Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32174—Circuits specially adapted for controlling the RF discharge
  • H01J37/32183—Matching circuits
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32137—Radio frequency generated discharge controlling of the discharge by modulation of energy
  • H01J37/32155—Frequency modulation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32137—Radio frequency generated discharge controlling of the discharge by modulation of energy
  • H01J37/32155—Frequency modulation
  • H01J37/32165—Plural frequencies
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P50/00—Etching of wafers, substrates or parts of devices
  • H10P50/20—Dry etching; Plasma etching; Reactive-ion etching
  • H10P50/24—Dry etching; Plasma etching; Reactive-ion etching of semiconductor materials
  • H10P50/242—Dry etching; Plasma etching; Reactive-ion etching of semiconductor materials of Group IV materials

Definitions

• Embodiments of the present disclosure generally relate to substrate processing systems and, more specifically, to methods and apparatus for fast and repeatable plasma ignition and tuning in plasma chambers.
• a plasma chamber is typically coupled to a radio frequency (RF) source to provide energy to ignite and/or maintain a plasma during substrate processing.
• RF radio frequency
• a matching network also referred to as a tunable matching circuit or match box is connected between the RF source and the plasma chamber.
• Past techniques for igniting (i.e., striking) the plasma in plasma chambers, or tuning across plasma transitions include using match boxes with motorized variable capacitors to ignite the plasma.
• this method can be slow due to the slow speed of the capacitor stepper motors ⁇ e.g., in the range of 0.5 - 2.0 seconds).
• this method suffers from poor repeatability.
• the inventors have observed that in plasma chambers that require high voltages to ignite a plasma, those high voltages may not be reachable using the match box.
• the trajectory of the match capacitor position of may miss the high voltage point or reach it with varying delay.
• Another technique for igniting plasmas, or tuning across plasma transitions is the use of frequency sweeping of the RF power generators to reach high voltages in plasma chamber to assist in plasma striking.
• the inventors have observed that although this method can be fast to ignite plasma ( ⁇ 0.5s), the variation in generator frequency can lead to variation in on-wafer process results and variation in RF measurement results. [0005] Therefore, the inventors believe that there is a need in the art for improved methods and apparatus for fast and repeatable plasma ignition and/or tuning across plasma transitions in plasma chambers.
• an apparatus for plasma processing in a process chamber may include a first RF power supply having frequency tuning, a first matching network coupled to the first RF power supply, and a controller to control the first RF power supply and the first matching network, wherein the controller is configured to: initiate a plasma transition by at least one of instructing the RF power supply to provide RF power to the process chamber, instructing the RF power supply to change a level of RF power delivered to the process chamber, or changing a pressure in the process chamber, wherein the RF power supply operate at a first frequency and the matching network is in a hold mode, instruct the RF power supply to adjust the first frequency to a second frequency during a first time period to ignite the plasma, instruct the RF power supply to adjust the second frequency to a known third frequency during a second time period while maintaining the plasma, and change an operational mode of the matching
• the method includes initiating a plasma transition by at least one of providing RF power to the process chamber, changing level of RF power delivered to the process chamber, or changing a pressure in the process chamber, wherein the RF power supply is operating at a first frequency and the matching network is in a hold mode, adjusting the first frequency, using the RF power supply, to a second frequency during a first time period to ignite the plasma, adjusting the second frequency, using the RF power supply, to a known third frequency during a second time period while maintaining the plasma, and changing an operational mode of the matching network to an automatic tuning mode to reduce a reflected power of the RF power provided by the RF power supply.
• a system for plasma processing in a process chamber may include a process chamber having an antenna assembly and a substrate support pedestal, a first matching network coupled to the antenna assembly;
• a first RF source coupled to the first matching network, a matching network, a second matching network coupled to the substrate support pedestal, a second RF source coupled to the second matching network, a controller to control the first RF source, the first matching network, the second RF source, and the second controller, wherein the controller is configured to: instructing the first RF source to provide RF power to the process chamber, wherein the first source operates at a first frequency and the first matching network is in a hold mode; instruct the first RF source to adjust the first frequency to a second frequency during a first time period to ignite the plasma; instruct the first RF source to adjust the second frequency to a known third frequency during a second time period while maintaining the plasma; and change an operational mode of the first matching network to an automatic tuning mode to reduce a reflected power of the RF power provided by the first RF source.
