WO2013059093A1

WO2013059093A1 - E-beam plasma source with profiled e-beam extraction grid for uniform plasma generation

Info

Publication number: WO2013059093A1
Application number: PCT/US2012/060018
Authority: WO
Inventors: Leonid Dorf; Shahid Rauf; Kenneth S. Collins; Nipun Misra; James D. Carducci; Gary Leray; Kartik Ramaswamy
Original assignee: Applied Materials, Inc.
Priority date: 2011-10-20
Filing date: 2012-10-12
Publication date: 2013-04-25
Also published as: CN103748970A; TW201320145A; KR20140078748A; US20130098552A1

Abstract

A plasma reactor that relies on an electron beam as a plasma source employs a profiled electron beam extraction grid in an electron beam source to improve uniformity.

Description

E-BEAM PLASMA SOURCE WITH PROFILED E-BEAM

EXTRACTION GRID FOR UNIFORM PLASMA GENERATION

Inventors: Leonid Dorf, Shahid Rauf, Kenneth S. Collins, Nipun Misra, James D. Carducci, Gary Leray and

Kartik Ramaswamy

FIELD OF THE INVENTION

[ 1 ] Embodiments of the invention relate to an e-beam plasma source for uniform plasma generation.

BACKGROUND

[ 2 ] A plasma reactor for processing a workpiece can employ an electron beam (e-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) due to non^¬ uniform distribution of electron density and/or kinetic energy within the electron beam. Such non-uniformities can be distributed along a direction transverse to the beam propagation direction.

SUMMARY

[3] A plasma reactor for processing a workpiece comprises a workpiece processing chamber having a

processing chamber enclosure comprising a ceiling and a side wall and an electron beam opening in the side wall, a workpiece support pedestal in the processing chamber having a workpiece support surface facing the ceiling and defining a workpiece processing region between the workpiece support surface and the ceiling, the electron beam opening facing the workpiece processing region.

Further, there is provided an electron beam source chamber comprising an electron beam source chamber enclosure and an emission opening between the electron beam source chamber and the workpiece processing chamber facing the electron beam opening, and a profiled

extraction grid is disposed in the emission opening and comprising plural grid openings each extending through the extraction grid, the grid openings having a non^¬ uniform distribution of a number of grid openings per unit length along an axis parallel with a plane of the workpiece support surface.

[4] In one embodiment, the non-uniform distribution of the grid openings is a decreasing function of a proximity of the grid openings to an edge of the profiled

extraction grid along the axis. In another embodiment, the non-uniform distribution of the grid openings is an increasing function of a proximity of the grid openings to an edge of the profiled extraction grid along the axis. Optionally, the grid openings may be arranged in regular row and columns, the columns being distributed along the axis, the rows extending parallel to the axis, wherein the number of grid openings in each the column varies with location of each column along the axis.

[5] The reactor in one embodiment further comprises a voltage source coupled to the extraction grid, the extraction grid comprising a conductive material.

[6] The non-uniform distribution of the number of grid openings per unit length in one embodiment is

complementary relative to a non-uniformity in plasma distribution along the axis in the electron beam source chamber . [7] The plasma reactor in one embodiment further comprises an electron beam source gas supply coupled to the electron beam source chamber, a workpiece process gas supply coupled to the workpiece processing chamber, a supply of plasma source power coupled to the electron beam source chamber and an electron beam extraction voltage supply coupled to the extraction grid.

[8] The plasma reactor in one embodiment further comprises an acceleration grid in the emission opening and located between the extraction grid and the workpiece processing chamber. The acceleration grid comprises plural acceleration grid openings having a non-uniform distribution of a number of grid openings per unit length along the axis parallel with a plane of the workpiece support surface. In one embodiment, the non-uniform distribution of the acceleration grid openings conforms with the non-uniform distribution of the extraction grid openings .

