Microwave magnetron with constant anode impedance and system using the same

Abstract

A microwave magnetron includes a cathode for emitting electrons, a filament for receiving a filament current to heat the cathode so that the cathode can emit electrons, and an anode capable of applying an anode power to affect the electron flow. The anode power input receives the anode power to be applied to the anode, and the anode power is characterized by an anode current, an anode voltage, and an anode impedance, where the anode impedance is the quotient of the anode voltage and the anode current. The electromagnet power input receives the electromagnet power and applies the electromagnet power to the electromagnet to control the magnetic field strength, and the electromagnet power is characterized by an electromagnet current. The controller adjusts at least one parameter of the magnetron to affect the electron flow while keeping the anode impedance constant.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Non - Provisional Application No. 16 / 593,942, filed on October 4, 2019, entitled "MICROWAVE MAGNETRON WITH CONSTANT ANODIC IMPEDANCE AND SYSTEMS USING THE SAME", the content of which is incorporated herein by reference as if fully set forth herein. Technical Field

[0003] The present disclosure relates to microwave magnetrons and systems using microwave magnetrons, and more particularly to microwave magnetrons and systems using microwave magnetrons in which the anodic impedance is controlled to provide improved magnetron performance and reliability. Background Art

[0004] A magnetron is a device that generates microwave energy by converting the power supplied to the anode into microwave radiation. They are essentially vacuum diodes, consisting of circular resonant cavities around a cathode immersed in a perpendicular magnetic field. This magnetic field generates a force that changes the motion of electrons from a straight - line path to a curved path. As the electrons move through a series of open metal cavities (i.e., cavity resonators), the magnetron uses this interaction between the electron flow and the magnetic field to generate microwaves. The electrons pass through the openings of these cavities and cause radio waves to oscillate therein. The frequency of the generated microwaves (i.e., the resonant frequency) is determined by the physical dimensions of the cavities. The magnetron produces a high - power microwave output signal from the direct current electricity supplied to the vacuum tube.

[0005] Magnetrons are used in many applications that employ microwave radiation. For example, the most common commercial application of a continuous - wave (CW) magnetron is in microwave ovens. An industrial application of magnetrons is in the field of plasma generation. In a plasma generator, a magnetron can be used to supply microwave excitation energy to a plasma chamber to initiate and sustain the generation of plasma. Plasma generators using magnetrons have many applications, including, for example, in semiconductor device manufacturing processes such as chemical vapor deposition (CVD). CVD can also be used in other processes such as synthetic diamond growth.

[0006] Many processes using plasma can be very complex and time-consuming. For example, the growth process of CVD synthetic diamond can last for multiple days, during which the synthetic diamond grows slowly layer by layer without interruption. During this long process, complex plasma generation steps are usually performed. These multiple steps may require adjustment of plasma generation, which in turn requires adjustment of the microwave plasma signal generated by the magnetron. For example, it is well known that the ignition of plasma requires a higher microwave signal power level than the power required to maintain the plasma at a constant level after ignition. Therefore, between plasma ignition and continuous plasma generation, one or more parameters in the magnetron need to be adjusted. Similarly, the amount of plasma required during the process may also need to be adjusted, which also drives the need to adjust the magnetron during the process.

[0007] If the magnetron operates under unstable conditions, such as by an accidental shutdown or experiencing a change in microwave output characteristics, an interruption or change in plasma generation may occur, which may then interrupt the entire process, such as CVD synthetic diamond growth. This can result in very costly time and product manufacturing losses, as the interrupted product batches may have to be discarded and the process will have to start from scratch. Therefore, even with multiple parameter adjustments during the process, it is very important for the magnetron to operate at a very high level of stability and reliability. Summary of the Invention

[0008] According to one aspect, a microwave magnetron is provided. The microwave magnetron includes a cathode for emitting electrons, a filament for receiving a filament current to heat the cathode to enable the cathode to emit electrons, and an anode to which anode power can be applied to affect the electron flow. The anode power input receives the anode power to be applied to the anode, and the anode power is characterized by an anode current, an anode voltage, and an anode impedance, where the anode impedance is the quotient of the anode voltage and the anode current. An electromagnet provides a magnetic field in which electrons flow. The electromagnet power input receives the electromagnet power and applies the electromagnet power to the electromagnet to control the magnetic field strength, and the electromagnet power is characterized by an electromagnet current. A controller controls the parameters of the microwave magnetron, and the controller adjusts at least one parameter of the magnetron to affect the electron flow while keeping the anode impedance constant.

