JP2007142003A - Manufacturing method of group iii nitride crystal, epitaxial substrate, warpage reduction method therein, and semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a group III nitride crystal capable of stably ensuring compatibility between high crystal quality and high specific resistance, and of reducing warpages in an epitaxial substrate. <P>SOLUTION: An underlaying substrate obtained by epitaxially forming a growing underlaying layer, consisting of AlN on a sapphire single crystal is placed in a manufacturing apparatus (step S1), then supply of hydrogen gas is started in a state of room temperature (step S2), and further rise in the temperature is started (step S3). Hydrogen gas is supplied and rise in its temperature is continued, until the underlaying substrate reaches a predetermined formation temperature (step S4). Once the temperature of the underlaying substrate reaches the formation one, supply mode of gases is changed over from only hydrogen gas to mixed gas of ammonia, nitrogen, and hydrogen, while keeping the temperature of the underlaying substrate (step S5). After the passage of a predetermined period, further supply of the group III stock gas is started, while continuing the supply of the mixed gas (step S6), to make a group III nitride crystal film grow epitaxially on the underlaying substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a group III nitride crystal on a single crystal base substrate, and more particularly to setting of an atmosphere according to a temperature change.

  Group III nitride crystals such as GaN have high band gaps, high breakdown electric field strengths, and high melting points, so they are expected as high-power, high-frequency, and high-temperature semiconductor device materials that can replace GaAs-based materials. Therefore, HEMT (High Electron Mobility Transistor) has been researched and developed as an electronic device that makes use of such physical properties. For example, a GaN layer or the like is epitaxially grown as a so-called semi-insulating layer (or buffer layer) on a substrate such as sapphire or SiC, and an AlGaN layer or an AlN layer or the like is epitaxially grown as a so-called carrier supply layer thereon. A heterostructure type HEMT obtained by forming a body has been researched and developed.

  In order to obtain good characteristics in such an electronic device, the crystal quality of each layer formed epitaxially is required to be good. For example, in the case of using a base substrate formed by epitaxially forming a base film such as an AlN film or an AlGaN film on a single crystal base material, in order to improve the crystal quality of each layer formed thereon, Techniques for reducing surface defects are known (see, for example, Patent Document 1 and Patent Document 2).

  In such an electronic device, it is required that the semi-insulating layer (buffer layer) has a small off-state leakage current. For this purpose, it is required to form a buffer layer so as to have a high specific resistance. A technique for realizing this is already known (see, for example, Patent Document 3).

  Therefore, after all, it is required to improve both the crystal quality and the realization of a high specific resistance. A technique for achieving this is already known (see, for example, Patent Document 4).

JP 2003-048799 A JP 2003-197541 A JP 2004-289905 A JP 2005-035869 A

  As described above, in an electronic device manufactured by obtaining a laminate in which a group III nitride crystal is epitaxially formed on a substrate, high crystal quality of each formed layer and high specific resistance of a semi-insulating layer are achieved. However, it is necessary to realize them stably or reliably for practical use and for mass production. For this purpose, it is necessary to minimize the variation in quality between laminates derived from different substrates.

  In addition, since a large number of these electronic devices are usually obtained by dividing one laminated body, in order to stably have a certain quality and characteristic of each electronic device, a single laminated body is Therefore, it is necessary to reduce the variation of the so-called in-plane variation as much as possible. This is because such a variation is indispensable in order to secure a yield when producing electronic devices.

  In addition, the group III nitride epitaxial film generally has better crystal quality as the film thickness is increased. On the other hand, as the film thickness is increased, the epitaxial formation is performed on different materials having different lattice constants. As a result, the laminate tends to warp. The existence of such warp causes problems such as difficulty in adsorbing and fixing the laminate during the steps after film formation, for example, during exposure by a stepper. Therefore, it can be said that it is preferable from the viewpoint of suppressing warpage that the above-described high crystal quality and high specific resistance are realized in a state where the thickness of the semi-insulating layer is thin.

  However, none of Patent Documents 1 to 3 discloses a technique for achieving both improvement in crystal quality and a technique for realizing a high specific resistance in the semi-insulating layer. In addition, there is no disclosure of a technique related to warpage reduction.

  Patent Document 4 discloses a technique for achieving both improvement in crystal quality of each layer constituting the laminated body and realization of a high specific resistance of the semi-insulating layer. However, realization of such quality and characteristics is disclosed. There is no disclosure about the realization of stability and certainty. Further, there is no disclosure about a technique related to warpage reduction.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a group III nitride crystal in which both high crystal quality and high specific resistance are stably realized. A second object is to reduce warpage in an epitaxial substrate using the group III nitride crystal as a semi-insulating layer.

  In order to solve the above-mentioned problem, the invention of claim 1 is a method for producing a group III nitride crystal, and a temperature raising step of raising a predetermined single crystal base substrate to a predetermined film formation temperature in a processing vessel. And a film forming step of epitaxially growing a first group III nitride crystal containing at least Ga on the single crystal base substrate heated to the predetermined film forming temperature, and in the temperature increasing step, Then, hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container until the temperature of the single crystal base substrate reaches the film formation temperature at the latest, and the temperature of the single crystal base substrate is set to the predetermined temperature. The film forming step is performed by starting the supply of the predetermined gas group necessary for forming the first group III nitride crystal into the processing container after the film forming temperature is reached. Features.

  The invention of claim 2 is a method for producing a group III nitride crystal, wherein a temperature raising step of raising a predetermined single crystal base substrate to a predetermined film formation temperature in a processing vessel, A film forming step of epitaxially growing a first group III nitride crystal containing at least Ga on the single crystal base substrate that has been heated to a film forming temperature. When the temperature of the substrate is equal to or higher than a predetermined hydrogen gas supply start temperature, hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container, and the temperature of the single crystal base substrate is the predetermined film formation temperature. After reaching the above, the film forming step is performed by starting supply of a predetermined gas group necessary for forming the first group III nitride crystal into the processing vessel.

  The invention of claim 3 is the method for producing a group III nitride crystal according to claim 1 or 2, wherein the temperature of the single crystal base substrate is 300 ° C. or higher in the temperature raising step. The hydrogen gas is supplied to

  The invention of claim 4 is the method for producing a group III nitride crystal according to claim 3, wherein the hydrogen gas is used when the temperature of the single crystal base substrate is 500 ° C. or higher in the temperature raising step. It is characterized by supplying.

  The invention of claim 5 is the method for producing a group III nitride crystal according to any one of claims 1 to 4, wherein the first group III nitride is added in the film forming step. First, supply of the first gas group including the group V source gas for forming is started, and after the temperature fluctuation has converged, the group III element gas for forming the first group III nitride is included. The supply of the second gas group is started.

  The invention of claim 6 is the method for producing a group III nitride crystal according to any one of claims 1 to 5, wherein in the film forming step, the first group III nitride is used. The predetermined gas group is supplied so that a Ga content ratio in all group III elements is 50% or more.

  The invention of claim 7 is a method for producing a group III nitride crystal according to claim 6, wherein in the film formation step, Ga in all group III elements in the first group III nitride is obtained. The predetermined gas group is supplied so that the content ratio of is not less than 80%.

  The invention of claim 8 is the method for producing a group III nitride crystal according to claim 7, wherein in the film forming step, the first group III nitride is GaN. A predetermined gas group is supplied.

  The invention of claim 9 is the method for producing a group III nitride crystal according to any one of claims 1 to 8, wherein the single crystal base substrate is formed on a predetermined single crystal base material. An underlayer made of a second group III nitride, which is an AlN group III nitride, is formed epitaxially, and the Al content in the first group III nitride is the second group III nitride. It is characterized by being smaller than the Al content ratio in the product.

