Diamond field effect transistor and preparation method thereof

Abstract

The invention provides a diamond field effect transistor and a preparation method thereof, and relates to the technical field of diamond field effect transistors. According to the method, the patterned hydrogen terminal can be prepared on the diamond substrate, and the Van der Waals dielectric layer covers the patterned hydrogen terminal, so that ionization impurity scattering of a hydrogen terminal interface is reduced, and the performance of a diamond device is improved. Meanwhile, after the patterned hydrogen terminal is prepared and before the Van der Waals dielectric layer is covered, source and drain electrodes are prepared in the source and drain regions in advance. The pre-prepared source and drain electrodes cover the diamond interface of the source and drain regions, so that the interface pollution to the source and drain regions when the Van der Waals dielectric layer is subsequently transferred is avoided, and the ohmic contact resistance of the source and drain electrodes can be reduced.

Description

Technical Field

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

[0002] A diamond field-effect transistor (DFET) is a field-effect transistor based on diamond material. Two-dimensional vacancies formed based on a hydrogen-terminated structure are a common method for achieving electrical conductivity in diamond devices. Hydrogen-terminated diamond can undergo charge transfer with gas molecules in the air, high-work-function materials, and other materials in contact with it, achieving "transfer doping" and forming two-dimensional vacancies on the lower surface of the diamond. However, the performance of hydrogen-terminated diamond devices is easily affected by the surrounding environment. The main factor affecting the performance of hydrogen-terminated diamond devices is the scattering of ionized impurities near the interface between the hydrogen-terminated diamond and the dielectric layer. The naturally dangling-bond-free van der Waals layered material h-BN can effectively reduce the interface defect density.

[0003] Currently, the fabrication method for diamond field-effect transistors (FETs) with van der Waals dielectric layers typically involves using a transfer table to transfer pre-prepared van der Waals material to a target location on a diamond substrate, using the van der Waals dielectric material as the gate dielectric. Source, drain, and gate electrodes are then fabricated to create the FET. However, the ohmic contact resistance of the source and drain electrodes of FETs fabricated using existing methods is relatively high. Summary of the Invention

[0004] An embodiment of the present invention provides a diamond field effect transistor and a method for manufacturing the same, so as to solve the problem of large ohmic contact resistance of source and drain electrodes of a diamond field effect transistor having a van der Waals dielectric layer.

[0005] In a first aspect, an embodiment of the present invention provides a method for preparing a diamond field-effect transistor, comprising: preparing a patterned hydrogen terminal covering a channel region on the upper surface of a diamond substrate; the left side of the channel region is a source region, and the right side is a drain region; after obtaining the patterned hydrogen terminal, preparing a first source electrode layer and a first drain electrode layer; the vertical projection of the first source electrode layer covers the source region, and the vertical projection of the first drain electrode layer covers the drain region; after obtaining the first source electrode layer and the first drain electrode layer, covering the channel region with a van der Waals dielectric layer; the vertical projection of the van der Waals dielectric layer covers the patterned hydrogen terminal; preparing a gate electrode on the van der Waals dielectric layer to obtain a diamond field-effect transistor.

[0006] In one possible implementation, the preparation of a patterned hydrogen terminal covering the channel region on the upper surface of the diamond substrate includes: sequentially preparing a hydrogen terminal and a sacrificial layer on the upper surface of the diamond substrate; after the sacrificial layer is prepared, removing the sacrificial layer outside the channel region to prepare a patterned sacrificial layer covering the channel region; and under the shielding of the patterned sacrificial layer, removing the hydrogen terminal outside the channel region to prepare a patterned hydrogen terminal covering the channel region.

[0007] In one possible implementation, before the channel region is covered with the van der Waals dielectric layer, the process further includes: after obtaining the first source electrode layer and the first drain electrode layer, preparing a second source electrode layer and a second drain electrode layer; wherein the thickness of the second source electrode layer is less than that of the first source electrode layer, and the thickness of the second drain electrode layer is less than that of the first drain electrode layer; the right side portion of the second source electrode layer covers the left side portion of the patterned hydrogen terminal in the channel region, and the left side portion covers the first source electrode layer; the left side portion of the second drain electrode layer covers the right side portion of the patterned hydrogen terminal in the channel region, and the right side portion covers the first drain electrode layer.

[0008] In a possible implementation, before forming the first source electrode layer and the first drain electrode layer, the method further includes: forming oxygen terminals on the exposed surface of the diamond substrate in the source region and the drain region outside the patterned hydrogen terminals;

[0009] Correspondingly, the preparation of the first source electrode layer and the first drain electrode layer includes: preparing the first source electrode layer on the oxygen terminal of the source region; and preparing the first drain electrode layer on the oxygen terminal of the drain region.

[0010] In one possible implementation, covering the channel region with a van der Waals dielectric layer includes: covering the surface of the patterned hydrogen terminal not covered by the second source electrode layer and the second drain electrode layer, as well as the surface of the second source electrode layer located in the channel region and the surface of the second drain electrode layer located in the channel region with the van der Waals dielectric layer; wherein the thickness of the second source electrode layer and the second drain electrode layer are both less than the thickness of the van der Waals dielectric layer.

