Atomic layer deposition

Chengcheng Li 2013/6/27

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

ALD Example Cycle for Al2O3 Deposition

Cambridge NanoTech Inc., Cambridge, MA 02139 USA www.cambridgenanotech.com/.../

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

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)

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

Criteria for ALD Precursors

•Reactivity with substrate•Reactivity with surface of growing film•Thermal decomposition allowed or even needed

Criteria for CVD 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

Usefulness of Precursors for CVD & ALDSome 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

To realize self-terminating, reactions must be irreversible and saturating

Self-terminating Reversiblesaturating

Ir/reversiblesaturating

Irreversiblenonsaturating

Effect of temperature

Effect of cycle numbers

Two dimension growth Random deposition Island growth

N-dope: N 2p

W-dope: increase visible activity reduce recombination

W,N-doped TiO2

Narrow Eg

Increase recombination (trap for charge carriers)

The Journal of Physical Chemistry C 113(20): 8553-8555

2.55eV

1

ALD for TiNx

Journal of Photochemistry and Photobiology A: Chemistry 177 (2006) 68–75

Precursors: TiCl4, NH3, H2ODeposition temperature: 500℃Substrate: ITON-TiO2 deposited by TiN/TiO2 ALD process

TiN will be partially oxided during TiO2 ALD Process, leading to TiO2-xNx

TiCl4+NH3 TiCl4+H2O

Process

2

substrate: n+ Siprecursor: TiCl4 and ammonia waterTemperature: 400℃Thickness ： 55nm after 1000 cycles (GPC 0.55A/cycle )

NH3 ： H2O in vapor 420 ： 1Film N concentration: 1.60 atom %

XPS

1.12%

0.48%

About 70% of total N

IPCE

2.25eV

Next Focus

+ doped TiO2

THANK YOU !