Paper PS1-FrM3
Mechanism of Plasma Ashing Damages on Porous SiOCH Films

Friday, October 24, 2008, 9:00 am, Room 304

The construction of integration process employing low dielectric constant (low-k) materials for interlayer dielectric is a key for the development of ULSI devices. Since the low-k films tend to be damaged during plasma processes, the damage free plasma processes are strongly required. Although many researchers have been studying on the plasma damage on the low-k films, there has been little in situ evaluation of plasma damages on the low-k films. The in situ evaluation is crucial for the clarification of damage generation mechanism because properties of damaged low-k films change when the low-k films are exposed to atmosphere. We built up an in situ measuring system to evaluate surface properties of the low-k films during plasma process. We investigated H₂/N₂ ashing plasma damages on porous SiOCH films and the correlation between the amount of damages and densities of radicals in the plasma which make large effects on low-k film properties during plasma process. The surface reaction was measured by using in situ Fourier transform infrared reflection absorption spectroscopy (FT-IR RAS) and spectroscopic ellipsometry. Absolute densities of H and N radicals were measured by vacuum ultraviolet absorption spectroscopy. The 100 MHz excited capacitively coupled plasma was used for the ashing process. The thickness of damaged layer was measured at a real time by the in situ spectroscopic ellipsometry and in situ FT-IR RAS during the ashing process. After the porous SiOCH were exposed to H₂/N₂ plasma at various flow rate ratios of H₂/(H₂+N₂) for 60s, the thickness of damaged layer was monotonically increased with the flow rate ratio and reached the maximum of 33nm at that of 100%. H radical densities were increased with the flow rate ratio and had the maximum of 7.5x10¹¹cm^-3 at that of 75 %, and then, decreased to 6.8x10¹¹cm^-3 at that of 100%. N radical densities had the maximum of 9.5x10¹¹cm^-3 at that of 25 %. The thickness of damaged layer agreed well with the H radical density in the region for 25% to 75%. Even though the H radical density decreased, the thickness of damage increased at the flow rate ratio of 100 %. On the basis of these results, we consider that damages on the porous SiOCH are determined by chemical reactions of H radicals which enhance the damage reaction and N radicals which have an effect of inhibition of the damages.