Influence of pulsed bias frequency on the etching of magnetic tunneling junction materials

• The effect of different bias frequencies during the etching of nanoscale masked MTJ stack by rf pulse biasing was investigated.
• For highly anisotropic etch profiles of magnetic materials, the lower rf pulse bias frequency is proposed.
• The lower rf pulse bias frequency also decreased the residue remaining on the sidewall of the etched MTJ features.
• The improvements obtained are related to the higher sputter yield of MTJ materials due to the wider ion energy distribution at the lower frequency.

The effect of different bias frequencies during the etching of magnetic tunneling junction materials in an inductively coupled plasma with rf pulse biasing (50% duty percentage) on etch characteristics was investigated. The decrease of rf bias frequency from 13.56 MHz to 400 kHz while keeping the same average dc bias voltage at −300 V increased not only the etch rates of MTJ related materials but also the etch selectivities. We observe improved etch characteristics of CoFeB and CoPt, and also improved etch profiles of CoPt, CoFeB and MTJ (CoPt/MgO/CoFeB) masked with nanoscale W(100 nm)/Ti(20 nm)/Ru(5 nm) at lower bias frequencies. The observed improvements are attributed to the higher sputter yields due to the wider ion energy distribution (with increase high energy component) for the metal carbonyl related compounds formed during the etching of MTJ materials with CO/NH3 etchant gas.