Surface modification of magnetic recording substrates to control

Abstract

Nonmagnetic substrate disks used to fabricate magnetic data storage media are surface treated prior to laser texturing, to enhance characteristics of the resulting texturing features and the surface topography provided by the features. In one approach, nickel-phosphorous plated aluminum substrates are maintained in an aqueous silicate solution, preferably sodium metasilicate at about a 5 percent concentration, by weight. An alternative approach involves maintaining the substrates in an aqueous borate solution, for example, sodium tetraborate decahydrate at about 5 grams per liter. In both cases a silicate or borate is deposited onto the substrate, forming an oxidation layer that changes the surface characteristics at and near the substrate surface, more particularly to a depth of 50-60 angstroms beneath the surface. The changes in surface composition include a reduction in the nickel concentration, and an increase in either silicon or boron. As a result, subsequent laser texturing produces features, e.g., rims or nodules, with reduced heights, substantially more uniformity in their heights, and more favorable diameter-to-height ratios. Alternative treatments include etching, followed by oxidation in aqueous oxidizing agents.