Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-09-29
2002-07-23
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230AN, C118S7230ER, C118S7230AN, C156S345480, C156S345510
Reexamination Certificate
active
06422173
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to semiconductor fabrication and, more particularly, to apparatus and methods for controlling the plasma behavior inside of plasma etching chambers.
In semiconductor manufacturing processes, etching processes, insulation film formation, and diffusion processes are repeatedly carried out. As is well known to those skilled in the art, there are two types of etching processes: wet etching and dry etching. Dry etching is typically implemented by using an inductively coupled plasma etching apparatus such as shown in FIG.
1
A.
In the inductively coupled plasma etching apparatus shown in
FIG. 1A
, a reactant gas is first led into chamber
20
through a gas lead-in port (not shown). High frequency power is then applied from a power supply (not shown) to coil
17
. Semiconductor wafer
11
is mounted on chuck
19
provided inside chamber
20
. Coil
17
is held on the upper portion of the chamber by spacers
13
, which are formed of an insulating material. In operation, high frequency (RF) current passing through coil
17
induces an electromagnetic current into chamber
20
, and the electromagnetic current acts on the reactant gas to generate a plasma.
The plasma contains various types of radicals and the chemical reaction of the positive
egative ions is used to etch semiconductor wafer
11
itself or an insulation film formed on the wafer. During the etching process, coil
17
carries out a function that corresponds to that of the primary coil of a transformer while the plasma in chamber
20
carries out a function that corresponds to that of the secondary coil of the transformer. The reaction product generated by the etching process is discarded via exhaust port
15
.
When etching one of the recently developed device materials (e.g., platinum, ruthenium, and the like), the reaction product generated may be a nonvolatile substance (e.g., RuO
2
). In some cases, the reaction product may adhere to surface
10
a
of TCP window
10
. If the reaction product is conductive, then the film of reaction product on surface
10
a
may electrically shield the electromagnetic current in the chamber. Consequently, the plasma does not strike well after several wafers are etched and the etching process must be discontinued.
In an effort to avoid this problem, a method for sputtering the reaction product adhered to surface
10
a
of TCP window
10
by using the plasma has been developed. In the inductively coupled plasma etching apparatus shown in
FIG. 1A
, however, the electromagnetic current induced by the RF current generates a distribution voltage having a standing wave in the vicinity of TCP window
10
. This is problematic because it causes the deposition and sputtering of the reaction product to become nonuniform.
FIGS. 1B and 1C
illustrate the inherent nonuniformity of the deposition and sputtering on the TCP window in the inductively coupled plasma etching apparatus shown in FIG.
1
A. In
FIG. 1B
, coil
17
is indicated by boxes having either an “x” or a “&Circlesolid;” therein. The boxes having an “x” therein indicate that the coil extends into the page. The boxes having a “&Circlesolid;” therein indicate that the coil extends out of the page. As shown in
FIG. 1B
, some portions of surface
10
a
of TCP window
10
are subjected to excess sputtering and other portions of the surface are subjected to excess deposition. Excess sputtering occurs in the regions where a relatively large amount of energy is added to the ions in the plasma because the amplitude of the acceleration voltage due to the standing wave at the location is high. As shown in the graph in the lower part of
FIG. 1C
, the amplitude of standing wave
24
is high at points
24
a
and
24
b,
which correspond to ends
17
a
and
17
b,
respectively, of coil
17
, as shown in the upper part of FIG.
1
C. Excess deposition occurs in the regions where only a relatively small amount of energy is added to the ions in the plasma because the amplitude of the standing wave is low. As shown in the graph in the lower part of
FIG. 1C
, the amplitude of standing wave
24
is low in the region proximate to point
22
, which is the node of the standing wave.
Nonuniform deposition and sputtering on the TCP window is undesirable for a number of reasons. Excessive deposition is undesirable because, as discussed above, the presence of an electrically conductive film on the surface of the TCP window can electrically shield the electromagnetic current in the chamber and thereby disable the etching process. In addition, excessive deposition often causes particle problems (particles flake off on the wafer) and, consequently, increases the frequency with which the chamber must be subjected to dry and wet cleanings. Frequent cleaning of the chamber is particularly undesirable because it sacrifices the tool's available up time and thereby reduces throughput. Excessive sputtering is undesirable because the ion bombardment can cause erosion of the TCP window, which is typically made of quartz or alumina. Such erosion not only shortens the lifetime of the TCP window, but also generates particles, which can contaminate the wafer and introduce unwanted chemical species into the process environment. The presence of unwanted chemical species in the process environment is particularly undesirable because it leads to poor reproducibility of the process conditions.
In view of the foregoing, there is a need for an inductively coupled plasma etching apparatus that prevents substantial deposition of electrically conductive reaction products on the surface of the TCP window without causing excess erosion of the TCP window.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention provides an inductively coupled plasma etching apparatus that uniformly adds energy to the ions in the plasma in the vicinity of a wall of the chamber in which the plasma is generated.
In one aspect of the invention, a first type of inductively coupled plasma etching apparatus is provided. This inductively coupled plasma etching apparatus includes a chamber and a window for sealing a top opening of the chamber. The window has an inner surface that is exposed to an internal region of the chamber. A metal plate, which acts as a Faraday shield, is disposed above and spaced apart from the window. A coil is disposed above and spaced apart from the metal plate. The coil is conductively connected to the metal plate at a connection location that is configured to generate a peak-to-peak voltage on the metal plate that optimally reduces sputtering of the inner surface of the window while substantially simultaneously preventing deposition of etch byproducts on the inner surface of the window.
In one embodiment, the inductively coupled plasma etching apparatus further includes a coil input terminal for receiving RF power and a coil output terminal. In this embodiment, the connection location is defined between the coil input terminal and the coil output terminal. In one embodiment, the connection location is more proximate to the coil output terminal than to the coil input terminal. In one embodiment, the inductively coupled plasma etching apparatus further includes an RF generator, a match circuit network coupled between the RF generator and the coil input terminal, and a variable capacitor coupled between ground and the coil output terminal.
In one embodiment, the inductively coupled plasma etching apparatus further includes an oscillation circuit coupled to the metal plate. The oscillation circuit is controllable so that the peak-to-peak voltage on the metal plate may be adjusted. In one embodiment, the oscillation circuit includes a variable capacitor that can be adjusted to control the peak-to-peak voltage along a harmonic point. In another embodiment, the inductively coupled plasma etching apparatus further includes a voltage divider circuit coupled to the metal plate. The voltage divider circuit is controllable so that the peak-to-peak voltage may be adjusted. In one embodiment, the voltage divider circuit i
Lam Research Corporation
Martine & Penilla LLP
Mills Gregory
Zervigon Rudy
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