Development of Line-Focus-Beam Acoustic Microscopy System for Evaluation of Electronic Device Materials

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A system of the line-focus-beam (LFB) acoustic microscope applicable to quantitative characterization of electronic device materials has been developed. Some serious problems, such as mechanical precision and temperature, has been experimentally and theoretically discussed from the point of view of measurement accuracy. It has been shown that stabilization of the temperature of coupling liquid of water in the LFB system is most important for accurate measurements, which are carried out by determining propagation characteristics of leaky surface acoustic waves (LSAWs) on the water/sample boundary. The system has been installed in a temperature controlled room around 23<plus-minus>0.1^ﾟC. The relative accuracy of LSAW velocity measurements has been estimated to be better than <plus-minus>0.005% at a point and <plus-minus>0.02% over a scanning area of 3-inch diameter.The system has been applied to investigate the elastic properties of piezoelectric LiNbO_3 and LiTaO_3 crystals. Experiment … More al relations between chemical composition ratios of Li/Nb and leaky surface acoustic wave (LSAW) velocities for 128^ﾟYX LiNbO_3 wafers have been determined. LSAW velocity measurements have been carried out for commercial wafers obtained from a series of crystal growths. Small changes of 0.092% have been detected due to the compositional variation. It has been estimated that the "effective" congruent composition in the production line is 48.440 Li_2O mol% with the density of 4647.4 kg/m^3. A serious problem regarding the elastic properties of X-112.2^ﾟY LiTaO_3 during industrial preparation has been examined with the system. Various types of elastic inhomogeneities have been detected quantitatively as a significant variation of LSAW velocities. In some wafers, large changes, about 2.5%, in LSAW velocities have been observed, which have corresponded to a difference between the velocities for single- and multi-domains. One of the causes has been found to be in the poling process during wafer fabrication.One of the potential applications is thin-film characterization. A new method of determining the elastic constants, density, and thickness of thin-film materials has been developed using propagation characteristics of leaky Sezawa and pseudo-Sezawa waves in the neighborhood of the cut-off region, in addition to those of leaky Rayleigh waves. It has been demonstrated for a sample of gold film on fused quartz that the values of the stiffness constant, C_<44>, and density have been, respectively, about 11% and 5.5% less than those for polycrystalline bulk gold, and the thickness has been determined as 6370A. Less