JP4552516B2 - Method for producing AlN single crystal - Google Patents

Description

The present invention relates to a method for producing a compound semiconductor single crystal, and more particularly to an improvement in a method for producing a hexagonal AlN single crystal.

In recent years, various electronic devices have been manufactured using compound semiconductor single crystals. Among compound semiconductor single crystals, hexagonal Al _x Ga _y In _{1- (x + y)} N (0 <x ≦ 1, 0 ≦ y <1, x + y ≦ 1) single crystals are used for various electronic devices. It can be preferably used for making. In the present specification, an Al _x Ga _y In _{1- (x + y)} N (0 <x ≦ 1, 0 ≦ y <1, x + y ≦ 1) semiconductor may be abbreviated as an AlGaInN-based semiconductor.

Incidentally, it is not easy to grow an AlGaInN-based semiconductor single crystal as compared to a silicon single crystal. Among the AlGaInN semiconductor single crystals, it is not easy to grow an AlN single crystal. More specifically, it is not easy to grow a large AlN single crystal capable of obtaining a large-diameter wafer. Further, it is not easy to efficiently grow an AlN single crystal at a high growth rate. Furthermore, it is not easy to grow a high-quality AlN single crystal having a low dislocation density and a low impurity concentration.

In relation to the method of manufacturing an AlN single crystal that is not easy to grow, in US Pat. No. 5,858,086 of Patent Document 1, AlN is grown at a relatively high growth rate (0.5 mm / hr) using a sublimation method. Methods for growing crystals have been reported. In addition, US Pat. No. 6,296,956 of Patent Document 2 reports a method of growing an AlN crystal having a diameter of 1 inch or more and an impurity amount of 450 ppm or less. Further, US Pat. No. 6,0017,481 of Patent Document 3 reports a method of growing an AlN crystal having a relatively large size of 10 mm × 10 mm × 0.3 mm or more.
US Pat. No. 5,858,086 US Pat. No. 6,296,956 US Patent No. 6,0017,481

  As described in Patent Documents 1 to 3, regarding the growth of AlN single crystals, a method of growing at a relatively high growth rate, a method of growing a single crystal having a relatively low impurity concentration, and a single crystal having a relatively large diameter There have been attempts to cultivate food.

However, in general, it is not easy to grow a large, high-quality AlN single crystal efficiently at a high growth rate, and improvement of the growing method is desired. In particular, hexagonal AlN crystals have anisotropy depending on crystallographic orientation with respect to the direction in which crystal growth is easy and the direction in which dislocations are easy to propagate. Therefore, it is not easy to grow a hexagonal AlN crystal from a small seed crystal to a large-diameter bulk single crystal or to grow a single crystal of good quality. Moreover, the hexagonal AlN crystal that can be used as a seed crystal is usually limited to a size of several millimeters square.

  More specifically, for example, as a method for growing an AlN crystal using a sublimation method, crystal growth by natural nucleation and heteroepitaxial crystal growth on a SiC substrate are known. However, in any of these cases, it is difficult to stably obtain a large and high-quality AlN crystal for the following reasons.

  For example, in natural nucleation, a single crystal of good quality can be obtained, but the single crystal size is limited. That is, since crystal nuclei are generated at a plurality of locations, there is a limit to the size that can be grown, and the crystal yield is low. Furthermore, since the generation location of crystal nuclei cannot be specified, it is difficult to control the growth rate and the reproducibility (stability) is low.

  On the other hand, in hetero-growth, relatively large-diameter crystals can be grown, but the quality of the crystals obtained is not sufficient. For example, the quality of the AlN crystal is likely to deteriorate due to lattice mismatch between the SiC substrate and the AlN crystal grown thereon. Further, warpage and cracks are likely to occur due to a difference in thermal expansion coefficient between the SiC substrate and the AlN crystal. In particular, the AlN single crystal has a problem that cracks are likely to occur among the AlGaInN single crystals. Furthermore, the purity of the AlN crystal tends to decrease due to the diffusion of impurities from the substrate.

