JP6307818B2 - Method for producing group 13 nitride crystal - Google Patents

Description

  The present invention relates to a technique for producing a group 13 nitride crystal.

Currently, InAlGaN-based (group 13 nitride) semiconductors used for ultraviolet, violet to blue-green laser diodes are manufactured using a GaN substrate on the c-plane. The GaN free-standing substrate was grown thickly on the dissimilar substrate such as sapphire substrate or GaAs substrate by HVPE method by making full use of the growth method that reduces dislocation density such as ELO, advance-DEEP method, VAS method, etc. Thereafter, it is manufactured by a method of separating the GaN thick film from the heterogeneous substrate. The GaN substrate manufactured in this way has a transition density reduced to about 10 ⁶ cm ^{−2, and a} substrate having a size of 2 inches has been put into practical use.

  On the other hand, as one method for realizing a GaN substrate by liquid phase growth, a flux method in which nitrogen is dissolved in a mixed melt containing metallic sodium and metallic gallium to grow GaN crystals has been researched and developed. The flux method enables crystal growth at a relatively low temperature of 700 to 900 ° C. and a relatively low internal pressure of 3 to 8 MPa, and is a crystal growth method that can be industrialized relatively easily. Although in the research and development stage, a method of manufacturing a GaN free-standing substrate by liquid-phase epitaxial growth on a φ2 inch template substrate using a flux method has been realized.

  Patent Document 1 discloses a method of growing by changing the stirring condition of the melt in order to suppress dislocation and inclusion when crystal growth is performed on a template substrate. In this method, first, the first stirring condition set so that the growth surface is uneven is adopted to grow the crystal, and then the second stirring condition is set so that the growth surface becomes smooth. To grow crystals.

  In Patent Document 2, for the purpose of providing a manufacturing method capable of manufacturing a group 13 nitride substrate having a low dislocation density and high surface flatness, (i) a step of preparing a group 13 nitride semiconductor layer (Ii) forming a patterned mask film on the semiconductor layer; and (iii) using a plurality of semiconductor layers exposed from the mask film as seed crystals on the semiconductor layer by a flux method. A method for manufacturing a group 13 nitride substrate including a step of growing a nitride crystal is disclosed.

  In Patent Document 3, as a method for solving the problem that it is difficult to obtain a thick c-plane GaN substrate because the growth rate is slow in the method of growing GaN on the c-plane on the c-plane, a crystal is formed on the a-plane of the seed crystal. A method of growing is disclosed. In this method, the a-plane of the group 13 nitride semiconductor is formed in a band shape whose longitudinal direction is the m-axis direction, and the group 13 nitride semiconductor crystal is grown in a plate shape in the a-axis direction on the a-plane of the seed crystal. Thus, a c-plane substrate of a group 13 nitride semiconductor is manufactured.

  A GaN free-standing substrate having a diameter of 2 inches or more that is currently in practical use is a c-plane substrate manufactured by the HVPE method. Ultraviolet, violet to blue-green laser diodes have been put into practical use using c-plane substrates.

  However, as the In composition of the InGaN quantum well of the active layer increases, the difference in lattice constant from GaN increases and the strain increases. Therefore, the c-plane is a polar plane, so a piezo electric field is applied and the luminous efficiency is greatly reduced. . That is, the emission efficiency decreases as the wavelength increases from blue to green, and laser oscillation in pure green becomes difficult. In addition, in the strong current injection, a so-called blue shift occurs in which the emission wavelength is shortened, which also inhibits laser oscillation in the green region.

  In order to solve the above problem, a pure green laser using a semipolar or nonpolar substrate other than the c-plane has been developed. Recently, a pure green laser fabricated on a semipolar {20-21} plane substrate has been reported. However, in order to manufacture a semipolar {20-21} plane substrate by the HVPE method, it is necessary to grow a thick crystal in the c-axis direction, and thus it is difficult to manufacture a large substrate.

Moreover, the defect of a board | substrate is also about> 10 ^{< 5} > cm ^<-2 >. In the flux method, an attempt is made to produce a bulk by growing a liquid layer epitaxially on the c-plane and growing a crystal in the c-axis direction. However, when the crystal is grown in the c-axis direction, melt components such as metal sodium, metal gallium, or a mixture of sodium and gallium are easily included in the crystal during crystal growth. It is necessary to control precisely.

  This invention is made | formed in view of the above, Comprising: It aims at enabling it to manufacture the semipolar or nonpolar board | substrate with which inclusion was suppressed using the flux method.

In order to solve the above-described problems and achieve the object, the present invention provides an independent seed crystal having a crystal plane on which a group 13 nitride grows by c-axis orientation, the seed crystal and the seed crystal The main surface is a first step of preparing a seed crystal having a shape in which the a-axis direction of the growing group 13 nitride is a longitudinal direction, and the seed crystal is mixed and mixed with an alkali metal and a group 13 metal. A second step of starting crystal growth in the c-axis direction with respect to the principal surface by dissolving nitrogen in the mixed melt, and a crystal growth condition that affects the crystal growth By adjusting the third growth step so that the main growth surface of the group 13 nitride crystal is parallel to the {10-11} plane, and the group 13 nitride crystal is converted to the {10 -11} includes a fourth step of plane parallel slices, the said first The group 13 nitride crystal grown in this step has six {10-11} planes and a hexagonal bottom surface that is composed of a c-plane nitrogen polar plane and is in contact with the six {10-11} planes. In addition, in the manufacturing method of a group 13 nitride crystal, two of the six {10-11} planes facing each other and the bottom face are long in the a-axis direction.

  According to the present invention, it is possible to manufacture a semipolar or nonpolar substrate in which inclusion is suppressed using a flux method.

