JP4741792B2 - Manufacturing method of nitride semiconductor MIS type field effect transistor - Google Patents

Description

  The present invention relates to a nitride semiconductor MIS type field effect transistor, and more particularly to a nitride semiconductor high-power device capable of operating at a high voltage by reducing the gate leakage current of the device.

  Conventionally, an MIS field effect transistor in which an insulating film of this type is sandwiched between a gate electrode and a nitride semiconductor is, for example, an AlGaN / GaN Metal Oxide Semiconductor Field Effect Transistor described in Patent Document 1 or Non-Patent Document 1. As shown in the paper by the title M. Asif Khan, it is used for the purpose of increasing the gate input voltage width and reducing the gate leakage current of the nitride semiconductor field effect transistor.

As shown in FIG. 2, the MIS field effect transistor in which the insulating film 1 is sandwiched between the gate electrode 2 and the nitride semiconductor 3 includes the insulating film 1 covering the surface of the AlGaN semiconductor between the source electrode 4 and the drain electrode 5. And the gate electrode 2 on the insulating film 1. Conventionally, as the insulating film 1, an AlN semiconductor crystal and oxides and nitrides such as Al ₂ O ₃ , SiO ₂ , SiN are used.

JP-A-10-223901 IE ELECTRON DEVICE LETTERS, published in 2000, pages 63 to 65

  However, in the MIS field effect transistor in which the conventional insulating film 1 is sandwiched between the gate electrode 2 and the nitride semiconductor 3, when an AlN crystal is used as the insulating film 1 as shown in FIG. As a result, the gate leakage current cannot be reduced. On the other hand, when the SiN film is used, the difference between the energy band gap value of SiN (5 eV) and the energy band gap value of AlGaN (for example, 4.1 eV when the Al composition is 0.3) is small. When Al is added, there is a problem in that electrons flow from AlGaN, which is the nitride semiconductor 3, to SiN and gate leakage current increases.

In addition, when an SiO ₂ film or Al ₂ O ₃ is used, a high-density interface state is generated at the interface between the insulating film 1 and the nitride semiconductor 3, so that the characteristics of the element deteriorate as shown in FIG. There was a problem.

  Accordingly, the present invention has been made in view of the above-mentioned problems of the prior art, and the object thereof is a high voltage with a small gate leakage current and a small interface state generated at the insulating film / nitride semiconductor interface. An object of the present invention is to provide a MIS field effect transistor that operates and exhibits high output characteristics.

  In the present invention, in the nitride semiconductor MIS field effect transistor having a gate insulating film between the nitride semiconductor surface and the gate electrode, the gate insulating film is an oxide of aluminum containing nitrogen.

  Here, the thickness of the gate insulating film is preferably 3 nm or more and 20 nm or less.

  The ratio of the number of oxygen atoms to the number of nitrogen atoms (number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms)) of the gate insulating film is preferably greater than 0.4 and less than or equal to 0.95.

  The gate insulating film preferably covers the nitride semiconductor surface from the source electrode end to the drain electrode end.

  The gate insulating film covers the nitride semiconductor surface directly under and around the gate electrode, and the nitride semiconductor surface from the gate insulating film end to the drain electrode end is a second layer other than the oxide of aluminum containing nitrogen. It is preferable to cover with an insulating film.

  Further, the dimension of the gate electrode is larger than the dimension of the gate insulating film, and the nitride semiconductor surface from the gate insulating film end to the drain electrode end is covered with a second insulating film other than the oxide of aluminum containing nitrogen. It is preferable that

  Furthermore, in the present invention, in the nitride semiconductor MIS field effect transistor having a gate insulating film between the surface of the nitride semiconductor and the gate electrode, the gate insulating film includes an oxide or nitride of aluminum containing nitrogen on the gate electrode side. The semiconductor surface side is formed of a two-layer insulating film of aluminum nitride.

  Here, it is preferable that the thickness of the oxide of aluminum containing nitrogen is 3 nm or more and 16 nm or less, and the thickness of the aluminum nitride is more than 0 nm and 4 nm or less.

