Etching & depositionMVP
Etch selectivity
The ratio of the target material's etch rate to the mask or underlayer's etch rate.
Inputs
Result
Enter values and calculate to see the result.
Interpretation
Enter the target and mask (or underlayer) etch rates, in the same units.
Formula
S = target etch rate / mask etch rate
Dimensionless ratio (same rate units).
Variables
| Symbol | Variable | Unit |
|---|---|---|
| S | Selectivity | dimensionless |
| target rate | Target material etch rate | m/s |
| mask rate | Mask/underlayer etch rate | m/s |
Assumptions & validity
This tool assumes:
- Both rates measured under the same process conditions and units.
- No universal 'good' value — required selectivity depends on the layer and stack.
Worked example
target = 300 nm/min, mask = 15 nm/min.
S = 300 / 15 = 20 (i.e. 20:1)