JP4600160B2 - Group III nitride crystal growth method - Google Patents

Description

The present invention relates to materials and large method of a group III nitride sintered crystallization growth composed for forming various semiconductor devices.

  Group III nitride crystals formed from Group III elements such as Al, Ga and In and nitrogen are very useful as materials for forming various semiconductor devices such as light emitting elements, electronic elements, and semiconductor sensors. There is a need to develop a method for growing a large group III nitride crystal.

  Various growth methods such as sublimation method, HVPE (hydride vapor phase epitaxy) method, MBE (molecular beam epitaxy) method, MOCVD (metal organic chemical vapor volume) method are proposed as growth methods for group III nitride crystals. Has been. Among these vapor phase growth methods, the sublimation method has been proposed a method for growing a group III nitride crystal by the sublimation method from the viewpoint of obtaining a crystal with good crystallinity (for example, a crystal having a small half width of X-ray diffraction). (For example, see Non-Patent Document 1 and Non-Patent Document 2).

However, when an AlN crystal is grown without using a seed crystal in the sublimation method, a needle-like AlN crystal is obtained (see FIG. 5 of Non-Patent Document 1), and the growth of the AlN crystal using the SiC seed crystal If only, an AlN crystal having irregularities on the surface is obtained (see FIG. 3 of Non-Patent Document 2, etc.), and a large group III nitride crystal serving as a material for forming various semiconductor devices is obtained. It was difficult.
B. Liu and 8 others, “The Durability of Various Crucible Materials for Aluminum Nitride Crystal Growth by Sublimation”, MRS Internet J. Nitride Semicond. Res. 9, 6 (2004) V. Noveski, 4 others, “Growth of AlN crystals on AlN / SiC seeds by AlN powder sublimation in nitrogen atmosphere”, MRS Internet J. Nitride Semicond. Res. 9, 2 (2004)

The present invention aims at providing a material with large III-nitride crystal growth method comprising for forming various semiconductor devices.

The present invention is a method for growing a group III nitride crystal by a sublimation method, wherein a group III nitride raw material is disposed inside a crystal growth chamber having an opening provided inside a crystal growth vessel having an opening. And supplying a mixed gas of nitrogen gas and inert gas to the outside of the crystal growth vessel, and performing gas exchange between the outside of the crystal growth vessel and the inside of the crystal growth chamber , and the group III nitridation inside the crystal growth chamber A method for growing a group III nitride crystal including a step of growing a physical crystal.

  In the group III nitride crystal according to the present invention, the mixed gas may have a ratio of an inert gas partial pressure to a nitrogen gas partial pressure of 0.1 or more. Furthermore, the crystal growth temperature can be 2000 ° C. or higher.

According to the present invention, a large group III-nitride crystal method growth as a material for forming various semiconductor devices can be provided.

  A method for growing a group III nitride crystal according to the present invention is a method for growing a group III nitride crystal by a sublimation method with reference to FIGS. 1 to 3, and includes an inside of a crystal growth vessel 12 having an opening 12 h. The group III nitride raw material 1 is disposed on the crystal growth vessel 12, a mixed gas of nitrogen gas and inert gas is supplied to the outside of the crystal growth vessel 12, and the crystal is exchanged between the outside and the inside of the crystal growth vessel 12. A step of growing the group III nitride crystal 3 inside the growth vessel 12 is included.

  The ratio of the nitrogen gas partial pressure to the group III element gas partial pressure by supplying a mixed gas so as to satisfy the above condition to the outside of the crystal growth vessel 12 having the opening 12h in which the group III nitride raw material 1 is accommodated. It is possible to carry out large-scale crystal growth under the conditions lower than in the prior art. This point will be described in detail below.

  The sublimation method in the present invention refers to a method of obtaining a group III nitride crystal 3 by sublimating the group III nitride raw material 1 and then solidifying it again with reference to FIGS. In crystal growth by the sublimation method, for example, high-frequency heating type vertical sublimation furnaces 10, 20, and 30 as shown in FIGS. A crystal growth vessel 12 having an opening 12 h is provided at the center of the reaction vessel 11 in these sublimation furnaces 10, 20, and 30. Around the crystal growth vessel 12, the inside and outside of the crystal growth vessel 12 are provided. A heat insulating material 15 is provided so as to ensure ventilation.

