JP5260831B2 - Group III nitride semiconductor crystal manufacturing method, group III nitride semiconductor substrate manufacturing method, and semiconductor device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group III nitride semiconductor crystal with a high resistance value, a group III nitride semiconductor substrate, a semiconductor device, and a manufacturing method of the group III nitride semiconductor crystal. <P>SOLUTION: A Fe-doped GaN layer 14 of a GaN substrate 1 comprises group III nitride semiconductor crystals with Fe atoms as transition metal atoms added, and Ga atom vacancy density is 1&times;10<SP>16</SP>cm<SP>-3</SP>or less. A density of the Fe atoms in the layer 14 is 5&times;10<SP>17</SP>to 10<SP>20</SP>cm<SP>-3</SP>. In addition, the density of the Fe atoms in the layer 14 is higher than a total of densities of oxygen atoms and silicon atoms in the layer 14. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a group III nitride semiconductor crystal to which a transition metal atom is added.

Group III nitride semiconductors are expected as electronic materials for light-emitting elements and transistors because of their large band gap and direct transition between bands.
It is desired to reduce the size of the system device by fabricating a device in which such a light-emitting element, a transistor, and the like composed of a group III nitride semiconductor are integrated on a single substrate.
In such a device, it is necessary to electrically isolate each element by a substrate. Therefore, a high resistance group III nitride semiconductor substrate exhibiting semi-insulating properties is required as the substrate.
Here, Patent Document 1 discloses a technique for obtaining a semi-insulating crystal by adding a transition metal to a III-V group semiconductor crystal such as GaAs or InP, although it is a material different from the group III nitride semiconductor substrate. It is disclosed.

Japanese Patent Laid-Open No. 4-164892

  As described above, a technique for obtaining a semi-insulating crystal by adding a transition metal to a III-V group semiconductor crystal such as GaAs or InP is disclosed in Patent Document 1 or the like. A group III nitride semiconductor crystal having a sufficiently high value has not been obtained. Conventionally used group III nitride semiconductor substrates are n-type semiconductor substrates for the purpose of imparting electrical conductivity, and high resistance group III nitride semiconductor substrates have hardly been proposed. .

  An object of the present invention is to provide a group III nitride semiconductor crystal, a group III nitride semiconductor substrate, a semiconductor device, and a method for producing a group III nitride semiconductor crystal having a high resistance value.

According to the present invention,
In the reaction chamber of the vapor phase growth apparatus,
A halogenated group III source gas,
Nitrogen source gas,
A doping gas containing halogenated Fe atoms;
A carrier gas of H ₂ ,
Supply
On the substrate held in the reaction chamber,
Forming a semi-insulating group III nitride semiconductor crystal doped with Fe ,
The supply amount of the nitrogen source gas, V / III ratio which is the ratio of the supply amount of the group III material gas is Ri 30 der below,
In the step of forming the group III nitride semiconductor crystal, the density of Fe atoms is 1.0 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, and the total of Si atoms and O atoms Higher than density,
There is provided a method for producing a group III nitride semiconductor crystal that forms a group III nitride semiconductor crystal containing Ga as an essential element .
Moreover, according to the present invention,
A method for producing a group III nitride semiconductor substrate having the group III nitride semiconductor crystal described above is provided.
Moreover, according to the present invention,
A manufacturing method of a semiconductor device including a manufacturing method of a group III nitride semiconductor crystal substrate described above,
There is provided a method of manufacturing a semiconductor device including a semiconductor layer forming step of forming a semiconductor layer on the group III nitride semiconductor substrate without supplying the doping gas of the Fe atoms.

According to the present invention, by adding a transition metal atom to the group III nitride semiconductor crystal, the transition metal atom enters the group III atom vacancy. Transition metal atoms enter Group III vacancies, function as acceptors, and compensate donors. As a result, a high resistance group III nitride semiconductor crystal is obtained.
Furthermore, when the transition metal atom enters the group III atom vacancy, the group III atom vacancy is filled with the transition metal atom, and the group III atom vacancy density decreases. In addition, the introduction of transition metal atoms reduces the residual electron density, and the Fermi level moves away from the conduction band edge and approaches the center of the band gap. Thereby, the vacancy formation energy of a group III atom increases. Therefore, it becomes difficult to form group III atomic vacancies. Accordingly, in the present invention, the group III atomic vacancy density can be set to 1 × 10 ¹⁶ cm ⁻³ or less. The resistance value of the group III nitride semiconductor crystal can also be increased by reducing the group III atomic vacancy density.
In addition, when a group III nitride semiconductor crystal having such a low group III atomic vacancy density is used to produce a semiconductor device or the like, it is possible to prevent a decrease in the function of the semiconductor device.
For example, the group III nitride semiconductor crystal of the present invention is used as a substrate, and a GaN channel layer or an AlGaN electron supply layer is formed on the substrate to constitute a transistor. Since the group III nitride semiconductor crystal of the present invention has a low group III atomic vacancy density, many holes do not move to the GaN channel layer, and the function of the GaN channel layer is hindered by the movement of holes. Can be prevented.

