JP2010215501A - Method for growing gallium nitride crystal, gallium nitride crystal substrate, method for producing epitaxial wafer, and epitaxial wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a gallium nitride crystal suppressing cracks generating upon processing for thinning, and allowing to grow a gallium nitride crystal with greater thickness; a gallium nitride crystal substrate, an epitaxial wafer, and a method for producing the epitaxial wafer. <P>SOLUTION: The method for growing a gallium nitride crystal to grow the gallium nitride crystal on a ground substrate by means of the hydride vapor phase epitaxy (HVPE) using a carrier gas, raw materials of gallium nitride and a gas including silicon as a dopant is characterized in that the carrier gas is purified by permeating the gas through a molecular membrane or an adsorbent during the growth of the gallium nitride crystal, and the dew point of the carrier gas during the growth of the gallium nitride crystal is -60°C or lower. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gallium nitride crystal growth method, a gallium nitride crystal substrate, an epiwafer manufacturing method, and an epiwafer.

  Gallium nitride (GaN) crystals are used as substrates for semiconductor devices such as light emitting diodes (LEDs) or laser diodes (LDs). Since a gallium nitride crystal having an energy band gap of 3.4 eV and high thermal conductivity can be provided with an electrode on the back surface thereof, the driving (operating) voltage of the semiconductor device can be reduced.

  As a method for manufacturing such a semiconductor device, for example, Japanese Patent Laying-Open No. 2005-251961 (Patent Document 1) describes the following method. First, an MOCVD (Metal Organic Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy) method, HVPE (Hydride Vapor Phase Epitaxy) is formed on the first main surface of the base substrate. A seed crystal layer made of a group III nitride crystal is grown by a vapor deposition method or the like. Thereafter, a group III nitride single crystal is grown on the seed crystal by a liquid phase growth method, and the base substrate is removed to manufacture a group III nitride single crystal wafer. Next, a semiconductor element is formed on the first main surface of the group III nitride single crystal wafer. Thereafter, for the purpose of improving the heat dissipation characteristics, the second main surface of the group III nitride single crystal wafer is subjected to removal processing by grinding, polishing, or the like, thereby thinning the wafer.

Further, for example, Japanese Patent Application Laid-Open No. 11-68156 (Patent Document 2) discloses that a group III nitride semiconductor layer is grown on a substrate by MOCVD. In this growth, an n-type GaN layer doped with silicon (Si) having a thickness of 0.2 μm using Si ₂ H ₆ (disilane) as a carrier gas with purified hydrogen gas having a dew point of −90 ° C. It is described that it has been grown.

JP 2005-251961 A JP-A-11-68156

  However, when the processing for thinning the second main surface of the group III nitride single crystal wafer as in Patent Document 1 is performed, cracks are caused due to impurities incorporated during crystal growth. There was a problem that occurred.

  Moreover, in the said patent document 2, since each layer was grown by MOCVD method, there existed a problem that the thickness of the layer to grow could not be enlarged.

  Therefore, the present invention provides a method for growing a gallium nitride crystal, a gallium nitride crystal growth method capable of suppressing a crack generated when processing for thinning and growing a gallium nitride crystal having a large thickness, It is to provide an epi-wafer and a method for manufacturing the epi-wafer.

As a result of diligent research, the present inventor has found that when a gallium nitride crystal is grown using silicon as a dopant by an HVPE method suitable for thickening, the cause of cracks is caused by oxygen in the carrier gas. It was. The reason for this is that silicon has a property of being easily oxidized. Therefore, if O (oxygen) is contained in the carrier gas, oxygen and silicon in the carrier gas are silicon dioxide (SiO ₂ ) or the like. Reacts to silicon oxide. When silicon oxide is incorporated into a GaN crystal, the silicon oxide does not function as an n-type impurity but becomes an impurity. As a result, the gallium nitride crystal becomes hard and brittle, and it is considered that cracking occurs when processing for thinning the gallium nitride crystal is performed.

The present inventor has also found that the generation of cracks by oxygen in the carrier gas is a problem specific to the HVPE method, and this problem does not occur in the MOCVD method. The reason is that an organic metal is used as a source gas in the growth of a gallium nitride crystal by the MOCVD method. Therefore, oxygen in the carrier gas reacts with carbon (C) in the organic metal before reacting with silicon, and as a carbon monoxide (CO) gas or carbon dioxide (CO ₂ ) gas, outside the reactor. Discharged. Furthermore, even if silicon oxide is taken in, cracks are unlikely to occur because the thickness of the gallium nitride crystal to be grown is as thin as several μm. Therefore, in Patent Document 2, since the crystal is grown by the MOCVD method, there is no problem that a crack is generated when a gallium nitride crystal is grown using silicon as a dopant. Therefore, even if a carrier gas having a low dew point is used, there is no effect of suppressing the generation of silicon oxide.

  Based on these findings, the present inventor has intensively studied to suppress the generation of cracks when a gallium nitride crystal is grown using silicon as a dopant in the HVPE method. It has been found that if the dew point is −60 ° C. or lower, the occurrence of the cracks can be suppressed. Therefore, the method for growing a gallium nitride crystal according to the present invention uses a carrier gas, a gallium nitride raw material, and a gas containing silicon as a dopant to gallium nitride on a base substrate by a hydride vapor phase epitaxy (HVPE) method. This is a method for growing a gallium nitride crystal to grow a crystal. The carrier gas has a dew point of −60 ° C. or lower during the growth of the gallium nitride crystal.

