IGBT cell with novel hole extraction structure

Abstract

The application discloses an IGBT cell with a novel hole extraction structure. By introducing alternating distribution of low-doped N-type buried layers and low-doped P-type buried layers on both sides of a groove, the concentration of the N-type buried layer is just right to form a threshold voltage close to 0 with two adjacent P-type regions, and an accumulation type PMOS is formed. When the device is turned off, the PMOS in the vertical direction is turned on to form a vertical hole path, connecting all P-type buried layers and Pbody. The path converts a higher barrier of the conventional IGBT hole extraction path into several lower barriers, improves the smoothness of the hole extraction path in energy change, and improves the extraction speed. The multiple P-type buried layers and the inversion channel in the vertical direction form a comb-shaped hole extraction structure, and the area of the structure is much larger than that of the conventional IGBT cell structure, thereby improving the hole extraction rate. Compared with the conventional IGBT cell, the application has faster turn-off speed and lower turn-off loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power semiconductor devices, in particular to an IGBT cell with a novel hole extraction structure. BACKGROUND

[0002] IGBT (Insulated Gate Bipolar Transistor) is a device with the combination of MOS voltage control and bipolar conduction modulation, which has the advantages of high input impedance, small control power and simple drive circuit of MOSFET, and the advantages of large current density, low saturation voltage drop and strong current handling capability of bipolar power transistor. It is an ideal power device for high-voltage, large-current and high-speed application fields. It is widely used in the fields of transportation, power grid, consumer electronics, etc.

[0003] As a bipolar device, IGBT has one obvious defect compared to MOSFET, which is a unipolar device. In the on state, a large number of holes are injected into the drift region, resulting in a large number of non-equilibrium minority carriers in the drift region. At the moment of device turn-off, these non-equilibrium minority carriers cannot be extracted from the emitter in time, but can only disappear in the drift region through slow recombination of electrons, resulting in a significant tail current in the turn-off process, increasing the turn-off time and turn-off loss. Therefore, the defect of IGBT in hole extraction capability is a key problem that must be solved in IGBT design. SUMMARY

[0004] The present application provides an IGBT cell with a novel hole extraction structure, which aims to solve the defects of low hole extraction rate and long turn-off time of the traditional IGBT cell structure. The reasons for the low hole extraction rate of the traditional IGBT cell structure are mainly two aspects: one is the small cross-sectional area of the hole extraction path, and the other is the high barrier on the hole extraction path. The present application will solve the defects of the traditional IGBT cell structure from these two aspects.

[0005] In a first aspect, an IGBT cell with a novel hole extraction structure is provided, which includes an emitter metal electrode and a collector metal electrode; a low-doped N-type drift region, a medium-doped P-type Pbody region, an oxide isolation layer and a P-type heavily doped collector are arranged between the emitter metal electrode and the collector metal electrode; the oxide isolation layer is located between the medium-doped P-type Pbody region and the emitter metal electrode, and the P-type heavily doped collector is located between the low-doped N-type drift region and the collector metal electrode;

[0006] On the side of the middle-doped P-type Pbody region close to the emitter metal electrode, an ohmic contact layer is formed by ion implantation in the middle-doped P-type Pbody region, the ohmic contact layer being in contact with both the oxide isolation layer and the emitter metal electrode; the ohmic contact layer comprises a heavily-doped N-type emitter and a heavily-doped P-type Pbody ohmic contact region; in the ohmic contact layer, the heavily-doped P-type Pbody ohmic contact region is located at the periphery of the heavily-doped N-type emitter;

[0007] On the side of the low-doped N-type drift region away from the collector metal electrode, at least one group of buried layers is formed by ion implantation in the low-doped N-type drift region, each group of buried layers comprising a lightly-doped N-type buried layer and a lightly-doped P-type buried layer; when the number of groups of buried layers is multiple, the lightly-doped N-type buried layers and the lightly-doped P-type buried layers are arranged alternately; the buried layer farthest from the collector metal electrode in the low-doped N-type drift region is a lightly-doped N-type buried layer;

[0008] The IGBT cell further comprises a gate oxide layer and a polysilicon gate; a trench is etched in the low-doped N-type drift region and the middle-doped P-type Pbody region, so that the trench passes through the heavily-doped N-type emitter, the middle-doped P-type Pbody region, and all the buried layers in the low-doped N-type drift region; the gate oxide layer is arranged on the inner wall of the trench and wraps around the periphery of the polysilicon gate.

[0009] With reference to the first aspect, in some implementations of the first aspect, when the number of groups of buried layers is multiple, the doping concentration of the lightly-doped P-type buried layer gradually decreases with the depth of the buried layer, and the doping concentration of the lightly-doped P-type buried layer decreases linearly with the depth of the buried layer after taking the logarithm to the base 10.

