Preparation method of low-damage hydrogen terminal diamond

Abstract

The invention discloses a preparation method of a low-damage hydrogen terminal diamond. The preparation method comprises the following steps: providing a diamond substrate; preparing a diamond epitaxial layer on the diamond substrate; pretreating the upper surface of the diamond epitaxial layer; depositing a silicon dioxide film on the pretreated diamond epitaxial layer; annealing the diamond substrate, the diamond epitaxial layer and the silicon dioxide film in vacuum to improve the strength of the silicon dioxide film; processing the diamond substrate, the diamond epitaxial layer and the silicon dioxide thin film by adopting a non-direct contact type hydrotreating mode, forming a carbon-rich film on the upper surface of the silicon dioxide thin film, and forming a hydrogen terminal on the upper surface of the diamond epitaxial layer; and removing the carbon-rich film and the silicon dioxide film to obtain the diamond substrate, the diamond epitaxial layer and the hydrogen terminal on the diamond epitaxial layer. According to the method, the etching damage of atomic hydrogen to the upper surface of the diamond epitaxial layer in the plasma hydrotreating atmosphere is reduced, and the hydrogen terminal diamond surface with lower surface damage is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors, and in particular relates to a method for preparing low-damage hydrogen-terminated diamond. Background Art

[0002] Diamond is an ultra-wide bandgap semiconductor material with excellent properties such as high breakdown electric field, high intrinsic mobility, and high thermal conductivity, making the application of diamond high-voltage and high-power devices in high-temperature and strong radiation environments extremely promising. However, it is difficult to form a conductive channel through body doping of diamond. Both n-type dopants represented by phosphorus and p-type dopants represented by boron have high activation energies and are difficult to activate at room temperature. Currently, the surface of diamond is mainly functionalized by means of surface modification to prepare various terminals, among which hydrogen termination is a very important and relatively mature terminal technology, which is widely used to prepare conductive channels and ohmic contacts for diamond field effect transistors and detection devices.

[0003] Normally, when diamond is directly exposed to hydrogen plasma for a period of time, a surface covered with carbon-hydrogen (CH) bonds is formed on the diamond surface, i.e., a hydrogen-terminated surface. This hydrogen-terminated diamond surface will produce a layer of two-dimensional hole gas (2DHG) when exposed to air. At room temperature, the carrier concentration of 2DHG is usually 10 12 ~10 14 cm -2 Range, Mobility Usually tens to 200 cm 2 / (V•s) range and has good p-type conductivity characteristics. Therefore, direct hydrogenation of diamond to form a hydrogen-terminated diamond surface has become the main method for fabricating diamond power devices with p-type channels. In the prior art, when preparing a hydrogen-terminated diamond, a diamond sample is directly placed into a microwave plasma chemical vapor deposition (MPCVD) apparatus. Using hydrogen as the gas source and during the glow discharge of the microwave plasma, the atomic hydrogen generated after the ionization of hydrogen replaces the carbon-oxygen (C-O) structure on the diamond surface, causing a hydrogen-terminated diamond with a carbon-hydrogen (C-H) structure to form on the surface of the diamond sample. However, during the process of preparing a hydrogen-terminated diamond using an MPCVD apparatus, hydrogen molecules will acquire sufficient energy to dissociate into hydrogen atoms, and the hydrogen atoms directly bombard the diamond surface, inevitably etching the surface of the diamond sample and reducing the crystal quality of the diamond. Therefore, in order to obtain better hydrogen-terminated diamond performance, the plasma direct-contact hydrogenation process requires a trade-off among parameters such as microwave power, pressure, and temperature. Generally, the surface roughness of the diamond obtained by plasma direct-contact hydrogenation treatment is about 1 nm or even larger, resulting in an aggravated carrier scattering behavior and a deteriorated mobility, which is not conducive to p-type conductivity. In addition, in order to avoid an aggravated etching degree on the diamond surface, the hydrogenation treatment temperature usually does not exceed 850 °C. Since the bond enthalpy of C-H is larger than that of C-O, a higher hydrogenation temperature should be used to remove the residual C-O bonds on the diamond surface, thereby increasing the coverage rate of C-H bonds.

