JP5013379B2 - Crystal growth equipment - Google Patents

Description

  The present invention relates to a crystal growth apparatus used in a flux method in which a group III nitride compound semiconductor is crystal-grown using a flux.

The group III nitride compound semiconductor flux method is a method in which sodium (Na) is used as a flux and a nitrogen source is introduced into a dissolved sodium / gallium solution to grow a gallium nitride crystal. A GaN single crystal can be grown at a relatively low temperature of 600 ° C. to 900 ° C. under a nitrogen (N ₂ ) pressure of about 5 MPa.

Further, as can be seen from the conventional techniques disclosed in the following Patent Documents 1 to 4, the conventional manufacturing method for growing a group III nitride compound semiconductor crystal by a flux method usually involves a seed crystal. For example, a template substrate in which a buffer layer is formed on a sapphire substrate and a group III nitride compound semiconductor is vapor-phase grown on the buffer layer, or a GaN single crystal free-standing substrate is used.
As a method for stirring the sodium / gallium solution under such a high temperature and high pressure, as shown in Patent Documents 5 and 6, etc., the rotation of the high pressure vessel in which the crucible containing the sodium / gallium solution is arranged, or the shaking of the external vessel is performed. The movement is known.

Japanese Patent Laid-Open No. 11-060394 JP 2001-058900 A JP 2001-064097 A JP 2004-292286 A WO2004 / 083498 WO2005 / 080648

The present inventors consider that an advanced solution stirring technique is necessary in order to obtain a high-quality group III nitride compound semiconductor crystal having good crystallinity, and a new sodium / gallium solution stirring method has been proposed. developed.
That is, an object of the present invention is to provide a crystal growth apparatus capable of obtaining a high-quality group III nitride compound semiconductor crystal having good crystallinity.

The invention according to claim 1 is a crystal growth apparatus using a group III nitride compound semiconductor flux method using a high-pressure vessel incorporating a reaction vessel or an oscillation device of an external vessel further incorporating the reaction vessel. The high pressure vessel or the external vessel incorporating the same can be held by a plurality of support points, and have a plurality of means for individually moving the plurality of support points up and down. It is characterized by causing the change to occur continuously.
In the invention according to claim 2, the plurality of support points are four, and the four means for moving the four support points up and down respectively move up and down in conjunction with a numerically controllable servo motor. And a ball screw.
The invention according to claim 3 is characterized in that the direction of inclination of the reference surface is rotated while the normal direction of the reference surface provided in the reaction vessel is maintained at a constant angle with respect to the vertical direction.
The invention according to claim 4 is characterized in that the inclination direction of the reference surface is rotated while the normal direction of the reference surface provided in the reaction vessel is maintained at a constant angle with respect to the vertical direction.

The present invention provides a device capable of swinging a pressure vessel of 1 ton or more safely, smoothly and freely. Here, “free” means not only rotational movement such as rotation and reversal, but also rotation that repeats reversal around the horizontal rotation axis, and more complicated movement. By swinging with such an apparatus, the flux in the crucible for crystal growth of the group III nitride compound semiconductor can be sufficiently stirred, and macro defects of the grown crystal, for example, a solution in the crystal As a result, the film thickness distribution and the uniformity of electrical characteristics due to doping are greatly improved.
Hereinafter, “a desired change in the tilted state is continuously generated in the reaction vessel” in the present invention will be described with reference to FIG. 1 and mathematical expressions.
A reference surface that is swung together with the reaction vessel and is fixed to the structure is set so as to include a point that does not move during the rocking of the supported structure (a fixed point). The n support points are arranged on the circumference of the radius r centered on the fixed point when the reference plane is horizontal. One of the n support points is set as a reference support point, and the other support points are indicated by an angle ψ _n between a line segment connecting the fixed support point and the fixed point and a line segment connecting the reference support point and the fixed point. The angle ψ ₁ of the reference support point is ψ ₁ = 0. Assuming that the angle between the normal vector of the reference plane and the vertical upward vector is θ, when the vertical movement of −rsinθcos (ωt−ψ _n ) is applied to each support point, the normal direction of the reference plane is In this way, the vehicle rotates around the vertical direction while maintaining the angle θ. That is, the reference plane is rotated while changing the inclination direction φ = ωt while maintaining the inclination angle θ.

