Atomic layer deposition

1. Atomic layer deposition Chengcheng Li 2013/6/27

2. What is ALD • ALD (Atomic Layer Deposition) • Deposition method by which precursor gases or vapors are alternately pulsed on to the substrate surface. • Precursor gases introduced on to the substrate surface will chemisorb or surface reaction takes place at the surface • Surface reactions on ALD are complementarity and self-limiting

3. ALD Example Cycle for Al2O3 Deposition Cambridge NanoTech Inc., Cambridge, MA 02139 USA www.cambridgenanotech.com/.../

4. ALD vs CVD Chemical vapor deposition(CVD) One or more gases or vapors react to form a solid product: Solid product can be: film particle nanowire nanotube Reaction started by: heat mix two vapors plasma

5. Atomic layer deposition(ALD) Sequential, self-limiting surface reactions make alternating layers: • Benefits of ALD: • Atomic level of control over film composition • Uniform thickness over large areas and inside narrow holes • Very smooth surfaces (for amorphous films) • High density and few defects or pinholes • Low deposition temperatures (for very reactive precursors)

6. Criteria for Both CVD & ALD Precursors •Sufficient volatility (> 0.1 Torr at T < 200 ℃) •No thermal decomposition during vaporization •Precursors and byproducts don’t etch films

7. Criteria for CVD Precursors •Reactivity with substrate •Reactivity with surface of growing film •Thermal decomposition allowed or even needed Criteria for ALD Precursors •Self-limited reactivity with substrate •Self-limited reactivity with the surface made by reaction of the film with the other precursor •Thermal decomposition not allowed

8. Usefulness of Precursors for CVD & ALD Some precursors work only in CVD, but not ALD: Ni(CO)4, W(CO)6, many alkoxides Some precursors work in both CVD and ALD: many beta-diketonates and amidinates Most ALD precursors also work in CVD Some CVD precursors also work in ALD

9. To realize self-terminating, reactions must be irreversible and saturating Irreversible nonsaturating Ir/reversible saturating Self-terminating Reversible saturating

10. Effect of temperature

11. Effect of cycle numbers Two dimension growth Island growth Random deposition

12. W,N-doped TiO2 Narrow Eg N-dope: N 2p W-dope: increase visible activity reduce recombination Increase recombination (trap for charge carriers)

13. 2.55eV The Journal of Physical Chemistry C 113(20): 8553-8555

14. ALD for TiNx 1 Journal of Photochemistry and Photobiology A: Chemistry 177 (2006) 68–75

15. Precursors: TiCl4, NH3, H2O Deposition temperature: 500℃ Substrate: ITO N-TiO2 deposited by TiN/TiO2 ALD process TiN will be partially oxided during TiO2 ALD Process, leading to TiO2-xNx TiCl4+NH3 TiCl4+H2O

17. Process

18. 2

19. substrate: n+ Si precursor: TiCl4 and ammonia water Temperature: 400℃ Thickness： 55nm after 1000 cycles (GPC 0.55A/cycle ) NH3：H2O in vapor 420：1 Film Nconcentration: 1.60 atom %

20. XPS 0.48% 1.12% About 70% of total N

21. IPCE

22. 2.25eV

23. Next Focus + doped TiO2

24. THANK YOU !