Junction barrier Schottky diode and method for manufacturing the same

Abstract

To provide a junction barrier Schottky diode with a trench structure that has an excellent surge resistance and a suppressed energy loss in switching operations, and to provide a method of manufacturing the same.SOLUTION: Provided is a junction barrier Schottky diode 1 that comprises: an n-type semiconductor layer 11 with a plurality of trenches 111; a p-type semiconductor film 12 provided in contact with inner surfaces of the plurality of trenches 111; an anode electrode 13 provided on a first surface 113 of the n-type semiconductor layer 11 so as to be in contact with mesa shape parts 112 of the n-type semiconductor layer 11, being partially covered with the p-type semiconductor film 12 in the plurality of trenches 111; and a cathode electrode 14 provided on a second surface 114 of the n-type semiconductor layer 11 directly or via other layers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a junction barrier Schottky diode and a method for manufacturing the same. [Background technology]

[0002] Conventionally, a trench-type junction barrier Schottky (JBS) diode is known, comprising: an n-type semiconductor layer formed on an n-type semiconductor substrate, having a trench opening on the side opposite to the n-type semiconductor substrate; a p-type semiconductor layer embedded in the trench of the n-type semiconductor layer; an anode electrode formed on the n-type semiconductor layer so as to be in contact with the p-type semiconductor layer; and a cathode electrode formed on the side of the n-type semiconductor substrate opposite to the n-type semiconductor layer (see Patent Document 1).

[0003] According to the trench-type JBS diode described in Patent Document 1, when a reverse voltage is applied between the anode electrode and the cathode electrode, no current flows due to the Schottky barrier. At this time, the depletion layer expands from the p-type semiconductor layer, and the channels between adjacent p-type semiconductor layers close, effectively suppressing leakage current. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-36593 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in the trench-type JBS diode described in Patent Document 1, the p-type semiconductor layer is embedded throughout the entire trench, resulting in high electrical resistance of the p-type semiconductor layer. This can lead to significant heat generation when a surge current occurs, potentially damaging the connection points around the p-type semiconductor layer. In other words, it can result in low surge resistance. Furthermore, high electrical resistance of the p-type semiconductor layer can hinder the movement of charge necessary for charging and discharging to form and eliminate the depletion region near the pn junction, potentially leading to increased energy loss during switching operation.

[0006] The object of the present invention is to provide a junction barrier Schottky diode with a trench structure that has excellent surge resistance and suppresses energy loss during switching operation, and a method for manufacturing the same. [Means for solving the problem]

[0007] One aspect of the present invention, in order to achieve the above objective, Note Junction barrier Schottky diode, and Biji This invention provides a method for producing a junction barrier Schottky oxide.