[0004] Therefore, the hydrogenation treatment is a core process step in the fabrication process of diamond field-effect transistors and detection devices. How to reduce the damage to the diamond surface during the hydrogenation treatment step while obtaining a hydrogen-terminated diamond sample with a high C-H bond coverage rate has become the basis and key technical node for obtaining high-performance diamond devices. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a method for preparing a low-damage hydrogen-terminated diamond. The technical problems to be solved by the present invention are achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing a low-damage hydrogen-terminated diamond, including: providing a diamond substrate; epitaxially growing a diamond layer on the upper surface of the diamond substrate to prepare a diamond epitaxial layer; irradiating the surface of the diamond epitaxial layer with ozone for pretreatment; depositing a silicon dioxide film on the upper surface of the pretreated diamond epitaxial layer; annealing the diamond substrate, the diamond epitaxial layer, and the silicon dioxide film in a vacuum to improve the strength of the silicon dioxide film; A non-direct contact hydrogenation treatment method is adopted to treat a diamond substrate, a diamond epitaxial layer, and a silicon dioxide thin film, forming a carbon-rich film on the upper surface of the silicon dioxide thin film and forming hydrogen termination on the upper surface of the diamond epitaxial layer; The carbon-rich film and the silicon dioxide thin film are removed to prepare a diamond substrate, a diamond epitaxial layer, and hydrogen termination on the diamond epitaxial layer.

[0006] Advantages of the present invention: A method for preparing low-damage hydrogen-terminated diamond provided by the present invention adopts a non-direct contact hydrogenation treatment method. The surface of the diamond epitaxial layer is not directly exposed to the plasma environment, reducing the etching damage of atomic hydrogen in the plasma atmosphere to the upper surface of the diamond epitaxial layer, obtaining a diamond surface with lower surface damage, improving the surface conductivity of the hydrogen-terminated diamond, thereby preparing higher-quality hydrogen-terminated diamond and higher-performance diamond field-effect transistors and detection devices, which is of great significance for the development of high-performance diamond devices.

[0007] The present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0008] Figure 1 is a flowchart of a method for preparing low-damage hydrogen-terminated diamond provided by an embodiment of the present invention; Figure 2 is a schematic diagram of the structure of hydrogen-terminated diamond provided by an embodiment of the present invention; Figure 3 is a schematic diagram of a hydrogen-terminated diamond field-effect transistor provided by an embodiment of the present invention; Figure 4 is a schematic diagram of the XPS test results of low-damage hydrogen-terminated diamond by non-direct contact hydrogenation treatment provided by an embodiment of the present invention; Figure 5 is a schematic diagram of the AFM test results of low-damage hydrogen-terminated diamond by non-direct contact hydrogenation treatment provided by an embodiment of the present invention; Figure 6 is a schematic diagram of the output characteristic curve of a depletion-type hydrogen-terminated diamond field-effect transistor prepared from low-damage hydrogen-terminated diamond by non-direct contact hydrogenation treatment provided by an embodiment of the present invention; Figure 7 is a schematic diagram of the transfer characteristic curve of a depletion-type hydrogen-terminated diamond field-effect transistor prepared from low-damage hydrogen-terminated diamond by non-direct contact hydrogenation treatment provided by an embodiment of the present invention. Detailed Embodiments

[0009] The present invention will be further described in detail below with reference to specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0010] Please refer to Figures 1 - 2 , Figure 1 which is a flowchart of a method for preparing low-damage hydrogen-terminated diamond provided by an embodiment of the present invention, Figure 2 and is a schematic diagram of the hydrogen-terminated diamond structure provided by an embodiment of the present invention. A method for preparing low-damage hydrogen-terminated diamond provided by the present invention includes: S101. Provide a diamond substrate 10.

[0011] Specifically, in this embodiment, the diamond substrate 10 is a Ib-type (001)-oriented single-crystal diamond substrate with a size of 3×3×0.5 mm 3 .

