JP5207073B2 - Crystal manufacturing method and manufacturing apparatus using the same - Google Patents

Description

  The present invention relates to a crystal manufacturing method and a manufacturing apparatus using the same. In particular, the present invention relates to a processing apparatus and method for taking out crystals from a flux in a short time in the production of GaN crystals using the sodium flux method.

  In recent years, group III nitride crystals, particularly gallium nitride (GaN) crystals, have been rapidly demanded for semiconductor devices such as heterojunction high-speed electronic devices, light-emitting diodes (LEDs) and laser diodes (LDs). A substrate of a GaN-based device such as an LD or LED is usually made of sapphire, and is formed by heteroepitaxially growing GaN on the substrate using a vapor phase epitaxial growth method.

  However, when GaN is grown on dissimilar substrates such as sapphire, the lattice constant and thermal expansion coefficient are different, so many lattice defects are generated in the grown GaN crystal, and device characteristics such as lifetime and light emission efficiency are reduced. The problem of doing is easy to occur. Therefore, attempts have been made to improve device characteristics by producing high-quality crystals by homoepitaxial growth of GaN on a GaN crystal substrate. The GaN crystal substrate is obtained by slicing and polishing a GaN crystal ingot.

  As a growth method of this GaN crystal ingot, in addition to vapor phase growth such as hydride vapor phase growth (HVPE) method, in recent years, liquid phase growth called sodium flux method using alkali metal or alkaline earth metal such as sodium. The (LPE) method has attracted attention. This is a method for obtaining a GaN crystal by reacting gallium with a nitrogen source such as nitrogen gas or ammonia at several tens of atmospheres and several hundred degrees in an alkali metal flux solution such as sodium. Here, when sodium is used as the flux and nitrogen gas is used as the nitrogen source, the reaction mechanism is considered as follows. Electrons move from the low electronegativity sodium to the antibonding orbitals of nitrogen molecules, and the binding force of conventionally stable nitrogen molecules decreases. As a result, nitrogen is dissolved in an atomic state in the sodium-gallium mixed melt, and gallium and atomic nitrogen react to generate GaN. The mechanism is that the generated GaN is supersaturated in the solution and precipitates as GaN crystals. In this method, since crystal growth proceeds by a mechanism close to thermal equilibrium, a high-quality GaN crystal with relatively few defects such as transition can be obtained as compared with the above-described vapor phase method.

  A conventional crystal manufacturing apparatus using liquid phase growth is shown in FIG. For the sake of explanation, the case of producing a GaN crystal is taken as an example. 18 is a raw material gas supply device for supplying nitrogen gas, which is a raw material gas, 27 is a hermetic crystal growth vessel for crystal growth, 21 is a connecting pipe for connecting the raw material gas supply device 18 and the crystal growth vessel 27, Reference numeral 17 denotes a growth furnace equipped with heating means. The connection pipe 21 has a pressure regulator 19, a stop valve 23, a leak valve 20, and a disconnecting portion 22. The growth furnace 17 is configured as an electric furnace provided with a heat insulating material 26 and a heater 25, is temperature-controlled by a thermocouple 24, and can swing as a whole.

  In the manufacturing apparatus having such a configuration, the seed substrate 16 is set in the crucible 3. This seed substrate 16 is arranged in a direction parallel to the bottom surface of the crucible 3. Further, a predetermined amount of metal gallium and Na as raw materials are weighed and set in the crucible 3. Then, the crucible 3 is inserted into the crystal growth vessel 27, and this crystal growth vessel 27 is set in the growth furnace 17 and connected to the source gas supply device via the connection rod 21, and the growth temperature is 850 ° C. and the nitrogen atmosphere. A GaN crystal is grown by dissolving nitrogen gas in a Ga / Na melt (hereinafter referred to as a raw material liquid) at a pressure of 40 atm.

  Since the produced GaN crystal is in the crucible together with the solidified raw material solution, the GaN crystal must be taken out from this state. FIG. 13 shows a method for extracting the GaN crystal manufactured by the manufacturing apparatus of FIG. In the state where the crucible 3 is taken out from the crystal growth container 27 at room temperature, the flux 29 as the raw material liquid is in a solid state, and the GaN crystal grown on the seed substrate 16 cannot be taken out as it is. Therefore, as shown in FIG. 13, the crucible 3 is placed in the flux treatment tank 4 filled with the flux treatment liquid 11, and the flux 29 is melted from the upper surface by causing a chemical reaction between the flux treatment liquid 11 and the flux 29. Here, when using Ga / Na as a raw material, by using ethanol as the flux treatment liquid 11, it becomes possible to dissolve the flux 29 while generating hydrogen 28 as a reaction gas, and the GaN crystal 16 is crucible. 3 can be taken out.

