IGBT (Insulated Gate Bipolar Translator) cell with gradient P base region doping and composite buffer layer

Abstract

The invention discloses an IGBT (Insulated Gate Bipolar Translator) cell with gradient P base region doping and a composite buffer layer. The IGBT cell comprises an emitter metal electrode 11, a heavily-doped N-type emitter 3, a heavily-doped P-type ohmic contact region 4, an N-type drift region 1, a trench gate 8, a P-type heavily-doped collector 9, a collector metal electrode 10 and a P base region 12, wherein the emitter metal electrode 11, the heavily doped N-type emitter 3, the N-type drift region 1, the P-type heavily doped collector 9 and the collector metal electrode 10 are stacked from top to bottom; the heavily-doped P-type ohmic contact region 4 and the heavily-doped N-type emitter 3 are arranged in parallel on the same layer; the trench gate 8 is of a strip-shaped structure and extends from the heavily doped N-type emitter 3 to the N-type drift region 1; the P base regions 12 are located on the two sides of the trench gate, the P base regions 12 are of a gradient doping structure, and the doping concentration of the P base regions 12 is monotonically decreased from the upper surface of the cell to the interior of the cell; and a composite buffer layer 5 is arranged at the interface of the P base region 12 and the N-type drift region 1.

Description

Technical Field

[0001] This invention relates to an IGBT cell with a gradient P-base doped and composite buffer layer, belonging to the field of power semiconductor device technology. Background Technology

[0002] IGBTs (Insulated Gate Bipolar Transistors) are core switching devices in modern power electronic systems, combining the easy controllability of MOS gates with the low on-state voltage drop of bipolar devices. They play a crucial role in new energy vehicle motor drives, photovoltaic inverters, and aerospace applications. They achieve high current carrying capacity through channel formation controlled by gate voltage and by utilizing conductivity modulation effects. However, traditional planar gate structures are limited by the inherent trade-off between on-state losses (Eon) and off-state losses (Eoff), and tail current and bulge effects at high switching frequencies constrain performance limits. Current technological development mainly focuses on innovations in trench gate design, carrier storage layer optimization, and terminal structures.

[0003] As a bipolar device, the IGBT combines the high input impedance of the MOSFET with the low conduction loss of the BJT. However, in traditional designs, there is an inherent trade-off between conduction loss and turn-off loss. Furthermore, at high switching frequencies, tail current causes a surge in turn-off loss, while the pilus effect caused by parasitic thyristors limits short-circuit robustness. Therefore, the loss-robustness trade-off limit and tail current of traditional IGBTs are key issues that must be addressed in IGBT design. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide an IGBT cell with a gradient P-base region doping and a composite buffer layer, thereby resolving the trade-off between conduction loss and turn-off loss.

[0005] The technical solution of this invention is:

[0006] This invention discloses an IGBT cell with a gradient P-base region doping and a composite buffer layer, comprising: an emitter metal electrode, a heavily doped N-type emitter, a heavily doped P-type ohmic contact region, an N-type drift region, a trench gate, a heavily doped P-type collector, a collector metal electrode, and a P-base region; wherein the emitter metal electrode, the heavily doped N-type emitter, the N-type drift region, the heavily doped P-type collector, and the collector metal electrode are stacked from top to bottom; the heavily doped P-type ohmic contact region and the heavily doped N-type emitter are arranged side by side in the same layer; the trench gate has a strip structure extending from the heavily doped N-type emitter to the N-type drift region; the P-base region is located on both sides of the trench gate, and the P-base region has a gradient doping structure, with the doping concentration of the P-base region monotonically decreasing from the upper surface of the cell towards the bulk; a composite buffer layer is provided at the interface between the P-base region and the N-type drift region.

