6-inch high thermal conductivity doped diamond wafer and method of making same

Abstract

The application discloses a 6-inch high-thermal-conductivity doped diamond wafer and a preparation method thereof, and relates to the technical field of diamond wafer preparation, in particular to a 6-inch high-thermal-conductivity doped diamond wafer and a preparation method thereof. In the application, in view of the problems that the existing 6-inch diamond wafer is prone to uneven doping in the center and the edge, surface impurity adsorption and the influence of a doped enrichment layer on surface quality in doping epitaxial growth, a cavity cover, a reaction cavity, a rotary carrier, a 6-inch single-crystal diamond seed crystal, an exhaust pipeline, a vacuum pump, a microwave generator, a gas input pipeline and a methane, hydrogen, phosphine, nitrogen and argon gas source are arranged, phosphorus-nitrogen composite doping epitaxial growth is carried out through microwave plasma CVD, and segmented argon cleaning, ion beam etching and chemical mechanical polishing are cooperated to obtain a 6-inch doped diamond wafer which is uniform in doping, low in surface roughness, and has high thermal conductivity and certain electrical conductivity.

Description

Technical Field

[0001] This invention relates to the field of diamond wafer fabrication technology, specifically to a 6-inch high thermal conductivity doped diamond wafer and its fabrication method. Background Technology

[0002] With the rapid development of high-power semiconductor devices, radio frequency devices, power modules, and high-performance chips, the heat flux density during device operation continues to increase, making heat dissipation capacity a crucial factor affecting device stability, lifespan, and power output. Diamond, with its high thermal conductivity, good chemical stability, and high mechanical strength, is considered an excellent thermal management material for high heat flux density devices. To better adapt diamond wafers to the heat sink, substrate, and packaging integration requirements of semiconductor devices, current technologies typically employ chemical vapor deposition (CVD) to prepare diamond wafers, introducing dopant gases during the growth process to obtain doped diamond wafers that possess both thermal conductivity and certain electrical properties.

[0003] Existing doped diamond wafers still have shortcomings in large-size fabrication. On the one hand, during the fabrication of 6-inch diamond wafers, differences in gas concentration, plasma distribution, and deposition environment within the reaction chamber can easily arise between the central and edge regions of the wafer, leading to uneven distribution of doped elements and consequently affecting the overall consistency of thermal conductivity and resistivity. On the other hand, during long-term CVD epitaxial growth, impurities are easily adsorbed on the wafer surface, forming a doped enrichment layer. If subsequent processing is insufficient, this can easily cause surface defects, high roughness, and unstable surface quality, thus affecting the reliability and compatibility of doped diamond wafers when used as heat sinks or substrates for high-power devices. Summary of the Invention

[0004] To achieve the above objectives, the present invention provides a technical solution: a 6-inch high thermal conductivity doped diamond wafer, a reaction chamber sealed to the lower side of the cavity cover, a rotating carrier rotatably connected to the lower side of the reaction chamber, a 6-inch single crystal diamond seed crystal placed on the upper side of the rotating carrier, an exhaust pipe connected to the lower side of the reaction chamber, and a vacuum pump connected to the lower end of the exhaust pipe; a microwave transmission pipe connected to the upper side of the cavity cover, a microwave generator connected to the end of the microwave transmission pipe away from the cavity cover, a gas input pipe connected to the left side of the reaction chamber, the gas input pipe communicating with the interior of the reaction chamber, and methane, hydrogen, phosphine, nitrogen, and argon gas sources respectively connected to the left side of the gas input pipe.

[0005] Furthermore, the cavity cover is disposed on the upper side of the reaction chamber, and a sealed connection is formed between the cavity cover and the reaction chamber. One end of the microwave transmission pipeline passes through the cavity cover and communicates with the interior of the reaction chamber. The microwave generator is connected to the reaction chamber through the microwave transmission pipeline.

[0006] Furthermore, the rotating carrier is located inside the lower side of the reaction chamber, and the rotating carrier is rotated along the vertical axis. The 6-inch single-crystal diamond seed is placed horizontally on the upper side of the rotating carrier, and the 6-inch single-crystal diamond seed is located below the microwave transmission pipeline.

