STUDY OF ULTRA-THIN HYDROGEN SILSESQUIOXANE FILMS USING X-RAY REFLECTIVITY

X-ray reflectivity was used to measure the coefficient of thermal expa nsion (CTE) and the density profile of hydrogen silsesquioxane thin fi lms deposited on silicon wafer substrates. This study has demonstrated that this technique is capable of measuring the thickness change of 4 0 nm thick films with a CTE in the 10(-5)/degrees C range. The CTE of ultra-thin hydrogen silsesquioxane films was found to be about 40 ppm/ degrees C from 20 to 175 degrees C. After-taking the substrate constra int into consideration, the calculated CTE of the films in their uncon strained condition was about 20 ppm/degrees C. In addition, the densit y of the films was found to be smaller than that of silica and was non -uniform along the thickness direction with a low density region adjac ent to the hydrogen silsesquioxane/silicon interface. (C) 1998 Elsevie r Science S.A.