JP2006173148A - Self-supported group iii nitride semiconductor substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably peel a high-quality GaN layer from a sapphire substrate after the GaN layer is formed on the substrate. <P>SOLUTION: A method of manufacturing a self-supported group GaN semiconductor substrate is provided including a step of forming a thick GaN film composed of an Si-doped GaN layer 714 and undoped GaN layer 715 on a sapphire substrate 711, and a step of separating and removing the sapphire substrate 711 without applying any external force by generating cracks in the thick GaN film by cooling the substrate 711 and thick GaN film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a group III nitride semiconductor free-standing substrate and a method for manufacturing the same.

  In manufacturing a semiconductor device, it is desirable to use a bulk crystal of the same material as the epitaxial layer to be grown as a substrate material. Attempts to make bulk crystals of gallium nitride (GaN) crystals have been made by many research institutions. However, crystals such as GaN have a high nitrogen dissociation pressure, making it difficult to obtain large bulk crystals from the melt like gallium arsenide (GaAs). Is very difficult to fabricate.

For this reason, a method of producing a GaN semiconductor substrate in a vapor phase using HVPE (hydride vapor phase epitaxy) is mainly used. That is, a GaN thin film (film thickness: about 2 μm) is formed on a sapphire (Al ₂ O ₃ ) substrate using a MOCVD apparatus, and a GaN layer (film thickness: about 400 μm) is formed on the GaN thin film using an HVPE apparatus. By growing or performing HVPE growth of GaN directly on the sapphire substrate, a structure composed of a GaN thick film-sapphire substrate (hereinafter referred to as a sapphire / GaN structure as appropriate) is obtained. Finally, a GaN semiconductor substrate for manufacturing a semiconductor device is obtained by separating the GaN layer from the sapphire / GaN structure.

  Patent Document 1 discloses a method of separating a GaN layer from a sapphire substrate by growing the GaN layer on a sapphire substrate and then irradiating a laser beam as a method for separating the GaN layer from the sapphire / GaN structure. Yes. However, since the sapphire / GaN structure is subjected to thermal strain due to the difference in thermal expansion coefficient, this method tends to cause defects such as dislocations during peeling, and the GaN layer is often damaged.

  On the other hand, Patent Document 2 discloses a method of growing a GaN layer using GaAs as a substrate material instead of sapphire and then removing GaAs by etching. According to this method, a GaN layer can be obtained while suppressing breakage. However, since the decomposition temperature of GaAs is low, GaAs is decomposed during the growth of the GaN layer, and As is mixed into the GaN layer as an impurity, which may deteriorate the quality of the GaN semiconductor substrate. Moreover, since toxic As is handled, it is not preferable in terms of safety.

  In Patent Document 3, a lift-off layer made of an AlGaN layer or an InGaN layer containing crystal defects or voids is grown on a sapphire substrate, a GaN layer is grown on the lift-off layer, and a lift-off layer containing crystal defects or voids is used. A method for peeling a GaN layer from a sapphire substrate is disclosed.

However, in order to stably form a large number of fine voids or crystal defects in a lift-off layer composed of an AlGaN layer or an InGaN layer, 1) a ratio of hydrogen (H ₂ ) and nitrogen (N ₂ ) of carrier gas, 2) The ratio of ammonia (NH ₃ ) to gallium chloride (GaCl) (V / III ratio), 3) the supply amount of aluminum (Al) or indium (In), and 4) the growth temperature must be precisely controlled. There is. Therefore, there is room for further improvement in terms of control stability. In addition, it is difficult to improve the crystallinity of the GaN layer formed on the lift-off layer having fine voids or crystal defects. Therefore, there is a problem in terms of the quality of the GaN substrate.

JP 2002-57119 A International Publication No. WO99 / 23693 Pamphlet JP 2004-112000 A

  As described above, conventionally, a free-standing (self-supporting) GaN substrate has been produced by growing a GaN single crystal on a base substrate such as sapphire and then removing the base substrate. However, it is difficult to remove the underlying substrate by any method while suppressing damage to the GaN substrate.

  The present invention has been made in view of the above circumstances, and a purpose thereof is to stably provide a high-quality group III nitride semiconductor free-standing substrate with little damage.

  According to the present invention, a first layer made of a group III nitride semiconductor containing an n-type impurity is provided on an upper portion of a base substrate, and an n-type impurity is provided on the upper portion of the first layer. A step of forming a group III nitride semiconductor film comprising: a second layer made of a group III nitride semiconductor having a low content of: a step of cooling the base substrate and the group III nitride semiconductor film; Separating and removing the structure including the base substrate within the layer or in the vicinity of the interface between the first layer and the second layer to obtain a free-standing substrate including at least a part of the group III nitride semiconductor film. A method of manufacturing a group III nitride semiconductor free-standing substrate is provided.

  According to this method, a crack is generated without applying external force in the first layer containing a high concentration of n-type impurities or in the vicinity of the interface between the first layer and the second layer due to a temperature drop. . For this reason, it becomes easy to peel the group III nitride semiconductor film from the base substrate, so that a high-quality group III nitride semiconductor free-standing substrate with little damage can be stably obtained.

  According to the present invention, the first layer made of a group III nitride semiconductor containing an n-type impurity and the second layer made of a group III nitride semiconductor provided on one side of the first layer are provided. And the first layer has a higher n-type impurity content than the second layer, and the first layer provides a group III nitride semiconductor free-standing substrate having an uneven surface.

  A group III nitride semiconductor self-supporting substrate having this configuration can be manufactured by the above-described manufacturing method. Therefore, it can be stably obtained as a high-quality group III nitride semiconductor free-standing substrate with little damage. In addition, since the first layer having an uneven surface and containing a high concentration of n-type impurities is provided, the contact property with an electrode or the like is excellent. Therefore, the group III nitride semiconductor free-standing substrate having such a configuration can be used as a substrate of a semiconductor device such as a semiconductor laser element.

  In the present invention, the base substrate means a substrate serving as a base for crystal growth of a group III nitride film. In the present invention, the structure means a three-dimensional structure including one or more layer structures. In the present invention, the layer is not limited to a film structure that is uniformly provided on the entire surface.

  According to the present invention, since the base substrate can be peeled and removed by cooling a structure having a specific configuration, a high-quality group III nitride semiconductor free-standing substrate with little damage can be provided.

  In the present invention, in the above-described step of cooling the group III nitride semiconductor film, the base substrate can be separated and removed without applying external force for the following reason. That is, a first layer formed of a group III nitride semiconductor containing an n-type impurity and formed on an upper portion of the base substrate, and an n-type impurity provided on the upper portion of the first layer. And cooling the III-nitride semiconductor film including the second layer made of a III-nitride semiconductor with a low content of the inside of the first layer or in the vicinity of the interface between the first layer and the second layer Cracks occur. Therefore, the base substrate can be removed by separating the group III nitride semiconductor film without applying any external force.

  The group III nitride semiconductor film may further include a third group III nitride layer having a lower n-type impurity content than the first layer below the first layer. According to this configuration, the first n-type impurity-rich first sandwiched between the second group III-nitride layer and the third group-III nitride layer having a low n-type impurity content by cooling. Cracks are likely to occur inside the layer or in the vicinity of the interface between the first layer and the second layer. For this reason, the base substrate can be removed without applying an external force inside the first layer or in the vicinity of the interface between the first layer and the second layer.

