JP2012182199A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation gate field-effect transistor with vertical field plate structure capable of alleviating concentration of an avalanche current caused by a parasitic bipolar transistor.SOLUTION: A semiconductor device according to an embodiment has an element part and a diode part. The element part has: a drain layer; a drift layer provided on the drain layer; a base region provided on the drift layer; a first conductivity type source region provided on a surface of the base region selectively; a first gate electrode provided in a plurality of first trenches penetrating from a surface of the source region through the base region and contacting with the drift layer; and a field plate electrode provided under the first gate electrode. The diode part shares the drain layer and the drift layer with the element part, and has a plurality of second trenches penetrating through the surface of the base region and contacting with the drift layer. The semiconductor device is formed so that a distance between the second trenches of the diode part is larger than a distance between the first trenches of the element part.

Description

  The present invention relates to a power semiconductor device.

  Conventionally, as a power semiconductor device, an insulated gate field effect transistor has been known which has a vertical field plate structure to alleviate electric field concentration and achieve a high breakdown voltage.

  In this semiconductor device, a trench is formed in the N-type semiconductor layer on the drain layer. In this trench, a field plate electrode is embedded via a thick field plate insulating film. The field plate electrode is electrically connected to the source layer.

  A gate electrode is embedded in the upper part of the trench so as to sandwich the field plate electrode with the gate insulating film interposed therebetween. A P-type base layer is formed on the N-type semiconductor layer adjacent to the trench, and an N-type source layer is formed on the base layer.

  If this structure is used, the base contact layer can be formed at a deeper position as well as the reduction of the photolithography process, so that the avalanche resistance can be increased.

US Pat. No. 5,998,833

  However, in the MOSFET having the buried field plate electrode structure, the field plate electrode is not completely buried in the trench, and a void may occur. When a void occurs, the contact resistance between the base region and the field plate electrode increases, an avalanche current flows through the base region, and a parasitic bipolar transistor is generated. When the parasitic bipolar transistor is generated, the avalanche current is concentrated in one place, which causes a problem that the avalanche resistance is lowered.

  According to the embodiment, the semiconductor device has an element part and a diode part. The element unit includes a drain layer of a first conductivity type, a drift layer of a first conductivity type provided on the drain layer, a base region of a second conductivity type provided on the drift layer, A source region of a first conductivity type selectively provided on the surface of the base region, and a first insulating film in a plurality of first trenches that penetrates the base region from the surface of the source region and contacts the drift layer And a field plate electrode provided in the first trench under the first gate electrode with a second insulating film interposed therebetween. The diode portion includes a drain layer of the first conductivity type, a drift layer of the first conductivity type provided on the drain layer, and a base region of the second conductivity type provided on the drift layer. A second gate electrode provided in a plurality of second trenches through the base region from the surface of the source region of the element portion and in contact with the drift layer via a third insulating film, and in the second trench And a field plate electrode provided via a fourth insulating film under the second gate electrode. The distance between the second trenches of the diode part is formed to be larger than the distance between the first trenches of the element part.

1 is a cross-sectional view showing a cross-sectional structure of a semiconductor device according to a first embodiment. The simple circuit diagram which shows the electrical connection relation of an element part and a diode part. The figure which illustrated the relationship between the breakdown voltage between the drain-source of the diode part in 1st Embodiment, and the cell pitch of a trench. Sectional drawing which shows the cross-section of the semiconductor device concerning 2nd Embodiment. The graph which illustrated the relationship between the proof pressure of the diode part B concerning 2nd Embodiment, and a gate electrode / source electrode insulation area | region. Sectional drawing which shows the cross-section of the semiconductor device concerning 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a semiconductor device 1 according to the first embodiment. The semiconductor device 1 is a power MOSFET having an upper and lower electrode structure, and includes an element part A and a diode part B adjacent to the element part A. As shown in FIG. 1, the element portion A is provided on the n-type (first conductivity type) drain layer 10, the n-type drift layer 11 provided on the drain layer 10, and the drift layer 11. P-type (second conductivity type) base region 12. An n-type source region 13 is selectively provided on the surface of the base region 12.

  In the element portion A, a plurality of first trenches 20 that penetrate the base region 12 from the surface of the source region 13 and are in contact with the drift layer 11 are provided. A first field plate electrode 22 is provided on the lower side in the depth direction in the first trench 20 via a first field plate insulating film 21 (first insulating film). A first gate electrode 23 is provided on the first field plate electrode 22. The first gate electrode 23 is provided in the first trench 20 via a first gate insulating film 24 (second insulating film). The film thickness of the first field plate insulating film 21 is thicker than the film thickness of the first gate insulating film 24.

