JP4588340B2 - Method for manufacturing group III nitride substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a group III nitride substrate (a substrate including a group III nitride semiconductor crystal) and a semiconductor 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 blue light or ultraviolet light. Laser diodes (LD) that emit blue light are applied to high-density optical discs and displays, and light-emitting diodes (LEDs) that emit blue light are applied to displays and illumination. 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 vapor phase epitaxial growth, for example, formed by heteroepitaxial growth of a group III nitride crystal on a sapphire substrate. Yes. However, the sapphire substrate and the GaN crystal have a difference of 13.8% in the lattice constant and a difference of 25.8% in the linear expansion coefficient. For this reason, the GaN thin film obtained by vapor phase epitaxial growth has insufficient crystallinity. 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. 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 or AlN is 10,000 atm (10,000 × 1.013 × 10 ⁵ Pa) or more, GaN has conventionally been in the liquid phase. In order to grow, a condition of 8000 atm (8000 × 1.013 × 10 ⁵ Pa) at 1200 ° C. has been required. On the other hand, it has recently 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.

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 1).

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). Has been.
JP 2002-293696 A

  A sapphire substrate or the like is usually used for manufacturing a group III nitride substrate. However, since these substrates and group III nitride crystals have different lattice constants and thermal expansion coefficients, when the group III nitride crystals are grown using these substrates, the substrates may be distorted or warped. It was.

  When a device is manufactured using a semiconductor substrate having a low surface flatness, the manufacture may be difficult. For example, in a stepper used in a device manufacturing process, mask alignment may be difficult.

  In view of such circumstances, the present invention provides a manufacturing method capable of manufacturing a group III nitride substrate having a low dislocation density and high surface flatness, and a semiconductor device manufactured using the same. With the goal.

  To achieve the above object, the present invention provides a group III nitride in which a group III element and nitrogen are reacted in an alkali metal melt to form and grow a group III nitride crystal in an atmosphere containing nitrogen. A method for manufacturing a substrate, wherein a plurality of portions of a group III nitride semiconductor layer prepared in advance are selected as seed crystals for generation and growth of a group III nitride crystal, and It is a manufacturing method which makes the surface of a seed crystal contact.

  In the manufacturing method of the present invention, since a group III nitride is used as a seed crystal and a group III nitride crystal is selectively grown from the seed crystal, a group III nitride substrate having a large low dislocation region can be easily manufactured. .

  Hereinafter, the manufacturing method of the present invention will be specifically described using the first to fourth manufacturing methods as examples. The present invention is not limited to these.

The first production method of the present invention is represented by (i) a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). Preparing a semiconductor layer; (ii) forming a patterned mask film on the semiconductor layer; and (iii) at least one selected from gallium, aluminum, and indium in an atmosphere containing nitrogen. By bringing the surface of the semiconductor layer into contact with a melt containing a group III element, an alkali metal, and the nitrogen, the semiconductor layer exposed from the mask film is used as a seed crystal, and a group III nitride crystal is formed on the semiconductor layer. It is preferable to include the process of growing. In this specification, the group III nitride crystal is a crystal represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1). means.

The second manufacturing method of the present invention includes (I) a step of forming a patterned mask film on the original substrate, and (II) a composition formula Al _u on the original substrate exposed from the mask film. A step of forming a semiconductor layer represented by Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1), and (III) under an atmosphere containing nitrogen The semiconductor layer is used as a seed crystal by bringing the surface of the semiconductor layer into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium, an alkali metal, and the nitrogen. And a step of growing a group III nitride crystal.

The third production method of the present invention is represented by (A) composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). A step of preparing a semiconductor layer to be formed; (B) a step of oxidizing part of the surface of the semiconductor layer to form an oxidized region; and (C) an atmosphere containing nitrogen, selected from gallium, aluminum, and indium. The semiconductor layer other than the oxidized region is used as a seed crystal by bringing the surface of the semiconductor layer into contact with a melt containing at least one group III element, an alkali metal, and the nitrogen, and the group III is formed on the semiconductor layer. A step of growing a nitride crystal.

Furthermore, the fourth manufacturing method of the present invention is as follows: (a) On the original substrate, the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) And (b) forming a patterned mask film on the semiconductor layer, and removing the semiconductor layer in a region exposed from the mask film up to the original substrate. A step of forming a convex seed semiconductor layer covered with the mask film, and (c) at least one group III element selected from gallium, aluminum and indium and an alkali metal in an atmosphere containing nitrogen It is preferable to include a step of growing a group III nitride crystal on the semiconductor layer using the seed semiconductor layer as a seed crystal by bringing the surface of the semiconductor layer into contact with a melt containing nitrogen and nitrogen.

In the first manufacturing method, the mask film is represented by, for example, diamond-like carbon, alumina (Al ₂ O ₃ ), composition formula Al _u Ga _1-u N (where 0 <u ≦ 1). Can be used.

In the first manufacturing method, when a material represented by the composition formula Al _u Ga _1-u N (where 0 <u ≦ 1) is used as the mask film, the Al film in the mask film The composition ratio is preferably larger than the Al composition ratio of the semiconductor layer. Moreover, it is preferable that the surface or the whole of the mask film is oxidized. The mask film being oxidized means a state in which, for example, GaO _x , AlO _x , or AlGaO _x is formed on the mask film. Moreover, that the surface of the mask film is oxidized means, for example, a state where half or less of the thickness of the mask film is oxidized. The oxidized region of the mask film may partially include an unoxidized portion, for example, a portion represented by Al _u Ga _1-u N (where 0 <u ≦ 1). It may be included.

  A method for oxidizing the surface of the mask film is not particularly limited, and examples thereof include a thermal oxidation method in which heat treatment is performed in an atmosphere containing oxygen, a method of injecting oxygen ions, and a method of processing with oxygen plasma. The thickness of the region where the surface of the mask film is oxidized is, for example, in the range of 0.01 μm to 1.0 μm, preferably 0.05 μm to 0.5 μm. The thickness of the oxidized region can be measured by, for example, a cross-sectional scanning electron microscope (SEM) or a cross-sectional transmission electron microscope (TEM).

In the first manufacturing method, the step (i) includes a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) on the original substrate. It is preferable to be a step of forming a semiconductor layer represented by:

In the first manufacturing method, the semiconductor layer is formed using GaN, and the mask film is represented by a composition formula Al _u Ga _1-u N (where 0.05 ≦ u ≦ 1). It is preferable.

  In the first to fourth manufacturing methods, it is preferable that a plurality of through holes are formed in the mask film, and the through holes are, for example, the through holes when the through holes are formed in the mask film. This means that the semiconductor layer is exposed from the mask film. Examples of the shape viewed from the upper surface of the through hole include a dot shape and a stripe shape.

  In the first to fourth manufacturing methods, the mask film is preferably patterned in a stripe shape, and as a result, the semiconductor layer may be exposed in a stripe shape.

  As the size of the through hole, for example, when the shape seen from the upper surface is a dot-like circle, the diameter is, for example, in the range of 1 μm to 1000 μm, preferably 10 μm to 500 μm. On the other hand, when the shape seen from the upper surface is a stripe shape, the length is not particularly limited, and the width is, for example, 1 μm to 100 μm, preferably 5 μm to 30 μm.

  In the manufacturing method of the present invention, it is preferable that the group III nitride crystal is grown while the original substrate is swung in the melt.

  In the first manufacturing method, it is preferable that the mask film is formed using Al, and the surface or the whole of the mask film is oxidized. The method for oxidizing the mask film is as described above.

  In the second manufacturing method, it is preferable that the mask film includes at least one selected from the group consisting of silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, and aluminum nitride oxide.

  In the second manufacturing method, the mask film preferably contains at least one of a refractory metal or a refractory metalized product.

  In the second manufacturing method, it is preferable that the mask film includes at least one selected from the group consisting of titanium, tungsten, molybdenum, niobium, tungsten silicide, molybdenum silicide, and niobium silicide.

In the third manufacturing method, the step (A) includes a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) on the original substrate. It is preferable to be a step of forming a semiconductor layer represented by:

  In the third manufacturing method, the step (B) includes (B-1) forming a patterned mask film on the surface of the semiconductor layer, and (B-2) exposing the mask film. It is preferable to include a step of forming the oxidized region by oxidizing the surface of the semiconductor layer. In addition, the said oxidation area | region can be formed similarly to the said oxidation method, The thickness is 0.01 micrometer-1.0 micrometer, for example, Preferably it is 0.05 micrometer-0.5 micrometer.