  The n-type impurity is preferably Si. According to this configuration, the base substrate can be easily removed inside the first layer or in the vicinity of the interface between the first layer and the second layer without applying external force by cooling.

  In the present invention, the undoped GaN layer means a GaN layer that is not intentionally doped with impurities such as Si during GaN film formation, and may contain a small amount of impurities mixed unintentionally.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

<Embodiment 1>
FIG. 1 is a process cross-sectional view illustrating the method for manufacturing a GaN substrate according to the first embodiment.

  First, a vapor phase growth apparatus used for growing a GaN layer in this embodiment will be described. FIG. 2 is a cross-sectional view showing the structure of the vapor phase growth apparatus used for manufacturing the GaN substrate according to the first and second embodiments.

  A vapor deposition apparatus particularly suitable for use in this film forming process is a hydride vapor deposition (HVPE) apparatus as shown in FIG. The GaN substrate according to the first embodiment can be formed by an MOCVD apparatus or the like. Hereinafter, the case of an HVPE apparatus will be described as a representative example with reference to FIG.

  The HVPE apparatus 120 includes a reaction tube 121 and a substrate holder 123 provided in the reaction tube 121. Further, the HVPE apparatus 120 includes a group III source gas supply unit 139 that supplies a group III source gas into the reaction tube 121, a nitrogen source gas supply unit 137 that supplies a nitrogen source gas into the reaction tube 121, and a doping gas. A gas supply pipe 125 for supplying the reaction pipe 121. Further, the HVPE apparatus 120 includes a gas exhaust pipe 135 and heaters 129 and 130.

  The substrate holder 123 is rotatably provided on the downstream side of the reaction tube 121 by a rotation shaft 132. The gas discharge pipe 135 is provided on the downstream side of the substrate holder 123 in the reaction pipe 121.

  The group III source gas supply unit 139 includes a gas supply pipe 126, a source boat 128, a Ga source 127, and a layer below the shielding plate 136 among the reaction tubes 121.

  The nitrogen source gas supply unit 137 includes a gas supply pipe 124 and a layer above the shielding plate 136 in the reaction pipe 121 (excluding the gas supply pipe 125 and the inside thereof).

The gas supply pipe 125 supplies dichlorosilane (SiH ₂ Cl ₂ ) gas (doping gas) into the reaction pipe 121.

  The group III source gas supply unit 139 generates GaCl and supplies it to the surface of the wafer 133 on the substrate holder 123. The group III source gas supply unit 139 includes a source boat 128 that houses a gas supply pipe 126 and a Ga source 127.

  The supply port of the gas supply pipe 126 is arranged on the upstream side in the group III source gas supply unit 139. For this reason, the supplied HCl gas comes into contact with the Ga source 127 in the source boat 128 in the group III source gas supply unit 139.

  Thereby, the halogen-containing gas supplied from the gas supply pipe 126 comes into contact with the surface of the Ga raw material 127 in the source boat 128 or volatilized Ga, and chlorinates Ga to generate a group III raw material gas containing Ga chloride. To do. A heater 129 is disposed around the group III source gas supply unit 139, and the inside of the group III source gas supply unit 139 is maintained at a temperature of about 800 to 900 ° C., for example.

  The upstream side of the reaction tube 121 is divided into two layers by a shielding plate 136. Ammonia supplied from the gas supply pipe 124 passes through the nitrogen source gas supply unit 137 located on the upper side of the shielding plate 136 in the drawing, and decomposition is accelerated by heat. A heater 129 is disposed around the nitrogen source gas supply unit 137, and the nitrogen source gas supply unit 137 is maintained at a temperature of about 800 to 900 ° C., for example.

  In the growth region 122 located on the right side in the drawing, a substrate holder 123 that holds the wafer 133 is disposed, and GaN is grown in the growth region 122. A heater 130 is disposed around the growth region 122, and the inside of the growth region 122 is maintained at a temperature of about 1000 to 1200 ° C., for example.

  The number of substrate holders 123 may be one, or two or more. The HVPE apparatus may be a horizontal type or a vertical type.

  Hereinafter, the process of the manufacturing method of the GaN free-standing substrate according to the present embodiment will be described in detail.

  FIG. 3 is a graph showing a growth temperature profile of the GaN layer in the GaN substrate manufacturing method according to the first and second embodiments. First, as shown in FIG. 1A, a 2-inch sapphire having a thickness of 430 μm and having an upper surface inclined by 0.2 ° from the (0001) plane that has been surface-cleaned with a mixed solution of an organic solvent, phosphoric acid, and sulfuric acid. A substrate 101 (sapphire substrate) is prepared.

  Next, the sapphire substrate 101 is set on the substrate holder 123 in the reaction tube 121 of the HVPE apparatus 120 as shown in FIG. This sapphire substrate 101 is displayed as a wafer 133 in the figure.

Then, the inside of the reaction tube 121 is purged by supplying N ₂ gas as a purge gas from the gas supply tubes 125 and 126. The purge gas supplied into the reaction tube 121 is discharged from the gas discharge tube 135. After sufficiently purging the inside of the reaction tube 121, the gas introduced from the gas supply tubes 125 and 126 is switched to H ₂ gas (carrier gas), and the temperature of the reaction tube 121 is raised by the heater 129 and the heater 130.

When the temperature of the growth region 122 reaches 500 ° C., NH ₃ gas is added to the carrier gas from the gas supply pipe 125 and supplied. Subsequently, as shown in FIG. 3, the temperature rise is continued until the temperature of the Ga material 127 reaches 850 ° C. and the temperature of the growth region 122 reaches 1040 ° C. After each temperature is stabilized, HCl gas is added to the carrier gas from the gas supply pipe 126 and supplied to react with the Ga raw material 127 to generate gallium chloride (GaCl) and transport it to the growth region 122.

In the growth region 122, NH ₃ gas and GaCl gas react to grow a low impurity concentration GaN layer 103 on the sapphire substrate 101.

When the thickness of the low impurity concentration GaN layer 103 reaches a predetermined thickness, SiH ₂ Cl ₂ gas (doping gas) is supplied from the gas supply pipe 126. In the growth region 122, NH ₃ gas, GaCl gas, and SiH ₂ Cl ₂ gas react to grow a high concentration Si-doped GaN layer 105 on the low impurity concentration GaN layer 103.

When the thickness of the high-concentration Si-doped GaN layer 105 reaches a predetermined thickness, the supply of SiH ₂ Cl ₂ gas from the gas supply pipe 126 is stopped. Thereafter, in the growth region 122, NH ₃ gas and GaCl gas react to grow a low impurity concentration GaN layer 107 on the high concentration Si-doped GaN layer 105.

  When the thickness of the low impurity concentration GaN layer 107 reaches a predetermined thickness, the supply of HCl gas from the gas supply pipe 126 is stopped, the power sources of the heaters 129 and 130 are shut off, and the temperature of the reaction tube 121 is lowered. To do.

Then, the NH ₃ gas is continuously supplied from the gas supply pipe 124 until the temperature of the growth region 122 is lowered to about 500 ° C., and after the temperature is lowered to about 200 ° C., the supply of NH ₃ gas from the gas supply pipe 124 is reduced to N _2. Switch to purge gas such as gas.

