GaN-based HEMT device with multi-gate structure and method of manufacturing the same

Abstract

The application provides a GaN-based HEMT device with a multi-gate structure and a preparation method thereof. A corresponding gate pattern is defined by forming a plurality of dummy gates, and a gate is formed in a gate groove after the dummy gates are removed, so that AlGaN barrier layers with different thicknesses are arranged under the plurality of gates without thinning the barrier layers by etching, and thus damage caused by etching is avoided. The GaN-based HEMT device provided by the application comprises a plurality of AlGaN barrier layers, a plurality of gate grooves arranged at intervals, and a gate arranged in the plurality of gate grooves. The AlGaN barrier layers are arranged in pairs with the gates arranged thereon. By arranging the barrier layers with different thicknesses under the plurality of gates, a plurality of gates with different threshold voltages can be formed in the same device, so that modulation of the threshold voltage is realized.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology and relates to a GaN-based high electron mobility transistor device and its fabrication method. Background Technology

[0002] As a representative of third-generation semiconductor materials, gallium nitride (GaN) possesses many excellent properties, such as a high critical breakdown electric field, high electron mobility, high two-dimensional electron gas concentration, and good high-temperature operating capability. Therefore, GaN-based third-generation semiconductor devices, due to their high voltage withstand capability and high power output, are now widely used in applications such as base stations, communications, radar, satellites, and navigation systems.

[0003] In traditional AlGaN / GaN heterojunction GaN-based high electron mobility transistors (HEMTs), the AlGaN / GaN heterojunction generates a high concentration of two-dimensional electron gas (2DEG) when undoped. The depletion effect applied by the gate voltage Vg controls the switching on and off of the 2DEG under the gate, thus enabling device turn-on and turn-off. Therefore, GaN-based power devices based on this heterojunction are depletion-mode devices, meaning their threshold voltage is negative. In applications, a negative polarity drive is required to control the device's switching, which not only complicates the gate drive circuit but also increases the device's application cost. Currently, one common approach is to etch the barrier layer, such as AlGaN, to thin the barrier layer, causing the threshold voltage of the GaN device to drift more positively until the barrier layer is completely etched, thus forming a normally-off device.

[0004] However, conventional dry etching, especially plasma-enhanced chemical plasma (ICP) etching, inevitably causes ion damage to the epitaxial layer when etching the AlGaN barrier layer, which affects the electrical performance and reliability of the device. Therefore, there is an urgent need in the field to propose a fabrication method that can modulate the threshold voltage of GaN-based HEMT devices without compromising device performance. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a GaN-based HEMT device with a multi-gate structure and its fabrication method, so as to solve the problems of difficulty in achieving high-quality electrical performance, low reliability, complex threshold voltage modulation method and high application cost in the fabrication methods of GaN-based HEMT devices in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a method for fabricating a GaN-based HEMT device with a multi-gate structure, comprising the following steps: providing a GaN channel layer; forming an epitaxial stack on the GaN channel layer, including intermittently growing a plurality of AlGaN barrier layers on the GaN channel layer, wherein the intermittent growth of the plurality of AlGaN barrier layers includes the following steps: forming an AlGaN barrier layer on the GaN channel layer; forming a dummy gate on the AlGaN barrier layer to define a corresponding gate pattern; and repeatedly forming the AlGaN barrier layer and... The process of forming dummy gates continues until a predetermined number of gate patterns are defined; after forming dummy gates on the next-top AlGaN barrier layer, a top AlGaN barrier layer is formed on the next-top AlGaN barrier layer; metal sources and metal drains are formed on the epitaxial stack, the metal sources and metal drains being located at both ends of the plurality of dummy gates; the plurality of dummy gates are removed to form a plurality of gate trenches through the top AlGaN barrier layer, a metal gate is formed in each gate trench, and each metal gate forms a Schottky contact with the corresponding AlGaN barrier layer.

[0007] Optionally, the plurality of AlGaN barrier layers have an Al composition that decreases layer by layer from the top AlGaN barrier layer downwards.

[0008] Optionally, any one of the steps for forming a dummy gate includes: spin-coating hydrogen silsesquioxane onto an AlGaN barrier layer; exposing the hydrogen silsesquioxane to define a gate pattern; and developing the exposed hydrogen silsesquioxane with a TMAH solution to form the dummy gate.

[0009] Optionally, after performing the photolithography process, the exposed hydrogen silsesquioxane is cured at a temperature of 350°C-400°C in an O2 atmosphere to form the dummy gate.

