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

The modification of silicon dioxide films by means of ion implantation of f luorine and carbon was studied. F-19(+) and C-12(+) ions were separately an d sequentially implanted in 250 nm thick thermal SiO2 films with energies r anging from 10 to 50 keV and fluences ill the interval 5 x 10(15) to 5 x 10 (16) cm(-2). Metal/oxide/semiconductor (MOS) capacitors were fabricated on half side of the wafers. The implanted SiO2/Si samples were characterized b y 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 wh en only fluorine was implanted or when fluorine with a higher dose was impl anted in combination with carbon. For the same conditions, a relative diele ctric 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. (C) 2000 E lsevier Science B.V. All rights reserved.