Improved ignition for inductively coupled plasma

Abstract

In one embodiment, the present disclosure relates to a system for generating an inductively coupled plasma. The system includes a dielectric tube and an induction coil circuit. The induction coil circuit includes induction coils surrounding the dielectric tube and connected in series with each other. An intervening capacitor is switchably coupled between the induction coils. The control circuit is configured to cause at least one of the intervening capacitors to be switched out of the induction coil circuit during ignition of the plasma when it is determined that the plasma is to be ignited.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to systems and methods for improved plasma ignition. BACKGROUND

[0002] Substrate processing systems can use inductively coupled plasma (ICP) to process substrates. Processes run by the systems can be short, and thus require fast and reliable ignition of the plasma. They can also require the ICP source to ignite process gases under a variety of chemical and pressure conditions. These requirements present various challenges. For example, in high power applications, the sustained high voltage on the ICP coil can cause heating of the dielectric tube due to ion bombardment. But high voltage is needed in ICP applications to ignite the plasma. SUMMARY

[0003] The present disclosure discusses systems and methods for preventing over-heating of the dielectric tube while ensuring sufficient voltage to reliably ignite inductively coupled plasma.

[0004] In one aspect, the present disclosure can relate to a system comprising: a dielectric tube; an induction coil circuit comprising: induction coils surrounding the dielectric tube and connected in series with each other; intervening capacitors coupled between the induction coils, each intervening capacitor comprising one fixed capacitor or a plurality of fixed capacitors coupled in parallel; and switches operably coupled to the intervening capacitors; and a control circuit configured to cause at least one of the switches to switch at least one of the fixed capacitors of the intervening capacitors out of the induction coil circuit during ignition of the plasma upon determining that the plasma is to be ignited.

[0005] In another aspect, a method of improved plasma ignition comprises: surrounding a dielectric tube with induction coils of an induction coil circuit, the induction coil circuit comprising: induction coils connected in series with each other; intervening capacitors coupled between the induction coils, each intervening capacitor comprising one or more fixed capacitors coupled in parallel; and switches operably coupled to the intervening capacitors; and causing at least one of the switches to switch at least one of the fixed capacitors of the intervening capacitors out of the induction coil circuit during ignition of the plasma upon determining that the plasma is to be ignited. BRIEF DESCRIPTION OF DRAWINGS

[0006] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0007] Figure 1 is a block diagram of a system for processing a substrate according to one embodiment.

[0008] Figure 2 is a block diagram of an inductively coupled plasma source according to one embodiment.

[0009] Figure 3is a schematic diagram of a first inductive coil circuit according to a first embodiment.

[0010] Figure 4 is a schematic diagram of a portion of a second inductive coil circuit according to a second embodiment.

[0011] Figure 5 is a schematic diagram of a portion of a third inductive coil circuit according to a third embodiment.

[0012] Figures 6A to 6C is a schematic diagram of a switch according to different embodiments.

[0013] Figure 7 is a flowchart of a method for improving plasma ignition according to one embodiment.

[0014] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. DETAILED DESCRIPTION

[0015] The following description of preferred embodiments is merely exemplary in nature and is in no way intended to limit the one or more applications, their application, or their uses. The description of illustrative embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The discussion herein describes and illustrates some possible non-limiting combinations of features that can exist alone or in other combinations of features. In addition, the term “or” as used herein, shall only be interpreted as a logical operator in terms of the greater than or equal to zero true outcome, that is, that the outcome of the logical operator is true whenever one or more of its operands are true. Additionally, the phrase “based on” as used herein shall not be construed as meaning “based only on” and thus is not limited to instrumentalities that operate “exclusively based on.” Further, the term “each” when used to refer to each of a plurality of items, does not require that every such item in the entire system or device be referred to, but can instead simply refer to each of the specifically recited items in the system.

[0016] As used throughout, ranges are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, all references cited herein are hereby incorporated by reference in their entireties. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure takes precedent.

[0017] In the following description of drawings and circuits, those skilled in the art will realize that, for clarity, not all peripheral components or circuits are shown or described in the drawings or in the specification. For example, common components such as memory devices and power supplies can not be discussed herein, as one of ordinary skill in the art will readily understand their role. Also, when two components are referred to as being “coupled” or “operably coupled,” this includes components that are related in any way, such that power or signal information can pass from one component to the other (directly or indirectly), and thus these terms do not require a direct connection between the components without intervening components.

