Temperature induced diffusion in Mo/Si multilayer mirrors

To optimize the growth process of Mo/Si multilayers, the effect of an elevated substrate temperature during deposition has been studied in the temperature range between 300 K and 550 K. Multilayer properties, such as interface roughness, d-spacing, and structure of the layers, have been investigated during deposition and cool-down, after cool-down, and during heating. A number of techniques have been used: small-angle, near-normal incidence, and in situ reflectivity measurements. It is found that the increased substrate temperature changes the interface roughness to a minimum value for samples produced at 488 K. Also, a change of the d-spacing as a function of time and temperature is observed and is explained by annihilation of free volume of the Si layer. The atomic structures of the layers deposited at different temperatures have been analyzed with high resolution electron microscopy (TEM), which shows that both materials are amorphous for the entire temperature range investigated. At the extremes of the temperature range investigated irregular layer structures, such as ripples and V-shaped structures, have been observed by TEM. (C) 1998 American Institute of Physics.