JP2005039248A - Method for manufacturing group iii nitride, method for manufacturing semiconductor substrate, group iii nitride crystal, semiconductor substrate, and electron device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing group III nitride crystals of high quality useful for the substrates used for a semiconductor manufacturing process. <P>SOLUTION: A semiconductor layer 12 with a crystalline nucleus growth region 12a is formed on the surface of a semiconductor represented by a compositional formula Al<SB>u</SB>Ga<SB>v</SB>In<SB>1-u-v</SB>N (wherein, 0≤u≤1, 0≤v≤1, u+v≤1). The crystalline nucleus growth region 12a of the semiconductor layer 12 is made in contact with a melt containing at least one of group III elements selected from a group consists of gallium, aluminum and indium and either of alkali metal or alkaline earth metal in an atmosphere containing nitrogen to grow a group III nitride crystal 13 on the layer 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a group III nitride crystal, a method for producing a semiconductor substrate, a group III nitride crystal, a semiconductor substrate, and an electronic device.

  Group III nitride compound semiconductors such as gallium nitride (GaN) (hereinafter sometimes referred to as group III nitride semiconductors or GaN-based semiconductors) are attracting attention as materials for semiconductor elements that emit green, blue and ultraviolet light. . Blue laser diodes (LD) are applied to high-density optical discs and displays, and blue light-emitting diodes (LEDs) are applied to displays and lighting. Further, ultraviolet LD is expected to be applied to biotechnology and the like, and ultraviolet LED is expected to be an ultraviolet source of fluorescent lamps.

A substrate of a group III nitride semiconductor (for example, GaN) for LD or LED is usually formed by heteroepitaxially growing a group III nitride crystal on a sapphire substrate using a vapor phase epitaxial growth method. The dislocation density of the crystal obtained by this method is usually 10 ⁸ cm ⁻² to 10 ⁹ cm ⁻² , and reduction of the dislocation density is an important issue. In order to solve this problem, efforts have been made to reduce the dislocation density. For example, an ELOG (Epitaxial lateral overgrowth) method has been developed (see, for example, Patent Document 1). According to this method, the dislocation density can be lowered to about 10 ⁵ cm ⁻² to 10 ⁶ cm ^−2, but the manufacturing process is complicated.

On the other hand, a method of performing crystal growth in a liquid phase instead of vapor phase epitaxial growth has been studied. However, since the equilibrium vapor pressure of nitrogen at the melting point of a group III nitride single crystal such as GaN is 10000 atm (10000 × 1.013 × 10 ⁵ Pa) or more, conventionally, 1200 has been used to grow GaN in the liquid phase. A condition of 8000 atm (8000 × 1.013 × 10 ⁵ Pa) at 0 ° C. has been required. On the other hand, in recent years, it has been clarified that GaN can be synthesized at a relatively low temperature and low pressure of 750 ° C. and 50 atm (50 × 1.013 × 10 ⁵ Pa) by using Na flux (see, for example, Patent Document 2). ).

Recently, a mixture of Ga and Na was melted at 800 ° C. and 50 atm (50 × 1.013 × 10 ⁵ Pa) in a nitrogen gas atmosphere containing ammonia, and this melt was used for a growth time of 96 hours. A single crystal having a maximum crystal size of about 1.2 mm is obtained (see, for example, Patent Document 3).

  Also reported is a method of growing a single crystal by liquid phase epitaxy (LPE) after forming a GaN crystal layer on the sapphire substrate by metal organic chemical vapor deposition (MOCVD). (For example, refer nonpatent literature 1).

However, in the conventional technique, the quality of the obtained group III nitride crystal is not sufficient, and a technique for producing a higher quality crystal is required.
JP-A-11-145516 US Pat. No. 5,868,837 JP 2002-293696 A Jpn. J. Appl. Phys., Vol42, (2003) pp4-6

  Therefore, an object of the present invention is to provide a method for producing a group III nitride crystal that can be stably grown in a flux and can be used as a substrate for a semiconductor production process.

In order to achieve the above object, the method for producing a group III nitride crystal of the present invention is a method comprising the following steps (i) and (ii).
(I) A semiconductor layer made of a semiconductor represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) and having a crystal nucleus generation region on the surface Forming.
(Ii) in an atmosphere containing nitrogen, the melt containing at least one group III element selected from the group consisting of gallium, aluminum and indium, at least one of an alkali metal and an alkaline earth metal, and nitrogen A step of growing a group III nitride crystal on the semiconductor layer by contacting the crystal nucleus generation region of the semiconductor layer;

  The inventors have conducted a series of studies on the growth of group III nitride crystals in the flux. In the process, we have found that crystal growth differs depending on the seed layer used in the growth of group III nitride crystals. After further studies on the relationship between the growth of group III nitride crystals and the seed layer, the growth of group III nitride crystals greatly depends on the surface state of the seed layer, and the crystal growth is stable in the flux. In order to achieve this, it has been found that it is necessary to control the surface of the seed layer. Since the generation of crystal nuclei is promoted in this crystal nucleus generation region by using a semiconductor layer (seed layer) having a crystal nucleus generation region on the surface as in the manufacturing method of the present invention, stable group III nitriding Growth of physical crystals is facilitated. Further, according to the production method of the present invention, crystal nuclei are selectively generated in the crystal nucleation generation region, so that the quality of the group III nitride crystal can be further improved.

  Next, the present invention will be described in detail.