[0007] Furthermore, in the aforementioned cell, the P-based region includes a highly doped P-based region, a moderately doped P-based region, and a lightly doped P-type base region; the surface doping concentration of the highly doped P-based region is 1 × 10⁻⁶. 18 / cm -3 Up to 3×10 18 / cm -3 The surface doping concentration of the moderately doped P-based region is 0.7 × 10⁻⁶. 18 / cm -3 Up to 1×10 18 / cm -3 The surface doping concentration of the lightly doped P-type base region is 0.5 × 10⁻⁶. 18 / cm -3 Up to 0.7×10 18 / cm -3 The doping concentration of the lightly doped p-type base region at a depth of 1.5 μm is less than or equal to 8 × 10⁻⁶. 17 / cm -3 .

[0008] Furthermore, in the aforementioned cell, the composite buffer layer is made of platinum-doped semiconductor or argon-ion irradiation-damaged semiconductor.

[0009] Furthermore, in the aforementioned cell, the thickness of the composite buffer layer is no greater than 30 nm, and the carrier lifetime of the composite buffer layer is less than 10 ns.

[0010] Furthermore, in the aforementioned cell, a P-based region with a doping concentration that monotonically decreases from the surface to the depth of the bulk is formed by tilted ion implantation. Before forming the P-based region, a composite buffer layer is formed on top of the N-type drift region by platinum diffusion or ion irradiation.

[0011] Furthermore, in the aforementioned cell, the tilted ion implantation process specifically includes:

[0012] The window for the P-based region is determined by photolithography, followed by vertical boron ion implantation. This process involves ion implantation with a maximum energy of 70–90 keV and a minimum ion implantation dose of 2 × 10⁻⁶ keV. 13 ~3×10 13 / cm -2 A low-concentration layer is formed within the cell;

[0013] Ion implantation angle tilted at 15°–25°, using a low energy of 40–60 keV, and an ion implantation dose of 3 × 10⁻⁶. 13 ~5×10 13 / cm -2 Boron ion implantation forms a gradient transition;

[0014] The ion implantation angle is tilted at 30°–35°, the implantation energy is further reduced to 20–40 keV, and the ion implantation dose is 5 × 10⁻⁶. 13 ~6×10 13 / cm -2 A high-concentration surface layer is formed;

[0015] Rapid thermal annealing activates doping and creates a gradient concentration.

[0016] Furthermore, in the aforementioned cell, the platinum diffusion process specifically involves: forming a buffer layer on the surface of the N-type drift region by means of platinum vapor diffusion; and performing a thermal annealing process on the buffer layer to form a composite buffer layer.

[0017] Furthermore, in the aforementioned cell, the ion irradiation process specifically involves: irradiating argon ions to generate high-energy ions; generating defects by bombarding the silicon lattice with high-energy ions to form a buffer layer on the surface of the N-type drift region; and performing a thermal annealing process on the buffer layer to form a composite buffer layer.

[0018] The advantages of this invention over the prior art are as follows:

[0019] (1) Compared to traditional IGBT cells (such as Figure 3 This invention achieves faster turn-off speed and lower turn-off loss with almost no sacrifice in conduction performance, and significantly improves dynamic robustness. It resolves the trade-off between conduction loss and turn-off loss in traditional IGBT chips, while simultaneously improving the device's anti-pilling capability and short-circuit withstand capability.

[0020] (2) This invention optimizes the doping concentration of the P-based region, transforming it into a region where the doping concentration decreases along the depth direction, with a surface doping concentration ≥ 1 × 10⁻⁶. 18 / cm -3 The concentration at a depth of 1.5 μm is ≤8 × 10⁻⁸. 17 / cm -3 To reduce the amount of holes stored in the cell during turn-off, a recombination buffer layer is added at the interface between the P-base region and the drift region to force electron-hole pairs at the recombination interface. The thickness of the recombination buffer layer should be ≤30nm, and the carrier lifetime ≤10ns. These two combined effects improve the hole extraction rate.

