Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
1997-05-08
2001-07-03
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C156S345420, C204S298060, C204S298320, C204S298340, C204S298010, C118S715000, C118S7230ER, C118S7230IR, C118S7230AN
Reexamination Certificate
active
06254746
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to plasma generators, and more particularly, to a method and apparatus for generating a plasma in the fabrication of semiconductor devices.
BACKGROUND OF THE INVENTION
Radio frequency (RF) generated plasmas have become convenient sources of energetic ions and activated atoms which can be employed in a variety of semiconductor device fabrication processes including surface treatments, depositions, and etching processes. For example, to deposit materials onto a semiconductor wafer using a sputter deposition process, a plasma is produced in the vicinity of a sputter target material which is negatively biased. Ions created within the plasma impact the surface of the target to dislodge, i.e., “sputter” material from the target. The sputtered materials are then transported and deposited on the surface of the semiconductor wafer.
Sputtered material has a tendency to travel in straight line paths from the target to the substrate being deposited at angles which are oblique to the surface of the substrate. As a consequence, materials deposited in etched trenches and holes of semiconductor devices having trenches or holes with a high depth to width aspect ratio, can bridge over causing undesirable cavities in the deposition layer. To prevent such cavities, the sputtered material can be “collimated” into substantially vertical paths between the target and the substrate by negatively charging the substrate or substrate support and positioning appropriate vertically oriented collimating electric fields adjacent the substrate if the sputtered material is sufficiently ionized by the plasma. However, material sputtered by a low density plasma often has an ionization degree of less than
1
% which is usually insufficient to avoid the formation of an excessive number of cavities. Accordingly, it is desirable to increase the density of the plasma to increase the ionization rate of the sputtered material in order to decrease the formation degree of unwanted cavities in the deposition layer. As used herein, the term “dense plasma” is intended to refer to one that has a high electron and ion density.
There are several known techniques for exciting a plasma with RF fields including capacitive coupling, inductive coupling and wave heating. In a standard inductively coupled plasma (ICP) generator, RF current passing through a coil surrounding the plasma induces electromagnetic currents in the plasma. These currents heat the conducting plasma by ohmic heating, so that it is sustained in steady state. As shown in U.S. Pat. No. 4,362,632, for example, current through a coil is supplied by an RF generator coupled to the coil through an impedance matching network, such that the coil acts as the first windings of a transformer. The plasma acts as a single turn second winding of a transformer.
In order to maximize the energy being coupled from the coil to the plasma, it is desirable to position the coil as close as possible to the plasma itself. At the same time, however, it is also desirable to minimize the number of chamber fittings and other parts exposed to the material being sputtered so as to facilitate cleaning the interior of the chamber and to minimize the generation of particles being shed from interior surfaces. These particles shed from interior surfaces can fall on the wafer itself and contaminate the product. Accordingly, many sputtering chambers have a generally annular-shaped shield enclosing the plasma generation area between the target and the pedestal supporting the wafer. The shield provides a smooth gently curved surface which is relatively easy to clean and protects the interior of the chamber from being deposited with the sputtering material. In contrast, it is believed by the present inventors that a coil and any supporting structure for the coil would of necessity tend to have relatively sharply curved surfaces which would be more difficult to clean away deposited materials from the coil and its supporting structures. In addition, it is believed that the smooth gently curved surface of the shield would tend to shed fewer particles than the sharply curved surfaces of the coil and its supporting structure.
Thus, on the one hand, it would be desirable to place the coil outside the shield (as described in copending application Ser. No. 08/559,345, pending filed Nov. 15, 1995 for METHOD AND APPARATUS FOR LAUNCHING A HELICON WAVE IN A PLASMA which is assigned to the assignee of the present application and is incorporated herein by reference) so that the coil is shielded from the material being deposited. Such an arrangement would minimize generation of particles by the coil and its supporting structure and would facilitate cleaning of the chamber. On the other hand, it is desirable to place the coil as close as possible to the plasma generation area inside the shield to avoid any attenuation by the spacing from the plasma or by the shield itself to thereby maximize energy transfer from the coil to the plasma. Accordingly, it has been difficult to increase energy transfer from the coil to the plasma while at the same time minimizing particle generation and facilitating chamber cleaning.
SUMMARY OF THE PREFERRED EMBODIMENTS
It is an object of the present invention to provide an improved method and apparatus for generating plasmas within a chamber, obviating, for practical purposes, the above-mentioned limitations.
These and other objects and advantages are achieved by, in accordance with one aspect of the invention, a plasma generating apparatus which inductively couples electromagnetic energy from a coil which is recessed with respect to the sputtering surface of a target so as to minimize the deposition of target material onto the coil. In addition, the coil is recessed with respect to the perimeter of the pedestal (support member) and the deposition surface of the workpiece supported on the pedestal such that any target material deposited upon, and subsequently shed by, the coil onto the workpiece is minimized. As a consequence, contamination of the workpiece by particulate matter shed by the coil is reduced.
In one embodiment, the coil is partially shielded from deposition material by a dark space shield which is positioned above the coil to prevent a substantial portion of the target material from being deposited onto the coil. In an alternative embodiment, the coil is carried by a separate adapter ring which has a coil chamber to protect the coil from deposition material. In addition, the coil chamber has a floor positioned below the coil to catch particulate matter shed by the coil to reduce contamination of the workpiece. Still further, the adapter ring coil chamber is separate from the shield. As a consequence, the shield may be separately cleaned or discarded thereby substantially facilitating the cleaning of the shield and chamber and reducing the cost of the shield itself.
In accordance with another aspect of the present invention, the coil is carried on the shield or in the adapter ring chamber by a plurality of novel coil standoffs and RF feedthrough standoffs which have an internal labyrinth structure. As explained below, the labyrinth structure permits repeated depositions of conductive materials from the target onto the coil standoffs while preventing the formation of a complete conducting path of deposited material from the coil to the shield which could short the coil to the shield which is typically at ground. In addition, the labyrinth structure permits the standoff to have a low height which can reduce the overall size of the chamber.
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patent: 4716491 (1987-12-01), Ohno et al.
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patent: 4844775 (1989-07-01), Keeble
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pa
Edelstein Sergio
Forster John C.
Grunes Howard
Stimson Bradley O.
Subramani Anantha
Applied Materials Inc.
Konrad Raynes & Victor LLP
McDonald Rodney G.
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