JP4597534B2 - 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), a group III nitride substrate obtained thereby, a semiconductor device, and a method for manufacturing the same.

  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 or 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 group III nitride semiconductor (for example, GaN) substrate for an LD or LED is usually formed by vapor phase epitaxial growth. For example, a substrate obtained by heteroepitaxially growing a group III nitride crystal on a sapphire substrate is used. 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 atmospheres or more, conventionally, a condition of 8000 atmospheres at 1200 ° C. is required for growing GaN in a liquid phase. It has been needed. 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 by using Na flux.

  Recently, a mixture of Ga and Na was melted at 800 ° C. and 50 atm in a nitrogen gas atmosphere containing ammonia, and a single crystal having a maximum crystal size of about 1.2 mm was grown using this melt for 96 hours. A crystal has been obtained (see, for example, Patent Document 1).

In addition, after a GaN crystal layer is formed on a sapphire substrate by metal organic chemical vapor deposition (MOCVD) method, a single crystal is grown by liquid phase epitaxy (LPE) method. It has been reported.
JP 2002-293696 A

  However, in order to manufacture a semiconductor device having high characteristics at a low cost, a method for manufacturing a group III nitride substrate having a lower dislocation density than the conventional method and a method for manufacturing a group III nitride substrate at a lower cost are required. ing. In view of such circumstances, an object of the present invention is to provide a novel manufacturing method for obtaining a group III nitride substrate and a manufacturing method of a semiconductor device.

In order to achieve the above object, the first production method of the present invention heats and melts a mixture containing at least one group III element selected from gallium, aluminum, and indium, an alkali metal, and a liquid nitrogen compound. A step of reacting the at least one group III element with the nitrogen compound to grow a group III nitride crystal. In this specification, the group III nitride is a semiconductor represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) unless otherwise specified. Means. Note that since the composition ratio never becomes a negative value, it goes without saying that 0 ≦ 1-xy ≦ 1 is satisfied (the same applies to other composition formulas).

In addition, another manufacturing method of the present invention includes (i) a composition formula Al _u Ga _v In _{1 -uv} N (where 0 (Ii) at least one group III element selected from gallium, aluminum, and indium in an atmosphere containing nitrogen, and (ii) forming a semiconductor layer made of a semiconductor represented by ≦ u ≦ 1, 0 ≦ v ≦ 1) And a step of growing a group III nitride crystal on the semiconductor layer by bringing the semiconductor layer into contact with a melt containing an alkali metal. The full width at half maximum of the two-crystal method X-ray rocking curve is, for example, 0.1 degree or more, preferably 0.3 degree or more, more preferably 1 degree or more. The full width at half maximum of the X-ray rocking curve of the two-crystal method is that the X-ray incident from the X-ray source is made highly monochromatic by the first crystal, irradiated to the semiconductor layer as the second crystal, and diffracted from the semiconductor layer. It can be measured by obtaining FWHM (Full width at half maximum) centered on the peak of X-ray. The X-ray source is not particularly limited, but for example, CuKα rays can be used. Also, the first crystal is not particularly limited, but for example, an InP crystal or a Ge crystal can be used.

  In the semiconductor layer of the substrate, the full width at half maximum of the two-crystal method X-ray rocking curve is preferably large. By bringing the semiconductor layer into contact with a melt containing one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen, a group III element nitride crystal is formed on the semiconductor layer. This is because the growth reproducibility of the group III element nitride crystal tends to be better when the crystallinity of the semiconductor layer is poor. The reason is that when the crystallinity of the semiconductor layer is poor, the semiconductor layer is dissolved in the melt, and the group III element nitride crystal tends to grow from the dissolved semiconductor surface. Conceivable. Accordingly, the full width at half maximum of the two-crystal X-ray rocking curve of the semiconductor layer is, for example, 0.1 degrees or more, preferably 0.3 degrees or more, more preferably 1 degree or more.

  As a method for forming a semiconductor layer on the substrate, for example, a method of forming under a certain temperature range of T ± 10 ° C. (500 ≦ T ≦ 1100) shown below, a method of forming by a sputtering method, a high pressure Below is a method of sublimating GaN.

In another manufacturing method of the present invention, (i) a substrate is made of a semiconductor represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1). Forming the semiconductor layer under a constant temperature range of T ± 10 ° C. (where 500 ≦ T ≦ 1100), and (ii) at least one selected from gallium, aluminum, and indium in an atmosphere containing nitrogen A step of growing a group III nitride crystal on the semiconductor layer by bringing the semiconductor layer into contact with a melt containing a group III element and an alkali metal.

In addition, another production method of the present invention includes (I) a step of forming an AlN layer on a substrate by sputtering, and (II) at least one group III selected from gallium and aluminum in an atmosphere containing nitrogen. By bringing the semiconductor layer into contact with a melt containing an element and an alkali metal, a group III nitride crystal represented by a composition formula Al _x Ga _1-x N (where 0 ≦ x ≦ 1) is converted into the AlN layer. And growing it on.

In another manufacturing method of the present invention, (i) a substrate is made of a semiconductor represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1). A step of forming a semiconductor layer, and (ii) contacting the semiconductor layer with a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal in an atmosphere containing nitrogen. And growing a group III nitride crystal on the semiconductor layer and melting the substrate in the melt.

According to another manufacturing method of the present invention, (i) a step of laminating a multilayer film including a first semiconductor layer and a second semiconductor layer, which are sequentially laminated from the substrate side, on a substrate; ) At least part of the second semiconductor layer by bringing the multilayer film into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen A group III nitride crystal is grown on the first semiconductor layer or the second semiconductor layer, and the first semiconductor layer has a composition formula Al _s Ga. _t In _1-st N (where 0 <s ≦ 1, 0 ≦ t <1), and the second semiconductor layer has a composition formula of Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1), and u and s satisfy u <s . By forming the second semiconductor layer on the first semiconductor layer, with the formula _{Al s Ga t In 1-st} N crystal is a seed layer is prevented better that all dissolved in a non-saturated solution When the group III nitride crystal is grown on the first semiconductor layer, there is an effect of surface protection such as oxidation.