[0021] (3) The present invention relates to an IGBT cell with a graded P-base region doping and a composite buffer layer, in order to improve the inherent contradiction between turn-on loss and turn-off loss in traditional IGBTs. The reason why the traditional IGBT cell structure has an inherent contradiction between turn-on loss and turn-off loss is mainly because reducing the on-state voltage drop requires increasing the carrier concentration, while the increase in carrier concentration will lead to an increase in tail current and loss during turn-off, forming a stalemate where one increases at the expense of the other.

[0022] (4) The technical solution of the present invention is to increase the gradient P-base region, and the doping concentration of the P-base region decreases layer by layer from the surface to the cell. This can maintain a high surface concentration to stabilize the threshold voltage, reduce the hole storage in the cell, accelerate the hole extraction speed during turn-off, and reduce turn-off loss. At the same time, a composite buffer layer of about 20 nm is inserted at the interface between the P-base region and the drift region. This composite buffer layer can force electron-hole pairs at the composite interface, significantly reduce the tail current, and shorten the turn-off tail time. Attached Figure Description

[0023] Figure 1 This is a schematic diagram showing the variation of P-type base region doping concentration with depth in an IGBT cell with gradient P-base region doping and composite buffer layer according to the present invention.

[0024] Figure 2 This is a schematic diagram of an IGBT cell with a gradient P-base region doping and a composite buffer layer according to the present invention; 1 is a lightly doped N-type drift region; 3 is a heavily doped N-type emitter; 4 is a heavily doped P-type Pbody ohmic contact region; 12-1 is a highly doped P-base region; 12-2 is a moderately doped P-base region; 12-3 is a lightly doped P-type base region; 5 is a composite buffer layer; 6 is a gate oxide layer; 8 is a polysilicon gate; 7 is an oxide isolation layer; 9 is a heavily doped P-type collector; 10 is a collector metal electrode; 11 is an emitter metal electrode.

[0025] Figure 3 This is a schematic diagram of a traditional IGBT cell. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 2 As shown, this invention discloses an IGBT cell with a gradient P-base region doped and a composite buffer layer, comprising: an emitter metal electrode 11, a heavily doped N-type emitter 3, a heavily doped P-type ohmic contact region 4, an N-type drift region 1, a trench gate 8, a heavily doped P-type collector 9, a collector metal electrode 10, and a P-base region 12; wherein, the emitter metal electrode 11, the heavily doped N-type emitter 3, the N-type drift region 1, the heavily doped P-type collector 9, and the collector metal electrode 10 are... The electrodes 10 are stacked from top to bottom; the heavily doped P-type ohmic contact region 4 and the heavily doped N-type emitter 3 are arranged side by side in the same layer; the trench gate 8 is a strip structure that extends from the heavily doped N-type emitter 3 to the N-type drift region 1; the P-base region 12 is located on both sides of the trench gate, and the P-base region 12 is a graded doping structure, with the doping concentration of the P-base region 12 decreasing monotonically from the upper surface of the cell towards the bulk; a composite buffer layer 5 is provided at the interface between the P-base region 12 and the N-type drift region 1.

[0028] Preferably, the P-base region 12 includes a highly doped P-base region 12-1, a moderately doped P-base region 12-2, and a lightly doped P-type base region 12-3; the surface doping concentration of the highly doped P-base region 12-1 is 1×10⁻⁶. 18 / cm -3 Up to 3×10 18 / cm -3 The surface doping concentration of the moderately doped P-based region 12-2 is 0.7 × 10⁻⁶. 18 / cm -3 Up to 1×10 18 / cm -3 The surface doping concentration of the lightly doped P-type base region 12-3 is 0.5 × 10⁻⁶. 18 / cm -3 Up to 0.7×10 18 / cm -3 The lightly doped p-type base region 12-3 has a bulk doping concentration of less than or equal to 8 × 10⁻⁶ at a depth of 1.5 μm. 17 / cm -3 .

