JP2014045174A - Nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor device arranged so that the leak of current can be reduced while suppressing the collapse of current.SOLUTION: A GaN-based HFET as an embodiment of a nitride semiconductor device comprises: a gate electrode 19; a drain electrode 18; a first insulator film 21 located between the gate electrode 19 and the drain electrode 18, and formed on a nitride semiconductor laminate 15; and a second insulator film 22 located between the gate electrode 19 and the drain electrode 18, and formed on the first insulator film 21 and the nitride semiconductor laminate 15. The first insulator film 21 is spaced apart from the gate electrode 19 by a first distance X1 which is 60-90% of a second distance X2 between the gate electrode 19 and the drain electrode 18 along a surface of the nitride semiconductor laminate 15.

Description

  The present invention relates to a nitride semiconductor device including a nitride semiconductor multilayer body having a hetero interface.

  Conventionally, as a nitride semiconductor device including a nitride semiconductor multilayer body having a hetero interface, a GaN layer is formed on an AlGaN layer in Patent Document 1 (Japanese Patent Application Laid-Open No. 2008-219054), and the GaN layer is formed on the GaN layer. A GaN-based field effect transistor is disclosed in which a source electrode, a gate electrode, and a drain electrode are formed, and a first protective layer made of a silicon nitride film is formed on the GaN layer between the gate electrode and the drain electrode. Yes.

  In the GaN-based field effect transistor, the first protective layer is made of SiN having a nitrogen (N) content of 20% or less, and an opening reaching the GaN layer is formed in the first protective layer. . A second protective layer 30 made of SiN having an N content of 20% or more is formed on the opening and the first protective layer.

  In the conventional nitride semiconductor device described above, current collapse is suppressed by the first protective film made of the Si-rich silicon nitride film. In addition, although an opening is formed in the first protective film to divide a leakage current path to suppress the leakage current, there is a problem that the leakage current cannot be sufficiently suppressed.

JP 2008-219054 A

  Accordingly, an object of the present invention is to provide a nitride semiconductor device capable of sufficiently reducing leakage current while suppressing current collapse.

  In the present invention, it is particularly important for the insulating film for suppressing current collapse to be formed near the drain electrode in order to suppress current collapse, and the insulating film is separated from the gate electrode beyond a specific distance. It was created based on the fact that the present inventors have newly discovered through experiments that it is particularly effective to suppress leakage current.

That is, the nitride semiconductor device of the present invention is
A nitride semiconductor laminate having a heterointerface;
A source electrode and a drain electrode that are formed at least partially on the nitride semiconductor multilayer body or in the nitride semiconductor multilayer body and spaced apart from each other;
A gate electrode formed on the nitride semiconductor multilayer body between the source electrode and the drain electrode;
A first electrode formed on the nitride semiconductor multilayer body between the gate electrode and the drain electrode and spaced apart from the gate electrode by a first distance along a surface of the nitride semiconductor multilayer body; An insulating film of
A second insulating film formed on the first insulating film and on the nitride semiconductor multilayer body between the gate electrode and the drain electrode;
The first distance is 60% or more and 90% or less of the second distance between the gate electrode and the drain electrode.

  According to the nitride semiconductor device of the present invention, the first insulating film formed on the nitride semiconductor multilayer body between the gate electrode and the drain electrode is nitrided with respect to the gate electrode. Along the surface of the physical semiconductor stacked body, the first distance is 60% or more and 90% or less of the second distance between the gate electrode and the drain electrode. Thus, according to the present invention, current collapse can be suppressed and the leakage current can be sufficiently reduced.

  Here, “current collapse” is a phenomenon in which the on-resistance of a transistor in a high voltage operation becomes higher than the on-resistance of the transistor in a low voltage operation.

  According to the nitride semiconductor device of the present invention, the first insulating film formed on the nitride semiconductor stacked body between the gate electrode and the drain electrode, and the above-mentioned between the gate electrode and the drain electrode. A second insulating film formed on the first insulating film and on the nitride semiconductor multilayer body, wherein the first insulating film has a surface of the nitride semiconductor multilayer body with respect to the gate electrode. , And a first distance that is 60% or more and 90% or less of the second distance between the gate electrode and the drain electrode. Thus, according to the present invention, current collapse can be suppressed and leakage current can be sufficiently reduced.

It is sectional drawing of 1st Embodiment of the nitride semiconductor device of this invention. It is process sectional drawing explaining the manufacturing process of the said 1st Embodiment. FIG. 3 is a process cross-sectional view subsequent to FIG. 2. FIG. 4 is a process cross-sectional view subsequent to FIG. 3. FIG. 5 is a process cross-sectional view subsequent to FIG. 4. FIG. 6 is a process cross-sectional view subsequent to FIG. 5. FIG. 7 is a process cross-sectional view subsequent to FIG. 6. FIG. 8 is a process cross-sectional view subsequent to FIG. 7. FIG. 9 is a process cross-sectional view subsequent to FIG. 8. FIG. 10 is a process cross-sectional view subsequent to FIG. 9. It is process sectional drawing following FIG. FIG. 12 is a process cross-sectional view subsequent to FIG. 11. It is a characteristic view showing the relationship between the ratio of the first distance X1 to the second distance X2 and the collapse value. FIG. 6 is a characteristic diagram showing a relationship between a ratio of a first distance X1 to a second distance X2 and a leakage current. It is a characteristic view showing the relationship between the composition ratio (Si / N, Al / N, Si / O, Al / O) of the first insulating film and the collapse value. It is a characteristic view showing the relationship between the composition ratio (Si / N, Al / N, Si / O, Al / O) of the first insulating film and the leakage current. It is sectional drawing of the 1st comparative example of the said 1st Embodiment. It is sectional drawing of the 2nd comparative example of the said 1st Embodiment. It is sectional drawing of 2nd Embodiment of the nitride semiconductor device of this invention. It is sectional drawing of 3rd Embodiment of the nitride semiconductor device of this invention. It is sectional drawing of 4th Embodiment of the nitride semiconductor device of this invention. It is sectional drawing of 5th Embodiment of the nitride semiconductor device of this invention. It is sectional drawing of 6th Embodiment of the nitride semiconductor device of this invention. It is sectional drawing of 7th Embodiment of the nitride semiconductor device of this invention.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

