Method and apparatus for controlled broadband microwave heating

• US 20140305934A1
• Filed: 04/16/2013
• Published: 10/16/2014
• Est. Priority Date: 04/16/2013
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: DeCamillis, Clayton R., Wander, Joseph M., Hazelhurst, Richard C., Hampton, Michael L.
• Granted Patent: US 10,470,256 B2
• Time in Patent Office: Days
• US Class Current: 219/709
• CPC Class Codes: H01L 21/67115 mainly by radiation
• CPC Class Codes: H05B 6/686 Circuits comprising a signal generator and power amplifier, e.g. using solid state oscillators
• CPC Class Codes: H05B 6/705 using microwave tuning
• CPC Class Codes: H05B 6/80 Apparatus for specific applications stoves or ranges F24C7/02

Abstract

A materials processing system comprises a thermal processing chamber and a broadband microwave power source. The power source includes an ovenized small-signal RF circuit, a high power microwave amplifier, and forward and reflected power detectors separated from one another by an isolator. The power detectors are also preferably ovenized. A control system provides control signals to the thermally stabilized VCO and VCA in the small-signal circuit to control output power based on detected forward power compared to demanded forward power. The system may be run in either open-loop or closed-loop modes.

Claims

1. A broadband microwave heating apparatus comprising:

an applicator cavity for exposing a workpiece to microwave energy;

a microwave power supply connected to said cavity, said power supply comprising;

a small signal RF source comprising at least a voltage controlled microwave oscillator and a voltage controlled attenuator that are both thermally stabilized at a selected temperature above ambient;

a high power microwave amplifier to amplify said small signal to a usable power level for heating;

forward and reflected power detectors, said detectors separated from one another by a microwave isolator; and

,

a control system using a power regulator to adjust output power using detected forward power compared to demanded forward power.

2. The apparatus of claim 1 wherein said small-signal RF source further includes a fixed attentuator and a bandpass filter.

3. The apparatus of claim 1 wherein all components of said small-signal RF source are mounted on a common thermal platform so that they are all maintained at a common temperature above ambient.

4. The apparatus of claim 1 wherein said forward and reflected power detectors are thermally stabilized at a selected temperature above ambient.

5. A broadband microwave power supply comprising:

a small signal RF source comprising at least a voltage controlled microwave oscillator and a voltage controlled attenuator that are both thermally stabilized at a selected temperature above ambient;

a high power microwave amplifier to amplify said small signal to a usable power level for heating;

forward and reflected power detectors, said detectors separated from one another by a microwave isolator; and

,

a control system including a power regulator to adjust output power using detected forward power compared to demanded forward power.

6. The apparatus of claim 5 wherein said small-signal RF source further includes a fixed attentuator and a bandpass filter.

7. The apparatus of claim 5 wherein all components of said small-signal RF source are mounted on a common thermal platform so that they are all maintained at a common temperature above ambient.

8. The apparatus of claim 5 wherein said forward and reflected power detectors are thermally stabilized at a selected temperature above ambient

9. An integrated, low power microwave source comprising:

a voltage controlled oscillator (VCO);

a voltage controlled attenuator (VCA);

a heater and temperature control circuit; and

,

a package containing said VCO, VCA, heater, and temperature control circuit and having external connections for DC power, DC frequency control voltage, DC amplitude control voltage, and RF signal out.

10. The microwave source of claim 9 wherein said package comprises a printed circuit board.

11. The microwave source of claim 9 wherein said package comprises a hybrid circuit module.

12. A method of heating materials using broadband microwave power, comprising the steps of:

placing a selected workpiece in a multi-mode microwave applicator cavity;

providing a microwave power supply in communication with said cavity, said power supply including a small-signal RF generating circuit, a high power microwave amplifier, and forward and reflected power detectors, said detectors separated from one another by an isolator;

heating at least some of the components of said small-signal RF circuit to a selected temperature above ambient;

providing a control system to perform the following functions;

run an autoleveling routine to automatically generate an autolevel table and download said autolevel table to said control system;

provide an automatic power control system to limit the rate of power adjustment; and

,

applying microwave power into said applicator cavity under the control of said control system to heat said workpiece.

13. The method of claim 12 wherein said autoleveling routine includes a spline-based surface fitting routine.

14. The method of claim 12 further including the step of heating said forward and reflected power detectors to a selected temperature above ambient.

15. The method of claim 12 wherein said automatic power control system further includes a limiter that prevents adjustments beyond a preset amount.

16. The method of claim 12 wherein said automatic power control system includes an alarm function to notify the master control if the system is not able to maintain accurate power control.