JP5249100B2 - Epitaxial substrate manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing an epitaxial substrate including a group III nitride film containing indium .

Nitride semiconductors are attracting attention as a semiconductor material constituting high-frequency and high-power semiconductor devices because of their high saturation electron velocity and high dielectric breakdown electric field. In particular, a semiconductor stacked structure in which a gallium nitride (GaN) film is used as a channel layer and an indium aluminum nitride (In _x Al _1-x N) film (hereinafter referred to as “InAlN film”) as a barrier layer is adopted in a semiconductor device. In this case, for example, in x to 0.18, a high concentration two-dimensional electron gas (2DEG; 2 Dimensional Electron Gas) can be generated without increasing the lattice mismatch between the channel layer and the barrier layer. The power that can be handled by the semiconductor device can be increased (see, for example, Non-Patent Document 1).

  As a method for forming an InAlN film, a metal organic chemical vapor deposition (MOCVD) method is known (see, for example, Non-Patent Document 1 and Non-Patent Document 2). Formation of a group III nitride film by MOCVD is performed by supplying a raw material containing elements constituting group III nitride together with a carrier gas to the inside of the reactor while heating the substrate accommodated in the reactor. In general, a nitride film is epitaxially grown on the surface of the substrate.

"International Electron Devices Meeting 2006 Technical Digest (USA), 2006, p.672-676 "Applied Physics Letter", (USA), July 28, 2003, Volume 83, Issue 4, p.668-670

  However, when a group III nitride film containing indium is formed by MOCVD, a large number of particles may adhere to the surface. Such particles are not preferable because they cause problems such as an increase in leakage current by preventing formation of a Schottky barrier between the group III nitride film and the electrode.

The present invention has been made to solve this problem, and provides an epitaxial substrate manufacturing method capable of suppressing particles from adhering to the surface of a group III nitride film containing indium. Objective.

To solve the above problems, a first aspect of the invention, contains at least indium composition by the general formula In _x Al _y Ga _z N in the first method for manufacturing an epitaxial substrate including a film of a group III nitride represented (A) While heating the substrate accommodated in the reactor, a raw material containing indium, a raw material containing a group III element other than indium, a raw material containing nitrogen and a carrier gas are introduced into the reactor. Supplying and epitaxially growing the first group III nitride film on the surface of the substrate; and (b) stopping the supply of the indium-containing material after the step (a); c) After the step (b), a step of continuing to supply a raw material containing a group III element other than the indium, a raw material containing the nitrogen, and the carrier gas.

In the first aspect of the present invention, the first group III nitride film further contains aluminum, and the epitaxial substrate contains at least gallium and has a composition of the general formula In _p Al _q Ga _r N. And a second group III nitride film that functions as a barrier layer in the epitaxial substrate, and wherein the second group III nitride film is a channel. And the composition of the first group III nitride film is x + y + z = 1, {y− (0.45 + q)} / 4.56 ≦ x ≦ {y− (0.27 + 0.51q)} /1.78, 0 ≦ z ≦ 0.4, and the composition of the second group III nitride film is p + q + r = 1, p = 0, 0 ≦ q ≦ 0.3. It is selected from the range shown.

  According to the invention of claim 1, since the raw material containing indium is removed by reaction with the raw material containing a group III element other than indium, the surface of the group III nitride film containing indium contains indium. Can be prevented from adhering.

According to the first aspect of the present invention, the concentration of the two-dimensional electron gas can be increased, lattice mismatch between the barrier layer and the channel layer can be reduced, and particles containing indium on the upper surface of the barrier layer can be obtained. It can suppress adhering.

It is sectional drawing which shows schematic structure of the semiconductor device which concerns on 1st Embodiment. It is a schematic diagram which shows schematic structure of a vapor phase growth apparatus. It is a flowchart explaining the manufacturing method of an epitaxial substrate. It is a time chart explaining the particle suppression process which concerns on 1st Embodiment. It is a time chart explaining the particle suppression process which concerns on 2nd Embodiment. It is a time chart explaining the particle suppression process which concerns on 3rd Embodiment. It is a time chart explaining the particle suppression process which concerns on 4th Embodiment. It is a time chart explaining the particle suppression process which concerns on 5th Embodiment. It is a figure which shows the evaluation result of an epitaxial substrate. It is a figure which shows the result of having observed the upper surface of the epitaxial substrate with the atomic force microscope. It is a figure which shows the result of having observed the upper surface of the epitaxial substrate with the atomic force microscope. It is a figure which shows the image obtained by observing the cross section of the particle | grains adhering to the InAlN film | membrane and its surface with a transmission electron microscope. It is a figure which shows the energy spectrum obtained by analyzing the composition of the particle adhering to the surface of the InAlN film. It is a figure which shows the result of having measured the density of the particle | grains containing an indium at the time of changing the composition of a channel layer and a barrier layer, and performing the particle | grain suppression process of Example 1. FIG. It is a figure which shows the result of having measured the density of the particle | grains containing an indium at the time of changing the composition of a channel layer and a barrier layer, and performing the particle | grain suppression process of Example 2. FIG. It is a figure which shows the result of having measured the density of the particle | grains containing an indium at the time of changing the composition of a channel layer and a barrier layer, and performing the particle | grain suppression process of Example 3. FIG. It is a figure which shows the result of having measured the density of the particle | grains containing an indium at the time of changing the composition of a channel layer and a barrier layer, and performing the particle | grain suppression process of Example 4. FIG. It is a figure which shows the result of having measured the density of the particle | grains containing an indium at the time of changing the composition of a channel layer and a barrier layer, and performing the particle | grain suppression process of Example 5. FIG. It is a figure which shows the result of having measured the density of the particle containing indium at the time of changing the composition of a channel layer and a barrier layer, and not performing a particle | grain suppression process.

