OFHC copper substrates for niobium sputtering: comparison of chemical etching recipes

Smoothening of the down-skin regions of copper components produced via Laser Powder Bed Fusion technology

“…The non-homogeneous behavior of the chemical polishing might be due to different grain orientation of the copper surface and/or the microscopic structures (pores or microscopic asperities) produced by AM. Literature [20,22,29] confirms the pitting produced by the treatment also on bulk copper samples; this could generate a higher surface roughness compared to the EP-treated surfaces. Samples 1 and 3 look similar, except for some dark areas on sample 1.…”

“…These darker regions look like oxidized copper. Recent works [22] revealed that dark brown color develops on the surface of the substrate when acid is completely consumed and oxide formation starts; this happens when the final cleaning stage is not performed properly and a small amount of acid remains on the surface, but further investigations need to be carried out to understand if these spots and their distribution are caused by SUBU5, by the prior smoothening treatments (conventional mass-finishing treatment + chemically assisted mass-finishing treatment) or by the manufacturing method. The first two hypotheses seem to be the most realistic, considering that sample 3 does not show any spots.…”

“…This treatment is usually done on traditionally produced copper cavities to clean and smooth the inner surface [19]. SUBU5 solution contains sulfamidic acid (H 3 NO 3 S -99.0%, 5 g/L), hydrogen peroxide (H 2 O 2 ; 30%, 50 mL/L), n-butanol (C 4 H 10 O -99.9%, 50 mL/L), and ammonium citrate (C 6 H 11 NO 7 -99.0%, 1 g/L) [19][20][21][22]. The treatment time can vary depending on the final requirements since the smoothening rate depends on the sample surface/solution volume ratio [20,21].…”

“…Before the treatment, the substrate is cleaned in the ultrasound bath with GP17.40 commercial soap. After SUBU5 polishing, the sample is placed into a diluted solution of sulfamidic acid (~ 5 g/L) for passivation [19,21,22]. The polishing technique removes up to some microns of material; usually, the entity of the material removed depends on the method used for shaping the copper to create a cavity [19].…”

A closed-circulation system for chemical polishing of the 1.3-GHz single-cell copper cavity substrate for niobium sputtering

“…A damaged layer of a few tens to a few hundred microns shall be removed from the copper substrate to obtain a clean and smooth surface before sputtering. Mechanical polishing and chemical etching are often adopted [9,10]. A mixed solution namely "SUBU" has been previously developed at CERN containing sulfamic acid, ammonium citrate, hydrogen peroxide, and n-butanol [11].…”