Semiconductor device

Abstract

Provided is a semiconductor device capable of suppressing occurrence of dielectric breakdown. A semiconductor device according to an embodiment comprises a semiconductor layer, a first electrode, a second electrode, a first insulating layer, a gate electrode, a second insulating layer, a third insulating layer, a first field plate electrode, and a fourth insulating layer. The first insulating layer is located between the first electrode and the second electrode in the first direction. The gate electrode is provided on the first insulating layer and includes a first portion and a second portion. A lower surface of the second portion is located above a lower surface of the first portion. The second insulating layer is provided between the first insulating layer and the second portion. The first and second insulating layers include a first insulating material. The third insulating layer is provided on the gate electrode, the first insulating layer, and the second insulating layer. The first field plate electrode is provided on the third insulating layer. The fourth insulating layer is provided on the third insulating layer and the first field plate electrode. The third and fourth insulating layers include a second insulating material.

Description

Semiconductor Devices

[0001] FIELD An embodiment of the present invention relates to a semiconductor device.

[0002] There are semiconductor devices that use gallium nitride, and there is a demand for technology that can suppress the occurrence of dielectric breakdown in these semiconductor devices.

[0003] JP 2023-38273 A

[0004] An object of the present invention is to provide a semiconductor device capable of suppressing the occurrence of dielectric breakdown.

[0005] A semiconductor device according to the embodiment includes a semiconductor layer, a first electrode, a second electrode, a first insulating layer, a gate electrode, a second insulating layer, a third insulating layer, a first field plate electrode, and a fourth insulating layer. The semiconductor layer includes gallium nitride. The first electrode is provided on a portion of the semiconductor layer. The second electrode is provided on another portion of the semiconductor layer and is spaced apart from the first electrode. The first insulating layer is provided on the semiconductor layer. The first insulating layer is located between the first electrode and the second electrode in a first direction from the first electrode to the second electrode. The first insulating layer includes a first insulating material. The gate electrode is provided on the first insulating layer and includes a first portion and a second portion. The position of the second portion in the first direction is between the position of the first portion in the first direction and the position of the second electrode in the first direction. The bottom surface of the second portion is located above the bottom surface of the first portion. The second insulating layer is provided between the first insulating layer and the second portion and includes the first insulating material. The third insulating layer is provided on the gate electrode, the first insulating layer, and the second insulating layer and includes a second insulating material. The first field plate electrode is provided on the third insulating layer and electrically connected to the first electrode. The position of the first field plate electrode in the first direction is between the position of the gate electrode in the first direction and the position of the second electrode in the first direction. The fourth insulating layer is provided on the third insulating layer and the first field plate electrode and includes the second insulating material.

[0006] FIG. 1 is a cross-sectional view showing a portion of a semiconductor device according to an embodiment. FIG. 2 is a cross-sectional view showing a portion of a semiconductor device according to a reference example. FIG. 3 is a cross-sectional view showing a portion of a semiconductor device according to a reference example. FIG. 4 is a graph showing characteristics of a semiconductor device according to a reference example. FIGS. 5(a) and 5(b) are schematic diagrams showing characteristics of a semiconductor device according to a reference example. FIG. 6 is a cross-sectional view showing a portion of a semiconductor device according to a modified example of the embodiment.

[0007] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In this specification and each drawing, elements similar to those already described are designated by the same reference numerals, and detailed description will be omitted as appropriate.

[0008] FIG. 1 is a cross-sectional view showing a portion of a semiconductor device according to an embodiment. The semiconductor device 1 according to the embodiment is a MOSFET. As shown in FIG. 1, the semiconductor device 1 according to the embodiment includes a semiconductor layer 10, a source electrode 21 (first electrode), a drain electrode 22 (second electrode), a gate electrode 23, a first insulating layer 31, a second insulating layer 32, a third insulating layer 33, and a fourth insulating layer 34. The semiconductor device 1 also includes a field plate electrode (FP electrode). Specifically, the semiconductor device 1 includes a first FP electrode 41, a second FP electrode 42, and a third FP electrode 43.