  Further, in the step (B-2) in the third manufacturing method, the method for forming the oxidized region is not particularly limited. For example, a method for implanting oxygen ions, a heat for performing heat treatment in an atmosphere containing oxygen. Examples thereof include an oxidation method and a method of treating with oxygen plasma.

  In the first, second, third and fourth manufacturing methods, it is preferable to further include a step of removing the mask film.

  In the first, second, third and fourth manufacturing methods, the original substrate is preferably a sapphire substrate whose surface is a (0001) plane.

  In the first, second, third and fourth manufacturing methods, the group III element is preferably gallium, and the group III nitride crystal is preferably a gallium nitride crystal.

  In the first, second, third and fourth manufacturing methods, the atmosphere is preferably a pressurized atmosphere.

  In the first, second, third and fourth manufacturing methods, the melt may further contain an alkaline earth metal. Examples of the alkaline earth metal include Ca, Mg, Sr, and Ba.

  In the first, second, third and fourth manufacturing methods, the period of the group III nitride semiconductor layer selected as the seed crystal is preferably 30 μm or more, more preferably 50 μm or more, and still more preferably. It is 100 μm or more, and particularly preferably 1000 μm or more. The period of the group III nitride semiconductor layer selected as the seed crystal is an average value of the distances between the centers (center lines) of the group III nitride semiconductor layer surfaces selected as the adjacent seed crystals. Examples of the measuring method include a cross-sectional scanning electron microscope (SEM) and a cross-sectional transmission electron microscope (TEM).

  Next, the group III nitride substrate of the present invention is a group III nitride substrate manufactured by the manufacturing method of the present invention.

In the substrate of the present invention, the period of the dislocation dense region is preferably 30 μm or more, more preferably 50 μm or more, still more preferably 100 μm or more, and particularly preferably 1000 μm or more. The dislocation dense region is a region where the number of edge dislocations and screw dislocations is 10 ⁷ to 10 ⁸ / cm ² or more. The period of the dislocation dense region is an average value of the distance between the portions having the highest dislocation density. As the measuring method, for example, by observing cathodoluminescence (CL) by electron beam irradiation, it is obtained from the number of dark spots, or after etching with an acid (200 ° C.) such as pyrophosphoric acid, unevenness is formed with AFM or the like. The observation method etc. can be given. The portion having a high dislocation density means, for example, a portion where dark transitions are most concentrated in a CL image.

  The group III nitride substrate of the present invention includes a group III nitride semiconductor layer having a partially oxidized region, and a group III nitride substrate formed by liquid phase growth on the semiconductor layer And it is preferable that the said oxidation area | region is the partial oxidation area | region formed by the (B) process in a 3rd manufacturing method.

  Further, the group III nitride substrate of the present invention includes a group III nitride semiconductor layer partially including at least one region of AlGaN or AlN, and a group III nitride crystal formed by liquid phase growth on the semiconductor layer. A group III nitride substrate containing is preferable.

  The group III nitride substrate of the present invention is a group III nitride including a group III nitride semiconductor layer partially containing diamond carbon and a group III nitride crystal formed by liquid phase growth on the semiconductor layer. A substrate is preferred.

In the present invention, when a GaN substrate is manufactured, a combination of a mask film and a semiconductor layer to be a seed crystal uses Al ₂ O ₃ as a mask film, and the semiconductor layer is formed of at least one of GaN or AlGaN. Preferably it is. This is because a GaN crystal grows selectively from the surface of the semiconductor layer exposed from the mask film (Al ₂ O ₃ ).

  The semiconductor device of the present invention is a semiconductor device comprising a substrate and a semiconductor element formed on the substrate, and the substrate is a group III nitride substrate manufactured by the manufacturing method of the present invention. is there.

  In the semiconductor device, the semiconductor element may be, for example, a laser diode or a light emitting diode.

  Hereinafter, embodiments of the present invention will be described with reference to examples. In the following description, the same parts may be denoted by the same reference numerals and redundant description may be omitted.

(Embodiment 1)
First, an example of the first manufacturing method of the present invention for manufacturing a group III nitride substrate will be described with reference to FIG.

FIG. 1 is a process sectional view showing an example of the process of the first manufacturing method of the present invention. First, a semiconductor layer represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) is prepared (step (i)). In this step, 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 the original substrate 11. You may form the semiconductor layer 12 represented by these. The semiconductor layer 12 is formed by, for example, metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). it can. As the original substrate 11, for example, a sapphire substrate, a GaAs substrate, a Si substrate, a SiC substrate, an AlN substrate, or the like can be used. As the sapphire substrate, for example, a sapphire substrate whose surface is a (0001) plane is preferably used.

For example, after growing a GaN crystal having a thickness of several hundreds μm or more on an original substrate such as sapphire by using the HVPE method or the like, a seed crystal of only the GaN crystal is obtained by separating the original substrate. Can do. Below, an example of the growth method of the GaN crystal using HVPE method is demonstrated. First, a GaN layer is formed on a sapphire substrate by MOCVD. Next, a metal Ti film is formed on the GaN layer, and the Ti film is heat-treated with NH ₃ to form a void TiN film. Then, for example, a GaN crystal having a thickness of 600 μm is grown on the TiN film by using the HVPE method. In the HVPE method, GaCl is put into a Ga port, and hydrogen gas and hydrogen chloride gas are blown into the Ga port to generate GaCl. A GaN crystal is grown on the sapphire substrate by blowing hydrogen gas and NH ₃ gas near the susceptor on which the sapphire substrate is placed. Thereafter, the GaN crystal is peeled off from the sapphire substrate to obtain a GaN substrate (crystal). This GaN substrate can be used as the semiconductor layer (seed crystal), for example. A GaN crystal or the like formed by liquid phase growth can also be used as the semiconductor layer (seed crystal).

Next, as shown in FIG. 1B, a patterned mask film 13 is formed on the semiconductor layer 12 (step (ii)). The mask film 13 is formed of a material that is not easily melted into the GaN melt, and is represented by, for example, diamond-like carbon or a composition formula Al _u Ga _1-u N (where 0 <u ≦ 1). For example, AlN, AlGaN, Al ₂ O _{3 and the} like can be used. When the semiconductor layer 12 is formed using GaN, the mask film 13 is a material represented by the composition formula Al _u Ga _1-u N (where 0.05 ≦ u ≦ 1). It is preferable. In the case of using a mask film represented by the composition formula Al _u Ga _1-u N (where 0 <u ≦ 1), the Al content (composition ratio) is the Al content of the semiconductor layer 12 ( It is preferable that it is larger than the composition ratio. Examples of the method for forming the mask film include a sputtering method, a CVD method, and a vapor deposition method.

  The thickness of the mask film is, for example, 0.05 μm to 10 μm, preferably 0.1 μm to 3 μm. The surface of the mask film is preferably oxidized.

Further, a plurality of through holes may be formed in the mask film 13. This is because when the through hole is formed, the semiconductor layer 12 is exposed from the mask film at the portion of the through hole, and a group III nitride crystal can be selectively grown using the exposed portion as a seed crystal. . The shape of the through hole is, for example, a dot shape or a stripe shape when the mask film is viewed from above. An example of a top view of the mask film 13 in this case is shown in FIGS. When the through hole is patterned in a dot shape as shown in FIG. 2A, the semiconductor layer 12 is exposed in a dot shape in the through hole 13h of the mask film 13, and as shown in FIG. When the through hole is patterned in a stripe shape, the semiconductor layer 12 is exposed in a stripe shape in the through hole 13 g of the mask film 13. For example, when the mask film 13 contains diamond-like carbon, the through-hole can be formed by forming a resist pattern by photolithography and performing dry etching using oxygen gas. Further, when the mask film 13 contains AlN or AlGaN, it can be formed, for example, by forming a resist pattern by photolithography and etching. Further, an Al layer is formed on the semiconductor layer, and a second mask film is further formed thereon. Next, the second mask film is patterned to form a through hole, and the Al layer exposed from the second mask film is oxidized through the through hole (for example, heat treatment in an oxygen atmosphere). Thus, the exposed portion can be oxidized to form Al ₂ O ₃ , and the Al ₂ O ₃ portion can be used as a mask film. The mask film on the Al layer can be removed together with the Al layer by a known method.

