A Water Polishing Process to Improve Ceria Abrasive Removal

Abstract

This study details the improved ceria abrasive removal on SiO 2 wafer during the post CMP water polishing (buff clean) process. Initially, the zeta potentials of the wafer and ceria abrasive were measured according to pH and compared with the zeta potential and pH change during water polishing. From these measurements, it was determined that the zeta potential difference between the ceria abrasive and the wafer decreased during water polishing. The electrical repulsion between them decreased as well. Additionally, ceria abrasive removal was measured using a surface defect inspection system. The abrasive removal increased when water polishing conditions such as pressure, rotation speed and processing time increased. Chemical enhancement and a pad cleaning process also increased the ceria abrasive removal. Consequently, the total defect counts were reduced by 91.8% with the optimized water polishing condition. These results provide useful data for determining optimal water polishing conditions for more effective post CMP cleaning.

The Effect of Surfactants on the Removal of Ceria Particles in the Buff Clean Process

“…It has been reported that in a water buff clean process, most of the ceria particles can be removed. 12,20 After the buff clean with DIW only, Fig. 2b shows that the number of the residual ceria particles on the SiO 2 surface reduces to 361.…”

“…1,4 As a result, it is critical to remove the remaining ceria particles from the SiO 2 dielectric film after the CMP procedure. 9,12 In the post-CMP cleaning process, a variety of methods are employed to remove the remaining particles from the wafer. Traditional standard cleaning solutions, such as alkaline SC1 (NH 4 OH:H 2 O 2 :H 2 O = 1:5:10) and acidic SPM (H 2 SO 4 :H 2 O 2 = 3 ∼ 4:1, contain strong acidic and alkaline substances (HCl, H 2 SO 4 and NH 4 OH), and need heating during the cleaning process.…”

Communication—Effect of Hydrogen Water on Ceria Abrasive Removal in Post-CMP Cleaning

“…After the CMP process was over, a buff clean was performed by using the water jet on the same pad. 8 During the buff clean, the effect of hydrogen water on the cleaning performance was evaluated while maintaining the other process conditions. KOH was used to control the pH of the hydrogen water for more effective cleaning.…”

“…6,7 Thus, the ceria abrasive removal has been an important process in post-CMP cleaning. 8 In this study, we propose the use of hydrogen water in the ceria CMP cleaning. The hydrogen water can remove the ceria abrasives by the reduction reaction.…”

Effect of Viscosity on Ceria Abrasive Removal during the Buff Clean Process

“…Our previous research showed that the removal efficiency of the ceria abrasive was improved by approximately 91% on including a water polishing (buff clean) process. 12 It was assumed that it would be more effective to remove the ceria abrasive if the chemicals are mixed with deionized (DI) water in the buff clean process. The chemical used as additive is glycerin.…”