This can be described more precisely as follows. Reference is now made to FIG.
The center of gravity of the structure is assumed to be a fixed point, and the origin O is set there. O-xyz is used as a fixed coordinate system fixed outside the floor or the like, and O-xyz is used as a coordinate system fixed to the structure that moves with the structure. Take x'y'z '. For simplicity, the reference plane is a unit disk surrounded by unit circles, the unit circle in the xy plane of the fixed coordinate system in the horizontal state is C0, and the unit circle in the x'y 'plane of the coordinate system that moves with the structure Is C0 ′.
Considering a point P (cos φ, sin φ, 0) on the unit circle C0, a plane including the z axis and the point P in the fixed coordinate system is referred to as a φ plane. It is assumed that the z axis of the fixed coordinate system and the z ′ axis of the coordinate system moving with the structure are both in the φ plane and form an angle θ. The unit vector of the z ′ axis is (sin θ cos φ, sin θ sin φ, cos θ) in the fixed coordinate system. At this time, a point P ′ where the angle POP ′ is θ can be considered on the circumference of the unit circle C0 ′. At this time, it can be seen that the unit circle C0 ′ and the z ′ axis are in a relationship in which the unit circle C0 and the z axis which is a normal line are inclined by θ in the φ plane.
The coordinates of P ′ are (cos θ cos φ, cos θ sin φ, −sin θ) in the fixed coordinate system.
Now, when θ is fixed and φ is changed, P ′ moves around the circle C1 having a radius cos θ parallel to the xy plane with (0, 0, −sin θ) as the center. The unit circle C0 ′ and the circle C1 have a common tangent at the point P ′.
Next, on the circumference of the unit circle C0 ′, the coordinates (x, y, z) in the fixed coordinate system of the points that form an angle of −φ with the line segment OP ′ are obtained. An arbitrary point (x, y, z) of the unit circle C0 ′ satisfies the relationship in which the inner product of the spherical equation with the radius 1 and the vector (x, y, z) and the unit vector of the z ′ axis is 0. . The inner product of the vector (x, y, z) and the vector OP ′ is cos φ. These conditions are shown as follows.

When this is solved, the coordinates (x, y, z) are obtained as follows.

  A vector (a point on the circumference of the unit circle C0 ′) represented by the expression (2) is x ′ of the unit circle C0 ′ corresponding to the unit vector (1, 0, 0) in the x-axis direction of the unit circle C0. This is a display of the unit vector in the axial direction in a fixed coordinate system.

Exactly in the same manner, the coordinates (x, y, z) in the fixed coordinate system of the point forming an angle of π / 2−φ with the line segment OP ′ are obtained on the circumference of the unit circle C0 ′. This condition is shown as follows.

When this is solved, the coordinates (x, y, z) are obtained as follows.

  The vector (point on the circumference of the unit circle C0 ′) represented by the equation (4) is y ′ of the unit circle C0 ′ corresponding to the unit vector (0, 1, 0) in the y-axis direction of the unit circle C0. This is a display of the unit vector in the axial direction in a fixed coordinate system.

As described above, the unit vector in the x′-axis direction of Ox′y′z ′ as a coordinate system that moves together with the structure changes in the y component when displayed in the fixed coordinate system O-xyz. Is not fixed in the zx plane. The x component also varies. Similarly, the unit vector in the y′-axis direction of Ox′y′z ′ as a coordinate system that moves together with the structure changes in the x component when displayed in the fixed coordinate system O-xyz. It is not fixed in the yz plane. The y component also varies.
The end point of the unit vector in the x′-axis direction is a radius with a radius of 1 centered on the origin O and a straight line passing through the coordinates ((1 + cos θ) / 2, 0, 0) and parallel to the z-axis. Draws the figure of the Arabic numeral 8, which is the line of intersection with the (1-cos θ) / 2 cylindrical surface. The end point of the unit vector in the y′-axis direction is exactly the same except that the central axis passes through the coordinates (0, (1 + cos θ) / 2, 0).
The same applies when the support point for supporting the reference surface is (-1, 0, sin θ cos ωt), (0, -1, sin θ sin ωt). The case where the above four points are used as support points is an example of four-point support.
The same is true if the support point is on a unit circle by simple consideration.
If φ is replaced with ωt−ψ _n , the motion at each support point of the reference plane can be uniformly described.
On the other hand, the z-direction component of the vertical motion is completely coincident with −r sin θ cos (ωt−ψ _n ) at the radius r already described.