(First embodiment)
FIG. 1 is a cross-sectional view of a GaN-based HFET (Hetero-junction Field Effect Transistor) as a first embodiment of the nitride semiconductor device of the present invention.

  In this GaN-based HFET, as shown in FIG. 1, an undoped GaN channel layer 13 and an undoped AlGaN barrier layer 14 are formed on a Si substrate 11. A 2DEG (two-dimensional electron gas) layer 16 is generated near the heterointerface between the undoped GaN channel layer 13 and the undoped AlGaN barrier layer 14. The undoped GaN channel layer 13 and the undoped AlGaN barrier layer 14 constitute a nitride semiconductor multilayer body 15.

  In place of the GaN channel layer 13, an AlGaN layer having a smaller band gap than the AlGaN barrier layer 14 may be used. Further, a layer having a thickness of about 1 nm made of GaN, for example, may be provided as a cap layer on the AlGaN barrier layer 14.

  A source electrode 17 and a drain electrode 18 are formed on the AlGaN barrier layer 14 at a predetermined interval. The source electrode 17 and the drain electrode 18 are ohmic electrodes. A gate electrode 19 is formed on the AlGaN barrier layer 14 and between the source electrode 17 and the drain electrode 18. This gate electrode 19 is a Schottky electrode. The source electrode 17 and the drain electrode 18 are made of Hf / Al / Hf / Au, Ti / Al / TiN, or the like. The gate electrode 19 is made of WN / W or the like.

  As an example, the gate electrode 19 may be made of TiN.

  A first insulating film 21 is formed on the AlGaN barrier layer 14 and between the gate electrode 19 and the drain electrode 18. The first insulating film 21 is separated from the gate electrode 19 by a first distance X1 along the surface of the nitride semiconductor multilayer body 15. As an example, the thickness of the first insulating film 21 is 20 nm. The first distance X1 is 60% or more and 90% or less (for example, 70%) of the second distance X2 between the gate electrode 19 and the drain electrode 18.

  The first insulating film 21 has a silicon composition ratio of silicon to nitrogen of 1.15 to 3.0 or a composition ratio of aluminum to nitrogen of 0.8 to 1.0. It is preferably made of aluminum nitride, aluminum oxide, silicon oxycarbide, or silicon oxynitride. In the following, the case where the first insulating film 21 is made of silicon nitride having a composition ratio of silicon to nitrogen of 1.15 or more and 3.0 or less will be mainly described. Considering that the composition ratio of aluminum with respect to aluminum is 0.8 or more and 1.0 or less of aluminum nitride, aluminum oxide, silicon oxycarbide, or silicon oxynitride, the difference is only in the material. For simplicity, the same reference number “21” is used with the aid of FIGS.

  A second insulating film 22 is formed on the AlGaN barrier layer 14 and the first insulating film 21 between the gate electrode 19 and the drain electrode 18. The second insulating film 22 is a silicon nitride film having a silicon composition ratio with respect to nitrogen of 0.75 or more and 1.0 or less and a silicon composition ratio smaller than the silicon composition ratio of the first insulating film 21. The thickness of the second insulating film 22 is, for example, 150 nm between the gate electrode 19 and the first insulating film 21.

  The second insulating film 22 can be made of silicon oxide, aluminum nitride, or aluminum oxide instead of silicon nitride. In the following, the case where the second insulating film 22 is a silicon nitride film will be mainly described, but the second insulating film 22 is also made of silicon oxide, aluminum nitride, or aluminum oxide. For the sake of brevity, considering the difference in material only, the same reference number “22” is used with the aid of FIGS.

  An insulating film 23 is formed on the AlGaN barrier layer 14 and between the source electrode 17 and the gate electrode 19. The insulating film 23 is the same insulating film as the first insulating film 21. An insulating film 24 is formed on the insulating film 23. The insulating film 24 is the same insulating film as the second insulating film 22.

  In the nitride semiconductor device configured as described above, a two-dimensional electron gas (2DEG) layer 16 is generated at the interface between the GaN channel layer 13 and the AlGaN barrier layer 14 to form a channel. This channel is controlled by applying a voltage to the gate electrode 19 to turn on and off the HFET having the source electrode 17, the drain electrode 18, and the gate electrode 19. The HFET is turned off when a depletion layer is formed in the GaN channel layer 13 below the gate electrode 19 when a negative voltage is applied to the gate electrode 19, while the gate is turned off when the voltage of the gate electrode 19 is zero. This is a normally-on type transistor in which the depletion layer disappears in the GaN channel layer 13 below the electrode 19 and is turned on.

