Patent Application
20160181355
This application claims priority to Japanese Patent Application No. 2014-259316 filed on Dec. 22, 2014, the contents of which are hereby incorporated by reference into the present application.
A technology disclosed herein relates to a Schottky barrier diode and a method for manufacturing the same.
Japanese Patent Application Publication No. 2009-94433 (hereinafter referred to as “patent document 1”) discloses a Schottky barrier diode (hereinafter referred to as “SBD”). The SBD includes: a semiconductor substrate and an anode electrode being in contact with the semiconductor substrate. The semiconductor substrate includes: p-type contact regions being in contact with the anode electrode; and an n-type drift region being in contact with the anode electrode by Schottky contact in a range where the p-type contact regions are not provided. The p-type contact regions include: a single circular region extending along an outer circumference of the anode electrode; and a plurality of stripe patterned regions located in an inner portion of the circular region. Each of the stripe patterned regions is connected to the circular region. Further provided around the anode electrode (i.e. in an outer portion of the circular region) are p-type FLRs (field limiting rings) extending so as to surround the anode electrode. The FLRs are not in contact with the anode electrode. Application of a forward voltage to the SBD causes electrons to flow from the n-type drift region to the anode electrode through a Schottky interface between the anode electrode and the n-type drift region. This causes the SBD to be turned on. On the other hand, application of a backward voltage to the SBD stops the aforementioned flow of electrons, thus causing the SBD to be turned off. Further, when the SBD is turned off, depletion layer spread from the p-type contact regions to a portion of the n-type drift region that is located around the p-type contact regions. The depletion layer spreads so as to cover the Schottky interface. This prevents generation of a high electric field in an area in vicinity of the Schottky interface.
In the SBD of the patent document 1, the circular region is provided at an outer edge of a contact surface between the semiconductor substrate and the anode electrode. Therefore, when the SBD is turned off, a depletion layer extends from the circular region into a region located outer than the anode electrode (i.e. a region that is not covered with the anode electrode; hereinafter referred to as “peripheral region”). Meanwhile, the stripe patterned regions are connected to the circular region. Areas in vicinity of connected portions of the circular region to which the stripe patterned regions are connected have a higher p-type region ratio than areas in vicinity of non-connected portions of the circular region to which the stripe patterned regions are not connected. Therefore, the depletion layer extends more easily around the connected portions than around the non-connected portions. For this reason, the depletion layer extends from the circular region into the peripheral region faster in the areas in vicinity of the connected portions than in the areas in vicinity of the non-connected portions. Therefore, as shown in
A Schottky barrier diode disclosed herein comprises: a semiconductor substrate; and an anode electrode being in contact with the semiconductor substrate. The semiconductor substrate comprises: p-type contact regions being in contact with the anode electrode; and an n-type drift region being in contact with the anode electrode by Schottky contact in a range where the p-type contact regions are not provided. The p-type contact regions comprise: a plurality of circular regions located so that the circular regions are arranged at intervals from an outer side to an inner side at a contact surface between the semiconductor substrate and the anode electrode; and an internal region located in an inner portion of the circular region located on an innermost side at the contact surface and connected to the circular region located on the innermost side at the contact surface.
The term “inner side” as used herein means a side with respect to a circular region on which a region surrounded by the circular region is located, and the term “outer side” as used herein means a side with respect to a circular region that is outside a region surrounded by the circular region. Further, the term “inner portion” as used herein means a region surrounded by a circular region, and the term “outer portion” as used herein means a region that is outside a region surrounded by a circular region.