[0012] S102. Epitaxially grow a diamond layer on the upper surface of the diamond substrate 10 to prepare a diamond epitaxial layer 20.

[0013] Specifically, in this embodiment, a microwave plasma chemical vapor deposition method is used to prepare an undoped diamond layer with a thickness of 400-600 nm on the upper surface of the diamond substrate 10 to prepare the diamond epitaxial layer 20. Optionally, the thickness of the diamond epitaxial layer 20 is 500 nm.

[0014] Next, the diamond substrate 10 and the diamond epitaxial layer 20 are treated with hot mixed acid, organic cleaning, etc.

[0015] S103. Pre-treat the surface of the diamond epitaxial layer 20 by irradiating it with ozone.

[0016] Specifically, in this embodiment, the upper surface of the diamond epitaxial layer 20 is irradiated with ultraviolet ozone. The purpose is to treat and form an oxygen-terminated diamond surface, which can increase the adhesion of the subsequent deposited silicon dioxide film 40, and at the same time facilitate the subsequent non-direct-contact hydrogenation treatment to convert the upper surface of the diamond epitaxial layer 20 into a hydrogen termination 30.

[0017] S104. Deposit a silicon dioxide film 40 on the upper surface of the pre-treated diamond epitaxial layer 20.

[0018] Specifically, in this embodiment, a plasma-enhanced chemical vapor deposition process is used to deposit a silicon dioxide film 40 on the upper surface of the pre-treated diamond epitaxial layer 20.

[0019] The thickness of the silicon dioxide film 40 is 280-320 nm. Optionally, the thickness of the silicon dioxide film 40 is 300 nm.

[0020] The purpose of depositing the silicon dioxide film 40 in this embodiment is to isolate the diamond epitaxial layer 20 from the plasma environment and protect the upper surface of the diamond epitaxial layer 20 from being etched.

[0021] S105. Anneal the diamond substrate 10, diamond epitaxial layer 20, and silicon dioxide thin film 40 in a vacuum to improve the strength of the silicon dioxide thin film 40.

[0022] S106. Treat the diamond substrate 10, diamond epitaxial layer 20, and silicon dioxide thin film 40 by means of non - direct - contact hydrogenation treatment to form a carbon - rich film 50 on the upper surface of the silicon dioxide thin film 40 and a hydrogen termination 30 on the upper surface of the diamond epitaxial layer 20.

[0023] Specifically, in this embodiment, the non - direct - contact hydrogenation treatment means transferring the diamond sample with the deposited silicon dioxide thin film 40 to an MPCVD apparatus and treating it under the conditions for synthesizing diamond (gas sources: H2 and CH4). During the MPCVD process at high temperature, carbon - containing derivatives derived from CH4 accumulate on the upper surface of the silicon dioxide thin film 40 and gradually form a carbon - rich film 50. The presence of the carbon - rich film 50 can reduce the etching effect of the plasma on the silicon dioxide thin film 40. As a sacrificial layer for the non - direct - contact hydrogenation process, the structure formed by the carbon - rich layer / silicon dioxide film layer protects the diamond surface from direct plasma etching, significantly reducing the surface damage of the diamond. At the same time, the atomic size of hydrogen is very small and can penetrate any insulating film, enabling atomic hydrogen to penetrate the carbon - rich film 50 and the silicon dioxide thin film 40 to form a hydrogen termination 30 on the upper surface of the diamond epitaxial layer 20. In addition, the protective effect of the silicon dioxide thin film 40 allows the hydrogenation process to be carried out at a higher reaction temperature (1000 °C), which can effectively remove the oxygen - termination structure on the diamond surface, resulting in a higher hydrogen coverage rate on the diamond surface; it can be understood that enabling the hydrogenation to be carried out at a higher reaction temperature increases the C - H bond coverage rate and effectively enhances the conductivity of the hydrogen - terminated diamond surface.

[0024] S107. Remove the carbon - rich film 50 and the silicon dioxide thin film 40 to prepare the diamond substrate 10, diamond epitaxial layer 20, and the hydrogen termination 30 on the diamond epitaxial layer 20.

