Chemical-mechanical polishing of copper interconnects and dielectric films for microelectronic applications.

摘要

Part-1. Copper (Cu) dual damascene process coupled with chemical mechanical planarization (CMP) of over burden Cu has emerged as the only viable technique for patterning Cu lines in the manufacture of Very Large Scale Integration (VLSI) & Ultra Large Scale Integration (ULSI) based devices. Conventional CMP of Cu/ultra low-k integration faces many technical challenges. The low-k dielectric films are porous, poorly adhere to the metal films and are mechanically weak. A key challenge is to significantly reduce the mechanical loading during CMP in order to minimize the external shear forces applied to the wafer while maintaining a high removal rates.; A better understanding of the roles of various chemicals used in typical Cu CMP slurries along with the search for novel chemicals that can form a thin film on the Cu surface which can be easily abraded by the polishing pad with very low pressure will therefore be very useful. The requirement of the new generation Cu CMP slurries is to possess not only high removal rates at low down force but also high planarization efficiency (PE) in order to minimize dishing. High PE can be achieved by protecting the recessed regions using an efficient inhibiting agent while only the protruded regions are polished. Benzotriazole (BTA), which is a very good passivating agent, is not acceptable by itself due to the formation of defects as well as challenges with post-CMP cleaning.; In this work, an anionic surfactant [ammonium dodecyl sulfate (ADS)], without and with a small amount of BTA (≤ 1 mM), was investigated as a potential inhibiting agent for several amino acids-H2O2 (glycine, beta-alanine, and gamma-amino butyric acid) at pH = 4 and carboxylic acids-H2O2 (acetic acid, and oxalic acid) based slurries at pH = 3. Fumed silica particles (Degussa Corporation) were the abrasives used in the slurry. It was observed that the dissolution rates for all amino acids/H2O2 and acetic acid/H2O2 except for oxalic acid/H2O2 system were suppressed by either ADS or BTA alone, but not enough to achieve high PE. Further, beta-Alanine/H 2O2 system was investigated in detail in terms of calculating the PE. The PE was determined by polishing at 2 psi patterns consisting of ∼ 5000 A deep and ∼ 20 mum wide Cu lines that are spaced about ∼ 100 mum, created using a diamond tipped stylus in 150 mm Cu wafers. In contrast, combination of ADS/BTA ( 1 mM) for all the systems gave better performance in terms of dissolution and polish rates. A very useful metric/rule of thumb appears to be that high PE's (∼93%) result only when the dissolution rates at 40°C for the slurry (beta-alanine-H2O2) are 1.6 nm/min.; Oxalic acid-H2O2 system behaves differently and the dissolution rates could be brought down to only 3 nm/min at 40°C using 0.5 mM ADS and 5 mm BTAH together in the slurry. Several cationic surfactants and tetrazoles were explored for oxalic acid/H2O2 based slurries. CTAB (a cationic surfactant) was the best among all the inhibiting agents for oxalic acid/H2O2 system. Potentiodynamic/Potentiostatic polarization experiments, and contact angle measurements were used to understand the nature of the passive film and the role of these inhibitors in surface protection of Cu. When both ADS and BTA were present in the slurry having several complexing agents (amino acids and acetic acid), the contact angle was high (∼90°) and the corrosion current density was the lowest. An understanding of the behavior of the slurry additives towards achieving a low Cu dissolution rates and high planarization efficiency is the objective of this work. Directions for future work have been stated at the end of the thesis.; Part-2. The effect of size and concentration of ceria abrasive particles (untreated and treated with a poly-acrylic acid (PAA) additive used as a dispersant) on oxide and nitride polish rates for STI CMP was investigated. It was observed that a significantly high oxide polish rate (∼