An Integrated Circuit is a small Silicon (Si) wafer over which electronic circuits are manufactured. It is mainly composed of transistors, capacitors and resistors. These circuits are then packaged into plastic or ceramic packages.

Integration made possible to build up circuits which contain thousands and even millions of transistors within sizes up to several square centimetres. Clear examples are (in descendant order): computer microprocessors, micro-controllers, noise reduction integrated filters and operational amplifiers.

In an integrated circuit are present transistors, interconnection conductors, polarization components and isolation layers and regions, all obeying the design architecture.

In this article we will explain the basic processes involved in the manufacturing in order to understand how they are constructed and built.

Manufacturing process

Integrated Circuits are manufactured in specialised facilities. Each facility will require certain layout design rules. These rules include: minimum distances between masks, minimum sizes, number of Metal layers the can manufacture, etc. These rules have to be followed by the designer and are given in a confidential document to the designer. With these rules also the facility gives to the designer their datasheets where parasitic capacities, resistances, maximum temperature, etc. are specified.

All facilities nowadays work with confidentiality with the designers and the designer is asked to sign a confidentiality agreement.

In figure 1 a classical process of manufacturing is show. Even though it is not the only way that exists, it clarifies the concepts in behind.

There are three main processes over the Silicon wafer:

1. Oxidation
2. Ion implantation
3. Chemical etching

The wafer sections were these processes are held are delimited by “masks”. This process is also called lithography.

The masks and processes:

1. A nitride layer is grown and etched so a so-called active region is delimited. Active region defines the MOSFETs locations.
2. The an oxide layer is grown around the active region. Thick field oxide electrically isolates transistors. Nitride prevents oxide field to grow.
3. Then the nitride layer is removed chemically. So a thin layer of oxide is left. This thin layer will be used for building the transistor's Gate terminal.
4. A polysilicon layer (conductor) is placed over the oxide thin layer (for connecting the Gate). The rest of the thin oxide layer is chemically removed. This leaves Silicon accessible for generating the Drain and Source terminals of the MOSFET.
5. This is done by an n-type implantation.
6. New oxide layer is grown. And etched in order to allow metal contacts to access Drain and Source terminals.
7. These metal contacts are also etched in order to have access to each terminal of the transistor. (Bulk terminal is a common terminal in the Silicon generally connected to GND.

The layout design of the integrated circuit will allow interconnection of transistors so at the end we can have a working electronic circuit. This part of electronics (as many others) is highly artistic, one can say. Since by only following the manufacturing rules, only your imagination and experience will help you to build a better integrated circuit.

After manufacturing

After manufacturing of the integrated circuit there are other steps to
take:

1. Packaging
2. Mechanical resistance tests
3. Electronic tests (to see whether the circuit works as it should and which percentage of the circuits manufactured do)

Just then, the circuits arrive to our hands like chips, i.e. OPAMP741.

Enjoy!