GaN high electron mobility transistor of composite channel passivation medium
By employing a composite channel passivation dielectric of alumina and silicon nitride in GaN HEMT devices with a stepped distribution, the problems of current collapse and parasitic capacitance are solved, thereby improving device stability and performance.
Patent Information
- Application Number
- CN202511511384.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-22
- Publication Date
- 2026-01-20
AI Technical Summary
GaN HEMT devices suffer from current collapse due to interface and surface states, and the high dielectric constant of commonly used passivation media leads to parasitic capacitance that affects device gain.
Alumina grown by ALD and silicon nitride grown by CVD are used as the composite channel passivation medium. The two are distributed in a stepped manner, with alumina on the lower step and silicon nitride on the upper step. The gate metal covers the openings of the two dielectric layers.
It effectively suppresses current collapse, improves device stability, balances parasitic characteristics and gate characteristics, adjusts stress and thermal expansion coefficient, and reduces device damage under high temperature and high field conditions.
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Figure CN121368151A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to a GaN high electronic mobility transistor (HEMT) with a composite channel passivation medium, and belongs to the fields of ferromagnetic materials and third-generation semiconductor microwave and millimeter wave devices. BACKGROUND
[0002] GaN is a wide band gap material, has high electron saturation velocity, high breakdown field strength, good heat conduction of SiC substrate, and radiation resistance, and has new physical effects such as self-polarization and piezoelectricity on the AlGaN / GaN interface, and the two-dimensional electron gas density is as high as 2x1013 cm-2, so the GaN HEMT device has the ability of high power density; at the same time, since GaN has a larger band gap and a higher working voltage, it has a broad application prospect in the field of microwave and millimeter wave chips. However, there is a problem in gallium nitride devices that is difficult to overcome, that is, the current collapse problem caused by the interface state and the surface state. The current collapse caused by the surface state is mainly due to the fact that the passivation of the surface of the epitaxial layer is not ideal, and there are defect points or vacancies, so that potential well traps are generated, and when the device works at high voltage or dynamic radio frequency, the channel electrons will be captured by the surface potential well, thereby causing the current collapse phenomenon. In addition, since the HEMT device is a voltage-controlled current device, in the device model, the gate-source and gate-drain parasitic capacitances will affect the gain and other characteristics of the device. In addition, since the HEMT device is a voltage-controlled current device, in the device model, the gate-source and gate-drain parasitic capacitances will affect the gain and other characteristics of the device. Generally, the passivation process uses silicon nitride material as the passivation medium, and the dielectric constant is relatively large, which will also cause the problem of large parasitic capacitance. SUMMARY
[0003] In view of the deficiencies of the prior art, the present application provides a GaN high electron mobility transistor with a composite channel passivation medium, which uses two different media as the composite channel passivation medium, the first layer of medium being aluminum oxide grown by ALD, and the second layer of medium being silicon nitride medium grown by CVD. The second layer of channel protection medium silicon nitride is opened by photolithography and ion etching, and has a large opening size, and the etching stops on the first layer of channel protection medium aluminum oxide by using the etching selectivity of the two media; the first layer of channel protection medium aluminum oxide is opened by photolithography and wet etching, and has a small opening size, and the etching stops on the surface of the epitaxial material. The first layer of channel protection medium aluminum oxide and the second layer of channel protection medium silicon nitride are in a stepped shape, i.e. the aluminum oxide is on the lower step and has a small opening, and the silicon nitride is on the upper step and has a large opening. The gate metal covers the stepped openings of the two layers of composite channel passivation medium. The aluminum oxide as the first layer of passivation medium in contact with the channel of the GaN device has high density and low dielectric constant, and can effectively suppress the current collapse of the GaN device. The device structure of the present application has good stability, and can balance the parasitic characteristics and gate field plate characteristics of the device. Meanwhile, the two media and the stepped structure thereof can also adjust the stress and the coefficient of thermal expansion of the device, so as to reduce the damage and degradation of the device caused by the mismatch of the stress and the coefficient of thermal expansion under the working conditions of high temperature and high field.
