Matchless plasma source for semiconductor wafer fabrication
A matchless plasma source is described. The matchless plasma source includes a controller that is coupled to a direct current (DC) voltage source of an agile DC rail to control a shape of an amplified square waveform that is generated at an output of a half-bridge transistor circuit. The matchless plasma source further includes the half-bridge transistor circuit used to generate the amplified square waveform to power an electrode, such as an antenna, of a plasma chamber. The matchless plasma source also includes a reactive circuit between the half-bridge transistor circuit and the electrode. The reactive circuit has a high-quality factor to negate a reactance of the electrode. There is no radio frequency (RF) match and an RF cable that couples the matchless plasma source to the electrode.
1 . A method for providing radio frequency (RF) power by a low impedance RF generator operating as a matchless plasma source to an electrode of a plasma chamber, comprising:
generating, by a signal generator, an input RF signal at an operating frequency in response to a setting received from a controller;
generating, by an amplification circuit, an amplified waveform based on the operating frequency, the amplification circuit having an agile direct current (DC) rail that is interfaced with the controller;
instructing, by the controller, to set voltage values for the agile DC rail to provide the amplified waveform from the amplification circuit in a shaped envelope;
extracting, by a reactive circuit, a shaped sinusoidal waveform from the amplified waveform, the shaped sinusoidal waveform being output based on the shaped envelope; and
sending, to the electrode via a connection between an output of the reactive circuit and the electrode, the shaped sinusoidal waveform for generating a plasma for processing of a substrate.
2 . The method of claim 1 , wherein a connection between the reactive circuit and the electrode lacks an RF cable.
3 . The method of claim 1 , wherein a connection between the reactive circuit and the electrode lacks an RF match.
4 . The method of claim 1 , further comprising reducing, by a reactance of the reactive circuit, a reactance of the electrode, or a reactance of the plasma when formed within the plasma chamber, or a reactance of the connection that couples the reactive circuit to the electrode, or a combination thereof.
5 . The method of claim 4 , wherein the plasma chamber is an inductively coupled plasma chamber and the reactive circuit is a capacitor, the method comprising controlling a capacitance of the capacitor to nullify the reactance of the electrode, or the reactance of the plasma when formed within the plasma chamber, or the reactance of the connection that couples the reactive circuit to the electrode, or the combination thereof, wherein the electrode is a transformer coupled plasma (TCP) coil.
6 . The method of claim 4 , wherein the plasma chamber is a capacitively coupled plasma chamber and the reactive circuit is an inductor, the method comprising controlling an inductance of the inductor to nullify the reactance of the electrode, or the reactance of plasma when formed within the plasma chamber, or the reactance of the connection that couples the reactive circuit to the electrode, or the combination thereof, wherein the electrode is a capacitive upper electrode of the plasma chamber.
7 . The method of claim 1 , further comprising producing, by a gate driver, a plurality of signals upon receiving the input RF signal from the signal generator, wherein the amplified waveform is generated upon receiving the plurality of signals.
8 . The method of claim 7 , wherein each of the plurality of signals is a pulsed waveform that pulses at the operating frequency between a low power level and a high power level.
9 . The method of claim 1 , wherein the amplification circuit includes a field-effect transistor, wherein the field-effect transistor is turned on and turned off within a pre-determined time period to be turned on or off in a nearly instantaneous manner.
10 . The method of claim 9 , wherein the pre-determined time period is less than 10 microseconds.
11 . The method of claim 9 , wherein the pre-determined time period is between 0.5 microseconds and 10 microseconds.
12 . The method of claim 1 , further comprising generating, by a DC voltage source, a voltage signal to shape the amplified waveform.
13 . The method of claim 1 , wherein the shaped envelope is a multi-state pulse-shaped envelope, or a triangular-shape envelope, or a continuous-shaped envelope, or an arbitrary-shaped envelope.
14 . The method of claim 1 , further comprising removing, by a quality factor of the reactive circuit, higher-order harmonics of the amplified waveform to generate a fundamental waveform, wherein the shaped sinusoidal waveform is the fundamental waveform having the shaped envelope.
15 . The method of claim 1 , further comprising:
receiving, from a voltage probe, a measurement of a voltage applied to the plasma chamber; and
controlling, by the controller, the operating frequency of the signal generator or one or more of the voltage values for the agile DC rail or a combination thereof to control the RF power of the shaped sinusoidal waveform based on the voltage.
