Millimeter wave-oriented low-noise GaN HEMT device and preparation method thereof

Abstract

The invention discloses a millimeter wave-oriented low-noise GaN HEMT device and a preparation method thereof, and relates to the technical field of semiconductors, the millimeter wave-oriented low-noise GaN HEMT device comprises a substrate, a nucleating layer, a channel layer, a barrier layer, a first passivation layer and a second passivation layer which are stacked in sequence; the source electrode and the drain electrode are located on the two sides of the first passivation layer in the first direction respectively, and the source electrode and the drain electrode make contact with the barrier layer; the grid electrode is located in the opening of the second passivation layer and located between the source electrode and the drain electrode, and the opening penetrates through the second passivation layer in the second direction; wherein the first direction intersects with the second direction. According to the invention, the noise performance of the GaN HEMT device can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a millimeter-wave oriented low-noise GaN HEMT device and a preparation method thereof. Background Art

[0002] As a representative of wide bandgap (WBG) power semiconductor devices, GaN HEMT (High Electron Mobility Transistors) has great potential in high-frequency power applications.

[0003] In the related art, GaN-based HEMT devices require a high-quality semi-insulating buffer layer to suppress buffer leakage under high-voltage working conditions. HEMT devices based on the third-generation semiconductor material GaN usually require a sufficiently thick buffer layer to reduce growth defects caused by the lattice mismatch between the substrate and GaN. The buffer layer is also doped with deep acceptor impurities such as carbon or iron to make the buffer layer highly semi-insulating, i.e., carbon doping (C-Doped) and iron doping (Fe-Doped), to limit leakage current, increase breakdown voltage, and reduce short channel effects. However, in the process of carbon doping and iron doping, different problems will be brought about, which will deteriorate the noise performance of the device.

[0004] Therefore, there is an urgent need to provide a low-noise GaN HEMT device to improve the above defects. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a millimeter-wave oriented low-noise GaN HEMT device and a preparation method thereof. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] In a first aspect, the present invention provides a millimeter-wave oriented low-noise GaN HEMT device, comprising:

[0007] A substrate, a nucleation layer, a channel layer, a barrier layer, a first passivation layer and a second passivation layer are sequentially stacked;

[0008] A source electrode and a drain electrode are respectively located on two sides of the first passivation layer along the first direction, and both the source electrode and the drain electrode are in contact with the barrier layer;

[0009] The gate is located in the opening of the second passivation layer and between the source and the drain, and the opening penetrates the second passivation layer along the second direction; wherein the first direction intersects with the second direction.

[0010] In a second aspect, the present invention further provides a method for preparing a millimeter-wave oriented low-noise GaN HEMT device, which is used to prepare the above-mentioned millimeter-wave oriented low-noise GaN HEMT device, comprising:

[0011] providing a substrate;

[0012] epitaxially growing a nucleation layer on the substrate; epitaxially growing a channel layer on the nucleation layer; epitaxially growing a barrier layer on the channel layer, and epitaxially growing a first passivation layer on the barrier layer;

[0013] Photolithography is performed on the surface of the first passivation layer on the side away from the substrate to form a source region and a drain region, etching away the first passivation layer of the source region and the drain region by an etching process, depositing metal in the region where the first passivation layer is etched away by electron beam evaporation, and forming a source electrode and a drain electrode on both sides of the first passivation layer along a first direction respectively;

[0014] A second passivation layer is grown between the source electrode and the drain electrode on the side of the first passivation layer facing away from the substrate;

[0015] Photolithography is performed to form a gate region on the surface of the second passivation layer on the side facing away from the substrate, and a hole is formed in the gate region by etching using an etching process to form an opening;

[0016] Electron beam evaporation is used to deposit metal in the opening to form a gate.

[0017] Beneficial effects of the present invention:

[0018] The present invention provides a millimeter-wave oriented low-noise GaN HEMT device and a preparation method thereof, comprising a stacked substrate, a nucleation layer, a channel layer, a barrier layer, a first passivation layer and a second passivation layer, wherein the first passivation layer is located on the upper surface of the barrier layer, the source and the drain are both located on the upper surface of the barrier layer, the source and the drain are located on both sides of the first passivation layer, an opening is etched in the second passivation layer, a gate is prepared in the opening, the opening passes through the second passivation layer, but does not pass through the first passivation layer, which can also be understood as a portion of the first passivation layer is reserved between the gate and the barrier layer. In the present invention, on the one hand, the buffer layer in the GaN HEMT device is eliminated and the thickness of the channel region is increased, which can effectively solve the problem of low device noise performance caused by buffer layer doping; on the other hand, an opening is etched in the second passivation layer, and a gate is prepared in the opening to form a MIS structure, which can achieve a lower noise coefficient of the device.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of a millimeter-wave oriented low-noise GaN HEMT device provided by an embodiment of the present invention;