[0004] To solve the technical problems, the present application adopts the following technical solutions: A GaN high electron mobility transistor with a composite channel passivation medium, comprising a GaN HEMT complete epitaxial structure, and a source metal, a drain metal, a composite channel passivation medium and a gate metal prepared on the GaN HEMT complete epitaxial structure; the GaN HEMT complete epitaxial structure comprises a substrate, a nucleation layer and a high-resistance buffer layer, a channel layer and a barrier layer; the composite channel passivation medium comprises a first layer of channel protection medium aluminum oxide and a second layer of channel protection medium silicon nitride.
[0005] Preferably, the substrate is any one of Si single crystal, sapphire, high-purity semi-insulating SiC, GaN single crystal and diamond substrate.
[0006] Preferably, the material of the nucleation layer and the high-resistance buffer layer is one or more of iron-doped GaN, alumina-doped GaN, carbon-doped GaN and AlN material.
[0007] Preferably, the material of the channel layer is one of GaN and InGaN.
[0008] Preferably, the material of the barrier layer is any one or combination of AlGaN, AlInN, AlN and AlInGaN.
[0009] Preferably, the first layer of channel protection medium aluminum oxide is prepared by atomic layer deposition (ALD) equipment, which has high density; and the second layer of channel protection medium silicon nitride is prepared by chemical vapor deposition (CVD) equipment.
[0010] Preferably, the second layer of channel protection medium silicon nitride is opened by photolithography and ion etching, and has large opening size, and is etched to stop on the first layer of channel protection medium aluminum oxide by using etching selectivity of the two mediums; the first layer of channel protection medium aluminum oxide is opened by photolithography and wet etching, and has small opening size, and is etched to stop on the surface of the epitaxial material. The first layer of channel protection medium aluminum oxide and the second layer of channel protection medium silicon nitride are in a stepped shape, that is, the first layer of channel protection medium aluminum oxide is in a lower step and has small opening to the gate metal, and the second layer of channel protection medium silicon nitride is in an upper step and has large opening to the gate metal.
[0011] Preferably, the metal material of the gate metal is one or a combination of Au, Al, Ta, Ti, Pt, Pd, Ru and Ni; and the gate metal covers the stepped openings of the two layers of composite channel passivation mediums.
[0012] The present application has the following advantages: 1. The present application uses ALD-grown aluminum oxide as the first layer of passivation medium in contact with the channel of a GaN device, which has high density and low dielectric constant, and can effectively inhibit current collapse of the GaN device.
[0013] 2. The present application uses two different mediums as channel passivation mediums, and the two passivation mediums are in a stepped distribution, with small opening in the lower layer and large opening in the upper layer, and the gate metal covers the two layers of mediums; the structure has good stability, and can balance parasitic characteristics and gate field plate characteristics of the device. Meanwhile, the device stress and thermal expansion coefficient can be adjusted, so as to reduce device damage and degradation caused by mismatch of the stress and thermal expansion coefficient when the device works under high temperature and high field conditions. BRIEF DESCRIPTION OF DRAWINGS
[0014] Figure 1 Figure 1 is a schematic diagram of a GaN epitaxial layer structure.
[0015] Figure 2 Figure 3 is a schematic diagram of a cross section of preparation of source-drain metal and two layers of channel passivation mediums.
[0016] Figure 3 Figure 4 is a schematic diagram of a cross section of forming a medium groove by opening process of the upper layer of silicon nitride medium of the gate part.
[0017] Figure 4 Figure 5 is a schematic diagram of a cross section of forming a medium groove by opening process of the lower layer of aluminum oxide medium of the gate part.
[0018] Figure 5A cross-sectional view of a Schottky contact formed after fabrication of the gate metal.
[0019] Wherein: 101: substrate; 102: nucleation layer and high resistance buffer layer; 103: channel layer; 104: barrier layer; 105: AlGaN back barrier layer; 106: AlN insertion layer; 107: GaN cap layer; 108: GaN HEMT complete epitaxial structure; 201: source metal; 202: second layer of channel protection medium silicon nitride; 203: first layer of channel protection medium aluminum oxide; 205: drain metal; 206: composite channel protection medium formed by 202 and 203; 301: gate metal. DETAILED DESCRIPTION
[0020] The application will be further described in detail below with reference to the accompanying drawings.
