ELECTRON BEAM PLASMA SOURCE WITH PROFILED CHAMBER WALL FOR UNIFORM PLASMA GENERATION
A plasma reactor that generates plasma in a workplace processing chamber by an electron beam, has an electron beam source chamber with a wall opposite to the electron beam propagation direction, the wall being profiled to compensate for a non-uniformity in electron beam density distribution.
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This application claims the benefit of U.S. Provisional Application Ser. No. 61/549,355, filed Oct. 20, 2011 entitled ELECTRON BEAM PLASMA SOURCE WITH PROFILED CHAMBER WALL FOR UNIFORM PLASMA GENERATION, by Kalloi Bera, et al.
BACKGROUNDA plasma reactor for processing a workplace can employ an electron beam as a plasma source. Such a plasma reactor can exhibit non-uniform distribution of processing results (e.g., distribution of etch rate across the surface of a workpiece) doe to non-uniform density distribution of the electron beam. Such non-uniformities can be distributed in a direction transverse to the beam propagation direction.
SUMMARYA plasma reactor for processing a workpiece, includes a workpiece processing chamber having a processing chamber including a chamber ceiling and a chamber side wall and an electron beam opening in the chamber side wall, a workpiece support pedestal in the processing chamber having a workpiece support surface facing the chamber ceiling and defining a workpiece processing region between the workpiece support surface and the chamber ceiling, the electron beam opening facing the workpiece processing region. The plasma reactor further includes an electron beam source chamber including a source enclosure, the source enclosure having an electron beam emission window that is open to the electron beam opening of the workpiece processing chamber, and defining an electron beam propagation path along a longitudinal direction extending through the electron beam emission window and through the electron beam opening and into the workpiece processing region, the source enclosure further including a back wall displaced from the electron beam emission window by a gap along the longitudinal direction, the electron beam emission window extending generally along a direction transverse to the longitudinal direction. An electron beam extraction grid extends across the electron beam emission window. An extraction voltage source is coupled to the electron beam extraction grid, and a supply of plasma source power is coupled to the electron beam source chamber. The back wall has a profile corresponding to a variance in the gap along the transverse direction. In one embodiment, the profile is selected to be complementary to a variance in electron beam density along the transverse direction. In a related embodiment, the variance in the gap corresponds to a measured variance in electron beam density distribution along the transverse direction. The profile may be actively configurable. For example, the back wall may consist of plural slats that are removably inserted into the source enclosure through a. particular selection of various slots. Each profile corresponds to a different selection of the slots. As another example, the back wall may be a flexible sheet that can be deformed to different curvatures.
So that the manner in which the exemplary embodiments of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
DETAILED DESCRIPTIONReferring to
The plasma is generated in process region 118 by an electron beam from an electron beam source 120. The electron beam source 120 includes a plasma generation chamber 122 outside of the process chamber 100 and having a conductive enclosure 124. The conductive enclosure 124 includes side wails 124b, a ceiling 124c, a floor 124d and a back wall 124e. The conductive enclosure 124 has a gas inlet or neck 125. An electron beam source gas supply 127 is coupled to the gas inlet 125. The conductive enclosure 124 has an opening 124a facing the process region 118 through an opening 102a in the sidewall 102 of the process chamber 100.
The electron beam source 120 includes an extraction grid 126 between the opening 124a and the plasma generation chamber 122, and an acceleration grid 128 between the extraction grid 126 and the process region 118, best seen in the enlarged view of
The electron beam source 120 further includes a pair of electromagnets 134-1 and 134-2 adjacent opposite sides of the chamber 100, the electromagnet 134-1 surrounding the electron beam source 120. The electromagnets 134-1 and 134-2 produce a magnetic field parallel to the direction of the electron beam along an electron beam path. The electron beam flows across the processing region 118 over the workpiece 110, and is absorbed on the opposite side of the processing region 118 by a beam dump 136. The beam dump 136 is a conductive body having a shape adapted to capture the wide thin electron beam.
A plasma D.C. discharge voltage supply 140 is coupled to the conductive cathode enclosure 124, and provides extraction voltage between cathode 124 and extraction grid 126. One terminal of an electron beam acceleration voltage supply 142 is connected to the extraction grid 126 and the other terminal to the acceleration grid 128 through the ground potential of the sidewall 102 of the process chamber 100. A coil current supply 146 is coupled to the electromagnets 134-1 and 134-2. Plasma is generated within the chamber 122 of the electron beam source 120 by a D.C. gas discharge produced by power from the voltage supply 140, to produce a plasma throughout the chamber 122. This D.C. gas discharge is the plasma source of the electron beam source 120. Electrons are extracted from the plasma in the chamber 122 through the extraction grid 126, and accelerated through the acceleration grid 128 due to a voltage difference between the acceleration grid and the extraction grid to produce an electron beam that flows into the processing chamber 100.
The distribution of electron density across the width of the beam (along the X-axis or direction transverse to beam travel) affects the uniformity of plasma density distribution in the processing region 118. The electron beam may have a measured non-uniform distribution, in the absence of features that correct such non-uniformities, which features are described below. Such non-uniformity may be measured from etch depth distribution measured on a workpiece or wafer processing in the reactor chamber described above. Such measured non-uniformity may be caused by electron drift due to the interaction of the bias electric field with the magnetic field, divergence of electron beam due to self electric field and/or electron collision with neutral gas in the process chamber. Such non-uniformity may also be caused by fringing of an electric field at the edge of the electron beam. The distribution of electron density across the width of the beam (across the X-axis or direction transverse to beam travel) is liable to exhibit non-uniformities due to the foregoing causes. Such non-uniformities may correspond to a variance in plasma electron density distribution in the electron beam across the width of the electron beam in a range of 1% to 20%, for example. Such a variance may be measured in that it may be inferred from the measurements of etch depth distribution in a test wafer referred to above.