  Next, as shown in FIG. 1C, a group III nitride crystal 14 is grown on the semiconductor layer 12 using the semiconductor layer 12 exposed from the mask film 13 as a seed crystal (step (iii)). The group III nitride crystal is made to contact the surface of the semiconductor layer 12 with a melt containing at least one group III element selected from gallium, aluminum and indium, an alkali metal and the nitrogen in an atmosphere containing nitrogen, It can be grown by reacting the at least one group III element with nitrogen dissolved in the melt. The melt can be prepared, for example, by putting a material into a crucible and heating. Then, after bringing the seed crystal and the melt into contact with each other, the group III nitride in the melt is supersaturated so that a group III nitride semiconductor crystal grows on the semiconductor layer. Adjust temperature and atmospheric pressure.

  The group III element dissolved in the melt is selected according to the group III nitride for crystal growth, and gallium, aluminum, indium, or some of them are used. In the case of forming a gallium nitride crystal, only gallium is used. As the alkali metal, at least one selected from sodium (Na), lithium (Li) and potassium (K) is used, that is, one of them or a mixture thereof, and these usually function as a flux (hereinafter referred to as “flux”). This is the same in the embodiment of FIG. Among these, it is more preferable to use a mixture of Na and Li. In liquid phase growth using a mixed flux of Na and Li, the growth rate in the direction perpendicular to the (0001) direction, that is, in the lateral direction with respect to the original substrate (seed crystal) is faster. The portion thus grown is desirable for selective growth as in the present invention because it has low dislocations.

Through the step (iii), the group III nitride crystal 14 is grown on the semiconductor layer 12 and the mask film 13. By this crystal growth, a group III nitride crystal (for example, a GaN single crystal) whose composition formula is expressed by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is obtained. Can be formed.

In the step (iii), as the atmosphere containing nitrogen, for example, a nitrogen gas (N ₂ ) atmosphere or a nitrogen gas atmosphere containing ammonia can be used. This atmosphere is preferably a pressurized atmosphere, preferably a pressurized atmosphere that is larger than 1 atm (1 × 1.013 × 10 ⁵ Pa) and smaller than 100 atm (100 × 1.013 × 10 ⁵ Pa). preferable. The material melting and crystal growth conditions vary depending on the flux components, the atmospheric gas components, and the pressure thereof. For example, the melt temperature is about 700 ° C. to 1100 ° C., and the pressure is 1 atm (1 × 1.013 ×). 10 ⁵ Pa) to 100 atm (100 × 1.013 × 10 ⁵ Pa).

  The melt may further contain an alkaline earth metal. As the alkaline earth metal, for example, Ca, Mg, Sr, Ba and the like can be used.

  According to the method of Embodiment 1, a group III nitride crystal having a low dislocation density is obtained because the crystal is selectively grown from the seed crystal as compared with the conventional vapor phase growth method. Further, according to the method of Embodiment 1, a group III nitride crystal having high surface flatness can be obtained. In addition, after growing the group III nitride crystal, a portion other than the group III nitride crystal (sapphire substrate) is removed by polishing or the like to obtain a substrate formed only of the group III nitride crystal.

(Embodiment 2)
Next, an example of the second manufacturing method of the present invention for manufacturing a group III nitride substrate will be described with reference to FIG.

  FIG. 3 is a process sectional view showing an example of the process of the second manufacturing method of the present invention. As shown in FIG. 3A, a patterned mask film 32 is formed on the original substrate 11 (step (I)). The mask film 32 can be formed of, for example, silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, or aluminum nitride oxide. The mask film may be formed of a refractory metal or a refractory metallized metal having a high melting point (melting point of 1000 ° C. or higher). For example, titanium, tungsten, molybdenum, niobium, tungsten silicide, molybdenum silicide, or niobium silicide Can be used. The thickness of the mask film 32 is, for example, 0.005 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. The mask film forming method, the mask film patterning method, and the shape are the same as those in the first embodiment.

Next, as shown in FIG. 3B, the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on the original substrate 11 exposed from the mask film 32. , U + v ≦ 1) is formed (step (II)). The semiconductor layer 33 can be formed by, for example, metal organic chemical vapor deposition (MOCVD) or hydride vapor deposition (HVPE). The shape of the semiconductor layer 33 can be changed by changing the growth temperature. 4A to 4C show examples of cross-sectional views of the semiconductor layer 33 grown in various shapes. For example, in the crystal growth using the MOCVD method, when the crystal is grown at a temperature of 1010 ° C., the semiconductor layer 33a grows in a conical shape (FIG. 4A). When the crystal is grown at a temperature of 1040 ° C., the semiconductor layer 33b grows in a trapezoidal shape (FIG. 4B). When the crystal is grown at a temperature of 1070 ° C., the semiconductor layer 33c grows in a columnar shape or a rectangular parallelepiped shape (FIG. 4C).

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 gallium, aluminum, and indium, an alkali metal, By bringing the surface of the semiconductor layer 33 into contact with a melt containing nitrogen, a group III nitride crystal is grown on the semiconductor layer 33 using the semiconductor layer 33 as a seed crystal (step (III)). Since step (III) can be performed by the same method as step (iii) described in the first embodiment, description thereof is omitted. Through this step, a group III nitride crystal 34 grows on the semiconductor layer 33 as shown in FIG. Note that the mask film 32 may be removed before the group III nitride crystal 34 is formed.

The melt may further contain an alkaline earth metal. As the alkaline earth metal, for example, Ca, Mg, Sr, Ba and the like can be used. According to this method, the group III element and nitrogen dissolved in the melt react to react with the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ A group III nitride crystal represented by 1) is obtained. For example, a GaN crystal or a crystal represented by the composition formula Al _x Ga _1-x N (where 0 ≦ x ≦ 1) is obtained.

  In this way, a substrate including a group III nitride crystal can be obtained. In the conventional liquid phase growth method, at the initial stage of GaN crystal growth, the GaN seed crystal substrate melts in the melt, and at this time, irregularities of the seed crystal surface occur, and crystal growth starts from that surface. In some cases, the surface flatness of the obtained GaN crystal substrate deteriorates, or dislocations occur randomly from a part of the crystal. On the other hand, in the method of the second embodiment (second manufacturing method of the present invention), since the crystal is selectively grown from the seed crystal, the flatness of the obtained substrate is improved and the dislocation density is reduced. There is a feature that can be planned. Thus, according to the method of Embodiment 2, a group III nitride crystal having high flatness and low dislocation can be produced at low cost.

  In the manufacturing method of this embodiment, the period of the original substrate exposed from the mask film is, for example, 30 μm or more, preferably 50 μm or more, more preferably 100 μm or more, and further preferably 1000 μm or more. .

(Embodiment 3)
Next, a third manufacturing method of the present invention for manufacturing a group III nitride substrate will be described.

In the manufacturing method of the third embodiment, a semiconductor layer represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) is prepared. (Step (A)). This step is the same as step (i) described in the first embodiment. The semiconductor layer may be formed on the original substrate, for example, as described above.

  Next, a part of the surface of the formed semiconductor layer is oxidized to form an oxidized region (step (B)). By forming the oxidized region, crystal growth from the oxidized portion can be suppressed. Step (B) can be performed, for example, by the following steps (B-1) to (B-3).

  First, a patterned mask film is formed on the surface of the semiconductor layer (step (B-1)). The patterned mask film can be formed by a known material and method common in a semiconductor process.

  Next, an oxidized region is formed in a part of the surface of the semiconductor layer by oxidizing the surface of the semiconductor layer exposed from the mask film (step (B-2)). A method for oxidizing the semiconductor layer is not particularly limited. For example, a thermal oxidation method in which heat treatment is performed in an atmosphere containing oxygen, a method of injecting oxygen ions, a method of processing with oxygen plasma, or the like can be applied. The thickness of the oxidized region is preferably 0.01 μm or more.

  Next, the mask film is removed. The method for removing the mask film is selected according to the type of the mask film, and a general method can be applied.

  Next to step (B), in an atmosphere containing nitrogen, the surface of the semiconductor layer is brought into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium, an alkali metal, and the nitrogen. By using the semiconductor layer other than the oxidized region as a seed crystal, a group III nitride crystal is grown on the semiconductor layer (step (C)). Since the crystal growth step of the step (C) is the same as the step (iii) described in the first embodiment, a duplicate description is omitted.