[0018] Note that, for the sake of clarity and convenience in describing like components or features, identical or similar components or features can be described using the same or similar reference numerals across different embodiments or drawings. This does not imply that the components or features identified by the same reference numerals must be identical in different embodiments. Rather, it is intended that the components or features identified by the same reference numerals in different embodiments play the same or similar role or perform the same or similar function.

[0019] Features of the present invention can be implemented in software, hardware, firmware, or a combination thereof. The computer programs described herein are not limited to any particular embodiment and can be implemented in an operating system, an application program, a foreground or background process, a driver, or any combination thereof. The computer programs can be executed on a single computer or server processor or multiple computers or server processors.

[0020] The processors described herein can be any central processing unit (CPU), microprocessor, microcontroller, computing or programmable device or circuit configured for executing computer program instructions (e.g., code). The various processors can be embodied in any suitable type of computer and / or server hardware (e.g., desktop, laptop, notebook, tablet, cellular phone, etc.) and can include all of the usual ancillary components required to form a functional data processing device, including but not limited to buses, software and data storage devices (such as volatile and non-volatile memory), input / output devices, graphical user interfaces (GUIs), removable data storage devices, and wired and / or wireless communication interface devices (including Wi-Fi, Bluetooth, LAN, etc.). As used herein, the term “processor” can refer to one or more processors.

[0021] The computer-executable instructions or programs (e.g., software or code) and data described herein can be programmed into and tangibly embodied in non-transitory computer- readable media that are accessible by and retrievable by the respective processors as described herein, which configure and direct the processors to perform the desired functions and processes by executing the instructions encoded in the media. A device embodying a programmable processor configured with such non-transitory computer-executable instructions or programs can be referred to as a “programmable device” or “device,” and a plurality of programmable devices in mutual communication can be referred to as a “programmable system.” It should be noted that the non-transitory “computer-readable media” as described herein can include, but is not limited to, any suitable volatile or non-volatile memory, including random access memory (RAM) and its various types, read-only memory (ROM) and its various types, USB flash drives, and magnetic or optical data storage devices (e.g., internal / external hard drives, floppy disks, magnetic tape CDs-ROM, DVD-ROM, optical disks, ZIP™ drives, Blu-ray disks, etc.), which can be written to and / or read by a processor operably connected to the media.

[0022] In certain embodiments, the present application can be embodied in the form of computer- implemented processes and apparatuses, such as processor-based data processing and communication systems or computer systems for practicing those processes. The present application can also be embodied in the form of software or computer program code embodied in non-transitory computer-readable storage media, which, when loaded into a data processing and communication system or computer system, configures the processor to create specific logic circuits configured for implementing the processes.

[0023] As described above, in high power applications, the sustained high voltage on the ICP coil can cause heating of the dielectric tube due to ion bombardment. To address this issue, a capacitor can be inserted, for example, between the inductors of the ICP coil to reduce the voltage. The capacitor cancels the voltage generated by the inductive coil, keeping the overall ICP coil voltage low. This is the approach taken in U.S. Patent No. 10,541,114, which is incorporated by reference in its entirety. This approach is effective in preventing heating of the dielectric tube. However, in ICP applications, a high voltage across the ICP coil is required to reliably ignite the plasma. Thus, by reducing the voltage, the plasma ignition becomes less reliable.

[0024] One can try to solve this low voltage ignition problem by using a separate secondary inductive coil structure for ignition and a separate generator attached to the ICP coil by which another frequency can be injected. But these components will add significant cost. One can also or alternatively inject a short high voltage DC pulse to start the plasma, but this method similarly requires a separate inductive coil structure or separate electrodes on both sides and will thus add significant cost.

[0025] The present disclosure discusses simpler and more cost effective systems and methods that prevent heating of the dielectric tube while also ensuring sufficient voltage to ignite the plasma. Turning to the drawings, Figure 1 is a block diagram of a system 100 for processing a substrate according to one embodiment. The system 100 includes an inductively coupled plasma (ICP) source (e.g., a remote plasma unit) that provides an ICP 207 to a process chamber 300. The process chamber 300 is shown to include standard components such as a chuck 304 for holding a substrate 302. It should be noted that process chambers are well known and thus will not be discussed in detail here. For more details regarding potential characteristics of process chambers, see, for example, U.S. Patent No. 10,541,114 (incorporated by reference).

