Silicon carbide power device with self-integrated reverse freewheeling transistor structure and preparation method of silicon carbide power device
The self-integrated reverse freewheeling transistor structure in silicon carbide power devices addresses high reverse conduction voltage issues by reducing turn-on voltage and switching losses, enhancing device performance in the third quadrant.
Patent Information
- Application Number
- CN202411294365.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-14
- Publication Date
- 2024-12-20
Smart Images
Figure CN119170639A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of integrated circuit device structure design, and in particular relates to a novel self-integrated reverse freewheeling transistor structure of silicon carbide power device and a preparation method thereof. Background Art
[0002] Silicon carbide is considered to be the next generation semiconductor device material that exceeds the limits of silicon due to its many excellent properties, including a critical electric field 10 times that of silicon, a thermal conductivity 3 times that of silicon, and an electron saturation drift velocity 2 times that of silicon. In addition, as the only compound semiconductor that can be obtained from silicon dioxide by thermal oxidation, silicon carbide is more compatible with existing silicon-based processes in terms of process implementation. With the growing demand for high-temperature, high-frequency, high-power and radiation-resistant devices, wide-bandgap semiconductors represented by silicon carbide are becoming more and more widely used in the field of electronic devices.
[0003] Power transistor devices based on silicon carbide are gradually replacing traditional silicon-based power devices with excellent performance. In practical applications, the conduction capability of power devices in the third quadrant is also worthy of attention. However, problems such as high body diode turn-on voltage caused by the wide bandgap properties of silicon carbide itself have hindered the further development of silicon carbide power devices. Designing a device structure with low reverse conduction voltage is urgent and has great practical application value.
[0004] In the face of the high reverse conduction voltage of silicon carbide power devices, the current solutions mainly include integrating a reverse freewheeling diode outside the device, integrating a Schottky diode inside the device, and integrating a p + Heterojunction diodes composed of polysilicon and n-type SiC, etc. However, external integrated freewheeling devices will cause a decrease in overall integration, and internal integrated diodes will have risks such as increased leakage current and decreased breakdown voltage. How to design new structures to improve the third quadrant conduction capability of silicon carbide power devices is a highly promising development direction in the future. Summary of the invention
[0005] The present invention discloses a silicon carbide power device with a self-integrated reverse freewheeling transistor structure, which comprises, from bottom to top, a silicon carbide substrate, an N-type drift layer, an N-type carrier storage layer and a P-type base region; an N-type carrier storage layer formed in the central region above the P-type base region; + The source region and the P + Ohmic contact area; gate trench, through N + A source region, a P-type base region and an N-type carrier storage layer; a freewheeling transistor, comprising a P-type base region of the freewheeling transistor, formed in the N-type drift layer below the gate trench; a drain N +The gate of the freewheeling transistor is formed in the central region of the upper part of the P-type base region of the freewheeling transistor; the gate oxide layer of the freewheeling transistor covers the sidewalls and the bottom of the gate trench on both sides; the gate of the freewheeling transistor is formed in the gate trench and connected to the drain N + The regions are short-circuited; the gate of the power device is formed above the gate of the freewheeling transistor in the gate trench and is isolated from each other; a top isolation layer covers the gate trench; a passivation layer is formed on both sides of the top of the device; and a source ohmic contact covers the surface of the device, wherein when the device operates in the third quadrant, the freewheeling transistor is turned on to achieve reverse freewheeling.
[0006] The silicon carbide power device of the self-integrated reverse freewheeling transistor structure of the present invention preferably further includes a P-type heavily doped region formed below the P-type base region of the freewheeling transistor.
[0007] In the silicon carbide power device of the self-integrated reverse freewheeling transistor structure of the present invention, preferably, the gate of the freewheeling transistor is polysilicon.
[0008] In the silicon carbide power device of the self-integrated reverse freewheeling transistor structure of the present invention, preferably, the gate of the power device is polycrystalline silicon.