[9] In one embodiment, the emission opening is located on one side of the workpiece processing chamber, and a beam dump is disposed at a side of the workpiece

processing chamber opposite the one side, the beam dump comprising a conductor electrically coupled to a

potential attractive to an electron beam. In one

embodiment, the beam dump is electrically coupled to the processing chamber enclosure.

[10] The profiled extraction grid in certain

embodiments comprises (a) a conductive sheet having the grid openings formed therethrough, or (b) a conductive mesh . BRIEF DESCRIPTION OF THE DRAWINGS

[11] 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.

[12] FIGS. 1A, IB and 1C depict a plasma reactor with an electron beam plasma source having a profiled e-beam extraction grid, of which FIGS. 1A is a side view, FIG. IB is an enlarged view of a portion of FIG. 1A, and FIG. 1C is a cross-sectional view taken along lines 1C-1C of FIG. IB, in accordance with a first embodiment.

[13] FIGS. 2A, 2B and 2C depict the profiled e-beam extraction grid in alternative embodiments.

[14] FIGS. 3A, 3B and 3C depict respective grid opening shapes in the profiled extraction grid, in accordance with different embodiments.

[15] FIGS. 4A and 4B are graphical depictions of the interaction of an edge-dense profiled extraction grid with a center-dense electron beam source.

[16] FIGS. 5A and 5B are graphical depictions of the interaction of a center-dense profiled extraction grid with an edge-dense electron beam source.

[17] 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 DESCRIPTION

[18] Referring to FIGS. 1A-1C, a plasma reactor includes a process chamber 100 enclosed by a cylindrical side wall 102, a floor 104 and a ceiling 106. A

workpiece support pedestal 108 supports a workpiece 110, such as a semiconductor wafer, the pedestal 108 being movable in the axial (e.g., vertical) direction. A gas distribution plate 112 is integrated with or mounted on the ceiling 106, and receives process gas from a process gas supply 114. A vacuum pump 116 evacuates the chamber through the floor 104. A process region 118 is defined between the workpiece 110 and the gas distribution plate 112. Within the process region 118, the process gas is ionized to produce a plasma for processing of the

workpiece 110.

[19] 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 has a gas inlet 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.

[20] The electron beam source 120 includes a profiled extraction grid 126 (best seen in FIG. 1C) 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. The profiled extraction grid 126 and the acceleration grid 128 may be formed as separate conductive sheets having apertures or holes formed therethrough or as meshes, for example. The extraction grid 126 and the acceleration grid 128 are mounted with insulators 130, 132, respectively, so as to be electrically insulated from one another and from the conductive enclosure 124. However, the acceleration grid 128 is in electrical contact with the side wall 102 of the chamber 100. The openings 124a and 102a and the extraction grid 126 and acceleration grid 128 are

mutually congruent, generally, and define a thin wide flow path for an electron beam into the processing region 118. The width of the flow path is about the diameter of the workpiece 110 (e.g., 100-500 mm), while the height of the flow path is less than about two inches.

[21] The electron beam source 120 further includes a pair of electromagnets 134-1 and 134-2 aligned with the electron beam source 120, and producing a magnetic field parallel to the direction of the electron beam. 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. The beam dump may be held at a selected electrical potential, such a ground .

[22] A negative terminal of a plasma D.C. discharge voltage supply 140 is coupled to the conductive enclosure 124, and a positive terminal of the voltage supply 140 is coupled to the extraction grid 126. In turn, a negative terminal of an electron beam acceleration voltage supply 142 is connected to the extraction grid 126, and a positive terminal of the voltage supply 142 is connected to the grounded 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 main plasma source of the electron beam source 120. Electrons are extracted from the plasma in the chamber 122 through the extraction grid 126 and the acceleration grid 128 to produce an electron beam that flows into the processing chamber 100. Electrons are accelerated to energies equal to the voltage provided by the acceleration voltage supply 142. Referring to FIG. 1C, the extraction grid 126 includes a frame 126-1 and a grid 126-2 with grid openings 126-3. The frame 126-1 defines a narrow aperture whose height H is relatively small (e.g., 2-4 cm) and whose width W

(e.g., on the order of the workpiece diameter, or 300 mm or more) is generally parallel to the workpiece support plane of the pedestal 108, so as to produce a

correspondingly thin wide electron beam.