<1 Causes of generation of particles containing indium>
FIG. 12 is a view showing an image obtained by observing a cross section of an InAlN film epitaxially grown by the MOCVD method and particles adhering to the surface with a transmission electron microscope (TEM). As shown in FIG. 12, the particles adhering to the surface of the InAlN film have a substantially hemispherical shape. In addition, despite the adhesion of particles to the surface, the InAlN film is substantially uniform and the surface thereof is also substantially flat, and there are no noticeable depressions or the like in the InAlN film.

  FIG. 13 is a diagram showing an energy spectrum obtained by analyzing the composition of particles using an energy dispersive X-ray spectrometer (EDX). The place where the composition analysis was performed is the portion of “x” in the image shown in FIG. FIG. 13 also shows elements that are the origins of the peaks that appear in the energy spectrum. As shown in FIG. 13, a peak originating from indium (In) appears strongly in the energy spectrum.

  Considering the result of the instrumental analysis described above, it is considered that the particles are mainly composed of indium and adhered after the InAlN film is formed.

  From these facts, the inventor of the present application left the raw material containing indium in the piping or the like of the MOCVD apparatus, and after the InAlN film was epitaxially grown, the raw material or the material derived from the raw material moved into the reactor, and the substrate When the temperature of the material is lowered, the raw material or a substance derived from the raw material aggregates and adheres to the surface of the InAlN film is considered to be the cause of generation of particles, and the particles containing indium described below are attached. It came to the process (henceforth "the particle suppression process") which suppresses this.

<2 First Embodiment>
<2-1 Configuration of Semiconductor Device 100>
FIG. 1 is a schematic diagram showing a schematic configuration of a semiconductor device 100 according to the first embodiment of the present invention. FIG. 1 is a cross-sectional view of the semiconductor device 100. The semiconductor device 100 is a high electron mobility transistor (HEMT). Note that the configuration of the semiconductor device 100, the configuration of the vapor phase growth apparatus 130, and the manufacturing method of the epitaxial substrate 101 described below may be employed in semiconductor devices other than the high electron mobility transistor.

  As shown in FIG. 1, a semiconductor device 100 includes a semiconductor stack in which a buffer layer 104, a channel layer 106, a spacer layer 108, and a barrier layer 110 made of a group III nitride film are stacked in this order on the surface of a substrate 102. It has a structure. A gate electrode 112, a drain electrode 114, and a source electrode 116 are formed on the upper surface of the barrier layer 110.

{Substrate 102}
The material constituting the substrate 102 and the orientation and polarity of the substrate 102 are selected from those capable of epitaxially growing a group III nitride film. For example, the material constituting the substrate 102 is silicon carbide (SiC), sapphire (Al ₂ O ₃ ), silicon (Si), spinel (MgAl ₂ O ₄ ), gallium arsenide (GaAs), ferrite (MnO—ZnO—Fe). Select from single crystals such as ₂ O ₃ ). In particular, if a single crystal of 6H—SiC or sapphire is selected as the material constituting the substrate 102 and a group III nitride film is epitaxially grown on the (0001) plane, a group III nitride film with good crystal quality can be obtained. Can be obtained.

  The thickness, planar shape, and planar dimensions of the substrate 102 are not limited. For example, a circular substrate or a square substrate having a diameter or a side of about 1 to 5 inches and a thickness of about 0.1 to 1 mm is adopted as the substrate 102. Is desirable.

{Buffer layer 104}
The buffer layer 104 suppresses deterioration of the crystal quality of the channel layer 106 due to lattice mismatch between the substrate 102 and the channel layer 106. The buffer layer 104 is preferably a group III nitride film having low crystallinity. The group III nitride constituting the buffer layer 104 is selected from, for example, gallium nitride (GaN) and aluminum nitride (AlN).

  The film thickness of the buffer layer 104 is preferably 10 to 1000 nm.

{Channel layer 106}
In the vicinity of the interface 118 with the spacer layer 108 inside the channel layer 106, a two-dimensional electron gas 120 that spreads substantially parallel to the interface 118 is generated. Thereby, the channel layer 106 becomes a channel through which electrons move.

The group III nitride constituting the channel layer 106 preferably has a composition represented by the general formula Al _y1 Ga _z1 N (y1 + z1 = 1, 0 ≦ y1 ≦ 0.3). The reason why the aluminum amount y1 is set to 0 ≦ y1 ≦ 0.3 is that when it exceeds this range, the flatness of the surface of the group III nitride film tends to deteriorate. However, this does not prevent selecting a composition outside this range.

{Barrier layer 110}
When an InAlN film is used as the barrier layer 110, the barrier layer 110 generates a two-dimensional electron gas 120 inside the channel layer 106 mainly due to the spontaneous polarization effect.

  The film thickness of the barrier layer 110 is desirably 1 to 35 nm. This is because the two-dimensional electron gas 120 tends to be difficult to be generated when the temperature is below this range, and the manufacture of the semiconductor device 100 tends to be difficult when the range is exceeded.

The group III nitride constituting the barrier layer 110 is desirably selected so that the concentration of the two-dimensional electron gas 120 generated in the channel layer 106 is increased and the lattice mismatch with the channel layer 106 is reduced. From these viewpoints, the group III nitride constituting the barrier layer 110 contains at least indium and aluminum, and has a general formula of In _x2 Al _y2 Ga _z2 N (x2 + y2 + z2 = 1, {y2− (0.45 + y1)} / 4. It is desirable to have a composition represented by .56 ≦ x2 ≦ {y2− (0.27 + 0.51y1)} / 1.78, 0 ≦ z2 ≦ 0.4). However, this does not prevent selecting a composition outside this range.

{Spacer layer 108}
The spacer layer 108 confines the two-dimensional electron gas 120 in the vicinity of the interface 118 with the spacer layer 108 inside the channel layer 106, thereby improving the concentration of the two-dimensional electron gas 120 and the mobility in the channel layer 106. However, the spacer layer 108 is not necessarily required and may be omitted.

  When the spacer layer 108 is provided, the film thickness is preferably 0.5 to 1.5 nm. This is because the effect of confining the two-dimensional electron gas 120 tends to be reduced if the range is below this range, and the crystal quality of the spacer layer 108 tends to be reduced due to internal stress if the range is exceeded.