[0021] Figure 2 It is a flow chart of a method for preparing a millimeter-wave oriented low-noise GaN HEMT device provided by an embodiment of the present invention;

[0022] Figure 3a to 3e It is a schematic diagram of a method for preparing a millimeter-wave oriented low-noise GaN HEMT device provided by an embodiment of the present invention;

[0023] Figures 4a to 4d is a schematic diagram of a comparative simulation device provided by an embodiment of the present invention;

[0024] Figure 5a to 5c It is a schematic diagram of a simulation result provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0026] See also Figure 1 , Figure 1 1 is a schematic diagram of a millimeter-wave oriented low-noise GaN HEMT device provided by an embodiment of the present invention. The millimeter-wave oriented low-noise GaN HEMT device provided by the present invention includes:

[0027] A substrate, a nucleation layer, a channel layer, a barrier layer, a first passivation layer and a second passivation layer are sequentially stacked;

[0028] A source electrode and a drain electrode are respectively located on two sides of the first passivation layer along the first direction, and both the source electrode and the drain electrode are in contact with the barrier layer;

[0029] The gate is located in the opening of the second passivation layer and between the source and the drain, and the opening penetrates the second passivation layer along the second direction; wherein the first direction intersects with the second direction.

[0030] For more details, please see Figure 1 The millimeter-wave oriented low-noise GaN HEMT device provided in this embodiment includes a stacked substrate, a nucleation layer, a channel layer, a barrier layer, a first passivation layer, and a second passivation layer, wherein the first passivation layer is located on the upper surface of the barrier layer, the source and the drain are both located on the upper surface of the barrier layer, the source and the drain are located on both sides of the first passivation layer, an opening is provided in the second passivation layer, and the gate is prepared in the opening, the opening passes through the second passivation layer but does not pass through the first passivation layer, which can also be understood as a portion of the first passivation layer is reserved between the gate and the barrier layer.

[0031] Considering the lattice mismatch between the substrate and GaN, the buffer layer needs to be thick enough to minimize growth defects. Defects extending to the channel region will affect the mobility of electrons in the two-dimensional electron gas (2DEG), thereby reducing the performance of HEMT. In addition, GaN-based HEMT devices require a high-quality semi-insulating buffer layer to suppress buffer leakage under high-voltage working conditions. The buffer layer is made highly semi-insulating by doping impurities such as carbon or iron in the buffer layer, namely carbon doping (C-Doped) and iron doping (Fe-Doped). However, during the C doping process, carbon will bring deep energy level traps, making the buffer layer floating, which may pinch off the active channel. The C doping concentration will aggravate the current collapse, resulting in the degradation of RF power characteristics. Compared with C doping, although Fe doping can achieve high breakdown voltage and low current collapse, the tail effect brought by Fe doping may introduce additional noise sources in HEMT devices, and the noise performance of the device will deteriorate, especially in high-frequency applications, the noise performance of the device is worse. In view of this, in this embodiment, on the one hand, the buffer layer in the GaN HEMT device is eliminated and the thickness of the channel region is increased, which can effectively solve the problem of low device noise performance caused by buffer layer doping; on the other hand, an opening is etched in the second passivation layer, and a gate is prepared in the opening to form a MIS structure, which can achieve a lower noise coefficient of the device.

[0032] It should be noted that the first direction is perpendicular to the second direction.

[0033] It should also be noted that Figure 1 The illustrated embodiment only schematically shows the positional relationship of various film layers of the device and does not represent the actual size.

[0034] In an optional embodiment of the present invention, along the second direction, the thickness of the first passivation layer is 8-12 nm, and the thickness of the second passivation layer is 98-102 nm.

[0035] Optionally, the thickness of the first passivation layer is 10 nm, and the thickness of the second passivation layer is 100 nm.

[0036] For more details, please see Figure 1 In this embodiment, the opening is set in the second passivation layer, and the opening does not penetrate the first passivation layer, so that the MIS structure can be realized, which enables the device to have a lower noise coefficient.

[0037] In an optional embodiment of the present invention, the channel layer is an unintentionally doped GaN channel layer.

[0038] In an optional embodiment of the present invention, along the second direction, the thickness of the channel layer is 230-280 nm. Optionally, the thickness of the channel region is 250 nm.

[0039] In an optional embodiment of the present invention, the nucleation layer is an AlN nucleation layer, and the thickness of the nucleation layer along the second direction is 60 nm.