[0009] In some exemplary embodiments, the parameters of the microwave magnetron controlled by the controller include the anode current, the filament current, and the electromagnet current. In some exemplary embodiments, the controller monitors the parameters of the microwave magnetron. In some exemplary embodiments, the controller is adapted to issue an alarm based on at least one monitored parameter of the microwave magnetron.

[0010] In some exemplary embodiments, the controller monitors the anode voltage. In some exemplary embodiments, the controller is adapted to issue an alarm based on the monitored anode voltage.

[0011] In some exemplary embodiments, the microwave magnetron further includes a filament control module between the controller and the filament. The filament control module generates a filament current monitoring signal and forwards the filament current monitoring signal to the controller, and the filament control module receives a filament current setting signal from the controller. In some exemplary embodiments, the microwave magnetron further includes a filament transformer between the filament control module and the filament.

[0012] In some exemplary embodiments, the microwave magnetron further includes an electromagnet control module between the controller and the electromagnet. The electromagnet control module generates an electromagnet current monitoring signal and forwards the electromagnet current monitoring signal to the controller, and the electromagnet control module receives an electromagnet current setting signal from the controller.

[0013] In some exemplary embodiments, the microwave magnetron further includes a microwave output for providing output microwave energy from the microwave magnetron. In some exemplary embodiments, the microwave output can be connected to a system for processing a substrate. In some exemplary embodiments, the system is a plasma generation system. In some exemplary embodiments, the system is a chemical vapor deposition (CVD) system. In some exemplary embodiments, the system is a synthetic diamond growth chemical vapor deposition (CVD) system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the following detailed description, the present disclosure is further described by way of non-limiting examples of embodiments of the present disclosure, with reference to the several figures indicated, wherein like reference numerals represent like parts in the several views of the figures.

[0015] Figure 1A and Figure 1B Schematic diagram including two magnetrons used according to some exemplary embodiments.

[0016] Figure 2 Schematic LC circuit equivalent diagram including the anode shown in FIG. 1.

[0017] Figure 3 Schematic diagram of the electron cloud between the cathode and the anode shown in FIG. 1.

[0018] Figure 4A Curve showing the relationship between the output power and the anode voltage and anode current of a typical conventional magnetron. Figure 4B Including showing Figure 4A Schematic diagram of certain parameters associated with the operation of the magnetron.

[0019] Figure 5 Curve showing the relationship between the output power and the magnetic field of a typical conventional magnetron.

[0020] Figure 6A Schematic block diagram of a system using a magnetron according to some exemplary embodiments. Figure 6B Including installed in one or more electrical cabinets according to some exemplary embodiments Figure 6B Schematic front view of the physical configuration of the system.

[0021] Figure 7 Is a graph including parameter curves of a magnetron according to some exemplary embodiments.

[0022] Figure 8A And Figure 8B Including a graph showing the relationship between the anode voltage and the magnetic field of a magnetron according to some exemplary embodiments.

[0023] Figure 9A And Figure 9C Including a schematic diagram of control module 202 according to some exemplary embodiments. Figure 9B Including according to some exemplary embodiments associated with Figure 9A And Figure 9C Schematic waveform diagram of signals associated with the operation of the circuit shown.

[0024] Figure 10 Is a graph showing the relationship between the anode impedance and the output power of a conventional magnetron and the magnetron of the present disclosure.

[0025] Figure 11 Is according to some exemplary embodiments Figure 6A And Figure 6B Schematic functional block diagram of the system shown, which shows additional functional details of the system.

[0026] Figure 12 Including a schematic diagram of a system 500 using the magnetron 100 of the present disclosure according to some exemplary embodiments. Detailed Description of the Invention

[0027] For a description of the well-known structure and function of a conventional magnetron, see Chapter 2 of Handbook of Microwave Technology, "Magnetron", written by Wayne Love, edited by T. Koryu Ishii, published by Academic Press, Inc., 1995. Figure 1A And Figure 1B Including schematic diagrams of two exemplary magnetrons 100 used according to some exemplary embodiments, respectively identified by reference numerals 100A and 100B in Figure 1A And Figure 1B It should be noted that the magnetron of the present disclosure is non-specifically referred to herein by reference numeral 100. Refer to Figure 1A And Figure 1B, the magnetrons 100A, 100B include an anode 102 and a permanent magnet 106 surrounding a cathode 104. The microwave radiation generated by the magnetrons 100A, 100B is emitted into a waveguide 103 at an output antenna 112, and the waveguide 103 includes an output flange 105 for coupling the microwave energy output from the magnetrons 100A, 100B to the system. Generally, the magnetrons 100A, 100B include a plurality of heat sinks 108 for heat dissipation. The magnetrons 100A, 100B are crossed-field vacuum tubes, which means that the electron flow, electric field, and magnetic field are perpendicular to each other.

