1. High Temperature Oxidation of TiAlN Thin Films for Memory Devices
Sang-Shik Park
Dept. of Materials Eng., Sangju National Univ.
Sangju, Kyungbuk , Korea

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 Formation of protective layer on surface (TiAlN, TiZrN)
 Properties of candidate materials
Barrier
Material
Processibility
Resistivity
(m Ω-cm)
Oxidation resistance
TiN
Easy
0.2
Poor
TaN -
TiAlN, TaAlN
Moderate
0.3~0.5
Good
TaSiN, TiSiN
1~10
Research trend for barrier layer
Formation of protective layer on surface (TiAlN, TiZrN)
Amorphous film (TaSiN, TiSiN, WSiN)

4. Introduction TiN TiAlN Ti Al N
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) mm
Base pressure ×10-7 torr
Deposition temperature oC
Working pressure ×10-2 torr
Rf power W (Ti)
DC power ~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 (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
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 650oC for 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 Oxidation kinetics D = D0 exp (- Ea / kT)
 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