Furthermore, the transition metal atom is Ru Oh in Fe atoms.
When producing a group III nitride semiconductor crystal by the HVPE method, Fe can be stably transferred as a chloride. Therefore, the group III nitride semiconductor crystal can be easily doped and the group III nitride semiconductor crystal to which Fe atoms are added can be stably produced.

Than the total density of the S i and O atoms, wherein the Fe atom density is rather high, and further, the density of Fe atoms Ru ^{1.0 × 10 18 cm -3 ~1 ×} 10 20 cm -3 der.
The density of Fe atoms is set to 1.0 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²⁰ cm ^−3, and the density is within a predetermined range, thereby suppressing high-resistance group III nitride semiconductor while suppressing deterioration of crystallinity. Crystals can be obtained.

Further, the nitride semiconductor crystal, ing a group III nitride semiconductor containing Ga as an essential element.
The group III nitride semiconductor containing Ga as an essential _{element, In x Al y Ga 1-} x-y N (0 ≦ x <1,0 ≦ y <1,0 ≦ x + y <1) can be mentioned.
Since transition metal atoms easily enter the vacancies of Ga atoms, a Group III nitride semiconductor containing Ga as an essential element can be used to make a Group III group III atom vacancy density of 1 × 10 ¹⁶ cm ⁻³ or less. A nitride semiconductor can be obtained reliably.

  According to the present invention, a group III nitride semiconductor crystal, a group III nitride semiconductor substrate, a semiconductor device, and a method for producing a group III nitride semiconductor crystal having a high resistance value are provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, in order to facilitate understanding of the present invention, a method for measuring Ga atom vacancy density in a group III nitride semiconductor (GaN) crystal will be described.

(Measurement method of Ga atom vacancy density)
(Positron annihilation method)
In this embodiment, Ga atom vacancy density is measured by the positron annihilation method.
The positron annihilation method will be described in detail below.
A positron is an antimatter of electrons and has the same rest mass (m ₀ ) as an electron, but its charge is positive. Usually, positrons are obtained by using radioactive isotopes that decay β ⁺ . When a positron enters a material, it annihilates with the electron. At this time, the mass is converted into energy, and two photons are mainly emitted in opposite directions. The energy of one photon is m ₀ c ² (511 keV), which corresponds to the γ-ray region (c is the speed of light). FIG. 1 shows how positrons emitted from a radioisotope ( ²² Na) disappear together with electrons and emit γ rays.

A positron incident on a solid loses energy and then disappears. Since momentum is preserved before and after annihilation, the energy of γ rays (E _γ ) is given by E _γ = m ₀ c ² ± ΔE _γ by the Doppler effect. Here, ΔE _γ = cp _L / 2, and p _L is the momentum distribution of electrons in the γ-ray emission direction. FIG. 2 schematically shows how positrons are trapped by vacancy-type defects.
In a solid, a positron receives a repulsive force from the ion shell and exists at an interstitial position (FIG. 2A), but may be trapped by a vacancy-type defect (FIG. 2B). Since the electron momentum distribution of the electrons in the defect is different from the electrons at the interstitial positions, a change appears in the Doppler broadening (ΔE _γ ). Therefore, it can be determined from the Doppler broadening of the γ rays whether the positrons have disappeared in the bulk or in the vacancies. In many cases, ΔE _γ is reduced by trapping positrons in defects, and Doppler broadening is sharpened.
In addition, the electron density in the substance having a vacancy type defect shown in FIG. 2B is lower than the electron density in the substance having no vacancy in FIG. . ^{When 22} Na decays β + and emits positrons, 99% or more moves to an excited state of ²² Na. In this state, a 1.28 MeV gamma ray is emitted with a lifetime of 3 × 10 ⁻¹² (s), and transitions to the ground state. This 1.28 MeV gamma ray is used as a start signal indicating that a positron has entered the material. The difference between the time when the 1.28 MeV gamma rays are emitted and the time when the 511 keV gamma rays emitted from the material due to the annihilation of positrons and electrons in the material are measured is measured. Thus, the positron lifetime can be grasped.

(S parameter)
The change of Doppler spread is evaluated with the S (Shape) parameter. The S parameter is obtained by dividing the count of the central portion of the Doppler spread (the portion filled in the graphs of FIGS. 2A and 2B) by the total count. That is, the value of S increases when positrons are captured by the vacancy-type defects, and the S parameter increases when the vacancy density is high.

(Relationship between pore density and S parameter)
The S parameter is expressed by Equation 1 below.

(Formula 1)
_{S = S f f f + S} 1 f 1
S ₁ : S value of hole type defect S _f : S value when positron is in a free state (defect-free sample) f _f : Rate at which positron trapped in hole type defect disappears (hole type) Rate of positrons trapped in defects)
f ₁ : the rate at which positrons in a free state disappear ff _f + f ₁ = 1

Therefore, f ₁ can be calculated if S _f and S _{1 in} Equation ₁ are known.
Here, f ₁ is expressed by the following formula 2.

(Formula 2)

  Further, Γ is expressed by Equation 3 below.

(Formula 3)
Γ = λ _f + κ ₁
λ _f is the reciprocal of the positron lifetime in a sample without vacancy-type defects. Here, the positron lifetime of GaN having no vacancy-type defects is 165 ps.