[0010] With reference to the first aspect, in some implementations of the first aspect, when the number of groups of buried layers is multiple, the doping concentration of the lightly-doped N-type buried layer does not change with the depth of the buried layer, and the doping concentration of the lightly-doped N-type buried layer is one to two orders of magnitude lower than the doping concentration of the low-doped N-type drift region.

[0011] With reference to the first aspect, in some implementations of the first aspect, the doping concentration of the low-doped N-type drift region is between 10 13 cm -3 and 10 14 cm -3 .

[0012] With reference to the first aspect, in some implementations of the first aspect, the doping concentration of the middle-doped P-type Pbody region is between 10 17 cm -3 and 10 18 cm -3 .

[0013] With reference to the first aspect, in some implementations of the first aspect, the doping concentration of the heavily-doped N-type emitter is between 1020 cm -3 above.

[0014] With reference to the first aspect, in some implementations of the first aspect, a doping concentration of the heavily doped P-type Pbody ohmic contact region is between 10 20 cm -3 above.

[0015] With reference to the first aspect, in some implementations of the first aspect, a doping concentration of the lightly doped N-type buried layer is between 10 13 cm -3 below.

[0016] With reference to the first aspect, in some implementations of the first aspect, a doping concentration of the lightly doped P-type buried layer is between 10 14 cm -3 and 10 17 cm -3 below.

[0017] With reference to the first aspect, in some implementations of the first aspect, a doping concentration of the P-type heavily doped collector is above 10 19 cm -3 above.

[0018] The second aspect provides a manufacturing method of the IGBT cell as described in any of the implementations of the first aspect, comprising:

[0019] The low-doped N-type Si-based substrate is used as a low-doped N-type drift region, and a middle-doped P-type Pbody region is formed by ion implantation on the front surface of the low-doped N-type drift region; then a heavily doped N-type emitter and a heavily doped P-type Pbody ohmic contact region are formed by ion implantation in a corresponding depth range of the middle-doped P-type Pbody region; then at least one set of buried layers (including a lightly doped N-type buried layer and a layer of lightly doped P-type buried layer) are implanted in the low-doped N-type drift region below the middle-doped P-type Pbody region by using a higher ion implantation energy to penetrate the middle-doped P-type Pbody region, and the implantation sequence of the buried layers is from shallow to deep in terms of depth; then a trench is etched, and a gate oxide layer and a polysilicon gate are formed in the trench; then an oxide insulating layer is formed on the upper surface of the cell, and a heavily doped collector is formed by ion implantation on the back surface; and finally, emitter metal electrodes and collector metal electrodes are formed by depositing metal on the upper and lower surfaces of the cell.

[0020] Compared with the prior art, the scheme provided by the present application has at least the following beneficial technical effects:

[0021] The technical scheme of the present application is to deepen the trench depth of an IGBT, introduce low-doped N-type buried layers and low-doped P-type buried layers alternately distributed in the vertical direction on both sides of the trench, and the doping concentration of the N-type buried layer is just enough to form an accumulation type PMOS with a threshold voltage close to 0 with the adjacent two P-type regions. When the device is turned off, the PMOS in the vertical direction is turned on to form a vertical hole path, which connects all the P-type buried layers and Pbody. Since the doping concentration of the P-type buried layer gradually decreases with the buried layer depth, the path converts a higher barrier of the conventional IGBT hole extraction path into several lower barriers, improving the smoothness of the hole extraction path in energy change and improving the extraction speed. In addition, the multiple P-type buried layers in the vertical direction and the inversion channel form a comb-shaped hole extraction structure, the area of which is much larger than that of the conventional IGBT cell structure, thereby improving the hole extraction rate. Compared with the conventional IGBT cell, the present application has faster turn-off speed and lower turn-off loss. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 FIG. 1 is a schematic diagram of an IGBT cell with a new hole extraction structure.

[0023] Figure 2 FIG. 2 is an embodiment of increasing the number of buried layers to n layers.

[0024] Figure 3 FIG. 3 is a schematic diagram of the doping distribution of the P-type buried layer of a multi-group buried layer. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0026] Figure 1 FIG. 1 shows an IGBT cell with a new hole extraction structure provided by the present application. The IGBT cell includes an emitter metal electrode 11 and a collector metal electrode 12. A low-doped N-type drift region 1, a medium-doped P-type Pbody region 2, an oxide isolation layer 9 and a P-type heavily doped collector 10 are arranged between the emitter metal electrode 11 and the collector metal electrode 12. The oxide isolation layer 9 is located between the medium-doped P-type Pbody region 2 and the emitter metal electrode 11, and the P-type heavily doped collector 10 is located between the low-doped N-type drift region 1 and the collector metal electrode 12.

