How Semiconductor Integrated Circuit Chips are Made – Dummies Guide

Basic building blocks for integrated circuits (IC), very large scale integrated circuit (VLSI)

And ultra large scale integrated circuits (ULSI) are diodes and transistors. Large numbers of this diodes and transistors are fabricated together in a tiny piece of silicon wafer to make the IC/VLSIC/ULSICs.

Semiconductor Integrated Circuit (IC) Manufacturing Process

Let’s assume we have to fabricate a chip which consists of a single N-P-N transistor, the steps typically are:

1. Sand to impure silicon: Sand or Silicon dioxide or Silica (SiO2) is mixed with carbon and heated above 2000 degree C. to get metallurgical grade silicon (97% purity).

SiO2 + 2C = Si + 2CO

2. Impure silicon to pure polycrystalline silicone: The semi-pure (97%) silicon is then powdered and first reacted at 300 degree C with gaseous hydrogen chloride (HCl) to make tricholorosilane (SiHCl3).

The tricholorosilane is then vaporized and reacted with hydrogen gas at 1100 degree C to get 99.999% pure polycrystalline Silicon (or Polysilicon).

Si + 3 HCl = SiHCl3 + H2

2SiHCl3+ 2H2 = 2Si + 6 HCl

Although its 99.999% pure but polycrystalline silicon is useless for chip fabrication, it needs pure crystalline silicon.

3. Polycrystalline to pure crystalline silicon ingot: Czochralski process is used for making pure N-type or P-Type silicon crystal ingot from polycrystalline silicone. The process is diagrammatically shown below:

Czochralski Process of Making Pure Polysilicon Crystal Ignot
Czochralski Process of Making Pure Polysilicon Crystal Ingot

Image source: Wiki

We have to make P-Type crystalline silicon ingot through this process for the purpose of making our N-P-N transistor chip.

4. Ingot to wafer: The P-Type silicon crystal ingot is sawed into thin silicon wafer.

5. Oxidization: The clean wafer is exposed to oxygen to convert the top layer into Silicon Dioxide film.

Silicon Dioxide Film Layer
Silicon Dioxide Film Layer

6. Applying photoresist layer: Thin photoresist material layer is then applied:

Applying Photo Resist Layer
Applying Photo Resist Layer

 

 

 

 

 

 

 

 

 

 

 

 

7. Glass masking: Glass masks are used to selectively expose the desired portion to the UV rays, the process is called photolithography:

Photolithography by Ultra Violet Ray
Photo lithography by Ultra Violet Ray

The UV rays soften the exposed photoresist areas, rest of the areas remain hard.

8. Etching: Special chemical is used in this process to remove the soften exposed photoresist portion:

Etching of Photoresist
Etching of Photoresist

9. Applying Silicon Dioxide Layer: Another thin layer of silicon dioxide is applied over the exposed portion of the wafer:

Applying Silicon Dioxide Layer - Second Time
Applying Silicon Dioxide Layer – Second Time

 

10. Polycrystalline silicon layer: Polycrystalline silicon layer is applied over the SiO2 layer:

Applying Polycrystalline silicon layer
Applying Polycrystalline silicon layer

 

11. Applying another photoresist layer: One more photoresist layer to be applied over the polycrystalline layer:

Applying Second Photo Resist Layer
Applying Second Photo Resist Layer

 

12. Photo lithography – Second time: Glass mask and UV lights are used for the photolithography for the second time:

Photolithography by Ultra Violet Ray Second Time
Photolithography by Ultra Violet Ray Second Time

13. Etching – Second time: Etching process is carried out once again:

Etching of Photoresist Second Time
Etching of Photoresist Second Time

14. N-Type Dopant implant: N-type Dopant materials (e.g., Phosphorus/ Arsenic) gas is used for implanting the Dopant to the suitable zones:

N-Type Dopant Implant
N-Type Dopant Implant

15. Applying silicon dioxide layer – Third time: Another layer of silicon dioxide or glass is applied all over:

Applying Silicon Dioxide or Glass Layer Third Time
Applying Silicon Dioxide or Glass Layer Third Time

16. Photolithography – Third time: For etching the required areas, again the photolithography is to be carried out, which will produce output like:

Photolithography by Ultra Violet Ray Third Time
Photolithography by Ultra Violet Ray Third Time

17. Making contacts : Metal layers are deposited to make the necessary contacts with the source, drain and gate of the final N-P-N chip:

Completely Fabricated N-P-N IC Chip
Completely Fabricated N-P-N IC Chip

 

Through this integrated circuit (IC) chip fabrication process we would be able to manufacture a chipset which consists of single N-P-N transistor. Actually the basic processes or steps for fabricating complex VLSIC or ULSIC chip is similar only repetition and scale changes.

Shibashis Ghosh

Hi, I am Shibashis, a blogger by passion and engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies.
Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.

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