• Figure 1 is a schematic diagram of a semiconductor wafer processing system in accordance with some embodiments of the present disclosure.
• Figure 2 is an exemplary matching network suitable for use in connection with some embodiments of the present disclosure.
• Figure 3 is a schematic chart showing the timing features of matching networks and RF generators in accordance with some embodiments of the present disclosure.
• Figure 4 is a schematic chart showing a timing diagram of frequencies provided by matching networks and RF generators in accordance with some embodiments of the present disclosure.
• Figure 5 depicts a flow diagram of a method for igniting a plasma and reducing a reflected power in a process chamber.
• Embodiments of the present disclosure include methods and apparatus for igniting a plasma and/or reducing a reflected power in a process chamber across a plasma transition.
• Exemplary embodiments of the present disclosure provide methods and apparatus that combine a mechanical matching network and a variable frequency RF power generator with a set of timing rules. By operating the two tuning techniques in the appropriate order and timing, fast and repeatable plasma ignition and/or tuning is possible, with a repeatable end frequency and plasma distribution.
• the combined system for fast and repeatable plasma ignition and/or tuning may facilitate better process performance in terms of run-to-run and wafer-to-wafer repeatability of on-wafer process results
• Embodiments of the present disclosure provide procedures that enable a repeatable and stable window of operation for using RF generators having frequency tuning (also referred to as frequency sweep) in combination with dynamic matching networks.
• frequency tuning also referred to as frequency sweep
• one advantage of these procedures is being able to ignite and tune a plasma within less than about 0.5 seconds, thereby minimizing the time during which the substrate is exposed to an unstable plasma or a plasma which is not well controlled.
• the description below may refer to certain processes, RF frequencies, and RF powers, the teachings provided herein may generally be utilized to advantage for other processes, other frequencies, and other power levels.
• FIG. 1 is a plasma enhanced substrate processing system 100 that in some embodiments is used for processing semiconductor wafers 122 (or other substrates and work pieces).
• ICP Inductively Coupled Plasma
• CCP Capacitively Coupled Plasma
• plasma annealing plasma enhanced chemical vapor deposition
• physical vapor deposition physical vapor deposition
• plasma cleaning and the like.
• This illustrative plasma enhanced substrate processing system 100 comprises a plasma reactor 101 , a process gas supply 126, a controller 1 14, a first RF power supply 1 12, a second RF power supply 1 16, a first matching network 1 10 (also referred to as a tunable matching circuit or a match box), and a second matching network 1 18.
• Either or both of the first and second RF power supplies 1 12, 1 16 may be configured for fast plasma ignition and fast frequency tuning ⁇ e.g., the source may be able to vary frequency within about +/- 5 percent in response to a sensed reflected power measurement in order to minimize reflected power).
• a forward power is the RF power supplied by the RF power supplies 1 12, 1 16 and the reflected power is the RF power that is reflected back to the RF power supplies 1 12, 1 16.
• the plasma reactor 101 comprises a vacuum vessel 102 that contains a cathode pedestal 120 that forms a pedestal for the wafer 122.
• a roof or lid 103 of the process chamber has at least one antenna assembly 104 proximate the lid 103.
• the lid 103 may be made of a dielectric material.
• the antenna assembly 104 in some embodiments of the disclosure, comprises a pair of antennas 106 and 108. Other embodiments of the disclosure may use one or more antennas or may use an electrode in lieu of an antenna to couple RF energy to a plasma.
• the antennas 106 and 108 inductively couple energy to the process gas or gases supplied by the process gas supply 126 to the interior of the vessel 102.
• the RF energy supplied by the antennas 106 and 108 is inductively coupled to the process gases to form a plasma 124 in a reaction zone above the wafer 122.
• the reactive gases will etch the materials on the wafer 122.