  As described above, the nitride semiconductor MIS field effect transistor of the present invention is a metal composed of an insulating film portion covering the nitride semiconductor surface between a source electrode and a drain electrode, and a gate electrode portion on the insulating film. In the / insulating film / semiconductor structure (MIS structure), an oxide of aluminum containing nitrogen (AlON) is provided as the insulating film.

  As described above, since the amorphous oxide containing aluminum containing nitrogen (AlO) is provided as the insulating film, the leakage current through the crystal defect penetrating the insulating film, which is a problem in the insulating film using the AlN crystal, is obtained. Is significantly reduced.

  In addition, since it has a high energy band gap similar to that of aluminum oxide, leakage current flowing from the nitride semiconductor into the insulating film can also be reduced. Further, since the insulating film contains nitrogen, when forming the insulating film / semiconductor interface, desorption of nitrogen from the nitride semiconductor is suppressed, and the interface state density generated by nitrogen desorption is also kept low. As a result, a gate leakage current does not occur even in a high voltage operation, and an excellent power characteristic can be obtained because there are few interface states.

  According to the present invention, by using an oxide of Al containing nitrogen as the insulating film, it is possible to provide a MIS transistor capable of operating at a high voltage with a small gate leakage current and no deterioration in characteristics due to interface states.

  Embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
Referring to FIG. 1, a cross-sectional view of a nitride semiconductor MIS field effect transistor is shown as a first embodiment of the present invention.

  A source electrode 4 and a drain electrode 5 are formed on the surface of the nitride semiconductor 3. On the surface of the nitride semiconductor 3 between the source electrode 4 and the drain electrode 5, an amorphous aluminum oxide 7 containing nitrogen is provided, and the gate electrode 2 is formed thereon.

In such a nitride semiconductor MIS field effect transistor, the aluminum oxide 7 containing nitrogen in an amorphous state serves as a gate insulating film. Therefore, when an aluminum nitride (AlN) crystal is used as the gate insulating film. There is no gate leakage current due to the crystal defect that has become a problem. Also, the energy band gap value of the insulating film is in the range of 7 to 9 eV, which is sufficiently higher than the energy band gap value of nitride semiconductors (for example, 4.1 eV for AlGaN having an Al composition of 0.3) (energy band gap value 5 eV). There is no generation of a gate leakage current in which electrons flow from the conduction band of the nitride semiconductor to the conduction band of the SiN insulating film, which is a problem when using as a gate insulating film. Furthermore, since the oxide 7 of aluminum containing nitrogen serves as the gate insulating film, the interface state generated at the interface between the insulating film such as SiO ₂ or Al ₂ O ₃ and the nitride semiconductor 3 is small.

  Therefore, as shown in FIG. 3, the gate leakage current is small and a high voltage operation is possible, and as shown in FIG. 4, the drain current fluctuation is reduced.

  By using the oxide of aluminum containing nitrogen according to the present invention for the gate insulating film, the gate leakage current and the insulating film / nitride semiconductor interface state are reduced. Therefore, a high voltage operation becomes possible, and the high frequency output characteristics are remarkably improved.

  As described above, the feature of the first embodiment resides in the use of an amorphous aluminum oxide 7 containing nitrogen as an insulating film, and the thickness is 3 nm or more and 20 nm or less, and the number of oxygen atoms / ( The ratio of the number of nitrogen atoms + the number of oxygen atoms is set to be larger than 0.4 and not more than 0.98. In particular, from the relationship between the leakage current and the threshold voltage of the FET, the film thickness is preferably 7 nm or more and 12 nm or less.

This is because, as shown in FIG. 5, there is a practically sufficient two-digit reduction in leakage current when the insulating film thickness is 3 nm or more. When the current is 20 nm or more, the threshold voltage of the transistor becomes deeper than −12 V and bias is applied. This is because it is not practical in terms of voltage setting. Desirably, 7 nm or more at which the leakage current is suppressed to 10 ⁻⁷ A / mm and 12 nm or less at which the threshold voltage is shallower than −10 V are preferable.

