Different cobalt surfaces (as-received, metallic, and oxidized Co) were characterized by contact angle measurements, FTIR (Fourier-transform infrared spectroscopy), XPS (X-ray photoelectron spectroscopy) and EIS (electrochemical impedance spectroscopy) to investigate the interaction of these surfaces with benzotriazole (BTA). A new sequential EIS technique was used to study the inhibition capabilities of BTA on the cobalt surface and its stability under de-ionized (DI) water rinsing. It was found that a Co-BTA complex passive layer was formed when exposed to a BTA solution for all types of Co surfaces. It was hypothesized that BTA could actively form a Co-BTA complex on metallic Co as well as on the Co oxide surface. Interestingly, most Co-BTA complexes could be easily removed by simply rinsing with DI water, which indicates that BTA might not produce an organic residue issue after the chemical mechanical planarization (CMP) process. This was also well supported by potentiodynamic studies.
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 use of polyvinyl acetal (PVA) brushes is one of the most effective and prominent techniques applied for the removal of chemical mechanical planarization (CMP) contaminants. However, the brush can be a source of defects by entrapping the abrasives inside its porous structure during brush scrubbing. In this study, the effect of brush top skin layer was extensively studied on contamination, cross-contamination, and cleaning performance by comparing brushes with and without skin layer. The presence of a dense top skin layer resulted in larger contact areas and high ceria particle adsorption on the skin layer. This leads to higher cross-contamination of the wafers during scrubbing along with high cleaning performances. Conversely, the brushes without skin layer showed lower contamination and negligible cross-contamination with a reduced cleaning performance (removal of ceria particles from oxide surface). Therefore, the role of the brush skin layer is significant and needs to be considered while designing a post-CMP cleaning process.
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