Cyclic etching of silicon oxide using NF3/H-2 remote plasma and NH3 gas flow

Selective isotropic cyclic dry etching of silicon oxide (SiO2) was investigated using a three-step cyclic process composed of hydrogen fluoride (HF) adsorption by NF3/H-2 remote plasma and reaction with NH3 gas flow to form ammonium fluorosilicate ((NH4)(2)SiF6), and desorption by heating. The variation of the ratio of NF3:H-2 (2:1 to 1:3) and adsorption time (10-180 s) showed the highest etch selectivity of SiO2 over Si3N4 at 1:2 ratio of NF3:H-2 and with the adsorption time of 20 s. The etch selectivity higher than 40 was observed with 20 s of adsorption time with a 1:2 ratio of NF3:H-2 remote plasma and the total etch depth was linearly increased with the increase of cycles with the SiO2 EPC of similar to 7.5 nm/cycle.