  As shown in FIG. 6, the ratio of the number of oxygen atoms / (number of nitrogen atoms + number of oxygen atoms) needs to be larger than 0.4, which can reduce the leakage current in the conventional aluminium nitride (AlN) rapidly. It is preferably 0.6 or more which can be obtained stably with a low gate leakage current. The ratio of the number of oxygen atoms / (the number of nitrogen atoms + the number of oxygen atoms) is 0.90 or less, in which the generation of interface states is small and the drain current does not fluctuate less than 0.95. desirable.

  Next, a first manufacturing method of the nitride semiconductor MIS field effect transistor according to the first embodiment will be described with reference to FIG.

  First, after the nitride semiconductor 3 is formed on the substrate 6 by crystal growth, aluminum nitride (AlN) 8 is grown on the surface (FIG. 7A). The aluminum nitride (AlN) 8 may be grown continuously or once taken out to the atmosphere and then grown by another growth apparatus. Next, aluminum nitride (AlN) 8 is oxidized to form an oxide 7 of aluminum containing nitrogen (FIG. 7B). Next, a part of the aluminum oxide 7 containing nitrogen is opened to form the source electrode 4 and the drain electrode 5 that form ohmic contact with the nitride semiconductor 3 (FIG. 7C). Finally, the gate electrode 2 is formed on the aluminum oxide 7 containing nitrogen (FIG. 7D).

  In the manufacturing method of the present embodiment, aluminum oxide (AlN) 8 formed by crystal growth is oxidized to form aluminum oxide 7 containing nitrogen, so that the insulating film / nitride semiconductor interface is in the process step. Since it is not exposed to the atmosphere and there is no influence such as surface contamination, the generation of interface states can be suppressed with particularly good controllability. Therefore, there is an advantage that the drain current does not fluctuate during the operation and operates stably (see FIG. 3).

  Next, this embodiment will be described using specific examples.

  A high resistance SiC substrate was used as the substrate 6, and an AlN buffer layer 4 nm, a GaN layer 2000 nm, and an AlGaN layer (Al composition ratio 0.25, thickness 30 nm) were formed as the nitride semiconductor 3. AlN is grown as an aluminum oxide 7 containing nitrogen by 8 nm, and then heat-treated in an oxygen atmosphere at 950 ° C. for 40 minutes to oxidize AlN to form an AlON film (number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms)) The element ratio of 0.92) was formed. Thereafter, the AlON film was removed with a phosphoric acid etching solution using the resist as a mask, and Ti and Al were successively deposited as the source electrode 4 and the drain electrode 5. Thereafter, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. Thereafter, Ni and Au were deposited and lifted off as the gate electrode 2.

  Next, a second manufacturing method of the nitride semiconductor MIS field effect transistor according to the first embodiment will be described with reference to FIG.

  First, after the nitride semiconductor 3 is formed on the substrate 6 by crystal growth, an aluminum oxide 7 containing nitrogen is formed by sputtering, CVD, or the like (FIG. 8A). Next, a part of the oxide 7 of aluminum containing nitrogen is opened to form the source electrode 4 and the drain electrode 5 that form ohmic contact with the nitride semiconductor 3 (FIG. 8B). Finally, the gate electrode 2 is formed on the aluminum oxide 7 containing nitrogen (FIG. 8C).

  In the manufacturing method of this embodiment, since the oxide 7 of aluminum containing nitrogen is formed by using a sputtering method or a vapor phase growth method, the deterioration of the electrode or the like is caused as compared with the growth temperature (about 1000 ° C.). The oxide 7 of aluminum containing nitrogen can be formed by a single film formation at a low temperature (400 ° C.) or less. For this reason, process steps and process equipment can be simplified. In this embodiment mode, it is desirable to incorporate a nitride semiconductor surface cleaning process to reduce the interface state before the film formation of the aluminum oxide 7 containing nitrogen.