  According to the gallium nitride crystal growth method of the present invention, since the HVPE method, which has a higher growth rate than the MOCVD method, is used, a thick gallium nitride crystal can be easily grown. Moreover, since the carrier gas of -60 degrees C or less is used, the oxygen in carrier gas is reduced by fully reducing the water | moisture content in carrier gas. Thereby, since it can suppress that oxygen reacts with silicon and produces | generates a silicon oxide, it can suppress that silicon is taken in as a silicon oxide in the gallium nitride crystal to grow. Therefore, it is possible to suppress the gallium nitride crystal to be grown from becoming hard and brittle, so that the generation of cracks can be suppressed when the gallium nitride crystal is thinned.

  Here, the “dew point” in the present invention means a value measured by a specular cooling type dew point meter.

  In the gallium nitride crystal growth method, the partial pressure of the carrier gas during the growth of the gallium nitride crystal is preferably 0.56 atm or more and 0.92 atm or less.

  By setting the carrier gas partial pressure to 0.56 atm or more, the gallium nitride raw material can be supplied uniformly to the base substrate, and the reaction of silicon to silicon oxide by oxygen contained in the raw material gas can be suppressed. On the other hand, by setting it to 0.92 atm or less, the gallium nitride raw material can be sufficiently supplied to the base substrate.

  The gallium nitride crystal substrate of the present invention is obtained by the above-described gallium nitride crystal growth method. The gallium nitride crystal substrate includes the base substrate and a gallium nitride crystal formed on the base substrate.

  The gallium nitride crystal substrate of the present invention includes a base substrate and a gallium nitride crystal formed on the base substrate and suppressed from taking in silicon as silicon oxide. Therefore, it is possible to suppress cracks that occur when processing for thinning the gallium nitride crystal. Further, a gallium nitride crystal having a large thickness can be obtained.

  In the method for manufacturing an epi-wafer of the present invention, the following steps are performed. First, a gallium nitride crystal is grown on a base substrate by the above-described gallium nitride crystal growth method. Then, at least the base substrate is removed to form a substrate made of gallium nitride crystal. Then, an epitaxial growth layer is formed on the substrate. Then, the surface of the substrate opposite to the surface on which the epitaxial growth layer is formed is processed for thinning.

  According to the epi-wafer manufacturing method of the present invention, the substrate processed for thinning is made of gallium nitride crystal in which silicon is prevented from being taken in as silicon oxide. Therefore, an epi-wafer in which generation of cracks is suppressed when the substrate is thinned is obtained.

  The epi-wafer of the present invention is manufactured by the above-described epi-wafer manufacturing method, and includes a substrate and an epitaxial growth layer formed on the substrate.

  According to the epi-wafer of the present invention, since the substrate made of gallium nitride crystals suppressed from being taken in as silicon oxide is provided, the generation of cracks is suppressed.

  According to the gallium nitride crystal growth method, gallium nitride crystal substrate, epi-wafer manufacturing method and epi-wafer of the present invention, since the dew point of the carrier gas used for growing the gallium nitride crystal is -60 ° C. or lower, the film thickness can be reduced. Thus, it is possible to suppress the cracks generated when processing is performed and grow a gallium nitride crystal having a large thickness.

It is the schematic which shows the HVPE apparatus used for the growth method of the gallium nitride crystal in Embodiment 1 of this invention. It is a flowchart which shows the growth method of the gallium nitride crystal in Embodiment 1 of this invention. It is the schematic which shows the gallium nitride crystal substrate in Embodiment 1 of this invention. 6 is a flowchart showing a method for manufacturing an epi-wafer in the second embodiment. FIG. 6 is a schematic diagram showing a substrate in a second embodiment. 5 is a schematic diagram showing an epi-wafer in a second embodiment. FIG. It is a schematic diagram which shows the gallium nitride crystal substrate in an Example. It is a figure which shows the relationship between the dew point of the carrier gas in an Example, and a crack generation rate. It is a figure which shows the relationship between the partial pressure of the carrier gas in an Example, and a crack generation rate. It is a figure which shows the relationship between the dew point of carrier gas, and the raise value of operating voltage.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
A method for growing a gallium nitride crystal according to an embodiment of the present invention will be described. The method for growing a gallium nitride crystal in this embodiment uses a carrier gas, a gallium nitride raw material, and a gas containing silicon as a dopant, and gallium nitride on a base substrate by a hydride vapor phase epitaxy (HVPE) method. Grow crystals.

  FIG. 1 is a schematic diagram showing an HVPE apparatus used in a gallium nitride crystal growth method according to an embodiment of the present invention. First, an HVPE apparatus 100 used in the gallium nitride crystal growth method in the present embodiment will be described with reference to FIG. As shown in FIG. 1, the HVPE apparatus 100 includes a first source gas cylinder 101, a second source gas cylinder 102, a first carrier gas cylinder 103, a second carrier gas cylinder 104, a first gas introduction pipe 105, Gas introduction pipe 106, source boat 107, susceptor 108, heater 109, crystal growth vessel 110, exhaust pipe 111, local heating mechanism (not shown), doping gas cylinder 112, and doping gas introduction pipe 113 And. The HVPE apparatus 100 is a horizontal reactor, for example.

