The fabrication of 3D high aspect ratio structures with positively sloped profiles has found extensive
applications both in the front-end and in the back-end semiconductor manufacturing. Often, high etch rates
are required and plasma etching processes with F-based chemistries need to be employed. However, plasma
etching of silicon in F-based chemistries generally results in so-called "cusping" due to its isotropic nature.
Of particular interest are the etch profiles with slope angles in the range of 50-80o and without "cusping" at
the top portion of etched structures. For 3D packaging applications, for example, even small cusping could
degrade the step-coverage of diffusion barrier layer and metal seed layer and cause void formation in
subsequent metal filling processes.
At Oerlikon USA Inc., a proprietary process scheme has been developed to etch deep and positively sloped
silicon structures (vias, trenches, etc.) at high etch rates while eliminating cusping with precise profile
control. The new process scheme employs main plasma etch steps using gas mixtures and deposition pulse
steps. And the deposition pulses intermittently punctuate the main etch steps. Using standard gases, such as
SF6 and C4F8, sloped Si trenches with slope angle of ~60o are etched in both 6" and 8" wafers, at etch rates
of ~7.0 (micron)m/min. Etch selectivity to photoresist mask materials exceeds 100:1. The process scheme and
underlying mechanism will be presented in this work.