JP5056147B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device including a DMOS element (Double diffused MOS-FET).

  2. Description of the Related Art Conventionally, as a switching power supply circuit such as a so-called DC-DC converter, a synchronous rectification type circuit using a MOS element as an output control unit is known as shown in Patent Document 1.

In such a synchronous rectification circuit, the high-side MOS element connected to the high potential side of the DC power supply and the low-side MOS element connected to the low potential side of the DC power supply are simultaneously turned on and have large penetrations. In order to prevent current from flowing, the gate voltage signal of each MOS element is turned on / off alternately between the high-side MOS element and the low-side MOS element while providing a dead time (period of simultaneous OFF). Yes.
JP 2004-312913 A

  As the operating frequency of the circuit is increased, a MOS element having a switching speed as high as possible is required, and the DMOS element is suitable for the above-mentioned use. However, for example, in the case where a current of 1 A or more flows, or in a system in which discrete components are connected by wires, the switching time of the MOS element becomes long due to parasitic inductance, so a relatively long dead time must be provided. In this case, current flows through the diode parasitic to the low-side MOS element during the dead time, and the high-side MOS element and the low-side MOS element pass through due to the delay in the recovery characteristics (reverse recovery time) of the diode. There is a problem that current flows.

  In view of the above problems, an object of the present invention is to provide a semiconductor device capable of controlling the operation of a parasitic diode and suppressing the generation of a through current.

  In order to achieve the above object, a semiconductor device according to claim 1 includes a first conductivity type semiconductor layer and a second conductivity type opposite to the first conductivity type formed on a surface layer on one surface side of the semiconductor layer. , A first conductivity type source region formed in a surface layer of the base region, and a second conductivity type having a higher impurity concentration in the surface layer of the base region than in the base region formed adjacent to the source region A semiconductor device including a DMOS element having a base contact region and a gate electrode disposed via a gate insulating film with respect to at least a part of the base region in the semiconductor layer. In the base region, by switching the applied potential to a predetermined potential with respect to the potential applied to the source region, one of the parasitic diode formed between the base region and the semiconductor layer and the high concentration region are provided. A depletion layer forming part for forming a depletion layer is formed in the base region so as to block a current path between the base region and the contact of the base region.

  Thus, according to the present invention, the depletion layer can be formed in the base region by setting the potential of the depletion layer forming portion formed in the base region to a predetermined potential with respect to the potential of the source region. This depletion layer is formed so as to block the current path between the parasitic diode formed between the base region and the semiconductor layer and the contact of the base region (part of the surface of the high concentration layer). The layer can block the flow of current from the contact to the anode of the parasitic diode. In other words, the operation of the parasitic diode can be suppressed depending on the presence or absence of the depletion layer, thereby suppressing the occurrence of a through current in the synchronous rectification type circuit.

  For example, as described in claim 2, when the first conductivity type is an n conductivity type, the depletion layer can be formed by setting the depletion layer forming portion to a positive potential with respect to the source region.

  As the depletion layer forming portion, for example, when a trench gate electrode in which a conductive material is filled through an insulating film in a trench formed from one surface of the semiconductor layer in the base region is employed as described in claim 3 good. Such a trench gate electrode can be formed by a known semiconductor process.

  In this case, as described in claim 4, it is preferable that the trench gate electrode is formed in the vicinity of the contact which is a starting point where current flows into the parasitic diode. With such a configuration, a depletion layer can be formed at a position close to the contact, and the current path between the contact and the parasitic diode can be efficiently blocked.

  Further, as described in claim 5, a plurality of trench gate electrodes may be formed so as to sandwich the contact therebetween. With such a configuration, the current path between the contact and the parasitic diode can be efficiently blocked by the depletion layer formed by the trench gate electrodes arranged to face each other via the contact.

  In the fifth aspect of the present invention, for example, as described in the sixth aspect, in the case where a plurality of contacts are formed in a row on the surface layer of the base region, the plurality of trench gate electrodes are contacted in the contact arrangement direction. It is preferable to have a configuration in which the two are alternately formed. With such a configuration, it is possible to uniformly form a depletion layer and completely block the current path between the plurality of contacts and the parasitic diode.

  Further, as described in claim 7, a plurality of trench gate electrodes may be formed so as to surround the contacts. Even in such a configuration, the current path between the contact and the parasitic diode can be efficiently blocked by the depletion layer formed by each trench gate electrode surrounding the contact.

