Abstract: A spin-on-glass sandwich layer planarization process where the spin-on-glass layer within the sandwich has been ion implanted through its entire thickness. The spin-on-glass sandwich layer is formed by successive deposition of a silicon oxide layer, followed by a spin-on-glass layer. The spin-on-glass layer is then thermally cured and ion implanted throughout its entire thickness. Various combinations of implanting ions, ion doses and implantation energies are used to implant the spin-on-glass layer. Finally, a second silicon oxide layer is formed upon the surface of the spin-on-glass layer to complete the spin-on-glass sandwich layer.