Silicon was etched with the Bosch process using C4F8 and C4F6 plasmas in the deposition step to show a feasibility of the use of UFC plasmas in the Bosch process. The use of C4F8 and C4F6 plasmas resulted in different characteristics of fluorocarbon films and radicals, affecting the etch profiles. It was shown that the use of a C4F6 plasma in the deposition step of the Bosch process produced thicker and more strongly bonded fluorocarbon films, compared to a C4F8 plasma. It was because more CF2 radicals and lower F/C ratio fluorocarbon films were generated in C4F6 plasmas than those in C4F8 plasmas, confirmed by OES and XPS measurements. By changing only the duration of the deposition step under the same process conditions, highly anisotropic deep etching of silicon was successfully achieved using both SF6/C4F8 and SF6/C4F6 plasmas in the etching and/deposition steps of the Bosch process. (C) 2008 American Vacuum Society.