JP2006165069A - Growing method and apparatus for compound semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a growing method and apparatus capable of achieving a high mobility high quality GaN-based heterojunction FET with less gate leakage. <P>SOLUTION: A low dislocation density high quality film is prepared as to a non-doped GaN layer using an MOCVD method such that secondary electrons can travel at a high speed. Further, for an n-type Al<SB>x</SB>Ga<SB>1-x</SB>N layer grown on the non-doped GaN layer it is grown with an MBE method in such a way that the n-type Al<SB>x</SB>Ga<SB>1-x</SB>N layer excellent in surface flatness is yielded in order to suppress gate leakage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention is directed to a compound semiconductor growth method and apparatus, and in particular, an n-type Al _x Ga _1-x N layer (x = 0.1 to 1.0) is epitaxially grown on a non-doped GaN single crystal layer. Method of growing a GaN-based heterojunction compound semiconductor for high-power / high-frequency devices, wherein two-dimensional electrons formed on the GaN side of the n-type Al _x Ga _1-x N layer / non-doped GaN interface run at high speed along the interface And an apparatus.

FIG. 5 of the accompanying drawings shows a general GaN-based heterojunction FET in a cross-sectional view. Reference numeral 41 denotes a substrate. Usually, sapphire (0001) or SiC (0001) is used as the substrate 41. Reference numeral 42 denotes a non-doped GaN layer, and reference numeral 43 denotes an n-type Al _x Ga _1-x N ( _{x to} 0.3) layer. As the non-doped GaN layer 42, a layer having a residual carrier concentration of 1 × 10 ¹⁶ / cm ³ or less and a film thickness of about 2 to ⁴ μm is used. For the n-type Al _x Ga _1-x N layer 43, the carrier concentration is about 10 ¹⁸ / cm ³ , the Al composition x is usually about 0.3, and the film thickness is about 20 to 30 nm. Reference numerals 44, 45, and 46 denote a source and a gate and drain made of a Schottky junction, respectively.

In the heteroepitaxial film having such a structure, as shown in the band diagram of FIG. 6 of the accompanying drawings, electrons in the n-type Al _x Ga _1-x N layer 43 fall into the non-doped GaN layer 42, Since there is no ionized impurity scattering in the GaN layer 42, it can travel at high speed along the interface.

Conventionally, the MOCVD method or the MBE method has been used to form such a heteroepitaxial film. However, when a film having such a structure is formed by the MOCVD method, the non-doped GaN layer can obtain a high-quality layer having a low defect density and a flat surface, but n-type Al _x Ga _1-x N The layer has a disadvantage that it tends to be a film having a rough surface where gate leakage is likely to occur due to thermal decomposition of TMAl in the gas phase (see Non-Patent Document 1).

That is, the MOCVD method is suitable for producing a high-quality non-doped GaN layer having high electron mobility, but is not suitable for producing an Al _x Ga _1-x N layer having a flat surface with little gate leakage. On the other hand, when an Al _x Ga _1-x N heteroepitaxial film is formed by the MBE method, an Al _x Ga _1-x N layer having excellent surface flatness can be obtained, but the non-doped GaN layer has crystal defects such as dislocations. There is a drawback that high electron mobility cannot be obtained.
Proceedings of the 65th Japan Society of Applied Physics, 3rd volume, P1253

  The present invention solves the above-described conventional problems, and an object thereof is to provide a growth method and apparatus capable of realizing a high mobility and high quality GaN-based heterojunction FET with little gate leakage. Yes.

In order to select the above object, according to the first aspect of the present invention, an n-type Al _x Ga _1-x N layer (x = 0.1 to 1.0) is epitaxially grown on a non-doped GaN single crystal layer. A heterojunction compound semiconductor growth method in which two-dimensional electrons formed on the GaN side of an n-type Al _x Ga _1-x N layer / non-doped GaN interface travel along the interface at high speed.
Using the MOCVD method to epitaxially grow the non-doped GaN layer on the substrate,
The MBE method is used to epitaxially grow the n-type Al _x Ga _1-x N layer on the non-doped GaN layer.