[0008] [1] An n-type semiconductor layer made of an n-type semiconductor having a plurality of trenches opening to a first surface; a p-type semiconductor film made of a p-type semiconductor provided in contact with the inner surfaces of the plurality of trenches; an anode electrode provided on the first surface of the n-type semiconductor layer in contact with the mesa-shaped portions between the plurality of trenches of the n-type semiconductor layer, with a portion thereof covered by the p-type semiconductor film within the plurality of trenches; and a cathode electrode provided directly or via another layer on a second surface of the n-type semiconductor layer opposite to the first surface, The upper surface of the mesa-shaped portion is in contact with the anode electrode over its entire width. The electron affinity χ of the aforementioned p-type semiconductor p and work function φ p , and the electron affinity χ of the n-type semiconductor n and work function φ n However, χ n -χ p >φ p -φ nA junction barrier Schottky diode that satisfies the conditions represented by the formula. [2] The junction barrier Schottky diode according to [1], wherein the n-type semiconductor layer and the p-type semiconductor film are made of different semiconductors. [3] The junction barrier Schottky diode according to [2], wherein the n-type semiconductor layer is made of a gallium oxide-based semiconductor. [4] The junction barrier Schottky diode according to any one of [1] to [3], wherein the p-type semiconductor contains Cu2O, NiO, Ag2O, polycrystalline Si, single crystal Si, amorphous Si, SnO, or CuO. [5] The junction barrier Schottky diode according to any one of the above [1] to [3], wherein the upper end of the p-type semiconductor film is lower than the first surface. [6] The junction barrier Schottky diode according to any one of the above [1] to [3], wherein the p-type semiconductor film is composed of a first p-type semiconductor film in contact with the inner surface of the trench and a second p-type semiconductor film laminated inside it, and the impurity concentration of the second p-type semiconductor film is higher than the impurity concentration of the first p-type semiconductor film. [7] A step of forming a plurality of trenches on a first surface of an n-type semiconductor layer made of an n-type semiconductor, a step of forming a p-type semiconductor film made of a p-type semiconductor that contacts the inner surfaces of the plurality of trenches, and on the first surface of the n-type semiconductor layer, The mesa-shaped portion between the plurality of trenches in the n-type semiconductor layer is in contact with the n-type semiconductor layer. A step of forming an anode electrode, a part of which is covered by the p-type semiconductor film in the plurality of trenches, and a step of forming a cathode electrode directly or through another layer on a second surface opposite to the first surface of the n-type semiconductor layer, and The upper surface of the mesa-shaped portion is in contact with the anode electrode over its entire width. the electron affinity χ of the p-type semiconductor p and the work function φ p , and the electron affinity χ of the n-type semiconductor n and the work function φ n satisfy the condition represented by the formula χ n -χ p >φ p -φ n A method for manufacturing a junction barrier Schottky diode. [8] A method for manufacturing a junction barrier Schottky diode according to [7], wherein the upper end of the p-type semiconductor film is lower than the first surface. [9] The method for manufacturing a junction barrier Schottky diode according to [7] above, wherein the p-type semiconductor film is composed of a first p-type semiconductor film in contact with the inner surface of the trench and a second p-type semiconductor film laminated inside it, and the impurity concentration of the second p-type semiconductor film is higher than the impurity concentration of the first p-type semiconductor film. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a junction barrier Schottky diode with a trench structure that has excellent surge resistance and suppresses energy loss during switching operation, as well as a method for manufacturing the same. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a vertical cross-sectional view of a junction barrier Schottky (JBS) diode according to an embodiment of the present invention. [Figure 2] Figures 2(a) and (b) are vertical cross-sectional views of a JBS diode showing a modified p-type semiconductor film. [Figure 3] Figures 3(a) and (b) are vertical cross-sectional views of a JBS diode showing other variations of the p-type semiconductor film. [Figure 4] Figures 4(a) to 4(c) are vertical cross-sectional views illustrating the manufacturing process of the JBS diode according to this embodiment. [Figure 5] Figures 5(a) to 5(c) are vertical cross-sectional views illustrating the manufacturing process of the JBS diode according to this embodiment. [Figure 6] Figures 6(a) and 6(b) are vertical cross-sectional views illustrating the manufacturing process of a JBS diode according to this embodiment. [Modes for carrying out the invention]

[0011] [Embodiment] (JBS diode configuration) Figure 1 is a vertical cross-sectional view of a junction barrier Schottky (JBS) diode 1 according to an embodiment of the present invention. The JBS diode 1 is a vertical JBS diode having a trench structure.

[0012] The JBS diode 1 comprises an n-type semiconductor layer 11 having a plurality of trenches 111 opening to a first surface 113, a p-type semiconductor film 12 provided in contact with the inner surface of the trenches 111 of the n-type semiconductor layer 11, an anode electrode 13 provided on the first surface 113 of the n-type semiconductor layer 11 in contact with the mesa-shaped portions 112 between the plurality of trenches 111 of the n-type semiconductor layer 11, with a portion 132 of the anode electrode 13 being covered by the p-type semiconductor film 12 within the plurality of trenches, and a cathode electrode 14 provided directly or via another layer on a second surface 114 opposite to the first surface 113 of the n-type semiconductor layer 11.

[0013] Typically, the JBS diode 1 comprises an n-type semiconductor substrate 10 as a base for the epitaxial growth of an n-type semiconductor layer 11, as shown in Figure 1, with a second surface 114 of the n-type semiconductor layer 11 in contact with the n-type semiconductor substrate 10. In this case, the cathode electrode 14 is provided on the surface of the n-type semiconductor substrate 10 opposite to the n-type semiconductor layer 11. That is, the cathode electrode 14 is provided on the second surface 114 of the n-type semiconductor layer 11 via the n-type semiconductor substrate 10.

[0014] The n-type semiconductor layer 11 and the anode electrode 13 form a Schottky junction, and the JBS diode 1 utilizes the rectifying properties of this Schottky junction. In the JBS diode 1, by applying a forward voltage (positive potential on the anode electrode 13 side) between the anode electrode 13 and the cathode electrode 14, the potential barrier at the interface between the anode electrode 13 and the n-type semiconductor layer 11 as seen from the n-type semiconductor layer 11 decreases, and current flows from the anode electrode 13 to the cathode electrode 14.

[0015] On the other hand, when a reverse voltage (negative potential on the anode electrode 13 side) is applied between the anode electrode 13 and the cathode electrode 14, no current flows due to the Schottky barrier. At this time, a depletion layer spreads from the p-type semiconductor film 12 in the trench 111, and a channel closes in the mesa-shaped portion 112 between adjacent trenches 111, thus effectively suppressing leakage current.