[0029] Preferably, the composite buffer layer 5 is made of platinum-doped semiconductor or argon ion irradiation-damaged semiconductor.

[0030] Preferably, the thickness of the composite buffer layer 5 is no greater than 30 nm, and the carrier lifetime of the composite buffer layer 5 is less than 10 ns.

[0031] Preferably, a P-based region 12 with a doping concentration that monotonically decreases from the surface to the depth of the bulk is formed by tilted ion implantation. Before forming the P-based region 12, a composite buffer layer 5 is formed on top of the N-type drift region 1 by platinum diffusion or ion irradiation.

[0032] Preferably, the tilted ion implantation process is as follows:

[0033] The window for the P-based region 12 was determined by photolithography, followed by vertical boron ion implantation. This process involved ion implantation with a maximum energy of 70–90 keV and a minimum ion implantation dose of 2 × 10⁻⁶. 13 ~3×10 13 / cm -2 A low-concentration layer is formed within the cell;

[0034] Ion implantation angle tilted at 15°–25°, using a low energy of 40–60 keV, and an ion implantation dose of 3 × 10⁻⁶. 13 ~5×10 13 / cm -2 Boron ion implantation forms a gradient transition;

[0035] The ion implantation angle is tilted at 30°–35°, the implantation energy is further reduced to 20–40 keV, and the ion implantation dose is 5 × 10⁻⁶. 13 ~6×10 13 / cm -2 A high-concentration surface layer is formed;

[0036] Rapid thermal annealing activates doping and creates a gradient concentration.

[0037] Preferably, the platinum diffusion process specifically involves: forming a buffer layer on the surface of the N-type drift region 1 by platinum vapor diffusion; and performing a thermal annealing process on the buffer layer to form a composite buffer layer 5.

[0038] Preferably, the ion irradiation process specifically involves: irradiating argon ions to generate high-energy ions; generating defects in the silicon lattice by bombarding the silicon lattice with high-energy ions to form a buffer layer on the surface of the N-type drift region 1; and performing a thermal annealing process on the buffer layer to form a composite buffer layer 5.

[0039] Example

[0040] This embodiment provides a technical solution for an IGBT cell structure and its fabrication method with a graded P-base region doping and a composite buffer layer. From top to bottom, it includes an emitter metal, an N+ source region, a P-type ohmic contact region, a P-base region, an N-drift region, a P+ collector region, and a collector metal. A trench gate penetrates the P-base region. The trench gate further includes: a graded doping distribution in the P-base region, with the highest concentration at the surface, decreasing sequentially from top to bottom; and a composite buffer layer added between the P-base region and the N-type drift region.

[0041] Furthermore, such as Figure 1 As shown, the surface doping concentration of the P-type base region is 1–3 × 10⁻⁶. 18 / cm -3 At a depth of 1.5 μm, the value drops to ≤8 × 10⁻⁸. 17 / cm -3 .

[0042] Furthermore, the composite buffer layer is made of a platinum-doped semiconductor layer or an argon ion irradiation-damaged semiconductor layer.

[0043] Furthermore, the thickness of the composite buffer layer is ≤30nm, and its carrier lifetime is less than 10ns.

[0044] By using gradient P-base doping and a composite buffer layer, the hole concentration accumulated in the cell during turn-off and the base resistance of the parasitic transistor are reduced, thereby reducing IGBT cell turn-off losses and increasing the peg current.

[0045] This embodiment discloses an IGBT cell with a gradient P-base doped region and a composite buffer layer, comprising: an emitter metal, an oxide insulating layer, an N-type emitter region, a P-type ohmic contact region, a P-base region, a gate oxide layer formed in the trench, a polysilicon gate, an N-type drift region, and a collector region. The trench IGBT further includes: changing the P-base region to a gradient doping pattern decreasing from top to bottom, and adding a composite buffer layer between the gradient P-base region and the N-type drift region. This invention can solve the problems of long tail current duration and high turn-off loss in existing IGBT cells, while also increasing the pillar current density and improving device reliability.

