Vacuum plasma processor having coil with intermediate...

Details Vacuum plasma processor having coil with intermediate... Vacuum plasma processor having coil with intermediate...

1997-09-16

2001-07-31

Bettendorf, Justin P. (Department: 2817)

Electric lamp and discharge devices: systems

Discharge device load with fluent material supply to the...

Plasma generating

C118S7230AN

Reexamination Certificate

active

06268700

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to vacuum plasma processors having improved plasma exciting coils and more particularly to such a coil having inter-connected interior, intermediate and peripheral winding portions having spatial geometries such that the intermediate portion couples a significantly lower magnetic flux density to the processor plasma than the magnetic flux density coupled to the plasma by the interior and peripheral portions.
BACKGROUND ART
Various structures have been developed to supply RF fields to an ionizable gas in a vacuum plasma processing chamber, to excite the gas to a plasma state. The excited plasma interacts with a workpiece in the vacuum plasma processing chamber to etch materials from an exposed workpiece surface or deposit materials on the surface. The workpiece is typically a semiconductor wafer having a planar circular surface, a metal planar surface or a dielectric workpiece, which can have a rectangular periphery, as in a flat panel display.
A processor for treating workpieces with an inductively coupled planar plasma (ICP) is disclosed, inter alia, by Ogle, U.S. Pat. No. 4,948,458, commonly assigned with the present invention. A magnetic field is derived from a coil positioned on or adjacent a single planar dielectric window extending in a direction generally parallel to the workpiece planar surface. In commercial devices, the window is usually quartz because quartz has low material impurity and provides optimum results for RF coupling. The coil is connected to be responsive to an RF source having a frequency in the range of 1 to 100 MHz, but which is typically 13.56 MHz. An impedance matching network is connected between the coil and source, to minimize RF reflections coupled back to the source from a load, including the coil and the plasma.
Barnes et al., U.S. Pat. No. 5,589,737 discloses a plasma processor including a coil for inductively deriving an RF plasma excitation field for processing relatively large substrates, for example, dielectric substrates forming rectangular flat panel displays. In the Barnes et al. patent, the RF field derived by the coil is coupled to the plasma via plural individually supported dielectric windows. In the preferred embodiment of the '737 patent, four such windows are positioned in four different quadrants. To maximize RF coupling from the coil through the windows to the plasma, the windows have a thickness substantially less than the thickness of a single window having the same combined area as the plural windows to withstand the differential pressure between the vacuum inside the chamber and atmospheric pressure on the chamber exterior.
Several different coil configurations are disclosed in the '737 patent. Some of these coils have plural winding segments connected electrically in parallel between first and second terminals coupled to an RF excitation source via a matching network. Some of the coil configurations of the '737 patent have parallel coil segments of the same electrical length between the first and second terminals.
To provide more uniform plasma flux density on the relatively large planar flat panel display surfaces having a rectangular periphery, the various coil configurations disclosed in the '737 patent were redesigned as illustrated in
FIG. 1
, a bottom view of the redesigned coil. The prior art coil
10
of
FIG. 1
includes two spiral-like, electrically parallel copper windings
12
and
14
, each having plural spiral-like turns substantially symmetrically arranged with respect to coil center point
16
.
Windings
12
and
14
are coplanar and have copper conductors with square cross-sections (with each side having a length of about 1.25 cm), including bottom edges spaced approximately 3 cms above the upper faces of the four rectangular quartz windows
21
,
22
,
23
and
24
, individually supported by one-piece, rigid frame
26
, made of a non-magnetic metal, preferably anodized aluminum. Frame
26
is preferably constructed in a manner similar to that illustrated and described in the '737 patent, except that interior mutually perpendicular rails
28
and
30
are substantially coplanar with the top coplanar faces of windows
21
-
24
. Coil
10
is suspended by dielectric hangers from the ceiling of a nonferrous metal (preferably anodized aluminum) electromagnetic shield cover of the type disclosed in Barnes et al. '737.
Windings
12
and
14
respectively include interior terminals
32
and
34
, equispaced from coil center point
16
along rail
28
. Terminals
32
and
34
are electrically driven in parallel and connected by metal strap
35
and cable
36
to output terminal
38
of matching network
40
, having an input terminal connected to be responsive to RF source
42
. Typically, strap
35
has an inverted U shape with a first leg of the U being spaced substantially farther from windows
21
and
24
than windings
12
and
14
, and the other legs running between the first leg and terminals
32
and
34
; strap
35
is shown offset to simplify the drawing.
Windings
12
and
14
also respectively include, at diametrically opposed corners thereof, terminals
44
and
46
, respectively connected to ground through capacitors
48
and
50
. Output terminal
52
of matching network
40
is also grounded to provide a return current path through capacitors
48
and
50
to the matching network grounded terminal for the parallel currents flowing through windings
12
and
14
. Windings
12
and
14
have a geometry and the values of capacitors
48
and
50
are selected so maximum standing wave currents occur along the lengths of windings
12
and
14
at positions that are somewhat electrically close to terminals
44
and
46
. Typically, the maximum standing wave currents occur in the outermost turn of each of windings
12
and
14
in proximity to rail
26
. The standing wave current is maximized close to the periphery of coil
10
to increase the magnetic flux density at the periphery of the coil and thereby increase the plasma flux density adjacent the workpiece periphery.
Each of windings
12
and
14
has a spiral-like configuration and is long enough that transmission line effects occur therein at the frequency of source
42
, as described in the previously mentioned co-pending applications. The configuration of each of the windings
12
and
14
is frequently referred to as a “square or rectangular” spiral. Each of windings
12
and
14
includes 2.125 turns, formed by nine straight segments. Each winding includes four straight metal conducting segments extending parallel to rail
28
and five straight metal conducting segments extending parallel to rail
30
, whereby each straight line segment intersects its abutting segment approximately at a right angle. Terminals
32
and
44
of coil
12
are on one side of rail
30
while terminals
34
and
46
of coil
14
are on the opposite side of rail
30
. The pitches of the turns of windings
12
and
14
are substantially the same throughout the lengths of the coils between terminals
32
,
34
and
44
,
46
.
The coil of
FIG. 1
can be thought of as having center, intermediate and peripheral portions respectively including approximately two, one and two turns. The turns of the center portion include straight metal conducting segments
61
-
64
of winding
12
, as well as straight metal conducting segments
71
-
74
of winding
14
. The one turn of the intermediate portion includes straight segments
75
and
76
of winding
12
as well as straight segments
77
and
78
of winding
14
. The turns of the peripheral portion include straight segments
81
-
83
of winding
12
as well as straight segments
84
-
86
of winding
14
.
The coil illustrated in
FIG. 1
has previously been used to excite a plasma for etching rectangular, dielectric flat panel display workpieces having straight, rectangular peripheral sides of 550×650 mm and 600×720 mm. Such workpieces were fixedly located on an electrostatic chuck so the top face of the substrate was approxim

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