JP 2002-293696 A

  However, since the timing for replacing the flux treatment liquid is not appropriate in the conventional configuration, it takes a very long time to take out a group III nitride crystal such as a GaN crystal formed by liquid phase growth from the solidified flux. It was hanging.

  The present invention solves the above-mentioned conventional problems, and a method for producing a crystal, which can take out a group III nitride crystal such as a GaN crystal formed by liquid phase growth from a raw material liquid in a short time, and It aims at providing the used manufacturing apparatus.

  In order to solve the above-mentioned conventional problems, the crystal manufacturing method of the present invention is a crystal manufacturing method in which the crystal is extracted from the flux as a post-process of growing the crystal, and the crucible is housed in the flux treatment tank. Before or after putting the crucible into the flux treatment tank, a flux treatment liquid is allowed to flow into the flux treatment tank, and a seed substrate and crystals grown on the seed substrate are placed in the crucible. And the flux covering the seed substrate and the crystal are stored, the electrical conductivity of the flux treatment liquid is measured, and when the electrical conductivity value is a predetermined value or less, the flux It has the process of replacing | exchanging a process liquid, It is characterized by the above-mentioned.

  According to the crystal manufacturing method of the present invention, the flux treatment liquid can be constantly maintained in a highly reactive state by evaluating the conductivity of the flux treatment liquid. Group III nitride crystals such as GaN crystals can be taken out of the raw material solution in a short time.

  Embodiments of a crystal manufacturing method and a manufacturing apparatus using the same according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
First, a crystal manufacturing method, in particular, a group III nitride crystal will be described. First, a group III material (for example, gallium, aluminum, indium) as a raw material and a flux 29 as an alkali metal (for example, lithium, sodium, potassium) or an alkaline earth metal (for example, calcium, strontium) , Barium, radium, beryllium, magnesium). These alkali metals and alkaline earth metals may be used alone or in combination of two or more. It is preferable that the group III material and alkali metal are weighed and handled in a glove box substituted with nitrogen gas, argon gas, neon gas, or the like in order to avoid alkali metal oxidation or moisture adsorption.

  Next, the crucible 3 is inserted into the crystal growth vessel 27 shown in FIG. 12, taken out from the glove box in a sealed state, and the crystal growth vessel 27 is fixed in the growth furnace 17. Thereafter, the crystal growth vessel 27 and the connecting pipe 21 are connected, the stop valve 23 is opened, and the source gas is injected from the source gas supply device 18 into the crystal growth vessel 27. Then, pressurization and heating are performed by controlling the temperature of the growth furnace 17 and the pressure of the growth atmosphere by the thermocouple 24 and the pressure regulator 19. Note that the conditions for melting and growing the raw material for generating the group III nitride crystal depend on the raw material of the group III material and the alkali metal, the raw material gas, and the pressure thereof. For example, the temperature is A relatively low temperature of 700 ° C. to 900 ° C. is used for the purpose of preventing the corrosion of the apparatus. The pressure is 20 atmospheres (20 × 1.01325 × 105 Pa) or more, preferably 30 atmospheres (5 × 1.01325 × 105 Pa) to 100 atmospheres (100 × 1.01325 × 105 Pa).

  In this way, by raising the temperature to the growth temperature, a melt of the alkali metal as the group III material and the flux 29, that is, a raw material liquid is formed in the crucible 3, and the raw material gas dissolves in this raw material liquid, and III The group material and the source gas react to grow a group III nitride crystal on the seed substrate 16.

  After the growth of the group III nitride crystal is completed after a predetermined time has elapsed, the growth furnace 17 is returned to normal pressure and room temperature, the crystal growth container 27 and the connecting pipe 21 are removed, and the crystal growth container 27 is removed from the growth furnace 17. Take out. Further, the crucible 3 is taken out from the crystal growth vessel 27.

  In the raw material liquid in the crucible 3 after growth, the Group III material is consumed and becomes crystals, so that it hardly remains, and most of them are alkali metals that are flux 29. Further, the flux 29 exists in a solid state at room temperature, and covers the grown group III nitride crystal. Therefore, in order to take out the group III nitride crystal from the crucible, it is necessary to remove the solidified flux 29 such as alkali metal. The alkali metal reacts with a liquid containing a hydroxyl group such as ethanol, isopropyl alcohol, and water. For example, when sodium is used as the alkali metal and ethanol is used as the treatment liquid 11 containing the hydroxyl group, the formula (1) Sodium ethoxide and hydrogen gas are generated.

