In this paper, the formation of Er disilicide (ErSi2-x) with a Ti cap on low doping n-type Si(100) is investigated. After deposition in ultrahigh vacuum, the solid-state reaction between Er and Si is performed ex situ by rapid thermal annealing between 450 and 600 °C in a forming gas ambience with a 10 nm thick Ti capping layer to protect Er from oxidation. X-ray diffraction analyses have confirmed the formation of ErSi2-x for all annealing temperatures. The formed films are found to be free of pinholes or pits and present a sharp and smooth interface with the Si bulk substrate. The extracted Schottky barrier height (SBH) corresponds to the state-of-the-art value of 0.28 eV if the annealing temperature is lower than or equal to 500 °C. This result demonstrates the possibility to form low SBH ErSi2-x/n-Si contacts with a protective Ti cap. However, when the annealing temperature is set to a higher value, the SBH concomitantly rises. Based on our experiments, this SBH increase can be mainly related to an enhanced diffusion of oxygen through the stack during the annealing, which degrades the quality of the ErSi2-x film.