Patent Publication Number: US-10332725-B2

Title: Systems and methods for reversing RF current polarity at one output of a multiple output RF matching network

Description:
FIELD 
     The present disclosure relates to substrate processing systems, and more particularly to substrate processing systems using inductively coupled plasma. 
     BACKGROUND 
     The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Substrate processing systems are typically used to deposit and etch thin film on substrates such as semiconductor wafers. Examples of etching include wet chemical etching and dry etching. Dry etching may be performed using plasma generated by inductively-coupled plasma (ICP). The inductively-coupled plasma may be generated by coils arranged outside of a processing chamber adjacent to a dielectric window. Process gas flowing inside the processing chamber is ignited to create plasma. 
     Some ICP systems use two coils and flow current in the same direction in both coils. Etch rate maps tend to show an “M” shape etch pattern on the substrate surface where the maximum etch rate is at a mid-radius. The non-uniformity is generally not acceptable for some processes. 
     SUMMARY 
     A substrate processing tool for processing a substrate includes a processing chamber including a substrate support. First and second coils are arranged outside of the processing chamber. Each of the first and second coils include first and second conductors. A coil driving circuit drives current through the coils to generate plasma in the processing chamber. A coil reversing circuit is configured to selectively reverse a polarity of current flowing through the first and second conductors of the first coil. The coil reversing circuit includes an H-bridge circuit. 
     In other features, the H-Bridge circuit includes a double-pole, double-throw relay. The H-Bridge circuit includes a first single-pole, double-throw relay and a second single-pole, double-throw relay. The H-Bridge circuit includes first, second, third and fourth switches and a controller configured to selectively switch states of the first, second, third and fourth switches. 
     In other features, the first, second, third and fourth switches include field effect transistors (FETs). The first, second, third and fourth switches include PIN diodes. The H-Bridge circuit includes a rotary switch. The H-Bridge circuit includes first, second third and fourth variable vacuum capacitors and a motor driver configured to drive gears to selectively adjust an impedance of the first, second third and fourth variable vacuum capacitors. 
     In other features, the H-Bridge circuit includes first, second third and fourth variable impedance circuits and a controller configured to selectively adjust an impedance of the first, second third and fourth variable impedance circuits. 
     In other features, the first, second third and fourth variable impedance circuits include a variable capacitance. The first, second third and fourth variable impedance circuits include a first variable capacitance in series with a parallel combination of a second variable capacitance and an inductance. 
     In other features, the coil driving circuit includes an RF source and a tuning circuit in communication with the RF source, the coil reversing circuit and the second coil. The tuning circuit includes a transformer capacitively coupled tuning circuit. The first coil is arranged inside of the second coil. The first coil is arranged outside of the second coil. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an example of an inductively coupled plasma (ICP) substrate processing system according to the present disclosure; 
         FIG. 2  is a plan view of an example of inner and outer coils; 
         FIG. 3  is electrical schematic of an example of a coil reversing circuit including H-bridge circuits according to the present disclosure; 
         FIGS. 4A and 4B  are electrical schematics of an example of an H-bridge circuit including a relay; 
         FIGS. 5A and 5B  are electrical schematics of an example of an H-bridge circuit including a rotary switch; 
         FIGS. 6A and 6B  are electrical schematics of an example of an H-bridge circuit including switches; 
         FIGS. 7A and 7B  are electrical schematics of an example of an H-bridge circuit including a motor drive and variable vacuum capacitors; and 
         FIGS. 8A to 8D  are electrical schematics of an example of an H-bridge circuit including a controller and variable capacitors or series/parallel resonant circuits. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     The present disclosure relates to a reversing circuit in an inductively coupled plasma substrate processing system. In some examples, the reversing circuit uses one or more H-bridge circuits to switch RF current polarity or phasing of one of the coils to allow processes to run with coil currents flowing in parallel and antiparallel directions. The dual current mode allows legacy process recipes and new process recipes to take advantage of RF current polarity-reversed modes for improved etch rate uniformity. 
     Referring now to  FIG. 1 , an example of a substrate processing system  10  according to the present disclosure is shown. The substrate processing system  10  includes a coil driving circuit  11 . In some examples, the coil driving circuit  11  includes an RF source  12  and a tuning circuit  13 . The tuning circuit  13  may be directly connected to one or more coils  16  or connected by a coil reversing circuit  15  to one or more coils  16 . The tuning circuit  13  is used to tune an output of the RF source  12  to a desired frequency and/or a desired phase. The coil reversing circuit  15  is used to selectively switch the polarity of current through one or more of the coils  16 . 
