A normally-off GaN HEMT structure with enhanced heat dissipation and a preparation method thereof
By etching T-shaped grooves and growing T-shaped polycrystalline diamond on the AlGaN barrier layer, combined with SiNx thin films, the heat dissipation difficulties and normally-on problems of gallium nitride materials were solved, realizing the functions of high-efficiency heat dissipation and normally-off GaN HEMT devices.
Patent Information
- Application Number
- CN202111397484.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-11-23
- Publication Date
- 2026-01-20
- Estimated Expiration
- 2041-11-23
AI Technical Summary
The low thermal conductivity of gallium nitride (GaN) materials makes heat dissipation difficult for GaN HEMT devices, and the traditional structure is normally open, resulting in unnecessary power loss.
By etching T-shaped grooves on the AlGaN barrier layer and growing T-shaped polycrystalline diamond, combined with SiNx thin film material, a normally-off GaN HEMT structure with enhanced heat dissipation is formed. The high thermal conductivity of diamond and the groove gate structure are used to reduce the polarization effect.
This improves the heat dissipation and saturation current output capability of GaN HEMT devices, while also realizing the function of normally off devices and reducing power loss.
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Figure CN114122108B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of semiconductors, and particularly relates to a normally-off GaN HEMT structure with enhanced heat dissipation. BACKGROUND
[0002] As one of the third-generation wide-bandgap semiconductor materials, gallium nitride has the advantages of wide bandgap, high critical breakdown field, high electron saturation drift speed, direct bandgap semiconductor, low dielectric constant, high temperature resistance, radiation resistance and good chemical stability, and is widely used in microelectronics, power electronics, optoelectronics and other fields.
[0003] Although gallium nitride has the above-mentioned advantages, there are still some problems in fully exerting the advantages of gallium nitride devices. On the one hand, gallium nitride material itself has low thermal conductivity, and the realization of normally-off GaN HEMT devices still faces some difficulties. In order to solve the problem of low thermal conductivity of gallium nitride material, gallium nitride devices generally use substrates with high thermal conductivity such as silicon carbide, silicon and sapphire. Even though silicon carbide has high thermal conductivity, it still cannot meet the heat dissipation requirements of gallium nitride power devices, which has become a key obstacle to the development of gallium nitride technology. On the other hand, due to the two-dimensional electron gas (2-DEG) generated by the piezoelectric polarization and spontaneous polarization of gallium nitride-based heterojunction, the traditional gallium nitride-based transistor is a depletion mode device (threshold voltage is negative), that is, the GaN HEMT structure we are familiar with is a normally-on device, which is not convenient for practical application in power electronic systems, and will cause unnecessary power loss. SUMMARY
[0004] The purpose of the present application is to provide a normally-off GaN HEMT structure with enhanced heat dissipation to solve the above-mentioned defects in the prior art.
[0005] A normally-off GaN HEMT structure with enhanced heat dissipation, comprising a substrate, a low-temperature AlN nucleation layer, a GaN channel layer, an AlGaN barrier layer, a dielectric layer, a T-shaped polycrystalline diamond and a gate electrode arranged in order from bottom to top, a source electrode and a drain electrode are located on the AlGaN barrier layer, a T-shaped groove is etched on the AlGaN barrier layer and a dielectric layer is grown, a T-shaped groove is etched on the dielectric layer and a T-shaped polycrystalline diamond is grown.
[0006] The preparation method of the above structure is as follows:
[0007] (1) AlGaN / GaN heterojunction epitaxy is carried out on the substrate by using MOCVD technology and equipment, which is a general traditional technology, and the AlGaN / GaN heterojunction structure includes a low-temperature AlN nucleation layer and a GaN channel layer in order;
[0008] (2) growing a certain thickness of AlGaN barrier layer on the GaN channel layer, taking out from the MOCVD device after the AlGaN barrier layer is grown, performing selective protection on the gallium nitride buffer layer through uniform glue development, photolithography and etching means, forming an AlGaN barrier layer T-shaped groove through dry etching and growing a certain thickness of dielectric layer;
[0009] (3) etching a T-shaped groove on the dielectric layer and growing T-shaped polycrystalline diamond, growing a polycrystalline diamond film by using a microwave plasma chemical vapor deposition device, and the specific growth conditions are: cavity pressure 95-105 Torr, methane flow 20-30 sccm, hydrogen flow 370-380 sccm, and the polycrystalline diamond growth thickness is 0.1-1 μm;
[0010] (4) depositing gate metal material on the T-shaped polycrystalline diamond to form a Schottky contact;
[0011] (5) etching the excess dielectric layer and depositing metal material of the source electrode and the drain electrode, wherein the source electrode and the drain electrode adopt a germanium / titanium / aluminum / titanium / gold (Ge / Ti / Al / Ti / Au) multilayer alloy, the thickness of the Ge metal layer is 1-20 nm, and the N-type heavy doping is formed with the AlGaN / GaN heterojunction to reduce the ohmic contact resistance.