  During this temperature decrease, the sapphire substrate 101 can be peeled without applying an external force in the high concentration Si-doped GaN layer 105 or in the vicinity of the interface with the adjacent low impurity concentration GaN layer 107.

  That is, the HVPE-GaN thick film 109 is separated at the peeling site 111 in the high-concentration Si-doped GaN layer 105. This upper and lower separation occurs without applying external force. By polishing the uneven surface of the GaN free-standing substrate composed of a part of the peeled high-concentration Si-doped GaN layer 105 and the low-impurity concentration GaN layer 107, a finally flattened GaN free-standing substrate can be produced.

Of the GaN thick films described above, the thickness of the low impurity concentration GaN layer 103 is 50 μm or more and 100 μm or less. The impurity concentration of the low impurity concentration GaN layer 103 is less than 1 × 10 ¹⁸ cm ⁻³ . The growth rate of the low impurity concentration GaN layer 103 is set to a constant rate. Therefore, by controlling the growth time, the film thickness of the low impurity concentration GaN layer 103 can also be accurately controlled. Note that the high concentration Si-doped GaN layer 105 may be formed directly on the sapphire substrate 101 without providing the low impurity concentration GaN layer 103.

The thickness of the high-concentration Si-doped GaN layer 105 is, for example, 100 μm or more and 500 μm or less. The impurity concentration of the high-concentration Si-doped GaN layer 105 is 1 × 10 ¹⁸ cm ⁻³ or more, particularly preferably 2 × 10 ¹⁸ cm ⁻³ or more, and most preferably 4 × 10 ¹⁸ cm ⁻³ or more. It is. If the impurity concentration of the high-concentration Si-doped GaN layer 105 is equal to or higher than these values, cooling is performed inside the high-concentration Si-doped GaN layer 105 or in the vicinity of the interface between the high-concentration Si-doped GaN layer 105 and the low-impurity concentration GaN layer 107. Even if no external force is applied during the process, the entire surface is easily peeled off. The upper limit of the impurity concentration is not particularly limited, but is particularly preferably 1 × 10 ²⁰ cm ⁻³ or less. The growth rate of the high-concentration Si-doped GaN layer 105 is a constant rate. Therefore, the film thickness of the high-concentration Si-doped GaN layer 105 can be controlled with high accuracy by controlling the growth time.

The thickness of the low impurity concentration GaN layer 107 is 300 μm or more. The impurity concentration of the low impurity concentration GaN layer 107 is less than 1 × 10 ¹⁸ cm ⁻³ . Note that the growth rate of the low impurity concentration GaN layer 107 is a constant rate. Therefore, by controlling the growth time, the film thickness of the low impurity concentration GaN layer 107 can be accurately controlled. The supply amount and partial pressure of HCl gas and NH ₃ gas are the same as described above.

  Note that the total thickness of the HVPE-GaN thick film 109 is 600 μm or more and 900 μm or less.

  As for the temperature drop rate after the growth of the GaN layer by the HVPE apparatus, the temperature is lowered from 1040 ° C. to 500 ° C. in about 8 minutes as shown in FIG. Then, the temperature is lowered from 500 ° C. to 200 ° C. in about 10 minutes. At this time, the HVPE-GaN thick film is cracked in the high concentration Si-doped GaN layer 105 or in the vicinity of the interface with the adjacent low impurity concentration GaN layer 107 at a temperature in the range of 800 ° C. to room temperature (25 ° C.). Cheap.

  As described above, in this embodiment, cracks are generated in the high concentration Si-doped GaN layer 105 or in the vicinity of the interface with the adjacent low impurity concentration GaN layer 107 in the cooling process after the growth of the GaN layer by the HVPE apparatus. The GaN layer is peeled off from the sapphire substrate 101. Thus, since the sapphire substrate 101 is peeled and removed without applying an external force due to a temperature drop, a high-quality GaN free-standing substrate with little damage can be stably obtained. In addition, according to the method of the present embodiment, high quality with little damage can be achieved for a self-standing GaN substrate having a large diameter exceeding 2 inches, as described above.

<Embodiment 2>
FIG. 4 is a cross-sectional view schematically showing a configuration of a structure including a sapphire substrate-GaN thick film according to the second embodiment. The manufacturing method of the GaN substrate according to the second embodiment is basically the same as that of the first embodiment, but the Si high concentration doping is performed between the undoped GaN layers by the ELO method instead of the FIELO method. The difference is that a GaN layer is formed.

  The structure includes a sapphire substrate 141 (underlying substrate) and a GaN thick film. This GaN thick film is provided on the sapphire substrate 141 and includes a Si-doped GaN layer 145 (first layer) containing Si element as an n-type impurity. The GaN thick film includes an undoped GaN layer 147 (second layer) provided on the Si-doped GaN layer 145 and having a lower Si element content than the Si-doped GaN layer 145. The GaN free-standing substrate according to the present embodiment cools this structure and forms a crack 146 in the Si-doped GaN layer 145 or in the vicinity of the interface between the Si-doped GaN layer 145 and the undoped GaN layer 147, It is obtained separately from the sapphire substrate 141.

  When this structure is cooled, the Si-doped GaN layer 145 containing a high concentration of n-type impurities or the interface between the Si-doped GaN layer 145 and the undoped GaN layer 147 in the process of temperature drop after the GaN thick film is formed. A crack 146 is generated without applying an external force in the vicinity, and the sapphire substrate 141 is peeled and removed.

  For this reason, a simple method of cooling the sapphire substrate 141 and the GaN thick film stably suppresses damage to the GaN substrate, and stably stabilizes a high-quality GaN free-standing substrate formed from the sapphire substrate 141 by the ELO method. Can get to.

  Hereinafter, the process of the manufacturing method of the GaN free-standing substrate according to the present embodiment will be described in detail.

  FIG. 5 is a process cross-sectional view illustrating the method for manufacturing the GaN substrate according to the second embodiment. First, as shown in FIG. 5A, a 2-inch sapphire substrate 141 having a thickness of 430 μm and tilted by 0.2 ° from the (0001) plane subjected to surface cleaning using a mixed solution of an organic solvent, phosphoric acid and sulfuric acid ( Prepare a sapphire substrate.

  Next, the sapphire substrate 141 is set on the substrate susceptor in the reaction tube of the MOCVD growth apparatus. Then, an undoped GaN layer 142 having a thickness of about 1.5 μm to 2 μm is formed on the sapphire substrate 141 by MOCVD.

Next, an SiO ₂ film having a thickness of 2 μm is formed on the surface of the undoped GaN layer 142 on the sapphire substrate 141 taken out from the MOCVD growth apparatus by using an electron beam (EB) evaporation method. Then, a stripe-like SiO ₂ mask 144 is formed by using a lithography technique so that the width of the opening is 3 μm and the width of the SiO ₂ film is 7 μm. Further, the surface of the undoped GaN layer 142 on which the SiO ₂ mask 144 is formed is cleaned using a mixed solution of organic detergent and nitric acid or a mixed solution of phosphoric acid and sulfuric acid.

The sapphire substrate 141 on which the undoped GaN layer 142 and the SiO ₂ mask 144 are formed is set on the substrate holder 123 in the reaction tube 121 of the HVPE apparatus shown in FIG. This sapphire substrate 141 is indicated as a wafer 133 in the drawing.