  Thus, when the support point that supports the reference plane moves, for example, at (1,0, −sin θ cos ωt) or (0, 1, −sin θ sin ωt) of the O-xyz coordinates, the support point is not between the structure and the structure. , Xy coordinates are different. For this reason, in order to drive as an apparatus, a play or a universal joint is needed in order to eliminate these differences.

The oscillating device of the present invention can change the tilting direction (φ plane in FIG. 1) of the high-pressure vessel or the outer vessel supporting the high-pressure vessel, for example, via a ball screw at a very low speed, for example, using a servo motor. . For this reason, it is possible to provide a crystal growth apparatus having a high stirring effect while stirring at a very low speed.
That is, for example, even a pressure vessel of 1 ton or more can stabilize the tilt angle, stabilize the height of the center of gravity, and perform synchronous control of the four servo motors.
Ball screws are available that can respond to the vertical movement of heavy objects. By operating four servomotors in synchronization with numerical control, smooth and continuous speed changes are achieved. Smooth rotation or rotation can be realized. For example, when the same operation is performed by using a hydraulic piston instead of the ball screw, it is difficult to perform synchronous control of the four support points, resulting in rattling.
The direction of inclination (φ surface in FIG. 1) may be rotated in one direction, or may be a rotation that reverses the direction of rotation every one or several weeks.

Explanatory drawing of the rotation which changes inclination direction (phi) used by this invention, maintaining inclination-angle (theta). The top view and front view which mainly show the structure of the rocking | fluctuation apparatus of the crystal growth apparatus 100 which concerns on one specific Example of this invention. The front view which shows two states of operation | movement of the rocking | fluctuation apparatus of the crystal growth apparatus 100. FIG.

The present invention includes a plurality of servo motors that can be numerically controlled, a ball screw that is linked to the drive shaft of each servo motor, and a high-pressure vessel or a built-in high-pressure vessel in any part that moves up and down by the ball screw. To the external container itself, or to a base that holds any of them. In the flux growth of the group III nitride compound semiconductor, since the reaction is performed at a high temperature and high pressure, the weight of the entire structure to be supported, such as the high pressure vessel, is about 1 ton. For this reason, sufficient strength is also required for the fixed portion of the servo motor.
This fixing portion may be assembled in a frame shape by combining, for example, an I-shaped beam.
For example, as an actual device, the outer frame is 1700 × 1700 × 2800 mm, the pressure vessel is made of SUS having a diameter of 700 mm and a height of 1300 mm, and the weight is 1 ton. Ball screw rod stroke is 10cm to 1m, rod moving speed is up to 150mm / sec, tilt angle is up to 20 degrees, 4 servomotors are synchronized, and rod position and moving speed are controlled smoothly The program control may be performed by one numerical control device.
Ideally, the joint has a joint with three degrees of freedom of rotation, but it is difficult because it costs as much as 1 ton. Therefore, it is preferable to use a bolt receiver having two joints having one degree of freedom of rotation each at the upper and lower ends of the link and having an inner diameter larger than the bolt diameter. At this time, for example, a copper bush may be provided on the outer periphery of the bolt to prevent seizure. This prevents sticking, eliminates abnormal noise, and enables smooth rocking.
In addition, it is preferable to provide X and Y degrees of freedom between the ball screw and the servo motor.

  In the practice of the present invention, the flux may be one or more elements selected from alkali metals and alkaline earth metals. Examples of the alkali metal include sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Alkaline earth metals are strontium (Sr), barium (Ba), and radium (Ra). These may be used alone or in combination of two or more.

The group III element to be dissolved is one or more of gallium (Ga), aluminum (Al), and indium (In). Of these, gallium is preferred. The group III element nitride semiconductor to be grown is preferably a gallium nitride (GaN) single crystal. However, binary, ternary, and quaternary Group III elements having an arbitrary composition ratio represented by the general formula Al _x Ga _y In _1-xy N (where x, y, and x + y are each 0 to 1) It may be a nitride single crystal. Further, a part of the group III element which is a constituent element of the group III element nitride semiconductor Al _x Ga _y In _1-xy N is substituted with B and Tl, and / or a part of the composition of the group V element is P. , As, Sb, and Bi may be substituted.