[23] Distribution of the plasma ion density and plasma electron density across the chamber 122 affects the uniformity of the electron beam that is introduced into the process region 118 of the processing chamber 100. Thus, non-uniformity in plasma distribution in the chamber 122 causes non-uniformity of the electron beam propagating through the process region 118. The

distribution of electron density across the width of the beam (i.e., along an axis, labeled "X" in FIG. 1C) is liable to exhibit non-uniformities. The X-axis is parallel to the workpiece support surface of the pedestal 108 and perpendicular to the propagation direction of the electron beam. For example, the electron density

distribution along this axis may be center high (center dense) or edge-high (edge-dense) . This is because the plasma density within the chamber 122 of the electron beam source 120 may itself exhibit non-uniform

distribution along the X-axis, which may be edge-dense or center-dense, for example. The profiled extraction grid 126 is configured to counteract such a non-uniformity, by having a distribution of the grid openings 126-3 along the X-axis that is complementary to the plasma electron (or ion) distribution along the X-axis of plasma in the electron beam source chamber 122. For example, the grid openings 126-3 through the profiled extraction grid of FIG. 1C are distributed so that the number of grid openings 126-3 per unit length along the X-axis of FIG. 1C is lower at the center and higher at each end of the profiled extraction grid. In this example, the

distribution of the grid openings 126-3 along the X-axis has an edge-high and center low profile, which may be referred to as an edge-dense profile. Such an edge-dense profile in the distribution of the openings 126-3 of the extraction grid 126 is suitable for reducing or

compensating for center-dense or center-high non-uniform distribution along the X-axis of plasma density in the chamber 122. This is because the edge-dense grid opening profile is complementary to (or is an inverse function of) the center-dense plasma distribution in the chamber 122.

[24] FIG. 2A depicts an alternative embodiment of the profiled extraction grid 126, in which the distribution of the grid openings 126-3 along the X-axis has a center- dense profile. Such a center-dense profiled extraction grid is useful for countering an edge-dense non- uniformity in the plasma electron (or ion) distribution in the electron beam source chamber 122. FIGS. 2B and 2C depict other possible configurations of the profiled extraction grid 126, in which the profile of the linear density of grid openings has two spaced-apart density peaks (FIG. 2B) or has a smoothly varying edge-peaked profile (FIG. 2C) .

[25] In the embodiments of FIGS. 1C, 2A, 2B and 2C, the profile or distribution of the number of grid openings 126-3 per unit length along the X-axis is realized by arranging the openings 126-3 in successive side-by-side columns extending parallel with a center line (labeled "Center" in FIGS. 1C and 2A) and rows extending parallel with the X-axis. The number of grid openings 126-3 varies from column to column in accordance with the desired profile. The desired profile is selected to compensate for a previously determined non-uniformity in the plasma distribution along the X-axis within the e- beam source chamber 122. Specifically, in the example of a center-dense plasma distribution in the chamber 122, an edge-dense profiled extraction grid such as that

illustrated in FIG. 1C is desired. In this example, the number of grid openings 126-3 per column is minimal at the center of the extraction grid 126 and is maximum at each edge. The number of grid openings 126-3 in each column is an increasing function of the nearness of the column to either edge of the frame 126-1 along the X-axis or a decreasing function of the nearness of the column to the center of the frame 126-1 along the X-axis. The columns may be arranged symmetrically with respect to the center line of the frame 126-1.

[26] In the example of an edge-dense plasma

distribution in the chamber 122, a center-dense profiled extraction grid such as that illustrated in FIG. 2A is desired. In this example, the number of grid openings 126-3 per column is minimal at the edge of the extraction grid 126. The number of grid openings 126-3 in each column is an increasing function of the nearness of the column to the center of the frame 126-1 along the X-axis or a decreasing function of the nearness of the column to either edge of the frame 126-1 along the X-axis.