  In addition, a high-frequency heating coil 16 for heating the crystal growth vessel 12 is provided at the outer central portion of the reaction vessel 11. Further, at the end of the reaction vessel 11, a gas introduction port 11 a and a gas exhaust port 11 b for supplying a mixed gas of nitrogen gas and inert gas or nitrogen gas to the outside of the crystal growth vessel 12 in the reaction vessel 11. A radiation thermometer 17 for measuring the temperature of the lower surface and the upper surface of the crystal growth vessel 12 is provided.

Here, inside the crystal growth vessel 12 of FIG. 1, there is provided a crystal growth chamber 13 partitioned into a raw material arrangement chamber 13a and a crystal growth chamber 13b, and an opening 13j is provided in the raw material arrangement chamber 13a. An opening 13k is also provided between the raw material arrangement compartment 13a and the crystal growth compartment 13b. Further, a crystal growth chamber 13 having an opening 13h is provided inside the crystal growth vessel 12 of FIGS. Note that the crystal growth chamber 13 in FIG. 3 is designed such that the upper space is narrowed in a spindle shape. As the material for the crystal growth vessel 12, when using high-frequency heating, graphite or refractory metal such as W or Ta that is easy to be high-frequency heated and can withstand a high-temperature atmosphere during crystal growth is used. The material constituting the crystal growth chamber 13 is not particularly limited as long as it is a material having heat resistance and mechanical strength with respect to the growth temperature of the group III nitride crystal, but a refractory metal such as W or Ta, WC, Carbides such as TaC, oxides such as Y ₂ O ₃ and ZrO _2, and nitrides such as BN are preferably used.

  The crystal growth chamber 13 of FIGS. 1 to 3 has the above-described structural differences, but in any case, the inside of the crystal growth chamber 13 and the crystal length only through the openings 13h, 13j, 13k, and 12h. It is a semi-closed room in which ventilation with the outside of the container 12 is ensured.

  Referring to FIGS. 1 to 3, group III nitride crystal raw material 1 is arranged in crystal growth chamber 13 having openings 13j, 13k, 13h inside crystal growth vessel 12 having opening 12h, and crystal growth is performed. A mixed gas of nitrogen gas and inert gas is supplied to the outside of the vessel 12 to exchange gases between the outside of the crystal growth vessel 12 and the inside of the crystal growth chamber 13, and the group III inside the crystal growth chamber 13. A nitride crystal 3 is grown.

  In a normal sublimation method, nitrogen gas is introduced into the crystal growth chamber 13 from the outside of the crystal growth vessel 12. If the nitrogen pressure is too high, the crystal will not grow. Conversely, if the nitrogen pressure is too low, the crystal will be crystallized although the growth rate is high. Therefore, it is necessary to grow under an appropriate nitrogen pressure.

On the other hand, the present inventors supply a mixed gas of an inert gas and a nitrogen gas instead of a nitrogen gas as a gas supplied to the outside of the crystal growth vessel 12, thereby reducing the nitrogen gas lower than the normal growth conditions. It was found that even when grown at partial pressure, it does not crystallize. More preferably, it has been found that good large crystals can be easily grown when grown at a low nitrogen gas partial pressure. Here, it is a preferable range of nitrogen pressure, but the following formula (1)
(V / III ratio) = p _N2 / p _III = (p _N2 ) ^1.5 / (K (T)) ^0.5 (1)
K (T) = exp {54.11- (151576 / T)}
(In formula (1), T represents an absolute temperature (unit: K))
(Source: Journal of Crystal Growth 220 (2000) 243)
It is preferable for the growth of a group III nitride crystal having a large size and good crystallinity to have a V / III ratio defined by ≦ 100. Specifically, a bulk AlN single crystal can be grown instead of needles. However, if the V / III ratio is less than 5, polycrystallization tends to occur, which is not preferable.