[0028] The cathode 104 is an electron source and has a negative electric potential relative to the anode 102. The cathode 104 is made of a conductive metal (such as tungsten), and it is wound in a helical shape. The cathode 104 is heated to emit electrons by: (i) passing a current directly through the cathode 104 to heat the cathode 104, or (ii) electrons in the oscillating magnetron returning to the cathode 104, thereby generating heat.

[0029] Figure 2 Schematic LC circuit equivalent diagram including the anode 102. Refer to Figure 2 , the anode 102 is made of a conductive metal (such as copper). It includes a set of resonant cavities 116 disposed around the cathode 104, and is characterized by a parallel LC circuit, where each cavity 116 is characterized by an inductance L and a capacitance C. Each cavity 116 is disposed between a pair of vanes 118. When the cavity 116 operates in the PI mode, the LC circuit has an oscillating resonant frequency, which is the most efficient operating mode, although there are other unwanted oscillation modes. The output of the magnetron 100 is achieved by coupling the microwave energy in the cavity 116 to the antenna 112.

[0030] In the absence of a magnetic field, the magnetron 100 will act as a diode, where electrons emitted from the cathode 104 will move radially outward in a straight path to the anode 102 under the action of the force exerted by the electric field between the cathode 104 and the anode 102. In the presence of a magnetic field provided by the permanent magnet 106 perpendicular to the electric field, in addition to the electric field force, there is also a force acting on the electrons, and this magnetic field hinders the path of the electrons. Under the action of the magnetic field, the path of the electrons is circular. At an anode voltage higher than the Hull cut-off voltage, in the presence of a magnetic field and an electric field, the electrons reach the anode 102 and current flows. Below this voltage, no current flows. The Hull cut-off voltage depends on the magnetic field, electric potential, radius of the anode 102, and radius of the cathode 104.

[0031] In the presence of a PI-mode electromagnetic field, alternating positive and negative voltages exist on the vane 118. If electrons leave the cathode and enter the accelerating field, the electrons will be accelerated and extract energy from the electromagnetic field. These higher-energy electrons will be greatly affected by the magnetic field and will return to the cathode 104, which causes heating of the cathode 104. As the anode 102 voltage increases, the cathode 104 filament voltage must be decreased to maintain a constant cathode temperature. Electrons entering the electromagnetic field from the decelerating field release some of their DC energy to the electromagnetic field. If the angular velocity of the electrons is such that it is always in the decelerating field, then almost all of the energy is released to the electromagnetic field and the electrons strike the anode 102.

[0032] Because there are regions of electrons that are in the decelerating field and not in the accelerating field, and because these regions move at an angular frequency proportional to the resonator frequency, there is an electron cloud 113 with spokes, as Figure 3 shown, Figure 3 is a schematic diagram of the electron "cloud" between the cathode 104 and the anode 102, which shows the spokes 115. As the spokes 115 move in the decelerating RF field, the electrons near the negatively charged vanes are decelerated while the electrons near the positively charged vanes are accelerated. This causes further bunching of the electrons in the spokes. The bunching of electrons in each spoke tends to keep the spokes 115 equally spaced. The electrons reaching the anode 102 have almost released their energy.

[0033] The magnetic field causes a circular path of the electrons in the electron cloud. In the interaction region, it must be as close as possible to being parallel to the cathode axis. To maintain a constant output power, it is also important that the magnetic field does not vary with time. The magnetic field can be formed by a permanent magnet 106 or an electromagnet.