Then, the inside of the reaction tube 121 is purged by supplying N ₂ gas as a purge gas from the gas supply tubes 125 and 126. The purge gas supplied into the reaction tube 121 is discharged from the gas discharge tube 135. After sufficiently purging the inside of the reaction tube 121, the gas introduced from the gas supply tubes 125 and 126 is switched from N ₂ gas to H ₂ gas (carrier gas), and the temperature of the reaction tube 121 is increased by the heater 129 and the heater 130. .

When the temperature of the growth region 122 reaches around 500 ° C., NH ₃ gas is added to the carrier gas from the gas supply pipe 125 and supplied. Subsequently, as shown in FIG. 3, the temperature rise is continued until the temperature of the Ga material 127 reaches 850 ° C. and the temperature of the growth region 122 reaches 1040 ° C. After each temperature is stabilized, HCl gas is added to the carrier gas from the gas supply pipe 126 and supplied to react with the Ga raw material 127 to generate gallium chloride (GaCl) and transport it to the growth region 122.

In the growth region 122, NH ₃ gas and GaCl gas react to grow an undoped GaN layer 143 on the undoped GaN layer 142 and the SiO ₂ mask 144. At this time, in this embodiment, the undoped GaN layer 143 is grown not by the FIELO method in which the undoped GaN layer 143 is grown in a facet shape but by the ELO method in which no facet is formed. Specifically, in the case of the FIELO method, the ELO method is performed by changing the V / III ratio or changing the film formation temperature.

When the thickness of the undoped GaN layer 143 reaches a predetermined thickness as shown in FIG. 5B, SiH ₂ Cl ₂ gas (doping gas) is supplied from the gas supply pipe 125. In the growth region 122, the NH ₃ gas, the GaCl gas, and the SiH ₂ Cl ₂ gas react to grow the Si-doped GaN layer 145 on the undoped GaN layer 143 as shown in FIG.

At this time, SiH ₂ Cl ₂ decomposes and changes to Si even at a low temperature. For this reason, SiH ₂ Cl ₂ gas is easily decomposed upstream of the HVPE vapor phase growth apparatus, falls as Si particles, and easily adheres to the inner wall of the introduction pipe. Therefore, in the following experimental examples, HCl gas is added to SiH ₂ Cl ₂ gas (3000 ppm). By doing so, decomposition of SiH ₂ Cl ₂ is suppressed and it is easy to reach the sapphire substrate.

When the thickness of the Si-doped GaN layer 145 reaches a predetermined thickness, the supply of SiH ₂ Cl ₂ gas from the gas supply pipe 125 is stopped. Thereafter, in the growth region 122, NH ₃ gas and GaCl gas react to grow an undoped GaN layer 147 on the Si-doped GaN layer 145 as shown in FIG.

  When the thickness of the undoped GaN layer 147 reaches a predetermined thickness, the supply of HCl gas from the gas supply pipe 126 is stopped, the power sources of the heaters 129 and 130 are shut off, and the temperature of the reaction tube 121 is lowered. .

Then, the NH ₃ gas is continuously supplied from the gas supply pipe 124 until the temperature of the growth region 122 is lowered to about 500 ° C., and after the temperature is lowered to about 200 ° C., the supply of NH ₃ gas from the gas supply pipe 124 is reduced to N _2. Switch to purge gas such as gas.

  FIG. 6 is a process cross-sectional view illustrating the method for manufacturing the GaN substrate according to the second embodiment.

  During this temperature decrease, as shown in FIG. 6D, a crack 146 is generated in the Si-doped GaN layer 145 or in the vicinity of the interface with the adjacent undoped GaN layer 147.

  The HVPE-GaN thick film can be separated into upper and lower Si-doped GaN layers 145a and 145b by a crack 146, as shown in FIG. This upper and lower separation occurs without applying external force due to cooling.

  As a result, as shown in FIG. 6F, a GaN substrate composed of the Si-doped GaN layer 145a and the undoped GaN layer 147 separated from the sapphire substrate 141 is obtained. It is to be noted that by polishing the surface of the GaN substrate that has been peeled off, the Si-doped GaN layer 145a can be removed, and a GaN free-standing substrate composed of an undoped GaN layer 147 that is finally planarized can be produced.

  In the above GaN layer thickness, the undoped GaN layer 143 has a thickness of 50 μm or more and 100 μm or less. The undoped GaN layer 143 is not doped with Si, but may contain a small amount of Si unintentionally. The growth rate of the undoped GaN layer 143 is set to a constant rate. Therefore, by controlling the growth time, the film thickness of the undoped GaN layer 143 can also be accurately controlled. Note that the Si-doped GaN layer 145 may be formed directly on the sapphire substrate 141 without providing the undoped GaN layer 143.

The thickness of the Si-doped GaN layer 145 is, for example, not less than 100 μm and not more than 500 μm. The impurity concentration of the Si-doped GaN layer 145 is, for example, 1 × 10 ¹⁸ cm ⁻³ or more, particularly preferably 2 × 10 ¹⁸ cm ⁻³ or more, and most preferably 4 × 10 ¹⁸ cm ⁻³ or more. is there. If the value of the impurity concentration is higher than these values, the entire surface is likely to be peeled off without applying any external force in the cooling process. The upper limit of the impurity concentration is not particularly limited, but a sufficient effect can be obtained at a concentration of 1 × 10 ²⁰ cm ⁻³ or less, for example. The growth rate of the Si-doped GaN layer 145 is a constant rate. Therefore, the film thickness of the Si-doped GaN layer 145 can be accurately controlled by controlling the growth time.

  If the value of the impurity concentration is equal to or higher than these values, the reason why the entire surface is likely to be peeled off without applying an external force in the cooling process is assumed as follows. That is, when the GaN layer is doped with Si, as the Si doping amount is increased, defects are generated throughout the Si-doped GaN layer during the cooling process when the sapphire / GaN structure is taken out from the film forming apparatus. It becomes easy to do. As a result, it is assumed that in the cooling process, the entire surface of the Si-doped GaN layer is likely to be peeled off without applying any external force due to defects generated throughout the Si-doped GaN layer.

The undoped GaN layer 147 has a thickness of 300 μm or more. The impurity concentration of the undoped GaN layer 147 is less than 1 × 10 ¹⁸ cm ⁻³ . The growth rate of the undoped GaN layer 147 is set to a constant rate. Therefore, by controlling the growth time, the film thickness of the undoped GaN layer 147 can also be accurately controlled. At this time, the supply amount and partial pressure of HCl gas and NH ₃ gas need not be changed.

  The total thickness of the HVPE-GaN thick film including the undoped GaN layer 143, the Si-doped GaN layer 145, and the undoped GaN layer 147 is, for example, 500 μm or more. The Si-doped GaN layer 145 is provided on the sapphire substrate 141 side with respect to the central portion of the GaN thick film.

<Embodiment 3>
FIG. 7 is a cross-sectional view schematically showing a configuration of a structure including the sapphire substrate-GaN thick film according to the third embodiment. The manufacturing method of the GaN free-standing substrate according to the third embodiment is basically the same as that of the second embodiment, but differs in that the Si-doped GaN layer 714 is directly provided on the SiO ₂ mask 713. .

