CMOS Fabrication

Step -1: Si substrate 

Start with P- type substrate.

Step - 2: Oxidation
Exposing to high purity Oxygen and silicon at approx 1000^oC in oxidation furnace.

Step - 3: Photo resist Coating
Photo resist is a light sensitive organic polymer softens when exposed to light.

Step - 4: Masking
Expose photo resist through N-well mask.

Step -5: Removal of Photo resist
Photo resist are removed by treating the wafer with acid or base solution.

Step - 6: Acid Etching
SiO2 is selectively removed from areas of wafer that are not covered by photo resist by using hydrofluoric acid.

Step - 7: Removal of Photo resist
Strip off the remaining photo resist.

Step - 8:Formation of N-well
N-well if formed with diffusion or ion implantation.

Step - 9: Removal of SiO2
Strip off the remaining oxide using HF

Step - 10: Polysilicon deposition

Deposit very thin layer of gate oxide using Chemical Vapor Deposition  (CVD) process.

Step - 11: N-Diffusion
N-Diffusion forms nMos source, drain, and n-well contact.

Oxidation

Masking

Dopants were diffusied or ion implanted.

Diffusion

Strip off oxide.

Step - 12: P - Diffusion
Similar set of steps form p+diffusion regions for pmos source, drain and substrate contact.

Step - 13: Contact cuts
The devices are to be wired together.
Cover chip with thick field oxide.
Etch oxide where contact cuts are needed.

Step - 14: Metallization:
Sputter on aluminium over whole wafer.
Pattern to remove excess metal, leaving wires.