C ₂ H ₅ OH + Na → C ₂ H ₅ ONa + H ₂ ↑ (1)
Since the alkali metal salt such as sodium ethoxide is dissolved in the flux treatment solution 11 such as ethanol as it is, the group III nitride crystal can be taken out from the crucible 3. However, as the reaction proceeds, ethanol as the flux treatment liquid 11 is consumed, that is, unreacted ethanol is reduced, and a product such as sodium ethoxide is excessively large. Therefore, the reaction rate of the chemical reaction is reduced, Eventually the reaction stops. Therefore, in order to remove the flux 29 such as alkali metal from the crucible 3 and take out the group III nitride crystal, it is necessary to appropriately replace the hydroxyl group-containing treatment liquid 11 such as ethanol. Conventionally, in the production of group III nitride crystals using the sodium flux method, the progress of this reaction has been carried out by visually confirming the amount of hydrogen gas generated. Therefore, it is difficult to quantitatively grasp the flux treatment status, the flux treatment liquid 11 cannot be replaced at an appropriate timing, and it takes a long time to take out the group III nitride crystal from the crucible 3. It was.

The flux processing apparatus according to the embodiment shown in FIG. 1 has a stirrer 2 and an electric conductivity meter 1 in a flux processing tank 4. Further, the flux processing liquid storage tanks 6 and 7 and the waste liquid storage tank 5 are connected to the flux processing tank 4. The electric conductivity meter 1 is not limited to this and may be an ion concentration meter or the like. Further, the stirrer 2 is not limited to this, and may be any one that can make the solution uniform, such as ultrasonic vibration and a magnetic stirrer. The flux treatment liquid storage tanks 6 and 7 store hydroxyl-containing compounds such as alcohol and water, respectively, but may be composed of one or three or more storage tanks. As described above, the produced alkali metal salt is dissolved in the flux treatment liquid 11 and ionized as shown in the formula (2), so that the solution exhibits conductivity.
C ₂ H ₅ O ⁻ + Na ⁺ ... (2)
Since this conductivity increases in proportion to the amount of alkali metal salt dissolved, that is, the amount of flux 29 treated, it is possible to quantitatively grasp the flux treatment status by installing the conductivity meter 1 in the flux treatment tank 4. It becomes. The stirrer 2 provided in the flux treatment tank 4 causes convection of the solution by stirring, and promotes the reaction between the flux 29 and the flux treatment liquid 11. Moreover, since the concentration unevenness of the dissolved metal salt in the solution can be alleviated by agitation, more accurate evaluation of the conductivity, that is, the flux treatment status can be performed.

  FIG. 2 shows an increment value of conductivity when Na 20 g is used as the flux 29 and 2 liters of ethanol is used as the flux treatment liquid 11 (here, the increment value is an increase in conductivity per unit time). . As shown in FIG. 2, the increment value of the conductivity of the flux treatment liquid 11 decreases with time. This is because, as described above, ethanol is consumed over time, that is, unreacted ethanol that removes Na decreases, products such as sodium ethoxide become excessively large, and the rate of chemical reaction decreases. It is.

  However, as shown in FIG. 3, the flux treatment liquid 11 is discarded, and the new value of the conductivity of the flux treatment liquid 11 is restored by re-adding new ethanol. In this way, the flux treatment solution is agitated by the stirrer 2 and the flux treatment solution 11 is discarded in the waste solution storage tank 5 while evaluating the flux treatment status with the increment of conductivity, and the new ethanol is stored in the treatment solution. By introducing from the tank 5, the flux can be efficiently processed without causing a decrease in the processing speed, so that the processing time can be significantly shortened as compared with the conventional case. Further, the larger the increment value, the better. However, if the increment value is equal to or greater than a predetermined value, that is, while the conductivity is increased to some extent, the flux treatment liquid 11 can sufficiently remove Na as described above. Processing can proceed. Therefore, when the increment value is equal to or smaller than the predetermined value, that is, when the change in conductivity is not noticeable, the guideline for exchanging the flux treatment liquid is used.

