Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-03-29
2004-11-09
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192170, C204S298060, C204S298080, C204S298110, C118S7230IR, C118S7230IR, C156S345480, C156S354000
Reexamination Certificate
active
06814838
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to vacuum treatment chambers for work pieces and for treatment methods using the same. In a preferred embodiment, a vacuum treatment chamber for work pieces comprises at least one induction coil for at least co-generating a treatment plasma in a discharge chamber which is located in the interior of the coil.
It is generally known in the art that plasmas can be generated inductively and/or capacitively in vacuum treatment chambers for work pieces.
In the context of capacitive plasma generation, electrodes that are envisioned inside the vacuum chamber are connected with different electric potentials, such as e.g. DC-or HF- potentials, which produces an electric field between the electrodes, similar to that of a capacitor that uses the vacuum as dielectric.
At least one induction coil is envisioned for the inductive plasma generation. The coil surrounds the plasma discharge chamber, and an induction field is generated inside the chamber.
As mentioned previously, frequently, the plasma undergoes a combination of capacitive and inductive excitement; in part this also applies for connected plasmas in which a virtual ‘stand by plasma’ is inductively generated and the capacitively injected power is switched on and off.
To inductively inject the induction field into the discharge chamber it is possible for the induction coil to be exposed vis-a-vis the discharge chamber; but preferably it is separated from the latter by way of a dielectric wall, and is, for the most past, arranged positioned on the outside in relation to the vacuum chamber, or it is, if necessary, embedded in the material of the dielectric wall. A vacuum treatment chamber in which capacitive and inductive plasma generation are used in combination is known in the art from, for example, European Patent No. 0 271 341.
If electrically conductive particles are released inside a chamber, in which a plasma is inductively at least co-produced, such as e.g. during sputter-etching of electrically conductive work piece surfaces or during sputter-coating of work pieces with electrically conductive layers or during PECVD processes that produce electrically conductive particles, the problems described below occur.
If the induction coil is freely exposed to the discharge chamber inside the treatment chamber, there results the formation of an interference layer on the induction coil. With increasing duration of the process this leads to the chipping of particles from the interference layer followed by the corresponding impairment of the process.
If, as preferred, the induction coil is separated from the discharge chamber by way of a dielectric material, the result is that with increasing duration of the process an increasingly thick layer of electrically conductive material is formed on the dielectric wall. This reduces the power that was inductively injected into the discharge chamber and converts it increasingly to heat in the electrically conductive interference layer.
U.S. Pat. No. 5,569,363 addresses these problems that occur inside a sputter treatment chamber with capacitive high frequency and inductive plasma excitement using an induction coil that is arranged outside of a dielectric wall. To resolve the problem of the dielectric inside wall becoming coated with an interference layer consisting of electrically conductive material that patent envisions a cylindrical steel screen with a thickness of approximately 0.1 mm between the discharge chamber and the dielectric wall. The screen is continuously slotted parallel to the axis of the induction coil. This longitudinal slot prevents rotating circular currents from developing inside the metallic cylinder screen, because their path is interrupted by the slot. Also with respect to the deposition of electrically conductive layers on the inside wall of the cylinder this interruption remains effective. It is in fact the screen that protects the dielectric wall from becoming coated with electrically conductive particles. A disadvantageous aspect of this method is the fact that the inductive power injection is considerably reduced if a conductive screen such as this is envisioned.
Similarly, a vacuum treatment chamber is known in the art from European Patent No. 0 782 172 which provides, again in combination, that a plasma is generated capacitively by way of DC-operation of a target as well as inductively by way of HF-operation of an induction coil for the sputter-treatment of work pieces. In one embodied example the induction coil is located inside the vacuum recipient, and in the other embodied example the induction coil is embedded in the dielectric wall. At any rate, at least one cylindrical screen, consisting of a dielectric or a metallic material, is envisioned between the discharge chamber and the induction coil. The screen is equipped with at least one slot running parallel to the axis or with a few continuous slots that are distributed around the circumference of the screen dividing the screen into separate segments.
On the basis of U.S. Pat. No. 5,569,363 and European Patent No. 0 782 172 it is assumed that, irrespective of the fact whether the slotted screen is manufactured from a metallic or from a dielectric material, the electrically conducting interference layer is caught on the screen. Already a single slot will prevent the development of circular currents in the conductive interference layer; however, several evenly distributed slots will, obviously, help achieve better symmetry of the discharge conditions. To avoid that electrically conducting interference layers become deposited on the induction coil or on the dielectric wall because they penetrated through the slots of the one screen, a second coaxial screen is envisioned in accordance with EP-A, which is realized like the screen referred to previously, but the slots are offset at an angle in relation to the former screen.
It can be noted that irrespective of whether the screen is manufactured from a dielectric material or from metal its surface area that is directed toward the discharge chamber will become electrically conducting due to the electrically conducting interference layer.
On the basis of a vacuum treatment chamber for work pieces with at least one induction coil, which is intended to produce a treatment plasma, at least in part, inside a discharge chamber and is located inside the coil, as well as a slotted screen, which is located between the discharge chamber and the coil, in particular arranged in a coaxial direction in relation to the axis of the coil, and whose slots have a direction component that is parallel to the axis, in accordance with the vacuum chamber that is described in European Patent No. 0 782 172 it is the subject matter of the current invention to decisively neutralize the reduction of inductively injected power into the discharge chamber if an electric interference layer is on the screen and, at the same time, to reduce the down-time of the treatment chamber due to the exchange of interference-coated screens.
For now, irrespective of the fact whether the screen consists of metal or of a dielectric material, the present invention relies on the realization that if the inside surface of the screen is electrically conductive—at least if an electrically conductive interference layer is present—it is in fact eddy currents that cause to a crucial degree of the losses of inductively injected power and not—at least not exclusively—circular currents, as outlined in particular in accordance with U.S. Pat. No. 5,569,369. Consequently, according to the invention the screen is equipped with a high slot density. This high density of slots can only be realized in a user-friendly fashion if the body that is used for the screen is self-contained, which, moreover, achieves the objective of allowing for a fast replacement of the screen.
In a preferred embodied example the selected slot density S (number of slots per cm) is
1≦S, preferably even
1.5≦S;
preferably the slot width d is
d≦2 mm, preferably
d≦1 mm.
The maximum lim
Crowell & Moring LLP
McDonald Rodney G.
Unaxis Balzers Aktiengesellschaft
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