  The group III nitride substrate of the present invention is produced by any one of the production methods of the present invention. In addition, in the group III nitride substrate of the present invention manufactured by a manufacturing method including the step of dissolving the substrate in the melt, at least one of the semiconductor layer and the group III nitride crystal has Si as an impurity. And at least one of As.

  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 any one of the group III nitride substrates of the present invention. The semiconductor element may be a laser diode or a light emitting diode.

In addition, a method for manufacturing a semiconductor device according to the present invention includes: (i) a semiconductor having a composition formula of Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on a substrate. And (ii) contacting the semiconductor layer with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen. And a step of growing a group III nitride crystal having a thickness of 1 μm or more and 50 μm or less on the semiconductor layer, and (iii) a step of forming a semiconductor element on the group III nitride crystal.

  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, according to the method for manufacturing a semiconductor device of the present invention, a semiconductor device having high characteristics can be easily manufactured.

  Embodiments of the present invention will be described below.

(Embodiment 1)
Embodiment 1 is an example of a method for producing a group III nitride substrate of the present invention.

  In the method of Embodiment 1, by heating and melting a mixture containing at least one group III element selected from gallium, aluminum and indium, an alkali metal and a liquid nitrogen compound, the at least one group III element and Reacting the nitrogen compound to grow a group III nitride crystal. A typical example method will be described below.

First, a Group III element, an alkali metal, and a liquid nitrogen compound are put into a crucible, and the crucible is melted by heating under pressure to form a melt thereof. The group III element to be input is selected according to the semiconductor to be crystal-grown, and gallium, aluminum, indium or some of these 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 a flux). This is the same in the embodiment of FIG. Of these, Na is often used. Hydrazine (H ₂ NNH ₂ ) can be used as the liquid nitrogen compound.

  Thereafter, after bringing the seed crystal into contact with the melt, the temperature and pressure are adjusted so that the group III nitride semiconductor crystal grows by being supersaturated. As the seed crystal, for example, a group III nitride crystal formed on a substrate can be used. As the substrate, a sapphire substrate, a GaAs substrate, a Si substrate, a SiC substrate, an AlN substrate, or the like can be used. Note that a substrate having a structure such as an ELOG structure may be used as the substrate (the same applies to the following embodiments).

  Group III nitride crystals, which are seed crystals, can be produced, for example, by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). Can be formed.

Through the above process, the group III element and nitrogen react to grow a group III nitride crystal on the seed crystal. By this crystal growth, a group III nitride crystal (for example, 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 formed. can do.

  In the above step, the group III nitride crystal is preferably grown under a pressurized atmosphere containing nitrogen. As the atmosphere containing nitrogen, a nitrogen gas atmosphere or a nitrogen gas atmosphere containing ammonia is used. This can prevent nitrogen from leaving the crystal. The material melting and crystal growth conditions vary depending on the flux component, the atmospheric gas component, and the pressure thereof. For example, the temperature is about 700 ° C. to 1100 ° C. and the pressure is about 1 to 100 atm.

  The mixture 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. 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 made of only the group III nitride crystal (embodiment) The same applies to the following embodiments excluding 3).

(Embodiment 2)
The second embodiment is another example of the method for producing a group III nitride substrate of the present invention.

  First, on a substrate, a semiconductor made of a semiconductor represented by a composition formula AluGavIn1-u-vN (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) in which the full width at half maximum of a two-crystal X-ray rocking curve is 1 degree or more. Form a layer. The method for measuring the full width at half maximum of the two-crystal method X-ray rocking curve is as described above.

  Next, the group III nitride is formed on the semiconductor layer by bringing the semiconductor layer into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen. Growing physical crystals.

  Hereinafter, a specific method for forming a semiconductor layer in which the half width of the X-ray rocking curve is 1 degree or more will be described.

In the method of Embodiment 2, first, 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) is formed on a substrate by T It is formed under a certain temperature range of ± 10 ° C. (however, 500 ≦ T ≦ 1100) (step (i)). Examples of the substrate include a GaAs substrate having a (111) surface, a Si substrate having a (111) surface, a sapphire substrate (Al ₂ O ₃ substrate) having a (0001) surface, or ( A SiC substrate having a (0001) plane can be used. The semiconductor layer is a crystal layer that becomes a seed crystal, and can be formed by a known method such as MOCVD, MBE, or HVPE.

Next, the semiconductor layer is brought into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm or less). Thus, a group III nitride crystal is grown on the semiconductor layer (step (ii)). As the atmosphere containing nitrogen, for example, a nitrogen gas atmosphere containing nitrogen gas or ammonia can be applied. As the alkali metal, at least one selected from sodium, lithium and potassium, that is, one of them or a mixture thereof is used. The melt is prepared, for example, by putting a material into a crucible and heating. After producing the melt, the semiconductor crystal grows 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 to 100 atm. 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, 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) is obtained. For example, a GaN crystal, A crystal represented by the composition formula Al _x Ga _1-x N (where 0 ≦ x ≦ 1) is obtained.

  An example of another method according to the second embodiment will be specifically described below. In this method, first, an AlN layer is formed on a substrate (step (I)). The AlN layer can be easily formed by sputtering, for example. The substrate described above can be used as the substrate.

Next, in a pressurized atmosphere containing nitrogen, the semiconductor layer is brought into contact with a melt containing at least one group III element selected from gallium and aluminum and an alkali metal, whereby the composition formula Al _x Ga _1-x A group III nitride crystal represented by N (where 0 ≦ x ≦ 1) is grown on the AlN layer (step (II)). Since this step is the same as the above-described step (ii) except that indium is not used, a duplicate description is omitted.