[0016] Since the JBS diode 1 according to this embodiment has a trench-type JBS structure, a high breakdown voltage can be obtained without increasing the resistance of the n-type semiconductor layer 11. That is, the JBS diode 1 is a Schottky barrier diode with high breakdown voltage and low loss.

[0017] The n-type semiconductor substrate 10 is made of a single crystal of an n-type gallium oxide-based semiconductor containing group IV elements such as Si and Sn as donors. The donor concentration of the n-type semiconductor substrate 10 is, for example, 1.0×10 16 cm -3 or more and 1.0×10 22 cm -3 or less, preferably 1.0×10 18 cm -3 or more and 1.0×10 22 cm -3 or less. The thickness of the n-type semiconductor substrate 10 is, for example, 5 μm or more and 650 μm or less.

[0018] Here, the gallium oxide-based semiconductor is Ga2O3, or Ga2O3 to which one or both of Al and In are added, and has a composition represented by (Ga x Al y In (1-x-y) )2O3 (0 < x ≦ 1, 0 ≦ y < 1, 0 < x + y ≦ 1). When Al is added to Ga2O3, the band gap widens, and when In is added, the band gap narrows. The single crystal of the above gallium oxide-based semiconductor typically has a β-type crystal structure. For example, the band gap energy of Ga2O3, which is a typical example of the gallium oxide-based semiconductor, is 4.5 to 4.9 eV, and the dielectric breakdown field strength is about 8.0 MV / cm.

[0019] The n-type semiconductor layer 11 is made of a single crystal of an n-type gallium oxide-based semiconductor containing group IV elements such as Si and Sn as donors. The donor concentration of the n-type semiconductor layer 11 is lower than that of the n-type semiconductor substrate 10. The n-type semiconductor layer 11 is, for example, an epitaxial layer epitaxially grown on the n-type semiconductor substrate 10.

[0020] Furthermore, a high-donor-concentration layer containing a high concentration of donors may be formed between the n-type semiconductor substrate 10 and the n-type semiconductor layer 11. This high-donor-concentration layer is used, for example, when epitaxially growing the n-type semiconductor layer 11 on the n-type semiconductor substrate 10. In the initial stages of growth of the n-type semiconductor layer 11, the amount of dopant uptake may be unstable, or acceptor impurities may diffuse from the n-type semiconductor substrate 10. Therefore, if the n-type semiconductor layer 11 is grown directly on the n-type semiconductor substrate 10, the region of the n-type semiconductor layer 11 near the interface with the n-type semiconductor substrate 10 may become highly resistive. To avoid such problems, a high-donor-concentration layer is used. The donor concentration of the high-donor-concentration layer is set, for example, higher than the donor concentration of the n-type semiconductor layer 11, and more preferably, 10 times or more the donor concentration of the n-type semiconductor layer 11.

[0021] As the donor concentration of the n-type semiconductor layer 11 increases, the electric field strength of each part of the JBS diode 1 increases. The donor concentration of the n-type semiconductor layer 11 is, for example, 2 × 10⁻⁶. 14 cm -3 The above and 4 × 10 17 cm -3 The following applies. Furthermore, in order for the JBS diode 1 to achieve a breakdown voltage of 400V or more, the donor concentration of the n-type semiconductor layer 11 must be 4 × 10 17 cm -3 The following is preferable: 8 × 10 15 cm -3 The above and 4 × 10 17 cm -3 The following is more preferable:

[0022] Furthermore, for JBS diode 1 to withstand a voltage of 600V or more, 2 × 10 17 cm -3 The following is preferable: 4 × 10 15 cm -3 The above and 2 × 10 17 cm -3 The following is more preferable: In order for the JBS diode 1 to obtain a breakdown voltage of 1200V or more, the donor concentration of the n-type semiconductor layer 11 should be 1 × 10⁻⁶ 17 cm -3 The following is preferable: 2 × 1015 cm -3 The above and 1 × 10 17 cm -3 The following is more preferable:

[0023] For the JBS diode 1 to achieve a breakdown voltage of 2200V or higher, the donor concentration of the n-type semiconductor layer 11 must be 8 × 10 16 cm -3 Preferably, it is 1.6 × 10 15 cm -3 The above and 8 x 10 16 cm -3 The following is more preferable: In order for the JBS diode 1 to withstand voltage of 3300V or more, the donor concentration of the n-type semiconductor layer 11 should be 5 × 10 16 cm -3 The following is preferable: 1 × 10 15 cm -3 The above and 5 x 10 16 cm -3 The following is more preferable:

