Coating processes – Coating by vapor – gas – or smoke – Metal coating
Reexamination Certificate
2000-02-24
2002-06-25
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Metal coating
C427S252000, C118S715000
Reexamination Certificate
active
06410089
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to plasma reactors and their operation. In particular, the invention relates to the reactors capable of plasma-enhanced chemical vapor deposition of copper using a showerhead gas dispenser.
BACKGROUND ART
Plasma-enhanced chemical vapor deposition (PECVD) is an important and widely practice method of depositing films in advanced semiconductor integrated circuits. In PECVD, a precursor gas is admitted into a reaction chamber held at a reduced pressure, and oscillatory electric energy at a radio frequency (RF) is applied to the chamber to excite the gas into a plasma. The gas reacts with the surface of a wafer exposed to the plasma to form a film on the wafer of a composition derived from that of the precursor gas.
Probably the widest use of PECVD for silicon integrated circuits involves the deposition of silicon dioxide (SiO
2
), also referred to as silica or simply oxide. The oxide forms an insulating layer, for example, between layers of electrical interconnects. The favored precursor for silicon dioxide formed by PECVD is tetraethyl orthosilicate (TEOS). PECVD is the favored technique for depositing oxide because the plasma supplies the activation energy rather than in a thermally activated process in which high temperature provides the energy. Therefore, the oxide can be deposited at relatively low temperatures over previously defined features, thereby reducing the thermal budget used for the oxide.
Sputtering (also called physical vapor deposition or PVD) has enjoyed the widest use in the deposition of layers of metals and other conductive materials because of its high deposition rate and low cost of precursor materials. However, sputtering is a generally ballistic process and has difficulty in coating narrow and deep apertures, of the sort required for via and contact holes between wiring layers. One favored technique for filling such holes is to first conformally coat the walls of the hole with a thin layer of titanium (Ti) and then to conformally coat the Ti-covered walls with a thin layer of titanium nitride (TiN). Thereafter, sputtered aluminum more easily fills into the hole. The Ti/TiN layer, generally referred to as a liner, provides good adhesion between the titanium and the oxide walls, and the TiN forms a barrier against aluminum migration.
It is possible to use sputtering to deposit an approximately conformal coating in holes of high aspect ratios, but much effort is being expended in using CVD or PECVD for one or both of these layers. It is known to deposit CVD TiN using tetrakis-dimethyl-amido titanium (TDMAT) as a precursor. This material is a metal-organic compound which is a liquid at room temperature. The TDMAT CVD process requires thermal decomposition, preferably around 450° C., and a subsequent plasma treatment to remove the carbon content in the as-deposited film. It is also known to deposit CVD Ti using titanium tetrachloride (TiCl
4
) as the precursor. TiCl
4
is also a liquid at the temperatures involved and so requires a bubbler or a liquid injector to produce a gas-phase precursor, but this difference does not directly affect most aspects of the plasma processing in which the gas entraining the TiCl
4
is energized into a plasma adjacent to the wafer so as to activate the reaction causing titanium to deposit on the wafer.
The chemical vapor deposition of a metal layer in a plasma chamber introduces problems not experienced in PECVD chambers used for the deposition of dielectrics. Almost inevitably, some of the metal is deposited on parts of the chamber other than the wafer. The metal may be deposited on dielectric members in the chamber intended to electrically isolate various portions of the chamber. At worst, the extra metal could short out the RF-biased gas showerhead. At a minimum, the changing extent of the grounding surfaces will cause the electrical fields to vary, thus causing the uniformity of the plasma and thus the uniformity of deposition to vary over time. Accordingly, the chamber must be designed to both minimize the effect of any metal deposited on chamber parts in the processing area and also to minimize the deposition of metal in areas away from the processing.
Very recent work of others has demonstrated that the titanium deposition rate and deposition uniformity using TiCl
4
as the precursor can be greatly increased by maintaining the wafer at a relatively high temperatures during the plasma deposition, despite the fact that deposition is primarily plasma activated. A desired temperature range extends between 600° C. and 750° C. At these temperatures, there are several problems not experienced at the lower temperatures experienced in dielectric deposition.
Zhao et al. have addressed some of these problems, at least for TiN, in U.S. Pat. No. 5,846,332, incorporated herein by reference in its entirety, which discloses the CVD reactor illustrated in cross-section in FIG.
1
. This figure illustrates many of the features of the TiNxZ CVD reactor available from Applied Materials, Inc. of Santa Clara, Calif.
A wafer
10
is supported on a surface
12
of a heater pedestal
14
illustrated in its raised, deposition position. In its lowered, loading position a lifting ring
16
attached to a lift tube
17
lifts four lift pins
18
slidably fitted into the heater pedestal
14
so that the pins
18
can receive the wafer
10
loaded into the chamber through a loadlock port
19
in the reactor body
20
. The heater pedestal
14
includes an electrical resistance heater
21
, which controllably heats the wafer
10
it supports. The temperatures experienced in a TiN reactor are low enough to allow the heater pedestal
14
and attached heater to be principally formed of aluminum. Often at least the upper part of the heater pedestal
14
is referred to simply as the heater.
In its upper, deposition position, the heater pedestal
14
holds the wafer
10
in close opposition to a lower surface
22
of a faceplate
24
, a processing region
26
being defined between the wafer
10
and the surface
22
. The faceplate
24
, often referred to as a showerhead, has a large number of apertures
28
in its lower surface
22
communicating between a lower distribution cavity
30
and the processing region
26
to allow the passage of processing gas. The processing gas is supplied through a gas port
32
formed at the center of a water-cooled gas box plate
36
made of aluminum. The upper side of the gas box plate
36
is covered by a water cooling cover plate
34
surrounding the upper portion of the gas box plate
36
that includes the gas port
32
. The gas port
32
supplies the processing gas to an upper cavity
38
separated from the lower cavity
30
by a blocker plate
40
, also having a large number of apertures
42
therethrough. One purpose of the cavities
30
,
38
, the perforated showerhead
24
, and blocker plate
40
is to evenly distribute the processing gas over the upper face of the wafer
10
.
A standard showerhead provided with the TiNxZ chamber has a somewhat irregular hole pattern, illustrated in the partial plan view of
FIG. 2
of the showerhead face
22
. A first set of holes
42
are arranged in two circles generally bracketing the periphery of the wafer
10
. A second set of holes
44
are arranged. in an hexagonal close packed array inside the two circles. The spacings of both sets of holes
42
,
44
equal about the same small value so that the distribution of holes is fairly uniform. Law et al. in U.S. Pat. No. 4,960,488 disclose a showerhead having two densities of holes, but different gases are injected through the two sets of holes.
Returning to
FIG. 1
, a single circular channel or moat
46
is formed in the top of the gas box plate
36
and is sealed by the cooling water cover plate
34
. Two water ports
48
,
50
are formed in the center portion of the gas box plate
36
also occupied by the gas port and respectively act as inlet and outlet for cooling water supplied to cool the showerhead
24
. Often a 50:50 mixture of water and glycol is used to efficiently r
Bhan Mohan K.
Chen Ling
Guo Xin Sheng
Koai Keith
Zheng Bo
Applied Materials Inc.
Guenzer, Esq. Charles S.
Meeks Timothy
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