Noriaki Toyoda

Abstract We would like to improve detection sensitivity by making photoelectron transmission window (SiNx membrane) of liquid cell ultra-thin for liquid measurement using XPS or X-ray PEEM at UHV. In this study, thinning of the membrane using gas cluster ion beams (GCIB) was demonstrated and the burst pressure was compared with those thinned with atomic 400 eV Ar+ ions. It was shown that SiNx membranes thinned by GCIB was 2.5 times higher burst pressure than the Ar+ ions. In addition, improvement of sensitivity of characteristic X-ray from liquid-water induced by low-energy electrons was investigated. By using 4.5 nm thick SiNx membrane etched by GCIB, the X-ray intensity became 1.6 times higher than those from 11 nm thick pristine membrane at electron beam energy of 1.5 keV. This result showed good agreement with Monte Carlo simulation results of the electron-beam-induced X-ray emission from liquid-water beneath SiNx membrane.

Abstract Atomic layer etching (ALE) of silicon nitride film (SiNx) was demonstrated using oxygen gas cluster ion beam (O2-GCIB) with acetylacetone (Hacac) as adsorption gas. GCIB is a beam of aggregates of several thousand atoms, enabling low damage and high energy density irradiation. In this study, we performed the characterization of the ALE, and revealed the etching mechanism. XPS results indicated the following etching process. (i) O2-GCIB irradiation oxidizes the surface of SiNx film, (ii) the oxide layer reacts with Hacac vapor, and (iii) the reaction layer is removed by the GCIB. The ALE can be executed by sequential repetition of the processes (i)~(iii). This technique enables highly accurate control of SiNx film thickness with low 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.