  In the production method of the present invention, the method for forming the semiconductor layer having the crystal nucleus generation region is not particularly limited. For example, as shown below, the surface of the semiconductor layer formed in advance is exposed to the atmosphere, or a method by surface processing, As described later, there is a method of forming a semiconductor layer by controlling the twist angle and carrier concentration. The crystal nucleus generation region may be formed partially or entirely on the surface of the semiconductor layer. The crystal nucleus generation region can be specified by a cross-sectional shape such as generation of carrier concentration or twist angle, exposure to the atmosphere, machining, etching, or the like.

  In the production method of the present invention, the twist angle of the crystal nucleus generation region is, for example, 680 seconds or less, and preferably 412 seconds or less.

  The twist angle means a full width at half maximum of a rocking curve of X-ray diffraction ((10-10) diffraction). For example, the full width at half maximum of an X-ray diffraction rocking curve is applied to a semiconductor layer from an X-ray source. It is obtained from FWHM (Full width at half maximum) centered on the X-ray peak diffracted from the layer. The X-ray source is not particularly limited, and for example, CuKα ray can be used.

  In the manufacturing method of the present invention, examples of the method for controlling the twist angle of the crystal nucleus generation region of the semiconductor layer include controlling conditions such as the growth rate, growth temperature, and growth film thickness. For example, a sample with a small twist angle can be produced by growing at a growth temperature under the optimum growth temperature under a condition where the growth film thickness is thick and the growth rate is low. In this way, samples with different twist angles can be produced.

In the production method of the present invention, the carrier concentration in the crystal nucleus generation region is, for example, 1 × 10 ¹⁷ cm ⁻³ or less, preferably 5 × 10 ¹⁶ cm ⁻³ , more preferably 1 × 10 ¹⁶ cm 3. ^-3 . The carrier concentration can be determined by, for example, hole measurement, CV measurement, or the like. In addition, it is thought that the generation | occurrence | production cause of the said carrier originates in the furnace member used for crystal growth, for example, the result of oxygen and Si etc. being taken in in the crystal | crystallization.

  In the manufacturing method of the present invention, as a method for controlling the carrier concentration in the crystal nucleus generation region of the semiconductor layer, for example, when the semiconductor layer is produced by vapor phase growth such as HVPE method or MOCVD method, Examples thereof include a method using a high source gas, a method using a well-dead quartz reaction tube, and a method of coating a quartz reaction tube of an HVPE apparatus or MOCVD apparatus with BN, AlN, SiC or the like. Among these, the coating method is particularly preferable, and if a quartz reaction tube is coated, for example, the incorporation of Si and oxygen from the surface of the reactor into the semiconductor layer can be further reduced, and the carrier concentration can be controlled very easily. become. In addition, the method of using a well-dead quartz reaction tube is, for example, using a quartz reaction tube or other constituent members, and growing a dummy crystal several times to several tens of times, thereby producing a quartz reaction tube or other members. In this method, the carrier concentration contained therein is reduced, and then the intended crystal growth is performed.

In the production method of the present invention, the step of said (i) is a (i-1) the composition formula _{Al s Ga t In 1-st} N ( provided that 0 ≦ s ≦ 1,0 ≦ t ≦ 1, s + t ≦ 1) (I-2) a step of exposing the surface of the underlayer to the atmosphere; and (i-3) a composition formula Al _u Ga _v on the underlayer. And a step of forming the semiconductor layer by growing a semiconductor represented by In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). In this case, the crystal nucleus generation region includes at least one of pits and hillocks.

In the production method of the present invention, the step (i) includes (i-a) composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). The method may include a step of forming a semiconductor layer formed of the represented semiconductor and (ib) a step of processing the surface of the semiconductor layer.

  In the manufacturing method of the present invention, the step (ib) may include a step of roughening the surface of the semiconductor layer by etching. Examples of the etching method include dry etching and wet etching.

  In the manufacturing method of the present invention, the step (ib) may include a step of mechanically processing the surface of the semiconductor layer. In this case, in the step (ia), the semiconductor layer is formed so that the surface of the semiconductor layer becomes a (0001) plane. In the step (ib), the surface is a (0001) plane. The surface of the semiconductor layer may be polished so that the surface is inclined with respect to the surface.

  In the manufacturing method of the present invention, the group III element may be gallium, and the group III nitride crystal may be gallium nitride.

  In the manufacturing method of the present invention, the atmosphere may be a pressurized atmosphere.

  In the manufacturing method of the present invention, the semiconductor layer is preferably formed on a substrate. The substrate is not particularly limited. For example, a GaAs substrate whose surface is a (111) plane, a Si substrate whose surface is a (111) plane, a sapphire substrate whose surface is a (0001) plane, and a surface having a (0001) plane. A SiC substrate or the like can be used. Of these, sapphire substrates and SiC substrates are preferred.

  The electronic device of the present invention is an electronic device including a semiconductor element formed on a substrate, and the substrate is a group III nitride crystal manufactured by the manufacturing method of the present invention.

  In the electronic device, the semiconductor element may be a laser diode, a light emitting diode, or a field effect transistor.

  The electronic device may be a high frequency device or a high power device.

  Next, the present invention will be described with reference to the drawings as appropriate with examples. However, the present invention is not limited to the following embodiments. Moreover, although the following embodiment is an example which formed the semiconductor layer on the board | substrate, this invention is not limited to this.

