Gyu Weon Hwang

Atomic Layer Deposition of Ru Thin Films Using 2,4-(Dimethylpentadienyl)(ethylcyclopentadienyl)Ru by a Liquid Injection System

Ru thin films were grown on Si, SiO 2 , TiO 2 , and TiN substrates by atomic-layer deposition using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru and O 2 as Ru precursor and reactant, respectively, at temperatures ranging from 230 to 280°C. A saturated growth rate of 0.04 nm/cycle and a low oxygen concentration (below the detection limit of Auger electron spectroscopy) were obtained at 250°C. The Ru film showed a negligible incubation period on all the different types of substrates, and an active nucleation behavior which resulted in a very smooth film surface morphology. The dimethylpentadienyl ligand enhanced the active nucleation of Ru and retarded the oxidation of the grown Ru layer. Good step coverage (>90%) was obtained from the Ru film grown on a capacitor hole with an aspect ratio of 17 and an opening diameter of 150 nm by a proper control of the Ar carrier gas flow rate.

Growth Characteristics of Atomic Layer Deposited TiO2 Thin Films on Ru and Si Electrodes for Memory Capacitor Applications

TiO 2 thin films were grown by an atomic-layer-deposition process at growth temperatures ranging from 200 to 300°C on Ru and Si substrates using Ti[OCH(CH 3 ) 2 ] 4 and H 2 O as metal precursor and oxygen source, respectively, for metal-insulator-metal capacitor application in dynamic random access memories. The saturated film growth rate on Ru and Si substrates was 0.034 and 0.046 nm/cycle, respectively. The TiO 2 film growth on a Ru substrate showed a rather long incubation period and the incubation period decreased with increasing Ti[OCH(CH 3 ) 2 ] 4 pulse time, whereas the H 2 O pulse time had almost no influence on the incubation period. A growth rate transition, from low to high values, (thickness 7-8 nm) was observed when the films were grown at temperatures >250°C, whereas the films grown at lower temperatures did not show the transition. The transition was due to the structural change of the film from an amorphous/nanocrystalline to the well-crystallized polycrystalline anatase phase. The TiO 2 films grown at temperatures >250°C showed a dielectric constant of ∼35. A 14-nm-thick TiO 2 film showed an equivalent oxide thickness of 1.7 nm and a leakage current density of 5 X 10 - 6 A/cm 2 at 1 V.

Transformation of the Crystalline Structure of an ALD TiO2 Film on a Ru Electrode by O3 Pretreatment

The influence of the thin RuO 2 surface layer, formed by oxidation of a Ru electrode using O 3 (250°C for 15 s), on the phase formation and dielectric properties of TiO 2 thin films grown by atomic layer deposition (ALD) is investigated. TiO 2 films grown on the as-received Ru electrode (no O 3 pretreatment) have an anatase structure and the dielectric constant is ∼30. However, the crystalline structure of the TiO 2 film grown on an O 3 pretreated Ru electrode is rutile, and the dielectric constant is >60. This is attributed to a structural compatibility between rutile TiO 2 and RuO 2 .

Characteristics of Amorphous Bi2Ti2O7 Thin Films Grown by Atomic Layer Deposition for Memory Capacitor Applications

Bi 2 Ti 2 O 7 films were deposited on sputtered Ru/SiO 2 /Si substrates by atomic layer deposition using tris(l-methoxy-2-methyl-2-propoxy)bismuth [Bi(mmp) 3 ], titanium tetraisopropoxide as Bi and Ti precursors, and H 2 O as oxidant, respectively. The wafer temperature was varied from 225 to 300°C. The growth rates decreased from 0.075 nm/cycle at 225°C to 0.055 nm/cycle at 300°C. The Bi concentration in the film decreased with increasing growth temperature and it could be controlled within a certain range by changing the Bi feeding at a given temperature. The as-grown Bi 2 Ti 2 O 7 films were amorphous but contained metallic Bi at high growth temperatures and high Bi concentrations. Bi and Ti piled-up on the film surface and the Ru interface, respectively. The electrical leakage property of the Bi 2 Ti 2 O 7 thin film became worse with increasing deposition temperature and Bi concentration due to the metallic Bi formation. The dielectric constant at the optimum deposition condition (225°C) was ∼40, and the leakage current level was < 10 - 7 A/cm 2 at 1.0 MV/cm at a film thickness of ∼15 nm. Reasonable conformal film thickness and cation composition over contact holes with a diameter of 0.15 μm and a depth of 1.1 μm were obtained.

Atomic Layer Deposition and Electrical Properties of PbTiO3 Thin Films Using Metallorganic Precursors and H2O

Atomic layer deposition of ferroelectric PbTiO 3 (PTO) thin films was attempted using lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) and titanium tetra(tert-butoxide) as Pb and Ti precursors, respectively, and H 2 O as the oxidant at a wafer temperature of 200°C on Ir/IrO 2 /SiO 2 /Si substrates. Cation stoichiometric PTO thin films were grown with a growth rate of 0.064 nm/cycle by a proper control of the cycle ratio of the PbO and TiO 2 cycles. A catalytic increase in the growth rate was observed for the PTO films compared to the component oxide films. The as-grown film was amorphous and postdeposition annealing at temperatures ranging from 500 to 600°C induced crystallization to the desired perovskite structure. However, the slow heating and cooling induced pyrochlore phase formation with a very fine grain size along the larger perovskite grain boundaries. Conductive atomic force microscopy showed that the pyrochlore material shows a high leakage current which adversely interferes with the ferroelectric properties. Fast heating and cooling effectively suppressed the pyrochlore phase formation. In this case, the main leakage current path was formed by the perovskite grains but the leakage current level was largely decreased. A remanent polarization of 11.2 μC/cm 2 at an applied bias voltage of 2.8 V was obtained.

