CMOS FABRICATION
Step1: Substrate
Primarily, start the process with a P-substrate.
Step2: Oxidation
The oxidation process is done by using high-purity oxygen and hydrogen, which are
exposed in an oxidation furnace approximately at 1000 degree centigrade.
Step3: Photoresist
Photoresist is a light-sensitive organic polymer Softens when exposed to light
Step4: Masking
The photoresist is exposed to UV rays through the N-well mask
Step5: Photoresist removal
A part of the photoresist layer is removed by treating the wafer with the basic or acidic
Step6: Removal of SiO2 using acid etching
The SiO2 oxidation layer is removed through the open area made by the removal of
photoresist using hydrofluoric acid
Step7: Removal of photoresist
Strip off the remaining photoresist
Step8: Formation of the N-well
n-well is formed with diffusion or ion implantation
Diffusion:
Place wafer in furnace with arsenic gas
Heat until As atoms diffuse into exposed Si
Place wafer in furnace with arsenic gas
Heat until As atoms diffuse into exposed Si
Ion Implanatation:
Blast wafer with beam of As ions
Ions blocked by SiO2, only enter exposed Si
Step9: Removal of SiO2
Using the hydrofluoric acid, the remaining SiO2 is removed
Using the hydrofluoric acid, the remaining SiO2 is removed
Step 10: Polysilicon deposition
Deposit very thin layer of gate oxide using Chemical
Vapor Deposition (CVD) process
Step11: Removing the layer barring a small area for the Gates
Except the two small regions required for forming the Gates of NMOS and PMOS, the
remaining layer is stripped off
Except the two small regions required for forming the Gates of NMOS and PMOS, the
remaining layer is stripped off
Next, an oxidation layer is formed on this layer with two small regions for the formation
of the gate terminals of NMOS and PMOS
Step13: Masking and N-diffusion
By using the masking process small gaps are made for the purpose of N-diffusion
By using the masking process small gaps are made for the purpose of N-diffusion
The n-type (n+) dopants are diffused or ion implanted, and the three n+ are formed for
the formation of the terminals of NMOS.
the formation of the terminals of NMOS.
Step14: Oxide stripping
The remaining oxidation layer is stripped off.
The remaining oxidation layer is stripped off.
Step15: P-diffusion
Similar to the above N-diffusion process, the P-diffusion regions are diffused to form
the terminals of the PMOS.
Similar to the above N-diffusion process, the P-diffusion regions are diffused to form
the terminals of the PMOS.
Step16: Thick field oxide
A thick-field oxide is formed in all regions except the terminals of the PMOS and
NMOS.
A thick-field oxide is formed in all regions except the terminals of the PMOS and
NMOS.
Step17: Metallization
Aluminum is sputtered on the whole wafer
Aluminum is sputtered on the whole wafer
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