[0010] Optionally, the fabrication method further includes: after removing multiple dummy gates, simultaneously depositing multiple layers of metal in multiple gate trenches using a patterned mask to form a metal gate, wherein the metal gate is formed as a T-shaped metal gate.

[0011] The present invention also provides a GaN-based HEMT device with a multi-gate structure, the GaN-based HEMT device comprising: a GaN channel layer; an epitaxial stack located on the GaN channel layer, the epitaxial stack including multiple AlGaN barrier layers; multiple gate trenches arranged at intervals, each gate trench being disposed in the top AlGaN barrier layer and paired with one of the other AlGaN barrier layers, each gate trench exposing the corresponding AlGaN barrier layer from the bottom; metal gates disposed in the multiple gate trenches, each metal gate forming a Schottky contact with the corresponding AlGaN barrier layer; and metal source and metal drain disposed on the epitaxial stack and located at both ends of the multiple metal gates.

[0012] Optionally, the fabrication method further includes: providing a substrate before providing the GaN channel layer, and sequentially growing a buffer layer and the GaN channel layer on the substrate.

[0013] Optionally, the plurality of AlGaN barrier layers have a thickness ranging from 5 nm to 25 nm, and the length of the metal gate ranges from 50 nm to 0.5 μm.

[0014] Optionally, the plurality of gate trenches are arranged at intervals in the direction of the connection between the source and the drain and have successively decreasing penetration depths, and each gate trench is provided with a T-shaped metal gate.

[0015] Optionally, the metal gates are provided in an even number, and adjacent metal gates have a common metal source or metal drain, so that each metal gate has a metal source and a metal drain at both ends.

[0016] As described above, the multi-gate semiconductor device and its fabrication method of the present invention have the following beneficial effects:

[0017] The fabrication method of the multi-gate GaN-based HEMT device of the present invention defines a corresponding gate pattern by forming multiple dummy gates, and then forms gates in the gate trench after removing the dummy gates. This results in multiple gates with AlGaN barrier layers of different thicknesses disposed below them, without the need for etching to thin the barrier layer. Therefore, there is no damage or interface state caused by etching, which is beneficial for obtaining high-quality epitaxial layers and improving the reliability of the device. The fabrication method of the present invention has the advantages of simple process and good repeatability.

[0018] The GaN-based HEMT device provided by this invention has a multi-gate structure, with multiple gates disposed on multiple AlGaN barrier layers. By disposing barrier layers of different thicknesses under the multiple gates, multiple gates with different threshold voltages can be formed within the same device, thereby achieving threshold voltage modulation. Furthermore, the source and drain are disposed on barrier layers with Al composition gradually increasing from bottom to top, thereby improving the overall linearity of the device and also contributing to improved IT. on / I off This also improves the device's ability to handle high voltage and high power. Attached Figure Description

[0019] Figure 1 The diagram shows the process flow for fabricating GaN-based HEMT devices according to an embodiment of the present invention.

[0020] Figure 2 The diagram shows a schematic of the structure for forming a first AlGaN barrier layer and a first dummy gate in an embodiment of the present invention.

[0021] Figure 3 The diagram shows a schematic of the structure for forming a second AlGaN barrier layer and a second dummy gate in an embodiment of the present invention.

[0022] Figure 4 The diagram shows a schematic of the structure for forming a third AlGaN barrier layer and a third dummy gate in an embodiment of the present invention.

[0023] Figure 5 The diagram shown is a schematic representation of the structure with multiple dummy gates removed in an embodiment of the present invention.

[0024] Figure 6 The diagram shown is an exemplary cross-sectional view of a GaN-based HEMT device with a multi-gate structure according to the present invention.

[0025] Figure 7 The diagram shown is another exemplary cross-sectional view of a GaN-based HEMT device with a multi-gate structure according to the present invention.

[0026] Component designation explanation

[0027] 200 - GaN channel layer; 300 - Epitaxial stack; 301 - First AlGaN barrier layer; 302 - Second AlGaN barrier layer; 303 - Third AlGaN barrier layer; 304 - Fourth AlGaN barrier layer; 305 - Fifth AlGaN barrier layer; 311 - First gate trench; 312 - Second gate trench; 313 - Third gate trench; 401 - First metal gate; 402 - Second metal gate; 403 - Third metal gate; 411 - First dummy gate; 412 - Second dummy gate; 413 - Third dummy gate; 501 - Metal source; 502 - Metal drain; 600 - Interconnect. Detailed Implementation

[0028] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0029] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0030] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for the device in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The phrase “between” as used herein includes both endpoint values.

