Ion-milling

Although crushing and cleaving is often the most favorable preparation technique with respect to the preservation of the structure, many times these 

Thickness measurement in sample preparation is quite important. Here we describe how to control the thickness precisely by observing color fringes. 

Color Wavelength X (nm) Complementary color Estimated thickness (nm) 

It is relatively easy to prepare a plan-view sample. The common way to prepare a plan-view sample is to grind the sample down to less than 10 pm and then ion mill the sample. For a bulk sample, the sample can be ion milled from both 

---

Figure Bl.19.32. AFM image of Blue Seript II plasmid (400 mu x 400 mu) in propanol, taken with super tip , prepared by earbon deposition on nomral tip in SEM, followed by ion milling. (Taken from [152], figure 1.)...

In the early days of TEM, sample preparation was divided into two categories, one for thin films and one for bulk materials. Thin-films, particularly metal layers, were often deposited on substrates and later removed by some sort of technique involving dissolution of the substrate. Bulk materials were cut and polished into thin slabs, which were then either electropolished (metals) or ion-milled (ceramics). The latter technique uses a focused ion beam (typically Ar+) of high-energy, which sputters the surface of the thinned slab. These techniques produce so-called plan-view thin foils. 

XPS is very useful for the study of surface layers and corrosion films. In the case of corrosion films and oxides it is important to do depth profiling by coupling XPS with ion milling of the surface. Another important aspect of XPS is that the incident X-rays cause negligible damage to the surface. 

In ion milling systems (143-145) a confined plasma is used to generate ions. A set of grids used for confinement is biased so that an ion beam can be extracted from the source. This beam is then directed to the substrate surface, where sputter etching or ion milling takes place. 

A number of advantages exist for ion milling compared to plasma etching or RIE. Because of the collimated beam of ions, essentially vertical profiles are possible. Also, profile tapering can be achieved by tilting the substrate relative to the ion beam. In addition, ion milling is performed at pressures at least 100 times lower than those used in plasma etching or RIE. Therefore, redeposition of sputtered material is reduced. 

Unfortunately, since ion milling is a purely physical process, selectivity is generally poor. Indeed, selectivity in such systems depends almost exclusively on differences in sputter yield between materials. Finally, since the etch products are not volatile, redeposition and trenching can be serious limitations (146). 

Biegelson, D. K., Ponce, F. A., and Tramontana, J. C. (1987). Ion milled tips for scanning tunneling microscopy. Appl. Phys. Lett. 50, 696-698. 

Resist reactive-ion etching (RIE) was performed with a totally modified Tegal Model 400 plasma reactor. Ion-milling (IM) was accomplished with a Veeco three inch system. All resist RIE and IM etch rates are measured versus the rate of Si02 and PMMA as outlined above. 

---