  Here, the inert gas means an inert gas in the sense that it does not react with the group III element gas and the nitrogen gas, and examples thereof include argon (Ar) gas and helium (He) gas.

  In the group III nitride crystal growth method according to the present invention, it is preferable that the ratio of the partial pressure of the inert gas to the partial pressure of the nitrogen gas is 0.1 or more. When the ratio of the partial pressure of the inert gas is less than 0.1, the effect of suppressing polycrystallization is reduced. From this viewpoint, it is more preferable that the ratio of the partial pressure of the inert gas to the partial pressure of the nitrogen gas is 1 or more. Further, the total pressure of the supplied mixed gas is preferably 1013 kPa (10 atm) or less from the mechanical strength of the sublimation furnace. From these, the ratio of the partial pressure of the inert gas to the partial pressure of the nitrogen gas is preferably 1000 or less, and more preferably 100 or less. If the ratio of the partial pressure of the inert gas exceeds 1000, the nitrogen gas introduced into the crystal growth chamber 13 is reduced, and the V / III ratio is extremely reduced. Be inhibited.

  In the group III nitride crystal growth method according to the present invention, the V / III ratio is preferably 5 or more and 100 or less. When the V / III ratio is less than 5, growth of the group III nitride crystal is inhibited, and when it exceeds 100, crystal growth in the c-axis direction of the group III nitride crystal occurs preferentially and a large group III nitride crystal. It becomes difficult to obtain.

  In the group III nitride crystal growth method according to the present invention, it is preferable to grow the crystal in the direction perpendicular to the c-axis in addition to the c-axis direction of the group III nitride crystal by satisfying the above conditions.

  In the group III nitride crystal growth method according to the present invention, the crystal growth temperature is preferably set to 2000 ° C. or higher. If the crystal growth temperature is less than 2000 ° C., the cause is unknown, but crystal growth in the direction perpendicular to the c-axis is difficult to occur.

  The group III nitride raw material used in the method for growing a group III nitride crystal according to the present invention is not particularly limited, but from the viewpoint of easy acquisition or production of the raw material, a group III nitride amorphous material, group III A nitride polycrystal is preferably used. Specifically, a group III nitride powder, a group III nitride sintered body, a polycrystal obtained by directly nitriding a group III metal at a high temperature, a sublimation / recrystallized polycrystal, and the like are preferably used. The seed crystal used in the method for growing a group III nitride crystal according to the present invention is not particularly limited, but from the viewpoint of good crystallinity of the crystal to be grown, a SiC seed crystal, a group III nitride seed crystal, etc. are preferable. Used.

  The group III nitride crystal according to the present invention is a crystal obtained by the above growth method. The obtained group III nitride crystal is sliced parallel to a plane (C plane) perpendicular to the c-axis, the surface is polished, and the work-affected layer is removed by etching to obtain a group III nitride crystal substrate. Here, the slice plane of the group III nitride crystal is not only a plane oriented in the C plane, but also a plane parallel to the A plane, R plane, M plane or S plane, or an arbitrary inclination with respect to these planes. It can be a surface having.

  The group III nitride crystal substrate obtained as described above includes light-emitting elements such as light-emitting diodes and laser diodes, electronic elements such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (high electron mobility transistors), and temperature sensors. , Pressure sensors, acceleration sensors, radiation sensors, semiconductor transistors such as visible-ultraviolet light detection groups, SAW devices (surface acoustic wave elements), MEMS (microelectromechanical system) parts, piezoelectric vibrators, resonators, piezoelectric actuators, etc. Can be used.

  The group III nitride crystal and its growth method according to the present invention will be described more specifically with reference to the following comparative examples and examples.

(Comparative Examples 1 and 2 and Example 1)
Comparative Examples 1 and 2 and Example 1 are examples in which an AlN crystal which is a group III nitride crystal was grown without using a seed crystal by a sublimation method.