[0011] In a possible implementation, the thickness of the second source electrode layer and the second drain electrode layer is no more than 10 nanometers.

[0012] In one possible implementation, preparing a gate electrode on the van der Waals dielectric layer includes: growing a metal oxide dielectric layer after covering the channel region with the van der Waals dielectric layer; and after growing the metal oxide dielectric layer, growing metal on the metal oxide dielectric layer in the channel region to prepare the gate electrode.

[0013] In a possible implementation, after growing the metal oxide dielectric layer, the method further includes: etching and removing the metal oxide dielectric layer in the source region and the drain region to form a source groove and a drain groove;

[0014] Correspondingly, after growing the metal oxide dielectric layer, the method further includes: growing metal on the metal oxide dielectric layer in the channel region to prepare a gate electrode, while growing metal in the source groove and the drain groove to prepare a third source electrode layer and a third drain electrode layer.

[0015] In a possible implementation, the material of the van der Waals dielectric layer includes a layered material or an inorganic molecular crystal material.

[0016] In a second aspect, an embodiment of the present invention provides a diamond field effect transistor, which is prepared based on the method for preparing a diamond field effect transistor as described in any one of the first aspects.

[0017] An embodiment of the present invention provides a diamond field-effect transistor and a method for fabricating the same. By forming a patterned hydrogen termination on a diamond substrate and covering the patterned hydrogen termination with a van der Waals dielectric layer, ionized impurity scattering at the hydrogen termination interface is reduced, thereby improving diamond device performance. Furthermore, after forming the patterned hydrogen termination and before covering the van der Waals dielectric layer, source and drain electrodes are prefabricated in the source and drain regions. These prefabricated source and drain electrodes cover the diamond interface in the source and drain regions, preventing contamination of the source and drain regions during the subsequent transfer of the van der Waals dielectric layer, thereby reducing the ohmic contact resistance of the source and drain electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flowchart of a method for preparing a diamond field-effect transistor according to an embodiment of the present invention;

[0019] Figure 2 1 is a schematic structural diagram of a diamond field-effect transistor provided by an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the structure after preparing the hydrogen terminal and sacrificial layer provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic structural diagram of a patterned hydrogen terminal after preparation according to an embodiment of the present invention;

[0022] Figure 5 is a schematic structural diagram after preparing the first source-drain electrode layer provided by an embodiment of the present invention;

[0023] Figure 6 is a schematic structural diagram after preparing the second source-drain electrode layer provided by an embodiment of the present invention;

[0024] Figure 7 1 is a schematic structural diagram after preparing a van der Waals dielectric layer according to an embodiment of the present invention;

[0025] Figure 8This is a schematic structural diagram of a metal oxide dielectric layer after preparation according to an embodiment of the present invention;

[0026] Figure 9 It is a schematic diagram of the structure after the source groove and the drain groove are prepared according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] The following is a detailed description of the implementation of the present invention with reference to the accompanying drawings:

[0030] Diamond-based field-effect transistors have the characteristics of high frequency and high power, and can be used in 5G / 6G base stations and satellite communications, microwave and millimeter wave systems, medical equipment, aerospace and other fields.

[0031] Van der Waals dielectric materials are often used as the gate dielectric layer of diamond field-effect transistors. Transferring them to the hydrogen-terminated diamond surface through methods such as van der Waals pickup transfer can significantly improve device parameters such as the mobility of diamond field-effect transistors, thanks to the excellent surface and dielectric properties of the van der Waals dielectric layer. When the van der Waals dielectric material is transferred to the surface of the diamond substrate, dielectric material contamination is inevitably introduced at the source and drain electrodes, adversely affecting electrode quality and device performance testing. For example, contamination of the source and drain electrodes and the diamond interface by the van der Waals dielectric material increases the ohmic contact resistance of the source and drain electrodes of the diamond field-effect transistor.

[0032] In the embodiment of the present invention, after preparing the patterned hydrogen terminal, the source and drain electrodes are first prepared, and then the van der Waals dielectric layer is prepared, thereby avoiding interface contamination of the source and drain regions during subsequent transfer of the van der Waals dielectric layer, thereby reducing the ohmic contact resistance of the source and drain electrodes.

[0033] Figure 1 A flowchart of a method for preparing a diamond field effect transistor according to an embodiment of the present invention. Figure 1 ,include:

[0034] Step 101: Prepare a patterned hydrogen terminal covering a channel region on the upper surface of a diamond substrate; the left side of the channel region is a source region, and the right side is a drain region;

[0035] Diamond is a material with excellent physical and chemical properties, such as high hardness, high thermal conductivity, wide band gap, and high carrier mobility.

[0036] Exemplarily, the side of the diamond substrate on which the device structure is prepared is the upper surface.

[0037] Field-effect transistors typically include a source electrode, a drain electrode, a gate electrode, and a conductive channel. The channel region is the area between the source and drain electrodes in a field-effect transistor and serves as a channel for carrier (electron or hole) transmission. With the channel region as a reference, the left side is defined as the source region, which is the area where carriers (such as electrons or holes) are injected; the right side is defined as the drain region, which is the area where carriers flow out. In a complete field-effect transistor structure, the source, drain, and channel regions work together to achieve functions such as current conduction and cutoff through gate control.

