SEMICONDUCTOR DEVICE WITH SCHOTTKY BARRIER DIODE

A semiconductor device includes a first conductivity-type drift region including an exposed portion, a plurality of second conductivity-type body regions, a first conductivity-type source region, a gate portion and a Schottky electrode. The drift region is defined in a semiconductor layer, and the exposed portion exposes on a surface of the semiconductor layer. The body regions are disposed on opposite sides of the exposed portion. The source region is separated from the drift region by the body region. The gate portion is disposed to oppose the body region. The exposed portion is formed with a groove, and the Schottky electrode is disposed in the groove. The Schottky electrode has a Schottky contact with the exposed portion.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described. The items described hereinafter each have technical usability.

According to an embodiment of the present disclosure, a semiconductor device includes a first conductivity-type drift region, second conductivity-type body regions, a first conductivity-type source region, a gate portion, and a Schottky electrode. The first conductivity-type drift region is defined in a semiconductor layer, and has an exposed portion exposing on a surface of a semiconductor layer. The second conductivity-type body regions are disposed on opposite sides of the exposed portion of the first conductivity-type drift region. The first conductivity-type source region is separated from the drift region by the second conductivity-type body region. The gate portion is opposed to the second conductivity-type body region, which separates the source region from the drift region. The Schottky electrode contacts the exposed portion of the first conductivity-type drift region to have a Schottky contact with the exposed portion. The exposed portion is formed with a groove. The Schottky electrode is disposed in the groove.

Examples of the semiconductor device may be a metal oxide semiconductor field effect transistor (MOSFET) and an insulated gate bipolar transistor (IGBT).

In the semiconductor device, the Schottky electrode has the Schottky contact with the exposed portion of the drift region. Therefore, a Schottky barrier diode is integrated in the exposed portion of the drift region.

The structure of the gate portion may not be limited to a specific one. For example, the gate portion may be a trench gate or a planar gate.

In the semiconductor device, the groove is formed in the exposed portion of the drift region, and the Schottky electrode is disposed in the groove.

The body region may include a contact region between the exposed portion of the drift region and the source region. The contact region has an impurity concentration higher than that of a remaining portion of the body region.

The Schottky electrode disposed in the groove may extend to a position deeper than the contact region. In this case, since the Schottky electrode disposed in the groove extends to a position deeper than a depletion layer that expands in the exposed portion of the drift region from the contact region, an influence of the depletion layer is restricted, and an increase in forward voltage of the Schottky barrier diode can be reduced.

The gate portion may extend in a first direction, when the semiconductor layer is viewed along a direction generally normal to a surface of the semiconductor layer, that is, in a direction normal to a plane surface of the semiconductor layer. The first direction is a direction included in the plane of the semiconductor layer. In this case, the exposed portion of the drift region has a width in a second direction that is perpendicular to the first direction and included in the plane of the semiconductor layer. Also, the contact region of the body region has a width in the second direction. The ratio of the width of the exposed portion and the width of the contact region may vary in the first direction.

The exposed portion of the drift region may have wide portions and narrow portions narrower than the wide portions, in the first direction. In other words, the contact region of the body region may have narrow portions and wide portions wider than the narrow portions, in the first direction. In this case, since the wide portions of the exposed portion or the narrow portions of the contact region exist, the increase in the forward voltage of the Schottky barrier diode is restricted. Also, since the narrow portions of the drift region or the wide portions of the contact region exist, it is less likely that a latch-up will occur.

The Schottky electrode disposed in the groove may extend to a position not deeper than the body region. In this case, an electric field concentration at a bottom surface of the Schottky electrode is alleviated, and a capacity improves.

The semiconductor layer may be a silicon carbide layer.

Hereinafter, exemplary embodiments of the present disclosure will be described more in detail with reference to the drawings.

A semiconductor device1according to an embodiment will be described with reference toFIG. 1toFIG. 3. The semiconductor device1is a metal oxide semiconductor field effect transistor (MOSFET) integrating a Schottky barrier diode therein. The semiconductor device1is, for example, used to an inverter that supplies alternating-current (AC) power to an AC motor. The Schottky barrier diode serves as a freewheel diode. As shown inFIGS. 1 and 2, the semiconductor device1includes a drain electrode10, a silicon carbide layer20, a source electrode30, and a trench gate40.

