximum diameter of 111 mm. When the growth stripes were observed in the same manner as in Example 1, as shown in FIG. 10, a prominent tendency to be recessed was observed in the peripheral portion of the solid-liquid interface, and polycrystallization was observed from the arrow portion.

[Comparative Example 2] In Example 1, when the inner diameter of the cylindrical body used was the target diameter of the growing crystal + 5 mm, the diameter of the crystal fluctuated and the crystal grew to the full extent of the cylindrical body and was caught by the cylindrical body. I couldn't continue. The inner diameter of the cylinder is the target diameter of the growing crystal + 40m
When m of m was used, depression was observed at the periphery of the solid-liquid interface, and polycrystal was generated.

Further, when the cylindrical body was fixed to the heat insulating material and the crucible was rotated at 5 rpm and the crystal was rotated at 2 rpm, the pitting at the peripheral portion of the solid-liquid interface was slightly improved, but the pitting still showed a tendency. . Furthermore, when the cylindrical body was fixed to the heat insulating material, the crucible was rotated at 10 rpm, and the crystal was rotated at 5 rpm, the pitting at the peripheral portion of the solid-liquid interface was slightly improved, but the pitting still showed a tendency.

Example 3 A GaA was prepared in the same manner as in Example 1 except that a cylindrical body having a closed upper end as shown in FIG. 5 was used, and an As reservoir was connected to the cylinder so that As vapor was loaded.
s single crystal was grown. The temperature gradient in the growth axis direction in B ₂ O ₃ before the growth was about 100 ° C./cm in Example 1, whereas the growth was performed under As vapor pressure.
In Example 3, it could be suppressed to as low as about 30 ° C./cm.

The obtained crystal was a single crystal having a length of 215 mm and an average diameter of 107 mm. Generally, when a GaAs single crystal was grown in a state where the temperature gradient was small, there was As loss, but the GaAs single crystal obtained here had a metallic luster on the surface, and no As evaporation was observed. Since the temperature gradient was small, the amount of protrusion in the central portion of the solid-liquid interface was small, but the peripheral portion of the solid-liquid interface was almost the same as in Example 1. A (100) wafer was cut out from the obtained crystal and etched with molten KOH, and the in-plane distribution of dislocation density was examined. The result is as shown by ▲ in Fig. 11, and the average dislocation density is 7750 cm ^-2 . there were.

Example 4 In Example 1, a PBN cylindrical body coated with a carbon heater was used to heat the cylindrical body, and other conditions were the same as in Example 1 for growth. It was As a result, the depression in the peripheral portion of the solid-liquid interface is further improved as compared with the first embodiment, as shown in FIG.
Similar to the above, the tendency of convexity was recognized. This effect is considered to be due to the fact that the heating of the cylindrical body suppressed the heat radiation from the crystal to the side.

[0044]

According to the present invention, by adopting the above-mentioned structure, it is possible to prevent depression of the peripheral portion of the solid-liquid interface of the growing crystal and prevent polycrystallization due to the accumulation of dislocations. .

[Brief description of drawings]

FIG. 1 is a diagram illustrating a convection state of a raw material melt when a lower end of a cylindrical body is immersed in a liquid sealant in the present invention.

FIG. 2 is a diagram illustrating a convection state of a raw material melt in a conventional LEC method.

FIG. 3 is an explanatory diagram for fixing the cylindrical body of the present invention to a heat insulating material.

FIG. 4 is an explanatory diagram of a case where a cylindrical body of the present invention is supported by an upper shaft.

FIG. 5 is an explanatory diagram of a crystal growth apparatus in which a group V source material reservoir is connected to the cylindrical body of the present invention.

FIG. 6 is a conceptual diagram of an apparatus for performing a conventional LEC method.

FIG. 7 is a diagram for explaining a state of polycrystallization at a conventional solid-liquid interface.

FIG. 8 is a schematic diagram showing growth fringes of the crystal obtained in Example 1.

FIG. 9 is a schematic view showing growth fringes of the crystal obtained in Example 2.

FIG. 10 is a schematic diagram showing growth fringes of a crystal obtained in Comparative Example 1 (conventional LEC method).

FIG. 11: Cut out from the crystals obtained in Examples 3, 4, and 5.
3 is a graph showing in-plane distribution of dislocation density of a (100) wafer.

Claims (14)

[Claims] 1. A method for growing a single crystal in which a crystal is pulled from a raw material melt by the liquid-encapsulated Czochralski method, wherein the tip of a cylindrical body having an inner diameter larger than the target diameter of the straight body of the grown crystal is sealed with a liquid sealant. A method for growing a single crystal, which is characterized in that the grown crystal is pulled up by a pulling shaft while being immersed in the solution and preventing the solid-liquid interface from being dented. 2. The method for growing a single crystal according to claim 1, wherein the cylinder is fixed and the grown crystal is pulled up. 3. The grown crystal is pulled while rotating the cylindrical body integrally with the pulling shaft.
The method for growing a single crystal described. 4. The method for growing a single crystal according to claim 1, wherein the growing crystal is pulled while rotating the cylindrical body at a rotation speed different from that of the pulling shaft and the crucible. 5. Instead of the cylinder, a cylinder having the same cross-sectional shape as the crystal habit of the grown crystal, or a cylinder having an elliptical cross-section when growing a crystal for cutting a wafer in a direction not perpendicular to the growth axis is used. The method for growing a single crystal according to any one of claims 1 to 4, which is used. 6. The method for growing a single crystal according to claim 1, wherein the cylinder is heated. 7. The unit according to claim 1, wherein an upper end of the cylinder is closed and a vapor pressure of a volatile element forming a growing crystal is applied to the cylinder. Crystal growth method. 8. A single crystal growing apparatus for pulling a crystal from a raw material melt by a liquid sealed Czochralski method, wherein a tip of a cylindrical body having a larger inner diameter than a target diameter of a straight body portion of the grown crystal is liquid sealed. Means for supporting so as to be immersed in the agent, means for supporting the crucible containing the raw material melt so as to be rotatable up and down with a lower shaft, means for supporting the seed crystal at the lower end of the upper shaft so as to be rotatable up and down, and An apparatus for growing a single crystal, which is provided with means for adjusting the number of rotations of the vertical shaft and the cylindrical body and the ascending / descending speed thereof in response to changes in the shape. 9. The apparatus for growing a single crystal according to claim 8, wherein the cylindrical body is fixed to a stationary portion of the growth apparatus. 10. An apparatus for growing a single crystal according to claim 8, further comprising means for supporting the cylindrical body so as to be rotatable integrally with the pulling shaft. 11. The single crystal growth apparatus according to claim 8, wherein the cylindrical body is rotatably supported independently of the vertical axis. 12. Instead of the cylinder, a cylinder having the same cross-sectional shape as the crystal habit of the grown crystal, or a cylinder having an elliptical cross-section for crystal growth for cutting a wafer in a direction not perpendicular to the growth axis is used. The single crystal growth apparatus according to any one of claims 8 to 11, which is used. 13. The apparatus for growing a single crystal according to claim 8, further comprising heating means for the cylindrical body. 14. A cylindrical body having a closed upper end is used as the cylindrical body, a reservoir containing a volatile element constituting a growing crystal is provided, and the reservoir is connected to the cylindrical body in a ventilable manner.
13. The single crystal growth apparatus according to claim 8, wherein the heater output of the reservoir is adjusted to adjust the vapor pressure of the volatile element in the cylinder.