Structural effect of PVA brush nodule on particle removal efficiency during brush scrubber cleaning

Polyvinyl acetal (PVA) brush cleaning is one of the most important processes in the post chemical mechanical planarization (CMP) cleaning process. However, PVA brush could be severely contaminated due to strong direct contact with a large amount of abrasive particles during the long-time post CMP cleaning, and the particles on the brush can be easily transported to the next wafer substrate. In this study, we tested four different types of conditioning processes to remove the particles from the brush to increase the cleaning efficiency of post CMP process and comparatively evaluated using FE-SEM. The physical scrubbing method showed higher cleaning efficiency than the chemically dipping method, but some abrasive particles remained on the non-contacted surface. The flow-through method using pH 11 showed the higher removal ability than pH 3 and 7 due to strong repulsive force between silica abrasive particle and PVA brush, but some abrasive particles remained due to non-uniform flow of chemicals. The ultrasonication method with DIW was found to be very effective to remove the particles completely from the brush without damage. Consequently, the new developed conditioning process provides an environmentally friendly and cost effective alternative conditioning process to the existing conditioning process of contaminated PVA brushes.

Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

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A Breakthrough Method for the Effective Conditioning of PVA Brush Used for Post-CMP Process

Lee

Ryu

Hwang

et al. 2019

“…22 Other researchers have presented the effects of zeta potential and friction forces between brush and wafer on crosscontamination during scrubbing. 23,24 Cross-contamination decreases brush lifetime by decreasing cleaning performance and can induce yield-reducing defects on the wafer surface such as circular rings, organic residue, and scratches. Hence, brush contamination mechanisms need to be investigated to avoid defects related to crosscontamination.…”

mentioning

confidence: 99%

Study on PVA Brush Loading and Conditioning during Shallow Trench Isolation Post-CMP Cleaning Process

Sahir

Cho

Kim

et al. 2022

Polyvinyl acetal (PVA) brush cleaning is a widely accepted and efficient process for removing contaminants of the chemical mechanical planarization process during semiconductor processing. However, contaminants can adhere to the PVA brush, due to its highly hydrophilic and porous nature, and deteriorates its performance. This contamination is a serious problem, especially for processing devices smaller than 10 nm. Here, the effect of cleaning solution pH was investigated for ceria removal from oxide wafers and subsequent transfer to the PVA brush during scrubbing. A cleaning solution of pH 7 resulted in lower ceria removal efficiency compared to pH 2 and 12. The pH 2 and 7 cleaning conditions resulted in high brush loading compared to the pH 12 condition. High brush contamination at pH 7 resulted in higher cross contamination, whereas very low cross-contamination was observed at pH 2 and 12. The effect of ultrasonication and scrubbing on improvement of brush performance and lifetime was evaluated. Scrubbing in the presence of NH4OH efficiently removed all ceria particles from contaminated brushes. Because the bonding between brush and ceria particles is strong, only a robust physical force combined with a high chemical action can remove ceria particles loaded onto a PVA brush.

“…The contact state between the brush and surface is very complex because of the soft nature of the brush, the asperities on the brush surfaces, and the porous structure of the brush surface. Generally, PVA brushes have a number of cylindrical nodules on their outer surfaces, and the mechanical effect of the brush nodule structure 1 and brush design [2][3][4] has been investigated. The factors dominating particle removal during scrubber-based cleaning differ depending on the size and type of particles, location and time of contact, and the contact state between the brush and surface.…”

mentioning

confidence: 99%

Effect of Surface Wettability on Frictional Conditions during Scrubbing Using Polyvinyl Acetal Brush

Hara

Sanada

Fukunaga

et al. 2015

To gain insight into the mechanisms of polyvinyl acetal (PVA) roller brush cleaning in semiconductor device fabrication, we measure the shear force between four types of PVA brushes and several surfaces and evaluate the effect of the brush rotation speed and surface wettability on the shear force. We simultaneously measure the normal force to evaluate the coefficient of friction (COF). The shear force between the brush and surface is affected by the surface wettability, and the COF is found to decrease and approach 0.5 as the brush rotation speed increases. At low rotation speeds, the COF of hydrophobic surfaces is large (almost 1.0), whereas that of hydrophilic surfaces is small. These results imply that the brush directly makes contact with the surface and that the real contact area of the PVA brush increases with the contact time. In addition, the contact and absorbed water behavior between a brush nodule and the surface was observed using a high-speed video camera. The amount and direction of water seeping out of the nodule depend on the rotation speed and surface wettability. The results indicate that the water motion during nodule contact plays an important role in determining the friction.