[0026] Figure 2 is a block diagram of the ICP source 200, and Figure 3 is a schematic diagram of a first inductive coil circuit 210 of the ICP source 200 according to one embodiment. The ICP source 200 is configured to generate an inductively coupled plasma such as (but not limited to) an inductively coupled hydrogen plasma. An example process gas source 202 provides a process gas 203 to a dielectric tube 206. The dielectric tube 206 is surrounded by inductive coils 211, 212, 213, 214 that form part of an inductive coil circuit 210 that receives RF power from an RF power source 204. The inductive coils 211-214 are connected in series with each other. Four inductive coils 211-214 are utilized, but the present invention is not limited to any particular number of inductive coils. Intervening capacitors 221, 222, 223 are coupled between the inductive coils 211-214, and switches 231-233 are operably coupled to the intervening capacitors 221-223 to enable the intervening capacitors 221-223 to be switched out of the inductive coil circuit 210 (in this example, by being shorted). In this embodiment, each of the intervening capacitors 221-223 is coupled between adjacent ones of the inductive coils 211-214 (e.g., intervening capacitor 221 is coupled between adjacent inductive coils 211 and 212), and the intervening capacitors 221-223 are in series with the inductive coils 211-214.

[0027] It should be noted that when the plasma ignites in the inductively coupled coil, the impedance of the coil changes significantly due to the interaction between the plasma and the electromagnetic field of the coil. When the plasma ignites, it becomes a conductive medium that interacts with the magnetic field of the coil. The interaction induces a current in the plasma, which affects the impedance of the coil. The ignited plasma will typically provide a path for the induced current, reducing the inductive reactance of the coil, causing the impedance of the coil to drop when the plasma ignites. After ignition, the impedance will stabilize at a new value that is lower than the initial impedance. The new impedance will depend on factors such as the plasma density, temperature, and the frequency of the applied electromagnetic field.

[0028] The control circuit 250 is configured to cause at least one of the switches 231-233 to switch at least one of the fixed capacitors 221-223 of the capacitor out of the inductive coil circuit 210 during ignition of the plasma 209 when it is determined that the plasma 209 is to be ignited. The exemplary control circuit 250 is also configured to switch the at least one of the fixed capacitors that was switched out of the inductive coil circuit back into the inductive coil circuit after the plasma ignites, enabling the inductive coil circuit 210 to have two modes of operation, one for the ignition period and one for the no ignition period. By enabling these two modes, the ICP source 200 is able to generate a high voltage across the inductive coils 211-214 during ignition to help ignite, and also bring the capacitors back into the circuit to lower the voltage in the inductive coils and prevent overheating of the dielectric tube. The high voltage across the inductive coils 211-214 increases the resonant frequency of the inductive coils 211-214. The frequency from the RF power source 204 can also be increased to further increase the voltage across the inductive coils 211-214, and the load can become resonant. Once the plasma 209 is ignited and the capacitors 221-223 are returned into the circuit, the resonant frequency of the inductive coils 211-214 will decrease, and the frequency from the RF power source 204 can also be reduced. The drive frequency of the RF power source 204 can vary, for example, from hundreds of kilohertz to several megahertz. Its RF power can also vary, for example, from tens of watts to tens of kilowatts.

[0029] The presence control circuit 250 can determine that the plasma 209 is to be ignited and that, therefore, at least one of the intervening capacitors 221-223 should be switched off in a number of possible ways. For example, the control circuit 250 can determine that the RF power from the RF power supply 204 that can be provided to the inductive coil circuit 210 is turned off or is in an off state. In response, the control circuit 250 can automatically switch off the at least one intervening capacitor in preparation for the next ignition. The control circuit 250 can know that the RF power is turned off based on a signal received from the RF power supply 204. For example, a matching network (not shown) coupled to the control circuit can receive an RF on signal that informs the matching (and thus the control circuit) when the RF power is on or off. Alternatively, a VI sensor or directional coupler can be used to detect the presence of the RF power. Ignition can occur quickly (e.g., every few hundred milliseconds) or less quickly (e.g., every 10 seconds).

[0030] In an example embodiment, the control circuit 250 includes a processor. The processor can be any type of suitably programmed processing device, such as a computer or microprocessor, configured to execute computer program instructions (e.g., code). The processor can be embodied in any suitable type of computer and / or server hardware (e.g., desktop, laptop, notebook, tablet, cellular phone, etc.) and can include all common ancillary components necessary to form a functional data processing device, including but not limited to a bus, software and data storage devices (such as volatile and non-volatile memory), input / output devices, a graphical user interface (GUI), removable data storage devices, and wired and / or wireless communication interface devices (including Wi-Fi, Bluetooth, LAN, etc.). The processor of the example embodiment is configured with a particular algorithm to enable the ICP source 200 to perform the functions described herein.

