JP5347228B2 - Field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high output nitride semiconductor transistor having a low current collapse and a low gate leakage current. <P>SOLUTION: In the transistor comprises a buffer layer 2, a GaN channel layer 3, and an AlGaN electron supply layer 4 formed on a substrate 1. A source electrode 5, a drain electrode 6 and a gate electrode 7 are formed on the surface of the AlGaN electron supply layer 4, the surface of the exposed AlGaN electron supply layer 4 is covered with a fluorine-containing insulating film 8 containing a fluorine, such as a fluorine-containing SiN film. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a field effect transistor, and more particularly to a nitride semiconductor field effect transistor whose surface is covered with an insulating film such as a SiN film.

  FIG. 6 is a cross-sectional view of a conventional hetero-junction field effect transistor (hereinafter referred to as HJFET). Such a conventional HJFET is reported in Non-Patent Document 1, for example. In this HJFET, a buffer layer 2 is formed on a substrate 1 made of sapphire or SiC. A GaN channel layer 3 is formed on the buffer layer 2, and an AlGaN electron supply layer 4 is formed thereon. A source electrode 5 and a drain electrode 6 are formed thereon, and these electrodes are in ohmic contact with the AlGaN electron supply layer 4. A gate electrode 7 is formed between the source electrode 5 and the drain electrode 6, and this gate electrode is in Schottky contact with the AlGaN electron supply layer 4. A SiN film 10 is formed on the uppermost layer as a surface protective film.

  In such an AlGaN / GaN HJFET, there is a trade-off between the current collapse amount and the gate breakdown voltage, and its control is very difficult. In an AlGaN / GaN heterojunction, piezoelectric polarization is generated by spontaneous polarization and stress caused by lattice mismatch between the AlGaN layer and the GaN layer, and a two-dimensional electron gas is supplied to the AlGaN / GaN interface. Therefore, it becomes sensitive to the surface charge, and the AlGaN surface state greatly affects the device characteristics of the HJFET. Collapse is a phenomenon in which, when the HJFET performs a large signal operation, negative charge is accumulated on the surface due to the response of the surface trap, and the maximum drain current is suppressed. When the collapse becomes significant, the drain current during large signal operation is suppressed, and the saturation output decreases. FIG. 6 is an explanatory diagram for explaining a method of calculating a collapse coefficient indicating a collapse amount. The collapse coefficient (CF) increases the maximum current: Imax (10 V) when Vds = 10 V after operating the transistor under the condition that Vds does not exceed 10 V, and increases Vds until it reaches 80 V to increase the transistor Is a coefficient indicating the rate of change of the maximum current when Vds = 10 V after the operation. That is, CF = [{Imax (10V) −Imax (80V)} / Imax (10V)] × 100. This collapse coefficient is 60% or more when there is no SiN film on the element surface (film thickness 0 nm), but can be suppressed to 10% or less when the SiN film thickness is 100 nm. In this way, in a GaN transistor that is sensitive to the surface state of the element, when a SiN film is formed on the surface of the element, the surface of the AlGaN is protected by the SiN film, which has the effect of suppressing the generation of negative charges due to the surface level. The amount of collapse can be reduced. On the other hand, the moderate surface negative charge has the effect of relaxing the electric field concentration between the gate and the drain and increasing the gate breakdown voltage. For this reason, when the surface of AlGaN is protected with a SiN film, there is a problem that when the surface negative charge is canceled, the electric field concentration between the gate and the drain becomes remarkable and the gate leakage current increases.

