Electrolyzed Sulfuric Acid Application in Semiconductor Cleaning Processes: An Advanced Substitution of SPM Cleaning

SPM cleaning, a mixture of Sulfuric Acid and Peroxide, is a commonly used cleaning method in the semicondutor industry. The main purpose of the SPM cleaning is remove unwanted metal and organic contamination by oxidation process. The removal rate of both metal and organic contamination depend on the density of peroxide. As the semiconductor technology node shrinks, processes require less amount of metal loss, while the removal of organic contamination is relatively maintained. It is impossible to meet the demand with the conventional SPM cleaning, in which the density of peroxide do not take part in improving the metal, polymer selectivity. Instead of using conventional SPM cleaning, where peroxide produces Caro's acid taking the main part in the oxidation process, electrolytic Sulfuric Acid is introduced. Electrolytic sulfuric acid produces Persulfate ion, which is more powerful oxidizer compared to peroxide used in conventional SPM cleaning. We used the Kurita's “Green Sulfaceed KD”(GS-KD) Module to supply the electrolytic sulfuric acid into the DNS batch type FC-3100 system. Electrolytic Sulfuric Acid, compared to conventional SPM Cleaning, showed improvement in the metal, organic removal selectivity. In this paper, cases of process integration challenges concerning the metal, organic removal selectivity are reviewed. In case of a metal residue removal process with metal disclosure, minimum removal is required, however excess metal removal results in contact disconnection. In case of a implant dosed photo resist residue stripping process with danger of metal disclosure, low peroxide SPM cleaning is required however it is insufficient to strip the photo resist residue. Using the Electrolytic Sulfuric Acid, it was possible to meet the requirements of the processes, removing the unneeded residues while maintaning the metal underlayers. The improvement in the removal selectivity became the key factor in overcoming the technical challenges in the processes.