[0038] Exemplarily, the patterned hydrogen termination covers the channel region. Areas outside the channel region are not covered with hydrogen termination. For example, the entire surface of the diamond substrate in the channel region is hydrogen terminated. Hydrogen termination refers to the state where the diamond surface is covered with hydrogen atoms, which can alter the electrical properties of the diamond surface. The following describes a method for preparing the patterned hydrogen termination.

[0039] In one possible implementation, the step of preparing a patterned hydrogen terminal covering the channel region on the upper surface of the diamond substrate includes:

[0040] Step 1011: sequentially preparing a hydrogen terminal and a sacrificial layer on the upper surface of the diamond substrate;

[0041] First, hydrogen termination is performed, covering the diamond surface with hydrogen atoms. A sacrificial layer is then deposited on top of the hydrogen-terminated surface. A sacrificial layer is an intermediate layer that is removed during subsequent processing, typically to protect certain areas or to serve as a foundation for subsequent patterning operations.

[0042] Step 1012: After the sacrificial layer is prepared, the sacrificial layer outside the channel region is removed to obtain a patterned sacrificial layer covering the channel region;

[0043] The sacrificial layer is removed from areas outside the channel region through specific process methods, such as photolithography and etching. The channel region is the key area for carrier transmission in the field-effect transistor, and only the sacrificial layer covering the channel region remains.

[0044] Step 1013: Under the shielding of the patterned sacrificial layer, remove the hydrogen termination outside the channel region to obtain a patterned hydrogen termination covering the channel region.

[0045] Under the shielding of the patterned sacrificial layer, the patterned sacrificial layer covering the channel region provides protection, preventing the hydrogen terminations in the channel region from being damaged during subsequent operations. Exemplarily, an oxygen plasma process is used to remove the hydrogen terminations in areas outside the channel region. Protected by the patterned sacrificial layer, the hydrogen terminations in the channel region are preserved. Ultimately, the desired structure is achieved, where only the channel region is covered by the hydrogen terminations, while the hydrogen terminations in other areas are removed, resulting in a patterned hydrogen termination covering the channel region.

[0046] For example, the sacrificial layer on the hydrogen-terminated diamond can be removed by wet etching.

[0047] Step 102: After the patterned hydrogen terminal is obtained, a first source electrode layer and a first drain electrode layer are prepared; a vertical projection of the first source electrode layer covers the source region, and a vertical projection of the first drain electrode layer covers the drain region;

[0048] It should be noted that in the present application, the source and drain electrodes are prepared in multiple times. In this step, the first layer, namely the first source electrode layer and the first drain electrode layer, is prepared. The first source electrode layer and the first drain electrode layer are also patterned and cover part of the area. For example, the vertical projection of the first source electrode layer covers the source region, and the vertical projection of the first drain electrode layer covers the drain region. Here, the first source electrode layer can completely cover the source region or only cover part of the source region. The first drain electrode layer can completely cover the drain region or only cover part of the drain region. As a result, the first source electrode layer and the first drain electrode layer do not cover the channel region, and may even be separated from the channel region by a certain distance.

[0049] It should also be noted that the first source electrode layer and the first drain electrode layer need to have a certain thickness to withstand probe testing and subsequent wire bonding processes. For example, the first source electrode layer and the first drain electrode layer are prepared to form ohmic contacts; after annealing to achieve ohmic contacts, contact resistance testing is usually required during the manufacturing process, usually by piercing the electrode layers with a probe.

[0050] In addition, in the subsequent steps, after covering the gate dielectric layer, ICP etching of source and drain electrode grooves is required at the source and drain electrode positions. The first electrode layer needs to have a certain thickness to ensure that the ICP etching does not completely etch the electrode.

[0051] Step 103: After obtaining the first source electrode layer and the first drain electrode layer, covering the channel region with a van der Waals dielectric layer; a vertical projection of the van der Waals dielectric layer covers the patterned hydrogen terminal;

[0052] Exemplarily, the material of the van der Waals dielectric layer includes a layered material or an inorganic molecular crystal material. For example, if the van der Waals dielectric material is a layered material, the van der Waals dielectric material can be applied to the hydrogen termination region between the source and drain electrodes using a dry transfer method. If the van der Waals dielectric material is an inorganic molecular crystal material, the van der Waals dielectric layer can be formed using a thermal evaporation method.

[0053] Exemplarily, the van der Waals layered material includes h-BN, Bi2SeO5, etc. When the selected van der Waals layered material is h-BN, plasma treatment can be used after the dry transfer.

[0054] Exemplarily, the thickness of the van der Waals dielectric material ranges from 1 nm to 500 nm.

[0055] A van der Waals dielectric layer is a material with special properties that interacts with other materials based on van der Waals forces. The purpose of covering this dielectric layer is usually to improve the electrical performance of the channel region, reduce interface scattering, and enhance device stability.

