沉积方法对颗粒去除效率的影响

In semiconductor manufacturing, wafer surface  cleaning is one of the most important processes as the  integration density of device increases.[1] To develop  cleaning process, various particles should be deposited  on wafer surfaces to measure particle removal efficiencies.  Particles can be suspended in air or liquid before  deposition on wafer surfaces in liquid and air enviroononmet.

In this article, removal efficiency of submicron  alumina particles from silicon wafer surfaces with  different deposition methods. Dry deposition and wet  spray deposition using IPA and DI water were used.

In order to understand the capillary effect between  the particle and the wafer surface theoretically, adhesion  force of the particle was calculated in term of van der  Waals force and capillary force. van der Waals force is  described as following equation (1).

where A is the Hamaker constant, r is the particle radius,  rc  is the radius of the contact surface area, and Z is the  atomic separation between the substrate and the  particle.[2] On the other hand, the capillary force  described as below (2). where γ is the surface energy, R is the radius of the particle adhering to a flat substrate.[3] In equation (1), Hamaker constant, particle size and radius of the contact surface area are important parameters in van der Waals force while capillary force is strongly dependent on surface energy of the liquid medium and particle size not by material characteristics. From the theoretical calculation, both adhesion forces become lager with an increase of the particle size. However adhesion force per unit area (calculated by the division of  increase significantly with a decrease of  the particle size as shown in Figure 1. This implies that  smaller particles are more difficult to remove from the  surface due to the increased van der Waals and capillary  pressures. In addition, the capillary force at DI water is  much stronger than IPA. This implies that the particles  deposited with DI water are more difficult to remove from  the wafer surface due to the larger capillary force than  IPA.

In order to verify the theoretical analysis, a laser  shock cleaning using a Q-switched Nd:YAG laser with a  wavelength of 1064nm was carried out for the different  particle status. A gap distance of between the laser focus  and wafer surface was changed to control the laser shock force. A spray gun with DI water and IPA was used to  deposit the particles on the silicon wafer surfaces.