[0009] The present invention also discloses a method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure, comprising the following steps: sequentially epitaxially growing an N-type drift layer, an N-type carrier storage layer and a P-type base region on a silicon carbide substrate; forming an N-type carrier storage layer located in the central region on the upper part of the P-type base region; + The source region and the P + Ohmic contact area; photolithography defines the gate trench and the base region of the freewheeling transistor, through the N + The gate trench is formed by forming a source region, a P-type base region, and an N-type carrier storage layer, and a base region window of a freewheeling transistor is formed in the N-type drift layer below the gate trench; a P-type base region of the freewheeling transistor is formed by epitaxy; and a drain N of the freewheeling transistor is formed in the P-type base region of the freewheeling transistor by photolithography and ion implantation. + region, and then perform high temperature annealing to activate the doped ions; form a gate oxide layer of the freewheeling transistor in the gate trench, so that it covers the sidewalls and both sides of the bottom of the gate trench, and form the gate of the freewheeling transistor and the drain N of the freewheeling transistor + The regions are in contact with each other to obtain a freewheeling transistor with a gate-drain short circuit; then the intermediate isolation layer, the gate of the power device, and the top isolation layer are filled in the gate trench in sequence; a passivation layer is formed, the source metal contact area is defined by photolithography, and the passivation layer is etched to retain only part of the passivation layer on both sides; a source ohmic contact is formed to cover the device surface, and then the top of the device is chemically mechanically polished to form a single cell structure.
[0010] In the method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure of the present invention, preferably, before forming the P-type base region of the freewheeling transistor, the following steps are also included: ion implantation is performed from the freewheeling transistor base region window to form a P-type heavily doped region.
[0011] In the method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure of the present invention, preferably, the gate of the freewheeling transistor is polysilicon.
[0012] In the method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure of the present invention, preferably, the gate of the power device is polycrystalline silicon.
[0013] Beneficial effects:
[0014] The self-integrated freewheeling transistor at the bottom of the gate can have a lower reverse turn-on voltage, which can effectively reduce the switching loss of the device.
[0015] The quasi-split-gate structure converts a portion of the gate-drain capacitance into gate-source capacitance, further reducing switching losses.
[0016] The heavily doped P-type region at the bottom of the local MOSFET can form a depletion region when the device withstands reverse voltage, effectively taking on the reverse voltage and improving the device's withstand voltage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 It is a flow chart of a method for preparing a silicon carbide trench MOSFET with a self-integrated reverse freewheeling transistor structure.
[0018] Figure 2 to Figure 10 It is a structural schematic diagram of each stage of a method for preparing a silicon carbide trench MOSFET with a self-integrated reverse freewheeling transistor structure. DETAILED DESCRIPTION
[0019] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.
[0020] In the description of the present invention, it should be noted that the terms "upper", "lower", "vertical", "horizontal", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.
[0021] In addition, many specific details of the present invention are described below, such as the structure, materials, dimensions, processing technology and techniques of the device, so that the present invention can be more clearly understood. However, as can be understood by those skilled in the art, the present invention can be implemented without following these specific details. Unless otherwise specified below, the various parts of the device can be made of materials known to those skilled in the art, or can be made of materials with similar functions developed in the future.
[0022] Figure 1 The figure is a flow chart of the method for preparing a silicon carbide trench MOSFET with a self-integrated reverse freewheeling transistor structure. Figure 1 As shown, the method for preparing a silicon carbide trench MOSFET with a self-integrated reverse freewheeling transistor structure comprises the following steps:
[0023] Step S1, epitaxially doping with a concentration of 7×10 15 cm -3 , N-type drift layer (N-Drift) 101 with a thickness of 10 microns and a doping concentration of 2×10 16 cm -3 The N-type carrier storage layer (N-CSL) 102 has a doping concentration of 1×10 17 cm -3 The P-base region (P-base) 103, the resulting structure is as follows Figure 2 Then, through two times of photolithography and ion implantation, an N type base region located in the central region is formed on the upper part of the P type base region 103. + The source region 104 and the P + Ohmic contact region 105, the resulting structure is as follows Figure 3 shown.
