Method and apparatus for anisotropic etching

A method of treating a substrate material or film present on the material surface comprising repeatedly performing an etching process cycle, wherein each etching process cycle increases a depth of an etched feature in the material or film, and wherein each etching process cycle includes performing the following sequential steps:

• (a) etching the material or film to increase the depth of the etched feature;
• (b) depositing or forming a passivation layer on the surfaces of the etched feature;
• and
• (c) partially and selectively removing the passivation layer from the surfaces of the etched feature in order that the etching of subsequent etching process cycles proceeds in a direction substantially perpendicular to the material or film surface,
• wherein at least one of steps (a) or (b) is performed in the absence of a plasma, and wherein step (c) of each cycle is performed separately from step (a) of each next cycle.