[0034] Typically, the output power of the magnetron needs to be adjusted during operation. Several methods are commonly used to change the power applied to the load. These methods include: (i) pulsing the output power of the magnetron, (ii) changing the anode current, (iii) changing the magnetic field, and (iv) adjusting the microwave energy supplied to the load. Regarding item (ii), a decrease in the input power will result in a change in the output power. The output power of the magnetron is proportional to the anode current. As the anode voltage begins to increase, the anode current becomes smaller. At a voltage determined in part by the magnetic field, current will begin to flow and the magnetron will begin to oscillate. The voltage known as the Hartree voltage depends on the magnetic field, the anode radius, the cathode radius, and the wavelength. In the oscillation region, a large change in the anode current will cause a small change in the anode voltage. Most power supplies are current-stabilized to maintain the output power. Figure 4A is a curve showing the relationship between the output power and the anode voltage and anode current of a typical conventional magnetron. Figure 4B includes showing the relationship with Figure 4ASchematic diagram of certain parameters associated with the operation of a magnetron. Refer to Figure 4A and Figure 4B , it can be seen from the curve of Figure 4A that as the anode current Ia decreases, the filament voltage must increase. It should be noted that the filament current If is the current flowing in the filament, which heats the filament so that the filament can emit electrons. In the context of the present disclosure, a typical value of the filament current If is 115 amperes at 12 volts. In the magnetron 100 of the present disclosure, one of the filament taps of the filament transformer T1 is also connected to the cathode negative high voltage. The anode current Ia is a DC current at the anode voltage Va, which has a typical value of 4 - 5 amperes in the context of the present disclosure. It should be noted that the filament is the same as the cathode, but the filament current If is different from the cathode current. Regarding item (iv) above, Figure 5 is a curve showing the relationship between the output power and the magnetic field of a typical conventional magnetron. It can be seen from this specific example that a 10% change in the magnetic field will cause a 60% change in the output power. Changing the magnetic field requires a separate power supply to power the electromagnet, but it can be a low - power power supply. This low - power power supply is isolated from the high - voltage power supply and can be easily adjusted to provide the required output power.

[0035] As described above, the magnetron 100 is a vacuum tube that converts anode electrical power into microwave radiation. The microwave output power in the magnetron 100 is proportional to the input electrical power, which is given by the product of the anode voltage Va and the anode current Ia. The hot filament emits electrons, and the electrons are affected by the electric field and the magnetic field. The electric field E is generated by the high anode voltage between the anode 102 and the cathode 104. The magnetic field B is generated by the magnet 106, which can be a permanent magnet or an electromagnet. Preferably, in order to allow magnetic field adjustment, the magnet 106 is an electromagnet. With an electromagnet, the intensity of the magnetic field B is controlled by adjusting the coil current intensity. When the applied E - field and B - field force the electrons into a curved trajectory, the tube or magnetron 100 emits microwave radiation. An interaction occurs between the resonant cavity structure and the electron cloud, and through this interaction, the electrons transfer their energy to the oscillating electromagnetic field. In typical large - scale commercial applications, the magnetron 100 generates radiation at nominal frequencies such as 2.45 GHz and 915 MHz. A typical magnetron 100 has an efficiency of about 65% at 2.45 GHz and about 85% at 915 MHz. It should be understood that the present disclosure applies to magnetrons operating at any microwave frequency.

[0036] A power supply for providing power to operate magnetron 100 supplies high voltage to magnetron 100. It also provides anode current Ia and filament current If, as well as the voltage required to heat the filament to emission. The power supply also provides magnetic current to generate the required magnetic field. The power supply can be in a switched configuration or a linear configuration. A switched-mode power supply can deliver energy in packets of 50,000 or more per second, while a linear power supply, on the contrary, is driven by line frequency and can deliver 100 to 120 packets per second (50 or 60 Hz). The use of a switched power supply provides a faster response time for events such as turn-on, power increase / decrease, restart after a fault, etc. It also results in a reduction in the stored energy delivered to magnetron 100 during a fault event (e.g., an arc).

[0037] Figure 6A Schematic block diagram of a system 200 using magnetron 100 according to some exemplary embodiments. Figure 6B Schematic front view of the physical configuration of a system 200 installed in one or more electrical cabinets 201A, 201B. Refer to Figure 6A and Figure 6B As shown in FIGS. and, system 200 includes a magnetron 100 connected to a power supply system 201. The power supply system 201 includes a control module 202 connected to a plurality (e.g., four) of power modules 204, 206, 208, 210 via a control bus 212. In some exemplary embodiments, the control module 202 can be an AC571 controller manufactured and sold by MKS Instruments of Andover, Massachusetts, USA, or other similar control modules. In some exemplary embodiments, each power module 204, 206, 208, 210 is an SM1818 power module manufactured and sold by MKS Instruments of Andover, Massachusetts, USA, or other similar power modules.

