Active control of electron temperature in an electrostatically shielded radio frequency plasma source

• US 20030045012A1
• Filed: 08/14/2002
• Published: 03/06/2003
• Est. Priority Date: 02/15/2000
• Status: Active Grant

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Tokyo Electron Limited
• Inventors: Johnson, Wayne L.
• Granted Patent: US 6,790,487 B2
• Time in Patent Office: Days
• US Class Current: 438/14
• CPC Class Codes: H01J 37/32082 Radio frequency generated discharge H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence
• CPC Class Codes: H01J 37/32165 Plural frequencies
• CPC Class Codes: H01J 37/32522 Temperature
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence

Abstract

A method and apparatus for generating a plasma having a selected electron temperature, by: generating electrical power having components at at least two different frequencies; deriving electromagnetic energy at the at least two different frequencies from the generated electrical power and inductively coupling the derived electromagnetic energy into a region containing an ionizable gas to ionize the gas and create a plasma composed of the resulting ions; and selecting a power level for the electrical power component at each frequency in order to cause the plasma to have the selected electron temperature.

Claims

1. A method for generating a plasma having a selected electron temperature, comprising:

generating electrical power having components at at least two different frequencies;

deriving electromagnetic energy at the at least two different frequencies from the generated electrical power and inductively coupling the derived electromagnetic energy into a region containing an ionizable gas to ionize the gas and create a plasma composed of the resulting ions; and

selecting a power level for the electrical power component at each frequency in order to cause the plasma to have the selected electron temperature.

2. The method according to claim 1, wherein said step of selecting is performed to maintain the total power coupled into the region substantially at a predetermined level.

3. The method according to claim 2, wherein one of the frequencies is a fundamental frequency and the other frequency is a harmonic of the fundamental frequency.

4. The method according to claim 2, wherein said step of inductively coupling comprises inductively coupling energy at more than two frequencies into the region.

5. The method according to claim 4, wherein one of the frequencies is a fundamental frequency and each of the other frequencies is a respective harmonic of the fundamental frequency.

6. The method according to claim 1, wherein the electrical power components are RF components.

7. The method according to claim 1 wherein said step of selecting comprises varying the power level for the electrical power component at each frequency in steps in order to cause the plasma to have different selected electron temperatures.

8. The method according to claim 1, further comprising measuring at least one of plasma electron density and plasma electron temperature to produce a control value, and controlling said generating step on the basis of the control value.

9. The method according to claim 1, further comprising:

determining power level values for the electrical power component at each frequency in order to cause the plasma to have a selected electron temperature for each of a plurality of different values of total electrical power generated and pressure in the region; and

storing data representing the determined power level values and associated values of total electrical power generated and pressure in the region; and

wherein said step of selecting is performed by using the stored data to select power level values for existing values of total electrical power generated and pressure in the region.

10. Apparatus for generating a plasma having a selected electron temperature, comprising:

generating means for generating electrical power having components at at least two different frequencies;

electromagnetic energy deriving and coupling means connected to said generating means for deriving electromagnetic energy at the at least two different frequencies from the generated electrical power and inductively coupling the derived electromagnetic energy into a region containing an ionizable gas to ionize the gas and create a plasma composed of the resulting ions; and

selecting means coupled to said electromagnetic energy deriving and coupling means for selecting a power level for the electromagnetic energy at each frequency in order to cause the plasma to have the selected electron temperature.

11. The apparatus according to claim 10, wherein said selecting means are operative to maintain the total power coupled into the region substantially at a predetermined level.

12. The apparatus according to claim 11, wherein one of the frequencies is a fundamental frequency and the other frequency is a harmonic of the fundamental frequency.

13. The apparatus according to claim 11, wherein said electromagnetic energy deriving and coupling means are operative for inductively coupling energy at more than two frequencies into the region.

14. The apparatus according to claim 13, wherein one of the frequencies is a fundamental frequency and each of the other frequencies is a respective harmonic of the fundamental frequency.

15. The apparatus according to claim 10, wherein said generating means comprise:

a plurality of oscillators each producing a signal at a respective frequency; and

a plurality of amplifiers each connected to a respective oscillator for amplifying the signal from the respective oscillator to produce electrical power at the respective frequency.

16. The apparatus according to claim 15, wherein said electromagnetic energy deriving and coupling means comprise a coil connected to receive electrical power from said amplifiers and to derive and couple the electromagnetic energy into the region containing an ionizable gas.

17. The apparatus according to claim 16, wherein said generating means further comprise a plurality of impedance matching networks each connected between a respective one of said amplifiers and said coil.

18. The apparatus according to claim 17, wherein said coil has a plurality of taps which are spaced from one another along said coil and each of said taps is connected to at least one of said matching networks.

19. The apparatus according to claim 16, wherein said coil has a plurality of taps which are spaced from one another along said coil and each of said taps is connected to receive electrical power from at least one of said amplifiers.

20. The apparatus according to claim 10, wherein said generating means comprise a free running oscillator.

21. The apparatus according to claim 20, wherein said electromagnetic energy deriving and coupling means comprise a coil connected to receive electrical power from said free running oscillator.

22. The apparatus according to claim 21, wherein said free running oscillator has a plurality of resonant circuits each producing electrical power at a respective one of the at least two different frequencies, said coil has a plurality of taps which are spaced from one another along said coil, and each of said taps is connected to receive electrical power from at least one of said resonant circuits.

23. The apparatus according to claim 10, wherein said selecting means are operative for varying the power level for the electrical power component at each frequency in steps in order to cause the plasma to have different selected electron temperatures.

24. The apparatus according to claim 10, further comprising means coupled to the plasma for measuring at least one of plasma electron density and plasma temperature to produce a control value, and means coupled to said generating means for controlling said generating means on the basis of the control value.