A superjunction MOSFET device with improved reverse recovery characteristics

Abstract

The present invention discloses a super junction MOSFET device with improved reverse recovery characteristics, comprising an N+ substrate layer and a plurality of P columns and N columns alternately arranged on the N+ substrate layer, wherein a drain is arranged at the bottom of the N+ substrate layer; an N epitaxial layer is arranged on the top of the P columns and the N columns, a P-type body region corresponding to the position and number of the P columns is arranged on the N epitaxial layer, the P columns in a part of the body of the super junction MOSFET device extend upward and form epitaxial P columns, the epitaxial P columns pass through the N epitaxial layer and are connected to the P-type body region at the corresponding position to maintain the same potential; a dielectric layer is arranged on the top of the P-type body region, a source metal layer and a first metal layer corresponding to the positions of the P columns and the epitaxial P columns are arranged on the top of the dielectric layer, a plurality of connection holes are arranged in the dielectric layer, and at least one diode is connected in forward series or reverse series between the epitaxial P columns and the source metal layer of the original cell.

Description

Technical Field

[0001] The invention relates to the field of design and process manufacturing of super junction MOSFET (SJ-MOSFET) devices, and in particular to a super junction MOSFET device with improved reverse recovery characteristics. Background Art

[0002] The basic structure of the superjunction MOSFET device is composed of alternating P columns and N columns. When the device is in the blocking state, the P columns and N columns in the superjunction structure are completely depleted, and under the modulation of the lateral electric field in the drift region, the longitudinal electric field of the device tends to be evenly distributed. In theory, the voltage resistance of the superjunction structure depends only on the thickness of the drift region, and has nothing to do with the doping concentration. Therefore, the superjunction structure breaks the "silicon limit" in which the on-resistance of traditional power devices is limited by the breakdown voltage, and changes the Ron-VB relationship from the 2.5th power to the 1.32th power. Therefore, superjunction MOSFET devices have lower on-resistance and faster switching speed, so they have been widely used in solar energy, wind power generation, server and communication power systems, medical and industrial control, power switches and other fields, and are key devices for high-power power electronics industry applications.

[0003] However, compared with traditional MOSFET, super junction devices have a larger parasitic body diode, which is composed of a PN junction between the body region, the P column and the N drift region. When the device is used as a freewheeling diode, the parasitic diode will start to work. At this time, the source of the device is connected to a high potential, the drain is connected to a low potential, the parasitic diode is in a forward conduction state, the body region and the P column emit holes into the N drift region, and the N+ substrate of the drain also begins to emit electrons into the drift region, and the parasitic diode is in a conducting state. Due to the introduction of the P column region of the super junction device, the emission efficiency is enhanced when hole injection occurs, that is, the holes injected into the N drift region are far more than those in the traditional MOSFET. When the parasitic diode is turned off, the residual carriers stored in the drift region need to be released, and this process takes a period of time, namely the reverse recovery time (Trr). Since the holes injected into the super junction MOSFET when the parasitic diode is turned on are far more than those of the traditional MOSFET, more energy will be lost in the process of reverse recovery to extract excess carriers. Summary of the invention

[0004] The technical problem to be solved by the present invention is that, in view of the above-mentioned defects of the prior art, a super junction MOSFET device with improved reverse recovery characteristics is provided. By designing the device structure, when the super junction MOSFET device works as a freewheeling diode, that is, when the parasitic diode is reversely conducted, the ability of the parasitic diode to emit holes and electrons is almost the same as that of a traditional MOSFET, so that the ability to extract residual carriers when the device is turned off will also be greatly improved.

[0005] The objective of the present invention is to achieve the following technical solution: a super junction MOSFET device with improved reverse recovery characteristics, comprising a super junction MOSFET device body, wherein the super junction MOSFET device body comprises an N+ substrate layer and a plurality of P columns and N columns alternately arranged on the N+ substrate layer, wherein a drain is arranged at the bottom of the N+ substrate layer; an N epitaxial layer is arranged on the top of the P columns and the N columns, wherein a P-type body region corresponding to the position and number of the P columns is arranged on the N epitaxial layer, wherein the P columns in a partial area of ​​the super junction MOSFET device body extend upward and form epitaxial P columns, wherein the epitaxial P columns are arranged on the top of the P columns and the N columns, wherein the P-type body region corresponding to the position and number of the P columns are arranged on the N epitaxial layer, wherein the P columns in a partial area of ​​the super junction MOSFET device body extend upward and form epitaxial P columns, wherein the epitaxial P columns are arranged on the top of the P columns and the N ... The epitaxial P column passes through the N epitaxial layer and is connected to the P-type body region at the corresponding position to maintain the same potential; a dielectric layer is arranged on the top of the P-type body region, and a source metal layer and a first metal layer corresponding to the positions of the P column and the epitaxial P column are arranged on the top of the dielectric layer, a gate and connection holes corresponding to the number of P-type body regions and penetrating between the P-type body region and the source metal layer or the P-type body region and the first metal layer are arranged in the dielectric layer, one or more diodes are connected in series between the epitaxial P column and the source metal layer of the original cell, and connection holes are arranged between the diode and the source metal layer and the first metal layer on the corresponding side.