[0046] 1. Gradient-doped p-type base region 12

[0047] Concentration distribution: High surface doping concentration (1~3×10⁻⁶) 18 / cm -3 This ensures the stability of the threshold voltage and the blocking capability of the device.

[0048] In vivo concentration: monotonically decreasing, decreasing to 5-8 × 10 at the shallowest point. 17 / cm -3 .

[0049] Process: A P-base region window is defined using photolithography. Vertical boron ion implantation is then performed, with the highest implantation energy and lowest ion concentration, forming a low-concentration layer within the cell. Next, the ion implantation angle is tilted at 15°, and lower energy is used to implant boron ions with increasing concentration, creating a gradient transition. Finally, the ion implantation angle is tilted at 30°, the implantation energy is further reduced, and the ion concentration increases, forming a high-concentration surface layer. Rapid thermal annealing then activates the doping and establishes the gradient concentration.

[0050] Mechanism of action: The gradient P-type region reduces the amount of holes stored, thereby accelerating the hole extraction speed during IGBT module turn-off and eliminating tail current. The high-concentration surface layer ensures that the IGBT's threshold voltage remains unaffected. Simultaneously, the low bulk concentration of the gradient P-base region also reduces the base resistance of parasitic NPN transistors, improving the chip's anti-pilling capability.

[0051] 2. Composite buffer layer

[0052] Location: At the interface between P-base region 12 and N-drift region 1;

[0053] Implementation Method 1: High-efficiency carrier recombination is achieved by introducing platinum atoms as deep-level recombination centers. Specifically, a recombination buffer layer is formed on the surface of the N-drift region through platinum vapor diffusion. Stable recombination centers are then formed through processes such as thermal annealing.

[0054] Implementation Method 2: Argon ion irradiation damage. High-energy ions bombard the silicon lattice to create defects and recombination centers. Annealing is performed after bombardment to stabilize the irradiation-introduced defects, allowing them to form stable recombination centers. Simultaneously, it prevents defects from excessively extending into the active region.

[0055] Thickness control: ≤30nm, to avoid excessive thickness affecting conduction characteristics.

[0056] Using a lightly doped N-type Si substrate as the low-doped N-type drift region 1, platinum diffusion or argon ion irradiation is performed on the front side of the low-doped N-type drift region 1. After annealing, a recombination center is formed. Then, through ion implantation, a lightly doped P-based region 12-3, a moderately doped P-based region 12-2, a heavily doped P-based region 12-1, a heavily doped N-type emitter 3, and a heavily doped P-type Pbody ohmic contact region 4 are formed sequentially. Then, trenches are etched to form a gate oxide layer 6 and a polysilicon gate 8. An oxide insulating layer 7 is formed on the upper surface of the cell. A heavily doped collector 9 is formed by ion implantation on the back side. Metals are deposited on the upper and lower surfaces of the cell to form a collector metal electrode 10 and an emitter metal electrode 11.

[0057] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

[0058] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. An IGBT cell with a graded P-based doped region and a composite buffer layer, characterized in that, include: Emitter metal electrode (11), heavily doped N-type emitter (3), heavily doped P-type ohmic contact region (4), N-type drift region (1), trench gate (8), heavily doped P-type collector (9), collector metal electrode (10), and P-base region (12); wherein, the emitter metal electrode (11), heavily doped N-type emitter (3), N-type drift region (1), heavily doped P-type collector (9), and collector metal electrode (10) are stacked from top to bottom; the heavily doped P-type ohmic contact region (4) is a P-type ohmic contact region (5), a P-type ohmic contact region (6), a P-type ohmic contact region (7), a P-type ohmic contact region (8), a P-type ohmic contact region (9), and a P-type base region (12). The ohmic contact region (4) and the heavily doped N-type emitter (3) are arranged side by side in the same layer; the trench gate (8) is a strip structure that extends from the heavily doped N-type emitter (3) to the N-type drift region (1); the P-base region (12) is located on both sides of the trench gate. The P-base region (12) is a gradient doped structure. The doping concentration of the P-base region (12) decreases monotonically from the upper surface of the cell to the bulk direction; a composite buffer layer (5) is provided at the interface between the P-base region (12) and the N-type drift region (1).