[0040] In an optional embodiment of the present invention, the substrate is a SiC substrate, and the thickness of the substrate along the second direction is 0.375 mm.

[0041] In an optional embodiment of the present invention, the barrier layer is an AlGaN barrier layer (Al component 30%), and the thickness of the barrier layer along the second direction is 10 nm.

[0042] Based on the same inventive concept, see Figure 2 and Figure 3, Figure 2 is a flow chart of a method for preparing a millimeter-wave oriented low-noise GaN HEMT device provided by an embodiment of the present invention, Figure 3a to 3e is a schematic diagram of a method for preparing a millimeter-wave oriented low-noise GaN HEMT device provided in an embodiment of the present invention. The present invention also provides a method for preparing a millimeter-wave oriented low-noise GaN HEMT device, which is used to prepare the millimeter-wave oriented low-noise GaN HEMT device provided in the above embodiment. The embodiment of the device is referred to above and will not be described in detail here. The preparation method comprises:

[0043] S101, providing a substrate;

[0044] S102, epitaxially growing a nucleation layer on the substrate; epitaxially growing a channel layer on the nucleation layer; epitaxially growing a barrier layer on the channel layer, and epitaxially growing a first passivation layer on the barrier layer;

[0045] S103, photolithography a source region and a drain region on a surface of the first passivation layer on a side facing away from the substrate, etching away the first passivation layer of the source region and the drain region by an etching process, depositing metal in the region where the first passivation layer is etched away by electron beam evaporation, and forming a source electrode and a drain electrode on both sides of the first passivation layer along a first direction, respectively;

[0046] S104, growing a second passivation layer between the source electrode and the drain electrode on a side of the first passivation layer facing away from the substrate;

[0047] S105, photolithography a gate region on the surface of the second passivation layer on the side facing away from the substrate, and etching a hole in the gate region by using an etching process to form an opening;

[0048] S106 , depositing metal in the opening by electron beam evaporation to form a gate.

[0049] For more details, please see Figure 2As shown in FIG. 3 , in the process of preparing the device, only one epitaxial growth process is required to prepare the device of the present invention, that is, a substrate is provided, a nucleation layer is epitaxially grown on the substrate, a channel layer is epitaxially grown on the nucleation layer, a barrier layer is epitaxially grown on the channel layer, a first passivation layer is epitaxially grown on the barrier layer, a second passivation layer is passivated and grown on the first passivation layer, and an opening is subsequently etched on the second passivation layer; on the one hand, an epitaxial structure without a buffer layer is adopted, and a SiN passivation layer is passivated under the gate as a dielectric layer to form a metal-dielectric-semiconductor (MIS) structure without a buffer layer, thereby improving the noise performance of the device; on the other hand, the MIS structure is not grown by atomic layer epitaxy (ALD), and the first passivation layer epitaxial process is realized by metal organic chemical vapor deposition (MOCVD), and the MIS structure and the epitaxial material are grown in an integrated manner, thereby reducing the cost and achieving higher efficiency; thus, the preparation process of the device provided in the present embodiment makes the device structure simple, and can realize an integrated epitaxial process, thereby effectively improving the efficiency and reducing the cost.

[0050] In an optional embodiment of the present invention, a source region and a drain region are respectively photolithographically formed on a surface of the first passivation layer on a side facing away from the substrate, the first passivation layer of the source region and the drain region is etched away by an etching process, metal is deposited in the region where the first passivation layer is etched away by electron beam evaporation, and a source electrode and a drain electrode are respectively formed on both sides of the barrier layer along a first direction, including:

[0051] The source region and the drain region are formed on the surface of the first passivation layer by using step-by-step photolithography, the first passivation layer of the source region and the drain region is etched away by using an etching process, and metal is deposited in the region where the first passivation layer is etched away by using electron beam evaporation to form a source electrode and a drain electrode;

[0052] In a nitrogen atmosphere, rapid annealing is performed at 850-870° C. for 55-65 seconds to form ohmic contacts between the source and drain electrodes and the barrier layer.

[0053] In an optional embodiment of the present invention, a gate region is photolithographically formed on a surface of the second passivation layer on a side facing away from the substrate, and a hole is etched in the gate region using an etching process to form an opening, including:

[0054] Electron beam lithography is used to etch a gate region on the surface of the second passivation layer, and an F-based dry etching process is used to open a hole in the gate region to form an opening.

[0055] In an optional embodiment of the present invention, the conditions of the F-based dry etching process include:

[0056] The flow rate of carbon tetrafluoride is 23-28 sccm, the flow rate of oxygen is 3-8 sccm, the applied pressure is 3-8 mT, the upper electrode power is 70-90 W, and the lower electrode power is 8-12 W.

