Method and apparatus for producing low pressure planar plasma using a coil with its axis parallel to the surface of a coupling window

• US 5,277,751 A
• Filed: 06/18/1992
• Issued: 01/11/1994
• Est. Priority Date: 06/18/1992
• Status: Expired due to Term

• Current Assignee: Ogle, John S.
• Original Assignee: Ogle, John S.
• Inventors: Ogle, John S.
• Primary Examiner(s): DANG, THI D
• Application Number:
  US07/900,131
• Time in Patent Office: 572 Days
• Field of Search: 156/345, 156/643, 118/723, 427/569, 204/298.02, 204/298.08, 204/298.19, 204/298.31, 204/298.34, 204/298.37, 204/192.12, 204/192.1, 204/192.32
• US Class Current: 216/70
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma

Abstract

An embodiment of the present invention is a plasma system that comprises a main coil with a flattened side and a capacitor in parallel that form a tuned circuit with radio frequency energy coupled to it through a radio frequency match by a generator. A process chamber with a quartz window and containing a low pressure gas is adjacent to the flat side of the main coil and a two-dimensional planar plasma in the shape of a circular disk is ignited and maintained by a high rate of change of the current flowing in the main coil. An electrode positioned in the chamber opposite to the window is used for attaching a semiconductor wafer for processing and a potential applied to the electrode independently controls the ion energy of ions attracted and accelerated out of the plasma.

Claims

1. A method of planar plasma generation comprising the steps of:

winding a main coil of soft copper tubing having between five and fifteen turns including a flattening of said coil on one side;

connecting a high-current high-voltage capacitor to said flattened main coil;

positioning said flattened main coil proximate to a gas enclosure with said one flattened side adjacent to said gas enclosure;

coupling a radio frequency power source to said flattened main coil;

optimally coupling said radio frequency power to the combination of said main coil and capacitor with a matching means to result in the generation of a planar plasma within said gas enclosure that lies in a plane substantially parallel to the axis of said flattened main coil; and

filtering out the magnetic field of said main coil from reaching inside said gas enclosure by separating said coil and gas enclosure and communicating the potentials existing on a series of voltage taps on said main coil to a series of planar electrodes parallel to said gas enclosure wherein said planar plasma is generated by the varying electric field of said main coil.

3. The apparatus of claim 1, wherein:

a side of said coil adjacent to said window is flattened to substantially improve coupling between the coil and said plasma within the enclosure.

4. The apparatus of claim 1, further comprising:

an electrode mounted inside the enclosure opposite to said insulating window and having a connection for a source of radio frequency power wherein ions created within said plasma may be imparted an acceleration energy in the direction of the electrode.

5. The apparatus of claim 1, wherein:

a source of radio frequency power is applied between a point of said coil and a ground defined by the potential of the conductive portions of said enclosure.

2. An apparatus for producing a plasma, comprising:

a gas-tight enclosure bounded at least in part by a substantially planar electrically insulating window;

means for introducing a plurality of process gases into the enclosure;

means for controlling the pressure of said process gases;

a coil with a plurality of winding turns that progress along a longitudinal axis and positioned proximate to the enclosure and outside adjacent to said insulating window with said longitudinal axis of the coil oriented substantially parallel to said insulating window; and

means for coupling a radio frequency power source to the coil to cause a current to flow through the coil wherein a planar plasma may be ignited and maintained parallel to said insulating window.

6. An apparatus for producing a plasma, comprising:

an enclosure having an interior bounded at least in part by an electrically insulating window;

means for introducing a process gas into the enclosure;

means for controlling the pressure of said process gas while in the chamber;

a resonant circuit including at least one inductor and one capacitor; and

a series of elongated plates positioned side-by-side on said insulating window such that plates are substantially parallel, each plate including an electrical connection to points on said resonant circuit wherein a portion of a voltage across said resonant circuit also is distributed across the plates for inducing a planar plasma within the enclosure that is parallel to said window.

7. The apparatus of claim 6, further comprising:

means for generating a stable magnetic field having a field direction that is substantially perpendicular to said window.