2. An IGBT cell with a gradient P-base doped region and a composite buffer layer according to claim 1, characterized in that: The P-type base region (12) includes a highly doped P-type base region (12-1), a moderately doped P-type base region (12-2), and a lightly doped P-type base region (12-3); the surface doping concentration of the highly doped P-type base region (12-1) is 1×10⁻⁶. 18 / cm -3 Up to 3×10 18 / cm -3 The surface doping concentration of the moderately doped P-based region (12-2) is 0.7 × 10⁻⁶. 18 / cm -3 Up to 1×10 18 / cm -3 The surface doping concentration of the lightly doped P-type base region (12-3) is 0.5 × 10⁻⁶. 18 / cm -3 Up to 0.7×10 18 / cm -3 The lightly doped p-type base region (12-3) has a bulk doping concentration of less than or equal to 8 × 10⁻⁶ at a depth of 1.5 μm. 17 / cm -3 .

3. An IGBT cell with a graded P-base doped region and a composite buffer layer according to claim 1, characterized in that: The composite buffer layer (5) is made of platinum-doped semiconductor or argon ion irradiation-damaged semiconductor.

4. An IGBT cell with a graded P-base doped region and a composite buffer layer according to claim 1, characterized in that: The thickness of the composite buffer layer (5) is no greater than 30 nm, and the carrier lifetime of the composite buffer layer (5) is less than 10 ns.

5. An IGBT cell with a gradient P-base doped region and a composite buffer layer according to claim 1, characterized in that: A P-based region (12) with a doping concentration that monotonically decreases from the surface to the depth of the bulk is formed by tilted ion implantation process; before forming the P-based region (12), a composite buffer layer (5) is formed on top of the N-type drift region (1) by platinum diffusion process or ion irradiation process.

6. An IGBT cell with a gradient P-based doped region and a composite buffer layer according to claim 5, characterized in that, The tilted ion implantation process is specifically as follows: The window of the P-based region (12) is determined by photolithography, and boron ions are implanted vertically. The highest ion implantation energy in this process is 70-90 keV, and the lowest ion implantation dose is 2×10⁻⁶. 13 ~3×10 13 / cm -2 A low-concentration layer is formed within the cell; Ion implantation angle tilted at 15°–25°, using a low energy of 40–60 keV, and an ion implantation dose of 3 × 10⁻⁶. 13 ~5×10 13 / cm -2 Boron ion implantation forms a gradient transition; The ion implantation angle is tilted at 30°–35°, the implantation energy is further reduced to 20–40 keV, and the ion implantation dose is 5 × 10⁻⁶. 13 ~6×10 13 / cm -2 A high-concentration surface layer is formed; Rapid thermal annealing activates doping and creates a gradient concentration.

7. An IGBT cell with a gradient P-based doped region and a composite buffer layer according to claim 5, characterized in that, The platinum diffusion process specifically involves: forming a buffer layer on the surface of the N-type drift region (1) by platinum vapor diffusion; and performing a thermal annealing process on the buffer layer to form a composite buffer layer (5).

8. An IGBT cell with a gradient P-based doped region and a composite buffer layer according to claim 5, characterized in that, The ion irradiation process specifically involves: irradiating argon ions to generate high-energy ions; generating defects by bombarding the silicon lattice with high-energy ions to form a buffer layer on the surface of the N-type drift region (1); and performing a thermal annealing process on the buffer layer to form a composite buffer layer (5).

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