[0024] For the JBS diode 1 to achieve a breakdown voltage of 5000V or more, the donor concentration of the n-type semiconductor layer 11 must be 3 × 10⁻¹⁰ 16 cm -3 The following is preferable: 6 × 10 14 cm -3 The above and 3 × 10 16 cm -3 The following is more preferable: For the JBS diode 1 to obtain a breakdown voltage of 10,000V or more, the donor concentration of the n-type semiconductor layer 11 should be 1 × 10⁻⁶ 16 cm -3 The following is preferable: 2 × 10 14 cm -3 The above and 1 × 10 16 cm -3 The following is more preferable:

[0025] When the thickness T of the n-type semiconductor layer 11 is designed such that the electric field generated in each part when a reverse voltage equal to the design breakdown voltage is applied to the JBS diode 1 is smaller than the dielectric breakdown electric field, the deeper the trench 111 D is, the more the electric field at the Schottky interface between the anode electrode 13 and the first surface 113 can be reduced when a reverse voltage is applied. On the other hand, if the depth D of the trench 111 is too deep, the electrical resistance between the anode electrode 13 and the cathode electrode 14 of the JBS diode 1 increases. For this reason, the depth D of the trench 111 is preferably 0.5 μm or more and 5 μm or less.

[0026] The thickness T of the n-type semiconductor layer 11 is, for example, a value obtained by adding 0.5 to 110 μm to the depth D of the trench 111 measured from the first surface 113. In order for the JBS diode 1 to obtain a breakdown voltage of 400 V or more, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 0.6 to 9 μm to the depth D of the trench 111, and more preferably a value obtained by adding 0.6 to 6 μm.

[0027] Furthermore, in order for the JBS diode 1 to achieve a breakdown voltage of 600V or higher, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 0.8 to 11 μm to the depth D of the trench 111, and more preferably a value obtained by adding 0.8 to 7 μm. In order for the JBS diode 1 to achieve a breakdown voltage of 1200V or higher, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 1.5 to 20 μm to the depth D of the trench 111, and more preferably a value obtained by adding 1.5 to 12 μm.

[0028] In order for the JBS diode 1 to achieve a breakdown voltage of 2200V or higher, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 4 to 40 μm to the depth D of the trench 111, and more preferably a value obtained by adding 4 to 25 μm. In order for the JBS diode 1 to achieve a breakdown voltage of 3300V or higher, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 5 to 50 μm to the depth D of the trench 111, and more preferably a value obtained by adding 5 to 30 μm.

[0029] For the JBS diode 1 to achieve a breakdown voltage of 5000V or more, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 7 to 90 μm to the depth D of the trench 111, and more preferably a value obtained by adding 7 to 55 μm. For the JBS diode 1 to achieve a breakdown voltage of 10000V or more, the thickness T of the n-type semiconductor layer 11 is preferably a value obtained by adding 12 to 180 μm to the depth D of the trench 111, and more preferably a value obtained by adding 12 to 110 μm.

[0030] Trench 111 width W t While a narrower gap reduces conductivity loss, it also increases manufacturing difficulty, which in turn lowers the manufacturing yield. Therefore, a gap of 0.3 μm or more and 5 μm or less is preferable.

[0031] Width W of the mesa-shaped portion 112 between adjacent trenches 111 in the n-type semiconductor layer 11 m The greater the reduction in the field strength, the greater the reduction in the field strength directly below the anode electrode 13 in the mesa-shaped portion 112 and the field strength at the junction between the n-type semiconductor layer 11 and the p-type semiconductor film 12. In order to effectively reduce these field strengths, the width W of the mesa-shaped portion 112 is reduced. m It is preferable that the width is 5 μm or less. On the other hand, the width W of the mesa-shaped portion 112 m The smaller the width W of the mesa-shaped section 112, the more difficult it is to manufacture the trench 111. m It is preferable that the particle size is 0.25 μm or larger.

[0032] The anode electrode 13 includes an outer portion 131 of the trench 111 and an inner portion 132 of the trench 111. The portion of the anode electrode 13 that contacts the n-type semiconductor layer 11 is made of a material that forms a Schottky junction with the n-type semiconductor layer 11. That is, if the anode electrode 13 has a single-layer structure, the entire anode electrode 13 is made of a material that forms a Schottky junction with the n-type semiconductor layer 11, and if it has a multilayer structure, at least the layer that contacts the n-type semiconductor layer 11 is made of a material that forms a Schottky junction with the n-type semiconductor layer 11.

[0033] As the material for the portion of the anode electrode 13 that contacts the n-type semiconductor layer 11, for example, Pt, Ni, Au, Cu, Mo, W, Fe, Pd, or Cr can be used to form a Schottky junction with the n-type semiconductor layer 11, which is made of a gallium oxide-based semiconductor.

[0034] For example, if the n-type semiconductor layer 11 is made of Ga2O3, and Pt or Ni is used as the material for the anode electrode 13, the rise voltage of the JBS diode 1 will be 0.7V or higher and 1.2V or lower, and if Mo is used as the material for the anode electrode 13, the rise voltage of the JBS diode 1 will be 0.3V or higher and 0.8V or lower.