Further, a specific method for forming a semiconductor layer in which the half width of the X-ray rocking curve is 0.1 degrees or more will be described. For example, a GaN seed layer formed by a sublimation method or the like can be used. A GaN powder is used as a raw material in a high-pressure chamber, the raw material is heated, supplied on a sapphire substrate with a carrier gas, reacted with ammonia gas on the sapphire substrate, recrystallized and grown. Thereby, a GaN layer as a seed layer can be formed on the sapphire substrate at high speed. The substrate is brought into contact with a melt containing at least one group III element selected from gallium and aluminum and an alkali metal in a pressurized atmosphere containing nitrogen, whereby the composition formula Al _x Ga _{1− A} group III nitride crystal represented by xN (where 0 ≦ x ≦ 1) is grown on the GaN layer.

  In this way, a substrate including a group III nitride crystal can be obtained. In the conventional crystal growth method, the crystallinity of the growing crystal is greatly influenced by the crystallinity of the seed crystal. Therefore, in the conventional method, in order to improve the crystallinity of the seed crystal, the seed crystal is grown on the buffer layer formed at a low temperature, or the seed crystal is formed using the ELOG method. It was necessary to form a seed crystal by a simple process. On the other hand, in the method of Embodiment 2, the group III nitride crystal is grown by the liquid phase growth method of step (ii) or step (II). This method is characterized in that crystals having a low dislocation density are easily obtained even if the crystallinity of the base is poor. For this reason, even if a seed crystal formed by a simple method is used, a crystal with a low dislocation density can be obtained. Thus, according to the method of Embodiment 2, a group III nitride crystal having high characteristics can be produced at low cost.

(Embodiment 3)
Embodiment 3 is still another example of the method for producing a group III nitride substrate of the present invention.

In the method of Embodiment 3, first, 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) is formed on a substrate. (Step (i)). As the substrate, a substrate that is melted into a melt in the following step (ii) is used. For example, a (111) -plane GaAs substrate or a (111) -plane Si substrate can be used. The semiconductor layer is a crystal layer that becomes a seed crystal and can be formed by a known method such as MOCVD, MBE, or HVPE.

  Next, the semiconductor layer is brought into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm or less). Thus, a group III nitride crystal is grown on the semiconductor layer, and the substrate is melted in the melt (step (ii)). Since this step (ii) is the same as the method described in the second embodiment except that the substrate is melted, a duplicate description is omitted. In step (ii) of the third embodiment, since the substrate that dissolves in the melt is used, the substrate is dissolved while the crystal growth proceeds. As a result, it is possible to manufacture a substrate made of only a group III nitride single crystal.

  In the group III nitride single crystal produced in Embodiment 3, Si or As is mixed as an impurity in the semiconductor layer or the group III nitride crystal. Since Si acts as an N-type dopant, it is not a problem. However, since a problem arises when an insulating substrate is manufactured, a method in which another Si or As shown below is not mixed as an impurity is used.

A semiconductor layer surface represented by Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on a substrate such as sapphire is brought into contact with the melt, and a group III nitride is formed on the semiconductor layer. After growing the physical crystal, everything including the substrate is immersed in the melt to dissolve the substrate. Thereby, it is possible to manufacture a substrate made of only a group III nitride single crystal.

(Embodiment 4)
Embodiment 4 is still another example of the method for producing a group III nitride substrate of the present invention. Specifically, on the substrate, said first semiconductor layer from the substrate side in this order (compositional formula _{Al s Ga t In 1-st} N ( provided that 0 <s ≦ 1,0 ≦ t < 1)) and the second A multilayer structure including a semiconductor layer (compositional formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1)), where u and s satisfy u <s And at least a part of the second semiconductor layer is melted in the melt, and a group III nitride crystal is grown on the first semiconductor layer or the second semiconductor layer. A group III nitride crystal substrate and a manufacturing method thereof will be described.

In the manufacturing method of Embodiment 4, first, a multilayer film including a first semiconductor layer and a second semiconductor layer that are sequentially stacked from the substrate side is stacked on a substrate (step (i)). As the substrate, a sapphire substrate, a GaAs substrate, a SiC substrate, a Si substrate, an AlN substrate, or the like can be used. On the substrate, a first semiconductor layer represented by a composition formula _{Al s Ga t In 1-st} N ( provided that 0 <s ≦ 1,0 ≦ t < 1), composition formula Al _u Ga _v In _{1- A} second semiconductor layer represented by _uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is sequentially stacked. The outermost surface of the multilayer film is the second semiconductor layer, and the first semiconductor layer is disposed adjacent to the second semiconductor layer. At this time, u and s satisfy u <s. That is, the first semiconductor layer is made of a semiconductor (for example, GaN) having a higher Al composition ratio than the second semiconductor layer. Specifically, u and s preferably satisfy 0 ≦ u ≦ 0.05 and 0.05 ≦ s ≦ 1, respectively. For example, a first semiconductor layer represented by a composition formula Al _0.07 Ga _0.93 N and a second semiconductor layer made of GaN can be used.

  These semiconductor layers are crystal layers that become seed crystals, and can be formed by a known method such as MOCVD, MBE, or HVPE. In the following step (ii), the thickness of the first semiconductor layer is preferably 1 μm or more in order to prevent the entire first semiconductor layer from melting. In order to melt the entire second semiconductor layer, the thickness of the second semiconductor layer is preferably 10 μm or less.

  Next, the multilayer film is brought into contact with a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm or less). Thus, at least a part (preferably all) of the second semiconductor layer is melted in the melt, and then a group III nitride crystal is grown on the first semiconductor layer (step (ii)). . Since this step (ii) is the same as the method described in the second embodiment except that the second semiconductor layer is melted, a duplicate description is omitted.