  The invention of claim 10 is a method for producing a group III nitride crystal according to claim 9, characterized in that the second group III nitride is AlN.

  The invention of claim 11 is a method for reducing warpage in an epitaxial substrate, wherein the group III includes at least Ga on a predetermined single crystal base substrate by the manufacturing method according to any one of claims 1 to 10. An epitaxial substrate is obtained by forming a crystal layer made of a nitride crystal.

  A twelfth aspect of the present invention is the method for reducing a warp in an epitaxial substrate according to the eleventh aspect, wherein the crystal layer is formed to have a film thickness of 2.0 μm or less.

  According to a thirteenth aspect of the present invention, an epitaxial substrate is formed on the predetermined single crystal base substrate by the Group III nitride crystal manufacturing method according to any one of the first to tenth aspects. A crystal layer made of nitride is formed.

  According to a fourteenth aspect of the present invention, in the epitaxial substrate, the underlayer is formed with a film thickness of 0.5 to 1.0 μm by the Group III nitride crystal manufacturing method according to the tenth aspect, and the first substrate is formed. A crystal layer made of Group III nitride is formed of GaN with a thickness of 1.0 to 2.0 μm, and an upper layer made of AlGaN is further epitaxially formed on the crystal layer. .

The invention of claim 15 is the epitaxial substrate according to claim 13 or claim 14, wherein the specific resistance of the crystal layer is 1 × 10 ⁶ Ω · cm or more.

  The invention according to claim 16 is the epitaxial substrate according to claim 15, wherein the crystal layer has an X-ray rocking curve half-width of (0002) plane of 200 seconds or less and no surface defects. It is formed.

  The invention according to claim 17 is characterized in that the semiconductor element is formed using the epitaxial substrate according to any one of claims 13 to 16.

  According to the inventions of claims 1 to 10, a group III nitride crystal having high crystal quality and high specific resistance can be stably formed on the base substrate. Further, in a semiconductor element having a crystal layer made of the group III nitride crystal as a semi-insulating layer, high crystal quality and high specific resistance are maintained even if the semi-insulating layer is thinned. Reduction of the warpage in the semiconductor element caused by the difference in lattice constant from the layer is realized.

  According to the eleventh and twelfth aspects of the present invention, in a semiconductor device in which a semi-insulating layer is formed of a crystal layer made of a group III nitride crystal on a base substrate, even if the semi-insulating layer is thinned, a high crystal Since the quality and high specific resistance are maintained, it is possible to reduce the warpage in the semiconductor element caused by the lattice constant difference between the base substrate and the semi-insulating layer.

  According to the thirteenth to seventeenth aspects of the present invention, an epitaxial substrate having a crystal layer made of a group III nitride crystal having a high crystal quality and a high specific resistance on a base substrate can be obtained. Further, in a semiconductor element formed using this epitaxial substrate and in which the crystal layer functions as a semi-insulating layer, high crystal quality and high resistivity are maintained even if the semi-insulating layer is thinned. Reduction of warpage in the semiconductor element caused by the difference in lattice constant between the insulating layer and the semi-insulating layer is realized.

<First Embodiment>
<Structure of HEMT element>
FIG. 1 is a schematic diagram showing a configuration of a laminate 10 obtained by the manufacturing method according to the present embodiment. For convenience of illustration, the ratio of the thickness of each layer in FIG. 1 does not reflect the actual ratio.

  The laminated body 10 is a so-called epitaxial substrate in which the growth base layer 2 and the semi-insulating layer 3 are epitaxially formed in this order on the single crystal substrate 1. In the present specification, the substrate in which the growth base layer 2 is formed on the single crystal substrate 1 may be referred to as a base substrate 1s. That is, the laminated body 10 can also be regarded as a semi-insulating layer 3 formed epitaxially on the base substrate 1s.

  FIG. 2 is a schematic diagram showing the configuration of the HEMT element 20 formed using the laminate 10. The HEMT device 20 has a carrier supply layer 4 formed on the laminate 10, more specifically on the semi-insulating layer 3, and further has a source electrode 5 and a drain electrode 6, a gate, An electrode 7 is formed.

The single crystal base material 1 is appropriately selected according to the composition and structure of each layer formed thereon or the forming method. For example, a single crystal such as SiC (silicon carbide) or sapphire cut into a predetermined thickness is used. Alternatively, various oxide materials such as ZnO, LiAlO ₂ , LiGaO ₂ , MgAl ₂ O ₄ , (LaSr) (AlTa) O ₃ , NdGaO ₃ , MgO, various IV group single crystals such as Si and Ge, and various IV-IV such as SiGe. It may be used by appropriately selecting from group III compounds, various III-V compounds such as GaAs, AlN, GaN, AlGaN, and various borides such as ZrB ₂ . Among such single crystals, a SiC substrate and a sapphire substrate are desirable. In particular, when a group III nitride layer having a C-plane as a main surface is obtained as the growth underlayer 2, it is desirable to use C-plane SiC or C-plane sapphire as the single crystal substrate 1. This is because the formation of a high quality growth underlayer 2 can be realized. Further, when a group III nitride layer having an A-plane as a main surface is obtained as the growth underlayer 2, it is desirable to use A-plane SiC or R-plane sapphire as the single crystal substrate 1. The thickness of the single crystal substrate 1 is not particularly limited in terms of material, but a thickness of several hundred μm to several mm is suitable for the convenience of handling.

  The growth underlayer 2 is formed of a group III nitride containing at least Al and having a molar fraction of Al with respect to all group III elements larger than the group III nitride (described later) constituting the semi-insulating layer 3. . Preferably, the growth underlayer 2 is formed of a group III nitride having a molar fraction of Al with respect to all group III elements of 50 atomic% or more. More preferably, the growth underlayer 2 is formed of a group III nitride having a molar fraction of Al with respect to all group III elements of 80 atomic% or more. Most preferably, it is made of AlN. The growth underlayer 2 is composed of the group III nitride having such a composition when the in-plane lattice constant is larger than that of the growth underlayer 2 in the semi-insulating layer 3. Threading dislocations mainly composed of edge dislocations from the growth base layer 2 are entangled with each other by the action of a substantially horizontal compressive stress generated in the vicinity of the interface portion of each, and as a result, dislocations in the semi-insulating layer 3 are reduced. This is because the effect is obtained. Here, the difference in the lattice constant can be adjusted by the molar fraction of group III elements B, Al, Ga, In or the addition amount of P and As that can be added to N as group V elements. . In particular, when the crystal quality, thermal conductivity, etc. of the growth base layer 2 are taken into consideration, it is desirable to adjust by the difference in the mole fraction of Al, and the mole fraction of Al between the growth base layer 2 and the semi-insulating layer 3 The greater the difference, the greater the dislocation reduction effect. Therefore, the effect is maximized when the growth underlayer 2 is formed of AlN, but the growth underlayer 2 is a group III nitride in which the molar fraction of Al with respect to all group III elements is 80 atomic% or more. It has been experimentally confirmed that the dislocation reduction effect is almost the same as that of AlN. In addition, when the growth base layer 2 is made of AlN, there is an advantage that variation in composition does not become a problem.