In this SBD, the internal region is connected to the circular region (hereinafter referred to as “first circular region”) located on the innermost side. For this reason, a depletion layer extends more easily around a connected portion of the first circular region to which the internal region is connected than around a non-connected portion of the first circular region to which the internal region is not connected. For this reason, the depletion layer, which extends from the first circular region into an outer portion of the first circular region, has its outer edge in a wavy shape. In this SBD, however, another circular region (hereinafter referred to as “second circular region”) is provided in the contact surface so as to surround the first circular region. As with the first circular region, the second circular region is in contact with the anode electrode. Therefore, a depletion layer extends from the second circular region at substantially a same time as the depletion layer extends from the first circular region. A portion of the n-type drift region that is located between the first circular region and the second circular region is pinched off by the depletion layers extending from the first circular region and the second circular region. That is, the wavy-edged depletion layer extending from the first circular region and the depletion layer extending from the second circular region are combined to make a single depletion layer. For this reason, electric field concentration due to the influence of the wavy-edged depletion layer does not occur in the pinched-off region. Further, a depletion layer extends from the circular region located on the outermost side into an outer portion (i.e. a peripheral region) of the circular region. The internal region is not connected to the circular region located on the outermost side. This allows the depletion layer to uniformly extend from this circular region over into the peripheral region. Therefore, the electric field concentration is suppressed also in the peripheral region. Therefore, this SBD is high in withstand voltage.
A method for manufacturing a Schottky barrier diode is disclosed herein. This method comprises formation of p-type regions and formation of an anode electrode. In the formation of p-type regions, p-type impurities are implanted into a semiconductor substrate being of n-type to form p-type regions exposed on a surface of the semiconductor substrate. The p-type regions comprise a plurality of ring regions and an internal region. The plurality of ring regions is arranged with intervals from an outer side to an inner side, and includes a first plurality of ring regions located on the inner side and a second plurality of ring regions located on the outer side. The internal region is located in an inner portion of the circular region located on an innermost side at the contact surface. The internal region is connected to the circular region located on the innermost side at the contact surface.
In this method, the first plurality of ring regions that are in contact with the anode electrode serves as circular regions, and the second plurality of ring regions that are not in contact with the anode electrode serves as FLRs. This method allows the internal region and the circular regions, which are in contact with the anode electrode, to be formed at the same time as the FLRs.
Provided in an inner part of the semiconductor substrate 12 are stripe patterned p-type contact regions 20, circular p-type contact regions 22a to 22e, FLRs 24, a drift region 26, and a cathode region 28. It should be noted that the following description may refer to the circular p-type contact regions 22a to 22e collectively as “circular p-type contact regions 22”.
The stripe patterned p-type contact regions 20, the circular p-type contact regions 22, and the FLRs 24 are provided in a range exposed on the upper surface 12a of the semiconductor substrate 12. As shown in
As shown in
As shown in
As shown in
The FLRs 24 are p-type semiconductor regions. Each of the FLRs 24 is provided in the peripheral region 13, and extends circularly so as to surround the anode electrode 14. The FLRs 24 are located so that the FLRs 24 are arranged at intervals from the outer side to the inner side. Each of the FLRs 24 has a quadrangular shape having corners chamfered in circular arcs. Each of the FLRs 24 has linear portions each shaped in a straight line and corner portions each shaped in a circular arc. As shown in
As shown in
The drift region 26 is an n-type semiconductor region. The drift region 26 has a low density of n-type impurities. In the present embodiment, the drift region 26 has a density of n-type impurities of 9.5×1015 atoms/cm3 or lower. The drift region 26 is located under the stripe patterned p-type contact regions 20, the circular p-type contact regions 22, and the FLRs 24. Further, in a position where the stripe patterned p-type contact regions 20 and the circular p-type contact regions 22 are not provided, the drift region 26 extends up to the upper surface 12a (i.e. the contact surface 15) of the semiconductor substrate 12 and is in contact with the anode electrode 14 by Schottky contact. Further, in a position in the peripheral region 13 where the FLRs 24 are not provided, the drift region 26 extends up to the upper surface 12a of the semiconductor substrate 12. As mentioned above, the stripe patterned p-type contact regions 20 are connected to the circular p-type contact region 22 located on the innermost side. Except for these connected portions, the drift region 26 is provided in regions between the p-type regions 20, 22, and 24. The circular p-type contact regions 22 and the FLRs 24 are separated from each other by the drift region 26.
The cathode region 28 is an n-type semiconductor region. The cathode region 28 has a density of n-type impurities higher than that of the drift region 26. In the present embodiment, the cathode region 28 has a density of n-type impurities of 3.0×1018 atoms/cm3 or higher. Further, the cathode region 28 has a resistivity of 15 to 25 mΩ·cm. The cathode region 28 is located under the drift region 26. The cathode region 28 is provided in a range exposed on the lower surface 12b of the semiconductor substrate 12. The cathode region 28 is in contact with the cathode electrode 16 by ohmic contact. The cathode region 28 is separated from the stripe patterned p-type contact regions 20, the circular p-type contact regions 22, and the FLRs 24 by the drift region 26. An interval W is provided between each of the p-type regions 20, 22, and 24 and the cathode region 28 in a thickness direction of the semiconductor substrate 12.