The group III nitride constituting the spacer layer 108 is preferably selected such that the band gap energy Eg3 of the spacer layer 108 is larger than the band gap energy Eg2 of the barrier layer 110 (Eg3> Eg2). From this viewpoint, the group III nitride constituting the spacer layer 108 preferably has a composition represented by the general formula In _x3 Al _y3 Ga _z3 N (x3 + y3 + z3 = 1, 0 ≦ z3 ≦ 0.05).

{Gate electrode 112, drain electrode 114, and source electrode 116}
The material forming the gate electrode 112 is selected from a metal that forms a Schottky junction with the barrier layer 110. For example, a Pd / Au electrode in which films of palladium (Pd) and gold (Au) are stacked can be suitably used as the gate electrode 112.

  The drain electrode 114 and the source electrode 116 are selected from metals that are in ohmic contact with the barrier layer 110. For example, a Ti / Al / Ni / Au electrode in which titanium (Ti), aluminum (Al), nickel (Ni), and gold (Au) films are stacked can be suitably used as the drain electrode 114 and the source electrode 116. .

<2-2 Vapor growth apparatus 130>
FIG. 2 is a schematic diagram showing a schematic configuration of a vapor phase growth apparatus 130 used for manufacturing the epitaxial substrate 101 having the above-described semiconductor laminated structure. The vapor phase growth apparatus 130 is an MOCVD apparatus for epitaxially growing a group III nitride film on the surface of a substrate by MOCVD.

  As shown in FIG. 2, the vapor phase growth apparatus 130 includes a reactor 132, a raw material supply unit 134, and a control unit 136.

  The reactor 132 contains a substrate 198 on which a group III nitride film is epitaxially grown. Inside the reactor 132, a susceptor 138 and a heater 140 are provided. The susceptor 138 holds the substrate 198. The heater 140 heats the substrate 198 held by the susceptor 138 by heating the susceptor 138.

  Hereinafter, literally, “heating” will be used as a word meaning that heat is applied to the substrate 102 from the heater 140 that has generated heat. Therefore, the “heating” of the substrate 198 is not only to raise the temperature of the substrate 198 but also to keep the temperature of the substrate 198 constant, or to lower the temperature of the substrate 198 at a slower rate than when natural cooling is performed. Is also done. That is, below, “heating” and “temperature increase” are conceptually used separately.

The raw material supply unit 134 is a raw material containing a group III element constituting a group III nitride, that is, trimethylindium (In (CH ₃ ) ₃ ; hereinafter referred to as “TMI”) containing indium (In), aluminum All of trimethylaluminum containing (Al) (Al (CH ₃ ) ₃ ; hereinafter referred to as “TMA”) and trimethylgallium containing Ga (Ga (CH ₃ ) ₃ ; hereinafter referred to as “TMG”) or A part of the vapor is supplied into the reactor 132 together with the carrier gas, and a raw material containing nitrogen (N) constituting group III nitride, that is, ammonia (NH ₃ ) gas is supplied into the reactor 132. Of course, other types of organometallic compounds may be selected as a raw material containing a group III element, and other types of nitrogen compounds may be selected as a raw material containing nitrogen. Further, the raw material supply unit 134 may further supply the raw material of the donor element and the acceptor element into the reactor 132.

  As shown in FIG. 2, the raw material supply unit 134 includes raw material supply systems 142, 144, and 146 that independently supply a raw material gas into the reactor 132.

  The raw material supply system 142 includes a bubbling unit 148 for bubbling TMI with nitrogen gas, a bubbling unit 150 for bubbling TMA with nitrogen gas, and a bubbling unit 152 for bubbling TMG with nitrogen gas from the nitrogen gas supply source 154 to the inside of the reactor 132. It is provided in the pipe 156 leading to The bubbling units 148, 150, and 152 serve as supply sources for TMI, TMA, and TMG, respectively, and mix vapors of these raw materials with nitrogen gas that is a carrier gas. The pipe 156 is connected to the inside of the reactor 132 from the nitrogen gas supply source 154 without passing through the bubbling parts 148, 150, and 152, and is branched from the pipe 1561 through the bubbling parts 148, 150, and 152. And a pipe 1562 returning to 1561.

  The raw material supply system 144 includes a bubbling unit 158 for bubbling TMI with hydrogen gas, a bubbling unit 160 for bubbling TMA with hydrogen gas, and a bubbling unit 162 for bubbling TMG with hydrogen gas from the hydrogen gas supply source 164 to the inside of the reactor 132. It is provided in the pipe 166 leading to. The bubbling units 158, 160, 162 serve as supply sources for TMI, TMA, and TMG, respectively, and mix the vapor of these raw materials with hydrogen gas that is a carrier gas. The piping 166 is routed from the nitrogen gas supply source 164 to the inside of the reactor 132 without passing through the bubbling portions 158, 160, 162, and from the piping 1661 to the piping via the bubbling portions 158, 160, 162. And a pipe 1662 for returning to 1661.

  The raw material supply system 146 includes a pipe 168 extending from the ammonia gas supply source 166 to the inside of the reactor 132.

  In any of the raw material supply systems 142 and 144, whether or not bubbling is actually performed in the bubbling units 148, 150, 152, 158, 160, and 162 can be switched by the mass flow controller.

  Depending on the composition of the group III nitride constituting the buffer layer 104, the channel layer 106, the spacer layer 108, and the barrier layer 110 and the carrier gas used when these layers are formed, the bubbling portions 150, 152, 158, In some cases, unnecessary items may appear in 160 and 162. In such a case, providing an unnecessary bubbling portion may be omitted.

  The control unit 136 heats the substrate 198 by the susceptor 138, supplies nitrogen gas from the supply source 154, supplies hydrogen gas from the supply source 164, supplies ammonia gas from the supply source 166, and bubbling units 148, 150, and 152. , 158, 160, 162 control bubbling and the like.