[0057] In an optional embodiment of the present invention, a second passivation layer is grown between the source and the drain on a side of the first passivation layer facing away from the substrate, comprising:

[0058] The second passivation layer is grown on the first passivation layer by low pressure chemical vapor deposition.

[0059] In an optional embodiment of the present invention, epitaxially growing a first passivation layer on the barrier layer comprises:

[0060] A first passivation layer is epitaxially grown on the barrier layer by chemical vapor deposition.

[0061] In an optional embodiment of the present invention, isolation photolithography and argon ion implantation are performed around the device to achieve isolation of the active region of the device.

[0062] In an optional embodiment of the present invention, the device is prepared by the following process, specifically:

[0063] S1. Epitaxially grow in sequence a 0.375 mm thick SiC substrate, a 60 nm thick AlN nucleation layer, a 250 nm thick unintentionally doped GaN channel layer, a 10 nm thick AlGaN barrier layer (Al component 30%), and a 10 nm thick first SiN passivation layer.

[0064] S2. Photolithography is performed on the first SiN passivation layer by step-by-step photolithography to etch out the source region and the drain region, and the first passivation layer of the source region and the drain region is etched away; ohmic metal (Ti / Al / Ni / Au) is deposited in the etched area by electron beam evaporation deposition, and then rapid annealing is performed at 860°C for 60 seconds in a nitrogen atmosphere to form ohmic contacts of the source and drain.

[0065] S3. Perform isolation lithography and argon ion implantation around the device to achieve isolation of the device active area.

[0066] S4. On the first passivation layer, between the source and the drain, a 100 nm thick SiN passivation layer is deposited on the surface of the first passivation layer by low pressure chemical vapor deposition (LPCVD) as the second passivation layer.

[0067] S5. Electron beam lithography is used to align and mark the gate metal. F-based dry etching technology is used with the following conditions: CF4=25sccm, O2=5sccm, pressure=5mT, upper electrode power=80W, lower electrode power=10W to perform hole etching on the second passivation layer.

[0068] S6. The stepper lithography machine aligns the gate metal mark and the gate metal (Ni / Au) is evaporated.

[0069] In an optional embodiment of the present invention, the performance of the millimeter-wave oriented low-noise GaN HEMT device provided in the above embodiment is verified by simulation experiments, specifically:

[0070] 1. Simulation process

[0071] The devices simulated in this embodiment include:

[0072] 1. Traditional heterojunction devices including Fe-doped buffer layers, such as Figure 4a As shown;

[0073] 2. Traditional heterojunction devices including MIS structures with Fe-doped buffer layers, such as Figure 4b As shown;

[0074] 3. The buffer-free heterojunction device of the present application, such as Figure 4c As shown;

[0075] 4. The heterojunction device of the MIS structure without buffer layer of the present application, such as Figure 4d shown.

[0076] 2. Simulation Results

[0077] In traditional GaN HEMTs, due to the lattice mismatch between the substrate and GaN, the buffer layer needs to be thick enough to minimize growth defects. Defects extending to the channel region will affect the mobility of electrons in the 2DEG, thereby reducing the performance of the HEMT. In order to limit leakage current, increase breakdown voltage, and reduce short channel effects, the buffer also needs to have high insulation properties. The GaN buffer layer is usually achieved by doping with deep acceptors, usually carbon or iron. However, deep acceptors can also form electron traps, affecting mobility and causing poor noise performance. In order to achieve a low noise coefficient of the channel, the two schemes proposed in the present invention and the traditional scheme are simulated and verified. The scheme is as follows: 1. A thin passivation layer SiN is passivated under the gate to reduce gate leakage and improve noise, such as Figure 5a , Fe-doped devices with MIS structure ( Figure 4b ) and conventional Fe-doped devices ( Figure 4a ) has better noise performance. 2. Adopting epitaxial structure without buffer layer ( Figure 4c ) to solve the noise deterioration problem caused by the doped buffer layer. Figure 5b The noise superiority of the device without buffer layer is demonstrated compared with the device with doped buffer layer. Finally, the present invention proposes a low-noise device with MIS structure without buffer layer ( Figure 4d ), through the simulation comparison of noise, it is found that the device structure has a lower noise coefficient, indicating that the noise performance of the device is optimal, such as Figure 5c This shows that the device structure proposed by the present invention is simple, and can realize an integrated epitaxial process, thereby effectively improving efficiency and reducing costs.

