Selective Alkaline Wet Etching of Al and AlCu Using a Phosphoric and Nitric Acid Free Formulation

In this study, a broad screening of alkaline solutions was conducted to evaluate the etching performance of Al and AlCu, as well as their compatibility with photoresist (PR) materials. The cations and anions in the alkaline salts were found to influence the etch rate (ER) of AlCu at equivalent pH levels, possibly due to differences in ion mobility and anionic complexation. At high pH, the ER has increased significantly; however, PR compatibility had been reduced. An optimal balance has been observed in the pH range of 12 to 13. The addition of chelating agents has shown to enhance the ER of the solution. Surfactants have lowered the contact angle of the solution but have adversely affected the PR on patterned wafers. This chemical screening effort has led to the formulation of TechniEtch D-BAL220. Using this solution, both the presence of Cu and the metal deposition temperature have been found to influence the ER. Full wafer tests have also been performed by immersion in a wet bench setup.