Precise depth control of silicon etching using chlorine atomic layer etching

In this study, the atomic layer etching (ALE) of Si was carried out using Cl(2) adsorption followed by Ar(+) ion beam irradiation with a low energy Ar(+) ion beam generated by an inductively. coupled plasma ion gun. A saturated silicon etch rate due to chlorine ALE could be obtained when the Ar(+) ion acceleration voltage of the ion gun was in the range of 70 to 90 V, as a result of the preferential etching of silicon chloride formed during the chlorine adsorption period by the Ar+ ions while the silicon sputter etch rate remains insignificant. This was attributed to the differences in the silicon-to-silicon and silicon-to-silicon chloride binding energies. The saturated silicon etch rate by ALE was dependent,on the chlorine flow rate, i.e. the surface coverage of chlorine and the Ar(+) ion irradiation time. In this experiment, a silicon etch rate of 1.36 A/cycle, which is a (100) silicon monolayer per cycle, could be obtained by flowing more than 10 sccm chlorine gas followed by bombarding the surface by Ar(+) ions with an acceleration voltage of 70 V for more than 40 seconds. Under this condition, when a 30 nm scale silicon etch profile was examined after 200 cycles, a silicon etch profile with no undercut could be obtained.