Diamond aluminum nitride heterojunction field effect transistor and preparation method thereof

Abstract

The invention provides a diamond aluminum nitride heterojunction field effect transistor and a preparation method thereof, and relates to the technical field of diamond devices. The source electrode and the drain electrode which are in ohmic contact are prepared on the surface of the diamond substrate firstly, then the aluminum nitride layer and the protection layer are grown in sequence, so that the diamond aluminum nitride heterojunction is formed in the channel region between the source electrode and the drain electrode, and the protection layer covers and protects the aluminum nitride layer at the same time. In the subsequent preparation step, under the shielding protection of the protective layer, the aluminum nitride outside the gate groove between the source and the drain is prevented from being exposed when the gate groove is etched, and the aluminum nitride is also prevented from being exposed when the gate electrode is prepared. According to the embodiment of the invention, the aluminum nitride growth step is carried out later, the source and drain electrodes are prepared firstly, then the aluminum nitride is grown, and then the gate electrode is prepared on the aluminum nitride. Therefore, the interval steps of aluminum nitride growth and gate electrode preparation are reduced, the exposure time of aluminum nitride is shortened, the failure probability of the heterostructure is reduced, and the reliability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of diamond devices, and in particular to a diamond aluminum nitride heterojunction field effect transistor and a preparation method thereof. Background Art

[0002] Diamond materials, with their wide bandgap, high carrier mobility and saturation drift velocity, low dielectric constant, and excellent radiation and corrosion resistance, offer advantages for use in high-frequency, high-power devices. However, due to the wide bandgap of diamond materials, the high activation energy and low activation rate of doping elements (such as B, N, and P) make achieving conductivity in diamond materials challenging using traditional doping strategies. Growing aluminum nitride on diamond to form a heterostructure can create a high-performance, two-dimensional carrier conduction channel within the diamond, resulting in a highly conductive diamond material.

[0003] The existing method for preparing diamond aluminum nitride heterojunction field-effect transistors generally involves first directly growing an aluminum nitride film on a diamond substrate, followed by cleaning, gluing, photolithography, development, metal evaporation, stripping, cleaning, and annealing to complete the preparation of source and drain electrodes, and then again cleaning, gluing, photolithography, development, metal evaporation, stripping, and cleaning to complete the preparation of the gate electrode. In the subsequent process steps of aluminum nitride growth, multiple contacts with solutions such as cleaning solutions, deionized water, photoresist, developer, and stripping solutions are required. However, due to the aluminum nitride material's easy hydrolysis and chemical reaction with alkali, the existing process methods for preparing diamond aluminum nitride heterojunction field-effect transistors cause significant damage to the diamond aluminum nitride heterojunction, which in turn affects the performance of the device and results in poor device reliability. Summary of the Invention

[0004] The embodiment of the present invention provides a diamond aluminum nitride heterojunction field effect transistor and a preparation method thereof, so as to solve the problem that the heterojunction structure in the existing diamond aluminum nitride heterojunction field effect transistor is prone to failure and has poor reliability.

[0005] In a first aspect, an embodiment of the present invention provides a method for preparing a diamond aluminum nitride heterojunction field effect transistor, comprising:

[0006] An ohmic contact layer is formed on the surface of a diamond substrate to obtain a wafer having the ohmic contact layer formed thereon; the ohmic contact layer includes a source electrode and a drain electrode isolated from each other;

[0007] On the surface of the wafer after the ohmic contact layer is prepared, an aluminum nitride layer and a protective layer are sequentially grown; wherein the aluminum nitride layer covering the area between the source electrode and the drain electrode forms a diamond aluminum nitride heterojunction with the diamond substrate; and the protective layer covers the aluminum nitride layer;

[0008] After growing the protective layer, selectively etching the protective layer in the region between the source electrode and the drain electrode to form a gate groove; wherein the aluminum nitride layer is exposed in the gate groove region;

[0009] The etched protective layer is used as a mask. Under the cover of the protective layer, a metal layer is grown on the surface of the wafer after the gate groove is prepared. A gate electrode is prepared in the gate groove to obtain a diamond aluminum nitride heterojunction field effect transistor.

[0010] In a possible implementation, the protective layer is selectively etched in the region between the source electrode and the drain electrode, and before the gate trench is formed, the following steps are further included:

[0011] After growing the protective layer, etching the protective layer and the aluminum nitride layer in the source electrode region and the drain electrode region to expose portions of the surfaces of the source electrode and the drain electrode;

[0012] Accordingly, growing a metal layer on the surface of the wafer after the gate trench is prepared also includes:

[0013] A metal layer is grown on the surface of the wafer after the gate groove is prepared, and the exposed surfaces of the source electrode and the drain electrode are thickened with electrode metal.

[0014] In a possible implementation, the material of the protective layer includes aluminum oxide, hafnium dioxide, or silicon nitride.

[0015] In a possible implementation, for each of the source electrode and the drain electrode, at the interface between the ohmic contact layer and the diamond substrate, a portion of the interface is hydrogen-terminated, and another portion of the interface is oxygen-terminated.

[0016] In a possible implementation, the step of preparing an ohmic contact layer on a surface of a diamond substrate to obtain a wafer having the ohmic contact layer prepared thereon comprises:

[0017] Performing hydrogen plasma treatment on the surface of the diamond substrate to obtain a diamond substrate with hydrogen terminals;

[0018] The surface of the diamond substrate after the hydrogen termination is prepared is subjected to oxygen plasma treatment under the protection of a patterned mask to prepare a patterned oxygen termination, wherein the area covered by the patterned oxygen termination includes a source region and a drain region that are isolated from each other; the portion between the source region and the drain region that is not covered by the oxygen termination is a hydrogen termination;

[0019] A patterned ohmic contact layer is prepared on the surface of the wafer after patterning the oxygen terminal to obtain a wafer after the ohmic contact layer is prepared, wherein in the patterned ohmic contact layer, the source electrode covers the source region and covers a portion of the hydrogen terminal connected to the source region, and the drain electrode covers the drain region and covers a portion of the hydrogen terminal connected to the drain region.

