JP2008085086A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which can improve the withstanding voltage in forming an floating electrode in a terminal area. <P>SOLUTION: A terminal area 42 of a semiconductor device 1 having an active region 41 in which a MOSFET is prepared and the terminal area 42 located in exterior of the active region 41 includes an end electrode 52 connected to a drain electrode 50 and formed in the end on an epitaxial layer 44, a plurality of trenches 53 formed in the surface of the epitaxial layer 44, a floating electrode 54 formed respectively in the plurality of trenches 53, and a plurality of Zener diodes 4 not only connected in series mutually between a source electrode 49 of the active region 41 and the end electrode 52 but also connected to the each floating electrode 54, each of which is composed of n-type conductor 2 and p-type conductor 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device with improved breakdown voltage.

Conventionally, as a semiconductor device with improved breakdown voltage, for example, in the terminal region outside the active region where a gate trench type MOSFET (Metal Oxide Field Effect Transistor) is provided, the epitaxial layer is formed on the surface of the epitaxial layer on the semiconductor substrate. In some cases, a semiconductor region of a conductor different from that of the layer, that is, a so-called FLR (Field Limiting Ring) is formed, and an end electrode connected to the drain electrode is formed at the terminal on the epitaxial layer. (For example, see Patent Document 1)
According to the semiconductor device described above, the depletion layer formed in the active region as the voltage between the drain electrode and the source electrode increases can be extended to the termination region by the FLR. Therefore, since the electric field concentrated on the corner of the gate trench at the end of the active region can be relaxed, breakdown current hardly flows in the active region, and the breakdown voltage can be improved.

  However, in the above semiconductor device, it is necessary to form the FLR deeply in order to extend the depletion layer to the termination region, and there is a possibility that the semiconductor substrate may be deteriorated by a long-time heat treatment at the time of forming the FLR.

Therefore, as a semiconductor device for solving this problem, for example, there is a semiconductor device in which a trench having a floating electrode inside is formed instead of the FLR in the termination region. (For example, see Patent Document 2)
FIG. 4 is a diagram illustrating a semiconductor device in which a trench having a floating electrode therein is formed in the termination region.

A semiconductor device 40 shown in FIG. 4 includes an active region 41 where a MOSFET is provided and a termination region 42 located outside the active region 41.
The MOSFET includes a semiconductor substrate 43 made of an n-type conductor, an n− epitaxial layer 44 formed on the semiconductor substrate 43, and a p− semiconductor region 45 formed by diffusion on the surface of the epitaxial layer 44. An n + semiconductor region 46 selectively diffused on the surface of the semiconductor region 45, a trench 47 formed from the surface of the semiconductor region 46 to the epitaxial layer 44, and an insulating film in the trench 47. A gate electrode 48 formed in this manner, a source electrode 49 connected to each surface of the semiconductor region 45 and the semiconductor region 46 (contact region formed by an insulating film 55 of a predetermined contact pattern), and a back surface of the semiconductor substrate 43 And a drain electrode 50 connected to the.

  The operation when the MOSFET is turned on will be described. First, when a positive voltage is applied to the gate electrode 48 with a voltage applied between the drain electrode 50 and the source electrode 49, an n-type channel is formed in the semiconductor region 45 around the trench 47. Then, the epitaxial layer 44 and the semiconductor region 46 are short-circuited, and a current flows between the drain electrode 50 and the source electrode 49.

  An end electrode 52 is formed at the termination of the termination region 42 on the epitaxial layer 44 via a semiconductor region 51 made of an n-type conductor. The end electrode 52 is electrically connected to the drain electrode 50. In the termination region 42, a plurality of trenches 53 that electrically divide the semiconductor region 45 are formed. Inside each of the plurality of trenches 53, a floating electrode 54 is formed of polysilicon or the like via an insulating film. In addition, an insulating film 55 is formed on the semiconductor region 45 and the trench 53 in the termination region 42.