[0031] Note that the inductive coil circuit 210 can also include capacitors 241 and 242 coupled to the RF power supply 204. In an example embodiment, the capacitor 241 is a first fixed capacitor coupled between a first output terminal (-V) of the RF power supply 204 and one end of the first inductive coil circuit 210, and the capacitor 242 is a second fixed capacitor coupled between a second output terminal (+V) of the RF power supply 204 and an opposite end of the first inductive coil circuit 210. However, in other embodiments, these capacitors can be omitted.

[0032] In Figures 2-3 In an example embodiment, each intervening capacitor 221-223 includes a single fixed capacitor. Further, each single fixed capacitor 221-223 is coupled to a corresponding switch of the switches 231-233, the corresponding switch configured to short the single fixed capacitor to switch the single fixed capacitor out of the inductive coil circuit. For example, the switch 231 is configured to short the fixed capacitor 221.

[0033] In other embodiments, one or more of the intervening capacitors can comprise a plurality of fixed capacitors coupled in parallel, for example Figure 4 and Figure 5 as shown. Figure 4 is a schematic diagram of a portion of a second inductor circuit 210B according to a second embodiment. In this embodiment, Figure 3 The first capacitor switching circuit 251 of the inductor circuit 210A is replaced by a second capacitor switching circuit 251B. This switching circuit 251B comprises three capacitors 221A, 221B, 221C coupled in parallel. Of these capacitors, the capacitor 221A is always maintained in the inductor circuit 210B, including during ignition. The other two capacitors 221B, 221C can be switched out of the inductor circuit 210B by switches 231B, 231C, respectively, during ignition. In this approach, the capacitor 221A can continuously provide voltage reduction for reducing the voltage in the inductors 211-214 and reducing overheating of the dielectric tube 206, while the switching capacitors 221B, 221C can be turned off to assist with ignition.

[0034] Figure 5 A third inductor circuit 210C is provided that utilizes a third capacitor switching circuit 251C. Unlike the existing switching circuit 251B, the switching circuit 251C includes a switch 231A positioned to short the capacitor 221A. In this arrangement, all three capacitors 221A-C are capable of being switched out of the inductor circuit 210C. Thus, the circuit 210C is capable of providing more significant voltage reduction to assist with ignition.

[0035] Note that the present invention is not limited to any particular number of capacitors coupled in parallel, or any number of those capacitors that can be switched, or any particular method of switching the capacitors out of the inductor circuit. Moreover, adjacent inductors can use different capacitor switching circuits with different numbers of capacitors and different switching arrangements. Thus, in some cases, certain intervening capacitors (e.g., intervening capacitor 221) between adjacent inductors (e.g., coils 211, 212) can be completely turned off during ignition, while other intervening capacitors (e.g., intervening capacitor 222) can remain turned on during ignition. The number of intervening capacitors to be turned off can depend on how much ignition support is needed, including considerations such as how much voltage is needed in the inductors and the size and number of inductors.

[0036] The present invention is not limited to any particular type of switch for turning on and off the intervening capacitors or the fixed capacitors that comprise the intervening capacitors. For example, the present invention can use PIN diodes, NIP diodes, or FETs. Figure 6AA schematic of example switches 601, 602, 603 that can be utilized is provided to FIG. C. Figure 6A A MOSFET switch is shown, Figure 6B A JFET switch is shown, and Figure 6C A PIN diode switch is shown. The inductive coil circuit can always use the same type of switch or different types of switches.

[0037] It should be noted that more common characteristics of ICP sources are not discussed in detail herein for the sake of clarity and efficiency. For more details on potential characteristics of ICP sources, see, for example, U.S. Patent No. 10,541,114 (incorporated by reference above) and its different ICP generation systems.

[0038] Figure 7 is a flowchart of a method 400 for improving ignition of a plasma according to one embodiment. In a first operation 401, a dielectric tube 206 can be surrounded by inductive coils 211-214, e.g. Figure 2 are shown. The inductive coils 211-214 form part of an inductive coil circuit, such as the inductive coil circuits 210, 210B, and 210C discussed above. In a second operation 402, it is determined that a plasma is to be ignited as described above. In operation 403, upon determining that the plasma 209 is to be ignited, at least one of the switches 231-233 is caused to switch at least one of the fixed capacitors 221-223 of the intervening capacitors out of the inductive coil circuit 210 during ignition of the plasma 209. Note that the method 400 is not limited to the embodiments discussed above.