(Embodiment 1)
In this method, first, as shown in FIG. 1A, a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) is formed on a substrate 11. The semiconductor layer 12 made of the semiconductor represented by the above and having the crystal nucleus generation region 12a on the surface is formed (step (i)). The semiconductor layer 12 is a seed layer that becomes a seed crystal, and is formed of, for example, GaN, Al _u Ga _1-u N (where 0 ≦ u ≦ 1), or the like. A method for forming the semiconductor layer 12 will be described later. The substrate 11 can be a sapphire substrate, a GaAs substrate, a Si substrate, a SiC substrate, or the like. For example, a GaAs substrate whose surface is a (111) plane, a Si substrate whose surface is a (111) plane, A sapphire substrate having a (0001) plane or a SiC substrate having a (0001) plane on the surface can be used. Note that another semiconductor layer may be included between the substrate 11 and the semiconductor layer 12. Further, the crystal nucleus generation region 12 a may be formed on the entire surface of the semiconductor layer 12.

Next, in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm (100 × 1.013 × 10 ⁵ Pa) or less), at least one group III element selected from the group consisting of gallium, aluminum, and indium; The surface of the semiconductor layer 12 (the surface including the crystal nucleus generation region 12a) is brought into contact with a melt containing at least one of an alkali metal and an alkaline earth metal and nitrogen, and a group III nitride crystal is formed on the semiconductor layer 12 Grow (step (ii)). Through the step (ii), a group III nitride crystal 13 is grown on the semiconductor layer 12 as shown in FIG. In the method of the present invention, the crystal nucleus generation region 12a in which crystal nuclei are likely to be generated is formed on the surface of the semiconductor layer 12 to be a seed layer. For this reason, in the step (ii), crystal nuclei are generated in the crystal nucleation generation region, and the growth of the group III nitride crystal is facilitated.

  The melt preferably contains an alkali metal or an alkaline earth metal or both. Examples of the alkali metal include sodium, lithium, potassium, rubidium and cesium, and these may be used alone or in combination of two or more. Examples of the alkaline earth metal include Ca, Mg, Sr, Ba, and Be. These may be used alone or in combination of two or more. Further, an alkali metal and an alkaline earth metal may be mixed and used. In this case, a mixture of sodium and calcium is preferred. As the atmosphere containing nitrogen, for example, a nitrogen gas atmosphere containing nitrogen gas or ammonia can be applied.

The melt can be prepared, for example, by putting a material such as a group III element into a crucible and heating it. After preparing the melt, a semiconductor crystal is grown by bringing the melt into a supersaturated state. The melting and crystal growth of the material are performed, for example, at a temperature of about 700 ° C. to 1100 ° C. and a pressure of about 1 atm (1 × 1.013 × 10 ⁵ Pa) to 100 atm (100 × 1.013 × 10 ⁵ Pa). Is called. According to this method, a group III nitride crystal represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1) is obtained. A crystal represented by GaN or a composition formula Al _x Ga _1-x N (where 0 ≦ x ≦ 1) is obtained.

  Hereinafter, the step (i) will be described with an example.

In the first example, first, on a substrate, is formed by a semiconductor which is represented by a composition formula _{Al s Ga t In 1-st} N ( provided that 0 ≦ s ≦ 1,0 ≦ t ≦ 1, s + t ≦ 1) An underlayer is formed (step (i-1)). The underlayer can be formed by, for example, MOCVD, MBE, HVPE, or the like.

  Next, the surface of the underlayer is exposed to the atmosphere (step (i-2)). The exposure to the atmosphere can be performed, for example, by taking out the substrate on which the base layer is formed from the film forming apparatus.

Next, a semiconductor layer is grown on the underlayer by growing a semiconductor represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). (Step (i-3)). At this time, pits and hillocks may be formed on the surface of the semiconductor layer formed on the base layer exposed to the atmosphere, and the pits and hillocks may be the crystal nucleus generation region.

In the second example, first, a semiconductor is formed on a substrate with a compositional formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). A semiconductor layer is formed (step (ia)). This semiconductor layer can be formed, for example, by MOCVD, MBE, or HVPE.

  Next, by processing the surface of the semiconductor layer, a crystal nucleus generation region is formed on the surface (step (ib)). By this processing, the surface of the semiconductor layer can be roughened, and the roughened surface becomes a crystal nucleus generation region. Such a rough surface tends to generate crystal nuclei. Examples of the processing method include dry etching, wet etching, and machining.

The dry etching can be performed by, for example, a method of treating the surface of the semiconductor layer at 80 W for 30 minutes using CF ₄ gas. The wet etching can be performed using, for example, a KOH aqueous solution or a phosphoric acid aqueous solution.

  When machining, for example, grooves may be formed on the surface of the semiconductor layer by scribing, dicing, or the like. In addition, after forming the semiconductor layer so that the surface becomes the (0001) plane in the step (ia), the semiconductor becomes so that the surface becomes a plane inclined with respect to the (0001) plane in the step (ib). The surface of the layer may be polished. By forming a surface other than the (0001) surface on the surface, crystal nuclei are easily generated. It is also possible to attach an impurity to the surface of the semiconductor layer and make that portion a crystal nucleus generation region.

  The crystal nucleus generation region can have various shapes such as a stripe shape, a dot shape, and a mesh shape. The crystal nucleus generation region may have a shape suitable for an applied device. For example, when applied to a semiconductor laser or the like, a stripe shape or the like is preferable.