  When growing a group III nitride semiconductor crystal, an oxide film or the like is easily formed on the surface of the semiconductor layer, and processing strain remains on the processed surface, so the surface of the seed crystal is in the melt. It is preferable to start crystal growth after dissolving in the solution. At this time, it is necessary to prevent the surface of the seed crystal from dissolving unevenly and from dissolving all the seed crystals. The group III nitride semiconductor has a slower dissolution rate in the melt as the Al composition ratio increases. Utilizing this property, in the method of Embodiment 4, the second semiconductor layer having a high Al composition ratio is used as the etch-back stopper layer. That is, when the first semiconductor layer having a relatively high dissolution rate is dissolved, a second semiconductor layer having a low dissolution rate appears. By starting crystal growth from the second semiconductor layer, crystal growth can be started from a relatively flat surface. Note that it is not always necessary to dissolve all of the second semiconductor layer, and there is no problem even if crystal growth is performed on the second semiconductor layer.

(Embodiment 5)
The fifth embodiment is an example of a method for manufacturing a semiconductor device of the present invention.

In the method of Embodiment 5, first, 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) is formed on a substrate. (Step (i)). As the substrate, a sapphire substrate, a GaAs substrate, a Si substrate, a SiC substrate, or an AlN substrate can be used. The semiconductor layer is a crystal layer that serves as a seed crystal and can be formed by MOCVD, MBE, or HVPE.

  Next, in a pressurized atmosphere containing nitrogen, the semiconductor layer is brought into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal to thereby form a thickness on the semiconductor layer. A group III nitride crystal having a thickness of 1 μm or more and 50 μm or less is grown (step (ii)). Since this step is the same as the step (ii) described in the second embodiment, a duplicate description is omitted. However, in the method of Embodiment 5, the crystal is grown so that the thickness of the crystal is in the range of 1 μm to 50 μm.

  Next, a semiconductor element is formed on the group III nitride crystal (step (iii)). The semiconductor element is, for example, a light emitting element such as a laser diode or a light emitting diode, a light receiving element, or the like. These elements can be formed by a known method.

  When a semiconductor element is formed on a group III nitride crystal, it is required that the crystal serving as a base is high in crystallinity. For this reason, in the conventional method using the vapor phase epitaxial growth method (HVPE method), a crystal layer having a thickness of 200 μm or more is usually formed. However, when a thick crystal layer is formed in this way, the substrate is warped, making it difficult to produce a device such as a laser diode. Specifically, there is a problem that defocus occurs during mask alignment in the photolithography process. On the other hand, in the manufacturing method of Embodiment 5, the group III nitride crystal is grown by the liquid phase epitaxial growth method of the step (ii). In this method, even if the epitaxial layer is very thin, a crystal with high crystallinity can be obtained. Therefore, according to this method, it is possible to form a semiconductor element having high characteristics while preventing the substrate from warping.

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 as an example. However, a compositional formula Al _x Ga _y In _1-xy N such as Al _x Ga _1-x N or AlN (where 0 ≦ x Group III nitride crystals represented by ≦ 1, 0 ≦ y ≦ 1) can also be formed by the same method.

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

First, a seed crystal substrate is formed. This substrate 10 is shown in FIG. The substrate 10 includes a sapphire substrate 11 made of sapphire (crystalline Al ₂ O ₃ ) and a seed layer 12 made of GaN. Here, the seed layer 12 may contain aluminum or indium as a group III element in addition to gallium. That is, the seed layer 12 may be 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).

Hereinafter, a method for manufacturing the substrate 10 will be described. First, a seed layer 12 made of GaN is grown on the sapphire substrate 11 by MOCVD. Specifically, the sapphire substrate is heated so that the substrate temperature is about 1020 ° C. to 1100 ° C., and trimethylgallium (TMG) and NH ₃ are supplied onto the substrate to grow the GaN layer. Other methods that can form a group III nitride semiconductor may be used. For example, a method such as HVPE (hydride vapor phase epitaxy) or MBE may be used.

  A GaN single crystal is grown by the LPE method using the seed crystal substrate thus obtained. The method will be described below.

  An example of an LPE apparatus (electric furnace) used in the method of the present invention is shown in FIG. The LPE apparatus includes a stainless steel chamber 21 and a furnace lid 22 and can withstand an atmospheric pressure of 50 atm. A heater 23 for heating is disposed in the chamber 21. The chamber 21 includes three zones, and thermocouples 24a to 24c 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 25 is arranged to improve the uniformity of the temperature in the furnace and prevent impurities from entering from the heater 23.

  A crucible 26 made of boron nitride (BN) is disposed inside the furnace tube 25. The melt 27 is prepared by putting the material into the crucible 26 and raising the temperature of the crucible. The substrate 10 serving as a seed crystal is attached to the substrate fixing unit 28. In the apparatus of FIG. 3, a plurality of substrates 10 can be fixed to the substrate fixing unit 28. The substrate 10 is rotated by a rotary motor 29a. A propeller 30 for stirring can be immersed in the melt 27. The propeller 30 is rotated by a rotary motor 29b. In this embodiment, since the atmospheric pressure is 10 atm or less, a normal rotary motor can be used. However, under an atmospheric pressure of 10 atm or more, an electromagnetic induction type rotating mechanism is used. The atmospheric gas is supplied from the gas source 31. The atmospheric pressure is adjusted by the pressure regulator 32. The atmospheric gas is sent into the furnace after impurities are removed by the gas purification unit 33.

  Hereinafter, a method of crystal growth will be described.

(1) First, Ga and flux Na are weighed by a predetermined amount and set in the crucible 26. Ga having a purity of 99.9999% (six nines) is used. As Na, purified Na is used. Na can be purified 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. In the present invention, liquid hydrazine (H ₂ NNH ₂ ) is mixed in the crucible as a nitrogen source.

(2) Next, in order to melt the raw materials in the crucible, the temperature in the electric furnace is raised to 900 ° C. At this stage, the seed crystal substrate is not yet put into the crucible. In order to stir Ga, Na and hydrazine, a propeller is put into the melt and the melt is stirred for several hours. In order to prevent the oxidation of GaN, nitrogen gas is used as the atmospheric gas. A feature of the present invention is that liquid hydrazine (H ₂ NNH ₂ ) is mixed in the crucible as a nitrogen source, thereby preventing desorption of nitrogen during crystal growth. Therefore, nitrogen defects in the obtained GaN single crystal can be reduced.