In the method according to the first aspect of the present invention, the non-doped GaN layer is epitaxially grown on the substrate by MOCVD and the n-type Al _x Ga _1-x N layer is epitaxially grown on the non-doped GaN layer by MBE. It can be configured to run continuously while maintaining.

  Further, in the method according to the first aspect of the present invention, after the non-doped GaN layer is epitaxially grown on the substrate using the MOCVD method, a surface protective film for preventing formation of an impurity layer or an oxide layer on the surface of the non-doped GaN layer is formed. The surface protective film formed and then formed on the non-doped GaN layer in a vacuum apparatus may be removed by heating.

  Preferably, a sapphire, SiC, GaN, GaAs, Si, or AlN substrate can be used as the substrate.

According to the second aspect of the present invention, an n-type Al _x Ga _1-x N layer (x = 0.1 to 1.0) is epitaxially grown on the non-doped GaN single crystal layer, and the n-type Al _x Ga _{1− In the} heterojunction compound semiconductor growth apparatus that causes two-dimensional electrons formed on the GaN side of the _xN layer / non-doped GaN interface to travel along the interface at high speed,
An MOCVD apparatus which includes respective flow rate control means for controlling the flow rates of trimethylgallium, ammonia and hydrogen, and forms a non-doped GaN layer on the substrate;
An MBE that is connected to a MOCVD apparatus via a gate valve and includes a gallium evaporation source, an aluminum evaporation source, a nitrogen plasma source, or an ammonia source, and forms an n-type Al _x Ga _1-x N layer on the non-doped GaN layer With the device;
It is characterized by having.

The MOCVD apparatus and the MBE apparatus can be connected via a vacuum transfer unit.

In the method according to the first aspect of the present invention, the MOCVD method is used to epitaxially grow the non-doped GaN layer on the substrate, and the MBE method is used to epitaxially grow the n-type Al _x Ga _1-x N layer on the non-doped GaN layer. Therefore, since the n-type Al _x Ga _1-x N layer is grown by the MBE method, a film having excellent surface flatness can be obtained and gate leakage can be suppressed. Further, since the two-dimensional electrons travel in the low dislocation density / high quality non-doped GaN layer grown by the MOCVD method, high electron mobility can be obtained. As a result, a high-quality GaN-based heterojunction compound semiconductor can be realized.

An apparatus according to a second aspect of the present invention comprises an MOCVD apparatus comprising a respective flow rate control means for supplying trimethylgallium, ammonia and hydrogen by controlling the flow rates thereof, and forming a non-doped GaN layer on the substrate. The n-type Al _x Ga _1-x N layer is formed on the non-doped GaN layer, which is connected to the MOCVD apparatus via a gate valve and includes a gallium evaporation source, an aluminum evaporation source and a nitrogen plasma source or an ammonia source. Since the MBE apparatus is included, the apparatus can be integrally formed. As a result, the epitaxial growth of the non-doped GaN layer by the MOCVD method on the substrate and the n-type Al _x Ga ₁ by the MBE method on the non-doped GaN layer. the epitaxial growth of _{-x N} layer successively with substantially maintaining the vacuum state actual It is possible to become.

Embodiments of the present invention will be described below with reference to FIGS.
FIG. 1 schematically shows the configuration of an embodiment of a compound semiconductor film forming apparatus according to the present invention. In FIG. 1, 1 is an MOCVD chamber of an MOCVD apparatus, 2 is an evaporation source chamber of an MBE apparatus, 3 is a gallium evaporation source, 4 is an aluminum evaporation source, 5 is a nitrogen plasma source, and 6 is a gate valve. Reference numerals 7, 8, and 9 denote mass flow controllers for trimethylgallium, ammonia, and hydrogen of the MOCVD apparatus, and reference numerals 10 to 13 denote valves. As shown, the MOCVD chamber 1 is connected to a trimethylgallium supply source (not shown) via a valve 10 and a trimethylgallium mass flow controller 7, and is not shown via a valve 11 and an ammonia massflow controller 8. It is connected to an ammonia supply source, and further connected to a hydrogen supply source (not shown) via a valve 12 and a mass flow controller 9. The valve 13 is connected to an appropriate evacuation system (not shown).