[27] While the illustrated embodiment involve an ordered distribution of the grid openings 126-3 in regular rows and columns arranged along an X-axis, the profiling of the number of grid openings per unit length along the X-axis may be realized without necessarily arranging the grid openings 126-3 in regular rows and column. Instead, the grid openings 126-3 may be arranged irregularly while still realizing the desired profiling of the number of grid openings per unit length along the X-axis, as center-dense, or edge-dense or any other desired profile.

[28] FIGS. 3A, 3B and 3C depict different embodiments of one grid opening 126-3, including a rectangular shape (FIG. 3A) , an oval shape (FIG. 3B) and a circular shape (FIG. 3C) . The extraction grid 126 may be formed as a metal sheet having the openings 126-3 formed through the sheet. In other embodiments, the extraction grid 126 and grid openings 126-3 may be formed using a wire-mesh structure, for example.

[29] FIGS. 4A and 4B graphically depict the effect of using the edge dense profiled extraction grid of FIG. 1C with a plasma source having a center-dense distribution along the X-axis. The non-uniformity or center peak exhibited by the plasma source is compensated by the profiled extraction grid, resulting in an electron distribution of the electron beam that has little or no center peak along the X-axis.

[30] FIGS. 5A and 5B graphically depict the effect of using the center dense profiled extraction grid of FIG. 2A with a plasma source having an edge-dense distribution along the X-axis. The non-uniformity or peak at each edge exhibited by the plasma source is compensated by the profiled extraction grid, resulting in an electron distribution of the electron beam that has little or no peak at each edge along the X-axis.

[31] In one embodiment, the acceleration grid 128 has a structure identical to that of extraction grid 126. For example, the acceleration grid may be formed as a

conductive sheet with openings formed therethrough and distributed in the manner of the openings 126-3 of the extraction grid of FIGS. 1C, 2A, 2B or 2C. In such a case, FIGS. 1C, 2A, 2B and 2C are representative of both the extraction grid 126 and the acceleration grid 128. In another embodiment, the acceleration grid 128 has a distribution of openings that is different from that of the extraction grid 126. For example, the acceleration grid opening distribution may be uniform along the X- axis, rather than being profiled, while only the

extraction grid opening distribution is profiled. Or, the reverse may be implemented, in which only the acceleration grid opening distribution is profiled while the extraction grid opening distribution is uniform.

[32] 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.

[33] 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

What is claimed is:

1. A plasma reactor for processing a workpiece, comprising :

a workpiece processing chamber having a

processing chamber enclosure comprising a ceiling and a side wall and an electron beam opening in said side wall, a workpiece support pedestal in said processing chamber having a workpiece support surface facing said ceiling and defining a workpiece processing region between said workpiece support surface and said ceiling, said electron beam opening facing said workpiece processing region;

an electron beam source chamber comprising an electron beam source chamber enclosure and an emission opening between said electron beam source chamber and said workpiece processing chamber facing said electron beam opening; and

a profiled grid in said emission opening and comprising plural grid openings each extending through said profiled grid, said grid openings having a non^¬ uniform distribution of a number of grid openings per unit length along an axis parallel with a plane of said workpiece support surface.

2. The plasma reactor of Claim 1 wherein said nonuniform distribution of said grid openings is a

decreasing function of a proximity of said grid openings to an edge of said profiled grid along said axis.

3. The plasma reactor of Claim 1 wherein said nonuniform distribution of said grid openings is an

increasing function of a proximity of said grid openings to an edge of said profiled grid along said axis.

4. The plasma reactor of Claim 1 wherein said grid openings are arranged in regular row and columns, said columns being distributed along said axis, said rows extending parallel to said axis, wherein the number of grid openings in each said column varies with location of each column along said axis.