  The structure includes a sapphire substrate 711 (underlying substrate) and a GaN thick film. This GaN thick film is provided on the sapphire substrate 711 and includes a Si-doped GaN layer 714 (first layer) containing Si element as an n-type impurity. The GaN thick film includes an undoped GaN layer 715 (second layer) that is provided on the Si-doped GaN layer 714 and has a lower Si element content than the Si-doped GaN layer 714. The GaN free-standing substrate according to the present embodiment cools this structure and forms a crack in the Si-doped GaN layer 714 or in the vicinity of the interface between the Si-doped GaN layer 714 and the undoped GaN layer 715, thereby reducing the sapphire. Obtained separately from the substrate 711.

  When this structure is cooled, the Si-doped GaN layer 714 containing a high concentration of n-type impurities or the interface between the Si-doped GaN layer 714 and the undoped GaN layer 715 in the process of temperature drop after the GaN thick film is formed. A crack is generated without applying an external force in the vicinity, and the sapphire substrate 711 is peeled and removed.

  For this reason, a simple method of cooling the sapphire substrate 711 and the GaN thick film stably suppresses damage to the GaN substrate, and stably stabilizes a high-quality GaN free-standing substrate formed from the sapphire substrate 711 by the FIELO method. Can be peeled off.

  Hereinafter, the process of the manufacturing method of the GaN free-standing substrate according to the present embodiment will be described in detail.

  FIG. 8 is a process cross-sectional view illustrating the method for manufacturing the GaN free-standing substrate according to the third embodiment. First, as shown in FIG. 8A, a 2-inch sapphire substrate 711 having a thickness of 430 μm and inclined by 0.2 ° from the (0001) plane that has been surface-cleaned using a mixed solution of an organic solvent, phosphoric acid, and sulfuric acid. (Sapphire substrate) is prepared.

  Next, a sapphire substrate 711 is set on the substrate susceptor in the reaction tube of the MOCVD growth apparatus. Then, an undoped GaN layer 712 having a film thickness of about 1.5 μm to 2 μm is formed on the sapphire substrate 711 by MOCVD.

Next, an SiO ₂ film having a thickness of 2 μm is formed on the surface of the undoped GaN layer 712 on the sapphire substrate 711 taken out from the MOCVD growth apparatus by using an electron beam (EB) vapor deposition method. Then, a striped SiO ₂ mask 713 was formed using a lithography technique so that the width of the opening was 3 μm and the width of the SiO ₂ film was 7 μm. Further, the surface of the undoped GaN layer 712 on which the SiO ₂ mask 713 is formed is cleaned using a mixed solution of organic detergent and nitric acid or a mixed solution of phosphoric acid and sulfuric acid.

The sapphire substrate 711 on which the undoped GaN layer 712 and the SiO ₂ mask 713 are formed is set on the substrate holder 123 in the reaction tube 121 of the HVPE apparatus shown in FIG. This sapphire substrate 711 is indicated as a wafer 133 in the drawing.

Then, the inside of the reaction tube 121 is purged by supplying N ₂ gas as a purge gas from the gas supply tubes 125 and 126. The purge gas supplied into the reaction tube 121 is discharged from the gas discharge tube 135. After sufficiently purging the inside of the reaction tube 121, the gas introduced from the gas supply tubes 125 and 126 is switched to H ₂ gas (carrier gas), and the temperature of the reaction tube 121 is raised by the heater 129 and the heater 130.

When the temperature of the growth region 122 reaches around 500 ° C., NH ₃ gas is added to the carrier gas from the gas supply pipe 125 and supplied. Subsequently, as shown in FIG. 3, the temperature rise is continued until the temperature of the Ga material 127 reaches 850 ° C. and the temperature of the growth region 122 reaches 1040 ° C. After each temperature is stabilized, HCl gas is added to the carrier gas from the gas supply pipe 126 and supplied to react with the Ga raw material 127 to generate gallium chloride (GaCl) and transport it to the growth region 122. At this time, SiH ₂ Cl ₂ gas (doping gas) is supplied from the gas supply pipe 125.

In the growth region 122, the NH ₃ gas, the GaCl gas, and the SiH ₂ Cl ₂ gas react to grow the Si-doped GaN layer 714 on the undoped GaN layer 712 and the SiO ₂ mask 713. At this time, in this embodiment, the Si-doped GaN layer 714 is grown by the FIELO method in which the Si-doped GaN layer 714 is grown in a facet shape.

At this time, SiH ₂ Cl ₂ decomposes and changes to Si even at a low temperature. For this reason, SiH ₂ Cl ₂ gas is easily decomposed upstream of the HVPE vapor phase growth apparatus, falls as Si particles, and easily adheres to the inner wall of the introduction pipe. Therefore, in the following experimental examples, HCl gas is added to SiH ₂ Cl ₂ gas (3000 ppm). By doing so, decomposition of SiH ₂ Cl ₂ is suppressed and it is easy to reach the sapphire substrate.

When the thickness of the Si-doped GaN layer 714 reaches a predetermined thickness, the supply of SiH ₂ Cl ₂ gas from the gas supply pipe 125 is stopped. Thereafter, in the growth region 122, NH ₃ gas and GaCl gas react to grow an undoped GaN layer 715 on the Si-doped GaN layer 714, as shown in FIG. 8C.

  When the thickness of the undoped GaN layer 715 reaches a predetermined thickness, the supply of HCl gas from the gas supply pipe 126 is stopped, the power sources of the heaters 129 and 130 are shut off, and the temperature of the reaction tube 121 is lowered. .

Then, the NH ₃ gas is continuously supplied from the gas supply pipe 124 until the temperature of the growth region 122 is lowered to about 500 ° C., and after the temperature is lowered to about 200 ° C., the supply of NH ₃ gas from the gas supply pipe 124 is reduced to N _2. Switch to purge gas such as gas.

  During this temperature decrease, a crack is generated in the Si-doped GaN layer 714 or in the vicinity of the interface with the adjacent undoped GaN layer 715.

  Then, as shown in FIG. 8D, the HVPE-GaN thick film can be separated into upper and lower Si-doped GaN layers 714a and 714b by cracks. This upper and lower separation occurs without applying external force due to cooling.

  As a result, a GaN free-standing substrate composed of the Si-doped GaN layer 714a and the undoped GaN layer 715 separated from the sapphire substrate 711 is obtained. The surface of the GaN free-standing substrate that has been peeled off is polished to remove the Si-doped GaN layer 714a, and a GaN free-standing substrate consisting of the undoped GaN layer 715 that is finally planarized can be produced.

In the GaN thick film, the thickness of the Si-doped GaN layer 714 is, for example, not less than 100 μm and not more than 500 μm. Further, the impurity concentration of the Si-doped GaN layer 714 is, for example, 2 × 10 ¹⁸ cm ⁻³ or more, and particularly preferably 4 × 10 ¹⁸ cm ⁻³ or more. If the value of the impurity concentration is higher than these values, the entire surface is likely to be peeled off without applying any external force in the cooling process. The impurity concentration is not particularly limited, but is particularly preferably 1 × 10 ²⁰ cm ⁻³ or less. Note that the growth rate of the Si-doped GaN layer 714 is constant. Therefore, the film thickness of the Si-doped GaN layer 714 can also be accurately controlled by controlling the growth time.

