## 2 Materials and Methods
### Development of a New Cleaning Agent  
Five targets needed to be achieved by the new cleaning agent developed in this research.  
* Full cleaning of the silicon contamination (Levels 1 to 3)
* No IC trace (Al) corrosion remaining after cleaning process
* No more UBM under cut to enhance
* No gel residue
* In mark area, residue is more than 80% and is readable.  
Existing agents used in the cutting process, such as the stripper and alkaline solvents, are mostly alkaline based. However, given the fact that the contaminants are primarily bound together by the interaction between water and silicic acid polymers (Figure 3), we would propose a cleaning agent based on the acidic properties of HF (BOE) [16].The chemical reactions involved are shown in Equations (5) and (6) below [17]:  
\[\text{SiO}_{2}+4\text{HF}+2\text{NH}_{4}\text{F}\rightleftharpoons(\text{NH}_{4}) _{2}\text{SiF}_{6}+2\text{H}_{2}\text{O} \tag{5}\]  
\[\text{SiO}_{2}+6\text{HF}\rightleftharpoons\text{H}_{2}\text{SiF}_{6}+2 \text{H}_{2}\text{O} \tag{6}\]  
Since HF is highly toxic to the human body, we used NH\({}_{4}\)F-HF instead to verify the cleaning effect against silicon contamination [18; 19; 20; 21].  
The IC metal is mostly aluminum and must be protected during the manufacturing process. The role of sulfuric acid in the cleaning agent is to provide hydrogen ions (H\({}^{+}\)) in solution. Additionally, as noted in the literature, metal can be passivized when the sulfuric acid exceeds a specific concentration; that will be prevented from occurring during the cleaning process [5; 22; 23].  
Figure 4: There are two main steps in the process of cleaning silicon contamination: the first is to dissolve the bonds of polysilicic acid, the particle-to-particle bonds, and the bonds between the particles and the surface of the IC; in the second step, water spray or a brush is used to cause agitation between the contamination particles, thus aiding the silicon contamination removal efficiency.  
In addition to the silicon element, there are other contaminants such as the adhesive glue, the dicing tape, the metal chips from the blade and other materials from the IC dicing assembly line (passivation material, SiO\({}_{2}\), Al, Cu, etc.) [24].  
Therefore, in order to successfully remove these contaminants, a proper solvent, in addition to ammonium bifluoride as an ingredient, must be added [25], but must not be so strong as to erode away the exposed IC metals [22]. Methane sulfonic acid (MSA) was selected as the solvent for this research. Since it is a derivative of sulfate, it formed a buffer solution of sulfuric acid, which allowed us to control the release of hydrogen ions (H\({}^{+}\)) and adjust the acidic acid level and prolong the lifespan of the cleaning agent [5]. MSA has an R group, which is -CH\({}_{3}\), giving it the ability to dissolve glues. The combination of the organic R group and an inorganic sulfate also gives it the properties of surfactant, further enhancing its cleaning strength [5].  
For a comprehensive review, N-methylethylamine (MEA) and propylene glycol methyl ether acetate (PGMEA) were included in the testing list. Four groups of tests were planned for this research. The first was to test the performance of the alkaline (MEA) formula, the second to test the solvent-based formula (PGMEA), the third to verify the surfactant additive, and the fourth to study the acidic formulas assumed in Section 2.4 (ammonium bifluoride/sulfuric acid/MSA).