Mechanistic Insights Into Microwave Annealing for Lattice Defect Recovery

The miniaturization of Si-MOS-FET logic integrated circuits necessitates the precise control of electron and hole densities through high-concentration impurity doping to realize transistors within the 2 nm technology node. Among the various thermal treatment techniques, microwave annealing (MWA) has emerged as a promising method for forming high-concentration active layers, offering advantages such as rapid processing and potential nonthermal effects. However, existing MWA systems suffer from interference and standing-wave effects because of their multimode cavity design, which makes it challenging to understand the underlying mechanisms. This study investigated the fundamental heating mechanisms of MWA, focusing on both the electric and magnetic field contributions. The role of Joule heating was examined, and the presence of nonthermal microwave effects was explored by applying MWA to Si substrates implanted with phosphorus or boron and comparing the results with those of conventional rapid thermal processing. The experimental evaluations included sheet resistance measurements, impurity distribution analysis, and defect assessments using slow-energy positron annihilation spectroscopy. The findings indicate that MWA enables the effective activation of implanted impurities at low temperatures, reduces defect formation, and minimizes impurity diffusion, highlighting its potential as a low-temperature processing technique for fabricating advanced semiconductor devices.