[0035] In the JBS diode 1, a potential barrier is formed in the mesa-shaped portion 112, so the rise voltage is the width W of the mesa-shaped portion 112. m Depends on width W m The smaller it gets, the larger it becomes.

[0036] The electric field strength in the JBS diode 1 is determined by the width W of the mesa-shaped portion 112 between two adjacent trenches 111, as described above. m Although it is affected by the depth D of the trench 111, it is hardly affected by the planar pattern of the trench 111. For this reason, the planar pattern of the trench 111 of the n-type semiconductor layer 11 is not particularly limited. Also, if the planar pattern of the trench 111 is a planar pattern (for example, a mesh pattern) that forms a mesa-shaped portion 112, then multiple trenches 111 may be included in a single continuous trench.

[0037] The cathode electrode 14 makes ohmic contact with the n-type semiconductor substrate 10 when the JBS diode 1 includes an n-type semiconductor substrate 10. The cathode electrode 14 is made of a metal such as Ti. The cathode electrode 14 may have a multilayer structure in which different metal films are stacked, for example, Ti / Au, Ti / Al, Ti / Ni / Au, or Ti / Al / Ni / Au. To ensure reliable ohmic contact between the cathode electrode 14 and the n-type semiconductor substrate 10, it is preferable that the layer of the cathode electrode 14 that contacts the n-type semiconductor substrate 10 is made of Ti. If the JBS diode 1 does not include an n-type semiconductor substrate 10 and the cathode electrode 14 is directly connected to the n-type semiconductor layer 11, it will make ohmic contact with the n-type semiconductor layer 11.

[0038] The p-type semiconductor film 12 is used to improve the surge resistance of the JBS diode 1. The p-type semiconductor film 12 is a deposited film formed by sputtering, CVD, or other deposition methods, and is not a region formed as part of the n-type semiconductor layer 11 by impurity implantation on the inner surface of the trench 111 using ion implantation.

[0039] Typically, pn diodes have a higher on-voltage (forward rise voltage) than Schottky diodes. Therefore, it is possible to design the circuit so that the pn diode portion (the pn junction between the p-type semiconductor film 12 and the n-type semiconductor layer 11) does not turn on at the voltage at which the JBS diode 1 turns on. For example, the on-voltage of the JBS diode 1 can be set to about 1V, and the on-voltage of the pn diode portion can be set to about 2V.

[0040] As a result, the pn diode portion of the JBS diode 1 does not turn on during normal operation, enabling the high-speed operation inherent to Schottky diodes. On the other hand, when an inrush current occurs, the voltage of the JBS diode 1 rises to the voltage at which the pn diode portion turns on, and current is injected from the p-type semiconductor film 12 to the n-type semiconductor layer 11.

[0041] At that time, the resistance of the drift layer decreases, and a large current called the inrush current flows through the JBS diode 1. However, since the increase in voltage is suppressed, the temperature rise is suppressed, and damage to the JBS diode 1 due to the inrush current can be prevented.

[0042] Since the p-type semiconductor film 12 is in a film shape, compared with the p-type semiconductor layer embedded in the entire region in the trench, such as the p-type semiconductor layer included in the trench-type JBS diode described in Patent Document 1 above, the electrical resistance is small. Therefore, the heat generation when a surge current occurs is small, and damage to the connection portion around the p-type semiconductor film can be suppressed. Also, since the electrical resistance of the p-type semiconductor film 12 is small, the energy loss during the switching operation of the JBS diode 1 can be suppressed.

[0043] The p-type semiconductor film 12 is made of a material that satisfies the conditions represented by the following Equation 1 in order to form a potential barrier between the p-type semiconductor film 12 and the n-type semiconductor layer 11. χ in Equation 1 p and φ p are the electron affinity and work function of the p-type semiconductor, which is the material of the p-type semiconductor film 12, respectively, and χ n and φ n are the electron affinity and work function of the n-type semiconductor, which is the material of the n-type semiconductor layer 11, respectively. The work function described above is the energy of the Fermi level as seen from the vacuum level. For example, χ n of Ga2O3, which is a typical material of the n-type semiconductor layer 11, is approximately 4.0 eV, and φ n varies depending on the carrier concentration of the n-type semiconductor layer 11. However, in the range of carrier concentration 1×10 14 cm -3 ~1×10 19 cm -3 it is approximately 4.3~4.0 eV.