[0056] The vertical projection of the van der Waals dielectric layer represents the projection of the van der Waals dielectric layer in the vertical direction, viewed from above. The vertical projection of the van der Waals dielectric layer covering the channel region must completely overlap the previously prepared patterned hydrogen termination. This positional relationship ensures sufficient contact and interaction between the van der Waals dielectric layer and the patterned hydrogen termination, thereby achieving the intended functions, such as further reducing ionized impurity scattering at the hydrogen termination interface and improving device mobility.

[0057] Step 104: Prepare a gate electrode on the van der Waals dielectric layer to obtain a diamond field effect transistor.

[0058] For example, a gate electrode may be manufactured on the van der Waals dielectric layer by using specific process methods, such as photolithography, metal deposition, lift-off, and the like.

[0059] The gate electrode is a key component of a field-effect transistor (FET). Its primary function is to control the conductivity of the channel region by applying a voltage. When different voltages are applied to the gate electrode, an electric field is generated between the gate electrode and the channel. This electric field affects the concentration and distribution of carriers (electrons or holes) within the channel, thereby controlling the on and off states of the transistor.

[0060] After a series of steps, including forming a patterned hydrogen termination on a diamond substrate, forming the first source and drain electrode layers, covering with a van der Waals dielectric layer, and forming a gate electrode on the van der Waals dielectric layer, the diamond field-effect transistor with a van der Waals gate dielectric layer is finally fabricated. At this point, the device has the basic structure of a source, drain, gate, and a diamond channel region.

[0061] The present invention utilizes a patterned hydrogen termination on a diamond substrate and covers it with a van der Waals dielectric layer, thereby reducing ionized impurity scattering at the hydrogen termination interface and improving diamond device performance. Furthermore, after forming the patterned hydrogen termination and before covering it with the van der Waals dielectric layer, source and drain electrodes are prefabricated in the source and drain regions. These prefabricated source and drain electrodes cover the diamond interface in the source and drain regions, preventing contamination of the source and drain regions during subsequent transfer of the van der Waals dielectric layer, thereby reducing the ohmic contact resistance of the source and drain electrodes.

[0062] The present invention alleviates the interface contamination problem between hydrogen-terminated diamond and van der Waals dielectrics caused by existing processes, ensures the performance of device electrodes, and has the technical effect of reducing the interface state density of diamond field-effect transistors and improving the DC and RF performance of the device.

[0063] The following describes how to prepare the second source electrode layer and the second drain electrode layer to improve the adhesion of the source and drain electrodes and reduce the contact resistance.

[0064] In one possible implementation, before the channel region is covered with the van der Waals dielectric layer, the process further includes: after obtaining the first source electrode layer and the first drain electrode layer, preparing a second source electrode layer and a second drain electrode layer; wherein the thickness of the second source electrode layer is less than that of the first source electrode layer, and the thickness of the second drain electrode layer is less than that of the first drain electrode layer; the right side portion of the second source electrode layer covers the left side portion of the patterned hydrogen terminal in the channel region, and the left side portion covers the first source electrode layer; the left side portion of the second drain electrode layer covers the right side portion of the patterned hydrogen terminal in the channel region, and the right side portion covers the first drain electrode layer.

[0065] Exemplarily, the thickness of the second source electrode layer and the second drain electrode layer is no more than 10 nanometers.

[0066] It should be noted that, from bottom to top, the channel region is provided with a patterned hydrogen terminal and a van der Waals dielectric layer.

[0067] The structure is illustrated by taking the second source electrode layer as an example. Exemplarily, the right portion of the second source electrode layer covers the left portion of the patterned hydrogen terminal in the channel region, and the left portion covers the first source electrode layer. That is, the second source electrode layer not only covers the first source electrode layer, but also extends to the channel region, extending to between the van der Waals dielectric layer and the patterned hydrogen terminal. In terms of the upper and lower order of the layers, the patterned hydrogen terminal, the second source electrode layer and the van der Waals dielectric layer are arranged from bottom to top. It should be noted that in order to maximize the mobility, the van der Waals dielectric layer covers the entire patterned hydrogen terminal, and here the second source electrode layer has to cover a portion of the patterned hydrogen terminal. Therefore, the van der Waals dielectric layer needs to cover a portion of the second source electrode layer. It should also be noted that although a portion of the second source electrode layer and the second drain electrode layer are both arranged on the patterned hydrogen terminal and in the channel region, the two are isolated from each other and not connected to each other.

[0068] Take the second source electrode layer as an example to illustrate its role. A portion of the second source electrode layer is arranged on the hydrogen terminal in the channel region, which can reduce the ohmic contact resistance of the source electrode. Another portion of the second source electrode layer is arranged on the first source electrode layer in the source region. The interface between the second source electrode layer and the first source electrode layer is metal-to-metal contact, and the interface adhesion is good. The contact interface between the first source electrode layer and the diamond substrate avoids contamination of the van der Waals dielectric layer, and the adhesion is also improved. As a result, the adhesion of the source electrode portion in the source region is ensured, and the contact between the source electrode and the hydrogen terminal reduces the contact resistance. The structure and working principle of the first drain electrode layer and the second drain electrode layer are similar to those of the above-mentioned source electrode.

