Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-07-16
2002-12-17
Ryan, Patrick (Department: 1745)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298060, C204S298110, C204S298140, C204S192260, C204S192290
Reexamination Certificate
active
06495000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to the fabrication of liquid crystal displays and, more particularly, to a system and method of using a finned anode in the deposition of oxide films in a direct current (DC) sputtering deposition process.
2. Description of the Related Art
As noted in U.S. Pat. No. 6,149,784 (Su et al.), sputtering, or physical vapor deposition (PVD), is the favored technique for depositing materials, particularly metals and metal-based materials, in the fabrication of semiconductor integrated circuits. Sputtering has a high deposition rate and, in most cases, uses relatively simple and inexpensive fabrication equipment and relatively inexpensive material precursors, targets in the case of PVD. The usual type of sputtering used in commercial applications is DC magnetron sputtering, which is limited to the sputtering of metallic target. Sputtering is widely used for the deposition of aluminum (Al) to form metallization levels in semiconductor liquid crystal displays. More recently, copper deposition by PVD has been developed. However, sputtering is applicable to a wider range of materials useful in the fabrication of semiconductor integrated circuits. Reactive sputtering is well known in which a target of a metal, such as titanium or tantalum, is sputtered in the presence of a reactive gas in the plasma, most typically nitrogen. Thereby, the sputtered metal atoms react with the reactive gas to deposit a metal compound on the wafer, most particularly, a metal nitride, such as titanium nitride using a titanium target in a nitrogen ambient or tantalum nitride using a tantalum target in a nitrogen ambient.
FIG. 1
is a schematic block diagram, partial cross-section of a DC sputtering chamber, or reactor
100
(prior art). The reactor
100
is vacuum-sealed and has a target or cathode
102
. Typically, the target
102
is a metal, but semiconductor and insulator materials can also be used. The target material is sputtered onto a substrate
104
held on a heater pedestal electrode
106
or an electrostatic chuck. An anode
108
acts as a dark space shield to protect the chamber wall
110
from the sputtered material and provides a return path or collection surface for the electrons emitted from the cathode target
102
. A controllable pulsed DC power supply (not shown) negatively biases the target
102
with respect to the anode
108
. Conventionally, the pedestal
106
and substrate
104
are left electrically floating, but a DC self-bias can be used to attract positively charged ions from the plasma.
Gas enters the reactor
100
from an inlet port
112
, and gas exits through an exhaust port
114
. The sputtering gas is often argon. The gas flow is regulated to maintain interior of the reactor
100
at a low pressure. The conventional pressure of the argon working gas is typically maintained at between about 1 and 1000 mTorr. When the argon is admitted into the reactor
100
, the DC voltage applied between the target
102
and the anode
108
ignites the argon into a plasma, and the positively charged argon ions are attracted to the negatively charged target
102
. The ions strike the target
102
at a substantial energy and cause target atoms or atomic clusters to be sputtered from the target
102
. Some of the target particles strike the substrate
104
and are thereby deposited on it, thereby forming a film of the target material. Alternately, the target material reacts with gas added to the argon to form a composite film including target material.
To provide efficient sputtering, opposing magnets
116
and
118
produce a magnetic field within the reactor
100
in the neighborhood of the magnets
116
,
118
. The magnetic field traps electrons and, for charge neutrality, the ion density also increases to form a high-density plasma region
120
within the reactor adjacent to the target
102
.
Plasma ignition can present a significant problem, especially in the geometries representative of a commercially significant plasma reactor. The initial excitation of a plasma requires a high voltage, though with essentially no current, to cause the working gas to be excited into the electrons and positive ions of an electron. This condition must persist for a time period and over a space sufficient to support a low-resistance, essentially neutral plasma between the two electrodes in the case of a capacitively coupled plasma. The maintenance of a plasma requires a feedback condition in which argon atoms must supply as many electrons to the anode as ions to target. If the flow of electrons to the anode is insufficient, the plasma collapses or is never formed.
Pulsed DC sputtering also provides a method for the low temperature (less than 2000 degrees C) deposition of oxide films, and should have advantages over the current plasma-enhanced chemical vapor deposition (PECVD) process. Low temperature processing is a critical when films are deposited on plastic substrates, such as the substrates used in the fabrication of flexible liquid crystal displays (LCDs). In addition, the pulsed DC sputtering of SiO2 and SiNx shows good promise from the viewpoint of high deposition rates and process flexibility. For example, the composition of the deposited film can be changed by simply changing gas mixture. However, the quality and deposition rate oxide films formed by pulsed DC sputtering is highly dependent on maintaining a good conductive anode for the electron return path.
FIG. 2
is a schematic block diagram of the chamber
100
of
FIG. 1
after the processing of a few substrates (prior art). The same oxide film that is being deposited on the substrate
104
is also being deposited on the anode
108
. Once the anode
108
is covered with oxide, a highly resistive material, the electron return path through the anode is eliminated. In response to the anode
108
being covered by the insulating film, changes occur in the plasma condition capacitance and electron flow in the chamber
100
. As the oxide layer on the anode
108
increases, electrons charge the anode surface, which produces a large capacitance the chamber. The large capacitance creates micro arcing as the capacitance builds ups and discharges. When the anode is heavily coated, the capacitance in the chamber becomes very large and severe arcing will occur along with damage to the target
102
.
Micro arcing is the first symptom that the anode is covered with insulator. Areas
200
of the substrate are damaged as a result of micro arcing. The resulting film can be nonuniform and of a poor quality. As the barrier layer on the anode increases in thickness, more severe arcing will take place in the vacuum chamber and eventually loss of plasma will occur. Severe arcing can cause damage. to the target
102
and result in the formation of large particles
202
on the substrate
104
. Such damage creates manufacturing problems, such as a short anode life cycle, poor film quality, and low production yield, all a result of arcing in the chamber. Because arcing aggravates film quality and production yield, conventional design anodes must be frequently changed and cleaned. These frequent anode changes are detrimental to production efficiency.
FIG. 3
is a schematic block diagram of the chamber of
FIG. 1
using an anode
108
having slits
300
on the anode surface (prior art). Alternately stated, the anode
108
has ribs
302
between the slits
300
. The principle behind this modification is to increase the aspect ratio of the anode surface and, therefore, increase anode life for manufacturing. Although the vertical section of the ribs appear to collect less deposition material than the horizontal surfaces, the overall ratio between cathode and anode still increases as the anode gets coated. As the ratio between the cathode and anode changes, so does the chamber capacitance and plasma. In other words, effective area of anode decreases during the process and causes changes to the plasma distribution and film uniformity. After the insulating oxide film covers the anode, arcing occurs
Atkinson James Mikel
Guthrie Patrick L.
Nishiki Hirohiko
Cantelmo Gregg
Krieger Scott C.
Rabdau Matthew D.
Ripma David C.
Ryan Patrick
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