[0027] On the side of the moderately doped P-type Pbody region 2 close to the emitter metal electrode 11, an ohmic contact layer is formed by ion implantation in the moderately doped P-type Pbody region 2, which is in contact with both the oxide isolation layer 9 and the emitter metal electrode 11. The ohmic contact layer comprises a heavily doped N-type emitter 3 and a heavily doped P-type Pbody ohmic contact region 4. In the ohmic contact layer, the heavily doped P-type Pbody ohmic contact region 4 is located at the periphery of the heavily doped N-type emitter 3.

[0028] On the side of the lowly doped N-type drift region 1 away from the collector metal electrode 12, at least one set of buried layers is formed by ion implantation in the lowly doped N-type drift region 1, each set of buried layers comprising a layer of lightly doped N-type buried layer 5 and a layer of lightly doped P-type buried layer 6. As shown in Figure 2 When the number of buried layer sets is n (n > 1), the lightly doped N-type buried layer 5 and the lightly doped P-type buried layer 6 are arranged alternately. The buried layer farthest from the collector metal electrode 12 in the lowly doped N-type drift region 1 is the lightly doped N-type buried layer 5.

[0029] The IGBT cell further comprises a gate oxide layer 7 and a polysilicon gate 8. A trench is etched in the lowly doped N-type drift region 1 and the moderately doped P-type Pbody region 2, so that the trench passes through the heavily doped N-type emitter 3, the moderately doped P-type Pbody region 2, and all the buried layers in the lowly doped N-type drift region 1. The gate oxide layer 7 is arranged on the inner wall of the trench, and the polysilicon gate 8 is wrapped around the outer periphery of the gate oxide layer 7.

[0030] In some embodiments, as shown in Figure 3 The doping concentration of the lightly doped P-type buried layer 6 gradually decreases with the depth of the buried layer (the deeper the buried layer, the closer to the emitter metal electrode 11), and the curve of the logarithm of the doping concentration of the buried layer with the depth of the buried layer is approximately linear.

[0031] In some embodiments, as shown in Figure 3 The doping concentration of the lightly doped N-type buried layer 5 does not change with the depth of the buried layer, and its value is one to two orders of magnitude lower than the doping concentration of the lowly doped N-type drift region 1.

[0032] In some embodiments, the doping concentration of the lowly doped N-type drift region 1 is between 10 13 cm -3 and 10 14 cm -3 .

[0033] In some embodiments, the doping concentration of the moderately doped P-type Pbody region 2 is between 10 17 cm -3 and 10 18 cm -3 .

[0034] In some embodiments, the doping concentration of the heavily doped N-type emitter 3 is between 10 20 cm -3 above.

[0035] In some embodiments, the doping concentration of the heavily doped P-type Pbody ohmic contact region 4 is between 10 20 cm -3 above.

[0036] In some embodiments, the doping concentration of the lightly doped N-type buried layer 5 is between 10 13 cm -3 below.

[0037] In some embodiments, the doping concentration of the lightly doped P-type buried layer 6 is between 10 14 cm -3 and 10 17 cm -3 .

[0038] In some embodiments, the doping concentration of the P-type heavily doped collector 10 is between 10 19 cm -3 above.

[0039] The application also provides a manufacturing method of an IGBT cell with a novel hole extraction structure.

[0040] A low-doped N-type Si-based substrate is used as a low-doped N-type drift region 1, and a middle-doped P-type Pbody region 2 is formed by ion implantation on the front surface of the low-doped N-type drift region 1. Then, a heavily doped N-type emitter 3 and a heavily doped P-type Pbody ohmic contact region 4 are formed by ion implantation in the corresponding depth range of the middle-doped P-type Pbody region 2. Then, at least one set of buried layers (including a lightly doped N-type buried layer 5 and a lightly doped P-type buried layer 6) are implanted in the low-doped N-type drift region 1 below the middle-doped P-type Pbody region 2 by using a higher ion implantation energy to penetrate the middle-doped P-type Pbody region 2, and the implantation sequence of the buried layers is from shallow to deep in terms of depth. Then, a trench is etched, and a gate oxide layer 7 and a polysilicon gate 8 are formed in the trench. Then, an oxide insulating layer 9 is formed on the upper surface of the cell, and a heavily doped collector 10 is formed by ion implantation on the back surface. Finally, an emitter metal electrode 11 and a collector metal electrode 12 are formed by depositing metal on the upper and lower surfaces of the cell.

