Primary ion energy

Ni(IIO). The top part of the figure shows the scattering geometry. The primary ion energy was 101 keV. 

Figure 4.4 Left sputter yields of copper under bombardment with Ne, Ar, Kr and Xe ions as a function of energy (data from [2]). Right, relative sputter yields of polycrystalline copper as a function of incident angle measured from the surface normal. The primary ion energy is 1.05 keV. The dashed line represents 1/cos (adapted from Oechsner [8]).

Molecular dynamics simulations have yielded a great deal of information about the sputtering process. First, they have demonstrated that for primary ion energies of a few keV or less, the dynamics which lead to ejection occur on a very short timescale on the order of a few hundred femtoseconds. This timescale means that the ejection process is best described as a small number of direct collisions, and rules out models which rely on many collisions, atomic vibrations and other processes to reach any type of steady state . Within this same short-timescale picture, simulations have shown that ejected substrate atoms come from very near the surface, and not from subsurface regions. 

In ISS, like in SIMS, gas ions such as helium or neon are bombarded on the sample surface at a fixed angle of incident. The ISS spectrum normally consists of a single peak of backscattered inelastic ion intensity at an energy loss that is characteristic of the mass of surface atom. From the pattern of scattered ion yield versus the primary ion energy, information about elements present on the sample surface can be obtained at ppm level. 

Fig. 10. Fractional energy loss (E — T)/E vs. primary ion energy. The scattering angle, 9, and the angle of incidence, are constant. (Data from Ref. )...

Primary ion energy Sample composition 500-10000 eV common Involatile organics, inorganics, and or ganomet al 1 ics semiconductors adsorbed gases... 

Figure 4. Total particle yields of glycerol versus primary ion energy In-LMI source.

Several authors believe that comparing LEIS spectra of one sample measured at different primary ion energies may also provide a means of determining which atoms are in the outer layer, and which are in the subsurface region [53-55], Because these arguments are based on a rather persistent misunderstanding, the... 

A profile of a 500-eV arsenic implant by Hitzman and Mount [127] shows the effect of Cs+ primary ion energy and incidence angle on depth resolution (Fig. 4.38). These As- profiles also demonstrate the high sensitivity of the SIMS technique. 

Figure 13 He Ion scattering spectrum of a physical mixture of AI2O3 and MoO, (7.6 wt%). Primary Ion energy E s 500 eV. scattering angle e = 137. ...

Figure 8.24 Sputtering yield data of copper atoms as a function of primary ion energy for different primary ions. (Reproduced with permission from J.C. Vickerman, Surface Analysis The Principal Techniques, John Wiley Sons Ltd, Chichester. 1997 John Wiley Sons Ltd.)...

The major difference between the two techniques lies in the energies of the incoming ion beam. In ISS. also called low-energy ion scattering, the primary ion energies are in the range of 0..5-5 keV, Noble gas ions, such as lie. Ar, and Ne. and alkali ions, such as l.i. Na, or K, are used. An electron-impact ion souree is most often used with an electrostatic or ttme-ol-fliglu analyzer. In the ISS technique, information is obtained from the topmost atomic layer or. in some cases, from one or two layers directly below. 

Bowers, Elleman and King have measured the rate constants and their dependence upon kinetic energy for the above reactions by the already described method. They showed that Aio, 11, i2a, i2b, isb and i4b increase initially with primary ion energy, reach a maximum and then decrease. Goode et have caUed this energy dependence... 

Figure 12 Useful ion yield of Si+ versus primary ion energy for normal Incidence bombardment of silicon in vacuum (from Ref. 7).

FIGURE 40.12 Dependence of the depth resolntion of various elements in Si on the primary ion energy, primary ion type in brackets. Reprinted from Vandervorst, W., (2008) Semiconductor profiling with siih-nm resolution challenges and solutions. Applied Surface Science, 255(4), 805-812. Copyright (2008), with permission from Elsevier. 

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