Reactive Ion Etching: Anisotropic Pattern Transfer

Plasma Etch Controls

Ion anisotropy A 70%

Etch rate Medium

Mask opening width 6 cells

Mask selectivity S 12×

Live readouts

Mixed profile

Etch depth

0.0 nm

Undercut

0.0 nm

Aspect ratio

0.00

Process time

0.0 s

How it works

Reactive-ion etching (RIE) removes a masked substrate by combining two independent attack mechanisms at every exposed surface cell:

R(surface) = R_phys · [direct line-of-sight to the ion source]
           + R_chem · [any exposed face, any direction]

Anisotropy   A = R_phys / (R_phys + R_chem)
Selectivity  S = R_substrate / R_mask

R_phys is directional ion sputtering — it only removes material that has an unobstructed vertical path up through the mask opening, which is why it carves straight, vertical sidewalls. R_chem is isotropic radical etching — it attacks any exposed surface regardless of direction, including material tucked sideways under a mask edge. That sideways attack is undercut: it grows the printed feature wider than the mask opening that defined it.

Ion anisotropy A — at A = 100% the process is purely physical (ion milling): vertical trenches, essentially zero undercut. At A = 0% it is purely chemical (wet-style etching): rounded, isotropic profiles that eat sideways as fast as they go down.
Etch rate — overall reaction speed; scales both R_phys and R_chem together.
Mask opening width — the lithographically defined aperture; combined with etch depth it sets the aspect ratio, a key limit on how deep a narrow feature can be etched before ions can no longer reach the bottom.
Mask selectivity S — how much slower the mask itself erodes compared with the substrate. Low selectivity lets the mask edges recede during the etch, silently widening the pattern — a real precision-control problem in nanofabrication.

The grid is a cellular automaton: each tick, every solid cell with at least one empty neighbor gets an etch probability built from these two terms, sampled independently, exactly mirroring how real RIE profiles evolve one exposed atomic layer at a time.

Photoresist mask Silicon substrate Reactive ions

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