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

  (4) During crystal growth, the substrate is 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 is raised and removed from the melt. After raising the substrate, the substrate is 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 is removed from the chamber. During crystal growth, the temperature of the crucible (melt temperature) may be kept constant. However, in order to keep the melt supersaturation constant, the temperature of the melt may be lowered at a constant rate. Good.

A GaN crystal was produced by the above method, and its dislocation density and PL intensity were measured. The dislocation density was 1 × 10 ² cm ⁻² or less. The PL intensity spectrum is shown in FIG. The intensity of the peak near 360 nm in the spectrum of FIG. 3B was 22 (V). For comparison, FIG. 3A shows the PL intensity of a GaN thin film produced by a normal MOCVD method. Note that FIG. 3A and FIG. 3B are spectra measured under different slit width conditions. The peak intensity around 360 nm in the spectrum of FIG. 3A was 0.48 (V). The crystal obtained by the method of the present invention has a PL strength about 50 times that of the crystal produced by the conventional method.

In the present invention, since liquid hydrazine (H ₂ NNH ₂ ) is mixed in the crucible as a nitrogen source, it is possible to prevent detachment of nitrogen during crystal growth and to reduce nitrogen defects in the obtained GaN single crystal. be able to. Further, a low dislocation density and a high PL intensity can be realized over the entire substrate.

  The GaN thick film growth by the general HVPE method is performed at a high temperature of 1050 ° C. In the present invention, since crystal growth can be performed at a low temperature of 800 ° C., wafer warpage caused by a difference in linear expansion coefficient from the sapphire substrate can also be reduced.

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

  When the grown GaN crystal layer is thick, a large strain is applied to the substrate due to a difference in linear expansion coefficient between the sapphire substrate and the GaN crystal. As a result, the substrate is warped. Therefore, it is desirable that the grown GaN crystal is thin to some extent. By setting the thickness to 1 μm or more and 50 μm or less, the warpage of the substrate can be reduced to a range where there is no problem in the process. However, in order to obtain a substrate without warping, the thickness is preferably set to 1 μm or more and 20 μm or less.

  As described above, according to the present invention, a GaN single crystal substrate with few nitrogen defects 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. In particular, since a substrate having a small number of nitrogen defects and dislocation density can be obtained in the entire region of the substrate, a device such as a semiconductor laser can be realized by homoepitaxial growth without requiring a complicated structure like ELOG as in the conventional configuration. The process can be simplified and devices can be manufactured with high yield.

In the present 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 operating wavelength of an 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. . 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 growing a GaN single crystal using various substrates as seed crystals will be described.

First, an example of a method for manufacturing a seed crystal substrate using GaN in order to realize an inexpensive and highly productive substrate will be described. GaN is deposited on the surface of the sapphire substrate C using the MOCVD method. Specifically, on a sapphire substrate, a trimethyl gallium is Ga source (TMG), a nitrogen source ammonia (NH ₃₎ and by supplying, to deposit a seed crystal layer made of GaN. The thickness of the GaN layer is, for example, about 1 μm. The set temperature (T) of the substrate may be in the range of 700 to 1100 ° C., and may be T ± 10 ° C. for temperature control. The substrate 40 to be formed is shown in FIG. The substrate 40 includes a sapphire substrate 41 and a GaN layer 42 formed on the sapphire substrate 41. The GaN layer 42 is a layer that becomes a seed crystal. In the subsequent steps, a group III nitride crystal 43 is grown on the GaN layer 42 as shown in FIG. The GaN layer 42 has many dislocations (1 × 10 ⁹ cm ⁻² ).

  When the full width at half maximum of the two-crystal method X-ray rocking curve of the produced GaN layer was measured, it was 2 degrees. The method for measuring the full width at half maximum of the two-crystal method X-ray rocking curve is as described above.

  The feature of the present invention is to grow the seed crystal while maintaining the substrate temperature within a certain temperature range. Thereby, the seed crystal layer can be easily formed. Although many dislocations exist in the seed crystal, in the present invention, since a single crystal is grown on this substrate by the LPE method described below, the crystallinity of the seed crystal is hardly affected and the dislocation density is low. Crystals can be grown.

Next, an example of a method for producing a seed crystal substrate having an AlN layer will be described. In this case, an AlN layer is formed on the (111) plane of the GaAs substrate using an ECR (electron cyclotron resonance) sputtering apparatus. The substrate temperature is 300 ° C., for example. Under this condition, the orientation to the C axis becomes high. The produced substrate 50 is shown in FIG. The substrate 50 includes a GaAs substrate 51 and an AlN layer 52 formed on the GaAs substrate 51. Instead of the GaAs substrate, a Si substrate having a (111) surface, a sapphire substrate (Al ₂ O ₃ substrate) having a (0001) surface, SiC having a (0001) surface, or the like can be used. . When the full width at half maximum of the two-crystal method X-ray rocking curve of the formed AlN layer was measured, it was 3 degrees. The method for measuring the full width at half maximum of the two-crystal method X-ray rocking curve is as described above.

  Next, a method for forming a GaN single crystal using the seed crystal substrate described above will be described. The GaN single crystal is grown by the LPE method similar to that in Example 1. However, in the following method, nitrogen gas is used as a nitrogen source.

  First, a prescribed amount of Ga and flux Na is weighed and set in a crucible. In order to melt the raw material in the crucible, the temperature in the electric furnace is raised to 900 ° C. At this stage, the seed crystal substrate is not put into the crucible. A propeller is placed in the melt of the material and the melt is stirred for several hours. The electric furnace has a nitrogen gas atmosphere. In order to avoid the reaction of Ga or Na with nitrogen gas at this stage, the N2 pressure at this stage is set to about 1 atm. Next, the temperature of the crucible is set to 800 ° C. to bring the melt into a supersaturated state. Also, the atmospheric pressure is increased. For example, the pressure is increased to 50 atm using only nitrogen gas as the atmospheric gas.