<2-3 Manufacturing Method of Epitaxial Substrate 101>
FIG. 3 is a flowchart for explaining a method for manufacturing the epitaxial substrate 101 having the above-described semiconductor multilayer structure. FIG. 4 is a time chart for explaining the particle suppression process according to the first embodiment. FIG. 4 shows the state of the vapor phase growth apparatus 130 when the barrier layer 110 is formed (timing t1 to t2) and the particle suppression process is performed (timing t2 to t3), that is, nitrogen controlled by the control unit 136. Presence / absence of gas supply (FIG. 4A), supply / non-supply of TMI bubbled with nitrogen gas (FIG. 4B), supply / non-supply of raw materials other than TMI bubbled with nitrogen gas (FIG. 4C) ), Whether ammonia gas is supplied (FIG. 4D), whether hydrogen gas is supplied (FIG. 4E), and the temperature of the substrate 198 (FIG. 4F).

{Thermal cleaning of substrate 102}
In manufacturing the epitaxial substrate 101, first, as shown in FIG. 3, the substrate 102 is accommodated in the reactor 132, and the surface of the substrate 102 is thermally cleaned (step S101). In the thermal cleaning, the substrate 102 is held on the susceptor 138, hydrogen gas is supplied to the inside of the reactor 132 to make the inside of the reactor 132 a hydrogen atmosphere, and the temperature of the substrate 102 is raised to 1000 to 1300 ° C. to 5 to 30. Do this by maintaining minutes. Note that thermal cleaning may be omitted if the surface of the obtained substrate 102 is sufficiently clean and flat. Thermal cleaning and other cleaning methods may be used in combination, or other cleaning methods may be employed instead of thermal cleaning.

{Formation of buffer layer 104}
Subsequently, the buffer layer 104 is formed (step S102). The buffer layer 104 is formed by lowering the temperature of the substrate 102 to 500 to 700 ° C., bubbling a necessary Group III element material with hydrogen gas, supplying the hydrogen gas into the reactor 132, And ammonia gas is supplied into the reactor 132. As a result, the raw materials of all elements constituting the group III nitride constituting the buffer layer 104 are supplied into the reactor 132 together with hydrogen gas, and the raw materials supplied into the reactor 132 react to react with the surface of the substrate 102. In addition, a group III nitride film is epitaxially grown.

{Formation of channel layer 106}
Subsequently, the channel layer 106 is formed (step S103). The channel layer 106 is formed by raising the temperature of the substrate 102 to 1050 to 1150 ° C., bubbling a necessary Group III element material with hydrogen gas, supplying the hydrogen gas into the reactor 132, and supplying nitrogen gas. Then, hydrogen gas and ammonia gas are supplied into the reactor 132. As a result, the raw materials of all the elements constituting the group III nitride constituting the channel layer 106 are supplied into the reactor 132 together with the nitrogen gas and the hydrogen gas, and the raw materials supplied into the reactor 132 react to react with the buffer. A group III nitride film is epitaxially grown on the surface of the layer 104.

{Formation of spacer layer 108}
Next, the spacer layer 108 is formed (step S104). The spacer layer 108 is formed by bubbling a necessary Group III element raw material with hydrogen gas while maintaining the temperature of the substrate 102 and then supplying the hydrogen gas into the reactor 132, and supplying hydrogen gas and ammonia gas. This is performed by supplying the inside of the reactor 132. As a result, the raw materials of all the elements constituting the group III nitride constituting the spacer layer 108 are supplied into the reactor 132 together with the hydrogen gas, and the raw materials supplied into the reactor 132 react to react with each other in the channel layer 106. A group III nitride film is epitaxially grown on the surface.

{Formation of barrier layer 110}
Subsequently, the barrier layer 110 containing indium is formed (step S105). In forming the barrier layer 110, first, the supply of hydrogen gas is stopped, the supply of nitrogen gas is started, and the temperature of the substrate 102 is lowered to 600 to 900 ° C. while the supply of ammonia gas is continued. After that, while continuing supply of nitrogen gas and ammonia gas, a necessary group III element material (a group III element material other than TMI and TMI) was bubbled with nitrogen gas, and then the nitrogen gas was passed into the reactor 132. To supply. As a result, the raw materials of all the elements constituting the group III nitride constituting the barrier layer 110 are supplied into the reactor 132 together with the nitrogen gas, and the raw materials supplied into the reactor 132 react to react with the spacer layer 108. A group III nitride film is epitaxially grown on the surface.

  Thus, if the carrier gas used when forming the barrier layer 110 is only nitrogen gas, the group III nitride dangling bonds constituting the barrier layer 110 can be terminated with nitrogen. The ideal electronic structure of the nitride can be maintained, and the concentration of the two-dimensional electron gas 120 can be increased.

  The vapor phase growth apparatus 130 described above uses the bubbling portions 148 and 150 used when forming the barrier layer 110 in the pipe 156 that leads the nitrogen gas used when forming the barrier layer 110 from the supply source 154 to the inside of the reactor 132. , 152, and independently, a bubbling portion 158 used when forming the spacer layer 108 in the pipe 166 that leads the hydrogen gas used when forming the spacer layer 108 from the supply source 144 to the inside of the reactor 132. , 160, 162 are provided. For this reason, carrier gas can be switched from hydrogen gas to nitrogen gas in a short time, and it can suppress that hydrogen gas mixes in the atmosphere at the time of forming barrier layer 110.

  However, these do not prevent the epitaxial substrate 101 from being manufactured using a vapor phase growth apparatus having a configuration different from that of the vapor phase growth apparatus 130 shown in FIG.

  Further, the above-described vapor phase growth apparatus 130 is used when forming the barrier layer 110 upstream, midstream, and downstream along the flow path of nitrogen gas used when forming the barrier layer 110, respectively. Bubbling portions 148, 150, and 152 are provided. For this reason, since it can suppress that only TMI remains in piping, it can control that the particle containing indium adheres to the surface of barrier layer 110. Of course, it is possible to change whether each of the bubbling portions 148, 150, 152 is provided upstream, midstream, or downstream.

