Magnetically enhanced plasma reactor system for semiconductor processing

• US 5,225,024 A
• Filed: 08/22/1991
• Issued: 07/06/1993
• Est. Priority Date: 05/08/1989
• Status: Expired due to Term

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Levy, Karl B., Savas, Stephen E., Donohoe, Kevin, Jha, Neeta, Hanley, Peter R.
• Primary Examiner(s): DANG, THI D
• Application Number:
  US07/750,720
• Time in Patent Office: 684 Days
• Field of Search: 156/345, 156/643, 156/646, 204/192.12, 204/192.32, 204/298.37, 204/298.16, 204/298.17, 118/723
• US Class Current: 156/345.46
• CPC Class Codes: H01J 37/32623 Mechanical discharge control means
• CPC Class Codes: H01J 37/3266 Magnetic control means
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence

Abstract

Magnetic confinement of electrons in a plasma reactor is effected using electro-magnetic coils and other magnets which generate respective magnetic fields which are mutually opposed and substantially orthogonal on their common axis to the major plane of a wafer being processed, instead of being aligned and parallel to the major plane as in prior magnetically enhanced plasma reactors. The respective magnetic fields combine to yield a net magnetic field which is nearly parallel to the wafer away from the magnetic axis so that electrons are confined in the usual manner. In addition, a magnetic mirror provides confinement near the magnetic axis. The E×B cross product defines a circumferential drift velocity urging electrons about a closed path about the magnetic axis. The magnetic and cross-product forces on plasma electrons have a rotational symmetry which enhances reaction uniformity across the wafer; this contrasts with the prior art in which lateral drift velocity disturbs plasma symmetry and thus reaction uniformity. Furthermore, the disclosed field geometry permits stronger electron confinement which enhances plasma reaction rates.

Claims

1. A plasma etch or CVD reactor having a pair of electrodes for plasma processing comprising:

plasma generation means for forming a plasma including energetic electrons near a major planar surface of a substrate mounted on a cathode, said plasma being selected to promote predetermined plasma processing at said surface; and

magnetic confinement means for defining a cusp magnetic mirror region which at least partially confines said energetic electrons to a region near said major planar surface of said substrate and a permanent magnet disposed within said cathode to enhance said plasma processing.

2. A plasma reactor having a pair of electrodes for plasma processing comprising:

substrate support means mounted on a cathode for supporting a substrate having a major planar surface at which plasma-based processing is to occur;

plasma generation means for forming a plasma including energetic electrons near said major planar surface; and

cusp magnetic mirror generation means for magnetically confining at least a portion of said energetic electrons proximate to said major planar surface, said mirror means defining a substantially axi-symmetric magnetic field with an axis substantially orthogonal to said major planar surface and a permanent magnet disposed within said substrate support.

3. A plasma reactor for semiconductor processing comprising:

plasma generation means for forming a plasma including energetic electrons near a major planar surface of a semiconductor substrate mounted on a cathode, said plasma being selected to promote predetermined etch or CVD processing at said surface;

plural magnetic means which develop a substantially timeinvariant cusp magnetic mirror region near said major planar surface, said plural magnetic means including a first magnet means and a second magnet means located on opposing sides of said substrate, said first magnet means providing a first magnetic field on a first side of said major planar surface having a first magnetic axis substantially orthogonal to said major planar surface, said second magnet means providing a second magnetic field on a second side of said major planar surface having a second magnetic axis substantially coaxial with said first magnetic axis; and

a permanent magnet located within said cathode.

4. A plasma reactor for semiconductor processing comprising:

a reaction vessel defining a CVD or etch plasma reaction chamber;

gas introduction means for introducing a reactive plasma precursor gas into said reaction chamber;

exhaust handling means for removing spent gases from said plasma reaction chamber and for maintaining a sub-ambient pressure within said chamber;

support means for supporting a substrate mounted on a cathode within said plasma reaction chamber, said substrate having a major planar surface on which plasma processing is to occur;

a permanent magnet disposed within said cathode;

power source means for generating an oscillating electric field to generate a plasma from said plasma precursor gas, said electric field being generally orthogonal to said major planar surface so that positive ions of said plasma are attracted to said surface; and

magnetic means for generating a substantially time-invariant net magnetic field which is at least partially symmetric about an axis orthogonal to said major planar surface, said net magnetic field being increasingly parallel to said surface at increasing radii from said axis, said magnet means including a first magnet means for generating a first magnetic field on a first side of said major planar surface having an axis substantially orthogonal to said surface and a second magnet means for generating a second magnet field on a second side of said major surface, said first magnetic field and said second magnetic field cooperating to confine at least a portion of energetic electrons proximate said major planar surface of said surface.

5. The plasma reactor of claim 4 wherein said plasma has a sheath boundary which moves back and forth across a boundary space under the influence of said plasma generation means, said first magnet means and said second magnet means being oriented so that said net magnetic field confines many of the more energetic electrons of said plasma to a region immediately above said boundary space.

6. The plasma reactor of claim 4 wherein said reaction vessel includes an exhaust manifold and wherein one of said first and second magnets means is at least partially positioned within said exhaust manifold.

7. A plasma reactor for semiconductor processing comprising:

plasma generation means for forming a CVD or etch plasma including energetic electrons near a surface of a semiconductor substrate mounted on a cathode, said plasma being selected to promote predetermined processing at said surface, said plasma generation means including means for generating a radio frequency electric field;

a permanent magnet disposed within said cathode; and

confinement means for magnetically confining a substantial proportion of said energetic electrons of said plasma, said confinement means defining a magnetic field which cooperates with said electric field to induce plasma drift which is azimuthal about an axis substantially orthogonal to said surface.

8. A plasma reactor comprising:

a CVD or etch reaction chamber;

substrate support means mounted on a cathode within said reaction chamber for supporting a substrate having a major planar surface to be processed;

plasma generation means for generating a plasma proximate to said major planar surface;

a permanent magnet means disposed within said cathode;

first magnet means having a first magnetic axis, said first magnetic means being disposed on a first side of said major planar surface such that said first magnetic axis is substantially perpendicular to said major planar surface; and

second magnet means having a second magnetic axis, said second magnet means being disposed on a second side of said major planar surface such that said second magnetic axis is substantially perpendicular to said major planar surface, wherein said first magnet means and said second magnet means cooperate to generate a substantially time-invariant cusp magnetic mirror region proximate said major planar surface to at least partial confine energetic electrons proximate to said major planar surface.

9. A plasma reactor as recited in claim 8 wherein said first magnetic axis and said second magnetic axis are substantially coaxial and ar substantially centered on said major plane of said semiconductor wafer.