[0024] Step S2, defining the gate trench and the freewheeling transistor base region by photolithography, so that the gate trench penetrates the N + The source region 104, the P-type base region 103 and the N-type carrier storage layer 102, the freewheeling transistor base region is formed in the N-type drift layer 101 below the gate trench, and the resulting structure is as shown Figure 4As shown. Ion implantation is performed from the freewheeling transistor base region window to form a 0.5-1 μm thick doping concentration of 10 18 cm -3 -10 19 cm -3 The P-type heavily doped region 106 is formed, and then the P-type base region 107 of the freewheeling transistor is epitaxially grown so that its top is flush with the top of the N-type drift layer 101. The doping concentration of the P-type base region 107 is controlled to be 10 13 cm -3 The low doping level is about 0.1 μm, so that the freewheeling transistor can achieve a lower turn-on voltage. The resulting structure is as follows Figure 5 As shown. By photolithography and ion implantation, a doping concentration of 10 19 cm -3 The drain of the freewheeling transistor N + Region 108 is then subjected to high temperature annealing at 1700°C to activate the doped ions. The resulting structure is as shown Figure 6 shown.
[0025] Step S3, depositing 50nm thick silicon dioxide in the gate trench to form a gate oxide layer 109 of the freewheeling transistor and the power device, so that it covers the sidewalls and the bottom of the gate trench, and fills the polysilicon layer 110 and the drain N of the freewheeling transistor. + The regions 108 are in contact with each other to form a freewheeling MOSFET with a gate-drain short circuit. The resulting structure is as follows Figure 7 Then, a silicon dioxide layer is deposited as an intermediate isolation layer 111 to isolate the gate of the freewheeling transistor from the gate of the power device; a polysilicon layer is deposited to form the gate 112 of the power device, and a silicon dioxide layer is formed to cover the gate trench as a top isolation layer 113. The structure is as shown in FIG. Figure 8 shown.
[0026] Step S4, deposit an oxide layer as a passivation layer 114, photolithography is used to define the source metal contact area, and the oxide layer is etched to retain only part of the oxide layer on both sides. The resulting structure is as follows: Fig. 9 shown.
[0027] Step S5, depositing metal to form a source ohmic contact 115, and then chemically mechanically polishing the top of the device to form a single cell structure of a silicon carbide trench MOSFET with a self-integrated reverse freewheeling transistor structure. The resulting structure is as shown in FIG. Fig.10 shown.
[0028] like Fig.10As shown, the silicon carbide power device of the self-integrated reverse freewheeling transistor structure includes, from bottom to top, a silicon carbide substrate 100, an N-type drift layer 101, an N-type carrier storage layer 102 and a P-type base region 103; an N-type carrier storage layer 102 formed in the central region above the P-type base region 103; + The source region 104 and the P + Ohmic contact region 105; gate trench, penetrating N + A source region 104, a P-type base region 103 and an N-type carrier storage layer 102; a freewheeling transistor, comprising a P-type base region 107 of the freewheeling transistor, formed in the N-type drift layer 101 below the gate trench; a drain N + Region 108 is formed in the central region of the upper part of the P-type base region 107 of the freewheeling transistor; the gate oxide layer 109 of the freewheeling transistor covers the sidewalls and the bottom of the gate trench on both sides; the gate 110 of the freewheeling transistor is formed in the gate trench and is connected to the drain N + Region 108 is short-circuited; a P-type heavily doped region is formed below the P-type base region of the freewheeling transistor; a gate 112 of the power device is formed above the gate 110 of the freewheeling transistor in the gate trench and is isolated from each other; a top isolation layer 113 covers the gate trench; a passivation layer 114 is formed on both sides of the top of the device; and a source ohmic contact 115 covers the surface of the device.