In carrying out the present invention, in order to obtain an n-type group III nitride compound semiconductor, it is preferable to further dissolve germanium (Ge) in the solution. The molar ratio of germanium to gallium is 0.05 mol% or more and 0.5 mol% or less. In this case, an n-type group III nitride system having a resistivity of 0.001 Ω · cm or more and 0.1 Ω · cm or less and an electron concentration of 1 × 10 ¹⁷ / cm ³ or more and 5 × 10 ¹⁹ / cm ³ or less. A compound semiconductor can be obtained.

In the case of dissolving germanium (Ge), it is preferable to further dissolve carbon in the solution. By setting the molar ratio of carbon in the solution to 0.1 mol% or more and 3.0 mol% or less, germanium can be favorably incorporated as a donor into the group III nitride compound semiconductor, and the resistivity is 0. An n-type group III nitride compound semiconductor having a density of 0.001 Ω · cm or more and 0.1 Ω · cm or less and an electron concentration of 1 × 10 ¹⁷ / cm ³ or more and 5 × 10 ¹⁹ / cm ³ or less can be obtained. In particular, at least one component of the flux is sodium, and the molar ratio of carbon to sodium in the solution is 0.1 mol% or more and 3.0 mol% or less, so that germanium as a donor to a group III nitride compound semiconductor N-type having a resistivity of 0.001 Ω · cm or more and 0.1 Ω · cm or less, and an electron concentration of 1 × 10 ¹⁷ / cm ³ or more and 5 × 10 ¹⁹ / cm ³ or less. A group III nitride compound semiconductor can be obtained.

The reaction temperature between the group III element and nitrogen in the flux is more preferably 500 ° C. or more and 1100 ° C. or less, and more preferably about 850 ° C. to 900 ° C. Further, the atmospheric pressure of the gas containing nitrogen is preferably 0.1 MPa or more and 6 MPa or less, and more preferably 3.5 MPa or more and 4.5 MPa or less. In the production method of the present invention, the gas containing nitrogen (N) is, for example, nitrogen (N ₂ ) gas, ammonia (NH ₃ ) gas, etc., and these may be mixed, and the mixing ratio is not limited. In particular, use of ammonia gas is preferable because the reaction pressure can be reduced. The nitrogen gas used may be in a plasma state. In addition, when carbon and germanium are added, the pressure during the growth of the semiconductor crystal is higher than the pressure at which the impurity-free group III nitride compound semiconductor can be grown on the seed crystal when carbon and germanium are not added. It is desirable to make it high in the range of 0.01 MPa or more and 0.2 MPa or less. Under these conditions, germanium is efficiently incorporated into the group III nitride compound semiconductor to be grown, the resistivity is 0.001 Ω · cm or more and 0.1 Ω · cm or less, and the electron concentration is 1 × 10 ¹⁷ / cm ^3. As described above, an n-type group III nitride compound semiconductor of 5 × 10 ¹⁹ / cm ³ or less can be obtained.

  In addition, as the seed crystal, a substrate (a heterogeneous substrate) made of a material different from that of the group III nitride compound semiconductor can be used. Further, a gallium nitride (GaN) single crystal was grown on a substrate (a heterogeneous substrate) made of a material different from the group III nitride compound semiconductor by, for example, the MOVPE method, the MBE method, the HVPE method, the LPE method, A so-called template substrate can also be used. Alternatively, a free-standing substrate made of gallium nitride (GaN) single crystal grown separately can be used. As a method for manufacturing a free-standing substrate, a flux method, HVPE method, MOVPE method, MBE method, LPE method, laser lift-off method, lateral growth method, and the like are effective. When using a seed crystal as a self-supporting substrate, it is desirable that the thickness of the substrate be 300 μm or more. The thickness of the substrate is more preferably 400 μm or more, and still more preferably 400 μm or more and 600 μm or less. In addition, when the seed crystal is a template substrate or a self-supporting substrate, the size and thickness of the substrate may be arbitrary, but considering industrial practicality, a circular substrate having a diameter of about 45 mm or about 27 mm square Or a square of about 12 mm square is more desirable. Further, the lower the dislocation density of these seed crystals, the better.

