Lecture3 IC fabrication process
- 2. IC Fabrication Process Sequence •Silicon Wafer manufacturing •Wafer processing •Oxidation •Photo Lithography •Etching •Diffusion & Ion implantation •Metallization •Testing •Assembly and packaging
- 3. 3 Transistor in side the IC IC 7400 No. of NAND gates=4 No. of transistors per gate=4 Total no of transistors=16 Size of chip in terms of mm Can you Imagine the size of the transistor in side IC
- 4. IC Fabrication Process- Video from Intel ‘From sand to silicon’ in youtube
- 5. 5 Creating Wafers -A Single Crystal Growth •Czochralski Method Silicon in nature
- 6. 6 Silicon Wafer Manufacturing Process
- 7. 7 Oxidation Si+O2 SiO2 1200 C 1. Wet Oxidation •Water vapour •Used to grow Thick Oxide •Oxygen gas •Used to grow Thin Oxide 2. Dry Oxidation Si+2H2O SiO2+2H2 900 C •Thickness depends on Temperature and Time •The process by which a layer of silicon di oxide is grown
- 8. 8 Photo Lithography •It uses light to transfer a geometric pattern from a photo mask to a photo sensitive chemical photo resist on the substrate •Photo resist: An organic polymer, sensitive to UV light and resistant to attack by acids.This is of 2 types. Positive &negative. If negative PR is used, the PR where it is exposed to UV light get hardened. •A solvent called developer is used to remove the soft PR Photo resist coating process
- 9. 9 •Mask: Photo mask is an opaque plate with holes or transparencies that allow light to shine throgh in a defined pattren •Lens: To scale the mask Photo Lithography
- 10. 10 Etching Etchants: KOH, HF,BF6,BCl3 SiO2 + 6HF H2SiF6+2H2O •To chemically remove layers from the surface of a wafer
- 11. 11 Diffusion & Ion Implantation •Diffusion and ion implantation are the two key methods of impurity doping •Diffusion: Dopant atoms move from the surface into Si by thermal means via substitutional or interstitial diffusion mechanism •It requires high temperature and hard mask •Dopant concentration and junction depth cannot be controlled
- 12. 12 •Ion implantation: Dopant atoms are forcefully added into Si in the form of energetic ion beam injection •Requires low temperature and PR mask •Dopant concentration and junction depth can be controlled Diffusion & Ion Implantation
- 13. 13 Metallization •Provides contacts and interconnections •Most commonly used material- Aluminium •Requirements •Low resistance Ohmic contacts •Low sheet resistance •Reliable interconnections
- 14. 14 Wafer Testing •A wafer prober is a machine (Automatic test equipment) used to test integrated circuits Wafer test setup Wafer inspection