JP2006318956A - Semiconductor device having schottky diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device having a Schottky diode for reducing steady loss when applying forward bias without increasing a leakage current when applying reverse bias. <P>SOLUTION: The Schottky diode 1 comprises a substrate 2, first and second semiconductors 3, 4, a Schottky metal 5, and an ohmic metal 6. The first semiconductor 3 is formed on the main surface of the substrate 2. A second semiconductor layer 4 is formed on the surface of a first semiconductor layer 3, has the same conductivity type as that of the first semiconductor layer 3, and has the concentration of impurities that is higher than that of the first semiconductor layer 3. The second semiconductor layer 4 is thin to the extent that a depletion layer 7 generated on the interface between the Schottky metal layer 5 and the second semiconductor layer 4 is extended in the thickness direction of the second semiconductor layer 4, for reaching the first semiconductor layer 3 when voltage is applied to cause the reverse bias. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor device having a Schottky diode, and more particularly to a semiconductor device having a Schottky diode that can reduce steady-state loss without increasing reverse leakage current.

  At present, silicon (Si) is generally used as a substrate material for power devices. However, when silicon is used as a semiconductor material, it is technically difficult to realize a Schottky diode having a withstand voltage exceeding 100 V due to the limit of physical properties.

Therefore, as a semiconductor material used for the Schottky diode, for example, silicon carbide (SiC) whose dielectric breakdown electric field is one digit larger than that of silicon is used. Due to the high breakdown electric field, silicon carbide can reduce the steady-state loss of the Schottky diode even at a high breakdown voltage exceeding 100 V compared to silicon, and the switching loss is small because it does not involve minority carrier injection. A smaller loss can be expected. The above contents are disclosed in Non-Patent Document 1, for example.
Hiroyuki Matsunami, “Semiconductor SiC Technology and Applications”, Nikkan Kogyo Shimbun, pp. 177-178

  However, with regard to the conventional Schottky diode using silicon carbide, if the steady-state loss is further reduced, the leakage current when the reverse bias is applied increases. Conversely, if the leakage current is reduced, the forward current is reduced. Steady loss will increase. This will be described below.

  In order to reduce the steady loss during forward bias application, it is necessary to use a metal having a low barrier height as the Schottky metal. However, in this case, since the barrier height is low, when a reverse bias is applied, the leakage current increases. On the other hand, when a metal having a high barrier height is used as the Schottky metal in order to reduce the leakage current when applying the reverse bias, the steady loss when applying the forward bias increases.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a semiconductor device having a Schottky diode that can reduce a steady loss when a forward bias is applied without increasing a leakage current when a reverse bias is applied.

  A semiconductor device having a Schottky diode according to the present invention includes a substrate, a first semiconductor layer, a second semiconductor layer, a Schottky metal layer, and an ohmic metal layer. The substrate has a main surface and a back surface opposite to the main surface. The first semiconductor layer is formed on the main surface of the substrate. The second semiconductor layer is formed on the surface of the first semiconductor layer, has an impurity concentration higher than that of the first semiconductor layer, and has the same conductivity type as the first semiconductor layer. In addition, the second semiconductor layer is generated at the interface between the Schottky metal layer and the second semiconductor layer when a voltage is applied to each of the Schottky metal layer and the ohmic metal layer so as to have a reverse bias. The depletion layer has such a thin thickness that it extends in the thickness direction of the second semiconductor layer and reaches the first semiconductor layer. The Schottky metal layer is in Schottky contact with the second semiconductor layer. The ohmic metal layer is in ohmic contact with the back surface of the substrate.

  According to the semiconductor device having a Schottky diode in the present invention, when a voltage is applied so as to be forward biased, the second semiconductor layer contains a large amount of impurities, so that there are many electrons serving as carriers, The key contact quality deteriorates and the current easily flows. Therefore, steady loss can be reduced. On the other hand, when a voltage is applied so as to be a reverse bias, since the thickness of the second semiconductor layer is thin, a depletion layer generated at the interface between the Schottky metal layer and the second semiconductor layer is The semiconductor layer extends in the thickness direction of the semiconductor layer and reaches the first semiconductor layer. Since the impurity concentration of the first semiconductor layer is low, the depletion layer further extends. Therefore, the spread of the depletion layer improves the breakdown voltage and does not increase the reverse leakage current. That is, it is possible to reduce the steady loss at the forward bias without increasing the leakage current at the time of applying the reverse bias.