  Next, a method for manufacturing the nitride semiconductor device will be described with reference to FIGS.

  First, as shown in FIG. 2, an undoped GaN channel layer 13 and an undoped AlGaN barrier layer 14 are sequentially formed on a Si substrate 11 by using MOCVD (Metal Organic Chemical Vapor Deposition). The thickness of the undoped GaN channel layer 13 is 1 μm, for example, and the thickness of the undoped AlGaN barrier layer 14 is 30 nm, for example. The GaN channel layer 13 and the AlGaN barrier layer 14 constitute a nitride semiconductor stacked body 15. In FIG. 2, 16 is a two-dimensional electron gas (2DEG) layer 16 formed in the vicinity of the heterointerface between the GaN channel layer 13 and the AlGaN barrier layer 14.

  Next, an insulating film 31 made of silicon nitride for forming the first insulating film 21 and the insulating film 23 is formed on the AlGaN barrier layer 14 by, for example, a plasma CVD (Chemical Vapor Deposition) method. To a film thickness of 20 nm. The growth temperature of the insulating film 31 is 225 ° C. as an example, but may be set in the range of 200 ° C. to 400 ° C. The thickness of the insulating film 31 is 20 nm as an example, but may be set in the range of 5 nm to 50 nm.

Further, the gas flow rate ratio of N ₂ / NH ₃ / SiH ₄ when the insulating film 31 which is a silicon nitride film for forming the first insulating film 21 and the insulating film 23 is formed by the plasma CVD method is adjusted. Thus, a silicon nitride film having a silicon Si ratio larger than that of a stoichiometric silicon nitride film can be formed. According to the silicon nitride film 31, current collapse can be further suppressed as compared with a stoichiometric silicon nitride film. Further, when the Si: N composition ratio of SiN forming the silicon nitride film 31 is Si: N = 0.9: 1.0 to 3.0: 1.0, Si: N = 0.75: 1. It is more effective in suppressing current collapse than a stoichiometric silicon nitride film.

1 and 2, the gas flow rate ratio of N ₂ / NH ₃ / TMA when the aluminum nitride film 31 serving as the first insulating film 21 and the insulating film 23 is formed by the plasma CVD method. By adjusting the above, it is possible to form an aluminum nitride film having a larger ratio of aluminum Al than the stoichiometric aluminum nitride film. According to the aluminum nitride film 31, the current collapse can be further suppressed as compared with the stoichiometric aluminum nitride film. Further, when the Al: N composition ratio of AlN forming the aluminum nitride film 31 is set to Al: N = 1.0: 0.8 to 1.0: 1.0, it is effective for suppressing current collapse.

  Next, a photoresist layer 33 is formed on the insulating film 31 and exposed and developed to pattern the photoresist layer 33 as shown in FIG. Wet etching is performed using the patterned photoresist layer 33 as a mask. As a result, as shown in FIG. 4, the insulating film 31 is patterned to form the first insulating film 21 and the insulating film 23. Next, the photoresist layer 33 is removed.

  Note that the first insulating film 21 and the insulating film 23 may be formed by patterning the insulating film 31 by dry etching instead of the wet etching.

  Next, the first insulating film 21 and the insulating film 23 are heat-treated. This heat treatment was performed, for example, at 500 ° C. for 5 minutes in a nitrogen atmosphere. Moreover, you may set the temperature of the said heat processing in the range of 400 to 850 degreeC as an example.

  Next, as shown in FIG. 5, another insulating film 35 for forming the second insulating film 22 and the insulating film 24 is formed on the first insulating film 21 and the insulating film 23 by, for example, plasma CVD. A film having a thickness of 150 nm is formed by a (Chemical Vapor Deposition) method. The other insulating film 35 is made of a silicon nitride film. The growth temperature of the other insulating film 35 is 225 ° C. as an example, but may be set in the range of 200 ° C. to 400 ° C. Moreover, although the film thickness of the said another insulating film 35 was 150 nm as an example, you may set it in the range of 50 nm-300 nm.

By adjusting the gas flow ratio of N ₂ / NH ₃ / SiH ₄ when forming the silicon nitride film 35 as another insulation by the plasma CVD method, the composition ratio of silicon to nitrogen is 0.75 or more and 1. A silicon nitride film having a silicon composition ratio less than 0 and smaller than that of the insulating films 21 and 23 can be formed.

  Next, a photoresist layer 36 is formed on the other insulating film 35, exposed, and developed to pattern the photoresist layer 36 as shown in FIG. Wet etching is performed using the patterned photoresist layer 36 as a mask. As a result, as shown in FIG. 6, the other insulating film 35 is patterned to expose the AlGaN barrier layer 14 in the region where the source electrode 17 and the drain electrode 18 are formed from the other insulating film 35. The other insulating film 35 may be patterned by dry etching instead of the wet etching.

  Next, the other insulating film 35 is heat-treated. This heat treatment was performed, for example, at 500 ° C. for 5 minutes in a nitrogen atmosphere. Moreover, you may set the temperature of the said heat processing in the range of 400 to 850 degreeC as an example.

  Next, as shown in FIG. 6, Ti and Al are sequentially stacked on the silicon nitride film 35 by sputtering, thereby stacking Ti / Al to form a stacked metal film 38 serving as an ohmic electrode. The Ti and Al may be deposited instead of the sputtering. Further, instead of sequentially stacking Ti and Al, Hf, Al, and Hf may be stacked in order to form the stacked metal film 38.