[0020] In a possible implementation, the surface of the diamond substrate after the hydrogen termination is prepared is subjected to oxygen plasma treatment under the shielding of a patterned mask to prepare the patterned oxygen termination, which includes:

[0021] A patterned sacrificial layer is prepared on the surface of the diamond substrate for preparing the hydrogen terminal; the uncovered areas on both sides of the patterned sacrificial layer are the source region and the drain region respectively;

[0022] Under the shielding of the patterned sacrificial layer, the surface of the diamond substrate not covered by the patterned sacrificial layer is subjected to oxygen plasma treatment to convert hydrogen terminals in the area not covered by the patterned sacrificial layer into oxygen terminals, thereby preparing patterned oxygen terminals;

[0023] Accordingly, a patterned ohmic contact layer is formed on the wafer surface after the patterned oxygen terminal is formed, including:

[0024] removing the patterned sacrificial layer to expose the hydrogen terminals covered by the patterned sacrificial layer;

[0025] After removing the patterned sacrificial layer, a patterned ohmic contact layer is prepared, wherein the patterned ohmic contact layer covers the patterned oxygen terminal and a portion of the hydrogen terminal close to the ohmic contact layer.

[0026] In a possible implementation, the preparing of the patterned ohmic contact layer includes:

[0027] After removing the patterned sacrificial layer, preparing a patterned photoresist mask, wherein the patterned photoresist mask exposes the patterned oxygen terminal and exposes a portion of the hydrogen terminal close to the ohmic contact layer;

[0028] A metal layer is grown, and a stripping process is used to remove the metal layer on the patterned photoresist mask to obtain a patterned ohmic contact layer.

[0029] In a possible implementation, after removing the metal layer on the patterned photoresist mask, the method further includes: annealing the patterned ohmic contact layer to form an ohmic contact.

[0030] In a possible implementation, the material of the ohmic contact layer includes gold, titanium gold, or titanium platinum gold.

[0031] In a second aspect, an embodiment of the present invention provides a diamond aluminum nitride heterojunction field effect transistor, which is prepared based on the preparation method of the diamond aluminum nitride heterojunction field effect transistor as described in any one of the first aspects.

[0032] An embodiment of the present invention provides a diamond aluminum nitride heterojunction field-effect transistor and a method for preparing the same. The method involves first preparing an ohmic contact source electrode and drain electrode on the surface of a diamond substrate, then sequentially growing an aluminum nitride layer and a protective layer, thereby forming a diamond aluminum nitride heterojunction in the channel region between the source and drain, and simultaneously covering the aluminum nitride layer with a protective layer. In subsequent preparation steps, under the shielding and protection of the protective layer, the aluminum nitride outside the gate groove between the source and drain is avoided when etching the gate groove, and the aluminum nitride is also avoided when preparing the gate electrode. In a first aspect, the aluminum nitride growth step is placed at a later stage, with the source and drain electrodes prepared first, the aluminum nitride grown, and then the gate electrode prepared on the aluminum nitride. This reduces the interval between aluminum nitride growth and gate electrode preparation, shortening the exposure time of the aluminum nitride. Secondly, in the steps after the aluminum nitride layer is prepared, the protective layer can both reduce the exposure time of the aluminum nitride layer in subsequent steps and continuously protect the aluminum nitride outside the gate groove between the source and drain. Third, directly using the etched protective layer as a mask to grow the metal layer and prepare the gate electrode avoids the use of photolithography masking processes, thereby preventing the aluminum nitride exposed by the etched gate trench from direct contact with the solution. This reduces the exposure time of the aluminum nitride and the impact of the preparation process solution and the external environment on the aluminum nitride, reducing the probability of heterostructure failure and improving reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is a schematic structural diagram of a diamond aluminum nitride heterojunction field effect transistor provided by an embodiment of the present invention;

[0034] Figure 2 This is a flow chart of a method for preparing a diamond aluminum nitride heterojunction field effect transistor provided by an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of the structure of a hydrogen preparation terminal provided in an embodiment of the present invention;

[0036] Figure 4 A schematic diagram of the structure after preparing a sacrificial layer according to an embodiment of the present invention;

[0037] Figure 5 A schematic diagram of the structure of the patterned sacrificial layer provided in an embodiment of the present invention;

[0038] Figure 6 A schematic diagram of the structure after preparing the ohmic contact layer according to an embodiment of the present invention;

[0039] Figure 7 A schematic diagram of the structure after the aluminum nitride layer is prepared according to an embodiment of the present invention;

[0040] Figure 8 A schematic diagram of the structure after preparing the protective layer provided in an embodiment of the present invention;

[0041] Figure 9 A schematic diagram of the structure after grooving provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] To help those skilled in the art better understand this solution, the following will clearly describe the technical solutions in the embodiments of this solution in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of this solution, not all of it. Based on the embodiments of this solution, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of this solution.

[0043] Throughout the specification, claims, and accompanying figures of this solution, the term "including" and any variations thereof mean "including, but not limited to," and are intended to cover non-exclusive inclusions and are not limited to the examples listed herein. Furthermore, the terms "first" and "second," etc., are used to distinguish between different objects, not to describe a specific order.

[0044] The following is a detailed description of the implementation of the present invention with reference to the accompanying drawings:

[0045] During actual research and development, the inventors of this application discovered that the reliability of diamond aluminum nitride heterojunction field-effect transistors prepared using existing process flows is low. They further discovered that due to the easy hydrolysis of aluminum nitride and its chemical reaction with alkali, the existing process for preparing diamond aluminum nitride heterojunction field-effect transistors involves multiple contacts with aqueous solutions and prolonged exposure to air. This significantly damages the diamond aluminum nitride heterojunction, thus affecting device performance and resulting in poor device reliability.

