Chemistry: electrical and wave energy – Processes and products – Vacuum arc discharge coating
Patent
1990-09-21
1992-05-05
Nguyen, Nam
Chemistry: electrical and wave energy
Processes and products
Vacuum arc discharge coating
20419212, 20429805, 20429806, C23C 1434
Patent
active
051104350
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for producing a thin layer of a coating material on a substrate with a vacuum chamber containing a holding means for the substrate, a cluster generating device for generating clusters of the coating material, an ionization device for ionizing the clusters and an accelerating device, which is provided with at least one electrode for accelerating the cluster ions by means of an electric field along an acceleration path in the direction towards the substrate.
The invention is further directed to a process for producing a thin layer of a coating material on a substrate which comprises generating clusters of the coating material and accelerating the clusters towards the substrate by means of an electric field.
Thin layers are produced under vacuum conditions according to different known processes. Examples are the vapor-deposition process and the sputtering process. During the vapor-deposition the substrate is placed near an open crucible in which the vaporization material is heated. In the sputtering process particles, perferably atomic ions, are shot on a solid surface of the coating material (sputter target), thereby releasing atomic or low molecular particles of the coating material which precipitate on the substrate placed near the sputter target. The sputtering is also called "atomizing", however, the English term is used as well in the German language so that in the following this term will be used exclusively.
A further known process is the cluster-ion-epitaxy in which not single atoms are deposited on the substrate surface but the atoms leaving a vaporization crucible first are combined to form so-called "clusters." Thereby the layer surface is said to be improved. The clusters are partially ionized and thereafter deposited on the substrate to be coated.
Cluster is a term used in physics for aggregations of a plurality of atoms or molecules. The number of atoms or molecules forming a cluster may vary considerably. In a typical case the order of magnitude is between 10 and 10.sup.5.
From German Auslegeschrift 26 28 366, there is known a cluster-ion-epitaxy process in which a closed melting crucible is used having a small aperture serving as injection nozzle. The crucible is heated under vacuum conditions and the particles passing through the injection nozzle expand very quickly. By this so-called adiabatic expansions clusters are formed which subsequently are ionized by means of an electron current from a heated wire. The ionized clusters are accelerated towards the substrate in an electric field.
For producing layers having excellent optical, electrical and mechanical properties it is very important that the layers are coated in a clean way and without impurities caused by the process. The cleaner the layers are the better is their quality in general.
The known cluster-ion-epitaxy processes do not satisfy the demands in this respect. The impurities caused by the process are especially high. They are caused e.g. by the crucible material, reaction products of the crucible material with the substance to be vaporized and reaction products of the crucible material with eventually present reactive gases. Moreover, incrustations of the nozzle may lead to disadvantageous alterations of the process parameters.
The invention therefore has the task to provide a process and an apparatus for the production of thin layers having improved quality at reasonable expense.
This problem is solved by an apparatus as described at the beginning in which the cluster generating device is provided with a sputter unit having a sputter target consisting of solid coating material for transferring the coating material into the gas phase and an aggregation chamber having a gas feeding conduit, the acceleration device being placed in an acceleration chamber separated from the aggregation chamber and being connected with the aggregation chamber by an aperture for the clusters arranged in an extension of the acceleration path, a vacuum pump being in communication with the acceleration chamber being
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