Fabrication of current generation integrated circuits involves the creation of multilevel copper/low-k dielectric structures during the back end of line processing. This is done by plasma etching of low-k dielectric layers to form vias and trenches, and this process typically leaves behind polymer-like post etch residues (PER) containing copper oxides, copper fluorides and fluoro carbons, on underlying copper and sidewalls of low-k dielectrics. Effective removal of PER is crucial for achieving good adhesion and low contact resistance in the interconnect structure, and this is accomplished using wet cleaning and rinsing steps. Currently, the removal of PER is carried out using semi-aqueous fluoride based formulations. To reduce the environmental burden and meet the semiconductor industry's environmental health and safety requirements, there is a desire to completely eliminate solvents in the cleaning formulations and explore the use of organic solvent-free formulations.The main objective of this work is to investigate the selective removal of PER over copper and low-k (Coral and Black Diamond®) dielectrics using all-aqueous dilute HF (DHF) solutions and choline chloride (CC) - urea (U) based deep eutectic solvent (DES) system. Initial investigations were performed on plasma oxidized copper films. Copper oxide and copper fluoride based PER films representative of etch products were prepared by ashing g-line and deep UV photoresist films coated on copper in CF4/O2 plasma. PER removal process was characterized using scanning electron microscopy and X-ray photoelectron spectroscopy and verified using electrochemical impedance spectroscopy measurements.A PER removal rate of ~60 Å/min was obtained using a 0.2 vol% HF (pH 2.8). Deaeration of DHF solutions improved the selectivity of PER over Cu mainly due to reduced Cu removal rate. A PER/Cu selectivity of ~20:1 was observed in a 0.05 vol% deaerated HF (pH 3). DES systems containing 2:1 U/CC removed PER at a rate of ~10 and ~20 Å/min at 40 and 70oC respectively. A mixture of 10-90 vol% de-ionized water (W) with 2:1 U/CC in the temperature range of 20 to 40oC also effectively removed PER. Importantly, etch rate of copper and low-k dielectric in DES formulations were lower than that in conventional DHF cleaning solutions.

Chemical systems containing oxidants are widely used at various stages in semiconductor processing, particularly for wet cleaning and polishing applications. This dissertation presents a series of studies related to oxidative removal of materials in the Front-End-Of-Line (FEOL) and Chemical Mechanical Planarization (CMP) processes during IC fabrication. In the first part of this study, stripping of photoresists exposed to high dose of ions (1E16 As/cm²) was investigated in activated hydrogen peroxide systems. Stripping of photoresists (PR) exposed to high dose (>1E15/cm²) ion beams is one of the most challenging steps in FEOL processing. This is due to unreactive crust layer that forms on the resist surface during ion implantation. The use of hydrogen peroxide systems activated by metal ion or UV light, for disrupting crust formed on deep UV resist to enable complete removal of crust as well as underlying photoresist was investigated. A systematic evaluation of variables such as hydrogen peroxide and metal ion concentration, UV intensity, temperature and time was conducted and an optimal formulation capable of attacking the crust was developed. A two step process involving pretreatment with activated hydrogen peroxide solution, followed by treatment with sulfuric acid-hydrogen peroxide mixture (SPM) was developed for complete removal of crusted resist films. In the second part of this study, electrochemically enhanced abrasive removal of Ta/TaN films was investigated in solutions containing 2,5 dihydroxy benzene sulfonic acid (DBSA) and potassium iodate (KIO₃). This method known as Electrically-assisted Chemical Mechanical Planarization (ECMP) is generating a lot of interest in IC manufacturing. Ta/TaN films were abraded at low pressures (<0.5 psi) on a polyurethane pad under galvanostatic conditions. The effect of variables including pH, KIO3 concentration, and current density has been explored. In the optimized formulation, tantalum and tantalum nitride removal rates of ~170 A⁰/min and ~200 A⁰/min, respectively have been obtained at a current density of 1 mA/cm². The use of benzotriazole as a copper inhibitor was required to obtain Ta to Cu selectivity of 0.8:1. Additionally, the nature of the oxide film formed on tantalum during the electrochemical abrasion process was characterized.