In situ atom-resolved observation of Si (111) 7×7 surface with F radical and Ar ion irradiation simulated atomic layer etching

Ar ions with controlled energy and doses, along with radicals in CF4 plasma, were irradiated separately onto a Si (111) 7 × 7 surface by using a plasma beam reactor. The crystal structure and the chemical bonds on the surface were analyzed by scanning tunneling microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy without air exposure of the samples. The SiF layer formed by F radical irradiation was completely removed by a desorption reaction induced by heating at 600 °C, resulting in an atomically flat surface that maintained the crystal structure. The 7 × 7 structure, which was reconstructed by each irradiation process alone, was not reconstructed because of the synergistic effects of F radicals and Ar ions in the cyclic CF4/Ar plasma used to simulate an atomic layer etching process. The cyclic CF4/Ar plasma process inhibited the reconstruction of the crystal structure by forming a mixture region that included Si, F, and C atoms.