Semiconductor devices

Abstract

A semiconductor device according to an embodiment of the present invention comprises a semiconductor portion including a first semiconductor layer of a first conductivity type, a first electrode provided on the back surface of the semiconductor portion, and a second electrode provided on the surface of the semiconductor portion. The second electrode includes a barrier layer and a metal layer, the barrier layer is in contact with the first semiconductor layer and includes vanadium or a vanadium compound as a main component. The metal layer is provided on the barrier layer.

Description

[0001] Related Application

[0002] This application claims priority based on Japanese Patent Application No. 2021-41019 (filing date: March 15, 2021), and the present application incorporates the entire contents of the basic application by reference. Technical Field

[0003] Embodiments relate to a semiconductor device. Background Art

[0004] Semiconductor devices are required to have improved electrical characteristics. For example, a Schottky barrier diode preferably has a low forward voltage and a low reverse current. Summary of the invention

[0005] Embodiments provide a semiconductor device capable of improving current / voltage characteristics.

[0006] A semiconductor device according to an embodiment includes a semiconductor portion including a first semiconductor layer of a first conductivity type, a first electrode provided on the back surface of the semiconductor portion, and a second electrode provided on the surface of the semiconductor portion. The second electrode includes a barrier layer that is in contact with the first semiconductor layer and contains vanadium as a main component, and a metal layer provided on the barrier layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a schematic cross-sectional view showing the semiconductor device according to the first embodiment.

[0008] Figure 2 (a) and (b) are graphs showing characteristics of the semiconductor device according to the first embodiment.

[0009] Figure 3 (a) to (c) are schematic cross-sectional views showing electrode structures of semiconductor devices according to modifications of the first embodiment.

[0010] Figure 4 This is a schematic cross-sectional view showing a semiconductor device according to a modification of the first embodiment.

[0011] Figure 5 This is a schematic cross-sectional view showing a semiconductor device according to a second embodiment. DETAILED DESCRIPTION

[0012] A semiconductor device according to an embodiment includes a semiconductor portion including a first semiconductor layer of a first conductivity type, a first electrode provided on the back surface of the semiconductor portion, and a second electrode provided on the surface of the semiconductor portion. The second electrode includes a barrier layer that is in contact with the first semiconductor layer and contains vanadium as a main component, and a metal layer provided on the barrier layer.

[0013] Hereinafter, the embodiments will be described with reference to the accompanying drawings. The same parts in the drawings are marked with the same numbers and their detailed descriptions are appropriately omitted, and the different parts are described. It should be noted that the drawings are schematic or conceptual drawings, and the relationship between the thickness and width of each part, the ratio of the size between the parts, etc. may not be the same as the actual situation. In addition, even when representing the same part, the sizes or ratios of each other are sometimes expressed differently according to the drawings.

[0014] (First embodiment)

[0015] Figure 1 1 is a schematic cross-sectional view showing a semiconductor device 1 according to a first embodiment. The semiconductor device 1 is, for example, a Schottky barrier diode.

[0016] like Figure 1 As shown in , the semiconductor device 1 includes a semiconductor portion 10 , a first electrode 20 , a second electrode 30 , and an insulating film 40 .

[0017] The semiconductor portion 10 includes, for example, a semiconductor substrate 11 of a first conductivity type and a first semiconductor layer 13 of the first conductivity type. The semiconductor substrate 11 is, for example, an n-type silicon carbide (SiC) substrate. The first semiconductor layer 13 is, for example, an n-type SiC layer or an n-type gallium nitride (GaN) layer. The first semiconductor layer 13 is epitaxially grown on the semiconductor substrate 11. In the following description, the first conductivity type is set to be n-type and the second conductivity type is set to be p-type.

[0018] The semiconductor portion 10 has a surface and a back surface on the opposite side thereof. The first electrode 20 is provided on the back surface of the semiconductor portion 10. The second electrode 30 is provided on the surface of the semiconductor portion 10. The semiconductor substrate 11 is located between the first semiconductor layer 13 and the first electrode 20. The first semiconductor layer 13 is located between the semiconductor substrate 11 and the second electrode 30. The first electrode 20 is, for example, a metal layer containing gold (Au) or aluminum (Al).

