Patterning of a hard disk can be performed using the Jet and Flash™ Imprint Lithography (J-FIL™) process. Conventional disk fabrication flow includes cleaning of the substrate, sputter of metal layers, sputter of the carbon over coat (CoC), followed by dip coating to add the lubricant, burnishing and finally fly testing. With the advent of patterned media several new steps will be required including post sputter disk wash, vapor deposition of an adhesion promoter, imprint patterning, pattern transfer, post etch cleaning followed by planarization. After planarization the anti corrosion CoC layer is applied before lubrication, burnish and fly testing as is typical for conventional media manufacturing.
Schematic of patterned media manufacturing flow. The manufacturing flow without patterned media does not have any lithography steps today. Patterning of media by J-FIL requires clean disks, coated with an adhesion promoter prior to imprint. After imprint the disks will be etched to open the metal pattern for ion milling. After the data tracks are defined by ion milling the substrate requires strip and cleaning followed by planarization to fill the etched areas with a dielectric material. After planarization the patterned disk will be subjected to the common process steps of unpatterned media, namely sputter coating of the anti corrsion carbon over coat, lubercation, burnishing and flytesting. Patterning of the media results in an addition of roughly six new to media manufacturing steps.
New to media manufacturing processes beginning with adhesion layer deposition using a vapor deposition process require new equipment sets, materials and processes. For example the vapor deposited adhesion layer called ValMat is put on using a simple chemical vapor deposition process so that a layer thickness of ~ 1nm with a uniformity of < 1nm is achieved.
Candela scan of a disk coated using a simple CVD process and ValMat. The thickness is ~1nm with uniformity of < 1nm, 3σ.
Vapor deposition tools such as Intevac’s Lithoprime tool can be used to cleanly and uniformly deposit Valmat to the disk surface.
ValMat is low cost, low volume usage material as it is applied via vapor deposition. The adhesion layer is critical for high adhesion of the imprint material to the substrate enabling thousands of imprints to be made from the single template. It is important that the vapor deposition process be clean and not add particles to the disk surface which could results in defects in the imprint process.
Figure One: Resist adhesion to Tantalum by adhesion layer type
Figure One reflects the adhesion of Molecular Imprints' resists to Tantalum (Ta) using a variety of adhesion promoters. DUV30J is a typical bottom anti-reflection coating with good adhesion to most substrates. This material enabled hundreds of imprints with a single template. ValMat and Transpin enabled thousands of imprints with a single template and provided good adhesion to most substrates.
After the vapor adhesion layer is deposited an imprint is performed, the J-FIL process is implemented across the active surface of the disk substrate. The template is lowered until contact is made with the liquid imprint resist which is then photo-polymerized via ultraviolet illumination. The template is then separated from the disk, which now contains a relief image corresponding to the template pattern. Following the imprint step, the resist pattern must be transferred into the underlying magnetic material to define the magnetic switching volumes. This can be accomplished by a number of processes, usually including a descum step to open the media surface so the space between the data tracks can be exposed for etching using either ion milling and ion irradiation. It is necessary to include a reactive ion etching step to remove the thin residual layer that forms at the base of the imprinted resist pattern.
Example of lines etched into thermal oxide. The etch process to for these lines in oxide is a convnetional RIE process using CF4/CHF3.
The inkjet-based IntelliJet™ Drop Pattern Generator approach to dispensing imprint material provides several significant advantages over a traditional spin-coating approach. First, it is a straightforward and fast method for depositing material on surfaces of arbitrary shape, such as the annular disk-type substrates used in the hard drive industry. The process is inherently cleaner than spin-coating methods, a separate resist coat tool is not required as the resist jetting system is part of the NuTera HD7000 imprint tool, and edge bead removal at the OD and ID of the front and backside of the disk is not required. Elimination of expensive two-sided spin coating and bake systems provides a compelling cost advantage. IntelliJet technology also allows the imprint tool to selectively place imprint resist to match the local pattern density of the template enabling excellent control of residual layer versus pattern density which is not accessible for spin coat based imprint approaches unless special features are patterned into the template to manage the volume variation in the pattern. Since Bit Patterned Media (BPM) patterns use nearly 100% of the available disk real estate this approach is not considered an option for BPM template modification. The J-FIL imprint material is dispensed in picoliter drops.