FIG. 1 is a flowchart showing an overall flow of a method for producing a group 13 nitride crystal according to Embodiment 1 of the present invention. FIG. 2 is a top view of the seed crystal according to Embodiment 1 and Example 1. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. FIG. 4 is a diagram illustrating a production apparatus for executing the method for producing a group 13 nitride crystal according to the first embodiment. FIG. 5 is a diagram showing a crystal growth process in the first embodiment. 6 is a diagram illustrating the shape of a GaN crystal obtained by crystal growth in Example 1. FIG. FIG. 7 is a bottom view of FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG. FIG. 9 is a diagram illustrating a crystal growth process according to the second embodiment. FIG. 10 is a top view of the seed crystal according to the second embodiment. 11 is a cross-sectional view taken along the line XI-XI in FIG. 12 is a diagram illustrating the shape of a GaN crystal obtained by crystal growth in Example 2. FIG. FIG. 13 is a bottom view of FIG. 14 is a cross-sectional view taken along line XIII-XIII in FIG. FIG. 15 is a view showing a cross section perpendicular to the longitudinal direction of the seed crystal used in the manufacturing process of the GaN substrate in Example 4. FIG. 16 is a diagram showing crystals manufactured in the manufacturing process of the GaN substrate in Example 4. FIG. 17 is a diagram showing a crystal obtained by further shaping the crystal shown in FIG. FIG. 18 is a diagram showing a GaN substrate manufactured in Example 4. FIG. 19 is a view showing a cross section perpendicular to the longitudinal direction of the seed crystal used in the manufacturing process of the GaN substrate in Example 5. FIG. 20 is a diagram showing crystals manufactured in the manufacturing process of the GaN substrate in Example 5. FIG. 21 is a diagram showing a crystal obtained by further shaping the crystal shown in FIG. FIG. 22 is a diagram showing a GaN substrate manufactured in Example 5. FIG. 23 is a view showing a cross section perpendicular to the longitudinal direction of the seed crystal used in the manufacturing process of the GaN substrate in Example 6. FIG. 24 is a diagram showing crystals manufactured in the manufacturing process of the GaN substrate in Example 6. FIG. 25 is a diagram showing a crystal obtained by further shaping the crystal shown in FIG. FIG. 26 is a view showing a GaN substrate manufactured in Example 6. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 shows an overall flow of a method for producing a group 13 nitride crystal according to the first embodiment (hereinafter abbreviated as the present production method). This production method is a method for producing a group 13 nitride crystal by a flux method. In the present embodiment, a case where a single crystal of gallium nitride (GaN) is manufactured as a group 13 nitride crystal will be described.

  This manufacturing method includes a seed crystal preparation step (first step) S1, a crystal growth start step (second step) S2, and a crystal growth continuation step 8 (third step) S3.

  The seed crystal preparation step S1 is a step of preparing a seed crystal that becomes the nucleus of crystal growth of the GaN crystal. FIG. 2 is a top view of the seed crystal 10, and FIG. 3 is a cross-sectional view taken along line III-III in FIG. The seed crystal 10 has a strip shape (a rectangular parallelepiped shape) and includes a sapphire substrate 11 and a main surface 12. The main surface 12 is formed on the upper surface of the sapphire substrate 11 and is composed of a GaN crystal. The main surface 12 is a surface serving as a main starting point for crystal growth of gallium nitride. An axis parallel to the longitudinal direction of the major surface 12 is defined as an a axis, an axis parallel to the lateral direction is defined as an m axis, and an axis perpendicular to the major surface 12 is defined as a c axis.

  The seed crystal 10 is a strip-shaped single crystal whose main surface 12 is a crystal plane on which group 13 nitride grows with c-axis orientation and whose longitudinal direction is substantially parallel to the a-axis of the growing group 13 nitride. Prepare a seed crystal. The material of the strip-shaped seed crystal 10 is not particularly limited as long as the main surface 12 is a crystal surface in which a group 13 nitride grows by c-axis orientation and becomes a single crystal. The seed crystal 10 may be a single crystal of the same material as a whole, or a structure in which a crystal in which a group 13 nitride is grown with c-axis orientation is stacked on a base substrate. The structure is not particularly limited.

  Moreover, the formation method of a strip-shaped seed crystal is not specifically limited, It can select suitably. For example, a crystal cut into a strip shape from a so-called template substrate in which a group 13 nitride crystal is epitaxially grown on the main surface of a different substrate can be used as the seed crystal 10. The material of the dissimilar substrate serving as the base of the template substrate is not particularly limited, and for example, a single crystal substrate such as sapphire, SiC, ZnO, MgAl 2 O 4 can be used.

  Considering the difference in thermal expansion coefficient between the group 13 nitride single crystal grown on the seed crystal 10 and the seed crystal 10, the group 13 nitride single crystal free-standing substrate from which the underlying heterogeneous substrate is removed is strip-shaped. It is preferable to use the cut-out crystal as a seed crystal. Furthermore, it is preferable to use, as the seed crystal 10, a crystal cut into a strip shape from a group 13 nitride crystal manufactured by LPE using a Na Flux method on a template substrate or a self-supporting substrate. Furthermore, a crystal produced by processing a bulk crystal grown by the same method as the crystal growth of the present embodiment (for example, Na Flux method using Na as an alkali metal) into a strip shape is used as a seed crystal 10. It is preferable to do.