[0021] The application proposes a GaN high electron mobility transistor with composite channel passivation medium, which uses two different media as the composite channel passivation medium 206, the first layer of medium uses ALD-grown aluminum oxide 203, and the second layer of medium uses CVD-grown silicon nitride medium 202. The first layer of channel protection medium aluminum oxide and the second layer of channel protection medium silicon nitride are in a stepped shape, that is, the aluminum oxide is in the lower step and has small openings; the silicon nitride (202) is in the upper step and has large openings. The gate metal 301 covers the stepped openings of the two layers of composite channel passivation medium. The aluminum oxide as the first layer of passivation medium in contact with the channel of the GaN device has high density and low dielectric constant, which can effectively suppress the current collapse of the GaN device. The two passivation media are in a stepped distribution, the lower layer has small openings and the upper layer has large openings, and the gate metal covers the two layers of medium; the structure has good stability and can balance the parasitic characteristics of the device and the gate field plate characteristics. At the same time, the two media and their stepped structure can also adjust the stress and the coefficient of thermal expansion of the device, thereby reducing the damage and degradation of the device caused by mismatch of stress and coefficient of thermal expansion when the device works under high temperature and high field conditions.
[0022] The structure and preparation method of the GaN high electron mobility transistor with composite channel passivation medium disclosed by the application are shown in Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 The GaN HEMT complete epitaxial structure 108 is shown in Figure 1As shown, the structure includes a substrate 101, a nucleation layer and a high-resistivity buffer layer 102, a channel layer 103, and a barrier layer 104. Due to the inverse piezoelectric effect, a two-dimensional electron gas is generated at the interface between the barrier layer 104 and the channel layer 103. The substrate 101 can be any one of Si single crystal, high-purity semi-insulating SiC, sapphire, GaN single crystal, or diamond substrate, and its size is not limited; it can be 4 inches or 6 inches. The nucleation layer and high-resistivity buffer layer 102 are composed of one or more of iron-doped GaN, carbon-doped GaN, vanadium-doped GaN, and AlN materials. The channel layer 103 is one of GaN or InGaN materials. The barrier layer 104 is any one of AlGaN, AlInN, AlN, and AlInGaN. The complete GaN epitaxial structure of this invention, from bottom to top, consists of a substrate 101 with a thickness of 300 μm to 1200 μm, a nucleation layer and high-resistivity buffer layer 102 with a thickness of 500 nm to 3000 nm, a channel layer 103 with a thickness of 10 nm to 200 nm, and a barrier layer 104 with a thickness of 4 nm to 50 nm. The thickness of each layer can be adjusted according to specific device requirements. When the barrier layer 104 is made of AlGaN material, the specific Al content can be determined by the device application requirements, such as 15% to 45%. Furthermore, other layers can be selectively inserted into the GaN epitaxial layer to meet different application environment requirements. For example, an AlGaN back barrier layer 105 can be inserted between the channel layer 103 and the nucleation layer and high-resistivity buffer layer 102; an AlN insertion layer 106 can be inserted between the barrier layer 104 and the channel layer 103; and a GaN cap layer 107 can be grown on the surface of the barrier layer 104. Since the typical epitaxial layer of the present invention includes a substrate 101, a nucleation layer and a high-resistivity buffer layer 102, a channel layer 103, and a barrier layer 104, other insertion layers are not discussed for the time being, and whether or not the selective structure is prepared does not affect the implementation of the novel composite channel passivated dielectric high electron mobility device of the present invention.
[0023] Furthermore, such as Figure 2 As shown, source metal 201 and drain metal 205 are then prepared on GaN epitaxial material. A first channel passivation protection medium 203, made of alumina, with a thickness adjustable from 2 nm to 100 nm, is grown using an ALD device. A second channel passivation medium 202, made of silicon nitride, with a thickness adjustable from 20 nm to 250 nm, is then grown using a PECVD (Plasma Enhanced Chemical Vapor Deposition) device. The first channel passivation protection medium 203 and the second channel passivation protection medium 202 together constitute a composite channel passivation medium 206.
[0024] Furthermore, such as Figure 3As shown, vias are created above the second layer of channel passivation protection dielectric using photolithography and etching processes. For example, the via linewidth can be 400 nm, and the size can be adjusted according to the frequency characteristics of the actual device. The via etching process can employ reactive ion etching or similar techniques; however, the specific implementation method is not within the scope of this patent and is not limited thereto.
