Apparatus for producing planar plasma using varying magnetic poles

• US 5,435,881 A
• Filed: 03/17/1994
• Issued: 07/25/1995
• Est. Priority Date: 03/17/1994
• Status: Expired due to Term

• Current Assignee: Ogle, John S.
• Original Assignee: Ogle, John S.
• Inventors: Ogle, John S.
• Primary Examiner(s): Breneman, R. Bruce
• Assistant Examiner(s): CHANG, JONI YUK YING
• Application Number:
  US08/210,173
• Time in Patent Office: 495 Days
• Field of Search: 118/723 MP, 118/723 MA, 156/345, 204/298.16, 204/298.17, 204/298.18, 204/298.19, 204/298.2, 204/298.21, 204/298.22, 204/298.37
• US Class Current: 156/345.42
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma

Abstract

A plasma generation system comprises a two-by-two or larger array of alternating magnetic poles set proximate to an insulating window in a chamber containing a process gas. The magnetic poles are ferromagnetic core coils driven by a radio frequency power source at sufficient energies to generate a plasma within the process gas chamber. The magnetic poles are included in ferromagnetic core coils that are wired to the radio frequency power source such that each magnetic pole is surrounded equally in the plane of the insulating window by adjacent magnetic poles of opposite magnetic polarity and uniform magnitudes. In a two-by-two array, the two sets of opposite corners have opposite magnetic polarities.

Claims

1. An apparatus for generating a low pressure plasma, comprising:

a chamber for enclosing process gases at reduced pressures and including means for controlling gas pressure and flow;

an approximately planar insulating window for passing varying magnetic fields at radio frequencies from outside the chamber into said process gases; and

means for four or more radio frequency varying magnetic poles in proximity to said insulated window, with adjacent varying magnetic poles of opposite polarity and approximately equally spaced for connection to an alternating current radio frequency power source, wherein a radio frequency varying magnetic field from said varying magnetic poles is coupled through said planar insulating window to create a plasma within said chamber.

2. The apparatus of claim 1, wherein:

the means for four or more radio frequency varying magnetic poles is such that each of the poles is elongated in one dimension with said approximately equal spacing in a dimension perpendicular to said magnetic pole elongation and parallel to said insulating window.

3. The apparatus of claim 1, wherein:

said adjacent opposite polarity magnetic poles are approximately equally spaced in two dimensions.

4. The apparatus of claim 1, further comprising:

steady-state magnetic means for passing a constant magnetic field through said window into said chamber providing for constant magnetic field lines that are approximately perpendicular to said window.

5. An apparatus for generating a low pressure plasma, comprising:

a chamber for enclosing process gases at reduced pressures and including means for controlling gas pressure and flow;

an approximately planar insulating window for passing varying magnetic fields from outside the chamber into said process gases; and

means for four or more varying magnetic poles in proximity to said insulated window, with adjacent varying magnetic poles of opposite polarity and approximately equally spaced, wherein each of the poles is elongated in one dimension with said approximately equal spacing in a dimension perpendicular to said magnetic pole elongation and parallel to said insulating window.

6. The apparatus of claim 5, wherein the means for four or more varying magnetic poles includes:

opposite polarity pairs of said elongated varying magnetic poles which comprise ferromagnetic cores with a U-shaped cross section with the dimension of said ferromagnetic core perpendicular to said cross section substantially larger than the dimension between the ends of said U-shaped cross section of said ferromagnetic core;

one or more turns of a conductor carrying a varying electric current through the inside of said U-shaped ferromagnetic core; and

the open side of said U-shaped cross section ferromagnetic core is placed adjacent to said insulating window.

7. The apparatus of claim 5, wherein the means for four or more varying magnetic poles includes:

opposite polarity pairs of said elongated varying magnetic poles are formed by non-magnetic cores with a U-shaped cross section with the dimension of said non-magnetic core perpendicular to said cross section larger than the dimension between the ends of said U-shaped cross section of said non-magnetic core;

four or more turns of a conductor carrying a varying electric current through the inside of said U-shaped non-magnetic core; and

the open side of said U-shaped cross section non-magnetic core is placed adjacent to said insulating window.

