Low damage ultra-low-k patterning using a high boiling point organic (HBPO) combined with NF3

Abstract

The plasma etching of a k = 2.3 periodic mesoporous ultra-low-k dielectric is studied, using a new gas mixture made of a high boiling point organic (HBPO) reagent and NF3. By decreasing the wafer temperature below 10 °C, the onset of micro-capillary condensation is observed, inducing pore wall passivation (∼10 °C < T < ∼ −20 °C, refractive index between 1.27 and 1.38) then complete pore filling (T < −20 °C, refractive index ∼1.38). The HBPO condensed phase is found to be stable for more than one minute for temperatures below −30 °C. The patterning capabilities of the discharge are studied on a 45 nm half pitch vehicle, leading to plasma etch conditions giving good morphological profiles and reduced sidewall damage. Due to HBPO condensation, the pristine carbon content of the film is maintained, preventing any drift in k-value. The absence of damage also prevents significant modifications of the mechanical properties of the ultra-porous low-k material. The present work shows that electrically and mechanically safe low-k etching can be achieved with an NF3/HBPO plasma, around −30 °C.