2.45 GHZ multimode upper inlet wave microwave plasma device and design method

Abstract

The invention discloses a 2.45 GHZ multimode upper wave inlet microwave plasma device and a design method.The device comprises a microwave excitation source, a rectangular waveguide, a short circuit piston, a mode conversion antenna, a quartz window, a deposition cavity, a deposition table and a deposition substrate, the rectangular waveguide and the short-circuit piston are arranged at the upper part of the mode conversion antenna, microwaves emitted by the microwave excitation source enter the mode conversion antenna through the rectangular waveguide, the short-circuit piston adjusts microwave energy reflected by an electric field and fed into the deposition chamber, and the quartz window is arranged between the mode conversion antenna and the deposition chamber; a deposition table is arranged in the center of the bottom in the deposition chamber, and a deposition substrate is arranged above the deposition table. According to the 2.45 GHZ microwave plasma device, a standing wave electric field larger than a conventional 2.45 GHZ microwave plasma device in coverage area can be generated in the central area, excitation of plasma on the deposition table in the reaction chamber is achieved, and then a larger diamond film can be deposited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diamond film deposition, and relates to a 2.45GHz multimode forward wave microwave plasma device and a design method. BACKGROUND

[0002] Microwave plasma chemical vapor deposition (MPCVD) technology has become the mainstream technology for preparing high-purity and high-quality diamond films due to its characteristics of no electrode pollution and the ability to generate high-density plasma. However, the traditional MPCVD equipment still faces challenges in practical applications. On the one hand, the energy distribution and spatial form of the plasma of the conventional resonant cavity type MPCVD system are strictly limited by the inherent resonant mode of the cavity, which leads to uneven energy distribution when growing large-size diamond, thereby introducing lattice defects in the edge region of the wafer and affecting product quality and yield.

[0003] In order to break through the limitation of resonant mode, researchers have developed plasma sources based on surface waves. In particular, the use of composite right and left-handed (CRLH) metamaterial waveguides to excite surface wave plasma has shown great potential. CRLH metamaterial is an artificial electromagnetic structure with unique dispersion characteristics that can precisely control the phase of electromagnetic waves. When working in a zero-order resonant state, the CRLH waveguide can form a phase-constant surface current on its surface, i.e., achieve infinite wavelength propagation. By slotting at the location of the surface current concentration, it can efficiently radiate electromagnetic waves of the same phase outward, thereby exciting large-area, high-density, and highly uniform surface wave plasma on the dielectric plate, effectively solving the problems of low energy utilization and non-uniform plasma of traditional MPCVD equipment.

[0004] However, the existing CRLH metamaterial waveguide devices still have obvious limitations in structural design. These devices are usually single-channel, single-surface radiation structures, i.e., only one surface of the waveguide is used for slotting and energy radiation. For the entire waveguide structure, the space on the other side is not utilized, resulting in waste of space resources and limiting the further improvement of production efficiency. If double-sided radiation can be achieved, it means that double production tasks (such as double-sided film deposition) can be carried out simultaneously based on a set of waveguide system, which will greatly improve the space utilization and production efficiency of the equipment.

[0005] However, it is a severe technical challenge to feed two output channels evenly and stably from a single input port in microwave engineering. Simple power distribution structures (such as T-junctions) often cannot guarantee that the power and phase of the two channels are completely consistent, and can easily cause unnecessary electromagnetic oscillation in one of the channels, leading to imbalance of the entire system and failure to form a stable in-phase surface current. Therefore, how to design a metamaterial waveguide structure that can be stably driven from a single input source and achieve uniform and in-phase radiation on both sides is a technical problem that needs to be solved in the field. SUMMARY

[0006] To solve the defects in the prior art, the purpose of the present application is to provide a 2.45GHz multimode upward wave microwave plasma device, and the technical scheme is as follows: The microwave excitation source, the rectangular waveguide, the short-circuit piston, the mode conversion antenna, the quartz window, the deposition chamber, the deposition table and the deposition substrate are provided, wherein The mode conversion antenna is a reverse trapezoidal ring antenna, the rectangular waveguide and the short-circuit piston are arranged at the upper part of the mode conversion antenna, the microwave emitted by the microwave excitation source enters the mode conversion antenna through the rectangular waveguide, the short-circuit piston adjusts the electric field reflection and the microwave energy fed into the deposition chamber, and the quartz window is arranged between the mode conversion antenna and the deposition chamber. The deposition table is arranged at the central position of the inner bottom of the deposition chamber, and the deposition substrate is arranged above the deposition table.

