Oxidation of Silicon
Objective: This experiment will demonstrate thin film formation through oxidation of
silicon to form a SiO2 thin film on silicon.
Theory:
The oxidation of silicon is a diffusion process as follows: Due to the relatively open
structure of SiO2, oxygen molecules or water molecules will diffuse through the growing
SiO2 layer and reach the silicon surface, whereupon these molecules will form SiO2.
Under exposure to oxygen (1), a silicon surface oxidizes to form silicon dioxide (SiO2).
Native silicon dioxide is a high-quality electrical insulator and can be used as a barrier
material during impurity implants or diffusion, for electrical isolation of semiconductor
devices, as a component in MOS transistors, or as an interlayer dielectric in multilevel
metallization structures such as multichip modules. The ability to form a native oxide was
one of the primary processing considerations which led to silicon becoming the dominant
semiconductor material used in integrated circuits today.
Thermal oxidation of silicon is easily achieved by heating the substrate to temperatures
typically in the range of 900-1200 degrees C. The atmosphere in the furnace where
oxidation takes place can either contain pure oxygen or water vapor. Both of these
molecules diffuse easily through the growing SiO2 layer at these high temperatures.
Oxygen arriving at the silicon surface can then combine with silicon to form silicon
dioxide. The chemical reactions that take place are either
for so-called "Dry Oxidation" or
"Wet Oxidation".
Thickness Determination:
Light reflected from the surface of an oxidized Si wafer will experience constructive
interference when the path length in the oxide is equal to an integer multiple of the
wavelength of the light.
2X0 = Kλ/n
Where X0 – Oxide thickness, K= 1,2,..
Wavelength of the incident light and ‘n’ is the refractive index (1.46) for SiO2
Color Chart
Growth Rate Chart
ELECTROMAGNETIC SPECTRUM