[0069] The following describes electrode layer thickness settings. Taking the second source electrode layer as an example, the second source electrode layer is thinner than the first source electrode layer. That is, the first source electrode layer is thicker and the second source electrode layer is thinner. This allows the thicker first source electrode layer to withstand probe testing, while the thinner second source electrode layer has smaller edge steps, making it easier for subsequent materials to cover the second source electrode layer.

[0070] In one possible implementation, before preparing the first source electrode layer and the first drain electrode layer, the process further includes: preparing oxygen terminals on the exposed surface of the diamond substrate in the source region and the drain region outside the patterned hydrogen terminals; correspondingly, preparing the first source electrode layer and the first drain electrode layer includes: preparing the first source electrode layer on the oxygen terminal in the source region; and preparing the first drain electrode layer on the oxygen terminal in the drain region.

[0071] For example, the exposed surface of the diamond substrate may be subjected to oxygen plasma treatment under the shielding of the sacrificial layer, thereby forming oxygen terminations in the portion not covered by the sacrificial layer and patterned hydrogen terminations in the portion covered by the sacrificial layer.

[0072] In this embodiment of the present invention, oxygen terminations are formed in the source and drain regions during the process of forming patterned hydrogen terminations. This improves electrode adhesion during the fabrication of the first source and drain electrode layers. Consequently, after the fabrication of the second source and drain electrode layers, adhesion can be improved in one portion of the source electrode while contact resistance is reduced in another portion. Furthermore, adhesion can be improved in one portion of the drain electrode while contact resistance is reduced in another portion.

[0073] In one possible implementation, covering the channel region with a van der Waals dielectric layer includes: covering the surface of the patterned hydrogen terminal not covered by the second source electrode layer and the second drain electrode layer, as well as the surface of the second source electrode layer located in the channel region and the surface of the second drain electrode layer located in the channel region with the van der Waals dielectric layer; wherein the thickness of the second source electrode layer and the second drain electrode layer are both less than the thickness of the van der Waals dielectric layer.

[0074] The following describes the electrode layer thickness setting. Taking the second source electrode layer as an example, the thickness of the second source electrode layer is less than that of the first source electrode layer, and the thickness of the second source electrode layer is less than that of the van der Waals dielectric layer. That is, the first source electrode layer is thicker and the second source electrode layer is thinner. The weak van der Waals interaction between the van der Waals layered material and the hydrogen-terminated diamond makes it easy for solvent molecules involved in the process to enter the interface, affecting the performance of the hydrogen-terminated diamond device. As a result, the thicker first source electrode layer can withstand probe testing; the thinner second source electrode layer has a smaller edge step, and when the van der Waals dielectric layer is covered on the second source electrode layer, it can ensure that the van der Waals dielectric layer is well covered, reducing gaps, thereby preventing the solution from invading under the van der Waals dielectric layer in subsequent process steps.

[0075] Due to the poor surface adhesion, the van der Waals dielectric layer is easily eroded by the solution and falls off, and is also easily fallen off by external force.

[0076] In one possible implementation, preparing a gate electrode on the van der Waals dielectric layer includes: growing a metal oxide dielectric layer after covering the channel region with the van der Waals dielectric layer; and after growing the metal oxide dielectric layer, growing metal on the metal oxide dielectric layer in the channel region to prepare the gate electrode.

[0077] For example, the metal oxide dielectric layer may be a high dielectric constant metal oxide dielectric layer, such as Al2O3, HfO2, etc.

[0078] Exemplarily, the thickness of the high dielectric constant metal oxide dielectric material ranges from 1 nm to 500 nm.

[0079] Exemplarily, the high dielectric constant metal oxide dielectric material is grown by atomic layer deposition.

[0080] For example, when the van der Waals dielectric material is a van der Waals layered material, an annealing treatment needs to be performed in the chamber of an atomic layer deposition device before growing the metal oxide dielectric material.

[0081] Exemplarily, preparing the gate electrode includes: depositing a gate metal to form the gate metal layer, and performing lift-off to form the gate electrode.

[0082] The embodiments of the present invention grow a metal oxide dielectric layer immediately after forming a van der Waals dielectric layer. On the one hand, the metal oxide dielectric layer serves as a gate dielectric, forming a double-layer gate dielectric with the van der Waals dielectric layer, thereby improving carrier mobility. On the other hand, the metal oxide dielectric layer covers the van der Waals dielectric layer, preventing subsequent process steps from invading the lower surface of the van der Waals dielectric layer, reducing damage to the van der Waals dielectric adhesion interface, and preventing external forces from directly acting on the upper surface of the van der Waals dielectric layer, further improving the adhesion and reliability of the van der Waals dielectric layer.

[0083] In a possible implementation, after growing the metal oxide dielectric layer, the method further includes: etching and removing the metal oxide dielectric layer in the source region and the drain region to form a source groove and a drain groove;

[0084] Correspondingly, after growing the metal oxide dielectric layer, the method further includes: growing metal on the metal oxide dielectric layer in the channel region to prepare a gate electrode, while growing metal in the source groove and the drain groove to prepare a third source electrode layer and a third drain electrode layer.

