Chapter 12: Surface Erosion During Implantation: Sputtering

12.1 Introduction

This chapter deals with the erosion of the sample by energetic particle bombardment. In this process, called sputtering, surface atoms are removed by collisions between the incoming particles and the atoms in the near surface layers of a solid. Sputtering limits the maximum concentration of atoms that can be implanted and retained in a target material. The yield of sputtered atoms the number of sputtered atoms per incident ion typically falls in the range of 0.5 20, depending on ion species, ion energy, and target material. For direct ion implantation into a target material, the maximum concentration of implanted species is inversely proportional to the sputter yield. Consequently, for ion-target combinations with high sputter yields, the maximum concentration may be only a few atom percent.

12.2 Sputtering of Single-Element Targets

Sputtering is the erosion of a sample by energetic particle bombardment and is characterized primarily by the sputtering yield, Y, which is defined as

(12.1)

The sputtering yield depends on the structure and composition of the target material, the parameters of the incident ion beam, and the experimental geometry. Sputtering yield experiments have measured values of Y that span more than seven decades; however, for the medium mass ion species and keV energies of general interest in ion-solid interactions, the typical values of Y are between one and ten. An extensive list of sputtering yields is given by Matsunami et al. (1984). Yields can also be calculated using SRIM Monte Carlo simulations.

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