[0019] The second electrode 30 includes, for example, a barrier layer 31 and a metal layer 33. The barrier layer 31 is in contact with the first semiconductor layer 13 and includes, for example, vanadium (V) as a main component. The metal layer 33 is provided on the barrier layer 31 and includes, for example, molybdenum (Mo) or aluminum (Al).

[0020] The barrier layer 31 is Schottky-connected to the first semiconductor layer 13. The barrier layer 31 includes, for example, at least one of a group consisting of metal vanadium (V), vanadium nitride (VN), silicon vanadium (SiV), aluminum vanadium (AlV), and vanadium carbide (VC). The barrier layer 31 is formed, for example, by sputtering. Here, silicon vanadium (SiV) is vanadium silicide or an alloy of silicon and vanadium. In addition, aluminum vanadium is an alloy of aluminum and vanadium.

[0021] The metal vanadium is formed, for example, by a sputtering method using a target containing vanadium with a purity of 99.9 wt % or more. The metal vanadium contains, for example, iron, chromium, nickel, etc. as impurities in an amount of 0.1 wt % or less.

[0022] Vanadium nitride is formed, for example, by a reactive sputtering method using a target containing vanadium with a purity of 99.9 wt % or more. Vanadium nitride contains, for example, iron, chromium, nickel, etc., or nitrides thereof as impurities.

[0023] Silicon vanadium (SiV) is formed by sputtering using a target containing vanadium silicide with a purity of 99.9 wt % or more, for example. Also, vanadium carbide (VC) is formed by sputtering using a target containing vanadium carbide with a purity of 99 wt % or more, for example.

[0024] The barrier layer 31 is not limited to the above-mentioned example, and may include, for example, an alloy layer of metal vanadium and the first semiconductor layer 13 .

[0025] The insulating film 40 is provided on the surface of the semiconductor portion 10. The insulating film 40 is, for example, a silicon oxide film, formed using CVD (Chemical Vapor Deposition). The second electrode 30 is connected to the first semiconductor layer 13 via a contact hole provided in the insulating film 40. The barrier layer 31 is in contact with the first semiconductor layer 13 exposed to the bottom surface of the contact hole.

[0026] Figure 2 It is a graph showing the characteristics of the semiconductor device 1 according to the first embodiment. Figure 2 (a) is a graph showing the forward characteristics of the semiconductor device 1 . Figure 2 (b) is a graph showing the relationship between the forward voltage VF and the reverse current IR.

[0027] Figure 2 (a) and (b) show characteristics EB of the semiconductor device 1 and characteristics CE of the semiconductor device of the comparative example. The barrier layer 31 of the semiconductor device 1 contains metal vanadium. The barrier layer of the semiconductor device of the comparative example contains titanium (Ti).

[0028] Figure 2 The horizontal axis of (a) is the forward voltage VF, and the vertical axis is the forward current IF.

[0029] like Figure 2 As shown in (a), the forward voltage VF of the semiconductor device 1 is lower than the forward voltage VF of the semiconductor device of the comparative example.

[0030] Figure 2 (b) The horizontal axis is the forward voltage VF, and the vertical axis is the reverse current IR.

[0031] like Figure 2As shown in (a) and (b), in the semiconductor device 1, by using the barrier layer 31 containing metal vanadium, the forward voltage VF can be reduced compared with the semiconductor device of the comparative example.

[0032] However, it is known that the reverse current IR increases in the semiconductor device 1. In order to further improve the current / voltage characteristics of the semiconductor device 1, it is preferable to reduce the reverse current IR.

[0033] Figure 3 (a) to (c) are schematic cross-sectional views showing electrode structures of the semiconductor device 1 according to a modification of the first embodiment. Figure 3 As shown in (a) to (c), the barrier layer 31 may have a stacked structure including at least two layers.

[0034] like Figure 3 As shown in (a), the barrier layer 31 includes a first layer 31a and a second layer 31b. The first layer 31a is provided so as to be in contact with the first semiconductor layer 13. The second layer 31b is provided between the first layer 31a and the metal layer 33. The first layer 31a includes, for example, vanadium nitride (VN). The second layer 31b includes, for example, metal vanadium (V).