{Particle suppression processing}
After the formation of the barrier layer 110, a particle suppression process is performed (step S106). In the particle suppression process according to the first embodiment, as shown in FIG. 4B, while the supply of TMI bubbling with nitrogen gas is stopped at the timing t2, FIG. 4A, FIG. As shown in FIG. 4D, the supply of nitrogen gas and ammonia gas and the supply of raw materials other than TMI bubbled with nitrogen gas are continued after timing t2. That is, the particle suppression process according to the first embodiment is performed by continuing the supply of the raw material other than TMI (the group III element raw material other than TMI and ammonia gas) and the nitrogen gas after the supply of TMI is stopped. As a result, TMI reacts with the Group III element raw material other than TMI in the gas phase and is removed, making it difficult to reach the saturated vapor pressure, thereby preventing the indium-containing particles from adhering to the surface of the barrier layer 110. Can do. Further, continuing the supply of raw materials other than TMI contributes to suppressing the occurrence of defects on the surface of the barrier layer 110 and preventing the flatness of the surface of the barrier layer 110 from being impaired. .

  The time for performing the particle suppression process according to the first embodiment is desirably 10 to 60 seconds. If the thickness falls below this range, removal of particles containing indium tends to be insufficient, and if the thickness exceeds this range, another group III nitride film is likely to be formed on the surface of the barrier layer 110.

  In the particle suppression process according to the first embodiment, during the formation of the barrier layer 110 and the particle suppression process, as shown in FIG. 4E, hydrogen gas is not supplied, as shown in FIG. In addition, the substrate 102 is continuously heated to maintain the temperature of the substrate 102 when the barrier layer 110 is formed. Thereby, since TMI reacts more easily than the case where the substrate 102 is naturally cooled, adhesion of particles containing indium can be more effectively suppressed. However, it is allowed to change the temperature of the substrate 102 within a range that does not hinder the removal of particles containing indium, or to stop the heating of the substrate 102 and start natural cooling during the particle suppression process.

  Note that while the barrier layer 110 is formed and the particle suppression process is performed, the flow rates of the nitrogen gas and the ammonia gas may be constant, but the nitrogen gas and the ammonia gas may be kept within a range that does not hinder the removal of the particles containing indium. Both or one of the flow rates may be changed.

  After the particle suppression processing according to the first embodiment is finished, the supply of raw materials other than TMI is also stopped, the heating of the substrate 102 is stopped, and then the supply of ammonia gas is also stopped. The epitaxial substrate 101 is recovered from the inside of the reactor 132.

<3 Second Embodiment>
The second embodiment relates to a particle suppression process that can be employed instead of the particle suppression process according to the first embodiment. FIG. 5 is a time chart for explaining the particle suppression process according to the second embodiment. FIG. 5 illustrates the state of the vapor phase growth apparatus 130 when the barrier layer 110 is formed (timing t1 to t2) and the particle suppression process is performed (timing t2 to t3), that is, nitrogen controlled by the control unit 136. Presence of gas supply (FIG. 5A), supply of TMI bubbled with nitrogen gas (FIG. 5B), supply of raw materials other than TMI bubbled with nitrogen gas (FIG. 5C) ), Whether ammonia gas is supplied (FIG. 5D), whether hydrogen gas is supplied (FIG. 5E), and the temperature of the substrate (FIG. 5F).

  In the particle suppression process according to the second embodiment, as shown in FIGS. 5B and 5C, the supply of raw materials other than TMI and TMI bubbled with nitrogen gas is stopped at timing t2. As shown in FIG. 5 (a) and FIG. 5 (d), the supply of nitrogen gas and ammonia gas is performed by continuing after timing t2. That is, the particle suppression process according to the second embodiment is performed by continuing the supply of ammonia gas and nitrogen gas after stopping the supply of Group III elements other than TMI and TMI. Thereby, since TMI is diluted by the carrier gas, it is possible to suppress adhesion of particles containing indium to the surface of the barrier layer 110. Further, continuing the supply of ammonia gas and nitrogen gas suppresses the occurrence of defects on the surface of the barrier layer 110 and contributes to not impairing the flatness of the surface of the barrier layer 110. Yes.

  The time for performing the particle suppression process according to the second embodiment is desirably 10 minutes or more, and more desirably 30 minutes or more. This is because if it falls below this range, removal of particles containing indium tends to be insufficient.

  In the particle suppression process according to the second embodiment, as shown in FIG. 5E, hydrogen gas is not supplied during the formation of the barrier layer 110 and the particle suppression process, as shown in FIG. In addition, the substrate 102 is continuously heated to maintain the temperature of the substrate 102 when the barrier layer 110 is formed. If the flow rates of the nitrogen gas and the ammonia gas are kept constant during the formation of the barrier layer 110 and the particle suppression treatment, the temperature change caused by the flow rate change and the particles containing indium from the inner wall of the reactor 132 The withdrawal of can be prevented. However, this does not prevent changing the flow rate of both or one of nitrogen gas and ammonia gas when performing the particle suppression process. When changing the flow rate of one or both of nitrogen gas and ammonia gas, it is desirable that the ratio of the ammonia gas supply amount to the total of the nitrogen gas supply amount and the ammonia gas supply amount be 10% or more. This is because, within this range, the nitrogen raw material is sufficiently supplied to the inside of the reactor 132, so that the occurrence of defects on the surface of the barrier layer 110 can be effectively suppressed.

  After the particle suppression process according to the second embodiment is finished, the heating of the substrate 102 is stopped and then the supply of ammonia gas is also stopped, the temperature of the substrate 102 is lowered to near room temperature, and the obtained epitaxial substrate 101 is reacted with the reactor. Collect from inside 132.