[0012] Further, the substrate adopts any one of sapphire, silicon, silicon carbide, gallium nitride, zinc oxide and diamond.
[0013] Further, the dielectric layer is SiN x Thin film material, thickness is 200 nm, used for isolating AlGaN and gate electrode from direct contact, reducing gate leakage, and improving device breakdown voltage.
[0014] The application proposes a normally-off GaN HEMT structure with enhanced heat dissipation and an implementation scheme based on the advantage of high thermal conductivity of diamond, which can effectively improve the heat dissipation capacity of the AlGaN / GaN HEMT power device, and realize the enhancement type GaN HEMT device on the basis of enhancing the heat dissipation.
[0015] The application has the following advantages:
[0016] (1) In the application, the diamond is directly deposited on the AlGaN barrier layer, so that the diamond is closer to the gallium aluminum nitride and gallium nitride channel heat source, and the heat dissipation capacity of the diamond can be efficiently exerted compared with the diamond substrate GaN HEMT device structure.
[0017] (2) The barrier layer with T-groove in this invention can not only grow diamond heat dissipation layer, but also facilitate the formation of thin barrier layer, thereby greatly reducing the two-dimensional electron gas generated by heterojunction polarization effect and realizing the function of enhancement GaN HEMT device.
[0018] (3) The GaN HEMT structure of the present invention not only enhances the heat dissipation capability of GaN HEMT, but also the trench gate structure can maintain a high saturation current output capability while realizing an enhanced GaN HEMT device.
[0019] (4) There are generally two methods for realizing enhancement-mode GaN HEMT devices. The first method is negative ion implantation, which causes lattice damage during ion implantation. The second method is p-GaN gate growth technology, which results in very low activation rate of doped magnesium. In contrast, this invention uses a thinning of the heterojunction barrier layer to form a groove, which depletes the two-dimensional electron gas in the channel to realize the enhancement-mode device. Compared with the first two methods, the groove barrier layer is easier to process and has higher stability, making it a more advantageous GaN enhancement-mode device realization method. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the structure of the present invention.
[0021] Figure 2 This is a schematic diagram of diamond growth.
[0022] Figure 3 This is a schematic diagram of the deposited medium layer.
[0023] Figure 4 This is a schematic diagram showing the sequential growth of an AlN nucleation layer, a GaN channel layer, and an AlGaN barrier layer on a substrate.
[0024] The structure consists of: 101 substrate, 102 low-temperature AlN nucleation layer, 103 GaN channel layer, 104 AlGaN barrier layer, 105 T-shaped polycrystalline diamond, 106 source electrode, 107 gate electrode, 108 drain electrode, and 111 dielectric layer. Detailed Implementation
[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.
[0026] Example 1
[0027] (1) An AlGaN / GaN heterojunction epitaxy is performed on a substrate 101 using MOCVD technology and equipment. This technology is a general traditional technology. The AlGaN / GaN heterojunction structure includes a low-temperature AlN nucleation layer 102 and a GaN channel layer 103 in sequence.
[0028] (2) An AlGaN barrier layer 104 of a certain thickness is grown in the GaN channel layer 103. After the AlGaN barrier layer 104 is grown, it is taken out from the MOCVD equipment. The gallium nitride buffer layer is selectively protected by means of homogenization, photolithography and etching. The AlGaN barrier layer 104 T-shaped groove is formed by dry etching and a dielectric layer 111 of a certain thickness is grown.
[0029] (3) T-shaped grooves are etched on the dielectric layer 111 and T-shaped polycrystalline diamond 105 is grown. The polycrystalline diamond film is grown using a microwave plasma chemical vapor deposition equipment. The specific growth conditions are: chamber pressure 100 Torr, methane flow rate 24 sccm, hydrogen flow rate 376 sccm, and polycrystalline diamond growth thickness 0.6 μm.