16 . The method of claim 15 , wherein the amplification circuit has an output that is coupled to the reactive circuit, wherein the voltage is measured at the output of the amplification circuit.
17 . The method of claim 1 , further comprising:
receiving, from a current probe, a measurement of a current supplied to the plasma chamber; and
controlling, by the controller, the operating frequency of the signal generator or one or more of the voltage values for the agile DC rail or a combination thereof to control the RF power of the shaped sinusoidal waveform based on the current.
18 . The method of claim 17 , wherein the amplification circuit has an output that is coupled to the reactive circuit, wherein the current is measured at the output of the amplification circuit or at the connection.
19 . The method of claim 1 , further comprising:
receiving, from a voltage probe, a measurement of a voltage applied to the plasma chamber;
receiving, from a current probe, a measurement of a current supplied to the plasma chamber;
determining, by the controller, a phase difference between the voltage and the current; and
controlling, by the controller, the operating frequency of the signal generator or one or more of the voltage values for the agile DC rail to adjust the phase difference to control the RF power of the shaped sinusoidal waveform.
20 . The method of claim 1 , further comprising, generating the shaped envelope of an arbitrary shape based on the voltage values for the amplified waveform, wherein the arbitrary shape has multiple slopes of the shaped envelope, wherein the slopes change from one state to another in a controlled manner that is determined by the controller.
21 . A low impedance radio frequency (RF) generator as a matchless plasma source, comprising:
an input section;
an output section coupled to the input section; and
a reactive circuit coupled to the output section and coupled via a connection to an inductively coupled plasma (ICP) coil of a plasma chamber,
wherein the input section includes:
a controller; and
a signal generator coupled to the controller,
wherein the output section includes:
a transistor circuit; and
a direct current (DC) voltage source coupled to the controller,
wherein the controller is configured to control the DC voltage source to change an envelope of an amplified waveform at an output of the transistor circuit,
wherein the reactive circuit is configured to reduce higher-order harmonics of the amplified waveform to produce a shaped sinusoidal waveform at an output of the reactive circuit, wherein the shaped sinusoidal waveform is supplied from the output of the reactive circuit to the ICP coil of the plasma chamber.
22 . The low impedance RF generator of claim 21 , wherein the controller is configured to receive, from a voltage probe, a measurement of a voltage applied to the ICP coil,
wherein the controller is configured to receive, from a current probe, a measurement of a current supplied to the ICP coil,
wherein the controller is configured to control an operating frequency of the signal generator to control power of the shaped sinusoidal waveform based on the current and voltage.
23 . The low impedance RF generator of claim 21 , wherein the connection lacks an RF cable between the reactive circuit and the ICP coil.
24 . The low impedance RF generator of claim 21 , wherein the connection lacks an RF match between the reactive circuit and the ICP coil.
25 . The low impedance RF generator of claim 21 , wherein the plasma chamber is an inductively coupled plasma chamber and the reactive circuit is at least a capacitor, wherein the capacitor has a capacitance that is controlled to nullify a reactance of the ICP coil, or a reactance of plasma when formed within the plasma chamber, or a reactance of the connection that couples the reactive circuit to the ICP coil, or a combination thereof.
26 . A method for using a low impedance radio frequency (RF) generator as a matchless plasma source for providing RF power to an inductively coupled plasma (ICP) coil of a plasma chamber, the method comprising:
providing, from a signal generator, an input RF signal at an operating frequency in response to a setting by a controller;
generating an amplified waveform using an amplification circuit, the amplification circuit uses one or more voltage values provided to an agile direct current (DC) rail, the controller is configured to set a level for the amplified waveform based on the one or more voltage values; and
generating a sinusoidal waveform as output from a reactive circuit that receives the amplified waveform as an input, the output of the reactive circuit is provided as said RF power delivered to the ICP coil for generating a plasma in said plasma chamber.
27 . The method of claim 26 , wherein a series resonance is provided between the reactive circuit and the ICP coil, wherein the reactive circuit is connected to an output of the amplification circuit and has an output connection that is electrically coupled to the ICP coil.
28 . The method of claim 26 , wherein the ICP coil is one coil of the plasma chamber, and wherein a second one of the low impedance RF generator is connected to another ICP coil of the plasma chamber.
29 . The method of claim 26 , further comprising adjusting said level for the amplified waveform to produce a shaped envelope for the amplified waveform.
30 . The method of claim 29 , wherein the shaped envelope provides for setting two or more levels during two or more states of operation, wherein power delivered during each one of said two or more states is settable via the controller.