  As a depletion layer forming portion other than the trench gate electrode, for example, as in claim 8, embedded diffusion of the first conductivity type embedded in a portion different from the high concentration region and the source region in the base region It is also possible to adopt a configuration having a first conductivity type connection region formed in a portion different from the high concentration region and the source region and connected to the buried diffusion layer, which is the surface layer of the base region and the source region.

  In this case, as described in claim 9, at least a part of the buried diffusion layer is preferably formed in the base region and immediately below the high concentration region. With such a configuration, the depletion layer can be formed as close to the contact as possible, and the current path between the contact and the parasitic diode can be efficiently blocked.

  Further, as described in claim 10, the plurality of buried diffusion layers may be formed so as to sandwich the contact therebetween. With such a configuration, the current path between the contact and the parasitic diode can be efficiently blocked by the depletion layer formed by the buried diffusion layer disposed so as to face the contact.

  In the invention according to claim 10, for example, when a plurality of contacts are formed in a row on the surface layer of the base region as in claim 11, a plurality of buried diffusion layers are arranged along the contact arrangement direction. It is preferable that the structure is formed. With such a configuration, it is possible to uniformly form a depletion layer and completely block the current path between the plurality of contacts and the parasitic diode.

  In the invention according to any one of claims 1 to 11, the drain of the first conductivity type formed as a DMOS element on the surface layer of the semiconductor layer apart from the base region as described in claim 12. A lateral DMOS device having a region can be employed. The lateral DMOS device has good process consistency with other devices such as CMOS, and is easy to integrate. As the DMOS element, besides the horizontal DMOS element, a vertical DMOS element having a configuration in which a drain region is stacked on the back side of one surface of a semiconductor layer in which a base region or the like is formed may be employed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a plan view showing a schematic configuration of the semiconductor device according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration along the line II-II in FIG. FIG. 3 is a cross-sectional view when the depletion layer is formed. In FIG. 1, for convenience, insulating films such as a LOCOS oxide film, an interlayer insulating film, and a protective film on the semiconductor substrate are omitted. Also in FIG. 2, insulating films such as an interlayer insulating film and a protective film are omitted.

As shown in FIGS. 1 and 2, the semiconductor device 100 includes a lateral DMOS element (Lateral Double Diffused MOS-FET, hereinafter referred to as an LDMOS element) as a DMOS element. In the present embodiment, a plurality of LDMOS elements are provided. Is formed on the semiconductor substrate 110. The semiconductor substrate 110 corresponds to the semiconductor layer of the first conductivity type described in the claims, and in this embodiment, for example, the n conductivity type (n of about 1 × 10 ¹⁶ cm ⁻³ ) is used. -) Bulk single crystal silicon substrate is adopted.

In the semiconductor substrate 110, a p conductivity type (p) base region 120 having, for example, an impurity concentration of about 1 × 10 ¹⁷ cm ⁻³ is formed in a part of the surface layer on one side. An n conductivity type (n +) source region 130 is formed on the surface layer of the base region 120. The impurity concentration of the source region 130 may be any concentration that can ensure ohmic characteristics with the source electrode. In this embodiment, it is about 1 × 10 ²⁰ cm ⁻³ . Further, on the surface layer of the base region 120, a p-conductivity type (p +) high concentration region 140 is formed adjacent to the source region 130. In the present embodiment, the high concentration region 140 is formed so as to enter the lower portion of the source region 130. The high concentration region 140 is a contact region with the source electrode (not shown) in the base region 120, and the impurity concentration may be a concentration that can ensure ohmic characteristics with the source electrode. In this embodiment, it is about 1 × 10 ²⁰ cm ⁻³ . In the present embodiment, adjacent source regions 130 of LDMOS elements are formed in one base region 120 with a high concentration layer 140 interposed therebetween.

  Further, as shown in FIG. 1, there are a plurality of contacts 131 with the source electrode in the source region 130 and contacts 141 with the source electrode in the high concentration region 140 along the longitudinal direction of the source region 130 and the high concentration region 140, respectively. Is formed. In other words, the plurality of contacts 131 are arranged in a row along the longitudinal direction of the source region 130, and the plurality of contacts 141 are arranged in a row along the longitudinal direction of the high concentration region 140. This contact 141 corresponds to the contact of the base region 120 described in the claims, and is hereinafter referred to as a base contact 141.

