Impact of Ions and Radicals on Etch Selectivity and Fluorocarbon Polymerization in the Selective Dry Etching of Si0.7Ge0.3

Abstract

Selective etching of Si0.7Ge0.3 was investigated in CF4 inductively coupled plasma using an ion-screening approach to decouple ion and radical contributions. Without ion screening, fluorocarbon polymer accumulation reduced etch selectivity, whereas ion screening suppressed polymer deposition and produced smoother surfaces with higher selectivity. Plasma simulations revealed that polymer deposition is governed by the balance between polymer-forming radicals (CF2·, CF·) and polymer-etching radicals (F·). Ion screening reduced CFx+ ion fluxes by 60%–85% while leaving radical fluxes nearly unchanged. Pressure-, power-, and geometry-dependent etch-rate and selectivity trends were analyzed using simulated F· radical and F+ ion fluxes. Under optimized ion-screened conditions, polymer deposition was minimized, and Si0.7Ge0.3/Si selectivity reached 30:1 in multilayer stacks.