[0030] (4) Deposit gate metal material on T-shaped polycrystalline diamond 105 to form a Schottky contact;
[0031] (5) Etch excess dielectric layer and deposit metal material for source electrode 106 and drain electrode 108. The source electrode 106 and drain electrode 108 are made of germanium / titanium / aluminum / titanium / gold (Ge / Ti / Al / Ti / Au) multilayer alloy. The thickness of the Ge metal layer is 12nm and it forms N-type heavy doping with AlGaN / GaN heterojunction to reduce ohmic contact resistance.
[0032] Example 2
[0033] The rest is the same as in Example 1, except that the growth conditions in step (3) are: cavity pressure 95 Torr, methane flow rate 20 sccm, hydrogen flow rate 370 sccm, T-shaped polycrystalline diamond 105 growth thickness is 0.1 μm, and the Ge metal layer thickness in step (5) is 1 nm.
[0034] Example 3
[0035] The rest is the same as in Example 1, except that the growth conditions in step (3) are: chamber pressure 105 Torr, methane flow rate 30 sccm, hydrogen flow rate 380 sccm, T-shaped polycrystalline diamond 105 growth thickness 1 μm, and Ge metal layer thickness in step (5) is 20 nm.
[0036] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.
Claims
1. A normally-off GaN HEMT structure with enhanced heat dissipation, characterized in that, The structure includes, from bottom to top, a substrate (101), a low-temperature AlN nucleation layer (102), a GaN channel layer (103), an AlGaN barrier layer (104), a dielectric layer (111), a T-shaped polycrystalline diamond (105), and a gate electrode (107). The source electrode (106) and the drain electrode (108) are located on the AlGaN barrier layer (104). A T-shaped groove is etched on the AlGaN barrier layer (104) and a dielectric layer (111) is grown thereon. A T-shaped groove is etched on the dielectric layer (111) and a T-shaped polycrystalline diamond (105) is grown thereon. The gate electrode (107) is located on the T-shaped polycrystalline diamond (105).
2. The normally-off GaN HEMT structure with enhanced heat dissipation according to claim 1, characterized in that, The substrate (101) is any one of sapphire, silicon, silicon carbide, gallium nitride, zinc oxide, and diamond.
3. The normally-off GaN HEMT structure with enhanced heat dissipation according to claim 1, characterized in that, The dielectric layer (111) is SiN x Thin film material with a thickness of 200 nm.
4. A method for preparing the heat-dissipating enhanced normally-off GaN HEMT structure of claim 1, characterized in that, Includes the following steps: (1) An AlGaN / GaN heterojunction is epitaxially grown on a substrate (101) using MOCVD technology and equipment. The AlGaN / GaN heterojunction structure includes a low-temperature AlN nucleation layer (102) and a GaN channel layer (103). (2) An AlGaN barrier layer (104) of a certain thickness is grown in the GaN channel layer (103). After the AlGaN barrier layer (104) is grown, it is taken out from the MOCVD equipment. The gallium nitride buffer layer is selectively protected by means of homogenization, photolithography and etching. The AlGaN barrier layer (104) T-shaped groove is formed by dry etching and a dielectric layer (111) is grown. (3) T-shaped grooves were etched on the dielectric layer (111) and T-shaped polycrystalline diamond (105) was grown. The polycrystalline diamond film was grown using a microwave plasma chemical vapor deposition equipment. The specific growth conditions were: cavity pressure 95-105 Torr, methane flow rate 20-30 sccm, hydrogen flow rate 370-380 sccm, and the growth thickness of the T-shaped polycrystalline diamond (105) was 0.1 μm-1 μm. (4) Deposit gate metal material on T-shaped polycrystalline diamond (105) to form a Schottky contact; (5) Etch excess dielectric layer and deposit metal materials for source electrode (106) and drain electrode (108), wherein the source electrode (106) and drain electrode (108) are made of germanium / titanium / aluminum / titanium / gold multilayer alloy, the thickness of the Ge metal layer is 1-20nm and it forms an N-type heavy doping with AlGaN / GaN heterojunction.
5. The method according to claim 4, characterized in that, The growth conditions in step (3) are: cavity pressure 100 Torr, methane flow rate 24 sccm, hydrogen flow rate 376 sccm, and polycrystalline diamond growth thickness 0.6 μm.