A silicon carbide MOSFET device with embedded integrated Schottky trench

Abstract

The application belongs to the technical field of power semiconductors, and particularly relates to a silicon carbide MOSFET device with embedded integrated Schottky trench. The application adopts a mode of integrating Schottky contact by multiple openings in a source trench, and provides a current path for reverse recovery by using the Schottky contact without increasing the lateral area of the device cell, thereby optimizing the switching characteristics and reverse recovery capability of the device, and having a lower specific on-resistance compared with a traditional structure.

Description

Technical Field

[0001] This invention belongs to the field of power semiconductor technology, specifically relating to a silicon carbide MOSFET device with an embedded integrated Schottky trench. Background Technology

[0002] Since the 1950s, power semiconductor devices have played an important role in energy conversion and control, providing us with smarter and more sustainable energy management solutions by offering efficient and reliable energy conversion solutions.

[0003] Metal-oxide-semiconductor field-effect transistors (MOSFETs) are an important type of power semiconductor device. MOSFET devices are characterized by low power consumption, high speed, and high voltage tolerance, enabling efficient current control and voltage conversion, thus achieving high energy conversion efficiency. They are widely used in fields such as power electronics, automotive electronics, and solar energy.

[0004] In high-power switching applications, a freewheeling diode is needed to provide a current path when the MOSFET is off. A common approach is to connect a Schottky diode in reverse parallel with the power MOSFET. There are generally two ways to achieve this reverse parallel connection: one is to add a Schottky diode outside the power MOSFET, but this increases the circuit size and introduces more parasitic capacitance and inductance. The other approach is to directly utilize the lightly doped epitaxial layer of the MOSFET to form a Schottky contact with the source metal, thus forming a Schottky diode structure inside the device. However, this method introduces a Schottky electrode laterally, increasing the unit area and affecting the forward conduction performance. This invention employs a method of integrating Schottky contacts through multiple openings in the source trench, aiming to solve the problem of increased unit area from integrated Schottky diodes. It achieves similar forward conduction capability with a smaller unit area, thereby optimizing the device's specific on-resistance. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by proposing an embedded integrated Schottky trench silicon carbide MOSFET device.

[0006] The technical solution of this invention is:

[0007] An embedded integrated Schottky trench silicon carbide MOSFET device includes a metal drain electrode 1, an N-type semiconductor substrate 2, and an N-type epitaxial layer 3 stacked sequentially from bottom to top; a P-type shielding region 4 is provided at one end of the upper layer of the N-type epitaxial layer 3, and a gate trench 10 is provided at the other end of the upper layer of the N-type epitaxial layer 3; a P-type well region 8 and an N+ source region 9 are stacked on the upper layer of the N-type epitaxial layer 3 between the P-type shielding region 4 and the gate trench 10, wherein the N+ source region 9 is located on the upper surface of the P-type well region 8;

[0008] Along the longitudinal direction of the device, a source trench 7 is provided in the upper middle layer of the P-type shielding region 4. The source trench 7 penetrates the P-type shielding region 4 in a direction parallel to the long side of the N+ source region 9 in the horizontal plane of the device. At the bottom of the source trench 7, there are alternately arranged source ohmic contact electrodes 6 and Schottky contact electrodes 5. The Schottky contact electrode 5 contacts the N-type epitaxial layer 3, and there is a gap between the source ohmic contact electrode 6 and the N-type epitaxial layer 3. The Schottky contact electrode 5 is formed by making an opening at the bottom of the P-type shielding region 4, filling the opening with the N-type epitaxial layer 3, and forming the Schottky contact electrode 5 on the surface.

[0009] The gate trench 10 is composed of a gate oxide layer 11 and a polysilicon gate 12 located in the gate oxide layer 11.

[0010] The longitudinal direction of the device proposed in the above scheme is a third-dimensional direction that is perpendicular to both the horizontal and vertical directions of the device.

[0011] Furthermore, silicon carbide MOSFET devices have a strip cell structure.

[0012] Furthermore, the Schottky contact electrode 5 and the source ohmic contact electrode 6 have the same width in the transverse direction of the device.

[0013] Furthermore, the source ohmic contact electrode 6 is made of nickel or a nickel alloy, and the Schottky contact electrode 5 is made of nickel.

[0014] The beneficial effects of this invention are as follows: by creating openings in the P-type shielding region along the longitudinal direction to bring out Schottky contact electrodes, a reverse-parallel Schottky diode is formed within the trench MOSFET. This transforms the traditional parasitic body diode freewheeling mode into a Schottky diode freewheeling mode. Due to the unipolar conductivity and low turn-on voltage of the Schottky diode, problems such as increased switching losses and reduced switching speed caused by the introduction of a large number of excess carriers inside the device are avoided. Compared with the structure of laterally integrated Schottky diodes, this invention does not increase the cell area of ​​the device laterally. Therefore, without affecting the device's breakdown voltage, it reduces the device's switching losses, improves the device's switching speed and reverse recovery capability, and avoids significantly increasing the on-resistance of the device cell. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the three-dimensional structure of the embedded integrated Schottky trench silicon carbide MOSFET provided by the present invention;

[0016] Figure 2 This is a top view of the embedded integrated Schottky trench silicon carbide MOSFET structure provided by the present invention;

[0017] Figure 3 This is a cross-sectional schematic diagram of the embedded integrated Schottky trench silicon carbide MOSFET provided by the present invention;

[0018] Figure 4 This is a schematic diagram of a traditional trench silicon carbide MOSFET device.