  The longitudinal direction of seed crystal 10 is parallel or substantially parallel to the a-axis of the growing group 13 nitride single crystal. The short direction is parallel to or substantially parallel to the m-axis. The length in the longitudinal direction of the strip crystal is not particularly limited. As the length in the longitudinal direction is longer, a larger crystal can be produced in a shorter time, so that a desired length can be appropriately selected. The width (length in the short direction) D of the strip-shaped crystal can be selected as appropriate. However, when the width D of the strip-shaped crystal is increased, the c-plane of the group 13 nitride single crystal is likely to be formed. Since raw materials are used, the growth rate is slow. In addition, since the c-plane is likely to be uneven, inclusion is likely to occur. Therefore, it is desirable that the width D of the strip-shaped crystal is not increased more than necessary. The thickness is preferably 5 mm or less, more preferably 2 mm or less, and even more preferably 1 mm or less. The minimum width D can be determined by the ease of handling and holding the seed crystal.

  The crystal growth start step S2 is a step of starting crystal growth in the c-axis direction of the GaN crystal on the main surface 12. The crystal growth is started by placing the seed crystal 10 in a mixed melt containing a group 13 metal (Ga in the present embodiment) and an alkali metal (Na in the present embodiment). This is performed by dissolving nitrogen in a supersaturated state.

  Although a plurality of seed crystals 10 can be installed, they are installed at intervals so as not to contact each other during crystal growth. This interval limits the number of seed crystals 10 installed in one reaction vessel. The material of the reaction vessel can be selected as appropriate, but alumina, YAG, BN, SiC, TaC or the like can be used.

  In the reaction vessel, an alkali metal serving as a flux and a group 13 metal serving as a raw material are placed, and the temperature is raised to a crystal growth temperature in a pressure vessel filled with a nitrogen raw material gas. In the temperature raising process, the alkali metal and the group 13 metal are dissolved to form a mixed melt. Then, under a predetermined crystal growth temperature and a predetermined nitrogen raw material gas pressure, nitrogen dissolved in the mixed melt from the gas phase reacts with a group 13 metal in the mixed melt to cause 13 on the main surface of the seed crystal 10. Group nitride crystal growth begins.

  Specifically, in step S2, the nitrogen partial pressure is preferably in the range of 1 MPa to 6 MPa. In step S2, the temperature of the mixed melt (crystal growth temperature) is preferably in the range of 800 ° C to 900 ° C. For example, the ratio of the number of moles of alkali metal to the total number of moles of group 13 metal (for example, gallium) and alkali metal (for example, sodium) is in the range of 50% to 90%, and the crystal growth temperature of the mixed melt is set to It is preferable that the temperature is in the range of 850 ° C. to 900 ° C. and the nitrogen partial pressure is in the range of 1.5 MPa to 6 MPa. In a more preferred embodiment, the molar ratio of gallium to alkali metal is 0.3: 0.7, the crystal growth temperature is in the range of 860 ° C. to 870 ° C., and the nitrogen partial pressure is in the range of 2 MPa to 3.5 MPa. More preferably.

  The group 13 nitride grown on the main surface 12 of the seed crystal 10 is a c-axis oriented single crystal. As the alkali metal, Na is mainly used, but other alkali metals such as Li and K can also be used. Moreover, these can also be mixed and used. The group 13 metal is B, Al, Ga, In, and these can be used alone or in combination.

  Nitrogen gas is generally used as nitrogen in the gas phase, but ammonia or other gas containing nitrogen can be used. In addition to the gas containing nitrogen, an inert gas such as Ar or other gas can be mixed in the gas phase.

  In the mixed melt, in addition to alkali metals, group 13 metals and nitrogen, dopant materials such as Ge, Mg, Fe, and Mn, alkaline earth metals that become fluxes such as Ca, Ba, and Sr, and reduction of miscellaneous crystals are reduced. Carbon having an effect may be mixed.

  In the crystal growth continuation step S3, the slope that is not parallel to the main surface 12 of the GaN crystal 20 that has started crystal growth in the above step S2, that is, the main growth surface 21 that is the main crystal growth surface after the start of crystal growth is {10-11. } This is a step of continuing crystal growth so as to be parallel to the plane. Such control of the growth surface is performed by adjusting crystal growth conditions that affect the crystal growth of the GaN crystal 20. The crystal growth conditions include the nitrogen partial pressure, the temperature of the mixed melt, the mixing ratio of gallium (Ga) and sodium (Na) in the mixed melt, and the like.

  In step S3, the group 13 nitride single crystal starting to grow from the main surface 12 of the seed crystal 10 is maintained at a predetermined temperature and pressure, and crystal growth is continued with the {10-11} plane as the main growth surface 12. A group 13 nitride crystal 20 larger than the seed crystal 10 protruding from the main surface 12 of the seed crystal 10 is grown. The grown group 13 nitride crystal 20 has a cross-sectional shape perpendicular to the longitudinal direction of the seed crystal 10 that forms a substantially triangular shape or a substantially trapezoidal shape with the seed crystal 10 side as a base, and is parallel to the main surface 12 of the seed crystal 10. If the slope is not flat or substantially flat {10-11} and the cross-sectional shape is trapezoidal, the c-plane is formed on the upper surface.

  Although a recess may be formed along the longitudinal direction of the strip-shaped seed crystal 10 on the grown group 13 nitride crystal 20, the cross-sectional shape is generally triangular or trapezoidal. Is also within the scope of the present invention. If the bottom is larger than the top of the crystal and the main growth surface 21 serving as a slope is a {10-11} plane, the application range of the present invention is obtained.

  The crystal growth conditions in step S3 can be realized by adjusting the nitrogen partial pressure, the temperature of the mixed melt, the ratio of the number of moles of alkali metal to the total number of moles of gallium and alkali metal (for example, sodium), and the like. Specifically, in step S3, the nitrogen partial pressure is adjusted to a partial pressure at which the nitrogen in the melt has a relatively low degree of supersaturation. Specifically, it is preferable to be within a range of 2 MPa to 3.5 MPa.

