Modification of the refractive index and the dielectric constant of silicon dioxide by means of ion implantation

Abstract

The modification of silicon dioxide films by means of ion implantation of fluorine and carbon was studied. 19F+ and 12C+ ions were separately and sequentially implanted in 250 nm thick thermal SiO2 films with energies ranging from 10 to 50 keV and fluences in the interval 5×1015 to 5×1016 cm−2. Metal/oxide/semiconductor (MOS) capacitors were fabricated on half side of the wafers. The implanted SiO2/Si samples were characterized by means of ellipsometry and Fourier transform infrared (FTIR) spectroscopy. The MOS capacitors were used to determine the relative dielectric constant. Our results indicate a considerable reduction of the dielectric constant and refractive index. The refractive index was reduced from 1.46 to 1.29 when only fluorine was implanted or when fluorine with a higher dose was implanted in combination with carbon. For the same conditions, a relative dielectric constant of 3.4 was obtained and a shift in the Si–O bond stretching mode from 1085 to 1075 cm−1 was observed by FTIR spectroscopy.