[0009] In the description of the embodiment, an XYZ Cartesian coordinate system is used. The direction from the source electrode 21 to the drain electrode 22 is defined as the X direction (first direction). The direction perpendicular to the X direction and from the semiconductor layer 10 to the source electrode 21 is defined as the Z direction (second direction). The direction perpendicular to the X direction and the Z direction is defined as the Y direction. For the sake of explanation, the direction from the semiconductor layer 10 to the source electrode 21 is referred to as "up" and the opposite direction is referred to as "down." These directions are based on the relative positional relationship between the semiconductor layer 10 and the source electrode 21 and are unrelated to the direction of gravity.

[0010] The semiconductor layer 10 includes gallium nitride. For example, the semiconductor layer 10 includes a first semiconductor region 11 and a second semiconductor region 12. The first semiconductor region 11 includes Al ｘ１ Ga １－ｘ１ N (0≦x1<1). The second semiconductor region 12 contains Al ｘ２ Ga １－ｘ２ N (0<x2<1, x1<x2). As an example, the first semiconductor region 11 is a GaN layer that does not substantially contain Al, and the second semiconductor region 12 is an AlGaN layer. The semiconductor layer 10 can be provided on a semiconductor substrate, a buffer layer, or the like (not shown).

[0011] The source electrode 21 is provided on a part of the semiconductor layer 10. The drain electrode 22 is provided on another part of the semiconductor layer 10. The drain electrode 22 is spaced apart from the source electrode 21 in the X direction. The source electrode 21 and the drain electrode 22 are electrically connected to the second semiconductor region 12 of the semiconductor layer 10.

[0012] The first insulating layer 31 is provided on the semiconductor layer 10 and is located between the source electrode 21 and the drain electrode 22. For example, the first insulating layer 31 is spaced apart from the source electrode 21 and the drain electrode 22 in the X direction. The first insulating layer 31 includes a first insulating material.

[0013] The gate electrode 23 is provided on a first insulating layer 31. The first insulating layer 31 functions as a gate insulating layer. The gate electrode 23 includes a first portion 23a and a second portion 23b. The position of the second portion 23b in the X direction is between the position of the first portion 23a in the X direction and the position of the drain electrode 22 in the X direction. In other words, when the semiconductor device 1 is viewed from the Z direction, the second portion 23b is located between the first portion 23a and the drain electrode 22 in the X direction. The lower surface of the second portion 23b is located higher than the lower surface of the first portion 23a.

[0014] The second insulating layer 32 is provided between the first insulating layer 31 and the second portion 23b. The first portion 23a is aligned with the second insulating layer 32 in the X direction. As shown in the figure, the second insulating layer 32 may be further provided in a region located on the drain electrode 22 side of the second portion 23b. The second insulating layer 32 includes the first insulating material. The thickness (dimension in the Z direction) of the second insulating layer 32 is greater than the thickness of the first insulating layer 31.

[0015] The third insulating layer 33 is provided on the gate electrode 23, the first insulating layer 31, and the second insulating layer 32. One end of the third insulating layer 33 in the X direction is located between the source electrode 21 and the first insulating layer 31, and is in contact with the semiconductor layer 10 and the source electrode 21. The other end of the third insulating layer 33 in the X direction is located between the drain electrode 22 and the first insulating layer 31, and is in contact with the semiconductor layer 10 and the drain electrode 22. The third insulating layer 33 includes a second insulating material. The second insulating material is different from the first insulating material.

[0016] The first FP electrode 41 is provided on the third insulating layer 33. The first FP electrode 41 is connected to the source electrode 21 at a portion not shown, and an electrical connection is formed between the source electrode 21 and the first FP electrode 41 as shown by the dashed line. The position of the first FP electrode 41 in the X direction is between the position of the gate electrode 23 in the X direction and the position of the drain electrode 22 in the X direction.

[0017] The second FP electrode 42 is provided on the third insulating layer 33 and is located on the gate electrode 23. The second FP electrode 42 is electrically connected to the gate electrode 23. An end E2 of the second FP electrode 42 in the X direction is located on the drain electrode 22 side of the gate electrode 23. In other words, the position of the end E2 in the X direction is between the position of the gate electrode 23 in the X direction and the position of the drain electrode 22 in the X direction.

[0018] The fourth insulating layer 34 is provided on the third insulating layer 33, the first FP electrode 41, and the second FP electrode 42. The fourth insulating layer 34 includes the second insulating material. The thickness of the fourth insulating layer 34 is greater than the thickness of the third insulating layer 33.