  In the case of producing a semiconductor element using a group III nitride crystal produced by the method of the present invention, an electronic device is formed by forming a semiconductor element on the group III nitride crystal following step (ii). Can be manufactured. The semiconductor element is, for example, a laser diode, a light emitting diode, a field effect transistor, or the like. The electronic device may be a high frequency device or a high power device.

(Embodiment 2)
In Embodiment 2, an example of manufacturing a field effect transistor will be described. First, a GaN semiconductor layer and an AlGaN semiconductor layer are formed by MOCVD on an insulating GaN crystal formed by a liquid phase growth method. Next, a source electrode, a gate electrode, and a drain electrode are formed on the AlGaN semiconductor layer. The GaN crystal formed by the liquid phase growth method is characterized in that it has excellent insulating properties because it has few dislocations and defects. By controlling the gate voltage, the two-dimensional electron gas concentration between the GaN semiconductor layer and the AlGaN semiconductor layer can be controlled, and a high-speed transistor can be realized.

(Embodiment 3)
In Embodiment 3, an example of manufacturing a semiconductor laser will be described. An n-type GaN layer is formed on a GaN crystal formed by a liquid phase growth method, an active layer composed of an InGaN layer is formed thereon, and a p-type GaN layer is further formed thereon. A light emitting device can be realized by forming electrodes on the n-type GaN layer and the p-type GaN layer, respectively.

(Embodiment 4)
This embodiment is an example of manufacturing a semiconductor laser using the semiconductor substrate of the present invention. The structure of this semiconductor laser is shown in the sectional view of FIG. This semiconductor laser can be manufactured, for example, as follows.

First, the contact layer 92 made of n-type GaN doped with Si so as to have a carrier concentration of 5 × 10 ¹⁸ or less is formed on the substrate 91 made of the GaN crystal obtained in the above embodiment. In a GaN-based crystal (a crystal containing Ga and N), Ga vacancies increase when Si is added as an impurity. Since these Ga vacancies diffuse easily, if a device is fabricated on this Ga, it has an adverse effect on the life and the like. Therefore, the doping amount is controlled so that the carrier concentration is 3 × 10 ¹⁸ cm ⁻³ or less.

Next, a clad layer 93 made of n-type Al _0.07 Ga _0.93 N and a light guide layer 94 made of n-type GaN are formed on the contact layer 92. Next, a multiple quantum well (MQW) constituted by a well layer (thickness: about 3 nm) made of Ga _0.8 In _0.2 N and a barrier layer (thickness 6 nm) made of GaN is formed as the active layer 95. Next, a light guide layer 96 made of p-type GaN, a clad layer 97 made of p-type Al _0.07 Ga _0.93 N, and a contact layer 98 made of p-type GaN are formed. These layers can be formed by a known method. The semiconductor laser 90 is a double heterojunction type semiconductor laser, and the energy gap of the well layer containing indium in the MQW active layer is smaller than the energy gap of the n-type and p-type cladding layers containing aluminum. On the other hand, the refractive index of light is the highest in the well layer of the active layer 95, and the light guide layer and the cladding layer are reduced in this order.

  Over the contact layer 98, an insulating film 99 constituting a current injection region having a width of about 2 μm is formed. A ridge portion serving as a current confinement portion is formed in the upper portion of the p-type cladding layer 97 and the p-type contact layer 98.

  A p-side electrode 100 that is in ohmic contact with the contact layer 98 is formed on the p-type contact layer 98. An n-side electrode 101 that is in ohmic contact with the contact layer 92 is formed on the upper side of the n-type contact layer 92.

  The device evaluation of the semiconductor laser manufactured by the above method was performed. When a predetermined voltage in the forward direction is applied between the p-side electrode and the n-side electrode to the obtained semiconductor laser, holes are injected from the p-side electrode into the MQW active layer, and electrons are injected from the n-side electrode, Recombination occurred in the MQW active layer to generate an optical gain, and laser oscillation occurred at an oscillation wavelength of 404 nm.

In the present embodiment, the GaN single crystal substrate has been described. However, it is desirable to supply a substrate that absorbs less light with respect to the used wavelength of the optical device manufactured on the substrate. Therefore, it is preferable to form an Al _x Ga _1-x N (0 ≦ x ≦ 1) single crystal containing a large amount of Al and having little light absorption in the short wavelength region as a semiconductor laser or light emitting diode substrate in the ultraviolet region. . In the present invention, such a group III nitride semiconductor single crystal can be formed by replacing a part of Ga with another group III element.

(Embodiment 5)
Further, an example of manufacturing a field effect transistor using the semiconductor substrate of the present invention will be described. The structure of the field effect transistor 110 is schematically shown in FIG. As the substrate, a non-doped GaN substrate 111 obtained by liquid phase growth using a flux is used. The GaN substrate 111 obtained by the liquid phase growth has an electrical resistance of 10 ¹⁰ Ω or more, for example, and exhibits characteristics close to an insulator. A GaN layer 112 and an AlGaN layer 113 are formed on the GaN substrate 111 by MOCVD. Further, a source electrode 114, a Schottky gate electrode 115, and a drain electrode 116 are formed thereon. By applying a voltage to the Schottky gate electrode 115, the two-dimensional electron gas concentration 117 formed at the interface between the GaN layer 112 and the AlGaN layer 113 is controlled to operate as a transistor.

  The GaN substrate formed by the method of the present invention has few defects and a low dislocation density. Therefore, it is possible to realize a field effect transistor that has high insulation properties, can reduce leakage current during transistor operation, and has excellent high-frequency characteristics.

