Investigation of ultrathin Pt/ZrO 2 –Al 2 O 3 –ZrO 2 /TiN DRAM capacitors Schottky barrier height by internal photoemission spectroscopy (original) (raw)
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Journal of Applied Physics, 2007
Engineered dielectrics combined with compatible metal electrodes are important materials science approaches to scale three-dimensional trench dynamic random access memory ͑DRAM͒ cells. Highly insulating dielectrics with high dielectric constants were engineered in this study on TiN metal electrodes by partly substituting Al in the wide band gap insulator Al 2 O 3 by Pr cations. High quality PrAlO 3 metal-insulator-metal capacitors were processed with a dielectric constant of 19, three times higher than in the case of Al 2 O 3 reference cells. As a parasitic low dielectric constant interface layer between PrAlO 3 and TiN limits the total performance gain, a systematic nondestructive synchrotron x-ray photoelectron spectroscopy study on the interface chemistry of Pr x Al 2−x O 3 ͑x =0-2͒ dielectrics on TiN layers was applied to unveil its chemical origin. The interface layer results from the decreasing chemical reactivity of Pr x Al 2−x O 3 dielectrics with increasing Pr content x to reduce native Ti oxide compounds present on unprotected TiN films. Accordingly, PrAlO 3 based DRAM capacitors require strict control of the surface chemistry of the TiN electrode, a parameter furthermore of importance to engineer the band offsets of Pr x Al 2−x O 3 / TiN heterojunctions.
Pt and RuO 2 Bottom Electrode Effects on Pb(Zr,Ti)O 3 Memory Capacitors
Japanese Journal of Applied Physics, 1999
This study examines the effects of bottom electrodes for metal ferroelectric metal (MFM) capacitor applications. We investigated the following parameters of bottom electrodes and Pb(Zr 0.53 Ti 0.47)O 3 (PZT) thin films: substrate temperature, rf power, gas flow rate, Ar/O 2 ratio, electrode material, and post-annealing effect. Bottom electrodes grown at 300 • C for Pt and 200 • C for RuO 2 exhibited a film resistivity of 10 −4 •cm, had a surface roughness of approximately 55 Å and a preferred crystal orientation. Rapid thermal annealing (RTA) treatments on a Pt electrode at 600 • C for 30 s improved the resistivity to 5 × 10 −6 •cm and generated the (111) preferred crystal orientation. PZT films exhibited a strong PZT (101) peak for an optimized Pt bottom electrode and (111), (200), (112) planes without preferred PZT orientations for the RuO 2 electrode. A well-fabricated Pd/PZT/Pt capacitor showed a leakage current density in the order of 6 × 10 −5 A/cm 2 , a dielectric constant (ε r) of 365, a remanent polarization (P r) of 27 µC/cm 2 , and a coercive field (E c) of 50.5 kV/cm. This paper discusses the bottom electrode properties as well as their recommended conditions in memory device applications of thin-film PZT capacitors.
Journal of Applied Physics, 2012
Al-doped ZrO 2 (Al-ZrO 2 ) films deposited by atomic layer deposition onto silicon substrates and the interface with the TaN metal gate are investigated. In particular, structural properties of asgrown and annealed films in the 6-26 nm thickness range, as well as leakage and capacitive behavior of metal-oxide-semiconductor stacks are characterized. As-deposited Al-ZrO 2 films in the mentioned thickness range are amorphous and crystallize in the ZrO 2 cubic phase after thermal treatment at 900 C. Correspondingly, the dielectric constant (k) value increases from 20 6 1 to 27 6 2. The Al-ZrO 2 layers exhibit uniform composition through the film thickness and are thermally stable on Si, whereas chemical reactions take place at the TaN/Al-ZrO 2 interface. A transient capacitance technique is adopted for monitoring charge trapping and flat band instability at short and long time scales. The role of traps nearby the TaN/Al-ZrO 2 interface is discussed and compared with other metal/high-k oxide films. Further, analytical modeling of the flat band voltage shift with a power-law dependence on time allows extracting features of bulk traps close to the silicon/oxide interface, which exhibit energy levels in the 1.4-1.9 eV range above the valence band of the Al-ZrO 2 . V C 2012 American Institute of Physics. [http://dx.
Thin Solid Films, 1996
ZrN and Pt/Ru thin films have been grown by an automated ion beam sputter-deposition system. Both materials were evaluated for use as barrier layers (ZrN) and bottom electrodes (Pt/Ru) in dynamic random access memory (DRAM) applications. The ZrN films had resistivities on the order of 250-300/.LO cm. The ZrN films were (002) oriented and were rather smooth with an average surface roughness of + 17 A,. Analysis of the oxidation kinetics of the ZrN thin films reveals a thermally activated, diffusion-limited oxidation process with an activation energy of 2.5 eV in the temperature range of 500-650 °C. This implies that there is an advantage in using ZrN as a barrier layer instead of TiN since the activation energy for oxidation of TiN is 2.05 eV. In addition, preliminary data suggest that a Pt/Ru double layer may be a promising bottom electrode and oxygen diffusion barrier for use in DRAMs with high-permittivity dielectrics.
Thin Solid Films, 2020
We investigate effects of bottom electrodes on ZrO 2 thin films formed through atomic layer deposition (ALD). We focus on the correlation between interfacial layer formation and electrical properties. For this comparative study, two different bottom electrodes consisting of TiN and Ru were employed. ALD ZrO 2 films are deposited on these bottom electrodes by using tris(dimethylamino)cyclopentadielnyl zirconium ((C 5 H 5)Zr[N(CH 3) 2 ] 3) and ozone as a precursor and oxidant, respectively. Based on detailed investigations using transmission electron microscopy and X-ray photoelectron spectroscopy, we are able to comparatively characterize the formations and chemical compositions of the interfacial layers between ALD ZrO 2 and both bottom electrodes. Based on the electrical properties of metal-insulator-metal capacitors fabricated using both the TiN and Ru bottom electrodes, we observe improved capacitance-voltage and current-voltage characteristics with the Ru bottom electrode, which are attributed to the suppressed formation of an interfacial layer. We also discuss the correlation between traps in the interfacial layer and electrical properties.
High-performance stacked TiO2-ZrO2 and Si-doped ZrO2 metal-insulator-metal capacitors
2014 IEEE International Conference on IC Design & Technology, 2014
Metal-insulator-metal (MIM) capacitors for DRAM applications have been realised using stacked TiO2-ZrO2 (TiO2/ZrO2 and ZrO2/TiO2) and Si-doped ZrO2 (TiO2/Si-doped ZrO2) dielectrics. High capacitance densities (> 42 fF/µm 2), low leakage current densities (< 5×10 −7 A/cm 2 at-1 V), and sub-nm EOT (< 0.8 nm) have been achieved. The effects of constant voltage stress on the device characteristics is studied. The structural analysis of the samples is performed by X-ray diffraction measurements, and this is correlated to the electrical characteristics of the devices. The surface chemical states of the films are analyzed through X-ray photoelectron spectroscopy measurements. The doped-dielectric stack (TiO2/Si-doped ZrO2) helps to reduce leakage current density and improve reliability, with a marginal reduction in capacitance density; compared to their undoped counterparts (TiO2/ZrO2 and ZrO2/TiO2). We compare the device performance of the fabricated capacitors with other stacked high-k MIM capacitors reported in recent literature. Index Terms-constant voltage stress (CVS), equivalent oxide thickness (EOT), metal-insulator-metal (MIM) capacitor, reliability, titanium oxide (TiO2), zirconium oxide (ZrO2).