     In some examples, a gas plenum  20  may be arranged between the coils  16  and a dielectric window  24 . The dielectric window  24  is arranged along one side of a processing chamber  28 . The processing chamber  28  further comprises a substrate support  32 . The substrate support  32  may include an electrostatic chuck, a mechanical chuck or other type of chuck. Process gas is supplied to the processing chamber  28  and plasma  40  is generated inside of the processing chamber  28 . The plasma  40  etches an exposed surface of the substrate  34 . An RF source  50  and a bias matching circuit  52  may be used to bias the substrate support  32  during operation. 
     A gas delivery system  56  may be used to supply a process gas mixture to the processing chamber  28 . The gas delivery system  56  may include process and inert gas sources  57 , a gas metering system  58  such as valves and mass flow controllers, and a manifold  59 . A gas delivery system  60  may be used to deliver gas  62  via a valve  61  to the gas plenum  20 . The gas may include cooling gas that is used to cool the coils  16  and the dielectric window  24 . A heater  64  may be used to heat the substrate support  32  to a predetermined temperature. An exhaust system  65  includes a valve  66  and pump  67  to remove reactants from the processing chamber  28  by purging or evacuation. 
     A controller  54  may be used to control the etching process. The controller  54  monitors system parameters and controls delivery of the gas mixture, striking, maintaining and extinguishing the plasma, removal of reactants, supply of cooling gas, etc. 
     Referring now to  FIG. 2 , an example of the coil  16  is shown. The coil  16  may include an inner coil  80  and an outer coil  82 . The inner coil  80  includes a first conductor  80 - 1  having an input end In 1  and an output end Out 1  and a second conductor  80 - 2  having an input end In 2  and an output end Out 2 . The first conductor  80 - 1  and the second conductor  80 - 2  are wound in a generally circular or looped path adjacent to each other. The outer coil  82  includes a first conductor  82 - 1  having an input end In 3  and an output end Out 3  and a second conductor  82 - 2  having an input end In 4  and an output end Out 4 . The first conductor  82 - 1  and the second conductor  82 - 2  are wound in a generally circular or looped path adjacent to each other. 
     In some examples, the tuning circuit  13  may include a transformer-coupled capacitive tuning circuit (TCCT), which is connected to first and second coils  16 , although other types of tuning circuits can be used. The TCCT circuit typically includes one or more fixed or variable capacitors. An example of a TCCT circuit is shown and described in commonly assigned U.S. Publication No. 2013/0135058 to Long et al., which is hereby incorporated by reference in its entirety. 
     Referring now to  FIG. 3 , the coil reversing circuit  15  is shown to include an H-bridge circuit. The tuning circuit  13  is shown to include a TCCT input circuit  102  and a TCCT output circuit  104 . At least some of the coils  16  are connected to the coil reversing circuit  15  between the TCCT input circuit  102  and the TCCT output circuit  104 . For example only, the coil reversing circuit  15  may include an H-bridge circuit  110 . The H bridge circuit  110  is connected between the TCCT input circuit  102 , the first conductor  80 - 1  of the inner coil  80  and the TCCT output circuit  104  and between the TCCT input circuit  102 , the second conductor  80 - 2  of the inner coil  80  and the TCCT output circuit  104 . 
     While the coil reversing circuit  15  is shown connected to the inner coil  80  in  FIG. 3 , the coil reversing circuit  15  may optionally be connected to the outer coil  82  or connected to both the inner coil  80  and the outer coil  82  (so that a reversing selection can be made between the inner coil  80  and the outer coil  82 ). As will be described further below, the coil reversing circuit  15  selectively switches the polarity of current flowing through the conductors  80 - 1  and  80 - 2  of the inner coil  80 . 
     Referring now to  FIGS. 4A and 4B , the H-bridge circuit  110  includes relays  120 - 1  and  120 - 2 . As can be appreciated, current reversal through one of the conductors  80 - 1  of the inner coil  80  is shown. A similar approach can be used to reverse current flowing through other conductors of other coils. 
     In  FIG. 4A , the relays  120 - 1  and  120 - 2  are shown in a first state to flow current through the conductor  80 - 1  in a first direction from the input end In 1  to the output end Out 1 . In  FIG. 4B , the relays  120 - 1  and  120 - 2  are shown in a second state to flow current through the conductor  80 - 1  in a second direction from the output end Out 1  to the input end In 1 . While high-voltage, high-current single-pole, double-throw relays are shown, a high-voltage, high-current double-pole, double-throw relay may be used. 
