Ho-Jung Sun

Effects of B2H6 Pretreatment on ALD of W Film Using a Sequential Supply of WF6 and SiH4

The effects of diborane pretreatment on atomic layer deposition (ALD) of tungsten (W) thin film using a sequential supply of and on thermally grown and TiN films at 300°C were investigated. The results show that the pretreatment reduces the incubation time for film growth. X-ray photoelectron spectroscopy and scanning electron microscopy analysis suggest that elemental B on , released during pretreatment, induce rapid W nucleation. The drastically improved step coverage of ALD-W film is achieved at the ultrahigh aspect ratio contact (height: and top diameter: ) by the enhanced nucleation and growth via pretreatment. The effects of pretreatment on the properties of ALD-W films such as roughness, phase, microstructure, and resistivity are also investigated.

(Bi, La)4Ti3O12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices

Using nanocrystalline perovskite nuclei, (117) oriented-(Bi,La)4Ti3O12(BLT) thin films were grown using a noble bake process for nonvolatile ferroelectric memory devices. The c-axis oriented BLT thin films have a remanent polarization (2Pr) of 8.0μC∕cm2 at a 3V driving voltage, and the (117) oriented films have a 2Pr value of about 25μC∕cm2. The BLT capacitors, grown on a platinum electrode via nanocrystalline perovskite nuclei, had fatigue and imprint free characteristics after applying 1×1011 switching cycles and for ten years at a 125°C stress. The average sensing margin of the (117) oriented BLT thin films was approximately 700mV for a 0.65μm2 cell size and a sufficient signal margin for ten years was indicated, based on the extrapolation of the measured data for high density ferreoelectric random access memory applications.

Properties of Ru Thin Films Fabricated on TiN by Metal-Organic Chemical Vapor Deposition

Ruthenium (Ru) thin films were fabricated on TiN, as well as on SiO2, by metal-organic chemical vapor deposition using tris(2,4-octanedionato)ruthenium. We characterized the Ru films grown on TiN, and compared them with the films prepared on SiO2. The Ru films deposited on TiN showed weak crystallinity and random grain orientation similar to the films on SiO2, but revealed notably rougher surfaces than the films on SiO2. Moreover, deposition rates on TiN were lower than those on SiO2. These properties of the Ru films grown on TiN originated from the difficulties in nucleation and growth at the initial stage of the deposition. The inferior surface flatness and deposition rate could cause structural instability and poor coverage of the Ru electrode at the bottom of a deep concave hole for a three-dimensional capacitor where the Ru film was in contact with a diffusion barrier metal TiN plug.

Fabrication of Highly Dense Ru Thin Films by High-Temperature Metal-Organic Chemical Vapor Deposition with NH3 Gas as Ru Oxidation Suppressing Agent

We attempted to fabricate highly dense Ru thin films by metal-organic chemical vapor deposition at an elevated temperature of 400°C, employing NH3 gas to suppress Ru oxidation. A solution of 0.2 mol/L tris(2,4-octanedionato)ruthenium [Ru(od)3, Ru(C8H13O2)3] dissolved in n-butylacetate was used as a Ru source and O2 as a reactant gas. It was revealed that NH3 gas effectively eliminated residual oxygen from the Ru films. However, at higher feeding rates of a metal-organic source, Ru films showed poor densities and high electrical resistivities mainly due to significant carbon incorporation. By optimizing Ru(od)3 flow rate to less than 0.3 g/min to reduce contaminating carbon supply, we successfully produced highly dense and conductive Ru films. The best Ru film had a density of 12.2 g/cm3 and a resistivity of 12.0 µΩcm, which were excellent values close to the bulk ones.

Pb(ZrxTi1-x)O3 Thin Film Fabricated on Heterogeneous Under-Layer of Pt and SiO2 in High Density Ferroelectric Random Access Memory (FeRAM) Capacitor

We investigated a Pb(ZrxTi1-x)O3 (PZT) thin film applied in ferroelectric random access memory (FeRAM) capacitor where under-layered structure was made up of patterned Pt/IrO2/Ir electrodes separated by inter-electrode dielectric (IED) SiO2. This capacitor structure is one of the promising candidates for realizing high density FeRAMs. The PZT film grown on IED-SiO2 appeared to have Pb-deficient pyrochlore phase due to significant Pb-diffusion into IED-SiO2, which would make a detrimental effect on PZT film in the capacitor region where the PZT film was grown on isolated Pt electrode, even though growth condition for perovskite PZT film with strong (111) preferred orientation was made when the film was deposited on continuous Pt electrode.