[0025] Furthermore, such as Figure 4 As shown, a second hole is created inside the first channel protection dielectric opening using photolithography and etching processes. For example, the size of the second hole can be 250nm. It should be noted that after the second channel passivation dielectric is opened, the topmost layer of the epitaxial material is exposed at the opening. Simultaneously, the first channel protection dielectric 203 (alumina) and the second channel protection dielectric 202 (silicon nitride) form a stepped structure at the opening; that is, alumina is on the lower step with a smaller opening, and silicon nitride is on the upper step with a larger opening.
[0026] Furthermore, such as Figure 5 As shown, gate metal 301 is fabricated through photolithography, electron beam evaporation, and lift-off processes. Gate metal 301 covers stepped openings in two layers of composite channel passivation dielectric. The gate metal material 301 is any one or a combination of Ni, W, Ir, Pt, Pd, Ru, and Co metals, with a total thickness ranging from 300 nm to 800 nm and a linewidth ranging from 300 nm to 1.5 μm. Other structures and processes are involved in microwave and millimeter-wave monolithic integrated circuits, such as active region isolation, resistor fabrication, capacitor and microstrip fabrication, etc. Since these are not the focus of this invention, their fabrication methods and sequences are not limited. After gate formation, a heat treatment process is performed to enhance the field-effect characteristics of the device gate. Other front and back processes are the same as those for general HEMT devices and are not the focus of this invention, so they will not be described further.
[0027] The embodiments described in this invention are intended to better explain a novel composite-channel passivated dielectric GaN high electron mobility transistor and its fabrication method. The process steps of this invention are relatively simple, and the fabrication process is compatible with GaN microwave and millimeter-wave chip manufacturing technologies.
[0028] The composite channel passivation medium described above with reference to the drawings is the focus of the present application, and embodies the substantial features and progress of the present application. Meanwhile, the epitaxial material system structure can be adjusted according to actual use needs, such as selectively introducing an AlN insertion layer 106, an AlGaN back barrier layer 105, and the like HEMT device structure. The thickness of each layer and the Al content and thickness of the AlGaN barrier layer can be adjusted according to the application characteristics of the actual device. In addition, the types and thicknesses of the composite channel passivation medium can be adjusted as needed. The medium thickness, material selection of the gate thickening metal system, and the material and thickness of the passivation layer can also be modified according to actual conditions, and will not be described here.
Claims
1. A GaN high electron mobility transistor with a composite channel passivation dielectric and its fabrication method, characterized in that, It includes a complete GaN HEMT epitaxial structure (108) and source metal (201), drain metal (205), composite channel passivation medium (206), and gate metal (301) prepared on the complete GaN HEMT epitaxial structure (108); the complete GaN HEMT epitaxial structure (108) includes: substrate (101), nucleation layer and high-resistivity buffer layer (102), channel layer (103) and barrier layer (104); the composite channel passivation medium (206) includes a first channel protection medium aluminum oxide (203) and a second channel protection medium silicon nitride (202).
2. The GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 1, characterized in that, The substrate (101) is any one of Si single crystal, sapphire, high-purity semi-insulating SiC, GaN single crystal, or diamond substrate.
3. The GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 1, characterized in that, The materials of the nucleation layer and the high-resistivity buffer layer (102) are one or more of the following: iron-doped GaN, vanadium-doped GaN, carbon-doped GaN, and AlN.
4. The GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 1, characterized in that, The channel layer (103) is made of either GaN or InGaN.
5. A GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 1, characterized in that, The material of the barrier layer (104) is any one or a combination of AlGaN, AlInN, AlN, and AlInGaN.
6. A GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 1, characterized in that: The first layer of channel protection medium, alumina (203), is prepared by atomic layer deposition (ALD) equipment; the second layer of channel protection medium, silicon nitride (202), can be prepared by chemical vapor deposition (CVD) equipment.
7. A GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 1, characterized in that: The second layer of channel protection medium, silicon nitride, is opened using photolithography and ion etching, resulting in a large opening size. Utilizing the etching selectivity ratio of the two media, the etching stops on the first layer of channel protection medium, alumina. The first layer of channel protection medium, alumina, is opened using photolithography and wet etching, resulting in a small opening size. The etching stops on the surface of the epitaxial material.
8. The GaN high electron mobility transistor with a composite channel passivation dielectric according to claim 7, characterized in that, The metal material of the gate metal (301) is one or a combination of Au, Al, Ta, Ti, Pt, Pd, Ru, and Ni; at the same time, the gate metal (301) covers the stepped openings of two layers of composite channel passivation medium.