[0046] To facilitate understanding of the preparation method according to the embodiment of the present invention, the structure of the diamond aluminum nitride heterojunction field effect transistor according to the embodiment of the present invention is first described.

[0047] Figure 1 A schematic structural diagram of a diamond aluminum nitride heterojunction field effect transistor provided by an embodiment of the present invention. Figure 1 The field-effect transistor includes a diamond substrate; an ohmic contact layer is provided on a portion of the upper surface of the diamond substrate; the ohmic contact layer includes a source electrode and a drain electrode that are isolated from each other; an aluminum nitride layer and a protective layer are provided on a portion of the upper surface of the ohmic contact layer and the upper surface of the region between the source and drain electrodes. The portion of the ohmic contact layer not covered by the aluminum nitride layer and the protective layer can serve as an electrode lead-out region. The protective layer in the region between the source and drain has a groove, and a gate electrode is provided in the groove. The aluminum nitride layer in the region between the source and drain forms a heterojunction with the diamond substrate. The gate electrode above the aluminum nitride layer is used to control the on / off state of the conductive channel between the source and drain.

[0048] An embodiment of the present invention provides a diamond aluminum nitride heterojunction field-effect transistor and a preparation method thereof, wherein the aluminum nitride growth step is placed at a later stage, a protective layer is provided on the aluminum nitride, and the protective layer is used as a mask to grow a metal layer, thereby solving the problem of easy failure and poor reliability of the heterojunction structure in existing diamond aluminum nitride heterojunction field-effect transistors.

[0049] Figure 2 This is a flow chart of a method for preparing a diamond aluminum nitride heterojunction field effect transistor according to an embodiment of the present invention. Figure 2 The embodiment of the present invention provides a method for preparing a diamond aluminum nitride heterojunction field effect transistor, the method comprising:

[0050] Step 201: preparing an ohmic contact layer on a surface of a diamond substrate to obtain a wafer having the ohmic contact layer formed thereon; the ohmic contact layer comprising a source electrode and a drain electrode isolated from each other;

[0051] Exemplarily, the upper surface of the diamond substrate is a (001) crystal plane.

[0052] Exemplarily, the material of the ohmic contact layer includes: gold, titanium gold, or titanium platinum gold. Exemplarily, the thickness of the ohmic contact layer ranges from 5 nm to 50 μm.

[0053] It should be noted that the chip manufacturing process involves simultaneously fabricating multiple chips with the same structure on the same wafer, which are then cut into individual chips. To facilitate understanding of the wafer-based chip manufacturing process, the structural manufacturing process of a single chip is used as an example.

[0054] An ohmic contact is a type of contact between a metal and a semiconductor whose current-voltage characteristics follow Ohm's law. The primary function of an ohmic contact is to provide a good electrical connection for semiconductor devices, ensuring efficient current transfer between the metal electrode and the semiconductor, thereby reducing contact resistance. The typical preparation steps for an ohmic contact layer include metal plating and annealing.

[0055] The source and drain electrodes are the main components of a field-effect transistor. To reduce contact resistance, an ohmic contact with the substrate is typically required. The source and drain electrodes are electrically connected via a conductive channel, and the gate electrode controls the on / off switching of the conductive channel. Therefore, isolated source and drain electrodes can be patterned on the surface of a diamond substrate to form an ohmic contact layer. The general steps for preparing an ohmic contact layer may include: patterning photolithography to form a mask, growing a metal layer, removing the metal layer between the source and drain electrodes, and finally annealing to obtain the ohmic contact layer.

[0056] The above describes the general steps for preparing an ohmic contact layer, namely growing metal directly on a diamond substrate to form an ohmic contact. The following examples illustrate an improved approach: reducing the ohmic contact resistance while improving the adhesion of the ohmic contact layer.

[0057] In a possible implementation, for each of the source electrode and the drain electrode, at the interface between the ohmic contact layer and the diamond substrate, a portion of the interface is hydrogen-terminated, and another portion of the interface is oxygen-terminated.

[0058] Illustratively, at the interface between the source electrode and the diamond substrate, part of the interface is hydrogen-terminated, while another part of the interface is oxygen-terminated. Furthermore, at the interface between the drain electrode and the diamond substrate, part of the interface is hydrogen-terminated, while another part of the interface is oxygen-terminated.

[0059] Furthermore, the portion where the source electrode and the drain electrode are close to each other is a hydrogen terminal, and the portion where the source electrode and the drain electrode are far from each other is an oxygen terminal.

[0060] Hydrogen termination refers to the process of attaching hydrogen atoms to surface atoms on the surface of a material through chemical bonding, thereby forming a surface termination state. There are unsaturated chemical bonds on the surface of diamond, and these chemical bonds are highly active. When diamond interacts with hydrogen or hydrogen-containing gases under certain conditions (such as high temperature, plasma environment, etc.), hydrogen atoms will form covalent bonds with carbon atoms on the diamond surface, thereby fixing the hydrogen atoms on the surface and achieving hydrogen termination on the diamond surface. The hydrogen-terminated diamond surface has some unique properties. First, hydrogen termination can significantly change the electrical properties of the diamond surface, making the surface exhibit a certain degree of conductivity. Second, hydrogen termination can also improve the chemical stability of the diamond surface, reduce surface oxidation and contamination, and improve the surface finish and quality.

[0061] Oxygen termination refers to a state in which the diamond surface interacts with oxygen atoms or oxygen-containing compounds, causing oxygen atoms to attach to the diamond surface, terminating chemical bonds on the diamond surface with oxygen atoms. Oxygen termination of the diamond surface can be achieved through a variety of methods. One common method is to expose the diamond to oxygen or an oxidizing atmosphere. Under certain temperature and pressure conditions, oxygen molecules adsorb on the diamond surface and chemically react with carbon atoms on the surface, forming carbon-oxygen chemical bonds, thereby achieving oxygen termination.

