Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Patent
1985-12-13
1988-03-01
Pianalto, Bernard D.
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
427294, B05D 306
Patent
active
047285290
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of producing diamond-like carbon coatings in which hydrocarbons and hydrogen, possibly in the presence of a noble gas, are ionized by plasma discharge.
Diamond-like carbon coatings are used in particular for coating IR optical systems, e.g. lenses, mirrors or the like. Coating of objects like this takes place under vacuum conditions, a gas mixture consisting of hydrocarbons, e.g. acetylene, and a noble gas, e.g. argon, being exposed to a plasma discharge. The coatings thus produced are not transparent in the visible spectrum; they are of yellow, brownish, blue or black color. This is why these coatings cannot be used as scratch-resistant coatings for optical systems in the visible spectral region but only for the IR spectrum. A method of despositing a diamond-like carbon film is described in GB-A-2 128 637, in which carbon ions and other ions are generated in separate stationary sources, directed toward the surface of the substrate to be coated, and accelerated. The second ion species has the function to remove the undesired carbon modifications from the deposited coating by chemical sputtering. For this purpose hydrogen is used among other materials. The substrate is heated to a temperature of 100.degree. to 200.degree. C. In this way, yellow to brown-colored coatings are obtained that are likewise suitable for IR optical systems. In conventional methods that use stationary sources the substrate has to be rotated relative to the sources in order to achieve homogenous all-round coating. The simultaneous coating of a large number of parts is technologically feasible, though at a high expenditure. A further disadvantage consists in the fact that the growth rate of typically 0.1 to 1 .mu.m that can be reached per hour is relatively low. Besides, only comparably thin coatings can be produced because the internal stresses in the diamond-like carbon coatings will lead to cracks at coating thicknesses higher than about 1 .mu.m. Hence, these diamond-like coatings have only a very limited wear reserve, so that their application is restricted. If thicker diamond-like coatings could be produced, they would have a much wider of application.
The object of the present invention is to provide a method of producing uncolored diamond-like carbon coatings which are transparent even in the visible region and in addition show low internal stresses. Moreover, the method should permit the simultaneous homogenous all-round coating of large production volumes.
This problem has been solved by the invention in that a hydrocarbon gas or a mixture of hydrocarbon gases and pure hydrogen is passed onto the substrate to be coated which is at room temperature and that around the substrate an oxygen-free plasma discharge is produced by high-frequency excitation which is sustained by the gases admitted, the gases being excited, dissociated, ionized, and accelerated toward the substrate during the plasma discharge. The partial pressure of the hydrocarbon gas is preferably between 10.sup.-3 and 1 mbar and the ratio of the partial pressures of hydrocarbon:hydrogen ranges between 0.05 and 20, preferably between 0.5 and 10. When carrying out the process in the presence of a noble gas, preferably argon, the ratio of the partial pressures of hydrocarbon:noble gas ranges between 0.1 and 10, preferably between 1 and 5.
Coating is initiated under vacuum conditions, preferably at a residual gas pressure of below 2.times.10.sup.-5 mbar.
Coating according to the invention is carried out without heating of the substrate being necessary prior to or during coating. The preferred substrate temperature is between 10.degree. and 20.degree. C. Cooling down to -100.degree. C. is possible.
Plasma discharge takes place at low voltages, e.g., between 50 and 600 V, preferably at 150 to 250 V. High-frequency excitation in the kilohertz to megahertz range, from 30 KHz to 14 MHz, is required to produce and sustain plasma discharge.
According to one embodiment of the method according to the invention, the coating process is carried ou
REFERENCES:
patent: 3167444 (1965-01-01), Baumann
patent: 3167449 (1965-01-01), Spacil
patent: 4410504 (1983-10-01), Galasso et al.
patent: 4434188 (1984-02-01), Kano et al.
J. M. Mackowski, "Comparison physiochimique des couches de carbone a large bande interdite (I-C) elaborees par differentes techniques plasma" pp. 99-106.
Etzkorn Heinz-Werner
Ronge Werner
Battelle-Institut e.V.
Pianalto Bernard D.
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