Impact of thermal treatments on the schottky barrier height reduction at the Ti-TiO<inf>x</inf>-Si interface for contact resistance reduction

Abstract

Metal-Insulator-Semiconductor (MIS) Schottky diodes were fabricated to study Fermi level unpinning by use of a thin TiO x insulator. For Ti-TiO x -n-Si junctions, the Schottky barrier height (SBH) was pinned due to O diffusion from TiO x into Ti during thermal anneals, as observed from XPS depth profiles. A thin AlO x barrier inserted between the Ti and the TiO x prevented O diffusion from TiO x into Ti, allowing SBH unpinning to be maintained after 450 °C anneals. IntroductionAs device dimensions shrink in CMOS technology, transistor performance is increasingly dominated by the external resistance (R ext ). Contact resistance at the metal-semiconductor interface is a primary contributor to this external resistance. The barrier height of the system is difficult to modulate since the Fermi level (FL) is pinned at this interface. Several studies have shown that a thin insulator can be inserted between the metal and silicon to create a metal-insulator-semiconductor (MIS) contact to unpin the FL, hence allowing for reduction in the Schottky barrier height (SBH) and R ext [1] [2] [3]. To be a viable process option for future nodes, this SBH unpinning at the MIS contact needs to survive the thermal budget of processes after contact formation. In this work using a thin TiO x insulator, we study the SBH unpinning of various metals on n-Si, and in particular the effects of anneals on the SBH at the Ti-TiO x -n-Si junction.

Thermal Stability Concern of Metal-Insulator-Semiconductor Contact: A Case Study of Ti/TiO2/n-Si Contact

“…Considering that the MIS contacts on n-type semiconductors are typically composed of low-WF metal and an ultrathin interlayer, their thermal stability is worrying. However, till now, the MIS thermal stability issue has only been incidentally mentioned in the literature [5], [8]- [10], and detailed experimental [11] and theoretical studies of this issue are still lacking. Therefore, we perform a systematic thermal stability study of a typical MIS contact: Ti/TiO 2 /n-Si.…”