Reduction of Reactive-Ion Etching-Induced Ge Surface Roughness by SF₆/CF₄ Cyclic Etching for Ge Fin Fabrication

An SF₆/CF₄ cyclic reactive-ion etching (RIE) method is proposed to suppress the surface roughness and to optimize the morphology of Ge fin, aiming at the fabrication of superior Ge FinFETs for future CMOS technologies. The surface roughness of the Ge after RIE can be sufficiently reduced by introducing SF₆-O₂ etching steps into the CF₄-O₂ etching process, while maintaining a relatively large ratio of vertical etching over horizontal etching of the Ge. As a result, an optimized rms roughness of 0.9 nm is achieved for Ge surfaces after the SF₆/CF₄ cyclic etching with a ratio of greater than four for vertical etching over horizontal etching of the Ge, by using a proportion of 60% for SF₆-O₂ etching steps.