JP2012180232A - Method for producing nitride semiconductor single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nitride semiconductor single crystal.SOLUTION: The method for producing a nitride semiconductor single crystal 9 includes: a step of preparing a base substrate 8 in a crystal growing furnace; and a step of growing a group III nitride semiconductor crystal 9 by reacting the halogenated product of a group III element with a compound containing a nitrogen element while mixing C surfaces and faceted surfaces other than the C surface on the base substrate 8. In the growing step, a substance containing nitride is introduced into a crystal growing furnace, and oxygen is incorporated in the area grown on the faceted surface other than the C surface to grow the group III nitride semiconductor crystal 9.

Description

  The present invention relates to a method for producing a nitride semiconductor single crystal used in light-emitting devices such as light-emitting diodes and semiconductor lasers and electronic devices.

  Nitride semiconductors typified by gallium nitride have a large band gap, and the transition between bands is a direct transition type. Therefore, light emitting diodes such as ultraviolet, blue and green, semiconductor lasers and the like on the relatively short wavelength side It is a material useful as a substrate for semiconductor devices such as light emitting elements and electronic devices.

  Various methods for manufacturing such a nitride semiconductor crystal have been proposed. For example, in Cited Document 1, a method for growing a gallium nitride crystal while simultaneously causing facets other than the C-plane and the C-plane to appear is proposed. ing. In this document, the C-plane of the nitride semiconductor crystal is hardly doped with oxygen. Therefore, by doping oxygen using a technique such as including water in the source gas during crystal growth, It has been proposed to dope oxygen through the facet plane.

On the other hand, it is known that Si is used to control the dopant concentration in the gallium nitride crystal. For example, in Cited Document 2, nitriding is performed by using silicon tetrafluoride (SiF ₄ ) gas as a doping gas. It has been proposed to control the resistivity in gallium crystals. In addition, in Cited Document 2, oxygen as a dopant is not efficiently incorporated into the C-plane and has poor controllability as an n-type dopant, so that the oxygen concentration is reduced to a concentration of 5 × 10 ¹⁶ cm ⁻³ or less. It has been proposed that the resistivity of a physical semiconductor crystal can be controlled more stably.

JP 2006-282504 A JP 2009-126721 A

In the cited document 1, in a method of growing a crystal while causing facets other than the C plane and the C plane to appear at the same time, the oxygen doping amount can be accurately controlled by doping oxygen. However, as a result of investigations by the present inventors, it has been found that even when oxygen doping is performed, the carrier concentration at the C-plane growth portion becomes extremely low, so that the carrier concentration becomes uneven within the crystal. . Therefore, when the obtained nitride semiconductor crystal is used as a semiconductor substrate or the like, a problem has been found that a portion having a low carrier concentration has a low resistivity and insufficient conductivity.
The portion where the carrier concentration in the crystal is low cannot satisfy the market demand for high-quality crystals and is not commercialized, resulting in a problem in manufacturing efficiency. The present invention has been made under such circumstances, and in the method for growing a crystal while causing facets other than the C-plane and the C-plane to appear at the same time, a nitride semiconductor crystal with less carrier concentration unevenness is produced in the crystal. It is an object of the present invention to provide a method for doing this.

The present inventors have intensively researched for nitride semiconductor crystals with less carrier concentration unevenness in the crystal, and when growing a group III nitride semiconductor crystal having a C-plane area and a facet area, C-plane growth is performed. In order to make up for the carrier concentration of the portion, the inventors have found that a nitride semiconductor crystal with less carrier concentration unevenness in the crystal can be obtained by growing the crystal while doping silicon element, and completed the invention.

That is, the present invention is as follows.
A step of preparing a base substrate in the crystal growth furnace, and a group III nitriding process while reacting a group III element halide and a compound containing a nitrogen element so that the facet surface other than the C plane and the C plane is mixed on the base substrate. A method for producing a group III nitride semiconductor crystal comprising a growth step of growing a compound semiconductor crystal,
The growth step is characterized in that a silicon-containing material is introduced into the crystal growth furnace and a group III nitride semiconductor crystal is grown while oxygen is contained in a region grown on a facet plane other than the C plane. A method for producing a group III nitride semiconductor crystal.

