Baffled perforated shield in a plasma sputtering reactor

Details Baffled perforated shield in a plasma sputtering reactor Baffled perforated shield in a plasma sputtering reactor

2000-06-22

2001-10-02

McDonald, Rodney G. (Department: 1753)

Chemistry: electrical and wave energy

Apparatus

Coating, forming or etching by sputtering

C204S298110, C204S298140

Reexamination Certificate

active

06296747

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to plasma sputtering. In particular, the invention relates to chamber parts optimized for supply of gases in plasma sputtering.
BACKGROUND ART
Magnetron plasma sputtering is widely practiced in the semiconductor industry for the deposition of metals and metal compounds. A recently developed technology of self-ionized plasma (SIP) sputtering allows plasma sputtering reactors to be only slightly modified but to nonetheless achieve efficient filling of metals into high aspect-ratio holes. This technology has been described by Fu et al. in U.S. patent application Ser. No. 09/546,798, filed Apr. 11, 2000, and by Chiang et al. in U.S. patent application Ser. No. 09/414,614, filed Oct. 8, 1999, both incorporated herein by reference in their entireties.
Such a reactor
10
is schematically illustrated in cross section in FIG.
2
. This reactor is based on a modification of the Endura PVD Reactor available from Applied Materials, Inc. of Santa Clara, Calif. The reactor
10
includes a vacuum chamber
12
, usually of metal and electrically grounded, sealed through a target isolator
14
to a sputtering target
16
, usually at least a metal surface portion composed of the material to be sputter deposited on a wafer
18
. A cover ring
20
shields the portion of a pedestal electrode supporting the wafer
18
between the wafer
18
and its edge. Unillustrated resistive heaters, refrigerant channels, and thermal transfer gas cavity in the pedestal
22
allow the temperature of the pedestal
22
to be controlled within a temperature range extending down to less than −40° C. to thereby allow the wafer temperature to be similarly controlled. However, for the materials being described here, the deposition temperature is typically in the range of 100 to 400° C.
An electrically floating shield
24
and a grounded shield
26
separated by a second dielectric shield isolator
28
are held within the chamber
12
to protect the chamber wall
12
from being coated by the sputtered material. When after extended use the shields
24
,
26
are instead coated, they can be quickly replaced by fresh shields. If desired, the coated shields can be refurbished for reuse. The shield replacement eliminates much of the need for cleaning the chamber wall, which consumes valuable production time not only for the cleaning itself but also for reestablishing the high vacuum in the chamber after cleaning fluid has been used on the chamber walls, which would be required in the absence of shields.
The grounded shield
26
includes a downwardly extending outer portion
30
, an inwardly extending bottom portion
32
and an upwardly extending inner portion
30
which terminates close to the wafer clamp
20
and to the top of the wafer pedestal with a narrow gap
34
extending from the backside of the pedestal
22
to the main processing area. The grounded shield
26
thereby acts as the anode grounding plane in opposition to the cathode target
16
, thereby capacitively supporting a plasma. Some electrons deposit on the floating shield
26
so that a negative charge builds up there. The negative potential not only repels further electrons from the shield but also confines the electrons to the main plasma area, thus reducing the electron loss, sustaining low-pressure sputtering, and increasing the plasma density.
A selectable DC power supply
36
negatively biases the target
16
to about −400 to −600 VDC with respect to the grounded shield
26
to ignite and maintain the plasma. A target power of between 1 and 5 kW is typically used to ignite the plasma while a power of greater than 10 kW is preferred for the SIP sputtering process described below. Conventionally, the pedestal
22
and hence the wafer
18
are left electrically floating, but a negative DC self-bias nonetheless develops on them. On the other hand, some designs use a controllable power supply
38
to apply a DC or RF bias to the pedestal
22
to further control the negative DC bias that develops on it. In the tested configuration, the bias power supply
38
is an RF power supply operating at 13.56 MHz.
A gas source
40
supplies a sputtering working gas, typically the chemically inactive noble gas argon, through a mass flow controller
42
to a gas inlet
44
located at the lower portion of the chamber
12
in back of and below the grounded shield
26
. The gas enters the main processing space between the target
16
and the wafer
18
through the gap
34
between the grounded shield
26
and the pedestal
22
and the clamp
20
. A vacuum pump system
46
connected to the chamber
12
through a wide pumping port
48
on the side of the chamber opposite the gas inlet
44
maintains the chamber at a low pressure. Although the base pressure can be held to about 10
−7
Torr or even lower, the pressure is typically maintained at about or below 1 milliTorr for SIP sputtering of metals. A computer-based controller
50
controls the reactor including the DC target power supply
36
, the bias power supply
38
, the mass flow controller
42
, and the vacuum system
46
.
To provide efficient sputtering, a magnetron
54
is positioned in back of the target
16
. It has opposed magnets
56
,
58
connected and supported by a magnetic yoke
60
. The magnetic field traps electrons and, for charge neutrality, the ion density also increases to form a high-density plasma region
62
close to the target
16
. The magnetron
54
is rotated about the center
64
of the target
16
by a motor-driven shaft
66
to achieve full coverage in sputtering the target
16
.
To decrease the electron loss, the inner magnetic pole represented by the inner magnet
56
and unillustrated magnetic pole face should be surrounded by a continuous outer magnetic pole represented by the outer magnets
58
and unillustrated pole face. Furthermore, to guide the ionized sputter particles to the wafer
18
and to minimize electron leakage to the grounded shield
26
, the magnets
58
of the outer pole should produce a much higher total magnetic flux integrated over the area of the pole face, particularly near its outer portions, than do the magnets
56
of the inner pole. The asymmetric magnetic field lines extend far from the target
16
toward the wafer and at least partially parallel to the grounded shield
26
. Such an axial magnetic field traps electrons and extends the plasma closer to the wafer
18
. Other means are available for generating such an axial field, such as auxiliary magnets or electromagnetic coils.
The above described sputtering reactor has been very effective at depositing copper into high aspect-ratio holes in the wafer
18
. It is possible to sputter copper by self-sustained sputtering (SSS), in which after the plasma has been established, the supply of argon is discontinued and the plasma is supported only by the sputtered plasma ions. The chamber pressure can be reduced essentially to zero. This same chamber has been effective also at depositing aluminum, tungsten, and titanium into such high aspect-ratio holes. Although sustained self-sputtering is not possible with Al and Ti, some of the same mechanisms allow SIP sputtering of these metals at very low pressures and high ionization fractions, thus facilitating deep hole filling.
A variant of the above SIP chamber is described by Fu et al. in U.S. patent application Ser. No. 09/581,180 filed on Mar. 2, 2000, also incorporated herein by reference in its entirely. This chamber uses a complexly shaped target having an annularly shaped vault and magnets disposed along sidewalls of the vault.
Titanium is used as part of a liner layer in vias and contacts to be later filled with aluminum or possibly copper. However, the barrier layer typically also includes a titanium nitride (TiN) layer. For copper metallization, the more usual barrier layer is based on tantalum, often a Ta/TaN bilayer. In either case, the same reactor can be used in the same sequence to deposit both the metal and metal nitride by, in a second portion of the sputter deposition, admitting

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