[0019] Figure 5 This is a schematic diagram of a trench silicon carbide MOSFET device with a source-integrated Schottky structure, based on existing technology.

[0020] Figure 6 These are the transfer characteristic curves of a traditional trench silicon carbide MOSFET device, an embedded integrated Schottky trench silicon carbide MOSFET device according to the present invention, and a trench silicon carbide MOSFET device with a source integrated Schottky structure in the prior art.

[0021] Figure 7 These are the forward IV characteristic curves of a conventional trench silicon carbide MOSFET device, an embedded integrated Schottky trench silicon carbide MOSFET device according to the present invention, and a trench silicon carbide MOSFET device with a source integrated Schottky structure in the prior art.

[0022] Figure 8 These are the body diode conduction characteristic curves of a traditional trench silicon carbide MOSFET device, an embedded integrated Schottky trench silicon carbide MOSFET device according to the present invention, and a trench silicon carbide MOSFET device with a source integrated Schottky structure in the prior art.

[0023] The attached diagram lists the components represented by each number as follows:

[0024] 1. Metal drain, 2. N-type semiconductor substrate, 3. N-type epitaxial layer, 4. P-type shielding region, 5. Schottky contact electrode, 6. Source ohmic contact electrode, 7. Source trench, 8. P-type well region, 9. N+ source region, 10. Gate trench, 11. Gate oxide layer, 12. Polysilicon gate. Detailed Implementation

[0025] The effectiveness and practicality of this invention will be explained below with reference to the accompanying drawings and simulation examples:

[0026] like Figure 4The diagram shows a conventional trench silicon carbide MOSFET device. To facilitate a comparison of its performance with the embedded integrated Schottky trench silicon carbide MOSFET of this invention, this embodiment uses a device fabricated with the same doping level and size, taking a long strip half-cell size as an example: Specifically, the silicon carbide N-type semiconductor substrate 2 has a doping concentration of 1E19cm-3 and a thickness of 1 micrometer; the silicon carbide N-type epitaxial layer 3 has a doping concentration of 8E15cm-3 and a thickness of 12 micrometers; a Ni alloy is used as the Schottky contact electrode 5, and a Ni alloy is used as the ohmic contact electrode 6; the surface doping concentration of the P-type well region 8 is 6E16cm-3, and its width is 0.6 micrometers; the channel length is 0.3 micrometers; and the gate oxide layer thickness is 60 nanometers.

[0027] like Figure 5 The image shows a trench silicon carbide MOSFET device with a source-integrated Schottky structure in the prior art. In addition to the structural parameters mentioned above, a Schottky contact electrode 5 with a width of 1 micrometer is formed above the outside of the P-type shielding region 4.

[0028] like Figure 1 The image shows an embedded integrated Schottky trench silicon carbide MOSFET device provided in this embodiment. Besides having the same structural parameters as a conventional trench silicon carbide MOSFET device, it features multiple discontinuous openings at the bottom of the P-type shielding region 4. Multiple discontinuous Schottky contact electrodes 5 are formed above these openings, spaced apart from ohmic contact electrodes 6. Each opening has a width of 1 micrometer and a length of 1 micrometer. Figure 2 The image shown is a top view of the embedded integrated Schottky trench silicon carbide MOSFET device provided in this embodiment, implemented as various ion implantation regions. The dashed lines represent the source trench 7 and the gate trench 10, respectively. Figure 3 The diagram shown is a cross-sectional view of the embedded integrated Schottky trench silicon carbide MOSFET device provided in this embodiment at AA' and BB'.

[0029] This embodiment uses the above parameters to produce the following: Figure 1 , Figure 4 , Figure 5 The device structures were tested, and the transfer characteristics of the three devices were measured under a drain voltage of 0.1V. The curves are shown below. Figure 6 As shown, the square-shaped curve represents the transfer characteristic curve of a conventional trench silicon carbide MOSFET device, the circular-shaped curve represents the transfer characteristic curve of the embedded integrated Schottky trench silicon carbide MOSFET device of this invention, and the triangular curve represents the transfer characteristic curve of a prior art trench silicon carbide MOSFET device with a source-integrated Schottky structure. Figure 6 It can be seen that, as Figure 4The threshold voltage of the conventional trench silicon carbide MOSFET device shown is approximately 3.22V under a 0.1V drain voltage condition. Figure 1 The threshold voltage of the embedded integrated Schottky trench silicon carbide MOSFET device shown in this embodiment of the invention is approximately 3.22V. Figure 5 The threshold voltage of the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure shown is approximately 3.22V. The threshold voltage of the embedded integrated Schottky trench silicon carbide MOSFET device in this embodiment is basically the same as that of the conventional trench silicon carbide MOSFET device and the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure, but the current conduction capability differs. Specifically, the embedded integrated Schottky trench silicon carbide MOSFET device in this embodiment has a higher current conduction capability than the conventional trench silicon carbide MOSFET device, which in turn has a higher current conduction capability than the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure.

