Plasma processing system for sputter deposition applications

Details Plasma processing system for sputter deposition applications Plasma processing system for sputter deposition applications

2000-11-21

2002-10-08

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Discharge device load with fluent material supply to the...

Plasma generating

C118S7230ER

Reexamination Certificate

active

06462482

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma processing system for sputter deposition applications, and more particularly, to a plasma processing system like a plasma assisted sputtering system having an improved plasma source capable of independently controlling plasma ion density and ion energy at the rf (high-frequency AC) electrodes useful for a sputtering process of metal or dielectric materials during the fabrication of integrated circuits in the semiconductor industry.
2. Description of the Related Art
Large-area and high-density plasma sources with higher radial uniformity are of great demand to process large area substrates without charge-induced damages to the devices fabricated on the substrate surface. Specially, development of new plasma sources for the sputtering process of metal and dielectric materials with enhanced uniformity of the deposited film is of important. Difficulties in obtaining the above-mentioned properties with conventional plasma sources are explained using two conventional configurations as shown in
FIGS. 10-13
, which are usually applied in 200 mm wafer or flat panel plasma processing systems.
FIG. 10
shows a simplified conventional magnetron-type plasma source that uses for sputter deposition applications in semiconductor industry. A reactor
101
is comprised of an upper electrode
102
made of a non-magnetic metal, a cylindrical side wall
103
and a lower electrode
104
. The upper electrode
102
forms a top plate of the reactor
101
and the lower electrode
104
is arranged on a bottom plate
105
of the reactor
101
. The upper electrode
102
and the lower electrode
104
are parallel to each other across at least over a portion of the reactor
101
. The side wall
103
and the bottom plate
105
are made of a metal, for example stainless steel. The upper part of the side wall
103
is made of an insulating material
106
on which the upper electrode
102
is placed. A target plate
107
made of a material needed to be sputtered is fixed to the lower surface of the upper electrode
102
. Usually, the target plate
107
has slightly smaller dimensions in comparison with the upper electrode
102
. On the upper surface of the upper electrode
102
as the top plate, two magnets
108
a
and
108
b
of circular and ring shapes are concentrically placed as shown in
FIGS. 10 and 11
. The central magnet
108
a
is of a cylindrical shape without any cavity as shown in FIG.
11
. The outer magnet
108
b
is of a ring shape. The height and widths of each of the magnets
108
a
and
108
b
are not critical and selected according to the other dimensions of the reactor
101
. The magnets
108
a
and
108
b
are placed on the upper electrode
102
so as to have opposite polarities facing the inside of the reactor
101
. This arrangement of the magnets
108
a
and
108
b
generates curved magnetic fields
109
between these two magnets.
The upper electrode
102
is connected to a high-frequency AC (rf) electric power source
110
through a matching circuit
111
. The frequency of the rf electric power source
110
is usually 13.56 MHz. When a rf electric power is applied to the upper electrode
102
, plasma is generated by the capacitively-coupled mechanism. Once the plasma is made, electrons in the plasma are confined within the curved magnetic fields causing an increase of plasma density in that region.
A substrate
112
is placed on the lower electrode
104
electrically isolated from the bottom plate
105
through an insulating material
113
. The lower electrode
104
may or may not be given a rf electric power from a rf power source. If a rf electric power is supplied to the lower electrode
104
by a rf electric power source
114
through a matching circuit
115
, as shown in
FIG. 10
, the frequency of the rf electric power source
114
usually lies in MF region. When a rf current is applied to the lower electrode
104
, it gets negatively biased causing an ion bombardment onto the surface of the substrate
112
. Though the ion bombardment causes an etching process on films deposited on the substrate
112
, the self-bias voltage of the lower electrode
104
is controlled so that the film deposition rate exceeds the film etching rate on the substrate
112
.
Another conventional magnetron type sputtering source shown in
FIG. 12
is a slight modification of the above-mentioned plasma source given in FIG.
10
. Here the central magnet
108
a
is placed in an off-axis mode in order to form an asymmetric magnetic field below the upper electrode
102
. A top view of this magnet arrangement is shown in FIG.
13
. This magnetic configuration is rotated around a central axis (shown as a dashed line
116
in
FIG. 12
) of the upper electrode
102
. The magnet arrangement formed by the magnets
108
a
and
108
b
shown in
FIGS. 12 and 13
rotates asymmetrically.
The parallel plate plasma reactor shown in
FIG. 10
has several advantages such as large area plasma between the parallel electrodes, readily ignition of the plasma, and the ability of controlling plasma ion energy at the lower electrode surface. With the magnet arrangement given in
FIG. 10
, a doughnut-shaped curved magnetic field is generated below the upper electrode
102
. Once the plasma is ignited, higher-density plasma of the doughnut-shaped is formed below the upper electrode
102
due to the magnetic confinement of electrons. Since this higher-density plasma is mainly confined within the region between the magnetic poles of the magnets
108
a
and
108
b,
there is a lower plasma density in the vicinity of the magnetic. poles.
Further, the strength of the magnetic field increases toward the magnetic poles. This causes a mirror reflection of the electrons that result in lower electron density at the magnetic poles of the magnets
108
a
and
108
b.
When the electron density is low, the ion density is also gets low since ions are trapped in the plasma by electrostatic fields generated by electrons.
Because of the two reasons explained above, the ion flux at the magnetic poles gets smaller to result in a lower sputtering rate. However, since there is a higher-density plasma in the doughnut-shape region between the respective magnetic poles of the magnets
108
a
and
108
b,
the area of the target plate
107
corresponding to the region between the two magnets gets strongly sputtered. A fraction of these sputtered atoms are reflected back due to the scattering by gas molecules and deposited again on the target plate
107
. Since the sputtering rate at the places of the target plate surface corresponding to the magnetic poles is relatively smaller, deposition of the sputtered atoms at these places gets dominant. The re-deposited film, however, has a lower density and stick loosely on the target plate
107
, thus it can be easily released as particles.
In order to avoid the re-deposition of sputtered materials on the target plate
107
, as shown in
FIG. 12
, the magnets
108
a
and
108
b
are placed asymmetrically and rotated around the central axis
116
of the upper electrode
102
. Even though there is the re-deposition of sputtered materials at the places corresponding to the magnetic poles, the re-deposited films are immediately sputtered back into the plasma due to the rotation of the magnets. Accordingly, the source of particles in the plasma can be eliminated.
However, the plasma generated with the configuration given in
FIG. 12
is radially non-uniform. This causes a non-uniform ion flux onto the surface of the substrate
112
. This may cause localized charge build up on the substrate surface, specially if the substrate
112
is negatively biased by applying the rf electric power to the lower electrode
104
, which eventually results in electrical breakdown of sub-micro scale elements on the substrate
107
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetically enhanced capacitively-coupled plasma processing system for sputter deposition applications with higher ion concentration, higher

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