8. The apparatus of claim 6, further comprising:

an electrode mounted inside the enclosure opposite to said insulating window; and

means for applying radio frequency power to said electrode.

9. An apparatus for treating articles with a plasma, said apparatus comprising:

an enclosure having an interior for supporting said articles to be treated, the enclosure being bounded at least in part by an electrically insulating window;

an electrically conductive coil mounted external to said enclosure adjacent to said window, with a longitudinal axis of said coil substantially parallel to the surface of said window for generating an intense varying internal magnetic field along said longitudinal axis and a weaker external return magnetic field outside the coil wherein a plasma may be maintained inside said plasma chamber by said weaker external return magnetic field passing through said window;

means for coupling radio frequency power to said coil to cause a radio frequency current to flow through said coil;

means for introducing process gases into said enclosure; and

means for controlling the pressure inside said chamber.

10. A plasma generation device for generating a substantially two-dimensional planar plasma parallel to a semiconductor wafer being processed, the device comprising:

a main coil including between five and fifteen turns wound along a longitudinal axis for generating an intense varying internal magnetic field along said longitudinal axis of the main coil and a weaker external return varying magnetic field outside the main coil, wherein said planar plasma may be maintained inside a plasma chamber by said weaker external return varying magnetic field passing through an adjacent insulating window;

a capacitor connected to the main coil for tuning the natural oscillating frequency of the combination of the main coil and capacitor;

a process chamber for receiving gas and supporting a substantially two-dimensional planar plasma parallel to the semiconductor wafer being processed, the process chamber having said adjacent insulating window in close proximity to the main coil and oriented with the axis of the main coil substantially parallel to the semiconductor wafer being processed;

means for radio frequency power injection coupled to the main coil wherein the two-dimensional planar plasma is generated; and

an electrode for accelerating ions produced from the two-dimensional planar plasma toward the semiconductor wafer in a direction normal to the plane of the semiconductor wafer.

11. The device of claim 10, wherein:

the main coil comprises soft copper tubing;

the capacitor is a vacuum variable type; and

said insulating window in the process chamber is a quartz window positioned between the main coil and the two-dimensional planar plasma.

12. The device of claim 10, further comprising:

an electrostatic shield is placed between the main coil and the two-dimensional planar plasma wherein only an electromagnetic field generated by the main coil is strong enough within the process chamber to ignite and maintain the two-dimensional planar plasma.

13. A system for generating a uniform planar plasma within a gas-tight, gas-filled plasma chamber with an electrically insulating window, comprising:

a coil with a plurality of winding turns that progress along a longitudinal axis and that is positioned proximate to the enclosure and outside adjacent to said insulating window with said longitudinal axis of the coil oriented substantially parallel to said insulating window for generating an intense varying internal magnetic field along said longitudinal axis and a weaker varying external return magnetic field outside the coil wherein a plasma may be maintained inside said plasma chamber by said weaker external return magnetic field passing through said insulating window.

14. A plasma generation device for generating a two-dimensional planar plasma parallel to a semiconductor wafer being processed, the device comprising:

a main coil including between five and fifteen turns wound along a longitudinal axis;

a capacitor connected to the main coil for tuning the natural oscillating frequency of the combination of the main coil and capacitor;

a process chamber for receiving gas and supporting a substantially two-dimensional planar plasma parallel to the semiconductor wafer being processed, the process chamber being in close proximity to the main coil and oriented with the axis of the main coil substantially parallel to the semiconductor wafer being processed;

means for radio frequency power injection coupled to the main coil wherein the two-dimensional planar plasma is generated;

an electrode for accelerating ions produced from the two-dimensional planar plasma toward the semiconductor wafer in a direction normal to the plane of the semiconductor wafer;

an electrostatic shield placed between the main coil and the two-dimensional planar system wherein only an electromagnetic field generated by the main coil is strong enough within the process chamber to ignite and maintain the two-dimensional planar plasma; and

an insulation layer that is placed between the main coil and the electrostatic shield for preventing electrical arcing of the main coil to the electrostatic shield.