Cryogenic etching of SiO<sub> <i>x</i> </sub>F<sub> <i>y</i> </sub> and SiO<sub>2</sub> in SF<sub>6</sub>/H<sub>2</sub> plasma
Rémi Dussart, Thomas Tillocher, Loı̈c Becerra, Philippe Lefaucheux, Lawrence Overzet
Abstract
Abstract The etching of the SiO x F y passivation layer during the etch step of the STiGer process was investigated to better understand and optimize the process. First: a 120 nm thick SiO x F y layer is grown on silicon using SiF 4 /O 2 plasma at low substrate temperature (−100 °C). Then, that 120 nm thick SiO x F y layer is etched using an SF 6 plasma without substrate bias and at different temperatures. The SiO x F y etch rate decreases as the substrate temperature is lowered. H 2 addition to the SF 6 plasma is also investigated and causes the opposite effect. We have also investigated SiO 2 etching at low temperatures using SF 6 /H 2 plasma. The formation of HF on a cooled SiO 2 surface combined with high energy ion bombardment can produce an etch rate as high as 1 μm min −1 at −130 °C. The results are in good agreement with recent experiments involving HF/H 2 O plasmas to deep-etch alternately stacked SiO 2 and Si 3 N 4 thin layers for 3D-NAND technology.