  Moreover, it is preferable that the silicon-containing substance in the growth step is introduced into the crystal growth furnace as a gas from a conduit.

  Since the nitride semiconductor crystal manufactured by the manufacturing method of the present invention has little variation in carrier concentration in the crystal, even if high conductivity is required, most of the crystal can be used as a product. Production efficiency is very high with little production loss. Moreover, since it is a crystal having a C-plane area and a facet area, it is a crystal having high crack resistance. According to the present invention, such a high quality nitride semiconductor crystal can be provided.

It is a conceptual diagram of the crystal growth which implement | achieves facet growth by comprising an unevenness | corrugation in a base substrate. It is a conceptual diagram of the crystal growth which implement | achieves facet growth by giving a mask pattern to a base substrate. It is the schematic which shows an example of the crystal manufacturing apparatus used for HVPE method.

  The method for producing a nitride semiconductor crystal of the present invention will be described in detail below. The description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

1) Step of preparing a base substrate in a crystal growth furnace The manufacturing method of the present invention includes a step of preparing a base substrate in a crystal growth furnace. The crystal growth furnace used in the production method of the present invention can be used without particular limitation as long as it can be used for crystal growth, and it is sufficient that at least the base substrate can be prepared in the crystal growth furnace. Then, the base substrate is disposed at a position where normal crystal growth is possible in the crystal growth furnace.

  The type of the base substrate used in the present invention is not particularly limited, and can be appropriately selected from silicon, sapphire, gallium arsenide, gallium nitride, aluminum nitride, zinc oxide, and the like.

2) Group III nitride semiconductor crystal growth step In the crystal growth step of the present invention, a group III element halide and a nitrogen element-containing compound are reacted to mix a C-face and a facet other than the C-face on the base substrate. This is a growth process for growing a group III nitride semiconductor crystal.

The group III element halide used in the production method of the present invention is not particularly limited as long as it is a raw material for the group III nitride semiconductor crystal. Specifically, the halide of gallium, the halide of indium, etc. Is mentioned. Examples of the halide include fluoride, chloride, and bromide.

  In addition, the compound containing a nitrogen element used in the production method of the present invention is not particularly limited as long as it can be used as a raw material for a group III nitride semiconductor, and ammonia is preferably used. In the manufacturing method of the present invention, a group III nitride semiconductor crystal can be grown by reacting a group III element halide and a nitrogen element compound on a base substrate in a crystal growth furnace.

In the crystal growth step of the present invention, a group III nitride semiconductor crystal is grown while mixing facets other than the C plane and the C plane (hereinafter also referred to as facet growth). Therefore, the group III nitride semiconductor crystal obtained by the manufacturing method of the present invention is a crystal having a C-plane area and a facet area. In the present invention, the C plane refers to a (0001) plane in hexagonal crystal and a plane equivalent thereto. Further, in the present specification, the C plane includes a C plane having an off angle in the a-axis and / or m-axis direction from the C plane. The off angle is preferably −10 to 10 °, more preferably −5 to 5 °.
A region grown while exposing the C plane during crystal growth on an arbitrary crystal surface is referred to as a C plane area. The facet plane refers to a plane other than the C plane, and a region grown while exposing the facet plane during crystal growth on an arbitrary crystal surface is referred to as a facet area. Normally, when an arbitrary crystal surface is observed with a fluorescence microscope, the C-plane area can be seen bright and the facet area can be seen dark.

  In facet growth, a crystal having a C-plane as an upper surface (main surface) is grown, but a crystal having a facet other than the C-plane can be obtained. Therefore, oxygen can be doped into the crystal through the facet. .