[0031] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0032] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0033] To achieve devices with multiple threshold voltages while avoiding damage to the epitaxial layer caused by etching processes, this invention provides a method for fabricating a GaN-based HEMT device with a multi-gate structure, comprising:

[0034] Provides a GaN channel layer;

[0035] Forming an epitaxial stack on the GaN channel layer includes intermittently growing a plurality of AlGaN barrier layers on the GaN channel layer. The intermittent growth of the plurality of AlGaN barrier layers includes the following steps:

[0036] An AlGaN barrier layer is formed on the GaN channel layer;

[0037] A dummy gate is formed on the AlGaN barrier layer to define the corresponding gate pattern;

[0038] Repeat the steps of forming the AlGaN barrier layer and forming the dummy gate until a predetermined number of gate patterns are defined;

[0039] After forming a dummy gate on the second-to-top AlGaN barrier layer, a top AlGaN barrier layer is formed on the second-to-top AlGaN barrier layer.

[0040] A metal source and a metal drain are formed on the epitaxial stack, and the metal source and the metal drain are located at both ends of a plurality of dummy gates;

[0041] Multiple dummy gates are removed to form multiple gate trenches that penetrate through the top AlGaN barrier layer. A metal gate is formed in each gate trench, and each metal gate forms a Schottky contact with the corresponding AlGaN barrier layer.

[0042] The fabrication method of the present invention includes repeatedly forming an AlGaN barrier layer and forming a dummy gate on the AlGaN barrier layer, defining a corresponding gate pattern using the dummy gate, removing multiple dummy gates, and forming gates in gate trenches of different depths, thereby obtaining a structure in which multiple gates are provided with AlGaN barrier layers of different thicknesses, without the need to thin the barrier layer through a dry etching process, thus avoiding damage to the epitaxial layer, which is beneficial for obtaining a high-quality epitaxial layer and improving the reliability of the device.

[0043] Unlike previous methods that used etching processes, especially dry etching, to thin the barrier layer, the GaN-based HEMT device fabricated in this invention achieves threshold voltage modulation by setting multiple thin barrier layers to positively shift the GaN device's threshold voltage. Different threshold voltages controlled by multiple gates within the same HEMT device can be achieved. Since the AlGaN barrier layer can control the density of the two-dimensional electron gas within the GaN channel layer, a higher Al content in the AlGaN barrier layer leads to a higher electron density polarized within the GaN channel layer; conversely, a thicker AlGaN barrier layer results in a higher polarized electron density. To achieve different threshold voltages within the same HEMT device, this invention employs multiple thin barrier layers, each paired with a gate on top of it. By modulating the thickness of the thin barrier layers and the Al content in the AlGaN barrier layers, the thickness of the barrier layer under different gates can be changed, thus achieving different threshold voltages within the same device.

[0044] The term "substrate" as used in this invention can refer to a semiconductor substrate used for heteroepitaxial growth of GaN layers, including but not limited to silicon substrates, sapphire substrates, SiC substrates, GaN substrates, or similar substrates.

[0045] The following sections, in conjunction with the accompanying drawings, describe in detail the steps involved in fabricating a GaN-based HEMT device with a multi-gate structure according to the present invention.

[0046] Example 1

[0047] This embodiment provides a method for fabricating a GaN-based HEMT device with a multi-gate structure, such as... Figure 1 As shown, the preparation method includes the following steps:

[0048] 1) Provide a GaN channel layer;

[0049] 2) An epitaxial stack is formed on the GaN channel layer, including the intermittent growth of multiple AlGaN barrier layers on the GaN channel layer;

[0050] 3) A metal source and a metal drain are formed on the epitaxial stack;

[0051] 4) Remove multiple dummy gates to form multiple gate trenches.

[0052] First, step 1) is performed: providing a GaN channel layer. Specifically, step 1) includes: 1-1) providing a substrate (not shown), and heteroepitaxially growing a buffer layer (not shown) on the substrate; 1-2) forming a GaN channel layer 200 on the buffer layer. By forming the buffer layer, the problems of lattice mismatch and thermal expansion coefficient mismatch between the GaN channel layer and the substrate can be alleviated. Preferably, the buffer layer may include one or a combination of an AlGaN buffer layer and a GaN buffer layer. As an example, the buffer layer may have a thickness range of 1-3 μm, and the GaN channel layer 200 may have a thickness range of 50-200 nm.

[0053] In this embodiment, the substrate can be a Si (111) substrate to meet the need for cost savings, and based on lattice adaptability, a Si substrate with (111) orientation is beneficial for the subsequent growth of GaN materials. The size of the substrate can be an 8-inch wafer, a 12-inch wafer, etc., without excessive limitation. The GaN channel layer 200 can be grown on this buffer layer by MOCVD or other suitable processes.

