What is diffusion process in VLSI fabrication and name the different techniques?
In VLSI fabrication, this is a method to introduce impurity atoms (dopants) into silicon to change its resistivity. The rate at which dopants diffuse in silicon is a strong function of temperature. Diffusion of impurities is usually carried out at high temperatures (1000–1200°C) to obtain the desired doping profile.
What are the main processes in IC fabrication?
The monolithic fabrication process consists of wafer preparation, epitaxial growth, diffused isolation, base and emitter diffusions, pre-ohmic etch, metallization, circuit probing, dicing, mounting and packaging, wire bonding, encapsulation and final testing.
How is diffusion used in semiconductors?
Atomic diffusion in semiconductors refers to the migration of atoms, including host, dopant and impurities. Diffusion occurs in all thermodynamic phases, but the solid phase is the most important in semiconductors. The diffusion of atoms and defects (both native and dopant) is at the heart of semiconductor processing.
What is metallization in IC fabrication?
Metallization is the process by which the components of IC’s are interconnected by aluminium conductor. This process produces a thin-film metal layer that will serve as the required conductor pattern for the interconnection of the various components on the chip.
What is diffusion in wafer fabrication?
Diffusion is the movement of impurity atoms in a semiconductor material at high temperatures. Diffusion is applied to anneal the crystal defects after ion implantation or to introduce dopant atoms into silicon from a chemical vapor source.
What is lithography in IC fabrication?
Lithography is the process of transferring patterns of geometric shapes in a mask to a thin layer of radiation-sensitive material (called resist) covering the surface of a semiconductor wafer. Figure 5.1 illustrates schematically the lithographic process employed in IC fabrication.
What is meant by diffusion current in semiconductor?
Diffusion Current is a current in a semiconductor caused by the diffusion of charge carriers (holes and/or electrons). This is the current which is due to the transport of charges occurring because of non-uniform concentration of charged particles in a semiconductor.
Why does diffusion occur in pn junction?
Diffusion is the process of movement of charge carriers due to concentration gradient along the semiconductor. In a p-n junction, n-side has excess of electrons and hence electrons diffuse from n-side to p-side. Similarly, holes diffuse from p-side to n-side.
What are the process steps used in the fabrication of IC’s?
Starting with an uniformly doped silicon wafer, the fabrication of integrated circuits (IC’s) needs hundreds of sequential process steps. The most important process steps used in the semiconductor fabrication are [1]: 1.1.1 Lithography Lithography is used to transfer a pattern from a photomask to the surface of the wafer.
Why is constant source diffusion used for isolation and emitter diffusion?
In the fabrication of monolithic IC’s, constant source diffusion is commonly used for the isolation and the emitter diffusion because it maintains a high surface concentration by a continuous introduction of dopant. There is an upper limit to the concentration of any impurity that can be accommodated at the semiconductor wafer at some temperature.
What is diffusion in semiconductor materials?
Diffusion is the movement of impurity atoms in a semiconductor material at high temperatures. The driving force of diffusion is the concentration gradient. There is a wide range of diffusivities for the various dopant species, which depend on how easy the respective dopant impurity can move through the material.
What is the use of diffusion in silicon wafers?
Impurity atoms are introduced onto the surface of a silicon wafer and diffused into the lattice because of their tendency to move from regions of high to low concentration. Diffusion is used to form base,emitters and resistors in bipolar device technology , to form source and drain regions and to dope polysilicon in MOS device technology.