(Formula 4)
κ ₁ = μ ₊ C

μ ₊ is a trapping ability and is 1 × 10 ¹⁴ to 1 × 10 ¹⁵ s ⁻¹ . Note that κ ₁ is a trapping speed and can also be obtained from measurement of the positron lifetime.
Accordingly, the hole density C can be calculated.

In this embodiment, the high-energy positron beam emitted by ²² Na is decelerated to near E = 0 using a moderator, and then an acceleration voltage is applied to inject it to an arbitrary depth in the crystal. Use the “annihilation” method.

(Detection limit of Ga atom vacancy density)
The detection limit of Ga atom vacancy density is 1 × 10 ¹⁶ cm ⁻³ . The detection limit of Ga atom vacancy density can be inferred from the detection limit of vacancy density in the case of Si. From FIG. 3, the lower limit of detection of neutral vacancy defects in Si is 10 ¹⁵ cm ⁻³ . Here, if the defect is negatively charged, the detection sensitivity is increased by one digit. Therefore, the detection sensitivity for Ga atomic vacancies (negatively charged) of GaN is 10 ¹⁴ cm ⁻³ .
On the other hand, the positron diffusion distance in GaN considered to have a low defect concentration is about 50 nm, and the positron diffusion distance in Si is about 200 nm. The ability of positrons to detect defects is considered to be a parameter of diffusion distance. In this case, the volume in which positrons can be seen in GaN is (0.25) ³ compared to Si. Considering this value and detection sensitivity, the detection limit of Ga atom vacancy density is 1 × 10 ¹⁶ cm ⁻³ .

(Group III nitride semiconductor substrate and semiconductor device)
FIG. 4 shows a GaN substrate 1 (group III nitride semiconductor substrate) of this embodiment.
The GaN substrate 1 includes a sapphire substrate 11 as a base substrate, a GaN layer 12 formed on the sapphire substrate 11, an undoped GaN layer 13 formed on the GaN layer 12, and an undoped GaN layer 13. And an Fe-doped GaN layer 14 (group III nitride semiconductor crystal) formed.
The undoped GaN layer 13 is a GaN layer to which no transition metal atom is added.
The Fe-doped GaN layer 14 is a group III nitride semiconductor crystal to which Fe atoms as transition metal atoms are added, and has a Ga atom vacancy density of 1 × 10 ¹⁶ cm ⁻³ or less.
Here, the Ga atom vacancy density is 1 × 10 ¹⁶ cm ⁻³ or less means that when there are only Ga atom vacancies, the density of Ga atom-only vacancies is 1 × 10 ¹⁶ cm 3. ^-3 or less, and when there are complex defects of Ga atoms and other impurity atoms (for example, oxygen atoms), only Ga atom vacancies and Ga atoms and other impurity atoms (for example, oxygen atoms) ) And the combined defect are 1 × 10 ¹⁶ cm ⁻³ or less.

Further, the density of Fe atoms in the Fe-doped GaN layer 14 is 5 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . In particular, the density of Fe atoms in the Fe-doped GaN layer 14 is preferably 7 × 10 ¹⁷ cm ⁻³ or more. By setting it as 7 * 10 < ¹⁷ > cm < ^-3 > or more, the Fe dope GaN layer 14 can be made semi-insulating reliably.
Further, the density of Fe atoms in the Fe-doped GaN layer 14 is higher than the total density of oxygen atoms and silicon atoms in the Fe-doped GaN layer 14. For example, the total density of oxygen atoms and silicon atoms is less than 5 × 10 ¹⁷ cm ⁻³ .
Here, oxygen atoms and silicon atoms are donor impurities and generate electrons.
The density of Fe atoms, the density of oxygen atoms, and the density of silicon atoms can be measured by, for example, secondary ion mass spectrometry, Auger spectroscopy spectrum, or the like.
Further, the threading dislocation density of the Fe-doped GaN layer 14 of the GaN substrate 1 is 1 × 10 ⁸ cm ⁻² or less. Further, the positron lifetime of the Fe-doped GaN layer 14 of the GaN substrate 1 is 165 ps or less.

FIG. 5 shows a semiconductor device 4 using such a GaN substrate 1.
The semiconductor device 4 includes a GaN substrate 1 and a semiconductor layer 41 stacked on the GaN substrate 1. The semiconductor layer 41 includes a GaN channel layer 411 and an AlGaN electron supply layer 412 provided on the GaN channel layer 411. A source electrode 42 and a drain electrode 43 are formed on the AlGaN electron supply layer 412. Further, a gate electrode 44 is also formed on the AlGaN electron supply layer 412 via a gate insulating film (for example, SiO ₂ film) (not shown).

(Method for manufacturing GaN substrate)
Next, a method for manufacturing the GaN substrate 1 will be described.
First, a silicon oxide (SiO ₂ ) film is formed on a (0001) -plane sapphire substrate 11 on which a GaN layer 12 having a thickness of 2 μm is formed. Next, the silicon oxide (SiO ₂ ) film is etched by using a lithography technique to form an opening 151 as shown in FIG.
Here, the longitudinal direction of the stripe of the mask 15 is a direction along the <1-100> direction of the sapphire substrate 11.
The GaN layer 12 is formed by MOCVD (metal organic chemical vapor deposition).