  The crystal growth vessel 110 is a vessel for holding a base substrate 11 inside and growing a gallium nitride crystal on the base substrate 11. The first source gas cylinder 101, the second source gas cylinder 102, and the source boat 107 are each supplied with a source containing an element constituting a gallium nitride crystal to be grown. The doping gas cylinder 112 is filled with a gas containing silicon as a dopant. Each of the first gas introduction pipe 105, the second gas introduction pipe 106, and the doping gas introduction pipe 113 includes the first and second source gases G1, G2, the first and second carrier gases G3, G4, and the doping gas G12. In order to introduce each from the outside to the inside of the crystal growth vessel 110, the crystal growth vessel 110 is provided. The source boat 107 accommodates and holds a metal raw material of gallium nitride and is disposed below the second gas introduction pipe 106. In the source boat 107, the second source gas G2 supplied from the second gas introduction pipe 106 is reacted with the metal source to generate a reaction gas G7. The first gas introduction pipe 105, the second gas introduction pipe 106, and the doping gas introduction pipe 113 are configured so that the reaction gas G7, the first source gas G1, and the doping gas G12 can be supplied to the surface of the base substrate 11.

  The susceptor 108 holds the base substrate 11. The susceptor 108 is disposed so that the surface on which the base substrate 11 is held by the susceptor 108 in the crystal growth vessel 110 is positioned below the first gas and second gas introduction pipes 105 and 106 and the doping gas introduction pipe 113. ing. The susceptor 108 is disposed horizontally inside the crystal growth vessel 110. The local heating mechanism is a heating member such as a resistance heater of the base substrate 11 and is embedded in the susceptor 108, for example.

  The heater 109 has the ability to heat the inside of the crystal growth vessel 110 as a whole to, for example, 700 ° C. or more and 1500 ° C. or less, and is disposed outside the crystal growth vessel 110. The exhaust pipe 111 is provided in the crystal growth vessel 110 in order to discharge the reacted gas to the outside of the crystal growth vessel 110.

  The HVPE apparatus 100 shown in FIG. 1 is configured to supply the carrier gas of the first and second carrier gas cylinders 103 and 104 to the inside through the first gas and the second gas introduction pipes 105 and 106. It is not limited to this. For example, one carrier gas cylinder may be prepared, and an inlet for supplying the carrier gas cylinder to the inside may be provided in the crystal growth vessel 110 separately from the first gas and the second gas introduction pipes 105 and 106. In this case, the HVPE apparatus 100 transports the first source gas G1, the second source gas G2, the reaction gas G7, and the doping gas to the base substrate 11 by supplying the carrier gas from the inlet to the base substrate 11. It is the structure that can be done. Further, although the doping gas cylinder 112 is disposed in the doping gas introduction pipe 113, a configuration in which a doping gas and a carrier gas are supplied may be employed.

  FIG. 2 is a flowchart showing a gallium nitride crystal growth method according to Embodiment 1 of the present invention. Next, a method for growing a gallium nitride crystal in the present embodiment will be described with reference to FIG.

As shown in FIG. 1, first, a carrier gas is prepared (step S1). The carrier gas is a gas for transporting the source gas to the base substrate 11. Although the carrier gas is not particularly limited, but is less reactive gas of the source gas, and for example, hydrogen (H ₂₎ gas, nitrogen (N ₂₎ gas, and such as argon (Ar) inert gas such as gas . Such a commercially available gas is prepared as a carrier gas, for example.

  Next, it refine | purifies so that the dew point of the prepared carrier gas may be -60 degrees C or less (step S2). By passing the prepared carrier gas through, for example, a molecular film or an adsorbent, water as an impurity is removed. Thereby, the dew point of the prepared carrier gas is purified to −60 ° C. or lower.

  The dew point of the carrier gas is −60 ° C. or lower, preferably −80 ° C. or lower, more preferably −90 ° C. or lower. By making it -60 degrees C or less, the production | generation of the silicon oxide formed by the silicon | silicone as a dopant reacting with oxygen in carrier gas can be prevented. By making it -80 degrees C or less, the reaction to the silicon oxide of silicon can be prevented more. By setting the temperature to −90 ° C. or lower, the reaction of silicon to silicon oxide can be further prevented. From the viewpoint of refining feasibility, the dew point of the carrier gas is, for example, −100 ° C. or higher.

  In the present embodiment, when purifying the carrier gas, the dew point of the carrier gas is controlled using a mirror-cooled dew point meter so that the dew point of the carrier gas is −60 ° C. or lower. Here, the mirror cooling type means a system in which a small mirror is provided in the carrier gas flow path, and the temperature of the mirror is raised or lowered to monitor whether the mirror is fogged. If the mirror starts to cloud when the temperature of the mirror reaches −60 ° C., it is determined that the dew point of the carrier gas has reached −60 ° C. When the dew point is −60 ° C., the water contained in the carrier gas is 0.0011%.

