Etch Selectivity Calculator
Divide the film etch rate by the mask etch rate to get the etch selectivity.
Description
Calculate target-film-to-mask etch selectivity from two removal rates measured in the same units.
Etch selectivity states how many units of target film are removed for each unit of mask material removed. The numerator and denominator convention matters: this calculator uses target film rate divided by mask rate.
When to use Etch Selectivity Calculator
- Compare candidate masks or stop layers for an etch recipe
- Estimate mask consumption from a measured film removal
- Report a dimensionless selectivity from paired rate measurements
How the calculation works
Both rates use nm/min, so their units cancel. A result of 50 means the target film removes 50 times as quickly as the mask under the paired measurement conditions.
film-to-mask selectivity = film etch rate / mask etch rate Interpreting the result
Zero film rate gives zero selectivity. Mask rate must be greater than zero because a zero denominator would imply an unbounded or unresolved ratio rather than a finite measurement.
Assumptions and limitations
- The two rates should come from comparable process conditions and measurement definitions.
- A very small measured mask loss can make the ratio highly sensitive to measurement uncertainty.
- Selectivity alone does not describe anisotropy, sidewall profile, residue, roughness, or device damage.