Ru Bottom Electrode Research Articles

Improved Properties of the Atomic Layer Deposited Ru Electrode for Dynamic Random-Access Memory Capacitor Using Discrete Feeding Method.

Ruthenium (Ru) thin films deposited via atomic layer deposition (ALD) with a normal sequence and discrete feeding method (DFM) and their performance as a bottom electrode of dynamic random-access memory (DRAM) capacitors were compared. The DFM-ALD was performed by dividing the Ru feeding and purge steps of the conventional ALD process into four steps (shorter feeding time + purge time). The surface morphology of the Ru films was improved significantly with the DFM-ALD, and the preferred orientation of the Ru films was changed from relatively random to a <101>-oriented direction. Under the DFM-ALD condition, the higher susceptibility of oxygen atoms to the Ru electrode resulted in a higher proportion of the RuO2 formation on the Ru film surface during the subsequent TiO2 ALD process. This higher RuO2 portion leads to higher crystallinity of the local-epitaxially grown TiO2 films with a rutile phase. Such improvement also decreased the interfacial component of equivalent oxide thickness (EOTi) by ∼0.1 nm compared with the cases on sputtered Ru film, which showed an even smoother surface morphology. Consequently, the minimum EOT values when the Ru bottom electrodes deposited via DFM-ALD were adopted were 0.76 and 0.48 nm for TiO2 and Al-doped TiO2 films, respectively, while still satisfying the DRAM leakage current density specification (<10-7 A/cm2 at a capacitor voltage of 0.8 V).

Influence of ALD Ru bottom electrode on ferroelectric properties of Hf0.5Zr0.5O2-based capacitors

We report the influence of an ultrathin Ru bottom electrode on ferroelectric properties of fully atomic layer deposition (ALD)-grown Hf0.5Zr0.5O2 (HZO) and La-doped Hf0.5Zr0.5O2 (HZLO)-based ferroelectric capacitors. We show that the Ru bottom electrode deposited by radical enhanced ALD (REALD) improves the remanent polarization of both capacitors considerably. The origin of such a phenomenon is established by grazing-incidence and symmetrical θ–2θ x-ray diffraction measurements. HZO films on Ru exhibit the orthorhombic phase, which is highly (002)-textured in the out-of-plane direction as compared to HZO on TiN. HZLO films demonstrate the rise of (111) intensity of the orthorhombic phase when it is grown on Ru. Both types of capacitors with Ru exhibit a lower wake-up degree as compared to the ones with TiN, which is assumed to be due to the difference in the bottom interface properties. At the same time, both HZO and HZLO on Ru suffer from the relatively early breakdown during electric field cycling, which is presumably due to the high surface roughness of REALD Ru. Taking into account the continuous search for the new precursor's chemicals and ALD processes for Ru, which would be able to provide smother films, ALD Ru might be promising for the hafnium oxide-based ferroelectric random access memory.

Improved interface quality of atomic-layer-deposited ZrO2 metal-insulator-metal capacitors with Ru bottom electrodes

We investigate effects of bottom electrodes on ZrO2 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 ZrO2 films are deposited on these bottom electrodes by using tris(dimethylamino)cyclopentadielnyl zirconium ((C5H5)Zr[N(CH3)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 ZrO2 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.

Improvement of sensing margin and reset switching fail of RRAM

To develop a high voltage read margin ΔVrd, deep reset engineering and defect engineering are proposed. To realize the defect engineering, the amount of oxygen vacancy of the resistor was controlled by optimizing the material of the reservoir (RSV) and switching oxide. We investigated the barrier height modulation, which was formed by the Ru bottom electrode (BE) having a high work function, to demonstrate the concept of deep reset engineering by reducing the set current (Iset) of the HfO2 resistor (1R) to the turn-on current (Ith) of the selector device (1S). Further, we identified the causes of the negative set fail through the chemical analysis of the HfO2/BE TiN interface to improve the reset switching fail. Unstable TiON and TiOx chemical species, which present in the interface of HfO2/BE TiN, take oxygen from the resistor HfO2 and create the parasitic defect (or filament), which was injected from BE TiN. To improve the negative set fail of RRAM, we proposed the O3 surface treatment of BE TiN at a high temperature (∼320 °C) and the BE Ru with a superior oxidation resistance. By using deep reset engineering, we successfully increased the ΔVrd of 1S1R by more than 0.5 V. We also demonstrated that Ru BE and the O3 surface treatment of BE TiN improved both the reset window and the negative set.