  In the semiconductor device having the above Schottky diode, preferably, the second semiconductor layer is composed of two or more separated regions, and the Schottky metal layer is shot on both the first semiconductor layer and the second semiconductor layer. The key is touching.

  Thereby, when a voltage is applied so as to be a forward bias, a current easily flows due to the presence of the second semiconductor layer. On the other hand, when a voltage is applied so as to provide a reverse bias, depletion layers generated at the interface between the first semiconductor layer and the Schottky metal layer, and the interface between the second semiconductor layer and the Schottky metal layer The depletion layer generated in step 1 is pinched off, and the depletion layer is more reliably spread, and the reverse leakage current is not increased.

The impurity concentration of the second semiconductor layer is preferably 1 × 10 ¹⁶ cm ^{−3 to} 1 × 10 ¹⁸ cm ⁻³ , and more preferably 5 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁷ cm ⁻³ . The reason for the above range is that when a forward bias voltage is applied, the number of electrons serving as carriers increases, so that the steady loss can be further reduced and the breakdown voltage can be maintained.

  The thickness of the second semiconductor layer is preferably 0.1 μm or more and 5.0 μm or less, and more preferably 0.1 μm or more and 2 μm or less. Within this range, when a forward bias voltage is applied, a current easily flows, and when a reverse bias voltage is applied, a depletion layer that is generated causes a region of the second semiconductor layer to flow. This is because the region of the first semiconductor layer can be more reliably exceeded.

  In the semiconductor device having the above Schottky diode, preferably, the first semiconductor layer and the second semiconductor layer have irregularities, and the Schottky metal layer is an irregular recess formed in the first semiconductor layer. And Schottky contact with both of the convex and concave portions formed in the second semiconductor layer.

  This increases the surface area of the interface between the Schottky metal layer and the semiconductor layer, considering that the ease of current flow is proportional to the current density and the surface area when applying a voltage so as to be forward biased. Therefore, the current easily flows, and the resistance decreases accordingly, and the steady loss can be reduced. On the other hand, when a voltage is applied so that the reverse bias is applied, the depletion layer of the semiconductor layer is expanded, so that the breakdown voltage is improved and the reverse leakage current is not increased. That is, the loss can be reduced without increasing the reverse leakage current.

  In the semiconductor device having the above Schottky diode, preferably, the surface of the second semiconductor layer has irregularities, and the Schottky metal layer is formed between the concave and convex portions and the convex portions formed in the second semiconductor layer. Both are in Schottky contact.

  As a result, it is possible to further reduce the steady loss at the time of applying the forward bias as a synergistic effect without increasing the leakage current at the time of applying the reverse bias.

  In the semiconductor device having the above Schottky diode, it is preferable that a plurality of concave portions and convex portions are alternately provided on the surface of the first semiconductor layer, and the thickness of the concave portions and the convex portions is increased and the height is increased.

  This is because the surface area of the interface between the Schottky metal layer and the semiconductor layer is further increased, so that a current in a forward bias can easily flow.

  In the semiconductor device having the above Schottky diode, the substrate, the first semiconductor layer, and the second semiconductor layer are preferably made of silicon carbide.

  As a result, the resistance at the same breakdown voltage can be greatly reduced, and the loss can be further reduced. Silicon carbide has a large band gap, a large dielectric breakdown electric field, a carrier mobility as high as that of silicon, and an electron saturation drift velocity larger than that of GaAs, and therefore, it becomes a better Schottky diode.

The impurity concentration of the first semiconductor layer is preferably 1 × 10 ¹³ cm ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less.

  Thereby, the spread of the depletion layer becomes appropriate at the time of reverse bias, the leakage current is not increased, and the steady loss at the time of forward bias can be reduced.