Thus, a group III nitride crystal (for example, a GaN single crystal) whose composition formula is represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is formed. can do. According to the manufacturing method of the third embodiment (the third manufacturing method of the present invention), the same effects as the manufacturing methods of the first and second embodiments can be obtained.

(Embodiment 4)
Also in the following method, a group III nitride crystal can be selectively grown.

First, a semiconductor layer represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on the original substrate (step (a)). . The semiconductor layer can be formed by, for example, the MOCVD method or the MBE method.

  Next, a patterned mask film is formed on the semiconductor layer, and the semiconductor layer in a region exposed from the mask film is removed to the original substrate, thereby forming a convex seed covered with the mask film. A semiconductor layer is formed, and the mask film is removed (step (b)). The convex portion can be formed by a known method in which photolithography and etching are combined. The upper surface of the convex portion is usually a C surface. As the shape of the convex portion, a shape that facilitates separation of the original substrate in the following steps is selected. For example, it can be formed in a stripe shape or a dot shape.

Furthermore, at least one selected from gallium, aluminum, and indinium is formed on the upper surface of the convex portion of the semiconductor layer in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm (100 × 1.013 × 10 ⁵ Pa) or less). By bringing the surface of the semiconductor layer into contact with a melt containing three elements III, an alkali metal, and the nitrogen, the at least one group III element and nitrogen dissolved in the melt are reacted to form a group III nitride Crystals are grown (step (c)).

  As a result, a gap is formed between the original substrate and the group III nitride crystal. In this embodiment, since a group III nitride crystal is grown in a liquid phase in a melt containing a group III element in which nitrogen is dissolved, an alkali metal, and the nitrogen, a conventional MOCVD method, HVPE method, or the like is used. Compared with phase growth, the lateral growth rate can be increased. Therefore, even if the area of the convex portion is, for example, 10% or less of the entire area, crystals grown from the convex portion can be combined with each other. For example, when forming a stripe-shaped convex part, the width of a convex part is 1 micrometer-5 micrometers, for example, and the width between adjacent convex parts is 20 micrometers-500 micrometers, for example. Moreover, the period of a convex part is 30 micrometers or more, for example, More preferably, it is 50 micrometers or more, More preferably, it is 100 micrometers or more, Most preferably, it is 1000 micrometers or more.

  In particular, a semiconductor laser having a wide stripe width of an active layer required for a high-power laser requires low dislocations over a wide region. Further, when a semiconductor element is formed on a substrate, it is necessary to align a mask with a low dislocation region, and a wide low dislocation region is preferable in terms of process. Therefore, a substrate having a wide low dislocation region has a large practical effect.

Hereinafter, the present invention will be described in more detail with reference to examples. In the following examples, a case where a GaN crystal is grown will be described. However, a 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 A group III nitride crystal represented by ≦ y ≦ 1, x + y ≦ 1) can also be formed by a similar method.

  In this embodiment, an example of a method of forming a GaN semiconductor layer on a sapphire substrate by MOCVD and forming a GaN single crystal layer by liquid phase epitaxy will be described with reference to the drawings.

Process sectional views showing an example of a method for manufacturing a seed crystal substrate are shown in FIGS. First, a seed crystal substrate was formed. Specifically, as shown in FIG. 6A, a group III nitride semiconductor layer (GaN semiconductor layer) 62 made of GaN was grown on the sapphire substrate 61 by MOCVD. Specifically, the sapphire substrate 61 is heated so that the substrate temperature is about 1020 ° C. to 1100 ° C., and trimethyl gallium (TMG) and NH ₃ are supplied onto the original substrate to grow the GaN layer. . At this time, the surface of the GaN semiconductor layer 62 is preferably a Ga plane. Note that other methods capable of forming a group III nitride semiconductor may be used. For example, a method such as HVPE (hydride vapor phase epitaxy) or MBE may be used. Further, a thick GaN crystal formed on a sapphire substrate by HVPE or the like may be separated from the sapphire substrate and used as the semiconductor layer. Also in this case, it is desirable that the surface of the GaN semiconductor layer is a group III surface.

The GaN semiconductor layer 62 may contain aluminum or indium as a group III element in addition to gallium. The GaN semiconductor layer 62 has a composition formula of Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, and u + v ≦ 1).

Next, a mask film was formed on the GaN semiconductor layer 62. Specifically, as shown in FIG. 6B, a mask film 63 was formed on the GaN semiconductor layer 62. The mask film is preferably made of a material that is difficult to melt into the GaN melt. For example, diamond-like carbon (DLC), AlGaN, AlN, or the like can be used. When AlGaN is used for the mask film, if the Al content of the mask film is high, the wettability of crystal growth is low and it is difficult to melt into the GaN melt. It is important that the content of is high. Specifically, the composition ratio of Al in the mask film is preferably 3 atomic% or more (Al _0.03 Ga _0.97 N), more preferably 5 atomic% or more (Al _0.05 Ga _0.95 N). Further, when AlGaN is used as the group III nitride semiconductor layer, the surface is desirably oxidized (the same applies to the following examples). In this embodiment, the mask film 63 made of Al _0.07 Ga _0.93 N is formed by the MOCVD method. Specifically, an organic metal (such as trimethylgallium and trimethylaluminum) and NH ₃ are supplied to a substrate (substrate temperature: 1050 ° C.) at 26,600 Pa (200 Torr) to grow a mask film 63 made of AlGaN. I let you.

Here, in order to examine the difference in solubility in Ga melt depending on the composition, a seed crystal substrate was mixed with GaN melt (800 ° C., 10 atm (10 × 1.013 × 10) mixed with Na and Ca as flux. ⁵ Pa)). As the seed crystal substrate, a substrate in which a GaN layer (thickness: 4 μm) and an Al _0.07 Ga _0.93 N layer (thickness: 1.4 μm) were stacked on a sapphire substrate was used. A photograph of the cross section after immersion is shown in FIG. 5, in which A represents a sapphire substrate, B represents a (GaN + AlGaN) layer, and C represents a mask film. The side surface of the GaN layer portion was melted, but the AlGaN layer was hardly melted, and the thickness of the (GaN + AlGaN) layer (B in the figure) after immersion was 5 μm. Further, no crystal growth was observed on the Al _0.07 Ga _0.93 N layer. Note that there is a difference in resistance to the GaN melt depending on the flux component.

Next, in order to evaluate the usefulness of AlN as a mask film, a comparative study was conducted on the dissolution characteristics of an AlN film and a GaN film with respect to a Ga-containing melt. First, a sapphire substrate laminated with an AlN layer (thickness: 3 μm) and a sapphire substrate laminated with a GaN layer (thickness: 3 μm) were prepared. Next, 5 grams of Ga, 4.4 grams of Na and the respective laminated substrates were put into an alumina crucible, and then the crucible was placed in a stainless steel container. The stainless steel container was heated in an electric furnace under a nitrogen atmosphere (pressure 10 atm (10 × 1.013 × 10 ⁵ Pa)) and held at 800 ° C. for 10 hours. Thereafter, when the laminated substrate was taken out and evaluated, the laminated GaN was almost dissolved in the substrate on which the GaN layer was laminated. On the other hand, almost no change in thickness was observed on the substrate on which the AlN layer was laminated.

The DLC has an amorphous structure including the same sp ₃ bond of carbon as that of natural diamond, the same sp ₂ bond of carbon as that of graphite, and a bond with hydrogen. DLC has high hardness and high resistance to various melts. The DLC film can be formed by a plasma CVD method using the energy of plasma generated using high-frequency power or the like in a vacuum vessel, or a sputtering method.

In order to verify that a DLC film can be used as a mask film, the resistance of diamond to a GaN melt mixed with flux was examined. Ga 1 gram, Na 0.88 gram, and diamond single crystal (0.038 gram) were put into a BN crucible, and 800 ° C., 24 ° C. in a 2.5 atm (2.5 × 1.013 × 10 ⁵ Pa) atmosphere. A melting experiment was conducted for a period of time. The surface of the diamond after the experiment was the same as before the experiment, and when the mass of the diamond crystal taken out was measured, it was 0.038 gram, which was the same as before the experiment. From this, it was found that diamond is resistant to GaN melt mixed with flux.

  Next, a resist pattern was formed by photolithography, a part of the mask film 63 was removed by dry etching, and the GaN semiconductor layer 62 was exposed as shown in FIG. Specifically, as shown in FIG. 6C, photolithography and etching were performed so that the GaN semiconductor layer 62 was exposed from the mask film 63 in the form of dots.

