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High Temperature Oxidation of TiAlN Thin Films for Memory Devices Sang-Shik Park

High Temperature Oxidation of TiAlN Thin Films for Memory Devices Sang-Shik Park Dept. of Materials Eng., Sangju National Univ. Sangju, Kyungbuk 742-711, Korea (sspark@sangju.ac.kr). Introduction. DRAM cell structure and problems.

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High Temperature Oxidation of TiAlN Thin Films for Memory Devices Sang-Shik Park

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  1. High Temperature Oxidation of TiAlN ThinFilms forMemory Devices Sang-Shik Park Dept. of Materials Eng., Sangju National Univ. Sangju, Kyungbuk 742-711, Korea (sspark@sangju.ac.kr)

  2. Introduction DRAM cell structure and problems Ref. : Kotecki, et al., IBM J. Res. Develop. Vol.43. No.3 (1999) Required conditions for barrier layers in DRAM applications Withstand at oxygen atmosphere above 650oC, 30min. Prevent oxygen diffusion and remain electrically conductive Total contact resistance after oxidation : 400 Ω

  3. Introduction  Properties of candidate materials Research trend for barrier layer Formation of protective layer on surface (TiAlN, TiZrN) Amorphous film (TaSiN, TiSiN, WSiN)

  4. Introduction Crystal Structure Ti Al N TiN TiAlN Solubility of Al in TiN (ref.) - Ti1-xAlxN film by sputtering ; x : 0.4 (Ts ; 500℃) - Ti1-xAlxN film by arc evaporation : x ; 0.6∼0.7 (Ts ; 400~450℃) Objective of this study Properties of TiAlN films with preparation condition Effects of Al content in TiAlN films Oxidation behavior of TiAlN films

  5. Experimental Conditions Deposition condition by sputtering Target Ti and Al Substrate poly-Si D (target-substrate) 50 mm Base pressure 5.0 ×10-7 torr Deposition temperature 400 oC Working pressure 1.0 ×10-2 torr Rf power 250 W (Ti) DC power 20~150 W (Al) Sputtering gas Ar, N2 OXIDATION CONDITION : O2(1 atm), 650~800 oC, 30∼60 min.(RTA)

  6. as-depo. films • Increase of Al content : • - Decrease of lattice parameter • Amorphous structure XRD patterns of Ti1-xAlxN thin films with various Al content.

  7. micro-structure (b) (a) (b) 200nm (c) • Increase of Al content : • - finer micro-stucture • - glass like structure • Difficulty in diffusion of adatom • due to compositional defects • Decrease of G.B. mobility SEM cross-section images of (a)TiN, (b)Ti0.89Al0.11N and (c) Ti0.48Al0.52N thin films.

  8. Effects of N2 gas ratio 83% ; Ti0.82Al0.18N 50% ; Ti0.74Al0.26N 9% ; Ti0.70Al0.30N XRD patterns of the Ti1-xAlxN films as a function of N2 flow ratio.

  9. Resistivity Effect of Al content (a) (b) Resistivity of Ti1-xAlxN films as a function of (a) Al content and (b) N2 flow ratio.

  10. After Oxidation (b) (a) XRD patterns of (a)Ti1-xAlxN films annealed at 800oC for 1hr and (b) Ti0.74Al0.26N films annealed at various temp. for 1hr.

  11. micro-structure after oxidation (c) (c) SEM cross-section images of Ti0.74Al0.26N films annealed at (a) 650oC, (b) 720oC and (c) 800oC.

  12. Oxidation of TiN film AES depth profile of TiN film annealed at 650oCfor 30min.

  13. Oxidation vs. temperature AES depth profile of Ti0.74Al0.26N films annealed at (a) 650oC, (b) 720oC and (c) 800oC for 1hr.

  14. Oxidation vs. Al content AES depth profile of Ti1-xAlxN films annealed at 800oC for 1hr.

  15. Oxidation behavior Film with higher Al content : - Decrease of oxide thickness - Oxide form ; AlTiNO (Incease of Al content) RBS spectra of Ti0.70Al0.30N and (b) Ti0.82Al0.18N films annealed at 800oC for 1hr.

  16. Oxidation Kinetics  650 oC / lower Al content  720 oC / higher Al content Ti-rich AlTiNO Al-rich AlTiNO TiO2 TiO2 TiAlN TiAlN Si Si Oxidation kinetics dox = 2 (Dt)1/2 D = D0 exp (- Ea / kT) dox; oxide thickness, D ; diffusion coefficient, t ; oxidation time, Ea; activation E., k ; Boltzmann’s const., T ; temperature

  17. Oxidation Kinetics Ti0.74Al0.26N films (a) (b) ref. : Wittmer, et al., JAP. .52, 11 (1981) (a) Dependence of the thickness of oxide layer on oxidation time and (b) Arrhenius plot of diffusion coefficient.

  18. TiZrN film for comparison As depo. annealed Annealed AES depth profile of Ti0.73Zr0.27N films annealed at 720oC for 30min.

  19. Summary • Ti1-xAlxN barrier layer was deposited by reactive magnetron sputtering • ▶Effects of Al content • - Resistivity increases with Al incorporation • - Excess Al(x=0.52) reduce the crystallinity of films due to lattice defects • - N2 flow rate affects the Al/Ti ratio of films • - Oxidation resistance increases with increasing the Al content • ▶ Oxidation Kinetics of TiAlN thin films • - Diffusion rate of Al ion to the surface is higher at high temperature • - Protective layer on the surface is AlTiNO layer • - Films with higher Al content forms thicker protective layer • - Thinner Al-rich surface layer results in easier O diffusion • - Oxidation of TiAlN layer is diffusion limited process • - Ti0.74Al0.26N layer show diffusion coefficient of ~10-15㎠/s at 800oC and • activation Energy of 2.12eV

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