[0007] Furthermore, the methane gas source, hydrogen gas source, phosphine gas source, nitrogen gas source, and argon gas source are arranged sequentially along the vertical direction on one side of the gas input pipeline. The methane gas source, hydrogen gas source, phosphine gas source, nitrogen gas source, and argon gas source are all connected to the gas input pipeline, and the end of the gas input pipeline away from each gas source is connected to the interior of the reaction chamber.

[0008] This invention also provides a technical solution: a 6-inch high thermal conductivity doped diamond wafer and its preparation method, comprising the following steps: S1: Seed crystal preparation: Select a 6-inch monocrystalline diamond seed crystal, and polish and clean the 6-inch monocrystalline diamond seed crystal; S2: Doped Epitaxial Growth: The treated 6-inch single-crystal diamond seed crystal is placed on the upper side of the rotating carrier. Methane, hydrogen, phosphine and nitrogen are introduced into the reaction chamber through methane, hydrogen, phosphine and nitrogen gas sources. Microwave energy is input into the reaction chamber through a microwave generator to make the surface of the 6-inch single-crystal diamond seed crystal undergo phosphorus-nitrogen composite doped CVD epitaxial growth. S3: Impurity control: During the phosphorus-nitrogen composite doped CVD epitaxial growth process, argon gas is introduced into the reaction chamber through an argon gas source to perform segmented cleaning of the growth surface. S4: Post-processing: Ion beam etching is performed on the grown doped diamond wafer, and then chemical mechanical polishing is performed on the etched doped diamond wafer to obtain a 6-inch high thermal conductivity doped diamond wafer.

[0009] Furthermore, the 6-inch single-crystal diamond seed crystal of S1 is a (100) crystal orientation single-crystal diamond seed crystal, the surface roughness Ra of the 6-inch single-crystal diamond seed crystal after polishing is ≤0.2nm, and the cleaning treatment is plasma cleaning.

[0010] Furthermore, the volume fraction of methane in S2 is 2-3%, the molar ratio of phosphine to methane is 0.5-2%, the molar ratio of nitrogen to methane is 0.2-0.8%, the phosphine is used to introduce phosphorus dopant into the doped diamond wafer, and the nitrogen is used to introduce nitrogen dopant into the doped diamond wafer.

[0011] Furthermore, the growth temperature of the phosphorus-nitrogen composite doped CVD epitaxial growth of S2 is 900-1000℃, the deposition pressure is 100-150 Torr, the microwave power is 8-12kW, the growth time is 30-45h, and the rotation speed of the rotating carrier is 5-10r / min.

[0012] Furthermore, in step S3, argon gas is introduced every 8 hours for plasma cleaning, with each cleaning session lasting 5 minutes.

[0013] Furthermore, in step S4, a 5-10 μm doped enrichment layer on the surface of the doped diamond wafer is removed by ion beam etching, and the surface roughness Ra of the doped diamond wafer is reduced to ≤0.4 nm by chemical mechanical polishing.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a rotating carrier within a reaction chamber, placing a 6-inch single-crystal diamond seed crystal on top of the carrier. This allows the 6-inch single-crystal diamond seed crystal to rotate along a vertical axis during phosphorus-nitrogen composite doping CVD epitaxial growth. This ensures more uniform contact between the wafer's central and edge regions and the reaction atmosphere formed by methane, hydrogen, phosphine, and nitrogen, reducing doping inhomogeneity caused by localized differences in gas concentration and plasma distribution within the reaction chamber. By combining this structure and method, the uniformity of phosphorus and nitrogen dopant distribution within the 6-inch diamond wafer can be improved, resulting in doped diamond wafers with more consistent thermal and electrical properties across different regions. This, in turn, enhances their stability when used as heat sinks or substrates for high-power devices.