  Next, the seed crystal substrate is lowered to just above the melt, and the temperature of the substrate is brought close to the temperature of the melt. After a few minutes, the seed crystal substrate is placed in the melt and crystal growth is started. During crystal growth, the substrate is 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 is raised and removed from the melt. After raising the substrate, the substrate is rotated at a rotation speed in the range of 300 rpm to 1500 rpm in order to remove the melt remaining on the substrate surface. Desirably, it is rotated at around 1000 rpm. Thereafter, the substrate on which the GaN single crystal is formed is taken out of the chamber. The temperature of the crucible may be kept constant, or the melt temperature may be lowered at a constant rate in order to make the supersaturation degree of the melt constant.

As another method, an example of a method for producing a GaN seed crystal substrate on a sapphire substrate by a sublimation method will be described. A crucible is placed in a pressure-resistant chamber, and GaN raw material is filled therein. As the GaN raw material, GaN powder or the like is used. A sapphire substrate is disposed in the crystal generation region above the crucible. The GaN powder in the crucible is heated by a raw material heater and supplied to the crystal generation region using nitrogen gas as a carrier gas. Ammonia, which is a reaction gas, flows on the surface of the substrate in the crystal generation region, and the reaction gas and Ga, which is a raw material, react on the substrate to grow a GaN crystal on the substrate. A mixed gas of NH ₃ and N ₂ is introduced into the pressure resistant chamber, and a GaN seed layer is grown in a pressurized state of 5 atm (5 × 1.013 × 10 ⁵ Pa). The raw material temperature was 1150 ° C and the substrate temperature was 1000 ° C. The growth rate was 100 μm / h, which was high-speed growth. A 50 μm thick film can be formed on sapphire in a short time for a growth time of 30 min. When the crystallinity of the obtained GaN semiconductor layer was evaluated, the full width at half maximum of the rocking curve obtained by ω scan measurement using an X-ray analyzer was 0.2 degree.

  Using this seed crystal, a GaN single crystal can be grown on the semiconductor layer formed by the sublimation method by the LPE method similar to that of the first embodiment.

  A feature of the present invention is that a GaN crystal is grown using a seed crystal substrate that can be easily formed. In this method, the group III nitride substrate can be formed by a simple process as compared with the method of forming the buffer layer at a low temperature and the method of forming the selective growth layer. In addition, high-quality semiconductor layers such as GaN, AlGaN, and AlN (for example, a semiconductor layer having a full width at half maximum of a two-crystal X-ray rocking curve of less than 0.1 degrees) formed through a buffer layer by MOCVD or the like are added to nitrogen. In the case where a group III nitride crystal is grown on the semiconductor layer by contacting with a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal in an atmosphere containing Since the semiconductor layer had good crystallinity, the semiconductor layer was difficult to dissolve in the melt, and the growth characteristics of group III element nitride crystals formed on the semiconductor layer were highly variable.

  As described above, when a semiconductor layer is formed on a substrate by a method of forming T ± 10 ° C. (where 500 ≦ T ≦ 1100), a sputtering method, a high-pressure sublimation method, or the like, the semiconductor layer Since the crystallinity of the semiconductor layer is worse than that of the film through the buffer layer, the semiconductor layer is easily dissolved in the melt. Since the group III element nitride crystal tends to grow from the dissolved semiconductor layer, crystal growth with good reproducibility can be obtained. If the full width at half maximum of the two-crystal method X-ray rocking curve is, for example, a semiconductor layer of 0.1 degree or more, the reproducibility of crystal growth in the melt is better, and the semiconductor layer thus formed is It also has the feature that it can grow at high speed. The full width at half maximum of the semiconductor layer is preferably 0.3 degrees or more, and more preferably 1 degree or more. However, when a GaN crystal is grown by liquid phase growth, a single crystal grows using the seed crystal as a seed, so that a good crystal can be obtained. For this reason, according to the present invention, a high-quality single crystal can be formed even by using an inexpensive seed crystal grown at high speed, and a semiconductor device can be formed at low cost. In addition, even if it uses a SiC substrate, a GaN single crystal can be grown similarly to a sapphire substrate.

  In this embodiment, a flux containing only Na is used, but the same effect can be obtained by using a mixed flux with an alkaline earth metal such as Li, Na, K flux or Ca. 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.

In this embodiment, a GaN single crystal substrate using gallium has been described. However, it is desirable to supply a substrate that absorbs less light with respect to the wavelength used for an optical device manufactured on the substrate. Therefore, as the semiconductor laser or a light emitting diode substrate in the ultraviolet range, it is preferable to form the Al a number included light absorption in the short wavelength region is small _{Al x Ga 1-x N (} 0 ≦ x ≦ 1) single crystal . 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.

  In Example 3, a method for producing a GaN single crystal using a GaAs substrate or a Si substrate will be described.

A manufacturing method will be described with reference to FIG. First, a GaAs substrate 61 having a (111) surface is prepared, and this substrate is heated so that the substrate temperature is about 1020 ° C. to 1100 ° C. A seed layer 62 is formed on the GaAs substrate 61 by MOCVD. Specifically, a seed layer 62 made of GaN is formed by supplying TMG and NH ₃ onto the substrate. In addition, you may form into a film using VPE method, MBE method, and HVPE method.

Next, an SiO ₂ layer 63 patterned in a stripe shape is formed on the seed layer 62 by a known method. GaN is grown again on the obtained substrate, and a selective growth layer 64 made of GaN crystal is formed. The selective growth layer 64 is selectively grown from the seed layer 62 in which the SiO ₂ layer 63 as a mask does not exist. The selective growth layer 64 is formed by a low pressure MOCVD method (26600 Pa (200 Torr), 1050 ° C.). A GaN single crystal is grown by the following method using the seed crystal substrate thus obtained.