The growth underlayer 2 thus formed usually has a hexagonal wurtzite structure. In particular, when a group III nitride having a C-plane as a main surface is used as the growth underlayer 2, the growth underlayer 2 has a half-width of (0002) plane of 200 seconds by X-ray rocking curve measurement (ω scan). The following is preferable. Furthermore, it is more preferable that it is 100 seconds or less. The realization of such a half width means that a state in which the growth orientation is less fluctuated, the C-plane is aligned, and the dislocation of the helical component is less is realized on the surface of the growth base layer 2. This is because it is more suitable for forming the semi-insulating layer 3 with good crystal quality on the growth underlayer 2. In order to realize this crystallinity, it is desirable not to insert a so-called low-temperature buffer layer on the single crystal substrate 1. The lower limit of the half-width of the (0002) plane by X-ray rocking curve measurement (ω scan) is not particularly defined, but is not less than the theoretical value (-10 seconds) calculated from the material and crystal structure. Further, the edge dislocation density in the growth base layer 2 is desirably 5 × 10 ¹⁰ / cm ² or less, and this state is realized by forming a nitride layer on the surface of the single crystal substrate 1. Depending on the condition setting, it is possible to realize a dislocation density of 1 × 10 ⁹ / cm ² . In this embodiment, the dislocation density is evaluated using a planar TEM.

The growth foundation layer 2 is preferably formed to a thickness of 10 nm to 100 μm. If the thickness is smaller than this, the growth underlayer 2 does not grow sufficiently, and a large amount of dislocations generated at the interface between the single crystal substrate 1 and the growth underlayer 2 remain up to the surface of the growth underlayer 2. It is not preferable. Therefore, it is desirable to form the growth underlayer 2 with a thickness of at least 5 × 10 ¹⁰ / cm ² or less in order to sufficiently eliminate internal dislocations. If the thickness is 300 nm or more, a dislocation density of 5 × 10 ¹⁰ / cm ² or less can be stably realized. However, if the thickness is too large, there are disadvantages in terms of cost, and cracks may occur inside the growth base layer 2, so the thickness is appropriately set within the range where cracks do not occur. A desirable thickness is 10 μm or less. Further, from the viewpoint of reducing the warpage in the laminate 10 or the HEMT element 20, the thickness of the growth base layer 2 is preferably thin, and is preferably 2 μm or less.

  The growth underlayer 2 can be formed by using, for example, the MOCVD method or the MBE method (molecular beam epitaxy). For the MOCVD method, a PALE method (Pulsed Atomic Layer Epitaxy), a plasma assist method or a laser assist method can be used in combination. The same technique can be used in combination with the MBE method. A growth method such as MOCVD method or MBE method is suitable for growing high-quality crystals because the production conditions can be controlled with high precision. As in this embodiment, AlN is formed on a dissimilar substrate. In the case of growing the high quality growth underlayer 2 by the above method, it is desirable to use such a method in which the decompression condition can be set at a heating temperature of 1100 ° C. to 1600 ° C. More specific manufacturing conditions are appropriately selected and set according to each forming method. Among these methods, it is particularly desirable to use the MOCVD method, which can realize a state closer to a thermal equilibrium state.

  Moreover, it is desirable that the outermost surface of the growth underlayer 2 be formed so as to be substantially flat at the atomic level. In this case, the surface of the growth underlayer 2 has such flatness that atomic steps can be clearly observed, and the surface roughness of the outermost surface evaluated by AFM (in this application, a square region of 5 μm × 5 μm) (Evaluated by the arithmetic average roughness Ra) of 0.5 nm or less, preferably 0.3 nm or less, which is substantially the same as the c-axis lattice constant of the group III nitride material constituting the growth underlayer 2. When the value of Ra is 0.3 nm or less, pits are hardly observed on the surface.

  In order to realize such flatness at the atomic level on the surface of the growth base layer 2, it is preferable to use a crystal growth technique in which local unevenness is less likely to occur. It can be said that the MOCVD method in which the formation rate is at most about several μm / hr is suitable as the method. When the above growth base layer 2 is formed by MOCVD using trimethylaluminum and ammonia, the temperature of the substrate itself is 1100 ° C. or more and 1250 ° C. or less, and the forming pressure is 6.5 mbar or more and 35 mbar or less, The supply ratio of trimethylaluminum to ammonia is 1: 500 or less, more preferably 1: 200 or less, and preferably 1: 1 or more. Here, the temperature of the substrate itself when the growth base layer 2 is formed is defined based on a temperature measurement experiment under the same conditions as the formation conditions using the thermocouple-attached substrate.

The semi-insulating layer 3 is preferably formed of a high resistance group III nitride. For example, in a group III nitride in which the Ga content ratio in all group III elements is 50% or more, preferably in a group III nitride in which the Ga content ratio in all group III elements is 80% or more More preferably, it is formed of GaN (i-GaN) that does not contain impurities that cause a reduction in resistance. By setting the Ga content ratio to 50% or more, a lateral growth effect during the formation of the semi-insulating layer 3 appears, and the effect of reducing dislocations in the semi-insulating layer 3 can be stably obtained. By making the content ratio of 80% or more, a dislocation density of 5 × 10 ⁹ / cm ² or less can be stably realized.

  The semi-insulating layer 3 can be generally formed by using a known film forming method such as MOCVD or MBE, but the method for forming the semi-insulating layer 3 according to the present embodiment will be described later. Will be described in detail. Since it forms by the method mentioned later on the growth base layer 2 which has the above high crystallinity, the semi-insulating layer 3 also has favorable crystal quality.

Note that the higher the surface flatness of the growth underlayer 2 is, the more effective the dislocation reduction effect in the semi-insulating layer 3 is. The dislocation density inside the semi-insulating layer 3 can be at least ½ or less of the dislocation density of the surface portion of the growth underlayer 2 and can be reduced to 5 × 10 ⁷ / cm ² . In order to realize this crystallinity, it is desirable not to insert a so-called low-temperature buffer layer on the growth base layer 2. Furthermore, when the semi-insulating layer 3 is formed on the growth base layer 2 that is flat enough to have almost no pits on the surface, the occurrence of a situation in which crystal defects are induced from the pits in the semi-insulating layer 3 is suppressed. In addition, the surface flatness of the carrier supply layer 4 can be improved.

  Further, in the vicinity of the upper surface of the semi-insulating layer 3, a two-dimensional electron gas region in which a high-concentration two-dimensional electron gas is generated is formed by supplying electrons serving as carriers from the carrier supply layer 4. . Therefore, the semi-insulating layer 3 needs to be thick enough to secure this two-dimensional electron gas region. On the other hand, if the thickness is too large, cracks are likely to occur, and the HEMT element 20 as a whole is likely to be warped. Therefore, it is required to have good crystal quality and high specific resistance while suppressing the thickness.

In the present embodiment, by forming the semi-insulating layer 3 by the method described later, the thickness is several μm or less, preferably 3 μm or less, more preferably about 1.5 μm, (0002) The half-width of the X-ray rocking curve on the surface is at most 100 seconds or less, and high crystal quality that the surface flatness is good and high specific resistance of 1 × 10 ⁷ Ω · cm or more are achieved, while in the laminated body or HEMT device Warpage can be reduced. Conventionally, when the semi-insulating layer is 3 μm or less, a decrease in the mobility of the HEMT element has been observed due to an increase in defects such as the pits, but in the case of the semi-insulating layer 3 formed by a method described later, No decrease in the mobility of the HEMT element is observed until the thickness is about 2 μm. Furthermore, it has been confirmed that in the region where the thickness of the semi-insulating layer 3 is 1 μm or more and less than 2 μm, the mobility is recovered more than when the conventional semi-insulating layer is used, and the mobility required for the device is satisfied. .

  FIG. 3 is a diagram for explaining a method for defining warpage in the present embodiment. In the present embodiment, the warpage amount BW is defined by the maximum lift amount of the surface WS of the stacked body 10 (or HEMT element 20), that is, the protruding distance of the surface WS from the horizontal position HR.