  Between the first trenches 20 of the element part A, a first trench contact 30 that penetrates the base region 12 from the surface of the source region 13 of the element part A and contacts the drift layer 11 is provided. That is, the first trench contacts 30 are alternately arranged in a direction substantially parallel to the surface of the base region 12. The lower end of the first trench contact 30 is shallower than the lower end of the trench 20, and a carrier extraction layer 31 is formed in a region immediately below the first trench contact 30.

  On the other hand, the diode part B, like the element part A, has an n-type (first conductivity type) drain layer 10 and an n-type drift layer 11 provided on the drain layer 10. That is, the diode part B shares the element part A and the semiconductor substrate (in the embodiment, the drain layer 10 and the drift layer 11). The selective source region 13 is not provided in the diode part B. That is, the second field plate electrode 42 is provided on the lower side in the depth direction in the second trench 40 of the diode portion B via the second field plate insulating film 41 (third insulating film). A second gate electrode 43 is provided directly on the field plate electrode 42. The second gate electrode 43 is provided in the second trench 40 via a second gate insulating film 44 (fourth insulating film), and the film thickness of the second field plate insulating film 41 is the second gate insulating film. It is thicker than the film 44.

  Between the second trenches 40 of the diode part B, a second trench contact 50 that penetrates from the surface of the base region 12 of the element part A and contacts the drift layer 11 is provided. That is, the trench contacts are alternately arranged in a direction substantially parallel to the surface of the base region 12. The lower end of the trench contact 30 is shallower than the lower end of the trench 20, and a carrier extraction layer 31 is formed in a region immediately below the trench contact.

  The drain layer 10 shared by the element part A and the diode part B is connected to the drain electrode 80, and the source region 81 is connected to the source region 13 and the base region 12.

  The first and second gate electrodes 23 and 43 share a gate contact (not shown) at the end of the semiconductor device 1 and are connected to a common gate wiring (not shown). Each of the first and second field plate electrodes 22 and 42 is connected to a common field plate wiring via the gate contact at the end of the first and second field plate electrodes 22 and 42.

The main component of the drain layer 10, the drift layer 11, the base region 12, and the source region 13 may be, for example, silicon (Si). The material of the first and second gate electrodes 23 and 43 and the first and second field plate electrodes 22 and 42 is, for example, polysilicon (poly-Si). The material of the first and second field plate insulating films 21 and 41 and the first and second source insulating films 24 and 44 is silicon oxide (SiO ₂ ). The material of the drain electrode 80 and the source electrode 81 may be, for example, aluminum (Al), copper (Cu), tungsten (W), or polysilicon.

  As described above, the semiconductor device 1 has the element portion A and the diode portion B on the drain layer 10, the drift layer 11, the gate layer 12, and each electrode of the same substrate.

  FIG. 2 is a simplified circuit diagram showing an electrical connection relationship between the element portion and the diode portion. Here, the N substrate (drain layer 10 and drift layer 11) is schematically shown as being biased to a positive voltage V, and is schematically shown as being grounded to the field plate electrode 22. . As shown in the figure, in the diode part B, the base layer 12 common to the element part A serves as an anode electrode and is connected to the source electrode 81 of the element part A. On the other hand, the drain layer 10 and the drift layer 11 common to the element part A serve as a cathode electrode and are electrically connected to the drain electrode 80 of the element part A. As described above, the semiconductor device 1 has a structure in which the element part A and the diode B are connected in parallel to each other.

Here, in the present embodiment, the pitch X1 between the plurality of first trenches 20 of the element portion A is set to 0.6 μm (microns) or more. For example, when the pitch X1 of the trench 20 is 0.6 μm, the impurity concentration of the drift layer 11 is designed to be 1 × 10 ¹⁷ (atoms / cm ³ ) or less. Note that the minimum value of the pitch X1 of the first trench 20 is 0.6 μm, and the maximum value of the impurity concentration of the drift layer 11 is 1 × 10 ¹⁷ (atoms / cm ³ ).

  On the other hand, the pitch Y1 between the second trenches 40 of the diode part B is set larger than the pitch of the first trenches 20 of the element part A, for example, set to 3.0 μm or more. That is, as shown in FIG. 1, X1 <Y1 is set. By doing so, the breakdown voltage Vdss in the diode part B becomes smaller than the drain-source breakdown voltage Vdss in the element part A. Therefore, avalanche breakdown occurs in the diode part B, and the generation of carriers in the diode part B Centralized. This makes it possible to reduce the on-resistance of the element portion A.

  FIG. 3 is a graph illustrating the relationship between the pitch Y1 of the diode part B and the withstand voltage Vdss of the diode part B in the present embodiment. As shown in this figure, when the cell pitch Y1 of the diode part B is 3.0 μm, the withstand voltage Vdss is 115.0V, but by setting the cell pitch Y to 3.20 μm, the withstand voltage Vdss is generated by 118.5V. Occurred.