  Group III nitride crystals were produced using this apparatus. First, as a flux 29, 23.4 g of sodium, 18 g of gallium, and a seed crystal 16 having a diameter of 50 mm are placed in an alumina crucible 3 having a diameter of 60 mm, and a group III nitride crystal is grown under a nitrogen flow of 850 degrees, 30 atm, and 100 sccm. I let you.

  Next, this crucible 3 was subjected to flux treatment using ethanol in the conventional method and the above-described embodiment of the present invention. FIG. 4 shows the processing time until the crystal is extracted when the conventional method is used. As shown in the figure, the conventional method required an average of 38 hours until the crystal was taken out. In addition, since the processing status of the flux could not be grasped quantitatively, the variation in processing time for all five times was very large. On the other hand, FIG. 5 shows the processing time when the embodiment of the present invention is used. As shown in the figure, it takes 21 hours on average until the crystal is taken out, and it becomes possible to grasp the treatment status based on the conductivity, and to appropriately supply and discharge the ethanol based on it, so that the treatment time can be greatly shortened. Also, the variation of the processing time for all five times is very small. This is because the processing status of the flux, which was unknown in the conventional method, can be grasped in the embodiment of the present invention, and the treatment liquid is stirred appropriately so that the increment value of the conductivity of the processing liquid becomes constant. This is because the ethanol effluent was charged.

(Embodiment 2)
FIG. 6 shows a view of a group III nitride crystal production apparatus according to the second embodiment of the present invention. In this apparatus, a chelate treatment tank 12 is connected to a flux treatment tank 4 with respect to the apparatus of the first embodiment. The chelate treatment tank 12 is a tank for treating the flux treatment liquid 11 with a chelating agent. In addition to the flux (for example, Na) 29, various ion species can be mixed in the flux treatment liquid 11. For example, when alumina is used as the crucible material, aluminum ions such as Al3 + are mixed, which causes a large error in grasping the flux treatment by the conductivity. A chelating agent forms a chelate ring with a specific metal ion and can deionize a specific ionic species. For example, by using a chelating agent that has a chelating action on aluminum ions or the like, it is possible to evaluate the conductivity of pure flux only, and improve the accuracy of evaluating the conductivity of the flux treatment. Moreover, the stirrer 2 provided in the chelate treatment tank 12 causes convection of the solution and promotes the reaction between the chelating agent and the chelate species.

  FIG. 7 shows the result of selective removal of aluminum ions by the chelating agent. The chelating agent used is Dianitrix Diafloc MT1006. As shown in the figure, the addition of a chelating agent can reduce aluminum ions by up to about 50%.

  Moreover, FIG. 8 shows the figure of the further another manufacturing apparatus in Embodiment 2 of this invention. In this apparatus, a neutralization tank 15, a chelate treatment tank 12, a hollow filter 14, and a measurement tank 13 are connected to the apparatus of the first embodiment. As shown in the figure, by providing a neutralization step with sulfuric acid or the like before the chelating agent treatment and a filtration step by hollow filtration after the chelation treatment, it becomes possible to more efficiently remove ionic species other than the flux such as aluminum ions. Further, the hollow filtration is not limited to this, and any filter that can remove aggregates generated by the chelate treatment may be used. Further, the neutralizing agent is not limited to sulfuric acid, and may be any acidic compound such as hydrochloric acid or phosphoric acid.

  FIG. 9 shows the concentration of aluminum ions after neutralization, chelation, and hollow filtration. The used chelating agent was Dianitrix Diafloc MT1006, the neutralizing agent was sulfuric acid, and the hollow filtration was a Mitsubishi Rayon polyethylene hollow fiber membrane filter, Stella Pore. As shown in the figure, by providing the processing step, the selective removal of aluminum can be further improved, and aluminum ions can be reduced by up to about 90%.

  Group III nitride crystals were produced using the above processing apparatus. As a flux 29, 23.4 g of sodium, 18 g of gallium, and a seed crystal 16 having a diameter of 50 mm were placed in an alumina crucible 3 having a diameter of 60 mm, and a group III nitride crystal was grown at 850 ° C., 30 atm, and 100 sccm nitrogen flow.

  Next, this crucible 3 is required for flux treatment by a method in which only a chelate treatment step is added to Example 1, and a method in which three steps of neutralization, chelate treatment and hollow filtration are added to Example 1. A time comparison experiment was conducted. FIG. 10 shows the treatment time when only the chelate treatment step is added. As shown in the figure, it took 19 hours on average until the crystals were taken out, and a further reduction in processing time was achieved with respect to Example 1. FIG. 10 shows the treatment time when three steps of neutralization, chelation treatment and hollow filtration are added. As shown in the figure, it took 17 hours on average until the crystals were taken out, and further reduction of the processing time was achieved as compared with the case where only Example 1 and the above-mentioned chelate treatment step were added. Moreover, the variation of the processing time of all 5 times could be further reduced.