[0035] like Figure 3 As shown in (b), the barrier layer 31 includes a first layer 31c and a second layer 31b. The first layer 31c is provided in contact with the first semiconductor layer 13. The second layer 31b is provided between the first layer 31c and the metal layer 33. The first layer 31c includes, for example, at least one of silicon vanadium (SiV) and vanadium carbide (VC). The second layer 31b includes, for example, metal vanadium (V).

[0036] like Figure 3 As shown in (c), the barrier layer 31 includes a first layer 31c and a second layer 31a. The first layer 31c is provided in contact with the first semiconductor layer 13. The second layer 31a is provided between the first layer 31c and the metal layer 33. The first layer 31c includes, for example, at least one of silicon vanadium (SiV) and vanadium carbide (VC). The second layer 31a includes, for example, vanadium nitride (VN).

[0037] In the semiconductor device 1 , for example, by using the barrier layer 31 having a single-layer structure or one of the above-mentioned stacked structures, the current / voltage characteristics can be improved.

[0038] Figure 4 It is a schematic cross-sectional view showing a semiconductor device 2 according to a modified example of the first embodiment.

[0039] The semiconductor device 2 includes a semiconductor portion 100 . The first electrode 20 is provided on the back surface of the semiconductor portion 100 . The second electrode 30 is provided on the front surface of the semiconductor portion 100 .

[0040] The semiconductor portion 100 includes a first conductivity type semiconductor substrate 11 , a first conductivity type first semiconductor layer 13 , a second conductivity type second semiconductor layer 15 , a second conductivity type third semiconductor layer 17 , and a second conductivity type fourth semiconductor layer 19 .

[0041] The second electrode 30 includes a barrier layer 31, a metal layer 33, and a contact layer 35. The second electrode 30 is provided so as to be in contact with the semiconductor portion 100 via a contact hole provided in the insulating film 40. The barrier layer 31 is provided between the semiconductor portion 100 and the metal layer 33. The contact layer 35 is provided between the semiconductor portion 100 and the barrier layer 31.

[0042] The semiconductor substrate 11 is located between the first electrode 20 and the first semiconductor layer 13 and is electrically connected to the first electrode 20. The first semiconductor layer 13 is located between the semiconductor substrate 11 and the second electrode 30.

[0043] The second semiconductor layer 15 is provided between the first semiconductor layer 13 and the second electrode 20. The second semiconductor layer 15 includes the same material as that of the first semiconductor layer 13. In addition, the second semiconductor layer 15 further includes an impurity of the second conductivity type.

[0044] The third semiconductor layer 17 is provided between the second semiconductor layer 15 and the second electrode 30. The third semiconductor layer 17 includes the same material as the first semiconductor layer 13. The third semiconductor layer 17 includes the second conductivity type impurity at a higher concentration than that of the second semiconductor layer 15.

[0045] The contact layer 35 of the second electrode 30 is provided between the third semiconductor layer 17 and the barrier layer 31. The contact layer 35 is in contact with the third semiconductor layer 17 and the barrier layer 31 and includes, for example, a material for ohmic contact. The contact layer 35 includes, for example, nickel (Ni).

[0046] The second electrode 30 is electrically connected to the third semiconductor layer 17 via the contact layer 35. Furthermore, the second electrode 30 is electrically connected to the second semiconductor layer 15 via the third semiconductor layer 17.

[0047] The second semiconductor layer 15 includes a portion provided between the first semiconductor layer 13 and the third semiconductor layer 17 and a portion in contact with the barrier layer 31 of the second electrode 30. The first semiconductor layer 13 includes an extension portion 13c extending in the second semiconductor layer 15 and in contact with the barrier layer 31 of the second electrode 30.

[0048] The first semiconductor layer 13 includes, for example, a plurality of extensions 13c. The extensions 13c of the first semiconductor layer 13 are, for example, Schottky-connected to the barrier layer 31 of the second electrode 30. The second semiconductor layer 15 includes a portion located between the extensions 13c adjacent to each other in the direction along the surface of the semiconductor portion 100 and in contact with the barrier layer 31 of the second electrode 30.