  As described above, according to the semiconductor device having the Schottky diode of the present invention, the semiconductor layer having a small thickness and a high impurity concentration is provided, or the surface area of the interface between the Schottky metal layer and the semiconductor layer is increased. Thus, the steady loss at the time of applying the forward bias can be reduced without increasing the leakage current at the time of applying the reverse bias.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a configuration of a semiconductor device having a Schottky diode according to Embodiment 1 of the present invention. Referring to FIG. 1, a Schottky diode 1 according to a first embodiment includes a substrate 2, a first semiconductor layer 3, a second semiconductor layer 4, a Schottky metal layer 5, and an ohmic metal layer 6. And.

The substrate 2 has a main surface and a back surface opposite to the main surface. Substrate 2 is made of, for example, n-type silicon carbide. The first semiconductor layer 3 is formed on the substrate 2. The first semiconductor layer 3 has a thickness of, for example, 4.9 μm and is made of n ^- silicon carbide into which nitrogen (N) is introduced as an impurity at a concentration of 5 × 10 ¹⁵ cm ⁻³ . The second semiconductor layer 4 is formed on the surface of the first semiconductor layer 3. The second semiconductor layer 4 has a thickness of, for example, 0.1 μm and is made of n ⁺ silicon carbide into which nitrogen (N) is introduced as an impurity at a concentration of 1 × 10 ¹⁷ cm ⁻³ . The Schottky metal layer 5 is in Schottky contact with the second semiconductor layer 4 and is made of, for example, titanium (Ti) having a Schottky barrier height of 0.95 eV. The ohmic metal layer 6 is in ohmic contact with the back surface of the substrate 2 and is made of, for example, Ti or Ni.

  When a voltage is applied to each of the Schottky metal layer 5 and the ohmic metal layer 6 so that the second semiconductor layer 4 is reverse-biased, the second semiconductor layer 4 is formed between the Schottky metal layer 5 and the second semiconductor layer 4. The depletion layer generated at the interface has a thickness that is thin enough to extend in the thickness direction of the second semiconductor layer 4 and reach the first semiconductor layer, for example, 0.1 μm in this embodiment. However, the thickness of the second semiconductor layer 4 is not limited to this, but is preferably 0.1 μm or more and 5.0 μm or less, and more preferably 0.1 μm or more and 2 μm or less.

  Note that the substrate 2, the first semiconductor layer 3, and the second semiconductor layer 4 are not limited to n-type, and may be p-type. The material of the substrate 2, the first semiconductor layer 3, and the second semiconductor layer 4 is not limited to silicon carbide, and may be, for example, silicon, gallium nitride, or gallium arsenide. Furthermore, the impurity introduced into the substrate 2, the first semiconductor layer 3, and the second semiconductor layer 4 is not limited to nitrogen, and may be, for example, phosphorus, aluminum, or boron. Furthermore, the material of the Schottky metal layer 5 is not limited to titanium, and may be aluminum, nickel, or the like, for example.

  Next, an operation method of the Schottky diode 1 will be described with reference to FIG. First, when a forward bias is applied to the Schottky diode 1, a relatively positive voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and a relatively negative voltage is applied to the ohmic metal layer 6 serving as the cathode electrode. Is applied. Thereby, a current flows from the anode electrode to the cathode electrode.

  Next, when a reverse bias is applied to the Schottky diode 1, a relatively negative voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and relative to the ohmic metal layer 6 serving as the cathode electrode. A positive voltage is applied. At the time of this reverse bias, the depletion layer 7 generated at the interface between the Schottky metal layer 5 and the second semiconductor layer 4 extends in the thickness direction of the second semiconductor layer 4 as shown in FIG. At this time, since the thickness of the second semiconductor layer 4 is set to be thin, the depletion layer 7 easily reaches the first semiconductor layer 3 beyond the second semiconductor layer 4. Furthermore, since the impurity concentration of the first semiconductor layer 3 is low, the depletion layer 7 that has reached the first semiconductor layer 3 easily extends in the first semiconductor layer 3. As a result, the depletion layer 7 is greatly expanded and the current flow is interrupted.