The mechanism for increasing the gate leakage current has not been clarified at present, but the interface state of SiN / AlGaN is low and the electric field concentration occurs at the drain end of the gate electrode, and there are N vacancies on the SiN / AlGaN surface. There is an idea that a tunnel current flows because it is generated and becomes a high-concentration n-type layer. As a technique for solving this problem, for example, in Patent Document 1, if the hydrogen content in the SiN protective film is 15% or less, the state change of the nitride semiconductor surface caused by the presence of hydrogen in the SiN protective film It is disclosed that the change in the charge state of the surface defect level is suppressed, and the gate leakage current and current collapse can be suppressed to a level that satisfies the user's characteristic requirements.
Y. Ando et al., IEDM 01-381-384, 2001 JP-A-2005-286135

As described above, the field effect transistor in which the surface of the nitride semiconductor is covered with the SiN film has a problem that the current leakage can be reduced but the gate leakage current increases. On the other hand, as disclosed in Patent Document 1, when the hydrogen content in the SiN protective film is 15% or less, the gate leakage current and the current collapse can be suppressed to a level that satisfies the user's characteristic requirements. . However, in the plasma CVD growth method using ordinary silane gas (SiH ₄ ), ammonia gas (NH ₃ ), and nitrogen gas (N ₂ ), the deposited SiN film easily contains about 15% hydrogen, and the hydrogen concentration For the reduction, it is necessary to greatly increase the ratio of nitrogen gas (N ₂ ) to ammonia gas (NH ₃ ). At this time, N ₂ gas is harder to decompose than NH _3, and sufficient N cannot be supplied to the SiN film, so that there is a shortage of N in the SiN film and sufficient insulation cannot be obtained with good reproducibility. It becomes.
An object of the present invention is to solve the above-mentioned problems of the prior art, and its purpose is to control a nitride semiconductor transistor having a high frequency power characteristic by solving a trade-off between current collapse and gate leakage current. It is to be able to provide well.

In order to achieve the above object, according to the present invention, a second nitride semiconductor having an energy band gap wider than that of the first nitride semiconductor is formed on and in contact with the first nitride semiconductor, the source electrode in contact with the nitride semiconductor of the second, is formed a drain electrode and a gate electrode, a field effect includes an insulating film containing fluorine in contact therewith on the crystal surface of the second nitride semiconductor In the transistor, a field effect transistor is provided in which the fluorine content in the fluorine-containing insulating film is 5 atom% or less and 0.001 atom% or more .

In order to achieve the above object, according to the present invention, a second nitride semiconductor having an energy band gap wider than that of the first nitride semiconductor is formed on and in contact with the first nitride semiconductor. A source electrode, a drain electrode and a gate electrode are formed in contact with the second nitride semiconductor, and an insulating film containing fluorine and carbon is provided on the crystal surface of the second nitride semiconductor in contact with the second nitride semiconductor. The field effect transistor is characterized in that the fluorine content in the insulating film containing fluorine and carbon is 5 atom% or less and 0.001 atom% or more .

In order to achieve the above object, according to the present invention, a second nitride semiconductor having an energy band gap wider than that of the first nitride semiconductor is formed on and in contact with the first nitride semiconductor. A source electrode, a drain electrode, and a gate electrode are formed in contact with the second nitride semiconductor, and an insulating film having a multilayer structure is formed on a crystal surface of the second nitride semiconductor. In the field effect transistor in which the first layer in contact with the semiconductor is composed of an insulating film containing fluorine, the fluorine content in the insulating film containing fluorine is 5 atom% or less and 0.001 atom% or more. A field effect transistor is provided.

In order to achieve the above object, according to the present invention, a second nitride semiconductor having an energy band gap wider than that of the first nitride semiconductor is formed on and in contact with the first nitride semiconductor. A source electrode, a drain electrode, and a gate electrode are formed in contact with the second nitride semiconductor, and an insulating film having a multilayer structure is formed on a crystal surface of the second nitride semiconductor . In the field effect transistor in which the first layer in contact with the semiconductor is composed of an insulating film containing fluorine and carbon, the fluorine content in the insulating film containing fluorine and carbon is 5 atom% or less and 0.001 atom% or more. field effect transistor, characterized in that there, is provided.

  Preferably, the fluorine content in the insulating film containing fluorine is 5 atom% or less. More preferably, the fluorine content in the insulating film containing fluorine is 0.001 atom% or more.