  Next, the base substrate 11 is prepared (step S3). The base substrate 11 is a substrate for growing a gallium nitride crystal thereon. The base substrate 11 is made of, for example, silicon, sapphire, silicon carbide, gallium nitride, aluminum nitride, or the like. In order to grow a good crystalline gallium nitride crystal with no difference in lattice constant, the base substrate 11 is preferably made of gallium nitride.

  Next, a gallium nitride crystal is grown on the base substrate 11 by the HVPE method using a carrier gas having a dew point of −60 ° C. or less, a gallium nitride raw material, and a gas containing silicon as a dopant (step S4). .

Specifically, as shown in FIG. 1, first, a first source gas cylinder 101 and a second source gas cylinder 102 filled with a first source gas and a second source gas, respectively, are prepared. Further, a metal raw material is supplied to the source boat 107. The first source gas, the second source gas, and the metal source are materials for growing gallium nitride crystals. For example, ammonia (NH ₃ ) gas can be used as the first source gas, hydrogen chloride (HCl) gas can be used as the second source gas, and gallium (Ga) can be used as the metal source supplied to the source boat 107.

Further, a doping gas cylinder 112 filled with a doping gas containing silicon is prepared. As doping gas containing silicon, silane (SiH ₄ ), disilane (Si ₂ H ₆ ), chlorosilane (SiHCl ₃ ), dichlorosilane (SiH ₂ Cl ₂ ), monochlorosilane (SiH ₃ Cl), tetrachlorosilane (SiCl ₄ ) Silane compounds such as can be used. The dew points of the first and second source gases G1, G2 and the doping gas G12 that are source gases are preferably low.

  Thereafter, the source boat 107 is heated. Then, the second source gas G2 supplied from the second gas introduction pipe 106 is reacted with the source material of the source boat 107 to generate a reaction gas G7. The first source gas G1, the reaction gas G7, and the doping gas G12 supplied from the first gas introduction pipe 105 are caused to flow so as to contact the surface of the base substrate 11 with the first and second carrier gases G3 and G4. React (provide).

  At this time, the heater 109 is used to heat the inside of the HVPE apparatus 100 to a temperature at which the gallium nitride crystal grows at an appropriate rate (for example, 700 ° C. or more and 1500 ° C. or less). Further, the reacted gas is discharged from the exhaust pipe 111 to the outside.

  Here, the partial pressure of the carrier gas (the sum of the partial pressure of the first carrier gas G3 and the partial pressure of the second carrier gas G4 in this embodiment) during the growth of the gallium nitride crystal is 0.56 atm or more and 0.00. It is preferably 92 atm or less, and more preferably 0.67 atm or more and 0.89 atm or less. By setting the carrier gas partial pressure to 0.56 atm or more, the gallium nitride raw material (first raw material gas G1 and reactive gas G7 in this embodiment) can be uniformly supplied to the base substrate 11. Further, the reaction of silicon to silicon oxide due to oxygen contained in the source gas can be suppressed. By setting the partial pressure of the carrier gas to 0.67 atm or more, the gallium nitride raw material can be supplied uniformly from the base substrate 11, and the reaction from silicon in the doping gas to silicon oxide can be further suppressed. On the other hand, by setting it to 0.92 atm or less, the source gas can be sufficiently supplied to the base substrate 11. By setting it to 0.89 atm or less, the source gas can be sufficiently supplied to the base substrate 11. The total pressure (total pressure) of the partial pressure of the carrier gas and the partial pressure of the source gas is 1 atm.

  By adjusting the flow rate of the first raw material gas G1, the flow rate of the second raw material gas G2, or the amount of the raw material in the source boat 107, the thickness of the gallium nitride crystal to be grown can be appropriately changed. The gallium nitride crystal is preferably grown to have a thickness of, for example, 200 μm or more. Since the HVPE method has a high crystal growth rate, a crystal having a large thickness can be grown by controlling the growth time. By setting the thickness to 200 μm or more, a gallium nitride crystal that can be used alone as a substrate for various semiconductor devices can be easily obtained.

  FIG. 3 is a schematic view showing the gallium nitride crystal substrate in the first embodiment of the present invention. As shown in FIG. 3, by performing the above-described method for growing a gallium nitride crystal, a nitridation comprising a base substrate 11 and a gallium nitride crystal 12 formed on the base substrate 11 and incorporating silicon as a dopant. A gallium crystal substrate 10 is obtained.

  As described above, the gallium nitride crystal growth method according to the present embodiment is nitrided on the base substrate 11 by the HVPE method using a carrier gas, a gallium nitride raw material, and a gas containing silicon as a dopant. A method for growing a gallium nitride crystal 12 for growing a gallium crystal 12, wherein the dew point of the carrier gas during the growth of the gallium nitride crystal 12 is −60 ° C. or lower.

  According to the GaN crystal growth method of the present invention, since the HVPE method, which has a higher growth rate than the MOCVD method, is used, the thick gallium nitride crystal 12 can be easily grown. Moreover, since the carrier gas of -60 degrees C or less is used, the oxygen in carrier gas is reduced by fully reducing the water | moisture content in carrier gas. Thereby, it can be suppressed that silicon as a dopant is taken in as silicon oxide in the gallium nitride crystal 12 to be grown. Therefore, it is possible to prevent the gallium nitride crystal 12 to be grown from becoming hard and brittle, so that the generation of cracks can be suppressed when the gallium nitride crystal is thinned.