[0015] This invention utilizes an argon gas source on one side of the gas input pipeline and introduces argon gas into the reaction chamber in stages during the phosphorus-nitrogen composite doping CVD epitaxial growth process to clean the growth surface. This reduces the adsorption and abnormal enrichment of impurities on the wafer surface during long-term epitaxial growth. Simultaneously, after epitaxial growth is completed, the doped enriched layer on the surface of the doped diamond wafer is first removed by ion beam etching, and then the wafer surface quality is improved by chemical mechanical polishing. This reduces the surface roughness of the wafer and minimizes the adverse effects of surface defects on subsequent packaging, bonding, and device integration. As a result, the fabricated 6-inch high thermal conductivity doped diamond wafer has better surface quality and application adaptability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the interior of the 6-inch high thermal conductivity doped diamond of this invention; Figure 3This is a schematic diagram of the overall process of the present invention.

[0017] In the diagram: 1. Chamber cover; 2. Reaction chamber; 3. Rotating carrier; 4. 6-inch single-crystal diamond seed crystal; 5. Exhaust pipe; 6. Vacuum pump; 7. Microwave generator; 8. Gas input pipe; 81. Methane; 82. Hydrogen; 83. Phosphine; 84. Nitrogen; 85. Argon. Detailed Implementation

[0018] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed merely to enable those skilled in the art to better understand and implement the subject matter described herein, and are not intended to limit the scope, applicability, or examples set forth in the claims. The function and arrangement of the elements discussed may be changed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the various examples. For example, the described methods may be performed in a different order than described, and steps may be added, omitted, or combined. Furthermore, features described in some examples may be combined in other examples.

[0019] As used herein, the term "comprising" and its variations are open terms meaning "including but not limited to". The term "based on" means "at least partially based on". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other definitions, whether explicit or implicit, may be included below. Unless explicitly indicated by the context, the definition of a term shall remain consistent throughout the specification.

[0020] Example Please see Figure 1-3 The present invention provides a technical solution: A 6-inch high thermal conductivity doped diamond wafer is used. A reaction chamber is sealed and connected to the lower side of the cavity cover. A rotating carrier is rotatably connected to the lower side of the reaction chamber. A 6-inch single crystal diamond seed is placed on the upper side of the rotating carrier. An exhaust pipe is connected to the lower side of the reaction chamber, and a vacuum pump is connected to the lower end of the exhaust pipe. A microwave transmission pipe is connected to the upper side of the cavity cover. A microwave generator is connected to the end of the microwave transmission pipe away from the cavity cover. A gas input pipe is connected to the left side of the reaction chamber and is connected to the interior of the reaction chamber. A methane gas source, a hydrogen gas source, a phosphine gas source, a nitrogen gas source, and an argon gas source are respectively connected to the left side of the gas input pipe.

[0021] Cavity cover: Located at the top of the reaction chamber, it is sealed to the reaction chamber using a stainless steel flange and vacuum O-ring to ensure a high vacuum environment. The cavity cover integrates microwave transmission pipeline interfaces and sealing valves, allowing the microwave generator to be connected to the cavity via a waveguide for microwave energy input; at the same time, the cavity cover can monitor the internal status of the cavity through interfaces such as vacuum gauges and viewing windows.

[0022] The reaction chamber is a hollow metal container and serves as the main cavity for CVD growth. Both the upper and lower ends of the chamber are flanged: the upper end is sealed to the chamber cover, the side wall has a gas inlet flange, and the bottom has an exhaust flange. The inner wall of the reaction chamber is polished or coated to reduce impurity deposition. A plasma region is formed inside the chamber: when microwaves and gas are introduced, a stable plasma is generated at the top of the chamber to drive diamond crystal growth.

[0023] Rotating Carrier: Installed in the lower part of the reaction chamber, it is connected to an external drive motor via a vacuum shaft, enabling rotation along the vertical axis. The rotating carrier is made of ceramic or metal and is resistant to plasma bombardment. A 6-inch single-crystal diamond seed crystal is placed on top of it and secured by fastening clamps or mechanical clamps. The rotation of the carrier keeps the seed crystal in motion during growth, thereby improving the regional uniformity of the wafer. The rotational seal between the rotating carrier and the chamber can be achieved using mechanically sealed bearings or a vacuum magnetic coupling structure.

[0024] 6-inch single-crystal diamond seed crystal: placed horizontally on a rotating carrier. The seed crystal is a (100) oriented diamond wafer, 6 inches in diameter and 400–800 μm thick, with a surface that has been precision polished and plasma cleaned to ensure growth quality.

