Hee Jae Kang

Nondestructive and quantitative depth profiling analysis of ion bombarded Ta2O5 surfaces by medium energy ion scattering spectroscopy

Ion beam sputtering has been widely used for sputter depth profiling with x‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). However, the problem of surface compositional change due to ion bombardment remains to be understood and solved. So far sputtering processes have been usually studied by surface analysis tools such as XPS, AES, and secondary‐ion mass spectrometry which use the sputtering process again. In this work, the altered surface layer of amorphous Ta2O5 thin films due to Ar+ ion bombardment was depth profiled nondestructively and quantitatively for the first time by medium energy ion spectroscopy (MEIS) as a function of the ion incidence angle and the ion dose with a depth resolution of better than 1.0 nm. The MEIS spectrum showed that the preferential sputtering of oxygen atoms developed with the ion dose and saturated in the ion dose of 3.1×1016 ions/cm2. The Ta mole fraction at the surface increased from 0.29 up to 0.42±0.03 at the saturation ion dose under norma...

Computer simulation of damage processes during ion implantation

A new version for the marlowe code, which enables dynamic simulation of damage processes during ion implantation to be performed, has been developed. This simulation code is based on uses of the Ziegler–Biersack–Littmark potential [in Proceedings of the International Engineering Congress on Ion Sources and Ion‐Assisted Technology, edited by T. Takagi (Ionic Co., Tokyo, 1983), p. 1861] for elastic scattering and Firsov’s equation [O. B. Firsov, Sov. Phys. JETP 61, 1453 (1971)] for electron stopping. By introducing a damage function u2009f(z)=l−exp[−ΔE(z)/Ecrit], where ΔE(z) is the deposition energy due to nuclear stopping per unit volume at depth z and Ecrit is the critical energy assessed from the experiment, the present code allows us to simulate how the crystalline structure at depth z transforms to the disordered structure, resulting in the marked change in the penetration of implanted ions as ion implantation proceeds. To examine the applicability of the present simulation code for practical ion implantat...

Dynamic Monte Carlo simulation of surface composition changes on TiC and AuCu under Ar+ ion bombardment

Abstract A dynamic Monte Carlo simulation code has been developed to describe the dynamic processes of surface composition changes in multi-component materials during ion bombardment. This code containing the simulations of not only the kinetic collision processes describing the preferential sputtering but also the radiation-induced segregation and radiation-enhanced diffusion. We applied it to Auue5f8Cu and TiC under 2 keV Ar+ ion bombardment. The results have indicated that the altered layer formation in TiC is caused by the preferential sputtering of the lighter atom, while in Auue5f8Cu, the above three major factors all play significant roles in the formation of an altered layer enriched with Au atoms at the topmost atomic layer followed by a depletion layer of Au approaching to the bulk composition. These calculations have described the experimental results very well.

Dynamic simulation of ion implantation with damaging processes included

Abstract Recent rapid progress in IC-manufacturing requires more accurate knowledge of the spatial distribution of implanted ions in crystalline targets, particularly on channeling and dechanneling processes of the implanted ions which causes disordering of target atoms. For this we have developed a new computer simulation code to simulate how the crystalline structure undergoes disordering due to ion implantation and how this disordering affects successive ion implantation, leading to considerably modified spatial distribution. The simulation program is based on the MARLOWE code which is widely used in calculating atomic binary collision problems either for crystalline targets or for amorphous targets. Besides all functions of the MARLOWE code, the present simulation code is capable of handling cases where the damage due to ion implantation plays an important role. The functional representation of the Ziegler—Biersack—Littmark (ZBL) potential is used in the present code instead of the original Moliere potential. The new simulation code also has an option to choose the approximate formula for calculating atom trajectories in order to reduce computation time.