[0029] In the silicon carbide trench gate structure, a local MOSFET with a gate-drain short circuit is formed at the bottom of the gate to act as a freewheeling transistor when the device is turned on in the third quadrant. When the device works in the third quadrant, the local MOSFET is turned on and enters a saturation state. By adjusting the threshold voltage of the local MOSFET, the reverse turn-on voltage is much lower than the turn-on voltage of the body diode, and a P-type heavily doped region is formed at the bottom of the local MOSFET, which can effectively improve the reverse breakdown characteristics of the device.
[0030] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.
Claims
1. A self-integrated reverse freewheeling transistor structure of silicon carbide power device, characterized in that: From bottom to top, it includes a silicon carbide substrate, an N-type drift layer, an N-type carrier storage layer and a P-type base region; The N-type base region located in the central region is formed on the upper part of the P-type base region. + The source region and the P + Ohmic contact area; Gate trench, through N + Source region, P-type base region and N-type carrier storage layer; A freewheeling transistor, comprising a P-type base region of the freewheeling transistor formed in an N-type drift layer below the gate trench; The drain of the freewheeling transistor N + The gate of the freewheeling transistor is formed in the central region of the upper part of the P-type base region of the freewheeling transistor; the gate oxide layer of the freewheeling transistor covers the sidewalls and the bottom of the gate trench; the gate of the freewheeling transistor is formed in the gate trench and connected to the drain N + The area phase is short-circuited; a gate of the power device, formed above the gate of the freewheeling transistor in the gate trench and isolated from each other; A top isolation layer covering the gate trench; a passivation layer, formed on both sides of the top of the device; The source ohmic contact covers the device surface. When the device operates in the third quadrant, the freewheeling transistor is turned on to achieve reverse freewheeling.
2. The silicon carbide power device of the self-integrated reverse freewheeling transistor structure according to claim 1, characterized in that: It also includes a P-type heavily doped region formed below the P-type base region of the freewheeling transistor.
3. The silicon carbide power device of the self-integrated reverse freewheeling transistor structure according to claim 1, characterized in that: The gate of the freewheeling transistor is polysilicon.
4. The silicon carbide power device of the self-integrated reverse freewheeling transistor structure according to claim 1, characterized in that: The gate of the power device is polysilicon.
5. A method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure, characterized in that: The following steps are involved: An N-type drift layer, an N-type carrier storage layer and a P-type base region are sequentially epitaxially grown on a silicon carbide substrate; The N type base region is formed in the central region on the upper part of the P type base region. + The source region and the P + Ohmic contact area; Photolithography is used to define the gate trench and base region of the freewheeling transistor, through the N + The source region, the P-type base region, and the N-type carrier storage layer form a gate trench, and a freewheeling transistor base region window is formed in the N-type drift layer below the gate trench; The P-type base region of the freewheeling transistor is formed by epitaxy; the drain electrode N of the freewheeling transistor is formed in the P-type base region of the freewheeling transistor by photolithography and ion implantation. + region, and then perform high temperature annealing to activate the doped ions; form a gate oxide layer of the freewheeling transistor in the gate trench, so that it covers the sidewalls and both sides of the bottom of the gate trench, and form the gate of the freewheeling transistor and the drain N of the freewheeling transistor + The regions are in contact with each other, and a freewheeling transistor with a gate-drain short circuit is obtained; Then, the middle isolation layer, the gate of the power device, and the top isolation layer are sequentially filled in the gate trench; Form a passivation layer, define the source metal contact area by photolithography, and etch the passivation layer to keep only part of the passivation layer on both sides; A source ohmic contact is formed to cover the device surface, and then the top of the device is chemically mechanically polished to form a single cell structure.
6. The method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure according to claim 5, characterized in that: Before forming the P-type base region of the freewheeling transistor, the following steps are also included: Ion implantation is performed from the base window of the freewheeling transistor to form a P-type heavily doped region.
7. The method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure according to claim 5, characterized in that: The gate of the freewheeling transistor is polysilicon.
8. The method for preparing a silicon carbide power device with a self-integrated reverse freewheeling transistor structure according to claim 5, characterized in that: The gate of the power device is polysilicon.