[0078] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant is intended to cover non-exclusive inclusion, so that the article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the article or device including the elements. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The orientation or position relationship indicated by "up", "down", "left", "right", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is 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 a limitation of the present invention.

[0079] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0080] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A millimeter-wave oriented low-noise GaN HEMT device, characterized in that: include: A substrate, a nucleation layer, a channel layer, a barrier layer, a first passivation layer and a second passivation layer are sequentially stacked; A source electrode and a drain electrode, respectively located on two sides of the first passivation layer along a first direction, and both the source electrode and the drain electrode are in contact with the barrier layer; The gate is located in the opening of the second passivation layer and between the source and the drain, and the opening penetrates the second passivation layer along a second direction; wherein the first direction intersects with the second direction.

2. The millimeter-wave oriented low-noise GaN HEMT device according to claim 1, characterized in that: Along the second direction, the thickness of the first passivation layer is 8-12 nm, and the thickness of the second passivation layer is 98-102 nm.

3. The millimeter-wave oriented low-noise GaN HEMT device according to claim 1, characterized in that: The channel layer is an unintentionally doped GaN channel layer.

4. The millimeter-wave oriented low-noise GaN HEMT device according to claim 1, characterized in that: Along the second direction, the thickness of the channel layer is 230-280 nm.

5. A method for preparing a millimeter-wave oriented low-noise GaN HEMT device, used for preparing the millimeter-wave oriented low-noise GaN HEMT device as claimed in any one of claims 1 to 4, characterized in that: include: providing a substrate; epitaxially growing a nucleation layer on the substrate; epitaxially growing a channel layer on the nucleation layer; epitaxially growing a barrier layer on the channel layer, and epitaxially growing a first passivation layer on the barrier layer; Photolithography is performed on the surface of the first passivation layer on the side away from the substrate to form a source region and a drain region respectively, etching away the first passivation layer of the source region and the drain region by an etching process, depositing metal in the region where the first passivation layer is etched away by electron beam evaporation, and forming a source electrode and a drain electrode on both sides of the first passivation layer along a first direction respectively; A second passivation layer is grown between the source electrode and the drain electrode on a side of the first passivation layer facing away from the substrate; Photolithography a gate region on a surface of the second passivation layer on a side facing away from the substrate, and etching a hole in the gate region using an etching process to form an opening; Metal is deposited in the opening by electron beam evaporation to form a gate.

6. The method for preparing a millimeter-wave oriented low-noise GaN HEMT device according to claim 5, characterized in that: A source region and a drain region are respectively photoetched on a surface of the first passivation layer on a side away from the substrate, the first passivation layer of the source region and the drain region is etched away by an etching process, metal is deposited in the region where the first passivation layer is etched away by electron beam evaporation, and a source electrode and a drain electrode are respectively formed on both sides of the barrier layer along a first direction, including: Using step-by-step photolithography to photoetch a source region and a drain region on the surface of the first passivation layer, using an etching process to etch away the first passivation layer of the source region and the drain region, and using electron beam evaporation to deposit metal in the region where the first passivation layer is etched away; forming the source electrode and the drain electrode; In a nitrogen atmosphere, rapid annealing is performed at 850-870° C. for 55-65 seconds to form ohmic contacts between the source electrode and the drain electrode and the barrier layer.

7. The method for preparing a millimeter-wave oriented low-noise GaN HEMT device according to claim 5, characterized in that: Photolithography is performed on a surface of the second passivation layer on a side facing away from the substrate to form a gate region, and an etching process is used to open a hole in the gate region to form an opening, including: Electron beam lithography is used to etch a gate region on the surface of the second passivation layer, and an F-based dry etching process is used to open a hole in the gate region to form an opening.

8. The method for preparing a millimeter-wave oriented low-noise GaN HEMT device according to claim 7, characterized in that: The conditions of the F-based dry etching process include: The flow rate of carbon tetrafluoride is 23-28 sccm, the flow rate of oxygen is 3-8 sccm, the applied pressure is 3-8 mT, the upper electrode power is 70-90 W, and the lower electrode power is 8-12 W.

9. The method for preparing a millimeter-wave oriented low-noise GaN HEMT device according to claim 5, characterized in that: A second passivation layer is grown between the source electrode and the drain electrode on a side of the first passivation layer away from the substrate, comprising: A second passivation layer is grown on the first passivation layer by low pressure chemical vapor deposition.

10. The method for preparing a millimeter-wave oriented low-noise GaN HEMT device according to claim 5, characterized in that: Epitaxially growing a first passivation layer on the barrier layer, comprising: A first passivation layer is epitaxially grown on the barrier layer by chemical vapor deposition.

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