Paper PS-ThP20
Atomic Layer Etching of SiO₂ Using Self-Limited Fluorocarbon Films

Thursday, October 22, 2015, 6:00 pm, Room Hall 3

Atomic Layer Etching (ALEt) with monolayer accuracy is a critical requirement for advancing nanoscience and nanotechnology. Current plasma etching techniques do not have the level of control or damage-free nature that is needed for patterning delicate sub-10 nm structures with uniform etching rates and higher selectivities. Here we present beam studies of ALEt of SiO₂. Substrates consisting of thin layers of SiO₂ on Si are placed in an ultrahigh vacuum (UHV) chamber, cleaned with an oxygen plasma beam, and then exposed first to a beam of species effusing from a C₄F₈ plasma, followed by bombardment by an Ar⁺ beam. The C₄F₈ plasma beam deposits a fluorocarbon (FC) film and the Ar⁺ beam removes the film along with a small amount of SiO₂. The process is then repeated. Multiple times between each step, the sample is moved under vacuum to another UHV chamber equipped with x-ray photoelectron spectroscopy (XPS). Changes in FC film thickness and composition are measured as a function of exposure time to the C₄F₈ plasma beam. Similarly, changes are measured in the FC film and SiO₂ film thickness and composition as a function of Ar⁺ beam exposure time. The FC film first deposits rapidly, then nearly saturates at a thickness of 0.8 nm and then continues to grow at a much slower steady rate. Stopping at this saturation FC film thickness and exposing the sample to a ~120 eV Ar⁺ beam removes 0.08 nm of SiO₂, concomitant with the loss of CF₃ and CF₂ moities (but not of C and F), and then continues to sputter SiO₂ at a much slower rate. The 7:1 F:C ratio observed after 0.8 nm FC film deposition is much higher than the F:C ratio computed from a peak fit of the C(1s) high resolution spectrum (1.3:1), indicating that most of the F is bound in the SiO₂ film. Further details and mechanisms for the ALEt process will be presented.