  Here, silicon oxide formed by reaction of silicon with oxygen has a function as a mask. Therefore, when silicon oxide can be suppressed from being taken into the gallium nitride crystal, inhibition of the growth of the gallium nitride crystal by the silicon oxide having a function as a mask can be suppressed. Therefore, according to the gallium nitride crystal growth method of the present embodiment, it is possible to grow gallium nitride crystal 12 having better crystallinity and a larger thickness.

  Moreover, since it can suppress that an insulating silicon oxide is taken in, the electroconductivity of the gallium nitride crystal 12 obtained can be improved. In particular, when processing for thinning (processing for thinning such as polishing or grinding is performed on one main surface of the substrate from which at least the base substrate 11 has been removed from the gallium nitride crystal substrate 10), silicon oxide is formed on the surface. An object can be prevented from being exposed. Therefore, when the electrode is formed on the surface, it is possible to suppress the deterioration of the contact property between the electrode and the GaN crystal, and when used as a semiconductor device, the increase in operating voltage can be reduced.

  Furthermore, since silicon as a dopant is taken into the gallium nitride crystal 12 without reacting with oxygen in the carrier gas, silicon can be efficiently doped into the gallium nitride crystal 12. Therefore, the gallium nitride crystal 12 that improves the carrier concentration is obtained.

(Embodiment 2)
FIG. 4 is a flowchart showing an epi-wafer manufacturing method in the second embodiment. FIG. 5 is a schematic diagram showing a substrate in the second embodiment. FIG. 6 is a schematic diagram showing an epi-wafer in the second embodiment. With reference to FIGS. 4-6, the manufacturing method of the epi wafer in this Embodiment is demonstrated.

  First, the gallium nitride crystal 12 is grown on the base substrate 11 by the gallium nitride crystal growth method in the first embodiment (S1 to S4). Thereby, the gallium nitride crystal substrate 10 shown in FIG. 3 is obtained.

  Next, as shown in FIGS. 4 and 5, at least the base substrate 11 is removed from the gallium nitride crystal substrate 10 to form a substrate 20 made of the gallium nitride crystal 12 (step S5). The crystallinity in the vicinity of the interface between the gallium nitride crystal 12 and the base substrate 11 is often not good. Therefore, it is preferable to further remove from the gallium nitride crystal substrate 10 a portion having poor crystallinity in the gallium nitride crystal 12. Thereby, as shown in FIG. 5, the board | substrate 20 which has the main surfaces 20a and 20b is obtained.

  As a removing method, for example, a method such as cutting or grinding can be used. The cutting means that at least the base substrate 11 is mechanically divided (sliced) from the gallium nitride crystal substrate 10 with a slicer or a wire saw having an outer peripheral edge of an electrodeposited diamond wheel. Grinding means that at least the base substrate 11 is mechanically removed by a grinding facility having a diamond grindstone.

  Further, the surface removed from the gallium nitride crystal substrate 10 is not limited to a surface parallel to the surface of the gallium nitride crystal 12 described above, and for example, a surface having an arbitrary inclination with respect to the surface may be sliced.

  Further, the main surfaces 20a and 20b of the substrate 20 may be further polished. The method for polishing is not particularly limited, and any method can be adopted.

  Next, as shown in FIG. 6, an epitaxial growth layer 31 is formed on the substrate 20 (step S6). In the present embodiment, epitaxial growth layer 31 is formed on one main surface 20a of substrate 20. The epitaxial growth layer 31 is preferably epitaxially grown on the substrate 20 using a carrier gas having a dew point of −60 ° C. or less. Further, it is preferable that the epitaxial growth layer 31 is formed by epitaxial growth by the HVPE method. The epitaxial growth layer 31 may be a plurality of layers.

  Next, the main surface 20b opposite to the main surface 20a on which the epitaxial growth layer 31 is formed in the substrate 20 is processed for thinning (step S7). As a method of processing for thinning, for example, a method such as cutting or grinding can be used. Since this method is the same as the method used when removing at least the base substrate 11 (step S6), the description thereof will not be repeated.

  Thus, by performing the epiwafer manufacturing method, as shown in FIG. 6, an epiwafer 30 including the substrate 20 and the epitaxial growth layer 31 formed on the substrate 20 can be manufactured. The epi-wafer 30 thus obtained can be used as a semiconductor device by further forming electrodes and the like.

  As described above, the manufacturing method of the epi-wafer 30 in the present embodiment includes the step of processing the main surface 20b on the opposite side of the main surface 20a on which the epitaxial growth layer 31 is formed on the substrate 20 for thinning. I have.

  According to the manufacturing method of epi-wafer 30 in the present embodiment, when main surface 20b is processed in order to make substrate 20 thin, substrate 20 is suppressed from being taken in as silicon oxide. Brittleness is suppressed. Therefore, an epi-wafer in which generation of cracks is suppressed when the main surface 20b is processed is obtained.

  Moreover, since it can suppress that a silicon oxide is exposed to the main surface 20b by the process for thinning the board | substrate 20, it can prevent that the contact at the time of forming an electrode on the main surface 20b deteriorates. In addition, since it is possible to prevent deterioration in conductivity when a voltage is applied, an increase in operating voltage can be suppressed.