[0038] The control module 202 provides control for the electromagnet 106 and the magnetron filament. The control module 202 also serves as a user interface by virtue of the display and various buttons, knobs, etc. on its front panel. It can be understood that any number of power modules can be used according to the requirements of a specific application. System power is provided to the control module 202 and the power modules 204, 206, 208, 210 via the power bus 214, such as a three-phase 480AC main power supply. The power supply system 201 provides signals from the control module 202 on the filament supply line 216 and the electromagnet supply line 218, and from the power modules 204, 206, 208, 210 on the high-voltage supply line 220 to operate the magnetron 100. In some exemplary embodiments, the current on the filament supply line 216 is 0 - 5 amperes and its function is to heat the filament. The electromagnet supply line 218 carries a 0 - 5 ampere DC current to generate a magnetic field for magnetron control. The high-voltage supply line 220 carries a 0 - 5 ampere DC current at a negative voltage of 6000 - 18000 volts to provide the main magnetron current for microwave power. The power modules 204, 206, 208, 210 provide anode current to the magnetron 100 at a rated voltage, and this rated voltage is adjusted by the electromagnet 106. The output power can be controlled within the range of 3% - 100% of the nominal power according to user requirements. According to the present disclosure, when controlling the output power, it can be understood that the magnetron output power depends on the magnetron anode power. Based on a look-up table, the system can set the anode voltage by changing the electromagnet current and can control the anode current. In this way, the system can control the anode electric power supplied to the magnetron, thereby indirectly controlling the output power of the magnetron. According to the present disclosure, for each of the parameters Ia (anode current), If (filament current), Ic (electromagnet current), Va (anode voltage), a look-up table is generated starting from eleven (11) values from 0% to 100% of the full scale.

[0039] Figure 7 is a diagram showing the parameter curves of the magnetron 100 according to some exemplary embodiments. Refer to Figure 7 , curve 231 represents the anode voltage Va (modulus, negative value), curve 233 represents the output microwave power Pmw in watts, curve 235 represents the electromagnet current Ic in mAdc, and curve 237 represents the anode current Ia in mAdc. Figure 8A and Figure 8B includes a graph according to some exemplary embodiments, which shows the relationship between the anode voltage and the magnetic field of the magnetron 100. Figure 8A and Figure 8B The curves of Figure 7 , Figure 8A and Figure 8BThe curve shows the life parameters of the magnetron 100 at different output power levels and the relationship between the magnetron magnetic field and the magnetron anode voltage. According to the present disclosure, the output power is controlled while keeping the ratio of the anode voltage to the anode current (i.e., Va / Ia) constant.

[0040] According to the present disclosure, the anode voltage is controlled by precisely controlling the electromagnet coil current. For each given output power set point, the control module 202 determines the required anode current level. It also determines the anode voltage required to maintain a constant anode impedance in order to maintain a constant Va / Ia ratio, and controls the anode voltage by changing the electromagnet coil current and thus the magnetic field. The anode voltage can be controlled by controlling the magnetic field (i.e., the electromagnet coil current). A system with dedicated electromagnet coil current control can set appropriate anode voltage and current levels at each power level.

[0041] Figure 9A and Figure 9C A schematic diagram including a control module 202 according to some exemplary embodiments. Figure 9B Including according to some exemplary embodiments Figure 9A and Figure 9C A schematic waveform diagram of signals associated with the operation of the circuit shown in. Refer to Figure 9A and Figure 9B , only two three-phase lines are used in this part of the circuit. The current in the primary coil of the filament transformer T1 is phase-cut by a line-synchronous gate driver that powers the gates of a pair of thyristors TR1 wired in an antiparallel configuration. Refer to Figure 9B The waveform of, the line voltage is a sine wave (A). The thyristor TR1 is triggered and turned on in synchronization with the line, with a variable delay dT inversely proportional to the average current in the primary coil of the transformer T1, i.e., the longer the delay, the lower the average value of the current, so it is similar to (B).

[0042] The line-synchronous gate driver circuit starts from the line-synchronous voltage provided by the transformer T3 to generate two different drive signals, one for each thyristor gate, as shown in (C) and (D). The primary side current is induced by the current transformer TA1, and a true RMS converter converts it to a DC value. This value is compared with the sawtooth signal (E) generated by the line-synchronous gate driver, and this comparison forces the gate driver pulses (C) and (D) to start. This has a stabilizing effect: if the RMS current value increases, the start of the drive pulse is delayed in a closed loop. The comparison level is also modified by the current set point signal received from the CPU: if the required current is larger, the circuit reduces the level, and vice versa.

[0043] The ENABLE input forces the comparison level shown in (E) to its maximum value, thereby zeroing the drive pulse and thus the current. The voltage on the primary side of the filament transformer T1 is sensed by the voltage transformer TV1, scaled by the resistive voltage dividers RA, RB, and converted to a DC value by another true RMS converter. Both the current and voltage RMS values are routed back to the CPU for monitoring.

[0044] Reference Figure 9C , the three-phase line is rectified by the full diode bridge B1 and then filtered by the capacitor C1. The DC bus is fed to a quasi-resonant power supply where the step-down transformer T1 in series with the resonant capacitor C2 is driven by an insulated gate bipolar transistor (IGBT) power module IGBT1 comprising a pair of IGBTs. The IGBT1 module is driven by a dedicated dual IGBT driver DRV1 and steered by a quasi-resonant zero-current switch (ZCS) integrated circuit controller CNT1. The controller alternately sends drive pulses to the upper IGBT via the HIGH signal and to the lower IGBT via the LOW signal.