Next, the sapphire substrate 11 having a mask formed thereon is set on the substrate holder 31 in the reaction tube 30 of the HVPE (Hydride Vapor Phase Epitaxy) apparatus 3 shown in FIG.
Then, nitrogen (N ₂ ) gas is supplied from the gas introduction pipes 33 and 34 to purge the inside of the reaction pipe (reaction chamber) 30. The gas supplied into the reaction tube 30 is discharged from the discharge port 38. After sufficiently purging the inside of the reaction tube 30, the reaction tube 30 is heated by the heater 35 by switching to hydrogen (H ₂ ) gas. When the temperature of the growth region 36 reaches around 500 ° C., the temperature is increased by adding ammonia (NH ₃ ) gas from the gas introduction pipe 33. Further, the temperature rise is continued until the temperature of the Ga source 37 region is 850 ° C. and the temperature of the growth region 36 is 900 ° C. or more and 1200 ° C. or less.

After the temperature of the Ga source 37 region and the temperature of the growth region 36 are stabilized, HCl gas is added from the gas introduction pipe 34 and supplied, and reacted with gallium (Ga) 37 in the source boat 39 to cause gallium chloride (GaCl). It is generated and transported to the growth region 36. In the growth region 36, NH ₃ gas and GaCl react to grow GaN.
As shown in FIG. 6B, a facet structure F is formed from the crystal nuclei of GaN formed in the opening 151 of the mask 15. This facet structure F has {1-102} as a side wall, has an inclined surface inclined with respect to the substrate surface of the sapphire substrate 11, and has a triangular cross section.
Thereafter, as shown in FIG. 6C, the adjacent facet structures F are united and begin to cover the mask 15. As a result, an undoped GaN layer 13 is formed as shown in FIG.

When the thickness of the undoped GaN layer 13 reaches a predetermined thickness (for example, 20 μm), HCl gas is introduced into the tube 32. In the pipe 32, rod-shaped iron raw materials (for example, purity 99.999%) 32A are arranged with a gap therebetween. As HCl gas flows through the tube 32, FeCl ₂ is generated. A desired amount of FeCl ₂ is supplied to the growth region 36 by adjusting the flow rate of the HCl gas (for example, 0.01 cc / min or more and 100 cc / min or less). The diameter of the tube 32 is preferably 1 mmφ or more and 100 mmφ. Moreover, the temperature of a rod-shaped iron raw material is 500 degreeC or more and 1200 degrees C or less.
As a result, the Fe-doped GaN layer 14 is formed on the undoped GaN layer 13.
At this time, the V / III ratio, which is the ratio between the supply amount of the nitrogen source gas (NH ₃ gas) and the supply amount of the group III source gas (HCl gas), is 30 or less. More preferably, the V / III ratio is 15 or less.
The growth temperature of the Fe-doped GaN layer 14 is 900 ° C. or more and 1200 ° C. or less.

Furthermore, the pressure in the reaction tube 30 when growing the Fe-doped GaN layer 14 is about normal pressure (for example, 0.050 MPa or more and 0.150 MPa or less).
By increasing the pressure in the reaction tube 30, the flow rate of the HCl gas becomes slow, and the reaction with the Ga source and the iron raw material can be sufficiently promoted. Thus, a large amount of GaCl or FeCl ₂ can be supplied to the growth region 36, and the Fe-doped GaN layer 14 having a low Ga atom vacancy density can be formed.
Furthermore, since it becomes difficult to supply unreacted HCl gas to the growth region 36, the crystal quality of the Fe-doped GaN layer 14 is improved, and the Fe-doped GaN layer 14 having a low Ga atom vacancy density can be formed.
Further, when the Fe-doped GaN layer 14 is grown, it is preferable to use H ₂ gas as a carrier gas. When the Fe-doped GaN layer 14 is grown, GaCl is supplied to the growth region 36. In order to form the Fe-doped GaN layer 14, it is necessary to separate Cl atoms from Ga atoms. At this time, when a large amount of H ₂ gas is present, Cl atoms are easily separated from Ga atoms. Thereby, the supply amount of Ga atoms can be increased, and the Fe-doped GaN layer 14 having a low Ga atom vacancy density can be formed.

Here, in this embodiment, an organic metal raw material is not used as the iron raw material, and high-purity iron (an inorganic compound containing an iron element) is used as the raw material. When an organic metal material is used as the iron material, a large amount of oxygen contained in the organic metal material is introduced into the Fe-doped GaN layer 14.
In contrast, in this embodiment, high-purity iron (an inorganic compound containing an iron element) is used as the iron raw material, so that a large amount of oxygen is prevented from being introduced into the Fe-doped GaN layer 14. Can do.
After the Fe-doped GaN layer 14 reaches a predetermined thickness (for example, 110 to 140 μm), the supply of HCl gas from the tubes 34 and 32 is stopped, the power supply to the heater 35 is shut off, and the temperature of the reaction tube 30 is lowered. When the temperature of the growth region 36 is about 500 ° C. or less, the supply of ammonia (NH ₃ ) gas from the gas introduction pipe 33 is stopped, and nitrogen (N ₂ ) gas is supplied from the gas introduction pipes 33 and 34 to react. After sufficiently purging the inside of the tube (reaction chamber) 30, the sapphire substrate 11 is taken out.
In the HVPE apparatus 3, the source boat 39 and the pipe 32 are arranged in a region partitioned by the cylindrical shielding member S.