The undoped GaN layer 715 has a thickness d of 300 μm or more. The impurity concentration of the undoped GaN layer 715 is less than 1 × 10 ¹⁸ cm ⁻³ . The growth rate of the undoped GaN layer 715 is set to a constant rate. Therefore, by controlling the growth time, the film thickness of the undoped GaN layer 715 can also be accurately controlled. At this time, the supply amount and partial pressure of HCl gas and NH ₃ gas need not be changed.

  Note that the total thickness D of the HVPE-GaN thick film including the Si-doped GaN layer 714 and the undoped GaN layer 715 is, for example, 500 μm or more. The Si-doped GaN layer 714 is provided on the sapphire substrate 711 side with respect to the central portion of the GaN thick film.

  According to the method for manufacturing a GaN free-standing substrate according to the present embodiment, as in the case of the first embodiment, the following effects are obtained in the present embodiment. That is, in the cooling process after the growth of the GaN layer by the HVPE apparatus, a crack is generated in the Si-doped GaN layer 714 or in the vicinity of the interface with the adjacent undoped GaN layer 715, and the GaN layer is peeled off from the sapphire substrate 711. Adopted. In this way, the sapphire substrate 711 is peeled and removed without applying an external force due to a temperature drop, so that a high-quality GaN free-standing substrate with little damage can be stably obtained.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

In the above embodiment, the direction of the SiO ₂ mask is formed in the (1-100) direction of the base substrate such as a sapphire substrate, but the same effect can be obtained even if it is formed in the (11-20) direction.

  Furthermore, in the above embodiment, the sapphire substrate has a thickness of 430 μm. However, the sapphire substrate has a thickness of 430 μm so that the stress is applied to the high-concentration Si-doped layer most during the cooling process. The thickness can be set as appropriate.

  Furthermore, in the above-described embodiment, the sapphire substrate is used as the base substrate. However, a different material substrate such as SiC or a silicon substrate can be suitably used.

  Further, in the above-described embodiment, a mode has been described in which cracks are formed without applying an external force by cooling, and the entire surface of the base substrate is peeled off. However, the entire surface may not be peeled off during the cooling process. Even in this case, the external force applied for peeling can be minimized, and a high-quality GaN free-standing substrate with little damage can be stably obtained.

  In the above embodiment, the semiconductor film having a specific thickness is formed under specific manufacturing conditions. However, the present invention is not particularly limited. That is, the above-described film thickness and manufacturing conditions are merely examples, and can be appropriately changed according to the structure or composition of the semiconductor film to be formed.

In addition, the undoped GaN layer 143 in the vicinity of the SiO ₂ mask 144 is considered to actually diffuse Si to some extent and contain a small amount of impurities. However, if the Si element concentration in the undoped GaN layer 143 and the undoped GaN layer 147 is less than 1 × 10 ¹⁸ cm ^−3, it is possible to ensure a sufficiently large difference in Si element concentration from the Si doped GaN layer 145. Is possible. For this reason, by cooling, a crack 146 is generated in the Si-doped GaN layer 145 or in the vicinity of the interface with the adjacent undoped GaN layer 147 without applying external force, and the GaN thick film is easily peeled up and down.

In the above embodiment, as a doping material gas, although using SiH ₂ Cl ₂ gas may be a gas containing a compound containing Si element and a halogen element. Among these, it is preferable to use a gas containing a compound containing Si element and Cl element.

In the above embodiment, SiH ₂ Cl ₂ gas is used as a doping source gas. However, SiH _x Cl _4−x (x = 1, 2, 3) or a mixture thereof may be used, and nitridation for performing Si doping may be performed. The group III-V compound semiconductor is In _x Ga _1-x N (0 ≦ x ≦ 1), Al _x Ga _1-x N (0 ≦ x ≦ 1), or Al _x In _y Ga _1-xy N ( Any nitride-based III-V group compound semiconductor of 0 ≦ x + y ≦ 1) or a layered structure thereof may be used.

  Further, in the above experimental example, a structure composed of a sapphire substrate-GaN thick film is produced, and cracks are generated in the high-concentration Si-doped GaN layer in the process of cooling the structure, and the base substrate is peeled and removed. The method for obtaining the GaN substrate by removing the sapphire substrate has been described, but the present invention is not limited to such a method.

  In the process of cooling a semiconductor laser, a light emitting element such as a light emitting diode, and an electronic device such as a field effect transistor on a structure composed of a sapphire substrate-GaN thick film, in the process of cooling them, a high concentration Si doped GaN layer The method of removing the sapphire substrate to obtain an electronic device by removing the base substrate is also included in the scope of the present invention.

  A GaN thick film was grown on a sapphire substrate, a crack was generated in the GaN thick film by cooling, and the sapphire substrate was peeled and removed to produce a GaN free-standing substrate in the following experimental example, and the degree of peeling was evaluated. .

  Hereinafter, first, a method for producing and evaluating an experimental sample will be described, and then each experimental example will be described in detail.

<Sample preparation method of Experimental Examples 1-3>
The growth of a GaN thick film on a sapphire substrate for producing samples used in Experimental Examples 1 to 3 was performed using the method described in the second embodiment. Specific growth conditions will be described below.

As the sapphire substrate, a sapphire / GaN structure with a SiO ₂ stripe mask (thickness: 430 μm) was used. Then, using the HVPE vapor phase growth apparatus as shown in FIG. 2, the following GaN thick film was grown.

  With the temperature profile shown in FIG. 3, the inside of the vapor phase growth apparatus was raised from room temperature to 1040 ° C., and an undoped GaN layer was formed on the sapphire substrate. Furthermore, a high-concentration Si-doped GaN layer was formed at the same temperature. Then, an undoped GaN layer was formed at the same temperature. At this time, each film thickness was controlled by setting the growth time to a predetermined time.

Specifically, the flow rate of HCl gas on Ga is 80 cc / min, the partial pressure is 0.01 to 0.015 atm, the flow rate of NH ₃ gas is 1200 cc / min, the partial pressure is 0.15 atm, and the flow rate of H ₂ gas is The GaN layer was grown by the HVPE method at 6800 cc / min or less.

In the growth of the high-concentration Si-doped GaN layer, HCl gas is used as a carrier gas, SiH ₂ Cl ₂ gas (3000 ppm) is supplied at a flow rate of ₂ to 4 cc / min, and a partial pressure of 7.5 × 10 ⁻⁷ to 4 Si was doped into the GaN layer by HVPE method as × 10 ⁻⁶ atm. As a result, the impurity concentration of the high impurity concentration layer (Si doped layer) could be controlled to about 2 to 3 × 10 ¹⁸ cm ⁻³ or more. On the other hand, the impurity concentration of the low impurity concentration layer (undoped layer) is set to 0.5 to 1 × 10 ¹⁸ cm ⁻³ or less, and in practice, about 1 × 10 ¹⁶ cm ^{−3 to} 1 × 10 ¹⁷ cm ^−3. I was able to control it.

  At this time, the growth rate of the GaN layer by the HVPE method was set to 100 μm / h or less, and the vapor phase growth was continued until the GaN layer thickness (total thickness) became 650 to 850 μm. This is because peeling is less likely to occur when the GaN layer thickness is less than 500 μm.