As described above, in the semiconductor device 40, the semiconductor region 45 is electrically divided into the plurality of the trenches 53 in the termination region 42, so that an electric field is applied to each insulating film between the semiconductor region 45 and each floating electrode 54. The electric field concentrated on the corner of the trench 47 at the end of the active region 41 can be relaxed. Accordingly, since the semiconductor device 40 can improve the breakdown voltage without forming the FLR in the termination region 42, the problem of deterioration of the semiconductor substrate 43 due to the long-time heat treatment at the time of forming the FLR can be solved.
JP-A-9-186315 JP-A-9-283754

  However, in the semiconductor device 40, when the potential of the floating electrode 54 becomes unstable due to the movement of electric charge in the floating electrode 54 after manufacture, the electric field is concentrated in a certain trench 53 and the breakdown current in the termination region 42. Is liable to flow and hinders the improvement of pressure resistance.

  Therefore, an object of the present invention is to provide a semiconductor device capable of improving the breakdown voltage when a floating electrode is formed in a termination region.

In order to solve the above problems, the present invention adopts the following configuration.
That is, the semiconductor device of the present invention includes a semiconductor layer made of a first conductor, a first semiconductor region formed on the surface of the semiconductor layer and made of a second conductor different from the first conductor, A second semiconductor region selectively formed on the surface of the first semiconductor region and made of the first conductor; a first trench formed from the surface of the second semiconductor region to the semiconductor layer; A first electrode formed in the first trench through an insulating film, a second electrode connected to the respective surfaces of the first and second semiconductor regions, and a back surface of the semiconductor layer A semiconductor device comprising: an active region provided with an active element including a third electrode connected to the side; and a termination region located outside the active region, wherein the third electrode Connected to said An end electrode formed at the end on the conductor layer, a plurality of second trenches formed on the surface of the semiconductor layer, and a floating formed in each of the plurality of second trenches via an insulating film An electrode and a first electrode or a second electrode of the active region and the end electrode are connected in series to each other and to each of the floating electrodes, and each of the first and second conductors. And a plurality of Zener diodes.

  Here, the “third electrode connected to the back surface side of the semiconductor layer” means a third electrode directly or indirectly on the back surface side opposite to the surface on which the first semiconductor region is formed. It means that the electrodes are connected. For example, it is a MOSFET if directly connected, and an IGBT (Insulated Gate Bipolar Transistor) if connected via a second conductor.

  In this manner, in the termination region, a predetermined electrode (for example, the first electrode or the second electrode) in the active region and the end electrode are connected by a plurality of Zener diodes, and each floating electrode is connected to the Zener diode. Therefore, the depletion layer formed in the semiconductor layer between the second trenches spreads along the second trench due to the potential difference between the second trenches, and the depletion layer formed in the active region becomes the termination region. Can be extended to. Therefore, the electric field concentrated on the corner of the first trench at the end of the active region can be relaxed. In addition, since each floating electrode is connected to a Zener diode connected between a predetermined electrode and an end electrode in the active region, the potential of the floating electrode is stabilized and the depletion layer formed in the termination region is uniform. Electric field concentration in the spreading termination region can be prevented. This makes it difficult for a breakdown current to flow in the active region and the termination region, thereby improving the breakdown voltage of the semiconductor device.

  When the predetermined electrode is the second electrode, the plurality of Zener diodes are applied between the second electrode and the third electrode when a breakdown current flows in the semiconductor layer. The number of the Zener diodes may be configured to be lower than the overall voltage.

  As a result, even if a surge voltage is applied to the semiconductor device, the Zener diode can be turned on before the breakdown current flows in the semiconductor layer due to the surge voltage, so that the energy due to the surge voltage is absorbed by the Zener diode. The surge resistance of the semiconductor device can be improved.

  When the predetermined electrode is the first electrode, the plurality of Zener diodes are applied between the first electrode and the third electrode when a breakdown current flows in the semiconductor layer. The number of the Zener diodes may be configured to be lower than the overall voltage.

  As a result, even if a surge voltage is applied to the semiconductor device, the active element can be turned on by turning on the Zener diode before the breakdown current flows in the semiconductor layer due to the surge voltage. It can be absorbed by the active element and the surge resistance of the semiconductor device can be improved.

  In the semiconductor device, the first semiconductor region may be formed on a surface of the semiconductor layer in the termination region.

  According to the present invention, when the floating electrode is formed in the termination region of the semiconductor device, the breakdown voltage of the semiconductor device can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A shows a semiconductor device according to an embodiment of the present invention. Moreover, FIG.1 (b) is an enlarged view in the broken-line frame A shown to Fig.1 (a). In FIG. 1A or FIG. 1B, the same components as those shown in FIG.