<4 Third Embodiment>
The third embodiment relates to a particle suppression process that can be employed instead of the particle suppression process according to the first embodiment. FIG. 6 is a time chart for explaining the particle suppression process according to the third embodiment. FIG. 6 shows the state of the vapor phase growth apparatus 130 when the barrier layer 110 is formed (timing t1 to t2) and the particle suppression process is performed (timing t2 to t3), that is, nitrogen controlled by the control unit 136. Presence or absence of supply of gas (FIG. 6A), Presence or absence of supply of TMI bubbled with nitrogen gas (FIG. 6B), Presence or absence of supply of raw materials other than TMI bubbled with nitrogen gas (FIG. 6C) ), Whether ammonia gas is supplied (FIG. 6D), whether hydrogen gas is supplied (FIG. 6E), and the temperature of the substrate (FIG. 6F).

  In the particle suppression process according to the third embodiment, as shown in FIGS. 6 (a), 6 (b), 6 (c), 6 (d) and 6 (e), supply of nitrogen gas, The supply of TMI bubbled with nitrogen gas, the supply of raw materials other than the TMI bubbled with nitrogen gas, the supply of ammonia gas, and the supply of hydrogen gas are performed in the same manner as in the second embodiment. Accordingly, the supply of the raw material and the carrier gas into the reactor 132 is performed in the same manner as in the second embodiment.

  However, in the particle suppression process according to the third embodiment, as shown in FIG. 6F, the temperature of the substrate 102 when the barrier layer 110 is formed by heating the substrate 102 more strongly after entering the particle suppression process. The temperature of the substrate 102 is raised above (hereinafter referred to as “barrier layer formation temperature”).

  The maximum temperature of the substrate 102 when the particle suppression process according to the third embodiment is performed is preferably 100 ° C. or more, and more preferably 300 ° C. or more higher than the barrier layer formation temperature. Further, the time from the start of the particle suppression process until the temperature of the substrate 102 reaches the maximum temperature is preferably 5 minutes or less, and more preferably 2 minutes or less. This is because, within this range, particles containing indium can be efficiently removed while suppressing the occurrence of defects on the surface of the barrier layer 110.

  As described above, when ammonia gas and nitrogen gas are supplied in a state where the temperature of the substrate 102 is higher than when the barrier layer 110 is formed, TMI is easily decomposed, so that the time required for the particle suppression process is shortened.

  In addition, after the temperature of the substrate 102 reaches the maximum temperature, the temperature may be maintained for a certain time.

  After the particle suppression process according to the third embodiment is finished, the heating of the substrate 102 is stopped and then the supply of ammonia gas is also stopped, the temperature of the substrate 102 is lowered to near room temperature, and the obtained epitaxial substrate 101 is reacted with the reactor. Collect from inside 132.

<5 Fourth Embodiment>
The fourth embodiment relates to a particle suppression process that can be employed instead of the particle suppression process according to the first embodiment. FIG. 7 is a time chart for explaining the particle suppression processing according to the fourth embodiment. FIG. 7 shows the state of the vapor phase growth apparatus 130 when the barrier layer 110 is formed (timing t1 to t2) and the particle suppression process is performed (timing t2 to t3), that is, nitrogen controlled by the control unit 136. Presence / absence of gas supply (FIG. 7A), supply / non-supply of TMI bubbled with nitrogen gas (FIG. 7B), supply / non-supply of TMI bubbled with nitrogen gas (FIG. 7C) ), Whether ammonia gas is supplied (FIG. 7D), whether hydrogen gas is supplied (FIG. 7E), and the substrate temperature (FIG. 7F).

  In the particle suppression process according to the fourth embodiment, as shown in FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D, and FIG. The supply of TMI bubbled with nitrogen gas, the supply of raw materials other than the TMI bubbled with nitrogen gas, the supply of ammonia gas, and the supply of hydrogen gas are performed in the same manner as in the second embodiment. Accordingly, the supply of the raw material and the carrier gas into the reactor 132 is performed in the same manner as in the second embodiment.

  However, in the particle suppression process according to the fourth embodiment, as shown in FIG. 6 (f), the substrate 102 is heated weakly after entering the particle suppression process, and the temperature of the substrate 102 is set higher than the temperature at the time of barrier layer formation. After the temperature is lowered, the temperature of the substrate 102 is kept constant.

  The difference between the minimum temperature of the substrate 102 and the barrier layer formation temperature when performing the particle suppression process according to the fourth embodiment is desirably 150 ° C. or less. This is because, within this range, the efficiency of removing particles is not significantly reduced.

  After completion of the particle suppression process according to the fourth embodiment, the supply of ammonia gas is stopped after heating of the substrate 102 is stopped, the temperature of the substrate 102 is lowered to near room temperature, and the obtained epitaxial substrate 101 is made into the reactor 132. Recover from inside.

  Thus, even if ammonia gas and nitrogen gas are supplied in a state where the temperature of the substrate 102 is lower than when the barrier layer 110 is formed, particles containing indium can be removed. In addition, if ammonia gas and nitrogen gas are supplied in a state where the temperature of the substrate 102 is lower than when the barrier layer 110 is formed, it is possible to suppress the occurrence of defects on the surface of the barrier layer 110. The flatness of the surface of the substrate 101 can be improved.

<6 Fifth Embodiment>
The fifth embodiment relates to a particle suppression process that can be employed instead of the particle suppression process according to the first embodiment. FIG. 8 is a time chart for explaining the particle suppression process according to the fifth embodiment. FIG. 7 shows the state of the vapor phase growth apparatus 130 when the barrier layer 110 is formed (timing t1 to t2) and the particle suppression process is performed (timing t2 to t3), that is, nitrogen controlled by the control unit 136. Presence / absence of gas supply (FIG. 7A), supply / non-supply of TMI bubbled with nitrogen gas (FIG. 7B), supply / non-supply of TMI bubbled with nitrogen gas (FIG. 7C) ), Whether ammonia gas is supplied (FIG. 7D), whether hydrogen gas is supplied (FIG. 7E), and the substrate temperature (FIG. 7F).