The carrier supply layer 4 is formed of a group III nitride containing at least Al. Preferably, it is formed of a group III nitride having a composition of Al _x Ga _1-x N. The carrier supply layer 4 is preferably formed to a thickness of about several tens of nm from the viewpoint of forming a two-dimensional electron gas region and device operation (that is, controllability of the main current with respect to gate voltage application). .

  The carrier supply layer 4 is formed by a known film formation method such as MOCVD method or MBE method. In the HEMT device 20, a semi-insulating layer 3 and a carrier supply layer 4 have a piezoelectric effect (piezoelectric effect) in which an electric field is generated from the surface to the substrate due to a lattice constant difference (a axis), and a spontaneous polarization effect. Two-dimensional electron gas is generated on the surface of the insulating layer 3, but the piezo effect increases as the carrier supply layer 4 is formed of a group III nitride having a large value of x, that is, an Al-rich group III nitride. The sheet carrier concentration in the two-dimensional electron gas region is improved. Preferably, the carrier supply layer 4 is formed of a group III nitride satisfying x ≧ 0.2. However, if x is large, cracks are likely to occur, so it is necessary to select growth conditions that do not cause cracks.

  The carrier supply layer 4 may be doped with an n-type dopant such as Si. In addition, a group III nitride layer acting as a barrier layer, a cap layer, or the like may be provided on the upper side or the lower side of the carrier supply layer 4.

The carrier supply layer 4 is formed so that the pit density on the surface thereof is 5 × 10 ⁸ / cm ² or less. The carrier supply layer 4 has such a good crystallinity after providing the semi-insulating layer 3 having a high crystallinity as described above, and changing the growth conditions of the semiconductor layer according to the film forming method used. It can be said that it is due to appropriate control.

  The source electrode 5 and the drain electrode 6 are formed on the surface of the carrier supply layer 4 by, for example, ohmic contact with Ti / Au / Ti / Au. The source electrode 5 and the drain electrode 6 may be formed after a predetermined contact process is performed on the electrode forming portion on the surface of the carrier supply layer 4. The gate electrode 7 is formed on the surface of the carrier supply layer 4 by, for example, Pt / Au by Schottky junction.

<Manufacturing equipment>
Next, an apparatus used when manufacturing the group III nitride according to the present embodiment, specifically, the epitaxial formation of the semi-insulating layer 3 using the MOCVD method will be described. FIG. 4 is a diagram schematically illustrating an example of the configuration of the manufacturing apparatus 100. That is, the manufacturing apparatus 100 is a so-called “MOCVD apparatus”.

  The manufacturing apparatus 100 is configured such that a source gas for epitaxially forming a group III nitride as the semi-insulating layer 3 on the base substrate 1s can be flowed over the main surface of the base substrate 1s. In addition to the formation of the semi-insulating layer 3, the growth base layer 2 and the carrier supply layer 4 can be formed using the manufacturing apparatus 100.

  The manufacturing apparatus 100 includes a reactive gas introduction pipe 31 for introducing a reactive gas into the main surface of the base substrate 1s. The reactive gas introduction pipe 31 is in an airtight processing vessel 21, and two external ends thereof are a reactive gas introduction port 22 and an exhaust port 24, respectively. In addition, the reactive gas introduction pipe 31 is provided with an opening 31h for contacting the reactive gas on the main surface of the base substrate 1s.

Piping systems L <b> 1 and L <b> 2 are connected to the introduction port 22 outside the processing container 21. The piping system L1 is a piping system for supplying ammonia gas (NH ₃ ), nitrogen gas (N ₂ ), and hydrogen gas (H ₂ ). On the other hand, the pipeline L2 is, TMA _{(trimethylaluminum; Al (CH 3) 3)} , TMG ( trimethyl _{gallium; Ga (CH 3) 3)} , TMI ( trimethyl _{indium; In (CH 3) 3)} , CP 2 Mg ( It is a piping system for supplying cyclopentadienyl magnesium; Mg (C ₅ H ₅ ) ₂ ), silane gas (SiH ₄ ), nitrogen gas and hydrogen gas. Further, TMA, TMG, TMI and CP ₂ Mg supply sources 24d to 24g are connected to the piping system L2.

The TMA, TMG, TMI, and CP ₂ Mg supply sources 24d to 24g are connected to a nitrogen gas supply source 24b for bubbling. Similarly, TMA, TMG, TMI, and CP2Mg supply sources 24d to 24g are connected to a hydrogen gas supply source 24c. In the present embodiment, since TMI and CP ₂ Mg are not used, the supply sources 24f and 24g may not be provided.

In the manufacturing apparatus 100, hydrogen (H ₂ ), nitrogen (N ₂ ), or a mixed gas thereof functions as a carrier gas. In all gas supply systems, the gas flow rate is controlled using a flow meter.

  Further, a vacuum pump 27 that forcibly exhausts the gas inside the processing container 21 is connected to the exhaust port 24.

  In addition, a base plate (susceptor) 28 on which the base substrate 1 s is placed and a support leg 29 that supports the base plate 28 inside the processing chamber 21 are provided inside the processing chamber 21. The temperature of the base table 28 can be controlled by a heater 30. In the manufacturing apparatus 100, the growth temperature of the base substrate 1s is changed by changing the temperature of the base 28 that is in close contact with the base substrate 1s. In other words, the temperature of the base substrate 1 s can be controlled by controlling the heater 30. Here, the temperature of the base substrate 1s when forming the semi-insulating layer 3 is such that the susceptor 28 having a thickness (5 mm) made of SiC-coated carbon has a radiation rate (0. It is defined by the temperature measured using the radiation thermometer set as 5).

<Method for forming semi-insulating layer>
Next, a method for producing a group III nitride using the manufacturing apparatus 100, specifically, a method for forming the semi-insulating layer 3 will be described. Here, the case where the semi-insulating layer 3 is generated on the base substrate 1s formed as described above by a predetermined method will be described. In the embodiment described later, for the sake of convenience, it is described that the production of the base substrate 1s by forming the growth base layer 2 and the creation of the semi-insulating layer 3 are performed continuously by the same manufacturing apparatus 100. The formation of the growth foundation layer 2, that is, the production of the foundation substrate 1s and the formation of the semi-insulating layer 3 thereon are preferably performed by different manufacturing apparatuses. When the conditions for forming the growth base layer 2 and the semi-insulating layer 3 are greatly different, for example, when the layers are formed of materials having greatly different compositions, these are continuously formed using the same manufacturing apparatus. This is because the quality of each layer may be greatly deteriorated due to the memory effect of the manufacturing apparatus. In addition, when both layers are formed by different apparatuses, it is possible to evaluate the crystal quality of the underlying layer when it is taken out from the manufacturing apparatus after the formation of the underlying layer, so that it is possible to eliminate defects. There is also. In this case, an oxide layer is formed on the outermost surface of the growth base layer 2 in the atmosphere, but the oxide layer is effectively removed by a process described later. FIG. 5 is a diagram showing a flow of forming the semi-insulating layer 3 according to the present embodiment.

  First, the base substrate 1s is placed on the base stand 28 (step S1). In that case, it is preferable that the surface of the growth base layer 2 of the base substrate 1s is ultrasonically cleaned using acetone and IPA (isopropyl alcohol), and then placed in a state of being washed with water and dried.

  After placing the base substrate 1s, supply of hydrogen gas is started from the hydrogen gas supply source 24c at room temperature (step S2). At that time, the flow velocity is set to a predetermined value in the range of 0.01 m / s to 100 m / s, and the pressure inside the manufacturing apparatus 100 is set to a predetermined value between 50 mbar and 300 mbar. For example, a preferred example is a flow rate of 4 m / s and a pressure of 200 mbar.

