A. Laszcz

Low Schottky barrier height for ErSi2−x/n-Si contacts formed with a Ti cap

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.

Schottky barrier lowering with the formation of crystalline Er silicide on n-Si upon thermal annealing

The evolution of the Schottky barrier height (SBH) of Er silicide contacts to n-Si is investigated as a function of the annealing temperature. The SBH is found to drop substantially from 0.43 eV for the as-deposited sample to reach 0.28 eV, its lowest value, at 450 degrees C. By x-ray diffraction, high resolution transmission electron microscopy, and x-ray photoelectron spectroscopy, the decrease in the SBH is shown to be associated with the progressive formation of crystalline ErSi2-x.

UHV fabrication of the ytterbium silicide as potential low Schottky barrier S/D contact material for n-type MOSFET

Ytterbium silicide provides a low Schottky barrier height to electron on n-type silicon. This property makes this material very attractive for the realization of Source/Drain contacts for n-type MOSFETs. In this communication, the study of structural and electrical properties of YbSi2-x fabricated at different temperature in Ultra-High Vacuum condition without any protective layers is presented. N-type SB-MOSFETs with ytterbium silicide based S/D contacts were fabricated at optimal silicidation temperatures on SOI substrate with an ultra thin body.

Transmission electron microscopy study of erbium silicide formation from Ti/Er stack for Schottky contact applications

In this paper, we present results of transmission electron microscopy studies on erbium silicide structures fabricated under various thermal conditions. A titanium cap has been used as a protective layer against oxidation during rapid thermal annealing of an erbium layer in a temperature range of 300–700°C. Both layers (200 nm Ti and 25 nm Er) were deposited by electron‐beam sputtering. The investigations have shown that the transformation of the 25‐nm‐thick erbium into erbium silicide is completed after annealing at 500°C. At higher temperatures, the formation of a titanium silicide layer above erbium silicide is observed. The lowest Schottky barrier has been measured in the sample annealed at 700°C.

Erbium silicide growth in the presence of residual oxygen

The chemical changes of Ti/Er/n-Si(100) stacks evaporated in high vacuum and grown ex situ by rapid thermal annealing were scrutinized. The emphasis was laid on the evolution with the annealing temperature of (i) the Er-Si solid-state reaction and (ii) the penetration of oxygen into Ti and its subsequent interaction with Er. For that sake, three categories of specimens were analyzed: as-deposited, annealed at 300°C, and annealed at 600°C. It was found that the presence of residual oxygen into the annealing atmosphere resulted in a substantial oxidation of the Er film surface, irrespective of the annealing temperature. However, the part of the Er film in intimate contact with the Si bulk formed a silicide (amorphous at 300°C and crystalline at 600°C) invariably free of oxygen, as testified by x-ray photoelectron spectroscopy depth profiling and Schottky barrier height extraction of 0.3 eV at 600°C. This proves that, even if Er is highly sensitive to oxygen contamination, the formation of low Schottky barrier Er silicide contacts on n-Si is quite robust. Finally, the production of stripped oxygen-free Er silicide was demonstrated after process optimization.