  As shown in FIGS. 8 (a), 8 (b) and 8 (c), the particle suppression process according to the fifth embodiment is performed by supplying nitrogen gas, and bubbling with nitrogen gas and raw materials other than TMI. While the supply is stopped at timing t2, as shown in FIG. 8 (d), the supply of ammonia gas is continued after timing t2, and the supply of hydrogen gas at timing t2 as shown in FIG. 8 (e). To start. That is, the particle suppression process according to the fifth embodiment is performed by continuing the supply of ammonia gas after stopping the supply of the group III element materials other than TMI and TMI and the supply of nitrogen gas and starting the supply of hydrogen gas. Thereby, since TMI is quickly diluted with hydrogen gas, it is possible to suppress adhesion of particles containing indium to the surface of the barrier layer 110.

  The time for performing the particle suppression process according to the fifth embodiment is desirably 60 to 300 seconds. This is because removal of particles containing indium tends to be insufficient if the thickness is below this range, and defects are likely to occur on the surface of the group III nitride constituting the barrier layer 110 if this range is exceeded. is there.

  In the particle suppression process according to the fifth embodiment, heating of the substrate 102 is stopped and the substrate 102 is allowed to cool naturally during the particle suppression process. However, it is allowed to heat the substrate 102 within a range where the surface of the barrier layer 110 is not etched and damaged. When the substrate 102 is heated, it is desirable that the maximum temperature of the substrate 102 does not exceed a temperature that is 150 ° C. higher than the barrier layer formation temperature.

  After the particle suppression process according to the fifth embodiment is finished, that is, after the temperature of the substrate 102 is lowered to near room temperature, the supply of hydrogen gas and ammonia gas is also stopped, and the obtained epitaxial substrate 101 is placed in the reactor 132. Collect from inside.

  Hereinafter, Examples 1 to 5 relating to the epitaxial substrate 101 manufactured through the particle suppression process according to the first to fifth embodiments and Comparative Examples regarding the epitaxial substrate manufactured without performing the particle suppression process will be described.

{Example 1}
In Example 1, a sapphire substrate having a diameter of 2 inches was thermally cleaned at 1150 ° C. for 10 minutes, and a gallium nitride (GaN) film having a thickness of 20 nm was epitaxially grown as a buffer layer 104 at 500 ° C. to form a channel layer 106. A gallium nitride (GaN) film having a thickness of 2.0 μm was epitaxially grown at 1100 ° C.

  Subsequently, an aluminum nitride (AlN) film having a thickness of 1 nm was epitaxially grown at 1100 ° C. as the spacer layer 108.

Subsequently, an indium aluminum nitride (In _0.18 Al _0.82 N) film having a thickness of 15 nm was epitaxially grown at 730 ° C. as the barrier layer 110. At this time, the flow rate of ammonia gas was 1500 sccm, the flow rate of nitrogen gas for bubbling TMI was 100 sccm, and the flow rate of nitrogen gas for bubbling TMA was 10 sccm.

  Finally, the particle suppression process according to the first embodiment was performed over 60 seconds.

{Example 2}
Similar to the case of Example 1, after the indium aluminum nitride (In _0.18 Al _0.82 N) film was epitaxially grown, the particle suppression process according to the second embodiment was performed over 30 minutes.

{Example 3}
Similar to the case of Example 1, after the epitaxial growth of the indium aluminum nitride (In _0.18 Al _0.82 N) film was performed, the particle suppression process according to the third embodiment was performed. At this time, the maximum temperature of the substrate 102 was 1100 ° C., and the heating rate was 300 ° C. per minute.

{Example 4}
As in the case of Example 1, after the indium aluminum nitride (In _0.18 Al _0.82 N) film was epitaxially grown, the particle suppression process according to the fourth embodiment was performed. At this time, the minimum temperature of the substrate 102 was 500 ° C., and the cooling rate was 100 ° C. per minute. The time for maintaining the minimum temperature of 500 ° C. was 60 minutes.

{Example 5}
Similar to the case of Example 1, after the epitaxial growth of the indium aluminum nitride (In _0.18 Al _0.82 N) film was performed, the particle suppression process according to the fifth embodiment was performed.

{Comparative example}
Similar to the case of Example 1, the epitaxial growth of an indium aluminum nitride (In _0.18 Al _0.82 N) film was performed. Particle suppression processing was not performed.

{Evaluation of epitaxial substrate 101}
FIG. 9 is a diagram showing the evaluation results of the epitaxial substrates 101 of Examples 1 to 5 and Comparative Example 1. In FIG. 9, for each of the epitaxial substrates 101 of Examples 1 to 5 and Comparative Example 1, sheet carrier concentration, mobility, sheet resistance, presence or absence of two-dimensional electron gas, depth of two-dimensional electron gas, constituent elements, Crystal density, surface roughness, gate leakage current, and density of particles containing indium are shown. Of these, the sheet carrier concentration, mobility and sheet resistance were measured by Hall measurement. The presence or absence of the two-dimensional electron gas and the depth of the two-dimensional electron gas were measured by CV measurement. The constituent elements are identified by analyzing the surface of the epitaxial substrate 101 with an X-ray photoelectron spectrometer (XPS), and the crystal species is the X-ray diffractometer (XRD; XRD) of the upper surface of the epitaxial substrate 101. The density of particles containing indium was determined by observing the upper surface of the barrier layer with an atomic force microscope. A gate leakage current is obtained by processing a source-drain voltage of 100 V on a transistor element having a gate width of 1 nm, a gate-source interval of 0.5 μm, a gate-drain interval of 7.5 μm, and a gate length of 1.5 μm, which is manufactured by processing the epitaxial substrate 101. It is a measured value in a state where a gate bias of −10 V is applied.