  The semiconductor device 1 shown in FIG. 1A includes an active region 41 where a MOSFET (active element) is provided, and a termination region 42, similarly to the semiconductor device 40 shown in FIG.

  The MOSFET includes a semiconductor substrate 43, an epitaxial layer 44, a semiconductor region 45 (first semiconductor region), a semiconductor region 46 (second semiconductor region), a trench 47 (first trench), a gate electrode. 48 (first electrode), a source electrode 49 (second electrode), and a drain electrode 50 (third electrode). The “semiconductor layer” recited in the claims may be constituted by the semiconductor substrate 43 and the epitaxial layer 44, or may be constituted by the semiconductor substrate 43 or the epitaxial layer 44.

  A plurality of trenches 53 (second trenches) are formed in the termination region 42, and floating electrodes 54 are formed in the respective trenches 53 via insulating films. Further, an end electrode 52 is formed at the end of the end region 42 on the epitaxial layer 44.

  A feature of the semiconductor device 1 of this embodiment is that a plurality of Zener diodes 4 each consisting of an n-type conductor 2 and a p-type conductor 3 are connected in series as shown in FIG. Thus, the connection is made between the source electrode 49 and the end electrode 52 of the active region 41, and each floating electrode 54 is connected to the n-type conductor 2 of the Zener diode 4. In the semiconductor device 1 of the present embodiment, a plurality of Zener diodes 4 are connected in series between cathodes or anodes, the n-type conductor 2 of the Zener diode 4 at one end and the source electrode 49 are connected, and the other end The n-type conductor 2 of the zener diode 4 and the end electrode 52 are connected. Each floating electrode 54 is connected to the n-type conductor 2 of each Zener diode 4 formed above the floating electrode 54.

  The spacing between the trenches 53 and the position of the floating electrode 54 connected to the Zener diode 4 (the number of stages of the Zener diode 4 when counted from the source electrode 49) are determined by the depletion layer formed in the epitaxial layer 44 in the termination region 42. It is assumed that it is set so as to spread uniformly along the trench 53.

  The total number of Zener diodes 4 is set such that the breakdown voltage of the entire Zener diode 4 is larger than the rated voltage of the semiconductor device 1. For example, when the rated voltage of the semiconductor device 1 is 60 V and the breakdown voltage of one Zener diode 4 is 6 V, the total number of Zener diodes 4 is 11 or more.

  When a voltage is applied between the drain electrode 50 and the source electrode 49, the potential of each trench 53 is determined in proportion to the voltage. Each potential of each trench 53 increases in order from the inner side (side closer to the source electrode 49) to the outer side (side closer to the end electrode 52). Each potential V of each trench 53 can be obtained by the following formula (1).

V = Vds × (Nd ÷ Nad) (1)
Vds indicates a voltage applied between the drain electrode 50 and the source electrode 49, Nd indicates the number of Zener diodes 4 counted from the source electrode 49, and Nad indicates the total number of Zener diodes 4. Yes.

  Thus, in the semiconductor device 1, in the termination region 42, the source electrode 49 and the end electrode 52 of the active region 41 are connected by the plurality of Zener diodes 4, and each floating electrode 54 is connected to the Zener diode 4. Therefore, the depletion layer formed in the epitaxial layer 44 between the trenches 53 spreads along each trench 53 due to the potential difference between the trenches 53, and the depletion layer formed in the active region 41 is extended to the termination region 42. The electric field concentrated on the corner of the trench 47 at the end of the active region 41 can be reduced. In the semiconductor device 1, each floating electrode 54 is connected to the Zener diode 4 connected between the source electrode 49 and the end electrode 52 of the active region 41, so that the potential of the floating electrode 54 is stabilized. The depletion layer formed in the termination region 42 spreads uniformly, and the electric field concentration in the termination region 42 can be reduced. This makes it difficult for a breakdown current to flow in the active region 41 and the termination region 42, thereby improving the breakdown voltage of the semiconductor device 1.

  In the semiconductor device 1, the depletion layer formed in the epitaxial layer 44 in the termination region 42 extends along each trench 53, and the depletion layer formed in the active region 41 can be extended to the termination region 42. Therefore, unlike the semiconductor device 40 shown in FIG. 4, it is not necessary to form the semiconductor region 45 on the surface of the epitaxial layer 44 in the termination region 42, and the degree of freedom in design can be increased.