  In FIG. 1, reference numerals 14, 15 and 16 denote shutters for the gallium evaporation source 3, the aluminum evaporation source 4, and the nitrogen plasma source 5, respectively. In the MOCVD chamber 1, a substrate holder 18 provided with a heater 17 for heating the substrate is set toward the evaporation source side, and a substrate 19 to be film-formed is mounted on the substrate holder 18.

The evaporation chamber source 2 of the MBE apparatus is evacuated by a 1500 liter / second turbo molecular pump (not shown), and the MBE provided between the MOCVD chamber 1 and the evaporation source chamber 2 is closed. The ultimate pressure of the evaporation source chamber 2 is 1 × 10 ⁻⁷ Pa, and 5 × 10 ⁻⁷ Pa when the gate valve 6 is opened. First, in the MOCVD chamber 1 with the gate valve 6 closed, the surface of the sapphire substrate 19 is heated at 1200 ° C. for 10 minutes while flowing hydrogen gas at 20 slm under the control of the valve 12 and the hydrogen mass flow controller 9 to clean the surface. Then, the sapphire substrate 19 is set to 550 ° C., and the flow rates of trimethylgallium, ammonia, and hydrogen are respectively set to 3 × 10 ⁻⁴ (mol / min), 40 slm, and 25 slm for 10 minutes to grow the low-temperature buffer layer by 300 Å. It was.

Thereafter, the temperature of the sapphire substrate 19 is increased to 1050 ° C., and the flow rates of trimethyl gallium, ammonia, and hydrogen are set to 5 × 10 ⁻⁴ (mol / min), 20 slm, and 20 slm for 60 minutes, respectively, and the non-doped GaN layer is grown to 4 μm. I let you.

Thereafter, the temperature of the sapphire substrate 19 was lowered to 400 ° C. Next, the valves 10 to 13 are closed, the gate valve 6 is opened, and the sapphire substrate 19 is irradiated with nitrogen plasma at an output of the nitrogen radical source 5 of 350 W and a nitrogen flow rate of 5 sccm. The shutters 14 and 16 of the gallium evaporation source 3 and the aluminum evaporation source 4 held at 900 ° C. and 1100 ° C., respectively, are opened for 3 minutes, and the n-type Al _x Ga _1-x N layer (x˜0.25) ) Was grown 250 angstroms.

The surface of the n-type Al _x Ga _1-x N layer obtained as described above is flat as shown in FIG. 2A, and the mobility of the two-dimensional electron gas is also 1450 (cm ² / Vs). Met.

On the other hand, when the non-doped GaN layer and the n-type Al _x Ga _1-x N layer are all formed by the MOCVD method, the mobility of the two-dimensional electron gas of 1420 (cm ² / Vs) was obtained, but the n-type On the surface of the Al _x Ga _1-x N layer, as shown in FIG. 2B, many recesses that are said to easily cause gate leakage were observed.

In addition, after growing the non-doped GaN layer by the MOCVD method, it is once taken out into the atmosphere and transferred to the MBE apparatus to grow the n-type Al _x Ga _1-x N layer. As a result, the interface states can be formed, and the mobility of the two-dimensional electron gas is only 60 (cm ² / Vs).

  3 and 4 schematically show the configuration of another embodiment of the compound semiconductor film forming apparatus according to the present invention. In each of these cases, the MOCVD apparatus and the MBE apparatus are connected by a vacuum transfer unit. Yes.

  In the embodiment shown in FIG. 3, 21 is an MOCVD apparatus, 22 is an MBE apparatus, and these apparatuses are connected to each other by a vacuum sample transport unit 23. A gate valve 24 is provided between the MOCVD apparatus 21 and the vacuum sample transport unit 23, and a gate valve 25 is provided between the MBE apparatus 22 and the vacuum sample transport unit 23.