  Further, in step S3, the temperature of the mixed melt (crystal growth temperature) may cause a problem in that crystals grow as a reaction vessel made of a material such as YAG or alumina dissolves or reacts in the melt. Adjust to no temperature. Specifically, it is preferable to set it within the range of 860 ° C to 870 ° C. Furthermore, when using a reaction vessel made of a material that is stable even at high temperatures, the temperature can be raised. Further, the ratio of the number of moles of alkali metal to the total number of moles of gallium and alkali metal (for example, sodium) is such that the main growth surface 21 that becomes the {10-11} plane is easily formed under the above-described conditions of nitrogen and temperature. In the range of 50% to 80%, more preferably 60% to 75%.

  In addition, by setting the step S2 to the same crystal growth conditions as the step S3 (conditions such as temperature, partial pressure, alkali metal molar ratio, etc.), the step S2 and the step S3 can be continued under the same conditions. it can.

  In the crystal growth of the group 13 nitride by the flux method, since the {10-11} plane is likely to form a flat crystal plane, the inclusion hardly enters the crystal. Therefore, in the crystal manufacturing method of the present embodiment, the precise control of the melt by means such as stirring required in the conventional flux method liquid phase epitaxial growth in which the crystal growth is performed with the c-plane as the main growth surface is possible. Inclusion is reduced and a group 13 nitride crystal can be produced. Further, since the seed crystal 10 has a strip shape, the time for growing a large crystal can be relatively short. Furthermore, the manufacturing method according to the present embodiment is different from the crystal manufacturing method in which a plurality of crystal start regions are formed on a substrate and adjacent crystals grown from the regions are combined to increase the size. Since a large single crystal is produced by growth, it is possible to produce a high-quality group 13 nitride single crystal 20 without generation of distortion or defects.

  FIG. 4 illustrates a manufacturing apparatus 100 for executing the manufacturing method. A reaction vessel 102 is installed in a closed pressure vessel 101 made of stainless steel. A mixed melt 103 containing gallium and sodium is held in the reaction vessel 102. A seed crystal 10 is placed in the mixed melt 103. In the mixed melt 103, the GaN crystal 20 grows using the seed crystal 10 as a nucleus.

The internal space 104 of the pressure vessel 101 is filled with nitrogen (N ₂ ) gas and argon (Ar) gas. The internal space 104 communicates with the gas supply pipe 105. The nitrogen pressure and the argon pressure in the internal space 104 are controlled by the pressure control devices 106 and 107 via the gas supply pipe 105. The gas supply pipe 105 is branched into a nitrogen supply pipe 108 and an argon supply pipe 109. Which of the nitrogen supply pipe 108 and the argon supply pipe 109 is connected to the internal space 104 can be determined by opening and closing the valves 110 and 111. The gas supply pipe 105 is provided with a pressure gauge 112 that monitors the total pressure in the pressure vessel 101. A valve 113 is installed between the pressure gauge 112 of the gas supply pipe 105 and the branch portion of both the pipes 108 and 109.

  Nitrogen gas is a raw material for gallium nitride. The reason why the nitrogen gas and the inert gas argon are mixed is to independently control the pressure of the nitrogen gas while increasing the total pressure and suppressing the evaporation of sodium. This makes it possible to control crystal growth with high accuracy.

  The reaction vessel 102 can be removed from the pressure vessel 101. The material of the reaction vessel 102 is not particularly limited, but BN sintered bodies, nitrides such as P-BN, oxides such as alumina and YAG, carbides such as SiC, and the like can be used. In this embodiment, YAG is used.

  A heater 115 is installed outside the pressure vessel 101. The temperature of the heater 115 can be controlled by a predetermined control device. The pressure vessel 101 can be removed from the manufacturing apparatus 100 at the valve 113 portion, and only the pressure vessel 101 portion can be put in the glove box for operation.

Example 1
Hereinafter, Example 1, which is an example of manufacturing a group 13 nitride crystal by the present manufacturing method, will be described. First, the first step S1 will be described. In the present example, a strip-shaped template substrate obtained by epitaxially growing a GaN layer serving as the main surface 12 on the sapphire substrate 11 by MOCVD was used as the seed crystal 10 (see FIG. 2).

  At this time, the strip-shaped seed crystal 10 was cut out so that the longitudinal direction thereof was substantially parallel to the a-axis of the GaN layer. After cutting along the m-axis from the back surface of the sapphire substrate 11 to the middle of the thickness direction of the substrate with a dicing device, the substrate was divided by applying pressure. By doing so, it was possible to cut out the strip-shaped seed crystal 10 whose longitudinal direction was along the m-axis of the sapphire substrate 11, that is, whose longitudinal direction was substantially parallel to the a-axis of the GaN layer (main surface 12). . In this example, the length of the seed crystal 10 in the longitudinal direction was 45 mm, and the length in the lateral direction (width D (see FIG. 3)) was 1 mm.

  Next, the second step S2 and the third step S3 will be described. In this example, the GaN crystal 20 was manufactured using the manufacturing apparatus 100 shown in FIG. The reaction vessel 102 was installed in a closed pressure vessel 101 made of stainless steel. A mixed melt 103 containing metallic sodium and metallic gallium was held in the reaction vessel 102.

The internal space 104 of the pressure vessel 101 was filled with nitrogen (N ₂ ) gas and argon (Ar) gas. A gas supply pipe 105 for controlling the nitrogen pressure and the argon pressure in the pressure vessel 101 was attached so as to penetrate the pressure vessel 101. The gas supply pipe 105 is branched into a nitrogen supply pipe 108 and an argon supply pipe 109, which can be separated by valves 110 and 111, respectively. The nitrogen pressure and the argon pressure were adjusted by pressure control devices 106 and 107, respectively.

