Microwave plasma applicator with improved power uniformity

Patent metadata

Field	Value
Publication number	US-9653266-B2
Application number	US-201514645837-A
Country	US
Kind code	B2
Filing date	Mar 12, 2015
Priority date	Mar 27, 2014
Publication date	May 16, 2017
Grant date	May 16, 2017

Abstract

An apparatus for generating plasma includes a plasma discharge tube and a conductive coil helically wound around an outer surface of the plasma discharge tube. A waveguide is coupled to a microwave cavity surrounding the plasma discharge tube to guide the microwave energy into the plasma discharge tube such that the plasma is generated in the plasma discharge tube. The waveguide is positioned such that an electric field of the microwave energy is oriented at a predetermined angle with respect to the longitudinal axis of the plasma discharge tube. A resulting induced electric current in the conductive coil affects power absorption in the plasma discharge tube, the predetermined angle being selectable such that power absorption in the plasma discharge tube is according to a predetermined profile with respect to the longitudinal axis of the plasma discharge tube.

First claim

The invention claimed is:

1. An apparatus for generating plasma, comprising:
a plasma discharge tube substantially transparent to microwave energy, the plasma discharge tube having a longitudinal axis;
a conductive coil wound around an outer surface of the plasma discharge tube, the conductive coil comprising an electrically conductive material;
a microwave cavity surrounding the plasma discharge tube;
a waveguide coupled to the microwave cavity for guiding the microwave energy into the plasma discharge tube such that the plasma is generated in the plasma discharge tube, the waveguide having a rectangular cross-section defining a narrower side of the rectangular cross-section and a wider side of the rectangular cross-section, a first cross-sectional axis of the rectangular cross-section being parallel to the wider side of the rectangular cross-section and a second cross-sectional axis of the rectangular cross-section being parallel to the narrower side of the rectangular cross-section, the second cross-sectional axis being positioned at a predetermined angle with respect to the longitudinal axis of the plasma discharge tube such that an electric field of the microwave energy induces an electric current in the conductive coil, the electric current affecting power absorption in the plasma discharge tube, the predetermined angle being selectable such that power absorption in the plasma discharge tube is according to a predetermined profile with respect to the longitudinal axis of the plasma discharge tube; and
an actuator for receiving a signal to control the predetermined angle.

2. The apparatus of claim 1 , wherein the predetermined angle is such that the second cross-sectional axis is oriented substantially perpendicular to the longitudinal axis of the plasma discharge tube.

3. The apparatus of claim 1 , wherein the predetermined angle is such that the second cross-sectional axis is oriented at an angle of 30° to 90° with respect to the longitudinal axis of the plasma discharge tube.

4. The apparatus of claim 1 , wherein the predetermined angle is such that the second cross-sectional axis is oriented at an angle of 45° to 90° with respect to the longitudinal axis of the plasma discharge tube.

5. The apparatus of claim 1 , wherein the predetermined angle is selected to increase uniformity of power absorption with respect to the longitudinal axis of the plasma discharge tube.

6. The apparatus of claim 1 , wherein the conductive coil comprises a plurality of loops around the plasma discharge tube, the plurality of loops defining a pattern of spacing between adjacent loops, the pattern of spacing being selectable based on a predetermined desired effect of the current induced in the conductive coil on the power absorption in the plasma discharge tube.

7. The apparatus of claim 6 , wherein the pattern of spacing between adjacent loops is selected to increase uniformity of power absorption with respect to the longitudinal axis of the plasma discharge tube.

8. The apparatus of claim 6 , wherein the spacing between selected adjacent loops can be decreased to increase the electric current induced in the conductive coil such that propagation of microwave energy in the plasma discharge tube in proximity to the selected adjacent loops increases.

9. The apparatus of claim 6 , wherein the spacing between selected adjacent loops can be increased to decrease the electric current induced in the conductive coil such that propagation of microwave energy in the plasma discharge tube in proximity to the selected adjacent loops decreases.

