Achieving Conduction Band-Edge Effective Work Functions by $\hbox{La}_{2}\hbox{O}_{3}$ Capping of Hafnium Silicates

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Conduction band-edge effective work functions (<formula formulatype="inline"><tex>$\phi_{m, {\rm eff}}$</tex> </formula>) are demonstrated with <formula formulatype="inline"><tex>$\hbox{TaC}_{x}$</tex></formula> and TiN by means of <formula formulatype="inline"><tex>$\hbox{La}_{2}\hbox{O}_{3}$</tex></formula> capping of <formula formulatype="inline"><tex>$\hbox{HfSiO}_{x}$</tex></formula> in a gate-first process flow with CMOS-compatible thermal budget. With <formula formulatype="inline"><tex>$\hbox{TaC}_{x}$</tex></formula>, a 10- <formula formulatype="inline"><tex>$\hbox{\bf \AA}$</tex></formula>-thick <formula formulatype="inline"><tex>$ \hbox{La}_{2}\hbox{O}_{3}$</tex></formula> cap results in a <formula formulatype="inline"><tex>$\phi_{m, {\rm eff}}$ </tex></formula> of 3.9 eV with a low equivalent oxide thickness (EOT) increase (1–2 <formula formulatype="inline"><tex>$\hbox{\bf \AA}$</tex></formula>) and unaffected electron mobility. With TiN, non-nitrided <formula formulatype="inline"><tex>$\hbox{La}_{2}\hbox{O}_{3}$</tex></formula> capping results in a smaller <formula formulatype="inline"><tex>$\phi_{m, {\rm eff}}$</tex></formula> reduction at a larger EOT increase, while with post-cap nitridation, the TiN <formula formulatype="inline"><tex>$\phi_{m, {\rm eff}}$</tex></formula> is lower at a smaller EOT increase. Results show that the choice of metal and nitridation conditions have significant effects on <formula formulatype="inline"><tex>$\hbox{La}_{2}\hbox{O}_{3}$</tex></formula> capped stacks. </para>