Impact of nanosecond laser energy density on the C40-TiSi2 formation and C54-TiSi2 transformation temperature

Abstract

The formation of Ti based contacts in new image sensor complementary metal–oxide–semiconductor technologies is limited by the requirement of a low thermal budget. The objectives of these new 3D-technologies are to promote ohmic, low resistance, repeatable, and reliable contacts by keeping the process temperature as low as possible. In this work, ultraviolet-nanosecond laser annealing was performed before classical rapid thermal annealing (RTA) to promote the formation at lower RTA temperatures of the low resistivity C54-TiSi2 phase. The laser energy density was varied from 0.30 to 1.00 J/cm² with three pulses in order to form the C40-TiSi2 phase and finally to obtain the C54-TiSi2 phase by a subsequent RTA at low temperatures. The formed Ti-silicides were characterized by four-point probe measurements, x-ray diffraction, transmission electron microscopy, and atom probe tomography. A threshold in the laser energy density for the formation of the C40-TiSi2 is observed at an energy density of 0.85 J/cm² for the targeted TiN/Ti stack on blanket wafers. The C40-TiSi2 formation by laser annealing prior to RTA enables to reduce the formation temperature of the C54-TiSi2 phase by 150 °C in comparison to a single RTA applied after the Ti/TiN deposition. This specific phase sequence is only observed for a laser energy density close to 0.85 J/cm². At higher energy densities, the presence of C49-TiSi2 or a mixture of C49-TiSi2 and C54-TiSi2 is observed. The underlying mechanisms of the phase sequence and formation are discussed in detail.