This embodiment will be described using specific examples. A high resistance SiC substrate was used as the substrate 6, and an AlN buffer layer 4 nm, a GaN layer 2000 nm, and an AlGaN layer (Al composition ratio 0.25, thickness 30 nm) were formed as the nitride semiconductor 3. Al ₂ O ₃ is sputter-deposited with a mixed gas of argon and nitrogen as an aluminum oxide 7 containing nitrogen by sputtering, and the ratio of oxygen atoms / (oxygen atoms + nitrogen atoms) is 0.8. An AlON film having a thickness of 10 nm was formed. Thereafter, the AlON film was removed with a phosphoric acid etching solution using the resist as a mask, and Ti and Al were successively deposited as the source electrode 4 and the drain electrode 5. Thereafter, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. Thereafter, Ni and Au were deposited and lifted off as the gate electrode 2.

  Next, a third manufacturing method of the nitride semiconductor MIS field effect transistor according to the first embodiment will be described with reference to FIG.

  First, after the nitride semiconductor 3 is formed by crystal growth on the substrate 6, the source electrode 4 and the drain electrode 5 that form ohmic contact with the nitride semiconductor 3 are formed (FIG. 9A). Next, aluminum-containing aluminum oxide 7 is formed by sputtering, CVD, or the like using nitrogen-containing aluminum oxide 7 (FIG. 9B). Next, the gate electrode 2 is formed on the aluminum oxide 7 containing nitrogen (FIG. 9C). Finally, a part of the source electrode 4 and the drain electrode 5 is opened to allow electrical connection with the outside (FIG. 9D).

  In the manufacturing method of the present embodiment, the ends of the source electrode 4 and the drain electrode 5 on the gate electrode 2 side are protected without gaps by the aluminum oxide 7 containing nitrogen, so that there is no long-term deterioration of the electrodes and reliability. High transistor can be realized.

  This embodiment will be described using specific examples.

A high resistance SiC substrate was used as the substrate 6, and an AlN buffer layer 4 nm, a GaN layer 2000 nm, and an AlGaN layer (Al composition ratio 0.25, thickness 30 nm) were formed as the nitride semiconductor 3. Next, Ti and Al were successively deposited as the source electrode 4 and the drain electrode 5 and heat-treated at 650 ° C. in a nitrogen atmosphere to form ohmic contacts. Thereafter, Al ₂ O ₃ is sputter-deposited as a nitrogen-containing aluminum oxide 7 with a sputtering apparatus using a mixed gas of argon and nitrogen by a sputtering apparatus, thereby obtaining AlON (number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms + number of nitrogen atoms). ) Of atomic ratio 0.85). Thereafter, Ni and Au were deposited and lifted off as the gate electrode 2.

(Second Embodiment)
In the above embodiment, the insulating film covering the surface of the nitride semiconductor between the electrodes can be composed of the aluminum oxide 7 containing nitrogen and the second insulating film. A configuration for this purpose is shown in FIG. 10A as a second embodiment.

  In this second embodiment, the aluminum oxide 7 containing nitrogen, which is characterized in that the interface state is low, is provided directly below and around the gate electrode 2 that requires a low interface state. The remaining nitride semiconductor surfaces up to the source electrode 4 and the drain electrode 5 are covered with a surface protective film 8 having high drain breakdown voltage characteristics.

  In the present embodiment, it becomes possible to operate the field effect transistor to a higher voltage than when the insulating film between the electrodes is a single layer of aluminum oxide 7 containing nitrogen, and the output is higher than that of the first embodiment. There is an extraordinary effect that a characteristic is obtained.

  Further, in the structure of the insulating film between the electrodes in this embodiment mode, a form in which the oxide film 7 made of aluminum containing nitrogen and the surface protective film 8 are formed is a gate to which a high voltage is applied as shown in FIG. You may change so that it may apply only between the electrode 2 and the drain electrode 5. FIG.

  Next, a method for manufacturing the nitride semiconductor MIS field effect transistor according to the second embodiment will be described with reference to FIG.

  First, an aluminum oxide 7 containing nitrogen is formed on the surface of the substrate 6 on which the nitride semiconductor 3 is formed by crystal growth, by the same method as the first or second manufacturing method of the first embodiment. (FIG. 11 (a)). Next, the oxide 7 of aluminum containing nitrogen is removed except for the region corresponding to the portion directly below and around the gate electrode 7 (FIG. 11B).