[0025] Specifically, in this embodiment, a wet etching method is used to remove the silicon dioxide thin film 40 and the carbon - rich film 50 above it with a hydrofluoric acid solution to obtain a hydrogen - terminated diamond surface with a high C - H bond coverage rate and low surface damage.

[0026] It can be understood that the hydrogen - terminated diamond 30 is disposed on the upper surface of the diamond epitaxial layer, and a two - dimensional hole gas channel is formed below the C - H structure of the hydrogen - terminated diamond 30.

[0027] In summary, the method for preparing a low-damage hydrogen-terminated diamond provided by the present invention adopts a non-direct-contact hydrogenation treatment method, in which the surface of the diamond epitaxial layer 20 is not directly exposed to the plasma environment, reducing the etching damage of atomic hydrogen in the plasma atmosphere to the upper surface of the diamond epitaxial layer 20, obtaining a diamond surface with lower surface damage, improving the surface conductivity of the hydrogen-terminated diamond, thereby preparing a higher-quality hydrogen-terminated diamond and a higher-performance diamond field-effect transistor and detection device, which is of great significance for the development of high-performance diamond devices.

[0028] In an optional embodiment of the present invention, please refer to Figure 3 , Figure 3 which is a schematic diagram of a hydrogen-terminated diamond field-effect transistor provided by an embodiment of the present invention. The hydrogen-terminated diamond field-effect transistor prepared by using the low-damage hydrogen-terminated diamond structure prepared in the above embodiment includes: Ib-type (001) crystal orientation diamond substrate 1, homoepitaxial diamond layer 2, P-type heavily doped diamond 3, source electrode 4, drain electrode 5, gate electrode 6, alumina 7, hydrogen-terminated diamond 8. The device adopts a stacked gate structure, and the length of the channel of the hydrogen-terminated diamond 8 L C-H is 4 μm, and the length of the gate electrode 6 L G is equal to the length of the source electrode 4 L S and the length of the drain electrode 5 L D , all of which are 4 μm. The length of the gate electrode 6 located above the P-type heavily doped diamond L D = L S = L G , all of which are 2 μm. L OV is 2 μm.

[0029] Please refer to Figure 4 and Figure 5 , Figure 4 which is a schematic diagram of the XPS test results of the low-damage hydrogen-terminated diamond prepared by non-direct-contact hydrogenation treatment provided by an embodiment of the present invention. Figure 4 In Figure 5It is a schematic diagram of the AFM test results of the low-damage hydrogen-terminated diamond by non-direct-contact hydrogenation treatment provided by an embodiment of the present invention. Thanks to the carbon-rich film 50 / silicon dioxide thin film 40 / diamond structure formed by the non-direct-contact hydrogenation treatment proposed by the present invention, the hydrogenation treatment can be carried out at a higher reaction temperature. The XPS test results show that the oxygen-terminated structure on the diamond surface has been completely removed, leaving a small amount of silicon-terminated structure (composition C3: C-Si structure; composition C4: C-Si-O structure), and the main component on the diamond surface is the hydrogen-terminated structure (composition C2). The AFM test results show that the average surface roughness Ra of the prepared hydrogen-terminated diamond is 0.38 nm, indicating its extremely high surface smoothness. The results of the above two tests can effectively show that the non-direct-contact hydrogenation treatment method proposed by the present invention can effectively reduce the etching damage caused during the hydrogenation treatment and effectively improve the C-H bond coverage rate on the diamond surface.

[0030] Please refer to Figure 6 and Figure 7 , Figure 6 It is a schematic diagram of the output characteristic curve of the depletion-mode hydrogen-terminated diamond field-effect transistor prepared from the low-damage hydrogen-terminated diamond by non-direct-contact hydrogenation treatment provided by an embodiment of the present invention. Figure 7 It is a schematic diagram of the transfer characteristic curve of the depletion-mode hydrogen-terminated diamond field-effect transistor prepared from the low-damage hydrogen-terminated diamond by non-direct-contact hydrogenation treatment provided by an embodiment of the present invention. The maximum output current I DMAX of the device reaches -1034 mA / mm, the threshold voltage is 4.7 V, and the hole mobility μ calculated for this field-effect transistor is 2 V -1 s -1 . This further shows that the non-direct-contact hydrogenation process proposed by the present invention can effectively improve the surface conductance characteristics of the hydrogen-terminated diamond.