As a specific method of facet growth, for example, as shown in FIG. 1 (1), the crystal growth surface of the substrate 21 is an uneven surface, and the crystal is grown while forming a facet structure from the recesses and / or protrusions. There is. In this method, a crystal growth surface in which concave and convex portions 22a and 22b are formed on the crystal growth surface of the substrate 21 is prepared, and a nitride semiconductor layer is grown by MOCVD or the like, as shown in FIG. The growth proceeds while forming facet surfaces in both the recesses 22a and the protrusions 22b. Under such circumstances, when the crystal growth continues, the crystal growth proceeds in both the concave portion and the convex portion, and eventually the films are connected to cover the uneven surface as shown in FIG.
Such facet growth is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-164296.

As another specific method of facet growth, for example, there is a method of providing a growth inhibition layer on a base substrate. In epitaxial growth of gallium nitride, a base substrate is prepared, an arbitrary mask pattern is partially formed on the base substrate with a material that inhibits epitaxial growth, and a covering portion covered by the mask and an exposed portion not covered by the mask are formed. Provide. For example, as shown in FIG. 2A, the mask covering portion 32 is provided on the base substrate 31 by CVD, sputtering, or the like. The shape of the mask is not particularly limited, as long as the mask covering portion and the substrate exposed portion can be distinguished on the base substrate. Specific examples include a pit shape and a stripe shape. In the case of a dot mask, the shape of the dot is not limited, such as a circle or a rectangle, but the diameter d is usually about 5 μm to 100 μm. In the case of a stripe mask, the width w of the covering portion is usually about 5 μm to 100 μm. The width of the exposed portion is usually about 200 μm to 400 μm.
The material of the mask is not particularly limited as long as it inhibits epitaxial growth, and specific examples include SiO ₂ , SiN, Al ₂ O ₃ , AlN, ZrO ₂ , Y ₂ O ₃ , MgO and the like.

  FIG. 2 (2) is a diagram showing epitaxial growth. Gallium nitride is epitaxially grown on the underlying substrate, and at the initial stage of the epitaxial growth, the nitride semiconductor single crystal 34 is grown in the exposed portion, but the epitaxial growth is not performed in the mask covering portion 32, and the end portion of the covering portion 32 extends from the end to the exposed portion. A slope formed of a facet surface of gallium nitride is formed, and from the slope, a gallium nitride protrusion having a polarity 180 degrees different from that of the exposed gallium nitride and inverted is formed above the fine polycrystalline grains of the mask covering portion. . By continuing the growth while maintaining the facet plane, the overall thickness increases as shown in FIG. 2 (3), and a polarity reversal region is formed only on the mask covering portion region. Growing facet. In addition, a C-plane growth region in which oxygen is not mixed may be mixed in part of the facet growth region. Such facet growth is disclosed in, for example, Japanese Patent No. 4182935.

  As another facet growth method, there is a method of forming crystals serving as facet nuclei and fine irregularities on a base substrate. In addition, the method for forming facet nuclei is not particularly limited as long as it can form nuclei having facet surfaces. Specifically, facet nuclei are formed by depositing small crystals on a base substrate in the early stage of growth. And a method of performing a polishing finish so that fine irregularities are generated on the surface of the base substrate.

  In the production method of the present invention, as described above, crystal growth is performed by facet growth. At this time, a silicon-containing substance is introduced into the crystal growth furnace, and oxygen is contained in a region grown on a facet surface other than the C plane. A group III nitride semiconductor crystal is grown. The crystal obtained by such a manufacturing method becomes a high-quality crystal with less uneven carrier concentration in the crystal.

  In the production method of the present invention, the method of introducing the silicon-containing substance into the crystal growth furnace is not particularly limited, and examples thereof include a method of flowing the silicon-containing substance into the crystal growth furnace from the outside as a gas.

Examples of the silicon-containing substance that flows into the crystal growth furnace from the outside include silane gas, monochlorosilane gas, dichlorosilane gas, trichlorosilane gas, tetrachlorosilane gas, and silicon tetrafluoride gas. These gases are appropriately introduced into the crystal growth furnace. At this time, it is preferable to introduce the halogen element-containing substance into the crystal growth furnace from the same conduit. By introducing the silicon-containing material from the same conduit as the halogen-containing material, the silicon-containing material is prevented from being decomposed before being incorporated into the crystal, and the resulting crystal is reliably doped with silicon. Higher quality crystals can be obtained with a more uniform carrier concentration in the crystals. Examples of the halogen element-containing gas include, but are not limited to, hydrogen halides such as HCl, HBr, and HF; halogen gases such as Cl ₂ , Br ₂ , and F ₂ ; gases that release halogen elements, and the like.