[0045] When the lower IGBT is turned on, the capacitor C2 charges through the primary coil of T1. Subsequent pulses will drive the upper IGBT, thereby discharging the capacitor C1 again through the primary winding of T1, but in this case the current will be reversed. Thus, the transformer is driven by a series of current pulses, each with a polarity opposite to the previous one. Each pulse has the same time width, but they are spaced in time to increase / decrease the average current in the primary coil of the transformer.

[0046] The secondary voltage of the transformer T1 is rectified by the diode bridge B2 and filtered by the capacitor C3. The positive pole of this voltage is directly connected to the electromagnet, while the negative pole is grounded through the current sensing device CSEN1. CSEN1 provides a voltage proportional to the current and feeds this information back to the controller CNT1, thus closing the control loop. A resistive voltage divider made up of the resistors RA and RB also senses the voltage across the electromagnet and provides information to the control circuit. The control circuit is driven by the control CPU via the ENABLE input (to turn the electromagnet current on and off) and the current SETPOINT input to set the desired current amount (from 0 amperes to 5 amperes). It also provides an alarm output in case the circuit fails to provide the desired current in the electromagnet. The electromagnet current value is also converted to a differential monitor output which is sent to the CPU for monitoring.

[0047] Reference Figure 6A 、 Figure 6B 、 Figure 7 、 Figure 8A 、 Figure 8B 、 Figure 9A and Figure 9B, the control module 202 performs the control functions required for the operating system 200 according to the present disclosure. For example, the control module 202 drives the filament heating current If, the anode current Ia, and the electromagnetic current Ic to set the operating anode voltage Va. The control module 202 also identifies alarms and forces the user through the correct restart sequence. It also protects the system from magnetron "modulation" events, in which oscillations other than the resonant frequency occur in the cavity. The control module 202 also manages the distribution of the power modules 204, 206, 208, 210. For example, if one of the power modules 204, 206, 208, 210 fails, the CPU takes action to replace the lost function with one or more other properly operating power modules 204, 206, 208, 210. The control module 202 also provides the ability to set the speed at which the system 200 changes power. The control module 202 also provides complete information about magnetron operation via the display and the fieldbus, which is a family of industrial computer network protocols for real-time distributed control.

[0048] In some exemplary embodiments, the power modules 204, 206, 208, 210 generate anode current at medium / high anode voltages. For example, in some exemplary embodiments, the anode voltage supplies current in the range of 0 - 5 amperes DC, and the anode voltage is in the range of negative 6000 - 18000 volts. The magnetron anode voltage is determined by the magnetron design and the magnetic field strength. In the magnetron 100 of the present disclosure, the anode current and the electromagnetic field strength of the electromagnet are independently controlled. The electromagnetic field is controlled by changing the magnetic drive current or the electromagnet current, so as to set the required operating anode voltage within the specified operating characteristics of the magnetron 100. Therefore, the electrical (anode) power fed to the magnetron 100 can be configured with any combination of anode current and voltage. For example, when the voltage V is 15 kV and the current I is 2.33 A, or when the voltage V is 12.5 kV and the current I is 2.8 A, an anode power P of 35 kW can be obtained. In these cases, the anode impedance Z = V / I will be 6.44 kohm and 4.46 kohm respectively.

[0049] According to the present disclosure, the anode voltage and the anode current are controlled simultaneously. Therefore, the magnetron 100 is capable of delivering any required power level, i.e., P = V x I, and the required anode impedance value Z = V / I, which remains constant according to the present disclosure.

[0050] The performance of a magnetron for a given load depends to a large extent on the equivalent impedance determined by dividing the anode voltage by the anode current. According to the present disclosure, a constant equivalent impedance is obtained by implementing a systematic calculation. This provides highly improved magnetron performance and spectral output. While the anode current is increasing, a constant impedance scheme is achieved by controlling the anode voltage. The anode voltage is controlled by precisely controlling the electromagnet coil current. For each given output power set point, the control module 202 determines the required anode current level and filament current. It also determines the anode voltage required to maintain a constant anode impedance and controls it by changing the electromagnet coil current and thus the magnetic field.

