Introduction
The basic interactions that occur between particles and wafer surfaces in solution are van der Waals forces ( molecular interactions ) and electrostatic forces ( interactions of electric double layers ) . In recent years, research related to the particle adhesion mechanism on the surface of wafer in solution that conforms to the above two effects has been booming, and a lot of work has been done to elucidate the particle adhesion mechanism.
Most substances acquire a surface charge when they come into contact with a solution, as is said in colloidal chemistry. This charge is thought to result from solid surface ionization, ion adsorption to the solid surface, and ion dissolution. The charged solid surface in the solution affects the ion distribution in the area around the interface; ions with the opposite sign to the charged solid surface are pulled toward the interface, while ions with the same sign are forced away from the interface. In this way, an electrical double layer forms at the electrical interface with in the solution and subsequently affects particle adsorption and removal associated with the wafer surface.
Next, the ζ potential will be briefly explained. If a solid is immersed in a solution, there is an electric double layer at the solid- liquid interface. Figure 10.1 shows a structural model of a solid-liquid interface based on Stern's theory for a positively charged surface.
In this electric double layer, in the almost solid part, there is a Stern layer that absorbs opposite ions. Furthermore, a diffusion layer is present on its exterior. There is a slip surface outside the stern layer. The potential at this slip surface is called the zeta potential. The slip plane is located somewhere in the liquid rather than right at the solid- liquid phase boundary. Zeta potential is used to account for particle adhesion and removal from the wafer surface.
Figure 10.2 shows a schematic of the particles in solution and the wafer surface. For example, due to the absorption of H" ions, it is speculated that both surfaces are positively charged. Near the charged surface, negative ions are affected by electrostatic attraction and irregular Brownian motion, forming an electric double layer. In this case
