The present invention relates generally to imprint lithography and, in particular, to structures and methods for improving imprint resist adhesion to protective carbon overcoats (COC) utilized in patterned magnetic media by introducing nitrogen into the COC to promote covalent bonding between an adhesion layer and the COC.
Imprint lithography is a low cost alternative for patterning nanometer features in the surface of a substrate. Nanoimprint lithography has been aggressively pursued by the magnetic recording industry for patterned media development.
Imprint lithography involves the utilization of an imprint template to pattern a thin film layer, typically a thermoplastic polymeric layer (e.g., resist), that is formed on a substrate. The template includes a molding surface that includes a plurality of features that form a desired topographical pattern. The molding surface of the template is pressed into the thin film layer, utilizing either mechanical or electrostatic force, to form compressed regions that correspond to the patterned features of the template. Thus, when the imprint template is separated from the thin film layer, a negative (or complementary) image of the topographical pattern of the template is transferred to the thin film layer. The patterned thin film layer is then used as a mask to pattern the underlying substrate for further processing.
As is well known, thin film magnetic recording discs and disc drives are conventionally employed for storing large amounts of data in magnetizable form. In conventional hard disc drives, for example, data are stored in terms of bits along tracks that have been defined in a thin film magnetic layer. The data are stored on the tracks by patterning the thin film magnetic layer using, for example, ion bombardment.
In the formation of a conventional thin film magnetic layer for magnetic recording disc applications, a non-magnetic substrate, e.g., a glass substrate, is typically selected. A multilayer magnetic thin film stack is then formed on a surface of the substrate. The magnetic thin film stack can comprise any of a number of well know structures. For example, the magnetic stack may comprise several layers of cobalt-based materials, such as a cobalt-platinum alloy, cobalt-chromium alloy, cobalt-platinum-chromium alloy, cobalt-platinum oxide, cobalt-platinum-chromium oxide, cobalt-platinum-silicon and cobalt-platinum-chromium-silicon. The magnetic stack material may also include additive elements such as B, Ta, Mo, Cu, Nd, Nb, Sm, Ru and Re.
With reference to
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However, formation of the adhesion layer 102 directly on the COC layer 108 fails to provide sufficient resist adhesion. The low surface energy of the COC layer 108 makes it less reactive to form covalent bonds with the carboxylic functional groups of the adhesion layer 102, resulting in poor adhesion when the imprint template 104 is removed from the resist 106. This poor adhesion results in resist 106 peeling off of the substrate 100 upon separation of the imprint template 104 from the resist 106, as schematically illustrated in
In view of the above, there exists a need for improved imprint lithography techniques for maintaining adhesion between the resist and the underlying substrate upon imprint template removal when a protective COC layer is formed on the substrate. These techniques are useful in nanoimprint lithography in the fabrication of bit patterned media “BPM”).
In accordance with the present invention, nitrogen is introduced into an upper surface region of a protective carbon overcoat (COC) layer formed on a substrate in a nanoimprint lithography process before application of an adhesion layer to the COC/substrate.
An embodiment of an imprint lithography method in accordance with the present invention comprises introducing nitrogen into an upper surface region of a carbon overcoat (COC) layer, forming an adhesion layer on the nitrogenated COC layer, forming resist on the adhesion layer, contacting the resist with an imprint template having patterned features formed therein such that the resist fills the patterned features of the imprint template, and separating the imprint template from the resist such that a negative image of the patterned features is formed in the resist.
An embodiment of an imprint structure in accordance with the present invention comprises a substrate, a carbon overcoat (COC) layer formed on the substrate, the COC layer having a nitrogenated upper surface region formed therein, an adhesion layer formed on the COC layer, and resist formed on the adhesion layer.
Additional features and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of the invention, wherein embodiments are shown and described by way of illustration. As will be realized by those skilled in the art, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from scope of the present invention. Accordingly, the drawings and description provided herein should be regarded as illustrative, not restrictive.
As shown in the
As an alternate to N2 plasma treatment as described above, N2 gas flow may be introduced during the deposition of the COC layer to provide a nitrogenated COC layer. However, while the nitrogen content of the COC layer is uniform when this approach is utilized, resist adhesion is improved less with this approach than with N2 plasma treatment, wherein a thin N2-rich layer is formed at the surface of the COC layer.
Another alternate approach to introducing nitrogen into the COC layer is nitrogen ion implantation. However, it is difficult to control the nitrogen implantation depth in a thin COC layer of the type utilized in the manufacture of magnetic media. Additionally, if not properly controlled, the tail of the nitrogen implantation profile could extend through the COC layer and into the magnetic layer of the media, resulting in magnetic property degradation.
As shown in
Resist 206 is then formed on the upper surface of the adhesion layer 204 in the conventional manner, e.g. by spin coating or by drop dispensing, resulting in the structure shown in
As shown in
The present invention will be used in some or all of the lithography processes used the fabrication of bit-patterned media (“BPM”). In particular, the present invention has use in the patterning of the magnetic media into the islands or bits that are associated with BPM. The characterization and specifications for BPM, as well as methods of manufacture, are known by the industry. See, e.g., Neil Robertson, “Magnetic Data Storage with Patterned Media,” presented May 2009 at the Nanomanufacturing Summitt 2009, and available at www.internano.org/ocs/index.php/NMS/NMS2009/paper. The manufacturing techniques for BPM are also reported in this publication, as well as in Rachid Sbiaa and Seidikkurippu N. Piramanayagam, “Patterned Media Towards Nano-Bit magnetic Recording: Fabrication and Challenges,” Recent Patents on Nanotechnology 2007, 1, 29-40. The relevant portions of these references are herein incorporated by reference, and if necessary, Applicants reserve the right to incorporate the text of some or all of these publications.
Since BPM has smaller and denser features than previously extant in other types of magnetic media, and since the commercial production throughput rates for BPM will be more demanding than those for other types of media fabrication, the present invention provides the ability for improved use of imprint lithography in BPM manufacture, while addressing overall BPM product and process market specifications.
For certain, current imprint lithography processes, we are presently unable to effectively remove the organic residues left behind by the lithography resists without sacrificing the nitrogenated COC layer. So, processing subsequent to the creation and/or use of the imprints using the methods of the claimed method, involves removal of the nitrogenated COC containing organic residues from the magnetic media with plasma etching of the carbon over coat and redeposition of a fresh layer of COC.
It should be understood that the particular embodiments of the invention described in this application have been provided as non-limiting examples and that other modifications and variations may occur to those skilled in the art without departing from the scope of the invention as expressed in the appended claims and their equivalents.