Sputter-induced damage

During the course of sputtering, a significant amount of kinetic energy can be dissipated via elastic (nuclear collisions) and inelastic (electronic excitation) processes into the substrate (only a small fi action of this energy is removed in the emission of photons, electrons, sputtered atoms/ions, and molecules). The remainder induces a myriad of processes that culminate in the modification of the composition and electronic structure of the solid. These can occur for any sufficiently energetic impacting ion. 

These processes are of importance in multicomponent solids as these will result in the redistribution of atoms, thereby altering any compositional gradient that may initially be present. These are discussed in greater detail in Section 5.3.2.4.I. 

Sputtering can also modify the lattice structure in the form of amorphization and re-crystallization, and introduction of surface roughening. This can occur on both single-component and multicomponent solids. Again, single-component solids are discussed only for the sake of simplicity. 

Recoil implantation describes the anisotropic redistribution of atoms within the solid resulting from energetic ion impact. In other words, this is an ion-atom knock-on event that transports atoms preferentially in the direction the ions are initially traveling in. This results in extensive defect formation. As indicated by Relation 3.3, recoil implantation depends primarily on the masses of the collision partners and the impact energy. As collisional cross sections decrease 

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Different secondary ions can also display different depth resolution values for the same substrate. As an example. Copper typically yields poor depth resolution because of its high diffusion coefficient, particularly when sputtered. This sputter-induced enhancement is otherwise referred to as radiation-enhanced diffusion. Radiation-induced segregation may also be initiated, with different primary ion/secondary ion combinations resulting in different trends. As a result, any emissions collected as a result of this form of sputtering will always emanate from what is termed an altered layer, as opposed to the initial intrinsic substrate layer. Exceptions are sometimes noted for large cluster ion impact, because, as mentioned in Section 4.1.1.3, these can remove sputter-induced damage. 

W.T. Pawlewicz, R. Busch, D.D. Hays, P.M. Martin and N. Laegreid Reactively Sputtered Optical Coatings for Use at 1064 nm, in Laser-Induced Damage in Optical Materials ... 

T.M. Donovan, J.O. Porteus, S.C. Seitel and P. Kratz,- Multithreshold HF/DF Pulsed Laser Damage Measurements on Evaporated and Sputtered Silicon Films, inrLaser-Induced Damage in Optical Materials, 1980, H.E. Bennett, A.J. Glass, A.H. Guenther and B.E. Newnam, (Eds.), NBS Spec. Publ. 620, (198 1) pp. 305 - 312. 

Galera, R., Biais, J.C., Boibach, G. (1991) Molecular sputtering and damage induced by kiloelectron ions in organic monolayer—metal systems. Int. J. Mass Spectrom. Ion Process., 107,531-543. 

The third major limitation is that the analysis process itself can change the composition of the surfaces to be analyzed. The two most common t5 es of this problem are analysis beam-induced damage and inhomogeneities caused by the sputtering process, which is used often to probe past the topmost surface of the sample. 

One way of controlling the effect of sputter-induced sample damage in the recorded signal is to ensure that the same localized area of the surface of interest is not impacted/sampled during the course of analysis. This can be implemented by... 

Even if all possible measures to improve depth resolution are applied, there still exist the effects of the primary ion beam-induced damage experienced by the substrate as a result of the sputtering process. These are discussed in Section 5.3.2.4.1. Crater edge effects and crater base effects can also result in the loss of depth resolution. These are discussed in Sections 5.3.2.4.2 and 5.3.2.4.3, respectively. Dynamic range pertains to the range of concentrations of a specific element or molecule that can be examined in a particular depth profile. As can be envisaged, this depends on the detection limit and on the detector type or combinations thereof (detectors are covered in Section 4.2.3.3). 

B. J. Pond, T. Du, J. Sobczak, and C. K. Carniglia, Comparison of the optical properties of oxide films deposited by reactive-dc-magnetron sputtering with those of ion-beam-sputtered and electron-beam-evaporated films, in Laser-Induced Damage in Optical Materials, vol. 2114 of Proceedings of SPIE, pp. 345-354, Boulder, Colo, USA, October 1993. 

While a lot of work has been done with heavy-ion induced radiation damage in metals and semiconductors, very little has been done on compounds, especially on covalent ones. In the following section we shall try to cover the most important work on the radiation chemistry of compounds. In the section on metals only a few selected examples will be mentioned. In the last part of this chapter we shall deal with changes in the composition of surfaces due to sputtering of compounds. 

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