[0007] Preferably, the lower half of the deposition chamber is cylindrical, and the upper half is circular truncated cone-shaped, so that the central plasma in the deposition process is in the shape of an ellipsoid.

[0008] Preferably, the slope of the reverse trapezoidal slope of the mode conversion antenna ranges from 5.5 to 5.9.

[0009] Preferably, the rectangular waveguide adopts BJ26 standard.

[0010] Preferably, the microwave propagates in the TE mode in the rectangular waveguide.

[0011] Preferably, the mode conversion antenna converts the TE wave into a TM wave.

[0012] Preferably, the resonance mode in the deposition chamber is TM031.

[0013] Preferably, the position of the short-circuit piston is adjustable to change the effective length of the deposition chamber.

[0014] Based on the above purpose, the present application also provides a design method of a 2.45GHz multimode upward wave microwave plasma device, which is used to design the above-mentioned 2.45GHz multimode upward wave microwave plasma device, and comprises the following steps: S10, selecting a microwave frequency based on diamond film deposition requirements; S20, designing a waveguide; S30, designing a mode conversion antenna; S40, designing a deposition chamber.

[0015] Preferably, the mode conversion antenna in S30 is designed as an inverted trapezoidal ring antenna, so that the radial electric field converges with the central electric field to form multi-mode coupling.

[0016] Compared with the prior art, the present application at least includes the following beneficial effects: 1. Compared with a common 2.45GHz single-mode cavity, the deposition area corresponding to the multi-mode coupling cavity based on TM031 mode in this paper is larger, and thus a larger size diamond film can be deposited.

[0017] 2. Compared with a multi-mode coupling cavity with a downward wave input mode, due to the pressure difference between the inside and outside of the cavity during deposition, the poor air tightness of the cavity leads to low deposition quality. The multi-mode resonant cavity of TM031 mode in this paper uses an upward wave input mode to feed microwaves, so the air tightness is better than that of the downward wave input mode.

[0018] 3. For a downward wave cavity, the quartz window is below the deposition table, so the deposition table cannot be adjusted up and down, i.e. it has no tunability. Compared with the downward wave cavity, the cavity structure of this application is an upward wave input mode, so the deposition table can be adjusted up and down, and it has tunability. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a structural schematic diagram of a 2.45GHz multi-mode upward wave microwave plasma device of an embodiment of the present application; Figure 2 is a resonant cavity electric field distribution diagram of a 2.45GHz multi-mode upward wave microwave plasma device of an embodiment of the present application; Figure 3 is a resonant cavity plasma distribution diagram of a 2.45GHz multi-mode upward wave microwave plasma device of an embodiment of the present application. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0021] On the contrary, the present application covers any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present application defined by the claims. Further, in order to make the public better understand the present application, some specific details are described in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0022] Referring to Figure 1 , a 2.45GHz multi-mode upward wave microwave plasma device of an embodiment of the present application is shown, which comprises a microwave excitation source 1, a rectangular waveguide 2, a short-circuit piston 3, a mode conversion antenna 4, a quartz window 5, a deposition chamber, a deposition table 71 and a deposition substrate 72, wherein, The mode conversion antenna 4 is a reverse trapezoidal ring antenna, the rectangular waveguide 2 and the short-circuit piston 3 are arranged at the upper part of the mode conversion antenna 4, the microwave emitted by the microwave excitation source 1 enters the mode conversion antenna 4 through the rectangular waveguide 2, the short-circuit piston 3 adjusts the electric field reflection and the microwave energy fed into the deposition chamber, and the quartz window 5 is arranged between the mode conversion antenna 4 and the deposition chamber; the deposition table 71 is arranged at the central position of the bottom of the deposition chamber, and the deposition substrate 72 is arranged above the deposition table 71. The lower half of the deposition chamber is a cylindrical cavity 62, and the upper half is a circular truncated cone cavity 61, so that the central plasma in the deposition process is in an ellipsoidal shape. The slope of the reverse trapezoidal slope of the mode conversion antenna 4 ranges from 5.5 to 5.9. The rectangular waveguide 2 adopts BJ26 standard. The microwave propagates in the rectangular waveguide 2 in TE mode. The mode conversion antenna 4 converts the TE wave into TM wave. The resonance mode in the deposition chamber is TM031. The position of the short-circuit piston 3 can be adjusted to change the effective length of the deposition chamber.