  In the conventional example in which the surface of the AlGaN electron supply layer is coated with a SiN film, as shown in the energy band diagram of FIG. 1B, the interface potential of the AlGaN electron supply layer decreases, and the interface between the AlGaN layer and the SiN film is reduced. Charge accumulates. As a result, a large surface leakage current 11 flows as shown in FIG. Thus, according to the present invention, fluorine is added to the surface protective insulating film such as the SiN film. EE Electron Device Letter Vol. 26, No. 7, pp. 435 shows that fluorine (F) is contained in the AlGaN layer by plasma treatment with a reactive gas containing fluorine (F) on the AlGaN surface immediately before forming the gate electrode. It has been reported that negative charges are formed by entering, and the threshold voltage moves to the positive side after the gate electrode is formed. If the configuration of the present invention is used, the ionized fluorine (F) and the AlGaN electron supply layer 4 existing at the interface between the source electrode, the gate electrode, and the drain electrode / AlGaN electron supply layer 4 are not directly under the gate electrode. Due to the diffused fluorine (F) ions, it is possible to prevent a decrease in the interface potential of the insulating film / AlGaN electron supply layer 4 which has been a problem in the conventional insulating film. That is, the addition of fluorine raises the interface potential of the AlGaN electron supply layer and eliminates the interface charge, as shown in the energy band diagram of FIG. For this reason, it is possible to suppress the concentration of the electric field at the gate electrode interface when the reverse voltage is applied, and to reduce the reverse leakage current. According to the present invention, the surface leakage current is reduced to about 1/100 or less of that of the conventional configuration, high voltage operation is possible, and high frequency output characteristics are remarkably improved. On the other hand, in the field effect transistor of the present invention, since the surface of the AlGaN electron supply layer is covered with the SiN film, current collapse can be reduced. Further, this SiN film can be easily formed with good reproducibility. Therefore, according to the present invention, it is possible to provide a transistor with good high-frequency power characteristics with low current collapse and reduced gate leakage current with good reproducibility.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 2 is a cross-sectional view showing a first embodiment of a nitride semiconductor field effect transistor of the present invention. As shown in FIG. 2, a buffer layer 2, a GaN channel layer 3, and an AlGaN electron supply layer 4 are sequentially grown on the substrate 1. A source electrode 5, a drain electrode 6 and a gate electrode 7 are formed on the surface of the AlGaN electron supply layer 4, and the exposed surface of the AlGaN electron supply layer 4 is covered with a fluorine-containing insulating film 8 containing fluorine.
Here, as the substrate, any substrate capable of crystal growth of GaN, such as a SiC substrate, a sapphire substrate, a silicon substrate, or a ZnO substrate, can be used. For the buffer layer 2, a material such as GaN or AlN having a lattice constant close to GaN is selected. SiN is preferably used as the insulator material of the fluorine-containing insulating film 8, but a high dielectric constant and high energy band gap material such as an Al ₂ O ₃ or HfO film can also be used. A desirable film thickness of the fluorine-containing insulating film 8 is 50 to 200 nm.

A desirable fluorine concentration in the fluorine-containing insulating film 8 is 5 atom% or less. If it exceeds this, the characteristics of the insulating film will deteriorate, and the original electrical insulation, surface shape and moisture resistance of the insulating film cannot be maintained.
On the other hand, the fluorine concentration in the insulating film needs to have a value sufficient to raise the surface potential, and the lower limit is selected as follows. Since d1 is the thickness of the insulating film containing fluorine, and N is the fluorine concentration, the polarization charge generated on the surface of the AlGaN electron supply layer 4 is about 1 × 10 ¹³ cm ⁻² , and this value varies depending on the surface state. The product d1xN of the thickness d1 of the insulating film and the fluorine concentration N needs to be 1 × 10 ¹³ cm ⁻² or more. For example, when the thickness of the insulating film is 100 nm, the necessary fluorine concentration is 1 × 10 ¹⁸ cm ⁻³ or more. Here, when the atomic density of the insulating film base material is estimated to be 1 × 10 ²³ cm ⁻³ , the above 1 × 10 ¹⁸ cm ⁻³ or more corresponds to 0.001 atom% or more.
Carbon (C) may be added to the fluorine-containing insulating film 8 in addition to fluorine. A desirable C concentration in the fluorine-containing insulating film 8 is 5 atom% or less. This is because even if it is added more than this, the improvement of the characteristics cannot be expected, and the characteristics of the insulating film are deteriorated, and the original electrical insulation, surface shape and moisture resistance cannot be maintained.