[0025] Gas input pipeline: Connected to the side wall of the reaction chamber via flanges or quick-connect fittings, entering the chamber interior. The gas input pipeline connects to the following gas sources via a multi-way valve system: methane, hydrogen, phosphine, nitrogen, and argon. Each gas source is connected to the pipeline via a high-precision mass flow controller and safety valve, achieving precise proportioning and flow control of carrier gases such as methane and hydrogen, as well as PH3 and N2 dopant gases. The pipeline has a good connection with the internal channels of the chamber, and sealing methods include welding or flanges and gaskets to ensure no leakage.

[0026] Exhaust piping and vacuum pump: An exhaust piping is installed at the bottom of the reaction chamber, with a vacuum pump connected to the lower end of the piping. The vacuum system can be a combination of an oil-lubricated rotary vane pump and a molecular pump, or an oil-free turbopump system. The vacuum pump reduces the base pressure within the chamber to the required deposition pressure and continuously exhausts waste gas. The exhaust piping should be connected to a fire damper and a tail gas purification device for dust and harmful gas treatment.

[0027] Microwave generator and matching system: A 2.45 GHz high-power microwave generator with an output power range of 8–12 kW is used. Microwaves are coupled into the reaction cavity through a transmission waveguide. The matching system is used to optimize the standing wave distribution in the cavity to ensure plasma stability. The microwave generator and power supply equipment must be anti-reflective and have automatic protection functions.

[0028] This invention also provides a technical solution: a 6-inch high thermal conductivity doped diamond wafer and its preparation method, comprising the following steps: S1: Seed crystal preparation: Select a 6-inch monocrystalline diamond seed crystal, and polish and clean the 6-inch monocrystalline diamond seed crystal; A 6-inch (100) crystal-oriented single-crystal diamond seed crystal (4) was selected as the epitaxial growth substrate. The seed crystal was subjected to precision chemical mechanical polishing to ensure a surface roughness Ra≤0.2. nm; then the surface is cleaned using argon ion plasma or O2 plasma to remove organic contaminants and micron-sized impurities. After polishing and cleaning, the seed crystal is placed horizontally on a rotating carrier and the chamber cover is closed to form a sealed reaction chamber.

[0029] S2: Doped Epitaxial Growth: The treated 6-inch single-crystal diamond seed crystal is placed on the upper side of the rotating carrier. Methane, hydrogen, phosphine and nitrogen are introduced into the reaction chamber through methane, hydrogen, phosphine and nitrogen gas sources. Microwave energy is input into the reaction chamber through a microwave generator to make the surface of the 6-inch single-crystal diamond seed crystal undergo phosphorus-nitrogen composite doped CVD epitaxial growth. Turn on the vacuum pump and exhaust line to evacuate the reaction chamber to a vacuum, then introduce high-purity hydrogen and stabilize to the target pressure. Introduce methane, hydrogen, phosphine, and nitrogen into the chamber using a mass flow controller to create the reaction atmosphere. Set the proportions as follows: methane volume fraction 2.0–3.0%, phosphine to methane molar ratio 0.5%–2.0%, nitrogen to methane molar ratio 0.2%–0.8%. For example, a mixture of 1000 sccm of hydrogen, 25 sccm of methane (2.5%), approximately 0.25 sccm of pH3 (pH3 / CH4=1%), and approximately 12.5 sccm of N2 (N2 / CH4=0.5%) can be used. At this point, a microwave generator sends microwaves to the chamber at a power of 8–12 kW to create a stable plasma. Rotate the rotating carrier at 5–10 r / min to continuously rotate the seed crystal. Maintain the growth temperature at 900–1000℃ for 30–45 hours. During this process, the reaction atmosphere is kept uniformly applied to the entire wafer surface by rotating the seed crystal, thereby achieving simultaneous phosphorus doping and nitrogen doping.