Therefore, in order to obtain a A l N single crystal having a large diameter, dissimilar substrate (SiC substrate, Al, etc. ₂ O ₃ substrate) of large-diameter amorphous layer as a buffer phase between the AlN single crystal to be grown and Attempts have been made to grow crystals of good quality by forming a mask layer or forming a mask layer for blocking dislocations, but sufficient crystal quality has not yet been obtained.

In view of such a state of the prior art, the present invention aims to improve a method for growing a hexagonal AlN crystal and efficiently provide a high-quality AlN single crystal having a relatively large diameter and a high growth rate. Is doing.

The method for producing an AlN single crystal according to the present invention is a method of growing a hexagonal AlN single crystal using at least one of a sublimation method and an HVPE (halide vapor phase epitaxy) method in the <0001> direction. a step of crystal growth in the preferred growing conditions, then the single crystal is characterized in that it comprises a step of crystal growth under conditions that preferentially grown in a direction intersecting the <0001> direction.

That is, the sublimation method can be preferably used for crystal growth of AlN. The HVPE (halide vapor phase epitaxy) method is preferably used for crystal growth in at least one direction of the thickness direction and the lateral direction of the single crystal to be grown, and can be preferably used particularly in combination with the sublimation method.

Note that the direction intersecting the <0001> direction may be the <10-10> direction. The grown AlN single crystal is preferably homoepitaxially grown on the same AlN seed crystal .

AlN single crystal of a hexagonal system obtained by the manufacturing method as above mentioned Ru good in the present invention can be utilized in the fabrication of various electronic devices. Such electronic devices include light emitting diodes, laser diodes, rectifiers, bipolar transistors, field effect transistors, HEMTs (high electron mobility transistors), temperature sensors, pressure sensors, radiation sensors, visible / ultraviolet light sensors, and surface acoustic waves. It can be a device or the like .

According to the crystal growth method of the present invention, an unprecedented large-diameter and high-quality AlN single crystal can be stably obtained with good reproducibility, and the single crystal can be used for manufacturing various electronic devices. .

For example, the dislocation density can be reduced to 1 × 10 ⁷ cm ⁻² or less in a range of 50% or more of the surface of the AlN single crystal (peripheral crystal quality is liable to deteriorate). It is also possible to reduce it to 10 ⁵ cm ⁻² or less.

In the present invention, in the process of growing a large-diameter AlN single crystal, the growth orientation is changed in at least two stages. By such a single crystal growth method, an AlN single crystal having a diameter of 1 inch or more and a thickness of 500 μm or more can be obtained. Under favorable conditions, a single crystal having a diameter of 2 inches or more and a thickness of 500 μm or more can also be obtained. In particular, it is preferable to homoepitaxially grow an AlN single crystal on an AlN seed crystal. With this method, a relatively small-sized seed crystal of about 5 mm square or less can be used as a base substrate.

  The crystal growth direction is changed in two stages at least in the thickness direction and the diameter direction of the crystal. For example, the {10} plane which is grown so that the thickness of the crystal increases in a direction perpendicular to the {0001} plane (abbreviated as C plane) and then intersects the {0001} plane (Abbreviated as M plane), {11-20} plane (abbreviated as A plane), {10-11} plane (abbreviated as S plane), or {10-12} plane (R plane) The crystal can be grown in a direction perpendicular to (abbreviated).

By the way, in order to grow an AlN crystal at a high speed, it is preferable to grow the surface in a direction perpendicular to the stable C-plane. Easy to propagate to. Therefore, by selecting a direction perpendicular to the c-axis (for example, a direction perpendicular to the M-plane or A-plane) as one of the crystal growth directions, a crystal with few dislocations can be easily obtained.

  As a specific example of the method for changing the crystal growth direction, the following sublimation method or HVPE method can be used.

  When an AlN single crystal is grown by the sublimation method, the crystal grows preferentially in the direction perpendicular to the C plane at a seed crystal temperature of less than about 2000 ° C., and the M plane (or C plane at a seed crystal temperature of about 2200 ° C. or higher). The crystal grows preferentially in the direction perpendicular to the other plane intersecting. Accordingly, two-stage crystal growth in different growth directions is possible by performing crystal growth at these different growth temperatures before and after the time.