  Further, in the semiconductor device 1, since it is not necessary to form the FLR in the termination region 42, the heat treatment process for forming the FLR can be omitted, and the generation of defects due to the deterioration of the semiconductor substrate 43 (quality deterioration) can be avoided. While suppressing, the cost for omitting the heat treatment step can be reduced.

  The semiconductor device 1 has such a number that the breakdown voltage of the entire Zener diode 4 is lower than the voltage applied between the drain electrode 50 and the source electrode 49 when a breakdown current flows in the epitaxial layer 44. A Zener diode 4 may be used.

  In such a configuration, even if a surge voltage is applied to the semiconductor device 1, the Zener diode 4 is turned on before the breakdown current flows in the epitaxial layer 44, and the energy due to the surge voltage can be absorbed by the Zener diode 4. Therefore, the surge resistance of the semiconductor device 1 can be improved.

Next, a method for manufacturing the semiconductor device 1 will be described.
FIG. 2A to FIG. 2E are diagrams for explaining a manufacturing process of the semiconductor device 1. 2A to 2E show the manufacturing process within the broken line frame B shown in FIG. 1, and the manufacturing process after the diffusion of the p− semiconductor region 45 on the surface of the epitaxial layer 44 is shown. Show.

  First, as shown in FIG. 2A, the trench mask pattern 20 is selectively formed on the epitaxial layer 44 and the semiconductor region 45. The trench mask pattern 20 in the termination region 42 becomes an insulating film between the Zener diode 4 and the epitaxial layer 44.

  Next, as shown in FIG. 2B, after performing Si anisotropic etching to form the trench 47 and the trench 53, the gate oxide film 21 is formed on the inner wall of the trench 47 and the trench 53. This gate oxide film 21 becomes an insulating film formed on the inner walls of the trench 47 and the trench 53.

  Next, as shown in FIG. 2C, after forming polysilicon doped in n-type on the inside of the trench 47 and the trench 53 and on the trench mask pattern 20 by CVD (Chemical Vapor Deposition) or the like, The trench mask pattern 20 in the region 41 and the polysilicon on the trench 47 are removed by etch back. The polysilicon formed in the trench 47 becomes the gate electrode 48. The polysilicon formed in the trench 53 becomes the floating electrode 54. The polysilicon formed on the trench mask pattern 20 becomes the n-type conductor 2 of the Zener diode 4.

  Next, as shown in FIG. 2D, after removing the trench mask pattern 20 in the active region 41, impurities are selectively diffused on the surface of the semiconductor region 45 in the active region 41 to form an n + semiconductor region 46. At the same time, impurities are diffused into a predetermined portion of the polysilicon on the trench mask pattern 20 in the termination region 42 to form the p + conductor 3 of the Zener diode 4.

  Then, as shown in FIG. 2E, after an insulating film 55 having a predetermined contact pattern is formed in the active region 41 and the termination region 42, the respective surfaces (contact regions) and one of the semiconductor regions 45 and 46 A source electrode 49 such as aluminum is formed so as to be connected to the n-type conductor 2 of the end Zener diode 4.

FIG. 3 is a diagram showing a semiconductor device according to another embodiment of the present invention. In FIG. 3, the same components as those shown in FIG.
The semiconductor device 30 shown in FIG. 3 is different from the semiconductor device 1 shown in FIG. 1 in that the gate electrode 48 and the end electrode 52 of the active region 41 are connected by a plurality of Zener diodes 4.

  Thereby, the semiconductor device 30 shown in FIG. 3 can extend the depletion layer formed in the active region 41 to the termination region 42 as well as the semiconductor device 1 shown in FIG. Since the potential of 54 can be stabilized and the depletion layer formed in the termination region 42 can be expanded uniformly, electric field concentration in the active region 41 and the termination region 42 can be reduced. Therefore, it is difficult for a breakdown current to flow in the active region 41 and the termination region 42, and the breakdown voltage of the semiconductor device 1 can be improved.

