Se-Hun Kwon

Plasma-enhanced atomic layer deposition of ruthenium thin films

This work was supported by the project of National Research Laboratory ~NRL!. Korea Advanced Institute of Science and Technology assisted in meeting the publication costs of this article.

PEALD of a Ruthenium Adhesion Layer for Copper Interconnects

Ruthenium thin films were produced by plasma-enhanced atomic layer deposition (PEALD) using an alternating supply of bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp) 2 ] and NH 3 plasma at a deposition temperature of 270°C. The film thickness per cycle was self-limited at 0.038 nm/cycle, which was thinner than the thickness obtained from the conventional ALD using oxygen instead of NH 3 plasma. The ruthenium thin film prepared with PEALD had a preferential orientation toward (002), and it was progressively promoted with NH 3 plasma power. The PEALD of ruthenium shows a merit in controlling ultrathin film thickness with less than 2 nm more precisely and more easily than the conventional ALD, due to the reduced transient period at the initial film growth stage. Also, ruthenium thin film improved the interfacial adhesion of metallorganic chemical vapor deposited copper to diffusion barrier metals by forming Cu-Ru chemical bonds at the interface without degrading the film resistivity of copper.

Plasma-Enhanced Atomic Layer Deposition of Ru–TiN Thin Films for Copper Diffusion Barrier Metals

Ruthenium-titanium nitride (Ru-TiN) thin films were grown by plasma-enhanced atomic layer deposition (PEALD) at a growth temperature of 200°C. For the Ru-TiN PEALD, Ru and TiN were sequentially deposited to intermix TiN with Ru. The composition of Ru-TiN films was controlled by changing the number of deposition cycles allocated to Ru, while the number of deposition cycles for TiN was fixed to one cycle. The microstructures of Ru-TiN films changed from polycrystalline to amorphous, as the intermixing ratio of Ru increased in the deposited Ru-TiN films. The resistivity of the Ru-TiN film was abruptly increased by adding Ru at the first stage, but after showing a peak resistivity, it decreased with the intermixing ratio of Ru in the films. Especially, the film of Ru 0.67 -(TiN) 0.33 showed an electrical resistivity of 190 μΩ cm. As a Cu diffusion barrier layer, amorphous Ru-TiN films showed a superior copper diffusion barrier property to TiN or Ru itself, which had a polycrystalline structure. Moreover, Ru-TiN films showed a good adhesion to both chemical vapor deposition copper and an underlayer of SiO 2 .

Improvement of the Morphological Stability by Stacking RuO2 on Ru Thin Films with Atomic Layer Deposition

Stacked RuO 2 /Ru structures were produced by atomic layer deposition (ALD) using an alternating supply of his(ethylcyclopentadienyl)ruthenium [Ru(EtCp) 2 ] and O 2 gas at a deposition temperature of 270°C. The type of the deposited film, either Ru or RUO 2 , was controlled by the total pressure in the ALD system as well as the ratio of the adsorbed Ru(EtCp) 2 to the partial pressure of O 2 in the following O 2 gas pulse. The resistivity of the deposited Ru and RuO 2 thin films was about 15 and 70 μΩ cm, respectively. The surface morphology of Ru films annealed in O 2 ambient was seriously degraded by surface oxidation. Moreover, RUO 2 films were also agglomerated due to the residual stress releasing during the annealing process. However, a stacked RUO 2 /Ru structure produced using ALD maintained a smooth surface even at an annealing temperature of 800°C in ambient O 2 . Auger electron spectroscopy confirmed that the stacked RuO 2 /Ru structure successfully blocked oxygen and silicon diffusion. Therefore, the stacked RuO 2 /Ru structure produced by ALD is suitable for use as the bottom electrode material for high dielectric applications.

Improvement of Copper Diffusion Barrier Properties of Tantalum Nitride Films by Incorporating Ruthenium Using PEALD

Ru-incorporated TaN (Ru-TaN) films were investigated as a Cu diffusion barrier material. Ru-TaN films were prepared by sequential deposition of Ru and TaN using plasma-enhanced atomic layer deposition (PEALD). The film composition was controlled by the number of Ru unit cycles. While the resistivity of Ru-TaN films was increased abruptly at low Ru composition (∼0.06), the resistivity of Ru-TaN films was decreased gradually as the Ru composition increased after that composition. The crystal structures of Ru-TaN films were amorphous at the Ru composition range from 0.19 to 0.52 due to disturbance of grain growth. However, the Ru-TaN films had TaN-like structure below this range and Ru-like structure above this range. The amorphous Ru-TaN films had nanocrystallite embedded structure in an amorphous matrix. This amorphous Ru-TaN barrier showed a better Cu diffusion barrier property (∼700°C) than the TaN barrier (∼650°C) because the Cu diffusion through the grain boundary was suppressed by the amorphization. In addition, the Ru-TaN barrier exhibited good adhesion to both Cu and SiO 2 .

