Laser thermal processing using an optical coating for ultra shallow junction formation

Abstract

Semiconductor doping is a critical step in microelectronic device fabrication. Particularly, ultra-shallow junction formation for the CMOS 45-nm node is today intensively studied. Laser thermal processing (LTP) has already shown potentiality to achieve abrupt and ultra-shallow junctions, with a very low resistivity. However, the laser process has to be integrated in the conventional process flow of a real CMOS device fabrication. Therefore, the laser treatment needs to preserve the integrity of the different irradiated structures like transistor gates. Optical coatings, including reflective and anti-reflective coatings, can be used to protect the structures and to control the lateral diffusion of the dopants. In this work, we have studied different optical coatings (different materials and thicknesses) irradiated by a long pulse SOPRA VEL 15 excimer laser (200 ns–15 J). Junctions have been characterized by 4-point probe, in situ reflectivity, UV photometry and secondary ion mass spectroscopy. The efficiency and the integrity of the different coatings have been studied for different laser irradiation conditions in solid and molten phases. The results show that a proper optical coating optimizes the coupling of the deposited laser energy and is promising for improving the integration of the laser activation process of future CMOS junctions.