On the other hand, an example of forming a mask film containing DLC will be described. First, a DLC film was formed on the GaN semiconductor layer by plasma CVD. For example, a DLC film was formed by using a hydrocarbon (C _x H _y ) -based gas as a source gas, a sapphire substrate temperature of 100 ° C., and performing plasma discharge at normal pressure. Next, a resist pattern was formed by photolithography, and a part of the DLC film was removed by dry etching using O ₂ to expose the GaN semiconductor layer. In this way, a mask film containing DLC can be formed.

  Using the seed crystal thus obtained, as shown in FIG. 6D, a GaN crystal 64 was grown from the GaN semiconductor layer 62 by the LPE method. Hereinafter, a method for growing a GaN crystal will be described.

FIGS. 7A and 7B are schematic views showing an example of the configuration of an LPE apparatus used in the manufacturing method of the present invention. The LPE apparatus of FIG. 7A is for adjusting the pressure of the growth atmosphere, and the source gas tank 71 for supplying the source gas such as nitrogen gas or the mixed gas of ammonia gas (NH ₃ gas) and nitrogen gas. Pressure regulator 72, leak valve 73, stainless steel container 74 for crystal growth, and electric furnace 75. FIG. 7B is an enlarged view of the stainless steel container 74, and a crucible 76 is set inside the stainless steel container 74. The crucible 76 is made of boron nitride (BN), alumina (Al ₂ O ₃ ), or the like. The crucible 76 can control the temperature to 600 ° C. to 1000 ° C. The atmospheric pressure (100 atm (100 × 1.013 × 10 ⁵ Pa) to 150 atm (150 × 1.013 × 10 ⁵ Pa)) supplied from the source gas tank 71 is adjusted to 100 atm (100 × 1.013) by the pressure regulator 72. X10 ⁵ Pa) or less can be controlled.

Hereinafter, a method for growing a GaN crystal will be described. First, a specified amount of Ga and Na as a flux were weighed and set in the crucible 76 together with the seed crystal substrate. In this example, the molar ratio of Ga and Na was 2.7: 7.3. Next, the crucible 76 was held at 800 ° C., and nitrogen gas mixed with ammonia (40%) was supplied at a pressure of ⁵ atm (5 × 1.013 × 10 ⁵ Pa).

By mixing ammonia, the atmospheric pressure during growth can be reduced, but it is not always necessary to mix ammonia. Even in a nitrogen gas atmosphere in which ammonia is not mixed, crystals can be grown under a pressure of 50 atm (50 × 1.013 × 10 ⁵ Pa). In this state, the temperature and pressure were kept constant, and LPE growth was performed for 96 hours to obtain a substrate provided with a GaN single crystal.

Moreover, an example of the large sized LPE apparatus (electric furnace) used with the method of this invention is shown in FIG. The LPE apparatus shown in FIG. 8 includes an electric furnace 80 having a stainless steel chamber 81 and a furnace lid 82 and can withstand an atmospheric pressure of 10 atm (10 × 1.013 × 10 ⁵ Pa). A heater 83 for heating is arranged in the chamber 81. The chamber 81 includes three zones including zones 800a, 800b, and 800c, and thermocouples 84a to 84c are attached to each of the zones. The three zones are controlled so that the temperature range is within ± 0.1 ° C., and the temperature in the furnace is uniformly controlled. The core tube 85 is arranged to improve the uniformity of the temperature in the furnace and prevent impurities from entering from the heater 83.

A crucible 86 made of boron nitride (BN) is disposed inside the furnace core tube 85. The melt 87 is prepared by putting the material into the crucible 86 and raising the temperature of the crucible. The substrate 10 serving as a seed crystal is attached to the substrate fixing portion 88. In the apparatus of FIG. 8, a plurality of substrates 10 can be fixed to the substrate fixing unit 88. The substrate 10 is rotated by a rotary motor 89a. A propeller 801 for stirring can be immersed in the melt 87. The propeller 801 is rotated by the rotary motor 89b. In this example, since the atmospheric pressure is 10 atm (10 × 1.013 × 10 ⁵ Pa) or less, a normal rotary motor can be used, but under an atmospheric pressure of 10 atm (10 × 1.013 × 10 ⁵ Pa) or more. Then, an electromagnetic induction type rotation mechanism is used. The atmospheric gas (source gas) is supplied from a gas source 802. The pressure of the atmospheric gas is adjusted by the pressure regulator 803. The atmospheric gas is sent into the furnace after impurities are removed by the gas purification unit 804.

  Hereinafter, a method of crystal growth will be described.

  (1) First, Ga and flux Na were weighed by a predetermined amount and set in the crucible 86. Ga having a purity of 99.9999% (six nines) was used. As Na, purified Na was used. It was possible to purify Na by heating and melting Na in a He-substituted glove box to remove oxides and the like 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 900 ° C. At this stage, the seed crystal substrate was not yet put into the crucible. In order to stir Ga and Na, a propeller was placed in the melt and the melt was stirred for several hours. Since Ga and Na have a large difference in specific gravity, Ga accumulates at the bottom of the melt unless the stirring of the melt is continued. Therefore, Ga in the melt becomes non-uniform and greatly affects the growth rate. In this example, the melt was stirred while the temperature in the electric furnace (crucible) was 900 ° C. However, in the case of a Na—Ga melt, the temperature in the electric furnace (crucible) should be 556 ° C. or higher. In this case, the Na—Ga alloy became a liquid phase and could be stirred more stably. Examples of the stirring method include a method using a propeller, a method in which a temperature distribution is given and heat convection is caused in an adjusted manner. In order to prevent GaN from being oxidized, nitrogen gas is preferably used as the atmospheric gas.

  (3) Next, the temperature of the crucible was set to 800 ° C., and the melt was brought into a supersaturated state. The seed crystal substrate was lowered to just above the melt, and the temperature of the substrate was brought close to the temperature of the melt. Several minutes later, the seed crystal substrate was put into the melt and crystal growth was started.

  (4) During crystal growth, the substrate was rotated at a rotation speed in the range of 10 rpm to 200 rpm. Preferably, it is rotated at around 100 rpm. After growing the crystals for 24 hours, the substrate was raised and removed from the melt. After raising the substrate, the substrate was rotated between 300 rpm and 1500 rpm in order to remove the melt remaining on the substrate surface. Desirably, it is rotated at around 1000 rpm. Thereafter, the substrate was taken out of the chamber. During crystal growth, the temperature of the crucible (melt temperature) may be kept constant, but the melt temperature may be lowered at a constant rate in order to keep the melt supersaturation constant. Good.

  In this example, a flux containing only Na was used, but the same effect was obtained even when a flux of Li, Na, K, or a mixed flux with an alkaline earth metal such as Ca was used. 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.

  As described above, according to the present invention, a GaN single crystal substrate having high flatness, good crystallinity, and low dislocation density can be manufactured with high productivity. In other words, a substrate that can supply a highly reliable device can be supplied at low cost. According to the present invention, since a substrate with high flatness can be obtained, a device process such as a semiconductor laser can be simplified, and a device can be manufactured with a high yield.

In this embodiment, the manufacture of a GaN single crystal substrate using gallium has been described. However, it is desirable to manufacture a substrate that absorbs less light with respect to the wavelength used for the optical device manufactured on the original 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. . According to 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.

  In this embodiment, an example of a method of forming a GaN semiconductor layer and a striped mask film on a sapphire substrate by MOCVD and forming a single crystal layer by liquid phase epitaxial growth will be described.

Using a sapphire (crystalline Al ₂ O ₃ ) substrate as the substrate, a group III nitride semiconductor layer containing GaN is formed on the sapphire substrate by MOCVD, and a stripe is formed on the group III nitride semiconductor layer. A mask film patterned in a shape was formed. As in the first embodiment, the mask film is preferably made of a material that does not melt in the GaN melt. Examples of the mask film include diamond-like carbon (DLC), AlGaN, and AlN. Among them, it is preferable to use AlN. When AlGaN is used, it is important that the Al content is higher than that of the group III nitride semiconductor layer. When the Al content is high, the wettability of crystal growth is low, and it is difficult to melt into the GaN melt, so that it is suitable as a mask film. The composition ratio of Al in the group III element is preferably 3 atomic% or more (Al _0.03 Ga _0.97 N), more preferably 5 atomic% or more (Al _0.05 Ga _0.95 N). In this example, Al _0.07 Ga _0.93 N was used. An AlGaN mask film was grown by supplying an organic metal (such as trimethylgallium and trimethylaluminum) and NH ₃ onto the original substrate by MOCVD. Then, an Al _0.07 Ga _0.93 N mask film was patterned in a stripe shape to expose the GaN semiconductor layer in a stripe shape.

