Substrate alignment through detection of rotating timing pattern

Abstract

Apparatus and method for aligning a rotatable substrate. In some embodiments, a circumferentially extending timing pattern is formed on a substrate. The timing pattern nominally extends about a center point of the substrate at a selected radius. The substrate is mounted to a support mechanism which rotates the substrate about a central axis. Due to mechanical tolerances, the central axis will be offset from the center point of the substrate as a result of an alignment error during the mounting of the substrate. The offset between the support mechanism central axis and the center point of the substrate is determined using a detector that detects two opposing cross-over transitions of the timing pattern during each revolution of the substrate. A feature may be written to the substrate by positioning a write element with respect to the substrate responsive to the detected offset.