[0044]

Equation

[0045] Materials that can be used as the material for the p-type semiconductor film 12 and that satisfy the conditions represented by the above formula 1 include, for example, p-type semiconductors such as Cu2O, NiO, Ag2O, polycrystalline Si, single-crystal Si, amorphous Si, SnO, and CuO. Alternatively, a mixture containing p-type semiconductors such as Cu2O, NiO, Ag2O, polycrystalline Si, single-crystal Si, amorphous Si, SnO, and CuO in a concentration sufficient to make the p-type semiconductor film 12 p-type can also be used as the material for the p-type semiconductor film 12.

[0046] In other words, the p-type semiconductor material for the p-type semiconductor film 12 includes, for example, Cu2O, NiO, Ag2O, polycrystalline Si, single-crystal Si, amorphous Si, SnO, or CuO. Cu2O, NiO, and SnO exhibit p-type conductivity even without the addition of dopants, but they may contain acceptor impurities such as Li and nitrogen (N). Polycrystalline Si, single-crystal Si, and amorphous Si preferably contain acceptor impurities such as B and Al.

[0047] The carrier concentration of the p-type semiconductor film 12 is preferably higher than that of the n-type semiconductor layer 11 in order to prevent the thickness of the depletion layer generated at the interface with the n-type semiconductor layer 11 from increasing and reaching the anode electrode 13 when a reverse voltage is applied to the JBS diode 1.

[0048] Furthermore, the thickness d of the p-type semiconductor film 12 is preferably such that it satisfies the condition expressed in the following equation 2 in order to obtain the desired breakdown voltage of the JBS diode 1. BR This is the desired pressure resistance (design pressure resistance), N D The carrier concentration of the n-type semiconductor layer 11 is N. A ε is the carrier concentration of the p-type semiconductor film 12. n is the dielectric constant of the n-type semiconductor layer 11, and q is the elementary charge.

[0049]

number

[0050] For example, when the carrier concentration of the n-type semiconductor layer 11 made of a gallium oxide-based semiconductor is 1×10 16 cm -3 and the carrier concentration of the p-type semiconductor film 12 is 1×10 19 cm -3 if the thickness of the p-type semiconductor film 12 is 200 nm or more, the breakdown voltage of the JBS diode 1 can be set to 1200 V or more.

[0051] Figs. 2(a) and (b) are vertical cross-sectional views of the JBS diode 1 showing modified examples of the p-type semiconductor film. In the JBS diode 1, the height of the upper end of the p-type semiconductor film 12 does not have to coincide with the height of the first surface 113. That is, as shown in Fig. 2(a), the upper end of the p-type semiconductor film 12 may be higher than the first surface 113, or as shown in Fig. 2(b), the upper end of the p-type semiconductor film 12 may be lower than the first surface 113.

[0052] Figs. 3(a) and (b) are vertical cross-sectional views of the JBS diode 1 showing other modified examples of the p-type semiconductor film. As shown in Fig. 3(a), the p-type semiconductor film 12 may be composed of a p-type semiconductor film 121 in contact with the inner surface of the trench 111 and a p-type semiconductor film 122 laminated inside thereof. The impurity concentration of the p-type semiconductor film 122 is higher than the impurity concentration of the p-type semiconductor film 121. Since the carrier concentration of the p-type semiconductor film 121 in the structure shown in Fig. 3(a) can be set lower than the constraint of the carrier concentration determined by the above (Equation 2), when a reverse voltage is applied to the JBS diode 1, the electric field applied to the trench corner portions of the p-type semiconductor film 121 and the n-type semiconductor layer 11 (portions close to the curved portion at the bottom edge of the trench 111) can be made smaller than that in the structure of Fig. 1.

[0053] Furthermore, the p-type semiconductor film 122 may have a shape that covers only the bottom periphery of the inner portion 132 of the trench 111 of the anode electrode 13, as shown in Figure 3(b). In this case as well, the carrier concentration of the p-type semiconductor film 121 in the structure shown in Figure 3(a) can be set lower than the carrier concentration constraint determined by (Equation 2) above, so when a reverse voltage is applied to the JBS diode 1, the electric field applied to the trench corner portion of the p-type semiconductor film 121 and the n-type semiconductor layer 11 can be made smaller compared to the structure in Figure 1.

[0054] (Manufacturing method for JBS diodes) The following is an example of a manufacturing method for JBS diode 1.

[0055] Figures 4(a)-(c), 5(a)-(c), and 6(a)-(b) are vertical cross-sectional views illustrating the manufacturing process of the JBS diode 1 according to this embodiment. First, as shown in Figure 4(a), a single crystal of gallium oxide semiconductor with a controlled donor concentration is epitaxially grown on an n-type semiconductor substrate 10 by methods such as HVPE, CVD, or MBE to form an n-type semiconductor layer 11.

