Analysis of Epitaxial Layers

Recent topics in SiC research in Japan are micropipes in wafers, control of polytype in epitaxy, surface analysis of epitaxial layers, application for power devices, device simulation, and others [10]. 

The SSMS point-to-plane surface technique has been shown to be particularly useful in the survey analysis of epitaxial films, heavy metal implant contamination, diflRision furnace contamination, and deposited metal layers. 

RBS and channeling are extremely useful for characterization of epitaxial layers. An example is the analysis of a Sii-j Gejc/Si strained layer superlattice [3.131]. Four pairs of layers, each approximately 40 nm thick, were grown by MBE on a <100> Si substrate. Because of the lattice mismatch between Sii-jcGe c (x a 0.2) and Si, the Sii-j Ge c layers are strained. Figure 3.51 shows RBS spectra obtained in random and channeling directions. The four pairs of layers are clearly seen in both the Ge and Si... 

In Chapter 3 we went as far as we could in the interpretation of rocking curves of epitaxial layers directly from the features in the curves themselves. At the end of the chapter we noted the limitations of this straightforward, and largely geometrical, analysis. When interlayer interference effects dominate, as in very thin layers, closely matched layers or superlattices, the simple theory is quite inadequate. We must use a method theory based on the dynamical X-ray scattering theory, which was outlined in the previous chapter. In principle that formrrlation contains all that we need, since we now have the concepts and formtrlae for Bloch wave amplitude and propagatiorr, the matching at interfaces and the interference effects. 

Chaimelling only requires a goniometer to inelude the effeet in the battery of MeV ion beam analysis teelmiques. It is not as eonnnonly used as tire eonventional baekseattering measurements beeause the lattiee loeation of implanted atoms and the aimealing eharaeteristies of ion implanted materials is now reasonably well established [18]. Chaimelling is used to analyse epitaxial layers, but even then transmission eleetron mieroseopy is used to eharaeterize the defeets. 

Analysis of stress distributions in epitaxial layers In-situ characterization of dislocation motion in semiconductors Depth-resolved studies of defects in ion-implanted samples and of interface states in heterojunctions. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

A ZnSe-on-GaAs epitaxial layer required a sensitive survey of near-surface contamination. PAI was selected for ZnSe analysis because its major constituents and many of the expected impurities are elements that have poor ion yields in conventional LIMS. Figures 8 and 9 are two mass spectra acquired from the ZnSe epitaxial layer. 

McPhail (1989) gives a detailed account of the experimental approach to depth profiling of semiconductors, including the quantification of the data. He illustrates the analysis of a silicon epilayer grown by molecular beam epitaxy (MBE) in which 11 boron-rich layers were incorporated by co-evaporation of boron. The intended structure is shown in Figure 4.8, and it was desirable to establish the concentration of boron in the layers, the inter-peak concentration and the sharpness of the doping transitions. 

In this chapter we discuss the measurement and analysis of simple epitaxial stractures. After showing how to select the experimental conditions we show how to derive the basic layer parameters the composition of ternaries, mismatch of quaternaries, misorientation, layer thickness, tilt, relaxation, indications of strain, curvature and stress, and area homogeneity. We then discuss the hmitations of the simple interpretation. 

When the epitaxial layer thickness is quite high, typically of the order of one micrometre, we can apply the simple criteria discussed in Chapter 3 to determine the layer parameters from the rocking curve. The effective mismatch can be determined by direct measurement of the angular splitting of the substrate and layer peaks and the differential of the Bragg law. This simple analysis catmot be applied when the layer becomes thin, typically less than about 0.25 //m, where, even for a single layer, interference effects become extremely important. We consider these issues in section 6.2 below. 

Figure 4.21 XPS survey obtained from a C-implanted p-type 4H-SiC epitaxial layer after a 1,600"C anneal. Besides the presence of O in the form of SiOj, the surface consists primarily of Si and C. The XPS data and analysis are courtesy of Dr. J. T. Wolan at the University of South Florida.

FIGURE 5 EDX composition analysis of GalnN on a GaN epitaxial layer for a thick GalnN layer with layer thickness of 2.0 pm. The open squares are the indium mole fractions of Region (I), and the closed circles are those of Region (II). 

The state-of-the-art analysis methods for the evaluation of structural, chemical and electrical properties of thin layers in processed Si substrates are discussed. The properties of inclanted p-n junctions, Si-SiO interface, Ge inplant amorphization of Si aid misfit dislocation interface in epitaxial Si are exenplified to illustrate the features and limitations of the techniques. 

BOU 04] BOULLE A., MASSON O., GUINEBRETIERE R DAUGER A., Two dimensional XRD profile modelling in imperfect epitaxial layers , in MITTEMEIJER E.J., Scardi P., Diffraction analysis of the microstructure of materials. Springer Series in Materials Science, vol. 68, p 505-526,2004. 

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