[0054] Next, step 2) is performed: an epitaxial stack is formed on the GaN channel layer. Specifically, the epitaxial stack 300 on the GaN channel layer 200 includes the epitaxial growth of multiple AlGaN barrier layers on the GaN channel layer 200. In this embodiment, multiple AlGaN barrier layers can be intermittently grown using a metal-organic chemical vapor deposition (MOCVD) process. These multiple AlGaN barrier layers are grown discontinuously; that is, between adjacent steps of forming AlGaN barrier layers, dummy gates are formed on the surface of the pre-formed AlGaN barrier layers to define the gate pattern. See also... Figure 1 The process of growing multiple AlGaN barrier layers at intervals includes: 2-1) growing an AlGaN barrier layer on the GaN channel layer; 2-2) forming a dummy gate on the AlGaN barrier layer; 2-3) repeating steps 2-1) and 2-2), forming a dummy gate on the surface of the AlGaN barrier layer after each growth of the AlGaN barrier layer, until a predetermined number of gate patterns are defined.

[0055] Specifically, in step 2-1), see... Figure 2 The first AlGaN barrier layer 301 can be formed by the following steps: growing the first AlGaN barrier layer 301 using MOCVD technology. The first AlGaN barrier layer 301 can have the expression Al x1 Ga 1- x1 N, the thickness t1 of the first AlGaN barrier layer 301 has a range of 1nm-5nm, and the value of Al component x1 ranges from 0.05 to 0.2.

[0056] Subsequently, in step 2-2), a negative photoresist can be used to perform a photolithography process and form a dummy gate on the AlGaN barrier layer. See, for example... Figure 2 The step of forming the first dummy gate 411 may include: spin-coating hydrogen silsesquioxane (HSQ) onto the first AlGaN barrier layer 301, defining a gate pattern on the first AlGaN barrier layer 301 using a photolithography process; then, curing the exposed HSQ at a temperature of 350°C-400°C in an O2 atmosphere; and cleaning for 10 minutes using tetramethylammonium hydroxide (TMAH) as a developing solution to remove residual oxides and other impurities on the photolithographic surface. Since the photosensitive portion of the HSQ layer will form a stable SiO2 layer after curing... x A well-defined pattern of the first gate can be defined on the first AlGaN barrier layer 301. As an example, a cleaning process can be performed using a 25% TMAH solution at 80°C for 10 minutes to remove residual oxides and other impurities from the photolithography surface.

[0057] Continuing with steps 2-3), a second AlGaN barrier layer 302 can be formed on the first AlGaN barrier layer 301, similar to the formation of the first AlGaN barrier layer 301, with the first dummy gate 411 protruding from the subsequently formed second AlGaN barrier layer 302. Next, after forming the second AlGaN barrier layer 302, a second dummy gate 412 is formed on the second AlGaN barrier layer 302 to define a corresponding second gate pattern on the second AlGaN barrier layer 302, such as... Figure 3 As shown. Similarly, multiple AlGaN barrier layers can be intermittently grown on the GaN channel layer, such as... Figure 4 and Figure 5 As shown, the epitaxial stack has four AlGaN barrier layers stacked together, namely, a first AlGaN barrier layer 301, a second AlGaN barrier layer 302, a third AlGaN barrier layer 303, and a fourth AlGaN barrier layer 304. The first AlGaN barrier layer 301, the second AlGaN barrier layer 302, the third AlGaN barrier layer 303, and the fourth AlGaN barrier layer 304 can have the same thickness. The number of AlGaN barrier layers and the thickness of each barrier layer can be appropriately determined according to the range and value of the threshold voltage required by the HEMT device, such as... Figure 5The AlGaN barrier layer shown has four layers, but this invention does not imply that the number of multiple AlGaN barrier layers is limited to this. The AlGaN barrier layer can have three or more layers, particularly four or more layers, such as five, seven, or nine layers. As an example, the first AlGaN barrier layer 301 has a thickness t1, the second AlGaN barrier layer 302 has a thickness t2, the third AlGaN barrier layer 303 has a thickness t3, and the fourth AlGaN barrier layer 304 has a thickness t4. The thicknesses t1, t2, t3, and t4 are in the range of 1 nm to 5 nm. Therefore, the multiple AlGaN barrier layers as a whole can have a thickness range of 5 nm to 20 nm.