In addition to conditions such as the V / III ratio when forming the Fe-doped GaN layer 14 and the growth temperature of the Fe-doped GaN layer 14, the surface of the sapphire substrate 11 is cleaned at 900 to 1200 ° C. Cycle (for example, filling the reaction tube 30 with ammonia before GaN growth, etc.), mask width, mask pitch, diameter of the tube 32, supply amount of HCl gas to the tube 32, temperature of the iron raw material, reaction tube 30 The Ga atom vacancy density of the Fe-doped GaN layer 14 can be reduced to 1 × 10 ¹⁶ cm ⁻³ or less by optimally adjusting various conditions such as the internal pressure and the supply of H ₂ carrier gas.

Such effects of the present embodiment will be described below.
The GaN substrate 1 of the present embodiment has a Fe-doped GaN layer 14 doped with Fe on the surface.
In this Fe-doped GaN layer 14, Fe atoms enter Ga atom vacancies. Fe atoms enter Ga vacancies, function as acceptors, and compensate donors. As a result, a high-resistance Fe-doped GaN layer 14 is obtained.

Furthermore, by introducing Fe atoms, the residual electron density is reduced, and the Fermi level moves away from the conduction band edge and approaches the center of the band gap. As a result, as shown in FIG. 8, the Ga atom vacancy formation energy increases (not only the Ga atom vacancy formation energy but also Ga atoms and other impurity atoms (for example, oxygen atoms) The energy of forming complex defects also increases. For this reason, it is considered that Ga atom vacancies are hardly formed. In FIG. 8, Ev represents the energy level of the conduction band, and Ec represents the energy level of the valence band.
Furthermore, by adding Fe to the GaN layer, Fe atoms enter Ga atomic vacancies, and the vacancy density decreases.
In addition, in this embodiment, the Fe-doped GaN layer 14 is formed using the HVPE method. In the HVPE method, the V / III ratio can be lowered, and in the present embodiment, the V / III ratio is set to 30 or less, preferably 15 or less, so that Ga atom vacancies that are Group III atoms are formed. It is hard to be done. In addition, since the undoped GaN layer 13 serving as the underlying layer of the Fe-doped GaN layer 14 is formed by FIELO (facet-initiated epitaxial lateral overgrowth) method, the undoped GaN layer 13 and further the Fe-doped GaN layer 13 on the undoped GaN layer 13 are formed. The GaN layer 14 has few threading dislocations and a small strain field due to threading dislocations. When a strain field is generated, point defects are likely to be generated around the strain field. However, in this embodiment, since the strain field is very small, point defects are hardly generated in the Fe-doped GaN layer 14. That is, Ga atom vacancies are hardly formed.
When the Fe-doped GaN layer 14 is formed under such various conditions, the Ga atom vacancy density in the Fe-doped GaN layer 14 can be set to 1 × 10 ¹⁶ cm ⁻³ or less. The semi-insulating Fe-doped GaN layer 14 having a high resistance value can also be obtained by reducing the Ga vacancy density.

Note that a high resistance value of the Fe-doped GaN layer does not necessarily mean that the group III atomic vacancy density is low. That is, for example, the resistance value of the Fe-doped GaN layer can be increased by increasing the threading dislocation density, grain growth, or the presence of substantially the same number of acceptors and donors. However, as in this embodiment, by controlling the Ga atom vacancy density to 1 × 10 ¹⁶ cm ⁻³ or less, the resistance value of the Fe-doped GaN layer 14 is increased, and the Fe-doped GaN layer 14 is formed on the Fe-doped GaN layer 14. When a transistor is formed by forming the GaN channel layer 411 or the AlGaN electron supply layer 412, many holes do not move to the GaN channel layer 411, and the function of the GaN channel layer 411 is hindered by the movement of holes. It can be prevented.

In the present embodiment, the Fe-doped GaN layer 14 is formed by adding Fe atoms.
Since Fe atoms easily enter Ga vacancies, and Fe atoms that have entered vacancies hardly move from the vacancies, the Ga atom vacancy density is 1 × 10 ¹⁶ cm ⁻³ or less and the resistance value is high. Thus, the Fe-doped GaN layer 14 is obtained.
In addition to this, by setting the density of Fe to 5 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ and a density within a predetermined range, a semi-insulating high-resistance Fe that suppresses deterioration of crystallinity. A doped GaN layer 14 can be obtained.
In the present embodiment, Fe atoms are employed as the metal atoms doped into the GaN layer 14. When the Fe-doped GaN layer 14 is produced by the HVPE method, Fe atoms can be stably transferred as chloride, and the Fe-doped GaN layer 14 can be produced stably.

