JP2006114655A - Semiconductor epitaxial wafer and field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor epitaxial wafer for realizing improved characteristics by preventing a highly conductive part (conductive layer) from being formed in a buffer layer due to the mixture of conductive impurities in the epitaxial layer, when manufacturing an electronic device, such as a field effect transistor and a hetero junction bipolar transistor including a high electron mobility transistor, on the semiconductor epitaxial wafer. <P>SOLUTION: In the semiconductor epitaxial wafer having the buffer layer 2 on a substrate 1, an Al<SB>X</SB>Ga<SB>1-X</SB>N buffer layer 23 (0≤X<1), an AlN buffer layer 22, and a GaN buffer layer 21 are formed successively in the buffer layer 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor epitaxial wafer, and more particularly to a semiconductor epitaxial wafer suitably used in the production of a field effect transistor (FET) including a high electron mobility transistor (HEMT) and the like and an FET obtained therefrom.

  In an FET including a HEMT, the current flowing between the source electrode and the drain electrode is controlled by the spread of the depletion layer from the gate electrode.

However, when manufacturing an epitaxial wafer on which an epitaxial layer made of gallium nitride (GaN) is grown, the technology for cleaning the interface between the epitaxial layer and the substrate is not well established, Due to the fact that one of the ammonia (NH ₃ ) gas, which is high purity, cannot be obtained, conductive impurities are easily mixed into the epitaxial layer.

  As a result, although the buffer layer is required to have higher insulation than other layers, the conductive impurities are mixed in the buffer layer, resulting in a degree close to the conductivity of the channel layer. However, this tendency is particularly remarkable in a portion near the substrate of the buffer layer.

  Such a problem causes the depletion layer to hardly spread from the gate electrode.

  Further, as a result of mixing conductive impurities in the buffer layer, a portion having high conductivity (conductive layer) is formed in a portion close to the substrate of the buffer layer, and a current flows therethrough, so that good characteristics (see FIG. 7). It has been difficult to obtain an electronic device having a pinch-off characteristic close to the ideal shown).

For example, Patent Document 1 and Patent Document 2 describe electronic devices (HEMT, FET) in which a buffer layer made of GaN is formed on a sapphire substrate or a silicon carbide (SiC) substrate. It is considered that sufficient characteristics are not obtained for the reason.
JP 2001-102564 A JP 2002-50758 A

  In the present invention, a defect that causes the deterioration of the characteristics as described above, more specifically, a portion having high conductivity in the buffer layer (conductive layer) by mixing conductive impurities into the epitaxial layer. ) Is formed, and as a result, a semiconductor epitaxial wafer that can be suitably used in manufacturing a field effect transistor (FET, HEMT, etc.) that realizes high characteristics is provided.

In order to achieve the above object, the present invention is configured as follows.
The semiconductor epitaxial wafer according to the invention of claim 1 is a semiconductor epitaxial wafer having a buffer layer on a substrate, wherein the buffer layer is an Al _x Ga _1-x N buffer layer (0 ≦ X <1), an AlN buffer layer, It has a structure in which GaN buffer layers are sequentially formed.

The semiconductor epitaxial wafer according to the invention of claim 2 is a semiconductor epitaxial wafer having a buffer layer on a substrate, wherein the buffer layer is an Al _x Ga _1-x N buffer layer (0 ≦ X <1), an AlN buffer layer, It has a structure in which a GaN buffer layer is formed in order, and 1 × 10 ¹⁸ cm ⁻³ or more of carbon and 5 × 10 ¹⁷ cm ⁻³ or more of an n-type dopant are added to the Al _x Ga _1-x N buffer layer. It is characterized by.

A semiconductor epitaxial wafer according to a third aspect of the present invention is a semiconductor epitaxial wafer having a buffer layer on a substrate, wherein the buffer layer is an In _Y Ga _1-Y N buffer layer (0 ≦ Y ≦ 1), Al _X Ga _{1 -X} N buffer layer (0 ≦ X <1), an AlN buffer layer, and a GaN buffer layer are formed in this order, and the Al _X Ga _1-X N buffer layer has a carbon of 1 × 10 ¹⁸ cm ⁻³ or more. And 5 × 10 ¹⁷ cm ⁻³ or more of an n-type dopant is added.

  A semiconductor epitaxial wafer according to a fourth aspect of the present invention is the semiconductor epitaxial wafer according to any one of the first to third aspects, wherein the substrate is a sapphire substrate or a SiC substrate.

  A field effect transistor according to a fifth aspect of the present invention is formed by forming a channel layer, an electron supply layer, a source electrode, a gate electrode, and a drain electrode on the semiconductor epitaxial wafer according to any one of the first to fourth aspects. It is characterized by having been produced.

