Coating apparatus – With heat exchange – drying – or non-coating gas or vapor... – Cooling
Reexamination Certificate
1999-10-19
2002-04-02
Mills, Gregory (Department: 1763)
Coating apparatus
With heat exchange, drying, or non-coating gas or vapor...
Cooling
C118S724000, C118S715000, C427S573000, C427S576000
Reexamination Certificate
active
06364949
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to semiconductor processing equipment. More specifically, this invention relates to a processing chamber for semiconductor processing and methods for confining plasma gas within a processing zone of the processing chamber.
2. Background of the Related Art
Semiconductor integrated circuits are fabricated with multiple layers of semiconductive, insulating, and conductive materials, as well as additional layers providing functions such as bonding, a migration barrier, and an ohmic contact. Thin films of these various materials are deposited or formed in a number of ways, the most common of which in modern processing are physical vapor deposition (PVD), also known as sputtering, and chemical vapor deposition (CVD).
In CVD, a substrate, for example a silicon substrate, which may already have patterned layers of silicon or other materials formed thereon, is exposed to a precursor gas which reacts at the surface of the substrate and deposits a product of the reaction, e.g. TiN, Al, etc., on the substrate to grow a film thereon. This surface reaction can be activated in at least two different ways. In a thermal process, the substrate is heated to a sufficiently high temperature to provide the activation energy necessary to cause the precursor gas adjacent to the substrate to react and deposit a layer on the substrate. In a plasma-enhanced CVD process (PECVD), the precursor gas is subjected to a sufficiently high electromagnetic field which excites the precursor gas into energetic states, such as ions or radicals, which react on the substrate surface to form the desired material.
One type of CVD chamber commercially available from Applied Materials, Inc., of Santa Clara, Calif., is known as a CVD DxZ Chamber and is illustrated in the cross-sectional side view of FIG.
1
. The CVD chamber
30
includes a pedestal
32
having a supporting surface
34
on which a substrate
36
is supported for chemical vapor deposition of a desired material thereon. Positioning the substrate
36
on the supporting surface is facilitated by vertically movable lift pins
38
.
A gas delivery assembly
31
is disposed on a lid rim
66
at an upper end of the chamber body
72
and includes a gas distribution faceplate
40
, often referred to as a showerhead, and a gas-feed cover plate
46
, or temperature control plate, disposed on the showerhead
40
and in thermal communication therewith. An annular flange
47
, (shown in
FIG. 2
) which is an integral component of the showerhead
40
, is disposed on an isolator
64
to support the gas delivery assembly
31
. A plurality of holes
42
arc formed in the showerhead
40
and are adapted to accommodate gas flow therethrough into the process region
56
. The gas is provided to the showerhead
40
by a central gas inlet
44
formed in the gas-feed cover plate
46
. The gas-feed cover plate
46
also includes a multi-turn cooling/heating channel
33
to accommodate the flow of water or other fluid therethrough during processing in order to maintain the gas delivery assembly
31
at a desired temperature. The gas delivery assembly
31
may be cooled or heated depending on the particular chemicals being delivered through the central gas inlet
44
. In operation, the temperature controlled gas delivery assembly
31
is intended to contribute to uniform deposition and prevents gas decomposition, deposition, or condensation within the gas distribution system upstream from the process zone.
In addition to assisting in gas delivery into the chamber
30
, the showerhead
40
also acts as an electrode. During processing, a power source
94
(
FIG. 1
) supplies power to the showerhead
40
to facilitate the generation of a plasma. The power source
94
may be DC or RF.
In operation, a substrate
36
is positioned on the pedestal
32
through cooperation of a robot (not shown) and the lift pins
38
. The pedestal
32
then raises the substrate
36
into close opposition to the showerhead
40
. Process gas is then injected into the chamber
30
through the central gas inlet
44
in the gas-feed cover plate
46
to the back of the showerhead
40
. The process gas then passes through the holes
42
and into the processing region
56
and towards the substrate
36
, as indicated by the arrows. Upon reaching the substrate
36
, the process gases react with the upper surface thereof. Subsequently, the process gas byproducts flow radially outwardly across the edge of the substrate
36
, into a pumping channel
60
and are then exhausted from the chamber
30
by a vacuum system
82
.
However, PECVD processes have demonstrated some problems with deposition uniformity, reproducibility and reliability. It is believed that the problems originate from temperature gradients over various chamber component surfaces as well as from extraneous metal depositions on the chamber surfaces affecting the plasma and producing excess particles within the chamber. With regard to extraneous metal deposition, it is believed that the deposition occurs in two different areas, an area at the top of the pedestal
32
outside of the substrate
36
and an area in and around the pumping channel
60
.
One problem associated with conventional CVD chambers is the temperature non-uniformity over the surface of the showerhead
40
. As a result of the power applied to the showerhead
40
by the power source
94
, the temperature of the showerhead
40
increases over time until reaching thermal stabilization which is determined, in part, by the thermal exchange between the showerhead
40
and the plasma, and the showerhead
40
and the gas-feed cover plate
46
. While acceptable results were achieved for 200 mm chambers, thermal stability and uniformity worsened as the chambers were scaled up to accommodate larger substrates, such as 300 mm substrates. Because the uniformity of deposition is at least partially dependent on temperature, the resultant temperature gradient over the surface of the showerhead
40
produces non-uniform deposition on the substrate.
One cause of temperature non-uniformity throughout the bulk of the showerhead
40
, is design features of conventional lid assemblies provided to accommodate thermal stresses during operation. For example, referring to
FIG. 2
, the gas-feed cover plate
46
is shown disposed on the showerhead
40
. The outer annular wall
35
of the gas-feed cover plate
46
is in facing relation to the inner annular wall
37
of the showerhead
40
to define a gap
39
therebetween. While preferably minimized or nonexistent at room temperature, the gap
39
is widened during processing due to the differing coefficients of expansion of the gas-feed cover plate
46
and the showerhead
40
which causes the showerhead
40
to expand to a greater degree. As a result, the gap
39
acts to insulate the gas-feed cover plate
46
and the showerhead
40
from one another, thereby inhibiting thermal exchange.
Temperature non-uniformity over the surface of the showerhead is also a result of the limitation of space which require that the dimensions of the gas delivery assembly
31
be minimized in order to reduced the cost of manufacturing and operation. In order to ensure the desired heating or cooling of the gas delivery assembly
31
, the gas-feed cover plate
46
requires sufficiently large dimensions to accommodate the cooling channel
33
. As a result of the large size of the gas-feed cover plate
46
, the showerhead thickness is minimized to achieve a compact gas delivery assembly
31
. In scaling up to accommodate larger substrates, it was initially believed that the ratio of dimensions could be maintained without a loss of deposition uniformity. However, 1:1 scale-up results in thermal non-uniformity over the surface of the showerhead
40
. In particular, the center of the showerhead
40
experiences considerably higher temperatures relative to the edge, thereby resulting in a temperature gradient from center to edge. As a result of the temperature gradient, deposition on the substrate is non-uniform
Chen Fufa
Koai Keith K.
Lei Lawrence C.
Or David T.
Applied Materials Inc.
Mills Gregory
Moser Patterson & Sheridan LLP
Zervigon Rudy
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