Further, an n conductivity type (n +) drain region 150 having an impurity concentration of about 1 × 10 ²⁰ cm ⁻³ is formed on the surface layer of the semiconductor substrate 110 apart from the base region 120. A portion of the base region 120 sandwiched between the source region 130 and the drain region 150 is a channel formation region of the LDMOS element. That is, in this embodiment, an n-channel type LDMOS element is formed as the LDMOS element. In the present embodiment, an n conductivity type (n) drift region 160 is formed on the surface layer of the semiconductor layer 110, which has a higher concentration than the semiconductor substrate 110 and becomes higher as the drain region 150 is approached. The drain region 150 is formed in the surface layer of the drift region 160.

  In addition, on the surface of the semiconductor substrate 110 on the side where the base region 120 and the like are formed and on the portion of the base region 120 sandwiched between the source region 130 and the drain region 150 (on the channel formation region), insulation is performed. A gate electrode 180 is formed through the film 170.

  The LDMOS element configured as described above has good process consistency with other elements such as CMOS, and can be easily integrated on the semiconductor substrate 110. 2 denotes a parasitic diode configured between the p-conductivity type (p) base region 120 and the n-conductivity type (n−) semiconductor substrate 110.

  Furthermore, in the semiconductor device 100 according to the present embodiment, a trench is formed so as to be included in the base region 120 constituting the LDMOS element, and an insulating film (not shown) such as a silicon oxide film is interposed in the trench. A trench gate electrode 200 filled with polycrystalline silicon doped with impurities or a metal material is formed. The trench gate electrode 200 corresponds to the depletion layer forming portion described in the claims.

  The trench gate electrode 200 is formed so that at least a part of the trench gate electrode 200 is located in a portion different from the source region 130 and the high concentration region 140 in the base region 120. Therefore, in the case of an n-channel type LDMOS element as shown in the present embodiment, the potential of the trench gate electrode 200 (the potential applied to the depletion layer forming pad K shown in FIG. 2) is applied to the source region 130. When the potential is positive with respect to the potential (potential applied to the source electrode pad S shown in FIG. 2), the depletion layer 210 extending from the trench gate electrode 200 to the base region 120, for example, as shown by a one-dot chain line in FIG. Can be formed.

  In addition, the trench gate electrode 200 forms a current path between the parasitic diode 190 formed between the base region 120 and the semiconductor substrate 110 and the base contact 141 which is a part of the high concentration region 140 by the depletion layer 210. It is formed (shape, arrangement, applied potential, etc. are determined) so as to be closed (blocked). That is, when the depletion layer 210 is formed, the trench gate electrode 200 is formed so that no current flows from the source electrode pad S to the anode of the parasitic diode 190 via the base contact 141. For example, if the trench gate electrode 200 is formed in the vicinity of the base contact 141 where the current flows into the parasitic diode 190, the depletion layer 190 can be formed at a position close to the base contact 141. The current path between the contact 141 and the parasitic diode 190 can be efficiently blocked. Further, when the base contact 141 is sandwiched between the plurality of trench gate electrodes 200, the base contact 141 and the parasitic diode 190 are formed by the depletion layer 210 extending from the trench gate electrode 200 disposed so as to face the base contact 141. The current path between the two can be efficiently blocked.

  In the present embodiment, in consideration of these points, as shown in FIG. 1, in the configuration in which a plurality of base contacts 141 are formed in a row on the surface layer of the base region 120, in the arrangement direction of the base contacts 141, A plurality of trench gate electrodes 200 are formed alternately with the base contacts 141. The plurality of trench gate electrodes 200 are substantially parallel to each other. Therefore, the depletion layer 210 can be uniformly formed in the vicinity of the plurality of base contacts 141, and the current path between the plurality of base contacts 141 and the parasitic diode 190 can be completely blocked. In the present embodiment, the depth of the trench gate electrode 200 is set so as to ensure a desired breakdown voltage when the depletion layer 210 is formed in consideration of the ESD tolerance. Specifically, when the distance between the trench gate electrodes 200 arranged opposite to each other with one base contact 141 interposed therebetween is D (see FIG. 1), the bottom of the trench gate electrode 200 and the bottom of the base region 120 are opposed to each other. The interval H (see FIG. 2) may be at least greater than D / 2, and preferably greater than D. In the present embodiment, the facing interval H is set larger than D.