  The total pressure in the pressure vessel 101 was monitored by a pressure gauge 112. The reason why the inert gas, argon, is mixed with the nitrogen gas, which is a gallium nitride raw material, is to independently control the pressure of the nitrogen gas while increasing the total pressure and suppressing the evaporation of sodium. Thereby, crystal growth with high controllability becomes possible.

  The reaction vessel 102 can be detached from the pressure vessel 101. The material of the reaction vessel 102 is not particularly limited, and nitrides such as BN aggregates and P-BN, oxides such as alumina and YAG, carbides such as SiC, and the like can be used. YAG was used.

  A heater 115 that can be controlled to an arbitrary temperature is installed outside the pressure vessel 101. The pressure vessel 101 can be detached from the manufacturing apparatus 100 at the valve 113 portion. Only the pressure vessel 101 part was put in the glove box and a predetermined operation was performed.

  Hereinafter, the process of crystal growth of the GaN crystal 20 in the second step S2 and the third step S3 using the manufacturing apparatus 100 will be described. FIG. 5 shows the process of crystal growth in this example. First, the pressure vessel 101 was separated from the manufacturing apparatus 100 at the valve 113 portion and placed in a glove box having a high purity Ar atmosphere with oxygen of 1 ppm or less and dew point of -80 ° C. or less.

  Next, the strip-shaped seed crystal 10 prepared in the first step S1 was placed in the reaction vessel 102 made of YAG having an inner diameter of 92 mm with the main surface 12 facing upward (see state A1 in FIG. 5). By setting the main surface 12 up, the rear surface side of the grown crystal, that is, the (000-1) c surface (see FIG. 3), which is a nitrogen polar surface, faces the bottom of the reaction vessel 102. Since the nitrogen polar plane is easily polycrystallized, it is desired to suppress the crystal growth on the nitrogen polar plane side in order to grow a GaN single crystal. By installing the seed crystal 10 so that the nitrogen polar surface faces the bottom of the reaction vessel 102, crystal growth on the nitrogen polar surface, that is, the (000-1) c-plane side can be suppressed, and polycrystallization is suppressed. We were able to.

  Next, gallium (Ga), which is a Group 13 metal raw material, and sodium (Na) as a flux were placed in the reaction vessel 102. In this example, 100 g of gallium and 77 g of sodium were added, and the molar ratio of gallium to sodium was set to 0.3: 0.7. Further, 0.34 g of carbon was added.

  Next, the reaction vessel 102 was installed in the pressure vessel 101. The pressure vessel 101 was sealed, the valve 113 was closed, and the reaction vessel 102 was shut off from the external atmosphere. Since these series of operations were performed in a glove box having a high-purity Ar gas atmosphere, the pressure vessel 101 was filled with Ar gas.

  Next, the pressure vessel 101 was taken out of the glove box and incorporated in the manufacturing apparatus 100. That is, the pressure vessel 101 was installed at a predetermined location adjacent to the heater 115 and connected to the nitrogen and argon gas supply pipe 105 at the valve 113 portion. The valve 113 and the valve 111 were opened, Ar gas was introduced from the argon supply pipe 109, the pressure was adjusted by the pressure control device 107, the total pressure in the pressure vessel 101 was set to 2.5 MPa, and the valve 111 was closed.

  Next, nitrogen gas was introduced from the nitrogen supply pipe 108, the pressure was adjusted by the pressure control device 106, the valve 110 was opened, and the total pressure in the pressure vessel 101 was 4 MPa. That is, the partial pressure of nitrogen in the internal space 104 of the pressure vessel 101 is 1.5 MPa. Thereafter, the valve 110 was closed and the pressure control device 106 was set to 8 MPa.

  Next, the heater 115 was energized to raise the temperature of the reaction vessel 102 to the crystal growth temperature. The crystal growth temperature was 870 ° C. Gallium and sodium in the reaction vessel 102 melted at the crystal growth temperature, and a mixed melt 103 was formed. The temperature of the mixed melt 103 became the same as the temperature of the reaction vessel 102. When the temperature was raised to the crystal growth temperature, the gas in the pressure vessel 101 was heated, and the total pressure became 8 MPa. That is, the nitrogen partial pressure was 3 MPa.

  Next, the valve 110 was opened, and a nitrogen gas pressure was applied at 8 MPa. This is because the partial pressure of nitrogen in the pressure vessel 101 is maintained at 3 MPa even when nitrogen is consumed by crystal growth of gallium nitride.

  In this way, nitrogen was dissolved in the mixed melt 103, and crystal growth of the GaN crystal 20 was started from the GaN layer on the main surface 12 of the seed crystal 10 (see state B1 in FIG. 5). Crystal growth was continued for 300 hours while maintaining the temperature in the reaction vessel 102 at 870 ° C. and the nitrogen gas partial pressure at 3 MPa.

  The GaN crystal 20 started growing from the main surface 12 of the seed crystal 10 and continued to grow out of the main surface 12. At this time, the main growth surface 21 which is the main crystal growth surface was a {10-10} plane (see FIG. 3). Crystal growth continued while the upper surface 22 parallel to the c-plane (main surface 12) was also slightly formed. Microcrystals 25 including polycrystals were formed on the bottom surface 23 serving as a nitrogen polar surface (see states C1 to E1 in FIG. 5).

  After the crystal growth was continued for 300 hours, the heater 115 was stopped and the mixed melt 103 was cooled to room temperature. After reducing the pressure in the pressure vessel 101, the pressure vessel 101 was opened. A single crystal GaN crystal 20 was grown on the seed crystal 10 in the reaction vessel 102.