Physical and electrical characteristics of physical vapor-deposited tungsten for bit line process

We attempted to explain the phenomenon that the electric resistivity of tungsten film increases as the thickness decreases and that physical vapor-deposited (PVD) tungsten shows a much lower resistivity than chemical vapor-deposited (CVD) tungsten. The crystallinity and electric conductivity of an under-layer does not affect the electric resistivity of tungsten film. The low resistivity of PVD tungsten originates from a large grain size. PVD tungsten with large grains is free from grain boundary scattering, while CVD tungsten with small grains exhibits grain boundary scattering. As film thickness decreases down to the mean free path of tungsten, the surface scattering effect surpasses the grain boundary scattering effect. Consequently, the resistivity of PVD and CVD tungsten becomes equal because surface scattering increases the resistivity of both large- and small-grained films. The same rule is adaptable for the resistance change of a narrow line structure. CVD tungsten shows a high resistance because of grain boundary scattering originating from a small grain size. However, if the line-width is reduced to the mean free path, grain boundary scattering disappears, making surface scattering only the factor that increases electric resistivity. Thus, CVD tungsten shows the same resistance as PVD tungsten in a very narrow line structure.

Effects of High-Temperature Metal-Organic Chemical Vapor Deposition of Pb(Zr,Ti)O3 Thin Films on Structural Stabilities of Hybrid Pt/IrO2/Ir Stack and Single-Layer Ir Bottom Electrodes

High-temperature Pb(Zr,Ti)O3 (PZT) metal-organic chemical vapor deposition (MOCVD) at 620°C was performed on two major bottom electrode candidates, namely, a hybrid Pt/IrO2/Ir stack electrode and a single-layer Ir electrode. The structural stabilities of both PZT/electrode stacks were investigated. Severe interaction between PZT and the underlayered Pt films was observed, and the interaction resulted in a pyrochlore phase in the PZT film and blister-type deformation in the Pt film. On the other hand, structural stability, which served as the basis for a well-crystallized perovskite PZT film, was preserved in the case of the Ir electrode. Therefore, it could be determined that the Ir electrode as a bottom electrode was better than the Pt electrode from the point of view of the structural stability of a capacitor stack, when high-temperature MOCVD is chosen as a preparation method.

Integration of Novel Capacitor Structure for High Density FeRAM With Barrier Metal TiAlN and (Bi,La)4Ti3O12

16M 1T1C ferroelectric random access memory was successfully integrated by newly proposed scheme named Recessed Open Barrier (ROB) structure with planar Pt/BLT/Pt/IrOx/Ir stacked capacitor. In conventional barrier metal scheme which bottom electrode was stacked, oxygen diffused through the bottom electrode interface formed during MTP structure integration, and oxidized the edge of barrier metal resulting compressive stress. The failure was accelerated by free oxygen diffusion as the stress built up to make the bottom electrode pop-up. In this paper, the barrier metal TiAlN was recessed and refilled by ALD Al2O3 after bottom electrode patterning. By this novel structure, oxidation resistance was greatly improved, because oxygen diffusion path to BM was much longer than conventional scheme. The contact resistance of storage node was below 10 kΩ/plug after all the thermal budget relevant to BLT capacitor.

Crystallographic Orientation Dependent Ferroelectric Characteristics of (Bi3.3,La0.8)Ti3O12 (BLT) Capacitors

ABSTRACT The 70 nm thick (Bi3.3,La0.8)Ti3O12 (BLT) thin films were fabricated by deposition multiple spin coating layers and then crystallized by RTA and FA on Pt/TiOx/SiO2/Si substrate. Films were synthesized by MOD (metal organic decomposition) derived precursor to easy mass production. The randomly oriented BLT thin films have resulted from newly developed noble bake process, while a highly c-axis preferred orientation occurs for conventional baked thin film. The texture coefficient of I(004), I(117), I(111) and I(200) of noble baked BLT capacitors has 0, 0.24, 1.35 and 1.92, respectively. The films were very dense with no apparent pore site. The switching polarization (P*-P∧) and coercive voltage (2 Vc) of randomly oriented BLT thin films were nearly saturated at 3 V to have 20.03 μ C/cm2 and 1.38 V, respectively. However, strongly c-axis oriented thin films have 10.1 μ C/cm2 and 1.42 V for drive 3 V. The random orientation BLT shows good insulating behavior (9.4E-7 A/cm2 at 3 V). Both randomly oriented capacitor and highly c-axis preferred orientation thin films show no degradation of polarization due to fatigue after 1E11 cycles using 3 V (428.5 kV/cm) bipolar square pulse at 1 MHz.

Preparation of Platinum Thin Films by Metalorganic Chemical Vapor Deposition Using Oxygen-Assisted Decomposition of (Ethylcyclopentadienyl)trimethylplatinum

Pt thin films were deposited by the O2-assisted decomposition of an (ethylcyclopentadienyl) trimethylplatinum [(EtCp)PtMe3] precursor, and their growth behavior was investigated by varying the amount of oxygen gas supply. An abrupt change from a very low growth rate to a significantly high growth rate was observed with an increase in O2 feeding rate, which indicated that an oxygen gas supply above a threshold was required to obtain a continuous Pt film with an acceptable growth rate. Under the deposition conditions of a substrate temperature of 340°C and an O2 flow rate of 1000 sccm, we successfully fabricated a Pt film with a smooth surface, (111)-preferred orientation, and low resistivity of 11.6 µΩ-cm on a 200-mm-diameter-wafer.