[0039] While this application has been described with respect to specific examples including presently preferred modes of carrying out the application, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments can be utilized and structural and functional modifications can be made without departing from the scope of the present application. Therefore, the spirit and scope of the application should be construed broadly as set forth in the appended claims.

Claims

1. A system comprising: Dielectric tube; Induction coil circuit, including: Induction coils, which are wrapped around a dielectric tube and connected in series with each other; Intervening capacitors, coupled between induction coils, each intervening capacitor comprising one fixed capacitor or multiple fixed capacitors coupled in parallel; and A switch, operablely coupled to an intervention capacitor; and A control circuit configured to, upon determining that the plasma will be ignited, cause at least one of the switches to switch at least one of the fixed capacitors of the intervening capacitor out of the induction coil circuit during the ignition of the plasma.

2. The system according to claim 1, wherein, The control circuit is also configured to switch at least one of the fixed capacitors that was switched out of the induction coil circuit back into the induction coil circuit after plasma ignition.

3. The system according to claim 1, wherein, Each intervening capacitor is coupled between adjacent induction coils in the induction coil.

4. The system according to claim 1, wherein, Each intervention capacitor is a single fixed capacitor.

5. The system according to claim 4, wherein, Each individual fixed capacitor is coupled to a corresponding switch in the switch, the corresponding switch being configured to short-circuit the individual fixed capacitor to switch the individual fixed capacitor out of the induction coil circuit.

6. The system according to claim 1, wherein, At least one of the intervention capacitors includes a plurality of fixed capacitors coupled in parallel, wherein, during plasma ignition, a portion of the plurality of fixed capacitors is switched out of the induction coil circuit, and a portion of the plurality of fixed capacitors is not switched out of the induction coil circuit.

7. The system according to claim 1, wherein, The induction coil circuit is configured to generate inductively coupled plasma.

8. The system according to claim 1, wherein, The intervention capacitor is connected in series with the induction coil, and the switch includes a PIN diode, a NIP diode, or a FET.

9. The system according to claim 1, wherein, Determining that the plasma will be ignited includes determining that the RF power supplied by the RF power source to the induction coil circuit has been turned off.

10. The system according to claim 1: It also includes an RF power supply that provides RF power to the induction coil circuit; in, When it is determined that the plasma will be ignited, the control circuit is also configured to reduce the frequency of the RF power supplied by the RF power source.

11. An improved method for plasma ignition, the method comprising: An induction coil circuit is used to wrap a dielectric tube with an induction coil. The induction coil circuit includes: Induction coils connected in series with each other; Intervening capacitors coupled between induction coils, each intervening capacitor comprising one or more fixed capacitors coupled in parallel; and A switch operablely coupled to the intervention capacitor; and When it is determined that the plasma will be ignited, at least one of the switches will switch at least one of the fixed capacitors of the intervening capacitor out of the induction coil circuit during the ignition of the plasma.

12. The method of claim 11, further comprising: After plasma ignition, at least one of the fixed capacitors that was switched out of the induction coil circuit is switched back into the induction coil circuit.

13. The method according to claim 11, wherein, Each intervening capacitor is coupled between adjacent induction coils in the induction coil.

14. The method according to claim 11, wherein, Each intervention capacitor is a single fixed capacitor.

15. The method according to claim 14, wherein, Each individual fixed capacitor is coupled to a corresponding switch in the switch, the corresponding switch being configured to short-circuit the individual fixed capacitor to switch the individual fixed capacitor out of the induction coil circuit.

16. The method according to claim 11, wherein, At least one of the intervention capacitors includes a plurality of fixed capacitors coupled in parallel, wherein, during plasma ignition, a portion of the plurality of fixed capacitors is switched out of the induction coil circuit, and a portion of the plurality of fixed capacitors is not switched out of the induction coil circuit.

17. The method according to claim 11, wherein, The induction coil circuit is configured to generate inductively coupled plasma.

18. The method according to claim 11, wherein, The intervention capacitor is connected in series with the induction coil, and the switch includes a PIN diode, a NIP diode, or a FET.

19. The method according to claim 11, wherein, Determining that the plasma will be ignited includes determining that the RF power supplied by the RF power source to the induction coil circuit has been turned off.

20. The method according to claim 11: It also includes an RF power supply that provides RF power to the induction coil circuit; and When it is determined that the plasma will be ignited, the frequency of the RF power supplied by the RF power source is reduced.

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