Sn thin film deposition using a vacuum arc plasma source with a refractory anode

A hot refractory anode vacuum arc (HRAVA) starts as a cathodic arc, which heats and deposits cathodic material on the anode. When the anode is hot, all the deposited cathode material is re-evaporated from the anode, forming a radially expanding plasma with reduced macroparticle (MP) contamination. This paper reports on the deposition of Sn films using this radially expanding arc plasma. The HRAVA current was I= 60-175 A and the duration was up to 180. s. Two electrode pairs were used. (1) A water-cooled Sn cathode with a diameter of D= 60. mm was used with a W anode having a thickness of d= 10. mm, diameter D= 60. mm and separated from the cathode by gaps of h= 10 and 15. mm. (2) A water-cooled Sn cathode with D= 30. mm was used with either of two graphite anodes, with d= 9 or 15. mm, D= 32. mm and h= 10. mm. The cathodes were recessed behind a boron nitride shield. A mechanical shutter controlled the deposition onset and exposure duration (15. s) on glass substrates. The distance from the arc axis to the substrate (L) was 80, 110, or 125. mm. Film thickness was measured with a profilometer. MPs on the coating surface were examined by optical microscopy. With D=60mm cathodes, L=125mm, and I=175 A, the deposition rate V_dep monotonically increased with time from 0.5 initially to 3.0μm/min after 120s. With the D=30mm cathode, L=110mm, I=175 A and d=9mm, V_dep increased with time to a peak of 0.84μm/min at 20s, and then decreased to a steady state of 0.69μm/min at 45s. The peak was due to re-evaporation from the hot anode of cathodic material, including MPs, which were deposited initially on the cold anode. The MP flux density decreased with I from 2.5 at I=80 A to about 1mm^-2s^-1 at I=175 A in case of D=30mm, L=110mm, d=9mm.