WO1997044812B1

WO1997044812B1 - Method of and apparatus for controlling reactive impedances of a matching network connected between an rf source and an rf plasma processor

Info

Publication number: WO1997044812B1
Application number: PCT/US1997/008610
Authority: WO
Filing date: 1997-05-23
Publication date: 1997-12-24

Abstract

An r.f. field is supplied by a reactive impedance element to a plasma in a vacuum plasma processing chamber. The element and source are connected via a matching network including first and second variable reactances that control loading of the source and tuning a load, including the reactive impedance element and the plasma, to the source. The values of the first and second variable reactances are changed to determine the amount the first variable reactance is to change for each unit change of the second variable reactance to attain the best match between the impedances seen looking into and out of output terminals of the r.f. source. Then the values of the first and second variable reactances are varied simultaneously based on the determination until the best impedance match between the impedances seen looking into and out of output terminals of the r.f. source is attained.

Claims

AMENDED CLAIMS

[received by the International Bureau on 19 November 1997 (19.11.97); original claims 2-12 cancelled; new claims 13-26 added; remaining claim unchanged (3 pages)]

13. The method of claim 1 wherein the best match between the impedances seen looking into and out of output terminals of the r.f. source is determined as a function of the power coupled between the source and a load including the reactive impedance element and the plasma.

14. The method of claim 13 wherein the function is maximum r.f. current flowing to the reactive impedance element.

15. The method of claim 13 wherein the function is based on maximum power delivered to the. load relative to source output power.

16. The method of any of claims 1 or 13-15 wherein the values of the first and second variable reactances are simultaneously changed during step (2).

17. The method of any of claims 1 or 13-16 wherein the values of the first and second variable reactances are sequentially changed during step (1) so the first variable reactance is changed while the second variable reactance is not changed and the second variable reactance is changed while the first variable reactance is not changed.

18. The method of any of claims 1 or 13-16 wherein the values of the first and second variable reactances are simultaneously changed during step (1).

19. The method of any of claims 1 or 13-18 wherein the best match attained during step (1) is a local best match.

20. The method of any of claims 1 or 13-19 wherein the best match attained during step (2) is a local best match.

21. The method of any of claims 1 or 13-17, 19 or 20 wherein step (1) is performed by (a) changing the value of only the first of said variable reactances until the best impedance match between the impedances seen looking into and out of output terminals of the r.f. source is attained; (b) then changing only the value of the second of said variable reactances until the best impedance match between the impedances seen looking into and out of output terminals of the r.f. source is attained; (c) then changing the value of only the first of said variable reactances until the best impedance match between the impedances seen looking into and out of output terminals of the r.f. source is attained; (d) from indications of the values of the first and second variable reactances at the completion of steps (a) and (c), determining the amount the first variable reactance is to change for each unit change in the value of the second variable reactance.

22. The method of any of claims 1 or 13-21 wherein the variations in values of step (5) result in a first straight line trajectory in a plot of the values of the first and second variable reactances, the method further including:

(a') determining if the best possible impedance match at the completion of step (2) meets a minimum criterion;

(b') in response to the determination of step (a') meeting the minimum criterion, maintaining the values of the first and second variable reactances constant;

(c') in response to the determination of step (a') not meeting the minimum criterion, changing the values of the first and second variable reactances so there is a second straight line trajectory at a right angle to the first trajectory until the best possible match between the impedances seen looking into and out of output terminals of the r.f. source is attained; and

(d') then simultaneously changing the values of the first and second variable reactances along a further straight line trajectory including a point on the first trajectory and a further point determined by the point on the second trajectory where the best possible match between the impedances seen looking into and out of output terminals of the r.f. source is attained.

23. The method of claim 22 wherein the point on the first and further trajectories is an intermediate point along the first trajectory.

24. The method of claim 22 or 23 wherein the further point on the further trajectory is the point on the second trajectory where the best possible match between the impedances seen looking into and out of output terminals of the r.f. source is attained.

25. Apparatus for performing the method of any of claims 1 or 13-24 characterized by a controller for automatically executing the claimed steps.

26. The apparatus of claim 25 wherein the controller includes a computer memory storing signals commanding execution of the claimed steps.