[0006] Furthermore, the diode is connected in forward series or reverse series between the epitaxial P column and the source metal layer of the original cell, that is, the diode is a PNPN diode or a NPNP diode.

[0007] Furthermore, a field oxide layer is provided at the bottom of the dielectric layer close to the epitaxial P column, and the diode is arranged on the field oxide layer or in the N epitaxial layer.

[0008] Furthermore, the P column and the N column in the super junction MOSFET device body are formed by multiple epitaxial implantations or by deep trench etching and epitaxial filling.

[0009] The beneficial technical effect of the present invention is that: the present invention adds an N epitaxial layer between the P-type body region and the P column of the super device to disconnect the P-type body region and the P column, and at the same time connects one or more diodes in series between the source and the P column of the super junction device, so that when the device is reverse-conducted, the parasitic diode is only the diode between the P-type body region and the N epitaxial, and the emission efficiency of holes and electrons is reduced to almost the same level as that of traditional MOSFET devices. Furthermore, when the parasitic diode is turned off, the turn-off time and energy loss are also similar to those of traditional MOSFETs, which greatly improves the reverse recovery characteristics of the super MOSFET; at the same time, the P column in the original cell area is at the same potential as the epitaxial P column at the far end, and the breakdown voltage of the device is completely unaffected. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic cross-sectional view of an existing super junction MOSFET structure;

[0011] Figure 2 A schematic cross-sectional view of the super junction MOSFET structure of the present invention;

[0012] Figure 3 It is a schematic diagram of the three-dimensional structure of the super junction MOSFET structure described in the present invention. DETAILED DESCRIPTION

[0013] In order to enable those skilled in the art to more clearly understand the objectives, technical solutions and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0014] In the description of the present invention, it is necessary to understand that the orientation or position relationship indicated by the terms such as "up", "down", "left", "right", "inside", "outside", "horizontal" and "vertical" is based on the orientation or position relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or original referred to must have a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0015] refer to Figure 1 As shown, Figure 1 This is the cross-section of an existing super junction MOSFET device. The parasitic diode is formed by a PN junction between a P-type body region, a P column and an N column. The area of ​​the diode is much larger than that of a traditional MOSFET device. Therefore, the emission efficiency of holes and electrons is much higher when the parasitic diode is reverse-conducted. Correspondingly, when the diode is turned off, more energy is lost in the process of reverse recovery to extract excess carriers, and the reverse recovery characteristics of the device are poor.

[0016] like Figure 2-3As shown, a super junction MOSFET device with improved reverse recovery characteristics described in the present invention includes a super junction MOSFET device body, wherein the super junction MOSFET device body includes an N+ substrate layer 1 and a plurality of P columns 2 and N columns 3 alternately arranged on the N+ substrate layer 1, and a drain 4 is arranged at the bottom of the N+ substrate layer 1; an N epitaxial layer 5 is arranged on the top of the P columns 2 and the N columns 3, and a P-type body region 6 corresponding to the position and number of the P columns 2 is arranged on the N epitaxial layer 5, and the P columns in a part of the area inside the super junction MOSFET device body extend upward and form epitaxial P columns 7, and the epitaxial P columns 7 pass through the N epitaxial layer 5 and are connected to the P-type body region 6 at the corresponding position. connected to maintain the same potential; a dielectric layer 8 is arranged on the top of the P-type body region 6, and a source metal layer 9 and a first metal layer 10 corresponding to the positions of the P column 2 and the epitaxial P column 7 are arranged on the top of the dielectric layer 8, a gate 11 and connection holes 12 corresponding to the number of the P-type body regions 6 and penetrating between the P-type body region 6 and the source metal layer 9 or the P-type body region 6 and the first metal layer 10 are arranged in the dielectric layer 8, a diode 13 is connected in series between the epitaxial P column 7 and the source metal layer 9 of the original cell, the number of the diodes 13 can be one, two or more, and a connection hole 12 is arranged between the diode 13 and the source metal layer 9 and the first metal layer 10 on the corresponding side.