  After the GaN thick film is formed on the sapphire substrate by the above film formation, the inside of the vapor phase growth apparatus is cooled from 1040 ° C. as shown in the temperature profile of FIG. Cracks were generated. The base substrate was peeled and removed using cracks generated by cooling.

  Then, the state of the upper peeled GaN layer was observed, the state of the lower GaN layer remaining on the sapphire substrate was observed, the thickness of the lower GaN layer was measured, and the degree of peeling was evaluated.

<Evaluation result of Experimental Example 1>
FIG. 9 is a graph showing the film thickness measurement result of the remaining GaN layer and a cross-sectional view of the GaN thick film for explaining the evaluation result of Experimental Example 1.

  FIG. 9B is a cross-sectional view schematically showing the thickness of each GaN layer of the GaN thick film.

In Experimental Example 1, an undoped GaN layer 51 μm, a Si-doped n + GaN layer 255 μm, and an undoped GaN layer 358 μm were formed in this order on the sapphire / GaN structure with a SiO ₂ stripe mask using an HVPE apparatus. The total thickness of the grown GaN film was 664 μm.

  When the obtained sapphire / GaN structure was cooled, a crack was generated in the GaN layer, and the sapphire substrate was peeled and removed over the entire surface.

  FIG. 9A is a graph showing the measurement results of the thickness of the remaining GaN layer (HVPE-GaN layer) on the sapphire substrate side separated by cracks. The horizontal axis of FIG. 9A represents the distance (mm) from the center of the GaN substrate, and the vertical axis represents the GaN layer thickness (μm).

  As shown in FIG. 9A, the average value by calculation of the GaN thickness remaining on the sapphire substrate side is about 133 μm, and cracks are formed in the high-concentration Si-doped GaN layer. It was peeled off.

<Evaluation result of Experimental Example 2>
FIG. 10 is a graph showing the film thickness measurement result of the remaining GaN layer and a cross-sectional view of the GaN thick film for explaining the evaluation result of Experimental Example 2.

  FIG. 10B is a cross-sectional view schematically showing the thickness of each GaN layer of the GaN thick film.

In Experimental Example 2, an undoped GaN layer 52 μm, a Si-doped n ⁺ GaN layer 157 μm, and an undoped GaN layer 471 μm were sequentially formed on a sapphire / GaN structure with a SiO ₂ stripe mask by an HVPE apparatus.

  Then, when the obtained sapphire / GaN structure was cooled, a crack was generated in the GaN layer, and the sapphire substrate was peeled and removed over the entire surface.

  FIG. 10A is a graph showing the measurement result of the thickness of the remaining GaN layer (HVPE-GaN layer) on the sapphire substrate side separated by the cracked portion. In FIG. 10A, the horizontal axis represents the distance (mm) from the center of the GaN substrate, and the vertical axis represents the GaN layer thickness (μm).

  Further, as shown in FIG. 10A, the average value of the GaN thickness remaining on the sapphire substrate side is about 133 μm, and cracks are formed in the high-concentration Si-doped GaN layer. The substrate was peeled off.

<Evaluation result of Experimental Example 3>
FIG. 11 is a graph showing the film thickness measurement result of the remaining GaN layer and a cross-sectional view of the GaN thick film for explaining the evaluation result of Experimental Example 3.

  FIG.11 (b) is sectional drawing which shows typically the thickness of each GaN layer of a GaN thick film.

In Experimental Example 3, an undoped GaN layer 52 μm, a Si-doped n ⁺ GaN layer 156 μm, and an undoped GaN layer 626 μm were sequentially formed on the sapphire / GaN structure with a SiO ₂ stripe mask by the HVPE method.

  Then, when the obtained sapphire / GaN structure was cooled, a crack was generated in the GaN layer, and the sapphire substrate was peeled and removed over the entire surface.

  FIG. 11A is a graph showing the measurement results of the thickness of the remaining GaN layer (HVPE-GaN layer) on the sapphire substrate side separated at the location where the crack occurred. In FIG. 11A, the horizontal axis represents the distance (mm) from the center of the GaN substrate, and the vertical axis represents the GaN layer thickness (μm).

  Moreover, as shown in FIG. 11A, the average value of the GaN thickness remaining on the sapphire substrate side is about 218 μm, and the interface between the high-concentration Si-doped GaN layer and the undoped GaN layer thereon is It was formed on the undoped GaN layer side near the interface. A part of the cracked portion was formed in the high-concentration Si-doped GaN layer near the interface beyond the interface between the high-concentration Si-doped GaN layer and the undoped GaN layer thereon.

<Sample Preparation Method for Experimental Example 4>
The growth of the GaN thick film on the sapphire substrate for producing the sample used in Experimental Example 4 was performed using the method described in the third embodiment. Specific growth conditions will be described below.

As the sapphire substrate, a sapphire / GaN structure with a SiO ₂ stripe mask (thickness: 430 μm) was used. Then, using the HVPE vapor phase growth apparatus as shown in FIG. 2, the inside of the vapor phase growth apparatus is raised from room temperature to 1040 ° C., and directly on the sapphire / GaN structure with the SiO ₂ stripe mask, high-concentration Si doping A GaN layer was formed. Then, an undoped GaN layer was formed at the same temperature. At this time, each film thickness was controlled by setting the growth time to a predetermined time.

Specifically, the flow rate of HCl gas on Ga is 80 cc / min, the partial pressure is 0.01 to 0.015 atm, the flow rate of NH ₃ gas is 1200 cc / min, the partial pressure is 0.15 atm, and the flow rate of H ₂ gas is The GaN layer was grown by the HVPE method at 6800 cc / min or less.

In the growth of the high-concentration Si-doped GaN layer, HCl gas is used as a carrier gas, SiH ₂ Cl ₂ gas (3000 ppm) is supplied at a flow rate of ₂ to 4 cc / min, and a partial pressure of 7.5 × 10 ⁻⁷ to 4 Si was doped into the GaN layer by HVPE method as × 10 ⁻⁶ atm. As a result, the impurity concentration of the high impurity concentration layer (Si doped layer) could be controlled to about 2 to 3 × 10 ¹⁸ cm ⁻³ or more. On the other hand, the impurity concentration of the low impurity concentration layer (undoped layer) is set to 0.5 to 1 × 10 ¹⁸ cm ⁻³ or less, and in practice, about 1 × 10 ¹⁶ cm ^{−3 to} 1 × 10 ¹⁷ cm ^−3. I was able to control it.

  At this time, the growth rate of the GaN layer by the HVPE method was set to 100 μm / h or less, and the vapor phase growth was continued until the GaN layer thickness (total thickness D) became 600 to 1500 μm. This is because peeling is less likely to occur when the GaN layer thickness (total thickness D) is less than 500 μm.

  After the GaN thick film was formed on the sapphire substrate by the above film formation, the inside of the vapor phase growth apparatus was cooled from 1040 ° C., and cracks were generated inside or near the interface of the high-concentration Si-doped GaN layer. The base substrate was peeled and removed using cracks generated by cooling.

  As variations of the sample, various film thicknesses of the Si-doped GaN layer 714 are set to 350 μm and the film thickness d of the undoped GaN layer 715 formed on the Si-doped GaN layer 714 can be varied by the above-described experimental sample manufacturing method. A sample having a total thickness D of a Ga thick film (thickness 350 μm of Si-doped GaN layer 714 + thickness d of undoped GaN layer 715) was produced.