Stabilizing Schemes for the Minority Failure Bits in Ta2O5-Based ReRAM Macro

A low-power 2-Mb Resistance random access memory (ReRAM) macro is developed in a 90-nm CMOS platform with a 3-nm-thick TaO x /Ta2O5 switching layer of the active area of $0.01~\mu \text{m}^{2}$ . Instability of the ON-state minority bits degrades the high-temperature retention lifetime. The oxygen vacancies in the filament are annihilated by oxygen ions, which have been generated mainly by the OFF-write bias repeated in the ON/OFF switching cyclesbefore the retention. This instability is improved by decreasing the oxygen concentration near Ru bottom electrode as well as lowering the OFF-write bias. Instability of the OFF-state minority bits narrows the memory window by random telegraph noise (RTN). Setting a statistically derived guard band with a pulse-modulated verify sequence is able to handle RTN to ensure the memory window. The 2-Mb ReRAMmacro with 1-b error-correcting code is confirmed to ensure ten years’ retention from −40 °C to 85 °C after 1E3 ON/OFF cycles.

Interfacial Contact Effects in Top Gated Zinc Oxide Thin Film Transistors Grown by Atomic Layer Deposition

Contact effects at the source/drain (S/D) electrodes in thin film transistors (TFTs) based on zinc oxide (ZnO) utilizing the top gate, bottom contact geometry are investigated using electrical and material studies. Low temperature atomic layer deposition (ALD) is employed to directly grow the ZnO active layer on Au, Ru, and TiW bottom electrodes. TFT performance varies significantly depending on the S/D metallization scheme. Au contacts are seen to uniquely promote the growth of a highly n-doped ZnO channel that degrades the TFT’s output impedance and controllability. On the other hand, TiW contacts suffer from poor carrier injection because of Schottky barrier formation. The best overall performance is demonstrated by Ru/ZnO TFTs based on their excellent switching capabilities alongside a moderately high mobility. From X-ray photoelectron spectroscopy measurements, the superior performance of Ru is the consequence of an oxidation-free interface that inhibits the adsorption of hydroxide surface dopants. Thus, the surface chemistry of the metal contact plays a large role on the ZnO growth and metal/ZnO interface energetics.

Endurance degradation mechanisms in TiN\Ta2O5\Ta resistive random-access memory cells

Impact of set/reset pulse duration and amplitude on the endurance failure modes of TiN\Ta2O5\Ta cells is investigated and is related to interaction between Oxygen and TiN bottom electrode during reset. Hourglass electrical switching simulation of conductive filament temperature during reset transient and ab-initio calculation of reaction energy further support this degradation mechanism. Based on this understanding, endurance improvement is achieved by using shorter reset pulse and/or using inert Ru bottom electrode.

Impact of bottom electrode and SrxTiyOz film formation on physical and electrical properties of metal-insulator-metal capacitors

