Rocking stages are used to reduce curtaining on FIB prepared cross-sections. The rocking stage tilts the stage backwards and forwards by a few degrees alongside the cross-sectioning surface whilst FIB milling/polishing. This allows the ion beam to intersect the sample at different incidence angles and thus reduce/avoid curtaining that is caused by surface roughness.
Surface topography leads to the ion beam intersecting the sample with different incidence angles. This effect is illustrated on the left. The different sputtering yields for the different incident angles result in different milling speeds. This leads to the vertical stripes along the cross-section, also known as curtaining (illustrated as orange lines). The illustration on the right shows how the rocking stage tilts the sample back and forth, allowing the surface topography to be milled with different incident angles. This reduces/avoids the formation of curtains.The SEM image on the left shows a cut and polished cross-section with curtaining. The actual cross-section is not visible. The SEM image on the right shows the same cross-section when polished using the cross-section. Curtaining can significantly be removed using a rocking stage, making it possible to image the actual cross-section.
