Impedance control of local areas of a substrate during plasma deposition thereon in a large PECVD chamber
Embodiments of the present disclosure generally relate to methods and apparatus for measuring and controlling local impedances at a substrate support in a plasma processing chamber during processing of a substrate. A substrate support includes a plurality of substrate support pins wherein the radio frequency voltage, current and phase of each of the plurality of substrate support pins are measured and impedances of the support pins are adjusted in real time. Each of the substrate support pins is coupled to an associated adjustable impedance circuit that may be remotely controlled. In one embodiment a variable capacitor is used to adjust the impedance of the impedance circuit coupled to the associated substrate support pin and may be remotely adjusted with a stepper motor. In another embodiment a microcontroller may control the impedance adjustments for all of the plurality of substrate support pins and may be used to track these impedances with each other and with a bulk impedance of the plasma processing chamber.
1. A plasma processing system, comprising:
a substrate support disposed within a processing volume of the plasma processing system, the substrate support comprising a body having a plurality of openings formed between a substrate support surface and backside opposite the substrate support surface;
a plurality of substrate support pins deposed in the plurality of openings of the substrate support, wherein when the substrate support is in a raised position, top portions of the plurality of substrate support pins are planar with or recessed below the substrate support surface, and when in a lowered position the substrate support pins extend above the substrate support surface;
a plurality of adjustable impedance circuits in electrical communications with associated ones of the plurality of substrate support pins; and
radio frequency (RF) voltage and RF current detectors electrically coupled to each of the plurality of adjustable impedance circuits.
2. The plasma processing system of claim 1 , further comprising:
a substrate support leg attached to the backside of the substrate support; and
an actuator attached to the substrate support leg and adapted to raise and lower the substrate support leg with the attached substrate support.
3. The plasma processing system of claim 2 , wherein phase angles ( 0 ) between each of the detected RF voltages and the detected RF currents are determined with a phase detector.
4. The plasma processing system of claim 1 , wherein each of the plurality of adjustable impedance circuits comprise an inductor and a capacitor having an adjustable capacitance.
5. The plasma processing system of claim 4 , wherein each of the plurality of adjustable impedance circuits comprise a position sensor coupled to a stepper motor.
6. The plasma processing system of claim 1 , wherein adjustment of each of the plurality of adjustable impedance circuits is remotely controlled.
7. The plasma processing system of claim 1 , wherein
the substrate support is adapted to support a substrate when in the raised position; and
the plurality of substrate support pins are adapted to support the substrate when the substrate support is in the lowered position.
8. The plasma processing system of claim 1 , wherein the RF voltage and RF current detectors comprise:
a voltage detection coil adapted for detecting a RF voltage on an electrical conductor; and
a Rogowski coil adapted for detecting RF current through the electrical conductor;
wherein the voltage detection coil and the Rogowski coil are fabricated on multiple layers of a printed circuit board (PCB).
9. The plasma processing system of claim 8 , further comprising RF conductive shielding on certain layers of the PCB.
10. The plasma processing system of claim 8 , wherein the voltage detection coil is disposed around a substrate support pin of the plurality of substrate support pins.
11. The plasma processing system of claim 8 , wherein the Rogowski coil comprises a helically wound coil having a lead from one end returning through the center of the coil.
12. The plasma processing system of claim 1 , wherein each adjustable impedance circuit of the plurality of adjustable impedance circuits is individually controlled.
13. A plasma processing system, comprising:
a plasma processing chamber;
at least one plasma generating radio frequency (RF) coil within an upper portion of the plasma processing chamber;
a RF power source;
a RF impedance matching network coupled between the RF power source and the at least one plasma generating RF coil;
a frequency detector;
first RF voltage and RF current detectors electrically coupled between the RF impedance matching network and the at least one plasma generating RF coil;
a substrate support disposed within the plasma processing chamber and below the at least one plasma generating RF coil, the substrate support comprising a body having a plurality of openings formed between a substrate support surface and a backside opposite the substrate support surface;
a plurality of substrate support pins deposed in the plurality of openings of the substrate support, wherein when the substrate support is in a raised position, top portions of the plurality of substrate support pins are planar with or recessed below the substrate support surface, and when in a lowered position the substrate support pins extend above the substrate support surface;
a plurality of adjustable impedance circuits in electrical communications with associated ones of the plurality of substrate support pins; and
second RF voltage and RF current detectors electrically coupled to each of the plurality of adjustable impedance circuits for detecting RF voltage and RF current thereof.
14. The plasma processing system of claim 13 , wherein each of the plurality of adjustable impedance circuits comprises an inductor and a capacitor having an adjustable capacitance.
15. The plasma processing system of claim 13 , further comprising a monitoring and control system providing:
a plurality of inputs coupled to the first RF voltage and RF current detectors, and the second RF voltage and RF current detectors associated with each of the plurality of adjustable impedance circuits;
an input coupled to the frequency detector; and
a plurality of outputs adapted to control impedance adjustments of the plurality of adjustable impedance circuits.
16. The plasma processing system of claim 15 , wherein the monitoring and control system:
determines phase angle (θ) between each pair of detected first and second RF voltages and RF currents;
determines a first impedance at an output of the RF impedance matching network;
determines second impedances of each of the plurality of adjustable impedance circuits; and
controls impedance adjustments of the plurality of adjustable impedance circuits.
17. The plasma processing system of claim 16 , wherein the monitoring and control system adjusts the second impedances of the plurality of adjustable impedance circuits to be proportional to the first impedance of the RF impedance matching network.
18. The plasma processing system of claim 16 , wherein the monitoring and control system remotely controls adjustment of each of the plurality of adjustable impedance circuits.
19. The plasma processing system of claim 15 , wherein the monitoring and control system comprises a microcontroller having:
a memory;
digital signal processing capabile of performing complex mathematical calculations and Fourier transform (FFT) capabilities;
general purpose inputs and outputs (GPIO) adapted for coupling to the plurality of inputs and the plurality of outputs; and
a communications interface for communicating with a master control system and a user interface.
20. The plasma processing system of claim 15 , wherein the communications interface is adapted for communicating with Ethernet for Control Automation Technology (EtherCAT).