[0019] The third FP electrode 43 is provided on the fourth insulating layer 34, and is located on the first FP electrode 41 and the second FP electrode 42. The third FP electrode 43 is electrically connected to the source electrode 21. An end E3 of the third FP electrode 43 in the X direction is located on the drain electrode 22 side with respect to the first FP electrode 41. In other words, the position of the end E3 in the X direction is between the position of the first FP electrode 41 in the X direction and the position of the drain electrode 22 in the X direction.

[0020] An example of the material of each component is as follows: The source electrode 21, the drain electrode 22, the gate electrode 23, the first FP electrode 41, the second FP electrode 42, and the third FP electrode 43 include a metal material such as titanium, copper, or aluminum. The first insulating material included in the first insulating layer 31 and the second insulating layer 32 is one selected from the group consisting of silicon nitride, silicon oxide, and silicon oxynitride. The second insulating material included in the third insulating layer 33 and the fourth insulating layer 34 is another one selected from the group. For example, the relative dielectric constant of the first insulating material is higher than the relative dielectric constant of the second insulating material.

[0021] The operation of the semiconductor device 1 will now be described. Two-dimensional electron gas (2DEG) is generated near the interface between the first semiconductor region 11 and the second semiconductor region 12. When a positive voltage is applied to the drain electrode 22 relative to the source electrode 21, electrons contained in the two-dimensional electron gas move from the source electrode 21 to the drain electrode 22, and a current flows between the source electrode 21 and the drain electrode 22. When a negative voltage is applied to the gate electrode 23, the potential difference between the semiconductor layer 10 and the gate electrode 23 repels electrons in the region below the gate electrode 23, depleting that region. This stops the current flowing through the semiconductor device 1.

[0022] 2 and 3 are cross-sectional views showing a portion of a semiconductor device according to a reference example. Advantages of embodiments of the present invention will be described with reference to the semiconductor device according to the reference example. The semiconductor devices r1 and r2 shown in FIGS. 2 and 3 include a semiconductor layer 10, a source electrode 21, a drain electrode 22, a gate electrode 23r, a first insulating layer 31, a third insulating layer 33, a fourth insulating layer 34, a first FP electrode 41, a second FP electrode 42, and a third FP electrode 43.

[0023] The semiconductor devices r1 and r2 do not have a second insulating layer 32. The gate electrode 23r also differs from the gate electrode 23 in that it does not have a second portion 23b. In the semiconductor device r1, the first insulating layer 31 contains silicon nitride, and the third insulating layer 33 and the fourth insulating layer 34 contain silicon oxide. In the semiconductor device r2, the first insulating layer 31 and the third insulating layer 33 contain silicon nitride, and the fourth insulating layer 34 contains silicon oxide. The gate electrode 23r includes an end e1 in the X direction. The first FP electrode 41 includes an end e2 in the X direction.

[0024] 4 is a graph showing the characteristics of a semiconductor device according to a reference example. In FIG. 4, the horizontal axis represents the thickness T of the third insulating layer 33, and the vertical axis represents the electric field strength S. The plots with "circle" symbols represent the electric field strength near the bottom end of end e1. The plots with "triangle" symbols represent the electric field strength near the bottom end of end e2. The solid line represents the characteristics of semiconductor device r1, and the dashed line represents the characteristics of semiconductor device r2. Note that in FIG. 4, the electric field strength S is expressed as a relative ratio.

[0025] The first insulating layer 31 is in contact with the semiconductor layer 10. An insulating material capable of suppressing reaction with the semiconductor layer 10 is selected as the material for the first insulating layer 31. As an example, when the oxygen concentration of the first insulating layer 31 is low, the reaction between the first insulating layer 31 and the semiconductor layer 10 can be suppressed. For this reason, the first insulating layer 31 is preferably a silicon oxynitride layer with a low oxygen concentration or a silicon nitride layer that is substantially free of oxygen.

