Oxidación Termal

Thermal oxidation

Máster ESF
01 10 2012

THERMAL OXIDATION
•Silicon oxide
•Oxidation systems in Silicon technology
•Kinetics of thermal oxidation

A. S. Grove Physics and technology ofsemiconductor devices
Wiley, N.Y., 1967
R.C. Jaeger, Introduction to microelectronic fabrication.
Addison-Wesley Publishing Co. 1988

SILICON OXIDE
amorphous SiO2

During oxide growth, Siliconis consumed
Original
surface

xox
xSi consumed=0,45 xox

Properties of thermal oxide
Simple technology – tight control of quality and thickness
Good dielectric material (insulator, MOS gates,AR coating…):
EG≈8eV; ρ≈1014Ωcm; ε=3,9
Mask for impurity diffusion (planar technology)
D(Si)/D(SiO2) ≈102-105 for typical dopants
Passivates the surfaces (decreases recombination)
S (bare Si) ≈105 cm s-1 → S (oxidized Si) ≈ 102 cm s-1

OXIDATION SYSTEMS IN SILICON TECHNOLOGY

O 2 N2

MASKING oxide:
>0,5 µm, dry – wet – dry
Quartz
tube

H2 O
95ºC

DRY: O2+Si→SiO2
WET: Si+2H2O→SiO2+ 2H2

PASSIVATING oxide:
>10 nm, dry

KINETICS OF THERMAL OXIDATION (1)
One or several chemical species carry the Oxygen atoms to the Silicon surface.
Depending on the atmosphere, O2,OH…
STEPS:
Atmosphere SiO2

Si

N(0) depends on the partial pressure, the temperature, the
chemical species…

1
Gas

1 TRANSPORT TO THE SURFACE IN THE GAS PHASE

N(0)

2 DIFUSSIONTHROUGH THE OXIDE

2

∂C D diffusion constant (depends on the
∂x temperature, the chemical species)
N ( 0 ) − N ( x0 )
If x0 N0 ,D (drt)
eg, a 1000ºC,

N0(wet)=3·1019 cm-3
N0(dry)=5·1016 cm-3… and on TEMPERATURE...
k y D activados en Tª (∝ exp-Ea/kT)
... and on crystal orientation,
and substrate doping, and...
NOTE. Initial oxide.
The first ~ 250 Å grow at a very high rate,
andforms even at room temperature.

B and B/A are the measured parameters

Show that when growing a SiO2 layer with x0 thickness, a Si layer with 0,45 x0
thickness is consumed.
DATA: Silicon...