Electric heating – Metal heating – By arc
Reexamination Certificate
1999-09-02
2001-09-18
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121410, C156S345420, C118S7230IR
Reexamination Certificate
active
06291793
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention is related to fabrication of microelectronic integrated circuits with an inductively coupled RF plasma reactor and particularly to such reactors having coiled RF antennas providing a highly uniform plasma distribution.
2. Background Art
Inductively coupled plasma reactors are employed where high density inductively coupled plasmas are desired for processing semiconductor wafers. Such processing may be etching, chemical vapor deposition and so forth. Inductively coupled reactors typically employ a coiled antenna wound around or near a portion of the reactor chamber and connected to an RF power source. In order to provide a uniform etch rate or deposition rate across the entire surface of a wafer, the plasma density provided by the coiled antenna must be *uniform across the surface of the semiconductor wafer. One attempt to provide such a uniform field is to wind the coiled antenna in a flat disk parallel to and overlying the wafer, as disclosed in U.S. Pat. No. 4,948,458 to Ogle. This concept is depicted in FIG. 1.
One problem with the flat coiled antenna of FIG. 1 is that there is a large potential difference between the center of the antenna and the circumferential edge thereof, with the result that the plasma can have a high ion density or “hot spot” over the center of the wafer and a lower ion density at the wafer periphery. This in turn causes the etch rate —or deposition rate—to be nonuniform across the wafer surface. One way of ameliorating this problem is to limit the power applied to the antenna coil to a few hundred watts so as to minimize the plasma non-uniformity. This approach is not completely satisfactory because it limits the etch rate (or deposition rate), thereby reducing throughput or productivity of the reactor, and moreover does not solve the problem of process non-uniformity across the wafer surface.
Another problem with inductively coupled reactors is that any high voltage applied to the antenna coil leads to capacitive coupling of RF power to the plasma. In other words, capacitive coupling of RF power from the coiled antenna to the plasma increases with the voltage on the coiled antenna. Such capacitive coupling can increase the ion kinetic energy which makes it difficult for the user to precisely control ion kinetic energy and thereby control sputtering rate or etch rate. Capacitive coupling is particularly pronounced in the flat disk coil antenna of FIG. 1.
Therefore, there is a need for an inductively coupled plasma reactor having a coiled antenna which provides a highly uniform plasma across the wafer surface at high power with only minimal capacitive coupling.
SUMMARY OF THE INVENTION
A coil antenna is provided for radiating RF power supplied by an RF source into a vacuum chamber of an inductively coupled plasma reactor which processes a semiconductor wafer in the vacuum chamber, the reactor having a gas supply inlet for supplying processing gases into the vacuum chamber, the coil antenna including plural concentric spiral conductive windings, each of the windings having an interior end near an apex of a spiral of the winding and an outer end at a periphery of the spiral of the winding, and a common terminal connected to the interior ends of the plural concentric spiral windings, the RF power source being connected across the terminal and the outer end of each one of the windings. In a preferred embodiment, the RF power source includes two terminals, one of the two terminals being an RF power terminal and the other of the two terminals being an RF return terminal which is connected to ground, the common terminal of the plural concentric spiral conductive windings being connected to one of the RF source terminals and the outer ends of the plural concentric spiral conductive windings being connected to the other RF source terminal.
In a first embodiment, the reactor chamber includes a planar ceiling and the antenna coil has a planar disk shape and lies on an exterior surface of the ceiling. In a second embodiment, the reactor chamber includes a cylindrical side wall and the antenna coil has a cylindrical shape and is helically wound around a portion of the cylindrical wall. In a third embodiment, the reactor includes a dome-shaped ceiling and the antenna coil has a dome shape and is helically wound around, lies on and is congruent with at least a portion of the dome-shaped ceiling. In a fourth embodiment, the reactor includes a truncated dome-shaped ceiling and the antenna coil has a truncated dome shape and is helically wound around, lies on and is congruent with at least a portion of the truncated dome-shaped ceiling. In a fifth embodiment, the reactor chamber includes a planar ceiling and a cylindrical side wall and one portion of the antenna coil is planar and overlies the planar ceiling while another portion of the antenna coil is cylindrical and is helically wound around at least a portion of the cylindrical side wall. In a sixth embodiment, the reactor includes a dome-shaped ceiling and a cylindrical side wall and one portion of the antenna coil is dome-shaped and overlies and is congruent with the dome-shaped ceiling and another portion of the coil antenna is cylindrical and is wound around at least a portion of the cylindrical side wall. In a seventh embodiment, the reactor includes a truncated dome-shaped ceiling and a cylindrical side wall and one portion of the antenna coil is truncated dome-shaped and overlies and is congruent with the truncated dome-shaped ceiling and another portion of the coil antenna is cylindrical and is wound around at least a portion of the cylindrical side wall.
Preferably, the plural windings are of about the same length. In one embodiment, the coil antenna includes three of the windings. Preferably, the inner ends are circumferentially spaced from one another at equal intervals and wherein the outer ends are circumferentially spaced from one another at equal intervals. A bias RF source may be connected to the wafer pedestal.
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Qian Xue-Yu
Sato Arthur H.
Appplied Materials, Inc.
Fish and Richardson
Paschall Mark
Prahl Eric L.
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