Fluorine-doped SiO2 and fluorocarbon low-k dielectrics investigated by SIMS

In this work, we present secondary ion mass spectrometry (SIMS) investigations of the incorporation of fluorine into thin SiO2 films adapted as low-k dielectrics in the metal-oxide-semiconductor (MOS) devices. The insulating SiOF oxides with the thickness ranging from 1 up to 15 nm have been prepared by plasma-enhanced chemical vapor deposition (PECVD) and/or by reactive ion etching (RIE) methods on 〈1 0 0〉 oriented p-Si substrates with the use of either CF4 or CHF3 source of the plasma. SIMS experiments were performed using ultra-low energy (1 keV) argon ion beam and quadrupole mass analyzer. Depth profiles of the resulting dielectric films illustrate: (i) the incorporation of F into the SiO2 matrix is accomplished by either the CHF3 or CF4 plasmas; (ii) no etching of SiO2 matrix is observed by using of CHF3; (iii) CHF3 is a source of fluorocarbon film deposition on top of the SiO2 that prevents the SiO2 etching; and (iv) fluorine quantifications done based on implantation criteria give the maximum concentrations within the films from 6.0 × 1018 to 2.4 × 1020 atoms/cm3 depending on the different fluoridation conditions. The F concentration in SiO2 increases with the r.f. power of CF4 or with decreasing a gas pressure of CHF3 plasma.