[0085] In some embodiments, a combination of wet etching and dry etching is used to etch the source trench and the drain trench, thereby exposing the electrode region to be contacted by the probe.

[0086] By etching source and drain grooves in the metal oxide dielectric layer, the embodiment of the present invention can simultaneously grow metal in the source and drain grooves when subsequently growing the gate electrode metal, thereby thickening the source and drain electrodes again. While improving the reliability of the source and drain electrodes, it not only saves metal materials but also simplifies the process steps. In addition, taking the source electrode as an example, because the first source electrode layer or the second source electrode layer is provided below the source groove, hard damage to the ohmic contact interface can be avoided during etching, thereby ensuring the contact resistance of the device.

[0087] The present invention is described below with a comprehensive embodiment.

[0088] Figure 2 is a schematic structural diagram of a diamond field effect transistor provided by an embodiment of the present invention; Figure 2An embodiment of the present invention provides a diamond field effect transistor with a double-layer gate dielectric structure, comprising a diamond substrate, a patterned hydrogen terminal, a first source electrode layer, a first drain electrode layer, a second source electrode layer, a second drain electrode layer, a van der Waals dielectric layer, a metal oxide dielectric layer, and a gate electrode. The patterned hydrogen terminal is formed on the upper surface of the diamond substrate; the first source electrode layer and the first drain electrode layer are formed on the upper surface of the diamond substrate, and a sufficient distance is maintained between the first source electrode layer and the first drain electrode layer; the second source electrode layer and the second drain electrode layer are above the patterned hydrogen terminal and the first source electrode layer and the first drain electrode layer. There is a certain gap between the second source electrode layer and the second drain electrode layer, which serves as a conductive channel; the van der Waals dielectric layer is above the patterned hydrogen terminal and the second source electrode layer and the second drain electrode layer, and the van der Waals dielectric layer can partially cover the second source electrode layer and the second drain electrode layer; the metal oxide dielectric layer covers the diamond substrate, the second source electrode layer, the second drain electrode layer, and the van der Waals dielectric layer; and the gate electrode is on the upper surface of the metal oxide dielectric layer.

[0089] Compared with the prior art, the diamond field-effect transistor with a double-layer gate dielectric structure provided by an embodiment of the present invention has the following advantages: the introduction of a first source electrode layer and a first drain electrode layer provides sufficient barriers for the subsequent removal of the van der Waals dielectric layer remaining in the source trench and the drain trench, avoids etching to the diamond substrate, ensures the interface quality of the source and drain electrodes, and improves the quality of the metal electrode; the second source electrode layer and the second drain electrode layer ensure the interface quality between the van der Waals dielectric layer and the hydrogen terminal, and has the technical effect of reducing the interface state density of the diamond field-effect transistor and improving the DC and RF performance of the device.

[0090] An embodiment of the present invention provides a method for preparing a diamond field-effect transistor having a double-layer gate dielectric structure, comprising:

[0091] Step 1: Forming a patterned hydrogen terminal on a diamond substrate.

[0092] Figure 3 This is a schematic diagram of the structure after preparing the hydrogen terminal and sacrificial layer provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the patterned hydrogen terminal provided in an embodiment of the present invention; Figure 3 、 Figure 4 In some embodiments, forming a patterned hydrogen termination on a diamond substrate comprises:

[0093] 1.1. A hydrogen-terminated diamond substrate was formed on a single-crystal diamond substrate using microwave plasma chemical vapor deposition equipment in a hydrogen plasma environment. The growth temperature was set to 650°C, the power was set to 1700W, and the time was set to 10 minutes.

[0094] 1.2. Using electron beam evaporation, metal Au was evaporated on the hydrogen-terminated diamond as a sacrificial layer with a thickness of 60 nm.

[0095] 1.3. Perform photolithography on the Au sacrificial layer, using photoresist as a mask. Remove the areas not covered by the photoresist with a potassium iodide / iodine solution wet etch. Place the Au sacrificial layer in a plasma etchant, and use oxygen plasma to remove the hydrogen termination areas not protected by the photoresist, achieving mesa isolation and forming patterned hydrogen terminations. Set the power to 120W and the etching time to 6 minutes.

[0096] Step 2: Form a first source electrode layer, a first drain electrode layer, and a second source electrode layer and a second drain electrode layer on the hydrogen-terminated diamond. The first source electrode layer and the first drain electrode layer are thick and spaced apart, not covering the patterned hydrogen terminal. The second source electrode layer and the second drain electrode layer are thin and spaced apart, partially covering the first source electrode layer, the first drain electrode layer, and the patterned hydrogen terminal. The space between the second source electrode layer and the second drain electrode layer serves as a conductive path.