[0058] Return to view Figure 3 After forming the second AlGaN barrier layer 302, a second dummy gate 412 is formed on the second AlGaN barrier layer 302. The steps of forming the second dummy gate 412 and the third dummy gate 413 can be performed using the same process parameters as in the formation of the first dummy gate 411. By forming a dummy gate on the corresponding AlGaN barrier layer after each AlGaN barrier layer is formed, and by repeatedly forming an AlGaN barrier layer and a dummy gate on that AlGaN barrier layer, defining the corresponding gate pattern using the dummy gates, and then forming gates in gate trenches of different depths after removing multiple dummy gates, a structure is obtained in which multiple gates are provided with AlGaN barrier layers of different thicknesses, without the need to thin the barrier layer through a dry etching process.

[0059] Further, step 2) also includes: after steps 2-3), performing step 2-4): after forming a dummy gate on the second outermost AlGaN barrier layer, forming the top AlGaN barrier layer on the second outermost AlGaN barrier layer. Figure 5 As shown, the multiple AlGaN barrier layers include a third AlGaN barrier layer 303 as the second-to-top layer and a fourth AlGaN barrier layer 304 as the top layer. In step 2-4), after the third AlGaN barrier layer 303 is formed, the fourth AlGaN barrier layer 304 is formed on the third AlGaN barrier layer 303. The first dummy gate 411, the second dummy gate 412, and the third dummy gate 413 have a height that protrudes beyond the fourth AlGaN barrier layer 304.

[0060] By way of example, the first AlGaN barrier layer 301, the second AlGaN barrier layer 302, the third AlGaN barrier layer 303 and the fourth AlGaN barrier layer 304 have Al compositions that increase layer by layer upward from the bottom AlGaN barrier layer (i.e., the first AlGaN barrier layer 301) grown on the GaN channel layer; in particular, the Al composition may increase linearly layer by layer from bottom to top. In other words, the plurality of AlGaN barrier layers have Al compositions that decrease layer by layer downward from the topmost AlGaN barrier layer. The design can be carried out according to the required linearity of the device, which can improve the polarization of the channel and ensure a slowly varying lattice constant at the same time. The larger the Al composition is, the stronger the polarization ability is, and the more two-dimensional electron gas is polarized in the GaN channel. However, since the larger the Al composition is, the more serious the lattice mismatch between AlGaN and GaN is, which will cause cracking of AlGaN and lead to performance degradation. With the graded multi-layer Al composition layers, the Al composition can be increased gradually. In addition, the design of graded Al composition in the barrier layer is beneficial to the linearity of the device, has high reliability, and can improve the comprehensive performance of the device.

[0061] In this embodiment, as Figure 5 shown, the first AlGaN barrier layer 301, the second AlGaN barrier layer 302, the third AlGaN barrier layer 303 and the fourth AlGaN barrier layer 304 can each be expressed as Al x1 Ga 1-x1 N, Al x2 Ga 1-x2 N, Al x3 Ga 1-x3 N and Al x4 Ga 1-x4 N, where x1, x2, x3 and x4 represent the Al composition content in each barrier layer, and satisfy the following relationship: 0<x1<x2<x3<x4≤1. Correspondingly, the n-th AlGaN barrier layer is expressed as Al xn Ga 1-xn N, where x n represents the Al composition content in the n-th AlGaN barrier layer, and the range of x n satisfies: (n-1)×0.2<x n <n×0.2. Specifically, the Al composition content in the first AlGaN barrier layer 301 is in the range of 0<x1<0.2, the Al composition content in the second AlGaN barrier layer 302 is in the range of 0.2<x2<0.4, the Al composition content in the third AlGaN barrier layer 303 is in the range of 0.4<x3<0.6, and the Al composition content in the fourth AlGaN barrier layer 304 is in the range of 0.6<x4<0.8. Preferably, the Al composition content in the first AlGaN barrier layer 301 is in the range of 0.05<x1<0.2.

[0062] Return to view Figure 1 The fabrication method of the GaN-based HEMT device further includes: step 3): forming a metal source and a metal drain on the epitaxial stack. Specifically, after forming the top AlGaN barrier layer in steps 2-4), step 3) is performed, forming a metal source and a metal drain on the top AlGaN barrier layer ( Figure 5 As shown, the metal source 501 and metal drain 502 are on the fourth AlGaN barrier layer 304.

[0063] As an example, the steps for forming the metal source 501 and metal drain 502 include: 3-1) performing a photolithography process using a mask to define the patterns of the metal source and metal drain; 3-2) depositing metal Ti / Al / Ni / Au and then removing the mask; 3-3) annealing at 850°C for 30 seconds to form ohmic contacts between the metal source 501 and metal drain 502 on the surface of the AlGaN barrier layer. It is understood that the method for forming the metal source 501 and metal drain 502 is not limited to this.

