Impact of bottom electrode and SrxTiyOz film formation on physical and electrical properties of metal-insulator-metal capacitors

Abstract

Metal-insulator-metal capacitors with SrxTiyOz (STO) dielectric films on TiN, Ru, and RuOx bottom electrodes with TiN top electrodes were studied. Metastable perovskite STO films with compositions in the Sr/(Sr+Ti)∼54–64 at. % range were obtained by crystallization at 600 °C in N2 of dielectric stacks grown by atomic layer deposition consisting of Sr-rich STO films [Sr/(Sr+Ti)∼64 at. %] on thin interfacial TiOx layers. The significant decrease in equivalent oxide thickness (EOT) and STO lattice parameter observed with increasing TiOx thickness indicates full intermixing of the TiOx and STO layers during the crystallization anneal, which results in the formation of an STO layer with higher Ti content and higher dielectric constant. The Sr-rich STO on TiOx stacks crystallize with small grain size, favorable for low leakage (JG). A significant improvement in JG for e-injection from the bottom electrode is obtained when using RuOx, as compared to TiN or Ru. A milder JG improvement with RuOx bottom electrode is also seen for e-injection from the top TiN electrode, indicating that higher quality perovskite STO films are formed on RuOx, or equivalently, that their trap density is lower. We propose oxygen scavenging from the STO by TiN or Ru electrodes, eliminated or reversed when using RuOx, as an explanation for the improvement. Using an optimized RuOx/TiOx/STO/TiN stack we obtained leakage of 10−7 A/cm2 (at 0.8 V) and 0.4 nm EOT.

(Invited) Plasma Enhanced Atomic Layer Deposited Ruthenium for MIMCAP Applications

“…Low pressure O 2 anneals can be used to form a Ru/RuO x bilayer stack without roughening the surface. Strongest oxidants such as O 3 have a more detrimental effect on the Ru surface. Surface roughening has been reported, but the origin of the roughening can have various reasons.…”

Process–property relationship in high-k ALD SrTiO3 and BaTiO3: a review

“…However, FLA has a significant drawback for 3-D structures due to the directionality of light and the consequent shading effect. PDA has been extensively studied for STO [70][71][72][73][74][75] and BTO. t Bu 3 Cp = tris(tert-butylcyclopentadienyl)), which is more chemically stable up to 340 1C and shows a higher deposition rate, showed the effect of PDA on the electrical performance of 32 nm stoichiometric BTO at 600 1C under O 2 to increase the permittivity of the film from 15 (as-deposited) to 70 (annealed) by forming the cubic phase of BTO while maintaining a low leakage current density ( J G ) of o10 À7 A cm À2 at 1 V. 66 With the same precursors and the PDA protocol, BTO films with various Ba stoichiometries (Ba/(Ba + Ti) = 33-52 at%) and thicknesses (32-140 nm) were prepared, and the degree of crystallization after post-deposition annealing was studied; more stoichiometric BTO tended to be more easily crystallized.…”

Medium energy ion scattering for the high depth resolution characterisation of high-k dielectric layers of nanometer thickness

“…These devices require EOT values of ≤ 0.4 nm in combination with very low leakage current densities, i.e. less than 10 -7 A/cm 2 [5,6] and, as for gate oxides, developments are driven by down scaling. Of the considerable range of materials and growth methods of these layers for memory applications investigated in recent years, Sr x Ti 1-x O 3 (STO) nanolayers either Sr enriched or stoichiometric (k ≥ 200), in combination with TiN electrodes [5,7] as well as TiO 2 (k ≥80), as an attractive alternative to STO, and combined with Ru/RuO 2 electrodes [8,9] have emerged as suitable, very high-k materials and have become the subject of intensive investigation and development.…”