Coating processes – Direct application of electrical – magnetic – wave – or... – Ion plating or implantation
Reexamination Certificate
2000-11-21
2003-12-09
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Ion plating or implantation
C427S523000, C427S525000, C427S528000
Reexamination Certificate
active
06660340
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a method for enhancing the adhesion of a diamond-like carbon (DLC) film to a substrate and for producing a strongly adhered DLC film on a metallic substrate or a metallic substrate having an oxide film on the surface and, more particularly, to cases where the substrate intended to receive the DLC film comprises a metal or metal alloy that does not readily form carbides or a metal or metal alloy that may form carbides, but has an oxide coating that does not readily form bonds with carbon. The invention causes strongly adhered DLC films on such metallic substrates or oxide films.
In order to improve the wear resistance or other properties of the surfaces of various substrates, it is desirable to overlay the substrate with a film of a harder material such as diamond-like carbon (DLC). Since the one of the goals in applying a hard DLC film on a substrate is to improve durability and lifetime, it is important that the hard DLC film be strongly adherent to the substrate so that it does not prematurely separate from it.
Of course, it is recognized that these concerns occur in many fields of application where it is desirable to improve adhesion of DLC films to metallic substrates or metallic films that have been deposited on other substrates, and especially so in cases where the substrate metal does not easily adhere to deposited DLC because it does not readily form strong carbide bonds at low temperatures, such as chromium, cobalt, nickel, copper, and alloys thereof or predominately thereof. An example is a magnetic data storage disk substrate having a chromium or copper film surface on which it is desired to deposit a durable DLC protective film coating. Another case is titanium or an alloy consisting primarily of titanium, but having an oxidized surface layer, which may be a native oxide layer. Although titanium may form carbide bonds, the oxide surface layer does not readily form strong carbide bonds at low temperatures and thus strongly adhered DLC films are not readily formed.
One of the problems encountered is that the DLC, when applied by conventional methods like chemical vapor deposition (CVD), physical vapor deposition (PVD), pulsed laser deposition (PLD), conventional ion beam assisted deposition (IBAD), or gas cluster ion beam assisted deposition (GCIBAD), does not produce DLC films that are sufficiently strongly adherent to the substrate metals and which therefore do not have long life and high wear resistance. Conventional methods investigated for improving the poor adhesion of a film include ion beam interface stitching, substrate pre-sputtering, post deposition interface ion implantation, and ion beam assisted deposition. These methods are all described by J. Baglin, in “Interface structure and thin film adhesion”, in
Handbook of Ion Beam Processing Technology
-
Principles, Deposition, Film Modification and Synthesis
, edited by J. Cuomo et. al., Noyes Publications, Park Ridge, N. J. (1989).
Furthermore, interface stitching and post-deposition interface ion implantation both require the ion beams employed be of sufficient energy to completely penetrate the deposited DLC film. This imposes thickness limitations on the DLC films due to the practical unavailability of ion beams of arbitrarily high energies. Other, more complex, treatments involve forming one or ore intermediate layers between the substrate metal and the DLC film of, for example, silicon (taught in U.S. Pat. No. 5,593,719, G. Dearnaly et. al., “Treatments to reduce frictional wear between components made of ultra-high molecular weight polyethylene and metal alloys”, 1997) or germanium (taught in U.S. Pat. No. 5,780,119, G. Dearnaly et. al., “Treatments to reduce frictional wear on metal alloy components” 1998) or a silicon compound or the like (as taught in U.S. Pat. No. 5,605,714, G. Dearnaly et. al., “Treatments to reduce thrombogeneticity in heart valves made from titanium and its alloys” 1997). In the prior art, when an oxide film covers a metal or metal alloy that otherwise might form carbide bonds, steps were required to remove the oxide film prior to DLC deposition and such steps often require the application of high temperatures (as also taught in U.S. Pat. No. 5,605,714, G. Dearnaly et. al., “Treatments to reduce thrombogeneticity in heart valves made from titanium and its alloys” 1997).
Such treatments, however, are complex and time consuming and thus, costly. Also, processes that employ additional materials such as silicon, germanium, or the like introduce foreign materials (Si, Ge, etc) which may detract from the suitability of the resulting structure for some applications. Furthermore, some of the existing processes require heating of the substrates and films during portions of the process, which allows the possibility of thermal degradation of materials or that differing thermal coefficients of expansion between substrate and film result in the introduction of stresses into the film when the materials are returned to room temperature.
In the example of a magnetic storage disk, there may be multiple stacked films of differing materials on the disk's base substrate. In such case, it is desirable to be able to deposit a DLC protective film without subjecting the disk to large temperature excursions that may produce undesirable results due to the different temperature coefficients of expansion of the various layers.
It is therefore an object of this invention to provide a method and system for producing a strongly adhered DLC coating for metals and metal alloys.
It is a further object of this invention to provide a method for causing improved adhesion of a DLC film to a substrate that does not readily form carbide bonds at low temperatures.
It is an additional object of this invention to provide DLC coating and improved DLC film adhesion by a process that is less costly than previous methods.
It is a further object of this invention to provide DLC coating and improved DLC film adhesion by a process that does not require high processing temperatures.
It is an additional object of this invention to provide a DLC film coating on metal or metal oxide substrates without introducing foreign materials.
SUMMARY OF THE INVENTION
The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow.
A substrate, being comprised of a metal or metal alloy that does not readily form carbides (for example chromium, cobalt, nickel, copper, and alloys thereof or predominately thereof) or a metal or metal alloy that may form carbides but is coated with an oxide coating that does not readily form bonds with carbon (for example titanium or an alloy consisting primarily of titanium, but having an oxidized surface layer) receives an ordinary solvent or chemical or other cleaning to assure surface cleanliness. It is then subjected to a pre-deposition adhesion enhancement process that includes the procedure of ion implantation of the surface of the metal substrate to which the DLC film will be deposited with carbon ions at a dose and energy sufficient to establish a volume concentration of carbon atoms at and near the surface of the substrate of not less than 5×10
18
atoms/cm
3
, and preferably of more than 4×10
19
atoms/cm
3
. Although the implantation energy is not critical, a preferred method is to implant the carbon ions at an energy of from 25 keV to 100 keV. The implantation may be done at room temperature or somewhat above room temperature as may result naturally from slight heating resulting from the implantation, with or without active cooling of the substrate. The carbon implantation is preferably done on an ion implanter that has mass analysis to select
12
C and reject other ion species—this assures that only pure carbon is introduced to the substrate being processed, thus avoiding the introduction of materials other than the carbon which forms the DLC that will be subsequently applied.
Although implantation of carbon
Cohen Jerry
Epion Corporation
Erlich Jacob N.
Padgett Marianne
Perkins Smith & Cohen LLP
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