  As described above, according to the semiconductor device 100 according to the present embodiment, the potential of the trench gate electrode 200 formed in the base region 120 is set to a predetermined potential (positive potential) with respect to the potential of the source region 130. A depletion layer 210 can be formed in the base region 120. The depletion layer 210 closes a current path between the parasitic diode 190 and the base contact 141 formed between the base region 120 and the semiconductor substrate 110, so that the base contact 141 is connected to the anode of the parasitic diode 190. Current flow can be cut off. That is, the trench gate electrode 200 functions as a switch that controls the conduction state in the current path between the base contact 141 and the parasitic diode 190.

  Note that, during normal operation of the semiconductor device 100 (LDMOS element), the potential of the trench gate electrode 200 is set to a negative potential with respect to the potential of the source region 130, whereby the n-conductivity type source region 130 and the p-conductivity type base. The base resistance of the npn parasitic bipolar transistor formed of the region 120 and the n-conductivity type semiconductor substrate 110 can be lowered to suppress the operation of the parasitic bipolar transistor, thereby making it difficult to deteriorate the characteristics of the LDMOS element.

  Next, effects obtained when the LDMOS element of the semiconductor device 100 according to the present embodiment is applied to a synchronous rectification switching circuit will be described with reference to FIGS. FIG. 4 is a diagram illustrating an example of a synchronous rectification switching circuit in which the LDMOS element of the semiconductor device according to the present embodiment is applied as a low-side MOS element. FIG. 5 is a diagram illustrating operation waveforms of the switching circuit.

  The switching circuit 10 (voltage step-down circuit) shown in FIG. 4 is a known switching circuit including a high-side MOS element and a low-side MOS element, and the LDMOS element of the semiconductor device 100 described above is applied to the low-side MOS element. It is a thing.

  Specifically, the MOS element 12 on the high side (high potential (positive electrode) side of the DC power supply 11) as a main switching element, and the LDMOS element 13 on the low side (low potential (negative electrode) side of the DC power supply) as an element for synchronous rectification. , An inductance 14 and a smoothing capacitor 15, and a control circuit 16 for controlling these circuit groups. 4 is the parasitic diode described above, and reference numeral 200 is the trench gate electrode as a switch for controlling the conduction state in the current path between the base contact 141 and the parasitic diode 190 as described above. It is.

  A series circuit of the MOS element 12 and the LDMOS element 13 is connected in parallel to the DC power supply 11. An inductance 14 and a smoothing capacitor 15 are connected in series between the drain and source of the LDMOS element 13. Further, as shown in FIG. 5, the control circuit 16 alternately turns on and off the MOS element 12 and the LDMOS element 13, whereby the voltage of the DC power supply 11 is lowered and the smoothed output VOUT is supplied to a load (not shown). It has come to be. Further, a parasitic diode 190 and a trench gate electrode 200 are connected in series between the drain and source of the LDMOS element 13.

  In such a switching circuit 10, as described above, in order to prevent the MOS element 12 and the LDMOS element 13 from being simultaneously turned on, a dead time is provided as shown in FIG. The gate signals Vg1 and Vg2 are alternately applied. Here, when the gate signal Vg2 of the LDMOS element 13 on the low side is to be turned off, the inductance 14 tries to draw a current from the drain in a transient state. The transient state is a state where the drain-source resistance is neither on-resistance nor high impedance. In the conventional configuration (configuration without the trench gate electrode 200 as a switch), current flows from the base contact 141 to the anode of the parasitic diode 190, and the recovery characteristics of the parasitic diode 190 delay the MOS element 12 and the LDMOS. There was a problem that the element 13 was turned on simultaneously and a through current flowed.

  On the other hand, in the present embodiment, as shown in FIG. 5, the trench gate as a switch in a predetermined period including a transient state when the control circuit 16 turns off the gate signal Vg <b> 2 of the LDMOS element 13 on the low side. A positive signal with respect to the source potential is given to the electrode 200 as the depletion layer signal Vk. Thereby, as described above, the depletion layer 210 is formed in the base region 120 so as to block the current path between the base contact 141 and the parasitic diode 190. Therefore, no current flows from the base contact 141 to the anode of the parasitic diode 190, and the parasitic diode 190 does not operate, so that generation of a through current can be suppressed.

  As described above, according to the semiconductor device 100 according to the present embodiment, the depletion layer 210 can be formed according to the applied potential of the trench gate electrode 200, and the operation of the parasitic diode 190 is controlled depending on the presence or absence of the depletion layer 210. Can do. Thereby, generation | occurrence | production of the through current in the synchronous rectification switching circuit 10 can be suppressed.