[0097] Figure 5 is a schematic structural diagram after preparing the first source-drain electrode layer provided by an embodiment of the present invention; Figure 6 is a schematic structural diagram after preparing the second source-drain electrode layer according to an embodiment of the present invention; Figure 5 、 Figure 6 In some embodiments, a first source electrode layer, a first drain electrode layer, a second source electrode layer, and a second drain electrode layer are sequentially formed on the hydrogen-terminated diamond, including:

[0098] 2.1. Evaporating Ti / Pt with a thickness of 20 / 10 nm on the upper surface of the diamond substrate to prepare a first source electrode layer and a first drain electrode layer;

[0099] 2.2. Use potassium iodide / iodine solution to remove the sacrificial layer;

[0100] 2.3. Evaporating Ti / Pt with a thickness of 5 / 5 nm to prepare the second source electrode layer and the second drain electrode layer;

[0101] 2.4. Perform an annealing process to alloy the first source electrode layer, the first drain electrode layer, the second source electrode layer, and the second drain electrode layer with the hydrogen-terminated diamond to form ohmic contacts. Set the annealing temperature to 850° C. and the duration to 10 minutes.

[0102] Step 3: Form a van der Waals dielectric layer on the hydrogen-terminated diamond and the second source electrode layer and the second drain electrode layer. The van der Waals dielectric layer must completely cover the conductive path between the second source electrode layer and the second drain electrode layer, and must partially cover the second source electrode layer and the second drain electrode layer.

[0103] Figure 7is a schematic diagram of the structure after preparing the van der Waals dielectric layer provided in an embodiment of the present invention; Figure 7 In some embodiments, a Bi2SeO5 van der Waals dielectric layer is formed on the hydrogen-terminated diamond and the second source electrode layer and the second drain electrode layer, including: transferring the Bi2SeO5 van der Waals dielectric layer that can completely cover the conductive channel to a specific position of the hydrogen-terminated diamond by dry transfer, and partially covering the second source electrode layer and the second drain electrode layer, with a thickness of 10 nm.

[0104] Step 4: directly forming a metal oxide dielectric layer after the van der Waals dielectric layer is introduced;

[0105] Figure 8 is a schematic diagram of the structure after the metal oxide dielectric layer is prepared according to an embodiment of the present invention; Figure 8 In some embodiments, forming an Al2O3 high dielectric constant metal oxide dielectric layer on the upper surface of the diamond substrate, the Bi2SeO5 van der Waals dielectric layer, the second source electrode layer, and the second drain electrode layer includes:

[0106] 4.1. Place the transferred hydrogen-terminated diamond with Bi2SeO5 van der Waals dielectric layer into the atomic layer deposition chamber at 300°C for 3 hours.

[0107] 4.2. Using trimethylaluminum and water as reaction sources, set the growth temperature to 300°C, and use an atomic layer deposition device to form an Al2O3 high dielectric constant metal oxide dielectric layer with a thickness of 120 nm on the hydrogen-terminated diamond with a Bi2SeO5 van der Waals dielectric layer.

[0108] Step 5: Etch the metal oxide dielectric layer in the areas corresponding to the second source electrode layer and the second drain electrode layer to form source grooves and drain grooves.

[0109] Figure 9 This is a schematic diagram of the structure after the source groove and drain groove are prepared according to an embodiment of the present invention. Figure 9 In some embodiments, forming a source trench and a drain trench on the Al2O3 high-k metal oxide dielectric layer includes:

[0110] 5.1. Coat photoresist on the Al2O3 high-k metal oxide dielectric layer and remove the photoresist within the area of the first source electrode layer and the first drain electrode layer. The area of the Al2O3 high-k metal oxide dielectric layer not covered by the photoresist should be smaller than the area of the first source electrode layer and the first drain electrode layer.

[0111] 5.2. Etch the Al2O3 high dielectric constant metal oxide dielectric layer and the Bi2SeO5 van der Waals dielectric layer that falls on the second source electrode layer and the second drain electrode layer during the dry transfer process by inductively coupled plasma etching.

[0112] Step 6: forming a gate electrode on the high-k metal oxide dielectric layer, and forming a third source electrode layer and a third drain electrode layer in the source trench and the drain trench.

[0113] In some embodiments, forming a gate electrode on the high-k metal oxide dielectric layer, and forming a third source electrode layer and a third drain electrode layer in the source trench and the drain trench include:

[0114] 6.1. Deposit a Ti / Au gate metal layer on the upper surface of the Al2O3 high-k dielectric layer at a specific location in the conductive path between the second source electrode layer and the second drain electrode layer to form a gate electrode. The thickness is 20 / 200 nm.

[0115] 6.2. A Ti / Au gate metal layer is simultaneously deposited in the source trench, the drain trench, and on the second source electrode layer and the second drain electrode layer to obtain a third source electrode layer and a third drain electrode layer for thickening the electrode.

[0116] The method for preparing a diamond field-effect transistor provided by the present invention has the following beneficial effects: compared with the prior art, the method for preparing a diamond field-effect transistor provided by the present invention comprises forming a hydrogen terminal on a diamond substrate; sequentially forming a pre-thickened first source electrode layer, a first drain electrode layer, a second source electrode layer, and a second drain electrode layer on the hydrogen-terminated diamond; forming a van der Waals dielectric layer on the second source electrode layer, the second drain electrode layer, and the hydrogen-terminated diamond; forming a high-dielectric-constant metal oxide dielectric layer on the upper surface of the diamond substrate, the van der Waals dielectric layer, and the second source electrode layer and the second drain electrode layer; forming a source trench and a drain trench on the high-dielectric-constant metal oxide dielectric layer; and growing a gate metal layer on the high-dielectric-constant metal oxide dielectric layer, the source trench, and the drain trench to form a gate electrode and a third source electrode layer and a third drain electrode layer.