  Then, the state of the upper peeled GaN layer was observed, the state of the lower GaN layer remaining on the sapphire substrate was observed, the thickness of the lower GaN layer was measured, and the degree of peeling was evaluated.

<Evaluation result of Experimental Example 4>
FIG. 12 is a graph showing a result of removing the sapphire substrate 711 from the sapphire / GaN structure according to Experimental Example 4. The horizontal axis indicates the total film thickness D (mm) of the Ga thick film. The vertical axis represents the remaining film thickness (mm) of the GaN layer remaining on the sapphire substrate 711 after the sapphire substrate is peeled off from the sapphire / GaN structure.

  As can be seen from the results of the above experimental examples, it can be seen that as the overall film thickness D (mm) of the Ga thick film increases, the remaining film thickness (mm) also tends to increase. It can also be seen that the layer where peeling occurs is inside the Si-doped GaN layer 714 or near the interface between the Si-doped GaN layer 714 and the undoped GaN layer 715.

  Moreover, although not shown in the drawing, the occurrence of cracks on the peeled surface of each sample peeled near the interface between the Si-doped GaN layer 714 and the undoped GaN layer 715 was suppressed. Further, the sapphire substrate 711 could be peeled and removed over the entire surface in the cooling process when the sample was taken out from the HVPE apparatus without applying any external force.

  That is, according to this experimental example, when a GaN thick film including a high-concentration Si-doped GaN layer 714 and an undoped GaN layer 715 is grown on a sapphire substrate 711 in order, and the obtained sapphire / GaN structure is cooled, Cracks occur in the high-concentration Si-doped GaN layer 714 or in the vicinity of the interface between the high-concentration Si-doped GaN layer 714 and the undoped GaN layer 715 thereon. As a result, the sapphire substrate can be peeled and removed at the location where the crack occurs without applying a particularly large external force. For this reason, a high-quality GaN free-standing substrate can be stably obtained.

  The present invention has been described based on experimental examples. This experimental example is merely an example, and it will be understood by those skilled in the art that various modifications are possible and that such modifications are within the scope of the present invention.

  For example, in the above experimental example, the thickness of the Si-doped GaN layer 714 is 350 μm, but the thickness of the Si-doped GaN layer 714 of the sapphire / GaN structure used in the present invention is not limited to this value.

  In the above experimental example, the sample was evaluated by setting the total film thickness of the GaN thick film in the range of 0.6 mm to 1.5 mm. However, the entire film of the GaN thick film of the sapphire / GaN structure used in the present invention was used. The thickness is not limited to this range. That is, the total thickness of the GaN thick film of the sapphire / GaN structure is not particularly limited and may exceed 1.5 mm.

FIG. 4 is a process cross-sectional view illustrating a method for manufacturing a GaN substrate according to Embodiment 1. 3 is a cross-sectional view showing a structure of a vapor phase growth apparatus used for manufacturing a GaN substrate according to Embodiments 1 and 2. FIG. 4 is a graph showing a growth temperature profile of a GaN layer in the method for manufacturing a GaN substrate according to Embodiments 1 and 2. 6 is a cross-sectional view schematically showing a configuration of a sapphire / GaN structure according to Embodiment 2. FIG. FIG. 6 is a process cross-sectional view illustrating a method for manufacturing a GaN substrate according to Embodiment 2. FIG. 6 is a process cross-sectional view illustrating a method for manufacturing a GaN substrate according to Embodiment 2. 6 is a cross-sectional view schematically showing a configuration of a sapphire / GaN structure according to Embodiment 3. FIG. It is process sectional drawing which shows the manufacturing method of the GaN substrate which concerns on Embodiment 3. It is a graph which shows the result of having peeled and removed the sapphire substrate from the sapphire / GaN structure used in Experimental Example 1 and the sapphire / GaN structure. It is a graph which shows the result of having peeled and removed the sapphire substrate from the sapphire / GaN structure used in Experimental Example 2 and the sapphire / GaN structure. It is a graph which shows the result of peeling and removing the sapphire substrate from the sapphire / GaN structure used in Experimental Example 3 and the sapphire / GaN structure. 10 is a graph showing a result of peeling off a sapphire substrate from a sapphire / GaN structure according to Experimental Example 4.

Explanation of symbols

101 sapphire substrate 103 low impurity concentration GaN layer 105 high concentration Si doping GaN layer 107 low impurity concentration GaN layer 109 HVPE-GaN thick film 111 exfoliation part 113 exfoliation direction 120 HVPE apparatus 121 reaction tube 122 growth region 123 substrate holder 124 gas supply tube 125 Gas supply pipe 126 Gas supply pipe 127 Ga raw material 128 Source boat 129 Heater 130 Heater 132 Rotating shaft 133 Wafer 135 Gas exhaust pipe 136 Shielding plate 137 Nitrogen raw material gas supply part 139 Group III raw material gas supply part 141 Sapphire substrate 142 Undoped GaN layer 143 undoped GaN layer 144 SiO ₂ mask 145 Si-doped GaN layer 146 crack 147 undoped GaN layer 711 sapphire substrate 712 the undoped GaN layer 713 SiO ₂ mask 7 4 Si-doped GaN layer 715 overall thickness of the film thickness D GaN thick film of undoped GaN layer d undoped GaN layer

Claims (7)

A first layer made of a group III nitride semiconductor containing an n-type impurity on an upper portion of the base substrate, and an upper portion of the first layer, the content of the n-type impurity being higher than that of the first layer; Forming a group III nitride semiconductor film comprising: a second layer comprising a low group III nitride semiconductor;
Cooling the base substrate and the group III nitride semiconductor film;
A self-supporting structure including at least a part of the group III nitride semiconductor film by separating and removing the structure including the base substrate in the first layer or in the vicinity of the interface between the first layer and the second layer. Obtaining a substrate;
A method for producing a group III nitride semiconductor free-standing substrate, comprising: In the manufacturing method of the group III nitride semiconductor free-standing substrate according to claim 1,
A method of manufacturing a group III nitride semiconductor self-supporting substrate, wherein the structure including the base substrate is separated and removed without applying an external force in the step of cooling the group III nitride semiconductor film. In the manufacturing method of the group III nitride semiconductor self-supporting substrate according to claim 1 or 2,
The method of manufacturing a group III nitride semiconductor free-standing substrate, wherein the n-type impurity is Si. In the manufacturing method of the group III nitride semiconductor free-standing substrate according to any one of claims 1 to 3,
The step of forming the group III nitride semiconductor film includes:
A method for producing a group III nitride semiconductor free-standing substrate, comprising a step of forming the group III nitride semiconductor film by a hydride vapor phase growth method.   A group III nitride semiconductor free-standing substrate obtained by the method for producing a group III nitride semiconductor free-standing substrate according to claim 1. a first layer made of a group III nitride semiconductor containing an n-type impurity;
A second layer made of a group III nitride semiconductor provided on one side of the first layer;
With
The first layer has a higher content of the n-type impurity than the second layer,
The group III nitride semiconductor free-standing substrate, wherein the first layer has an uneven surface. In the group III nitride semiconductor free-standing substrate according to claim 6,
A group III nitride semiconductor free-standing substrate, wherein the n-type impurity is Si.

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