The present invention is described in further detail using the following examples. In the following examples, the production of GaN crystals will be described. However, the composition formula Al _x Ga _y In _1-xy N such as Al _x Ga _1-x N or AlN (where 0 ≦ x ≦ 1, 0 ≦ y ≦ The group III nitride crystal represented by 1, x + y ≦ 1) can be formed by the same method.

  Example 1 is an example in which a group III nitride crystal was produced by the method described in the second example of the first embodiment.

As shown in FIG. 2, the group III nitride crystal formed in this example has a sapphire substrate 21 made of sapphire (crystalline Al ₂ O ₃ ), a semiconductor layer 22 containing GaN, and LPE-GaN. Layer 23 is formed. Here, the semiconductor layer 22 is formed of a group III nitride that satisfies the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). The feature of this embodiment is that a crystal nucleus generation region 22 a is formed on the surface of the semiconductor layer 22.

The manufacturing method of the group III nitride crystal used in the present example will be described with reference to FIG. First, as shown in FIG. 2A, the semiconductor layer 22 containing GaN was formed on the sapphire substrate 21. Specifically, the semiconductor layer 22 was formed by heating the sapphire substrate 21 to about 1020 ° C. to 1100 ° C. and then supplying trimethylgallium (TMG) and NH ₃ onto the substrate 21. .

  Next, as shown in FIG. 2B, a striped resist pattern 24 was formed on the surface of the semiconductor layer 22 by photolithography.

Then, as shown in FIG. 2C, the surface of the semiconductor layer 22 is processed by dry etching using CF ₄ gas, and a portion of the surface of the semiconductor layer 22 where the resist pattern 24 is not formed is processed. A crystal nucleus generation region 22a was formed. The dry etching was performed by using a parallel plate type reactive dry etching (RIE) apparatus at 80 W for 30 minutes. A large number of pits are formed on the surface of the semiconductor layer 22 by dry etching, and these pits become crystal nucleus generation regions. Note that the shape of the crystal nucleus generation region is not limited to the stripe shape, and a dot-like crystal nucleus generation region may be formed depending on the application. Further, a crystal nucleus generation region may be formed on the entire surface of the semiconductor layer 22.

The resist pattern 24 is removed, and a crystal nucleus generation region is formed in a melt containing gallium, Na, and nitrogen in a nitrogen atmosphere (preferably in a pressurized atmosphere of 100 atm (100 × 1.013 × 10 ⁵ Pa) or less). An LPE-GaN layer 23 was grown on the semiconductor 22 by bringing the surface of the semiconductor layer 22 on which 22a was formed into contact with each other and maintaining the melt in a supersaturated state.

  Note that the crystal nucleus generation region may be formed by a method other than dry etching. An example of another method for forming a crystal nucleus generation region is shown below.

  FIG. 4 shows a method for forming a crystal nucleus generation region by wet etching. Since the steps in FIGS. 4A and 4B are the same as the steps in FIGS. 2A and 2B, redundant description is omitted. Next, as shown in FIG. 4C, the sapphire substrate 21 having the resist pattern 24 formed on the semiconductor layer 22 is immersed in a hot phosphoric acid solution at 200 ° C. for 30 minutes to treat the surface of the semiconductor layer 22. To do. Since the semiconductor layer formed by the MOCVD method has dislocations and defects, a large number of pits are formed in the portion where the resist pattern 24 is not formed by this treatment, and the portion is formed in the crystal nucleus generation region 22a. It becomes. Thereafter, after removing the resist pattern 24, the LPE-GaN layer 23 is grown.

Next, an example of an oscillating LPE apparatus used in the method of the present invention is shown in FIG. The oscillating LPE apparatus 300 includes a stainless steel growth furnace 301 and can withstand an atmospheric pressure of 50 atm (50 × 1.013 × 10 ⁵ Pa). The growth furnace 301 is provided with a heater 302 and a thermocouple 303 for heating. The crucible fixing base 304 is disposed in the growth furnace 301, and a mechanism that rotates around the rotation shaft 305 in the direction of the arrow 310 is attached. A crucible 306 made of boron nitride (BN) or alumina (Al ₂ O ₃ ) is fixed in the crucible fixing base 304. In the crucible 306, a melt 307 and a seed crystal 308 are disposed. When the crucible fixing base 304 rotates, the melt in the crucible 306 moves to the left and right, and thereby the melt can be stirred. The atmospheric pressure is adjusted by the flow rate adjuster 309. Nitrogen gas, which is a raw material gas, or a mixed gas of ammonia gas (NH ₃ gas) and nitrogen gas is supplied from a raw material gas tank, and after impurities are removed by a gas purification unit, it is sent into a growth furnace. The growth of GaN crystals using this apparatus is performed, for example, as follows.

(1) First, Ga and flux Na were weighed by a predetermined amount and set in a crucible. Ga having a purity of 99.9999% (six nines) or higher was used. As Na, purified Na was used. Na was purified by heating and melting Na in a glove box substituted with He (which may be N ₂ or Ar) to remove oxides appearing on the surface layer. Na may be purified by a zone refining method. In the zone refining method, impurities are precipitated by repeating melting and solidification of Na in a tube, and the purity of Na can be increased by removing it.