  According to the present embodiment, at the time of forward bias, the second semiconductor layer 4 bonded to the Schottky metal layer 5 has a high impurity concentration and a large number of electrons serving as carriers exist. Current tends to flow through the interface between the layer 5 and the second semiconductor layer 4. Therefore, it is possible to reduce the steady loss at the time of forward bias. On the other hand, when the reverse bias is applied, since the thickness of the second semiconductor layer 4 is thin, the depletion layer 7 easily penetrates the second semiconductor layer 4 and reaches the first semiconductor layer 3. Since the first semiconductor layer 3 has a low impurity concentration, the depletion layer 7 easily extends in the first semiconductor layer 3. Thus, the presence of the wide depletion layer 7 suppresses the occurrence of reverse leakage current.

  As described above, according to the present embodiment, the second semiconductor layer 4 having a small thickness and a high impurity concentration is provided to control the spread of the depletion layer, thereby increasing the leakage current at the time of reverse bias. Therefore, the steady loss at the time of forward bias can be reduced.

(Embodiment 2)
FIG. 3A is a cross-sectional view showing a configuration of a semiconductor device having a Schottky diode in Embodiment 2 of the present invention. Referring to FIG. 3, the configuration of Schottky diode 10 according to the second embodiment is different from that of the first embodiment in that the second semiconductor layer 4 is composed of a plurality of separated regions 4a, and a Schottky metal layer is formed. 5 is different in that it is in Schottky contact with both the second semiconductor layer 4 and the first semiconductor layer 3 where the second semiconductor layer 4 is not formed.

  Specifically, the second semiconductor layer 4 includes a plurality of regions 4a separated from each other, and the thickness of each region 4a is 0.1 μm. The thickness of the first semiconductor layer 3 in the region where the second semiconductor layer 4 is not formed is 5.0 μm, and the thickness of the first semiconductor layer 3 in the region where the second semiconductor layer 4 is formed. Is 4.9 μm.

  In addition, as shown in FIG. 3B, the Schottky diode 10 may have a region 4a extending in a straight line, or as shown in FIG. 3C, the region 4a may have an island shape. good.

  Next, an operation method of the Schottky diode 10 will be described with reference to FIG. First, when a forward bias is applied to the Schottky diode 10, a relatively positive voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and a relatively negative voltage is applied to the ohmic metal layer 6 serving as the cathode electrode. Is applied. Thereby, a current flows from the anode electrode to the cathode electrode.

  Next, when a reverse bias is applied to the Schottky diode 10, a relatively negative voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and relative to the ohmic metal layer 6 serving as the cathode electrode. A positive voltage is applied. At the time of this reverse bias, as shown in FIG. 4, the depletion layer 7 generated at the interface between the Schottky metal layer 5 and the second semiconductor layer 4 is set so that the thickness of the second semiconductor layer 4 is thin. The first semiconductor layer 3 extends in the thickness direction of the second semiconductor layer 4 to reach the first semiconductor layer 3 and easily spreads in the first semiconductor layer 3. On the other hand, the depletion layer 7 generated at the interface between the Schottky metal layer 5 and the first semiconductor layer 3 is larger than the depletion layer 7 generated at the interface of the second semiconductor layer 4 in the thickness direction of the first semiconductor layer 3. Extend. Therefore, the depletion layer 7 is pinched off and the thickness becomes larger. Therefore, the current flow is blocked by the presence of the wide depletion layer 7.

  According to the present embodiment, at the time of forward bias, the second semiconductor layer 4 bonded to the Schottky metal layer 5 has a high impurity concentration and a large number of electrons serving as carriers exist. Current is particularly likely to flow through the interface between the layer 5 and the region 4a. Therefore, it is possible to reduce the steady loss at the time of forward bias. On the other hand, at the time of reverse bias, since the first semiconductor layer 3 is in direct contact with the Schottky metal layer 5 and the thickness of the second semiconductor layer 4 is thin, the depletion layer 7 is the configuration of the first embodiment. Since it spreads further, generation | occurrence | production of the reverse leakage current is further suppressed.