[0064] In this embodiment, the metal source and metal drain are formed on multiple AlGaN barrier layers with Al composition increasing from the bottom layer upwards, thereby improving the overall linearity of the device and also contributing to improved IL of the device. on / I off .

[0065] Next, proceed to step 4): remove multiple dummy gates to form multiple gate trenches. See [link to step 4]. Figure 5 As shown, multiple dummy gates are removed to form a first gate trench 311, a second gate trench 312, and a third gate trench 313. The first gate trench 311 penetrates the top fourth AlGaN barrier layer to the surface of the first AlGaN barrier layer; the second gate trench 312 penetrates the top fourth AlGaN barrier layer to the surface of the second AlGaN barrier layer; and the third gate trench 313 penetrates the top fourth AlGaN barrier layer to the surface of the third AlGaN barrier layer. Each gate trench corresponds one-to-one with a multiple dummy gate, and each gate trench has a depth penetrating to the corresponding AlGaN barrier layer surface. Specifically, the multiple dummy gates can be removed using a wet etching process. In this embodiment, a certain ratio of HF:NH4F(BOE) etching solution can be used to remove SiO2. xThe virtual gate. Step 4) further includes: performing a photolithography process to expose the openings of multiple gate trenches, redefining the pattern of the gate to be formed; and simultaneously depositing multiple layers of metal in the multiple gate trenches using a pattern mask to form a metal gate, for example, the multiple layers of metal can be Ni / Au. As an example, the metal gate can have a length range of 50nm-0.5um. Preferably, the metal gate can have a T-gate structure that modulates the electric field strength in the channel, which can effectively reduce the peak electric field strength in the device channel and improve device reliability. In other examples, the metal gate can be formed as a rectangular metal gate. Further, before depositing the metal gate, a cleaning process can be performed using a 25% TMAH solution at a temperature of 80°C for 5 minutes to clean the surface of the gate trenches and impurities thereon. Further, after forming the metal gate, metal interconnects can be formed between the multiple metal gates.

[0066] The fabrication method of this embodiment further includes: after step 4), forming an interconnect between the metal source 501 and the metal drain 502 to obtain a HEMT device structure with modulated threshold voltage.

[0067] Example 2

[0068] See Figures 6-7 This embodiment provides a GaN-based HEMT device with a multi-gate structure, which includes: a GaN channel layer 200, an epitaxial stack 300 located on the GaN channel layer, and a metal source 501 and a metal drain 502 disposed on the epitaxial stack 300, wherein the epitaxial stack 300 includes a plurality of AlGaN barrier layers.

[0069] As an example, multiple AlGaN barrier layers can each have a uniform thickness, with each AlGaN barrier layer having a thickness range between 1 nm and 5 nm. Figure 6As shown, the epitaxial stack has four AlGaN barrier layers stacked together: a first AlGaN barrier layer 301, a second AlGaN barrier layer 302, a third AlGaN barrier layer 303, and a fourth AlGaN barrier layer 304. The first AlGaN barrier layer 301, the second AlGaN barrier layer 302, the third AlGaN barrier layer 303, and the fourth AlGaN barrier layer 304 can have the same thickness. The number of AlGaN barrier layers and the thickness of each barrier layer can be appropriately determined based on the range and value of the threshold voltage required by the HEMT device. As an example, the first AlGaN barrier layer 301 has a thickness t1, the second AlGaN barrier layer 302 has a thickness t2, the third AlGaN barrier layer 303 has a thickness t3, and the fourth AlGaN barrier layer 304 has a thickness t4, with thicknesses t1, t2, t3, and t4 ranging from 1 nm to 5 nm, allowing the multiple AlGaN barrier layers to have an overall thickness range of 5 nm to 20 nm. Similarly, Figure 7 This embodiment shows an alternative to the multi-gate GaN-based HEMT device. The epitaxial stack has five stacked AlGaN barrier layers. A fifth AlGaN barrier layer 305 is also disposed on the fourth AlGaN barrier layer 304. The fifth AlGaN barrier layer 305 has a thickness t5 and is in the range of 1nm-5nm. The multiple AlGaN barrier layers as a whole can have a thickness range of 5nm-25nm.

