Masaya Takeuchi

Abstract We aimed to improve the detection sensitivity for liquid measurement by developing an ultrathin photoelectron transmission window (SiNx membrane) for liquid cells via X-ray photoelectron spectroscopy or X-ray photoelectron emission microscopy at an ultrahigh vacuum. The membrane using gas-cluster ion beams (GCIB) was thinned, and its burst pressure was compared with those of membranes thinned with atomic 400 eV Ar⁺ ions. The SiNx membranes thinned by GCIB had approximately 2.5 times higher burst pressure than Ar⁺ ions. In addition, the improved sensitivity of the characteristic X-ray from liquid water induced by low-energy electrons was investigated. With the use of the 4.5 nm-thick SiNx membrane etched by GCIB, the X-ray intensity became 1.6 times higher than those of the 11 nm-thick pristine membrane at the electron beam (EB) energy of 1.5 keV. This result showed a good agreement with Monte Carlo simulation results of the EB-induced X-ray emission from liquid water beneath the SiNx membrane.

Abstract The atomic layer etching (ALE) of silicon nitride (SiN _x ) film was demonstrated using an oxygen gas cluster ion beam (O₂-GCIB) with acetylacetone (Hacac) as the adsorption gas. A GCIB is a beam of aggregates of several thousand atoms, and it enables high energy density irradiation with little damage. In this study, we characterized the ALE to reveal the etching mechanism. The XPS results indicated the following etching process: (i) O₂-GCIB irradiation oxidizes the surface of SiN _x film; (ii) the oxynitride layer reacts with Hacac vapor; (iii) the reaction layer is removed by the GCIB. The ALE can be executed by the sequential repetition of the processes (i) to (iii). This technique enables highly accurate control of thickness of SiN _x film with little irradiation damage.