[0062] It should be noted that when an ohmic contact layer is prepared on the interface of the hydrogen terminal, the contact resistance can be reduced. However, the adhesion of the ohmic contact layer is not high. When an ohmic contact layer is prepared on the hydrogen terminal interface, the electronic state of the hydrogen terminal surface can be well matched with the electronic state of the ohmic contact layer material, which is conducive to the transmission of electrons at the interface, thereby reducing the contact resistance. The hydrogen atoms on the hydrogen terminal interface are relatively active, and the main bonding mode with the diamond surface is covalent bonding, which makes the hydrogen terminal diamond surface saturated and free of redundant dangling bonds. Although this covalent bond plays an important role in maintaining the electrical properties of the surface, it is not conducive to the formation of strong physical or chemical adsorption for the adhesion of the ohmic contact layer material, and thus hinders the formation of close contact and chemical bonding between the ohmic contact layer material and the diamond surface. In addition, the steric hindrance effect of hydrogen atoms may also make it difficult for the molecules or atoms of the ohmic contact layer material to get close enough to the diamond surface, resulting in low adhesion.

[0063] When an ohmic contact layer is prepared on the oxygen terminal, adhesion can be improved. The chemical properties of the oxygen-terminated diamond surface are different from those of the hydrogen-terminated surface due to the presence of oxygen atoms. Oxygen atoms can form a variety of chemical bonds with carbon atoms on the diamond surface, such as carbon-oxygen single bonds (CO). The presence of these chemical bonds makes the surface more chemically active and polar. When the ohmic contact layer is prepared, the atoms or molecules in the ohmic contact layer material are more likely to chemically react with the oxygen atoms or carbon atoms on the oxygen-terminated surface, forming chemical bonds or strong physical adsorption, thereby improving the adhesion of the ohmic contact layer to the diamond surface.

[0064] The embodiment of the present invention reduces the contact resistance of the ohmic contact layer, improves the adhesion of the ohmic contact layer, and improves the reliability of the device by setting the interface of a part of the electrode and the diamond substrate as a hydrogen terminal and the interface of another part of the electrode as an oxygen terminal.

[0065] The interface structure of the ohmic contact layer is described above, and the corresponding preparation method is described below.

[0066] In a possible implementation, the step of preparing an ohmic contact layer on a surface of a diamond substrate to obtain a wafer having the ohmic contact layer prepared thereon comprises:

[0067] Step 2011: performing hydrogen plasma treatment on the surface of the diamond substrate to obtain a diamond substrate for preparing hydrogen terminals;

[0068] Exemplarily, the hydrogen plasma processing equipment is a microwave plasma chemical vapor deposition equipment.

[0069] The diamond substrate is placed in an environment containing hydrogen plasma, typically generated in a vacuum chamber through radio frequency discharge, microwave discharge, or other methods. During the treatment process, hydrogen atoms in the high-energy hydrogen plasma interact with carbon atoms on the surface of the diamond substrate, forming hydrogen terminations across the entire upper surface of the diamond substrate.

[0070] Step 2012: The surface of the diamond substrate after the hydrogen termination is treated with oxygen plasma under the protection of a patterned mask to obtain a patterned oxygen termination, wherein the area covered by the patterned oxygen termination includes the isolated source and drain regions; the portion between the source and drain regions not covered by the oxygen termination serves as the hydrogen termination;

[0071] A patterned mask covers the surface of the diamond substrate at the hydrogen terminal. The pattern on the mask determines the area that will be subsequently treated with oxygen plasma. For example, the material of the patterned mask can be photoresist. For example, the mask can be produced using a photolithography process. Another example is that the material of the patterned mask can be metal. For example, a metal layer can be grown first, and then a patterned metal mask can be prepared using a photolithography process.

[0072] Regarding the process of oxygen plasma treatment to form patterned oxygen terminations, it should be noted that after the substrate is masked with a mask, it is placed in an oxygen plasma environment. Oxygen plasma is generated by discharge and other means, and contains highly active particles such as oxygen atoms, oxygen ions, and electrons. During the treatment process, the surface of the hydrogen-terminated diamond substrate that is not masked by the mask reacts with the oxygen plasma. The oxygen atoms undergo a replacement reaction with the hydrogen atoms on the surface, or directly combine with carbon atoms to form a carbon-oxygen chemical bond, thereby converting the hydrogen termination into an oxygen termination. The area shielded by the mask is not affected by the oxygen plasma and remains in the hydrogen termination state.

[0073] It should be noted that the oxygen termination pattern corresponds to the source and drain electrodes to be formed later. The oxygen termination pattern consists of two separate parts: one can be called the source region and the other can be called the drain region. The area between the source and drain regions remains the original hydrogen termination. It is important to note that, from the perspective of occupied area, the oxygen termination source region is part of the subsequently formed source electrode region, and the oxygen termination drain region is part of the subsequently formed drain electrode region.

[0074] Step 2013: Prepare a patterned ohmic contact layer on the surface of the wafer after preparing the patterned oxygen terminal, to obtain a wafer after preparing the ohmic contact layer, wherein in the patterned ohmic contact layer, the source electrode covers the source region and covers a portion of the hydrogen terminal connected to the source region, and the drain electrode covers the drain region and covers a portion of the hydrogen terminal connected to the drain region.

[0075] Illustratively, after patterning the oxygen terminal, an ohmic contact layer is formed on the source region oxygen terminal and a portion of the hydrogen terminal to obtain a source electrode; an ohmic contact layer is formed on the drain region oxygen terminal and a portion of the hydrogen terminal to obtain a drain electrode.

[0076] In some embodiments, a method for preparing a patterned ohmic contact layer may include: growing an ohmic contact metal on the surface of a wafer after preparing a patterned oxygen terminal; preparing a patterned mask using a photolithography process after growing the ohmic contact metal; and etching the ohmic contact metal under the shielding of the patterned mask to obtain a patterned ohmic contact layer.