     Referring now to  FIGS. 5A and 5B , the H-bridge circuit  110  includes a rotary switch  130 . In  FIG. 5A , the rotary switch  130  is shown in a first state to flow current through the conductor  80 - 1  in a first direction from the input end In 1  to the output end Out 1 . In  FIG. 5B , the rotary switch  130  is shown in a second state to flow current through the conductor  80 - 1  in a second direction from the output end Out 1  to the input end In 1 . In some examples, the rotary switch  130  includes a two-pole, two-position rotary switch capable of withstanding high voltage and high current. 
     Referring now to  FIGS. 6A and 6B , the H-bridge circuit  110  includes switches SW 1 , SW 2 , SW 3 , and SW 4 . In  FIG. 6A , the switches SW 1  and SW 4  are in a closed state and the switches SW 2  and SW 3  are in an open state to flow current through the conductor  80 - 1  in a first direction from the input end In 1  to the output end Out 1 . In  FIG. 6B , the switches SW 1  and SW 4  are in an open state and the switches SW 2  and SW 3  are in a closed state to flow current through the conductor  80 - 1  in a second direction from the output end Out 1  to the input end In 1 . A controller  140  may be used to control states of the switches SW 1 , SW 2 , SW 3 , and SW 4 . 
     Examples of switches SW 1 , SW 2 , SW 3 , and SW 4  include high voltage, high current PIN diode switches and high voltage, high current field effect transistors (FETs). 
     Referring now to  FIGS. 7A and 7B , the H-bridge circuit  110  includes a motor driver  150 , gears  152 - 1 ,  152 - 2 ,  152 - 3  and  152 - 4  (collectively gears  152 ) and variable vacuum capacitors (VVC)  160 - 1 ,  160 - 2 ,  160 - 3 , and  160 - 4 . In  FIG. 7A , the motor driver  150  drives the VVC  160 - 1  and  160 - 4  using gears  152 - 1  and  152 - 4  to a low impedance state and the VVC  160 - 2  and  160 - 3  using gears  152 - 2  and  152 - 3  to a high impedance state to flow current through the conductor  80 - 1  in a first direction from the input end In 1  to the output end Out 1 . In  FIG. 7B , the motor driver  150  drives the VVC  160 - 1  and  160 - 4  using gears  152 - 1  and  152 - 4  to a high impedance state and the VVC  160 - 2  and  160 - 3  using gears  152 - 2  and  152 - 3  to a low impedance state to flow current through the conductor  80 - 1  in a second direction from the output end Out 1  to the input end In 1 . 
     In this example, the VVCs can be linked to the same motor driver  150  (or two or more motor drivers) with gearing such that two of the VVCs are driven to a minimum capacitance while the other two of the VVCs are driven to a maximum capacitance. Use of the VVCs in this way mimics variation of a switch element from low to high impedance and approximates normal relay operation. 
     Referring now to  FIGS. 8A to 8D , the H-bridge circuit  110  includes a controller  180  and variable impedance circuits  190 - 1 ,  190 - 2 ,  190 - 3  and  190 - 4  (collectively variable impedance circuits  190 ). In  FIG. 8A , the controller  180  sets the variable impedance circuits  190 - 1  and  190 - 4  to a low impedance state and the variable impedance circuits  190 - 2  and  190 - 3  to a high impedance state to flow current through the conductor  80 - 1  in a first direction from the input end In 1  to the output end Out 1 . In  FIG. 8B , the controller  180  sets the variable impedance circuits  190 - 1  and  190 - 4  to a high impedance state and the variable impedance circuits  190 - 2  and  190 - 3  to a low impedance state to flow current through the conductor  80 - 1  in a second direction from the output end Out 1  to the input end In 1 . 
     In  FIG. 8C , an example of the variable impedance circuit  190  includes a variable capacitor Cv. In  FIG. 8D , an example of the variable impedance circuit  190  includes a first variable capacitor Cv 1  in series with a parallel combination of a second variable capacitor Cv 2  and an inductor L 1 . In some examples, the variable impedance circuits  190  vary from nearly 0 Ohms to very large impedances on order 103 Ohms. 
     During operation, the motor driver or the controller can switch between driving current in the same direction through both of the coils or reversing the direction of current through one of the coils. 
     The relays and rotary switches provide mechanical switch implementations of the H-bridge circuits. These implementations may require RF power to be turned off prior to switch operation in order to avoid arcing at switch contacts of the relays and rotary switches. The remaining H-bridge implementations described herein allow the flexibility to switch operation while RF power is being supplied. 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. 
     In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, radio frequency (RF) generator settings, RF matching circuit settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system. 
     Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer. 
     The controller, in some implementations, may be a part of or coupled to a computer that is integrated with the system, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber. 
     Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers. 
     As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory.