Ferroelectric And Stability Of Hf_0.5Zr_0.5O_2-δ Thin Films Prepared By Oxygen Vacancy Control

Due to its low power consumption,high scalability,and excellent CMOS compatibility,hafnium oxide（HfO₂）based ferroelectric memory is increasingly concerned in recent years,with a wide application prospect.Nonetheless,the metastable ferroelectric phase,so-called wake-up effect,limited endurance under filed cycling,and many other issues correlated with oxygen vacancies impeded it to attain greater accomplishment.In this paper,oxidizer dose change during atomic layer deposition（ALD）and oxygen plasma treatment implemented after the deposition are used to adjust oxygen vacancy in HfO₂ based ferroelectric thin film,for exploring the effect of oxygen vacancy on the ferroelectric polarization stability of Hf_0.5Zr_0.5O_2-δ（HZO）thin film.Ferroelectric thin films with excellent comprehensive properties were prepared.The main contents are as follows:（1）The effect of oxidizer dose on HZO ferroelectric thin film was studied.After the ALD oxidation reaction tends to be complete,oxygen plasma treatment was implemented to further decrease oxygen vacancy content in HZO thin film.Electrical experiment,XRD and XPS are carried out on Ti N/HZO/Ti N specimens fabricated by different parameters,and theδin different samples is speculated ranging between 0.11and 0.04.The result showed that proportion of orthogonal ferroelectric phase could be expanded with the increase of oxygen vacancies,enhancing remnant polarization of the film.The remnant polarization of HZO deposited at 0.1 s oxidizer dose time reached15.4μC/cm².Decrease the oxidizer dose time to 0.06 s,remnant polarization will rise up to 17.8μC/cm².After 900 s oxygen plasma treatment,the remnant polarization of the sample with 0.1 s oxidizer dose time fell into 7.9μC/cm².However,when the oxidizer dose time decrease to 0.03 s,remnant polarization of the film did not grow as usual since the precursor was not completely oxidized by insufficient distilled water.Lessen the oxygen vacancies in HZO thin films can ameliorate their imprint behavior as well.（2）The effect of oxygen vacancies on stability of HZO thin films under filed cycling were also studied.Samples with higher oxygen vacancy concentration or oxygen vacancies clusters will perform more significant wake-up effect.We also observed that the relative dielectric constant dropped during the wake-up,perhaps lead by phase transition.To a certain extent,the re-distribute of oxygen vacancies after partly wake-up brought leakage current density to a lower level.The HZO with 0.1 s oxidizer dose time can endure 6.3×10⁸ cycles when the test waveform is 4 V,100 k Hz,and after10⁸ cycles fatigue it will its leakage current density increase to 5.0×10^-3 A/cm².Our HZO capacitor broke down earlier during the endurance test as we increased their oxygen vacancy concentration.Sample with 0.03 s oxidizer dose time preform worst during the test,and can endurance only 2.5×10⁶ cycles.Suppress the oxygen vacancies in HZO thin films is good for their endurance reliability.All films treated by oxygen plasma did not break down during endurance test.Endurance test with the waveform of4 V,16.7 MHz was carried out on the sample treated by 270 s oxygen plasma.The sample did not breakdown after 10¹² cycles,and the polarization remained more than90%.Leakage current density of the sample with 900 s treatment is only 4.9×10^-4A/cm² after 10⁸ cycles of fatigue.