VARIATION OF LAYER SPACING IN SELF-ASSEMBLED HAFNIUM-1,10-DECANEDIYLBIS(PHOSPHONATE) MULTILAYERS AS DETERMINED BY ELLIPSOMETRY AND GRAZING ANGLE X-RAY-DIFFRACTION

Grazing angle X-ray diffraction and ellipsometry have been used to cha racterize the film thickness, thickness uniformity, density, and index of refraction of multilayer hafnium-1,10-decanediylbis(phosphonate) ( Hf-DBP) films grown on silicon wafers. Grazing angle X-ray diffraction is a powerful technique that can be used to assess thickness, density , and thickness uniformity of a wide variety of thin films. Grazing an gle diffraction of Hf-DBP multilayer films generally gives a series of peaks (fringes) in the range 0.5-4.0 degrees 2 theta, which arise fro m interference between X-rays reflected off the front and back of the film. Analysis of the fringes allows an assessment of film thickness w hich is independent of the physical properties of the films. With less accuracy, these data also permit an assessment of film density and th ickness uniformity. Indexes of refraction at optical wavelengths can b e determined by comparison of X-ray and ellipsometry data. For a given sample, a plot of film thickness as a function of the number of Hf-DB P layers deposited gives a straight line, indicating that individual l ayers within a given sample are uniform in thickness. However, large v ariations in thickness per Hf-DBP layer are observed from sample to sa mple (ranging from 15 to 21 Angstrom/layer), indicating that substrate effects are important in determining the layer spacing. Estimates of film density indicate that multilayer films are only similar to 75% as dense as the calculated density of the bulk material. Consistent with this finding, the indexes of refraction of all films studied fall in the 1.485-1.500 range, significantly smaller than the refractive index determined for the bulk compound (1.544). These findings indicate tha t Hf-DBP multilayers vary substantially in individual layer thickness from sample to sample and in general are not as similar to the assumed structure of the bulk compound with respect to the density and mode o f metal-phosphonate binding as has been previously suggested for the a nalogous Zr-DBP films.