The SOI planar photonic crystal fabrication: patterning of Cr using Cl2/O2 plasma etching

RIE-plasma etching of sub-micron structures in 150-200-nm thick Cr layers deposited on 4-inch SiO2/Si/SiO2 wafers was investigated as a function of the gas composition, RF power, and resist type. An optimal recipe is obtained yielding a Cr etching rate of about 7 nm/min and a ratio of the resist to the Cr etching rates of about 2 in case of etching the sub-micron structures in Cr with a ZEP 520 resist mask. SEM investigations show nearly vertical sidewalls of features etched in Cr layers with a lateral size ranging from 0.3 to 0.5 μm.