  Subsequently, the source electrode 4 and the drain electrode 5 that form an ohmic contact with the nitride semiconductor 3 are formed (FIG. 13C). Next, the gate electrode 2 is formed on the aluminum oxide 7 containing nitrogen (FIG. 11D). Finally, the surface is covered with the surface protective film 8, and the surface protective film 8 in the current extraction region of the source electrode 4, the drain electrode 5, and the gate electrode 2 is removed.

  This embodiment will be described using specific examples.

A high resistance SiC substrate was used as the substrate 6, and an AlN buffer layer 4 nm, a GaN layer 2000 nm, and an AlGaN layer (Al composition ratio 0.25, thickness 30 nm) were formed as the nitride semiconductor 3. Sputter deposition of Al ₂ O ₃ with argon and nitrogen mixed gas as an aluminum oxide 7 containing nitrogen by sputtering is performed to form an AlON film (number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms)) of 10 nm. An atomic ratio of 0.8) was formed. Thereafter, using the resist as a mask, the portions other than the peripheral portion of the gate electrode 2 of the AlON film were removed with a phosphoric acid etching solution.

Ti and Al were continuously deposited on the source electrode 4 and drain electrode 5 portions in the opening of the AlON film, and heat-treated at 650 ° C. in a nitrogen atmosphere to form ohmic contacts. On the AlON film, Ni and Au were deposited and lifted off as the gate electrode 2. Finally, 200 nm of SiO ₂ was formed as a surface protective film 8 on the entire surface, and the electrode portion in the current extraction region was opened. By using this structure, the MISFET can operate up to 80V.

(Third embodiment)
In the embodiment in which the insulating film between the electrodes is composed of the aluminum oxide 7 containing nitrogen and the surface protective film 8, only the aluminum oxide 7 containing nitrogen can be covered directly under the gate electrode. A configuration for this purpose is shown in FIG. 12 as a third embodiment.

  In the third embodiment in which the insulating film between the electrodes is composed of the aluminum oxide 7 containing nitrogen and the second insulating film, the nitrogen is formed only directly under the gate electrode 2 that requires a low interface state. The surface of the nitride semiconductor up to the source electrode 4 and the drain electrode 5 is covered with a surface protective film 8 having high breakdown voltage characteristics.

  In the present embodiment, the single layer of the surface protective film 8 is a field effect transistor than the case where the insulating film between the electrodes has a two-layer structure of a single layer of aluminum oxide 7 containing nitrogen or the surface protective film 8. There is an extraordinary effect of operating stably up to a high voltage and enabling higher output.

  In addition, in the structure of the insulating film between the electrodes in this embodiment mode, a structure in which two kinds of films, that is, an aluminum oxide 7 containing nitrogen and a second insulating film are used, is applied to the gate electrode 2 and the drain to which a high voltage is applied. You may change so that it may apply only between the electrodes 5. FIG.

  Next, with reference to FIG. 13, a method for manufacturing the nitride semiconductor MIS field effect transistor according to the third embodiment will be described.

  First, an aluminum oxide 7 containing nitrogen is formed on the surface of the substrate 6 on which the nitride semiconductor 3 is formed by crystal growth, by the same method as the first or second manufacturing method of the first embodiment. (FIG. 12A). Next, the gate electrode 2 is formed by vapor deposition or sputtering (FIG. 12B). Subsequently, the aluminum oxide 7 containing nitrogen is removed by etching using the gate electrode as a mask, and then the source electrode 4 and the drain electrode 5 are formed on the surface of the nitride semiconductor 3 (FIG. 12C). Finally, the surface is covered with the surface protective film 8, and the surface protective film 8 in the current extraction region of the source electrode 4, the drain electrode 5 and the gate electrode 2 is removed (FIG. 12D).

  This embodiment will be described using specific examples.

