Seed Layer and Multistack Approaches to Reduce Leakage in SrTiO3-Based Metal–Insulator–Metal Capacitors Using TiN Bottom Electrode (original) (raw)
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Japanese Journal of Applied Physics, 2010
Leakage reduction is crucial for metal–insulator–metal (MIM) capacitors for future dynamic random access memory (DRAM) nodes. In previous investigations we showed that increasing the Sr-content would result in leakage reduction of SrTiO3 (STO) films deposited on TiN. [1,2] In this work we demonstrate for thin (10 nm) stoichiometric SrTiO3 films that the leakage properties can be significantly lowered (while keeping high capacitance densities) by using stacking approaches such as seed layer (thin STO layer crystallized before the “bulk” STO deposition) and multistack SrTiO3/GdAlO3/SrTiO3. In this work, SrTiO3 films are deposited using a low temperature ALD process enabling the use of low-cost, manufacturable-friendly TiN-bottom electrode.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2011
SrTiO 3 thin films were grown to thicknesses in the range of 18-30 nm by atomic layer deposition using Sr͑ i Pr 3 Cp͒ 2 and ͑CpMe 5 ͒Ti͑OMe͒ 3 as strontium and titanium precursors at 250 and 300°C. Water or ozone was used as oxygen precursor. The films were amorphous in as-deposited state, but crystallized as cubic SrTiO 3 after annealing at 650°C. The highest permittivity values, 60-65, were achieved in the films deposited with ozone at 300°C. The films grown at 250°C tended to possess markedly lower leakage currents than those grown at 300°C.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2011
Metal-insulator-metal structures for dynamic random access memory capacitor applications were prepared by atomic layer deposition. Rutile TiO 2 dielectric layers were grown on top of RuO 2 electrodes. TiO 2 layers were doped in different ways by aluminum and these structures were compared to undoped ones. C-V and J-V measurements show that Al doping reduces the capacitance density of the stacks while reducing leakage current. Varying the initial Al doping profile did not change the electrical properties of the stacks. Leakage current analysis revealed that the current in the doped samples is controlled by Schottky emission.
Thin Solid Films, 2011
Metal-Insulator-Metal (MIM) capacitors are one of the most essential components of radio frequency devices and analog/mixed-signal integrated circuits. In order to obtain high capacitance densities in MIM devices, high-k materials have been considered to be promising candidates to replace the traditional insulators. The challenging point is that the dielectric material must demonstrate high capacitance density values with low leakage current densities. In this work, SrTiO 3 based MIM capacitors have been investigated and the electrical performance of the devices have been optimized by using bilayered systems of Sr 2 Ta 2 O 7−x /SrTiO 3 with different thicknesses of Sr 2 Ta 2 O 7−x . Sputtering X-Ray photoelectron spectroscopy (XPS) measurements have been applied to investigate the interfaces between the thin film constituents of the MIM stacks. The optimized bilayered system provides a leakage current density of 8 10 − 8 A/cm 2 at 2 V (bottom electrode injection) and a high capacitance density of 13 fF/μm 2 .
(Ba,Sr)TiO3 dielectrics for future stacked- capacitor DRAM
IBM Journal of Research and Development, 2000
dielectrics for future stackedcapacitor DRAM Thin films of barium-strontium titanate (Ba,Sr)TiO 3 (BSTO) have been investigated for use as a capacitor dielectric for future generations of dynamic random-access memory (DRAM). This paper describes progress made in the preparation of BSTO films by liquid-source metal-organic chemical vapor deposition (LS-MOCVD) and the issues related to integrating films of BSTO into a DRAM capacitor. Films of BSTO deposited on planar Pt electrodes meet the electrical requirements needed for future DRAM. The specific capacitance and charge loss are found to be strongly dependent on the details of the BSTO deposition, the choice of the lower electrode structure, the microstructure of the BSTO, the post-electrode thermal treatments, BSTO dopants, and thin-film stress. Films of BSTO deposited on patterned Pt electrodes with a feature size of 0.2 m are found to have degraded properties compared to films on large planar structures, but functional bits have been achieved on a DRAM test site at 0.20-m ground rules. Mechanisms influencing specific capacitance and charge loss of BSTO films are described, as are the requirements for the electrode and barrier materials used in stacked-capacitor structures, with emphasis given to the properties of the Pt/TaSi(N) electrode/barrier system. Major problems requiring additional investigation are outlined.
