Nitride etching with hydrofluorocarbons. II. Evaluation of C4H9F for tight pitch Si3N4 patterning applications
A novel etch chemistry, C4H9F was evaluated for highly selective patterning of SiN using both organic and SiOx masks for line/space and cylindrical geometries. Patterning of 80 nm of SiN using 65 nm of the organic planarization layer (OPL) mask with a C4H9F:O2:CF4 admixture yielded line edge roughness (LER) and line width roughness (LWR) values of 1.9 and 2.8 nm on sub-25 nm critical dimension (CD) SiN lines at 50 nm pitch, with >50 nm mask retention up to 40% overetch values. The LER and LWR values were 60% and 66% lower than features patterned using a CF4:CHF3 admixture, which also exhibited complete OPL mask loss and nitride erosion of 27 nm even at the endpointed etch condition. Using 20 nm of SiOx as a mask and removing CF4 from the chemistry admixture, LER and LWR values of 2.7 and 3.3 nm were achieved with nearly full SiOx retention for features of identical dimensions. At smaller mask pitches (21 and 24 nm) formed by directed self-assembly of high-χ block copolymers, the highly selective nature of C4H9F to organic masks facilitated SiN pattern transfer where CF4 based admixtures failed, achieving line CDs of ∼12 nm with LWR and LER of 1.6 and 2.2 nm. Applied to alternate geometry, hole patterning in SiN at ∼30 nm CD and 60 nm pitch was demonstrated. A subsequent image reversal process yielded pillars by filling the hole pattern with OPL and etching back the surrounding SiN layer, reaffirming the extremely high selectivity of C4H9F to organic masks.