Semiconductor device fabrication

From ArticleWorld

Semiconductor device fabrication refers to the steps used in the manufacture of integrated circuits which are required in vast applications of electrical, electronic, optical and biomedical engineering. It involves several stages which consist of chemical reactions. Semiconductor devices are thus fabricated on substrates of pure silicon, gallium arsenide or germanium.

Processing of wafers

A wafer is basically made of a pure silicon crystal which is cut into slices 0.75 mm in thickness. The wafers are highly polished to be completely flat and regular. After the preparation of wafers by using the Czochralski process, a number of steps are carried out to prepare the final integrated circuit.

Making integrated circuits

The first step of processing involves ‘front end’ steps in which a large number of transistors are created. Initially, the wafer surface is prepared for the growth of silica (silicon dioxide). Thereafter, the desired conductivity in the wafer is brought about by the addition of ‘dopants’. Techniques such as molecular beam epitaxy (MBE) or chemical vapour deposition (CVD) are used. The growth of the gate dielectric is also done. Isolation of adjacent semiconducting material is ensured by depositing appropriate insulating material like silicate glass.

Interconnections to form desired circuits are done in the next step by the technique of ‘back-end processing’. Layers of metals like aluminium or copper and silicate glass (as insulating material) are etched into set patterns.

Further steps involve the testing of the prepared devices to check for any discrepancies. Several electrical tests are performed for this purpose. Separate dice are cut from the original wafer once testing is accomplished. The dice are then packaged using plastic or ceramic. Pins are provided on the outside so that the devices can be connected to others in an electronic circuit. The final prepared chips are subjected to further tests to ensure complete reliability.

Development of fabrication techniques

Semiconductor fabrication techniques developed in the 1960s soon after the invention of the transistor. Molecular beam epitaxy was developed during this period by Arthur and Cho of the Bell Telephone Laboratories. It uses a technique involving a stream of the metal particles to be directed onto the substrate where layers are to be built. Other processes such as the chemical vapour deposition, using a so-called ‘fluid precursor’, were also developed.

It is not just the United States that has seen growing development in this technology. Countries like Japan, China, Singapore and Taiwan also have leading companies today that manufacture semiconductor products.