JPH04292500A - Growth of crystal - Google Patents

Abstract

PURPOSE:To increase a crystal growth rate and a composition-controlling property by applying an electric current in a specific direction to a melted solution for crystallizing a solute thereof, and applying a Lorentz's force to the melted solution in a specific direction based on the growth direction of the crystal. CONSTITUTION:A crystallization substrate 10 for determining the direction of the epitaxial growth of a crystal is fixed on the bottom of a solution reservoir 8, and electrodes 5, 6 are fixed at both the ends. The direction B of a magnetic field is designated as the arrow B, and an electric current is applied between the electrodes 5, 6 in the direction I orthogonal to the direction of the magnetic field, consequently generating a Lorentz's force F. The crystallization substrate 10, the solution and the electrodes 5, 6 are arranged so as to effectively utilize the Lorentz's force F. When the Lorentz's force is directed in the direction of the substrate, the rate of the growth is increased, and when the Lorentz's force is directed in the opposite direction, the rate of the growth is decreased, thereby permitting to enhance the reproductibility of the thickness of the crystal. The direction of the Lorentz's force F is therefore determined in response to the property of the objective crystal layer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth technique, and more specifically to a crystal growth method such as a boat growth method or a pulling growth method in which a solute is crystallized from a melt.

0002

[Prior Art] Method of growing crystals from melt (hereinafter referred to as
In the case of "liquid phase growth"), the crystal growth rate is controlled by supplying solute to the growth interface. Solute supply depends on the solute concentration in the solvent and the temperature. Conventionally, when these factors are regulated, solute supply cannot be controlled by other factors.

0003

[Problems to be Solved by the Invention] Although the liquid phase growth method has advantages such as less damage to the substrate crystal and good crystallinity of the grown crystal, it is inferior to methods such as MBE in crystal growth controllability. This results in the fact that it is very difficult to control the growth rate or control the composition since it is not possible to control the diffusion rate externally.

[0004] Therefore, in order to stack ternary compound semiconductors or quaternary compound semiconductors as thin films of several tens of Å to several thousand Å, methods with excellent crystal growth controllability, such as MBE and MOVPE, have conventionally been adopted. However, it was difficult to adopt liquid phase growth method.

[0005] In addition, in liquid phase growth using the conventional method, when the diffusion rates of each component of the ternary compound are different, for example, Ga and As
When growing InGaAs crystals with different diffusion rates, the composition of Ga and As is almost determined by determining the concentration in the melt, and there is no other method for controlling the composition. Here, since the concentration in the melt cannot be arbitrarily controlled during crystal growth, the controllability of the composition is extremely low, and is far lower than MOCVD, MBE, etc., which can grow ternary or quaternary compounds with arbitrary compositions.

In view of the above-mentioned current state of the liquid phase growth method, the present invention aims to improve the controllability of the crystal growth rate and composition compared to the conventional method, that is, to accurately control the rate from high-speed growth to low-speed growth; The aim is to enable control of elementary or quaternary compounds.

[0007]

[Means for Solving the Problems] The present invention provides a crystal growth method for growing a crystal by crystallizing a solute from a melt.
A current is applied to the melt or solution in a second direction having a perpendicular component to the first direction of a magnetic field applied from the outside, and the Lorentz force generated by the magnetic field and current is directed against the direction of crystal growth. The second direction is determined so as to be in a predetermined direction. The configuration of the present invention will be explained below.

[0008] In liquid phase growth, a growth furnace for melting a melt (sometimes called a solution in the field of liquid phase growth) is usually equipped with a heater, which has a coil shape that surrounds the object to be heated. When an alternating current is applied, an alternating magnetic field is generated,
In the case of direct current, a direct current magnetic field is generated within the coil.

FIG. 1 shows such a growth furnace using an AC heater. In the figure, 1 is a reaction tube, 2 is a heater coil that heats the melt resistance, 3 is a boat that holds the melt, 4 is an AC power source that supplies electricity to the heater coil, and 8 is a solution reservoir provided in the boat. . In such a growth reactor, a magnetic field is generated in the direction indicated by B in the figure. The feature of the liquid phase growth method of the present invention is that the power source 8 is connected to the boat 3 and a current is passed through the solution so that the Lorentz force acts on the magnetic field B in a desired direction. The relationship between current and magnetic field will be explained below with reference to FIG. 2.

A crystal substrate 10 for determining the epitaxial growth direction is fixed at the bottom of the solution reservoir 8, and electrodes 5,
6 is fixed. The direction B of the magnetic field in FIG. 1 is indicated in FIG. 2 by arrows B in the same direction. When a current is passed between the electrodes 5 and 6, its direction is I, that is, a direction perpendicular to the direction of the magnetic field, and as a result, a Lorentz force F is generated. The principle of the present invention is to perform growth by arranging the crystal substrate 10, solution, and electrodes 5 and 6 so as to effectively utilize such Lorentz force. This results in an increase in one control factor (Lorentz force) compared to conventional diffusion-only control. Since the Lorentz force F applies a force to the melt in the direction of the crystal substrate 10, the solute is moved in the direction of the crystal substrate 10.