Metal-insulator-metal capacitors with SrxTiyOz (STO) dielectric films on TiN, Ru, and RuOx bottom electrodes with TiN top electrodes were studied. Metastable perovskite STO films with compositions in the Sr/(Sr+Ti)∼54–64 at. % range were obtained by crystallization at 600 °C in N2 of dielectric stacks grown by atomic layer deposition consisting of Sr-rich STO films [Sr/(Sr+Ti)∼64 at. %] on thin interfacial TiOx layers. The significant decrease in equivalent oxide thickness (EOT) and STO lattice parameter observed with increasing TiOx thickness indicates full intermixing of the TiOx and STO layers during the crystallization anneal, which results in the formation of an STO layer with higher Ti content and higher dielectric constant. The Sr-rich STO on TiOx stacks crystallize with small grain size, favorable for low leakage (JG). A significant improvement in JG for e-injection from the bottom electrode is obtained when using RuOx, as compared to TiN or Ru. A milder JG improvement with RuOx bottom electrode is also seen for e-injection from the top TiN electrode, indicating that higher quality perovskite STO films are formed on RuOx, or equivalently, that their trap density is lower. We propose oxygen scavenging from the STO by TiN or Ru electrodes, eliminated or reversed when using RuOx, as an explanation for the improvement. Using an optimized RuOx/TiOx/STO/TiN stack we obtained leakage of 10−7 A/cm2 (at 0.8 V) and 0.4 nm EOT.

Influence of composition and bottom electrode properties on the local conductivity of TiN/HfTiO2 and TiN/Ru/HfTiO2 stacks

HfTiO 2 layers of various stoichiometries where deposited by physical vapor depostion on TiN and TiN/Ru bottom electrodes (BE) in order to determine the influence of composition, conduction band offset, and BE morphology on the overall leakage current characteristics. Current-voltage spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and conductive atomic force microscopy studies show increased leakage current and charge trapping with increased Ti content. The interplay of conduction band offset and trap density were studied. The influence of Ru bottom electrode roughness on the leakage current is higher than the influence of Ti content and low conduction band offset.

Controlled growth of rutile TiO2 by atomic layer deposition on oxidized ruthenium

Crystalline rutile TiO2 films were grown by atomic layer deposition on oxidized Ru electrodes using a titanium methoxide as the metal precursor and O3 as the oxidant. A protective layer of ∼0.3 nm TiO2 grown with H2O as the oxidant was first deposited in order to avoid etching of the Ru bottom electrode by the O3 used for the growth of the TiO2 (bulk) layer. Electrical evaluation of the capacitor stacks with TiO2 as dielectric, RuO2/Ru and Pt as the bottom and top electrodes respectively, resulted in superior characteristics of the rutile phase as compared to the anatase. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of pH in Ru Slurry with Sodium Periodate on Ru CMP

In this study, sodium periodate was chosen as both oxidant and etchant on ruthenium (Ru) chemical mechanical planarization (CMP) slurry for the formation of Ru bottom electrodes in dynamic random access memory capacitors. The effect of on etching and polishing behavior was investigated as a function of slurry pH. Below pH 7.5, the high static etch rate was measured due to the dissolution of soluble . Above pH 7.5, the static etch rate decreased due to the formation of insoluble and the depletion of periodate ions. The highest etching of was obtained at pH 6. In a slurry of and alumina particles at pH 6, the removal rate of Ru was about . Even though the highest removal rate was obtained at pH 6, Ru overetching occurred on Ru-patterned wafers due to the high static etch rate of Ru. A selectivity of Ru to oxide of about 23:1 was achieved at pH 8–9. In slurry of pH 9, the planarity and isolation of each capacitor were reached successfully because Ru overetching was prevented due to a low etch rate of Ru.

Effect of Sodium Periodate in Alumina-Based Slurry on Ru CMP for Metal–Insulator–Metal Capacitor

In this study, a ruthenium (Ru) chemical mechanical planarization (CMP) slurry was developed and characterized to fabricate Ru bottom electrodes in capacitor structures. Sodium periodate (NaIO 4 ) was chosen as both the oxidant and etchant due to its strong oxidizing power. The effect of NaIO 4 on Ru etching and polishing behaviors was investigated as a function of its concentration and polishing condition. The largest removal rate of 70 nm/min was obtained in a slurry of 0.1 M NaIO 4 and 2 wt % alumina particles at pH 9 and a polishing pressure of 4 psi. Planarization and isolation of each capacitor was successfully performed with the developed Ru slurry.