[0030] Under a gate voltage of 20V, the forward IV characteristics of the three devices were tested, and the curves were obtained as follows: Figure 7 As shown, the square-shaped curve represents the forward IV characteristic curve of a conventional trench silicon carbide MOSFET device, the circular-shaped curve represents the forward IV characteristic curve of the embedded integrated Schottky trench silicon carbide MOSFET device of this invention, and the triangular curve represents the forward IV characteristic curve of a prior art trench silicon carbide MOSFET device with a source-integrated Schottky structure. Figure 7 It can be seen that, as Figure 4 The conventional trench silicon carbide MOSFET device shown has a specific on-resistance of 2.183 mΩ·cm² under a gate voltage of 20V. Figure 1 The embedded integrated Schottky trench silicon carbide MOSFET device shown in this embodiment of the invention has a specific on-resistance of 2.05 mΩ·cm². Figure 5 The prior art trench silicon carbide MOSFET device with source-integrated Schottky structure shown has a specific on-resistance of 2.833 mΩ·cm². The specific on-resistance of the device of the present invention is reduced by 6.1% compared to the conventional device and by 27.6% compared to the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure. The embedded integrated Schottky trench silicon carbide MOSFET device of the present invention has a better current capability than the conventional trench silicon carbide MOSFET device and the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure. This is because, without increasing the device cell width, the embedded integrated Schottky trench silicon carbide MOSFET device of this embodiment increases the area of ​​the N-type epitaxial layer 3 by increasing the opening in the P-type shielding region 4, increasing the current conduction path, and thus increasing the forward current capability of the device.

[0031] Under the condition of 0V gate voltage, the body diode conduction characteristics of the three devices were tested, and the curves were obtained as follows: Figure 8 As shown, the square-shaped curve represents the body diode conduction characteristic curve of a conventional trench silicon carbide MOSFET device, the circular-shaped curve represents the body diode conduction characteristic curve of the embedded integrated Schottky trench silicon carbide MOSFET device of this invention, and the triangular curve represents the body diode conduction characteristic curve of a prior art trench silicon carbide MOSFET device with a source-integrated Schottky structure. Figure 8 It can be seen that, as Figure 4 The turn-on voltage of the conventional trench silicon carbide MOSFET device shown is approximately 2.71V, such as... Figure 1 The embedded integrated Schottky trench silicon carbide MOSFET device shown in this embodiment of the invention has a turn-on voltage of approximately 1.14V. Figure 5 The turn-on voltage of the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure shown is about 1.14V. The turn-on voltage of the body diode of the embedded integrated Schottky trench silicon carbide MOSFET device in the embodiment of the present invention is basically the same as that of the prior art trench silicon carbide MOSFET device with source-integrated Schottky structure. The current capability and conduction voltage are similar, which is because the Schottky contact area is basically the same.

Claims

1. A silicon carbide MOSFET device with an embedded integrated Schottky trench, comprising a metal drain electrode (1), an N-type semiconductor substrate (2), and an N-type epitaxial layer (3) stacked sequentially from bottom to top; characterized in that, A P-type shielding region (4) is provided at one end of the upper layer of the N-type epitaxial layer (3), and a gate trench (10) is provided at the other end of the upper layer of the N-type epitaxial layer (3). A P-type well region (8) and an N+ source region (9) are stacked on the upper layer of the N-type epitaxial layer (3) between the P-type shielding region (4) and the gate trench (10), wherein the N+ source region (9) is located on the upper surface of the P-type well region (8). Along the longitudinal direction of the device, a source trench (7) is provided in the upper middle layer of the P-type shielding region (4); along the direction parallel to the long side of the N+ source region (9) in the horizontal plane of the device, the source trench (7) penetrates the P-type shielding region (4), and at the bottom of the source trench (7) there are alternately arranged source ohmic contact electrodes (6) and Schottky contact electrodes (5); wherein the Schottky contact electrode (5) contacts the N-type epitaxial layer (3) and there is a gap between the source ohmic contact electrode (6) and the N-type epitaxial layer (3); The gate trench (10) is composed of a gate oxide layer (11) and a polysilicon gate (12) located in the gate oxide layer (11).

2. The silicon carbide MOSFET device with an embedded integrated Schottky trench according to claim 1, characterized in that, Silicon carbide MOSFET devices have a bar-shaped cell structure.

3. The silicon carbide MOSFET device with an embedded integrated Schottky trench according to claim 1, characterized in that, The Schottky contact electrode (5) and the source ohmic contact electrode (6) have the same width in the transverse direction of the device.

4. The silicon carbide MOSFET device with an embedded integrated Schottky trench according to claim 1, characterized in that, The source ohmic contact electrode (6) is made of nickel or a nickel alloy, and the Schottky contact electrode (5) is made of nickel.

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