[0011] When the Lorentz force is substantially in the direction of the substrate, the growth rate is increased, and when the Lorentz force is in the direction substantially opposite to the substrate, the growth rate is decreased, thereby increasing the reproducibility of the film thickness. Therefore, the direction of the Lorentz force is determined depending on the properties of the target crystal layer.

[0012] Above, an example of a growth furnace equipped with a heater coil has been explained, but since a magnetic field is generated in the case of a rod-shaped heater as well, the current should be adjusted by considering the relationship between B and I shown in Fig. 2. By flowing, Lorentz force F can be generated. Further, in addition to the heater, a magnet or the like that separately generates a magnetic field may be provided.

When the heater is an AC heater, FIG.
As shown in , when an alternating current (I) with the same frequency and phase as the magnetic field B of the heater is passed through the melt or solution, the Lorentz force (F=I×B) always acts in the positive (+) direction, resulting in the most efficient Good. When alternating current is represented by a perfect sine curve,
I, B in-phase Lorentz force (F=I×B, where I=50
Hz) is expressed by the following formula.

[0014]

[Math 1]

On the other hand, as shown in FIG.
When I) and the frequency (B) of the alternating magnetic field differ, the Lorentz force (I×B) oscillates and cancels each other out (I×B=0). ■When I=100Hz, B=50Hz and ■I=150
Calculations when Hz and B=50Hz are shown below.

[0016]

[Math 2]

[0017]

[Math 3]

The larger the current for generating the Lorentz force, the more effective it is. FIG. 5 shows the dependence of the amount of InP dissolved on the current value in the case of an AC heater and AC current supply. It can be seen from this figure that there is a linear relationship between the current value and the amount of dissolved InP. Note that the amount of dissolution is measured by the weight of the substrate. If the current value becomes excessive, the influence of heat generation in the electrode section becomes large, and the effects of convection other than the Lorentz force become larger, so it is necessary to set it below this upper limit. This upper limit is 3 to 20 A when compound semiconductor crystal growth is performed using the boat growth method.

The current applied to the melt according to the present invention has the greatest effect when its frequency (fi) matches the frequency (fm) of the alternating magnetic field, and f1 < fm,
Alternatively, if f1 > f, there is an effect, but the effect is small.

FIG. 6 shows the frequency dependence of the dissolution rate when 6 A of alternating current is applied to an InP solution heated by a 50 Hz AC heater, and the InP is brought into contact with the InP substrate to dissolve InP. From this figure, the current flowing into the solution is 50Hz.
It is clear that the amount of dissolution is frequency dependent.

Furthermore, when the current of the heater is direct current, it is preferable that the magnetic field is also direct current. Table 1 shows the effect of electricity on the InP dissolution process for each combination of the current flowing through the heater and the current flowing into the solution.

[0022] In the table, DC (pulse) refers to direct current ON and OF.
F means a pulsed heater current that repeats at 50 cycles/sec, substrate + and substrate - mean when the direction of the direct current flowing into the solution changes, and ++ means the most effective and 0 means no effect. means.

[0023]

[Table 1] In the table, the relative amount of dissolution is shown, with the value of no electricity being 1. This result shows that it is effective when the electric current in the heater and solution is a combination of direct current and direct current, and alternating current and alternating current. In other words, it can be seen that the amount of dissolution increases due to the Lorentz force.

When the alternating current flowing through the heater passes through the thyristor and causes waveform deformation as shown in FIG.
0Hz), the Lorentz force (I
×B) can always work in the plus (+) direction.

In the liquid phase growth of ternary or higher compound semiconductors, each element has a different diffusion coefficient, so the solute concentration at the growth interface changes during growth, and the conventional method has a problem in that the composition of the growth layer changes. In the present invention, the Lorentz force is a force determined by the charge of solute atoms, so unlike the distribution coefficient, it does not depend on the atoms as much as the distribution coefficient.Also, it can be controlled by changing the flowing current value and the magnitude of the magnetic field, so the growth layer The composition can be controlled to be constant. Therefore, the present invention is preferably applied to crystal growth of ternary or more compounds.

[0026] Furthermore, in the conventional method, the growth rate becomes extremely slow when low-temperature growth is performed. However, if the degree of supercooling of the melt is increased to accelerate the growth rate, solute precipitation will occur even at a distance from the substrate, and low-temperature growth has advantages such as less thermal denaturation when manufacturing devices with complex structures. However, it was difficult to implement. On the other hand, when the Lorentz force is used in the present invention, it is possible to grow a binary or higher compound semiconductor without destabilizing the growth system even at a growth temperature of 400 to 500K.