  FIG. 6 illustrates the shape of the GaN crystal 20 obtained by the crystal growth. FIG. 7 is a bottom view of FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG. The GaN crystal 20 has a trapezoidal shape having a hexagonal bottom surface 23 and a top surface 22 having long two sides parallel to the longitudinal direction of the seed crystal 10. A recess 24 is formed in the upper surface 22 along the longitudinal direction. The cross section of the GaN crystal 20 was substantially trapezoidal. The six slopes (main growth surface 21) were {10-11} planes that were relatively flat. The bottom surface 23 was formed on a nitrogen polar surface ((000-1) c surface). Microcrystals 25 (see FIG. 5) were attached to the bottom surface 23. However, the amount of microcrystals 25 was small because the crystal growth was limited on the bottom surface of the reaction vessel 102. The sapphire substrate 11, which is a template substrate for the seed crystal 10, was located in the approximate center of the bottom surface 23. The sapphire substrate 11 was cracked.

  The grown GaN crystal 20 has a size of about 59 mm in the longitudinal direction of the bottom surface 23, about 12 mm in the length (width) in the short direction of the bottom surface 23, and about 45 mm in the longitudinal direction of the top surface 22. The height was about 10 mm.

By SIMS analysis, 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of sodium was detected in the GaN crystal 20. Moreover, although GaN crystal 20 contained sodium at an impurity level, there was no inclusion such as metal gallium, metal sodium, or an alloy of gallium and sodium that would cause cracks or voids.

(Example 2)
Hereinafter, Example 2 of the present embodiment will be described. In addition, the same code | symbol may be attached | subjected about the location which show | plays the same or similar effect as the said Example 1, and the description may be abbreviate | omitted.

  FIG. 9 shows the process of crystal growth in this example. FIG. 10 is a top view of the seed crystal 30 according to the present embodiment. 11 is a cross-sectional view taken along the line XI-XI in FIG. FIG. 12 illustrates the shape of the GaN crystal 40 obtained by crystal growth in this example. FIG. 13 is a bottom view of FIG. 14 is a cross-sectional view taken along line XIII-XIII in FIG.

  First, the process of preparing the strip-shaped seed crystal 30 by 1st process S1 is demonstrated. In the present example, a seed crystal 30 made of a crystal cut out in a strip shape from a φ2 inch GaN free-standing substrate made of HVPE and having a (0001) c plane as the main surface 12 was used. A strip-shaped crystal could be easily cut out by hanging the back surface of the GaN substrate several times along the a-axis (m-plane) of the GaN free-standing substrate with a diamond pen. In this way, a strip-shaped seed crystal 30 whose longitudinal direction was approximately parallel to the a-axis of GaN was cut out (see FIG. 10).

  In this example, a seed crystal 30 having a length in the longitudinal direction of 45 mm and a length (width) in the lateral direction of 0.8 mm was used. The difference from Example 1 is that a crystal cut from a HVPE GaN free-standing substrate was used as the seed crystal 30 and that the length in the short direction of the seed crystal 30 was 0.8 mm.

  Next, the second step S2 and the third step S3 will be described. Since the manufacturing apparatus 100 used in this example is the same as that used in Example 1 and the crystal growth conditions are the same, only the differences from Example 1 will be described below. In this example, an alumina container having an inner diameter of 92 mm and a purity of 99.99% was used as the reaction container 102. The seed crystal 30 was placed so that the main surface 12 ((0001) c plane) was on top (see state A2 in FIG. 9). Crystal growth conditions such as raw material charge, growth temperature, nitrogen gas partial pressure, and growth time were the same as in Example 1 (see states B2 to E2 in FIG. 9).

  A GaN crystal 40 as shown in FIG. 12 was obtained by the above process. The GaN crystal 40 is a single crystal having a hexagonal bottom surface 23 with two long sides parallel to the longitudinal direction of the seed crystal 30 and a cross section perpendicular to the longitudinal direction of the seed crystal 30 having a generally triangular shape ( (See FIGS. 13 and 14). In the upper portion 41 of the GaN crystal 40, a slight recess 24 was formed along the longitudinal direction thereof. The six slopes (main growth surface 21) were {10-11} planes that were relatively flat. The bottom surface 23 was formed on a nitrogen polar surface ((000-1) c surface). Microcrystals 25 (see FIG. 9) were attached to the bottom surface 23. However, the amount of microcrystals 25 was small because the crystal growth was limited on the bottom surface of the reaction vessel 102. The seed crystal 30 was located approximately at the center of the bottom surface 23. No cracks or the like were found in the seed crystal 30.

  The size of the grown GaN crystal 40 is such that the length in the longitudinal direction of the bottom surface 23 is about 59 mm, the length (width) in the short direction of the bottom surface 23 is about 12 mm, and the length in the longitudinal direction of the upper portion 41 is about 45 mm. The height was about 11 mm.

By SIMS analysis, 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of sodium was detected in the GaN crystal 40. Further, although GaN crystal 40 contained sodium at an impurity level, there was no inclusion such as metal gallium, metal sodium, or an alloy of gallium and sodium that would cause cracks or voids.

(Example 3)
In this example, a seed crystal 50 made of a crystal cut out in a strip shape from a GaN substrate manufactured by processing a bulk GaN crystal manufactured by a flux method was used. The GaN substrate is manufactured from a bulk crystal that is enlarged using a GaN crystal spontaneously grown by a flux method as a seed crystal.

Since the bulk GaN substrate manufactured in this manner grows crystals without using a heterogeneous substrate, unlike the HVPE GaN free-standing substrate shown in Example 2, the residual stress and warpage are small and the locality radius is large. The c-axis and a-axis are more aligned. Moreover, the dislocation density of the c-plane which is the main surface 12 of the bulk GaN substrate is 10 ² cm ⁻² or less, whereas the dislocation density of the HVPE self-supporting substrate is about 10 ⁶ cm ⁻² , and the bulk GaN The dislocation density of the substrate is 4 or more orders of magnitude smaller than that of a free-standing substrate made of HVPE.