[0049] The fourth semiconductor layer 19 is provided between the first semiconductor layer 13 and the insulating film 40. The fourth semiconductor layer 19 includes the same material as the first semiconductor layer 13. The fourth semiconductor layer 19 is provided so as to surround the second semiconductor layer 15. In addition, the fourth semiconductor layer 19 is provided so as to be connected to the second semiconductor layer 15 and includes the second conductive type impurity having a higher concentration than the second conductive type impurity of the second semiconductor layer 15.

[0050] The fourth semiconductor layer 19 relaxes the electric field concentration around the second semiconductor layer 15, thereby improving the reverse withstand voltage of the semiconductor device 2. The fourth semiconductor layer 19 forms a so-called RESURF (Reduced Surface Field) structure.

[0051] In the semiconductor device 2, by providing, for example, a Schottky junction and a pn junction between the semiconductor portion 100 and the second electrode 30, the forward voltage VF can be reduced and the reverse current IR can be reduced. That is, the forward voltage VF becomes a value lower than the built-in voltage of the pn junction. On the other hand, when a reverse voltage is applied between the first electrode 20 and the second electrode 30, the action of the pn junction becomes dominant, and the reverse current can be reduced.

[0052] Furthermore, by using a material containing vanadium (V) as a main component for the barrier layer 31 of the second electrode 30, the forward voltage VF can be reduced. In addition, when a reverse voltage is applied between the first electrode 20 and the second electrode 30, the extension 13c of the first semiconductor layer 13 is depleted by the depletion layer extending from the pn junction at a low bias. Therefore, the electric field of the pn junction becomes higher than the electric field of the Schottky junction. Thus, the increase in the reverse current of the semiconductor device 2 caused by the reverse current IR of the Schottky junction can be suppressed.

[0053] In addition, in the semiconductor device 2, an increase in the reverse current IR when metal vanadium is used in the barrier layer 31 of the second electrode 30 can be prevented (see Figure 2 (b)). As a result, the current / voltage characteristics of the semiconductor device 2 can be improved.

[0054] (Second embodiment)

[0055] Figure 5 It is a schematic cross-sectional view showing a semiconductor device 3 according to the second embodiment. Figure 5It has a structure in which a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a Schottky barrier diode are integrated.

[0056] The semiconductor device 3 includes a semiconductor portion 200. The first electrode 20 is provided on the back surface of the semiconductor portion 200. The second electrode 30 is provided on the surface of the semiconductor portion 200. The first electrode 20 serves as a drain electrode and a cathode electrode, for example. The second electrode 30 serves as a source electrode and an anode electrode, for example.

[0057] The semiconductor device 3 further includes a control electrode 50. The control electrode 50 is provided on the surface of the semiconductor portion 200, for example, via a gate insulating film 51. The control electrode 50 is provided between the second electrode 30 and the semiconductor portion 200. The control electrode 50 is electrically insulated from the second electrode 30 by an interlayer insulating film 53, for example.

[0058] The semiconductor portion 200 includes a first conductivity type semiconductor substrate 11 , a first conductivity type first semiconductor layer 13 , a second conductivity type second semiconductor layer 15 , a second conductivity type third semiconductor layer 17 , a first conductivity type fifth semiconductor layer 21 , and a first conductivity type sixth semiconductor layer 23 .

[0059] The semiconductor substrate 11 is located between the first electrode 20 and the first semiconductor layer 13, and is electrically connected to the first electrode 20. The first semiconductor layer 13 is located between the semiconductor substrate 11 and the second electrode 30. The semiconductor substrate 11 contains a first conductive type impurity having a higher concentration than the first conductive type impurity of the first semiconductor layer 13. The first semiconductor layer 13 is, for example, an n-type drift layer.

[0060] The second semiconductor layer 15 is provided between the first semiconductor layer 13 and the second electrode 20. The second semiconductor layer 15 includes the same material as the first semiconductor layer 13. In addition, the second semiconductor layer 15 further includes second conductivity type impurities. The second semiconductor layer 15 is, for example, a p-type diffusion layer.

[0061] The third semiconductor layer 17 is provided between the second semiconductor layer 15 and the second electrode 30. The third semiconductor layer 17 includes the same material as the first semiconductor layer 13. The third semiconductor layer 17 includes the second conductivity type impurity at a higher concentration than that of the second semiconductor layer 15.

