Citric Acid and NaIO(4) Based Alkaline Cleaning Solution for Particle Removal during Post-Ru CMP Cleaning

Abstract

Post Ru CMP cleaning solution for particle (alumina) removal was successfully developed by controlling surface zeta potentials and choosing the proper Ru etchant. The zeta potentials of both alumina particles and Ru surface were measured as a function of pH. It was found that 1000 ppm of citric is good enough to modify the zeta potentials of both alumina particles and Ru surface at pH 10. At this condition, both Ru and alumina particles will have negative zeta potentials which will cause repulsion between them. This effect was confirmed by measuring the adhesion force between Ru and alumina particle by using force distance method at different pH values. The lowest adhesion force between an alumina particle and the Ru surface was observed in citric acid solution at pH 10. However, this effect can be magnified by adding an etchant to the cleaning solution which can lift off the particles. NaIO4 was chosen as Ru etchant and added to citric acid solution at pH 10. The highest PRE of 97% was achieved in citric acid solution at and slightly below 0.01 M of NaIO4 concentration at pH 10.