Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
1996-10-18
2001-10-30
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C156S345420
Reexamination Certificate
active
06308654
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to equipment for the fabrication of semiconductor integrated circuits and for similar processes. In particular, the invention relates to the chamber shape and to the heating and cooling of the reaction chamber for the processing of semiconductors and to controlling the temperature of the chamber surface exposed to the process in such chambers while simultaneously providing electrical inductive and capacitive effects in the chamber.
BACKGROUND ART
The fabrication of silicon integrated circuits was originally based upon thermally activated processes for both the deposition of material layers and their subsequent etching to form horizontally defined features. In a thermal process, the uniformity of deposition is dependent on the temperature of surfaces exposed to the process, and variations in the temperature cause a variation in the rate of the process. Such temperature dependence detracts from process repeatability. Because of the increasing complexity and decreasing feature sizes, more and more semiconductor processing is being performed in plasma reaction chambers. The plasma, rather than equilibrium heat, provides the necessary activation energy for various types of chemical processes and physical processes (sputter deposition and sputter cleaning), while still maintaining the silicon wafer at moderate temperatures so that deleterious thermally driven subsidiary effects are avoided. That is, an increased number of fabrication steps can be performed without producing deleterious effects due to temperature, both the maximum temperature and the integrated thermal profile.
Some early plasma reactors, particularly for etching and chemical vapor deposition (CVD) of single wafers, resemble the reactor illustrated in
FIG. 1. A
wafer
50
is supported on a pedestal
52
enclosed within a vacuum chamber
54
having metallic walls
55
, which are grounded. An RF electrical power supply
56
is connected to the pedestal
52
to excite a plasma of the gas supplied into the interior of the chamber
54
. The grounded chamber walls
55
act as a counter electrode to the pedestal
52
. The plasma-excited gas acts upon the wafer
50
to either etch it or to deposit a product of a plasma-activated reaction upon it. The pedestal
50
and chamber walls
55
act as two electrodes to capacitively couple RF energy into the plasma.
The geometry dictates that the RF-driven pedestal
50
acts as a cathode and the large grounded chamber wall
55
acts as an anode. As discussed by Lii in “Etching”,
ULSI Technology
, eds. Chang et al. (McGraw-Hill, 1996), pp. 330-333, the pedestal
50
develops a negative DC potential V
a
relative to the grounded wall
55
of magnitude given by
V
c
V
P
=
1
-
(
A
a
A
c
)
4
,
(
1
)
where V
p
is the plasma potential, typically on the order of a hundred volts positive or less, A
a
is the surface area of the chamber wall
55
adjacent to the plasma, and A
c
is the area of the top surface of the pedestal
50
. In the common case of
FIG. 1
with a small RF-powered cathode
52
and a large grounded anode
54
, the area ratio is quite large and the cathode voltage V
c
is negative because the DC plasma voltage is always positive. Thus, the equation can be simplified to
&LeftBracketingBar;
V
c
&RightBracketingBar;
V
p
≈
(
A
a
A
c
)
4
,
(
2
)
It is thus seen that for large grounded chamber walls surrounding the plasma, the voltage V
c
on the pedestal
50
can reach several hundred negative volts relative to both the plasma and the chamber wall
50
, creating a significant diode effect and causing positive ions in the plasma to strike the wafer on the pedestal
50
at high energy.
As wafer sizes have increased and demands for uniformity have intensified, the chamber geometry has changed to present a more planar geometry. See, for example, U.S. Pat. No. 4,892,753 to Wang et al. for a CVD chamber and U.S. Pat. No. 4,948,458 to Ogle for an etch chamber. As illustrated in
FIG. 2
, a counter electrode
58
is positioned opposite to the pedestal
52
and its supported wafer
50
across a gap that is substantially less than the diameter of the wafer
50
. For example, the gap may be a few centimeters for a 200 mm wafer. The counter electrode
58
is typically grounded for etch applications while the RF powering configuration is usually reversed for CVD. Often the counter electrode
58
includes a shower head gas dispenser to uniformly supply reaction gas to the reaction zone adjacent to the wafer
50
. In this design, the walls of the chamber
54
, although usually grounded, assume less importance in the plasma and the chemical reactions.
Chapman discusses the sheath voltages for the symmetric configuration in
Glow Discharge Processes: Splittering and Plasma Etching
(Wiley-Interscience, 1980), pp. 156-171. He also gives a more general version of Equation (1) which does not assume a grounded cathode,
V
p
-
V
1
V
p
-
V
2
=
(
A
2
A
1
)
4
,
where V
1
, and A
1
, are the DC self-bias and the area of the first electrode and V
2
and A
2
are the corresponding values for the second electrode.
Ogle et al. in the U.S. Pat. No. 4,871,421 teaches the advantages of splitting RF power in a 50:50 ratio between the pedestal
52
and the counter electrode
58
with respect to the grounded chamber wall
54
so as to avoid arcing to the chamber walls. In the Ogle reference we observe vastly different sizes of the counter electrode and pedestal electrode, such as shown in FIG.
1
. Such a difference in the electrode sizes creates the above described diode effect even for split RF power. Again, the differently sized electrodes cause high-energy charged ions to be ejected across the sheath of the plasma, causing increased physical sputtering (ion etching) rather than purely chemical activation.
Recent developments in plasma reaction chambers have been directed to high-density plasma (HDP) reactors in which large amounts of RF energy create a plasma having a very high ion density, typically above 10
11
cm
−3
. HDP reaction chambers provide high deposition and etching rates as well as other advantages. There are several types of HDP reaction chambers, but the most popular involve induction coupling of RF energy into the source plasma. Inductively coupled plasma reaction chambers can be divided into three main types.
The first type, as illustrated in
FIG. 3
, includes a helical coil
60
wrapped around a dielectric sidewall
62
, typically of quartz, and powered by an RF electrical source
64
. The pedestal
52
continues to have its own RF source
56
. For oxide etching, a counter electrode
66
is grounded and is composed of silicon in order to scavenge fluorine from the fluorocarbon plasma gas performing the etching. This approach is described generally by Collins et al. in U.S. Pat. No. 5,556,501 and European Patent Application 552,491. A1 and Rice et al. describe a specific embodiment in U.S. Pat. No. 5,477,975. Their specific embodiments will be described later in more detail in
FIGS. 7 and 8
. The configuration including a helical coil necessarily increases the size of the walls surrounding the sides of the plasma region. As a result, unlike in reactors with closely spaced capacitive electrodes, wall interactions become important both for forming the plasma and for the deposition or etching chemistry.
The second type of inductively coupled plasma reactor chambers, as illustrated in
FIG. 4
, includes a planar, spiral coil
70
, often referred to as a pancake coil or stove top coil, placed outside a top, planar dielectric wall
72
to be close and parallel to the wafer
50
. The pancake coil
70
is similarly powered by the RF source
64
to inductively couple power into the chamber plasma. For process control, the pedestal
52
may be RF biased. In the closely spaced configuration of
FIG. 4
, the chamber walls
74
, which are typically conductive and grounded, are effectively decoupled from the plasma and its chemistry because of their physical displacement and small size relative to the closely spaced planar coil
7
Nguyen Andrew
Schneider Gerhard
Shel Viktor
Wu Robert W.
Yin Gerald Z.
Alejandro Luz L.
Applied Materials Inc.
Guenzer Charles
Mills Gregory
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