Focused Ion Beam Milling: Sidewall Angle & Redeposition

Beam Setup

Beam energy 20 keV

Beam current / dose 2.0 pA

Scan pattern

Redeposition of sputtered atoms

Live Readouts

Milled volume

0 ×10³ nm³

Sputter yield here

0.00 at/ion

Sidewall taper angle

0.0°

How it works

A focused Ga⁺ beam is rastered over the substrate; every ion impact knocks a few surface atoms loose (sputtering). The number of atoms ejected per ion — the sputter yield — depends strongly on the local angle θ between the beam and the surface normal, following the empirical Yamamura form:

Y(θ) = Y₀ · cos(θ)⁻ᶠ · exp[ −Σ·(cos(θ)⁻¹ − 1) ]
f ≈ 1.7,  Σ ≈ 1.0   (typical for Ga⁺ on Si/metals)

At normal incidence (θ=0) the yield is just Y₀. As θ rises the yield first increases — ions deposit their energy closer to the surface — peaking near 60–75°, then collapses toward grazing incidence as ions increasingly reflect off the surface instead of sputtering it.

This simulator computes θ at every grid cell from the local slope of the milled surface itself, each frame, so the feedback is real: as a trench floor deepens, its walls tilt and present a higher θ to the vertical beam than the floor does — walls mill faster than floors, which is exactly why real FIB-cut features end up with curved, tapered sidewalls (V-grooves) rather than perfect vertical walls, and why deep structures need staircase-compensated scanning.

Beam energy — scales the base yield Y₀ (higher energy, more atoms per ion, up to the point of ion channeling losses).
Beam current / dose — sets how much material is removed per unit dwell time (ions delivered per second).
Redeposition — a fraction of sputtered atoms don't escape; they land back on nearby low-yield (flatter) surfaces, building the debris ridges seen around real milled features. Toggle it off to see the idealised, redeposition-free profile.

Ga⁺ ion beam Substrate (unmilled) Redeposited material

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