[0056] Next, as shown in Figure 4(b), a plurality of trenches 111 are formed on the first surface 113 of the n-type semiconductor layer 11 by photolithography and dry etching. Preferred conditions for dry etching used to form the trenches 111 are, for example, BCl3 (30 sccm) as the etching gas, a pressure of 1.0 Pa, an antenna power of 160 W, a bias power of 17 W, and a time of 90 minutes.

[0057] Next, as shown in Figure 4(c), a p-type semiconductor is deposited on the entire surface of the first surface 113 side of the n-type semiconductor layer 11 by sputtering, CVD, or the like to form a p-type semiconductor film 12. At this point, the p-type semiconductor film 12 covers the inner surface of the trench 111 and the first surface 113.

[0058] For example, when Cu2O is used as the material for the p-type semiconductor film 12, the method described in the non-patent document “Appl. Phys. Lett. 111, 093501 (2017), Fabrication and characterization of sputtered Cu2O :N / c-Si heterojunction diode” can be used. Also, when NiO is used as the material for the p-type semiconductor film 12, the method described in the non-patent document “Appl. Phys. Lett. 117, 022104 (2020), A 1.86-kV double-layered NiO / β-Ga2O3-vertical pn heterojunction diode” can be used. Furthermore, when polycrystalline Si, amorphous Si, or single-crystal Si is used as the material for the p-type semiconductor film 12, known film deposition methods can be used for each.

[0059] Next, as shown in Figure 5(a), photoresist 20 is deposited over the entire surface of the p-type semiconductor film 12 by a method such as spin coating, up to a height that fills at least the voids in the trench 111. At this time, the difference in height of the surface irregularities of the photoresist 20 is made smaller than the difference in height of the surface irregularities of the p-type semiconductor film 12.

[0060] Next, as shown in Figure 5(b), the photoresist 20 is etched back to expose the p-type semiconductor film 12 on the first surface 113. For etching the photoresist 20, a plasma asher apparatus using, for example, oxygen plasma is used.

[0061] Next, as shown in Figure 5(c), the p-type semiconductor film 12 is etched to expose the first surface 113 of the n-type semiconductor layer 11. For example, if the p-type semiconductor film 12 is made of Cu2O, a wet etching method using an acidic solution such as buffered hydrofluoric acid solution, dilute hydrofluoric acid, diluted aqua regia, or dilute sulfuric acid, or a dry etching method can be used to etch the p-type semiconductor film 12, or the wet etching method and dry etching method may be used in combination.

[0062] Next, the photoresist 20 is removed as shown in Figure 6(a). For removing the photoresist 20, an organic agent such as NMP or acetone is used.

[0063] Next, as shown in Figure 6(b), an anode electrode 13 is formed on the first surface 113 of the n-type semiconductor layer 11 such that a portion 132 of it is covered by a p-type semiconductor film 12 within a plurality of trenches 111, and a cathode electrode 14 is formed on the bottom surface of the n-type semiconductor substrate 10. For example, electron beam deposition is used to form the anode electrode 13 and the cathode electrode 14.

[0064] Since the p-type semiconductor film 12 is a film that covers the inner surface of the trench 111, the time required for material deposition is shorter compared to when the trench 111 is filled with a p-type semiconductor, and the time required for removing the portion formed on the outside of the trench 111 is also shorter.

[0065] Furthermore, in the above method, the portion formed outside the trench 111 of the p-type semiconductor film 12 is removed by a resist etch-back method using photoresist 20, but it may also be removed by polishing treatment such as CMP.

[0066] (modified version) The n-type semiconductor layer 11 may be made of a material other than a gallium oxide-based semiconductor. In this case as well, the electron affinity χ of the material of the n-type semiconductor layer 11 n and work function φ n And the electron affinity χ of the p-type semiconductor film 12 material p and work function φ p The above equation 1 satisfies the conditions expressed in equation 1.

[0067] As described above, the p-type semiconductor film 12 is a deposited film and is not formed as part of the n-type semiconductor layer 11 by ion implantation. Therefore, even if the n-type semiconductor layer 11 is made of a material that is difficult to convert to p-type, such as a gallium oxide-based semiconductor, the p-type film 12 can be formed using a different material (matrix) than the n-type semiconductor layer 11.

[0068] If the dielectric breakdown field strength of the n-type semiconductor layer 11 is high, the breakdown voltage can be increased while suppressing the increase in on-resistance. For this reason, for example, it is preferable that the n-type semiconductor layer 11 is made of a material with a dielectric breakdown field strength of 1 MV / cm or more, or a bandgap energy of 1 or more.