[0051] Figure 10 is a graph showing the relationship between the anode impedance and the magnetron output power for a conventional magnetron and the magnetron 100 of the present disclosure. Refer Figure 10 , curve 271 represents a conventional magnetron, and curve 273 represents the magnetron 100 of the present disclosure. As Figure 10 shown, a substantially constant anode impedance is implemented according to an exemplary embodiment. This method provides highly improved magnetron performance and spectral output. For example, under the constant anode impedance method of the present disclosure, system reliability and availability are improved. In addition, a clearer and narrower microwave spectrum is obtained in the magnetron output. This results in improved process efficiency, especially in the resonant cavity. According to an exemplary embodiment, the power control schedule will operate within the anode current and voltage specifications of the magnetron system. This improved method of the present disclosure is particularly effective in applications involving long-duration, 24-hour-a-day, 7-day-a-week, continuous high-value processes such as CVD synthetic diamond growth. According to the present disclosure, using an equivalent constant impedance, the broadband of the magnetron spectral output is significantly reduced or eliminated. This provides a significant improvement in operating the magnetron 100 under safe and reliable conditions.

[0052] Figure 11 is according to some exemplary embodiments of Figure 6A and Figure 6B shown in the system 200 of the schematic functional block diagram, which shows additional functional details of the system 200 using the magnetron 100. Refer Figure 11, the control module 202 includes a central processing unit (CPU) 215, which performs the required processing, data / instruction storage, input / output, and other required tasks to execute the functions of the exemplary embodiments. As shown, the CPU 215 monitors and controls the filament current If via a filament control module or board 217, and monitors and controls the electromagnet current Ic via an electromagnet control module or board 219. The filament control board 217 drives the filament transformer T1 to generate the required filament current If. The electromagnet control board 219 drives the electromagnet 106 to generate the required electromagnet current Ic. The CPU 215 also monitors and controls the anode current Ia and monitors the anode voltage Va. As described above, the power supply modules 204, 206, 208, 210 generate high voltages and drive the total anode current Ia, which is the sum of individual currents Ia1, Ia2, Ia3, Ia4, respectively.

[0053] Continuing to refer to Figure 11 , the CPU 215 issues three setpoint signals: SET_Ia, the magnetron anode current setpoint; SET_If, the magnetron filament current setpoint; and SET_Ic, the magnetron electromagnet current setpoint. The CPU 215 also monitors four monitoring signals: MON_Ia, the magnetron anode current monitor; MON_If, the magnetron filament current monitor; MON_Ic, the magnetron electromagnet current monitor; and MON_Va, the magnetron anode voltage monitor. All the monitoring signals are routed back to the CPU 215 for monitoring and alarm purposes. Note that in the exemplary embodiments, the anode voltage Va is not a controlled value because it depends on the other three controlled values, namely Ia, If, and Ic. The anode voltage Va is monitored via MON_Va for inspection and alarm. In some exemplary embodiments, the setpoint values are calculated by interpolation from the values stored in the memory of the CPU 215. These values are stored at 10% setpoint intervals, i.e., for each of the parameters Ia, If, Ic, Va, eleven (11) values from 0% to 100% of full scale. According to the exemplary embodiments, the stored setpoint values are the reason for being able to drive the magnetron with a constant impedance. There are many different combinations of the three main setpoint values (Ia, If, Ic) that can produce the same microwave power, but not all combinations are at a constant impedance. According to the present disclosure, the combinations that maintain a constant impedance (i.e., constant Va / Ia) are selected. Table 1 below is an exemplary look-up table for a 75 kW full-scale magnetron according to some exemplary embodiments. Table 1 includes eleven exemplary setpoint values for the parameters Va (volts), Ia (mA), If (A), and Ic (mA) for eleven microwave powers (watts) from 0% to 100%.

[0054]

[0055]

[0056] Table 1

[0057] Figure 12 Schematic diagram of a system 500 using a magnetron 100 of the present disclosure according to some exemplary embodiments. The system 500 can be, for example, a chemical vapor deposition (CVD) system, a CVD synthetic diamond growth system, or other such systems. Referring Figure 12 , the system 500 includes a chamber 517, in which a substrate 509 to be processed can be mounted on a platform 511, and the platform 511 can be heated by a heater 513 (such as a carbon heater). During processing, the pressure in the chamber 517 can be reduced, such as by a vacuum pump (not shown), which is connected to the chamber 517 via a pressure controller 507, and the pressure controller 507 monitors and controls the pressure in the chamber 517.