  (2) Next, in order to melt the raw materials in the crucible, the temperature in the electric furnace was raised to 800 ° C. At this stage, as shown, the seed crystal substrate is not present in the melt. In order to stir Ga and Na, the crucible was swung so that the melt did not adhere to the seed crystal substrate. In order to prevent the oxidation of GaN, nitrogen gas was used as the atmospheric gas.

  (3) Next, the crucible was rotated around the rotation axis, the seed crystal substrate was placed in the melt, and crystal growth was started.

(4) During crystal growth, the crucible was swung at a speed of one cycle per minute in order to stir the melt. However, the seed crystal substrate was present in the melt during the growth. The crucible was kept at 800 ° C., the pressure was kept at 40 atm (40 × 1.013 × 10 ⁵ Pa), and LPE growth was performed for 10 hours to 48 hours.

  (5) After completion of the growth, the crucible was rotated as shown in the figure, the substrate was taken out of the melt, and the melt temperature was lowered.

  When a GaN crystal was grown by the above method, crystal growth started from the crystal nucleus generation region, and a good GaN single crystal could be grown by lateral (lateral direction) growth.

  In this embodiment, a flux containing only Na is used, but the same effect can be obtained by using Li, Na, K flux, Ca, Sr, Ba flux, or a mixed flux of alkali metal and alkaline earth metal. It is done. For example, in a mixed flux of Na and Ca, it is possible to grow crystals at a lower pressure by mixing about 10% of Ca.

  Example 2 is an example in which a group III nitride crystal was produced by the method described in the first example of the first embodiment.

First, as shown in FIG. 5A, a base layer 51 made of GaN was formed on the sapphire substrate 21. The underlayer 51 was formed by heating the sapphire substrate 21 to a temperature of about 1020 ° C. to 1100 ° C. and then supplying trimethylgallium (TMG) and NH ₃ onto the substrate. Next, the sapphire substrate 21 on which the underlayer 51 was formed was taken out of the growth apparatus and exposed to the atmosphere. Then, again set the substrate in the apparatus, after heating so that the temperature of the sapphire substrate 21 to approximately 1020 ° C. C. to 1100 ° C., by supplying the NH ₃ and trimethylgallium (TMG) on the substrate, a GaN A semiconductor layer 52 was formed. At this time, since the surface of the underlayer 51 is exposed to the atmosphere, pits, hillocks, and the like are formed on the surface of the semiconductor layer 52 crystal-grown from the underlayer 51, and the portion where these are formed is a crystal nucleus generation region. 52a.

  The semiconductor layer 52 was produced by the above-described method, and further, crystal growth was performed by using the LPE method. When the obtained crystal was evaluated, crystal growth started from the crystal nucleus generation region, and a good single crystal could be grown by lateral (lateral) growth.

  Example 3 is an example in which a group III nitride crystal was manufactured by a method of forming a crystal nucleus generation region by machining.

  First, as shown in FIG. 6A, the semiconductor layer 22 was formed on the sapphire substrate 21. The process of FIG. 6A is the same as the process of FIG. Next, grooves with a pitch of 500 μm and a depth of 10 μm were formed in a grid pattern on the surface of the semiconductor layer 22 by a scriber. As shown in FIG. 6B, the groove portion (scribe mark) becomes a crystal nucleus generation region 22a. Diamond was used for the scriber needle. The groove may be formed using a dicing apparatus.

  In addition, the crystal nucleation region was formed by forming the GaN semiconductor layer at high speed. As a method for growing at high speed, the HVPE method is more suitable than the MOCVD method. FIG. 7A shows a photoluminescence (PL) emission spectrum of a GaN semiconductor layer formed by the MOCVD method, and FIG. 7B shows a PL emission spectrum of a GaN semiconductor layer grown at a high speed by the HVPE method. Indicates. PL emission was excited by a 0.5 mW 325 nm He—Cd laser, and the PL emission intensity was measured with a spectrometer. It can be seen that the PL emission intensity of the 420 nm band blue band is high in the GaN layer manufactured by the HVPE method. Nitrogen defects are considered as a factor. A substrate with many nitrogen defects has many crystal nucleus generation regions, and crystal growth by the LPE method can be easily realized. When LPE crystal growth was performed by this method and the obtained crystal was evaluated, crystal growth started from the crystal nucleus generation region, and a good single crystal could be grown by lateral (lateral) growth.

  In this example, a group III nitride crystal is formed on a semiconductor layer having a crystal nucleus generation region with an X-ray diffraction twist angle of 680 seconds or less.

(Examples 4-1 to 4-6)
The twist angle was 60 seconds (Example 4-1), 120 seconds (Example 4-2), 312 seconds (Example 4-3), 355 seconds (Example 4-4), 412 seconds (Example 4). -5), using a semiconductor layer having a crystal nucleus generation region of 680 seconds (Example 4-6), 850 ° C., 35 atm (35 × 1.013 × 10 ⁵ Pa) to 40 atm (40 × 1.013) Under conditions of × 10 ⁵ Pa), a gallium nitride crystal was grown on the semiconductor layer for 96 hours to 200 hours using nitrogen gas as a reaction gas.

(Comparative Examples 1-2)
As Comparative Examples 1 and 2, a semiconductor layer having a crystal nucleus generation region with a twist angle of 752 seconds (Example 4-1) and 882 seconds (Example 4-2) was used, and Example 4-1 was used. In the same manner as described above, a gallium nitride crystal was grown.