Applied Surface Science, 2020
Selective and localized process technology is a key enabler for the monolithic three-dimensional (M3D) integration of high-performance oxide-based resistive random access memory (RRAM) which is emerging as a post-flash nonvolatile memory solution. In this work, a photo-thermal laser process in a ZnO/Pt multi-layered structure is proposed as a new strategy to modulate the crystallinity at the ZnO/Pt interface and the oxygen vacancy (V O) distribution in the ZnO layer. Intensive optical and thermal simulation has been utilized for the optimized laser processing of the ZnO/Pt interface. It is verified that the optimized laser process can produce a thin ZnO crystallized layer on the ZnO/Pt interface and a significant concentration gradient of V O within the ZnO layer, without any deformation of the multi-layered structure. The switching characteristics of the laser-processed Pt/ZnO/Pt RRAM reveal that the laser process can increase the R HRS /R LRS ratio by up to tenfold and decrease the V SET by about 25%. The reliability of the RRAMs is also considerably improved. Our research demonstrates that the photo-thermal approach is a very promising method for improving oxide-based RRAM performance while meeting the critical requirements of M3D integration.
Electrical characteristics of ferroelectric PZT thin films for DRAM applications
Electron Devices, IEEE …, 1992
Ferroelectric lead zirconate titanate (PZT) films with as much as 2.5 times the storage capacity of the best reported silicon oxidelnitrideloxiPe (ONO) stacked dielectrics have been fabricated. A 2OOO-fi PbZr0.STi0.S03 film with an effective SiOz thickness of 10 A is demonstrated. Because of the extremely high dielectric constant (er L lOOO), even larger storage capacities can be obtained by scaling the ferroelectric film thickness whereas the thickness of ONO films is limited by direct tunneling through the film. Electrical conduction in the PZT films studied here is ohmic at electric fields below 250 kV/cm and follows an exponential field dependence at higher fields. This type of behavior is shown to be consistent with a simple model for electronic hopping through the film. Leakage current as low as 9 x lo-* A/cmZ at 2.5 V for a 4000 A film is obtained with the addition of lanthanum and iron to compensate for lead and oxygen vacancies in the film. Further improvement in both leakage current and time-dependent dielectric breakdown characteristics are necessary to ensure reliable DRAM operation.
Memory Properties of Zr-Doped ZrO2 MOS-like Capacitor
Coatings
The high-k-based MOS-like capacitors are a promising approach for the domain of non-volatile memory devices, which currently is limited by SiO2 technology and cannot face the rapid downsizing of the electronic device trend. In this paper, we prepare MOS-like trilayer memory structures based on high-k ZrO2 by magnetron sputtering, with a 5% and a 10% concentrations of Zr in the Zr–ZrO2 floating gate layer. For crystallization of the memory structure, rapid thermal annealing at different temperatures between 500 °C and 700 °C was performed. Additionally, Al electrodes were deposited in a top-down configuration. High-resolution transmission electron microscopy reveals that ZrO2 has a polycrystalline–columnar crystallization and a tetragonal crystalline structure, which was confirmed by X-ray diffraction measurements. It is shown that the tetragonal phase is stabilized during the crystallization by the fast diffusion of oxygen atoms. The capacitance–voltage characteristics show that the...
2004
An overview is given on the use of ALD deposition technologies for high-k dielectrics and electrodes in MIM capacitors for embedded-DRAM in 90 nm technology and beyond. ALD-Al 2 O 3 and ALD-HfO 2 dielectrics have been evaluated together with MOCVD-Ta 2 O 5 for capacitors targeted at EOT < 18 A. Improved leakage performance was obtained through control of the dielectric/electrode interface. This includes the use of ALD-Al 2 O 3 as a thermo-dynamic and electronic barrier between Ta 2 O 5 and electrode and the use of ALD-TiN as electrode material. ALD-Al 2 O 3 and ALD-HfO 2 both give good leakage performance and stability with temperature, with HfO 2 offering most robust capacitance performance for next generation embedded-DRAM processes.