  In the above example, referring to FIG. 1, a crystal growth chamber 13 partitioned into a raw material placement chamber 13a and a crystal growth chamber 13b by a partition material made of BN is provided inside a C crucible which is a crystal growth vessel 12. The sublimation furnace 10 having was used. Here, the inner diameter of the raw material arrangement compartment 13a was 50 mm and the height was 50 mm, and the inner diameter of the crystal growth compartment 13b was 50 mm and the height was 20 mm. The diameters of the openings 13j, 13k, and 12h were 3 mm, 3 mm, and 5 mm, respectively.

  When a group III nitride crystal is grown by a sublimation method without using a seed crystal, a large number of group III nitride crystals tend to be generated rapidly and disorderly. Is provided with a partition having an opening 13k that is divided into a raw material arrangement compartment 13a and a crystal growth compartment 13b for growing a group III nitride crystal 3, whereby the gas of the group III nitride raw material 1 into the crystal growth compartment 13b is provided. By reducing the supply rate, the crystal growth rate of the group III nitride crystal 3 was reduced to facilitate the growth of a group III nitride crystal of good quality.

  In the above example, an AlN crystal was grown as follows. First, 100 g of an AlN sintered body having an oxygen concentration of 500 ppm as the group III nitride material was stored in the material arrangement compartment 13a. Nitrogen gas or mixed gas (nitrogen gas and argon gas) inside the reaction vessel 11 and outside the crystal growth vessel 12 so as to satisfy the conditions shown in Table 1 for each of Comparative Examples 1 and 2 and Example 1. The temperature of the crystal growth chamber 13 inside the crystal growth vessel 12 is raised using the high-frequency heating coil 16, and the temperature of the lower surface of the crystal growth vessel 12 (AlN sintered body (group III nitride raw material 2)) is increased. An AlN crystal (Group III nitride crystal 3) was grown at a heating temperature of 2120 ° C. and an upper surface temperature (corresponding to the growth temperature of the AlN crystal (Group III nitride crystal 3)) of 2100 ° C. The crystal growth time was 50 hours. The crystal growth conditions and the results are summarized in Table 1.

  Referring to Table 1, in the comparative example 1 in which only the nitrogen gas of 101.3 kPa (1 atm) was supplied and the V / III ratio was 132, the needle-like AlN crystal was formed, but it was 20.26 kPa (0 In Comparative Example 2 in which only the nitrogen gas of .2 atm) was supplied and the V / III ratio was 11.8, a porous AlN crystal containing many pores was obtained. In contrast, a mixed gas of 20.26 kPa (0.2 atm) nitrogen gas and 81.04 hPa (0.8 atm) argon gas was supplied to set the V / III ratio to 11.8. In No. 1, several massive AlN crystals were obtained. The maximum AlN crystal obtained in Example 1 was a single crystal having a maximum length in the c-axis direction of 20 mm, a maximum length in the a-axis direction of 15 mm, and a weight of 5.2 g. Here, whether or not the obtained crystal was a single crystal was confirmed by measuring an X-ray diffraction pattern.

  In Comparative Example 1, nitrogen gas was supplied and the V / III ratio was made larger than 100, so that only acicular crystals were obtained. In Comparative Example 2, even if nitrogen gas was supplied and the V / III ratio was 5 or more and 100 or less, argon gas was obtained. Since there is no (inert gas), it is considered that Al gas was transported too quickly and only porous polycrystallized crystals were obtained. On the other hand, in Example 1 in which a mixed gas of nitrogen gas and argon gas was supplied and the V / III ratio was 5 or more and 100 or less, a massive single crystal was obtained.

(Comparative Example 3, Example 2)
Comparative Example 3 and Example 2 are examples in which an AlN crystal that is a group III nitride crystal was grown using a seed crystal by a sublimation method.

  In the above example, referring to FIG. 2, a sublimation furnace 20 having a crystal growth chamber 13 formed of a partition material made of BN inside a C crucible which is a crystal growth vessel 12 was used. Here, the inner diameter of the crystal growth chamber 13 was 50 mm, and the height was 70 mm. The diameters of the openings 13h and 12h were 3 mm and 5 mm, respectively.

  In the above example, since a seed crystal is used, a crystal with good quality is easily obtained as compared with the case where no seed crystal is used. Therefore, the crystal growth chamber 13 is not divided into a raw material arrangement chamber and a crystal growth chamber.