In addition, the semiconductor layer used in Examples 4-1 and 4-2 uses a thick film crystal manufactured by HVPE or LPE, and its tilt angle (half-value width of rocking curve of X-ray (0002) diffraction) is It was about 50 seconds to 150 seconds. The semiconductor layers used in Examples 4-3 to 4-6 and Comparative Examples 1 and 2 had a tilt angle of about 150 seconds to 300 seconds. The carrier concentration was 1 × 10 ^{16 to} 5 × 10 ¹⁶ (cm ⁻³ ).

  The growth results (average film thickness and quality) of Examples 4-1 to 4-6 and Comparative Examples 1 and 2 are shown in Table 1 below together with the twist angle of the crystal nucleus generation region used. When the thickness of the obtained gallium nitride crystal is 100 μm to 1500 μm, a thick film is formed, and when the thickness is 5 μm to 99 μm, a thin film is formed. Moreover, coloring means that the crystal | crystallization was black or brown.

(Table 1)
Twist angle (seconds) Crystal color Thickness Remarks
Example 4-1 60 Transparent thick film Example 4-2 120 Transparent thick film Example 4-3 312 Transparent thick film Example 4-4 355 Transparent thick film Example 4-5 412 Transparent thick film Example 4-6 680 Almost transparent thick film Comparative example 1 752 Colored thin film Reproducibility decline Comparative example 2 880 Colored thin film Reproducibility decline

  As shown in Table 1, in Examples 4-1 to 4-6 in which the twist angle of the crystal nucleus generation region was 680 seconds or less, transparent and thick gallium nitride crystals were obtained. In Comparative Examples 1 and 2, since the twist angle of the crystal nucleus generation region exceeds 680 seconds despite being grown under the same conditions, the obtained crystal is colored from brown to black and is a thin film. Cases were often observed. From these results, it has been found that when the twist angle of the nucleation layer is 680 seconds or less, a thicker gallium nitride crystal can be obtained with higher quality.

This example is an example in which a group III nitride crystal is formed on a semiconductor layer having a crystal nucleus generation region having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less.

(Examples 5-1 to 5-5)
Carrier concentration is 1 × 10 ¹⁶ cm ⁻³ (Example 5-1), 3 × 10 ¹⁶ cm ⁻³ (Example 5-2), 5 × 10 ¹⁶ cm ⁻³ (Example 5-3), 8 Using a semiconductor layer having a crystal nucleus generation region of × 10 ¹⁶ cm ⁻³ (Example 5-4) and 1 × 10 ¹⁷ cm ⁻³ (Example 5-5), 850 ° C., 35 atm (35 × 1 A gallium nitride crystal is grown on the semiconductor layer for 96 hours to 200 hours using nitrogen gas as a reaction gas under the conditions of .013 × 10 ⁵ Pa) to 40 atm (40 × 1.013 × 10 ⁵ Pa) I let you. In this example, the carrier concentration was controlled by using, for example, quartz reaction tubes having different growth rates, growth temperatures, and conditions. As the quartz reaction tube having different conditions, for example, a quartz reaction tube immediately after replacement or a sufficiently dead quartz reaction tube was used.

(Comparative Examples 3-4)
As Comparative Examples 3 and 4, a semiconductor layer having a crystal nucleus generation region having a carrier concentration of 3 × 10 ¹⁷ cm ⁻³ (Comparative Example 3) and 5 × 10 ¹⁷ cm ⁻³ (Comparative Example 4) was used. A gallium nitride crystal was grown in the same manner as in Example 5-1. In addition, the twist angle of the crystal nucleus generation region used in Examples 5-1 to 5-5 and Comparative Examples 3 to 4 was about 500 seconds, and the tilt angle was 200 seconds to 300 seconds.

  The growth results (average film thickness and quality) of the gallium nitride crystals of Examples 5-1 to 5-5 and Comparative Examples 3 to 4 are shown in Table 2 below together with the carrier concentration in the crystal nucleus generation region used. When the thickness of the obtained gallium nitride crystal is 100 μm to 1500 μm, a thick film is formed, and when the thickness is 5 μm to 99 μm, a thin film is formed. Moreover, coloring means that the crystal | crystallization was black or brown.

(Table 2)
Carrier concentration Crystal color Thickness Remarks
(Cm ^-3 )
Example 5-1 1 × 10 ¹⁶ transparent thick film Example 5-2 3 × 10 ¹⁶ transparent thick film Example 5-3 5 × 10 ¹⁶ transparent thick film Example 5-4 8 × 10 ¹⁶ transparent thick film Example 5-5 1 × 10 ¹⁷ Almost transparent thick film Comparative Example 3 3 × 10 ¹⁷ colored thick film Reproducibility decreased Comparative Example 4 5 × 10 ¹⁷ colored thin film Reproducible decreased

As shown in Table 2, in Examples 5-1 to 5-5 in which the carrier concentration in the crystal nucleus generation region was 1 × 10 ¹⁷ cm ⁻³ or less, transparent and thick gallium nitride crystals were obtained. . In Comparative Examples 5-1 and 5-2, although the carrier concentration in the crystal nucleus generation region exceeded 1 × 10 ¹⁷ cm ⁻³ even though it was grown under the same conditions, the obtained crystal was brown. It was often observed that the film was colored from black to black and was a thin film. From these results, it was found that when the carrier concentration of the nucleation layer is 1 × 10 ¹⁷ cm ⁻³ or less, a thicker gallium nitride crystal can be obtained with higher quality.