In manufacturing the transistor element, first, the boundary portion of each transistor element was removed to a depth of 400 nm by using photolithography and reactive ion etching (RIE). Subsequently, a silicon dioxide (SiO ₂ ) film having a thickness of 10 nm is formed on the surface of the epitaxial substrate 101, and the silicon dioxide film formed in the region where the source electrode and the drain electrode are provided is removed by photolithography. did. Subsequently, Ti / Al / Ni / Au (film thickness 25/75/15/100 nm) electrodes are formed as drain and source electrodes by vacuum deposition and photolithography, improving the ohmic properties of the drain and source electrodes. In order to achieve this, heat treatment at 850 ° C. was performed for 30 seconds in a nitrogen atmosphere. Next, the silicon dioxide film formed in the region where the gate electrode is provided is removed by photolithography. Subsequently, a Pd / Au (film thickness 30/100 nm) electrode was formed as a gate electrode by vacuum deposition and photolithography. Finally, a silicon nitride (Si ₃ N ₄ ) passivation film is formed by chemical vapor deposition (CVD) and photolithography, and contact holes are formed in the gate electrode, drain electrode, and source electrode portions. Wire bonding was performed.

  10 and 11 are diagrams showing the results of observation of the surface of the epitaxial substrate 101 of Example 5 and Comparative Example 1 with an atomic force microscope (AFM), respectively. FIGS. 10 and 11A show images of a 5 μm square region when the top surface of the epitaxial substrate 101 is viewed from the front, and FIG. 11B shows irregularities in the 1 μm square region.

As shown in FIG. 10, step flow growth was observed on the upper surface of the epitaxial substrate 101 of Example 5, and particles containing indium could not be found. On the other hand, as shown in FIG. 11, particles containing approximately 1.9 × 10 ⁸ pieces / cm ² of indium were scattered on the upper surface of the epitaxial substrate 101 of Comparative Example 1. Although not shown, even if the surface of the epitaxial substrate 101 of Examples 1 to 4 is observed with an atomic force microscope, an image similar to that of the epitaxial substrate 101 of Example 5 is obtained.

  As is clear from the comparison between Examples 1 to 5 and Comparative Example 1, it is possible to suppress adhesion of particles containing indium on the surface of the barrier layer by performing the above-described particle suppression treatment. Further, as is clear from the comparison between Examples 1 to 4 and Example 5, the surface roughness can be reduced by making the atmosphere when performing the particle suppression process a mixed atmosphere of nitrogen gas and ammonia. it can. This is considered to mean that the mixed atmosphere of nitrogen gas and ammonia suppresses the generation of surface defects. Further, as is clear from the comparison of Examples 2 to 4, when the atmosphere when performing the particle suppression process is a mixed atmosphere of nitrogen gas and ammonia, the surface roughness is lower when the temperature at which the particle suppression process is performed is lower. Get smaller. This seems to mean that the lower the temperature, the easier it is to suppress the occurrence of defects.

FIGS. 14-18 is a figure which shows the result of having measured the density of the particle | grains containing indium at the time of changing the composition of a channel layer and a barrier layer, and performing the particle | grain suppression process of Examples 1-5, respectively. . Moreover, FIG. 19 is a figure which shows the result of having measured the density of the particle | grains containing an indium when the composition of a channel layer and a barrier layer was changed and the particle suppression process was not performed like the comparative example 1. FIG. As shown in FIGS. 14 to 18, the composition of the channel layer is changed within the range represented by the general formula Al _y1 Ga _z1 N (y1 + z1 = 1, 0 ≦ y1 ≦ 0.3). formula _{In x2 Al y2 Ga z2 N (} x2 + y2 + z2 = 1, {y2- (0.45 + y1)} / 4.56 ≦ x2 ≦ {y2- (0.27 + 0.51y1)} / 1.78,0 ≦ z2 ≦ 0 .4) Even if it is changed within the range represented by (4), it is possible to suppress adhesion of particles containing indium on the upper surface of the barrier layer by performing the same particle suppression treatment as in Examples 1 to 5. is there. However, as shown in FIG. 19, when the particle suppression process is not performed, it is not possible to prevent particles containing indium from adhering to the upper surface of the barrier layer, and 0.8 × 10 ^{8 to} 3.5 Particles containing × 10 ⁸ particles / cm ² of indium were scattered on the upper surface of the barrier layer.

  Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention. In particular, when the group III nitride film containing indium is not present in the uppermost layer of the epitaxial substrate 101, the above-described particle suppression process is naturally scheduled.

DESCRIPTION OF SYMBOLS 100 Semiconductor device 101 Epitaxial substrate 102 Substrate 104 Buffer layer 106 Channel layer 108 Spacer layer 110 Barrier layer 112 Gate electrode 114 Drain electrode 116 Source electrode 120 Two-dimensional electron gas 130 Vapor phase growth apparatus 132 Reactor 140 Heater 154,164,166 Supply source 156, 166, 168 Piping 148, 150, 152, 158, 160, 162 Bubbling part 198 Substrate

Claims (1)

A method of manufacturing an epitaxial substrate including a first group III nitride film containing at least indium and having a composition represented by a general formula In _x Al _y Ga _z N,
(a) While heating the substrate accommodated in the reactor, a raw material containing indium, a raw material containing a group III element other than indium, a raw material containing nitrogen and a carrier gas are supplied into the reactor, Epitaxially growing the first group III nitride film on the surface of the substrate;
(b) after the step (a), stopping the supply of the raw material containing indium;
(c) after the step (b), continuing the supply of the raw material containing a group III element other than the indium, the raw material containing the nitrogen, and the carrier gas;
Equipped with a,
The first group III nitride film comprises:
Further containing aluminum,
The epitaxial substrate is
A second group III nitride film containing at least gallium and having a composition represented by the general formula In _p Al _q Ga _r N;
In the epitaxial substrate,
The first group III nitride film functions as a barrier layer, and the second group III nitride film functions as a channel layer;
The composition of the first group III nitride film is x + y + z = 1, {y− (0.45 + q)} / 4.56 ≦ x ≦ {y− (0.27 + 0.51q)} / 1.78, Selected from the range represented by 0 ≦ z ≦ 0.4,
The composition of the second group III nitride film is selected from the range represented by p + q + r = 1, p = 0, 0 ≦ q ≦ 0.3.
Epitaxial substrate manufacturing method.