Effect of etching on dielectric constant and surface composition of SiCOH low-k films in inductively coupled fluorocarbon plasmas

SiCOH low-k (k = 2.8) film etched in fluorocarbon (CF4 and CHF3) inductively coupled plasmas was characterized in this work. The surface composition and molecular structures of the low-k films after etching in the CF4, CHF3, CF4/Ar, and CHF3/Ar plasmas were characterized. A higher etch rate was observed with the CF4 plasmas than with the CHF3 plasmas. The etch rate of the low-k film in the CF4 plasmas was decreased and the etch rate in the CHF3 plasmas was increased by the Ar addition. After etching the low-k films, a decrease in the dielectric constant of up to 0.19 was observed. The thickness of the fluorocarbon (CFx) layer and CFx (x = 1, 2, 3)-to-carbon ratio obtained from the XPS C 1s peak increased with decreasing etch rate. The k-value was correlated with amount of Si–CH3 and Si–O related groups determined from the Fourier transform infrared (FT-IR) spectrum. The Si–O related peaks were markedly decreased after etching in the CF4 and CF4/Ar plasmas. The lower k-value was attributed to the increase of the Si–CH3/Si–O ratio after etching low-k film.