  As described above, according to the present embodiment, a plurality of regions 4a each including the second semiconductor layer 4 having a small thickness and a high impurity concentration are provided, and the spread of the depletion layer is controlled, so that the reverse bias can be achieved. The steady loss during forward bias can be reduced without increasing the leakage current.

(Embodiment 3)
FIG. 5 is a diagram showing a configuration of a semiconductor device having a Schottky diode according to the third embodiment of the present invention. Referring to FIG. 5, in the Schottky diode 20 according to the third embodiment, compared to the first embodiment, the second semiconductor layer 4 includes a plurality of separated regions 4a, and the Schottky metal layer 5 is The difference is that the second semiconductor layer 4 and the first semiconductor layer 3 where the second semiconductor layer 4 is not formed are in Schottky contact.

Specifically, the first semiconductor layer 3 is formed on the substrate 2. The second semiconductor layer 4 has a plurality of regions 4 a formed on the surface of the first semiconductor layer 3. The region 4a is convex. Region 4a has, for example, a width W1 of 1 μm and a thickness T1 of 1 μm. The thickness T2 of the first semiconductor layer 3 in the region where the recess is formed is 5.0 μm, and the thickness T3 of the first semiconductor layer 3 in the region where the region 4a is formed is 5.1 μm. The first semiconductor layer 3 is made of, for example, n ^- silicon carbide into which nitrogen is introduced as an impurity at a concentration of 5 × 10 ¹⁵ cm ⁻³ . Second semiconductor layer 4 is made of, for example, n silicon carbide into which nitrogen is introduced as an impurity at a concentration of 1 × 10 ¹⁷ cm ⁻³ . The Schottky metal layer 5 is in Schottky contact with both the region 4a of the second semiconductor layer 4 and the first semiconductor layer 3 where the region 4a of the second semiconductor layer 4 is not stacked. For example, Ti is used. The ohmic metal layer 6 is in ohmic contact with the back surface of the substrate 2 and is made of, for example, Ti or Ni.

  Next, an operation method of the Schottky diode 20 will be described. First, when a forward bias is applied to the Schottky diode 20, a relatively positive voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and a relatively negative voltage is applied to the ohmic metal layer 6 serving as the cathode electrode. Is applied. Thereby, a current flows from the anode electrode to the cathode electrode.

  Next, when a reverse bias is applied to the Schottky diode 20, a relatively negative voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and a relatively positive voltage is applied to the ohmic metal layer 6 serving as the cathode electrode. Is applied. At this time, since the first semiconductor layer 3 has a low impurity concentration, a depletion layer generated at the interface between the Schottky metal layer 5 and the first semiconductor layer 3 easily extends over a wide range. Therefore, the current flow is interrupted.

  According to the present embodiment, in consideration of the fact that the current is proportional to the surface area and the current density at the time of forward bias, the first semiconductor layer 3 is provided with the convex region 4a on the surface to increase the surface area. As a result, the amount of current increases. For this reason, when the same voltage is applied, the resistance is reduced, so that the steady loss can be reduced. On the other hand, since the impurity concentration of the first semiconductor layer 3 is low at the time of reverse bias, the presence of the wide depletion layer 7 generated at the interface between the Schottky metal layer 5 and the first semiconductor layer 3 causes reverse leakage current. Is suppressed.

  As described above, according to the present embodiment, the second semiconductor layer 4 having unevenness on the surface is provided, and the surface area to be brought into Schottky contact is increased, so that the leakage current at the time of reverse bias is not increased. The steady loss at the time of forward bias can be reduced.

(Embodiment 4)
FIG. 6 is a diagram showing a configuration of a semiconductor device having a Schottky diode according to the fourth embodiment of the present invention. Note that the cross-sectional view of the Schottky diode 30 according to the fourth embodiment is the same as that shown in FIG. With reference to FIG. 6, the Schottky diode 30 according to the fourth embodiment has a configuration in which the rectangular parallelepiped is removed from the region 4 a of the second semiconductor layer 4 as compared with the third embodiment. It differs only in increasing the number.