  In this example, since such a high-quality crystal was used as the seed crystal 50, a high-quality GaN crystal 60 could be grown. The strip-shaped seed crystal 50 could be easily cut out by hanging the back surface of the bulk GaN substrate several times along the a-axis (m-plane) with a diamond pen. In this example, four seed crystals 50 having a length in the longitudinal direction of 15 mm and a length (width) in the lateral direction of 0.8 mm were used.

  Next, the second step S2 and the third step S3 will be described. Since the manufacturing apparatus 100 used in this example is the same as that used in Example 1 and the crystal growth conditions are the same, only the differences from Example 1 will be described below. In this example, an alumina container having an inner diameter of 92 mm and a purity of 99.99% was used as the reaction container 102. Four seed crystals 50 were placed with the main surface 12 ((0001) c plane) facing upward and spaced apart. Regarding the amount of raw material charged, 165 g of gallium and 127 g of sodium were added, and the molar ratio of gallium to sodium was set to 0.3: 0.7. Further, 0.57 g of carbon was added.

  In both the second step S2 and the third step S3, the temperature and pressure are set to the same crystal growth conditions as in Example 1, the temperature in the reaction vessel 102 is maintained at 870 ° C., the nitrogen gas partial pressure is maintained at 3 MPa, and crystallization is performed for 700 hours. Continued growth. Similar to Example 2, the GaN crystal 60 obtained by this process has a hexagonal bottom surface 23 having two long sides parallel to the longitudinal direction of the seed crystal 50 (30). The vertical cross section was a single crystal having a substantially triangular shape (see FIGS. 13 and 14). In the upper portion 41 of the GaN crystal 40, a slight recess 24 was formed along the longitudinal direction thereof. The six slopes (main growth surface 21) were {10-11} planes that were relatively flat. The bottom surface 23 was formed on a nitrogen polar surface ((000-1) c surface). Microcrystals 25 (see FIG. 9) were attached to the bottom surface 23. However, the amount of microcrystals 25 was small because the crystal growth was limited on the bottom surface of the reaction vessel 102. The seed crystal 50 was located approximately at the center of the bottom surface 23. No cracks or the like were found in the seed crystal 50.

  The size of the grown GaN crystal 20 is such that the length in the longitudinal direction of the bottom surface 23 is about 47 to 50 mm, the length (width) in the short direction of the bottom surface 23 is about 28 to 30 mm, and the length in the longitudinal direction of the upper portion 41. Was about 15 mm and the height was about 24-26 mm.

By SIMS analysis, 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of sodium was detected in the GaN crystal 40. Moreover, although GaN crystal 20 contained sodium at an impurity level, there was no inclusion such as metal gallium, metal sodium, or an alloy of gallium and sodium that would cause cracks or voids.

Example 4
In the following, by processing the GaN crystals 20, 40, 60 manufactured as in Example 1, Example 2, or Example 3, these {10-11} planes or {10-1-1} planes An example of manufacturing a semipolar GaN substrate (a group 13 nitride crystal substrate) having the main surface 12 as a base material is shown.

  15 to 18 show the manufacturing process of the GaN substrates 73 and 74 in this embodiment. In this example, the GaN substrates 73 and 74 were manufactured using the GaN crystal 20 manufactured in Example 1. FIG. 15 shows a cross section perpendicular to the longitudinal direction of the seed crystal 10 of the GaN crystal 20 according to the first embodiment.

First, both side portions in the longitudinal direction of the GaN crystal 20 are cut to form the GaN crystal 20 into a quadrangular prism shape. Next, as shown by a broken line in FIG. 15, a GaN crystal 20 formed into a quadrangular prism shape was sliced in parallel with the {10-11} plane, thereby producing a crystal 71 as shown in FIG. 16. The maximum size of the crystal 71 was about 45 × 11 mm ² . The surface of the crystal before slicing is defined as the (10-11) plane, and the back surface that appears after slicing is defined as the (10-1-1) plane. The (10-11) plane is a semipolar plane in which the nitrogen polarity is dominant, and is expressed as {10-11} as an equivalent crystal plane.

  Next, as shown in FIG. 17, a crystal 72 was produced by further shaping the crystal 71 obtained by slicing into a desired size. The (10-11) plane or (10-1-1) plane of the crystal 72 was polished and then subjected to CMP treatment. Thus, as shown in FIG. 18, square semipolar GaN substrates 73 and 74 having the (10-11) plane or the (10-1-1) plane as the main surface 12 were manufactured.

  When the cross sections of the GaN substrates 73 and 74 were observed with a fluorescence microscope, growth fringes 75 were observed. The growth stripes 75 were formed in parallel with the {10-11} plane which is the main surface 12 of the GaN substrates 73 and 74.

By SIMS analysis, 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of sodium was detected in the GaN substrates 73 and 74. Moreover, although GaN substrates 73 and 74 contained sodium at an impurity level, there was no inclusion of metal gallium, metal sodium, or an alloy of gallium and sodium that would cause cracks and voids.

(Example 5)
In this example, the GaN crystal 40 manufactured in Example 2 was cut out differently from Example 4, so that a square semipolar GaN substrate having a {20-21} plane as the main surface 12 was obtained. Manufactured.

  19 to 22 show the manufacturing process of the GaN substrate 83 in this embodiment. In this example, the GaN substrate 83 was manufactured using the GaN crystal 40 manufactured in Example 2. FIG. 19 shows a cross section perpendicular to the longitudinal direction of the seed crystal 30 of the GaN crystal 40 according to the second embodiment.