[0058] The system 500 operates by igniting and maintaining a plasma 515 within the chamber 517 in the presence of the substrate 509 to be processed. The excitation microwave energy generated by the magnetron 100 ignites and maintains the plasma 515. The excitation microwave energy is coupled from the magnetron 100 through its connected waveguide 103 and output flange 105, through an optional power monitor and / or stub tuner 501, through another waveguide 503, which is connected to the interior of the chamber 517 via a microwave port 527 through a microwave transparent window 505, where the plasma 515 is excited. Process gases for the plasma and / or for processing the substrate 509 can be introduced into the interior of the chamber 517 from a gas source through a process gas port 521. The gas (such as, for example, hydrogen (H2) and / or methane (CH4)) can be routed from the gas source (not shown) through a valve 523. The flow rate of the gas is controlled by a mass flow controller 519.

[0059] Long processes, such as CVD synthetic diamond growth, require microwaves at different power levels for several weeks. Therefore, in such an environment, stability, reliability, and availability are very important. In traditional high-power magnetron systems, the output power is controlled by changing the anode current. This scheduling is effective in controlling the power, but it provides an unnecessarily high voltage at lower power levels and a wider spectrum, and increases the risk of arcing and discharging. In contrast, the scheduling of the present disclosure (i.e., the relationship between the life parameters of the magnetron and different output power levels) achieves a constant anode impedance (i.e., voltage / current ratio) at different power levels, thus overcoming these disadvantages of the traditional method, thereby providing higher value to the owner / user. The clearer and narrower spectrum provided by the method of the present disclosure is also highly valuable in these applications using resonant cavities.

[0060] Although many changes and modifications of the present disclosure will become apparent to those of ordinary skill in the art after reading the foregoing description, it should be understood that the specific embodiments shown and described by way of illustration are not intended to be considered limiting. In addition, the subject matter has been described with reference to specific embodiments, but those skilled in the art will envision variations within the spirit and scope of the present disclosure. It should be noted that the foregoing examples are provided for illustrative purposes only and are not to be construed as limiting the present disclosure in any way.

[0061] Although the concepts of the present disclosure have been specifically shown and described with reference to exemplary embodiments thereof, those of ordinary skill in the art will understand that various changes may be made to its form and details without departing from the spirit and scope of the concepts of the present disclosure as defined by the following claims.

Claims

1. A microwave magnetron, comprising: a cathode for emitting electrons; a filament for receiving a filament current to heat the cathode so that the cathode can emit the electrons; an anode capable of applying anode power to affect the electron flow; an anode power input for receiving the anode power to be applied to the anode, the anode power being characterized by an anode current, an anode voltage, and an anode impedance, the anode impedance being the quotient of the anode voltage and the anode current; an electromagnet for providing a magnetic field in which the electrons flow; an electromagnet power input for receiving an electromagnet power and applying the electromagnet power to the electromagnet to control the intensity of the magnetic field, the electromagnet power being characterized by an electromagnet current; and a controller for controlling parameters of the microwave magnetron, the controller adjusting at least one of the parameters of the magnetron to affect the electron flow while keeping the anode impedance constant.

2. The microwave magnetron according to claim 1, wherein, The parameters of the microwave magnetron controlled by the controller include the anode current, the filament current, and the electromagnet current.

3. The microwave magnetron according to claim 1, wherein, The controller monitors the parameters of the microwave magnetron.

4. The microwave magnetron according to claim 3, wherein, The controller is adapted to issue an alarm based on at least one of the monitored parameters of the microwave magnetron.

5. The microwave magnetron according to claim 1, wherein, The controller monitors the anode voltage.

6. The microwave magnetron according to claim 3, wherein, The controller is adapted to issue an alarm based on the monitored anode voltage.

7. The microwave magnetron according to claim 1, further comprising a filament control module between the controller and the filament, the filament control module generating a filament current monitoring signal and forwarding the filament current monitoring signal to the controller, and the filament control module receiving a filament current set signal from the controller.

8. The microwave magnetron according to claim 7, further comprising a filament transformer between the filament control module and the filament.

9. The microwave magnetron according to claim 1, further comprising an electromagnet control module between the controller and the electromagnet, the electromagnet control module generating an electromagnet current monitoring signal and forwarding the electromagnet current monitoring signal to the controller, and the electromagnet control module receiving an electromagnet current set signal from the controller.

10. The microwave magnetron according to claim 1, further comprising a microwave output for providing output microwave energy from the microwave magnetron.

11. The microwave magnetron according to claim 10, wherein, The microwave output can be connected to a system for processing a substrate.

12. The microwave magnetron according to claim 11, wherein, The system is a plasma generation system.

13. The microwave magnetron according to claim 11, wherein, The system is a chemical vapor deposition (CVD) system.

14. The microwave magnetron according to claim 11, wherein, The system is a synthetic diamond growth chemical vapor deposition (CVD) system.

Images