[0077] The above embodiment illustrates a method for preparing a patterned ohmic contact layer. With respect to step 2012 and step 2013, another method for preparing a patterned ohmic contact layer is provided below: preparing the patterned ohmic contact layer through a sacrificial layer.

[0078] In one possible implementation, the surface of the diamond substrate after preparing the hydrogen termination is subjected to oxygen plasma treatment under the shielding of a patterned mask to prepare the patterned oxygen termination, which includes: preparing a patterned sacrificial layer on the surface of the diamond substrate on which the hydrogen termination is prepared; the uncovered areas on both sides of the patterned sacrificial layer are the source region and the drain region, respectively; and under the shielding of the patterned sacrificial layer, performing oxygen plasma treatment on the surface of the diamond substrate not covered by the patterned sacrificial layer to convert the hydrogen terminations in the areas not covered by the patterned sacrificial layer into oxygen terminations, thereby preparing the patterned oxygen terminations.

[0079] Exemplarily, the material of the sacrificial layer is gold. Exemplarily, the thickness of the sacrificial layer ranges from 10 nm to 100 nm. Exemplarily, the sacrificial layer is evaporated by electron beam evaporation or thermal evaporation. In the embodiments of the present invention, by using gold as the sacrificial layer, gold has good chemical stability and machinability. In subsequent processes, the gold can be precisely etched away by a specific gold etching solution without causing significant damage to the diamond substrate and other key structures, thereby ensuring process reliability and repeatability.

[0080] It should be noted that, in the embodiment of the present invention, the patterned oxygen terminal is prepared by using the sacrificial layer as a mask for oxygen plasma treatment in step 2012. The patterned sacrificial layer can be prepared by patterned photolithography, which will not be described in detail here.

[0081] In some embodiments, after the patterned oxygen terminal is prepared, step 2013: preparing a patterned ohmic contact layer on the surface of the wafer after the patterned oxygen terminal is prepared, can include: removing the patterned sacrificial layer to expose the hydrogen terminal covered by the patterned sacrificial layer; after removing the patterned sacrificial layer, preparing a patterned ohmic contact layer, wherein the patterned ohmic contact layer covers the patterned oxygen terminal and covers a portion of the hydrogen terminal close to the ohmic contact layer.

[0082] In the embodiment of the present invention, a patterned oxygen terminal is formed by performing an oxygen plasma treatment using a sacrificial layer as a mask. Furthermore, after removing the sacrificial layer, an ohmic contact layer is formed in a specific area, so that a portion of the ohmic contact layer covers the oxygen terminal and another portion covers the hydrogen terminal.

[0083] In one possible implementation, the preparation of the patterned ohmic contact layer includes: after removing the patterned sacrificial layer, preparing a patterned photoresist mask, wherein the patterned photoresist mask exposes the patterned oxygen terminal and exposes a portion of the hydrogen terminal close to the ohmic contact layer; growing a metal layer, and using a stripping process to remove the metal layer on the patterned photoresist mask to obtain a patterned ohmic contact layer.

[0084] In a possible implementation, after removing the metal layer on the patterned photoresist mask, the method further includes: annealing the patterned ohmic contact layer to form an ohmic contact.

[0085] Step 202: On the surface of the wafer after the ohmic contact layer is formed, an aluminum nitride layer and a protective layer are sequentially grown; wherein the aluminum nitride layer covering the area between the source electrode and the drain electrode forms a diamond aluminum nitride heterojunction with the diamond substrate; and the protective layer covers the aluminum nitride layer;

[0086] Exemplarily, the thickness of the aluminum nitride layer ranges from 1 nm to 500 nm.

[0087] Exemplarily, the material of the protective layer includes aluminum oxide, hafnium dioxide, or silicon nitride. Exemplarily, the thickness of the protective layer ranges from 1 nm to 500 nm.

[0088] In some embodiments, the aluminum nitride layer is grown by an epitaxial process, for example, pulsed vapor deposition or metal organic chemical vapor deposition.

[0089] It should be noted that the diamond substrate is exposed in the area between the source electrode and the drain electrode of the ohmic contact layer. Therefore, after growing the aluminum nitride layer, the aluminum nitride is in direct contact with the diamond, forming a diamond aluminum nitride heterojunction. The diamond aluminum nitride heterojunction serves as the conductive path of the final device. The protective layer is grown directly on the aluminum nitride layer, covering the entire aluminum nitride layer. After growing the aluminum nitride layer, directly growing the protective layer can isolate the aluminum nitride layer from the outside air, reduce the exposure time of the aluminum nitride layer, and reduce the probability of aluminum nitride hydrolysis.

[0090] Step 203: After growing the protective layer, selectively etching the protective layer in the region between the source electrode and the drain electrode to form a gate groove; wherein the aluminum nitride layer is exposed in the gate groove region;

[0091] The gate trench is prepared by selectively etching the protective layer between the source and drain electrodes to create a recessed structure in a specific area for subsequent fabrication of device structures such as the gate. The gate trench provides space for subsequent gate fabrication. The gate trench can be filled with gate material, such as metal.

[0092] For example, selective etching can be achieved through photolithography and etching processes. First, a photoresist mask is formed in the area to be etched using photolithography technology to accurately define the pattern of the gate groove. Then, a suitable etching process, such as reactive ion etching (RIE), is used to etch the protective layer according to the pattern of the photoresist mask. Due to the use of a selective etching process, the protective layer in the area between the source electrode and the drain electrode can be accurately removed without affecting the protective layer in other areas, thereby exposing the aluminum nitride layer underneath.

[0093] For example, a photoresist is coated on the protective layer, and the protective layer at a specific position is etched away by dry etching to form a gate groove, exposing the aluminum nitride. A gate metal layer is deposited on the aluminum nitride surface exposed by the gate groove.

