Objects of type 'COME etching monitor' (managed in the SCOUT list of distributions) compute the reflectance of a layer stack vs. time while the complete stack is reduced by an etching process. COME stands for Charts for Optical Monitoring of Etching. These objects are very similar to the previously discussed objects of type 'Opt. growth mon. (time)'. In fact, COME objects just do the reverse, starting the computation for the complete stack and finishing at the blank substrate.
Etching rates
To compute charts displaying the reflectivity of a stack vs. time during etching the etching rate for each material in the stack must be known. Like in the case of deposition rates SCOUT stores etching rates of materials in a text file that must be in the same directory as the program file (scout_98.exe). The file holding etching rate information is called etch_rates.txt. As before, you do not have to look at this file but you can wait until SCOUT asks you to provide etching rate information for a certain material.
Example
The COME result for the anti-reflection coating discussed above is this:
The following etch rates (based on pure imagination) have been used:
Material Etch rate [nm/s]
SiO2 0.5
ZrO2 1.2
TiO2 0.1