• the power provided to the antenna assembly 104 ignites the plasma 124 and power coupled to the cathode pedestal 120 controls the plasma 124.
• RF energy is coupled to both the antenna assembly 104 and the cathode pedestal 120.
• the first RF power supply 1 12 also referred to as a source RF power supply
• a second RF power supply 1 16 also referred to as a bias RF power supply
• a controller 1 14 controls the timing and level of activating and deactivating the RF power supplies 1 12 and 1 16 as well as tuning the first and second matching networks 1 10 and 1 18.
• the power coupled to the antenna assembly 104 known as the source power and the power coupled to the cathode pedestal 120 is known as the bias power.
• a link 140 may be provided to couple the first and second RF supplies 1 12, 1 16 to facilitate synchronizing the operation of one source to the other.
• Either RF source may be the lead, or master, RF generator, while the other generator follows, or is the slave.
• the link 140 may further facilitate operating the first and second RF supplies 1 12, 1 16 in perfect synchronization, or in a desired offset, or phase difference.
• a first indicator device, or sensor, 150 and a second indicator device, or sensor, 152 are used to determine the effectiveness of the ability of the matching networks 1 10, 1 18 to match to the plasma 124.
• the indicator devices 150 and 152 monitor the reflective power that is reflected from the respective matching networks 1 10, 1 18. These devices are generally integrated into the matching networks 1 10, 1 18, or power supplies 1 12, 1 15; However, for descriptive purposes, they are shown here as being separate from the matching networks 1 10, 1 18. When reflected power is used as the indicator, the devices 150 and 152 are coupled between the supplies 1 12, 1 16 and the matching networks 1 10 and 1 18.
• the devices 150 and 152 are directional couplers coupled to a RF detector such that the match effectiveness indicator signal is a voltage that represents the magnitude of the reflected power. A large reflected power is indicative of an unmatched situation.
• the signals produced by the devices 150 and 152 are coupled to the controller 1 14.
• the controller 1 14 produces a tuning signal (matching network control signal) that is coupled to the matching networks 1 10, 1 18. This signal is used to tune the capacitor or inductors in the matching networks 1 10, 1 18.
• the tuning process strives to minimize or achieve a particular level of, for example, reflected power as represented in the indicator signal.
• the matching networks 1 10, 1 18 typically may require between about 100 microseconds to about a few milliseconds to minimize reflected power from a plasma in a given steady state.
• Figure 2 depicts a schematic diagram of an illustrative matching network used, for example, as the first RF matching network 1 10 or second RF matching network 1 18.
• the matching network shown in Figure 2 is just one example of a type of matching network that may be used in embodiments of the present disclosure. Other designs of matching networks may be used in embodiments of the present disclosure.
• the particular embodiment in Figure 2 has a single input 200 and a dual output (i.e., main output 202 and auxiliary output 204). Each output is used to drive one of the two antennas.
• the matching circuit 206 is formed by C1 , C2 and L1 and a capacitive power divider 208 is formed by C3 and C4.
• the capacitive divider values are set to establish a particular amount of power to be supplied to each antenna.
• values of capacitors C1 and C2 are automatically tuned to adjust the matching of the network 1 10.
• the capacitors may be adjusted to minimize reflected power.
• the values may be tuned by adjusting a position of either or both C1 and C2. Either C1 or C2 or both may be tuned to adjust the operation of the network.
• a hold mode the position, and thus the values, of C1 and C2 are held fixed.
• Other embodiments of a matching network may have a tunable inductor or a different topology of variable or fixed elements such as capacitors and inductors.
• the source power that is matched by the network 1 10 is at about 13.56 MHz and has a power level of up to about 3000 watts.
• a matching network is available under model NAVIGATOR 3013-ICP85 from AE, Inc. of Fort Collins, Colo. Still other various configurations of match networks may be utilized in accordance with the teachings provided herein.
• the controller 1 14 comprises a central processing unit (CPU) 130, a memory 132 and support circuits 134.