The following describes how the SBD 10 operates. Application of a forward voltage (i.e. a voltage that causes the anode electrode 14 to be higher in potential than the cathode electrode 16) to the SBD 10 causes electrons to flow from the drift region 26 to the anode electrode 14 through a Schottky interface between the anode electrode 14 and the drift region 26. That is, electrons flow from the cathode electrode 16 to the anode electrode 14 via the cathode region 28 and the drift region 26. This causes the SBD 10 to be turned on. Further, in the SBD 10, no current flows through the p-type regions 20 and 22. That is, the SBD 10 is a JBSD.
Thereafter, application of a backward voltage to the SBD 10 stops the flow of electrons, thus causing the SBD 10 to be turned off. Further, when the SBD 10 is turned off, depletion layer spreads from the p-type contact regions 20 and 22 to portions of the drift region 26 that are located around the p-type contact regions 20 and 22.
The application of a backward voltage causes the drift region 26 exposed on the contact surface 15 to be pinched off by the depletion layers spreading from the p-type regions 20 and 22 on both sides of the drift region 26. This prevents application of a high voltage to the Schottky interface between the anode electrode 14 and the drift region 26. In
Further, as mentioned above, the radiuses of the corner portions of the circular p-type contact regions 22a to 22e decrease as the circular p-type contact regions 22a to 22e are located closer to the inner side. Therefore, the corner portions have substantially constant widths. This allows depletion layers to evenly spread from the corner portions to areas near the corner portions, respectively. This suppresses the generation of a high electric field in the areas in vicinity of the corner portions.
Further, in the peripheral region 13, a depletion layer spreads from the circular p-type contact region 22e located on the outermost side to an outer portion of the circular p-type contact region 22e. The depletion layer spreads over to a further outer side via the plurality of FLRs 24. This causes the peripheral region 13 to be depleted. In this way, the depletion layer extends from the inner side toward the outer side in the peripheral region 13. If the depletion layer extending from the circular p-type contact region 22e to the outer portion of the circular p-type contact region 22e has its outer edge in a wavy shape, the depletion layer spreads into the peripheral region 13 while keeping its wavy outer edge to some extent. For this reason, there is a risk that a high electric field may be generated locally in the peripheral region 13. In the present embodiment, however, no other p-type region is connected to the circular p-type contact region 22e located on the outermost side. That is, unlike the circular p-type contact region 22a, the circular p-type contact region 22e does not have a connected portion 40. Therefore, the depletion layer extending from the circular p-type contact region 22e to the outer portion of the circular p-type contact region 22e has its outer edge not in a wavy shape, but in a flat shape. This prevents the generation of a high electric field in the peripheral region 13.
Further, the waviness of the depletion layer extending from the circular p-type contact region 22a located on the innermost side may influence electric field distribution in the peripheral region 13. In the SBD 10 according to the present embodiment, however, an interval Lr between the circular p-type contact region 22a and the circular p-type contact region 22e is larger than the radius Rmin of the corner portion located on the innermost side. The interval Lr is thus secured sufficiently wide. This curbs the influence on the peripheral region 13 by the wavy-edged depletion layer extending from the circular p-type contact region 22a. Further, in the SBD 10 according to the present embodiment, the number of the circular p-type contact regions 22 is larger than the number of the FLRs 24. That is, the many circular p-type contact regions 22b to 22d are provided between the circular p-type contact region 22a and the circular p-type contact region 22e. This also curbs the influence on the peripheral region 13 by the wavy-edged depletion layer extending from the circular p-type contact region 22a. Therefore, in the SBD 10, it is harder for electric field concentration to occur in the peripheral region 13.