The drain electrode10is formed to cover a rear surface (e.g., lower surface inFIG. 1) of the silicon carbide layer20. The drain electrode10contacts the rear surface of the silicon carbide layer20and forms an ohmic contact with the silicon carbide layer20. As a material of the drain electrode10, for example, nickel (Ni), titanium (Ti), molybdenum (Mo), or cobalt (Co) may be used.

The silicon carbide layer20includes an n-type substrate21, an n-type drift region22, p-type body regions23, and n-type source regions24. The n-type substrate21is a silicon carbide substrate having a surface in a plane direction [0001]. The n-type substrate21is also referred to as a drain region. A rear surface (e.g., lower surface inFIG. 1) of the substrate21contacts the drain electrode10and forms an ohmic contact with the drain electrode10.

The drift region22is disposed on the substrate21. The drift region22has an exposed portion26on its top. The exposed portion26is formed as a projection. A top surface of the exposed portion26exposes on a part of the surface of the silicon carbide layer20. In other words, the top surface of the exposed portion26forms a part of the surface of the silicon carbide layer20. The exposed portion26extends parallel to a longitudinal direction (e.g., arrow L inFIG. 1) of the trench gate40arranged in a stripe shape. The longitudinal direction L corresponds to a first direction that is defined in a plane of the silicon carbide layer20. The drift region22is formed by a crystal growth from the substrate21using an epitaxial growth technique.

The exposed portion26of the drift region22is interposed between the body regions23. That is, the body regions23are disposed on opposite sides of the exposed portion26of the drift region22. The body region23has a contact region25on its top. The contact region25is disposed between the exposed portion26of the drift region22and the source region24. The contact region25exposes at a part of the surface of the silicon carbide layer20. The contact region25has a relatively high impurity concentration.

The contact region25has a function of restricting a latch-up. The contact region25restricts a part of holes toward the source electrode30from flowing into the source region24, when the Schottky barrier diode carries out a recovery operation. Therefore, the contact region25is disposed adjacent to the source region24and has a certain amount of area. The contact region25extends in the longitudinal direction L. The body region23is formed by introducing a p-type impurity from the surface of the silicon carbide layer20. The p-type impurity is introduced two or more times by an ion implantation technique while changing a range distance. For example, the p-type impurity is aluminum.

The source region24is disposed on the body region23, and is separated from the drift region22by the body region23. Also, the source region24exposes at a part of the surface of the silicon carbide layer20. The source region24extends parallel to the longitudinal direction L. The source region24is formed by introducing an n-type impurity from the surface of the silicon carbide layer20by an ion implantation technique. For example, the n-type impurity is phosphorous (P).

The source electrode30covers the surface of the silicon carbide layer20. The source electrode30contacts the source region24, the contact region25of the body region23, and the exposed portion26of the drift region22, which expose on the surface of the silicon carbide layer20.

The exposed portion26of the drift region22is formed with a groove34. A part of the source electrode30is disposed in the groove34. Hereinafter, the part of the source electrode30disposed in the groove34is referred to as a trench Schottky electrode32.

The trench Schottky electrode32extends parallel to the longitudinal direction L. The source electrode30forms an ohmic contact with the source region24and the contact region25of the body region23. The source electrode30forms a Schottky contact with the exposed portion26of the drift region22. As a material of the source electrode30, for example, Ni, Ti, or Mo may be used. As another example, the source electrode30may be formed in such a manner that the portion forming the ohmic contact with the source region24and the contact region25and the portion forming the Schottky contact with the exposed portion26are made of different materials.

The trench gate40is opposed to the body region23, which separates the source region24from the drift region22. The trench gate40includes a trench gate electrode42and a gate insulation film44. The trench gate electrode42and the gate insulation film44are disposed in a trench that extends through the body region23from the surface of the silicon carbide layer20. The gate insulation film44covers an inner surface of the trench. The gate insulation film44is formed by a chemical vapor deposition (CVD) technique. The trench gate electrode42is filled on the gate insulation film44in the trench by a chemical vapor deposition (CVD) technique.

FIG. 3illustrates an enlarged cross-sectional view of a part of the exposed portion26of the drift region22. To increase a current density of the semiconductor device1, for example, an area of the MOS structure per unit area need to be increased by reducing a distance between adjacent MOS structures. In such a high density semiconductor device1, however, a distance W25between the contact regions25of the adjacent body regions23is short.

For example, in a semiconductor device without having the trench Schottky electrode32, a conduction path of the exposed portion26is narrowed due to a depletion layer expanding from the contact regions25, as shown by a dashed line inFIG. 3. As a result, a forward voltage of the Schottky barrier diode increases.