  The method for producing a crystal according to the present invention and the production apparatus using the same have an effect of taking out a group III nitride crystal such as a GaN crystal formed by liquid phase growth from a raw material solution in a short time, It is useful for manufacturing a substrate of a semiconductor device used for a blue laser diode, a blue light emitting diode, or the like.

Diagram of the crystal manufacturing apparatus in Embodiment 1 of the present invention The figure of the time change of the electrical conductivity of the flux solution in Embodiment 1 of this invention The figure of the time change of the electric conductivity of the further another flux solution in Embodiment 1 of the present invention Diagram showing the time required for conventional flux processing The figure which shows the required time of the flux process in Embodiment 1 of this invention Diagram of crystal manufacturing apparatus in Embodiment 2 of the present invention The figure which shows the selective removal of the aluminum ion in Embodiment 2 of this invention The figure of the further another crystal manufacturing apparatus in Embodiment 2 of this invention The figure which shows the selective removal of the other aluminum ion in Embodiment 2 of this invention The figure which shows the required time of the flux process in Embodiment 2 of this invention The figure which shows the time required for the further another flux process in Embodiment 2 of this invention. Diagram of an apparatus for growing general crystals Diagram of conventional crystal manufacturing equipment Diagram of crucible for growing common crystals

DESCRIPTION OF SYMBOLS 1 Conductivity meter 2 Stirrer 3 Crucible 4 Flux processing tank 5 Waste liquid tank 6 Flux processing liquid storage tank 1
7 Flux processing liquid storage tank 2
8 Pump 9 Piping 10 Thermometer 11 Flux treatment liquid 12 Chelate treatment tank 13 Measurement tank 14 Hollow filter 15 Neutralization tank 16 Seed substrate 17 Growth furnace 18 Raw material gas supply device 19 Pressure regulator 20 Leak valve 21 Connecting rod 22 Detaching part 23 Stop valve 24 Thermocouple 25 Heater 26 Heat insulation material 27 Crystal growth vessel 28 Hydrogen 29 Flux and group III material

Claims (7)

As a post-process for growing a crystal, this is a method for producing a crystal that takes this crystal out of a flux,
A crucible is housed in the flux treatment tank, and before or after the crucible is placed in the flux treatment tank, a flux treatment liquid is allowed to flow into the flux treatment tank, and in the crucible, a seed substrate, The crystal grown on the seed substrate and the flux covering the seed substrate and the crystal are stored, the electrical conductivity of the flux treatment liquid is measured, and the increment value of the electrical conductivity is a predetermined value. The crystal manufacturing method which has the process of replacing | exchanging the said flux processing liquid when it becomes below the value of this. The crystal manufacturing method according to claim 1, further comprising a step of performing a chelate treatment before measuring the electrical conductivity of the flux treatment liquid. The crystal manufacturing method according to claim 1, further comprising a step of stirring the flux treatment liquid before measuring the electrical conductivity of the flux treatment liquid. The method for producing a crystal according to claim 2, wherein the chelating agent used for the chelation treatment is non-chelating to an alkali metal, an alkaline earth metal, or both. The crystal production method according to claim 2 or 4, wherein the chelating agent used for the chelation treatment is nonionic, cationic, anionic, or a mixture thereof. It is a crystal manufacturing apparatus used for the manufacturing method of the crystal of Claims 1-5, Comprising: For making a flux processing liquid flow in into the installation stand of the above-mentioned flux processing tank, and the flux processing tank put on this installation stand A crystal manufacturing apparatus comprising an inflow means and a take-out means for taking out a crystal and a seed substrate from the flux treatment tank after dissolving the flux in the crucible with a flux treatment liquid. A flux treatment liquid storage tank connected to the flux treatment tank provided with an electric conductivity meter, and a waste liquid storage tank, and the flux treatment tank when the electric conductivity meter becomes a predetermined value or less. The crystal manufacturing apparatus according to claim 6, further comprising an exchanging unit that discharges the flux treatment liquid to the waste liquid storage tank and flows the flux treatment liquid in the flux treatment liquid storage tank into the flux treatment tank.

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