Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
1999-04-22
2001-05-29
Shingleton, Michael B (Department: 2817)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S111810, C118S7230IR, C118S7230AN
Reexamination Certificate
active
06239553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to plasma processing. More particularly, the present invention relates to a radio frequency (RF) plasma source for use in plasma material processing.
2. Background of the Related Art
Plasma material processes are widely used in the fabrication of integrated circuits on semiconductor substrates. These processes typically include etching, chemical vapor deposition, physical vapor deposition and other vacuum processes. During these processes, the semiconductor substrates are exposed to a gaseous plasma within a vacuum processing chamber. Radio frequency energy (RF between 3-30 MHz), typically at 13.56 MHz, is used to excite a processing gas that is supplied to the processing chamber and generate a plasma. The plasma may be generated within the processing chamber and/or introduced from a remote plasma generator to the processing chamber. Plasma generation within the processing chamber and remote plasma generation are both well known in the art. Each method of plasma generation has been utilized in a variety of plasma material processes. For example, remote plasma generation of a cleaning gas, such as NF
3
, has been successfully utilized to clean deposition chambers or process kit components (e.g., gas distributors, clamp rings, etc.) made of ceramic or aluminum.
FIG. 1
is a simplified schematic view of a typical remote inductively coupled plasma source. The plasma source
100
generally comprises a tube
102
, a coil
104
spirally wound outside and along the length of the tube
102
and an RF power source
106
connected to the coil
104
. Generally, inductive coupling, as shown in
FIG. 1
, is preferred over capacitive coupling because the plasma density generated by inductive coupling for a given power is higher than that generated by capacitive coupling with the same power. The higher plasma density generally results in an increased reaction rate, shorter processing time and higher throughput. The RF power source
106
supplies to the coil
104
the RF energy needed to generate a plasma within the tube. Typically, an RF match network
108
is connected between the RF power source
106
and the coil
104
to provide an impedance match between the RF power source
106
and the coil
104
. The impedance match ensures that the RF power supplied to the coil
104
is not reflected back to the RF power source
106
and provides optimal power transfer between the RF power source
106
and the coil
104
. The tube
102
includes a process gas inlet
110
disposed on one end and a plasma outlet
112
disposed on the other end. The process gas inlet
110
is fluidly connected to a processing gas source (not shown), and the plasma outlet
112
is fluidly connected to a processing chamber (not shown). The remote plasma source
100
is generally mounted on a surface of the chamber enclosure, typically on top of a lid to the chamber enclosure.
During processing, the processing gas is introduced into the tube
102
through the process gas inlet
110
, and the RF power source
106
is activated to supply an RF power to the coil
104
. The RF power energizes the coil
104
and produces an RF field within the tube
102
that excites the processing gases to a plasma state. The plasma then flows out of the plasma outlet
112
into the processing chamber. Typically, the processing gas is continuously introduced into the tube
102
and excited to a plasma to provide a continuous plasma supply into the processing chamber throughout the processing period.
Typically, the RF power source supplies a high peak-to-peak voltage on the order of a few kilo volts to one end of the coil
104
while the other end of the coil
104
is grounded. A problem with the inductive RF coil having one end grounded and the other end connected to a high voltage is that the high RF peak-to-peak potential causes strong capacitive coupling of RF power into the plasma generated within the tube
102
. The strong capacitive coupling of RF power into the plasma is undesirable because it reduces the RF energy being inductively coupled to the plasma as intended by the coil
104
. Capacitive coupling generally presents a large sheath voltage near the dielectric tube. The high voltage near the tube
102
causes significant erosion of the interior surface of the tube
102
as ions from the plasma are accelerated by the large sheath voltage to impinge on the dielectric tube material. The erosion on the tube
102
reduces the useful life of the tube and leads to contaminant generation during processing that may cause defects on substrates. The erosion also reduces the useful life of the tube as well as the remote inductively coupled plasma source, which results in additional costs and processing down-time for repairs and/or replacements. Furthermore, it is desirable to reduce or minimize the capacitive coupling because minimizing the capacitive coupling generally leads to a higher density plasma for a given power.
Therefore, there is a need for a remote inductively coupled plasma source that maintains a low coil voltage in the vicinity of the plasma tube, thereby reducing the capacitive coupling between the coil and the plasma and the erosion from the internal surfaces of the plasma tube.
SUMMARY OF THE INVENTION
The present invention provides a plasma source that maintains a low coil voltage in the vicinity of the plasma tube, thereby reducing the capacitive coupling between the coil and the plasma and significantly reducing the erosion from the internal surfaces of the plasma tube.
The plasma source generally comprises a coil having a first coil segment and a second coil segment, an RF power source connected to the coil and an enclosure disposed between the first coil segment and the second coil segment. Preferably, a first RF match network is connected between the RF power source and the first coil segment, and a second RF match network is connected between the second coil segment and a ground.
Alternatively, each coil segment is connected to a capacitor to operate in a self-resonant mode to simplify the RF match network. Preferably, one capacitor is connected to each outer end of the coil segments, and the RF power source is connected to one of the coil segments or to the middle segment between the first and second coil segments.
Another aspect of the invention provides a zero-voltage in the vicinity of the enclosure by grounding the inner ends of the coil segments. In this coil configuration, the RF power source is connected to the outer ends of the coil segments, and preferably, an RF match network is connected between the RF power source and the coil segments. As an alternative to separately grounding the inner ends of the coil segments, a middle coil segment connecting the first and second coil segments is grounded to provide a zero-voltage in the vicinity of the enclosure.
The invention also provides a method for generating a plasma, comprising: disposing an enclosure between a first coil segment and a second coil segment of a coil; introducing a gas into the enclosure; and supplying an RF power to the coil to excite the gas into a plasma. The invention provides a variety of coil operations, including symmetrical coil configuration, asymmetrical coil configuration with the matching networks adjusted to provide a low voltage near the plasma chamber, self-resonant configuration, grounded coil center configuration having coil segments driven in parallel and physically grounded near the plasma chamber, and pairs configurations having a plurality of coil segment pairs driven in series or parallel. In addition, the inductive coupling between the coils and the plasma can be enhanced by using coil segments having ferrite cores.
REFERENCES:
patent: 3705091 (1972-12-01), Jacob
patent: 4849675 (1989-07-01), Müller
patent: 4988644 (1991-01-01), Jucha et al.
patent: 5194731 (1993-03-01), Turner
patent: 5241245 (1993-08-01), Barnes
patent: 5540824 (1996-07-01), Yin et al.
patent: 5554223 (1996-09-01), Imahashi
patent: 5641359 (1997-06-01), Y
Barnes Mike
Ishikawa Tetsuya
Niazi Kaveh
Tanaka Tsutomu
Applied Materials Inc.
Shingleton Michael B
Thomason Moser & Patterson
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