A high resistance SiC substrate was used as the substrate 6, and an AlN buffer layer 4 nm, a GaN layer 2000 nm, and an AlGaN layer (Al composition ratio 0.25, thickness 30 nm) were formed as the nitride semiconductor 3. Sputter deposition of Al ₂ O ₃ with argon and nitrogen mixed gas as an aluminum oxide 7 containing nitrogen by sputtering is performed to form an AlON film (number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms)) of 10 nm. An atomic ratio of 0.8) was formed. On the AlON film, Ni and Au were deposited and lifted off as the gate electrode 2. Thereafter, using the gate electrode 2 as a mask, the AlON film was removed with a phosphoric acid etching solution. Ti and Al were continuously deposited on the source electrode 4 and the drain electrode 5 and heat-treated at 650 ° C. in a nitrogen atmosphere to form ohmic contacts. Finally, 200 nm of SiO ₂ was formed as a surface protective film 8 on the entire surface, and the electrode portion in the current extraction region was opened. By using this structure, the MISFET can operate up to 100V.

(Fourth embodiment)
In each of the above embodiments, a single layer of aluminum oxide 7 containing nitrogen is used under the gate electrode, but aluminum nitride (AlN) 9 is interposed between the aluminum oxide 7 containing nitrogen and the nitride semiconductor 3. It can be configured by the inserted structure. A configuration for this purpose is shown in FIG. 14 as a fourth embodiment.

  A source electrode 4 and a drain electrode 5 are formed on the surface of the nitride semiconductor 3. On the surface of the nitride semiconductor 3 between the source electrode 4 and the drain electrode 5, an aluminum nitride (AlN) 9 and an amorphous aluminum oxide 7 containing nitrogen are stacked, and a gate is formed thereon. An electrode 2 is formed.

In such a nitride semiconductor MIS field effect transistor, the two-layer film of aluminum nitride 7 containing aluminum nitride (AlN) 9 and amorphous aluminum containing nitrogen is an insulating film for the gate 2, so that aluminum nitride ( No gate leakage current is generated due to crystal defects which are a problem when the AlN) 9 crystal is used as a single layer for the gate insulating film.

  Also, the energy band gap value of the insulating film is in the range of 7 to 9 eV, which is sufficiently higher than the energy band gap value of nitride semiconductors (for example, 4.1 eV for AlGaN having an Al composition of 0.3) (energy band gap value 5 eV). There is no generation of a gate leakage current in which electrons flow from the conduction band of the nitride semiconductor to the conduction band of the SiN insulating film, which is a problem when using as a gate insulating film.

  Further, the nitride semiconductor 3, the aluminum nitride 9, and the oxide 7 of aluminum containing nitrogen sequentially form a heterointerface, and the interface state between the nitride semiconductor 3 and the aluminum nitride (AlN) 9 through which the current flows is nitride. Since it is composed of crystals, the interface state density is the smallest.

Furthermore, an interface state generated at the interface between aluminum nitride (AlN) 9 and nitrogen-containing aluminum oxide 7 is also used instead of aluminum-containing aluminum oxide 7 using an insulating film such as SiO ₂ or Al ₂ O ₃ . It can be greatly reduced compared with the case where it was. This occurs when the insulating film / aluminum nitride (AlN) 9 interface is formed by using nitrogen-containing aluminum oxide 7 to suppress the desorption of nitrogen from the aluminum nitride (AlN) 9 and by nitrogen desorption. This is because the interface state density is reduced.

  Therefore, the gate leakage current is small (see FIG. 2), high voltage operation is possible, and the drain current fluctuation is small (see FIG. 3).

  The presence of the nitrogen-containing aluminum oxide gate insulating film according to the present invention reduces the gate leakage current and the insulating film / nitride semiconductor interface state. Therefore, a high voltage operation becomes possible, and the high frequency output characteristics are remarkably improved.

  As described above, the fourth embodiment is characterized in that a two-layer film of aluminum-containing aluminum oxide 7 and aluminum nitride 9 is used as the insulating film. In this case, the thickness of aluminum nitride (AlN) 9 is 4 nm or less, and the thickness of the oxide 7 of aluminum containing nitrogen is 3 nm or more and 16 nm or less, and the number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms). The ratio is set to be greater than 0.4 and less than or equal to 0.98.