  As described above, according to the present embodiment, since the breakdown voltage Vdss in the diode part B is smaller than the drain-source breakdown voltage Vdss in the element part A, the avalanche breakdown occurs in the diode part B, and the generation of carriers is reduced to the diode. It is concentrated in part B. Therefore, the on-resistance of the element part A can be reduced. In particular, when the cell pitch Y of the diode part B is set to 3.20 μm and the cell pitch X of the element part A is set to be smaller than that, the above effect can be more easily realized.

  Note that the terminal part of the semiconductor device 1 according to the present embodiment may be terminated at either the element part A or the diode part B. However, it is preferable to perform a process of laminating the final end of the side surface of the first trench 20 or the second trench 40 only with the drain layer 11.

(Second Embodiment)
FIG. 4 is a diagram illustrating the semiconductor device 1 according to the second embodiment. As shown in the figure, in this embodiment, when the film thickness X2 of the first field plate insulating film 21 of the element portion A is compared with Y2 of the second field plate insulating film 41 of the diode portion B, X2> Y2 is formed so as to satisfy the relationship. By doing so, the withstand voltage Vdss of the diode part B becomes smaller than the withstand voltage between the drain and source of the element part A, so that the avalanche breakdown occurs in the diode part B and the generation of carriers is concentrated in the diode part B. Be made. Therefore, the on-resistance of the element portion A can be reduced. Carrier generation is concentrated on the diode part B.

  FIG. 5 is a diagram illustrating the relationship between the breakdown voltage Vdss of the diode part B and the film pressure Y2 of the second field plate insulating film 41. In this figure, by setting the film thickness Y2 of the diode portion B to 640 nm, the effect of generating the greatest breakdown voltage Vdss occurred.

As described above, according to the present embodiment, since the breakdown voltage Vdss in the diode part B is smaller than the drain-source breakdown voltage Vdss in the element part A, the avalanche breakdown occurs in the diode part B, and the generation of carriers is reduced to the diode. It is concentrated in part B. Therefore, the on-resistance of the element part A can be reduced. In particular, when the film thickness Y2 of the diode part B is 640 nm and the cell pitch X of the element part A is more than that, the above effect can be more easily realized.
(Third embodiment)
FIG. 6 is a diagram showing a semiconductor device according to the third embodiment. As shown in the figure, in this embodiment, when the depth X3 of the first trench 20 of the element part A and the depth Y3 of the second trench 40 of the diode part B are compared, X3> Y3 is established. First and second trenches 20 and 40 are formed. According to the present embodiment, since the breakdown voltage Vdss in the diode portion B is smaller than the drain-source breakdown voltage Vdss in the element portion A, avalanche breakdown occurs in the diode portion B, and carriers are concentrated in the diode portion B. Be made. Therefore, the on-resistance of the element part A can be reduced.

  Semiconductor device 1, drain layer 10, drift layer 11, gate region 12, source region 13, first trench 20, first field plate insulating film (first insulating film) 21, first field plate electrode 22, first gate electrode 23, first gate insulating film (second insulating film) first trench contact 30, carrier extraction layer 31, 51, second trench 40, second field plate insulating film (third insulating film) 41, second field plate electrode 42, second gate electrode 43, second gate insulating film (fourth insulating film), first trench contact 50, drain electrode 80, source electrode 81

Claims (3)

A drain layer of a first conductivity type; a drift layer of a first conductivity type provided on the drain layer; a base region of a second conductivity type provided on the drift layer; and a surface of the base region A source region of a first conductivity type selectively provided in the first region and a plurality of first trenches through the base region from the surface of the source region and in contact with the drift layer via a first insulating film A first gate electrode provided in the first trench and a first field plate electrode provided under the first gate electrode via a second insulating film;
The drain layer of the first conductivity type, the drift layer of the first conductivity type provided on the drain layer, the base region of the second conductivity type provided on the drift layer, and the base region A second gate electrode provided through a third insulating film in a plurality of second trenches that are in contact with the drift layer, and provided below the second gate electrode through a fourth insulating film A second field plate electrode, and a diode portion having
The semiconductor device is characterized in that the distance between the second trenches adjacent to the diode part is larger than the distance between the first trenches adjacent to the element part.   A part of the third insulating film or the fourth insulating film provided in the second trench of the diode part has a part of the first insulating film or the second insulating film provided in the first trench of the element part. The semiconductor device according to claim 1, wherein the semiconductor device is formed to be thinner than the thickness of the semiconductor device.   4. The semiconductor device according to claim 3, wherein the second trench of the diode part is formed to be shallower than the first trench of the element part.

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