Controlling the formation and stability of ultra-thin nickel silicides - An alloying strategy for preventing agglomeration

Abstract

The electrical contact of the source and drain regions in state-of-the-art CMOS transistors is nowadays facilitated through NiSi, which is often alloyed with Pt in order to avoid morphological agglomeration of the silicide film. However, the solid-state reaction between as-deposited Ni and the Si substrate exhibits a peculiar change for as-deposited Ni films thinner than a critical thickness of t c =5 nm. Whereas thicker films form polycrystalline NiSi upon annealing above 450 • C, thinner films form epitaxial NiSi 2 films which exhibit a high resistance towards agglomeration. For industrial applications, it is therefore of utmost importance to assess the critical thickness with high certainty and find novel methodologies to either increase or decrease its value, depending on the aimed silicide formation. This paper investigates Ni films between 0 and 15 nm initial thickness by using of 'thickness gradients', which provide semi-continuous information on silicide formation and stability as a function of as-deposited layer thickness. The alloying of these Ni layers with 10 % Al, Co, Ge, Pd or Pt renders a significant change in the phase sequence as a function of thickness and dependent on the alloying element. The addition of these ternary impurities therefore change the critical thickness t c. The results are discussed in the framework of

Highly Stable Self-Aligned Ni-InGaAs and Non-Self-Aligned Mo Contact for Monolithic 3-D Integration of InGaAs MOSFETs

“…It would be a possible origin of low film resistivity even at thin film thickness region unlike NiSi films [44]. Furthermore, this would be a possible origin of the difference of phase stability from Ni-Si system with changing initial Ni thickness [45].…”

Further insights into the growth mechanism of the non-stoichiometric θ-Ni2Si phase

“…However, diffusion may play a role on its growth mechanism. Indeed, it was observed that -Ni2Si forms during isothermal annealing at lower temperature (180°C) [4,5 ] than that reported, in several investigations during isochronal annealing (280°C) for different preparation conditions [1,2,6] .…”

“…The formation of NiSi phase, via solid state reaction between Ni film (ec > 4,8nm) and Si(100), is preceded by a simultaneous formation of Ni-rich phases [1]. Recent studies have shown that the sequence of Ni-rich phases and their characteristics (texture, resistivity and interface quality) is altered by the substrate orientation [2], film thickness [1,3,4], the presence of dopants [5] and alloy elements [1,6,7]. The formation of Ni-rich phases is albeit evidenced for all preparation conditions.…”

Inter-diffusion, melting and reaction interplay in Ni/4H-SiC under excimer laser annealing

“…While diffusing, Ni and Si could react with the formation of different silicide phases whose stoichiometry depends on the relative amount of the species and on the local temperature. They arise from the thermodynamic equilibrium and the kinetic conditions during the annealing process and during the cooling ramp down [22,25,26,27,28]. Rum-up and down are likewise important in time-dependent temperature fields that are also locally changeable.…”