(Second Embodiment)
FIG. 3 is a cross-sectional view showing a second embodiment of the nitride semiconductor field effect transistor of the present invention. As shown in FIG. 3, a buffer layer 2, a GaN channel layer 3, and an AlGaN electron supply layer 4 are sequentially grown on the substrate 1. A source electrode 5, a drain electrode 6 and a gate electrode 7 are formed on the surface of the AlGaN electron supply layer 4, and the exposed AlGaN electron supply layer 4 includes a fluorine-containing insulating film 8 containing fluorine and an upper insulating film 9 covering the fluorine-containing insulating film 9. It is covered with a multilayer insulating film consisting of
Here, since the configuration other than the protective insulating film covering the transistor surface is the same as that of the first embodiment shown in FIG. 2, only the multilayer insulating film will be described. SiN is preferably used as the insulator material of the fluorine-containing insulating film 8, but a high dielectric constant and high energy band gap material such as an Al ₂ O ₃ or HfO film can also be used. A desirable film thickness of the fluorine-containing insulating film 8 is 50 to 150 nm. The desirable fluorine concentration in the fluorine-containing insulating film 8 is 0.001 atom% or more and 5 atom% or less, as in the case of the first embodiment. Carbon may be added to the fluorine-containing insulating film 8 at a concentration of 5 atom% or less.
The upper insulating film 9 is composed of an insulating film to which fluorine is not added, and is preferably formed of SiN, SiON, SiO ₂ , Al ₂ O ₃ , HfO, or the like. The desirable film thickness is 30 to 150 nm. For example, in a case where the parasitic capacitance is to be kept low, SiO ₂ having a low dielectric constant is used, a multilayer film having a SiN—F / SiO ₂ structure is used, and if it is desired to increase moisture resistance, SiN—F / An appropriate material may be selected depending on the application, such as using a multilayer film having a SiN structure. Further, by using a combination of the above insulating materials, the upper insulating film 9 itself may be a multilayer film of two or more layers so as to meet various requirements. For example, the surface protective film may be made of SiN—F / SiO ₂ / SiN, SiN—F / Al ₂ O ₃ / SiN, SiN—F / HfO / SiN, or the like.

Next, specific examples will be described. The device structure of Example 1 is that of the first embodiment shown in FIG. The substrate 1 is a high resistance SiC substrate, the buffer layer 2 is an AlN buffer layer of 4 nm, the GaN channel layer 3 is a GaN layer of 2000 nm, the AlGaN electron supply layer 4 is an AlGaN with an Al composition ratio of 0.25 to a thickness of 30 nm. Crystals were grown by metal organic vapor phase epitaxy. Here, Ti and Al were vapor-deposited as the source electrode 5 and the drain electrode 6, and after forming a pattern using a lift-off process, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. The gate electrode 7 having a gate length Lg = 0.5 μm was formed by vapor-depositing Ni of 20 nm and Au of 200 nm and lifting off.
After that, SiN-F is used as the fluorine-containing insulating film 8 to a thickness of 100 nm, and a plasma CVD apparatus having parallel plate electrodes is used, and N ₂ diluted 2% SiH ₄ gas 200 SCCM, 100% SiF ₄ gas is 0 1 to 5 SCCM, 100% NH ₃ gas 50 SCCM, N ₂ gas 500 SCCM was flowed to form a substrate at a temperature of 300 ° C. and a PR power of 200 W.

