Particle bombardment surface

R. Behrisch, ed., "Sputtering by Particle Bombardment II Sputtering of Alloys and Compound, Electron and Neutron Sputtering, Surface Topography," in Topics in Applied Physics, Vol. 52, Springer-Vedag, Berlin, 1983. 

Unlike traditional surface science techniques (e.g., XPS, AES, and SIMS), EXAFS experiments do not routinely require ultrahigh vacuum equipment or electron- and ion-beam sources. Ultrahigh vacuum treatments and particle bombardment may alter the properties of the material under investigation. This is particularly important for accurate valence state determinations of transition metal elements that are susceptible to electron- and ion-beam reactions. Nevertheless, it is always more convenient to conduct experiments in one s own laboratory than at a Synchrotron radiation focility, which is therefore a significant drawback to the EXAFS technique. These focilities seldom provide timely access to beam lines for experimentation of a proprietary nature, and the logistical problems can be overwhelming. 

There are several methods in use for producing these clusters. Particle bombardment or laser vaporization of a graphite surface leads to direct formation of ions that can be detected by mass spectrometry. These are normally of relatively small size (n<30). By laser vaporization of graphite into a molecular beam neutral... 

Molecular dynamics simulations yield an essentially exact (within the confines of classical mechanics) method for observing the dynamics of atoms and molecules during complex chemical reactions. Because the assumption of equilibrium is not necessary, this technique can be used to study a wide range of dynamical events which are associated with surfaces. For example, the atomic motions which lead to the ejection of surface species during keV particle bombardment (sputtering) have been identified using molecular dynamics, and these results have been directly correlated with various experimental observations. Such simulations often provide the only direct link between macroscopic experimental observations and microscopic chemical dynamics. 

Stability of sputtered molecules. In order to further mimic experimental conditions, many trajectories are evaluated by choosing an ensemble of impact points for the energetic particle within the surface unit cell. The experiments with which the simulations are compared are performed so that the majority of the bombarded surface is undamaged This makes direct comparisons between the simulated and experimental results possible. 

As demonstrated in this section, the agreement between simulation and experimental results for keV particle bombardment of solids is remarkable. This is especially true when one considers the rather crude potentials used in the calculations. To understand the reason for this agreement, the underlying features of the dynamics should be reviewed. The surface structures which are... 

The dominant role of asperity contact is also apparent from analysis of the texture of polished surfaces. Figure 9 illustrates a typical post CMP surface as examined via atomic force microscopy (AFM). Surface texture is composed of innumerable randomly oriented nanogrooves of a width and depth consistent with traveling Hertzian loaded contact [12] particle bombardment during turbulent liquid flow produces profoundly different texture. All classes of semiconductor materials examined show similar textures, indicating the general nature of the process. From the data to date, it appears that asperity contact is the dominant wear mechanism in CMP. 

The important point to recognize is that the etch rate of surfaces subjected to energetic particle bombardment (bottom surfaces) will be larger than the etch rate of surfaces not subjected to this bombardment (sidewalls) because of the ion-assisted (or electron-assisted) gas-surface chemistry. The relationship between the shape of an etched profile and the dependence of the etch rate on ion bombardment is shown in... 

Fig. 7.2. Diagram of the PDS-1000/He, a stationary particle bombardment machine that is connected to a helium gas container. Controlled by adjustable valves, the gas stream (He) terminates in an acceleration tube, which is mounted on the top of a target chamber. This chamber is closed by a door and set under vacuum shortly before bombardment. When gas flows into the acceleration tube, the rupture disc bursts releasing the shock wave into the lower part of the tube. The gas pressure then accelerates the macrocarrier sheet containing the microprojectiles on its lower surface. The net-like stopping screen holds the macrocarrier sheet back and serves to block the shock wave, while the microprojectiles slip through the pores of the grid and continue on towards their final target.

The technique of secondary Ion mass spectrometry (SIMS) Is one of extremely large scope. By using energetic particle bombardment of a surface and detecting with a mass spectrometer the charged particles which are emitted, one can... 

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