  Next, a photoresist layer 40 is formed on the laminated metal film 38, exposed and developed, thereby patterning the photoresist layer 40 as shown in FIG. Dry etching is performed using the patterned photoresist layer 40 as a mask. Thereby, as shown in FIG. 7, the pattern of the source electrode 17 and the drain electrode 18 is formed.

  Then, by annealing the substrate on which the source electrode 17 and the drain electrode 18 are formed, for example, at 400 ° C. or more and 500 ° C. or less for 10 minutes or more, the two-dimensional electron gas (2DEG) layer 16, the source electrode 17, the drain electrode 18, An ohmic contact is obtained between the two. In this case, the contact resistance can be greatly reduced as compared with the case where annealing is performed at a high temperature exceeding 500 ° C. (for example, 600 ° C. or more). Further, by annealing at a low temperature of 400 ° C. or higher and 500 ° C. or lower, the diffusion of the electrode metal into the insulating films 21, 23, 35 can be suppressed, and the characteristics of the insulating films 21, 23, 35 are not adversely affected. . Further, the low temperature annealing can prevent the current collapse from deteriorating due to nitrogen desorption from the GaN channel layer 13 and the characteristic fluctuation. Although the annealing time is 10 minutes or longer here, the annealing time may be set to a time for obtaining ohmic contact.

  Next, as shown in FIG. 8, a photoresist layer 41 is formed on the source electrode 17, the drain electrode 18 and the silicon nitride film 35, and is exposed and developed to pattern the photoresist layer 41. . Wet etching is performed using the patterned photoresist layer 41 as a mask. As a result, as shown in FIG. 9, an opening 35A is formed in the silicon nitride film 35, and the AlGaN barrier layer 14 in the region where the gate electrode 19 is formed is exposed. By forming an opening 35 </ b> A in the silicon nitride film 35, the second insulating film 22 and the insulating film 24 are formed from the silicon nitride film 35.

  Next, as shown in FIG. 10, the metal that becomes the gate electrode 19 by sputtering WN on the AlGaN barrier layer 14 exposed in the source electrode 17, the drain electrode 18, the silicon nitride film 35, and the opening 35A. A film 43 is formed. The metal film 43 may be formed by sputtering TiN or Ni instead of WN. The metal film 43 may be formed by vapor deposition instead of sputtering.

  Next, a photoresist layer is formed on the metal film 43 and patterned by exposure and development to form a photoresist layer 45 on the gate electrode formation region as shown in FIG.

  Next, the metal film 43 is dry etched using the photoresist layer 45 as a mask to form the gate electrode 19 as shown in FIG.

  FIG. 13 shows a first distance X1 (μm) between the gate electrode 19 and the first insulating film 21 with respect to a second distance X2 (μm) between the gate electrode 19 and the drain electrode 18 in the GaN-based HFET. ) On the horizontal axis, and the vertical axis is the collapse value.

In the characteristic diagram of FIG. 13, the composition ratio Si: N = 1.15: 1.0 of the silicon nitride film forming the first insulating film 21 is set, and the silicon nitride film forming the second insulating film 22 is used. The composition ratio Si: N = 0.8: 1.0 is represented by □, and the composition ratio Al: N = 1: 0.9 of the aluminum nitride film forming the first insulating film 21 is The result obtained when the second insulating film 22 is made of SiO ₂ is represented by ◯, the first insulating film 21 is made of aluminum oxide, and the second insulating film 22 is made of aluminum nitride of Al: N = 1: 1. Indicated by Δ.

  The collapse value was measured as follows. First, the on-resistance Ron (1) when a voltage of 1 V is applied between the source electrode 17 and the drain electrode 18 in the on state is measured. Next, after applying a voltage of 400 V between the source electrode 17 and the drain electrode 18 in the off state where a negative voltage is applied to the gate electrode 19, the voltage of the gate electrode 19 is set to zero and the gate electrode 19 is in the on state. In a state where a voltage of 1 V is applied between the source electrode 7 and the drain electrode 8, the on-resistance Ron (2) after 5 microseconds from the switching from the off state to the on state is measured. A value Ron (2) / Ron (1) obtained by dividing the on-resistance Ron (2) by the on-resistance Ron (1) is defined as a collapse value.

  As apparent from FIG. 13, when the ratio (X1 / X2) × 100% of the first distance X1 (μm) to the second distance X2 is between 0% and 90%, the collapse value gradually increases. On the other hand, when the ratio (X1 / X2) × 100% exceeds 90%, the collapse value increases rapidly.

Next, FIG. 14 is a characteristic diagram in which the horizontal axis represents the ratio (%) of the first distance X1 to the second distance X2, and the vertical axis represents leakage current. This leakage current was measured in a state where 600 V was applied between the source electrode 17 and the drain electrode 18 at an atmospheric temperature of 150 ° C., and −10 V was applied to the gate electrode.
In the characteristic diagram of FIG. 14, the composition ratio Si: N = 1.15: 1.0 of the silicon nitride film forming the first insulating film 21 and the silicon nitride film forming the second insulating film 22 is set. The composition ratio Si: N = 0.8: 1.0 is represented by ◇, and the composition ratio Al: N = 1: 0.9 of the aluminum nitride film forming the first insulating film 21 is The result obtained when the second insulating film 22 is Al ₂ O ₃ is represented by ◯, the first insulating film 21 is aluminum oxide, and the second insulating film 22 is Al: N = 1: 1 aluminum nitride. The result was represented by Δ.