  Further, the Miller index of the crystal growth surface of the seed crystal (including the seed substrate) is arbitrary, but if a nonpolar surface such as a-plane, m-plane, and r-plane is used, a nonpolar group III nitride compound semiconductor is used. Can be obtained, piezoelectric distortion can be eliminated, and characteristics as a semiconductor element can be improved. When a nonpolar surface is used for the seed crystal, it is desirable to add strontium (Sr) to the flux. When sodium is used for the flux, the amount of strontium (Sr) added to sodium is preferably 0.001 mol% or more and 0.1 mol% or less. By adding strontium, a nonpolar plane which is a crystal growth plane parallel to the main surface of the growth substrate of the group III nitride compound semiconductor can be flattened. Of course, the crystal growth surface of the seed crystal may be the c-plane if a group III nitride compound semiconductor having the c-plane as the main surface is obtained.

To alleviate or prevent the seed crystal (group III nitride compound semiconductor crystal) that is part of the base substrate from melting in the flux before the start of the target crystal growth based on the flux method For example, nitrides such as Ca ₃ N ₂ , Li ₃ N, NaN ₃ , BN, Si ₃ N ₄ , and InN may be included in the flux in advance. By containing these nitrides in the flux, the concentration of nitrogen in the flux increases, so the melting of the seed crystal into the flux before the start of the desired crystal growth is prevented or alleviated. It becomes possible. The ratio of these nitrides in the flux is, for example, 0.0001 mol% to 99 mol%, preferably 0.001 mol% to 50 mol%, and more preferably 0.005 mol% to 5 mol%.

It is desirable that the temperature of the reaction chamber of the crystal growth apparatus when performing crystal growth according to the flux method can be arbitrarily controlled to rise and fall to about 1000 ° C. Further, it is desirable that the pressure in the reaction chamber can be arbitrarily controlled to increase or decrease to about 100 atm (about 1.0 × 10 ⁷ Pa). In addition, the electric furnace, stainless steel container (reaction container), raw material gas tank, and piping of these crystal growth apparatuses are made of a material having high heat resistance and high pressure resistance such as stainless steel (SUS) material or alumina material. It is desirable to form. As a container requiring pressure resistance such as a high-pressure container, a high-strength steel subjected to chrome plating or the like can be used in order to reduce the weight.

  For the same reason, the crucible is required to have high heat resistance and alkali resistance. For example, it is desirable to form from metal such as tantalum (Ta), tungsten (W), molybdenum (Mo), alumina, sapphire, or pyrolytic boron nitride (PBN), ceramics, or the like.

The rocking means of the present invention provides a stirring action for the flux, so that the flux can be supplied more uniformly on the crystal growth surface. Further, the number of swings in the case of the swing depends on the swing angle, but for example, 10 times / minute or less is sufficient. The swing angle may be, for example, 2 degrees or more and 30 degrees or less, and may be 5 degrees or more and 20 degrees or less.
If a heating means is used, a thermal gradient is generated in the flux, and the flux causes thermal convection, which also helps stirring.

Before crystal growth of the group III nitride compound semiconductor crystal, hydrogen (H ₂ ) gas, nitrogen (N ₂ ) gas, ammonia (NH ₃ ) gas, rare gas (He, Ne, Ar, Kr, Xe) Or Rn) or a mixed gas obtained by mixing two or more kinds of these gases at an arbitrary mixing ratio, using a cleaning gas at a temperature of 900 ° C. or higher and 1100 ° C. or lower and taking a time of 1 minute or longer, It is desirable to clean the crystal growth surface of the seed crystal. However, it is more preferable that the time for the cleaning process is 2 minutes or more and 10 minutes or less.

Depending on the method for producing a group III nitride compound semiconductor crystal, it is desirable that the dislocation density on the surface is 1 × 10 ⁵ / cm ² or less and the maximum diameter is 1 cm or more. The lower the dislocation density, the better, and the larger the maximum diameter, the better. In the present invention, a dislocation density of 10 ² / cm ² or more and 10 ⁵ / cm ² or less can be realized in an n-type group III nitride compound semiconductor to which germanium is added.

