半导体加工中注入的光刻胶和阻挡金属的氧化去除

ABSTRACT

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 wereabraded 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.

                                                                                  Figure 1. Trends in logic and memory devices