  Furthermore, in this embodiment, the density of Fe atoms is made higher than the density of donor impurities (oxygen atoms and silicon atoms). Since Fe atoms function as an acceptor, by making the density of Fe atoms higher than the density of donor impurities, residual donors can be compensated for and high-resistance Fe-doped GaN layer 14 can be obtained.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the above-described embodiment, the GaN substrate 1 having the Fe-doped GaN layer 14 is manufactured. However, the present invention is not limited thereto, and the Fe-doped GaN layer 14 may be used as an element isolation film that performs isolation between elements, for example. Good.
Further, for example, the Fe-doped GaN layer 14 may be used as a current confinement layer of a semiconductor laser device. By using such a Fe-doped GaN layer 14 having a high resistance value as a current confinement layer, current can be effectively blocked.

Furthermore, in the said embodiment, although the GaN board | substrate 1 shall have the sapphire board | substrate 11, it is not restricted to this, You may peel the sapphire board | substrate 11 and use it as a GaN self-supporting board | substrate.
In the embodiment, the GaN substrate 1 is used to configure the semiconductor device 4 that is a transistor. However, the present invention is not limited to this. For example, light emission in which a number of fine LEDs arranged in a matrix are arranged on the GaN substrate 1. It is good also as an apparatus.
In the above embodiment uses the sapphire substrate as the base substrate, a spinel substrate, SiC substrate, ZnO substrate, _Ga 2 _{O 3} substrate, may be a silicon substrate or the like.

Furthermore, in the said embodiment, although the Fe atom was illustrated as a transition metal atom added to a GaN layer (III group nitride semiconductor crystal), it is not restricted to this, For example, Ti, V, Cr, Mn, Fe, Co One or two or more transition metal atoms selected from the group consisting of, Ni and Cu may be used.
As shown in FIG. 9, these transition metal atoms form a Fermi level in the forbidden band between the conduction band and the valence band (the arrows on the right end of FIG. 9 indicate the group III nitride semiconductor crystals). Shows the band gap. Therefore, by using such a transition metal atom, the vacancy formation energy of the group III atom is increased. Therefore, the group III atom vacancies are hardly formed, and the group III atom vacancy density can be 10 ¹⁶ cm ⁻³ or less.
Of these, one or more transition metal atoms selected from the group consisting of Ti, V, Cr, Fe, Co, and Ni are preferable. Since these transition metal atoms easily enter the vacancies of group III atoms and are difficult to move from the vacancies, by selecting such transition metal atoms, a group III nitride semiconductor crystal having a high resistance value can be obtained. Will be obtained.
Further, other atoms may be added in addition to the transition metal atom.

Moreover, in the said embodiment, although GaN was illustrated as a group III nitride semiconductor crystal, it is not restricted to this. For example, InAlGaN or AlGaN may be used. That may be _{In x Al y Ga 1-x} -y N (0 ≦ x <1,0 ≦ y <1,0 ≦ x + y <1).
Furthermore, AlN, InN, or the like may be used.
Moreover, in the said embodiment, although the undoped GaN layer 13 used as the base layer of the Fe dope GaN layer 14 was formed by FIELO (facet-initiated epitaxial lateral overgrowth) method, it does not restrict to this, For example, the undoped GaN layer 13 is provided. Alternatively, the Fe-doped GaN layer 14 itself may be formed by FIELO (facet-initiated epitaxial lateral overgrowth) method.
Furthermore, in the said embodiment, although the organometallic raw material was not used as an iron raw material, but high purity iron (inorganic compound containing an iron element) was used as the raw material, for example, ferrocene etc. can be adjusted by adjusting manufacturing conditions suitably. Organic metal raw materials may be used.

Next, examples of the present invention will be described.
Example 1
A GaN substrate was manufactured using the HVPE (Hydride Vapor Phase Epitaxy) apparatus shown in FIG. 7 by the same method as in the previous embodiment.
An SiO ₂ layer is formed by EB (electron beam) evaporation on a (0001) sapphire substrate on which a GaN layer having a thickness of 2 μm is formed, and the same as in the previous embodiment by photolithography and hydrofluoric acid-based wet etching. A mask was formed.
Next, a sapphire substrate was mounted on the HVPE apparatus, and an undoped GaN layer was formed by the FIELO method and an Fe-doped GaN layer was formed by the same method as in the previous embodiment.
The temperature of the iron raw material when forming the Fe-doped GaN layer was 850 ° C.
The V / III ratio when forming the Fe-doped GaN layer is 15, and the growth temperature of the Fe-doped GaN layer is 1040 ° C. The HCl (Fe) partial pressure (partial pressure of HCl on the iron raw material with respect to the total growth gas) was set to 6.3 Pa. The thickness of the Fe-doped GaN layer was 110 μm. Further, the Fe atom concentration in the Fe-doped GaN layer was 1.0 × 10 ¹⁸ cm ⁻³ .
Furthermore, the donor impurity density (total density of oxygen atoms and silicon atoms) was 5 × 10 ¹⁷ cm ⁻³ . The dislocation density was 2.3 × 10 ⁷ cm ⁻² .
The other growth conditions for the Fe-doped GaN layer are as follows.
・ Mask width 3μm
・ Mask pitch 7μm
・ Diameter of pipe 32 6mmφ
・ Iron raw material temperature 850 ℃
-Pressure in reaction tube 0.099MPa
・ Carrier gas H ₂ gas

