Saturday , October 23 2021

Basic model for thermal oxidation of silicon

Explain the basic model for thermal oxidation of silicon?

 

Solution:

basic model for thermal oxidation of silicon

 

Model assumptions:
This model is valid for a temperature range of 700-1300C, 0.2 – 1 atm pressure, and oxide thickness of 300 – 20,000 Angstrom.

The oxidizing species-

1. are transported from the bulk gas phase to gas-oxide interface with flux F1 (Flux means a number of species crossing a unit area per unit time).

2. are transported across the existing oxide towards the silicon with flux F2.

3. react at the Si-SiO2 interface with the silicon with flux F3. And

4. at steady-state F1=F2=F3

Here

F1 = h (C* C0),

F2 = D (C0-Ci)/d ,

F3 = ks Ci

Where
C0: equilibrium concentration in the oxide at the outer surface,
C*: equilibrium bulk concentration in the oxide,
h: gas-phase mass transfer coefficient,

D: diffusion coefficient
Ci: oxidizing species concentration in the oxide adjacent to the Si-SiO2 interface,
d: oxide thickness and
ks: reaction rate constant.
After solving at steady state, values of C0
 and Ci can be obtained.

 

Limiting cases:
When D is very small, Ci →0 and C0→ C* (diffusion-controlled case) Oxidation rate depends on the supply of oxidant to the interface through the oxide layer.

When D is large, Ci=C0 (reaction controlled case). Oxidation rate depends on the reaction rate constant and Ci or
C0(Ci = C0 because D is high).

Basic model for thermal oxidation of silicon

Read:Explain different oxide charges?

Check Also

Explain body effects in MOS transistor

Explain body effects in MOS transistor?

Explain body effects in MOS transistor?   body effects in MOS transistor Normally, we considered …