The vacuum sample transport unit 23 is maintained at a pressure of 1 × 10 ⁻⁶ Pa or less in order to suppress oxidation of the sample surface as much as possible. Although not shown, the MOCVD apparatus 21 is provided with a valve and a mass flow controller for supplying trimethylgallium, ammonia, and hydrogen to the MOCVD chamber, as in the embodiment of FIG. Although not shown, an evaporation source chamber is provided, and a gallium evaporation source, an aluminum evaporation source, and a nitrogen plasma source are coupled to the evaporation source chamber.

In the operation of the apparatus shown in FIG. 3, in order to prevent the formation of an adsorption layer or an oxide layer on the non-doped GaN layer that causes a decrease in the mobility of two-dimensional electrons, an undoped GaN layer grown by MOCVD is used in the atmosphere. A method is employed in which an n-type Al _x Ga _1-x N layer is grown on the non-doped GaN layer by the MBE method without being exposed to. That is, first, the surface of the sapphire substrate is cleaned by heating it at 1200 ° C. for 10 minutes while flowing hydrogen gas in the MOCVD chamber 21 at 25 slm, then the sapphire substrate is set at 550 ° C., and the flow rates of trimethylgallium, ammonia, and hydrogen are changed. The low temperature buffer layer was grown by 300 angstroms by flowing for 10 minutes at 3 × 10 ⁻⁴ (mol / min), 40 slm, and 25 slm, respectively.

Thereafter, the temperature of the sapphire substrate is raised to 1050 ° C., and the flow rates of trimethyl gallium, ammonia, and hydrogen are respectively set to 5 × 10 ⁻⁴ (mol / min), 20 slm, and 20 slm for 60 minutes to grow a non-doped GaN layer by 4 μm. It was.

Thereafter, the temperature of the sapphire substrate was lowered to room temperature. Next, the non-doped GaN layer grown on the sapphire substrate 9 was transferred to the MBE apparatus 22 through the vacuum sample transfer chamber 23. The pressure in the vacuum sample transfer chamber 23 during transfer was 5 × 10 ⁻⁶ Pa.

In the MBE apparatus 22, the sapphire substrate temperature was raised to 800 ° C. while irradiating nitrogen plasma with a nitrogen radical source output of 350 W and a nitrogen flow rate of 5 sccm, and a gallium evaporation source held at 900 ° C. and 1100 ° C., respectively. The shutter of the aluminum evaporation source was opened for 3 minutes, and an n-type Al _x Ga _1-x N layer (x˜0.25) was grown by 250 Å.

The surface of the n-type Al _x Ga _1-x N layer obtained as described above is flat as shown in FIG. 2A, and the mobility of the two-dimensional electron gas is 1430 (cm ² / Vs). Met.

On the other hand, when the non-doped GaN layer and the n-type Al _x Ga _1-x N layer are all formed by the MOCVD method, the mobility of the two-dimensional electron gas of 1420 (cm ² / Vs) was obtained, but the n-type On the surface of the Al _x Ga _1-x N layer, as shown in FIG. 2B, many recesses that are said to easily cause gate leakage were observed.

Further, after the non-doped GaN layer is grown by MOCVD, it is once taken out into the atmosphere and transferred to the MBE apparatus 22 to grow the n-type Al _x Ga _1-x N layer. Since the interface states can be formed along with the oxidation, the mobility of the two-dimensional electron gas is only 60 (cm ² / Vs).

  In the embodiment shown in FIG. 4, the compound semiconductor film forming apparatus according to the present invention is incorporated in a multi-chamber apparatus. That is, in FIG. 4, 31 is an MOCVD chamber, 32 is an MBE chamber, and these chambers 31 and 32 are arranged around a common vacuum transfer section 36 together with other processing chambers 33, 34 and 35. The MOCVD chamber 31, the MBE chamber 32, and the other processing chambers 33, 34, and 35 are each connected to a common vacuum transfer section 36 via a gate valve 37.