[0031] In summary, a low-damage hydrogen-terminated diamond preparation process proposed by the present invention can be used to prepare a smooth hydrogen-terminated diamond surface with a high hole mobility at high temperatures. The XPS results show that the C-H bond coverage rate on the diamond surface is very high. The (001) diamond MOSFET prepared by using a low-damage diamond hydrogenation process of non-direct-contact hydrogenation treatment proposed by the present invention achieves a high output current density greater than 1 A / mm. These results indicate that the low-damage diamond hydrogenation process of non-direct-contact hydrogenation treatment proposed by the present invention has great potential in manufacturing diamond field-effect transistors and detection devices based on (001) diamond substrates.

[0032] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant are intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the article or device comprising said element. Similar words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The orientation or positional relationship indicated by "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0033] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0034] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing low-damage hydrogen-terminated diamond, characterized in that: include: providing a diamond substrate; epitaxially growing a diamond layer on the upper surface of the diamond substrate to prepare a diamond epitaxial layer; irradiating the surface of the diamond epitaxial layer with ozone for pretreatment; Depositing a silicon dioxide film on the upper surface of the pretreated diamond epitaxial layer; Annealing the diamond substrate, the diamond epitaxial layer and the silicon dioxide film in a vacuum to improve the strength of the silicon dioxide film; The diamond substrate, the diamond epitaxial layer and the silicon dioxide film are treated by a non-direct contact hydrogenation treatment method to form a carbon-rich film on the upper surface of the silicon dioxide film and a hydrogen terminal on the upper surface of the diamond epitaxial layer; The carbon-rich film and the silicon dioxide film are removed to prepare the diamond substrate, the diamond epitaxial layer and the hydrogen termination on the diamond epitaxial layer.

2. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The indirect contact hydrogenation treatment method is used to treat the diamond substrate, the diamond epitaxial layer and the silicon dioxide film, to form a carbon-rich film on the upper surface of the silicon dioxide film, and to form a hydrogen terminal on the upper surface of the diamond epitaxial layer, including: The diamond substrate, the diamond epitaxial layer and the silicon dioxide film are placed in a microwave plasma chemical vapor deposition device, and in an atmosphere of H2 and CH4, carbon-containing derivatives are accumulated on the upper surface of the silicon dioxide film layer to form the carbon-rich film. At the same time, atomic hydrogen penetrates the carbon-rich film and the silicon dioxide film to form a hydrogen terminal on the upper surface of the diamond epitaxial layer.

3. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The removing of the carbon-rich film and the silicon dioxide film comprises: The carbon-rich film and the silicon dioxide film are removed by a wet etching method using a hydrofluoric acid solution.

4. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The step of depositing a silicon dioxide film on the upper surface of the pre-treated diamond epitaxial layer comprises: A silicon dioxide film is deposited on the upper surface of the pretreated diamond epitaxial layer by using a plasma enhanced chemical vapor deposition process.

5. The method for preparing low-damage hydrogen-terminated diamond according to claim 4, characterized in that: The thickness of the silicon dioxide film is 280-320 nm.

6. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The method of irradiating the surface of the diamond epitaxial layer with ozone for pretreatment comprises: The upper surface of the diamond epitaxial layer is irradiated with ultraviolet ozone to increase the adhesion of the deposited silicon dioxide film.

7. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The thickness of the diamond epitaxial layer is 400-600 nm.

8. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The diamond epitaxial layer is a non-doped diamond layer.

9. The method for preparing low-damage hydrogen-terminated diamond according to claim 1, characterized in that: The diamond substrate is 3×3×0.5 mm 3 Type Ib single crystal diamond substrate.

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