Electron beam ablation of materials

The channelspark, a low accelerating voltage, high current electron beam ac celerator, has been used for ablation of materials applied to thin film dep osition. The channelspark operates at accelerating voltages of 10 to 20 kV with similar to 1500 A beam currents. The electron beam ionizes a low-press ure gas fill (10-20 mTorr Ar or N-2) to compensate its own space charge, al lowing ion focused transport. Ablation of TiN, Si, and fused silica has bee n studied through several plasma diagnostics. In addition, thin films of Si O2 have been deposited and analyzed. Strong optical emission from ionized s pecies, persisting for several microseconds, was observed in the electron b eam ablated plumes. Free electron temperatures were inferred from relative emission intensities to be between 1.1 and 1.2 eV. Dye-laser-resonance-abso rption photography showed Si atom plume expansion velocities from 0.38 to 1 .4 cm/mu s for several pressures of Ar or N-2 background gas. A complex, mu ltilobed plume structure was also observed, yielding strong indications tha t an electron beam instability is occurring, which is dependent upon the co nductivity of the target. Nonresonant interferometry yielded line-averaged electron densities from 1.6 to 3.7 x 10(23) m(-3) near the target surface. Resonant UV interferometry performed on Si neutral atoms generated in the a blation plumes of fused silica targets measured line integrated densities o f up to 1.6 x 10(16) cm(-2), with the total number of ablated silicon neutr als calculated to be in the range 2.0 x 10(15) to 5.0 x 10(13). Electron be am deposited films of fused silica were microscopically rough, with a thick ness variation of 7%. The average SiO2 deposition rate was found to be abou t 0.66 nm/shot. The electron beam-deposited fused silica films had accurate ly maintained stoichiometry. Ablated particulate had an average diameter ne ar 60 nm, with a most probable diameter between 40 and 60 nm. For SiO2 targ ets, the mass of material ablated in the form of particulate made up only a few percent of the deposited film mass, the remainder being composed of at omized and ionized material. (C) 1999 American Institute of Physics. [S0021 -8979(99)01324-9].