| The possibility of achieving a keff (effective dielectric constant) of 2.1 with an etch-back and gapfill process, and a Cu interconnect without the barrier/cap layer requires evaluation of novel low- k dielectrics for chemical mechanical polishing (CMP) compatibility. The primary goal of this investigation is to check for the CMP compatability (removal rates, surface roughness, and wetting characteristics) of methyl silsesquioxane (MSQ), a potential low-k material for the 45/32 nm technology nodes. Two types of MSQ films were investigated, porous and nonporous, with k values of 2.25 and 3.1, respectively. The factors studied include pH, pad hardness (IC-1400 and politex), hydrophobicity, abrasive particles (single and mixed), downforce, velocity, and additives. zeta-potentials of the MSQ films were measured using the electroosmosis technique. The interactions between the abrasives and the MSQ films, which play a major role in determining the removal rates and the post-CMP surface characteristics, were evaluated using the packed column technique. Particle adhesion, contact angle, and Fourier transform infrared spectroscopy (FTIR) measurements were utilized to explain the CMP results. It is concluded that the electrostatic interactions between the abrasive particles and the MSQ films play an important role in controlling the removal rates. The number of particles adhered increases in direct proportion to the removal rates, and in inverse proportion to the contact angles with/without additives. Mixed abrasive particles with ceria as the shell can be effectively used to polish MSQ films without inducing defects. The removal rate of nonporous MSQ increased linearly with an increase of both the downforce and velocity. The use of hard IC-1400 pad induces defects/scratches on nonporous MSQ films, and the removal rates did not change compared to that with soft politex pad. |