[0026] The first FP electrode 41 is provided to reduce the electric field strength near the end e1 of the gate electrode 23r. The first FP electrode 41 is provided on the third insulating layer 33. The distance in the Z direction between the semiconductor layer 10 and the first FP electrode 41 is longer than the distance in the Z direction between the semiconductor layer 10 and the gate electrode 23. Therefore, the electric field strength near the end e2 of the first FP electrode 41 may be higher than the electric field strength near the end e1 of the gate electrode 23r. On the other hand, if the electric field strength near the end e2 is high, the insulating properties of the third insulating layer 33 may deteriorate over time, reducing the semiconductor device's withstand voltage. Therefore, an insulating material that can improve long-term reliability is selected for the third insulating layer 33. For example, a low nitrogen concentration in the third insulating layer 33 can suppress deterioration of the insulating properties of the third insulating layer 33 over time and reduce the semiconductor device's withstand voltage. For this reason, the third insulating layer 33 is preferably a silicon oxynitride layer with a low nitrogen concentration or a silicon oxide layer that is substantially free of nitrogen.

[0027] 5A and 5B are schematic diagrams showing the characteristics of a semiconductor device according to a reference example. The relative dielectric constant of silicon nitride is higher than that of silicon oxide. In a semiconductor device r1 in which the first insulating layer 31 contains silicon nitride and the third insulating layer 33 contains silicon oxide, as shown in FIG. 5A, electric field lines are distributed so as to avoid the third insulating layer 33. This makes it easier for the electric field strength near the end e1 to increase, increasing the possibility of dielectric breakdown of the first insulating layer 31.

[0028] 5B, in the semiconductor device r2 in which the third insulating layer 33 contains silicon nitride, the bias of the electric field lines caused by the difference in the relative permittivity between the first insulating layer 31 and the third insulating layer 33 is alleviated. As can be seen from a comparison between the solid-lined circle plot and the dashed-lined circle plot in FIG. 4, the electric field intensity near the end e1 can be alleviated.

[0029] On the other hand, for semiconductor device r2, the relative dielectric constant of silicon nitride contained in the third insulating layer 33 is higher than the relative dielectric constant of silicon oxide contained in the fourth insulating layer 34. Therefore, near the lower end of end e2, the electric field lines are distributed so as to avoid the fourth insulating layer 34. As can be seen from a comparison between the triangular plots marked with solid lines and the triangular plots marked with dashed lines, the electric field strength near end e2 increases. Furthermore, an increase in the nitrogen concentration in the third insulating layer 33 may reduce the long-term reliability of the semiconductor device.

[0030] To address these issues, as shown in FIG. 1 , the semiconductor device 1 according to the embodiment includes a second insulating layer 32. The gate electrode 23 includes a first portion 23a and a second portion 23b. The second insulating layer 32 is provided between the first insulating layer 31 and the second portion 23b. An end E of the first portion 23a in the X direction contacts the first insulating layer 31 and the second insulating layer 32. The first insulating layer 31 and the second insulating layer 32 contain the same first insulating material. Therefore, the relative dielectric constant of the second insulating layer 32 is substantially the same as the relative dielectric constant of the first insulating layer 31. The provision of the second insulating layer 32 can reduce the electric field strength near the end E, thereby suppressing dielectric breakdown of the first insulating layer 31.

[0031] The first FP electrode 41 is provided on the third insulating layer 33, and the fourth insulating layer 34 covers the first FP electrode 41. The lower end of the end E1 of the first FP electrode 41 contacts the third insulating layer 33 and the fourth insulating layer 34. The third insulating layer 33 and the fourth insulating layer 34 contain a common second insulating material. Therefore, the relative dielectric constant of the fourth insulating layer 34 is substantially the same as the relative dielectric constant of the third insulating layer 33. This reduces the electric field strength near the end E1 of the first FP electrode 41 in the X direction, and suppresses the occurrence of dielectric breakdown of the third insulating layer 33.

[0032] Furthermore, according to the embodiment, the first insulating material and the second insulating material can be individually optimized. For example, the first insulating material may be silicon oxynitride having a lower oxygen concentration than the second insulating material, or silicon nitride containing substantially no oxygen. This can prevent the first insulating material contained in the first insulating layer 31 from reacting with the semiconductor layer 10. The second insulating material may be silicon oxynitride having a lower nitrogen concentration than the first insulating material, or silicon oxide containing substantially no nitrogen. This can improve the long-term reliability of the third insulating layer 33 and prevent the degradation of the semiconductor device 1's withstand voltage over time.