[0070] Preferably, the multiple AlGaN barrier layers can have an Al composition that decreases layer by layer from the top AlGaN barrier layer downwards. For example... Figure 7 As shown, the first AlGaN barrier layer 301, the second AlGaN barrier layer 302, the third AlGaN barrier layer 303, the fourth AlGaN barrier layer 304, and the fifth AlGaN barrier layer 305 can each have the expression Al x1 Ga 1-x1 N, Al x2 Ga 1-x2 N, Al x3 Ga 1-x3 N, Al x4 Ga 1-x4 N and Al x5 Ga 1-x5N, wherein x1, x2, x3, x4 and x5 represent the Al composition content in each barrier layer, and satisfy the following relationship: 0<x1<x2<x3<x4<x5≤1. Preferably, the Al composition content in the first AlGaN barrier layer 301 is in the range of 0.05<x1<0.2, the Al composition content in the second AlGaN barrier layer 302 is in the range of 0.2<x2<0.4, the Al composition content in the third AlGaN barrier layer 303 is in the range of 0.4<x3<0.6, the Al composition content in the fourth AlGaN barrier layer 304 is in the range of 0.6<x4<0.8, and the Al composition content in the fifth AlGaN barrier layer 305 is in the range of 0.8<x5<1. By arranging a plurality of barrier layers with linearly varying Al composition, the problem of lattice mismatch between AlGaN and GaN caused by excessively high Al composition content can be suppressed; at the same time, since the metal source electrode and the metal drain electrode are formed on a plurality of AlGaN barrier layers with consistent thickness, the linearity of the device can be improved as a whole, which is also beneficial to improving the comprehensive performance and reliability of the device. In this embodiment, the metal source electrode 501 and the metal drain electrode 502 can be arranged at both ends of the plurality of metal gate electrodes, such as Figure 6 shown in

[0071] The GaN-based HEMT device further comprises: a plurality of gate trenches arranged at intervals, each gate trench is arranged in the topmost AlGaN barrier layer and paired with one of the other AlGaN barrier layers, each gate trench exposes the corresponding AlGaN barrier layer from the bottom; and metal gate electrodes arranged in the plurality of gate trenches, each metal gate electrode forms a Schottky contact with the corresponding AlGaN barrier layer. As an example, the length of the metal gate electrode 401 ranges from 50 nm to 0.5 μm. As shown in Figure 6 , metal interconnection 600 is formed between a plurality of metal gate electrodes, the first metal gate electrode 401 forms a Schottky contact with the corresponding first AlGaN barrier layer 301, the second metal gate electrode 402 forms a Schottky contact with the corresponding second AlGaN barrier layer 302, and the third metal gate electrode 402 forms a Schottky contact with the corresponding third AlGaN barrier layer 303.

[0072] As an example, the plurality of gate trenches are arranged at intervals in the connecting line direction of the metal source electrode and the metal drain electrode and have sequentially decreasing penetration depths, so that the thickness of the AlGaN barrier layer under the gate electrode increases along the direction of decreasing gate-drain spacing, which is beneficial to the voltage withstand performance of the device as a whole. The plurality of said metal gate electrodes 800 formed in the plurality of gate trenches can have different heights. Since AlGaN barrier layers with different thicknesses are arranged under the plurality of metal gate electrodes, and the plurality of metal gate electrodes are interconnected, a plurality of gate electrodes with different threshold voltages are formed in the GaN-based HEMT device. The shape of the metal gate electrode can be T-shaped or rectangular. Refer to Figure 7The metal gate 800 located between the metal source 501 and the metal drain 502 includes four metal gates, and all four metal gates 800 are rectangular metal gates with the same length. However, this invention does not mean that the number, structure and / or morphology of the metal gates 800 are limited thereto.

[0073] In other examples, adjacent metal gates can share a common metal source or metal drain, so that each metal gate has both a metal source and a metal drain at its ends, such as... Figure 7 The metal source 501 and metal drain 502 are shown. In this configuration, the GaN-based HEMT device has an even number of metal gates, such as 4, 6, or 8, with interconnects formed between the multiple metal sources and between the multiple metal drains. As an example, interconnects between the multiple metal sources and between the multiple metal drains can be formed using metal air bridges.

[0074] In summary, the GaN-based HEMT device with a multi-gate structure and its fabrication method of the present invention have the following beneficial effects:

[0075] The fabrication method of the multi-gate GaN-based HEMT device of the present invention defines a corresponding gate pattern by forming multiple dummy gates, and then forms gates in the gate trench after removing the dummy gates. This results in multiple gates with AlGaN barrier layers of different thicknesses disposed below them, without the need for etching to thin the barrier layer. Therefore, there is no damage or interface state caused by etching, which is beneficial for obtaining high-quality epitaxial layers and improving the reliability of the device. The fabrication method of the present invention has the advantages of simple process and good repeatability.