[0030] S3: Impurity control: During the phosphorus-nitrogen composite doped CVD epitaxial growth process, argon gas is introduced into the reaction chamber through an argon gas source to perform segmented cleaning of the growth surface. During epitaxial growth, to suppress the accumulation of organic or metallic impurities on the wafer surface, Ar is introduced into the cavity for 5 minutes every 8 hours for plasma cleaning. Specifically, the PH3 and N2 channels are temporarily shut off, leaving only Ar and H2 to form plasma for cleaning the wafer surface. Ar cleaning removes residual impurities and unstable hydrocarbons from the surface, keeping the grown surface clean and stable. Studies have indicated that PH3 is a highly toxic gas with an explosion limit of only 1.79%, therefore its concentration must be strictly controlled and rapidly diluted; using diluted gas is safer. Throughout the growth process, the cavity pressure, temperature, and current are continuously monitored to ensure the plasma remains stable and does not extinguish.

[0031] S4: Post-processing: Ion beam etching is performed on the grown doped diamond wafer, and then chemical mechanical polishing is performed on the etched doped diamond wafer to obtain a 6-inch high thermal conductivity doped diamond wafer.

[0032] After growth is complete, all gas sources and microwaves are shut off, and the reaction chamber is slowly cooled to room temperature. The grown 6-inch doped diamond wafer is then removed, and its surface is subjected to further processing: first, ion beam etching is used to remove 5–10% of the surface surface. A doped enrichment layer or surface damage layer of μm is formed, followed by chemical mechanical polishing to obtain a mirror-smooth surface. The polishing goal is to achieve a double-sided roughness Ra ≤ 0.4 on the wafer. nm is selected to ensure its suitability as a heat sink or substrate for devices. After the above processing, the final 6-inch high thermal conductivity phosphorus-nitrogen co-doped diamond wafer is obtained.

[0033] Those skilled in the art will understand that the various embodiments disclosed above can be modified and altered in various ways without departing from the spirit of the invention. Therefore, the scope of protection of this invention should be defined by the appended claims.

[0034] It should be noted that not all steps and units in the above processes are necessary; some steps or units can be omitted as needed. The execution order of each step is not fixed and can be determined as required. The device structure described in the above embodiments can be a physical structure or a logical structure. That is, some units may be implemented by the same physical entity, or some units may be implemented by multiple physical entities, or they may be jointly implemented by certain components in multiple independent devices.

[0035] The specific embodiments described above are exemplary embodiments, but do not represent all embodiments that can be implemented or fall within the scope of the claims. The term "exemplary" as used throughout this specification means "serving as an example, instance, or illustration" and does not imply that it is "preferred" or "advantageous" compared to other embodiments. Specific details are included to provide an understanding of the described techniques. However, these techniques can be practiced without these specific details. In some instances, well-known structures and apparatuses are shown in block diagram form to avoid obscuring the concepts of the described embodiments.

[0036] The foregoing description of this disclosure is provided to enable any person skilled in the art to implement or use this disclosure. Various modifications to this disclosure will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but is consistent with the widest scope of the principles and novel features disclosed herein.

Claims

A 1.6-inch high thermal conductivity doped diamond wafer, including a cavity cap (1), characterized in that: The lower side of the cavity cover (1) is sealed to the reaction chamber (2). The lower side of the inside of the reaction chamber (2) is rotatably connected to the rotating carrier (3). A 6-inch single crystal diamond seed crystal (4) is placed on the upper side of the rotating carrier (3). The lower side of the reaction chamber (2) is connected to the exhaust pipe (5). The lower end of the exhaust pipe (5) is connected to the vacuum pump (6). The upper side of the cavity cover (1) is connected to the microwave transmission pipe. The end of the microwave transmission pipe away from the cavity cover (1) is connected to the microwave generator (7). The left side of the reaction chamber (2) is connected to the gas input pipe (8). The gas input pipe (8) is connected to the inside of the reaction chamber (2). The left side of the gas input pipe (8) is connected to the methane gas source (81), the hydrogen gas source (82), the phosphine gas source (83), the nitrogen gas source (84), and the argon gas source (85).

2. The 6-inch high thermal conductivity doped diamond wafer according to claim 1, characterized in that: The cavity cover (1) is placed on the upper side of the reaction chamber (2), and a sealed connection is formed between the cavity cover (1) and the reaction chamber (2). One end of the microwave transmission pipeline passes through the cavity cover (1) and communicates with the inside of the reaction chamber (2). The microwave generator (7) is connected to the reaction chamber (2) through the microwave transmission pipeline.

