In a certain process, it is desired that the pitch of metal lines be equal to or less than 1.0 µm (the pitch equals one metal linewidth plus one spacing between metal lines, measured at top of features).

Assume that the metal linewidth and spacing are equal (that is, 0.5 µm each). The height of such structures is also 0.5 µm, and the minimum lithographic dimension is 0.25 µm.

a. What minimum degree of anisotropy is needed in an etch process in order to produce such a structure?

b. What minimum pitch could be obtained for such a structure with wer etching? (Again with minimum lithograph dimension of 0.25 µm, thickness of 0.5 µm, and equal metal width and spacing.)