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

FIG. A is a plan view of a crystal growth apparatus 100 according to a specific embodiment of the present invention, FIG. B is a front view thereof. FIG. A and FIG. In B, the structure of the crystal growth apparatus 100 as an oscillation device will be mainly described.
FIG. Actuators MA1, MA2, MA3, and MA4 each having a servo motor are arranged at the four corners of the upper rectangular frame 101 of the frame-shaped housing portion 10 as shown in FIG. FIG. In the plan view of A, the lid portion 21 of the outer container 20 can be seen. Let O be the fixed point of the axisymmetric outer container 20 and consider the reference plane C0. The outer periphery of the reference plane C0 passes through the rotation axes of actuators MA1, MA2, MA3 and MA4 having servo motors.

FIG. As shown in the front view of B, the upper rectangular frame 101, the lower rectangular frame 102, and the ridge frame 103 of the frame-shaped housing unit 10 are arranged in a square shape.
In the actuator MA1 having a servo motor, a support shaft 61 fixed to the base 60 is vertically moved via a shaft 31, a universal joint portion 411, a joint 51, and a universal joint portion 412 for moving up and down via a ball screw. It is possible to exercise. At this time, since the universal joint portion 411, the joint 51, and the universal joint portion 412 exist, the universal joint portion 412 (the upper end of the support shaft 61) whose relative position does not change from the base 60 is viewed from the universal joint portion 411. , The degrees of freedom of angles in all directions in the xyz directions are guaranteed.
Exactly the same, the actuator MA2 having a servo motor has a support fixed to the base 60 via a shaft 32, a universal joint 421, a joint 52 and a universal joint 422 for moving up and down via a ball screw. The shaft 62 can move up and down.
The actuators MA3 and MA4 having servo motors are also connected to the bases via shafts 33 and 34, universal joints 431 and 441, joints 53 and 54, and universal joints 432 and 442 for moving up and down via ball screws. Support shafts 63 and 64 fixed to 60 can move up and down. These are shown in FIG. B is invisible.
In this way, the outer container 20 is fixed to the base 60 by the fixtures 261, 262, 263, and 264 (only the position of 264 is not visible in FIG. 2.B).

FIG. 3 is a front view showing how the crystal growth apparatus 100 swings.
First, FIG. A shows actuators MA1 and MA3 having servo motors (MA3 is not visible in FIG. 3.A), and the shafts 31 and 33 are moved downward by the same lowering amount. FIG. 3A shows the case where the shafts 32 and 34 are moved upward by the same increase amount. It can be seen that the outer container 20 has its z ′ axis, which is the normal line of the reference plane C0 ′, inclined to the left in the figure. Although the outer container 20 is inclined, it does not rotate around the z ′ axis.

  FIG. B shows that actuators MA1 and MA3 having servo motors (MA3 is not visible in FIG. 3.A) move the shafts 31 and 33 upward by the same amount of increase, and actuators MA2 and MA4 having servo motors (MA4 is MA4). FIG. 3A shows the case where the shafts 32 and 34 are moved downward by the same descending amount. It can be seen that the outer container 20 has the z ′ axis, which is the normal line of the reference plane C0 ′, inclined in the right direction in the figure. The outer container 20 is tilted but is not rotated about the z 'axis.

Although not shown in the other cases, as described with reference to FIG. 1, the outer container 20 does not rotate around the z ′ axis by continuously moving the φ plane on which the z ′ axis should be inclined. The inclination direction can be smoothly moved (rotated).
At this time, if the high-pressure vessel built in the external vessel 20 and further the reaction vessel (crucible) inside thereof are inclined according to the inclination of the external vessel 20, for example, a plate-shaped seed crystal is a reaction vessel (crucible). Tilt as the tilts. On the other hand, the sodium / gallium solution placed in the reaction vessel (crucible) so as to cover the seed crystal keeps its top surface in a horizontal plane, so that the sodium / gallium solution always moves relative to the seed crystal. Will be.
At this time, if the seed crystal is plate-shaped, it is preferable to contact the sodium / gallium solution with the surface with the fastest crystal growth facing upward. The tilt direction of the seed crystal changes, and the sodium / gallium solution always moves on the top surface of the seed crystal.
This results in the same situation as stirring the sodium / gallium solution over the seed crystal at very low speed. Thereby, when a group III nitride compound semiconductor is grown by flux using the crystal growth apparatus 100 of the present invention, an extremely high quality group III nitride compound semiconductor crystal can be obtained.
Actually, crystal growth was performed as follows.