Increment of dielectric properties of SrTiO3 thin films by SrO interlayer on Ru bottom electrodes

Sr Ti O 3 thin films were deposited on Ru using plasma-enhanced atomic layer deposition with and without a SrO interlayer. When the SrTiO3 films were deposited on Ru directly, the dielectric constants of the films decreased abruptly from 65 to 16 as the thickness fell below 20nm. This change was related to film crystallinity. Conversely, when a seed layer was prepared by depositing 2.7nm SrO and postannealing before SrTiO3 deposition, the crystallinity of the SrTiO3 films was enhanced and the thickness dependency of the dielectric constant was reduced. As a result, the dielectric constant of 10nm SrTiO3 films was improved from 16 to 50.

Bottom electrodes dependence of microstructures and dielectric properties of compositionally graded (Ba 1− xSr x)TiO 3 thin films

Compositionally graded (Ba 1− x Sr x )TiO 3 (BST) thin films, with x decreasing from 0.3 to 0, were deposited on Pt/Ti/SiO 2/Si and Ru/SiO 2/Si substrates by radio frequency magnetron sputtering technology. The microstructure and dielectric properties of the graded BST thin films were investigated. It was found that the films on Ru electrode have better crystallization, and that RuO 2 is present between the Ru bottom electrode and the graded BST thin films by X-ray diffraction and SEM analysis. Dielectric measurement reveals that the graded BST thin films deposited on Ru bottom electrode have higher dielectric constant and tunability. The enhanced dielectric behavior is attributed to better crystallization as well as smaller space charge capacitance width and the formation of RuO 2 that is more compatible with the BST films. The graded BST films on Ru electrode show higher leakage current due to lower barrier height and rougher surface of bottom electrode.

Development and Optimization of Slurry for Ru CMP

ABSTRACTIn this study, Ruthenium (Ru) chemical mechanical planarization (CMP) slurry was studied and developed to apply it for the formation of Ru bottom electrode in DRAM capacitor. An acidic chemical was chosen as both oxidant and etchant. The effects of the chemical on polishing and etching behavior were investigated as functions of chemical concentration and pHs. The static etch rate of Ru increased with increase of chosen chemical concentration. Also, thin Ru oxide was generated in chemical solution. The highest etching and removal rate were obtained in slurry of pH 6. Ru over etching was generated due to the high etch rate of Ru, and then good planarity was not obtained. However, because Ru over etching was prevented due to low etch rate of Ru, the plarnarity and isolation of each capacitor in slurry of pH 9 was acquired successfully.

Characterization of Metal Insulator Metal Electrical Properties of Electron Cyclotron Resonance Plasma Deposited Ta2O5

The electrical properties of tantalum pentaoxide (Ta2O5) films deposited by an electron cyclotron resonance (ECR) plasma sputtering have been investigated using metal–insulator–metal (MIM) capacitor structures. The deposition conditions of Ta2O5 films and the bottom electrode materials of the MIM have been examined from the point of view of both the low leakage current and the high capacitance. On the TiN bottom electrode, additional postdeposition plasma irradiation on the first thin Ta2O5 layer was effective in ensuring a high breakdown strength of the MIM, because of the stabilization of the interlayer between the Ta2O5 film and the TiN bottom electrode film. However, the MIM using a Ru bottom electrode, which shows the characteristics of conductive films even for oxides, showed the high breakdown characteristics of approximately 4.5 MV/cm for as-deposited Ta2O5 in metal-mode deposition in ECR sputtering. In both cases, the dielectric constant of Ta2O5 was approximately 25, so that a high capacitance of approximately 3 fF/µm2 was for frequencies of up to 1 MHz for a MIM with a Ru bottom electrode and 20-nm-thick Ta2O5 film.

TRIAL FOR MAKING THREE DIMENSIONAL PZT CAPACITOR FOR HIGH DENSITY FERROELECTRIC RANDOM ACCESS MEMORY

ABSTRACT Three dimensional capacitors of Pb(Zr,Ti)O3 [PZT] together with the Ru electrodes were tried to deposit by metal organic chemical vapor deposition for realizing high density ferroelectric random access memory (FeRAM). Good conformability was obtained for both of CVD-Ru and PZT layers on the trenched substrates by optimizing the deposition conditions. In addition, PZT films deposited on Ru bottom electrode showed the good compositional conformability. Finally we demonstrated the Ru/PZT/Ru three dimensional capacitor. These data accelerate the development of three dimensional PZT capacitors.