[0033] According to the semiconductor device 1 of the embodiment, it is possible to suppress the occurrence of dielectric breakdown in the first insulating layer 31 while suppressing the decrease in the withstand voltage over time.

[0034] The semiconductor device 1 preferably includes at least one of the second FP electrode 42 and the third FP electrode 43. This makes it possible to further reduce the electric field strength near the end E or the electric field strength near the end E1.

[0035] Furthermore, a portion of the third insulating layer 33 is provided between the first insulating layer 31 and the drain electrode 22 in the X direction and is in contact with the semiconductor layer 10. This portion of the third insulating layer 33 is located between the semiconductor layer 10 and a portion of the drain electrode 22 in the Z direction. In other words, the third insulating layer 33, which has a low nitrogen concentration and is less likely to trap electrons, is provided below a portion of the drain electrode 22. This makes it possible to suppress the generation of electron traps below that portion of the drain electrode 22. For example, electron traps are suppressed when a high voltage is applied to the drain electrode, and an increase in on-resistance (so-called collapse) is suppressed.

[0036] 6 is a cross-sectional view showing a portion of a semiconductor device according to a modified example of the embodiment. In the semiconductor device 2 according to the modified example shown in FIG. 6, the first FP electrode 41 is provided at a lower position than in the semiconductor device 1. Specifically, the second insulating layer 32 is provided between the first insulating layer 31 and the second portion 23b, and is not provided directly below the first FP electrode 41. When comparing the semiconductor device 1 and the semiconductor device 2, the first FP electrode 41 is located lower by the thickness of the second insulating layer 32.

[0037] For example, the third insulating layer 33 includes a first insulating portion 33a and a second insulating portion 33b. The first insulating portion 33a is located on the second portion 23b. The second insulating portion 33b is located below the first FP electrode 41. The upper surface of the second insulating portion 33b is located lower than the upper surface of the first insulating portion 33a. Furthermore, the lower surface of the first FP electrode 41 is located lower than the lower surface of the end E2 of the second FP electrode 42.

[0038] In semiconductor device 1 and semiconductor device 2, the insulating material contained in second insulating layer 32 is different from the insulating material contained in third insulating layer 33. That is, the relative dielectric constant of second insulating layer 32 is different from the relative dielectric constant of third insulating layer 33. As a result, the electric field strength increases near the end of second portion 23b in the X direction, which may cause dielectric breakdown of second insulating layer 32. However, in semiconductor device 2, first FP electrode 41 is located at a lower position than in semiconductor device 1. This reduces the electric field strength near the end of second portion 23b, thereby suppressing dielectric breakdown of second insulating layer 32.

[0039] The semiconductor device 2 according to the modified example can further suppress the occurrence of dielectric breakdown compared to the semiconductor device 1 .

[0040] An embodiment of the present invention includes the following features: (Feature 1) A semiconductor layer including gallium nitride, a first electrode provided on a portion of the semiconductor layer, a second electrode provided on another portion of the semiconductor layer and spaced apart from the first electrode, a first insulating layer provided on the semiconductor layer and located between the first electrode and the second electrode in a first direction from the first electrode toward the second electrode, the first insulating layer including a first insulating material, a gate electrode provided on the first insulating layer and including a first portion and a second portion, the position of the second portion in the first direction being between the position of the first portion in the first direction and the position of the second electrode in the first direction, and the bottom surface of the second portion being located higher than the bottom surface of the first portion, a second insulating layer provided between the first insulating layer and the second portion, the second insulating layer including the first insulating material, and a third insulating layer provided on the gate electrode, the first insulating layer, and the second insulating layer and including a second insulating material. a first field plate electrode provided on the third insulating layer and electrically connected to the first electrode, the first field plate electrode having a position in the first direction between a position of the gate electrode in the first direction and a position of the second electrode in the first direction, and a fourth insulating layer provided on the third insulating layer and the first field plate electrode and including the second insulating material. (Feature 2) The semiconductor device according to Feature 1, wherein the third insulating layer includes a first insulating portion located on the second portion and a second insulating portion located below the first field plate electrode, and an upper surface of the second insulating portion is located lower than an upper surface of the first insulating portion. (Feature 3) The semiconductor device according to Feature 1, further comprising a second field plate electrode provided on the third insulating layer and electrically connected to the gate electrode, wherein a position in the first direction of a portion of the second field plate electrode is between a position of the gate electrode in the first direction and a position of the first field plate electrode in the first direction. (Feature 4) The semiconductor device according to Feature 3, wherein a lower surface of the first field plate electrode is located lower than a lower surface of the portion of the second field plate electrode.(Feature 5) The semiconductor device according to any one of Features 1 to 4, wherein a portion of the third insulating layer is provided between the first insulating layer and the second electrode in the first direction and is in contact with the semiconductor layer. (Feature 6) The semiconductor device according to Feature 5, wherein the portion of the third insulating layer is located between the semiconductor layer and a portion of the second electrode in a second direction perpendicular to the first direction. (Feature 7) The semiconductor device according to any one of Features 1 to 6, wherein the first insulating material is silicon nitride, and the second insulating material is silicon oxide. (Feature 8) The semiconductor device according to any one of Features 1 to 7, wherein the relative dielectric constant of the first insulating material is higher than the relative dielectric constant of the second insulating material. (Feature 9) The semiconductor device according to any one of Features 1 to 8, wherein the second insulating layer is thicker than the first insulating layer, and the fourth insulating layer is thicker than the third insulating layer.