  As apparent from FIG. 14, when the ratio (X1 / X2) × 100% is in the range of 60% to 100%, the leakage current is about 1.8 μA or less. On the other hand, when the ratio (X1 / X2) × 100% is less than 60%, the leakage current increases rapidly.

  From FIG. 13 and FIG. 14, the collapse value is suppressed by setting the ratio (X1 / X2) × 100% of the first distance X1 (μm) to the second distance X2 in the range of 60% to 90%. It can be seen that the leakage current can be reduced.

  Next, FIG. 15 shows the composition ratio (Si / N) of the silicon nitride film forming the first insulating film 21, the composition ratio of aluminum nitride (Al / N), and the composition ratio of aluminum oxide (Al / O = 2). / 3) is a characteristic diagram in which the horizontal axis represents the horizontal axis and the vertical axis represents the collapse value.

  FIG. 16 shows the composition ratio (Si / N) of the silicon nitride film forming the first insulating film 21, the composition ratio of aluminum nitride (Al / N), the composition ratio of aluminum oxide (Al / O = 2 / 3) is a characteristic diagram in which the horizontal axis is taken and the vertical axis is the leakage current. In the characteristic diagrams of FIGS. 15 and 16, the ratio of the first distance X1 (μm) to the second distance X2 (X1 / X2) × 100% is 70%, and the second insulating film 22 is formed. The composition ratio of the silicon nitride film was set to Si: N = 0.8: 1.0.

  From FIG. 15, it can be seen that when the composition ratio (Si / N) of the silicon nitride film forming the first insulating film 21 is less than 0.9, the collapse value rapidly increases. Similarly, it can be seen that when the composition ratio (Al / N) of the aluminum nitride film forming the first insulating film 21 exceeds 1.0, the collapse value rapidly increases.

  On the other hand, as shown in FIG. 16, when the composition ratio (Si / N) of the silicon nitride film exceeds 3.0, the leakage current increases rapidly. Similarly, when the composition ratio (Al / N) of the aluminum nitride film is less than 0.8, the leakage current increases rapidly.

  Therefore, from the characteristic diagrams of FIGS. 15 and 16, the composition ratio (Si / N) of the silicon nitride film forming the first insulating film 21 is in the range of 0.9 or more and 3.0 or less, or aluminum nitride. It can be seen that by setting the composition ratio in the range of 0.8 to 1.0, the leakage current can be sufficiently reduced while suppressing the collapse value.

(First comparative example)
Next, FIG. 17 shows a cross section of a first comparative example for the first embodiment. The first comparative example includes first insulating films 121A and 121B and a second insulating film 122 in place of the first insulating film 21 and the second insulating film 22 of the first embodiment. Only the first embodiment is different.

  In the first comparative example, the first insulating film 121A has a dimension X30 that is 30% of the second distance X2 between the gate electrode 19 and the drain electrode 18 from the gate electrode 19 toward the drain electrode 18. It is extended in. The second insulating film 121B extends from the drain electrode 18 toward the gate electrode 19 with a dimension X30 that is 30% of the second distance X2. Therefore, the first insulating film 121A and the second insulating film 121B are separated by a distance of 40% of the second distance X2.

  The second insulating film 122 is formed on the first insulating films 121A and 121B and the AlGaN barrier layer 14 exposed between the first insulating films 121A and 121B.

  In the first comparative example, the thickness of the first insulating films 121A and 121B is set to 20 nm, which is the same as that of the first insulating film 21. The composition ratio (Si / N) of the first insulating films 121A and 121B was 1.15. The composition ratio (Si / N) of the second insulating film 122 is the same as the composition ratio (Si / N) of the second insulating film 22, and is exposed between the first insulating films 121A and 121B. The thickness of the portion on the AlGaN barrier layer 14 was set to 150 nm, which is the same as that of the second insulating film 22.

  In the first comparative example, as shown in (Table 1), the collapse value was 1.21, and the leakage current was 4.23 μA.

(Table 1)

(Second comparative example)
Next, FIG. 18 shows a cross section of a second comparative example with respect to the first embodiment. The second comparative example includes only the first insulating film 121A among the first insulating films 121A and 121B of the first comparative example, and the second comparative example is replaced with a second insulating film 122. The difference from the first comparative example described above is that the insulating film 125 is provided. The composition ratio (Si / N) of the second insulating film 125 is the same as that of the second insulating film 122 of the first comparative example, and the portion on the AlGaN barrier layer 14 exposed from the first insulating film 121A. The thickness of the first insulating film was 150 nm, which was the same as that of the second insulating film 122.

  As shown in the above (Table 1), the second comparative example had a collapse value of 1.54 and a leakage current of 2.27 μA.

  As shown in Table 1 above, in the first embodiment, the composition ratio (Si / N) of the first insulating film 21 is 1.15, and the first distance X1 (μm) with respect to the second distance X2. In the first example in which the ratio (X1 / X2) × 100% is 90%, the collapse value was 1.35 and the leakage current was 0.71 μA.

  Further, as shown in Table 1 above, in the first embodiment, the composition ratio (Si / N) of the first insulating film 21 is 1.15, and the first distance X1 with respect to the second distance X2 is set. In the second example in which the ratio (X1 / X2) × 100% of (μm) was 60%, the collapse value was 1.25 and the leakage current was 1.15 μA.