  Referring to FIG. 6, for example, a first groove group and a second groove group formed of a plurality of grooves running in parallel intersect with each other. Thereby, the first semiconductor layer 4 remaining in an island shape forms the region 4a. With this structure, the contact area between the Schottky metal layer 5 and the first semiconductor layer 3 and the contact area between the Schottky metal layer 5 and the second semiconductor layer 4 are further increased.

  Since the operation method of the Schottky diode 30 is the same as that of the third embodiment, the description thereof is omitted.

  According to the present embodiment, by providing irregularities on the surface of the second semiconductor layer 4, the contact area between the Schottky metal layer 5 and the first semiconductor layer 3, and the Schottky metal layer 5 and the second semiconductor layer 4 are increased. Since the contact area with the semiconductor layer 4 is further increased, the steady loss at the forward bias can be further reduced without increasing the leakage current at the reverse bias.

(Embodiment 5)
FIG. 7 is a cross-sectional view showing a configuration of a semiconductor device having a Schottky diode in the fifth embodiment of the present invention. Referring to FIG. 7, the configuration of the Schottky diode 40 according to the fifth embodiment has the second semiconductor layer 4 on the bottom surface of the recess as compared with the third embodiment, and the Schottky metal layer 5. Is different in that the second semiconductor layer 4 is in Schottky contact with the convex region 4a and the bottom surface of the concave portion.

  7, the configuration of the Schottky diode 40 according to the fifth embodiment has a region 4a on the surface of the second semiconductor layer 4 as compared with the first embodiment, and The key metal layer 5 is different in that the key metal layer 5 is in Schottky contact with the second semiconductor layer 4 at the convex region 4a and the bottom of the recess.

  Specifically, the Schottky diode 40 according to the fifth embodiment has irregularities on the surface of the second semiconductor layer 4, and the Schottky metal layer 5 is irregularities formed in the second semiconductor layer 4. Schottky contact is made with both the concave and convex portions. The thickness T4 of the first semiconductor layer 3 is, for example, 4.9 μm. The thickness T5 of the second semiconductor layer 4 is, for example, 0.1 μm. The thickness T6 of the region 4a of the second semiconductor layer 4 is, for example, 1 μm.

  Next, an operation method of the Schottky diode 40 will be described. First, when a forward bias is applied to the Schottky diode 40, a relatively positive voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and a relatively negative voltage is applied to the ohmic metal layer 6 serving as the cathode electrode. Is applied. Thereby, a current flows from the anode electrode to the cathode electrode.

  Next, when a reverse bias is applied to the Schottky diode 40, a relatively negative voltage is applied to the Schottky metal layer 5 serving as the anode electrode, and relative to the ohmic metal layer 6 serving as the cathode electrode. A positive voltage is applied. During the reverse bias, the depletion layer 7 generated at the interface between the Schottky metal layer 5 and the second semiconductor layer 4 reaches the first semiconductor layer 3 as shown in FIG. When the depletion layer 7 reaches the first semiconductor layer 3, it easily extends greatly in the thickness direction of the first semiconductor layer 3. Therefore, the current flow is interrupted.

  According to the present embodiment, when the forward bias is applied, the second semiconductor layer 4 has a high impurity concentration, so that current easily flows through the interface between the Schottky metal layer 5 and the second semiconductor layer 4. In addition, since the region 4a of the second semiconductor layer 4 has a large surface area, a larger amount of current flows than when the region 4a is not provided. Therefore, it is possible to reduce the steady loss at the time of forward bias. On the other hand, when the reverse bias is applied, since the thickness of the second semiconductor layer 4 is thin, the depletion layer 7 easily penetrates the second semiconductor layer 4, and the depletion layer 7 easily spreads in the first semiconductor layer 3. Thus, the presence of the wide depletion layer 7 suppresses the occurrence of reverse leakage current.

