Surface analysis instrumental, electronic materials

Problems and Prospects of Instrumental Surface Analysis of Electronic Materials and Processes... 

Ultra-high vacuum conditions are important for two reasons. Firstly the material to be analysed is bombarded with particles or photons, and particles (electrons or ions) leaving the surface are detected these particles suffer collisions with residual gas molecules if the pressure is >10 torr. Secondly, and more important, surfaces to be analysed can be rapidly contaminated by adsorption of residual gas molecules if the pressure is >10 torr. Hence, surface-analysis instrumentation is constructed routinely to achieve 10 ° torr (after bake-out). 

The student should be aware that there is another class of surface analysis instruments based on analytical microscopy, including scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and scanning tunneling microscopy. A discussion of these microscopy techniques is beyond the scope of this chapter. Most industrial materials characterization laboratories will have some combination of electron spectroscopy. X-ray analysis, surface mass spectrometry, and analytical microscopy instrumentation available, depending on the needs of the industry. 

In this review, the process steps in IC fabrication and the major new technologies utilized are discussed. Numerous examples of the application of instrumental surface analysis in the Study of electronic materials and processing are given. 

Plasma emission spectrometers have shown a rapid growth. This holds also for NMR spectrometer sales because of new applications in biomedical research and more sophisticated experimental methods using increased computing power. Similarly, Raman spectroscopy, traditionally used in academic research, is gaining acceptance in industrial R D and quality control applications. Materials research and surface analysis in a variety of industries keeps the sales of electron microscopic, electron spectroscopic, ion spectroscopic, and X-ray instruments growing. Details of the various techniques on surface and interface characterization which are also important in R D of chemical sensors themselves, can be found in Chapter 3, Section 3.4.2. 

The analysis of these materials by XPS included the use of valence band spectra. The use of valence band spectra has become more popular due to the ability to fingerprint polymer structure [21,34,35]. Spectra taken with monochromatic source XPS instruments allow analysis of the photoelectron emission from the molecular orbitals. The valence electrons are involved only in chemical bonding and not core level ionization. They give rise to valence band spectra (0-50 eV). This type of spectrum is more sensitive to changes in molecular structure than the core lines because it reflects only changes in the valence electron distribution. The valence band spectrum can act as the fingerprint of a particular valence electron arrangement in a polymer surface. The valence band spectra for the dry plasma-... 

Surfaces are investigated with surface-sensitive teclmiques in order to elucidate fiindamental infonnation. The approach most often used is to employ a variety of techniques to investigate a particular materials system. As each teclmique provides only a limited amount of infonnation, results from many teclmiques must be correlated in order to obtain a comprehensive understanding of surface properties. In section A 1.7.5. methods for the experimental analysis of surfaces in vacuum are outlined. Note that the interactions of various kinds of particles with surfaces are a critical component of these teclmiques. In addition, one of the more mteresting aspects of surface science is to use the tools available, such as electron, ion or laser beams, or even the tip of a scaiming probe instrument, to modify a surface at the atomic scale. The physics of the interactions of particles with surfaces and the kinds of modifications that can be made to surfaces are an integral part of this section. 

The scanning electron microscope (SEM) has been shown to be an effective instrument for the analysis of physical evidence materials. Both topographical, i.e. surface characterization, and compositional, i.e. elemental constitution, analyses have been successfully reported in several recent studies (l—8). The utilization of this instrumentation has widely increased. 

From a materials perspective there are two possible reasons why dental enamel shows the large variations in mechanical properties shown in figure 1 firstly, chemical variations in apatite composition and, secondly, changes in enamel structure with position from the occlusal surface to the EDJ. The chemical composition of enamel can be examined with a lateral resolution of 1-10 pm with electron microprobe analysis. Enamel structure can be obtained with SEM. To perform an accurate microprobe analysis, natural and synthetic minerals are used as standards to calibrate the instrument. This is fairly routine for geologists and earth scientists who are able to obtain chemical compositions with an accuracy of <0.1% for a wide range of elements simultaneously (including Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Hf, Ta, Pb, Th, U, F and Cl). In enamel only a few of these (Na, Mg, Al, P, K, Ca, Ti, Cl and F) are above the detection limit. The Ti is likely to be an impurity or contaminant rather than a constituent of enamel. This technique does not work for lighter elements such as C, S, O and N which may be present in enamel. 

---