[0094] Step 204 : Using the etched protective layer as a mask, under the shielding of the protective layer, a metal layer is grown on the surface of the wafer after the gate groove is prepared, and a gate electrode is prepared in the gate groove to obtain a diamond aluminum nitride heterojunction field effect transistor.

[0095] Exemplarily, the shape of the gate electrode includes a straight gate or a T-shaped gate. Exemplarily, the material of the gate electrode includes aluminum, aluminum gold, nickel gold, or titanium gold. Exemplarily, the thickness of the gate electrode ranges from 5 nm to 500 nm.

[0096] After the previous etching process, the protective layer forms a specific pattern of openings between the source and drain electrodes, namely the gate groove, while other areas where metal growth is not required remain covered by the protective layer. At this time, the etched protective layer acts as a mask to precisely define the areas where the metal layer grows, preventing metal deposition in unwanted areas and ensuring that metal grows only in the gate groove and other specific areas where it is needed, thereby achieving precise control over the device structure.

[0097] It should be noted that the etched protective layer is used as a mask, and a metal layer is grown on the surface of the wafer after the gate groove is prepared under the cover of the protective layer. This means that after the gate groove is obtained by etching the protective layer, the mask is not photolithographically formed again, but the metal layer is directly grown using the protective layer as a mask.

[0098] For example, if a photoresist is used as a mask to etch the protective layer in step 203, the remaining photoresist is not removed after etching the protective layer, and then a metal layer is directly grown in step 204 to form a gate electrode. This prevents aluminum nitride from contacting an aqueous solution after forming the gate trench and before forming the gate electrode, thereby reducing hydrolysis.

[0099] An embodiment of the present invention provides a diamond aluminum nitride heterojunction field-effect transistor and a method for preparing the same. The method involves first preparing an ohmic contact source electrode and drain electrode on the surface of a diamond substrate, then sequentially growing an aluminum nitride layer and a protective layer, thereby forming a diamond aluminum nitride heterojunction in the channel region between the source and drain, and simultaneously covering the aluminum nitride layer with a protective layer. In subsequent preparation steps, under the shielding and protection of the protective layer, the aluminum nitride outside the gate groove between the source and drain is avoided when etching the gate groove, and the aluminum nitride is also avoided when preparing the gate electrode. In a first aspect, the aluminum nitride growth step is placed at a later stage, with the source and drain electrodes prepared first, the aluminum nitride grown, and then the gate electrode prepared on the aluminum nitride. This reduces the interval between aluminum nitride growth and gate electrode preparation, shortening the exposure time of the aluminum nitride. Secondly, in the steps after the aluminum nitride layer is prepared, the protective layer can both reduce the exposure time of the aluminum nitride layer in subsequent steps and continuously protect the aluminum nitride outside the gate groove between the source and drain. Third, directly using the etched protective layer as a mask to grow the metal layer and prepare the gate electrode avoids the use of photolithography masking processes, thereby preventing the aluminum nitride exposed by the etched gate trench from direct contact with the solution. This reduces the exposure time of the aluminum nitride and the impact of the preparation process solution and the external environment on the aluminum nitride, reducing the probability of heterostructure failure and improving reliability.

[0100] The following describes how to process the aluminum nitride layer and protective layer in the source and drain electrode regions.

[0101] In some embodiments, after the gate electrode is prepared in step 204, the aluminum nitride layer and the protective layer in the region above the source and drain electrodes can be removed by photolithography and etching to expose the source and drain electrodes. Furthermore, after the source and drain electrodes are exposed, the source and drain electrodes can be thickened.

[0102] Another method for processing the aluminum nitride layer and the protective layer in the source and drain electrode regions is provided below.

[0103] In a possible implementation, the protective layer is selectively etched in the region between the source electrode and the drain electrode, and before forming the gate trench, the method further includes: after growing the protective layer, etching the protective layer and the aluminum nitride layer in the source electrode region and the drain electrode region to expose portions of the surface of the source electrode and the drain electrode;

[0104] It should be noted that after growing the protective layer and before etching the gate trench, the protective layer and aluminum nitride layer are etched in the source and drain electrode regions to expose portions of the source and drain electrode surfaces. This avoids etching the source and drain regions after etching the gate trench, and avoids steps such as photolithography mask preparation and cleaning.

[0105] Exemplarily, after growing the protective layer, the method of etching the protective layer and the aluminum nitride layer in the source electrode region and the drain electrode region includes: using photoresist as a mask to expose the protective layer at part of the ohmic contact layer position, and covering the rest of the position with photoresist; using wet etching or dry etching or a combination of wet etching and dry etching to remove the protective layer and the aluminum nitride layer at specific positions, exposing the ohmic contact metal layer in the specific area.

[0106] In some embodiments, correspondingly, growing a metal layer on the wafer surface after forming the gate trench further includes: growing a metal layer on the wafer surface after forming the gate trench, and performing electrode metal thickening on the exposed surfaces of the source electrode and the drain electrode.

[0107] It should be noted that source and drain etching is completed before preparing the gate groove. When the metal layer is grown on the wafer surface after preparing the gate groove, metal can be filled in the gate groove to form a gate electrode, and the electrode can be thickened in the exposed area of the source and drain electrodes.

[0108] It should be further noted that when the metal layer is grown on the wafer surface after the gate trench is formed, in addition to the gate trench and the exposed source and drain areas, excess metal layer will also grow on the surface of other areas. The excess metal layer can be removed in a variety of ways. For example, it can be removed through photolithography and etching processes. In another example, it can also be removed through chemical mechanical polishing.