  In the present embodiment, the semiconductor device 100 includes an LDMOS element as a low-side MOS element. However, the semiconductor device 100 may include not only the low-side LDMOS element but also the high-side MOS element 12. Further, the switching circuit 10 may be integrated on the same semiconductor substrate 110.

  In this embodiment, the source potential is supplied as the depletion layer signal Vk to the trench gate electrode 200 as a switch in a predetermined period including a transient state when the gate signal Vg2 of the LDMOS element 13 on the low side is turned off. An example in which a positive signal is given is shown. However, a positive signal with respect to the source potential may be applied as the depletion layer signal Vk to the trench gate electrode 200 as a switch in a predetermined period including a transient state when the gate signal Vg2 is turned on. Further, as shown in FIG. 6, as a depletion layer signal Vk to the trench gate electrode 200 as a switch in a predetermined period including a transient state when the gate signal Vg1 of the high-side MOS element 12 is turned off, A positive signal may be given to the source potential. As a result, even when the parasitic diode 190 operates to supply a current to the inductance 14, the current to the parasitic diode 190 is cut off and the occurrence of a through current can be suppressed. Note that a positive signal with respect to the source potential may be given as the depletion layer signal Vk to the trench gate electrode 200 as a switch in a predetermined period including a transient state when the gate signal Vg1 is turned off.

  In the present embodiment, an example in which the trench gate electrode 200 and the base contact 141 are alternately formed has been described. However, the aspect of the trench gate electrode 200 is not limited to the above example. For example, as shown in FIG. 7, a plurality of trench gate electrodes 200 may be formed so as to surround the base contact 141. Even in such a configuration, the current path between the base contact 141 and the parasitic diode 190 can be efficiently blocked in the vicinity of the base contact 141 by the depletion layer 210 extending from each trench gate electrode 200 surrounding the base contact 141. it can. In FIG. 7, each trench gate 200 is formed so as to straddle the source region 130 and the high concentration region 140, and one base contact 141 is surrounded by four trench gate electrodes 200. FIG. 7 is a plan view showing a modification.

  Further, as shown in FIG. 8, two trench gate electrodes 200 are formed across the source region 130 and the high concentration region 140 along the arrangement direction of the base contacts 141, and a plurality of base gates 200 are formed between the trench gate electrodes 200. A configuration in which the contact 141 is sandwiched is also possible. Also in this case, the current path between the base contact 141 and the parasitic diode 190 can be efficiently blocked in the vicinity of the base contact 141. However, the base resistance of the parasitic bipolar transistor including the source region 130, the base region 120, and the semiconductor substrate 110 is larger than the configuration shown in this embodiment and the configuration shown in FIG. 7, and the parasitic bipolar transistor operates. It becomes easy. Therefore, in consideration of this point, it is preferable to adopt the configuration shown in the present embodiment or the configuration shown in FIG. FIG. 8 is a plan view showing a modification.

  In the present embodiment, an example in which the source region 130 and the high-concentration region 140 are formed is shown. However, as described above, the trench gate electrode 200 may be formed so that at least a part of the trench gate electrode 200 is located in a portion different from the source region 130 and the high concentration region 140 in the base region 120. For example, it may be formed through only the high concentration region 140 or may be formed through only the source region 130. Furthermore, it may be formed only in a portion different from the source region 130 and the high concentration region 140 in the base region 120. However, in view of efficient current path, it is preferable that the structure be formed in the vicinity of the base contact 141 as described above.

(Second Embodiment)
Next, 2nd Embodiment of this invention is described based on FIG.9 and FIG.10. FIG. 9 is a plan view illustrating a schematic configuration of the semiconductor device according to the second embodiment. FIG. 10 is a cross-sectional view showing a schematic configuration along the line XX of FIG. In FIG. 9, for convenience, insulating films such as a LOCOS oxide film, an interlayer insulating film, and a protective film on the semiconductor substrate are omitted. Also in FIG. 10, insulating films such as an interlayer insulating film and a protective film are omitted.

  Since the semiconductor device according to the second embodiment is often in common with the semiconductor device shown in the first embodiment, the detailed description of the common parts will be omitted below, and different parts will be described mainly. In addition, the same code | symbol shall be provided to the element same as the element shown in 1st Embodiment.