  In the first and second embodiments, the collapse values are 1.35 and 1.25, which is slightly larger than the collapse value 1.21 of the first comparative example. 0.71 μA and 1.15 μA, which are much lower than the leakage current of 4.23 μA of the first comparative example.

  In the second comparative example, the collapse value is 1.54 and the leakage current is 2.27 μA. Therefore, according to the first and second embodiments, both the collapse value and the leakage current can be significantly reduced as compared with the second comparative example.

  As described above, according to the embodiment of the present invention, it is possible to reduce the leakage current while suppressing the collapse value as compared with the comparative example in which the first insulating film is in contact with the gate electrode.

(Second embodiment)
FIG. 19 shows a cross section of a GaN-based HFET as a second embodiment of the nitride semiconductor device of the present invention.

  This second embodiment differs from the first embodiment described above in the following points (1), (2), and (3).

    (1) The source electrode 17 and the drain electrode 18 are formed in the recesses 15A and 15B formed in the nitride semiconductor multilayer body 15.

    (2) A GaN-based buffer layer 51 is provided between the GaN channel layer 13 and the Si substrate 11.

    (3) An insulating film 52 having the same composition as that of the second insulating film 22 is provided in place of the insulating films 23 and 24 between the source electrode 17 and the gate electrode 19.

  Since the recesses 15A and 15B penetrate the two-dimensional electron layer 16 from the AlGaN barrier layer 14, and the source electrode 17 and drain electrode 18 penetrate the two-dimensional electron layer 16, the source electrode 17 and drain The ohmic contact of the electrode 18 can be ensured.

  The GaN buffer layer 51 is a superlattice layer formed by alternately laminating AlGaN and GaN, for example. This GaN-based buffer layer 51, which is a superlattice layer, can suppress lattice mismatch and can reduce the leakage current in the vertical direction.

  In the second embodiment, the insulating film 52 between the source electrode 17 and the gate electrode 19 is an insulating film similar to the second insulating film 22, so that the leakage current between the gate and the source is reduced. Suppression can be achieved.

(Third embodiment)
FIG. 20 shows a cross section of a GaN-based HFET as a third embodiment of the nitride semiconductor device of the present invention.

  The third embodiment is different from the first embodiment only in that a gate insulating film 61 is provided between the gate electrode 19 and the AlGaN barrier layer 14. According to the third embodiment, a GaN-based HFET having an insulated gate structure can be realized.

As the gate insulating film 61, for example, SiN, SiO ₂ , Al ₂ O ₃ , SiON, SiO, or the like is used.

(Fourth embodiment)
FIG. 21 shows a cross section of a GaN-based HFET as a fourth embodiment of the nitride semiconductor device of the present invention.

  The fourth embodiment includes a field plate structure gate electrode 71 having a field plate portion 71A in place of the gate electrode 19 of the first embodiment, and the gate electrode 71 and the AlGaN barrier layer 14. The only difference from the first embodiment is that a gate insulating film 72 is provided between the insulating films 22, 23, and 24.

  In the fourth embodiment, the second distance X2 between the gate electrode 71 and the drain electrode 18 is a distance between the gate electrode base 71B and the drain electrode 18, as shown in FIG. . In the fourth embodiment, the first distance X1 between the gate electrode 71 and the first gate insulating film 21 is the same as the gate electrode base 71B and the first gate insulating film as shown in FIG. This is the distance between 21.

  According to the fourth embodiment, the field plate portion 71 A of the gate electrode 71 extends toward the drain electrode 18 and the source electrode 17 on the insulating film 22. The field plate structure gate electrode 71 can alleviate electric field concentration in the vicinity of the gate electrode, suppress leakage current, and improve breakdown voltage.

  Further, since the gate insulating film 72 is formed not only between the gate electrode 71 and the AlGaN barrier layer 14, but also between the gate electrode 71 and the insulating film 22 and the insulating films 23 and 24, gate leakage Current can be reduced.

As the gate insulating film 72, for example, SiN, SiO ₂ , Al ₂ O ₃ , SiON, SiO, or the like is used.

(Fifth embodiment)
FIG. 22 shows a cross section of a GaN-based HFET as a fifth embodiment of the nitride semiconductor device of the present invention.

  The fifth embodiment is different from the fourth embodiment in that the second insulating film 75 and the third insulating film 76 are provided instead of the second insulating film 22 of the fourth embodiment. Different.

  The fifth embodiment includes a third insulating film 76 formed on the AlGaN barrier layer 14 and below the second insulating film 75 between the gate electrode 19 and the first insulating film 21. . The composition of the second insulating film 75 is the same as the composition of the second insulating film 22 described above.

  On the other hand, although the third insulating film 76 is a silicon nitride film, the silicon composition ratio (Si / N) is smaller than the silicon composition ratio (Si / N) of the first insulating film 22, 2 is larger than the silicon composition ratio (Si / N) of the insulating film 75.

  According to the fifth embodiment, the silicon composition ratio (Si / N) is equal to the silicon composition ratio (Si / N) of the first insulating film 22 and the silicon composition ratio (Si / N) of the second insulating film 75. With the third insulating film 76 having a value between the values, a balance between suppression of leakage current and suppression of current collapse can be achieved, and both suppression of leakage current and suppression of current collapse can be achieved.

