Dual-beam focused ion beam/electron microscopy processing and metrology of redeposition during ion–surface 3D interactions, from micromachining to self-organized picostructures

Abstract

Focused ion beam (FIB) tools have become a mainstay for processing and metrology of small structures. In order to expand the understanding of an ion impinging a surface (Sigmund sputtering theory) to our processing of small structures, the significance of 3D boundary conditions must be realized. We consider ion erosion for patterning/lithography, and optimize yields using the angle of incidence and chemical enhancement, but we find that the critical 3D parameters are aspect ratio and redeposition. We consider focused ion beam sputtering for micromachining small holes through membranes, but we find that the critical 3D considerations are implantation and redeposition. We consider ion beam self-assembly of nanostructures, but we find that control of the redeposition by ion and/or electron beams enables the growth of nanostructures and picostructures.

Focused ion beam milling of microchannels in lithium niobate

“…The reason for this decrease in material removal rate at high aspect ratios can be attributed to material redeposition. [33][34][35] It becomes more and more difficult to remove material from a deep yet narrow (i.e., high aspect ratio) structure because the material has to be expelled a long way to escape the top surface of the substrate, and there is a high probability that the material will be redeposited along the sidewalls within the structure itself. Alternatively, we can also explain the reduced material removal rate observed for high aspect ratio structures kinematically.…”

“…As can be seen from the figure, the channel walls are V-shaped, which suggests that it is quite difficult to remove material from the bottom of this high aspect ratio channel due to material redeposition. [33][34][35] Consequently, in this case, milling any deeper than about 3 lm in depth does not result in any further increase in the depth of the structure actually milled.…”

Nanostructures on surfaces by ion irradiation

“…Typically, FIBs are based on liquid-metal ion sources (LMIS) forming Ga + ion beams; because of the very high brightness (>10 6 A/cm 2 sr) and small virtual source size (<100 nm) [139,140] of LIMS, very small spot sizes (~10 nm) and extremely high current densities (>1 A/cm 2 ) can be achieved using suitable electrostatic focusing columns. These irradiation conditions may lead to the formation of quite specific surface structures [137,[141][142][143][144][145][146][147].…”

New micro-cones targets can efficiently produce higher energy and lower divergence particle beams

“…This results in a modification of the divergence of the output particle beam by effectively modifying the accelerating sheath shape, and can be adjusted by adjusting the amount of curvature. This efficiently produces a beam with extremely relevant characteristics to fast ignition , laser based accelerators (Dunne, 2006), proton beams for proton radiography of plasmas (Borghesi et al, 2002(Borghesi et al, , 2010Kodama et al, 2004), isochoric heating (Patel et al, 2003) shocks (Koenig et al, 2004), proton therapy (Bulanov & Khoroshkov, 2002;Fourkal et al, 2002;Noda et al, 2002;Pegoraro et al, 2004;Nishiushi et al, 2009, Yogo et al, 2009, micro-beam radiation therapy (Slatkin et al, 1992), positron emission tomography (Spencer et al, 2001), focused ion beam milling machines (Reyntjens & Puers, 2002), ion beam microscopes (Li, 2007), and dual beam electron/ion microscopes (MoberlyChan, 2009). For applications such as proton therapy, control of the characteristics of the beam are important (Toncian et al, 2006) and a micro-magnetic device (Schollmeier et al, 2008) separates the electron and or proton beam from the X-rays, or focus them (Nishiuchi et al, 2002;Kanazawa et al, 2009).…”