Chemical Mechanical Polishing of Ruthenium and Several Dielectric Films.

摘要

Chemical mechanical planarization (CMP) is an enabling technology that plays a crucial role in the integrated circuit fabrication and is used to planarize a variety of materials such as metals, semiconductors, polymer films, dielectrics, composite materials, etc. In this thesis work, we investigated three such applications of CMP: a) polishing of Ru barrier liner for advanced interconnects, b) smoothening of extreme ultraviolet (EUV) mask substrates for next generation lithography and c) selective removal of silicon dioxide over silicon nitride for shallow trench isolation.;Ru polishing is challenging due to its hardness and inertness. Here, colloidal silica-based slurries containing guanidine carbonate (GC) and hydrogen peroxide (H2O2) are shown to enhance the Ru removal rates (RRs). Interestingly, neither GC nor H2O2 alone enhances the Ru RRs but their combination does due to the formation of Ru oxide-guanidinium complexes which can be polished by silica abrasives. Furthermore, even though Ru on TiN and Ru on Ta/TaN substrates were deposited at the same conditions, RRs of Ru on TiN were enhanced more compared to those on TaN/Ta. This is shown to be a consequence of the difference in the crystalline structure of the oxide films formed due to a difference in the structure of the Ru films themselves. Using X-ray diffraction, X-ray photoelectron spectroscopy, nanoindentation, zeta potential measurements, thermo gravimetric analysis and contact angle measurements, the role of GC and crystalline structure in enhancing the RRs of the films will be discussed.;Achieving angstrom level surface roughness and defectivity in single digits on extreme ultraviolet (EUV) mask substrates is a challenging task. Using an abrasive-free solution for surface smoothening can eliminate the potential defects that will be caused by abrasives in conventional slurry. Abrasive-free CMP of a-silicon films using poly (ethyleneimine) solution showed that both the final surface roughness and RR are strongly dependent on polishing pressure. We developed a hybrid two-step CMP process consisting of polishing first at 1 psi to remove sufficient material to eliminate the underlying defects, followed by polishing at 0.5 psi to achieve low surface roughness. Under these polishing conditions, CMP of a-silicon films deposited on EUV mask substrates resulted in a RMS surface roughness of ∼ 0.09 nm.;As silica abrasives are inexpensive, abundantly available and less prone to creating defects compared to ceria abrasives, there is a growing need for colloidal silica-based slurries to enable shallow trench isolation schemes. We investigated colloidal silica-based slurries containing anionic surfactants, namely dodecylbenzenesulfonic acid (DBSA) and dodecyl phosphate (DP), and anionic polymers, namely poly (styrene sulfonic acid) (PSSA), poly (acrylic acid) (PAA), and poly (acrylic acid-co-maleic) acid) (PAAMA), to selectively polish oxide films over nitride films. It is shown that dispersions containing 5wt% silica + 150 ppm DBSA, 5wt% silica + 150 ppm DP and 5wt% silica + 0.5 wt% PSSA slurries at pH 2 can achieve the desired selectivity (SiO2 removal rate /SiN removal rate) of ∼ 80-100 : 1 with a nitride loss of < 1nm/min and good surface quality (RMS surface roughness < 1 nm). Interestingly, nitride removal rates (RRs) were suppressed only in the pH range 2-4 while the oxide RRs remained high. Using zeta potential (ZP) and thermo-gravimetric analysis (TGA) measurements and pKa values of the additives, a polishing mechanism is proposed to explain the observed selective polishing behavior.