Characteristics of Polycrystalline SrRuO3 Thin-Film Bottom Electrodes for Metallorganic Chemical-Vapor-Deposited Pb ( Zr0.2Ti0.8 ) O3 Thin Films

In situ and ex situ crystallized polycrystalline SrRuO 3 (SRO) thin-film electrodes are fabricated by dc magnetron sputtering at a substrate temperature of 550 and 350°C, respectively, followed by postannealing for application as bottom electrodes of metallorganic chemical-vapor-deposited Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin films. The in situ crystallized SRO electrode shows a negligible change in film composition during the subsequent annealing and works as a good electrode for the ferroelectric PZT films. However, the ex situ crystallization by postannealing largely decreases the Ru content in the SRO film and consequently the PZT film grown on top has a poor ferroelectric performance. In addition, the Zr component in the PZT film initially reacts with the excessive SrO in the electrode, resulting in a deposition of PbTiO 3 at the initial stage of the PZT deposition which largely deteriorates the ferroelectric performance. Therefore, it is crucial to have in situ crystallized SRO for a reliable electrode of a PZT capacitor.

Characterization of Pb x Pt y Alloy Formation on a Pt Substrate during Liquid-Delivery MOCVD of Pb ( Zr , Ti ) O3 Thin Films

Pb x Pt y alloy formation and its influence on Pb(Zr,Ti)O 3 (PZT) film growth during liquid-delivery metallorganic chemical vapor deposition (MOCVD) of ferroelectric PZT thin films on Pt electrodes are investigated. When an excessive amount of Pb precursor and a deficient amount of oxygen are supplied during MOCVD at temperatures near 550°C, Pb diffuses along the grain boundaries into the Pt substrate, causing the formation of an alloy layer. Compared to a thicker Pt electrode (150 nm), a thinner Pt substrate (50 nm) enhances the alloy layer formation due to the higher diffusion of Pb along the more abundant Pt grain boundaries. The alloy layer enhances the Pb incorporation into the PZT film and improves the crystallization of the PZT layer on top due to better structural compatibility between PZT and the alloy. When the deposition temperature is 570°C the alloy formation is initiated in the early stage of the film deposition but undergoes thermal decomposition in the later stage (> ∼ 15 min). Therefore, a constant Pb concentration is obtained after the initial decrease for a deposition period <15 min.

Atomic Layer Deposition of Bi1 − x − y Ti x Si y O z Thin Films Using H2O Oxidant and Their Characteristics Depending on Si Content

Bi 1-x-y Ti x Si y O z (BTSO) films were deposited on sputtered Ru/SiO 2 /Si substrates by the atomic layer deposition method using tris(l-methoxy-2-methyl-2-propoxy)bismuth, titanium tetraisopropoxide, and tetraethylorthosilicate as Bi, Ti, and Si precursors, respectively, arid H 2 O as an oxidant at temperatures ranging from 225 to 300°C. The film thickness ranged from 13 to 18 nm. The Si contents in the films ranged from 10 to 25 atom % and the dielectric constants ranged from 29 to 43 depending on the Si content. All of the BTSO films had very low carbon contents (<0.5 atom %), X-ray diffraction showed that the as-grown films were amorphous and, after annealing at 600°C for 30 min the films were crystallized to the pyrochlore structure.

Atomic layer deposition of PbTiO 3 and its component oxide films

Atomic layer deposition of ferroelectric PbTiO₃ (PTO) thin films and its component oxide films were attempted using the Pb(DMAMP)₂ and Ti(Oi-Pr)₄ or Ti(Ot-Bu)₄, as the Pb-and Ti-precursors, respectively, and H₂O as oxidant at a wafer temperature of 200 on Ir/IrO₂/SiO₂/Si substrate. The stoichiometric PTO thin films were grown by a proper control of the cycle ratio of the PbO and TiO₂ cycles. The increase of the PTO film growth rate due to the cayalytic effect was observed compared to its component oxide films for both processes using Ti(Oi-Pr)₄ or Ti(Ot-Bu)₄. The as-deposited PTO film was amorphous so that two different post-deposition annealing method, i.e. slow and fast furnace annealing at 600 , were used to crystallize PTO film. The higher growth rate of PTO film grown using Ti(Oi-Pr)₄ due to the higher growth rate of TiO₂ film compared to the case using Ti(Ot-Bu)₄ resulted in less dense PTO film with the higher density of micro-pores inside as well as surface of film after the fast furnace annealing. Slow furnace annealing improved the surface morphology of PTO film and reduced the micro-pore density. Post-deposition annealing transformed amorphous film to polycrystalline film of perovskite sturcure with an a-axis preferred crystallographic orientation.