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Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-19

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In standard applications of material removal by ion milling, the substrate is rotating at a constant rotational speed during the milling to help achieve best uniformity of material removal across the substrate. When the process is used during the later stages of a wafer build, for example in the case of the ion milling operation during the write element build for a magnetic recording head structure, surface topography will cause localized variations in the milling removal rate due to shadowing effects. For the case where there is normal incidence for the ion beam, divergence within the beam results in some shadowing of the off-normal components of the ion beam. The shadowing effect is even larger when the ion beam is intentionally set at an off-normal angle of incidence. One example commonly observed in fabrication of magnetic recording head wafers is the NiFe plating seedlayer extension, or “foot”, which can be left at the thick write head pole track edge. Any ion milling process capable of reducing this shadowing effect in critical regions of the magnetic head would be desirable. An improvement to the ion milling removal process, where topography is present, is the use of variable rotational speed of the substrate within a complete 360 degree revolution while keeping all other ion milling parameters constant. The angular speed of the substrate as a function of its angular position would be predetermined by the location of critical features on the wafer surface. The rotational speed is set at a higher rate when a critical subject region is in the shadow of an adjacent raised feature. Conversely, the rate is lower when this same region is fully exposed to the ion beam. In the previously mentioned example of a NiFe seedlayer foot, a total removal of the foot in the sensitive region is achieved with less total ion milling time when using a variable angular speed process than by using the usual uniform rotational speed process. A second variation of this process improvement is to vary the milling angle as a function of the rotational angle position of the substrate. This produces a similar effect of variable shadowing effects at different orientations of the substrate. 1