[0069] As the material for the n-type semiconductor layer 11, in addition to gallium oxide-based semiconductors, other materials such as SiC with a dielectric breakdown field strength of 2.5 MV / cm and a bandgap energy of 3.3 eV, GaN with a dielectric breakdown field strength of 3.3 MV / cm and a bandgap energy of 3.4 eV, and Al with a dielectric breakdown field strength of 1.2 to 12 MV / cm and a bandgap energy of 0.6 to 6.2 eV are also used. x In y Ga 1-x-y N, or diamond with a dielectric breakdown field strength of approximately 8.0 MV / cm and a bandgap energy of 5.5 eV, can be used.

[0070] Furthermore, the n-type semiconductor substrate 10 may also be made of a material other than a gallium oxide-based semiconductor. The same material as that used for the n-type semiconductor layer 11 can be used for the n-type semiconductor substrate 10.

[0071] (Effects of the embodiment) According to the above embodiment, a JBS diode 1 with a trench structure that exhibits excellent surge resistance and suppresses energy loss during switching operation, and a method for manufacturing the same, can be provided. Since the JBS diode 1 has high surge resistance and a low rise voltage, it can be suitably used in power conversion circuits such as AC / DC converters.

[0072] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the embodiments described above do not limit the invention as claimed. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. [Explanation of Symbols]

[0073] 1...Junction barrier Schottky diode, 10...n-type semiconductor substrate, 11...n-type semiconductor layer, 111...Trench, 112...Mesa-shaped region, 113...First surface, 114...Second surface, 12...p-type semiconductor film, 13...Anode electrode, 14...Cathode electrode

Claims

1. An n-type semiconductor layer made of an n-type semiconductor having a plurality of trenches opening to the first surface, A p-type semiconductor film made of a p-type semiconductor is provided in contact with the inner surface of the plurality of trenches, An anode electrode is provided on the first surface of the n-type semiconductor layer in contact with the mesa-shaped portion between the plurality of trenches of the n-type semiconductor layer, and a portion of it is covered by the p-type semiconductor film within the plurality of trenches. A cathode electrode provided directly or via another layer on a second surface opposite to the first surface of the n-type semiconductor layer, Equipped with, The upper surface of the mesa-shaped portion is in contact with the anode electrode over its entire width. The electron affinity χ of the p-type semiconductor ｐ and work function φ ｐ , and the electron affinity χ of the n-type semiconductor ｎ and work function φ ｎ However, χ ｎ -χ ｐ >φ ｐ -φ ｎ Satisfying the conditions expressed by the formula, Junction barrier Schottky diode.

2. The n-type semiconductor layer and the p-type semiconductor film are made of different semiconductors. The junction barrier Schottky diode according to claim 1.

3. The n-type semiconductor layer is made of a gallium oxide-based semiconductor. The junction barrier Schottky diode according to claim 2.

4. where the p-type semiconductor contains Cu ２ O, NiO, Ag ２ O, polycrystalline Si, single-crystalline Si, amorphous Si, SnO, or CuO A junction barrier Schottky diode according to any one of claims 1 to 3.

5. The upper end of the p-type semiconductor film is lower than the first surface, A junction barrier Schottky diode according to any one of claims 1 to 3.

6. The p-type semiconductor film is composed of a first p-type semiconductor film in contact with the inner surface of the trench and a second p-type semiconductor film laminated inside it. The impurity concentration of the second p-type semiconductor film is higher than that of the first p-type semiconductor film. A junction barrier Schottky diode according to any one of claims 1 to 3.

7. A step of forming a plurality of trenches on the first surface of an n-type semiconductor layer made of an n-type semiconductor, A step of forming a p-type semiconductor film made of a p-type semiconductor that is in contact with the inner surface of the plurality of trenches, A step of forming an anode electrode on the first surface of the n-type semiconductor layer, which is in contact with the mesa-shaped portion between the plurality of trenches of the n-type semiconductor layer, and a portion thereof is covered by the p-type semiconductor film within the plurality of trenches, A step of forming a cathode electrode directly or via another layer on a second surface opposite to the first surface of the n-type semiconductor layer, Includes, The upper surface of the mesa-shaped portion is in contact with the anode electrode over its entire width. The electron affinity χ of the p-type semiconductor ｐ and work function φ ｐ , and the electron affinity χ of the n-type semiconductor ｎ and work function φ ｎ However, χ ｎ -χ ｐ >φ ｐ -φ ｎ Satisfying the conditions expressed by the formula, A method for manufacturing a junction barrier Schottky diode.

8. The upper end of the p-type semiconductor film is lower than the first surface, A method for manufacturing a junction barrier Schottky diode according to claim 7.

9. The p-type semiconductor film is composed of a first p-type semiconductor film in contact with the inner surface of the trench and a second p-type semiconductor film laminated inside it. The impurity concentration of the second p-type semiconductor film is higher than that of the first p-type semiconductor film. A method for manufacturing a junction barrier Schottky diode according to claim 7.

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