Alternatively, even when SiO ₂ or Al ₂ O ₃ is used as the third insulating film 76, a balance between suppression of leakage current and suppression of current collapse is achieved, and suppression of leakage current and suppression of current collapse are achieved. Achieving balance.

(Sixth embodiment)
FIG. 23 shows a cross section of a GaN-based HFET as a sixth embodiment of the nitride semiconductor device of the present invention.

  The sixth embodiment is different from the first embodiment in the following points (1) and (2).

    (1) A mesa-shaped p-type AlGaN layer 81 is provided between the gate electrode 19 and the AlGaN barrier layer 14.

    (2) An insulating film 52 having the same composition as that of the second insulating film 22 is provided in place of the insulating films 23 and 24 between the source electrode 17 and the gate electrode 19.

  According to the sixth embodiment, normally-off can be realized by the configuration in which the mesa-shaped p-type AlGaN layer 81 is provided under the gate electrode 19.

  Further, since the insulating film 52 between the source electrode 17 and the gate electrode 19 is an insulating film similar to the second insulating film 22, leakage current can be suppressed.

  Instead of the mesa-shaped p-type AlGaN layer 81, a mesa-shaped InGaN layer or a GaN layer with an adjusted thickness may be used.

(Seventh embodiment)
FIG. 24 shows a cross section of a GaN-based HFET as a seventh embodiment of the nitride semiconductor device of the present invention.

  In the seventh embodiment, instead of the first insulating film 21 in the above-described fourth embodiment, a first insulating film 85 having a distance X3 from the drain electrode 18 is provided. The second embodiment differs from the fourth embodiment in that a second insulating film 86 is provided in place of the insulating film 22.

  The first and second insulating films 85 and 86 are the same as the first and second insulating films 21 and 22 in terms of materials.

  The first distance X1 between the first insulating film 85 and the gate electrode 71 is the same as that in the first embodiment described above, and the second distance between the gate electrode 71 and the drain electrode 18 is the same. 60% or more and 90% or less of X2.

  Further, the distance X3 between the first insulating film 85 and the drain electrode 18 is about several percent (for example, 3%) of the second distance X2. A second insulating film 86 extends between the first insulating film 85 and the drain electrode 18.

  When the first insulating film 85 is not in contact with the drain electrode 18 as in the seventh embodiment, the element breakdown voltage is increased from 800V to 900V. At the time of a high voltage at which element breakdown occurs, a high electric field is generated at a portion in contact with the drain electrode 18 to prevent the first insulating film 85 from being destroyed and to suppress the collapse value while reducing the leakage current. It is possible.

In the first to seventh embodiments, the second insulating film 22 is a silicon nitride film having a silicon composition ratio of 0.75 or more and 1.0 or less, but from the first insulating film 21. Alternatively, a SiON film or a SiO ₂ film having a small silicon composition ratio may be used.

  In the first to seventh embodiments, the nitride semiconductor device using the Si substrate has been described. However, the present invention is not limited to the Si substrate, and a sapphire substrate or a SiC substrate may be used, and the sapphire substrate or the SiC substrate may be used. A nitride semiconductor layer may be grown, or a nitride semiconductor layer may be grown on a substrate made of a nitride semiconductor, such as growing an AlGaN layer on a GaN substrate. In addition, a buffer layer may be formed between the substrate and the nitride semiconductor layer, or an AlN hetero characteristic having a layer thickness of about 1 nm between the AlGaN barrier layer 14 and the GaN channel layer 13 of the nitride semiconductor stacked body 15. An improvement layer may be formed.

The nitride semiconductor of the nitride semiconductor device according to the present invention may be any material as long as it is represented by Al _x In _y Ga _1-xy N (x ≦ 0, y ≦ 0, 0 ≦ x + y ≦ 1).

  The present invention and the embodiment are summarized as follows.

The nitride semiconductor device of the present invention is
A nitride semiconductor multilayer body 15 having a hetero interface;
A source electrode 17 and a drain electrode 18 formed at least partially on the nitride semiconductor multilayer body 15 or in the nitride semiconductor multilayer body 15 and spaced apart from each other;
Gate electrodes 19 and 71 formed on the nitride semiconductor laminate 15 between the source electrode 17 and the drain electrode 18;
It is formed on the nitride semiconductor multilayer body 15 between the gate electrodes 19 and 71 and the drain electrode 18 and along the surface of the nitride semiconductor multilayer body 15 with respect to the gate electrodes 19 and 71. First insulating films 21 and 85 separated by a first distance X1,
Second insulating films 22, 75, 86 formed on the first insulating films 21, 85 and on the nitride semiconductor multilayer body 15 between the gate electrodes 19, 71 and the drain electrode 18; With
The first distance X1 is 60% or more and 90% or less of the second distance X2 between the gate electrodes 19 and 71 and the drain electrode 18.

  According to the nitride semiconductor device of the present invention, the first insulating films 21 and 85 formed on the nitride semiconductor stacked body 15 between the gate electrodes 19 and 71 and the drain electrode 18 include: 60% or more and 90% or less of the second distance X2 between the gate electrodes 19 and 71 and the drain electrode 18 along the surface of the nitride semiconductor multilayer body 15 with respect to the gate electrodes 19 and 71. Are separated by a first distance X1. Thus, according to the present invention, current collapse can be suppressed and leakage current can be sufficiently reduced.

  In one embodiment, the second insulating film 86 is formed on the nitride semiconductor stacked body 15 between the drain electrode 18 and the first insulating film 85.