  First, a GaN free-standing substrate having a diameter of 50 mm and a thickness of 0.5 mm was prepared. The GaN free-standing substrate may be partially dissolved in the flux until the desired semiconductor crystal is grown by the flux method. In this case, a self-supporting substrate having a thickness that does not disappear is required.

Hereinafter, the crystal growth process of Example 1 using the crystal growth apparatus will be described.
First, a GaN free-standing substrate was placed horizontally at the bottom of the reaction vessel (crucible) with the Ga polar face up. Next, 30 g of sodium (Na), 30 g of gallium (Ga), 80 mg of carbon (C), and 50 mg of germanium (Ge) are placed, and the reaction vessel (crucible) is used as the reaction chamber (stainless steel vessel) of the crystal growth apparatus. The gas in the reaction chamber is exhausted after being placed in the chamber. That is, the ratio of the molar amount of germanium to the molar amount of gallium was 0.16 mol%, and the ratio of the molar amount of carbon to the molar amount of sodium was 0.51 mol%.
However, when these operations are performed in the air, Na is immediately oxidized. Therefore, the operation of setting the substrate and raw materials in the reaction vessel is performed in a glove box filled with an inert gas such as Ar gas. . In addition, if necessary, any of the above-mentioned additives such as alkaline earth metals may be introduced into the crucible in advance.

Next, while adjusting the temperature of the crucible to about 875 ° C., in parallel with the temperature adjustment step, nitrogen gas (N ₂ ) is newly fed into the reaction chamber of the crystal growth apparatus, and this reaction is thereby performed. The gas pressure of nitrogen gas (N ₂ ) in the chamber is maintained at about 4.3 MPa. This gas pressure is set to 0.2 MPa higher than the optimum gas pressure when crystal growth is performed without adding carbon and germanium.

Thereafter, while stirring and mixing the mixed flux by the swing as described above, the crystal growth was continued for about 200 hours. At this time, the tilt angle was fixed at 10 degrees, and the tilt direction was rotated once per minute (1 rpm).
At this time, the maximum moving speed of the rod was 12 mm / second, the rotation speed of the servo motor was 350 rpm, the stroke of the rod was 300 mm, and an inclination angle θ = 10 degrees was realized. The four servo motors were program controlled by the control unit, and were surely synchronized to achieve smooth rotation.

Next, after the temperature of the reaction chamber of the crystal growth apparatus is lowered to near room temperature, the grown GaN single crystal (desired semiconductor crystal) is taken out, and its periphery is also maintained at 30 ° C. or less to surround the GaN single crystal. The flux (Na) adhering to is removed with ethanol.
By executing the above steps, a high-quality semiconductor single crystal (grown GaN single crystal) can be manufactured at a low cost. This semiconductor single crystal had substantially the same area as the seed crystal GaN free-standing substrate 10 and had a thickness in the c-axis direction of about 2 mm, high transparency, and good crystallinity. The increase in GaN was 11.4 g, and the film thickness distribution showed that the maximum film thickness increased by 8% relative to the minimum film thickness.
The resistivity of this semiconductor crystal was 0.02 Ω · cm. The electron concentration was 1.5 × 10 ¹⁸ / cm ³ .
In this embodiment, the center of gravity does not fluctuate and it is possible to swing freely, smoothly and freely. By growing with this apparatus, a very good n-type GaN free-standing substrate having almost no so-called macro defects was obtained. The film thickness distribution was also good, and Ge was uniformly doped throughout the n-type GaN free-standing substrate, improving the in-plane uniformity of electrical characteristics.

In this embodiment, the tilting direction is not rotated but the swinging is reversed every round.
In the same manner as in Example 1, while maintaining an inclination angle of 10 degrees at 875 [deg.] C. and 4.3 MPa, growth was continued for 200 hours with a rotation that reverses the direction of rotation every cycle. The increase in GaN was 23.8 g, and the film thickness distribution showed an increase of 11% in the maximum film thickness relative to the minimum film thickness. Further, the in-plane distribution of electrical characteristics was improved as compared with Example 1.

