Basics Of Integrated Circuit.
Monolithic means single stone so IC's are often referred to as Monolithic Integrated circuit because entire electronic system is built on single silicon substrate(silicon bulk).
Steps are as follows:
- Substrate Formation.
- Epitaxy growth.
- Oxidation.
- Lithography.
- Etching.
- Diffusion.
- Metallization.
- Passivation.
1) Formation of Silicon Wafer " Czochralski Process " : In this method there is one heating arrangement in which silicon is heated at high temperature, a part called puller (used to pull silicon from molten silicon) containing a single crystal at its tip is dip into molten silicon and then slowly pulled up so as it is pulled up its temperature decreases and it become solid then silicon crystal are cut in the form of wafer by Diamond saw.Sometime a Boron is added into Silicon this forms P-type Substrate wafer which basically used to provide the strong base for forming millions of device.(Analogy for Czochralski :- Consider a small pot filled with water in which you had placed 4 magnets now assume water to be molten silicon and magnets to be atom of silicon crystal. Now assume you are holding one magnet in your hand (this will act as puller ), bring hand closer to water surface you will find that magnet inside water stick to magnet in your hand Czochralski Method work on same principle.)
2).
Epitaxy Layer : Now this is most important step because now we will form silicon layer from which entire circuit will be formed. Even Epitaxy means "Above". we will have substrate on which we will form silicon layer and th
at is simply Epitaxy layer.
3) Oxidation : Forming a oxide layer on top of epitaxial layer so as to form pattern on oxide to remove selected portion. There are two types of oxidation 1) Thermal Oxidation. 2) Wet oxidation.
Wet oxidation is faster process but quality of oxide form is not as good as thermal oxidation.(even to get thick oxide layer we used Dry oxidation).
4)Lithography : It is process of coating with oxide layer with photo-resist material. next step is to placed mask (pattern to form on silicon) it consist of transparent and black area then it is illuminated with UV. Now those part on mask which is transparent allow light to fall on Photo-resist because of this some photo resist harden(Negative Photoresisit) and some soften or polymerised (Positive photo-resist).
5) Etching : Now removing the soften portion which will form the window or opening through required impurity is diffused.
6) Diffusion : Adding required amount of dopant so as to form different region.(Good property of semiconductor suppose that we have p-type substrate of impurity concentration 10 hen if i add phosphorus of impurity concentration 11 then p-type substrate will become N-type substrate ! Amazing. )
7) Metallization : Placing metal on different layer so that require connection can be done.
8) Sealing : Covering entire wafer by depositing SiO2 so that entire chip can be protected from dust and moisture.