[0041] The application optimizes the barrier distribution of the hole extraction path, improves the smoothness of the hole extraction path in terms of energy, forms a comb-shaped structure with a large extraction area in the vertical direction, and improves the hole extraction rate in both aspects.

[0042] Although the present application is disclosed with reference to the preferred embodiments above, it is not intended to limit the present application, and any person skilled in the art can make possible variations and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application should be defined by the scope of the claims.

Claims

1. An IGBT cell having a novel hole extraction structure, characterized by, The IGBT cell comprises an emitter metal electrode (11) and a collector metal electrode (12); a low-doped N-type drift region (1), a medium-doped P-type Pbody region (2), an oxide isolation layer (9) and a P-type heavily-doped collector (10) are arranged between the emitter metal electrode (11) and the collector metal electrode (12); the oxide isolation layer (9) is located between the medium-doped P-type Pbody region (2) and the emitter metal electrode (11), and the P-type heavily-doped collector (10) is located between the low-doped N-type drift region (1) and the collector metal electrode (12); On the side of the medium-doped P-type Pbody region (2) close to the emitter metal electrode (11), an ohmic contact layer is formed by ion implantation in the medium-doped P-type Pbody region (2), and the ohmic contact layer is in contact with the oxide isolation layer (9) and the emitter metal electrode (11); the ohmic contact layer comprises a heavily-doped N-type emitter (3) and a heavily-doped P-type Pbody ohmic contact region (4); in the ohmic contact layer, the heavily-doped P-type Pbody ohmic contact region (4) is located at the periphery of the heavily-doped N-type emitter (3); On the side of the low-doped N-type drift region (1) away from the collector metal electrode (12), at least one group of buried layers is formed by ion implantation in the low-doped N-type drift region (1), each group of buried layers comprising a layer of lightly-doped N-type buried layer (5) and a layer of lightly-doped P-type buried layer (6); when the number of groups of buried layers is multiple, the lightly-doped N-type buried layer (5) and the lightly-doped P-type buried layer (6) are arranged alternately, and the doping concentration of the N-type buried layer is configured to form an accumulation-type PMOS with a threshold voltage close to 0 with the adjacent two P-type regions; the buried layer farthest from the collector metal electrode (12) in the low-doped N-type drift region (1) is a lightly-doped N-type buried layer (5); The IGBT cell further comprises a gate oxide layer (7) and a polysilicon gate (8); a groove is etched in the low-doped N-type drift region (1) and the medium-doped P-type Pbody region (2) so that the groove passes through the heavily-doped N-type emitter (3), the medium-doped P-type Pbody region (2) and all the buried layers in the low-doped N-type drift region (1); the gate oxide layer (7) is arranged on the inner wall of the groove and wraps around the outer periphery of the polysilicon gate (8).

2. The IGBT cell of claim 1, wherein, When the number of groups of buried layers is multiple, the doping concentration of the lightly-doped P-type buried layer (6) gradually decreases with the depth of the buried layer, and the doping concentration of the lightly-doped P-type buried layer (6) decreases linearly with the depth of the buried layer after taking the logarithm to the base 10.

3. The IGBT cell according to claim 1 or 2, characterized in that, When the number of groups of buried layers is multiple, the doping concentration of the lightly-doped N-type buried layer (5) does not change with the depth of the buried layer, and the doping concentration value of the lightly-doped N-type buried layer (5) is one to two orders of magnitude lower than the doping concentration of the low-doped N-type drift region (1).

4. The IGBT cell of claim 1, wherein, The doping concentration of the low-doped N-type drift region (1) is between 10 13 cm -3 and 10 14 cm -3 .

5. The IGBT cell of claim 1, wherein, The doping concentration of the middle doped P-type Pbody region (2) is between 10 17 cm -3 and 10 18 cm -3 .

6. The IGBT cell of claim 1, wherein, The doping concentration of the heavily doped N-type emitter (3) is in the range of 10 20 cm -3 above.

7. The IGBT cell of claim 1, wherein, The doping concentration of the heavily doped P-type Pbody ohmic contact region (4) is in the range of 10 20 cm -3 above.

8. The IGBT cell of claim 1, wherein, The doping concentration of the lightly doped N-type buried layer (5) is 10 13 cm -3 below.

9. The IGBT cell of claim 1, wherein, The doping concentration of the lightly doped P-type buried layer (6) is between 10 14 cm -3 and 10 17 cm -3 .

10. The IGBT cell of claim 1, wherein, The doping concentration of the P-type heavily doped collector (10) is 10 19 cm -3 above.

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