[Example]
In this example, the effect of growing a gallium nitride crystal using a carrier gas having a dew point of −60 ° C. or less was examined. Specifically, each epi-wafer of Examples 1 to 15 and Comparative Examples 1 to 3 was manufactured, and the crack generation rate and the operating voltage increase value were measured.

(Examples 1 to 15)
In Examples 1 to 15, epiwafers were manufactured according to the epiwafer manufacturing method in Embodiment 2 of the present invention. Specifically, first, carrier gases of the types shown in Table 1 were prepared (Step S1). Next, it refine | purified so that the dew point of the prepared carrier gas might become the dew point of Table 1 (step S2). The prepared carrier gas was allowed to permeate the molecular film so that the dew point in Table 1 was obtained.

Next, a base substrate made of 2-inch sapphire was prepared (step S3). A mask made of SiO ₂ was formed in stripes in the <1-100> direction by photolithography on the (0001) plane of the base substrate. The width of the mask was 5 μm, and the distance between adjacent masks was 5 μm.

  Next, with the HVPE apparatus 100 shown in FIG. 1, a carrier gas having a dew point of −60 ° C. or less, hydrogen chloride gas, ammonia gas and gallium as raw materials for gallium nitride, and dichlorosilane as a gas containing silicon as a dopant. Then, a gallium nitride crystal was grown on the base substrate by the HVPE method (step S4).

Specifically, ammonia gas was prepared as the first source gas G1, and hydrogen chloride gas was prepared as the second source gas G2. Thereafter, gallium was supplied to the source boat 107 to heat the source boat 107. Then, the hydrogen chloride gas supplied from the second gas introduction pipe 106 and the gallium in the source boat 107 were reacted as Ga + HCl → GaCl + 1 / 2H ₂ to generate GaCl (gallium chloride) gas as the reaction gas G7. .

Then, an ammonia gas and a gallium chloride gas supplied from the first gas introduction pipe 105 are caused to flow so as to hit the surface of the base substrate 11 on which the gallium nitride crystal is grown, and GaCl + NH ₃ → GaN + HCl + H ₂ on the surface. To react. As shown in FIG. 7, a buffer layer made of gallium nitride having a thickness of 30 mm was grown on the base substrate 11. FIG. 7 is a schematic view showing a gallium nitride crystal substrate in the example.

  In order to grow the buffer layer, the carrier gas partial pressure was 0.899 atm, the HCl gas partial pressure was 0.001 atm, and the ammonia gas partial pressure was 0.1 atm. The inside of the crystal growth vessel 110 was heated by the heater 109 so that the temperature was 500 ° C. The growth time of the buffer layer 13 was 0.5 hour.

  Thereafter, the partial pressures of the carrier gas, hydrogen chloride gas, and ammonia gas were respectively supplied to the base substrate 11 as shown in Table 1. Further, the heater 109 was heated so that the temperature inside the crystal growth vessel 110 was 1050 ° C. The growth time of the gallium nitride crystal 12 was 80 hours. As a result, a gallium nitride crystal 12 having the thickness shown in Table 1 was grown on the buffer layer 13. Thus, a gallium nitride crystal substrate including the base substrate 11 shown in FIG. 7, the buffer layer 13 grown on the base substrate 11, and the gallium nitride crystal 12 grown on the buffer layer 13 was obtained.

  Here, carrier concentration and dislocation density were measured for the gallium nitride crystal 12 of the obtained gallium nitride crystal substrate. The results are shown in Table 2. The carrier (silicon) concentration was measured using a Hall measuring device. The dislocation density was measured by the following method. The surface of the gallium nitride crystal 12 was etched with a KOH-NaOH (potassium hydroxide-sodium hydroxide) mixed melt at 350 degrees Celsius. Etch pits appeared at positions corresponding to dislocations on the etched surface, and the number of etch pits was counted to evaluate the dislocation density.

  Next, by polishing, the base substrate 11 and the buffer layer 13 were removed from the obtained gallium nitride crystal substrate to form a substrate made of the gallium nitride crystal 12 (step S5).

  Here, the rate of occurrence of cracks that occurred when the substrate made of the gallium nitride crystal 12 was formed was measured. The results are shown in Table 2. The method for measuring the crack occurrence rate is to observe using a 20 times objective lens of a differential interference optical microscope. There are 30 or more cracks with a length of 100 μm or more on the entire surface of a 2 inch substrate excluding the outer periphery of 5 mm. If there was a crack. The ratio of the number of cracks to the number of samples was defined as the crack occurrence rate.

Next, an n-type GaN layer having a thickness of 5 μm, an In _0.2 Ga _0.8 N layer having a thickness of 3 nm, an Al _0.2 Ga _0.8 N layer having a thickness of 60 nm, and a thickness are formed on the substrate by MOCVD. A 150 nm p-type GaN layer was sequentially grown.