  When the crystal is colored as in the comparative example, for example, when used as a substrate of a light emitting element, it becomes a light absorbing layer and absorbs light, which causes heat generation and deterioration of output characteristics. In addition, a reduction in the film thickness that can be grown reduces crystal productivity.

  In addition, the following reasons can be considered that the thickness of the crystal to be grown differs depending on the carrier concentration. A semiconductor layer having a high carrier concentration is considered to have a high impurity concentration on the surface. For this reason, as a result of the occurrence of pinning that prevents growth in the direction perpendicular to the C-axis (lateral growth), growth in the horizontal direction is hindered. As a result, even when grown under the same conditions, it is considered that the amount of incorporation of the impurity amount of the crystal becomes large, and the crystal is colored and the growth rate is reduced.

  As described above, according to the present invention, it is possible to provide a method for producing a group III nitride crystal that has high quality, high production efficiency, is useful as a substrate for a semiconductor production process, and can be used as a semiconductor substrate. Thereby, a semiconductor substrate and a semiconductor device using the same can be provided.

1A to 1C are process cross-sectional views illustrating an example of the manufacturing method of the present invention. 2A to 2D are process cross-sectional views illustrating another example of the manufacturing method of the present invention. FIG. 3 is a schematic diagram showing a configuration of an example of a manufacturing apparatus used in the manufacturing method of the present invention. 4A to 4D are process cross-sectional views illustrating still another example of the manufacturing method of the present invention. 5A to 5C are process cross-sectional views illustrating still another example of the manufacturing method of the present invention. 6A to 6B are process cross-sectional views showing still another example of the manufacturing method of the present invention. FIG. 7A shows a PL emission spectrum of a GaN semiconductor layer formed by MOCVD in Example 3 of the present invention, and FIG. 7B shows high-speed growth by HVPE in Example 3 of the present invention. It is the spectrum of PL light emission of the made GaN semiconductor layer. FIG. 8 is a schematic cross-sectional view showing an example of the semiconductor element of the present invention. FIG. 9 is a schematic cross-sectional view showing another example of the semiconductor element of the present invention.

Explanation of symbols

11 Substrate 12, 22, 52 Semiconductor layer 12a, 22a, 52a Crystal nucleus generation region 13 Group III nitride crystal 21 Sapphire substrate 23 LPE-GaN layer 24 Resist pattern 51 Underlayer

Claims (18)

(I) A semiconductor layer made of a semiconductor represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) and having a crystal nucleus generation region on the surface Forming a step;
(Ii) in an atmosphere containing nitrogen, the melt containing at least one group III element selected from the group consisting of gallium, aluminum and indium, at least one of an alkali metal and an alkaline earth metal, and nitrogen And a step of growing a group III nitride crystal on the semiconductor layer by bringing the crystal nucleus generation region of the semiconductor layer into contact with each other.   The manufacturing method according to claim 1, wherein a twist angle of the crystal nucleus generation region is 680 seconds or less. The manufacturing method according to claim 1, wherein a carrier concentration in the crystal nucleus generation region is 1 × 10 ¹⁷ cm ⁻³ or less. The step (i)
(I-1) forming a base layer formed of a semiconductor represented by the composition formula _{Al s Ga t In 1-st} N ( provided that 0 ≦ s ≦ 1,0 ≦ t ≦ 1, s + t ≦ 1) ,
(I-2) exposing the surface of the base layer to the atmosphere;
(I-3) By growing a semiconductor represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) on the underlayer. Forming the semiconductor layer,
The manufacturing method according to claim 1, wherein the crystal nucleus generation region includes at least one of pits and hillocks. The step (i)
(Ia) forming a semiconductor layer formed of a semiconductor represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1); ,
(Ib) The manufacturing method in any one of Claim 1 to 3 including the process of forming the said crystal nucleus generation | occurrence | production area | region by processing the surface of the said semiconductor layer.   The manufacturing method according to claim 5, wherein the step (ib) includes a step of roughening the surface of the semiconductor layer by etching.   The manufacturing method according to claim 5, wherein the step (ib) includes a step of mechanically processing a surface of the semiconductor layer. In the step (ia), the semiconductor layer is formed so that the surface of the semiconductor layer is a (0001) plane,
The manufacturing method according to claim 5, wherein in the step (ib), the surface of the semiconductor layer is polished so that the surface is inclined with respect to the (0001) plane.   The manufacturing method according to claim 1, wherein the group III element is gallium and the group III nitride crystal is gallium nitride.   The manufacturing method according to claim 1, wherein the atmosphere is a pressurized atmosphere.   The manufacturing method according to claim 1, wherein the semiconductor layer is formed on a substrate.   The substrate is a GaAs substrate having a (111) surface, a Si substrate having a (111) surface, a sapphire substrate having a (0001) surface, or a SiC substrate having a (0001) surface. The manufacturing method according to claim 11.   A group III nitride crystal produced by the production method according to claim 1.   A semiconductor substrate comprising a group III nitride crystal, wherein the group III nitride crystal is the group III nitride crystal according to claim 13.   A method for manufacturing a semiconductor substrate including a group III nitride crystal, comprising the step of growing a group III nitride crystal by the manufacturing method according to claim 1. An electronic device comprising a semiconductor element formed on a substrate,
An electronic device, wherein the substrate is a group III nitride crystal according to claim 13 or 14.   The electronic device according to claim 16, wherein the semiconductor element is a laser diode, a light emitting diode, or a field effect transistor.   The electronic device according to claim 16, wherein the electronic device is a high-frequency device or a high-power device.

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