In particular, from the relationship between the leakage current and the threshold voltage of the FET, the film thickness is preferably 7 nm or more and 11 nm or less. This is because, as shown in FIG. 16, there is a practically sufficient two-digit reduction in leakage current when the insulation film thickness is 3 nm or more. When the thickness is 16 nm or more, the threshold voltage of the transistor becomes deeper than −12 V and the bias voltage is increased. This is because it is not practical in terms of setting. Desirably, 7 nm or more at which the leakage current is suppressed to 10 ⁻¹⁰ A / mm and 11 nm or less at which the threshold voltage is shallower than −10 V are preferable.

  The ratio of the number of oxygen atoms / (the number of oxygen atoms + the number of nitrogen atoms) is larger than 0.4, which can rapidly reduce the leakage current in the conventional aluminum nitride (AlN) as shown in FIG. 5 of the first embodiment. It is necessary, and preferably 0.6 or more, which can be obtained stably with a low gate leakage current. The ratio of the number of oxygen atoms / (the number of oxygen atoms + the number of nitrogen atoms) needs to be 0.95 or less with little generation of interface states and little fluctuation of drain current, and a stable low interface state can be obtained. Is desirable.

  Next, with reference to FIG. 15, a method for manufacturing the nitride semiconductor MIS field effect transistor according to the fourth embodiment will be described.

  First, after the nitride semiconductor 3 is formed on the substrate 6 by crystal growth, aluminum nitride (AlN) 9 is grown on the surface (FIG. 15A). The aluminum nitride (AlN) 9 may be grown continuously or once taken out to the atmosphere and then grown by another growth apparatus. Next, the aluminum oxide layer 7 containing nitrogen is formed by oxidizing the surface layer of aluminum nitride (AlN) 9 (FIG. 15B). At this time, the oxidation is finished while leaving a layer of aluminum nitride (AlN) 9 having a thickness of 4 nm or less. Next, a part of the aluminum oxide 7 containing nitrogen and aluminum nitride (AlN) 9 are opened to form the source electrode 4 and the drain electrode 5 that form ohmic contact with the nitride semiconductor 3 (FIG. 15 ( c)). Finally, the gate electrode 2 is formed on the aluminum oxide 7 containing nitrogen (FIG. 15D).

  In the manufacturing method of the present embodiment, aluminum oxide 7 containing nitrogen is formed by oxidizing the surface side while leaving 4 nm or less of aluminum nitride (AlN) 9 formed by crystal growth, so that the insulating film / Since the nitride semiconductor interface is not exposed to the atmosphere during the process, and there is no influence such as surface contamination, the generation of interface states can be suppressed particularly with good controllability.

Further, by using an aluminum oxide 7 containing nitrogen without using a conventional oxide film such as Al ₂ O ₃ or SiO ₂ , desorption of nitrogen from aluminum nitride (AlN) 9 is suppressed, and nitrogen desorption is caused. The interface state density generated is also low. Therefore, there is an advantage that the drain current does not fluctuate during the operation and operates stably (see FIG. 17).

  Next, this embodiment will be described using specific examples.

  A high resistance SiC substrate was used as the substrate 6, and an AlN buffer layer 5 nm, a GaN layer 2000 nm, and an AlGaN layer (Al composition ratio 0.25, thickness 30 nm) were formed as the nitride semiconductor 3. After 8 nm of AlN is grown as an oxide 7 of aluminum containing nitrogen, the upper layer of AlN is oxidized by heat treatment in an oxygen atmosphere at 950 ° C. for 30 minutes to obtain AlON (oxygen atomic concentration 85%, thickness 5 nm) / AN A two-layer film (thickness 3 nm) was formed.

  Thereafter, using the resist as a mask, the two-layer film of AlON / AlN was removed with a phosphoric acid etching solution, and Ti and Al were successively deposited as the source electrode 4 and the drain electrode 5. Thereafter, an ohmic contact was formed by heat treatment at 650 ° C. in a nitrogen atmosphere. Thereafter, Ni and Au were deposited and lifted off as the gate electrode 2.

