Method of calibrating a nanometrology instrument

A method comprising:

• providing a calibration reference comprising a substrate and a plurality of bi-layer stacks on the substrate, the substrate being parallel to the plurality of bi-layer stacks, each bi-layer stack of the plurality of bi-layer stacks comprising a plurality of bi-layer steps, the plurality of bi-layer stacks comprising at least ten bi-layer stacks, each bi-layer step of said plurality of bi-layer steps comprising a run and a riser, said run being at least ten times greater than the riser, at least one bi-layer step of the plurality of bi-layer steps comprising two materials, said at least one bi-layer step of the plurality of bi-layer steps comprising an etch stop layer and a bulk layer, the calibration reference comprising a calibration reference step profile comprising a plurality of predetermined bi-layer stack heights,
• measuring the calibration reference step profile and the predetermined bi-layer stack heights using a topography metrology instrument;
• and
• calibrating the topography metrology instrument based on the measured calibration reference step profile and the measured bi-layer stack heights,
• wherein said measuring the calibration reference step profile and the predetermined bi-layer stack heights using a topography metrology instrument comprises measuring data points corresponding to a number of bi-layers steps,
• wherein said calibrating the topography metrology instrument based on the measured calibration reference step profile and the measured bi-layer stack heights comprises calibrating the topography metrology instrument until a calibration reference fit curve and the measured data points match.