Influence of stoichiometry on the performance of MIM capacitors from plasma‐assisted ALD SrxTiyOz films. Issue 2 (9th September 2013)

• Record Type: Journal Article
• Authors: Aslam, N.; Longo, V.; Keuning, W.; Roozeboom, F.; Kessels, W. M. M.; Waser, R.; Hoffmann‐Eifert, S.
• Is Part Of: Physica status solidi. Volume 211:Issue 2(2014:Feb.)
• Page Start: 389
• Page End: 396
• Publication Date: 2013-09-09
• Subjects: Solid state physics -- Periodicals; Solids -- Industrial applications -- Periodicals; 530.41
• DOI: 10.1002/pssa.201330101
• Languages: English
• ISSNs: 1862-6300

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="pssa201330101-sec-0001" sec-type="section"> <p>Strontium titanate, Sr<sub><italic>x</italic></sub>Ti<sub><italic>y</italic></sub>O<sub><italic>z</italic></sub> (STO), thin films with various cation stoichiometries were deposited by plasma‐assisted atomic layer deposition (ALD) using cyclopentadienyl‐based metal precursors and oxygen plasma as counter‐reactant. [Sr]/([Sr] + [Ti]) compositions ranging from 0.46 to 0.57 were obtained by changing the (SrO)/(TiO<sub>2</sub>) ALD cycle ratios. As‐deposited 15–30 nm thick Sr<sub><italic>x</italic></sub>Ti<sub><italic>y</italic></sub>O<sub><italic>z</italic></sub> films prepared at 350 °C on Pt‐coated silicon substrates were amorphous. Post‐annealing at 600/650 °C for 10 min under N<sub>2</sub> gas resulted in a crystallization into the perovskite phase. Stoichiometric STO and Sr‐rich STO films exhibited a certain degree of (111) texture while the Ti‐rich STO films showed a lower degree of crystallization. Crystallized layers exhibited a smaller band gap <italic>E</italic><sub>g</sub> than amorphous ones, while within the stoichiometry series the value of <italic>E</italic><sub>g</sub> increased with increasing Sr‐content. Within the stoichiometry series Pt/STO/Pt structures with Sr‐rich STO films showed the lowest leakage current densities. At 1.0 V values of about 2 × 10<sup>−8</sup> and 5 × 10<sup>−6</sup> A cm<sup>−2</sup> were obtained for the as‐deposited and the annealed films, respectively. Highest capacitance density was obtained for 15 nm polycrystalline stoichiometric SrTiO<sub>3</sub> films resulting in a capacitor equivalent thickness CET of about 0.7 nm. Pt/Sr<sub><italic>x</italic></sub>Ti<sub><italic>y</italic></sub>O<sub><italic>z</italic></sub>/Pt capacitors with the STO being in amorphous state exhibited a positive voltage nonlinearity factor <italic>α</italic> of about 400 ppm V<sup>−2</sup>, while the negative <italic>α</italic>‐values for crystallized films showed a systematic variation with the stoichiometry, the degree of crystallization and the thickness of the STO layer. This demonstrates that a broad performance range of MIM capacitors is accessible by controlling the stoichiometry and the degree of crystallization of plasma‐assisted ALD Sr<sub><italic>x</italic></sub>Ti<sub><italic>y</italic></sub>O<sub><italic>z</italic></sub> thin films.</p> </sec> </abstract>