Initial stages of ruthenium film growth in plasma-enhanced atomic layer deposition

The initial stages of ruthenium film growth in plasma-enhanced atomic layer deposition (PEALD) on titanium nitride (TiN) substrate were investigated in detail. During the initial stages of ruthenium film growth, the influence of the substrate surface was significant and controlling thickness by counting the number of deposition cycles is no longer valid. The time required for saturated adsorption of Ru(EtCp) 2 as well as the amount of deposited ruthenium atoms per cycle changed during the initial stage. The time required for saturated adsorption of Ru(EtCp) 2 on homogeneous ruthenium surfaces was 7 s. However, it increased up to 25 s during the initial stage of the ruthenium film growth where the film growth on heterogeneous TiN substrate is dominant. By considering these changes during the initial stages of ruthenium PEALD growth, the full coverage of PEALD ruthenium can be obtained at a minimum thickness of 2.7 nm.

Improvement of Morphological Stability of PEALD-Iridium Thin Films by Adopting Two-Step Annealing Process

Plasma-enhanced atomic layer deposition PEALD of iridium Ir films was investigated using Ir EtCp COD and NH3 plasma. Deposited Ir films had smooth surface and preferred 111 orientation. After simple annealing in ambient oxygen, surface roughening occurred because Ir was oxidized above 550°C, and the oxidized IrO2 during temperature rising was reduced to Ir at 850°C. However, by adopting two-step annealing, Ir films showed excellent thermal and morphological stability at 850°C. During two-step annealing at 850°C, the oxidation during temperature rising was suppressed by supplying argon, and annealing in ambient oxygen progressed after the temperature reached 850°C.

Dispersion of acoustic surface waves by velocity gradients

The perturbation theory of Auld [Acoustic Fields and Waves in Solids (Wiley, New York, 1973), Vol. II, p. 294], which describes the effect of a subsurface gradient on the velocity dispersion of surface waves, has been modified to a simpler form by an approximation using a newly defined velocity gradient for the case of isotropic materials. The modified theory is applied to nitrogen implantation in AISI 4140 steel with a velocity gradient of Gaussian profile, and compared with dispersion data obtained by the ultrasonic right‐angle technique in the frequency range from 2.4 to 14.8 MHz. The good agreement between experiments and our theory suggests that the compound layer in the subsurface region plays a dominant role in causing the dispersion of acoustic surface waves.

Sub-0.5 nm equivalent oxide thickness scaling for Si-doped Zr1-xHfxO2 thin film without using noble metal electrode.

The dielectric properties of the Si-doped Zr1-xHfxO2 thin films were investigated over a broad compositional range with the goal of improving their properties for use as DRAM capacitor materials. The Si-doped Zr1-xHfxO2 thin films were deposited on TiN bottom electrodes by atomic layer deposition using a TEMA-Zr/TEMA-Hf mixture precursor for deposition of Zr1-xHfxO2 film and Tris-EMASiH as a Si precursor. The Si stabilizer increased the tetragonality and the dielectric constant; however, at high fractions of Si, the crystal structure degraded to amorphous and the dielectric constant decreased. Doping with Si exhibited a larger influence on the dielectric constant at higher Hf content. A Si-doped Hf-rich Zr1-xHfxO2 thin film, with tetragonal structure, exhibited a dielectric constant of about 50. This is the highest value among all reported results for Zr and Hf oxide systems, and equivalent oxide thickness (EOT) value of under 0.5 nm could be obtained with a leakage current of under 10(-7) A·cm(-2), which is the lowest EOT value ever reported for a DRAM storage capacitor system without using a noble-metal-based electrode.

Theoretical Simulation of Surface Evolution Using the Random Deposition and Surface Relaxation for Metal Oxide Film in Atomic Layer Deposition

Atomic layer deposition (ALD) has become an essential deposition method for forming nanometer scale thin films in the microelectronics industry, and its applications have been extended to multi-component thin films, as well as to single metal oxide films. In order to investigate the development of the surface structure of ultra-thin film qualitatively as well as quantitatively, ALD processes are simulated with a molecular scale. For this simulation, the film materials are deposited on a imaginary substrate that consists of small lattice. The deposition behaviors are described by using random deposition (RD) model or random deposition with surface relaxation (RDSR) model as the ALD growth mode, and the proposed model was applied to the deposition of SrO-TiO 2 thin films. Through this work, growth characteristics such as surface morphology, deposited film coverage can be predicted.