Author:

Keywords:

Science & Technology, Technology, Engineering, Manufacturing, Engineering

Abstract:

We have studied how dilute HF-based cleaning recipes could be optimized in order to have a good particle removal efficiency and at the same time to minimize the (re-)deposition of particles. For this purpose, the removal of different particles (Si3N4, Al2O3, SiO2 and PSL) from thermal oxide substrates was studied. It was observed that the positively charged Si3N4 and Al2O3 particles were difficult to remove from the wafer substrate using a dilute HF-clean. When the pH of the following rinse was decreased to pH 2, the removal was significantly increased. This is explained in terms of preventing the re-deposition of the particles during the rinse using a simplified model. It is postulated that during a neutral rinse after an HF-based clean, the Si3N4 and Al2O3 particles will deposit on the oxide substrate because of electrostatic attraction forces during the rinse. When the pH is lowered during the rinse, the electrostatic attraction forces are replaced by repulsion forces that prevent these particles from re-deposition. For the SiO2 and PSL particles a decrease in removal efficiency was observed when the pH of the final rinse was lowered. This can be explained using the same model and is attributed to a decrease in electrostatic repulsion at lower pH for the SiO2 particle or to an electrostatic attraction at lower pH for the PSL particles. Best cleaning efficiency for all particles was obtained using an overflow rinse at a low pH in combination with megasonics.