3. The 6-inch high thermal conductivity doped diamond wafer according to claim 1, characterized in that: The rotating carrier (3) is located inside the reaction chamber (2) on the lower side. The rotating carrier (3) is rotated along the vertical axis. The 6-inch single crystal diamond seed crystal (4) is placed horizontally on the upper side of the rotating carrier (3). The 6-inch single crystal diamond seed crystal (4) is located below the microwave transmission pipeline.

4. The 6-inch high thermal conductivity doped diamond wafer according to claim 1, characterized in that: The methane gas source (81), hydrogen gas source (82), phosphine gas source (83), nitrogen gas source (84), and argon gas source (85) are arranged sequentially along the vertical direction on one side of the gas input pipeline (8). The methane gas source (81), hydrogen gas source (82), phosphine gas source (83), nitrogen gas source (84), and argon gas source (85) are all connected to the gas input pipeline (8). The end of the gas input pipeline (8) away from each gas source is connected to the inside of the reaction chamber (2). A method for fabricating 5.6-inch high thermal conductivity doped diamond wafers, characterized in that, Includes the following steps: S1: Seed crystal preparation: Select a 6-inch single crystal diamond seed crystal (4) and polish and clean the 6-inch single crystal diamond seed crystal (4); S2: Doped epitaxial growth: The treated 6-inch single crystal diamond seed crystal (4) is placed on the upper side of the rotating carrier (3). Methane, hydrogen, phosphine and nitrogen are introduced into the reaction chamber (2) through methane gas source (81), hydrogen gas source (82), phosphine gas source (83) and nitrogen gas source (84). Microwave energy is input into the reaction chamber (2) through microwave generator (7) so that phosphorus-nitrogen composite doped CVD epitaxial growth is performed on the surface of the 6-inch single crystal diamond seed crystal (4). S3: Impurity control: During the phosphorus-nitrogen composite doped CVD epitaxial growth process, argon gas is introduced into the reaction chamber (2) through the argon gas source (85) to perform segmented cleaning of the growth surface; S4: Post-processing: Ion beam etching is performed on the grown doped diamond wafer, and then chemical mechanical polishing is performed on the etched doped diamond wafer to obtain a 6-inch high thermal conductivity doped diamond wafer.

6. The method for preparing a 6-inch high thermal conductivity doped diamond wafer according to claim 5, characterized in that: The 6-inch single-crystal diamond seed crystal (4) of S1 is a (100) crystal orientation single-crystal diamond seed crystal. The surface roughness Ra of the 6-inch single-crystal diamond seed crystal (4) after polishing is ≤0.2nm. The cleaning process is plasma cleaning.

7. The method for preparing a 6-inch high thermal conductivity doped diamond wafer according to claim 5, characterized in that: The volume fraction of methane in S2 is 2-3%, the molar ratio of phosphine to methane is 0.5-2%, the molar ratio of nitrogen to methane is 0.2-0.8%, the phosphine is used to introduce phosphorus dopant into the doped diamond wafer, and the nitrogen is used to introduce nitrogen dopant into the doped diamond wafer.

8. The method for preparing a 6-inch high thermal conductivity doped diamond wafer according to claim 5, characterized in that: The growth temperature of the phosphorus-nitrogen composite doped CVD epitaxial growth of S2 is 900-1000℃, the deposition pressure is 100-150Torr, the microwave power is 8-12kW, the growth time is 30-45h, and the rotation speed of the rotating carrier (3) is 5-10r / min.

9. The method for preparing a 6-inch high thermal conductivity doped diamond wafer according to claim 5, characterized in that: In step S3, argon gas is introduced every 8 hours for plasma cleaning, with each cleaning session lasting 5 minutes.

10. The method for preparing a 6-inch high thermal conductivity doped diamond wafer according to claim 5, characterized in that: In step S4, a 5-10 μm doped enrichment layer on the surface of the doped diamond wafer is removed by ion beam etching, and the surface roughness Ra of the doped diamond wafer is reduced to 0.4 nm by chemical mechanical polishing.

Images