Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2002-08-22
2004-11-23
Versteeg, Steven (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298170, C204S298190, C204S298200
Reexamination Certificate
active
06821397
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling plasma density or its distribution over the target configuration of a magnetron source, a method for the production of coated workpieces, as well as magnetron sources.
Definition
By magnetron source is understood a sputter source, on which the discharge is operated with DC, AC or mixed AC and DC, or with pulsed DC, wherein AC is to be understood as extending up into the HF range. The source is conventionally operated under vacuum with a working gas, such as for example argon, at pressures of a few mbar up to 10
−3
mbar. In known manner, reactive additional gases can be mixed in for reactive processes.
Over the sputter surface of the target configuration at a magnetron source, a tunnel-form magnetic field is generated, which, in a view onto the surface to be sputtered, the sputter surface, forms a closed loop. Viewed in the cross sectional direction of the target configuration, at least a portion of the magnetic field emerges from the sputter surface and enters back into it again in the form of a tunnel arch. The sputter surface, also referred to as the target surface, forms the one electrode, the cathode, of the plasma discharge gap, since positive ions must be accelerated onto the target surface for the sputtering process. This electrode can also be subdivided and its components can be individually electrically supplied.
Consequently, in the region of the loop of the tunnel-form magnetic field an electric field obtains, which is substantially at an angle with respect to the tunnel field. A tunnel-form electron trap results and a pronounced electron current, which substantially circulates in and along the loop of the tunnel-form magnetic field. In the region of said loop-form circulating magnetic field this electron current produces a pronounced increase of the plasma density compared to the plasma density further outside of said magnetic field loop.
Therewith along the circulating electron current, referred to in the technical field as “race track” a substantially increased sputter rate, results which leads to an increasingly more developed erosion trench in the sputter surface, i.e. at the base of the tunnel-form circulating magnetic field.
Apart from fundamentally the great advantages of magnetron sources, this increasingly developing erosion trench, has negative effects on
Coating homogeneity on the coated substrate,
Degree of utilization of the target material.
In order to avoid at least partially these disadvantages, it is known to move, in particularly cyclically, entire or major portions of the magnetic field circulating tunnel-form in a loop with respect to the target configuration or its sputter surface. Thereby is obtained a temporal distribution of the “race track” electron current effect along the traversed sputter surface regions.
If it is taken into consideration that the looped magnetic field circulating in the form of a tunnel is conventionally realized by a configuration of strong permanent magnets beneath the target configuration, it is evident that, on the one hand, an existent permanent magnet configuration which, for shifting said magnetic field, is mechanically moved beneath the target configuration, can only be geometrically changed with relatively high expenditures, in order to realize different erosion profile distributions, and that in sputter operation a variation of this distribution or of the geometry of the permanent magnetic configuration is hardly possible.
SUMMARY OF THE INVENTION
The present invention addresses the problem of being able to control the plasma density or plasma density distribution over the sputter surface of the target configuration differently or additionally and therein also to be able to carry out this control during the coating process.
This is achieved with the method of the above described type thereby that locally, i.e. along a limited partial segment of the circulating loop of the tunnel-form magnetic field, this magnetic field and/or the electric field is varied under control. In a second solution formulation the posed problem is solved thereby that onto the tunnel-form magnetic field basically a controlling magnetic field is superimposed. Under the first formulation, the corresponding field is thus locally varied, under the second an additional magnetic field is superimposed onto the tunnel-form one.
U.S. Pat. No. 5,512,150 discloses a magnetron sputter source, in which the tunnel-form magnetic field over the target configuration can be varied with respect to its radial extension. For this purpose beneath the target configuration an electromagnet is disposed in the form of a pot, whose poles can be reversed by reversing the current direction. This electromagnet itself generates the tunnel-form magnetic field: for that reason, it must be extremely strong, which leads to a large voluminous coil with corresponding heat development.
The disadvantages of this known process according to the invention are circumvented under both formulations.
It was found according to the invention that through the exclusively local change of the electrical and/or of the tunnel-form magnetic field the electron trap is more or less disturbed, which corresponding to the particular operating point and the selected variation, leads to an increase or decrease of the plasma density along the entire electron trap.
With respect to the average periphery of the electron trap therein the described local intervention is realized in a peripheral region, in top view, of maximally ⅓ of the perimeter, preferably on a region of maximally ¼ of the perimeter, preferably in a region which is significantly shorter.
Relative to the average pole distance d of the pole regions out of which the tunnel-form magnetic field emerges from the sputter surface and enters it again, a preferred length l
B
of the “local” region on which the intervention is carried out, preferably results as:
0<l
B
≦4d
preferably
0<l
B
≦2d
in particular of
0<l
B
≦d.
When the term “local” is used, then preferably with the above addressed geometric reference to average loop perimeter and/or to average pole distance, in particular averaged in the considered intervention region.
Even if, under the second formulation of the present invention, onto the tunnel-form magnetic field a controlling magnetic field is superimposed no longer necessarily locally, such that the degree to which the anode intervenes in the resulting magnetic field is varied under control, a controlling effect is exerted onto the action of the electron trap and the circulating electron current and consequently onto the plasma density and sputter rate along the entire circulating loop.
According to the first listed formulation of the present invention in a preferred embodiment the tunnel-form magnetic field and/or the electric field is varied locally with control such that said degree is varied.
Since according to the first formulation of the invention the magnetic field and/or the electric field is only locally intervened upon, it is entirely possible to vary the tunnel-form magnetic field and/or the electric field through the controlling intervention on their particular generators themselves, thus without superposition.
If, according to the second formulation of the invention onto the circulating tunnel-form magnetic field a controlling magnetic field is superimposed, this takes place in a preferred embodiment along at least one major portion of the loop of the tunnel-form magnetic field. The superimposed field is preferably established substantially perpendicularly to the target sputter surface and, in a further preferred embodiment, substantially homogeneously, i.e. with locally constant field strength distribution. But it is entirely possible to develop this superimposed field also locally of different amplitude and/or to vary it such that its controlling strengths differ.
The two formulations, according to the invention, can be entirely realized in combination.
In terms of equivalent circu
Notaro&Michalos PC
Unaxis Balzers Aktiengesellschaft
Versteeg Steven
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