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.

Abstract Surface-activated bonding (SAB) of Cu by gas cluster ion beam (GCIB) irradiation with acetic acid vapor was studied. GCIB irradiation realizes surface smoothing and surface reaction enhancement without severe damage. Therefore, it is promising for SAB. In this study, acetic acid vapor was introduced during Ar-GCIB irradiation to assist the removal of surface oxides on the Cu surface. XPS results showed that Cu(OH)₂ was effectively removed by reaction with adsorbed acetic acid, and there was no residue by acetic acid adsorption. In addition, surface roughness decreased by Ar-GCIB irradiation with acetic acid because of the preferential removal of protrusion. Preliminary bonding experiments showed an increase of Cu–Cu bond strength by Ar-GCIB irradiation with acetic acid vapor.