PZT MIM Capacitor With Oxygen-Doped Ru-Electrodes for Embedded FeRAM Devices

An add-on-type, Pb(Zr,Ti)O/sub 3/ (PZT) metal-insulator- (MIM) capacitor on Al multilevel interconnects is developed for embedded FeRAM devices, concluding that the oxygen-doping into the ruthenium (Ru) electrodes is crucial for obtaining large remnant polarization under a limited process temperature below 450/spl deg/C. The oxygen-doped, Ru bottom-electrode with a granular structure reduces the PZT sputtering temperature below 450/spl deg/C to obtain the ferroelectric perovskite-phase. On the other hand, oxygen doping into the Ru top-electrode suppresses the reductive damage at the interface between the top-electrode and the PZT, keeping the leakage current low. The PZT MIM capacitor with these oxygen-doped, Ru electrodes exhibits the remnant polarization of 21 /spl mu/C/cm/sup 2/ on the Al multilevel interconnects with no degradation of the interconnect reliability, thus applicable to the embedded FeRAM in 0.25 /spl mu/m-CMOS logic LSIs.

Chemically conformal deposition of SrTiO3 thin films by Atomic Layer Deposition using conventional metal organic precursors and remote-plasma activated H2O

Chemically conformal deposition of SrTiO3 (STO) thin films was successfully achieved by ALD using conventional metal organic precursors and remote-plasma activated H2O. It was found that the ALD behavior of the STO film was critically dependent on the Sr(thd)2 source bubbling temperature. When the Sr-source bubbling temperature was <∼200 °C (Sr(thd)2 melting temperature), the deposition proceeded in a genuine ALD mode and stoichiometric STO films were deposited with a good process reliability. Relatively good electrical properties were obtained from a planar capacitor structure with Pt top and Ru bottom electrodes. A 19.5-nm-thick STO film showed an equivalent oxide thickness (EOT) of 0.8 nm and a leakage current density of 1.98×10−6 A/cm2 at 1V after post-annealing.

Thin Pt layer insertion into the Ru bottom electrode: effects on the surface morphology of a (Ba, Sr)TiO3 dielectric film and on the performance of the TiN barrier in the pt/Ru/TiN/p-Si/Si heterostructure

We have investigated the effects of inserting a thin Pt layer into the bottom electrode heterostructure and of post-treatment by rapid thermal oxidation (RTO) on the surface morphology of Ba1−xSrxTiO3 (BST) films and on the thermal stability of the TiN barrier under oxygen exposure in a Pt/Ru/TiN/Si structure. In the case of the Ru/TiN/p-Si/Si structure without a Pt thin layer, the surface morphology of the Ru layer was rough due to heterogeneous grain growth formation, which resulted in the degradation of the BST/Ru interface. When a thin Pt layer was inserted on top of the Ru layer, the number of faceted protrusions observed for the Ru layer was either largely decreased for the Pt/Ru/TiN/p-Si/Si structure or unobserved for the BST/Pt/Ru/TiN/p-Si/Si structure. For the BST/Pt/Ru/TiN/p-Si/Si structure, the oxygen in-diffusion can be reduced by the BST/Pt layers during RTO in the two-step annealing process, resulting in the observed smooth surface morphology of the BST/Pt layer. The thermal stability of the TiN barrier for the Pt/Ru/TiN/poly-Si/Si layer structure was found to be up to 650 °C. This was attributed to the role of the thin oxidized RuOx layer formed at the surface of the Ru film and the thin Pt layer. Consequently, the surface morphology of the BST film and the performance of the TiN barrier can be simultaneously improved by the introduction of a thin Pt layer and by post-treatment for a Ru/TiN/p-Si/Si structure.