Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-06-27
2003-09-16
Ryan, Patrick (Department: 1745)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C204S298080, C204S298180, C204S298260
Reexamination Certificate
active
06620299
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and a device for the coating of substrates by way of bipolar pulsed magnetron sputtering in the frequency range of 10 kHz to 100 kHz. The invention is particularly intended to deposit layers with poor electrical conductivity or insulating layers onto substrates. Such layers are preferably used as optical, electrical, or mechanical functional layers as are needed for optical components, electrical components, or for friction-reducing and wear-retarding protective layers.
2. Discussion of Background Information
Magnetron sputtering is widely used for depositing metallic and electrically insulating layers. The recent introduction of reactive pulsed magnetron sputtering brought about significant progress, especially for the economical deposition of layers with poor electrical conductivity or insulating layers (Schiller et al., Society of Vacuum Coaters, 38th Annual Technical Conference Proceedings 1995, pages 293-297).
Processes for unipolar and bipolar pulsed magnetron sputtering are known. In unipolar pulsed magnetron sputtering, the energy is fed into the target in the form of direct current pulses. A special manner of feeding unipolar pulsed energy using several targets sputtered in a unipolar fashion is described in DE 197 02 187. Here, at least one of two magnetron electrodes is connected cathodically and at least one is connected anodically and the discharge energy is fed in a unipolar fashion during a defined period of time with a pulse frequency of 10 to 150 kHz. Then the power supply is interrupted and a polarity reversal is performed.
Particularly high process stability and the possibility of coating large areas of largely uniform surfaces can be achieved by means of reactive sputtering with a double magnetron arrangement using a bipolar pulsed power supply with a frequency for the polarity change of 10 kHz to 100 kHz. Here, it is less significant for the process whether a clocked direct current source or a medium frequency generator is selected as the type of pulsed power source.
In a double magnetron arrangement that has been introduced in the field of coating technology as a dual magnetron system or TwinMag (Bräuer et al., Proc. of the 3rd ISSP, Tokyo 1995, pages 63-70), each target of the double magnetron arrangement acts alternately as a cathode or an anode of a gas discharge burning between the targets in the rhythm of the polarity reversal. Known arrangements consist of two magnetron sources arranged parallel to one another with rectangular targets that lie in a plane or are inclined toward one another at a particular angle in the shape of a roof. The overlapping of the magnetic fields of the two magnetron sources occurring here requires special measures or devices for compensating for the uneven erosion speed of the various regions of the target. In general, however, despite these measures, target erosion occurs with greater speed in the region of the closely adjacent erosion channels than in the region of erosion channels that are more widely separated from one another. This leads to a shortening of the useful life of the cost-intensive target.
A deciding factor for the quality of the layers deposited by-means of sputtering is the plasma density, i.e., the density of charged particles in the region of the substrates. It influences the average energy of the condensing particles and thus the structure of the layers and many other physical layer characteristics. In the region near the target, the plasma density is very high during magnetron sputtering. However, it decreases very quickly in the direction of the substrates and is less by orders of magnitude in the region of the substrate.
Various processes and/or devices are known from coating technology with single magnetron sources that have the purpose of increasing the plasma density in the region of the substrates. Thus, the spatial plasma density is changed by means of asymmetrical formation of the magnetic field of the magnetron source in such a way that the plasma density is increased in the region of the substrates (Window and Savvides, Unbalanced DC Magnetrons as Sources . . . , J.Vac.Sci.Technol. A4 (3) 1986, pages 453-456).
Similar effects are achieved with magnetic fields that are produced by means of additional coils, or so-called plasma booster arrangements (Hofmann, New Multilayer PVD Coating Techniques for Cutting Tools, Surf.Coat.Technol., No. 61 (1993), pages 326-330). Arrangements with four direct current magnetron sources are also known whose magnetic field poles are arranged such that their overlapping achieves a closed magnetic field with increased plasma density in the vicinity of the substrate.
In pulsed magnetron sputtering with double magnetron arrangements, the region of higher plasma density is located near the surface of the targets, in particular also in the vicinity of the gap between the targets. The layers deposited on the substrates condense under the influence of a comparatively low plasma density and therefore have quality defects in many cases. There is no known adaptation of the methods or arrangements for displacing the region of high plasma density in the direction of the substrate to double magnetron arrangements. Of these measures, only the introduction of large-area additional coils would be conceivable to one skilled in the art. However, a higher equipment expense and only limited effectiveness could be expected.
The concentration of the plasma in the immediate vicinity of the double magnetron arrangement has a particularly disadvantageous effect when three-dimensional extended substrates or substrates that are arranged on movable holders such as rotating cages or rotating substrate receptacles with several parallel rotational axes for the purpose of even coverage are to be coated in the immediate vicinity of the double magnetron arrangement. According to the prior art, the condensation of the layers on such substrates during pulsed magnetron sputtering occurs with a plasma density that differs greatly locally and, in the case of movable substrates, with a plasma density that differs over time. Serious disadvantages in terms of layer structure and local uniformity of layer characteristics result from this.
SUMMARY OF THE INVENTION
The invention provides for a process and a device for coating of substrates by way of bipolar pulsed magnetron sputtering that guarantees high-quality deposition of the layers. In particular, substrates that are extended in three dimensions and/or substrates and groups of substrates in the form of substrate arrangements that are arranged during coating on holders, preferably movable holders, such as rotating cages or rotating substrate receptacles with several parallel rotational axes, should also be coated at high quality. Moreover, the invention also provides for applications for the process and the device according to the invention.
The invention provides for a process for coating substrates utilizing bipolar pulsed magnetron sputtering in the frequency range between 10 kHz and 100 kHz in a device which includes at least three targets, the process comprises connecting at least two targets at a time to a potential-free bipolar power supply device, sputtering the at least two targets in a bipolar manner for a predetermined period of time, changing the connecting of the at least two targets to the bipolar power supply device according to a technologically predetermined program, and arranging the at least two targets relative to the substrate in a manner such that during each of a reversing discharge, the substrates being located at least partially inside a discharge current between the targets which are active at the time.
The changing may occur one of temporally periodically and aperiodically. The predetermined period of time may comprise at least 10 polarity reversals of a bipolar magnetron discharge. The predetermined period of time may comprise between 1,000 and 100,000 polarity reversals. At least one of a material of the targets and the technologicall
Fietzke Fred
Goedicke Klaus
Schiller Siegfried
Cantelmo Gregg
Fraunhofer-Gesellschaft zur Förderung der Angewandten Forschung
Greenblum & Bernstein P.L.C.
Ryan Patrick
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