[0062] The third semiconductor layer 17 is, for example, a p-type contact layer. The third semiconductor layer 17 is electrically connected to the second electrode 30. The second semiconductor layer 15 is electrically connected to the second electrode 30 via the third semiconductor layer 17.

[0063] The fifth semiconductor layer 21 is provided between the second semiconductor layer 15 and the second electrode 30. The fifth semiconductor layer 21 includes the same material as that of the first semiconductor layer 13.

[0064] The sixth semiconductor layer 23 is provided between the second semiconductor layer 15 and the second electrode 30. The sixth semiconductor layer 23 includes the same material as that of the first semiconductor layer 13.

[0065] The third semiconductor layer 17, the fifth semiconductor layer 21, and the sixth semiconductor layer 23 are arranged between the second semiconductor layer 15 and the second electrode 30, for example, along the surface of the semiconductor portion 200. The third semiconductor layer 17 is provided between the fifth semiconductor layer 21 and the sixth semiconductor layer 23. In addition, the fifth semiconductor layer 21 is electrically connected to the second electrode 30.

[0066] like Figure 5 As shown in , a plurality of second semiconductor layers 15 are provided along the surface of the semiconductor portion 200. The plurality of second semiconductor layers 15 are provided separately from each other. The first semiconductor layer 13 includes a first portion 13a extending between two adjacent second semiconductor layers 15, and a second portion 13b extending between another two adjacent second semiconductor layers 15. In addition, the second semiconductor layer 15 includes a channel portion 15c, and the first portion 13a of the first semiconductor layer 13 and the channel portion 15c of the second semiconductor layer 15 are arranged along the surface of the semiconductor portion 200.

[0067] The control electrode 50 is provided in a manner opposite to the first portion 13a of the first semiconductor layer 13 and the channel portion 15c of the second semiconductor layer 15 via the gate insulating film 51. In addition, the fifth semiconductor layer 21 is provided in a manner opposite to the first portion 13a of the first semiconductor layer 13 via the channel portion 15c of the second semiconductor layer 15. That is, the first portion 13a of the first semiconductor layer 13, the channel portion 15c of the second semiconductor layer 15, and the fifth semiconductor layer 21 are arranged along the surface of the semiconductor portion 200. In this way, the MOS gate structure is composed of the first portion 13a of the first semiconductor layer 13, the channel portion 15c of the second semiconductor layer 15, the fifth semiconductor layer 21, the control electrode 50, and the gate insulating film 51.

[0068] The barrier layer 31 is provided so as to be in contact with the second portion 13 b of the first semiconductor layer 13. In addition, the barrier layer 31 is provided so as to be in contact with a portion of the second semiconductor layer 15 located between the second portion 13 b of the first semiconductor layer 13 and the third semiconductor layer 17.

[0069] The second electrode 30 includes a barrier layer 31 and a metal layer 37. The barrier layer 31 is provided between the second portion 13b of the first semiconductor layer 13 and the metal layer 37. The metal layer 37 covers the surface side of the semiconductor portion 200, for example, and is in contact with the third semiconductor layer 17, the fifth semiconductor layer 21, and the barrier layer 31. The metal layer 37 is electrically connected to the third semiconductor layer 17, the fifth semiconductor layer 21, and the barrier layer 31. In addition, the control electrode 50 is electrically insulated from the metal layer 37 by the interlayer insulating film 53.

[0070] The barrier layer 31 is, for example, a metal layer containing vanadium as a main component, and is in contact with the second portion 13b of the first semiconductor layer 13. The barrier layer 31 is, for example, in Schottky contact with the first semiconductor layer 13. The barrier layer 31 includes, for example, at least one of the group consisting of metal vanadium (V), vanadium nitride (VN), silicon vanadium (SiV), aluminum vanadium (AlV), and vanadium carbide (VC).

[0071] As described above, the semiconductor device 3 has a structure in which a MOS gate structure and a Schottky junction are integrated on the surface of the semiconductor portion 200. In addition, the barrier layer 31 having vanadium as a main component can achieve a low VF of the Schottky junction. As a result, the forward current density of the Schottky junction can be increased, and the area occupied by the Schottky junction on the surface of the semiconductor portion 200 can be reduced.