Preferentially Oriented Crystal Growth in Dynamic Mixing Process–An Approach by Monte Carlo Simulation–

Titanium nitride films produced by a dynamic mixing method have a preferential crystallographic orientation, and the orientation varies with the arrival ratio of the depositing elements. For this study, we performed a Monte Carlo simulation of the damaging process caused by nitrogen ion irradiation onto (111) and (100) planes of a TiN single crystal. The simulation predicts that in (100)TiN, N+ penetrates through the open channel, losing its kinetic energy mainly by electronic stopping, while N+ loses its kinetic energy mainly by nuclear stopping in (111)TiN, leading the crystal to be amorphous. The contribution of this dynamic mixing process to the development of preferred orientation is discussed.

Secondary ion generation mechanism studied by ISS-SIMS and work function measurements

Abstract Oxygen enhancement effects in secondary ion generation were studied in polycrystalline Ni at different partial pressures of oxygen, Po2, by sequential ISS-SIMS and work function measurements. The investigation has revealed that the enhancement undergoes three stages: (I) The secondary ion intensity increases monotonically with an increase of work function which is described very well by the electron tunneling model. (II) This tendency abruptly changes, i.e. the work function decreases and the secondary ion intensity increases rapidly, for a slight increase of Po2 (III) The secondary ion intensities gradually increase and become saturated with a further increase of Po2. It has also been found that the critical coverage, θc, corresponds exactly to the stage (II) behaviour, which was observed by Blaise and Bernheim for a single crystal (100)Ni surface.

Sequential SIMS-ISS analysis of oxygen-enhanced secondary ion generation

Abstract A special arrangement for ISS signal detection has enabled the sequential analysis by SIMS and ISS to be performed with SIMS apparatus. Using a mixed ion beam of He + and Ar + ions, the He + ions provide ISS signals while the Ar + ions generate secondary ions as usual. We have applied this approach to oxygen-enhanced secondary ion generation. ISS monitors the surface coverage of oxygen on a Ni sample and SIMS the generation of secondary ions, Ni + ions, for different partial pressures of oxygen in the specimen chamber. The present SIMS-ISS analysis has led to the conclusion that the electron tunneling model describes the experimental results with considerable success.

MOLECULAR DYNAMICS SIMULATION FOR IONIZED CLUSTER BEAM DEPOSITION

Abstract The mechanism of ionized cluster beam deposition has been studied using Molecular Dynamics Simulation. The Embedded Atom Method (EAM) potential was used in the simulation. The impact of an Au 95 -cluster on a Au(100) substrate was studied for impact energies of 0.15–10 eV/atom. The dependence of the impact energy of the cluster beam was observed. For a cluster energy impact of 10 eV per atom, defects on the surface were created and the cluster embedded into a substrate as an amorphous state. For an energy of 0.5 eV per atom, a defect-free homoepitaxial growth was observed and atomic-scale nucleation was formed, which are in good agreement with experiment. Thus the molecular dynamics simulation is very useful to study the mechanism of ionized cluster beam deposition.

Basic Study of Quantitative Ion Scattering Spectroscopy I Correction Factors for Quantification

Basic problems in quantification by ion scattering spectroscopy (ISS), i.e., energy dependence of the detection efficiency of a micro channel plate (MCP) and neutralization probabilities, have been studied using a newly constructed time of flight (TOF)-ISS apparatus. For primary ion energy below keV (1) marked dependence of the detection efficiency of MCP on the signal energy, and (2) strong contribution, to the ISS spectrum, of those neutral signals that are backscattered through the collision with the second or subsequent atomic layer atoms have been clearly revealed. It has also been pointed out that the energy dependence of the detection efficiency is described very well by a simple statistical treatment of secondary electron generation in the detector.

A study of secondary ionization mechanism for LiF on Au by time‐of‐flight secondary ion mass spectrometry and direct recoil measurements

We have studied the change of Li+ and F− secondary ion intensiters with the matrix transition from submonolayer LiF on gold to thick LiF by time‐of‐flight secondary ion mass spectrometry. Based on direct recoil particle measurements and Monte Carlo simulations, we estimated that the ratio of Li+/F− secondary ion yields did not change significantly with the matrix. From the results, it is suggested that the bond breaking model can be applied for submonolayer LiF on gold as well as for thick LiF.