  As described above, according to the present embodiment, the leakage current at the time of reverse bias is increased by providing the second semiconductor layer 4 having a small thickness and a high impurity concentration and controlling the spread of the depletion layer 7. Without increasing the contact loss between the Schottky metal layer 5 and the second semiconductor layer 4 by increasing the contact area between the second semiconductor layer 4 and the surface of the second semiconductor layer 4. be able to.

Examples of the present invention will be described below.
Example 1
In Example 1, the steady loss at the time of forward bias in Examples 1 to 4 of the present invention having the same structure as that of the first embodiment of the present invention was examined. The thicknesses and impurity concentrations of the second semiconductor layers of Invention Examples 1 to 4 are as follows.

In Example 1 of the present invention, the thickness of the second semiconductor layer 4 was 0.1 μm, and the impurity concentration of nitrogen in the second semiconductor layer 4 was 1 × 10 ¹⁷ cm ⁻³ . In Example 2 of the present invention, the thickness of the second semiconductor layer 4 was 0.2 μm, and the impurity concentration of nitrogen in the second semiconductor layer 4 was 1 × 10 ¹⁷ cm ⁻³ . In Inventive Example 3, the thickness of the second semiconductor layer 4 was 0.1 μm, and the impurity concentration of nitrogen in the second semiconductor layer 4 was 1 × 10 ¹⁸ cm ⁻³ . In Example 4 of the present invention, the thickness of the second semiconductor layer 4 was 0.1 μm, and the impurity concentration of nitrogen in the second semiconductor layer 4 was 1 × 10 ¹⁶ cm ⁻³ .

(Comparative example)
A comparative example is a Schottky diode 100 including a substrate 102, a first semiconductor layer 103, a Schottky metal layer 105, and an ohmic metal layer 106 with reference to FIG. 10. Referring to FIG. 10, the configuration of Schottky diode 100 is different from that of the first embodiment in that there is no second semiconductor layer 4. Specifically, the first semiconductor layer 103 has an impurity concentration of 5 × 10 ¹⁵ cm ⁻³ and a thickness of 5 μm. The substrate 102 and the first semiconductor layer 103 are made of silicon carbide, the Schottky metal layer 105 is Ti, and the ohmic metal layer 106 is NiAl.

  The forward current with respect to the forward voltage was measured using the manufactured Example 1 and the comparative example. The result is shown in FIG.

  Referring to FIG. 10, all of the inventive examples 1 to 4 having the second semiconductor layer had a larger amount of current than the comparative example when a forward voltage was applied. Therefore, it turned out that the present invention examples 1-4 can reduce the steady loss at the time of forward bias.

(Example 2)
In Example 2, the steady loss at the time of forward bias of Example 5 of the present invention having the same structure as that of Embodiment 3 of the present invention and Examples 6 and 7 of the present invention having the same structure as Embodiment 6. Investigated about. The thickness and impurity concentration of the region 4a of Examples 5 to 7 of the present invention are as follows.

In Example 5 of the present invention, the nitrogen impurity concentration in the region 4a was 5 × 10 ¹⁵ cm ⁻³ , the width was 1 μm, and the thickness was 1 μm. In Example 6 of the present invention, the impurity concentration of nitrogen in the region 4a was 1 × 10 ¹⁷ cm ⁻³ , the width was 1 μm, and the thickness was 1 μm. In Inventive Example 7, the impurity concentration of nitrogen in the region 4a was 1 × 10 ¹⁷ cm ⁻³ , the width was 1 μm, and the thickness was 2 μm.

  The forward current with respect to the forward voltage was measured using the inventive examples 5 to 7 and the comparative example. The result is shown in FIG.

  Referring to FIG. 11, Example 5 of the present invention increased the surface area where the Schottky metal layer and the first semiconductor layer were in contact with each other. Therefore, when a forward voltage was applied, the amount of current was slightly larger than that of the comparative example. In the inventive examples 6 and 7, since the region 4a having a high impurity concentration is provided, the number of electrons serving as carriers is large. Therefore, when a forward voltage is applied, the amount of current is larger than that of the comparative example.

