High Resolution Auger Depth Profiles using a Dual Ion Gun System
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A dual ion gun system has been proposed (D.E. Sykes et al, Appl. Surf. Sci. 5(1980)103) to reduce texturing and improve depth resolution during Auger sputter depth profiling. We have evaluated this ion gun configuration by profiling a variety of multilayer structures. With careful alignment of the guns, we have obtained a dramatic decrease in ion-induced texturing often seen when a single ion gun is used. This effect was particularly pronounced for polycrystalline Al films on Si where an order of magnitude improvement in depth resolution was achieved. Further refinements of the technique include the use of low energy (IkeV) grazing incidence xenon ions and a small electron beam probe area. Depth profiles obtained from Ni/Cr, W/Si, and GaAs/GaAlAs multilayer structures will also be discussed. INTRODUCTION A major problem associated with ion beam sputtering to access buried interfaces for Auger analysis is the formation of ion induced topography (1-5). The formation of uneven ion etched surfaces is due to a number of effects including inhomogeneities in surface composition, uneven formation of native oxides or other contaminant layers, initial surface topography which may be enhanced by ion beam shadowing and/or deposition of material from forward sputtering, localized differences in sputtering rate due to different crystal orientations and effects of impurities concentrated in the region of crystalline defects. It is generally accepted that the effect of ion beam induced topography could be significantly reduced if the impinging ions approached the surface from all possible angles, since there is a general tendency for the surface structure to be oriented with reference to the direction of the impinging ions. There are two techniques which partially fulfil this requirement. The sample might be rotated, or multiple ion guns could be used. The former is not easy to accomplish while maintaining the mechanical alignment necessary for high spatial resolution analysis. Dual ion guns were shown to reduce ion beam induced degradation of interface resolution and layer composition accuracy in Au/Cr multilayer structures (6), but since this work very little has appeared in the literature. In this paper we report new studies using single and dual ion guns during Auger analysis of interfaces in materials ranging from large-grain polycrystalline films to epitaxial MBE layers. EXPERIMENTAL Four test structures were studied: I. Annealed polycrystalline Al contacts on silicon in integrated circuits. The Al thickness was 500nm and the contact windows in the field oxide were 5tm diameter. 2. Silicon(3nm)/tungsten(6nm) multilayers e-beam evaporated onto (100) GaAs.
Mat. Res. Soc. Symp. Proc. Vol. 54.
1986 Materials Research Society
700
3.
NBS standard reference material 2135 Ni(63nm)/Cr(50nm) multilayers on
silicon. 4. Molecular beam epitaxy (MBE)
layers of GaAs/Ga.5AI.
Cross-sectioned samples were spectroscopy (TEM) to determine
prepared thickness,
5 As.
for transmission el
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