5. The plasma reactor of Claim 1 further

comprising a voltage source coupled to said profiled grid, said profiled grid comprising a conductive

material .

6. The plasma reactor of Claim 1 wherein said nonuniform distribution of a number of grid openings per unit length is complementary relative to a non-uniformity in plasma distribution along said axis in said electron beam source chamber.

7. The plasma reactor of Claim 1 further

comprising :

an electron beam source gas supply coupled to said electron beam source chamber;

a workpiece process gas supply coupled to said workpiece processing chamber;

a supply of plasma source power coupled to said electron beam source chamber; and

an electron beam extraction voltage supply coupled to said profiled grid.

8. The plasma reactor of Claim 7 wherein said profiled grid comprises an extraction grid and said grid openings comprises extraction grid openings, said plasma reactor further comprising an acceleration grid in said emission opening and located between said extraction grid and said workpiece processing chamber.

9. The plasma reactor of Claim 8 wherein said acceleration grid comprises plural acceleration grid openings having a non-uniform distribution of a number of grid openings per unit length along said axis parallel with a plane of said workpiece support surface.

10. The plasma reactor of Claim 9 wherein said nonuniform distribution of said acceleration grid openings conforms with the non-uniform distribution of said extraction grid openings.

11. The plasma reactor of Claim 1 wherein said emission opening is located on one side of said workpiece processing chamber, said plasma reactor further

comprising :

a beam dump at a side of said workpiece

processing chamber opposite said one side, said beam dump comprising a conductor electrically coupled to a

potential attractive to an electron beam.

12. The plasma reactor of Claim 11 wherein said beam dump is electrically coupled to said processing chamber enclosure.

13. The plasma reactor of Claim 1 wherein said profiled extraction grid comprises one of:

(a) a conductive sheet having said grid

openings formed therethrough; or

(b) a conductive mesh.

14. For use in a plasma reactor that includes a workpiece processing chamber having a workpiece support pedestal in said processing chamber with a workpiece support surface, an electron beam source chamber coupled to said workpiece processing chamber through a chamber- to-chamber opening:

a profiled extraction grid adapted for placement in said chamber-to-chamber opening and

comprising plural grid openings, each of said grid openings extending through said profiled extraction grid, said grid openings having a non-uniform distribution of a number of grid openings per unit length along an axis parallel with a plane of said workpiece support surface.

15. The profiled extraction grid of Claim 14 wherein said non-uniform distribution of said grid openings is a decreasing function of a proximity of said grid openings to an edge of said profiled extraction grid along said axis.

16. The profiled extraction grid of Claim 14 wherein said non-uniform distribution of said grid openings is an increasing function of a proximity of said grid openings to an edge of said profiled extraction grid along said axis.

17. The profiled extraction grid of Claim 14 wherein said grid openings are arranged in regular row and columns, said columns being distributed along said axis, said rows extending parallel to said axis, wherein the number of grid openings in each said column varies with location of each column along said axis.

18. A plasma reactor comprising: a workpiece processing chamber having a

workpiece support pedestal in said processing chamber with a workpiece support surface;

an electron beam source chamber and a supply of plasma source power coupled to said electron beam source chamber;

a chamber-to-chamber opening between said workpiece processing chamber and said electron beam source chamber; and

a profiled extraction grid in said chamber-to- chamber opening and comprising plural grid openings, each of said grid openings extending through said profiled extraction grid, said grid openings having a non-uniform distribution of a number of grid openings per unit length along an axis parallel with a plane of said workpiece support surface; and

a beam extraction voltage supply coupled to said profiled extraction grid.

19. The plasma reactor of Claim 18 wherein said non-uniform distribution of said grid openings is a decreasing function of a proximity of said grid openings to an edge of said profiled extraction grid along said axis .

20. The plasma reactor of Claim 18 wherein said non-uniform distribution of said grid openings is an increasing function of a proximity of said grid openings to an edge of said profiled extraction grid along said axis .