First, both side portions in the longitudinal direction of the GaN crystal 40 are cut to form the GaN crystal 40 into a triangular prism shape. Next, as shown by a broken line in FIG. 19, the GaN crystal 40 formed into a triangular prism shape is sliced in parallel to the {20-21} plane, thereby producing a crystal 81 as shown in FIG. The maximum size of the crystal 81 was about 45 × 11 mm ² .

  Next, as shown in FIG. 21, a crystal 82 obtained by further shaping the crystal 81 obtained by slicing into a desired size was manufactured. The surface of the crystal 82 was polished and then subjected to CMP treatment. In this way, as shown in FIG. 22, a square semipolar GaN substrate 83 having the (20-21) plane as the main surface 12 was manufactured.

  When the cross section of the GaN substrate 83 was observed with a fluorescence microscope, growth stripes 85 were observed. The growth stripes 85 were formed in parallel with the {10-11} plane.

By SIMS analysis, 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of sodium was detected in the GaN substrate 83. Further, although GaN substrate 83 contained sodium at an impurity level, there was no inclusion of metal gallium, metal sodium, or an alloy of gallium and sodium that would cause cracks or voids.

(Example 6)
In this example, the GaN crystal 60 manufactured in Example 3 was cut out differently from Example 4 and Example 5 to obtain a square half with a {10-10} m plane as the main surface 12. A polar GaN substrate 93 was manufactured.

  23 to 26 show the manufacturing process of the GaN substrate 93 in the present embodiment. In this example, the GaN substrate 93 was manufactured using the GaN crystal 60 manufactured in Example 3. FIG. 23 shows a cross section perpendicular to the longitudinal direction of the seed crystal 50 of the GaN crystal 60 according to the third embodiment.

First, both side portions in the longitudinal direction of the GaN crystal 60 are cut to form the GaN crystal 60 into a triangular prism shape. Next, as shown by a broken line in FIG. 23, a GaN crystal 60 formed into a triangular prism shape is sliced in parallel with the {10-10} plane, thereby producing crystals 91 of various sizes as shown in FIG. did. Among these, the size of the largest crystal 91A was about 15 × 26 mm ² .

  Next, as shown in FIG. 25, a crystal 92 was manufactured by further shaping the crystal 91 obtained by slicing into a desired size. The surface of the crystal 92 was polished and then subjected to CMP treatment. In this way, as shown in FIG. 26, a square semipolar GaN substrate 93 having the (10-10) plane as the main surface 12 was manufactured.

  When the cross section of the GaN substrate 93 was observed with a fluorescence microscope, growth fringes 95 were observed. The growth stripes 95 were formed in parallel with the {10-11} plane.

By SIMS analysis, 10 ¹⁴ to 10 ¹⁵ cm ⁻³ of sodium was detected in the GaN substrate 93. Further, although GaN substrate 93 contained sodium at an impurity level, there was no inclusion of metal gallium, metal sodium, or an alloy of gallium and sodium that would cause cracks or voids.

10, 30, 50 Seed crystal 11 Sapphire substrate 12 Main surface 20, 40, 60 GaN crystal (Group 13 nitride crystal)
21 Main growth surface 22 Upper surface 23 Bottom surface 24 Recess 25 Microcrystal 41 Upper portion 71, 72, 81, 82, 91, 92 Crystal 73, 74, 83, 93 GaN substrate (Group 13 nitride crystal substrate)
75, 85, 95 Growth stripes 100 (Group 13 nitride crystal) production apparatus 101 Pressure vessel 102 Reaction vessel 103 Mixed melt 104 Internal space 105 Gas supply pipe 106,107 Pressure control device 108 Nitrogen supply pipe 109 Argon supply pipe 110 , 111, 113 Valve 112 Pressure gauge 115 Heater

International Publication No. 2010/092736 JP 2005-12171 A JP 2010-37153 A

Claims (5)

An independent seed crystal having a crystal plane on which a group 13 nitride grows with c-axis orientation as a main surface, wherein the seed crystal and the main surface are longitudinal in the a-axis direction of the group 13 nitride to be grown A first step of preparing a seed crystal having a shape of
The seed crystal is placed in a mixed melt containing an alkali metal and a group 13 metal, and nitrogen is dissolved in the mixed melt to start crystal growth in the c-axis direction with respect to the main surface. Two steps;
Adjusting the crystal growth conditions affecting the crystal growth, a third step of continuing the crystal growth so that the main growth surface of the group 13 nitride crystal is parallel to the {10-11} plane;
Slicing the group 13 nitride crystal parallel to the {10-11} plane ,
The group 13 nitride crystal grown in the third step is composed of six {10-11} planes and a hexagonal bottom surface in contact with the six {10-11} planes, which are c-plane nitrogen polar planes. Have
A method for producing a group 13 nitride crystal, wherein two opposing faces and the bottom face of the six {10-11} faces are long in the a-axis direction. The method for producing a group 13 nitride crystal according to claim 1, wherein the crystal growth conditions are adjusted so that the degree of supersaturation of nitrogen in the mixed melt is within a predetermined range. The group 13 nitride crystal according to claim 2, wherein the crystal growth conditions include a nitrogen partial pressure, a temperature of the mixed melt, and a mixing ratio of the alkali metal and the group 13 metal in the mixed melt. Manufacturing method. In the third step,
The nitrogen partial pressure is 2 to 3.5 MPa,
The temperature of the mixed melt is 860 to 870 ° C.,
The method for producing a group 13 nitride crystal according to claim 3, wherein a ratio of the number of moles of the alkali metal to the total number of moles of the alkali metal and the group 13 metal is 50 to 80%. The main surface of the seed crystal is rectangular,
The method for producing a group 13 nitride crystal according to any one of claims 1 to 4, wherein a length of the rectangular shape in a short direction is 1 mm or less.

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