Next, an example of an oscillating LPE apparatus used in the method of the present invention is shown in FIG. This oscillating LPE apparatus 90 includes a growth furnace 91 and a flow rate regulator 98 made of stainless steel, and the growth furnace 91 and the flow rate regulator 98 are connected by a pipe 99. The growth furnace 91 is provided with a heater 92 and a thermocouple 93 for heating, and can withstand an atmospheric pressure of 50 atm (50 × 1.013 × 10 ⁵ Pa). Further, in the growth furnace 91, there is a crucible fixing base 94, and a mechanism that rotates around the rotation shaft 902 in the direction of the arrow 901 in the figure is attached. A crucible 95 made of boron nitride (BN) is fixed in the crucible fixing base 94, and a melt 96 and a seed crystal 97 are placed in the crucible 95. As the crucible fixing base rotates, the melt in the crucible 95 moves to the left and right, and thereby the growth direction on the seed crystal is controlled in a fixed direction. In the present embodiment, it is desirable that the GaN seed crystal substrate 97 is fixed so that the swinging direction of the melt is parallel to the stripe-shaped mask film on the seed crystal 97. The atmospheric pressure is adjusted by the flow rate adjuster 98. The atmosphere gas supplied in the direction of the arrow 900 in the drawing from the source gas tank for supplying the source gas nitrogen gas or the mixed gas of ammonia gas (NH ₃ gas) and nitrogen gas has impurities introduced by the gas purification unit. After being removed, it is sent into the growth furnace 91.

  Hereinafter, a method of crystal growth will be described.

  A material containing Ga and Na was prepared by the same method as in Example 1. Next, in order to melt the raw material in the crucible 95, the temperature in the growth furnace 91 was raised to 800 ° C. In order to prevent GaN oxidation, nitrogen gas was used as the atmospheric gas. During crystal growth, the crucible fixing base 94 was swung to the left and right at one cycle per minute. After growing the crystals for 24 hours, the substrate was removed from the melt.

  In this method, the crucible fixing base 94 was swung in one cycle per minute, and the crystal was grown so that the seed crystal substrate 97 came out of the GaN melt every time it was swung. However, the crystal may be grown while the seed crystal substrate 97 is always present in the melt during oscillation.

  In this example, the crystal growth direction could be controlled by rocking the melt. That is, by controlling the crystal growth in a direction parallel to the stripe-shaped mask film, crystal growth starts from the group III nitride semiconductor layer exposed in the stripe shape, and dislocations are concentrated only in that portion. I was able to. As a result, it was possible to grow a GaN single crystal with particularly low dislocations in a portion other than the group III nitride semiconductor layer exposed from the mask film.

In the conventional method, it is difficult to control the dislocation, and the dislocation of the obtained group III nitride substrate varies in the range of 10 ⁴ to 10 ⁶ cm ⁻² depending on the portion of the substrate. By selectively growing the group III nitride crystal as in the manufacturing method, the portion where the group III nitride crystal has grown in the lateral direction (the portion not in contact with the semiconductor layer (seed crystal) exposed from the mask film) Dislocations could be stably controlled to 10 ⁴ cm ^-2 or less.

  In this example, the flux of only Na was used, but the same effect was obtained even when a flux of Li, Na, K, or a mixed flux with an alkaline earth metal such as Ca was used. For example, in the mixed flux of Na and Ca, about 10% of Ca can be mixed to grow crystals at a lower pressure.

  In this embodiment, an example of a method of forming a single crystal layer by liquid phase epitaxial growth after forming a mask film and a group III nitride semiconductor layer on a sapphire substrate will be described.

A sapphire (crystalline Al ₂ O ₃ ) substrate was used as the original substrate, and SiN _x was used as the mask film. As the mask film, silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, aluminum nitride oxide, titanium oxide, zirconium oxide, or niobium oxide can be used. Among these, silicon nitride is particularly preferable because it has a GaN growth suppressing action and GaN is not deposited on the silicon nitride.

First, on a sapphire substrate, SiN _{x serving} as a mask film was grown to 100 nm by a CVD method at atmospheric pressure. Next, a dot-shaped window (sapphire substrate exposed portion) was opened in the mask film by photolithography and etching. The window may be striped.

Next, on the sapphire substrate exposed from the mask film, the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1) is applied by MOCVD. The seed crystal represented was deposited. In this example, the sapphire substrate was heated so that the substrate temperature was about 1020 ° C. to 1100 ° C., and trimethylgallium (TMG) and NH ₃ were supplied onto the original substrate to grow the GaN layer. The shape of the growing GaN layer could be changed by changing the growth temperature. 4A to 4C show the shapes of GaN layers grown at various temperatures. As shown in FIGS. 4A to 4C, when the crystal is grown at a temperature of 1010 ° C., the GaN layer grows in a conical shape (FIG. 4A), and when the crystal is grown at a temperature of 1040 ° C., GaN The layer grew in a trapezoidal shape (FIG. 4B), and when the crystal was grown at a temperature of 1070 ° C., the GaN layer grew in a cylindrical shape or a rectangular parallelepiped shape (FIG. 4C). In this example, growth was performed at 1070 ° C. to form a cylindrical seed crystal.

A GaN single crystal was grown by the LPE method using the obtained GaN seed crystal in the same manner as in Example 1. The SiN _x mask film may be left as long as there is no problem in crystal growth, but since Si becomes an n-type dopant, it is preferably removed by wet etching with hydrofluoric acid or dry etching.

  Since the sapphire substrate does not melt in the GaN melt having a flux component, the GaN crystal was selectively grown from the seed crystal. It has been experimentally found that when silicon (Si) or gallium arsenide (GaAs) is used as the original substrate, the original substrate is melted in the GaN melt. Therefore, a sapphire substrate is desirable as an original substrate that can be selectively grown. By using a seed crystal substrate in which a group III nitride semiconductor layer is selectively formed on an original substrate that does not melt into a GaN melt, such as a sapphire substrate, selective GaN crystal growth becomes possible, and lower dislocations are better. A GaN single crystal substrate was obtained.

  In Example 4, an example in which a semiconductor laser is manufactured using the original substrate obtained in the above example will be described. The structure of the semiconductor laser 100 is shown in FIG.

First, a contact layer 102 made of n-type GaN doped with Si so as to have a carrier density of 5 × 10 ¹⁸ cm ⁻³ or less was formed on the original substrate 101 made of the GaN crystal obtained in the above example. The original substrate 101 is a substrate in which a group III nitride crystal is formed on sapphire or a substrate made of a group III nitride crystal. In GaN-based crystals (crystals containing Ga and N), Ga vacancies increased when Si was 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 was controlled so that the carrier density was 5 × 10 ¹⁸ cm ⁻³ or less.

Next, a cladding layer 103 made of n-type Al _0.07 Ga _0.93 N and a light guide layer 104 made of n-type GaN were formed on the contact layer 102. Next, a multiple quantum well (MQW) composed of a well layer (thickness of about 3 nm) made of Ga _0.8 In _0.2 N and a barrier layer (thickness 6 nm) made of GaN was formed as the active layer 105. Next, a light guide layer 106 made of p-type GaN, a clad layer 107 made of p-type Al _0.07 Ga _0.93 N, and a contact layer 108 made of p-type GaN were formed. These layers can be formed by a known method. The semiconductor laser 100 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 105, and the light guide layer and the cladding layer are reduced in this order.

  An insulating film 109 constituting a current injection region having a width of about 2 μm is formed on the contact layer 108. On the p-type cladding layer 107 and the p-type contact layer 108, a ridge portion serving as a current confinement portion is formed.

  A p-side electrode 110 that is in ohmic contact with the contact layer 108 is formed on the p-type contact layer 108. An n-side electrode 111 that is in ohmic contact with the contact layer 102 is formed on the upper side of the n-type contact layer 102.

  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.