Also in the semiconductor device 30 shown in FIG. 3, since it is not necessary to form the semiconductor region 45 on the surface of the epitaxial layer 44 in the termination region 42, the degree of freedom in design can be increased.
Also, in the semiconductor device 30 shown in FIG. 3, since it is not necessary to form the FLR in the termination region 42, the heat treatment process for forming the FLR can be omitted, and defects due to the deterioration of the semiconductor substrate 43 are generated. While suppressing, the cost for omitting the heat treatment step can be reduced.

  Also in the semiconductor device 30 shown in FIG. 3, as in the semiconductor device 1 shown in FIG. 1, the voltage applied between the drain electrode 50 and the gate electrode 48 when a breakdown current flows through the epitaxial layer 44. Alternatively, a number of Zener diodes 4 may be used so that the overall breakdown voltage of the Zener diode 4 is lowered.

  In this configuration, even if a surge voltage is applied to the semiconductor device 30, the Zener diode 4 can be turned on and the MOSFET can be turned on before the breakdown current flows in the epitaxial layer 44. Can be absorbed by the MOSFET, and the surge resistance of the semiconductor device 30 can be improved.

  In the semiconductor device 1 shown in FIG. 1 or the semiconductor device 30 shown in FIG. 3, the semiconductor region 45 may be formed on the surface of the epitaxial layer 44 in the termination region 42 in the same manner as the semiconductor device 40 shown in FIG. Good.

  Further, in the semiconductor device 1 shown in FIG. 1 or the semiconductor device shown in FIG. 3, the plurality of Zener diodes 4 are connected to each other between the anodes or the cathodes. May be.

  In the semiconductor device 1 shown in FIG. 1 or the semiconductor device shown in FIG. 3, the n-channel MOSFET is provided in the active region 41, but a p-channel MOSFET may be provided in the active region 41.

  In the above embodiment, an IGBT (Insulated Gate Bipolar Transistor) may be provided in the active region 41 instead of the MOSFET.

It is a figure which shows the semiconductor device of embodiment of this invention. It is a figure which shows the manufacturing process of the semiconductor device of this embodiment. It is a figure which shows the semiconductor device of other embodiment of this invention. It is a figure which shows the existing semiconductor device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor device 2 N-type conductor 3 P-type conductor 4 Zener diode 20 Trench mask pattern 21 Gate oxide film 30 Semiconductor device 40 Semiconductor device 41 Active region 42 Termination region 43 Semiconductor substrate 44 Epitaxial layer 45 Semiconductor region 46 Semiconductor region 47 Trench 48 Gate electrode 49 Source electrode 50 Drain electrode 51 Semiconductor region 52 End electrode 53 Trench 54 Floating electrode 55 Insulating film

Claims (4)

A semiconductor layer made of a first conductor, a first semiconductor region made of a second conductor different from the first conductor formed on the surface of the semiconductor layer, and a surface of the first semiconductor region; A second semiconductor region selectively formed and made of the first conductor, a first trench formed from the surface of the second semiconductor region to the semiconductor layer, and insulation in the first trench A first electrode formed through a film; a second electrode connected to the respective surfaces of the first and second semiconductor regions; and a third electrode connected to the back side of the semiconductor layer A semiconductor device having an active region provided with an active element comprising: and a termination region located outside the active region,
In the termination region,
An end electrode connected to the third electrode and formed at a terminal end on the semiconductor layer;
A plurality of second trenches formed in a surface of the semiconductor layer;
A floating electrode formed in each of the plurality of second trenches via an insulating film;
A plurality of first and second conductors each connected in series between the first electrode or the second electrode of the active region and the end electrode and connected to each of the floating electrodes. Zener diode
A semiconductor device comprising: The semiconductor device according to claim 1,
The plurality of Zener diodes have an overall breakdown voltage of the plurality of Zener diodes higher than a voltage applied between the second electrode and the third electrode when a breakdown current flows in the semiconductor layer. It is composed of numbers that are low,
A semiconductor device. The semiconductor device according to claim 1,
The plurality of Zener diodes have an overall breakdown voltage of the plurality of Zener diodes higher than a voltage applied between the first electrode and the third electrode when a breakdown current flows in the semiconductor layer. Is composed of numbers that are low,
A semiconductor device. The semiconductor device according to claim 1,
The first semiconductor region is formed on a surface of the semiconductor layer in the termination region;
A semiconductor device.