[0072] It should be noted that the first and second embodiments are examples, and the present invention is not limited to these examples. For example, the materials of the semiconductor substrate 11 and the first semiconductor layer 13 are not limited to silicon carbide (SiC) and gallium nitride (GaN), and may also be nitride semiconductors other than gallium nitride, or oxide semiconductors such as gallium oxide. Figure 5 In the example shown in , the MOS gate structures and the Schottky junctions are arranged alternately, but the embodiment is not limited to this. For example, a plurality of MOS gate structures may be provided between two adjacent Schottky junctions.

[0073] Several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the subject matter of the invention. These embodiments and their variations are included in the scope and subject matter of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. A semiconductor device comprising: a semiconductor portion including a first semiconductor layer of a first conductivity type; a first electrode provided on the back surface of the semiconductor portion; and a second electrode disposed on the surface of the semiconductor portion, the second electrode comprising a barrier layer and a metal layer, the barrier layer being in contact with the first semiconductor layer and comprising vanadium or a vanadium compound as a main component, the metal layer being disposed on the barrier layer, The barrier layer comprises a first layer and a second layer, The first layer is provided in contact with the first semiconductor layer and includes at least one of silicon vanadium and vanadium carbide. The second layer is disposed between the first layer and the metal layer, and includes metal vanadium or vanadium nitride.

2. The semiconductor device according to claim 1, in, The first semiconductor layer is a silicon carbide layer.

3. The semiconductor device according to claim 1, in, The first semiconductor layer is a gallium nitride layer.

4. The semiconductor device according to claim 1, in, The semiconductor portion includes a nitride semiconductor or an oxide semiconductor.

5. The semiconductor device according to claim 1, in, The semiconductor portion further includes a second semiconductor layer of a second conductivity type provided between the first semiconductor layer and the second electrode. The first semiconductor layer has a portion extending in the second semiconductor layer and in contact with the barrier layer of the second electrode.

6. The semiconductor device according to claim 5, in, The second electrode further includes a contact layer that is in contact with and electrically connected to the second semiconductor layer.

7. The semiconductor device according to claim 6, in, The barrier layer includes a first portion in contact with the first semiconductor layer and a second portion provided between the contact layer and the metal layer.

8. The semiconductor device according to claim 7, in, The semiconductor portion further includes a third semiconductor layer of the second conductivity type and a fourth semiconductor layer of the second conductivity type. The third semiconductor layer is provided between the second semiconductor layer and the contact layer of the second electrode, The fourth semiconductor layer surrounds the second semiconductor layer along the surface of the semiconductor portion, The third semiconductor layer and the fourth semiconductor layer each contain a second conductivity type impurity having a higher concentration than the second conductivity type impurity concentration of the second semiconductor layer. The contact layer of the second electrode is electrically connected to the second semiconductor layer via the third semiconductor layer.

9. The semiconductor device according to claim 8, in, The fourth semiconductor layer is provided so as to cover the outer edge of the second semiconductor layer.

10. The semiconductor device according to claim 5, further comprising a control electrode, the control electrode being provided on the surface side of the semiconductor portion, the control electrode being provided separately from the barrier layer of the second electrode, being electrically insulated from the semiconductor portion by a first insulating film, and being opposed to a portion of the first semiconductor layer via the first insulating film, The semiconductor portion further includes a second semiconductor layer of the second conductivity type and a fifth semiconductor layer of the first conductivity type. The second semiconductor layer includes a portion provided between the first semiconductor layer and the second electrode and facing the control electrode via the first insulating film. The fifth semiconductor layer is provided between the second semiconductor layer and the second electrode, is in contact with the first insulating film, and is electrically connected to the metal layer of the second electrode.

11. The semiconductor device according to claim 10, in, The second electrode is arranged so as to cover the control electrode. The control electrode is electrically insulated from the second electrode by a second insulating film provided between the second electrode and the control electrode.

12. The semiconductor device according to claim 10, in, The semiconductor portion further includes a third semiconductor layer of the second conductivity type. The third semiconductor layer is provided between the second semiconductor layer and the second electrode, and contains a second conductivity type impurity having a higher concentration than a second conductivity type impurity in the second semiconductor layer. The metal layer of the second electrode is electrically connected to the third semiconductor layer between the barrier layer and the control electrode.

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