  In the sublimation method, the crystal growth rate in the direction perpendicular to the M plane is smaller than the direction perpendicular to the C plane under the same conditions such as the amount of source gas supply. Here, in the direction perpendicular to the M plane, if conditions such as the supply amount of the source gas are changed so as to obtain the same growth rate as that in the direction perpendicular to the C plane, polycrystals and defects are easily generated. In this case, the generation of polycrystals and defects can be suppressed by supplying the source gas substantially parallel to the M plane.

  When crystal growth is performed by gradually changing the growth temperature in the sublimation method, if it takes a long time to change the growth temperature, a transition region in which the crystal growth mode changes is generated, or impurity gas is contaminated on the growth surface. There is a risk that good crystals cannot be obtained. Therefore, for example, after the crystal growth in one direction is completed, the transport of sublimation seeds to the seed crystal is interrupted, and the crucible (seed crystal and raw material) is instantaneously moved to the temperature zone for crystal growth in the next direction. Therefore, it is desirable to suppress changes in other conditions accompanying changes in the growth temperature.

  In the HVPE method, crystals grow almost depending on the crystal plane of the seed crystal. Therefore, for example, if the C plane of the seed crystal is opposed to the transport direction of the source gas, the crystal can be grown mainly in the direction perpendicular to the C plane. Similarly, if the M plane of the seed crystal is opposed to the transport direction of the source gas, it is possible to grow a crystal mainly in a direction perpendicular to the M plane. Note that the HVPE method has a feature that the single crystal to be grown is highly purified and various types of doping are relatively easy compared to the sublimation method.

  The above-described sublimation method and HVPE method according to the present invention can be particularly preferably applied to the growth of AlN single crystals in which large-diameter seed crystals are difficult to obtain and the crystal growth anisotropy is strong.

(Embodiment 1)
In the block diagram of FIG. 1, an example of a single crystal growing apparatus that can be preferably used for manufacturing a compound semiconductor single crystal by the sublimation method of the present invention is schematically illustrated. This single crystal growing apparatus includes a quartz tube 1, and a graphite crucible 4 is housed in a heat insulating material container 3 supported by a support base 2 in the quartz tube 1. A coil 6 connected to an RF (high frequency) power source 5 is disposed on the outer periphery of the quartz tube 1. Note that the relative positional relationship between the graphite crucible 4 and the high-frequency coil 6 can be changed by changing the height of the support base 2 whose height can be adjusted from the outside of the quartz tube 1 or by changing the position of the coil 6. The temperature distribution of the graphite crucible 4 can be changed. Further, the temperature distribution of the graphite crucible 4 can be changed by dividing the coil 6 into an upper part and a lower part and individually controlling the high frequency power applied to each part by the RF power source 5.

If the seed crystal and the sublimation raw material powder are set in the crucible 4, the inside of the quartz tube 1 is evacuated by the rotary pump 8 through the valve 7. When the inside of the quartz tube 1 is evacuated, the valve 7 is closed, and nitrogen gas is introduced into the quartz tube 1 from the nitrogen gas (N ₂ ) cylinder 9 through the flow meter 10. Maintained in a nitrogen gas atmosphere under pressure.

  In a state where the inside of the quartz tube 1 is maintained in a nitrogen gas atmosphere at normal pressure, high frequency power is applied from the RF power source 5 to the coil 6, and the graphite crucible 4 can be induction heated. The heat insulating material container 3 has holes (not shown in FIG. 1) for measuring the temperature of the crucible 4 at the upper part and the lower part thereof. The temperature of the upper part of the crucible 4 can be measured by the upper optical thermometer 12a through the upper mirror 11a. Similarly, the temperature of the lower part of the crucible 4 can be measured by the lower optical thermometer 12b through the lower mirror 11b.