[0109] The following is a comprehensive embodiment to illustrate the technical solution of the present invention. Figure 1 In a field-effect transistor structure, the diamond aluminum nitride heterojunction field-effect transistor provided in an embodiment of the present invention includes: a diamond substrate, a hydrogen terminal, an ohmic contact layer, an aluminum nitride layer, a protective layer, and a gate electrode. The ohmic contact layer is formed on the upper surface of the diamond substrate, with a portion of the ohmic contact layer on the hydrogen terminal. A certain gap exists between the two portions of the ohmic contact layer, serving as a conductive path. The aluminum nitride layer is located on the diamond substrate and the ohmic contact layer; the protective layer is located on the aluminum nitride layer. The gate electrode is located on the upper surface of the aluminum nitride layer. A thickened source electrode and a thickened drain electrode are provided on the ohmic contact layer.

[0110] The preparation method provided by an embodiment of the present invention includes: forming a hydrogen terminal on a diamond substrate; forming an ohmic contact layer on the hydrogen-terminated diamond; forming an aluminum nitride layer on the diamond substrate and the ohmic contact layer; growing a protective layer after introducing the aluminum nitride layer; setting a gate groove in a portion of the protective layer and the aluminum nitride layer; and forming a gate metal layer in the gate groove.

[0111] An embodiment of the present invention provides a method for preparing a diamond aluminum nitride heterojunction field-effect transistor, in which an ohmic contact layer is prepared on the hydrogen-terminated diamond before the epitaxial growth of the aluminum nitride layer, and a protective layer is grown on the aluminum nitride layer immediately after the growth of the aluminum nitride layer, thereby providing protection for the aluminum nitride layer and the diamond aluminum nitride heterojunction, improving the impact of the process on the aluminum nitride layer and the diamond aluminum nitride heterojunction, and having the technical effect of improving the DC and RF performance of the diamond aluminum nitride heterojunction field-effect transistor.

[0112] Figures 3 to 9 This is a schematic diagram of the structure after each step of the preparation method provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the hydrogen terminal after preparation provided by the embodiment of the present invention. Figure 3 , forming hydrogen terminations on a diamond substrate. For example, a hydrogen-terminated diamond substrate was formed on a (001) single-crystal diamond substrate using microwave plasma chemical vapor deposition equipment in a hydrogen plasma environment. The growth temperature was set at 600°C, the power was 1600W, the flow rate was 800sccm, the chamber pressure was 70mbar, and the time was 10 minutes.

[0113] Figure 4 This is a schematic diagram of the structure after the sacrificial layer is prepared according to an embodiment of the present invention. Figure 4 , a 50nm Au sacrificial layer was deposited on the hydrogen-terminated diamond using electron beam evaporation.

[0114] Figure 5 This is a schematic diagram of the structure of the patterned sacrificial layer provided in an embodiment of the present invention. Figure 5 Photolithography was performed on the Au sacrificial layer, using a photoresist as a mask. Areas uncovered by the photoresist were removed using a potassium iodide / iodine solution. Hydrogen terminations in the exposed areas of the photoresist were removed using an oxygen plasma, achieving mesa isolation. The power was set to 100 W for 5 minutes. The photoresist mask was then removed.

[0115] Figure 6 This is a schematic diagram of the structure after preparing the ohmic contact layer according to an embodiment of the present invention. Figure 6 The ohmic contact layer is formed on the hydrogen-terminated diamond, including: evaporating Ti / Au to a thickness of 50 / 200 nm on the top surface of the hydrogen-terminated diamond; removing the sacrificial layer using a potassium iodide / iodine solution before evaporating the ohmic contact layer; and performing an annealing treatment at 800°C for 10 minutes to alloy the Ti / Au metal layer with the hydrogen-terminated diamond, forming the Ti / Au ohmic contact layer.

[0116] Figure 7 This is a schematic diagram of the structure after the aluminum nitride layer is prepared according to an embodiment of the present invention. Figure 7In some embodiments, an aluminum nitride layer is formed on the hydrogen-terminated diamond substrate and the Ti / Au ohmic contact layer, specifically comprising: placing the hydrogen-terminated diamond with the Ti / Au ohmic contact layer into a pulsed laser deposition device, setting the growth temperature to 600°C and the number of laser pulses to 10,000 times, thereby epitaxially growing a 10 nm thick aluminum nitride layer on the surface of the hydrogen-terminated diamond to form a diamond-aluminum nitride heterojunction.

[0117] Figure 8 This is a schematic diagram of the structure after the protective layer is prepared according to an embodiment of the present invention. Figure 8 In some embodiments, growing an Al2O3 protective layer on the aluminum nitride layer includes: using trimethylaluminum (TMA) and water as reaction sources, setting the growth temperature to 300°C, and growing 50nm Al2O3 on the aluminum nitride layer through an atomic layer deposition device to form an Al2O3 protective layer.

[0118] Figure 9 This is a schematic diagram of the structure after the groove is engraved according to the embodiment of the present invention. Figure 9 In some embodiments, etched grooves are formed on the Al2O3 protective layer and the aluminum nitride layer. The etched grooves include gate grooves, source grooves, and drain grooves. For example, a photoresist is coated on the Al2O3 protective layer, and the photoresist within the Ti / Au ohmic contact layer is removed. The exposed Al2O3 protective layer should be smaller than the Ti / Au ohmic contact metal layer. The exposed Al2O3 protective layer and the aluminum nitride layer on the ohmic contact layer that are not covered by the photoresist are removed by a reactive ion etching process to form the source groove and drain groove.

[0119] In some embodiments, after removing the photoresist, photoresist is re-coated on the Al2O3 protective layer, and the photoresist is removed at a specific area between the Ti / Au ohmic contact metal layers to expose a portion of the Al2O3 protective layer; the exposed Al2O3 protective layer is removed by a reactive ion etching process to form a gate groove.

[0120] In some embodiments, a metal layer is grown on the aluminum nitride layer to form a gate electrode, a thickened source electrode, and a thickened drain electrode. For example, Ni / Au is deposited on the upper surface of the aluminum nitride layer at the location of the gate groove to a thickness of 50 / 100 nm. Ni / Au is also deposited on the gate groove and the Ti / Au ohmic contact layer to thicken the electrodes.

