| AVS 54th International Symposium | |
| Nanomanufacturing Topical Conference | Wednesday Sessions |
| Session NM-WeM |
| Session: | Nanomanufacturing for Information Technologies |
| Presenter: | V. Parekh, University of Houston |
| Authors: | V. Parekh, University of Houston A. Ruiz, University of Houston Ch. E, University of Houston P. Ruchhoeft, University of Houston D. Litvinov, University of Houston |
| Correspondent: | Click to Email |
We describe the fabrication of patterned medium substrates consisting of 50nm diameter Co/Pd multilayer pillars in a densely packed array with 100nm pitch using ion beam proximity lithography (IBPL) to pattern a resist followed by argon ion milling to transfer the pattern into the magnetic stack. These pattern medium samples serve as test structures to develop a fundamental understanding of the switching behavior of isolated magnetic islands and as a test-bed for developing next-generation magnetic recording media. In our fabrication approach, substrates are first coated with a Ta buffer layer, followed by deposition of alternating Co (0.3nm) and Pd (0.7nm) layers (repeated 10 times). Hydrogen silsesquioxane, a negative tone, ion sensitive resist, is deposited onto the multilayer structure and patterned using IBPL, in which an energetic helium ion beam irradiates a stencil mask, placed in front of the resist-coated sample, and ions passing through the stencil openings damage the resist and copy, in a single exposure, the entire mask pattern. After developing the resist, the HSQ pillars are transferred into the multilayers by argon ion milling. In developing this process, we have concentrated on the uniformity of the lithographically defined bits to improve the switching field distribution of the magnetic medium. To this end, we have developed stencil masks fabricated from 250nm thick, 1cm2 area, free standing silicon nitride membranes. The blank membranes are coated with palladium, silicon dioxide and resist. Electron beam lithography is used to define 100nm circular openings on a 200nm pitch in the resist, which are then transferred into the membrane using a series of reactive ion etching and ion milling steps. A conformal gold coating allows for further reduction of the mask features without significantly increasing the feature size variation. Measurements using scanning electron microscopy reveal a 3nm standard deviation in the sizes of the mask openings over a 1mm2 area. The standard deviation of the island structures that are formed using this mask have a similar standard deviation in size (4.5nm), indicating that our printing process is primarily limited by our ability to fabricate masks. A six-fold increase in the coercivity of the multilayer samples (from 900Oe for continuous samples to 6kOe for the patterned samples) and a switching field distribution of ~15% in the patterned sample was measured using magneto-optical kerr effect.