  According to this embodiment, the element breakdown voltage can be increased.

  In one embodiment, the first insulating films 21 and 85 have a composition ratio of silicon to nitrogen of 0.9 or more and 3.0 or less.

  According to this embodiment, current collapse can be suppressed while suppressing leakage current by the first insulating films 21 and 85 having a composition ratio of silicon to nitrogen of 0.9 or more and 3.0 or less.

  In one embodiment, the first insulating films 21 and 85 have a composition ratio of silicon to nitrogen of 1.15 or more and 3.0 or less.

  According to this embodiment, the current insulation can be further suppressed while the leakage current is suppressed by the first insulating films 21 and 85 in which the composition ratio of silicon to nitrogen is 1.15 or more and 3.0 or less.

  In one embodiment, the first insulating films 21 and 85 have a composition ratio of aluminum to nitrogen of 0.8 or more and 1.0 or less.

  According to this embodiment, the current insulation can be suppressed while the leakage current is suppressed by the first insulating films 21 and 85 whose composition ratio of aluminum to nitrogen is 0.8 or more and 1.0 or less.

  In one embodiment, the first insulating films 21 and 85 are aluminum oxide.

  According to this embodiment, the current insulation can be suppressed while the leakage current is suppressed by the first insulating films 21 and 85 made of aluminum oxide.

In one embodiment, the second insulating films 22, 75, 86 are
The silicon nitride film has a composition ratio of silicon to nitrogen of 0.75 or more and 1.0 or less.

  According to this embodiment, the leakage current can be reduced by the second insulating films 22, 75 and 86.

  In one embodiment, the second insulating films 22, 75, 86 are silicon oxide.

  According to this embodiment, the leakage current can be reduced by the second insulating films 22, 75 and 86.

  In one embodiment, the second insulating films 22, 75, 86 are aluminum oxide. However, this is limited to the case where the first insulating films 21 and 85 are not aluminum oxide.

  According to this embodiment, the leakage current can be reduced by the second insulating films 22, 75 and 86.

  In one embodiment, the second insulating films 22, 75, 86 are aluminum nitride. However, this is limited to the case where the first insulating films 21 and 85 are not aluminum nitride.

  According to this embodiment, the leakage current can be reduced by the second insulating films 22, 75 and 86.

  In one embodiment, the second insulating films 22, 75, 86 are formed on the nitride semiconductor multilayer body 15 between the drain electrode 18 and the first insulating films 21, 85. Yes.

  According to this embodiment, the element breakdown voltage can be increased.

In one embodiment, the third insulating film 76 formed on the nitride semiconductor stacked body 15 and below the second insulating film 75 between the gate electrode 71 and the first insulating film 21. With
The third insulating film 76 is made of silicon oxide.

In one embodiment, the third insulating film 76 formed on the nitride semiconductor stacked body 15 and below the second insulating film 75 between the gate electrode 71 and the first insulating film 21. With
The third insulating film 76 is made of silicon nitride, and the silicon composition ratio of the silicon nitride is smaller than the silicon composition ratio of the first insulating film 21 and the silicon composition ratio of the second insulating film 75. large.

In one embodiment, the third insulating film 76 formed on the nitride semiconductor stacked body 15 and below the second insulating film 75 between the gate electrode 71 and the first insulating film 21. With
The third insulating film 76 is made of aluminum oxide.

In one embodiment, the third insulating film 76 formed on the nitride semiconductor stacked body 15 and below the second insulating film 75 between the gate electrode 71 and the first insulating film 21. With
The third insulating film 76 is made of aluminum nitride.

  According to this embodiment, the third insulating film 76 can achieve a balance between the suppression of the leakage current and the suppression of the current collapse, thereby achieving both the suppression of the leakage current and the suppression of the current collapse.

  Although specific embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

11 Si substrate 13 Undoped AlGaN channel layer 14 Undoped GaN barrier layer 15 Nitride semiconductor laminate 15A, 15B Recess 16 Two-dimensional electron gas layer 17 Source electrode 18 Drain electrode 19, 71 Gate electrode 21, 85, 121A, 121B First Insulating films 22, 75, 86, 122, 125 Second insulating films 23, 24, 52 Insulating films 31, 35 Silicon nitride films 33, 36, 40, 41, 45 Photoresist layer 38 Multilayer metal film 43 Metal film 51 GaN System buffer layers 61, 72 Gate insulating film 71A Field plate portion 71B Base portion 76 Third insulating film 81 Mesa-shaped p-type AlGaN layer

Claims (2)

A nitride semiconductor laminate having a heterointerface;
A source electrode and a drain electrode that are formed at least partially on the nitride semiconductor multilayer body or in the nitride semiconductor multilayer body and spaced apart from each other;
A gate electrode formed on the nitride semiconductor multilayer body between the source electrode and the drain electrode;
A first electrode formed on the nitride semiconductor multilayer body between the gate electrode and the drain electrode and spaced apart from the gate electrode by a first distance along a surface of the nitride semiconductor multilayer body; An insulating film of
A second insulating film formed on the first insulating film and on the nitride semiconductor multilayer body between the gate electrode and the drain electrode;
The nitride semiconductor device, wherein the first distance is 60% or more and 90% or less of a second distance between the gate electrode and the drain electrode. The nitride semiconductor device according to claim 1,
The nitride semiconductor device, wherein the second insulating film is formed on the nitride semiconductor multilayer body between the drain electrode and the first insulating film.

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