The back wall 124e of the conductive enclosure 124 is profiled along the transverse direction (X-axis). The profiling is chosen to compensate for a measured non-uniformity along the transverse direction in electron density distribution of the electron beam. For example, in the embodiment of
In the embodiment of
It is believed that such profiling changes the effective cathode area along the transverse direction, which changes the distribution of ion current to the cathode (i.e., the conductive envelope 124) along the transverse direction. This creates a corresponding change in distribution along the transverse direction of electron current through the extraction grid 126. For example, a constriction in volume reduces plasma electron density. Thus, in the embodiment of
profiling of
While the main plasma source in the electron beam source 120 is a D.C. gas discharge produced by the voltage supply 140, any other suitable plasma, source may be employed instead as the main plasma source. For example, the main plasma source of the electron beam source 120 may be a toroidal RF plasma source, a capacitively coupled RF plasma source, or an inductively coupled RF plasma source.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims
1. A plasma reactor for processing a workpiece, comprising:
- a workpiece processing chamber having a processing chamber comprising a chamber ceiling and a chamber side wall and an electron beam opening in said chamber side wall, a workpiece support pedestal in said processing chamber having a workpiece support surface facing said chamber ceiling and defining a workpiece processing region between said workpiece support surface and said chamber ceiling, said electron beam opening facing said workpiece processing region;
- an electron beam, source chamber comprising a source enclosure, said source enclosure having an electron beam emission window that is open to said electron beam opening of said workpiece processing chamber, and defining an electron beam propagation path along a longitudinal direction extending through said electron beam emission window and through said electron beam opening and into said workpiece processing region, said source enclosure further comprising a back wall displaced from said electron beam emission window by a gap along said longitudinal direction, said electron beam emission window extending generally along a direction transverse to said longitudinal direction;
- an electron beam extraction grid, across said electron beam emission window, an extraction voltage source coupled to said electron beam extraction grid, and the said electron beam source chamber; and
- said back wall having a profile corresponding to a distribution of said gap along said transverse direction.
2. The plasma reactor of claim 1 wherein said distribution of said gap corresponds to a distribution in electron beam density along said transverse direction.
3. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction corresponds to a measured distribution in electron beam density distribution along said transverse direction.
4. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction is center-low, wherein said gap has a minimum value at a center location of said back wall along said transverse direction.
5. The plasma reactor of claim 4 wherein said distribution of said gap along said transverse direction of said electron beam source chamber compensates for a measured distribution of plasma density along said transverse direction that is center-high.
6. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction is center-high, wherein said gap has a maximum value at a center location of said back wall along said transverse direction.
7. The plasma reactor of claim 6 wherein said distribution of said gap along said transverse direction of said electron beam source chamber compensates for a measured distribution of plasma, density distribution along said transverse direction that is center-low.
8. The plasma reactor of claim 1 wherein said, distribution of said gap along said transverse direction has a variance of least 1%.
9. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction has a variance of at least 5%.
10. The plasma reactor of claim 1 wherein back wall is configurable for changing said profile.
11. The plasma reactor of claim 1 wherein said back wall comprises a flexible member capable of deforming between different curvatures, and an actuator coupled to said flexible member.
12. The plasma reactor of claim 11 wherein said different curvatures comprise a curvature corresponding to a concave profile or a curvature corresponding to a convex profile.
13. The plasma reactor of claim 1 wherein said source enclosure further comprises a ceiling, a floor facing said ceiling, plural elongate slots in one of said floor and ceiling, said slots spaced apart from one another and at least some of said slots extending in different directions relative to said transverse and longitudinal directions, and plural slats removably inserted into selected ones of said slots to form respective barriers extending from said floor to said ceiling and through the selected, slots, said back wall comprising the slats inserted through said slots.
14. The plasma reactor of claim 13 wherein said selected slots comprises a set of said plural slots corresponding to one of plural profiles.
15. The plasma reactor of claim 14 wherein said plural profiles comprise a convex profile or a concave profile.
16. The plasma reactor of claim 14 wherein said plural profile corresponds to a measured distribution in electron beam density distribution along said transverse direction.
17. The plasma reactor of claim 11 wherein said different curvatures comprise a curvature corresponding to a measured distribution in electron beam density distribution along said transverse direction.
18. The plasma reactor of claim 1 further comprising:
- an electron beam acceleration grid or slot separated by a dielectric from the said electron beam extraction grid, an acceleration voltage source coupled to said electron beam acceleration grid or slot, and the said extraction grid.
Type: Application
Filed: Aug 27, 2012
Publication Date: Apr 25, 2013
Applicant: Applied Materials, Inc. (Santa Clara, CA)
Inventors: Kallol Bera (San Jose, CA), Kenneth S. Collins (San Jose, CA), Shahid Rauf (Pleasanton, CA), Leonid Dorf (San Jose, CA)
Application Number: 13/595,351
International Classification: C23F 1/08 (20060101);