To compare the effects of the present invention, then the SiN film 10 as an insulating film containing no fluorine, with a plasma CVD apparatus having a parallel plate electrode, N ₂ dilution 2% SiH ₄ gas 200 SCCM, 100% NH ₃ A transistor having the device structure of FIG. 6 was formed by flowing 50 SCCM of gas and 500 SCCM of N ₂ gas to form a film thickness of 100 nm at a substrate temperature of 300 ° C. and RF power of 200 W. For comparison, a sample without a surface protective film was also prepared as a conventional example.
FIG. 4 shows the evaluation results of gate leakage current characteristics of the transistor of this example in which a SiN film containing fluorine (F) was formed at a gas flow rate of 0.2 SCCM of SiF ₄ and a conventional transistor. As a result of analysis, the F concentration in the SiN film of the transistor of this example was 1 × 10 ¹⁹ cm ⁻³ . A conventional transistor having SiN not containing F has a large gate leakage current, and a good high-frequency output characteristic cannot be obtained. On the other hand, in the example of the present invention, since the leakage current is greatly reduced (approximately two digits), good high-frequency output characteristics were obtained.
Although a SiN film containing fluorine (F) The above embodiments was formed at a gas flow rate 0.2SCCM of SiF _4, the F concentration in the SiN is a SiF ₄ gas flow rate at the deposition sample was 4 sccm 8% At that time, the surface shape of the SiN was rough, the electric resistance was not sufficiently high, and the gate leakage current increased.

The device structure of Example 2 is shown in FIG. A high resistance SiC substrate is used as the substrate 1, an AlN buffer layer is 4 nm as the buffer layer 2, a GaN layer is 2000 nm as the GaN channel layer 3, and an AlGaN layer with an Al composition ratio of 0.25 is 30 nm as the AlGaN electron supply layer 4. Each was formed by metal organic vapor phase epitaxy. Here, Ti and Al metals were vapor-deposited as the source electrode 5 and the drain electrode 6, and after forming a pattern using a lift-off process, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. A gate electrode 7 having a gate length Lg = 0.5 μm was formed by vapor-depositing Ni to a thickness of 20 nm and Au to a thickness of 200 nm and lifting off. Then fluorine-containing insulating film 8 as a SiN -C-F, for example, by a plasma CVD method with parallel plate electrodes _{N 2} dilution 2% SiH ₄ gas 200SCCM, 100% CF ₄ gas, a range of 0.1 to 5SCCM 100% NH ₃ gas 50 SCCM, N ₂ gas 500 SCCM were flowed, and the substrate temperature was 300 ° C. and the PR power was 200 W.

To compare the effects of the present invention, the SiN as SiN film 10 containing no fluorine, with a plasma CVD apparatus having a parallel plate electrode, N ₂ dilution 2% SiH ₄ gas 200 SCCM, 100% NH ₃ gas 50 SCCM, N ₂ gas of 500 SCCM was flowed to form a transistor having a device structure shown in FIG. 6 with a substrate temperature of 300 ° C. and an RF power of 200 W to a thickness of 100 nm. For comparison, a sample without a surface protective film was also prepared as a conventional example.
FIG. 5 shows the evaluation results of the gate leakage current characteristics of the transistor of this example and the conventional transistor. As a result of analysis, the F concentration and the C concentration in the SiN—C—F film of the transistor of this example were 1 × 10 ¹⁹ cm ⁻³ and 5 × 10 ¹⁸ cm ⁻³ , respectively. In addition to F, the SiN film contains impurities C that form a level for capturing electrons, and the SiN / AlGaN interface is lifted by the negative charge of the captured electrons, thereby further reducing the gate leakage current. A conventional transistor having SiN not containing F has a large gate leakage current, and a good high-frequency output characteristic cannot be obtained. On the other hand, in the example of the present invention, since the leakage current was reduced to 1/100 or less, good high frequency output characteristics were obtained.

