Oxidation in device fabrication

1. Oxidation in
Semiconductor Device
Fabrication
Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
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2. Oxidation
Oxidation is a process which converts silicon
on the wafer into silicon dioxide (SiO2)
Specifically, it means the substance that gives
away electrons is oxidized
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3. Types of Oxidation
Dry oxidation – Si reacts with O2 to form SiO2
Si (s) + O2 (g) SiO2 (s)
Wet oxidation – Si reacts with water/steamto form SiO2
Si (s) + 2H2O (g) SiO2 (s) + 2H2 (g)
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4. Dry and wet oxidation need high temperature (900 –
1200 °C) for growth, though the kinetics are different,
which is why this process is called thermal oxidation
Thermal Oxidation
In both cases. Si is
consumed from the surface
of the substrate
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5. Characteristic of the dry oxidation:
 slow growth of oxide
 high density
 high breakdown voltage
Characteristics if wet oxidation:
 fast growth even on low temperatures
 less quality than dry oxides
Characteristics of Oxidation
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6. Importance of SiO2 layer
It acts as a diffusion mask permitting selective
diffusions into Si wafer through the window etched
into oxide
It is used for surface passivation which is nothing but
creating protective SiO2 layer on the wafer surface. It
protects the junction from moisture and other
atmospheric contaminants.
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7. It serves as an insulator on the water surface. Its
high relative dielectric constant, which enables
metal line to pass over the active silicon regions.
SiO2 acts as the active gate electrode in MOS device
structure.
It is used to isolate one device from another. It
provides electrical isolation of multilevel
metallization used in VLSI.
Importance of Oxidation
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8. Classification of Oxidation: time-dependent
I. Diffusion limited case:
supply of the oxidizing species to the Si-SiO2
interface is the rate limiting step
This determines the growth rate of the oxide layer.
The diffusion limiting case occurs when there is a
thick oxide layer, or at long oxidation time
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9. Classification of Oxidation: time-dependent
If diffusivity is large or if the oxide thickness
is small, growth is controlled by the formation
of the oxide layer
The diffusion limiting case occurs when there
is a thin oxide layer, or at short oxidation time
II. Reaction Controlled case:
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