[0121] The present invention first prepares a hydrogen-terminated diamond structure with an ohmic contact metal layer, then epitaxially grows an aluminum nitride layer on the surface of the hydrogen-terminated diamond. A protective layer is then directly grown to protect the aluminum nitride layer and the diamond-aluminum nitride heterostructure from subsequent process steps. Finally, a gate metal layer is formed, ultimately resulting in a field-effect transistor. Compared to existing technologies, the present invention helps protect the diamond-aluminum nitride heterostructure, ensuring the optimal performance of the diamond-aluminum nitride heterojunction field-effect transistor device, and has the technical effect of improving the DC and RF performance of the diamond-aluminum nitride heterojunction field-effect transistor.

[0122] An embodiment of the present invention provides a diamond aluminum nitride heterojunction field effect transistor, which is prepared based on the method for preparing a diamond aluminum nitride heterojunction field effect transistor as described in any one of the above.

[0123] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a diamond aluminum nitride heterojunction field effect transistor, characterized in that: include: forming an ohmic contact layer on a surface of a diamond substrate to obtain a wafer having the ohmic contact layer formed thereon; The ohmic contact layer includes a source electrode and a drain electrode isolated from each other; On the surface of the wafer after the ohmic contact layer is prepared, an aluminum nitride layer and a protective layer are sequentially grown; wherein the aluminum nitride layer covering the area between the source electrode and the drain electrode forms a diamond aluminum nitride heterojunction with the diamond substrate; and the protective layer covers the aluminum nitride layer; After growing the protective layer, selectively etching the protective layer in the region between the source electrode and the drain electrode to form a gate groove; wherein the aluminum nitride layer is exposed in the gate groove region; The etched protective layer is used as a mask. Under the cover of the protective layer, a metal layer is grown on the surface of the wafer after the gate groove is prepared. A gate electrode is prepared in the gate groove to obtain a diamond aluminum nitride heterojunction field effect transistor.

2. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 1, wherein: The protective layer is selectively etched in the region between the source electrode and the drain electrode, and before the gate trench is prepared, the following steps are also included: After growing the protective layer, etching the protective layer and the aluminum nitride layer in the source electrode region and the drain electrode region to expose portions of the surfaces of the source electrode and the drain electrode; Accordingly, growing a metal layer on the surface of the wafer after the gate trench is prepared also includes: A metal layer is grown on the surface of the wafer after the gate groove is prepared, and the exposed surfaces of the source electrode and the drain electrode are thickened with electrode metal.

3. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 1, wherein: The material of the protection layer includes aluminum oxide, hafnium dioxide or silicon nitride.

4. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 1, wherein: For each of the source electrode and the drain electrode, a portion of the interface between the ohmic contact layer and the diamond substrate is hydrogen-terminated, and another portion of the interface is oxygen-terminated.

5. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 4, wherein: The step of preparing an ohmic contact layer on the surface of a diamond substrate to obtain a wafer having the ohmic contact layer prepared thereon comprises: Performing hydrogen plasma treatment on the surface of the diamond substrate to obtain a diamond substrate with hydrogen terminals; The surface of the diamond substrate after the hydrogen termination is prepared is subjected to oxygen plasma treatment under the protection of a patterned mask to prepare a patterned oxygen termination, wherein the area covered by the patterned oxygen termination includes a source region and a drain region that are isolated from each other; the portion between the source region and the drain region that is not covered by the oxygen termination is a hydrogen termination; A patterned ohmic contact layer is prepared on the surface of the wafer after patterning the oxygen terminal to obtain a wafer after the ohmic contact layer is prepared, wherein in the patterned ohmic contact layer, the source electrode covers the source region and covers a portion of the hydrogen terminal connected to the source region, and the drain electrode covers the drain region and covers a portion of the hydrogen terminal connected to the drain region.

6. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 5, wherein: The surface of the diamond substrate after the hydrogen termination is prepared is subjected to oxygen plasma treatment under the shielding of a patterned mask to prepare the patterned oxygen termination, which includes: A patterned sacrificial layer is prepared on the surface of the diamond substrate for preparing the hydrogen terminal; the uncovered areas on both sides of the patterned sacrificial layer are the source region and the drain region respectively; Under the shielding of the patterned sacrificial layer, the surface of the diamond substrate not covered by the patterned sacrificial layer is subjected to oxygen plasma treatment to convert hydrogen terminals in the area not covered by the patterned sacrificial layer into oxygen terminals, thereby preparing patterned oxygen terminals; Accordingly, a patterned ohmic contact layer is formed on the wafer surface after the patterned oxygen terminal is formed, including: removing the patterned sacrificial layer to expose the hydrogen terminals covered by the patterned sacrificial layer; After removing the patterned sacrificial layer, a patterned ohmic contact layer is prepared, wherein the patterned ohmic contact layer covers the patterned oxygen terminal and a portion of the hydrogen terminal close to the ohmic contact layer.

7. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 6, wherein: The step of preparing the patterned ohmic contact layer comprises: After removing the patterned sacrificial layer, preparing a patterned photoresist mask, wherein the patterned photoresist mask exposes the patterned oxygen terminal and exposes a portion of the hydrogen terminal close to the ohmic contact layer; A metal layer is grown, and a stripping process is used to remove the metal layer on the patterned photoresist mask to obtain a patterned ohmic contact layer.

8. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 7, wherein: After removing the metal layer on the patterned photoresist mask, the method further includes: The patterned ohmic contact layer is annealed to form an ohmic contact.

9. The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to claim 1, wherein: The material of the ohmic contact layer includes: gold, titanium gold or titanium platinum gold.

10. A diamond aluminum nitride heterojunction field effect transistor, characterized in that: The method for preparing a diamond aluminum nitride heterojunction field effect transistor according to any one of claims 1 to 9 is used for preparing the diamond aluminum nitride heterojunction field effect transistor.

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