  2 schematically illustrates the inside of the graphite crucible 4 set in the crystal growth apparatus of FIG. 1 in Embodiment 1 of the present invention. As shown in FIG. 2, the heat insulating material container 3 in FIG. 1 includes a heat insulating material container main body 3a and a heat insulating material cover 3b. The central portion of the heat insulating material lid 3b includes a hole 3c for measuring the temperature of the upper portion of the graphite crucible 4 with the upper optical thermometer 12a. Similarly, the bottom of the heat insulating material container body 3a includes a hole 3d for measuring the temperature of the lower part of the graphite crucible 4 with the lower optical thermometer 12b.

  The graphite crucible 4 accommodated in such a heat insulating material container 3 includes a graphite container 4a and a graphite lid 4b, and accommodates a sublimation deposition reaction container 13a and its lid 13b. These reaction vessel 13a and its lid 13b are preferably formed of carbon or BN (boron nitride) coated with PG (pyrolytic graphite), for example. The reaction vessel 13a is loaded with AlN powder. The lid 13b has a hole 13c with an enlarged lower portion, and the AlN seed crystal 15a is placed on the lid 13b so as to face the hole 13c.

  In the first embodiment, an AlN seed crystal 15a having a C-plane as a main surface and a diameter of 5 mm and a thickness of 500 μm is placed on the lid 13b of the reaction vessel 13a as shown in FIG. In this state, the following two stages of crystal growth (A) and (B) are performed.

  First, in crystal growth (A), the upper part of the crucible 4 in a nitrogen atmosphere is heated to 1900 ° C. and the lower part is heated to 2000 ° C. by the RF heating coil 6 to sublimate AlN from the AlN powder 14 and seed. It is deposited on the C-plane which is the main surface of the crystal 15a. By continuing such heating for about 10 hours, an AlN single crystal having a diameter of about 5 mm and a thickness of 4 mm can be formed. That is, in the case of crystal growth (A), it can be seen that the crystal grows mainly only in the thickness direction and is preferential growth in the direction perpendicular to the C plane.

  Thereafter, in the crystal growth (B), the upper portion of the crucible 4 is further heated to 2300 ° C. and the lower portion thereof is heated to 2400 ° C., thereby further sublimating AlN. By continuing such heating for about 20 hours, an AlN crystal having a diameter of about 1 inch and a thickness of 5 mm can be formed. That is, in the case of crystal growth (B), it can be seen that the crystal grows mainly only in the lateral direction and is preferential growth in the direction perpendicular to the M plane.

(Embodiment 2)
In the second embodiment, crystal growth (A) and (B) in the first embodiment are performed in reverse order. In Embodiment 2 like this, as in Embodiment 1, an AlN single crystal having a diameter of about 1 inch and a thickness of 5 mm can be obtained.

(Embodiment 3)
In the schematic cross-sectional view of FIG. 3, an example of a single crystal growing apparatus that can be preferably used for manufacturing a compound semiconductor single crystal by the HVPE method of the present invention is schematically illustrated. This single crystal growing apparatus includes a quartz tube 21 in which a seed crystal 15b is supported on a support base 22. The support table 22 is coupled to a support bar 22a inserted from the side of the quartz tube 21, and the orientation of the seed crystal 15b can be changed by rotating the support bar 22a. A heater (not shown) is disposed around the quartz tube 21. The raw material gas for HVPE is introduced into the quartz tube 21 from the first and second gas introduction pipes 23 and 24, and the remaining gas that has not contributed to HVPE is discharged from the discharge port 25.

In the third embodiment, the AlN wafer obtained by the first or second embodiment can be used as the seed crystal 15b. For example, the AlN seed crystal 15b has a C-plane main surface and may have a diameter of about 1 inch and a thickness of 1.5 mm. Crystals are grown on such an AlN wafer 15b in the direction perpendicular to the C-plane using the HVPE method. That is, AlCl ₃ is introduced into the quartz tube 21 from the first gas introduction tube 23 and simultaneously NH ₃ is introduced from the second gas introduction tube 24. These gases are blown onto the C surface, which is the main surface of the seed crystal 15b held at 1000 ° C. As a result, an AlN single crystal having a diameter of about 1 inch and a thickness of 3.5 mm is obtained by HVPE. In this case, it can be seen that preferential growth occurs in a direction perpendicular to the C-plane of the seed crystal 15b to which the source gas is sprayed.

