Part I.
In recent years, backscattering spectrometry has become an importanttool for the analysis of thin films. An inherent limitation,though, is the loss of depth resolution due to energy straggling ofthe beam. To investigate this, energy straggling of 4He has beenmeasured in thin films of Ni, Al, Au and Pt. Straggling is roughlyproportional to square root of thickness, appears to have a slightenergy dependence and generally decreases with decreasing atomicnumber of the adsorber. The results are compared with predictionsof theory and with previous measurements. While Ni measurements arein fair agreement with Bohr's theory, Al measurements are 30% aboveand Au measurements are 40% below predicted values. The Au and Ptmeasurements give straggling values which are close to one another.
Part II.
MeV backscattering spectrometry and X-ray diffraction are used toinvestigate the behavior of sputter-deposited Ti-W mixed films on Sisubstrates. During vacuum anneals at temperatures near 700°C for severalhours, the metallization layer reacts with the substrate. Backscatteringanalysis shows that the resulting compound layer is uniform in compositionand contains Ti, Wand Si. The Ti:W ratio in the compound correspondsto that of the deposited metal film. X-ray analyses withReed and Guinier cameras reveal the presence of the ternary TixW(1-x)Si2compound. Its composition is unaffected by oxygen contamination duringannealing, but the reaction rate is affected. The rate measured onsamples with about 15% oxygen contamination after annealing is linear, ofthe order of 0.5 Å per second at 725°C, and depends on the crystallographicorientation of the substrate and the dc bias during sputter-depositionof the Ti-W film.
Au layers of about 1000 Å thickness were deposited onto unreactedTi-W films on Si. When annealed at 400°C these samplesunderwent a color change,and SEM micrographs of the samples showedthat an intricate pattern of fissures which were typically 3µm widehad evolved. Analysis by electron microprobe revealed that Au hadsegregated preferentially into the fissures. This result suggeststhat Ti-W is not a barrier to Au-Si intermixing at 400°C.