[0041] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0042] 1, 2: semiconductor device, 10: semiconductor layer, 11: first semiconductor region, 12: second semiconductor region, 21: source electrode, 22: drain electrode, 23: gate electrode, 23a: first portion, 23b: second portion, 23r: gate electrode, 31: first insulating layer, 32: second insulating layer, 33: third insulating layer, 33a: first insulating portion, 33b: second insulating portion, 34: fourth insulating layer, 41: first FP electrode, 42: second FP electrode, 43: third FP electrode, E, E1 to E3, e1, e2: end portion, r1, r2: semiconductor device

Claims

1. A semiconductor layer including gallium nitride; a first electrode provided on a portion of the semiconductor layer; a second electrode provided on another portion of the semiconductor layer and spaced apart from the first electrode; a first insulating layer provided on the semiconductor layer and located between the first electrode and the second electrode in a first direction from the first electrode toward the second electrode, the first insulating layer including a first insulating material; a gate electrode provided on the first insulating layer and including a first portion and a second portion, the position of the second portion in the first direction being between the position of the first portion in the first direction and the position of the second electrode in the first direction, and the bottom surface of the second portion being located higher than the bottom surface of the first portion; a second insulating layer provided between the first insulating layer and the second portion, the second insulating layer including the first insulating material; and a third insulating layer provided on the gate electrode, the first insulating layer, and the second insulating layer, the third insulating layer including a second insulating material. a first field plate electrode provided on the third insulating layer, electrically connected to the first electrode, and having a position in the first direction between a position of the gate electrode in the first direction and a position of the second electrode in the first direction; and a fourth insulating layer provided on the third insulating layer and the first field plate electrode, the fourth insulating layer including the second insulating material.

2. The semiconductor device described in claim 1, wherein the third insulating layer includes a first insulating portion located above the second portion and a second insulating portion located below the first field plate electrode, and an upper surface of the second insulating portion is located lower than an upper surface of the first insulating portion.

3. The semiconductor device described in claim 1, further comprising a second field plate electrode provided on said third insulating layer and electrically connected to said gate electrode, wherein a position of a portion of said second field plate electrode in said first direction is between a position of said gate electrode in said first direction and a position of said first field plate electrode in said first direction.

4. The semiconductor device according to claim 3, wherein a lower surface of said first field plate electrode is located lower than a lower surface of said portion of said second field plate electrode.

5. A semiconductor device according to any one of claims 1 to 4, wherein a portion of the third insulating layer is provided between the first insulating layer and the second electrode in the first direction and contacts the semiconductor layer.

6. The semiconductor device according to claim 5, wherein said portion of said third insulating layer is located between said semiconductor layer and a portion of said second electrode in a second direction perpendicular to said first direction.

7. The semiconductor device according to claim 1, wherein the first insulating material is silicon nitride, and the second insulating material is silicon oxide.

8. The semiconductor device according to claim 1, wherein the first insulating material has a higher relative dielectric constant than the second insulating material.

9. The semiconductor device according to claim 1, wherein the second insulating layer is thicker than the first insulating layer, and the fourth insulating layer is thicker than the third insulating layer.

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