[0117] The diamond field-effect transistor and preparation method provided by the present invention improve the interface contamination problem between the hydrogen-terminated diamond and the van der Waals gate dielectric layer during the process, improve the quality of the metal electrode, and have the technical effect of reducing the interface state density of the diamond field-effect transistor and improving the DC and RF performance of the device.

[0118] An embodiment of the present invention provides a diamond field-effect transistor, which is prepared based on the method for preparing a diamond field-effect transistor as described in any one of the above items.

[0119] 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 field effect transistor, characterized in that: include: A patterned hydrogen terminal covering a channel region is formed on the upper surface of the diamond substrate; the left side of the channel region is a source region, and the right side is a drain region; After the patterned hydrogen terminal is obtained, a first source electrode layer and a first drain electrode layer are prepared; a vertical projection of the first source electrode layer covers the source region, and a vertical projection of the first drain electrode layer covers the drain region; After the first source electrode layer and the first drain electrode layer are formed, a van der Waals dielectric layer is formed in the channel region; a vertical projection of the van der Waals dielectric layer covers the patterned hydrogen terminal; A gate electrode is prepared on the van der Waals dielectric layer to obtain a diamond field effect transistor.

2. The method for preparing a diamond field effect transistor according to claim 1, wherein: The step of preparing a patterned hydrogen terminal covering the channel region on the upper surface of the diamond substrate comprises: A hydrogen termination layer and a sacrificial layer are sequentially prepared on the upper surface of the diamond substrate; After the sacrificial layer is prepared, the sacrificial layer outside the channel region is removed to obtain a patterned sacrificial layer covering the channel region; Under the shielding of the patterned sacrificial layer, the hydrogen termination outside the channel region is removed to obtain a patterned hydrogen termination covering the channel region.

3. The method for preparing a diamond field effect transistor according to claim 1, wherein: Before the channel region is covered with the van der Waals dielectric layer, it also includes: After obtaining the first source electrode layer and the first drain electrode layer, a second source electrode layer and a second drain electrode layer are prepared; wherein the thickness of the second source electrode layer is less than that of the first source electrode layer, and the thickness of the second drain electrode layer is less than that of the first drain electrode layer; the right side of the second source electrode layer covers the left side of the patterned hydrogen terminal in the channel region, and the left side covers the first source electrode layer; the left side of the second drain electrode layer covers the right side of the patterned hydrogen terminal in the channel region, and the right side covers the first drain electrode layer.

4. The method for preparing a diamond field effect transistor according to claim 3, wherein: Before preparing the first source electrode layer and the first drain electrode layer, the method further includes: Oxygen terminations are prepared on the exposed surface of the diamond substrate in the source and drain regions outside the patterned hydrogen terminations; Accordingly, the step of preparing the first source electrode layer and the first drain electrode layer includes: A first source electrode layer is prepared on the oxygen terminal of the source region; and a first drain electrode layer is prepared on the oxygen terminal of the drain region.

5. The method for preparing a diamond field effect transistor according to claim 3, wherein: The van der Waals dielectric layer covering the channel region includes: A van der Waals dielectric layer is covered on the surface of the patterned hydrogen terminal not covered by the second source electrode layer and the second drain electrode layer, as well as on the surface of the second source electrode layer in the channel region and the surface of the second drain electrode layer in the channel region; wherein the thickness of the second source electrode layer and the second drain electrode layer are both less than the thickness of the van der Waals dielectric layer.

6. The method for preparing a diamond field effect transistor according to claim 3, wherein: The thickness of the second source electrode layer and the second drain electrode layer is no more than 10 nanometers.

7. The method for preparing a diamond field effect transistor according to claim 1, wherein: The gate electrode is formed on the van der Waals dielectric layer, comprising: After the channel region is covered with a van der Waals dielectric layer, a metal oxide dielectric layer is grown; After growing the metal oxide dielectric layer, metal is grown on the metal oxide dielectric layer in the channel region to prepare a gate electrode.

8. The method for preparing a diamond field effect transistor according to claim 7, wherein: After growing the metal oxide dielectric layer, the following steps are also included: Etching and removing the metal oxide dielectric layer in the source region and the drain region to obtain a source groove and a drain groove; Accordingly, after growing the metal oxide dielectric layer, the following steps are also included: While growing metal on the metal oxide dielectric layer in the channel region to prepare a gate electrode, metal is grown in the source groove and the drain groove to prepare a third source electrode layer and a third drain electrode layer.

9. The method for preparing a diamond field effect transistor according to claim 1, wherein: The material of the van der Waals dielectric layer includes layered material or inorganic molecular crystal material.

10. A diamond field effect transistor, characterized in that: The diamond field effect transistor is prepared according to the preparation method of any one of claims 1 to 9.

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