Effect of top power on a low-k film during oxygen strip in a TCP etch chamber

The modification of a SiOCH based low-k by oxygen plasma in a transformer coupled plasma (TCP) is reported. Modification of the film is studied as function of TCP power and time. Spectroscopic ellipsometry (SE) and Fourier transformed infrared absorption spectroscopy (FTIR) measurements are used for characterization. Both techniques show that the modification (damage) depth increases with increasing TCP power. Optical emission spectroscopy (OES) indicates that adding TCP power increases the O/O2+ ratio in the plasma. By means of FTIR and OES, evidence is found for the removal of hydrogen and carbon from the low-k during plasma exposure. Using a two-layer SE fitting model, and no TCP power a refractive index (RI) of 1.44 for the chemically altered top layer was found. This RI decreases with TCP power. Presumably, at increased TCP power, relatively more radicals are generated and they penetrate more easily because of a less dense top layer.