Since the semiconductor laser of this example uses a substrate having a low dislocation density of 1 × 10 ² cm ⁻² or less as a substrate, the threshold is higher than that of a semiconductor laser manufactured on a GaN substrate having a high dislocation density. A decrease in value current, an improvement in luminous efficiency, and an improvement in reliability were observed.

  It is also possible to remove a sapphire portion other than the GaN crystal by polishing or the like to produce a GaN substrate and to produce a device thereon.

In the method of the above embodiment, a c-plane Al _x Ga _1-x N (where 0 ≦ x ≦ 1) substrate can be used as a seed crystal, but Al _x Ga _1-x N ( However, even when a substrate of 0 ≦ x ≦ 1) is used as a seed crystal substrate, a single crystal substrate represented by the composition formula Al _x Ga _1-x N (where 0 ≦ x ≦ 1) is obtained. For example, when an A-plane GaN substrate is used as a seed crystal, if a light emitting diode is formed using the obtained single crystal substrate, there is no piezo effect, so holes and electrons can be efficiently recombined, Luminous efficiency can be improved.

  By using a substrate obtained by the manufacturing method of the present invention and epitaxially growing a group III nitride crystal on this substrate, a semiconductor device including a semiconductor element such as an LD or LED can be obtained. The following can be cited as an effect of manufacturing an LD or LED using the substrate of the present invention. Since the dislocation density is small throughout the substrate, higher reliability can be realized in wide stripe LDs and surface emitting LDs.

  In this embodiment, a method of forming an oxide layer on the surface of a GaN semiconductor layer and selectively growing it will be described.

11A to 11E are process cross-sectional views illustrating an example of the process of the third manufacturing method of the present invention. First, as shown in FIG. 11A, first, a group III is formed on one main surface of an original substrate 1100 made of sapphire (single crystal Al ₂ O ₃ ) by, for example, metal organic chemical vapor deposition (MOCVD). A semiconductor layer 1101 made of gallium nitride (GaN) having a thickness of about 5 μm was grown using trimethyl gallium (TMG) as an element source and ammonia (NH ₃ ) as a nitrogen source. In this embodiment, the semiconductor layer 1101 is grown on the original substrate 1100. However, a thick GaN crystal formed on the sapphire substrate by HVPE or the like is separated from the sapphire substrate to obtain the semiconductor layer 1101. May be used as

Subsequently, as shown in FIG. 11B, a mask film 1102 patterned in a stripe shape was formed on the semiconductor layer 1101. The mask film 1102 was formed as follows, for example. First, a mask formation film made of silicon (Si) having a thickness of about 100 nm was deposited on the semiconductor layer 1101 by a chemical vapor deposition (CVD) method using monosilane (SiH ₄ ). Then, after forming a striped resist pattern on the mask forming film by photolithography, the mask forming film was dry-etched using the formed resist pattern as a mask. Etching can be performed by, for example, reactive ion etching (RIE) containing hydrogen bromide (HBr) or chlorine gas (Cl ₂ ) as a reactive gas. Thereafter, the resist pattern was removed by ashing or the like. Although the planar shape of the mask film is a stripe shape, it is not limited to the stripe shape and may be a dot shape.

Next, in an oxidizing atmosphere, for example, an atmosphere containing oxygen gas (O ₂ ) or water vapor (H ₂ O), about 4 at a temperature of 900 ° C. with respect to the original substrate on which the semiconductor layer and the mask film are formed. Heat treatment for hours was performed. Gallium oxide of about 300 nm in an oxygen gas atmosphere and about 40 nm in a water vapor atmosphere could be formed on the original substrate. By this heat treatment, an oxide region 1103 made of gallium oxide was formed on the surface of the semiconductor layer 1101 not covered with the mask film 1102 as shown in FIG. In this oxidation step, by using an atmosphere containing oxygen gas or water vapor as the oxidizing atmosphere, a rapid and uniform oxidation treatment could be realized with good reproducibility.

  Next, as shown in FIG. 11D, the mask film was removed by, for example, hydrofluoric acid or RIE.

  Using the seed crystal substrate thus obtained, as shown in FIG. 11E, the GaN crystal 1104 is formed on the exposed surface of the semiconductor layer 1101 by the LPE method in a GaN melt using a flux. Grown up. The GaN crystal 1104 could be grown using the LPE apparatus as in the above example.

  As in this embodiment, crystal growth from the oxidized portion can be suppressed by oxidizing the surface of the GaN semiconductor layer. That is, as shown in FIG. 11E, crystals with few dislocations can be grown by selectively growing crystals from the semiconductor layer 1101 and growing the crystals on the oxide region 1103 in the lateral direction. Above the oxidized region 1103, lateral crystal growth is dominant. Therefore, the oxide region 1103 is not affected by dislocations on the surface of the semiconductor layer 1101 which is a seed crystal, so that the crystal defect density of the GaN crystal grown by the LPE method can be further reduced.

In the conventional method, it is difficult to control the dislocation, and the dislocation of the obtained group III nitride substrate varies in the range of 10 ⁴ to 10 ⁶ cm ⁻² depending on the portion of the substrate. By selectively growing the group III nitride crystal as in the manufacturing method, the portion where the group III nitride crystal has grown in the lateral direction (the portion not in contact with the semiconductor layer (seed crystal) exposed from the mask film) Dislocations can be stably controlled to 10 ⁴ cm ^-2 or less. In addition, since the GaN crystal obtained by the LPE method grows quickly in the lateral direction, the period of the oxidized region can be increased and a low dislocation region can be formed over a wide area. Note that the period of the oxidized region is an average value of the distance between the centers (center lines) of adjacent oxidized regions. Examples of the measuring method include a cross-sectional scanning electron microscope (SEM) and a cross-sectional transmission electron microscope (TEM).

In this embodiment, the oxidation of the surface of the GaN semiconductor layer has been described. However, AlGaN and AlN are easier to oxidize than this, and are advantageous for selectively growing crystals. In this embodiment, the method for forming an oxide film by thermal oxidation has been described. However, the same effect can be obtained by forming an oxide film by ion implantation. A photoresist material can be used as the mask material. In the oxide film, for example, oxygen ions of 5 × 10 ¹⁴ (atoms / cm ² ) per unit area are implanted at about 200 nm from the surface of the semiconductor layer exposed from the mask film at an acceleration voltage of 150 kVe. Thus, an oxide region can be selectively formed in the semiconductor layer exposed from the mask film. As the peak oxygen ion concentration, for example, 3 × 10 ¹⁹ (atoms / cm ³ ) can be implanted. The peak oxygen ion concentration means the maximum value of oxygen ion concentration that can be implanted into the mask film.

FIGS. 12A to 12D are process cross-sectional views illustrating an example of the process of the third manufacturing method of the present invention. As shown in FIG. 12A, a semiconductor layer 1202 made of GaN was formed on a sapphire substrate 1201 made of sapphire (crystalline Al ₂ O ₃ ) by MOCVD. Specifically, after the sapphire substrate 1201 is heated so that the substrate temperature is about 1020 ° C. to 1100 ° C., trimethyl gallium (TMG) and NH ₃ are supplied onto the original substrate, whereby a semiconductor made of GaN. Layer 1202 was deposited. Note that the group III element of the semiconductor layer 1202 is not limited to gallium, and may contain aluminum or indinium. That is, the semiconductor layer 1202 may be a semiconductor crystal represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1 and 0 ≦ v ≦ 1).

  Next, as shown in FIG. 12C, the semiconductor layer 1202 was etched to the sapphire substrate to form stripe-shaped convex portions. Specifically, first, a resist film (mask film) was applied to the upper surface of the semiconductor layer 1202, and then the applied resist film 1203 was patterned in a stripe shape by a photolithography method to form a resist pattern. Subsequently, by performing dry etching on the semiconductor layer 1202 using the resist pattern as a mask, convex portions having a width of about 5 μm were formed with a period of about 300 μm as shown in FIG. In the present embodiment, the convex portion has a stripe structure, but there is no problem even if it has another structure. For example, a dot-like structure may be arranged in the plane.

Next, as shown in FIG. 12D, an LPE-GaN crystal 1204 made of GaN crystal was grown by liquid phase growth using the upper surface of the convex portion as a seed crystal. Liquid crystal growth was performed using the LPE apparatus shown in FIG. Sodium and gallium are weighed in a crucible, and the template shown in FIG. 12 (c) is inserted into the crucible. A nitrogen pressure atmosphere of 50 atm (50 × 1.013 × 10 ⁵ Pa), 800 ° C., 100 hours. The LPE-GaN crystal shown in FIG. 12 (d) was grown. In the liquid phase growth, since the lateral growth rate is fast, as shown in FIG. 12 (d), LPE-GaN crystals grown from the convex portions could be combined.