  In the above example, an AlN crystal was grown as follows. First, a 6H—SiC seed crystal having a diameter of 50 mm × thickness of 0.3 mm is disposed as a seed crystal 2 in the upper part of the crystal growth chamber 13, and an oxygen concentration of 500 ppm as a group III nitride material 1 is provided in the lower part of the crystal growth chamber 13 100 g of an AlN sintered body was stored. Nitrogen gas or mixed gas (nitrogen gas and argon gas) was allowed to flow inside the reaction vessel 11 and outside the crystal growth vessel 12 so that the conditions shown in Table 2 were satisfied for each of Comparative Example 3 and Example 2. However, the temperature of the crystal growth chamber 13 inside the crystal growth vessel 12 is raised using the high-frequency heating coil 16, and the temperature of the lower surface of the crystal growth vessel 12 (heating temperature of the AlN sintered body (group III nitride raw material 2)) is increased. And an upper surface temperature (corresponding to the growth temperature of the AlN crystal (Group III nitride crystal 3)) of 1900 ° C. to grow an AlN crystal (Group III nitride crystal 3). The crystal growth time was 30 hours. The crystal growth conditions and the results are summarized in Table 2.

  Referring to Table 2, in Comparative Example 3 in which only the nitrogen gas of 50.65 kPa (0.5 atm) was supplied and the V / III ratio was 882, there was a region where no AlN crystal grew on the seed crystal. Unevenness was also observed on the surface of the grown AlN crystal. On the other hand, in Example 2 in which a mixed gas of nitrogen gas of 10.13 kPa (0.1 atm) and argon gas of 91.17 kPa (0.9 atm) was supplied and the V / III ratio was 79. Obtained an AlN single crystal having a smooth surface and a diameter of 50 mm and a thickness of 2.5 mm.

  In the case of growing an AlN crystal using a seed crystal by the sublimation method, in Comparative Example 3, since the V / III ratio was made larger than 100 by supplying nitrogen gas, only an AlN crystal having irregularities on the surface was obtained. In Example 2, since a mixed gas of nitrogen gas and argon gas was supplied to make the V / III ratio 5 or more and 100 or less, an AlN single crystal having a smooth surface was obtained.

(Comparative Example 4, Example 3)
Comparative Example 4 and Example 3 are examples in which an AlN crystal that is a group III nitride crystal was grown using a seed crystal by a sublimation method, and whether or not crystal growth occurred in a direction perpendicular to the c-axis of the AlN crystal This is an example of a comparative study.

  In the above example, with reference to FIG. 3, a sublimation furnace 30 having a crystal growth chamber 13 formed of a partition material made of BN inside a C crucible which is a crystal growth vessel 12 was used. The upper portion of the crystal growth material 3 in FIG. 3 is formed in a weight shape in order to confirm the presence or absence of crystal growth in the direction perpendicular to the c-axis of the AlN crystal. Here, the crystal growth chamber 13 is formed of a frustoconical space having an upper surface inner diameter of 30 mm, a height of 20 mm, and a lower surface of 50 mm, and a cylindrical space having an inner diameter of 50 mm and a height of 50 mm. The diameters of the openings 13h and 12h were 3 mm and 5 mm, respectively.

  In the above example, since a seed crystal is used, a crystal with good quality is easily obtained as compared with the case where no seed crystal is used. Therefore, the crystal growth chamber 13 is not divided into a raw material arrangement chamber and a crystal growth chamber.

  In the above example, an AlN crystal was grown as follows. First, an AlN seed crystal having a diameter of 30 mm and a thickness of 0.3 mm is disposed as the seed crystal 2 in the upper part of the crystal growth chamber 13 (the crystal growth surface is an Al plane that is a (0001) plane), As Group III nitride raw material 1, 100 g of an AlN sintered body having an oxygen concentration of 500 ppm was stored. Nitrogen gas or mixed gas (nitrogen gas and argon gas) was allowed to flow inside the reaction vessel 11 and outside the crystal growth vessel 12 so that the conditions shown in Table 3 were satisfied for each of Comparative Example 4 and Example 3. However, the temperature of the crystal growth chamber 13 inside the crystal growth vessel 12 is raised using the high-frequency heating coil 16, and the temperature of the lower surface of the crystal growth vessel 12 (heating temperature of the AlN sintered body (group III nitride raw material 2)) is increased. And an upper surface temperature (corresponding to the growth temperature of the AlN crystal (Group III nitride crystal 3)) of 2100 ° C. to grow an AlN crystal (Group III nitride crystal 3). The crystal growth time was 30 hours. The crystal growth conditions and the results are summarized in Table 3.