• the controller 1 14 is coupled to various components of the plasma enhanced substrate processing system 100 to facilitate control of the process, such as an etch process or other suitable plasma-enhanced substrate process.
• the controller 1 14 regulates and monitors processing in the process chamber via interfaces that can be broadly described as analog, digital, wire, wireless, optical, and fiber optic interfaces.
• the CPU 130 may be one of any form of general purpose computer processor that can be used in an industrial setting for controlling various chambers and subprocessors.
• the memory 132 is coupled to the CPU 130.
• the memory 132, or a computer readable medium may be one or more readily available memory devices such as random access memory, read only memory, floppy disk, hard disk, or any other form of digital storage either local or remote.
• the support circuits 134 are coupled to the CPU 130 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and related subsystems, and the like.
• Etching, or other, process instructions are generally stored in the memory 132 as a software routine typically known as a process recipe.
• the software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU 130.
• the software routine when executed by CPU 130, transforms the general purpose computer into a specific purpose computer (controller) 1 14 that controls the system operation such as that for controlling the plasma during a substrate process, for example, an etch process.
• the process of the present disclosure can be implemented as a software routine, some of the method steps that are disclosed therein may be performed in hardware as well as by the software controller.
• embodiments of the disclosure may be implemented in software as executed upon a computer system, and hardware as an application specific integrated circuit or other type of hardware implementation, or a combination of software and hardware.
• an integrated matching network may be embedded within the RF generator with frequency tuning capability (e.g., the first or second RF source 1 12 or 1 16) while the algorithms used for tuning the matching network as well as the frequency with the RF cycle may both be controlled based on the same readings as measured at the generator output (e.g., using a shared sensor).
• the first RF source 1 12 and the first matching network 1 10 may be physically integrated or may merely share a controller directing the tuning process for the pair of devices to eliminate the tuning competition between the two and to maximize the tuning efficiency of the overall system.
• the first RF source 1 12 and the first matching network 1 10 may merely share a common sensor for reading the reflected power such that they are at least tuning to minimize reflected power off of the same reading.
• Figures 3 and 4 depicts a diagram of variables that may be independently controlled over time or set to predetermined values to facilitate fast and repeatable plasma ignition and matching the impedance of the plasma to the impedance of the RF source generator over a wide range of plasma processes.
• Figures 3 and 4 show time independent operational parameters for an RF source generator, such as first RF source 1 12, and a tunable matching network (i.e., a match box), such as first matching network 1 10. These parameters are decoupled and may be independently controlled.
• the RF source generator may be operated in a frequency sweep (or frequency tuning) mode.
• the matching network i.e., match box
• f 0 is the RF source generator starting RF frequency at Tstart
• varjreq is the time duration during which the RF source generator frequency allowed to tune after power on, power level change, or other transitions started at Tstart
• Tfreq ramp is the time duration during which for the RF source generator frequency transitions back to fo or other known frequency value
• T h0 id is the time duration for the matching network to be fixed in hold mode
• Poso is the initial fixed value/position of the matching network (e.g., in some embodiments, the fixed initial position of the capacitors in the matching network).
• a timing diagram of frequencies is provided by the tunable matching circuits and RF generators in accordance with some embodiments.
• the RF generator starts outputting power, or changes its output level, at time Tstart, with f 0 starting RF frequency of the generator.
• a plasma transition such as pressure change is started in the chamber at T s tart.
• the starting RF frequency fo is a known predetermined value that may be within 5% to 10% of the generator center frequency.
• the generator center frequency could be about 2MHz, 13.56MHz or higher.
• the match box capacitors/inductors are held in a fixed position/value (Poso), while the generator frequency is allowed to tune to minimize reflected power.
• a minimized reflected value may be about 0% to about 20% of the forward power, depending on the process and hardware requirements.
• the lowest reflected power possible can be provided if the matching network operation is controlled properly. That is, the match can be controlled to be either one of two main modes: Automatic tuning mode or Hold mode (e.g., fixed position mode).
• the RF generator frequency is allowed to tune for a duration of T var _freq -
• T var _freq may be about 1 millisecond to about 1 second.
