Chapter 5 Neutralization of Deep Levels in Silicon

Abstract

This chapter describes the hydrogen (H) neutralization of deep levels in silicon. These are defects because of the so-called “deep” impurities, such as the metals gold (Au), iron (Fe), nickel (Ni), copper (Cu), platinum (Pt), palladium (Pd), molybdenum (Mo), and silver (Ag). The removal of the deep levels associated with these defects normally requires annealing temperatures of at least 400°C but can be achieved by H neutralization at much lower temperatures. The thermal evolution of H from these defects has activation energy of at least 2.2 eV. The chalcogens, sulfur (S), selenium (Se), and tellurium (Te), also form deep levels. The chapter discusses the problem of oxygen thermal donors that form two levels near the conduction band. These oxygen defects can be neutralized by monatomic H (that is, their states removed from the energy bandgap), but the microstructure of the oxygen-related defect is still unknown. The chapter also discusses process-related defects, such as those because of sputter etching and deposition, and reactive-ion etching. There is a useful table of energy levels associated with various defects and the reactivation energy of these defects by thermal dehydrogenation treatment. In some cases, prehydrogenation treatments may last through subsequent processing steps to provide protection against further defect formation, such as during silicide formation that is equivalent to damage hardening. The chapter presents a list of the deep-level centers passivated by atomic hydrogen in the major elemental semiconductor, such as silicon (Si), and discusses their thermal stability and the possible passivation mechanisms.