(Example 2)
A GaN substrate was manufactured in the same manner as in Example 1.
The V / III ratio when forming the Fe-doped GaN layer is 15, and the growth temperature of the Fe-doped GaN layer is 1040 ° C. The HCl (Fe) partial pressure was 12.5 Pa. Other conditions are the same as those in the first embodiment.
The thickness of the Fe-doped GaN layer was 120 μm.
The Fe atom concentration in the Fe-doped GaN layer was 4.0 × 10 ¹⁸ cm ⁻³ .
Furthermore, the donor impurity density (total density of oxygen atoms and silicon atoms) was 5 × 10 ¹⁷ cm ⁻³ . The dislocation density was 1.4 × 10 ⁷ cm ⁻² .

(Example 3)
A GaN substrate was manufactured in the same manner as in Example 1.
The V / III ratio when forming the Fe-doped GaN layer is 15, and the growth temperature of the Fe-doped GaN layer is 1040 ° C. The HCl (Fe) partial pressure was 62.5 Pa. Other conditions are the same as those in the first embodiment.
The thickness of the Fe-doped GaN layer was 90 μm.
Further, the Fe atom concentration in the Fe-doped GaN layer was 9.5 × 10 ¹⁹ cm ⁻³ .
Furthermore, the donor impurity density (total density of oxygen atoms and silicon atoms) was 5 × 10 ¹⁷ cm ⁻³ . The dislocation density was 2.5 × 10 ⁷ cm ⁻² .

Example 4
A low-temperature GaN buffer layer having a thickness of 70 nm was formed on the (0001) sapphire substrate by MOCVD.
Specifically, after heat-treating the sapphire substrate at 1050 ° C. for 10 minutes, the temperature was lowered and stabilized at 500 ° C., and TMG (trimethylgallium) and ammonia gas were supplied. The supply amounts of TMG and ammonia gas were 10 μmol / min and 5000 cc / min, respectively, and the low-temperature GaN buffer layer had a thickness of 70 nm.
Next, an Fe-doped GaN layer was formed by the same method as in the above embodiment using the same HVPE apparatus as in the above embodiment.
The Fe-doped GaN layer here is not formed by the FIELO method.
The V / III ratio when forming the Fe-doped GaN layer is 15, and the growth temperature of the Fe-doped GaN layer is 1040 ° C. The HCl (Fe) partial pressure was 12.5 Pa.
The thickness of the Fe-doped GaN layer was 30 μm.
The Fe atom concentration in the Fe-doped GaN layer was 4.0 × 10 ¹⁸ cm ⁻³ .
Furthermore, the donor impurity density (total density of oxygen atoms and silicon atoms) was 5 × 10 ¹⁷ cm ⁻³ . The dislocation density was 1.2 × 10 ⁸ cm ⁻² .
The other growth conditions for the Fe-doped GaN layer are as follows.
・ Diameter of pipe 32 6mmφ
・ Iron raw material temperature 850 ℃
-Pressure in reaction tube 0.099MPa
・ Carrier gas H ₂ gas

(Comparative Example 1)
A GaN substrate was manufactured by the same method as in the previous embodiment.
The V / III ratio when forming the Fe-doped GaN layer is 15, and the growth temperature of the Fe-doped GaN layer is 1040 ° C. The HCl (Fe) partial pressure was 3.8 Pa.
The thickness of the Fe-doped GaN layer was 90 μm.
Further, the Fe atom concentration in the Fe-doped GaN layer was 3.2 × 10 ¹⁷ cm ⁻³ .
Furthermore, the donor impurity density (total density of oxygen atoms and silicon atoms) was 5 × 10 ¹⁷ cm ⁻³ .

(Comparative Example 2)
The Fe-doped GaN layer was not formed, and the thickness of the undoped GaN layer was 180 μm. Other conditions are the same as those in the first embodiment.

The Ga atom vacancy densities of Examples 1 to 4 and Comparative Examples 1 and 2 were measured by the positron annihilation method described in the above embodiment, and the results were as follows. In Examples 1 to 4, the Ga atom vacancy density is below the detection limit. Moreover, when the resistivity was measured, it was as shown in Table 1.
FIG. 10 shows the relationship between HCl (Fe) partial pressure and Fe atom concentration in Examples 1 to 3 and Comparative Example 1, and the relationship between HCl (Fe) partial pressure and resistivity.
Furthermore, in FIG. 11, the measurement result of the S parameter of the GaN substrate of Example 4 and Comparative Example 2 is shown. In FIG. 11, white circles are Comparative Example 2, and black squares are Example 4. In FIG. 11, the S parameter of Example 4 (the saturated value in FIG. 11, that is, the average value of the region having a horizontal axis of 0.5 μm or more) is 0.4370, and the S parameter of Comparative Example 2 (FIG. 11). Of the saturated region, that is, the average value of the region having a horizontal axis of 0.5 μm or more) is 0.4403.
In addition, the resolution of the apparatus which measured by the positron annihilation method is FWHM (full width of half maximum) 1.3 keV, and the calculation range of S parameter is 511 ± 0.76 keV.