Next, the surface of the substrate opposite to the surface on which the epitaxial growth layer was formed was processed for thinning (step S7). In this example, as processing for thinning, after the surface of the p-type GaN layer was bonded to a polishing holder, a slurry containing SiC abrasive grains having an average grain size of 30 μm was used to obtain the thickness of the substrate. Polishing was performed until the thickness became 100 μm. Thus, an epi-wafer comprising a substrate made of gallium nitride crystal and an n-type GaN layer, an In _0.2 Ga _0.8 N layer, an Al _0.2 Ga _0.8 N layer and a p-type GaN layer as an epitaxial growth layer formed on the substrate. Manufactured.

  Here, the crack generation rate was measured about the epitaxial wafer after the process for film thickness reduction. The results are shown in Table 2. The crack occurrence rate shown in Table 2 indicates the total value of the crack occurrence rate for removing the base substrate 11 and the buffer layer 13 and the crack occurrence rate after processing for thinning. Further, the crack generation rate after processing for thinning was measured in the same manner as the crack generation rate for removing the base substrate 11 and the buffer layer 13.

  Next, an n-type electrode having a thickness of 100 nm in which gold and nickel were laminated was formed on the surface of the substrate opposite to the surface on which the epitaxial growth layer was formed. Further, a 100-nm-thick p-type electrode in which gold and nickel were stacked was formed on the epitaxial growth layer (p-type GaN layer). Thereby, the semiconductor device in Examples 1-15 was manufactured.

  Here, the operating voltage of the obtained semiconductor devices in Examples 1 to 15 and the operating voltage when 50 hours passed at a temperature of 100 ° C. were measured. Then, the value obtained by subtracting the first operating voltage from the operating voltage after 50 hours was defined as the increased operating voltage (ΔVop). The results are shown in Table 2.

(Comparative Examples 1-3)
The epiwafers of Comparative Examples 1 to 3 basically have the same configuration as the epiwafer manufacturing method of Examples 1 to 15, but differ in that the dew point of the carrier gas is higher than those of Examples 1 to 15.

  Specifically, the types and dew point carrier gases listed in Table 1 were prepared for the epiwafers of Comparative Examples 1 to 3. Next, the same base substrate as in Examples 1 to 15 was prepared, and a buffer layer was grown under the same conditions as in Examples 1 to 15 except that a carrier gas having a dew point shown in Table 1 was used. Next, gallium nitride crystals doped with silicon were grown using carrier gas, hydrogen chloride gas, and ammonia gas having a dew point exceeding −60 ° C. under the partial pressures shown in Table 1, respectively. Thereby, the gallium nitride crystal substrate provided with the gallium nitride crystal in Comparative Examples 1 to 3 was obtained.

  Next, similarly to Examples 1 to 15, the base substrate and the buffer layer were removed to manufacture a substrate. Then, the epitaxial growth layer was grown on this board | substrate like Examples 1-15. Next, the surface of the substrate opposite to the surface on which the epitaxial growth layer was formed was processed for thinning, as in Examples 1-15. Thereby, the epiwafer in Comparative Examples 1-3 was manufactured.

  Next, an n-type electrode and a p-type electrode were formed in the same manner as in Examples 1 to 15, and semiconductor devices in Comparative Examples 1 to 3 were manufactured.

  For Comparative Examples 1 to 3, as in Examples 1 to 15, the crack generation rate, carrier concentration and dislocation density of the gallium nitride crystal, crack generation rate of the epiwafer, and operating voltage of the semiconductor device were measured. The results are shown in Table 2.

(Reference Examples 1-3)
The epi-wafers of Reference Examples 1 to 3 basically have the same configuration as the epi-wafer manufacturing method of Examples 1 to 15, except that oxygen is not used as a dopant and the dew point of the carrier gas. Is different in that it is expensive.

  Specifically, the epiwafers of Reference Examples 1 to 3 were prepared with carrier gases having the types and dew points listed in Table 1. Next, the same base substrate as in Examples 1 to 15 was prepared, and the same as in Examples 1 to 15 except that the carrier gas having the dew point shown in Table 1 and oxygen gas were used as the doping gas. The buffer layer was grown under the conditions of: Next, gallium nitride crystals doped with oxygen were grown by using carrier gas, HCl gas, and ammonia gas having a dew point exceeding −60 ° C. at partial pressures shown in Table 1, respectively. Thereby, the gallium nitride crystal substrate provided with the gallium nitride crystal in Reference Examples 1 to 3 was obtained.

  Next, similarly to Examples 1 to 15, the base substrate and the buffer layer were removed to manufacture a substrate. Then, the epitaxial growth layer was grown on this board | substrate like Examples 1-15. Next, as in Examples 1 to 15, the surface opposite to the surface on which the epitaxial growth layer was formed on the substrate was processed for thinning. Thereby, the epiwafers in Reference Examples 1 to 3 were manufactured.

  Next, an n-type electrode and a p-type electrode were formed in the same manner as in Examples 1 to 15, and semiconductor devices in Reference Examples 1 to 3 were manufactured.

  For Reference Examples 1 to 3, as in Examples 1 to 15, the crack generation rate, carrier concentration and dislocation density of the gallium nitride crystal, crack generation rate of the epiwafer, and the operating voltage of the semiconductor device were measured. The results are shown in Table 2.

