Criteria of Atomic Intermixing during Thin Film Growth 김상필*, 유승석§, 이승철, 정용재*, 이광렬 한국과학기술연구원, 미래기술연구본부 * 한양대학교, 세라믹스 공학과, § 서울대학교, 재료공학부 Thank you Prof. song? chairman. I am Kwang-Ryeol Lee of KIST working in the division of future technology research division. First of all, I would like to thank organizing committee for inviting me to this excellent symposium that covers very wide range of science and technology. Today, I will present our recent molecular dynamics simulation work of thin film deposition with the title, “””””. This is the part of Mr. Sangpil’s work for his master degree. And another coworker of this result is Dr. Seung-cheol Lee in my group. 2004. 7. 2. 상변태 열역학 통합심포지움, 포항공과대학교

GMR Spin Valve Major Materials Issue is the interfacial structure This would be an extreme case where the interface becomes very significant in the nano-scale devices. This is the schematic of GMR devices, one of typical nanodevice. GMR is composed of multilayers of thickness of few nanometer. Hence, the atomic structure of the interface should be well controlled to obtain high performance devices, and actually one of the major material issue in the development of GMR device is the atomic scale structure of the interface and interdiffusion. Major Materials Issue is the interfacial structure and chemical diffusion in atomic scale

Co on Al (001) Substrate N.R. Shivaparan, et al. Surf. Sci. 476, 152 (2001)

TEM Cross-section In the present work, we employed the molecular dynamic simulation to understand the atomic scale phenomena during thin film process for spintronic devices. This is the schematic of spin FET devices. The spintronic devices utilize the transfer a spin information from here to there using a nanoscale magnetic elements. Typically, this device is composed of nanoscale multilayer of various materials.

Conventional Thin Film Growth Model 흥미롭게도 기존의 증착메커니즘은 기판 위에서 원자는 depositon diffusion nucleation and growth만이 발생한다고 하였지만 본 실험에서는 기존의 개념과는 다른 새로운 형태의 증착 메커니즘을 발견할 수 있었습니다. Conventional thin film growth model simply assumes that intermixing between the adatom and the substrate is negligible.

Substrate Adatom (0.1eV, normal incident) Program : XMD 2.5.30 300K Initial Temperature Substrate 300K Constant Temperature Fixed Atom Position [100] [001] [010] z y x Program : XMD 2.5.30 x,y-axis : Periodic Boundary Condition z-axis : Open Surface Atom flux : 5ps/atom MD calc. step : 0.5fs This schematic shows the simulation condition used in the present work. Atdatom is deposited on the substrate with normal incident. The initial kinetic energy of the adatom was 0.1eV which is to simulate the case of evaporation or effusion in the MBE cell. The substrate was 6x6x4 lattice composed of 576 atoms. Periodic boundary condition was applied in x, y direction and the atoms in bottom 1 lattice was fixed to simulate wide and thick substrate. The temperature of bottom 2 lattice was kept at 300K to dissipate the heat generated on the growing surface. However, all other atoms were fully relaxed with initial temperature at 300K. Time step for MD calculation of 0.5 fs. We observed that after arrival of adatom, some agitation occurs on the surface. But most of significant reaction occurs within 1 ps, after that, the system becomes to a steady state. Every 5 ps, atom was added to the system.

Deposition Behavior of Al on Co (001)

Deposition Behavior of Co on Al (001)

CoAl compound layer was formed spontaneously. Structural Analysis CoAl CoAl compound layer was formed spontaneously.

Co on Al (100) 1.4 ML 2.8 ML 4.2 ML N.R. Shivaparan, et al Surf. Sci. 476, 152 (2001)

Deposition Behavior on (111) Al on Co Co on Al TOP VIEW

Asymmetry in Interfacial Intermixing Al on Co Co on Al

Energy Barrier for Co Penetration (1) (2) (3) Reaction Coordinate (1) (2) (3) Activation barrier is larger than the incident kinetic energy (0.1eV) of Co. How can the deposited Co atom get the sufficient energy to overcome activation barrier?

Acceleration of Deposited Co Near Al Substrate 1 2 3 4 3.5eV Co Hollow site Al (1) (2) (3) (4)

Deposition Behavior on (001) Al on Co Co on Al

Contour of Acceleration Al on Co (001) Co on Al (001)

Deposition Behavior on (001) Co on Al (001) Reaction Coordinate

Deposition Behavior on (001) Al on Co (001)

Deposition Behavior on (001) Al on Al (001) Al on Al (100)

Two Different Systems Au-Pt & Co-Cu

M.I. Haftel et al., Phys. Rev. B 53, 8007 (1996). Au on Pt (001) Pt on Au (001) M.I. Haftel et al., Phys. Rev. B 53, 8007 (1996).

2.19 eV 0.18 eV Local Acceleration Contour for Au on Pt(001) Local Acceleration Contour for Pt on Au (001)

Deposited Atom of 0.1 eV Co on Cu (100) Cu on Co (100)

Deposited Atom of 5.0 eV Cu on Co (100) Co on Cu (100)

Kinetic Energy of Co near Cu (100) Hollow site Top site 2.63 eV 1.81 eV

Energy Barrier for Intermixing 0.553 eV 1.21 eV Co on Cu(001) Cu on Co(001)

Conventional Thin Film Growth Model Conclusions In nano-scale processes, the model need to be extended to consider the atomic intermixing at the interface. Conventional Thin Film Growth Model Calculations of the acceleration of adatom and the activation barrier for the intermixing can provide a criteria for the atomic intermixing.

Conclusions

0.1 eV Co on Cu(001) 1ML 2ML 3ML 0.1 eV Cu on Co(001)

5 eV Co on Cu(001) 1ML 2ML 3ML 5 eV Cu on Co(001)