Further, the substrate of Example 4 was heat-treated in an electric furnace in a nitrogen atmosphere. The results are shown in Table 2.

Referring to Table 1, in Comparative Examples 1 and 2 where the Ga atom vacancy density exceeds 1 × 10 ¹⁶ cm ⁻³ , the resistivity is low, less than 1 × 10 ⁷ (Ωcm), and it is semi-insulating. I understand that there is no. On the other hand, in Examples 1 to 4 where the Ga atom vacancy density is 1 × 10 ¹⁶ cm ⁻³ or less, the resistivity is high and is 1 × 10 ⁷ (Ωcm) or more and is semi-insulating. I understand.
Further, referring to Table 2, it can be seen that the heat resistance does not decrease by heat treatment and the heat resistance is high.

Is a diagram for explaining the positron annihilation method, it is a diagram showing a state in which positrons emitted from a radioisotope ⁽²² Na) disappears with electron emits γ-rays. It is a schematic diagram which shows a mode that a positron is trapped by a void | hole type | mold defect. It is a figure which shows the detection limit of the void density in Si. It is a figure which shows the GaN board | substrate concerning embodiment of this invention. It is a figure which shows the semiconductor device which uses a GaN substrate. It is a figure which shows the manufacturing process of a GaN substrate. It is a schematic diagram which shows a HVPE (Hydride Vapor Phase Epitaxy) apparatus. It is a figure which shows the relationship between the energy which forms Ga atom vacancy, and Fermi level. It is a figure which shows a mode that each transition metal atom forms a Fermi level in the forbidden band between a conduction band and a valence band. It is a figure which shows the relationship between Examples 1-3 and the HCl (Fe) partial pressure and Fe atom concentration in Comparative Example 1, and the relationship between HCl (Fe) partial pressure and resistivity. It is a figure which shows the measurement result of the S parameter of the GaN substrate of Example 4 and Comparative Example 2.

Explanation of symbols

1 GaN substrate (Group III nitride semiconductor substrate)
3 HVPE device 4 Semiconductor device 11 Sapphire substrate 12 GaN layer 13 Undoped GaN layer 14 Fe-doped GaN layer 15 Mask 30 Reaction tube 31 Substrate holder 32 Tube 32A Iron raw material 33 Gas introduction tube 34 Gas introduction tube 35 Heater 36 Growth region 37 Ga source 38 discharge port 39 source boat 41 semiconductor layer 42 source electrode 43 drain electrode 44 gate electrode 151 opening 411 channel layer 412 electron supply layer F facet structure S shielding member

Claims (6)

In the reaction chamber of the vapor phase growth apparatus,
A halogenated group III source gas,
Nitrogen source gas,
A doping gas containing halogenated Fe atoms;
A carrier gas of H ₂ ,
Supply
On the substrate held in the reaction chamber,
Forming a semi-insulating group III nitride semiconductor crystal doped with Fe atoms,
The supply amount of the nitrogen source gas, V / III ratio which is the ratio of the supply amount of the group III material gas is Ri 30 der below,
In the step of forming the group III nitride semiconductor crystal, the density of Fe atoms is 1.0 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, and the total of Si atoms and O atoms Higher than density,
A method for producing a group III nitride semiconductor crystal comprising forming a group III nitride semiconductor crystal containing Ga as an essential element . In the manufacturing method of the group III nitride semiconductor crystal of Claim 1,
A method for producing a group III nitride semiconductor crystal, wherein the growth temperature of the group III nitride semiconductor crystal is 900 ° C. or higher and 1200 ° C. or lower. In the manufacturing method of the group III nitride semiconductor crystal of Claim 1 or 2,
A method for producing a group III nitride semiconductor crystal, wherein a group III atom vacancy density in the group III nitride semiconductor crystal is 1 × 10 ¹⁶ cm ⁻³ or less. In the manufacturing method of the group III nitride semiconductor crystal as described in any one of Claims 1 thru | or 3 ,
Before the step of forming the Fe atom is added, group III nitride semiconductor crystal, on the substrate, forming a base layer composed of a group III nitride semiconductor containing no transition metal atom,
A mask layer forming step of forming a mask having an opening on the underlayer;
Further including
After the mask layer forming step, performing a step of forming a group III nitride semiconductor crystal to which the Fe is added,
A method for producing a group III nitride semiconductor crystal, comprising the step of selectively growing a layer made of a group III nitride semiconductor from the opening in the step of forming a group III nitride semiconductor crystal to which the Fe atom is added. The manufacturing method of the group III nitride semiconductor substrate which has the said group III nitride semiconductor crystal in any one of Claims 1 thru | or 4 . A manufacturing method of a semiconductor device including the manufacturing method of a group III nitride semiconductor crystal substrate according to claim 5 ,
A semiconductor device manufacturing method including a semiconductor layer forming step of forming a semiconductor layer on the group III nitride semiconductor substrate.