  According to the present invention, it is possible to prevent a portion having high conductivity (conductive layer) from being formed in the buffer layer by mixing conductive impurities in the epitaxial layer, and as a result, high characteristics can be obtained. It is possible to provide a semiconductor epitaxial wafer that is suitably used when producing a realized field effect transistor (FET, HEMT, etc.).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Example 1>
FIG. 1 is a sectional view showing a first embodiment of a semiconductor epitaxial wafer of the present invention.

  Specifically, the structure shown in FIG. 1 is used to measure the characteristics (conductivity) of the buffer layer 2 including the AlGaN buffer layer 23, the AlN buffer layer 22, and the GaN buffer layer 21. A device for measuring characteristics manufactured using the first embodiment, on a substrate 1 made of sapphire, an AlGaN buffer layer 23 made of undoped AlGaN, an AlN buffer layer 22 made of undoped AlN, and an undoped layer having a thickness of 2 μm. It consists of a GaN buffer layer 21 made of GaN, and measurement electrodes 11 and 12 formed thereon.

In the element structure for characteristic measurement, the combination of carbon and silicon (n-type dopant) added to the AlGaN buffer layer 23 is changed to carbon addition amounts 5 × 10 ¹⁷ cm ⁻³ , 1 × 10 ¹⁸ cm ⁻³ , 1 The element for characteristic measurement was produced with respect to .5 × 10 ¹⁸ cm ⁻³ with silicon (n-type dopant) added in an amount 0.1, 0.5, and 1 times that of carbon, respectively.

  Here, the thicknesses of the AlGaN buffer layer 23 and the AlN buffer layer 22 were set to 0.05 μm and 0.25 μm, respectively.

  A metal organic vapor phase epitaxy (MOVPE) method was used for the epitaxial growth of the semiconductor epitaxial wafer used for the characteristic measuring element. Here, trimethylgallium (TMG) is used as the gallium source, trimethylaluminum (TMA) is used as the aluminum source, trimethylindium (TMI) is used as the indium source, ammonia gas is used as the nitrogen source, and carrier gas is used. Hydrogen was used.

  FIG. 4 is a diagram showing the relationship between the amount of carbon and silicon (n-type dopant) added to the AlGaN buffer layer 23 and the conductivity (indicated by current value, the unit is A / mm) in this case. is there. As a method for evaluating conductivity, a voltage of 10 V was applied to the semiconductor epitaxial wafer shown in FIG. 1, and the current flowing at that time was measured and compared.

As a result, when the buffer layer 2 composed of the AlGaN buffer layer 23, the AlN buffer layer 22, and the GaN buffer layer 21 is formed, the ratio of the amount of carbon and silicon (n-type dopant) added to the AlGaN buffer layer 23 (silicon When the addition amount of carbon / the addition amount of carbon (hereinafter referred to as doping ratio) is 0.5, a very small current value (low conductivity) could be obtained. Specifically, in the AlGaN buffer layer 23 having a carbon concentration of 1 × 10 ¹⁸ cm ⁻³ , the current value was 1 × 10 ⁻⁶ A / mm when the doping ratio was 0.1. On the other hand, when the doping ratio was 0.5, the current value was 1 × 10 ⁻⁸ A / mm, and when the doping ratio was 1, the current value was 5 × 10 ⁻⁴ A / mm.

Therefore, when the FET is actually manufactured using the first embodiment of the semiconductor epitaxial wafer of the present invention, the amount of carbon added is 1 × 10 ¹⁸ cm ⁻³ or more and silicon (n-type dopant) is used. The addition amount is preferably 5 × 10 ¹⁷ cm ⁻³ or more. This is because the current value that is considered to cause no problem in practice is 1 × 10 ⁻⁷ A / mm or less.

  FIG. 2 is a sectional view showing a HEMT manufactured using the first embodiment of the semiconductor epitaxial wafer of the present invention.

The HEMT shown in FIG. 2 is made of a sapphire substrate 1 having a thickness of 0.05 μm, an Al composition ratio of 0.1, a carbon addition amount of 1.5 × 10 ¹⁸ cm ⁻³ , and silicon (n-type dopant). AlGaN buffer layer 23 made of undoped AlGaN with an addition amount of 7.5 × 10 ¹⁷ cm ⁻³ , AlN buffer layer 22 made of undoped AlN with a thickness of 0.2 μm, GaN buffer layer 21 made of undoped GaN with a thickness of 2 μm, thickness A channel layer 4 made of undoped GaN having a thickness of 0.1 μm and a carrier supply layer 5 made of n-type AlGaN having a thickness of 0.025 μm were sequentially formed, and a cap layer 6 having a thickness of 0.002 μm was formed thereon. A gate electrode 8 was formed on the carrier supply layer 5, and a source electrode 7 and a drain electrode 9 were formed on the cap layer 6.