In this embodiment, the rotation in the tilt direction is about 5 times. The maximum moving speed of the rod was 60 mm / second, and the rotation speed of the servo motor was 1750 rpm.
In the same manner as in Example 1, while maintaining an inclination angle of 10 degrees at 875 ° C. and 4.0 MPa, the growth was continued for 200 hours while rotating and swinging at a period of 4.6 rpm. The increase in GaN was 23.7 g, and in the film thickness distribution, the maximum film thickness increased by 14% with respect to the minimum film thickness.

[Comparative Example 1]
For comparison, the reaction was performed without shaking and without tilting the outer container 20.
That is, the growth was continued for 200 hours without rotating and swinging while keeping the level of the external device 20 of Example 1 at 875 ° C. and 4.3 MPa. No increase in GaN was detected and no growth occurred.
[Comparative Example 2]
In FIG. 1, the reaction was performed by swinging the z ′ axis fixed to the structure in the xz plane of the fixed coordinate system.
That is, FIG. The actuators MA4 and MA2 having servo motors were fixed at A, and the y ′ axis fixed to the structure was fixed to the y axis of the fixed coordinate system, and swinging around the y ′ axis was performed. The actuators MA1 and MA3 moved up and down in a cycle of 1 minute. The maximum inclination angle of the z axis was 10 degrees.
In the obtained crystal, about 5% of macro defects existed in the plane, the film thickness distribution was 20%, and the in-plane distribution of electrical characteristics was also deteriorated as compared with Example 1.
[Others]
In addition, when the ball screw was replaced with a hydraulic piston, the position stability was poor, the center of gravity of the structure was shaken, and it was not possible to swing smoothly. When the universal joint was replaced with a simple one, abnormal noise was generated, heat was generated, and smooth rocking was not possible. If smooth speed control by numerical control is not performed, a time lag occurs, polygonal rotational motion occurs, and it stops once at the corner apex.

[Modification]
In all the above examples, nitrogen gas (N ₂ ), ammonia gas (NH ₃ ), or a mixed gas of these gases can be used as the gas containing nitrogen (N) as a crystal raw material. In the above composition formula of the group III nitride compound semiconductor constituting the desired semiconductor crystal, at least a part of the above group III elements (Al, Ga, In) is boron (B) or thallium ( Tl) or the like, or at least part of nitrogen (N) can be replaced with phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), or the like.

  The present invention is useful for manufacturing a semiconductor device using a semiconductor crystal made of a group III nitride compound semiconductor. Examples of these semiconductor devices include other general semiconductor devices such as FETs in addition to light emitting elements and light receiving elements such as LEDs and LDs.

10: Frame-shaped casing 20: External container 31, 32, 33, 34: Shaft 411, 412, 421, 422, 431, 432, 441, 442: Universal joint part 51, 52, 53, 54: Joint 60: Base 61, 62, 63, 64: Support shaft C0: Initial position of reference plane (unit circle) C0 '; Reference plane (unit circle) during swinging

Claims (4)

In a crystal growth apparatus by a flux method of a group III nitride compound semiconductor using a high-pressure vessel incorporating a reaction vessel, or an oscillating device of an external vessel further incorporating the reaction vessel,
The rocking device can hold the high-pressure vessel or an external vessel incorporating the high-pressure vessel by a plurality of support points,
A plurality of means for individually moving the plurality of support points up and down;
A crystal growth apparatus characterized in that a desired change in an inclined state is continuously generated in the reaction vessel. The plurality of support points are four, and each of the four means for moving the four support points up and down includes a numerically controllable servo motor and a ball screw that moves up and down in conjunction therewith. The crystal growth apparatus according to claim 1. 3. The crystal according to claim 1, wherein the tilt direction of the reference surface is rotated while maintaining the normal direction of the reference surface provided in the reaction vessel at a constant angle with respect to the vertical direction. Growth equipment. The tilt direction of the reference surface is rotated while maintaining the normal direction of the reference surface provided in the reaction vessel at a constant angle with respect to the vertical direction. Crystal growth equipment.

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