Etching a substrate: processes – Gas phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
1997-04-16
2001-01-16
Dang, Thi (Department: 1763)
Etching a substrate: processes
Gas phase etching of substrate
With measuring, testing, or inspecting
C216S068000, C216S071000, C156S345420, C315S111210, C118S7230IR, C118S7230ER, C438S010000, C438S017000, C438S729000
Reexamination Certificate
active
06174450
ABSTRACT:
TECHNICAL FIELD
The present invention relates to plasma processing systems and, more particularly, to methods and apparatus for controlling the amount of ion energy and/or the plasma density in an inductively coupled plasma processing system.
BACKGROUND ART
Ionized gas, or plasma, is commonly used during the processing and fabrication of semiconductor devices. For example, plasma can be used to etch or remove material from semiconductor integrated circuit wafers, and sputter or deposit material onto semiconducting, conducting or insulating surfaces. Creating a plasma for use in manufacturing or fabrication processes, typically begins by introducing various process gases into a plasma chamber within a plasma reactor wherein the gases are in contact with a workpiece, such as an integrated circuit wafer. The molecules of the gases in the chamber are ionized into plasma by a radio frequency (rf) energy supplied to the plasma chamber from an external power source. During processing, the plasma and ionized particles contact the workpiece.
The rf energy applied to the plasma chamber introduces an electric field that accelerates electrons which then collide with individual gas molecules causing further production of electrons and ions. There are several ways to introduce an electric field within the plasma reactor. Two common types of plasma processing systems are capacitively coupled plasma processing systems and inductively coupled plasma processing systems.
FIG. 1
is an illustration of a typical capacitively coupled plasma processing system
10
for use in processing and fabrication of semiconductor devices. As shown, plasma processing system
10
includes a plasma reactor
12
having within it a plasma chamber
13
. Within plasma processing chamber
13
there are two electrodes
14
a
and
14
b
which form a capacitor. Electrode
14
a
is coupled to ground and electrode
14
b
is connected to receive rf energy from a power supply
16
via a matching network
18
. When power supply
16
is energized the rf energy is applied to the capacitive circuit formed between electrodes
14
a
and
14
b.
If ionizable gases are provided within plasma chamber
13
then a plasma
22
is formed when the rf energy is applied.
Since plasma processing system
10
has only one power supply
16
, increasing the power of the rf signal produced by power supply
16
tends to increase both the density of the plasma (i.e., plasma density) and the direct current (dc) bias at electrode
14
b
and wafer
24
. An increase in the dc bias usually causes a corresponding increase in the potential drop across the plasma sheath
26
which increases the energy (i.e., ion energy) of the ionized particles contacting wafer
24
.
FIG. 2
is an illustration of a conventional inductively coupled plasma processing system
30
for processing and fabrication of semiconductor devices the system illustrated in
FIG. 2
is of the type disclosed in U.S. Pat. Nos. 4,948,458 and 5,571,366. Inductively coupled plasma processing system
30
includes a plasma reactor
32
having a plasma chamber
33
therein. Unlike the plasma processing system
10
of
FIG. 1
, inductively coupled plasma processing system
30
includes two power supplies,
34
and
36
, which influence the plasma created within plasma chamber
33
. Power supply
34
is configured to supply an rf energy, via a match network
38
, to an electrode, chuck i.e., workplace holder)
40
, located within plasma reactor
32
. The rf energy for power supply
34
supplies to electrode
40
develops a dc bias on a wafer
42
which is typically located on a top surface
44
of chuck
40
.
Power supply
36
is configured to supply an rf energy, via a match network
46
, to a coil
48
located near plasma chamber
33
. Window
50
, for example a ceramic plate, separates coil
48
from plasma chamber
33
. Also shown, there is typically a gas supply mechanism
52
that supplies the proper chemistry required for the manufacturing process to the plasma reactor
32
. A gas exhaust mechanism
54
removes particles from within plasma chamber
33
and maintains a particular pressure within plasma chamber
33
. As a result, the rf energy generated by power supply
36
creates a plasma
56
provided ionizable gases are supplied to plasma chamber
33
.
The control and delivery of the rf power in a plasma discharge is of fundamental importance in plasma processing. The amount of actual power in the plasma chamber greatly affects the process conditions. Significant variance in actual power delivered to the plasma chamber can unexpectedly change the anticipated contribution of other process variable parameters such as pressure, temperature and etch rate.
As illustrated in
FIGS. 1 and 2
, the most commonly used method of obtaining a predetermined rf power within the plasma chamber is to provide a match network within the power circuit. The match network essentially transforms the impedance (capacitive or inductive reactance) of the plasma discharge into a substantially resistive load for the power supply. The power supply (or power supplies) can then be set to a predetermined power level dependent upon the desired process parameters.
By way of example, a typical match network includes variable capacitors and/or inductors as matching components (for low to high rf frequencies), and variable cavity taps or matching stubs (for use at microwave frequencies). Match networks may be adjusted manually or automatically, however, most match networks adjust automatically to changing load conditions.
In an effort to further control the amount of rf power provided to the plasma chamber, in a typical plasma processing system the output from the power supply (or power supplies) is monitored and controlled. This usually occurs at the output of the power supply itself based in part on the assumption that the power losses in the match network are negligible.
However, rf power delivered to the plasma chamber has been found to be substantially less than the rf power supply output because of unexpected losses in, for example, the match network itself. To account for losses in the match network in capacitively coupled plasma processing systems, additional sensing and controlling circuitry has been added to the power circuit. For example, U.S. Pat. Nos. 5,175,472, 5,474,648 and 5,556,549 disclose different ways to use of an rf sensor and a controller to provide an additional feedback control loop circuit that adjusts the output of the power supply to reach a desired rf power level within the plasma chamber.
Such feedback techniques have not been used in inductively coupled plasma processing systems because it has long been believed that the two power supplies are independent of each other in that the rf power supplied to the coil controls the plasma density and the rf power supplied to the chuck controls the energy of the ions contacting the wafer (i.e., by controlling the dc bias). Therefore, by having the two power supplies it was assumed that additional control over the process was inherently provided by independently setting the outputs of the two power supplies and operating them in an open loop mode (i.e., without feedback).
However, in reality the plasma density and ion energy are not truly independent since there is coupling between the power supplied at the source and the wafer chuck. This coupling is illustrated in
FIG. 3
, for example, which is a graph of the dc bias versus the rf power supplied to the wafer for various rf power settings of the rf power supplied to the coil, and various gaps (i.e., 4 or 6 cm) between the top of the plasma chamber and the surface of the wafer. The data plotted in
FIG. 3
were collected from a TCP™ 9600SE processing system available from Lam Research Corporation of Fremont, Calif. As shown, when the rf power supplied to the chuck (i.e., bottom power) increases, the magnitude of the dc bias tends to increase. However, for a given bottom power, the dc bias which is developed also depends on the rf power supplied to the coil (i.e., TCP™ power), and to some extent on the gap
Patrick Roger
Williams Norman
Dang Thi
Lam Research Corporation
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