Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1992-08-21
2002-02-19
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S113000, C427S123000, C427S304000
Reexamination Certificate
active
06348240
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for modifying oxidizable surfaces, including diamond surfaces, including methods for metallizing these surfaces, where these methods include plasma oxidation of these surfaces. The present invention also relates to the products of these methods.
2. Description of the Related Art
Modified surfaces are increasingly of great technological importance. In particular, modified diamond surfaces have increasing technological importance because of the attractive physical properties of diamond, including hardness, broad wavelength transparency, high thermal conductivity and sound propagation velocity, variable electrical resistivity, low friction coefficient, high refractive index, and chemical and biological inertness. Applications for modified diamond surfaces exist or are foreseen in a number of areas, including microelectronics (semiconductive layers, optical and x-ray masks, and heat dissipators), optics (transparent or antireflective coatings), machine tools (abrasion resistant coatings), and biotechnology (biocompatible coatings for implants, biosensors).
Of particular interest is the deposition of adherent, conductive metal coatings (including metal contacts) onto these surfaces for microelectronic and mechanical applications. For instance, metal-coated dielectric, such as polymers and ceramics (including diamond) have increasing technological importance in a variety of applications. These applications include use in circuit boards, use for shielding, lithographic masks, etc.
Surfaces coated with various chemical functional groups also are of increasing technological importance. Chemical sensing, including biosensing, is just one area where surfaces coated with chemical functional groups may be employed. For instance, a surface is coated with a particular antigen may be used in testing for a particular antibody.
For many of these applications, it is desirable for these surfaces to be modified in a pattern. The terms “pattern” and “patterning” have meanings that vary from application to application. However, for each area of application, these terms are well-understood by skilled practitioners in the art. For example, in the context of fabricating circuit boards, patterned metallization means laying down conductive pathways on a circuit board, preferably with through-holes and other useful structures. In the context of microelectronic applications, patterned metallization means laying down conductive pathways with linewidths in the sub-0.5 &mgr;m range, consistent with VLSI applications. Preferably, in the context of microelectronics, these linewidths are about 0.1 &mgr;m, using currently available lithographic techniques. As x-ray lithographic techniques improve, it is anticipated that the present invention will produce microelectronic circuits with linewiths of about 0.05 &mgr;m. In the context of lithography, patterning means creating a pattern of lines on a mask with sufficient resolution and packing density for the particular application at hand. In the context of chemical applications (such as chemical sensing) patterned chemical modification means attaching chemical groups in a pattern consistent with the specific application and system at hand.
A problem associated with patterned metallization is that it is typically accomplished by means of a “lift-off” process, in which metal is evaporated or sputtered over a lithographically defined photoresist, and then dissolution of the remaining resist removes metal from selected regions of the metallized surface. This process, which is subtractive in nature, wastes metal and is more difficult and expensive than a process in which metal is deposited in an additive fashion, i.e. only in regions where it is required.
Various workers have fabricated contacts and metal patterns on diamond using sputter deposition or evaporation of Ag, Cu and Au, Al, W and numerous alloys. The principal problems with forming diamond/metal interfaces fabricated with conventional methods are obtaining reproducible and controllable electrical characteristics and obtaining satisfactory adhesion of the metal to the diamond surface.
Acceptable adhesion of metal to diamond and good ohmic contact can be obtained if the metallized substrate is annealed at high temperature (800-900° C.), forming a metal carbide layer at the interface. However, such high temperature is also problematic for metal/diamond contact formation because the diamond surface is subject to graphitization, which can degrade the electrical properties of the interface. Vacuum metallization is another available method for metallizing diamond surfaces, but this method requires complex, expensive equipment.
A problem with forming polymer/metal interfaces is that currently employed techniques for surface modification result in a surface that is roughened on the microns scale. For many applications, especially microwave and millimeter wave applications, a much smoother surface is desired.
The principal problem encountered in modifying diamond and other surfaces, both for metallization and other types of functionalization, is putting a sufficient density of functional groups on the diamond surface to carry out a chemisorption reaction. As is shown below in the summary of the invention, plasma oxidation processes are useful for this purpose. Other processes may also be useful. Diamond surfaces may be modified by detergents and acids, which produce oxygen-containing functionalities on the diamond surface. However, these processes may not result in a sufficient concentration of the type of oxygen-containing functional groups needed to carry out a commercially viable chemisorption reaction. Only oxidation processes that result in high concentrations of oxygen-containing functional groups that participate in chemisorption reactions are useful for modifying oxidizable surfaces.
Adhesive metal patterns can be deposited selectively on a wide variety of surfaces using ultrathin film (UTF)-based metallization processes. See co-pending application Ser. No. 07/691,565; see also Schnur et al., U.S. Pat. No. 5,077,085, issued Dec. 31, 1991; Schnur et al., U.S. Pat. No. 5,079,600, issued Jan. 7, 1992; Calvert et al.,
New Surface Imaging Techniques for Sub
-0.5
Micrometer Optical Lithography,
Solid State Technology 34, 77 (October 1991); Dressick et al.,
Selective Electroless Metallization of Patterned Ligand Surfaces,
Proc. Materials Research Soc'y 1992 Spring Meeting Symposium C: Advanced Metallization & Processing for Semiconductor Devices (in press); Calvert et al.,
Top Surface Imaging Using Selective Electroless Metallization of Patterned Monolayer Films,
ACS Symposium Series on Polymers for Microelectronics (invited paper), which are incorporated by reference herein.
These references describe methods and materials for the attachment (by chemisorption) of ultrathin film (UTF) precursor materials (such as organosilanes or organotitanates) to surfaces that either intrinsically possess, or are treated to have, highly reactive polar surface groups. The references also teach patterning the chemisorbed UTF layers with actinic radiation, catalyzing the patterned UTF layers by exposure to either a Pd/Sn colloidal catalyst or a tin-free Pd catalyst, then selectively metallizing by immersion in an electroless plating bath. Omission of the irradiation step leads to a homogeneously metallized, rather than a patterned, surface.
Many surfaces, however, do not intrinsically possess a suitable density of reactive surface groups to carry out a commercially viable chemisorption reaction to attach UTFs. These surfaces include diamond and polymers such as polyethylene (PE) and polyethersulfone (PES). Direct treatment of these substrates with UTF precursors does not lead to a useful degree of surface functionalization. To modify or metallize these surfaces, a different approach is needed.
These surfaces can be rendered amenable to chemisorption reactions by carefully chosen surface oxidation pretreatment. Many methods for oxi
Calvert Jeffrey M.
Peckerar Martin C.
Pehrsson Pehr E.
Barrow Jane
Karasek John J.
Padgett Marianne
The United States of America as represented by the Secretary of
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