  In the fourth embodiment, a layer in which aluminum nitride (AlN) 9 is inserted between oxide 7 of aluminum containing nitrogen and nitride semiconductor 3 covers the entire region between source electrode 4 and drain electrode 5. As in the second or third embodiment, the two-layer film exists only in the vicinity of the gate 2 and the remaining region between the source electrode 4 and the drain electrode 5 is formed by the second insulating film. If the structure covered with is used, there is an effect of further increasing the operating voltage.

1 is a cross-sectional view showing a nitride semiconductor MIS field effect transistor structure according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the conventional nitride semiconductor MIS type | mold field effect transistor. It is a gate leakage current-gate voltage characteristic view which shows the subject of a prior art. It is a drain current fluctuation | variation figure which shows the subject of a prior art. FIG. 6 is a relationship diagram of AlON film thickness and device characteristics showing the effect of the present invention. It is a relationship diagram between oxygen concentration of AlON film and device characteristics showing the effect of the present invention. It is sectional drawing which shows the manufacturing method of the nitride semiconductor MIS type | mold field effect transistor which concerns on this invention. It is sectional drawing which shows the manufacturing method of the nitride semiconductor MIS type | mold field effect transistor which concerns on this invention. It is sectional drawing which shows the manufacturing method of the nitride semiconductor MIS type | mold field effect transistor which concerns on this invention. It is sectional drawing which shows the structure of the nitride semiconductor MIS type | mold field effect transistor which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the manufacturing method of the nitride semiconductor MIS type | mold field effect transistor of this invention. It is sectional drawing which shows the structure of the nitride semiconductor MIS type field effect transistor which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the manufacturing method of the nitride semiconductor MIS type | mold field effect transistor of this invention. It is sectional drawing which shows the structure of the nitride semiconductor MIS type field effect transistor which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the manufacturing method of the nitride semiconductor MIS type | mold field effect transistor of this invention. It is a relationship diagram between the thickness of the AlON film and the device characteristics showing the effect of the present invention. It is a drain current fluctuation | variation figure which shows the effect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gate insulating film 2 Gate electrode 3 Nitride semiconductor 4 Source electrode 5 Drain electrode 6 Substrate 7 Aluminum oxide containing nitrogen (AlON)
8 Surface protective film 9 Aluminum nitride (AlN)

Claims (5)

In a method of manufacturing a nitride semiconductor MIS field effect transistor having a gate insulating film between a nitride semiconductor surface and a gate electrode,
After forming the nitride semiconductor,
On the nitride semiconductor surface, an oxide of aluminum containing nitrogen is formed using a sputtering method or a vapor phase growth method, and the gate insulating film is formed into a single layer in an amorphous state.
A thickness of the gate insulating film is 3 nm or more and 20 nm or less;
The ratio of the number of oxygen atoms to the number of nitrogen atoms (number of oxygen atoms / (number of oxygen atoms + number of nitrogen atoms)) of the gate insulating film is greater than 0.4 and less than or equal to 0.95. Type field effect transistor manufacturing method.   2. The method of manufacturing a nitride semiconductor MIS field effect transistor according to claim 1, wherein the gate insulating film covers a nitride semiconductor surface from a source electrode end to a drain electrode end. The gate insulating film covers the nitride semiconductor surface directly under and around the gate electrode,
2. The nitride semiconductor MIS according to claim 1 , wherein a surface of the nitride semiconductor from the end of the gate insulating film to the end of the drain electrode is covered with a second insulating film other than an oxide of aluminum containing nitrogen. Type field effect transistor manufacturing method. The dimension of the gate electrode is larger than the dimension of the gate insulating film, and the surface of the nitride semiconductor from the gate insulating film end to the drain electrode end is covered with a second insulating film other than an oxide of aluminum containing nitrogen. The method of manufacturing a nitride semiconductor MIS field effect transistor according to claim 1 , wherein:   2. The method for manufacturing a nitride semiconductor MIS field effect transistor according to claim 1, further comprising a step of cleaning the surface of the nitride semiconductor before the film formation of the oxide of aluminum containing nitrogen.

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