High-Aspect-Ratio TSiCV Etch Development in 4H-SiC for RF Interposer Applications

This work focused on the inductively coupled plasma (ICP) etching of$30 \mu \mathrm{m}$diameter,$90 \mu \mathrm{m}$deep ThroughSiC Vias (TSVs) in$200 \text{mm} 4 \mathrm{H}$monocrystalline SiC wafers, utilizing a$12 \mu \mathrm{m}$electroplated Nickel (Ni) hard mask. Impact of the addition of$\mathrm{O}_{2}$flow and chamber pressure on the process has been characterized to achieve SiC Via profile. Results confirmed that the presence of$\mathrm{O}_{2}$is key process knob for achieving clean surfaces by reacting with carbon byproducts to suppress “grass” formation. Furthermore, exploring a lower chamber pressure regime to enhance bombardment and improved etch depth, achieving a 25% higher etch rate compared to a higherpressure regime. Similar to TSV, SiC via formation also observed Aspect ratio dependent etching (ARDE) i. e, etch rate of SiC via etch rate declined from$0.87 \mu \mathrm{m}/\min$to$0.62 \mu \mathrm{m}/\min$as the via depth increases from$52.1 \mu \mathrm{m}$to$111 \mu \mathrm{m}$with the reduction of sidewall angle from 87.8° to 84.0°. Unlike Si etching, ARDE effect and profile angle strongly influenced by Ni redeposition within SiC via.