## 3 Results and Discussion  
The combination of MEA and ammonium bifluoride rendered the cleaning agent ineffective in removing Level-1 contamination, but this preparation was good for the other concerns, such as leaving no CI trace corrosion, no UBM under cut, and no gel residue and not attacking ink marks. The combination of propylene glycol methyl ether acetate (PGMEA) solvent and ammonium bifluoride (Figure 5) rendered the cleaning agent ineffective in removing Level-1 contamination as well as other contaminants such as glues from the dicing tape. As seen in Figure 6, ammonium bifluoride in acidic conditions (H\({}_{2}\)SO\({}_{4}\) + NH\({}_{4}\)F-HF) could effectively remove Level-1 silicon contamination. This result proved the assumptions of Section 2.4. Figure 5: PGMEA, as a solvent, not only obstructed ammonium bifluoride from cleaning Level-1 silicon contaminants (shown by the red arrow) but also dissolved the UV glue from the dicing tapes, leaving more residues on the IC surface. In Test 3 of Table 4, the results confirmed that the combination of ammonium bifluoride in high concentration with sulfuric acid could effectively remove Level-1 contaminants (Figure 6), without corroding the aluminum metal [8; 22]. Additionally, no signs of disruption of the adhesive materials from the dicing tape and ink dot were observed, but when the solution came in contact with under-bump metal (UBM), the peel-off of the bumps was noticeable (Figure 7). \begin{table}
\begin{tabular}{l l l l l l l} \hline \multirow{2}{*}{**Test**} & \multirow{2}{*}{**Composition**} & \multicolumn{3}{c}{**Performance**} \\ \cline{3-8}  & & **Si** & **Al Corrosion** & **UBM** & **Gel Residue** & **Ink Marks** \\  & & **Level 1** & **Al Corrosion** & **Under Cut** & **Gel Residue** & **Ink Marks** \\ \hline
1 & 40\% MEA + 4\% NH4F-HF + 56\% H2O & NG & OK & OK & OK & OK \\ \hline
2 & 40\% PGMEA + 4\% NH4F-HF + 56\% H2O & NG & OK & OK & NG & NG \\ \hline
3 & 10\% H2 SO4 + 4\% NH4F-HF + 86\% H2O & OK & OK & NG & OK & OK \\ \hline
4 & 15\% H2 SO4 + 1\% NH4F-HF + 84\% H2O & NG & OK & NG & OK & OK \\ \hline
5 & 15\% H2 SO4 + 4\% C NH4F-HF + 7\% non-ionic surfactant + 74\% H2O & NG & NG & NG & NG & NG \\ \hline
6 & 20\% H2 SO4 + 6\% NH4F-HF + 74\% H2O & OK & OK & NG & OK & OK \\ \hline
7 & 20\% H2 SO4 + 3\% NH4F-HF + 77\% MSA & NG & OK & OK & NG & NG \\ \hline
8 & 20\% H2 SO4 + 3\% NH4F-HF + 30\% MSA + 47\% H2O & OK & NG & \(\triangle\)OK & OK & NG & NG \\ \hline
9 & 10\% H2 SO4 + 1.5\% NH4F-HF + 8.5\% MSA + 80\% H2O & OK & OK & \(\triangle\)OK & OK & OK & NG \\ \hline \end{tabular}
\end{table} 
Table 4: Summary of Cleaning Performance for Si Contaminants. Figure 6: Cleaning results with ammonium bifluoride in acid formula, with the right side showing clear removal of all contaminants. The comparison of Test 3, 4, and 6 in Table 4 showed that the mixture of H\({}_{2}\)SO\({}_{4}\) and NH\({}_{4}\)F-HF left the ultraviolet (UV) glue of the cutting tape and ink marks intact, while it only removed Level-1 silicon contamination. Higher concentrations of H\({}_{2}\)SO\({}_{4}\) could indeed protect the aluminum metal, but not UBM (Ti/TiW) [5; 26; 27]. Test 5 in Table 4 found that the non-ionic surfactant additive did not remove the contaminants by a general ionic mechanism, as expected, but by the chemical reaction of micro-etching, as illustrated below in Equation (7) [26; 28; 29]. \[\mathrm{H_{2}SiO_{3}+6 NH_{4}F-HF\to H_{2}SiF_{6}+3H_{2}O+6 NH_{4}F} \tag{7}\]  
The reaction product of H\({}_{2}\)SiF\({}_{6}\) is soluble in water, so NH\({}_{4}\)F-HF could effectively remove the polysilicic acid to free the silicon powder from bonds with the wafer surface, which in turn could be easily removed [1; 30]. The NH\({}_{4}\)F solution served as a chemical buffer to ammonium bifluoride, such that it slowed down and stabilized the etch efficiency [17; 20].