[0027]

[Operation] In Figure 8, the graph for "no current" corresponds to the conventional method in which solute is supplied for crystal growth only by diffusion, and the "AC 6A" graph is for solute to be supplied by Lorentz force and diffusion. This corresponds to the present invention. Both, InG
The results of an experiment in which aAs was grown are shown. From these results and FIG. 5, it is clear that according to the present invention, the growth rate can be controlled during crystal growth by controlling the current value from outside the growth system. The reason why control using electric current became possible in this way is thought to be due to the Lorentz force acting on the ionized solute in the solution, accelerating its diffusion.

The second aspect of the present invention enables control to increase the crystal growth rate as shown in FIG. According to a third aspect of the present invention, by suppressing diffusion, the amount of solute supplied can be reduced, and control can be performed to form an extremely thin film. Claims 4 to 7 indicate the most preferred method of applying current according to the magnetic field from the heater. Claim 8 relates to application to crystals whose composition is most difficult to control by liquid phase growth. Claim 9 is a method for producing crystals with good crystallinity by low-temperature growth. The present invention will be explained below with reference to Examples.

[0029]

EXAMPLES Example 1 InP was grown using a boat growth apparatus shown in FIG. In the figure, 11 is a substrate slider, and 13 is a PBN-coated boat, both of which are known. The ends of stainless steel electrodes 14 and 15 were welded to the electrodes 5 and 6 fixed to both ends of the solution reservoir 8. A boat growth device consisting of the above-mentioned components 5, 6, 8, 11, and 13 was installed with an inner diameter of 80 mm, an outer diameter of 90 mm, and a length of 1.
It was set in a reaction tube with a diameter of 500 mm and a heater with 50 turns. A 600°C saturated melt of InP (
XP (liquid phase molar concentration of P) = 3.7 x 10-3) is 1
0 g was added, and growth was performed for 5 minutes under conditions of a supercooling degree of 4° C. while flowing a current of 6 A from the AC power source 4. At this time, the furnace heater (not shown) was a 50 Hz AC heater, and the current flowing into the solution was also 50 Hz, and the phases were matched (
(see Figure 3). As a result, a film thickness of only 1.6 μm could be obtained in 5 minutes of growth when no current was applied, whereas a film thickness of 11 μm could be obtained when an alternating current was applied.

Example 2 In1-x Gax A was grown using the boat growth apparatus shown in FIG.
FIG. 10 shows the results of growing s. From this result, it is clear that the composition of the InGaAs crystal is stable in the present invention.

[0031]

[Effects of the Invention] As explained above, by using the present invention, the transport of solutes in a solution can be controlled by external control, so that the growth rate, film thickness controllability, and A growth method that is advanced in terms of temperature setting, composition stability, etc. is provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a growth apparatus used in the method of the present invention.

FIG. 2 is a diagram explaining the principle of the present invention.

FIG. 3 is a diagram of Lorentz force due to alternating current and alternating magnetic field having the same frequency.

FIG. 4 is a diagram similar to FIG. 3 for a case where the frequencies are different;

FIG. 5 is a graph showing the current dependence of the amount of InP dissolved.

FIG. 6 is a graph showing the frequency dependence of the amount of InP dissolved.

[Figure 7] Figure 3 when the frequency of alternating current is an odd multiple of the magnetic field
This is a similar diagram.

FIG. 8 is an explanatory diagram of the action of the present invention.

FIG. 9 is a diagram of a boat growth apparatus.

FIG. 10 is a graph showing the Ga distribution of In1-x Gax As.

[Explanation of sign]

1 Reaction tube 2 Heater coil 3 Boat 4 AC power supply 5 Electrode 6 Electrode 8 Solution reservoir 10 Crystal substrate 11 Board slider 12 InP solution 13 PBN coated boat

Claims (9)

[Claims] Claim 1. A crystal growth method in which a solute is crystallized from a melt to grow a crystal, in which a magnetic field is applied to the melt from the outside, and a second direction having a perpendicular component to the first direction. A crystal growth method characterized by flowing an electric current through the melt and determining a second direction so that the Lorentz force generated by the magnetic field and the electric current is in a predetermined direction with respect to the crystal growth direction. 2. The crystal growth method according to claim 1, wherein the predetermined direction is substantially the same direction as the crystal growth direction. 3. The crystal growth method according to claim 1, wherein the predetermined direction is substantially equal to a direction opposite to the crystal growth direction. 4. The crystal growth method according to claim 1, wherein the magnetic field is generated by a heater that heats the melt. 5. The crystal growth method according to claim 4, wherein when the heater is an alternating current heater, an alternating current having the same frequency and phase as that of the heater is passed into the melt or into the melt. 6. The crystal growth method according to claim 4, wherein an alternating current having a frequency that is an odd multiple of the frequency of the heater is passed through the melt. 7. The crystal growth method according to claim 4, wherein when the heater is a direct current heater, direct current is passed through the melt. 8. The crystal growth method according to claim 1, wherein crystal growth of a ternary or higher compound semiconductor is carried out. 9. The crystal growth method according to claim 8, wherein the crystal growth is performed with the degree of supercooling of the melt being 0<ΔT≦10k.