[0076] The GaN-based HEMT device provided by this invention has a multi-gate structure, with multiple gates disposed on multiple AlGaN barrier layers. By disposing barrier layers of different thicknesses under the multiple gates, multiple gates with different threshold voltages can be formed within the same device, thereby achieving threshold voltage modulation. Furthermore, the source and drain are disposed on barrier layers with Al composition gradually increasing from bottom to top, thereby improving the overall linearity of the device and also contributing to improved IT. on / I off This also improves the device's ability to handle high voltage and high power.

[0077] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0078] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fabricating a GaN-based HEMT device with a multi-gate structure, characterized in that, Includes the following steps: Provides a GaN channel layer; Forming an epitaxial stack on the GaN channel layer includes intermittently growing a plurality of AlGaN barrier layers on the GaN channel layer. The intermittent growth of the plurality of AlGaN barrier layers includes the following steps: An AlGaN barrier layer is formed on the GaN channel layer; A dummy gate is formed on the AlGaN barrier layer to define the corresponding gate pattern; Repeat the steps of forming the AlGaN barrier layer and forming the dummy gate until a predetermined number of gate patterns are defined; After forming a dummy gate on the second-to-top AlGaN barrier layer, a top AlGaN barrier layer is formed on the second-to-top AlGaN barrier layer. A metal source and a metal drain are formed on the epitaxial stack, and the metal source and the metal drain are located at both ends of a plurality of dummy gates; Multiple dummy gates are removed to form multiple gate trenches, and a metal gate is formed in each gate trench. Each metal gate forms a Schottky contact with the corresponding AlGaN barrier layer.

2. The method for fabricating a GaN-based HEMT device according to claim 1, characterized in that: The plurality of AlGaN barrier layers have an Al composition that decreases layer by layer from the top AlGaN barrier layer downwards, and the nth AlGaN barrier layer has the expression Al xn Ga 1-xn N, where x n This represents the content of the Al component in the nth barrier layer, and x n The range satisfies: (n-1)×0.2 <x n <n×0.2。 3. The method for fabricating a GaN-based HEMT device according to claim 1, characterized in that, The process of forming a dummy gate includes the following steps: spin-coating hydrogen silsesquioxane onto an AlGaN barrier layer; exposing the hydrogen silsesquioxane to define a gate pattern; and developing the exposed hydrogen silsesquioxane with a TMAH solution to form the dummy gate.

4. The method for fabricating a GaN-based HEMT device according to claim 3, characterized in that, After performing the photolithography process, the exposed hydrogen silsesquioxane is cured at a temperature of 350℃-400℃ in an O2 atmosphere to form the dummy gate.

5. The method for fabricating a GaN-based HEMT device according to claim 4, characterized in that, The fabrication method further includes: after removing multiple dummy gates, simultaneously depositing multiple layers of metal in multiple gate trenches using a pattern mask to form a metal gate, wherein the metal gate is formed as a T-type metal gate.

6. The method for fabricating a GaN-based HEMT device according to claim 1, characterized in that, The fabrication method involves providing a substrate before providing the GaN channel layer, and sequentially growing a buffer layer and the GaN channel layer on the substrate.

7. A GaN-based HEMT device with a multi-gate structure, characterized in that, The GaN-based HEMT device is prepared by the method for preparing a GaN-based HEMT device according to any one of claims 1 to 6, and the GaN-based HEMT device comprises: GaN channel layer; An epitaxial stack is located on the GaN channel layer, the epitaxial stack includes multiple AlGaN barrier layers, the multiple AlGaN barrier layers having an Al composition that decreases layer by layer from the top AlGaN barrier layer downwards; Multiple gate slots are arranged at intervals. Each gate slot is set in the top AlGaN barrier layer and is paired with one of the other AlGaN barrier layers. Each gate slot exposes the corresponding AlGaN barrier layer from the bottom. A metal gate is disposed in the plurality of gate trenches, and each metal gate forms a Schottky contact with the corresponding AlGaN barrier layer; A metal source and a metal drain are disposed on the epitaxial stack and located at both ends of the plurality of metal gates.

8. The GaN-based HEMT device according to claim 7, characterized in that: The plurality of AlGaN barrier layers have a thickness ranging from 5 nm to 25 nm, and the length of the metal gate ranges from 50 nm to 0.5 μm.

9. The GaN-based HEMT device according to claim 7, characterized in that: The plurality of gate trenches are arranged at intervals along the line connecting the source and drain and have progressively decreasing penetration depths. Each gate trench is provided with a T-shaped metal gate.

10. The GaN-based HEMT device according to claim 7, characterized in that: The metal gates are provided in an even number, and adjacent metal gates have a common metal source or metal drain, so that each metal gate has a metal source and a metal drain at both ends.

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