  In the LPE-GaN crystal obtained in this example, many dislocations were observed on the convex portion and the merged portion, but low dislocations were observed in other portions. In the present invention, since the period of the convex portion is 300 μm, a low dislocation region can be realized in a wide region of 100 μm or more. Therefore, for example, when fabricating a semiconductor laser or the like, the accuracy of mask alignment for forming a waveguide can be relaxed, and a wide stripe waveguide necessary for a high-power semiconductor laser can be formed. Is big.

  Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

  As described above, according to the method for manufacturing a semiconductor substrate of the present invention, a substrate including a group III nitride crystal having high characteristics can be easily manufactured. Further, by using this semiconductor substrate, a semiconductor device having high characteristics can be obtained.

It is process sectional drawing which shows an example of the manufacturing method of this invention. It is the top view of (a) an example which shows 1 process of the manufacturing method of this invention, and (b) the top view of another example. It is process sectional drawing which shows another example of the manufacturing method of this invention. (A)-(c) is sectional drawing which shows the example of 1 process of the manufacturing method of this invention. It is sectional drawing which shows the solubility of the group III nitride to GaN melt. (A)-(d) is process sectional drawing which shows another example of the manufacturing method of this invention. It is a schematic diagram which shows a structure of an example about the manufacturing apparatus used for the manufacturing method of this invention. It is a schematic diagram which shows a structure of an example about the manufacturing apparatus used for the manufacturing method of this invention. It is a schematic diagram which shows a structure of an example about the manufacturing apparatus used for the manufacturing method of this invention. It is sectional drawing which shows an example of the semiconductor device manufactured with the manufacturing method of this invention. It is process sectional drawing which shows another example of the manufacturing method of this invention. It is process sectional drawing which shows another example of the manufacturing method of this invention.

Explanation of symbols

11, 1100 substrate 12, 33, 33a, 33b, 33c, 1101 semiconductor layer 13, 32, 63, 1102 mask film 14, 34 group III nitride crystal 13g, 13h through-hole 61, 1201 sapphire substrate 62, 1202 semiconductor layer 64 DESCRIPTION OF SYMBOLS 1104 GaN crystal 1103 Oxidized region 1203 Resist film 1204 LPE-GaN crystal A Sapphire substrate B Semiconductor layer C Mask film 71 Gas tank 72, 802 Pressure regulator 73 Valve 74 Container 75, 80 Electric furnace 76, 95 Crucible 81 Chamber 82 Furnace 83, 92 Heater 84a, 84b, 84c, 93 Thermocouple 85 Core tube 86 Crucible 87 Melt 88 Substrate fixing part 89a, 89b Motor 800a, 800b, 800c Zone 800 Propeller 801 Gas source 803 Gas purification part 91 Growth furnace 4 Fixing table 95 Crucible 96 Melt 97 Seed crystal 98 Flow controller 99 Tube 900, 901 Arrow 902 Rotating shaft 100 Semiconductor laser 101 Substrate 102, 108 Contact layer 103, 107 Clad layer 104, 106 Light guide layer 105 Active layer 109 Insulation Membrane 101, 110 electrode

Claims (22)

A method for producing a Group III nitride substrate in which a Group III element and nitrogen are reacted in an alkali metal melt to form and grow a Group III nitride crystal in an atmosphere containing nitrogen,
Manufacturing a plurality of portions of a group III nitride semiconductor layer prepared in advance as a seed crystal for at least one of generation and growth of a group III nitride crystal and bringing the surface of the seed crystal into contact with the melt Including the process, the manufacturing process,
(I) A step of preparing a group III nitride semiconductor layer represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). When,
(Ii) forming a patterned mask film on the semiconductor layer;
(Iii) by bringing the surface of the semiconductor layer into contact with a melt containing at least one group III element selected from the group consisting of gallium, aluminum, and indium, an alkali metal, and the nitrogen in an atmosphere containing nitrogen. And a step of growing a group III nitride crystal on the semiconductor layer using the semiconductor layer exposed from the mask film as a seed crystal . The mask film, III-nitride substrate manufacturing method according to claim 1 comprising a diamond-like carbon. The method for producing a group III nitride substrate according to claim 1 , wherein the mask film is represented by a composition formula Al _u Ga _1-u N (where 0 <u ≦ 1). 4. The method for producing a group III nitride substrate according to claim 3 , wherein the Al composition ratio of the mask film is larger than the Al composition ratio of the semiconductor layer. The step (i) is 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 original substrate III. The method for producing a group III nitride substrate according to claim 1 , which is a step of forming a group nitride semiconductor layer. 3. The III according to claim 1 , wherein the semiconductor layer is formed using GaN, and the mask film is represented by a composition formula Al _u Ga _1-u N (where 0.05 ≦ u ≦ 1). A method for manufacturing a group nitride substrate. The method for producing a group III nitride substrate according to any one of claims 3 to 6 , wherein the surface or the whole of the mask film is oxidized. The method for manufacturing a group III nitride substrate according to claim 1 , wherein the mask film is formed using Al, and the surface or the whole of the mask film is oxidized. A method for producing a Group III nitride substrate in which a Group III element and nitrogen are reacted in an alkali metal melt to form and grow a Group III nitride crystal in an atmosphere containing nitrogen,
Manufacturing a plurality of portions of a group III nitride semiconductor layer prepared in advance as a seed crystal for at least one of generation and growth of a group III nitride crystal and bringing the surface of the seed crystal into contact with the melt Including the process, the manufacturing process,
(A) A step of preparing a group III nitride semiconductor layer represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, u + v ≦ 1). When,
(B) oxidizing a part of the surface of the semiconductor layer to form an oxidized region;
(C) by bringing the surface of the semiconductor layer into contact with a melt containing at least one group III element selected from the group consisting of gallium, aluminum, and indium, an alkali metal, and the nitrogen in an atmosphere containing nitrogen. , the semiconductor layer other than the oxidized region as a seed crystal, the semiconductor layer on the III-nitride crystal process and the including growing, III-nitride substrate manufacturing method. The step (A) is 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 original substrate III. The method for producing a group III nitride substrate according to claim 9 , which is a step of forming a group nitride semiconductor layer. The step (B)
(B-1) forming a patterned mask film on the surface of the semiconductor layer;
(B-2) The method for producing a group III nitride substrate according to claim 9 , further comprising: oxidizing the surface of the semiconductor layer exposed from the mask film to form the oxidized region. The method of manufacturing a group III nitride substrate according to claim 11 , wherein the step (B-2) is a step of forming an oxidized region by implanting oxygen into the surface of the semiconductor layer exposed from the mask film. . The mask film has a plurality of through holes are formed, the manufacture of III-nitride substrate according to any one of the through-hole portions in claim 1, wherein the semiconductor layer is exposed 8, 11 and 12 Method. The mask film is patterned in stripes, III-nitride substrate manufacturing method according to any one of the semiconductor layer from claim 1 exposed in stripes 8, 11 and 12. The group III element is gallium, III-nitride substrate manufacturing method according to any one of the III claims 1 to 14 nitride crystal is a crystal of gallium nitride. The atmosphere, III-nitride substrate manufacturing method according to any one of claims 1 a pressurized atmosphere 15. The method for producing a group III nitride substrate according to any one of claims 1 to 16 , wherein the melt further contains an alkaline earth metal. The method for producing a group III nitride substrate according to any one of claims 1 to 17, growing the III-nitride crystal with rocking in the melt. The method for producing a group III nitride substrate according to any one of claims 1 to 18 , wherein a period of the group III nitride semiconductor layer selected as the seed crystal is 30 µm or more. The seed cycle the selected group III nitride semiconductor layer as a crystal, III-nitride substrate manufacturing method according to any of claims 1 18 is 50μm or more. The method for producing a group III nitride substrate according to any one of claims 1 to 18 , wherein a period of the group III nitride semiconductor layer selected as the seed crystal is 100 µm or more. The method for producing a group III nitride substrate according to any one of claims 1 to 18 , wherein a period of the group III nitride semiconductor layer selected as the seed crystal is 1000 µm or more.