The obtained seed crystal substrate, gallium and sodium are put in a crucible, and the crucible is heated to 800 ° C. The atmosphere gas is, for example, a pressurized atmosphere (5 atm) of nitrogen gas partially substituted with ammonia gas (NH ₃ gas). By reacting Ga and nitride in this state, a GaN single crystal 65 is formed on the selective growth layer 64 (GaN seed crystal) as shown in FIG. 6B. On the other hand, the GaAs substrate 61 is dissolved in the melt.

  A feature of the present invention is that a GaAs substrate, which is a seed crystal substrate, melts during crystal growth. Thereby, a GaN single crystal substrate with less distortion and warpage can be obtained. By using a substrate having no warpage and having a low dislocation density over the entire substrate, a semiconductor element having high characteristics can be manufactured with high productivity. An Si substrate can be used instead of the GaAs substrate.

  When the impurities of the obtained crystal were evaluated by SIMS (Secondary ion mass spectroscope), it was found that Si and As were mixed. However, since it becomes a problem when an insulating substrate is manufactured, a method in which another Si or As is not mixed as an impurity is used below.

The said method is demonstrated using FIG. Using a seed crystal in which a semiconductor layer 102 represented by Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on a substrate 101 such as sapphire, nitrogen is included. In a pressurized atmosphere, a group III nitride crystal 105 is grown in a melt 103 in which an alkali metal, a group III metal, and nitrogen are dissolved. The crucible 104 containing the melt 103 is held in a nitrogen atmosphere at 850 ° C. and 50 atm. The substrate 101 is held by the holding member 106, and only the semiconductor layer 102 is brought into contact with the melt 103. After the group III nitride crystal 105 is grown on the semiconductor layer 102, the holding member is moved in the direction of the arrow, the substrate 101 is also immersed in the melt 103, and the substrate 101 is dissolved. Thereby, it is possible to manufacture a substrate made of only the group III nitride single crystal 105.

  In Example 4, another example for obtaining a group III nitride substrate will be described.

  The Ga melt mixed with Na flux melts in the vicinity of the surface of the GaN seed crystal formed on the sapphire substrate in a pressurized nitrogen gas atmosphere (melt back). For this reason, it is difficult to set initial crystal growth conditions. On the other hand, by melting back the seed crystal, irregularities on the substrate surface of the seed crystal can be reduced, and the uniformity and quality improvement of the grown crystal can be realized. In this embodiment, crystal growth is performed using a seed crystal having a layered structure in order to stably melt back the seed crystal.

The seed crystal used in this example will be described with reference to FIG. A seed layer 72 made of GaN is formed on a sapphire substrate 71 made of sapphire (crystalline Al ₂ O ₃ ). On top of the seed layer 72, the composition formula _{Al s Ga t In 1-st} N ( provided that 0 <s ≦ 1,0 ≦ t < 1) the first semiconductor layer 73 represented by is formed. On the first semiconductor layer 73, a second semiconductor layer 74 represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed. Yes. Here, the Al composition ratio of the first semiconductor layer 73 is higher than the Al composition ratio of the second semiconductor layer 74. AlN is harder than GaN, and AlN is less likely to melt into a melt composed of Ga and Na flux. Therefore, for example, when the first semiconductor layer 73 made of Al ₁ Ga _1-x N and the second semiconductor layer 74 made of GaN are used, the first semiconductor layer 73 has a meltback stopper at the initial stage of crystal growth. Acts as a layer. Specifically, after a part or all of the second semiconductor layer 74 is melted before crystal growth, a group III nitride crystal 75 is formed on the first semiconductor layer 73 as shown in FIG. 7B. Grow. Hereinafter, an example of a specific manufacturing method will be described.

  First, a sapphire substrate whose surface is a C plane (that is, a (0001) plane) is prepared.

  After raising the substrate temperature to about 1020 ° C. to 1100 ° C., TMG and ammonia are supplied onto the substrate to form a seed layer made of GaN. Next, the second semiconductor layer is formed as a stopper layer on the seed layer. Next, a GaN layer is formed again as a second semiconductor layer. The GaN layer is formed by a low pressure MOCVD method (26600 Pa (200 Torr), 1050 ° C.).

  The GaN single crystal layer can be formed using the LPE apparatus shown in FIG. However, since the seed crystal substrate has a stopper layer in this embodiment, meltback is performed at an early stage of growth, the seed crystal layer is slightly melted, and then crystal growth is performed.

  Specifically, a prescribed amount of Ga and Na, which is a flux, are weighed and set in a crucible. In order to melt the raw material in the crucible, the temperature in the electric furnace is raised to 900 ° C. to prepare a raw material melt. At this stage, the seed crystal substrate is not put into the crucible. In order to stir Ga and Na, a propeller is put in the melt and the melt is stirred for several hours. Next, the temperature of the crucible is set to 830 ° C. The seed crystal substrate is lowered to just above the melt to bring the temperature of the substrate closer to the temperature of the melt. After a few minutes, the seed crystal substrate is placed in the melt. In this state, since the melt is not supersaturated, the seed crystal layer of the substrate is slightly melted. Then, while raising atmospheric pressure, the temperature of a solution is set to 800 degreeC. In this embodiment, the atmosphere is 50 atm with only nitrogen gas.

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

  According to the present invention, since the seed crystal having a layered structure includes a stopper layer having a high Al composition ratio, the seed crystal can be stably melted back, and crystal growth can be started from a flat surface. it can. Therefore, a GaN single crystal having a flat and uniform surface can be grown. In addition, it is possible to prevent the seed crystal on the sapphire substrate from being lost when meltback is performed in a melt that is not supersaturated.

