Material Science and Metallurgy

6

Diffusion

6.1 INTRODUCTION

Diffusion is defined as a natural tendency of the molecules to flow from higher concentration to lower concentration. Impurity diffusion is the process by which impurity particles move from a region of high concentration near the surface of a crystal to the region of low concentration within the crystal. Diffusion is the net action of matter (atoms or molecules) in the form of heat, momentum or light, whose purpose is to minimize concentration gradient.

Diffusion of various impurities into selected regions of a semiconductor allows to fabricate complex electronic circuits in a single semiconductor crystal. A beam of impurity ions is accelerated to kinetic energy level of 50 keV or more and then directed to the surface ...