10. The apparatus of claim 1 , wherein:
the conductive coil is thermally coupled to the plasma discharge tube;
the conductive coil comprises a channel through which a cooling fluid can flow, such that the cooling fluid removes heat from the plasma discharge tube.

11. The apparatus of claim 1 , further comprising a microwave choke at each of two ends of the conductive coil, the microwave chokes substantially preventing leakage of the microwave energy from the plasma discharge tube.

12. The apparatus of claim 1 , wherein the conductive coil is helically wound around the outer surface of the plasma discharge tube.

13. The apparatus of claim 1 , further comprising at least one of an electromagnetic field sensor for generating a first signal indicative of electromagnetic field intensity in the plasma discharge tube or a temperature sensor for generating a second signal indicative of temperature in the plasma discharge tube, the actuator controlling the predetermined angle based on at least one of the first and second signals.

14. The apparatus of claim 1 , wherein the actuator rotates the waveguide with respect to the plasma discharge tube about an axis which is parallel to a longitudinal axis of the waveguide to adjust the predetermined angle, a controller controlling the actuator to control the predetermined angle.

15. An apparatus for generating plasma, comprising:
a plasma discharge tube substantially transparent to microwave energy, the plasma discharge tube having a longitudinal axis;
a conductive coil wound around an outer surface of the plasma discharge tube, the conductive coil comprising an electrically conductive material, an electric field of the microwave energy inducing an electric current in the conductive coil, the electric current affecting power absorption in the plasma discharge tube;
a microwave cavity surrounding the plasma discharge tube;
a waveguide coupled to the microwave cavity for guiding the microwave energy into the plasma discharge tube such that the plasma is generated in the plasma discharge tube, the waveguide having a rectangular cross-section defining a narrower side of the rectangular cross-section and a wider side of the rectangular cross-section, a first cross-sectional axis of the rectangular cross-section being parallel to the wider side of the rectangular cross-section and a second cross-sectional axis of the rectangular cross-section being parallel to the narrower side of the rectangular cross-section;
a rotational coupling device for coupling the waveguide to the plasma discharge tube, the rotational coupling device allowing the waveguide to be rotated with respect to the plasma discharge tube about an axis which is parallel to a longitudinal axis of the waveguide to adjust an angle between the second cross-sectional axis of the waveguide and the longitudinal axis of the plasma discharge tube, such that power absorption in the plasma discharge tube is adjustable via the rotational coupling device to a predetermined profile with respect to the longitudinal axis of the plasma discharge tube; and
an actuator for receiving a signal to adjust the angle between the second cross-sectional axis and the longitudinal axis of the plasma discharge tube.

16. The apparatus of claim 15 , further comprising at least one of an electromagnetic field sensor for generating a first signal indicative of electromagnetic field intensity in the plasma discharge tube or a temperature sensor for generating a second signal indicative of temperature in the plasma discharge tube, the actuator controlling the angle between the second cross-sectional axis and the longitudinal axis of the plasma discharge tube based on at least one of the first and second signals.

17. The apparatus of claim 15 , wherein the actuator rotates the waveguide with respect to the plasma discharge tube to adjust the angle between the second cross-sectional axis and the longitudinal axis of the plasma discharge tube, a controller controlling the actuator to control the angle between th

Assignees

• Mks Instr Inc

Inventors

• Chen Xing
• Ji Chengxiang
• Madden Erin
• Pokidov Ilya
• Wenzel Kevin W

Classifications

• H01J37/32201

  Generating means · CPC title

• H01J37/32229 Primary

  Waveguides · CPC title

• H05H1/46

  using applied electromagnetic fields, e.g. high frequency or microwave energy (H05H1/26 takes precedence) · CPC title

• H01J37/32522

  Temperature · CPC title

• H01J37/32311

  Circuits specially adapted for controlling the microwave discharge · CPC title