In the production method of the present invention, crystals may be grown by a sublimation method. That is, a Group III element or a compound thereof and nitrogen or a compound thereof are reacted to form a Group III nitride, which is deposited on a substrate to form a Group III nitride semiconductor layer. As an example of the crystal growth apparatus in this case, a crystal growth apparatus 80 is shown in FIG. The crystal growth apparatus 80 includes an electric furnace 81. A quartz tube 82 is installed inside the electric furnace 81, and a boron nitride (BN) crucible 84 containing GaN powder 83 is placed therein. The electric furnace 81 has a nitrogen gas atmosphere containing about 10% by volume of NH ₃ gas. When the temperature of the crucible 84 is raised, the GaN powder 83 reacts with nitrogen gas (NH ₃ gas) and decomposes, jumps upward, and adheres to the substrate 86 heated by the substrate heater 85. As the substrate mounted on the substrate heater, for example, a seed crystal substrate whose surface is polycrystalline GaN or a seed crystal substrate whose surface is AlN can be used. After growing the GaN single crystal on the GaN seed crystal substrate, when the temperature in the electric furnace is lowered and the temperature of the substrate heater is also lowered, the linear expansion coefficient of the sapphire substrate and the linear expansion coefficient of the grown GaN crystal are Due to the difference, the grown GaN single crystal can be separated from the sapphire substrate. In FIG. 8, 87 indicates a flow rate regulator, and 88 indicates a thermocouple.

  In Example 5, an example in which a semiconductor laser is manufactured using the substrate obtained in the above example will be described. The structure of the semiconductor laser 90 is shown in FIG.

First, a contact layer 92 made of n-type GaN doped with Si so as to have a carrier density of 5 × 10 ¹⁸ or less is formed on the substrate 91 containing the GaN crystal obtained in the above embodiment. The substrate 91 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 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 density is 3 × 10 ¹⁸ or less.

Then, on the contact layer 92, to form the optical guide layer 94 made of the cladding layer 93 and the n-type GaN made of n-type Al _0.07 Ga _0.93 N. 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. The p-side electrode 100 is made of a laminate of nickel (Ni) and gold (Au).

  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 n-side electrode 101 is composed of a laminate of titanium (Ti) and aluminum (Al).

  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-type electrode for 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 over the entire area of the substrate, high reliability can be realized in wide stripe LDs and surface emitting LDs. In addition, since the device can be realized with a configuration that does not require a complicated structure like ELOG as in the conventional configuration, the manufacturing process can be simplified and the device can be manufactured at low cost.

  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, according to the method for manufacturing a semiconductor device of the present invention, a semiconductor device having high characteristics can be easily manufactured.

It is sectional drawing which shows 1 process of an 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 figure which shows PL intensity | strength of (a) GaN crystal obtained by the conventional method, and (b) GaN crystal obtained by this invention. It is process sectional drawing which shows an example about the manufacturing method of this invention. It is sectional drawing which shows 1 process of another example about the manufacturing method of this invention. It is process sectional drawing which shows another example about the manufacturing method of this invention. It is process sectional drawing which shows another example about the manufacturing method of this invention. It is a schematic diagram which shows the structure of another 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 a schematic diagram which shows an example of the manufacturing method of this invention.

Explanation of symbols

10, 40, 50 substrate 11,41,71 sapphire substrate 12,62,72 seed layer 63 SiO ₂ layer 64 selective growth layer 42 GaN layer 43,75 III nitride crystal 51 GaAs substrate 52 AlN layer 61 GaAs substrate 65 GaN Single crystal 73 First semiconductor layer 74 Second semiconductor layer 90 Semiconductor laser 101 Substrate 102 Semiconductor layer 103 Melt 104 Crucible 105 Group III nitride crystal 106 Holding member

Claims (9)

(I) A composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) in which the full width at half maximum of a two-crystal method X-ray rocking curve is 0.1 degree or more on a substrate Forming a semiconductor layer made of a semiconductor represented by:
(Ii) Group III nitridation on the semiconductor layer by bringing the semiconductor layer into contact with a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal in an atmosphere containing nitrogen. And III-nitride substrate manufacturing method including a step of growing a physical crystal. 2. The method for producing a group III nitride substrate according to claim 1, wherein in the step (i), the full width at half maximum of the two-crystal method X-ray rocking curve is 0.3 degrees or more. 2. The method for producing a group III nitride substrate according to claim 1, wherein in the step (i), the full width at half maximum of the two-crystal X-ray rocking curve is 1 degree or more. In the step (i) , a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦) is formed on the substrate , wherein the full width at half maximum of the two-crystal method X-ray rocking curve is 0.1 degree or more. 4. The step of forming a semiconductor layer made of a semiconductor represented by v ≦ 1) under a constant temperature range of T ± 10 ° C. (where 500 ≦ T ≦ 1100). A method for producing a group III nitride substrate as described in 1. The step (i) is a step of forming an AlN layer having a full width at half maximum of a two-crystal X-ray rocking curve of 0.1 degrees or more on a substrate by a sputtering method ,
In the step (ii), the semiconductor layer is brought into contact with a melt containing at least one group III element selected from gallium and aluminum and an alkali metal in an atmosphere containing nitrogen, whereby a composition formula Al _x Ga _{1 The} group III nitride substrate according to any one of claims 1 to 3, which is a step of growing a group III nitride crystal represented by _-xN (where 0≤x≤1) on the AlN layer. Manufacturing method. In the step (i) , a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦) is formed on the substrate , wherein the full width at half maximum of the two-crystal method X-ray rocking curve is 0.1 degree or more. The group III nitride according to any one of claims 1 to 3, which is a step of forming a semiconductor layer made of a semiconductor represented by v ≦ 1) by heating a group III nitride crystal material and sublimating it. Manufacturing method of physical substrate. The method for producing a group III nitride substrate according to any one of claims 1 to 6, wherein the atmosphere containing nitrogen is a pressurized atmosphere. 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 method for producing a group III nitride substrate according to any one of claims 1 to 7. The method for producing a group III nitride substrate according to any one of claims 1 to 8, wherein the melt further contains an alkaline earth metal.

Images