E-beam

We need to point out that, if the wavelengths of laser radiation are less than the size of typical structures on the optical element, the Fresnel model gives a satisfactory approximation for the diffraction of the wave on a flat optical element If we have to work with super-high resolution e-beam generators when the size of a typical structure on the element is less than the wavelengths, in principle, we need to use the Maxwell equations. Now, the calculation of direct problems of diffraction, using the Maxwell equations, are used only in cases when the element has special symmetry (for example circular symmetry). As a rule, the purpose of this calculation in this case is to define the boundary of the Fresnel model approximation. In common cases, the calculation of the diffraction using the Maxwell equation is an extremely complicated problem, even if we use a super computer. 

Fig. 36. Representative bilayer resist systems. Both CA and non-CA approaches are illustrated (116—119). (a) Cross-linking E-beam resist, 193-nm thin-film imaging resist (b) acid-cataly2ed negative-tone cross-linking system (c) positive-tone CA resist designed for 193-nm appHcations and (d) positive-tone...

Fig. 39. Schematic showing the basics of cell projection. The desired beam shape is selected by steering the electron beam through the appropriate pattern in the aperture plate. By using a rectangular aperture the system can operate like a conventional direct-write e-beam tool, so any shape of pattern can be...

The basic principle of e-beam SNMS as introduced by Lipinsky et al. in 1985 [3.60] is simple (Fig. 3.30) - as in SIMS, the sample is sputtered with a focused keV ion beam. SN post-ionization is accomplished by use of an e-beam accelerated between a filament and an anode. The applied electron energy Fe a 50 20 eV is higher than the range of first ionization potentials (IP) of the elements (4—24 eV, see Fig. 3.31). Typical probabilities of ionization are in the 0.01% range. SD and residual gas suppression is achieved with electrostatic lenses before SN post-ionization and energy filtering, respectively. 

Positive secondary ions (SI" ) are repelled by an electrode in e-beam SNMS or completely (in DBM) or widely (in HFM, see below) re-attracted by the sample surface in HF-plasma SNMS. Ionized plasma species (Ar", contamination) are suppressed by energy filtering. 

With useful yields typically in the 10 range - a value also valid for e-beam SNMS -typical measured intensities are in the lO -lO range for HF-plasma SNMS, depending on the material and Udbm- With a typical plasma and low Udbm near -300 V one effects ultimate depth resolution and low intensities, whereas Udbm 800 V enables bulk analysis in the ppm range (apart from C, N, and O being implanted from contamination) but no longer with good depth resolution. 

Figure 3.37 gives an example of the depth resolution routinely achieved with both e-beam and HF-plasma SNMS on suitable samples. If Eq. (3.21) is applicable, i.e. all sputtered material has been recorded with Hi, then YeollA,y equals Sli/Si [3.75], and depths 2 can be calculated according to ... 

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

E-beam is a relatively cold process and so is more suitable for heat-sensitive substrates. UV lamps emit about one third UV light and the rest is visible and IR. Consequently substrates can get very hot, even causing fires if they become stuck beneath the lamp. Safety shutters which close if the line stops are installed on many UV bulbs. 

While electron beams can produce cations, they are not effective at producing cationic cure in the absence of suitable photoinitiators. The same cationic photoinitiators used for UV cure are often also e-beam sensitive. Examples are triaryl sulfonium or diaryl iodonium salts [41]. 

Polyisoprene can be UV or e-beam cured [43,44]. The 3,4 units are particularly prone to crosslinking at low dose [45]. SIS and SBS are also crosslinkable, even conventional linear materials with low vinyl content however, small amounts of liquid trithiol or triacrylate compounds speed cure dramatically [44]. Like UV, e-beam cure is strongly affected by tackifier choice. Hydrogenated, non-aromatic resins provide much less interference with cure [36,37]. 

Kraton Polymers has developed a multiarm SIS (Kraton 1320X [37,46,47,50]) and SBS (Kraton KX-222C, [48,49]) for rapid UV/e-beam cure. Besides heat resistance improvements, plasticizer resistance is also improved in cured rubber-based systems. The dioctyl phthlate plasticizer common in PVC backing films is soluble in the styrenic domains of SBCs. Crosslinking of the mid-block provides cohesion even after plasticizer attack [51]. 

Functionalized rubbers. Butyl rubber (isobutylene with about 2% iso-prene) has been functionalized through the residual double bonds via the bro-mobutyl intermediate to produce a material with 2% conjugated diene (see Fig. 19). This resin shows high reactivity towards e-beam or UV (free radical or cationic [53]). The bromo butyl intermediate has also been used to attach acrylate or photoinitiator groups to the butyl backbone [54]. 

Fluoropolymers utilizing high molecular weights and copolymerized and alloyed with polyethylene, should be used in most radiation applications. High-dose-rate E-beam processing may reduce oxidative degradation. When irradiated, PTFE and PFA are... 

As argued above, it is not reasonable to expect that new polymer developments will easily stay away from the use of additives. In this respect e-beam processing of plastics constitutes an alternative to chemical additives, but is very limited in scope [15]. Table 10.12 gives the current status for several additive groups. 

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