As a method for producing the nitride semiconductor crystal of the present invention,
1) Halide vapor phase epitaxy (HVPE method),
2) Metalorganic chemical vapor deposition (MOCVD)
3) Organometallic chloride vapor phase growth method (MOC method)
4) A known method such as a sublimation method can be appropriately employed. In the production method of the present invention, it is preferable to employ a vapor phase growth method, more preferably the HVPE method or the MOCVD method from the viewpoint of mass productivity, and particularly preferably the HVPE method.
Hereinafter, the manufacturing apparatus in the manufacturing method which employ | adopted HVPE method is demonstrated using FIG.

In FIG. 3, the conceptual diagram of the manufacturing apparatus used for the manufacturing method which employ | adopted HVPE method is shown. The nitride semiconductor manufacturing apparatus of FIG. 3 includes a reaction vessel (reactor) 1, a support unit 7 that is disposed in the reaction vessel 1 and supports a base substrate 8, and a heater 11. The type of the base substrate is not particularly limited, and can be appropriately selected from silicon, sapphire, gallium arsenide, gallium nitride, aluminum nitride, zinc oxide, and the like. A carrier gas (for example, H ₂ gas, N ₂ gas, or a mixed gas thereof) G2 and a group V source gas (for example, NH ₃ gas) G3 are supplied to the reaction vessel 1 through conduits 2 and 3, respectively. A reaction gas (for example, HCl gas) is supplied to the reservoir 5 in the reaction vessel 1 through the conduit 4. The reaction gas reacts with the group III source material (for example, Ga) in the reservoir 5 to generate a group III source gas (for example, GaCl gas) G1 and is supplied through the conduit 6. When supplying a silicon-containing substance as a gas for Si doping, for example, dichlorosilane gas can be introduced from the conduit 2 together with HCl gas. Here, the method of introducing the silicon-containing substance gas into the reaction vessel 1 is not limited, and may be introduced from the same conduit as the group III source gas, but is introduced from the same conduit as the halogen element-containing substance. It is preferable.

  With such a configuration, the base substrate 8 supported by the support portion 7 is supplied with the group III source gas G1, the carrier gas G2, and the group V source gas G3, and the target nitride is formed on the base substrate 8. The semiconductor 9 can be grown. The gas in the reaction vessel 1 is exhausted out of the manufacturing apparatus through the exhaust pipe 10. The flow rate of each gas is typically controlled by a mass flow controller (MFC). The conduit here is a concept including a nozzle. Further, a plurality of substances may be mixed and reacted in the conduit.

Hereinafter, the crystal manufacturing method using the manufacturing apparatus of FIG. 3 will be described in more detail.
First, the reaction container 1 of the production apparatus is heated to 900 to 1150 ° C. in the presence of NH ₃ , and the temperature of the reservoir 5 is adjusted to 750 to 850 ° C. Thereafter, HCl gas is introduced into the Ga in the reservoir 5 through the conduit 4, and the generated GaCl gas G 1 is supplied to the base substrate 8 together with the mixed carrier gas G 2 and NH ₃ gas G _{3 of} H ₂ and N _2. A GaN crystal 9 is grown on the substrate 8. In this growth step, the growth pressure is 5 × 10 ^{4 to} 5 × 10 ⁵ Pa, the partial pressure of the GaCl gas G1 is 3 × 10 ^{1 to} 3 × 10 ⁴ Pa, and the partial pressure of the NH ₃ gas G3 is 1 × 10. ³ is preferably set to ~3 × 10 ⁵ Pa. The partial pressure of the carrier gas is preferably 4.9 × 10 ^{4 to} 4.9 × 10 ⁵ Pa. Further, when dichlorosilane gas is introduced for doping Si, the efficiency of Si incorporation into the crystal varies depending on the dichlorosilane gas introduction method, but the partial pressure of dichlorosilane gas is 1 × 10 ⁻³ to 1 × 10 ¹ Pa. It is preferable to do. After the completion of this growth step, the temperature is lowered to a temperature at which the reaction vessel 1 can be taken out.