  After the supply of hydrogen gas is started, the temperature rise is started by the heater 30 (step S3). The temperature rising rate at that time is set to a predetermined value between 50 ° C./min and 400 ° C./min. For example, 150 ° C./min is a suitable example.

  The supply of hydrogen gas and the temperature increase are continued until the base substrate 1s reaches a predetermined formation temperature (the formation temperature of the group III nitride crystal constituting the semi-insulating layer 3) (step S4). Here, the formation temperature is appropriately set within a temperature range of 1000 ° C to 1200 ° C. For example, 1100 ° C. is a suitable example. If a sufficient hydrogen gas atmosphere is formed in the processing container until the formation temperature is reached, the supply of hydrogen gas may be terminated during the temperature increase, but the control parameters are reduced as much as possible. From this viewpoint, it is preferable that the supply is terminated after the temperature is stabilized at a constant temperature. However, due to the problem of temperature stability, a temperature deviation of about ± 10 ° C. from the predetermined formation temperature is allowed within the range of the formation temperature.

  That is, in this embodiment, it can be said that the hydrogen gas is supplied so that the hydrogen gas atmosphere is formed in the processing container until the temperature of the base substrate reaches the formation temperature at the latest. In addition, it can be said that hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container in a temperature range of room temperature or higher, which is a hydrogen gas supply start temperature.

  The hydrogen gas atmosphere refers to a gas atmosphere containing hydrogen gas as a main component, but also indicates a case where a trace amount of other gas such as ammonia or nitrogen is intentionally included or an impurity is included. And The heating in the hydrogen gas atmosphere is a process having an action of removing the oxide layer formed on the outermost surface of the base substrate 1s, but other gases may be included as long as the oxide layer can be removed. Permissible. However, in order to make maximum use of the action of removing the oxide film, it is desirable that the atmosphere be formed only with hydrogen gas. Further, the effect of removing the oxide layer becomes remarkable when the growth underlayer 2 is formed of AlN group III nitride that is easily oxidized when stored in the air, particularly when formed with AlN. This is the case. However, if the heating in the hydrogen gas atmosphere is continued for a long time, defects may be induced on the surface of the base substrate 1s and the crystal quality of the semi-insulating layer 3 may be deteriorated. It is desirable to set the time so as not to induce one surface defect.

  When the temperature of the base substrate 1s reaches the formation temperature (until the formation of the semi-insulating layer 3 is completed), while maintaining the temperature of the base substrate 1s, the gas supply mode is changed from only hydrogen gas to ammonia, nitrogen, and Switching to a mixed gas of hydrogen (step S5). The flow rate of each gas supplied from each of the supply sources 24a to 24c when supplying such a mixed gas is appropriately determined. For example, 2 m / s, 1 m / s, and 1 m / s are sequentially set. Is a suitable example.

  After a predetermined time (for example, about 30 seconds) has passed since the supply of the mixed gas has started, the supply of the group III source gas is further started while the supply of the mixed gas is maintained (step S6). Here, the reason for waiting for a predetermined time to elapse is that the switching of the supply gas is likely to cause a temperature fluctuation, so that the fluctuation is converged in order to avoid a malfunction due to this switching. This is to stabilize the temperature of the base substrate at the set formation temperature.

  The type of gas to be supplied is determined according to the composition of the substance to be formed as the semi-insulating layer 3. When the semi-insulating layer 3 is formed of GaN, TMG is supplied from the supply source 24e. Further, when the semi-insulating layer 3 having a composition containing Al or In is formed, TMA and TMI as raw materials for these elements are also supplied from the respective supply sources 24d and 24f.

  The group III source gas is supplied so that the supply ratio to the ammonia gas (group III source gas: ammonia gas) is a predetermined ratio of 1: 500 to 1: 3000. For example, 1: 1000 is a suitable example.

  By such gas supply, the group III nitride crystal film is epitaxially grown on the base substrate 1 s, specifically, on the growth base layer 2. That is, the semi-insulating layer 3 is formed. Such gas supply is performed until the semi-insulating layer 3 is formed to a desired thickness.

  In the present embodiment, by using such a method, the semi-insulating layer 3 having good crystal quality and high specific resistance can be formed more stably than when the mixed gas is supplied at the time of temperature rise. it can. Thereby, the HEMT device 20 having such a semi-insulating layer 3 can be stably obtained.

For example, as shown in the examples to be described later, a sapphire is used as the single crystal base material 1, and a base substrate 1s formed to a thickness of 1 μm of a high crystal quality AlN layer as the growth base layer 2 is prepared. When the semi-insulating layer 3 is formed by the method, the half-value width of the X-ray rocking curve on the (0002) plane is 110 seconds or less at most in any of the plurality of different laminated bodies 10 and 1 × 10 ⁷ Ω · cm. It has been confirmed that the above high specific resistance is stably realized and that in-plane variation in one laminated body is small. In addition, it has been confirmed that the warpage of the laminate 10 in this case is about 25 to 30 μm when the thickness is 3 μm and about 15 μm when the thickness is 1.5 μm.

  Note that the apparatus used in the above-described method is not limited to the manufacturing apparatus 100, and it is needless to say that a semi-insulating layer can be formed using another apparatus as long as it has necessary components.

  As described above, by using the manufacturing method according to the present embodiment, a semi-insulating layer made of a group III nitride crystal that is stably high crystal quality and high resistivity with respect to the base substrate. Can be formed. Furthermore, in a HEMT device having the group III nitride crystal as a semi-insulating layer, even if the semi-insulating layer is thin, high crystal quality and high specific resistance are maintained, so that the lattice between the base substrate and the semi-insulating layer can be maintained. Reduction of warpage in the HEMT element caused by the constant difference is realized.

<Second Embodiment>
Next, a method for forming the semi-insulating layer 3 according to an aspect different from the first embodiment will be described. Specifically, an aspect in which the atmosphere in the temperature raising process prior to the formation of the group III nitride crystal is different from the first embodiment will be described. In the present embodiment, it is also assumed that the semi-insulating layer 3 is generated using the manufacturing apparatus 100 on the base substrate 1s that has been prepared in advance by a predetermined method. FIG. 6 is a diagram showing a flow of forming the semi-insulating layer 3 according to the present embodiment.

  First, similarly to step S1 of the first embodiment, the base substrate 1s is placed on the base stand 28 (step S101). Thereafter, supply of a mixed gas of ammonia, nitrogen, and hydrogen is started at room temperature (step S102). The flow rates of the respective gases supplied from the respective supply sources 24a to 24c are appropriately determined. For example, 2 m / s, 1 m / s, and 1 m / s are preferable in order. In that case, the pressure inside the manufacturing apparatus 100 is set to a predetermined value between 50 mbar and 300 mbar. For example, a preferable example is a pressure of 200 mbar.

  After the supply of the mixed gas is started, the heating is started by the heater 30 (step S103). The temperature increase rate at that time is set to a predetermined value between 50 ° C./min and 400 ° C./min. For example, 150 ° C./min is a suitable example.

  When the temperature reaches 300 ° C. after starting the temperature increase (step S104), the gas supply mode is switched from the mixed gas to only hydrogen gas (step S105). At that time, the flow velocity is set to a predetermined value in the range of 0.01 m / s to 100 m / s, and the pressure inside the manufacturing apparatus 100 is set to a predetermined value between 50 mbar and 300 mbar. For example, a preferred example is a flow rate of 4 m / s and a pressure of 200 mbar.

  The supply of hydrogen gas and the temperature increase are continued until the base substrate 1s reaches a predetermined formation temperature (deposition temperature of the group III nitride crystal constituting the semi-insulating layer) (step S106). Here, the formation temperature is appropriately set within a temperature range of 1000 ° C to 1200 ° C. For example, 1100 ° C. is a suitable example.