  In the first embodiment, the example of the trench gate electrode 200 is shown as the depletion layer forming part for forming the depletion layer 210 in the base region 120. On the other hand, in the present embodiment, as shown in FIGS. 9 and 10, the depletion layer forming portion is embedded in the base region 120 and in a portion different from the high concentration region 140 and the source region 130. An n conductivity type connection region 221 that is formed on a surface layer of the n conductivity type buried diffusion layer 220 and the base region 120 and is different from the high concentration region 140 and the source region 130 and connected to the buried diffusion layer 220. It is characterized by having Other configurations are the same as those shown in the first embodiment.

Such a buried diffusion layer 220 can be formed by, for example, an ion implantation method. In the present embodiment, the high concentration region 140 and the source region 130 are separated from the high concentration region 140 and the source region 130 so as to straddle the high concentration region 140 and the source region 130 by high acceleration implantation. ing. The impurity concentration may be at least higher than that of the semiconductor substrate 110, and is approximately the same as that of the base region 120 (about 1 × 10 ¹⁷ cm ⁻³ ) in this embodiment. The connection region 221 is a contact region of the buried diffusion layer 220, and the impurity concentration thereof is approximately the same as that of the source region 130 (approximately 1 × 10 ²⁰ cm ⁻³ ).

  Therefore, the potential applied to the buried diffusion layer 220 and the connection region 221 formed in the base region 120 is set to a predetermined potential (positive potential) with respect to the potential of the source region 130, thereby depleting the base region 120. A layer (not shown) can be formed. The depletion layer blocks a current path between the parasitic diode 190 and the base contact 141 formed between the base region 120 and the semiconductor substrate 110, so that a current from the base contact 141 to the anode of the parasitic diode 190 can be obtained. Can be cut off. That is, the depletion layer forming portion including the buried diffusion layer 220 and the connection region 221 functions as a switch that controls the conduction state in the current path between the base contact 141 and the parasitic diode 190. Therefore, generation of a through current in the synchronous rectification switching circuit 10 can be suppressed.

  In the present embodiment, the plurality of base contacts 141 are formed in a row, and the two buried diffusion layers 220 are substantially parallel to each other with the plurality of base contacts 141 interposed therebetween along the arrangement direction of the base contacts 141. Is formed. Therefore, the depletion layer 210 can be uniformly formed in the vicinity of the plurality of base contacts 141, and the current path between the plurality of base contacts 141 and the parasitic diode 190 can be completely blocked. Note that only a part of the buried diffusion layer 220 (both ends in the present embodiment) is connected to the connection region 221. Therefore, the operation of the parasitic bipolar transistor including the source region 130, the base region 120, and the semiconductor substrate 110 is performed more than the trench gate electrode 200 having a similar configuration, although the configuration is formed along the arrangement direction of the base contacts 141. Can be suppressed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the present embodiment, an example of an LDMOS element is shown as the DMOS element. However, a configuration in which the present invention is applied (depletion layer formation) to a vertical DMOS device (so-called VDMOS device) in which a drain region is stacked on the back side of one surface of a semiconductor layer in which a base region and the like are formed. It is also possible to adopt a configuration in which a part is provided. However, in the VDMOS element, since design factors in the thickness direction of the semiconductor substrate 110 are included, it is difficult to integrate with other elements such as a CMOS. Therefore, in consideration of process consistency and integration with other elements such as CMOS, it is preferable to employ an LDMOS element.

  In the present embodiment, an example in which the DMOS element (LDMOS element) is an n-channel type is shown. However, the present invention can also be applied to a p-channel type. In the case of the p-channel type, the potential applied to the depletion layer formation portion is set to a negative potential with respect to the potential applied to the p-conduction type source region, so that the depletion layer formation portion is transferred to the n-conduction type base region A spreading depletion layer can be formed. Further, the semiconductor device 100 may include an n-channel type and a p-channel type DMOS element (LDMOS element) as the high-side and low-side MOS elements constituting the switching circuit 10. An example of a synchronous rectification switching circuit to which a p-channel DMOS element is applied is shown in FIG. In FIG. 11, the same reference numerals are given to the same elements as those of the switching circuit described above. 11 includes a p-channel DMOS element (LDMOS element) as a high-side MOS element 12, an n-channel MOS element 13 on the low-side, an inductance 14, and a smoothing capacitor 15. And a control circuit 16 for controlling these circuit groups. Further, reference numeral 190 shown in FIG. 11 is the parasitic diode described above, and reference numeral 200 is the trench gate electrode as a switch for controlling the conduction state in the current path between the base contact 141 and the parasitic diode 190 as described above. It is.