  Also in this case, as in the case of the embodiment of FIG. 1, the MOCVD chamber 31 is provided with a valve and a mass flow controller for supplying trimethylgallium, ammonia and hydrogen, although not shown, and MBE. Although not shown, the chamber 32 is provided with an evaporation source chamber, and a gallium evaporation source, an aluminum evaporation source, and a nitrogen plasma source are coupled to the evaporation source chamber.

In the MOCVD chamber 31, the sapphire substrate was heated at 1200 ° C. for 10 minutes while flowing hydrogen gas at 20 slm to clean the surface, then the sapphire substrate was brought to 550 ° C., and the flow rates of trimethylgallium, ammonia, and hydrogen were 3 ×, respectively. 10 ⁻⁴ (mol / min), 40 slm, 25 slm was applied for 10 minutes to grow a low temperature buffer layer by 300 Å.

Thereafter, the temperature of the sapphire substrate is raised to 1050 ° C., and the flow rates of trimethyl gallium, ammonia, and hydrogen are respectively set to 5 × 10 ⁻⁴ (mol / min), 20 slm, and 20 slm for 60 minutes to grow a non-doped GaN layer by 4 μm. It was.

Thereafter, the temperature of the sapphire substrate was lowered to 500 ° C., and the flow rates of trimethylgallium, ammonia, and hydrogen were set to 3 × 10 ⁻⁴ (mol / min), 20 slm, and 20 slm, respectively, and InN for surface protection was grown to 100 Å. .

  Next, the grown sample was transported in the atmosphere and set in the MBE chamber 32 of the MBE apparatus. In the MBE chamber 32, the sample was heated to 700 ° C. for 1 hour to evaporate only InN for surface protection. .

The non-doped GaN layer having a clean surface thus obtained is irradiated with nitrogen plasma with a nitrogen radical source output of 350 W and a nitrogen flow rate of 5 sccm, and the substrate temperature is raised to 800 ° C. The shutters of the gallium evaporation source and the aluminum evaporation source maintained at ° C. were opened for 3 minutes, and an n-type Al _x Ga _1-x N layer (x˜0.25) was grown on the non-doped GaN layer by 250 Å.

The surface of the n-type Al _x Ga _1-x N layer obtained as described above is flat, as shown in FIG. 2A, and the mobility of the two-dimensional electron gas is 1410 (cm ^2). / Vs).

On the other hand, when the non-doped GaN layer and the n-type Al _x Ga _1-x N layer are all formed by the MOCVD method, the mobility of the two-dimensional electron gas of 1420 (cm ² / Vs) was obtained, but the n-type On the surface of the Al _x Ga _1-x N layer, as shown in FIG. 2B, many recesses that are said to easily cause gate leakage were observed.

However, after a non-doped GaN layer is grown by MOCVD, it is once taken out into the atmosphere and transferred to another MBE apparatus to grow an n-type Al _x Ga _1-x N layer. Since interface states could be formed along with oxidation, the mobility of the two-dimensional electron gas was 60 (cm ² / Vs).

In the illustrated embodiment, the InN film is formed in the MOCVD apparatus after growing the non-doped GaN layer, and the InN film is removed by heating in the MBE apparatus. However, the surface protective film is formed in the film forming apparatus connected to the MOCVD apparatus. Formed on the layer, transported in the atmosphere to the MBE apparatus, heat-removed the surface protective film formed on the non-doped GaN layer in a vacuum apparatus connected to the MBE apparatus, transported the sample to the MBE apparatus, n A type Al _x Ga _1-x N layer may be grown.

In the illustrated embodiment, sapphire is used as the substrate, but other substrates such as SiC, GaN, GaAs, Si, and AlN may be used. As the nitrogen source for growth of the n-type Al x _Ga 1-x _N layer by the MBE method, using nitrogen plasma may be used ammonia.