The device structure of Example 3 is shown in FIG. A high resistance SiC substrate is used as the substrate 1, an AlN buffer layer is 4 nm as the buffer layer 2, a GaN layer is 2000 nm as the GaN channel layer 3, and an AlGaN layer with an Al composition ratio of 0.25 is formed as the AlGaN electron supply layer 4 to a thickness of 30 nm. Each was formed by metal organic vapor phase epitaxy. Here, Ti and Al were vapor-deposited as the source electrode 5 and the drain electrode 6, and after forming a pattern using a lift-off process, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. The gate electrode 7 having a gate length Lg = 0.5 μm was formed by evaporating Ni to a thickness of 20 nm and Au to a thickness of 200 nm and lifting off, for example. After that, SiN 4 -F is used as the fluorine-containing insulating film 8 to a thickness of 50 nm using a plasma CVD apparatus having parallel plate electrodes, N ₂ diluted 2% SiH ₄ gas 200 SCCM, 100% SiF ₄ gas 0.2 SCCM 100% NH ₃ gas 50 SCCM, N ₂ gas 500 SCCM are flown to form a substrate at a temperature of 300 ° C. and RF power 200 W, the discharge is stopped once, and only the flow rate of SiF ₄ gas is set to 0 SCCM, again without changing other conditions. The film formation was started, and an SiN film having a thickness of 50 nm was formed as the upper insulating film 9.

To compare the effects of the present invention, then the SiN film 10 as an insulating film containing no fluorine in a thickness of 100 nm, using a plasma CVD device having parallel plate electrodes, N ₂ dilution 2% SiH ₄ gas 200 SCCM, A transistor having the device structure shown in FIG. 6 was formed by flowing 100% NH ₃ gas 50 SCCM and N ₂ gas 500 SCCM at a substrate temperature of 300 ° C. and a PR power of 200 W.
The gate leakage current characteristics of the transistor of the present invention in which a SiN film containing fluorine (F) was formed at a gas flow rate of 0.2 SCCM of SiF ₄ and a transistor having a conventional structure were evaluated. As a result of analysis, the F concentration in the SiN-F film was 1 × 10 ¹⁹ cm ⁻³ . As in FIG. 4, the conventional transistor having SiN not containing F has a large gate leakage current, and good high-frequency output characteristics cannot be obtained. On the other hand, in this example, since the leakage current was greatly reduced, good high frequency output characteristics were obtained. In addition, the SiN film on the surface has an advantage that it can be formed under conditions with excellent long-term reliability among conventional growth conditions.

The device structure of Example 4 is shown in FIG. A high resistance SiC substrate is used as the substrate 1, an AlN buffer layer is 4 nm as the buffer layer 2, a GaN layer is 2000 nm as the GaN channel layer 3, and an AlGaN layer with an Al composition ratio of 0.25 is 30 nm as the AlGaN electron supply layer 4. Each was formed by metal organic vapor phase epitaxy. Here, Ti and Al were vapor-deposited as the source electrode 5 and the drain electrode 6, and after forming a pattern using a lift-off process, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. A gate electrode 7 having a gate length Lg = 0.5 μm was formed by vapor-depositing Ni to a thickness of 20 nm and Au to a thickness of 200 nm and lifting off. Thereafter, Ar ₂ O ₃ -F is used as the fluorine-containing insulating film 8 to a thickness of 100 nm, and Al ₂ O ₃ is used as a target, and an ECR (Electron Cyclotron Resonance) sputtering method is used. Ar gas 20 SCCM, CF ₄ gas 0. It was formed with 2 SCCM, a substrate temperature of 200 ° C., and an ECR power of 200 W.

In order to compare the effects of the present invention, an ECR sputtering method was used on a transistor having the same structure as in Example 4 with an Al ₂ O ₃ film having a thickness of 100 nm as an insulating film not containing fluorine and with Al ₂ O ₃ as a target. A sample formed with Ar gas 20 SCCM, a substrate temperature of 200 ° C., and an ECR power of 200 W was prepared.
The gate leakage current characteristics of the transistor of this example in which an Al ₂ O ₃ film containing fluorine (F) was formed and a conventional transistor were evaluated. As a result of analysis, the F concentration in the film was 4 × 10 ¹⁸ cm ⁻³ . As in FIG. 4, the conventional transistor having Al ₂ O ₃ not containing F has a large gate leakage current, and good high-frequency output characteristics cannot be obtained. On the other hand, in the embodiment of the present invention, since the leakage current is greatly reduced, good high frequency output characteristics were obtained. Further, a similar effect of adding F was also obtained in an HfO film formed by ECR sputtering instead of Al ₂ O ₃ . Further, the same effect was obtained when carbon was added to the Al ₂ O ₃ film or HfO film in addition to fluorine.