By the depletion layer spreading as described above, the drift region 26 is depleted in a range indicated by a dotted line 50 in
Once the depletion layer reaches the cathode region 28 (i.e. the region having a high density of n-type impurities), downward spreading of the depletion layer stops. Therefore, the interval W in
In manufacturing an SBD 10, stripe patterned p-type contact regions 20, circular p-type contact regions 22, and FLRs 24 can be formed by a single implantation of p-type impurities. In this case, a mask having openings corresponding in shape to the p-type regions 20, 22, and 24 is formed on a surface of an n-type semiconductor substrate. Next, p-type impurities are implanted into the n-type semiconductor substrate via the mask. This causes the stripe patterned p-type contact regions 20 and a plurality of ring p-type regions (i.e. the circular p-type contact regions 22 and FLRs 24) to be formed. Next, an anode electrode 14 is formed so as to be in contact with the stripe patterned p-type contact regions 20 and a first plurality of the ring p-type regions located on an inner side and so as not to be in contact with a second plurality of the ring p-type regions located on an outer side. This causes the anode electrode 14 to be in contact by Schottky contact with the p-type and n-type regions located under the anode electrode 14. The first plurality of the ring p-type regions which are in contact with the anode electrode 14 by Schottky contact serve as the circular p-type contact regions 22. Further, the second plurality of the ring p-type regions which are not in contact with the anode electrode 14 serve as the FLRs 24. In this way, the single implantation of p-type impurities can form the stripe patterned p-type contact regions 20, the circular p-type contact regions 22, and the FLRs 24.
Although, in the above embodiment, a JBSD has been described, a similar structure may alternatively be employed in an MPSD. Further, although, in the above embodiment, the p-type contact regions 20 and 22 are in contact with the anode electrode 14 by Schottky contact, the p-type contact regions 20 and 22 may alternatively be in contact with the anode electrode 14 by ohmic contact.
Further, in the above embodiment, the stripe patterned p-type contact regions 20 are provided in an inner portion of the circular p-type contact region 22a located on the innermost side. Alternatively, a grid like p-type contact region 20 shown in
A relationship between the components of above embodiment and the components of the claims will be described. The “stripe patterned p-type contact regions 20” and the “circular p-type contact regions 22” of the embodiment are an example of the “p-type contact regions” of the claims. The “circular p-type contact regions 22” of the embodiment are an example of the “circular regions” of the claims. The “stripe patterned p-type contact regions 20” of the embodiment are an example of the “internal region” of the claims. The “interval W” of the embodiment is an example of the “interval between the p-type contact region and the high density n-type region” of the claims. The “radius Rmax” of the embodiment is an example of the “radius of the corner portion located on an outermost side”. The “interval Lr” of the embodiment is an example of the “interval between the circular region located on the innermost side and the circular region located on an outermost side”. The “radius Rmin” of the embodiment is an example of the “radius of the corner portion located on the innermost side”.
The following enumerates technical elements disclosed herein. It should be noted that the following technical elements are each independently useful.
In a configuration disclosed herein as an example, each of the circular regions may comprise a corner portion shaped in a circular arc. Radiuses of the circular arcs may decrease as the circular regions are located closer to an inner side.
This configuration makes it possible to better uniform the widths of the corner portions.
In a configuration disclosed herein as an example, an interval between the circular region located on the innermost side and the circular region located on an outermost side may be larger than a radius of the corner portion located on the innermost side.
In a configuration disclosed herein as an example, the semiconductor substrate may comprise a plurality of Field Limiting Rings (FLRs) each of which extends so as to surround the anode electrode. A number of the circular regions may be larger than a number of the FLRs.
In a configuration disclosed herein as an example, the semiconductor substrate may comprise a high density n-type region located under the n-type drift region and having a density of n-type impurities higher than that of the drift region. The p-type contact region may be separated from the high density n-type region by the n-type drift region. A radius of the corner portion located on an outermost side may be larger than an interval between the p-type contact region and the high density n-type region.
The embodiments have been described in detail in the above. However, these are only examples and do not limit the claims. The technology described in the claims includes various modifications and changes of the concrete examples represented above. The technical elements explained in the present description or drawings exert technical utility independently or in combination of some of them, and the combination is not limited to one described in the claims as filed. Moreover, the technology exemplified in the present description or drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of such objects.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-259316 | Dec 2014 | JP | national |
