Plasma confinement by use of preferred RF return path

Details Plasma confinement by use of preferred RF return path Plasma confinement by use of preferred RF return path

2001-04-30

2003-08-05

Hassanzadeh, Parviz (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

C156S345430, C118S715000, C118S7230ER, C315S111710

Reexamination Certificate

active

06602381

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to plasma etching apparatus. More particularly, the present invention relates to improved techniques for controlling plasma formation in a plasma processing chamber.
BACKGROUND OF THE INVENTION
The use of plasma-enhanced processes in the manufacture of semiconductor-based products (such as integrated circuits or flat panel displays) is well known. Generally speaking, plasma-enhanced processes involve the processing of a substrate (e.g., a glass panel or a semiconductor wafer) in a plasma processing chamber. Within the plasma processing chamber, a plasma may be formed out of appropriate etchant or deposition source gases to respectively etch or deposit a layer of material on the surface of the substrate.
FIG. 1
depicts a capacitively-coupled plasma processing chamber
100
, representing an exemplary plasma processing chamber of the types typically employed to etch a substrate. A chuck
104
represents the workpiece holder on which a substrate
106
is positioned during etching. The chuck
104
may be implemented by any suitable chucking technique, e.g., electrostatic, mechanical, clamping, vacuum, or the like. During etching, the chuck
104
is typically supplied with RF power having a frequency of, for example, about 400 Khz to about 27 Mhz, by an RF power supply
110
. In some systems, chuck
104
may be supplied with dual frequencies, e.g., 2 MHz and 27 MHz simultaneously during etching.
A reactor top
112
, formed of a conductive material such as aluminum, is disposed above substrate
106
. Confinement rings
102
may be coupled in a fixed manner to reactor top
112
or may be coupled to cam-based plungers (not shown in
FIG. 1
) that allow confinement rings
102
to be raised and lowered without moving reactor top
112
.
In general, confinement rings
102
help confine the etching plasma to the region above substrate
106
to improve process control and to ensure repeatability. Although only two confinement rings are shown in the example of
FIG. 1
, it should be understood that any number of confinement rings may be provided.
An upper electrode
114
and a baffle
116
are also coupled to reactor top
112
. The upper electrode
114
may be grounded (as in the case of
FIG. 1
) or may be powered by another RF power source
120
during etching. If the upper electrode
114
is powered, it may be insulated from the remainder of the reactor to isolate the electrode from ground. During etching, plasma is formed from etchant|source gas supplied via a gas line
122
and the baffle
116
.
When RF power is supplied to the chuck
104
(from the radio frequency generator
110
), equipotential field lines are set up over the substrate
106
. During plasma processing, the positive ions accelerate across the equipotential field lines to impinge on the surface of substrate
106
, thereby providing the desired etch effect (such as improving etch directionality). Due to geometry factors, however, the field lines may not be uniform across the substrate surface and may vary significantly at the edge of substrate
106
. Accordingly, a focus ring is typically provided to improve process uniformity across the entire substrate surface. With reference to
FIG. 1
, chuck
104
is shown disposed within a focus ring
108
, which is typically formed of a suitable dielectric material such as ceramic, quartz, or plastic.
The equipotential field lines that are set up during plasma etching may be seen more clearly in FIG.
1
B. In
FIG. 1B
, the presence of focus ring
108
allows the equipotential field lines to be disposed substantially uniformly over the entire surface of the substrate, thereby allowing etching to proceed in a uniform manner across the substrate. As seen by
FIG. 2
, however, some of the equipotential field lines also extend into the region
160
outside of focus ring
108
. The presence of the equipotential field lines in region
160
may cause any charged particles that leak past the confinement rings to accelerate in a direction perpendicular to the equipotential field lines toward the chamber walls. This acceleration and the subsequent collision between the charged particles and the chamber walls may generate secondary electrons, which may ignite and/or sustain unconfined plasma in the region
160
(i.e., unintended plasma that is not confined to region directly above the substrate).
Furthermore, current return paths have relied on the chamber wall
118
for a return path or a return path outside the chamber. Magnetic fields are generated from the return paths and cause magnetic fields that can light and sustain a plasma outside the confined region. The dotted lines in
FIGS. 1A and 1B
illustrate the current return path along the chamber wall
118
.
The inadvertent generation of plasma in the region
160
renders the etch process difficult to control and may damage components within this region. By way of example, this unconfined plasma, which may be unplanned and/or intermittent, changes the location of power absorbed by the plasma within the plasma processing chamber, thereby making it difficult to control the delivery of power to the chuck to achieve consistent, repeatable etch results. As another example, the presence of unwanted plasma in region
160
may cause damage to the chamber door (not shown), particularly to the seals that are provided therewith. The chamber door is necessary for substrate transport into and out of the chamber, and if the seals are damaged, accurate control of the chamber pressure may be difficult. When the seals and/or other components in the region
160
are inadvertently attacked by the plasma, particulate and/or polymeric contaminants may form along the chamber walls, potentially leading to contamination of the etch environment.
Accordingly, it would be desirable to provide techniques for minimizing and/or eliminating the unwanted plasma formation in the region outside of the focus ring of the plasma processing chamber.
BRIEF DESCRIPTION OF THE INVENTION
A confinement assembly for confining a discharge within an interaction space of a plasma processing apparatus comprising a stack of rings and at least one electrically conductive member. The rings are spaced apart from each other to form slots therebetween and are positioned to surround the interaction space. At least one electrically conductive member electrically couples each ring. The electrically conductive member contacts each ring at least at a point inside of the outer circumference of each ring.


REFERENCES:
patent: 5534751 (1996-07-01), Lenz et al.
patent: 5744049 (1998-04-01), Hills et al.
patent: 5904800 (1999-05-01), Mautz
patent: 5998932 (1999-12-01), Lenz
patent: 6019060 (2000-02-01), Lenz
patent: 6129808 (2000-10-01), Wicker et al.
patent: 6178919 (2001-01-01), Li et al.
PCT International Search Report for PCT/US 02/10460, date of mailing Jul. 23, 2002.

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