The energy band figure of this invention and the conventional transistor for demonstrating the effect of this invention and the trouble of a prior art example. Sectional drawing which shows the structure of the 1st Embodiment of this invention. Sectional drawing which shows the structure of the 2nd Embodiment of this invention. FIG. 3 is a characteristic diagram of gate leakage current of Example 1 of the present invention and a conventional example. FIG. 6 is a characteristic diagram of gate leakage current of Example 2 of the present invention and a conventional example. Sectional drawing of a structure of a conventional example. The figure explaining the current collapse which is a problem of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 GaN channel layer 4 AlGaN electron supply layer 5 Source electrode 6 Drain electrode 7 Gate electrode 8 Fluorine-containing insulating film 9 Upper insulating film 10 SiN film 11 Surface leakage current

Claims (7)

A second nitride semiconductor having a wider energy band gap than the first nitride semiconductor is formed on and in contact with the first nitride semiconductor, and the source electrode and the drain are in contact with the second nitride semiconductor. It is electrodes and a gate electrode is formed, in a field effect transistor which includes an insulating film containing fluorine in contact therewith on the crystal surface of the second nitride semiconductor, the fluorine in the insulating film containing the fluorine A field effect transistor having a content of 5 atom% or less and 0.001 atom% or more . A second nitride semiconductor having a wider energy band gap than the first nitride semiconductor is formed on and in contact with the first nitride semiconductor, and the source electrode and the drain are in contact with the second nitride semiconductor. In the field effect transistor, in which an electrode and a gate electrode are formed, and an insulating film containing fluorine and carbon is in contact with the crystal surface of the second nitride semiconductor, the insulating film containing fluorine and carbon A field effect transistor having a fluorine content of 5 atom% or less and 0.001 atom% or more . A second nitride semiconductor having a wider energy band gap than the first nitride semiconductor is formed on and in contact with the first nitride semiconductor, and the source electrode and the drain are in contact with the second nitride semiconductor. An electrode and a gate electrode are formed, an insulating film having a multilayer structure is formed on a crystal surface of the second nitride semiconductor, and a first layer in contact with the second nitride semiconductor is formed of an insulating film containing fluorine. The field effect transistor according to claim 1, wherein the fluorine content in the fluorine-containing insulating film is 5 atom% or less and 0.001 atom% or more. A second nitride semiconductor having a wider energy band gap than the first nitride semiconductor is formed on and in contact with the first nitride semiconductor, and the source electrode and the drain are in contact with the second nitride semiconductor. An electrode and a gate electrode are formed, an insulating film having a multilayer structure is formed on the crystal surface of the second nitride semiconductor, and a first layer in contact with the second nitride semiconductor is an insulating film containing fluorine and carbon The field effect transistor according to claim 1, wherein the fluorine content in the insulating film containing fluorine and carbon is 5 atom% or less and 0.001 atom% or more. 5. The field effect transistor according to claim 2, wherein the carbon content in the insulating film containing carbon is 5 atom% or less. The insulating film containing fluorine or the insulating film containing fluorine and carbon is any one of a silicon nitride (SiN) film, an aluminum oxide (Al ₂ O ₃ ) film, and a hafnium oxide (HfO) film. field effect transistor according to any one of claims 1 to 5, characterized in. In order to form the insulating film having the multilayer structure, the insulating film containing fluorine or another insulating film laminated with the insulating film containing fluorine and carbon is formed of a silicon oxide (SiO ₂ ) film, an acid 4. The silicon nitride (SiON) film, the aluminum oxide (Al ₂ O ₃ ) film, the hafnium oxide (HfO) film, or the silicon nitride (SiN) film is any one layer or a plurality of layers. 7. The field effect transistor according to any one of items 1 to 6 .

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