[0023] The present application designs a multi-mode coupling upward wave microwave resonance cavity based on TM031 mode which has simple structure and can be used for depositing large-area diamond. Compared with single-mode coupling cavity, the main advantage of the present application is to achieve multi-mode coupling effect of electric field, thereby increasing the coverage area of strong electric field and improving the electric field strength, resulting in improved uniformity of electric field and stable deposition of diamond film with larger area than single-mode. In the design of the central resonance cavity, the corresponding cylindrical cavity of TM031 mode is designed. The TM031 mode corresponds to three strong electric field distributions in the radial direction of the corresponding cylindrical cavity, and one strong electric field distribution in the axial direction, and the corresponding cylindrical resonance cavity has a radius of 184mm and a cavity height of 150mm, and the electric field distribution can be seen in the electromagnetic simulation software.

[0024] Secondly, the waveguide transmission part is designed, since the microwave frequency used by the device is 2.45GHz, the waveguide size of BJ26 standard is used as the size of the microwave transmission part. The part includes the microwave excitation source 1, the rectangular waveguide 2 and the short-circuit piston 3.

[0025] Since the microwave propagates in the rectangular waveguide 2 in the TE mode, the microwave in the TE mode cannot excite a strong electric field in the central area of the resonant cavity, and thus the diamond cannot be deposited, so it is necessary to design a mode conversion antenna 4 to convert the microwave TE transmission mode into the TM transmission mode, and a coaxial antenna is used as the mode conversion antenna 4 to couple the microwave into the resonant cavity. Compared with the ordinary disc-shaped annular antenna, the lower half of the antenna has a slope (the slope range is 5.5-5.9) in the present application, forming an inverted trapezoidal structure of the annular antenna, so that the radial electric field and the central electric field form a coupling effect, resulting in the enhancement of the central electric field intensity and the expansion of the coverage area of the electric field.

[0026] Then, the structure of the cylindrical chamber in the prior art is changed, and on the basis of the structure of the traditional TM031 mode cylindrical cavity, the two sides of the cavity are cut at an angle, so that the cavity is formed into two parts, the lower half is a cylindrical cavity 62, and the upper half is a circular truncated cone cavity 61. Through optimization of the slope parameter of the cut angle side, the central plasma tends to be ellipsoidal, and the extension characteristic of the long axis can deposit a larger area of diamond film compared with the spherical shape and improve the uniformity of film deposition. A deposition table 71 that can be adjusted up and down is arranged in the lower half cylindrical cavity 62, and the height of the deposition table 71 is adjusted to tune the plasma, so that the area of the deposited diamond film remains uniform.

[0027] The present application also provides a design method of a 2.45GHz multi-mode upward wave microwave plasma device, and the 2.45GHz multi-mode upward wave microwave plasma device is designed by using the method, and the method comprises the following steps: S10, selecting a microwave frequency based on the diamond film deposition requirement; S20, designing a waveguide; S30, designing a mode conversion antenna; S40, designing a deposition chamber.

[0028] In S30, the mode conversion antenna is designed as an inverted trapezoidal annular antenna, so that the radial electric field converges to the central area and the central electric field, forming multi-mode coupling.

[0029] The working process is as follows: 2.45GHz microwave is generated from the microwave excitation source 1 and transmitted through the rectangular waveguide 2. The TE is converted into TM wave by the mode conversion antenna 4 (inverted trapezoidal annular antenna) to be coupled into the resonant cavity (deposition chamber). The radial electric field is coupled with the central electric field through the reflection of the inclined edge of the inverted trapezoidal annular antenna and the circular truncated cone cavity 61, and finally a stable standing wave electric field is formed. The gas added to the deposition chamber excites the plasma above the deposition table 71 under the condition of standing wave, so as to realize the deposition of diamond film. The adjustment of the short-circuit piston 3 above the deposition chamber can reduce the reflection of the electric field, thereby increasing the absorption of microwave energy by the plasma. For specific electric field results, see Figure 2 . As can be seen from the results, a strong electric field region with a wide coverage area is formed above the deposition table 71, and the maximum electric field can reach 50,000 V / M. For the plasma results, see Figure 3 , the coverage area of the plasma can reach about 45-50 mm (the coverage area of the single-mode cavity under 2.45GHz is generally 30mm).

[0030] Design of the central cavity of the application: the resonant cavity part adopts a cylindrical structure design, and is divided into an upper half circular truncated cone part and a lower half cylindrical part. The deposition table 71 is arranged in the lower half cylindrical cavity 62, and the deposition table 71 is adjustable up and down to adjust the position of the plasma to stabilize its distribution, so as to realize the demand of large-area deposition of diamond.