In the semiconductor device1having the trench Schottky electrode32, on the other hand, the influence by the narrowing of the conduction path due to the depletion layer can be reduced. Therefore, the increase of the forward voltage of the Schottky barrier diode can be restricted.

As described above, the forming of the trench Schottky electrode32is useful in the high density semiconductor device1.

As shown inFIG. 3, the depletion layer widely expands on the sides of the contact regions25, which are located at a surface layer portion and have the high impurity concentration. Therefore, the trench Schottky electrode32extends to a position deeper than the contact regions25. In this case, the influence by the narrowing of the conduction path due to the depletion layer can be suitably restricted.

The trench Schottky electrode32is disposed at a position shallower than the body regions23. For example, the trench Schottky electrode32ends at a position higher than a bottom end of the body region23. In this case, an electric field applied to the bottom surface of the trench Schottky electrode32can be alleviated.

As shown inFIG. 4, an insulation region36may be disposed at the bottom of the trench Schottky electrode32. The insulation region36contacts the bottom surface of the trench Schottky electrode32. The insulation region36is filled at the bottom of the groove34by a chemical vapor deposition (CVD) technique, for example. In the case where the insulation region36is disposed at the bottom of the trench Schottky electrode32, a breakdown due to the concentration of electric field at the bottom surface of the trench Schottky electrode32can be restricted.

The configuration of the trench Schottky electrode32formed at the exposed portion of the drift region22is not limited to a specific one. For example, as shown inFIG. 5, a plurality of trench Schottky electrodes32may be disposed at the exposed portion26of the drift region22. For example, as shown inFIG. 6, the trench Schottky electrode32may be disposed separately or discontinuously in the longitudinal direction L. Also in these cases, the effect of restricting the increase in the forward voltage of the Schottky barrier diode can be achieved.

As shown inFIG. 7, the exposed portion26of the drift region22may have narrow portions26aand wide portions26b.The narrow portions26aand the wide portions26bare alternately arranged in the longitudinal direction L. In other words, the contact region25of the body region23may have wide portions25aand narrow portions25balternately in the longitudinal direction L. That is, the exposed portion26and the contact regions25may be formed in such a manner that, when viewed in a direction perpendicular to the longitudinal direction L, a ratio of the width of the exposed portion26and the width of the contact region25discontinuously varies in the longitudinal direction L.

In this case, it is less likely that the latch-up will occur at the narrow portions26aof the exposed portions26, that is, at the wide portions25aof the contact region25. Therefore, the increase of the forward voltage of the Schottky barrier diode is restricted at the wide portions26bof the exposed portion26, that is, the narrow portions25bof the contact region25.

The ratio of the width of the exposed portion26and the width of the contact region25may be varied in the longitudinal direction L in any other ways. For example, a layout shown inFIG. 8may be employed. In the example ofFIG. 8, the width of the exposed portion26continuously or gradually varies in the longitudinal direction L. Also in this case, the occurrence of the latch-up is reduced, and the increase of the forward voltage is restricted.

In place of or in addition to the change of the surface layout, the thickness of the contact region25may be changed. For example, as shown inFIG. 9, the thickness of the contact region25may be smaller than the source region24. In this case, the width of the depletion layer expanding from the contact region25can be reduced. Therefore, the increase of the forward voltage of the Schottky barrier diode can be restricted.

As shown inFIG. 10, a p-type high impurity corner region27may disposed at a corner portion of the body region23that is adjacent to the exposed portion26of the drift region22. The p-type high impurity corner region27has an impurity concentration higher than that of the corner of the body region23. In the case where the high impurity corner region27is disposed, the electric field concentration at the corner portion of the trench gate40is alleviated. Thus, the breakdown due to the electric field concentration at the corner portion of the trench gate40can be restricted.

While only the selected exemplary embodiment and examples have been chosen to illustrate the present disclosure, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the disclosure as defined in the appended claims. Furthermore, the foregoing description of the exemplary embodiment and examples according to the present disclosure is provided for illustration only, and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents. The technical elements described hereinabove and illustrated in the drawings are useful by itself or in any combinations, and are not limited to the combinations of the appended claims described at the time of filing the application. The features exemplified hereinabove and illustrated the drawings can achieve a plurality of objectives, but can be technically useful even only by achieving one of the objectives.