  In this embodiment, an example in which a bulk single crystal silicon substrate is employed as the semiconductor substrate 110 has been shown. However, a semiconductor layer of an SOI structure substrate in which a semiconductor layer is disposed on a supporting substrate with an insulating layer interposed may be adopted as the semiconductor substrate.

1 is a plan view showing a schematic configuration of a semiconductor device according to a first embodiment. It is sectional drawing which shows schematic structure in alignment with the II-II line | wire of FIG. It is sectional drawing at the time of depletion layer formation. It is a figure which shows an example of the switching circuit of the synchronous rectification system which applied the LDMOS element of the semiconductor device which concerns on 1st Embodiment as a MOS element by the side of a low side. It is a figure which shows the operation | movement waveform of a switching circuit. It is a figure which shows the modification of an operation waveform. It is a top view which shows a modification. It is a top view which shows a modification. It is a top view which shows schematic structure of the semiconductor device which concerns on 2nd Embodiment. It is sectional drawing which shows schematic structure in alignment with the XX line of FIG. It is a figure which shows the other example of the switching circuit of a synchronous rectification system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Switching circuit 12 ... High side MOS element 13 ... Low side LDMOS element (semiconductor device)
14 ... Inductance 13 ... Smoothing capacitor 100 ... Semiconductor device 110 ... Semiconductor substrate (semiconductor layer)
120 ... base region 130 ... source region 140 ... high concentration region 141 ... base contact 150 ... drain region 160 ... drift layer 180 ... gate electrode 190 ... parasitic diode 200 ... Trench gate electrode (depletion layer forming part)
210 ... depletion layer

Claims (12)

A first conductivity type semiconductor layer;
A base region of a second conductivity type opposite to the first conductivity type formed on a surface layer on one surface side of the semiconductor layer;
A source region of a first conductivity type formed in a surface layer of the base region;
A second conductivity type high concentration region having a higher impurity concentration than the base region formed adjacent to the source region in a surface layer of the base region;
A semiconductor device comprising a DMOS element having a gate electrode disposed through a gate insulating film for at least a partial region of the base region in the semiconductor layer,
In the base region, a parasitic diode configured between the base region and the semiconductor layer and the high concentration are switched by switching the applied potential to a predetermined potential with respect to the potential applied to the source region. A semiconductor device, wherein a depletion layer forming part for forming a depletion layer is formed in the base region so as to block a current path between the base region and a contact of the base region which is a part of the region. The first conductivity type is an n conductivity type,
The semiconductor device according to claim 1, wherein the depletion layer is formed by setting the depletion layer formation portion to a positive potential with respect to the source region.   The depletion layer forming portion is a trench gate electrode in which a conductive material is filled in an insulating film in a trench formed from one surface of the semiconductor layer in the base region. The semiconductor device according to claim 2.   The semiconductor device according to claim 3, wherein the trench gate electrode is formed in the vicinity of the contact.   5. The semiconductor device according to claim 3, wherein the plurality of trench gate electrodes are formed so as to sandwich the contact therebetween. In the surface layer of the base region, a plurality of the contacts are formed in a row,
6. The semiconductor device according to claim 5, wherein a plurality of the trench gate electrodes are alternately formed with the contacts in the arrangement direction of the contacts.   The semiconductor device according to claim 3, wherein the plurality of trench gate electrodes are formed so as to surround the contact.   As the depletion layer forming part, a buried diffusion layer of a first conductivity type embedded in a portion different from the high concentration region and the source region in the base region, and a surface layer of the base region, 3. The semiconductor device according to claim 1, further comprising a connection region of a first conductivity type that is formed at a site different from the high concentration region and the source region and connected to the buried diffusion layer. .   9. The semiconductor device according to claim 8, wherein the buried diffusion layer is formed at least in part in the base region and immediately below the high concentration region.   The semiconductor device according to claim 9, wherein the plurality of buried diffusion layers are formed so as to sandwich the contact therebetween. In the surface layer of the base region, a plurality of the contacts are formed in a row,
The semiconductor device according to claim 9, wherein a plurality of the buried diffusion layers are formed along an arrangement direction of the contacts.   12. The DMOS device according to claim 1, wherein the DMOS device is a lateral DMOS device having a drain region of a first conductivity type formed in a surface layer of the semiconductor layer apart from the base region. A semiconductor device according to 1.

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