  The MOVPE method was used for the epitaxial growth of this HEMT. The raw materials used for the growth were TMG as the gallium raw material, TMA as the aluminum raw material, TMI as the indium raw material, ammonia gas as the nitrogen raw material, and hydrogen as the carrier gas. Used, monosilane was used as the n-type dopant. Epitaxial growth was performed using a face-up heater-heated decompression furnace (not shown) and setting the pressure in the furnace to 13332 Pa (100 Torr).

  As a result of measuring the characteristics of the HEMT fabricated as described above, it was confirmed that the buffer layer had a good pinch-off characteristic (pinch-off voltage −4.1 V) as a result of a decrease in the conductivity of the buffer layer.

<Example 2>
FIG. 3 is a cross-sectional view showing a HEMT manufactured using the second embodiment of the semiconductor epitaxial wafer of the present invention.

The HEMT shown in FIG. 3 has an InGaN buffer layer 34 made of undoped InGaN having a thickness of 0.01 μm and an In composition ratio of 0.05 on a substrate 1 made of sapphire, a thickness of 0.05 μm, and an Al composition ratio of 0.1. An AlGaN buffer layer 33 made of undoped AlGaN having an added amount of carbon of 1 × 10 ¹⁸ cm ⁻³ or more and an added amount of silicon (n-type dopant) of 5 × 10 ¹⁷ cm ⁻³ or more, and an undoped AlN of 0.2 μm in thickness. An AlN buffer layer 32, a GaN buffer layer 31 made of undoped GaN having a thickness of 2 μm, a channel layer 4 made of undoped GaN having a thickness of 0.1 μm, and a carrier supply layer 5 made of n-type AlGaN having a thickness of 0.025 μm are sequentially formed. Then, a cap layer 6 having a thickness of 0.002 μm was formed thereon. A gate electrode 8 was formed on the carrier supply layer 5, and a source electrode 7 and a drain electrode 9 were formed on the cap layer 6.

  For the HEMT epitaxial growth, the MOVPE method was used in the same manner as in Example 1. As in Example 1, the raw materials used for the growth were TMG as the gallium raw material, TMA as the aluminum raw material, TMI as the indium raw material, and ammonia gas as the nitrogen raw material. Nitrogen was used as the carrier gas, and monosilane was used as the n-type dopant. Epitaxial growth was performed using a face-up heater-heated decompression furnace (not shown) and setting the pressure in the furnace to 13332 Pa (100 Torr).

  As a result of measuring the characteristics of the HEMT fabricated as described above, it was confirmed that the buffer layer had a good pinch-off characteristic (pinch-off voltage −4.0 V) as a result of a decrease in the conductivity of the buffer layer.

<Comparative Example 1>
FIG. 5 is a cross-sectional view showing a semiconductor epitaxial wafer as a comparative example of the semiconductor epitaxial wafers of Examples 1 and 2 above.

  Specifically, the structure shown in FIG. 5 is a characteristic measuring element manufactured for measuring the characteristics (conductivity) of the buffer layer 10 made of GaN, and has a thickness on the substrate 1 made of sapphire. It consists of a buffer layer 10 made of 2 μm of GaN, and measurement electrodes 11 and 12 formed thereon. The epitaxial growth method of the semiconductor epitaxial wafer used for this characteristic measuring element and the raw materials used for the epitaxial growth are the same as those used for growing the GaN buffer layer in Examples 1 and 2 above. is there.

As a result, the obtained current value was 1 × 10 ⁻¹ A / mm, and only a large current value (high conductivity) could be obtained as compared with Examples 1 and 2 above.

  FIG. 6 is a cross-sectional view showing a HEMT fabricated using a semiconductor epitaxial wafer as a comparative example of the semiconductor epitaxial wafers of Examples 1 and 2 above.

  The HEMT shown in FIG. 6 is formed on a substrate 1 made of sapphire, a buffer layer 10 made of undoped GaN having a thickness of 2 μm, a channel layer 4 made of undoped InGaN having a thickness of 0.1 μm, and an n-type having a thickness of 0.025 μm. A carrier supply layer 5 made of AlGaN was sequentially formed, and a cap layer 6 having a thickness of 0.002 μm was formed thereon. A gate electrode 8 was formed on the carrier supply layer 5, and a source electrode 7 and a drain electrode 9 were formed on the cap layer 6.

