Coating apparatus – Gas or vapor deposition – With treating means
Patent
1992-08-10
1994-06-28
Breneman, R. Bruce
Coating apparatus
Gas or vapor deposition
With treating means
118723AN, 118723VE, 20429838, C23C 1650, C23C 1400
Patent
active
053243625
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
German patent specification 2 625 448 discloses a method by which optical reflectors, preferably headlight reflectors vapour-coated with aluminium, can be protected against corrosion by a plasma polymer layer. For this purpose, the reflectors are exposed in a vacuum bell jar to a monomeric vapour of organic compounds, preferably an organosilicon substance, and the protective layer is deposited by polymerisation from the vapour phase with the aid of radiation from a non-self-maintained glow discharge using a tungsten filament wire. The deposition rates which can be achieved by this method are frequently insufficient to achieve the minimum layer thickness necessary for an increased resistance to condensation water. Moreover, it is necessary to ensure not only that a minimum layer thickness is deposited, but that a maximum layer thickness is not exceeded at particularly exposed points, for example at plane surfaces of the reflector. Troublesome interference colours may otherwise be produced from a maximum layer thickness of approximately 70 nm upwards because the phase condition for destructive interference of blue light is fulfilled (refractive index of the protective layer n.apprxeq.1.5). The reflector does therefore not meet the quality requirements. For this reason, the ratio between maximum protective layer thickness, for example at the front surface plane areas, and minimum thickness, for example in the neck region of the lamp must be not more than 2.8:1 even in the case of deep-drawn reflectors. Otherwise, the required resistance to condensation water over several hundred hours without optical impairment as a result of variegated interference colours cannot be achieved.
This condition can frequently not be fulfilled with the specified method (incandescent tungsten wire--non-self-maintained glow discharge). The reason for the inadequacy of the layer thickness distribution in some cases is the relatively high process pressure necessary for an economical deposition of the layers, which is in the order of magnitude of 10.sup.-3 -10.sup.-2 mbar and at which the free path length of the reactive species is less than the extension in depth of the reflector to be coated. A further disadvantage of this method is the relatively high expenditure due to the consumption of tungsten filament wires.
The literature discloses plasma-generated methods which have a particularly high efficiency and which permit, in principle, a reduction in pressure down to approximately 10.sup.-5 mbar. These include electron cyclotron resonance plasma generation (ECR) at excitation frequencies in the gigahertz range. Since the free path length of the reactive species at these low process pressures becomes much larger than the extension in depth of the parts to be coated, a profound improvement in the layer thickness distribution on the reflectors is expected.
German Offenlegungsschrift 37 05 666 has disclosed a device for generating a plasma and for treating substrates therein. The plasma generated with the aid of microwaves serves to coat a substrate which is situated in an evacuable housing. With the aid of permanent magnets mounted in the vicinity of the substrate to be coated it is possible to generate inside the housing an electron cyclotron resonance which makes possible a locally controlled triggering of the plasma (German Offenlegungsschrift 37 05 666 deals with the principles of electron cyclotron resonance in detail so that it is not necessary to go into them here). To couple the microwaves in, there is constructed in a side wall of the housing a large rectangular window which extends in the longitudinal direction of the same and which is hermetically sealed by a quartz-glass pane. For this purpose, the housing has to be cut open over virtually its entire length. Mounted behind the window at a very small distance from the substrates to be coated is a closed magnet configuration in order to generate an ECR plasma at that point. The apparatus is also suitable for coating markedly three-dimensional objects.
SUMMARY AND
REFERENCES:
patent: 4085248 (1978-04-01), Zehender et al.
patent: 4339326 (1982-07-01), Hirose et al.
patent: 4683838 (1987-08-01), Kimura et al.
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patent: 5126635 (1992-06-01), Doehler et al.
patent: 5180436 (1993-01-01), Ueda et al.
Benz Gerhard
Schneider Guenter
Baskin Jonathan D.
Breneman R. Bruce
Robert & Bosch GmbH
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