MEMS & Semiconductor

MEMS DRIE Bosch Process Etch Lag (ARDE) & Scallop Height Calculator

Model time-multiplexed Bosch etching/passivation cycles, aspect ratio dependent etch lag, and sidewall scalloping for deep silicon microstructures.

Process & CAM Parameters

Etch Step Duration (t_etch in s):

SF6 isotropic chemical/ion etching cycle time.

Passivation Step Duration (t_pass in s):

C4F8 fluorocarbon polymer sidewall passivation time.

Trench Opening Width (W_trench in um):

Target Etch Depth (H_target in um):

Silicon Etch Rate (R_Si in um/min):

Photoresist Mask Selectivity (S_PR : 1):

Engineering Calculations

Aspect Ratio (AR)

15.0:1AR

ARDE Etch Lag

-18.5%

Scallop Wavelength

525nm

Req Photoresist Mask

2.4um

Dynamic CAM Toolpath & Vector Preview

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Engineering Principles & Formulations

Deep Reactive Ion Etching (DRIE) via the pulsed time-multiplexed Bosch process alternates between an aggressive isotropic chemical etching cycle ($ ext{SF}_6$) and a conformal Teflon-like polymer passivation cycle ($ ext{C}_4 ext{F}_8$). This enables vertical silicon structures with extreme aspect ratios ($>30:1$) for MEMS comb-drive actuators, micro-gyroscopes, and through-silicon vias (TSVs).

Aspect Ratio Dependent Etching (ARDE / RIE Lag): Governed by Knudsen gas transport in deep trenches: $R_{ ext{eff}} = R_{ ext{Si}} \cdot (1 - K_{ ext{lag}} \cdot \ln(AR))$. Narrow trenches etch slower than wide open fields.
Sidewall Scallop Wavelength ($\lambda_{ ext{scallop}}$): Calculated as $\lambda = R_{ ext{Si}} \cdot rac{t_{ ext{etch}}}{60}$. Minimizing cycle duration creates ultra-smooth optical mirrors.
Photoresist Mask Thickness: Required mask thickness $T_{ ext{mask}} = rac{H_{ ext{target}}}{S_{ ext{PR}}} imes 1.20$ safety margin.