  Referring to Table 3, in Comparative Example 4 in which a nitrogen gas of 101.3 kPa (1 atm) was supplied and the V / III ratio was 132, an AlN crystal grew from the seed crystal in a columnar shape in the c-axis direction, Crystal growth was not observed in the direction perpendicular to the c-axis. Further, the grown AlN crystal was brought into contact with the AlN sintered body as a raw material to be polycrystallized, and the growth mass could not be measured. On the other hand, Example 3 in which a mixed gas of 20.26 kPa (0.2 atm) nitrogen gas and 81.04 kPa (0.8 atm) argon gas was supplied to set the V / III ratio to 11.8. In FIG. 5, an AlN single crystal grew from the seed crystal in the c-axis direction and the plane direction perpendicular to the c-axis, and grew in a truncated cone shape along the inner wall of the crystal growth material 3. Thus, a truncated cone-shaped AlN single crystal having an upper surface diameter of 30 mm, a lower surface diameter of 50 mm, and a height of 16 mm was obtained.

  In Comparative Example 4, nitrogen gas was supplied to increase the V / III ratio from 100, so that only a cylindrical AlN crystal grown only in the c-axis direction was obtained, whereas in Example 3, nitrogen gas and argon gas were obtained. And a V / III ratio of 5 or more and 100 or less was obtained, and a frustoconical AlN single crystal grown in the c-axis direction and the direction perpendicular to the c-axis direction was obtained.

  Further, the AlN crystal (single crystal) obtained in the above Example 3 was sliced parallel to the (0001) plane (C plane), the surface was polished, and the work-affected layer was etched to obtain a diameter of 30 mm × An AlN single crystal substrate having a thickness of 1 mm was obtained. This AlN single crystal substrate has an RMS (Root Mean Square: square root of a value obtained by averaging the squares of deviations from the average line to the measurement curve) observed by an AFM (atomic force microscope) within a 10 μm square mirror surface roughness of 50 nm. (500cm) or less, which can be applied to various semiconductor devices.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a model which shows one specific example of the growth method of the group III nitride crystal by a sublimation method. It is a model which shows the other specific example of the growth method of the group III nitride crystal by the sublimation method. It is a model which shows the other specific example of the growth method of the group III nitride crystal by a sublimation method.

Explanation of symbols

  1 Group III nitride raw material, 2 seed crystal, 3 Group III nitride crystal, 10, 20, 30 sublimation furnace, 11 reaction vessel, 11a gas introduction port, 11b gas exhaust port, 12 crystal growth vessel, 12h, 13j, 13k , 13h opening, 13 crystal growth chamber, 13a raw material placement compartment, 13b crystal growth compartment, 15 heat insulating material, 16 high-frequency heating coil, 17 radiation thermometer.

Claims (3)

A method for growing a group III nitride crystal by a sublimation method,
A group III nitride raw material is disposed inside a crystal growth chamber having an opening provided inside a crystal growth vessel having an opening, and a mixed gas of nitrogen gas and inert gas is placed outside the crystal growth vessel. And a step of growing a group III nitride crystal inside the crystal growth chamber while performing gas exchange between the outside of the crystal growth vessel and the inside of the crystal growth chamber. Method.   2. The method for growing a group III nitride crystal according to claim 1, wherein the mixed gas has a ratio of a partial pressure of the inert gas to a partial pressure of the nitrogen gas of 0.1 or more.   The method for growing a group III nitride crystal according to claim 1 or 2, wherein the crystal growth temperature is 2000 ° C or higher.

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