  The MOVPE method was used for the epitaxial growth of HEMT, as in Examples 1 and 2. As in Example 1, the raw materials used for the growth were TMG as the gallium raw material, TMA as the aluminum raw material, ammonia gas as the nitrogen raw material, and hydrogen as the carrier gas. Monosilane was used as the n-type dopant. Epitaxial growth was performed using a face-up heater-heated decompression furnace (not shown) and setting the pressure in the furnace to 13332 Pa (100 Torr).

  As a result of measuring the characteristics of the HEMT produced in this way, it was not possible to pinch off. That is, since the conductivity of the buffer layer does not decrease as in Examples 1 and 2, it was confirmed that it did not have good pinch-off characteristics as in Examples 1 and 2.

<Other embodiments and modifications>
In the first and second embodiments, the sapphire substrate is used as the substrate. However, a silicon carbide (SiC) substrate may be used as the substrate. In this case, the same effect as when the sapphire substrate is used as the substrate 1 may be used. Can be obtained.

  In the first and second embodiments, an AlGaN buffer layer having an Al composition ratio of 0.1 is used. However, the present invention is not particularly limited to this, and an AlGaN buffer having an Al composition ratio of 0 to less than 1 is used. Includes layers. That is, the case where the Al composition ratio is 0 (GaN) is also included.

  In Example 2, an InGaN buffer layer having an In composition ratio of 0.05 is used. However, the present invention is not particularly limited to this, and includes an AlGaN buffer layer having an In composition ratio of 0 to 1. It is a waste. That is, the case where the In composition ratio is 0 (GaN) and the case where the In composition ratio is 1 (InN) is also included.

It is sectional drawing which shows the element for a characteristic measurement produced using 1st Embodiment of the semiconductor epitaxial wafer of this invention. It is sectional drawing which shows the high electron mobility transistor (HEMT) produced using 1st Embodiment of the semiconductor epitaxial wafer of this invention. It is sectional drawing which shows the high electron mobility transistor (HEMT) produced using 2nd Embodiment of the semiconductor epitaxial wafer of this invention. It is the figure which showed the relationship between the addition amount of carbon and silicon (n-type dopant) of the AlGaN buffer layer in the semiconductor epitaxial wafer of this invention, and electroconductivity. It is sectional drawing which shows the element for a characteristic measurement produced using the semiconductor epitaxial wafer of a prior art example. It is sectional drawing which shows the high electron mobility transistor (HEMT) produced using the semiconductor epitaxial wafer of a prior art example. It is a figure which shows the pinch-off characteristic of the high electron mobility transistor produced using the semiconductor epitaxial wafer of a prior art example, and the ideal pinch-off characteristic in a high electron mobility transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 21 GaN buffer layer 22 AlN buffer layer 23 AlGaN buffer layer 3 Buffer layer 31 GaN buffer layer 32 AlN buffer layer 33 AlGaN buffer layer 34 InGaN buffer layer 4 Channel layer 5 Carrier supply layer 6 Cap layer 7 Source electrode 8 Gate electrode 9 Drain electrode 10 Buffer layer 11 Measuring electrode 12 Measuring electrode

Claims (5)

In a semiconductor epitaxial wafer having a buffer layer on a substrate,
Semiconductor epitaxial wafer, characterized by comprising the buffer layer is Al _X Ga _1-X N buffer layer (0 ≦ X <1), AlN buffer layer to form a GaN buffer layer in order. In a semiconductor epitaxial wafer having a buffer layer on a substrate,
The buffer layer has a structure in which an Al _X Ga _1-X N buffer layer (0 ≦ X <1), an AlN buffer layer, and a GaN buffer layer are formed in this order, and the Al _X Ga _1-X N buffer layer is 1 × A semiconductor epitaxial wafer characterized by adding carbon of 10 ¹⁸ cm ⁻³ or more and an n-type dopant of 5 × 10 ¹⁷ cm ⁻³ or more. In a semiconductor epitaxial wafer having a buffer layer on a substrate,
The buffer layer has a structure in which an In _Y Ga _1-Y N buffer layer (0 ≦ Y ≦ 1), an Al _X Ga _1-X N buffer layer (0 ≦ X <1), an AlN buffer layer, and a GaN buffer layer are formed in this order. A semiconductor epitaxial wafer comprising: 1 × 10 ¹⁸ cm ⁻³ or more of carbon and 5 × 10 ¹⁷ cm ⁻³ or more of n-type dopant added to the Al _x Ga _1-x N buffer layer. In the semiconductor epitaxial wafer according to any one of claims 1 to 3,
A semiconductor epitaxial wafer, wherein the substrate comprises a sapphire substrate or a SiC substrate.   A field effect transistor produced by forming and cutting a channel layer, an electron supply layer, a source electrode, a gate electrode, and a drain electrode on the semiconductor epitaxial wafer according to claim 1.

Images