Mesh shield in a sputter reactor

Details Mesh shield in a sputter reactor Mesh shield in a sputter reactor

2001-11-05

2003-11-11

VerSteeg, Steven H. (Department: 1753)

Chemistry: electrical and wave energy

Apparatus

Coating, forming or etching by sputtering

Reexamination Certificate

active

06645357

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to sputter deposition of materials. In particular, the invention relates to a shield used in a sputter reactor.
2. Background Art
Sputtering, alternatively called physical vapor deposition (PVD), is the most prevalent method of depositing layers of metals and metal nitrides in the fabrication of silicon integrated circuits. Recently developed technology has enabled sputtering to be applied to many difficult structures, such as depositing thin barrier layers in high aspect-ratio holes.
In U.S. Pat. No. 6,296,747, Tanaka describes one such advanced plasma sputter reactor
10
, illustrated schematically in the cross-sectional view of FIG.
1
. The reactor
10
includes an aluminum reactor body
12
defining a vacuum chamber. A metal target
14
is supported on the wall
12
through an isolator
16
and faces a wafer
18
to be sputter coated. A wafer clamp
20
holds the wafer
18
on a pedestal electrode
22
. A vacuum pump system
26
connected to the chamber through a pumping port
28
is capable of maintaining the interior of the chamber at a very low pressure of down to about 10
−8
Torr. However, a sputter working gas, such as argon is supplied from a gas source
30
and metered by a mass flow controller
32
to flow through an inlet
34
into the chamber at a pressure typically in the low milliTorr range. When a DC power supply
36
applies a negative voltage of about −600 VDC to the metal target
14
, the argon working gas is excited into a plasma and the positively charged argon ions are attracted to the target
14
at high energy and sputter metal atoms from the target
14
. Some of these metal ions strike the wafer
18
and are deposited in a thin layer thereon.
The reactor
10
is configured for self-ionized plasma (SIP) sputtering. A small magnetron
40
is positioned at the back of the target
14
and includes an inner magnetic pole
42
of one magnetic polarity surrounded by an outer magnetic pole
44
of the opposite polarity and of a substantially greater total magnetic intensity. The poles
42
,
44
are supported on and magnetically coupled by a magnetic yoke
46
, which is itself supported on a motor driven shaft
48
positioned along a center axis
50
of the chamber so that the magnetron
40
is rotated about the center axis. The magnetron
40
creates a magnetic field adjacent the interior face of the target
14
and thereby creates a region of high-density plasma next to the target
14
, which intensifies the sputtering rate in the portion of the target
14
adjacent the high-density plasma. The magnetron rotation produces a more uniform sputtering pattern.
The sputtering process not only coats the wafer
18
with the sputtered metal atoms, it also coats any other body exposed to the target
14
, such as the chamber wall
12
. Cleaning sputtered material from the interior of the chamber wall
12
is difficult and time consuming. Accordingly, it is standard practice to include sputter shields, such as the illustrated upper and lower shields
54
,
56
, typically formed of aluminum or stainless steel, which protect the chamber wall
12
from sputter deposition and are instead themselves coated with the sputtered material. A topmost shield
58
protects the isolator and is positioned close to the target
14
to form a plasma dark space between it and target
14
. When the shields
54
,
56
,
58
become excessively coated to the point that the coating tends to flake and produce deleterious particles, they are replaced with fresh shields in a preventative maintenance (PM) procedure. At least the lower shield
54
is usually electrically grounded to act as the anode in opposition to the target cathode in the plasma generation process.
In SIP sputtering, the magnetic field and the target power are increased to the extent that a large fraction of the sputtered metal atoms are ionized to produce two effects. First, the metal ions are themselves attracted back to the target to sputter yet further metal atoms in a process referred to as self-sputtering. As a result, the argon supply and chamber pressure can be decreased. In the case of copper sputtering, it is possible to stop the supply of argon once the plasma has been ignited. Secondly, the metal ions can be accelerated towards the wafer by an RF power supply
60
connected to the pedestal electrode
22
, which results in a negative DC self bias on the wafer
18
. A controller
62
controls the power supplies
36
,
60
and the flow of gas to set the processing conditions. Further, the magnetic field created by the unbalanced intensities of the magnetic poles
42
,
44
can guide the metal ions to the wafer
18
.
Such ionized sputtering and controlled directionality is advantageous for sputtering material into deep and narrow holes, that is, holes having a high aspect-ratio. Aspect ratios of 5:1 are becoming common for inter-level electrical vias through silica-based dielectric layers, and aspect ratios are increasing for advanced products. As a result, sputtering can be used to deposit thin liner layers on the bottom and sidewalls of the via holes. One such liner layer is a barrier layer required to be interposed between the metal filled into the via and the silica dielectric to prevent the metal from diffusing into the silica and making it conductive. For aluminum metallization, a titanium-based barrier of Ti/TiN is typically used, where TiN is titanium nitride. For copper metallization, a tantalum-based barrier of Ta/TaN is more typical, although other barrier materials are possible. The titanium or tantalum is usually deposited first to act as a glue layer to the underlying silica while the nitride acts as the actual barrier material.
Sputtering, particularly ionized sputtering, can be used to deposit both the metal portion and the metal nitride portion of the barrier. The target
14
has at least its front surface composed of the metal, whether it be titanium, tantalum, or other barrier metals such as tungsten. In a first phase, called metal sputtering, a thin metal layer is deposited on the wafer
18
under biasing conditions that favor sidewall deposition. In a second phase, called reactive sputtering, nitrogen is additionally admitted into the chamber from a nitrogen source
66
through its mass flow controller
68
. The nitrogen reacts with the metal atoms at or near the surface of the wafer to deposit a coating of metal nitride.
Reactive sputtering increases the problems associated with the sputtering shields. A first problem addressed by Tanaka is that nitrogen, unlike argon, is consumed in reactive sputtering. The gas inlet
34
is preferably located behind the shields
54
,
56
, and the gas flows into the main processing area through a gap
70
between the lower shield
56
the clamp
20
, and the pedestal electrode
22
. While this flow pattern is sufficient for argon, it constrains the supply of nitrogen and it is possible that the nitriding is incomplete. Accordingly, Tanaka forms a ring of perforations
74
in the lower shield
12
to facilitate the flow of nitrogen into the main processing region. However, to protect the chamber wall in back of the perforations, he additionally includes the upper shield
54
to cover the perforations
74
with a downwardly facing gap
76
between the two shields
54
,
56
to flow the nitrogen from the perforations
74
into the main processing region. While the structure is effective, it is complicated.
Particulate flaking of shields in reactive sputtering is a particularly troublesome effect. Nitrides tend to be much harder and less pliable than metals Accordingly, they are more prone to flaking at lesser coating thicknesses. It has become typical to roughen the shield surface exposed to sputter coating. Machined grooves are disclosed by Koyama et al. in U.S. Pat. No. 5,837,057 and by Visser in U.S. Pat. No. 6,059,938. A more commercially popular approach is to form the shield of stainless steel and to coat the areas of the shield exposed to sputter coating with

Affiliated with

Also associated with

Rating

Mesh shield in a sputter reactor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Mesh shield in a sputter reactor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mesh shield in a sputter reactor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3153372