(Measurement result)
FIG. 8 is a diagram showing the relationship between the dew point of the carrier gas and the crack generation rate in this example. As shown in FIG. 8 and Table 2, in Examples 1 to 15 having a dew point of −60 ° C. or less, the crack occurrence rate after processing for thinning (Step S7) is higher than that in Comparative Examples 1 to 3. It was made lower than 15%. In particular, by setting the dew point of the carrier gas to −80 ° C. or less, the crack occurrence rate of the gallium nitride crystal can be reduced to 6% or less, and the crack occurrence rate after processing for thinning can be reduced to 9% or less. .

  FIG. 9 is a diagram showing the relationship between the partial pressure of the carrier gas and the crack occurrence rate in this example. As shown in FIG. 9 and Table 2, by making the partial pressure of the carrier gas 0.92 atm or less, the crack occurrence rate of the gallium nitride crystal is 6%, and the crack occurrence rate after processing for thinning is performed. Was reduced to 9%.

  FIG. 10 is a diagram showing the relationship between the dew point of the carrier gas and the increase value of the operating voltage in this example. As shown in FIG. 10 and Table 2, Examples 1 to 15 in which the dew point of the carrier gas was −60 ° C. or less were able to be 0.36 V or less where the increase value of the operating voltage was lower than those of Comparative Examples 1 to 3.

  As shown in Table 2, the crack generation rate could be reduced for Examples 1 to 15 in which the dew point of the carrier gas was −60 ° C. or lower regardless of the type of the carrier gas.

  Furthermore, in Examples 1 to 15, gallium nitride was grown by the HVPE method, so that the film thickness could be increased.

  Furthermore, as shown in Table 2, the carrier concentrations of Examples 1 to 15 were higher than those of Comparative Examples 1 to 3. From this, it can be seen that the reaction of silicon with silicon oxide is suppressed and the silicon is taken into the gallium nitride crystal as a carrier. Moreover, in Examples 1-15, the low dislocation density was able to be maintained.

  Here, according to Reference Examples 1 to 3 shown in Table 2, when oxygen is used as the dopant, the occurrence of cracks can be suppressed without depending on the temperature, even when the dew point of the carrier gas is high. It was. From this, it was found that when oxygen is used as a dopant, it is not incorporated as an impurity in the gallium nitride crystal to be grown, and therefore does not have the problem of the present invention when silicon is used as the dopant. Note that when silicon is used as the dopant, there is an advantage that it is easily taken into the c-plane ({0001} plane) as compared with the case where oxygen is used.

  As mentioned above, according to the present Example, it has confirmed that the crack which generate | occur | produces at the time of the process for thinning can be suppressed by making the dew point of carrier gas into -60 degrees C or less.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

  The gallium nitride crystal obtained by the method for growing a gallium nitride crystal according to the present invention can suppress the generation of cracks when processing for thinning and grow a thick gallium nitride. Therefore, gallium nitride crystals are used in light emitting elements such as light emitting diodes and laser diodes, electronic devices such as rectifiers, bipolar transistors, field effect transistors, and HEMTs, temperature sensors, pressure sensors, radiation sensors, and visible-ultraviolet light detectors. It can be suitably used for semiconductor sensors, SAW devices, and the like.

  DESCRIPTION OF SYMBOLS 10 Gallium nitride crystal substrate, 11 Ground substrate, 12 Gallium nitride crystal, 13 Buffer layer, 20 Substrate, 20a, 20b Main surface, 30 Epi wafer, 31 Epitaxial growth layer, 100 HVPE apparatus, 101 1st source gas cylinder, 102 2nd source gas cylinder 103 First carrier gas cylinder, 104 Second carrier gas cylinder, 105 First gas introduction pipe, 106 Second gas introduction pipe, 107 Source boat, 108 Susceptor, 109 Heater, 110 Crystal growth vessel, 111 Exhaust pipe, 112 Doping gas cylinder, 113 doping gas introduction pipe, 114 heater, G1 first source gas, G2 second source gas, G3 first carrier gas, G4 second carrier gas, G7 reaction gas, G12 doping gas.

Claims (5)

In the method for growing a gallium nitride crystal, a gallium nitride crystal is grown on a base substrate by a hydride vapor phase growth method using a carrier gas, a gallium nitride raw material, and a gas containing silicon as a dopant.
A method for growing a gallium nitride crystal, wherein the carrier gas during the growth of the gallium nitride crystal is purified by passing through a molecular film or an adsorbent, and the dew point of the carrier gas is −60 ° C. or lower.   2. The method for growing a gallium nitride crystal according to claim 1, wherein a partial pressure of the carrier gas during the growth of the gallium nitride crystal is 0.56 atm or more and 0.92 atm or less. Obtained by the method for growing a gallium nitride crystal according to claim 1 or 2,
The base substrate;
A gallium nitride crystal substrate comprising the gallium nitride crystal formed on the base substrate. A step of growing the gallium nitride crystal on the base substrate by the method of growing a gallium nitride crystal according to claim 1;
Removing at least the base substrate to form a substrate made of the gallium nitride crystal;
Forming an epitaxially grown layer on the substrate;
A method for manufacturing an epi-wafer, comprising a step of processing a surface opposite to the surface on which the epitaxial growth layer is formed on the substrate for thinning. Manufactured by the method for producing an epi-wafer according to claim 4,
The substrate;
An epi-wafer comprising the epitaxial growth layer formed on the substrate.

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