Chemistry of Materials, 2012
SrRuO 3 (SRO) film was deposited by sequential executions of atomic layer deposition of SrO and chemical vapor deposition of RuO 2 layers at a low growth temperature of 230°C using Sr( i Pr 3 Cp) 2 , RuO 4 precursors, and O 2 gas. A wide range of Sr (Ru) concentration could be obtained by modulating the SrO/RuO 2 subcycle ratio, and a high growth rate of ∼2.0 nm/supercycle was achieved with the stoichiometric SRO composition. The as-deposited SRO film was amorphous, and crystallized SRO film was obtained by post deposition annealing in N 2 ambient at temperatures ranging from 600 to 700°C. Crystallized SRO film was adopted as a seed layer for the in situ crystallization of ALD SrTiO 3 (STO) film for application to capacitors for next generation dynamic random access memory. Consequently, a crystalline STO film was grown on crystallized SRO in the as-deposited state, and the dielectric constant of the STO film was largely improved compared to that of the amorphous STO, from 12 to 44.
Impact of Electrode Composition and Processing on the Low-Frequency Noise in SrTio3 MIM Capacitors
IEEE Electron Device Letters, 2014
Strontium titanate (STO) has been proposed as dielectric material in metal-insulator-metal (MIM) capacitors for future DRAM generations due to its higher dielectric constant and corresponding lower equivalent oxide thickness. In this letter, we show for the first time the impact of electrode composition and processing on the low-frequency noise (LFN), hence on the device material defectiveness, in large area (1000 μm × 1000 μm) MIM capacitors with STO dielectric (EOT is ∼0.4nm, physical thickness is ∼8.5nm) and Ru/TiN or TiN as metal electrodes. LFN measurements show that the power spectral density (S IG) associated with gate current (I G) fluctuations follows a 1/f shape and that S IG ∝I α G with α measured between 1.6 and 1.9. In particular, it is shown that PVD processing for top electrode Ru in place of chemical vapor deposition processing results in a significant (more than three decades) noise reduction (lower trap density) according to the observed lower gate leakage (< 10 −7 A/cm 2 at ±1 V).
Thin Solid Films, 2009
The properties of SrTiO 3 thin films, grown by liquid injection metal organic chemical vapor deposition on Si/SiO 2 , using a mixture of precursors, have been investigated at the nanoscale using an Atomic Force Microscope in the so-called Conductive Atomic Force Microscopy mode. Maps of the leakage currents with a nanometric resolution have been obtained on films elaborated at different temperatures and stoichiometries in order to discriminate the role of each parameter on the onset of leakage currents in the resulting layers. It appears that the higher the deposition temperature, the higher the leakage currents of the films. The mapping with a nanometric precision allows to show a heterogeneous behaviour of the surface with leaky grains and insulating boundaries. The study of films elaborated at the same temperature with different compositions supports the assumption that the leakage currents on Ti-rich layers are far higher than on Sr-rich layers.
physica status solidi (RRL) - Rapid Research Letters, 2019
SrTiO 3 (STO) films are grown via atomic layer deposition at 370 C with a two-step growth method. A 5-nm-thick seed layer is first deposited and annealed via rapid thermal annealing (RTA) at temperatures ranging from 450 to 650 C, and the main layer is subsequently grown on the annealed seed layer for in situ crystallization. When the RTA temperature is 500 C or lower, the seed layer remains amorphous, and the main layer is also grown in the amorphous phase. At the 550 C seed annealing temperature, the STO film is partially crystallized, and at the higher annealing temperature, the STO main layer is fully crystallized. The oxygen diffuses through the vertically aligned grain-boundaries during the crystallized film growth, which induces the oxidation-reduction reaction of the underlying Ru substrate. This reaction causes a higher growth rate in the crystalline phase. The large growth rate difference between the amorphous and crystalline regions induces a severe roughening of the main layer. When RTA is done at 600 C, the film is mostly crystallized, and the main layer becomes smooth again. Consequently, a 0.52 nm equivalent oxide thickness is achieved with the low leakage current of 2.5 Â 10 À8 A cm À2 at the 0.8 V applied bias.
Chinese Physics B, 2017
SrTiO 3 (STO) and TiO 2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage (α). Insertion of a TiO 2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO 2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO 2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. TiN was deposited as the top and bottom metal electrodes to form a metal-insulator metal (MIM) structure, which exhibited a very large linear capacitance density of 21 fF/um 2 that decreased by increasing the thickness of the TiO 2 film. The leakage current decreased with an increase in the thickness of TiO 2 , and for a 27-nm-thick film, the measured leakage current was 2.0 × 10 −10 A. X-ray diffraction and Raman spectroscopy revealed that TiN, STO, and TiO 2 films are crystalline and TiO 2 has a dominant anatese phase structure.