(Example 3)
In Example 3, the steady loss at the time of forward bias of Example 8 of the present invention having the same structure as that of Embodiment 5 of the present invention was examined.

  The forward current with respect to the forward voltage was measured using the present invention example 8 and the comparative example. The result is shown in FIG.

  Referring to FIG. 12, Example 8 of the present invention provided the second semiconductor layer, which is a thin high-concentration layer, and provided a convex portion to increase the surface area. Therefore, when a forward voltage was applied, The amount of current was larger than that of the comparative example. In particular, the current density when the forward voltage was 0.9 V was 1.4 times that of the comparative example.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is sectional drawing of the Schottky diode in Embodiment 1 of this invention. FIG. 3 is a cross-sectional view in which a reverse bias is applied to the Schottky diode in the first embodiment. (A) is sectional drawing of the Schottky diode in Embodiment 2 of this invention, (B) is a schematic perspective view except the Schottky metal layer in the Schottky diode in Embodiment 2, (C) ) Is another schematic perspective view of the Schottky diode according to Embodiment 2 except for the Schottky metal layer. FIG. 6 is a cross-sectional view in which a reverse bias is applied to the Schottky diode in the second embodiment. (A) is sectional drawing of the Schottky diode in Embodiment 3, (B) is the schematic perspective view except the Schottky metal layer in the Schottky diode in Embodiment 3. FIG. 6 is a schematic perspective view of a Schottky diode according to a fourth embodiment, excluding a Schottky metal layer. FIG. It is sectional drawing of the Schottky diode in Embodiment 5 of this invention. FIG. 10 is a cross-sectional view in which a reverse bias is applied to the Schottky diode in the fifth embodiment. It is sectional drawing of the Schottky diode in a comparative example. It is a figure which shows the relationship between the forward voltage and forward current in Example 1 of this invention. It is a figure which shows the relationship between the forward voltage and forward current in Example 2 of this invention. It is a figure which shows the relationship between the forward voltage and forward current in Example 3 of this invention.

Explanation of symbols

  1, 10, 20, 30, 40 Schottky diode, 2 substrate, 3 first semiconductor layer, 4 second semiconductor layer, 5 Schottky metal layer, 6 ohmic metal layer, 7 depletion layer.

Claims (5)

A substrate having a main surface and a back surface opposite to the main surface;
A first semiconductor layer formed on the main surface of the substrate;
A second semiconductor layer formed on a surface of the first semiconductor layer and having an impurity concentration higher than that of the first semiconductor layer and having the same conductivity type as the first semiconductor layer;
A Schottky metal layer in Schottky contact with the second semiconductor layer;
An ohmic metal layer in ohmic contact with the back surface of the substrate;
When applying a voltage to each of the Schottky metal layer and the ohmic metal layer so that the second semiconductor layer has a reverse bias, the second semiconductor layer is formed between the Schottky metal layer and the second semiconductor layer. A semiconductor device having a Schottky diode, wherein a depletion layer generated at an interface extends in a thickness direction of the second semiconductor layer and is thin enough to reach the first semiconductor layer. The second semiconductor layer comprises two or more separated regions;
2. The semiconductor device having a Schottky diode according to claim 1, wherein the Schottky metal layer is in Schottky contact with both the first semiconductor layer and the second semiconductor layer. There are irregularities in the first semiconductor layer and the second semiconductor layer,
The Schottky metal layer is in Schottky contact with both the concave and convex concave portions formed in the first semiconductor layer and the concave and convex convex portions formed in the second semiconductor layer. A semiconductor device having a Schottky diode according to claim 1. The surface of the second semiconductor layer has irregularities,
2. The Schottky diode according to claim 1, wherein the Schottky metal layer is in Schottky contact with both the concave and convex portions of the concave and convex portions formed in the second semiconductor layer.   The semiconductor device having a Schottky diode according to claim 1, wherein the substrate, the first semiconductor layer, and the second semiconductor layer are made of silicon carbide.

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