A Thermodynamic Approach to Selecting Alternative Gate Dielectrics

Abstract

As a first step in the identification of suitable alternative gate dielectrics for metal oxide semiconductor field-effect transistors (MOSFETs), we have used tabulated thermodynamic data to comprehensively assess the thermodynamic stability of binary oxides and nitrides in contact with silicon at temperatures from 300 K to 1600 K. Sufficient data exist to conclude that the vast majority of binary oxides and nitrides are thermodynamically unstable in contact with silicon. The dielectrics that remain are candidate materials for alternative gate dielectrics. Of these remaining candidates, the oxides have a significantly higher dielectric constant (ĸ) than the nitrides. We then extend this thermodynamic approach to multicomponent oxides comprising the candidate binary oxides. The result is a relatively small number of silicon-compatible gate dielectric materials with ĸ values substantially greater than that of SiO2 and optical bandgaps ≥ eV.

Amorphous lanthanum lutetium oxide thin films as an alternative high-κ gate dielectric

“…As shown by Schlom and Haeni, 3 single crystals of these oxides show values of 20-35 which were also observed for amorphous LaScO 3 , GdScO 3 , and DyScO 3 films deposited on silicon ͑ =22-23͒. 4,5 In addition, these materials fulfill the requirements for large optical band gaps ͑5.6 eV͒ and band offsets ͑2 -2.5 eV͒, 6 while their amorphous phase is stable up to 1000°C ͑for GdScO 3 and DyScO 3 ͒.…”

“…4,5 Lanthanum lutetium oxide ͑LaLuO 3 ͒, as a member of this class of ternary oxides, is predicted to have similar properties. 3,7 Experimental data related to high-gate applications of amorphous LaLuO 3 films are, however, still not available. In this letter, we present the results of a systematic study on the microstructural and electrical properties of amorphous LaLuO 3 thin films, deposited on silicon substrates by means of pulsed laser deposition ͑PLD͒.…”

Molecular volume and electronic and vibrational polarizibilities for amorphous LaAlO3

“…We note first than the film refractive index is directly related to its density [Eq. (2)] and that for our samples deposited with and without a substrate bias, the refractive indices are close. It is generally assumed that one of the roles of substrate bias is to ion-assist the deposition of the film and that this usually leads to a more densified form.…”

Interfacial reaction in the growth of epitaxial SrTiO3 thin films on (001) Si substrates

“…Although the thermodynamic calculations for SrO in contact with silicon could not be completed due to the absence of thermodynamic data for SrSi 2 and Sr 3 SiO 5 , it is possible that SrO and silicon are thermodynamically stable in contact with each other at temperatures in the 300-1200 K range over which relevant thermodynamic data exist. 13,14,41 In contrast, all oxides of titanium, including TiO 2 , are unstable in contact with silicon 13,14 as exemplified by the reaction 13,42,43 TiO 2 + 3Si → TiSi 2 + SiO 2 ͑⌬G 1000 K ‫ؠ‬ = − 23.014 kcal/mol͒.…”

“…SrTiO 3 is thermodynamically unstable in contact with silicon owing to its strong chemical reactivity with silicon. [13][14][15] Thermodynamic issues are of greater importance in oxide/silicon systems than in other heteroepitaxial systems, particularly in cases where a high-temperature treatment ͑ϳ900°C or higher͒ is traditionally used to fully activate the implanted dopant species in a self-aligned process. 16,17 Even if this high-temperature step is circumvented by avoiding a self-aligned process or employing a gate-last process, the processing temperatures encountered in deposition or postdeposition processing ͑to achieve the desired electronic performance͒ can also be high.…”