[0031] Design of the inverted trapezoidal annular antenna: the mode conversion antenna 4 adopts an inverted trapezoidal design, so that the lower part of the cylindrical annular antenna in the prior art produces an inclined edge with a certain slope, so that the radial electric field can converge to the central area with the central electric field, forming a multi-mode coupling effect (the central electric field intensity is enhanced and the coverage area is increased).

[0032] Design of the quartz window 5: the excited plasma will etch the annular quartz window 5, and the product will contaminate the deposition area. Therefore, the application designs a curved channel to place the quartz window 5 on the basis of the upper wave, which not only keeps the quartz away from the plasma to prevent etching and contamination of the diamond film, but also provides a supporting effect for the inverted trapezoidal annular antenna. Moreover, the gravity of the annular antenna and the pressure difference between the inside and outside of the vacuum chamber can better maintain the air tightness of the chamber to prevent atmospheric pollution deposition.

[0033] Operation mode: start the motor, adjust the position of the deposition table 71, place the substrate sample, start the vacuum pump to pump the chamber to low pressure (below 100Pa). Then slowly add hydrogen or argon gas to the deposition chamber under low pressure to 0.5~1kPa. Turn on the microwave power supply and the cooling water system, increase the power by 1000W every 1 minute, to the target power of 5000~10000W and keep stable, and then start depositing diamond film on the substrate of the deposition table 71.

[0034] During deposition, the shorting piston 3 is adjusted every certain time to improve the absorption of microwave energy by the plasma. The shape of the plasma is observed through the observation window, and the height of the deposition table 71 is adjusted by the motor to keep the plasma stable.

[0035] After the diamond quality and thickness grow to the target requirement, the gas valve is closed to stop adding hydrogen or argon into the reaction chamber, the microwave power is slowly reduced, the microwave power supply is turned off, and the cooling system is cooled down. After a period of time, the deposition table 71 is slowly raised by the motor, the quartz cover is opened, and the sample is taken out. All the systems are turned off, and the whole deposition process is completed.

[0036] The above only describes the preferred embodiments of the present application and is not used to limit the present application. Any modification, equivalent replacement, and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A 2.45 GHz multimode upward wave microwave plasma apparatus, characterized by, The microwave excitation source, the rectangular waveguide, the short-circuit piston, the mode conversion antenna, the quartz window, the deposition chamber, the deposition platform and the deposition substrate, wherein, The mode conversion antenna is an inverted-trapezoidal ring antenna, the rectangular waveguide and the short-circuit piston are arranged at the upper part of the mode conversion antenna, the microwave emitted by the microwave excitation source enters the mode conversion antenna through the rectangular waveguide, the short-circuit piston adjusts the electric field reflection and the microwave energy fed into the deposition chamber, and the quartz window is arranged between the mode conversion antenna and the deposition chamber. The deposition platform is arranged at the central position of the inner bottom of the deposition chamber, and the deposition substrate is arranged above the deposition platform.

2. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 1, wherein The lower half of the deposition chamber is in a cylindrical shape, and the upper half is in a circular truncated cone shape, so that the central plasma in the deposition process is in an ellipsoidal shape.

3. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 1, wherein The slope of the oblique side of the inverted-trapezoidal mode conversion antenna ranges from 5.5 to 5.

9.

4. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 1, wherein The rectangular waveguide adopts the BJ26 standard.

5. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 1, wherein The microwave propagates in the TE mode in the rectangular waveguide.

6. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 5, wherein The mode conversion antenna converts the TE wave into the TM wave.

7. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 1, wherein The resonance mode in the deposition chamber is TM031.

8. The 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 1, wherein The position of the short-circuit piston is adjustable to change the effective length of the deposition chamber.

9. A method of designing a 2.45 GHz multimode upward wave microwave plasma apparatus, characterized by, The method comprises the following steps: S10, selecting the microwave frequency based on the requirement of the diamond thin film deposition; S20, designing the waveguide; S30, designing the mode conversion antenna; S40, designing the deposition chamber.

10. The method of designing a 2.45 GHz multimode upward wave microwave plasma apparatus according to claim 9, wherein In the step S30, the mode conversion antenna is designed as an inverted-trapezoidal ring antenna, so that the radial electric field converges to the central area and the central electric field, forming a multi-mode coupling.

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