The schematic diagram which shows the structure of the principal part of the compound semiconductor growth apparatus by one Embodiment of this invention comprised as a MOCVD and MBE compound apparatus. (A) The figure which shows the surface of the AlGaN film layer created with the apparatus of FIG. (B) The figure based on the AFM photograph of the surface of the AlGaN film layer produced by MOCVD method. The schematic diagram which shows the structure of the compound semiconductor growth apparatus by another embodiment of this invention which comprised the MOCVD apparatus and the MBE apparatus by connecting with the vacuum conveyance part. The schematic diagram which shows the structure of the compound semiconductor growth apparatus by another embodiment of this invention comprised as a cluster type apparatus. The schematic sectional drawing which shows an example of general GaN-type FET. The figure which shows the band structure in a n-type AlGaN / non-doped GaN heterojunction.

Explanation of symbols

1: MOCVD chamber of MOCVD apparatus 2: Evaporation source chamber of MBE apparatus 3: Gallium evaporation source 4: Aluminum evaporation source 5: Nitrogen plasma source 6: Gate valve 7: Mass flow controller of trimethyl gallium 8: Mass flow controller of ammonia 9: Hydrogen Mass flow controller 10: Valve 11: Valve 12: Valve 13: Valve 14: Shutter 15 of gallium evaporation source 3: Shutter 16 of aluminum evaporation source 4: Shutter 17 of nitrogen plasma source 5: Heater 18 for substrate heating: Substrate holder 19: Substrate 21: MOCVD apparatus 22: MBE apparatus 23: Vacuum sample transfer section 24: Gate valve 25: Gate valve 31: MOCVD chamber 32: MBE chamber 36: Common vacuum transfer section 37: Gate valve

Claims (6)

An n-type Al _x Ga _1-x N layer (x = 0.1 to 1.0) is epitaxially grown on the non-doped GaN single crystal layer, and on the GaN side of the n-type Al _x Ga _1-x N layer / non-doped GaN interface. In the method of growing a heterojunction compound semiconductor in which the formed two-dimensional electrons travel along the interface at high speed,
Using the MOCVD method to epitaxially grow the non-doped GaN layer on the substrate,
A method for growing a compound semiconductor, comprising using an MBE method to epitaxially grow an n-type Al _x Ga _1-x N layer on a non-doped GaN layer. Epitaxial growth of a non-doped GaN layer by MOCVD on a substrate and epitaxial growth of an n-type Al _x Ga _1-x N layer by MBE on a non-doped GaN layer are continuously performed while maintaining a vacuum state. The method for growing a compound semiconductor according to claim 1.   After the non-doped GaN layer is epitaxially grown on the substrate using the MOCVD method, a surface protective film for preventing the formation of an impurity layer or mono-oxide layer on the surface of the non-doped GaN layer is formed, and then on the non-doped GaN layer in a vacuum apparatus. 2. The method for growing a compound semiconductor according to claim 1, wherein the formed surface protective film is removed by heating.   The method for growing a compound semiconductor according to any one of claims 1 to 3, wherein any one of sapphire, SiC, GaN, GaAs, Si, and AlN is used as the substrate. An n-type Al _x Ga _1-x N layer (x = 0.1 to 1.0) is epitaxially grown on the non-doped GaN single crystal layer, and on the GaN side of the n-type Al _x Ga _1-x N layer / non-doped GaN interface. In the heterojunction compound semiconductor growth apparatus that causes the formed two-dimensional electrons to travel along the interface at high speed,
An MOCVD apparatus which includes respective flow rate control means for controlling the flow rates of trimethylgallium, ammonia and hydrogen, and forms a non-doped GaN layer on the substrate;
An MBE that is connected to a MOCVD apparatus via a gate valve and includes a gallium evaporation source, an aluminum evaporation source, a nitrogen plasma source, or an ammonia source, and forms an n-type Al _x Ga _1-x N layer on the non-doped GaN layer With the device;
An apparatus for growing a compound semiconductor, comprising: 6. The compound semiconductor growth apparatus according to claim 5, wherein the MOCVD apparatus and the MBE apparatus are connected via a vacuum transfer unit.