  The type of nitride semiconductor thus obtained is not particularly limited as long as it is a group III nitride semiconductor, and specific examples thereof include gallium nitride, indium nitride, and mixed crystals thereof.

3) Group III nitride semiconductor crystal of the present invention The group III nitride semiconductor crystal obtained by the production method of the present invention is a high-quality crystal with no uneven carrier concentration in the same crystal.
Specifically, the crystal obtained by the production method of the present invention has an oxygen content of the C-plane area of 1 × 10 ¹⁸ cm ⁻³ or less and a silicon content of 2 × 10 ¹⁷ cm ⁻³ or more. It is preferable that More preferably, the oxygen content in the C-plane area is 1 × 10 ¹⁷ cm ⁻³ or less, and more preferably 2 × 10 ¹⁶ cm ⁻³ or less. The silicon content in the C-plane area is more preferably 5 × 10 ¹⁷ cm ⁻³ or more.

The difference between the total oxygen content and silicon content in the C-plane area and the total oxygen content and silicon content in the facet area is preferably 4 × 10 ¹⁸ cm ⁻³ or less. The difference is more preferably 2 × 10 ¹⁸ cm ⁻³ or less.
The oxygen content in the facet area is preferably 1 × 10 ¹⁸ cm ⁻³ or more and the silicon content is preferably 1 × 10 ¹⁹ cm ⁻³ or less. The oxygen content in the facet area is more preferably 2 × 10 ¹⁸ cm ⁻³ or more, and the silicon content is more preferably 1 × 10 ¹⁸ cm ⁻³ or less.

  The content of the dopant contained in the C-plane area and the facet area in the crystal can be measured using secondary ion mass spectrometry (SIMS).

The nitride semiconductor crystal produced by the production method of the present invention preferably has an intracrystalline carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less. When the carrier concentration in the crystal is within the above range, the resistivity in the crystal is low and the semiconductor crystal is excellent in conductivity. The carrier concentration in the crystal can be measured using hole measurement by the van der Pauw method.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, it is not limitedly interpreted only to the specific form shown in the following Examples.

<Example 1>
As a base substrate, a GaN crystal having a polarity inversion region is polished by CMP to prepare a GaN semiconductor substrate having fine irregularities on the surface, and the GaN semiconductor crystal is formed by the HVPE method using the manufacturing apparatus shown in FIG. Manufactured.
A GaN semiconductor substrate was placed on the support portion 7 of the apparatus with the + C (0001) plane facing upward. At this time, the -C (000-1) plane is in contact with the support portion 7 and is not in direct contact with the raw material gas. The temperature of the reaction vessel 1 in the reactor is set to 1005 ° C., a GaCl gas is supplied from the conduit G1, a mixed gas of H ₂ and N ₂ is supplied as a carrier gas from the conduit G2, and an NH ₃ gas is supplied from the conduit G3. HCl and NH ₃ gas were supplied from the conduit G2 so that dichlorosilane and the substrate surface merged. These source gases are supplied from the + C plane direction of the nitride semiconductor substrate.
In this crystal growth process, oxygen doping is realized by facet growth of a GaN semiconductor crystal, and Si doping is realized by supplying dichlorosilane gas.
After growing for 34 hours, the temperature of the reactor was lowered to room temperature, and a GaN single crystal 1 was obtained. The shape of the obtained GaN single crystal 1 was a circular shape with no abnormal growth, and the thickness in the c-axis direction was 4.3 mm. Also, no cracks were observed.