  As described above, the method of providing the atmosphere in the temperature raising process in the present embodiment is different from that in the first embodiment, but hydrogen gas in the processing container is not reached until the temperature of the base substrate reaches the formation temperature at the latest. It can be said that it is common in that hydrogen gas is supplied as an atmosphere is formed. In addition, although the hydrogen gas supply start temperature itself is different, it is common in that hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container in a temperature range higher than the hydrogen gas supply start temperature. It can be said.

  After the temperature of the base substrate 1s reaches the formation temperature, the same processing as in the first embodiment is performed. That is, while maintaining the temperature of the base substrate 1s, the gas supply mode is switched from only hydrogen gas to a mixed gas of ammonia, nitrogen, and hydrogen (step S107). Then, after a predetermined time (for example, about 30 seconds) has elapsed since the start of the supply of the mixed gas, the supply of the group gas is further started while the supply of the mixed gas is maintained (step S108). Thus, a group III nitride crystal film is epitaxially grown on the base substrate 1 s, specifically, on the growth base layer 2. That is, the semi-insulating layer 3 is formed. Such gas supply is performed until the semi-insulating layer 3 is formed to a desired thickness.

Also in this embodiment, as illustrated in the examples described later, the half-value width of the X-ray rocking curve on the (0002) plane is 130 seconds or less and the surface flatness is good, and the crystal quality is 1 × 10. It is possible to form the semi-insulating layer 3 that can reduce the warpage in the laminate while simultaneously achieving a high specific resistance of ⁷ Ω · cm or more. Thereby, the HEMT device 20 having such a semi-insulating layer 3 can be stably obtained. Further, when the temperature increase rate is the same as or faster than that in the first embodiment, the heating time in the hydrogen atmosphere is shorter in the present embodiment than in the first embodiment. The aspect of the atmosphere formation at the time of temperature increase in the present embodiment is also suitable in that the deterioration of the crystal quality of the semi-insulating layer 3 due to the induction of defects on the surface of 1 s is less likely to occur. Also in this embodiment, the apparatus to be used is not limited to the manufacturing apparatus 100.

  As described above, by using the manufacturing method according to this embodiment, a semi-insulating layer having high crystal quality and high specific resistance and reducing warpage in a stacked body can be formed over a base substrate. Can be formed.

<Third Embodiment>
FIG. 7 is a diagram showing a flow of forming the semi-insulating layer 3 according to the third embodiment. FIG. 7 shows an aspect in which processing similar to that in FIG. 6 is performed except that step 204 is provided instead of step 104 in FIG. That is, the third embodiment is a mode in which the same processing as that of the second embodiment is performed except that the timing of switching the gas supplied to the processing container from the mixed gas to the hydrogen gas at the time of temperature rise is set to 500 ° C. It is.

  That is, also in the present embodiment, hydrogen gas is supplied so that the hydrogen gas atmosphere is formed in the processing container until the temperature of the base substrate reaches the formation temperature at the latest in the temperature raising process. It can be said that it is common with other embodiments. Further, although the hydrogen gas supply start temperature itself is different, other implementations are also performed in that hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container in a temperature range higher than the hydrogen gas supply start temperature. It can be said that it is common with the form.

Also in this embodiment, as illustrated in the examples described later, the half-value width of the X-ray rocking curve in the (0002) plane is 150 seconds or less and the surface flatness is good, and the crystal quality is 5 × 10 5. It is possible to form the semi-insulating layer 3 that can reduce the warpage in the laminated body while simultaneously realizing a high specific resistance of ⁶ Ω · cm or more. That is, by using the manufacturing method according to this embodiment mode, a semi-insulating layer having high crystal quality and high specific resistance and reduced warpage in the stacked body can be formed over the base substrate. . In addition, when the rate of temperature increase is the same as or faster than that in the first or second embodiment, the heating time in the present embodiment is shorter in the hydrogen atmosphere than in the first or second embodiment. The aspect of atmosphere formation at the time of temperature increase in the present embodiment is also preferable in that the crystal quality of the semi-insulating layer 3 is less likely to be deteriorated due to the induction of defects on the surface of the base substrate 1s because it is shorter. It is.

Example 1
In this example, the laminated body 10 was produced by the method according to the first embodiment. Specifically, first, in order to prepare the base substrate 1s, a C-plane sapphire substrate having a diameter of 2 inches and a thickness of 630 μm is prepared as the single crystal substrate 1, and ultrasonically cleaned with acetone and IPA, and further washed with water and dried. After that, it was installed in the manufacturing apparatus 100. The pressure in the processing vessel was set to 50 mbar, and the single crystal substrate 1 was heated to 1200 ° C. while flowing hydrogen gas at a flow rate of 1 m / sec. Thereafter, ammonia gas was allowed to flow along with the hydrogen carrier gas for 5 minutes to nitride the main surface of the single crystal substrate 1. As a result of analysis by XPS (X-ray photoelectron spectroscopy), a nitride layer is formed on the main surface of the substrate by this surface nitriding treatment, and the nitrogen content at a depth of 1 nm from the main surface is 7 atomic%. There was found.

Next, TMA and ammonia gas were combined and flowed at a flow rate of 5 m / sec, and an AlN layer as a growth underlayer 2 was epitaxially grown to a thickness of 1 μm. Thereby, the base substrate 1s was obtained. The dislocation density of this AlN layer was 2 × 10 ¹⁰ / cm ² , and the half width of the X-ray diffraction rocking curve on the (0002) plane was 60 seconds. Furthermore, when the surface flatness of the AlN layer was confirmed by AFM (atomic force microscope), the average roughness Ra in the range of 5 μm × 5 μm was 0.15 nm.

  Next, the AlN layer was quickly ultrasonically washed with acetone and IPA, then washed with water and dried, and placed in the manufacturing apparatus 100 again. Subsequently, the internal pressure of the manufacturing apparatus 100 was set to 200 mbar, the supply of hydrogen gas was started at a flow rate of 4 m / sec at room temperature, and then the heating was started by the heater 30 at a heating rate of 150 ° C./min. When the temperature reached 1100 ° C., the atmospheric gas was switched to a mixed gas of hydrogen gas, nitrogen gas, and ammonia gas. Each flow velocity was 2 m / sec, 1 m / sec, and 1 m / sec. After maintaining this state for 30 seconds, TMG supply was further started, and a GaN layer as a semi-insulating layer was epitaxially grown to a thickness of 3 μm. Thereby, the laminated body 10 was obtained.

Next, in order to measure the specific resistance, silane gas is added so that the carrier density becomes 1 × 10 ¹⁹ / cm ³ , and an n-GaN layer serving as a contact layer with the electrode is grown on the semi-insulating layer 3 by 10 nm. I let you. After completion of the growth, after forming an electrode for four-terminal measurement composed of Ti / Al / Ti / Au on the surface of the n-GaN layer, and removing the n-GaN portion that is not covered with the electrode by etching, Placed in an annealing furnace. Next, nitrogen gas was flowed into the annealing furnace at a flow rate of 0.1 m / sec, the substrate temperature was set to 500 ° C. or higher, maintained for 1 minute, and then cooled to room temperature. After the above treatment, the specific resistance value of the GaN layer as the semi-insulating layer 3 was measured and found to be 1 × 10 ⁸ Ω · cm. In the following, the process for measuring the specific resistance is performed in the same manner, but the description thereof is omitted.

  The amount of substrate warpage was 28 μm. The full width at half maximum of the X-ray rocking curve on the (0002) plane of the GaN layer was 70 seconds.