[0017] Reference Figure 2-3 As shown, the diode 13 is connected in series in a forward direction or in a reverse direction between the epitaxial P column 7 and the source metal layer 9 of the original cell, that is, the diode is a PNPN diode or an NPNP diode. A field oxide layer 14 is provided at the bottom of the dielectric layer close to the epitaxial P column 7. The diode 13 can be made of polysilicon on the field oxide, or it can be made in the N epitaxial layer 5.

[0018] In the super junction MOSFET device described in the present invention, the thickness of the N epitaxial layer 5 can be adjusted according to actual needs, specifically to meet the breakdown voltage requirements of the device, and it is appropriate that the P column does not participate in the emission of holes when the parasitic diode direction is turned on. The concentration of the N epitaxial layer 5 can also be adjusted according to actual needs, and can be the same as the concentration of the N column, or it can be different, specifically to ensure that the P column and the N column can be completely depleted so that the breakdown voltage of the device meets the requirements. The preparation method of the super junction MOSFET device body is not only suitable for the process preparation method of multiple epitaxy and multiple injection to form P column and N column, but also suitable for the process preparation method of deep trench etching epitaxial filling to form P column and N column.

[0019] The present invention adds an N epitaxial layer between the P-type body region and the P-column of the super device to disconnect the P-type body region and the P-column, and simultaneously connects one or more diodes in series between the source and the P-column of the super junction device, so that when the device is reverse-conducted, the parasitic diode is only the diode between the P-type body region and the N epitaxial layer, and the emission efficiency of holes and electrons is reduced to almost the same level as that of traditional MOSFET devices. When the parasitic diode is turned off, the turn-off time and energy loss are also similar to those of traditional MOSFETs, greatly improving the reverse recovery characteristics of the super MOSFET; at the same time, the P-column in the original cell region is at the same potential as the epitaxial P-column at the far end, so the breakdown voltage of the device is completely unaffected. Figure 2 As shown, the P column in the original cell area is isolated from the P-type body area by the N epitaxial layer. At the same time, the P column in the original cell area is led to the surface through the remote P column and connected to the source of the device through one or more diodes. The potential difference between the P column and the source is only ~0.7V or several times 0.7V, so that the device can still withstand the same breakdown voltage when reverse cutoff.

[0020] The specific embodiments described herein are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A super junction MOSFET device with improved reverse recovery characteristics, comprising a super junction MOSFET device body, characterized in that: The super junction MOSFET device body includes an N+ substrate layer and a plurality of P columns and N columns alternately arranged on the N+ substrate layer, a drain is arranged at the bottom of the N+ substrate layer; an N epitaxial layer is arranged on the top of the P columns and the N columns, a P-type body region corresponding to the position and number of the P columns is arranged on the N epitaxial layer, the P columns in some areas of the super junction MOSFET device body extend upward and form epitaxial P columns, the epitaxial P columns pass through the N epitaxial layer and are connected to the P-type body regions at corresponding positions to maintain the same potential; a dielectric layer is arranged on the top of the P-type body region, a source metal layer and a first metal layer corresponding to the positions of the P columns and the epitaxial P columns are arranged on the top of the dielectric layer, a gate and connection holes corresponding to the number of P-type body regions and penetrating between the P-type body region and the source metal layer or the P-type body region and the first metal layer are arranged in the dielectric layer, one or more diodes are connected in series between the epitaxial P columns and the source metal layer of the primitive cell, and connection holes are arranged between the diode and the source metal layer and the first metal layer on the corresponding side.

2. The super junction MOSFET device with improved reverse recovery characteristics according to claim 1, characterized in that: The diode is connected in forward series or reverse series between the epitaxial P column and the source metal layer of the original cell, that is, the diode is a PNPN diode or a NPNP diode.

3. The super junction MOSFET device with improved reverse recovery characteristics according to claim 1 or 2, characterized in that: A field oxide layer is provided on the top of the dielectric layer close to the epitaxial P column, and the diode is arranged on the field oxide layer or in the N epitaxial layer.

4. The super junction MOSFET device with improved reverse recovery characteristics according to claim 3, characterized in that: The P column and the N column in the super junction MOSFET device body are formed by multiple epitaxial implantations or by deep trench etching epitaxial filling.

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