The carrier concentration of the GaN single crystal 1 measured by Resitest 8300 manufactured by Toyo Technica was 4.15 × 10 ¹⁸ / cm ³ .
Next, oxygen concentration and silicon concentration were measured for each of the C-plane area and facet area by SIMS measurement using ims-4f manufactured by CAMECA. The results are shown in Table 2. In addition, since the C plane area in the crystal manufactured in Reference Example 1 was very narrow, the oxygen concentration and silicon concentration in the C plane area could not be measured. However, since the presence of the C-plane area has been confirmed, it is estimated that the oxygen concentration in the portion is low. Moreover, since the carrier concentration of the crystal is high, it is presumed that the silicon concentration in the C-plane area is sufficiently high.

<Example 2>
A GaN single crystal 2 having a thickness in the c-axis direction of 2.4 mm was obtained in the same manner as in Example 1 except that the reactor temperature, the raw material gas partial pressure, and the crystal growth time were changed as shown in Table 1. Got. No cracks were observed in the GaN single crystal 2. For the GaN single crystal 2, the oxygen concentration and the silicon concentration were measured for each of the C-plane area and the facet area by SIMS measurement. The results are shown in Table 2.

<Comparative Example 1>
A GaN single crystal 3 having a thickness in the c-axis direction of 2.1 mm is the same as in Example 1 except that the temperature of the reactor, the partial pressure of the source gas, and the crystal growth time are changed as shown in Table 1. Got. The carrier concentration of the GaN single crystal 3 measured by Resitest 8300 manufactured by Toyo Technica was 5.99 × 10 ¹⁸ / cm ³ .
Next, the oxygen concentration and the silicon concentration were measured for each of the C-plane area and the facet area by SIMS measurement. The results are shown in Table 2. In the C-plane area where oxygen is not doped, Si doping is not sufficient.

<Comparative example 2>
In Example 1, the GaN semiconductor substrate on the support portion 7 was not subjected to facet growth, and the reactor temperature, source gas partial pressure, and crystal growth time were changed as shown in Table 1. Obtained a GaN single crystal 4 having a thickness in the c-axis direction of 2.4 mm in the same manner as in Example 1.
When the carrier concentration of the GaN single crystal 4 was measured, it was 5.80 × 10 ¹⁷ / cm ³ , which was significantly lower than that of the GaN crystal produced by facet growth and the conductivity was low.

<Comparative Example 3>
In the same manner as in Comparative Example 2, except that dichlorosilane gas and HCl were not mixed in the source gas, and the reactor temperature, source gas partial pressure, and crystal growth time were changed as shown in Table 1, c-axis A GaN single crystal 5 having a thickness in the direction of 4.7 mm was obtained.
When the carrier concentration of the GaN single crystal 5 was measured, it was 1.30 × 10 ¹⁷ / cm ³ , which was significantly lower than that of the GaN crystal produced by facet growth and the conductivity was low.

1 reaction vessel (reactor)
2, 3, 4, 6 6 Conduit 5 Reservoir 7 Support 8 Base substrate 9 Nitride semiconductor crystal 10 Exhaust pipe 11 Heater G1 Group III source gas G2 Carrier gas G3 Group V source gas 21 Base substrate 22a Concave portion 22b Convex portion 23 Nitride Semiconductor layer 31 Base substrate 32 Covering portion 33 Seed crystal 34 Nitride semiconductor crystal

Claims (2)

A step of preparing a base substrate in the crystal growth furnace, and a group III nitriding process while reacting a group III element halide and a compound containing a nitrogen element so that the facet surface other than the C plane and the C plane is mixed on the base substrate. A method for producing a group III nitride semiconductor crystal comprising a growth step of growing a compound semiconductor crystal,
The growth step is characterized in that a silicon-containing material is introduced into the crystal growth furnace and a group III nitride semiconductor crystal is grown while oxygen is contained in a region grown on a facet plane other than the C plane. A method for producing a group III nitride semiconductor crystal.   2. The method for producing a group III nitride semiconductor crystal according to claim 1, wherein the silicon-containing material in the growth step is introduced into the crystal growth furnace as a gas from a conduit. 3.

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