(Example 2)
In this example, the laminated body 10 was produced by the method according to the second embodiment. Specifically, the base substrate 1s produced in the same manner as in Example 1 is placed in the manufacturing apparatus 100, the pressure in the manufacturing apparatus 100 is set to 200 mbar at room temperature, hydrogen gas, nitrogen gas, And the supply of a mixed gas of ammonia gas was started. Each flow velocity was 2 m / sec, 1 m / sec, and 1 m / sec. Thereafter, the heating was started by the heater 30 at a heating rate of 150 ° C./min. After the point where the temperature of the base substrate reached 300 ° C., the supply gas was switched to hydrogen gas only. The flow rate at that time was 4 m / sec. Thereafter, the temperature was continued to rise, and after the base substrate reached 1100 ° C., a GaN layer as a semi-insulating layer was grown to a thickness of 3 μm as in Example 1. Further, the formation of the contact layer and the electrode for measuring the specific resistance was performed in the same manner as in Example 1. In this way, 10 laminates were produced.

About the obtained ten laminated bodies, when the specific resistance value of the GaN layer was evaluated, it was 1 to 5 × 10 ⁷ Ω · cm. Further, the amount of warpage of the substrate was 25 to 30 μm, and the half width of the X-ray rocking curve on the (0002) plane of the GaN layer was 70 to 90 seconds.

(Example 3)
In this example, the laminated body 10 was produced by the method according to the third embodiment. Specifically, 10 laminates were formed in the same manner as in Example 2 except that the gas supply switching temperature was 500 ° C.

When the specific resistance value of the GaN layer was evaluated for the obtained 10 laminates, it was 5 to 10 × 10 ⁶ Ω · cm. The amount of warpage of the substrate was 25 to 30 μm, and the half width of the X-ray rocking curve on the (0002) plane of the GaN layer was 80 to 110 seconds.

(Comparison of Examples 1 to 3)
From these examples, it is confirmed that a high specific resistance of at least 5 × 10 ⁶ Ω · cm is obtained, and that a semi-insulating layer of good crystal quality is formed.

  In these examples, the method of providing the atmosphere in the temperature raising process is different, but hydrogen gas is supplied so that the hydrogen gas atmosphere is formed in the processing container until the temperature of the base substrate reaches the formation temperature at the latest. In other words, in other words, the hydrogen gas is supplied in such a manner that the hydrogen gas atmosphere is formed in the processing container in a temperature range equal to or higher than the hydrogen gas supply start temperature. That is, it can be said that forming an atmosphere that reaches the formation temperature of the semi-insulating layer in this manner is effective in achieving both high crystal quality and high specific resistance.

Further, according to Examples 1 to 3, if the supply of hydrogen gas is started when the temperature of the base substrate 1s reaches 500 ° C. at the latest after the temperature increase is started, the specific resistance becomes 1 × 10 ⁶ Ω. It can be said that the semi-insulating layer 3 having a high specific resistance of cm or more can be obtained. From the viewpoint of obtaining a higher specific resistance, it is effective to start the supply before reaching 300 ° C., and more preferably to start at room temperature. It is considered that the condition setting including the temperature rising rate should be set so that the crystal quality is not deteriorated due to the long heating time in the atmosphere.

Example 4
A GaN layer as the semi-insulating layer 3 was grown on the base substrate 1s under the same conditions as in Example 1, but the thickness was set to 1.5 μm.

The specific resistance of the obtained GaN layer was 1 × 10 ⁸ Ω · cm. The full width at half maximum of the X-ray rocking curve on the (0002) plane of the GaN layer was 70 seconds. When the density of pits having a diameter of 1 μm or more on the surface of the GaN layer was evaluated by a differential interference microscope image, it was 0 / mm ² . Further, the amount of warpage of the substrate at this time was 15 μm.

(Comparative Example 1)
A base substrate 1s is prepared under the same conditions as in Example 1, placed in the manufacturing apparatus 100, and the pressure in the manufacturing apparatus 100 is set to 200 mbar at room temperature, and then hydrogen gas, nitrogen gas, and ammonia are prepared. Supply of gas mixture started. Each flow velocity was 2 m / sec, 1 m / sec, and 1 m / sec. Thereafter, the heating was started by the heater 30 at a heating rate of 150 ° C./min. After the temperature of the base substrate reached 1100 ° C., a GaN layer as a semi-insulating layer was grown by the same method as in Example 1, but the thickness was set to 1.5 μm.

The specific resistance of the obtained GaN layer was 2 × 10 ⁵ Ω · cm. The amount of warpage of the substrate at this time was 15 μm, and the half width of the X-ray rocking curve on the (0002) plane of the GaN layer was 130 seconds. Further, the density of pits evaluated in the same manner as in Example 4 by using a differential interference microscope image was 1500 pieces / mm ² . FIG. 11 is a diagram illustrating a differential interference microscope image for this comparative example. In FIG. 11, it is confirmed that a large number of pits exist as indicated by arrows.

(Comparison between Example 4 and Comparative Example 1)
In Example 4, the specific resistance and crystal quality almost equivalent to those in Example 1 are realized. Also, pits as shown in FIG. 11 were not confirmed in Example 4. In Comparative Example 1, both specific resistance and crystal quality were inferior to Example 4. Further, with respect to the warpage amount, the smaller value was obtained in Example 4 than in Example 1, and there was no difference in Comparative Example 1, and this reflected the fact that the film thickness of the semi-insulating layer was thin. It is thought that it was done. However, since there is a large difference in crystal quality between Example 4 and Comparative Example 1, when the method according to the above-described embodiment, the crystal quality is good even when the semi-insulating layer is thinner. It is considered that a high specific resistance can be secured. As a result, it can be said that it is possible to realize the stacked body 10 and the HEMT element 20 in which warpage is further reduced.

(Example 5)
It was fabricated under the following three different conditions, with the thickness of sapphire used as the single crystal substrate 1 and the type of growth furnace used for the formation of the AlN layer as the growth base layer 2 (epitaxial formation by MOCVD method) being different. Ten base substrates 1s were prepared for each. The thickness of each AlN layer was 1 μm.

Condition 1: 430 μm thickness, growth furnace 1;
Condition 2: 630 μm thick, growth furnace 1 (same conditions as the base substrate used in Example 1);
Condition 3: thickness 430 μm, growth furnace 2.

  Using these, a GaN layer as the semi-insulating layer 3 was formed to a thickness of 3 μm by the same method as in Example 1 to obtain a laminate 10.

(Comparative Example 2)
A base substrate 1s is prepared under the same three conditions as in the fifth embodiment, placed in the manufacturing apparatus 100, and after setting the pressure in the manufacturing apparatus 100 to 200 mbar at room temperature, hydrogen gas, nitrogen gas, And the supply of a mixed gas of ammonia gas was started. Each flow velocity was 2 m / sec, 1 m / sec, and 1 m / sec. Thereafter, the heating was started by the heater 30 at a heating rate of 150 ° C./min. After the temperature of the base substrate reached 1100 ° C., a GaN layer as a semi-insulating layer was formed to a thickness of 3 μm by the same method as in Example 1 to obtain a laminate.

(Comparison between Example 5 and Comparative Example 2)
8, FIG. 9, and FIG. 10 are diagrams showing the specific resistance of the GaN layer for each of the 10 stacked bodies according to Example 5 and Comparative Example 2. FIG. Each figure corresponds to the case where the substrate is manufactured using the base substrates of Condition 1, Condition 2, and Condition 3, and (A) shows the case of Example 5. (B) shows the case of Comparative Example 2. Moreover, the error bar shown in each figure has shown the grade of the in-plane variation of the specific resistance in each laminated body.