8. An apparatus for generating a low pressure plasma, comprising:

a chamber for enclosing process gases at reduced pressures and including means for controlling gas pressure and flow;

an approximately planar insulating window for passing varying magnetic fields from outside the chamber into said process gases; and

means for four or more varying magnetic poles in proximity to said insulated window, with adjacent varying magnetic poles of opposite polarity and approximately equally spaced, wherein said adjacent opposite polarity magnetic poles are approximately equally spaced in two dimensions.

9. The apparatus of claim 8, wherein:

the means for four or more varying magnetic poles includes two or more sets of two opposite polarity varying magnetic poles, each set of which is formed by the ends of a U-shaped ferromagnetic core about which is wound one or more turns of a conductor carrying a varying electric current.

10. The apparatus of claim 8, wherein:

the means for four or more varying magnetic poles includes varying magnetic poles formed by I-shaped ferromagnetic cores about which are wound one or more turns of a conductor carrying a varying electrical current, with said I-cores mounted approximately perpendicular to said window and the direction of current flow opposite for adjacent ferromagnetic I-cores.

11. The apparatus of claim 10, wherein:

the means for four or more varying magnetic poles further includes additional ferromagnetic cores for coupling the varying magnetic fields between two or more of the ends of said I-cores opposite to said window.

12. The apparatus of claim 8, further comprising:

a conductive sheet placed between said varying magnetic poles and said window and having holes corresponding to the position and size of said varying magnetic poles and having slots cut through said conductive sheet that join each hole to an adjacent hole, and having means for connecting said conductive sheet to a ground or to a source of radio frequency power.

13. The apparatus of claim 8, wherein:

the means for four or more varying magnetic poles includes two or more sets of two opposite polarity varying magnetic poles, each set of which is formed by the ends of a U-shaped non-magnetic core about which is wound four or more turns of a conductor for carrying a varying electric current.

14. An apparatus for generating a low-pressure plasma in a chamber containing-a process gas through an insulating window in the chamber, comprising:

a plurality of ferromagnetic core coils having respective magnetic poles placed proximate to said insulating window in at least a two-by-two array in a plane and connected with each magnetic pole surrounded by adjacent magnetic poles of opposite magnetic polarity, wherein in each two-by-two array, the two sets of opposite corners instantaneously have opposite magnetic polarities.

15. The apparatus of claim 14, wherein:

the plurality of ferromagnetic core coils comprises ferromagnetic core coils having a U-shaped ferromagnetic core with open ends of said core oriented in a single direction to face said insulating window and having approximately equal spacings between each open end of each core and open ends of adjacent cores.

16. The apparatus of claim 14, further comprising:

a variable capacitor in series with the plurality of ferromagnetic core coils; and

a variable transformer having a secondary winding connected to the series combination of the variable capacitor and the plurality of ferromagnetic core coils and having a primary winding for receiving a radio frequency power input.

17. The apparatus of claim 14, further comprising:

a direct current bias coil surrounding the plurality of ferromagnetic core coils in a plane parallel to said insulating window and having connections for a source of direct current, wherein a migration of electrons within said plasma is controlled to avoid the inner walls of said process chamber.

18. The apparatus of claim 14, further comprising:

a conductive sheet having holes at positions corresponding to said magnetic poles which provide access for each ferromagnetic core coil to said insulating window and an open slot between pairs of said holes.

19. An apparatus for generating a low-pressure plasma in a chamber containing a process gas through an insulating window in the chamber, comprising:

a plurality of ferromagnetic core coils in a row having respective elongated magnetic poles placed proximate to said insulating window in at least a one-by-four array in a plane and connected with each magnetic pole surrounded on either side by adjacent magnetic poles of opposite magnetic polarity, wherein said magnetic poles are elongated in a direction orthogonal to said row.

20. The apparatus of claim 19, wherein:

the plurality of ferromagnetic core coils comprise ferromagnetic core coils having a U-shaped ferromagnetic core with open ends of said core oriented in a single direction to face said insulating window and having approximately equal spacings between each open end of the core and open ends of adjacent cores.

21. The apparatus of claim 19, further comprising:

a variable capacitor in series with the plurality of ferromagnetic core coils; and

a variable transformer having a secondary winding connected to the series combination of the variable capacitor and the plurality of ferromagnetic core coils and having a primary winding for receiving a radio frequency power input.