E.2.II - Cleaning of Trace Metallic Impurities from Solid Substrates Using Liquid Media

Abstract

This chapter reviews the different mechanisms of metallic impurity adsorption on various surfaces and especially those surfaces that are important in the manufacturing of semiconductors. From a technological point of view, the liquid chemical environment is the environment that is most worthy of analysis. Wet chemistry is the most powerful and the most versatile process available today to remove metallic and other ionic impurities from surfaces. The different aspects of wet chemistry are described in this chapter. The state of the elements in the solution is the first important aspect of any wet cleaning chemistry. This is thoroughly investigated together with the engineering tools available to predict any contaminants' state in any kind of solution. The next important aspect is the state of the surfaces on wafers. It is shown that almost all surfaces of interest could be divided into two main groups: the hydroxide- or silanol-terminated oxide or silica-type surface, and the hydride-terminated silicon surface. Both surfaces react very differently with metallic impurities and, therefore, an in-depth review of the adhesion mechanisms, the adsorption forces, and the cleaning solutions is provided for each surface.