8A to 10B are compared with each other in the case of (A), that is, in the stacked body of Example 5, 1 × 10 ⁷ Ω · It can be seen that a high specific resistance of cm or more can be stably obtained, and that both individual variation and in-plane variation are small. That is, it can be said that a high specific resistance is stably obtained regardless of the type of the base substrate 1s. Since the difference between Example 5 and Comparative Example 2 is only the way of providing the atmosphere in the temperature raising process, this result shows that the temperature rise by the hydrogen atmosphere is effective for the stable realization of a high specific resistance. ing.

(Example 6)
A HEMT device 20 having the structure shown in FIG. 2 was produced. Specifically, a laminate having a semi-insulating layer thickness of 1.5 μm is manufactured under the same conditions as in Example 1, and subsequently, TMA and TMG are supplied to form an AlGaN layer as the carrier supply layer 4. And a thickness of 30 nm. Thereafter, a source electrode 5 and a drain electrode 6 made of Ti / Au / Ti / Au and a gate electrode 7 made of Pt / Au were formed on the surface of the AlGaN layer. The amount of warpage of the HEMT element 20 was 15 μm.

  The drain electrode 6 of the obtained HEMT device 20 is grounded, −5V is applied to the gate electrode 7 to be turned off, and the voltage + 50V is applied to the source electrode 5 to cause leakage between the source electrode 5 and the drain electrode 6. When the electric current was evaluated, it was 1 nA / mm.

(Comparative Example 3)
A laminated body having a semi-insulating layer thickness of 1.5 μm was produced under the same conditions as in Comparative Example 1, and then a HEMT element was produced by performing the same treatment as in Example 6. The amount of warpage of the obtained HEMT device was 15 μm, and the leakage current evaluated in the same manner as in Example 6 was 2 mA / mm.

(Comparison between Example 6 and Comparative Example 3)
In Example 6, a good HEMT element having a very small leakage current is obtained. That is, according to the method according to the above-described embodiment, a HEMT element including a semi-insulating layer in which both good crystal quality and high specific resistance are realized is realized even though the thickness is small. In addition, since the thickness of the semi-insulating layer is reduced, a HEMT element in which warpage is further reduced can be realized.

1 is a schematic diagram illustrating a configuration of a laminated body 10. 1 is a schematic diagram showing a configuration of a HEMT element 20 formed using a laminated body 10. FIG. It is a figure for demonstrating the definition method of curvature. It is a figure which shows an example of a structure of the manufacturing apparatus 100 typically. It is a figure which shows the flow of formation of the semi-insulating layer 3 which concerns on 1st Embodiment. It is a figure which shows the flow of formation of the semi-insulating layer 3 which concerns on 2nd Embodiment. It is a figure which shows the flow of formation of the semi-insulating layer 3 which concerns on 3rd Embodiment. 6 is a diagram showing specific resistance of a GaN layer according to condition 1 of Example 5 and Comparative Example 2. FIG. 6 is a graph showing specific resistance of a GaN layer according to condition 2 of Example 5 and Comparative Example 2. FIG. FIG. 6 is a diagram showing specific resistance of a GaN layer according to condition 3 of Example 5 and Comparative Example 2. 10 is a diagram illustrating a differential interference microscope image for Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal base material 1s Ground substrate 2 Growth base layer 3 Semi-insulating layer 4 Carrier supply layer 5 Source electrode 6 Drain electrode 7 Gate electrode 10 Laminated body 20 HEMT element 21 Processing container 24a-24g (various) gas supply source 28 Base plate 30 Heater 100 Manufacturing equipment

Claims (17)

A method for producing a group III nitride crystal,
A temperature raising step of raising a predetermined single crystal base substrate to a predetermined film formation temperature in a processing container;
A film forming step of epitaxially growing a first group III nitride crystal containing at least Ga on the single crystal base substrate heated to the predetermined film forming temperature;
With
In the temperature raising step, hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container until the temperature of the single crystal base substrate reaches the film formation temperature at the latest,
After the temperature of the single crystal base substrate reaches the predetermined film forming temperature, supply of a predetermined gas group necessary for forming the first group III nitride crystal into the processing container is started. The film forming step is performed by
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal,
A temperature raising step of raising a predetermined single crystal base substrate to a predetermined film formation temperature in a processing container;
A film forming step of epitaxially growing a first group III nitride crystal containing at least Ga on the single crystal base substrate heated to the predetermined film forming temperature;
With
In the temperature raising step, when the temperature of the single crystal base substrate is equal to or higher than a predetermined hydrogen gas supply start temperature, hydrogen gas is supplied so that a hydrogen gas atmosphere is formed in the processing container,
After the temperature of the single crystal base substrate reaches the predetermined film forming temperature, supply of a predetermined gas group necessary for forming the first group III nitride crystal into the processing container is started. The film forming step is performed by
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to claim 1 or claim 2,
Supplying the hydrogen gas when the temperature of the single crystal base substrate is 300 ° C. or higher in the temperature raising step;
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to claim 3,
Supplying the hydrogen gas when the temperature of the single crystal base substrate is 500 ° C. or higher in the temperature raising step;
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to any one of claims 1 to 4,
In the film forming step, the supply of the first gas group including the group V source gas for forming the first group III nitride is started in advance, and after the temperature fluctuation has converged, Starting to supply a second gas group containing a group III element gas to form a group III nitride of
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to any one of claims 1 to 5,
In the film forming step, the predetermined gas group is supplied so that a Ga content ratio in all Group III elements in the first Group III nitride is 50% or more.
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to claim 6,
In the film forming step, the predetermined gas group is supplied so that a Ga content ratio in all Group III elements in the first Group III nitride is 80% or more.
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to claim 7,
In the film forming step, the predetermined gas group is supplied so that the first group III nitride is GaN.
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to any one of claims 1 to 8,
The single crystal base substrate is formed by epitaxially forming a base layer made of a second group III nitride which is an AlN group III nitride on a predetermined single crystal base material,
The Al content ratio in the first Group III nitride is smaller than the Al content ratio in the second Group III nitride.
A method for producing a group III nitride crystal characterized by the above. A method for producing a group III nitride crystal according to claim 9,
The second group III nitride is AlN;
A method for producing a group III nitride crystal characterized by the above. An epitaxial substrate is obtained by forming a crystal layer made of a group III nitride crystal containing at least Ga on a predetermined single crystal base substrate by the manufacturing method according to any one of claims 1 to 10. thing,
A method for reducing warpage in an epitaxial substrate, characterized by: A method for reducing warpage in an epitaxial substrate according to claim 11,
Forming the crystal layer to have a thickness of 2.0 μm or less;
A method for reducing warpage in an epitaxial substrate, characterized in that: A crystal layer made of the first group III nitride is formed on a predetermined single crystal base substrate by the method for producing a group III nitride crystal according to any one of claims 1 to 10.
An epitaxial substrate characterized by that. The underlayer is formed with a film thickness of 0.5 to 1.0 μm by the method for producing a group III nitride crystal according to claim 10, and the crystal layer made of the first group III nitride is 1. It is formed with a film thickness of 0 to 2.0 μm, and an upper layer made of AlGaN is further epitaxially formed on the crystal layer.
An epitaxial substrate characterized by that. The epitaxial substrate according to claim 13 or 14,
The specific resistance of the crystal layer is 1 × 10 ⁶ Ω · cm or more,
An epitaxial substrate characterized by that. The epitaxial substrate according to claim 15, wherein
The crystal layer is formed so that the X-ray rocking curve half-value width of the (0002) plane is 200 seconds or less and there are no surface defects.
An epitaxial substrate characterized by that. It is formed using the epitaxial substrate according to any one of claims 13 to 16.
The semiconductor element characterized by the above-mentioned.