• the generator frequency will move away from the initial frequency fo.
• the generator will have frequency fi .
• the frequency may be adjusted from f 0 to fi in a non-monotonic manner.
• the RF frequency fi may be about 5% to about 10% different from f 0 .
• fi is shown as being a higher frequency than f 0 , in some embodiments fi may be less than f 0 .
• At least one of fo, fi and T var _freq are known predetermined values prior to the start of the ignition process.
• the starting frequency f 0 and T var _freq are known predetermined values, while fi is not known.
• the reflected power may be a predetermined threshold that, when reached, denotes the end of the T var _freq time period.
• the RF source generator frequency starts monotonically changing back towards the RF source generator starting frequency f 0 .
• the transition from fi back towards fo may be linear or any other monotonic relation, and is completed within the time T fr eq_ ram p.
• the Tf re q_ ra mp time period may be about 10 milliseconds to about 1 second.
• the frequency at the end of Tf re q_ ra mp may be a third frequency f x that is not equal to fo.
• f x may be equal, or substantially equal, to fo.
• the RF frequency f x may be about 5% to about 10% different from f 0 .
• the third frequency f x and Tf re q_ ra mp are known predetermined values, leading to a well-defined final plasma and chamber condition at a specified time.
• the matching network is allowed to move/adjust values and tune after T h0 id from T s t ar t.
• the T h0 id time period may be about 10 milliseconds to about 2 seconds.
• T h0 id is shown in Figure 3 and 4 as ending after T var _freq (i.e., T h0 id > T var _freq)
• the matching network is allowed to move/adjust values and tune during T var _freq (i.e., T h0 id ⁇ T var _freq)-
• the RF source generator frequency is ramped back to fixed frequency f x , which may be equal to fo in some embodiments, and the matching network is automatically tuning.
• FIG. 5 depicts a flowchart having a series of steps for igniting a plasma, or tuning across a plasma transition, and reducing a reflected power in a process chamber using a source RF power supply coupled to a process chamber via a matching network.
• the method 500 starts at 502 and proceeds to 504 where a transition in plasma conditions is initiated while RF power is provided to the process chamber by the RF power supply at a first frequency while the matching network is in a hold mode.
• the plasma transition may be initiated by the delivery of RF power, a change of the RF power level, a change of chemistry or pressure in the chamber, or other transition affecting the plasma.
• the first frequency may be fo as described above with respect to Figures 3 and 4.
• a hold mode the position and/or values of the matching network are held fixed.
• the RF power supply frequency is adjusted from the first frequency (e.g., f 0 ) to a second frequency (e.g., fi ) during a first time period (e.g., T var _freq) to ignite the plasma or tune during a transition and reduce the reflected power in the process chamber using the RF power source.
• the frequency may be increased, or decreased, from first frequency to the second frequency in a non-monotonic manner (that is, with possible intermediate frequencies during the first time period as shown in Figure 4) and the plasma may be ignited at some frequency between the first frequency and the second frequency.
• the frequency may continue to be adjusted to the second frequency until the reflected power is minimized to a certain level during the first time period.
• the matching network is maintained in the hold mode.
• the frequency is adjusted from the second frequency (e.g., fi ) to a third frequency (e.g., f x ) during a second time period (e.g., T fr eq_ ra mp)-
• the third frequency is different from the second frequency and, in some embodiments, may be a predetermined known quantity (e.g., a target value).
• an operation mode of the matching network is changed from the hold mode to automatic tuning mode (e.g., after a T h0 id time period, wherein T h0 id > T var _freq) to further reduce the reflected power while the frequency provided by the RF power source is adjusted to the third known frequency at 510.
• an operation mode of the matching network is changed from the hold mode to automatic tuning mode (e.g., after a T h0 id time period, wherein T h0 id ⁇ T var _freq) to further reduce the reflected power while the frequency provided by the RF power source is adjusted to the third known frequency at 510.
• the method 500 ends at 514.

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• 2014
  • 2014-05-27 US US14/287,480 patent/US20140367043A1/en not_active Abandoned
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