(Embodiment 4)
In the fourth embodiment, the HVPE method using the apparatus shown in FIG. 3 is used as in the third embodiment. For example, an AlN wafer having a diameter of about 5 mm and a thickness of 300 μm is used as the seed crystal 15b. However, the seed crystal 15b in the fourth embodiment has an M plane as its main surface.

  First, the M surface, which is the main surface of the seed crystal 15b of Embodiment 4, is made to face the raw material gas flow, and a crystal is grown to about 25 mm in a direction perpendicular to the M surface. Thereafter, the support rod 22a is rotated around its axis, so that the C-plane of the crystal faces the source gas flow. Then, a crystal is further grown to about 25 mm in the direction perpendicular to the C plane. From the AlN single crystal thus obtained, an AlN wafer of about 25 mm × 25 mm × 500 μm can be cut out.

Note that growth of AlN single crystals in various embodiments described above it has been describes, supplying GaCl and / or InCl from the gas inlet pipe of another system in addition to the conditions for growing the AlN single crystal by HVPE Thus, a crystal of Al _x Ga _y In _{1- (x + y)} N (0 <x ≦ 1, 0 ≦ y <1, x + y ≦ 1) can be formed in the same manner.

From the AlN single crystal obtained as described above according to the present invention, it is possible to obtain a wafer sliced by tilting in any direction from the C plane, A plane, R plane, M plane, S plane or those planes. Also, if the surface is processed so that the root mean square roughness is 500 mm or less in the range of 10 microns square on the main surface of those wafers, various electronic devices can be formed using that region. . Such electronic devices include light emitting diodes, laser diodes, rectifiers, bipolar transistors, field effect transistors, HEMTs, temperature sensors, pressure sensors, radiation sensors, visible / ultraviolet light sensors, surface acoustic wave devices, and the like.

As described above, according to the present invention, it is possible to efficiently provide high quality hexagonal AlN single crystal at a high growth rate in large diameter, such AlN single crystal for the production of various electronic devices Can be used .

It is a block diagram which shows an example of the single crystal growth apparatus which can be preferably used for manufacture of the AlN single crystal by the sublimation method of this invention. It is typical sectional drawing illustrating an example of the inside of a crucible in the single crystal growth apparatus of FIG. It is typical sectional drawing which shows an example of the single crystal growth apparatus which can be preferably used for manufacture of the AlN single crystal by the HVPE method of this invention.

  DESCRIPTION OF SYMBOLS 1 Quartz tube, 2 support stand, 3 heat insulation container, 3a heat insulation material container main body, 3b heat insulation material cover, 3c, 3d temperature measurement hole, 4 graphite crucible, 4a graphite container, 4b graphite cover, 5 RF (high frequency) power supply, 6 coil, 7 valve, 8 rotary pump, 9 nitrogen gas cylinder, 10 flow meter, 11a upper mirror, 11b lower mirror, 12a upper optical thermometer, 12b lower optical thermometer, 13a reaction vessel, 13b reaction vessel lid, 14 AlN powder, 15a, 15b AlN seed crystal, 21 quartz tube, 22 support base, 22a support rod, 23, 24 gas introduction tube, 25 gas exhaust port.

Claims (3)

In the process of growing the sublimation method and the HVPE method at least one of using hexagonal AlN single crystal, wherein the steps of the single crystal is grown under conditions that preferentially grown in the <0001> direction, then the single crystal method of manufacturing AlN single crystal but which comprises a step of crystal growth under conditions that preferentially grown in a direction intersecting the <0001> direction. The manufacturing method according to claim 1, wherein a direction intersecting with the <0001> direction is a <10-10> direction. The single crystal production method according to claim 1 or 2, characterized in that it is homoepitaxially grown on the AlN seed crystal.

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