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Semiconductor Ion Implantation

Ion Implantation Overview

Ion implantation is a process used to alter the surface properties of semiconductor materials. It does this by shooting atoms at high-speed onto the surface and bombarding the surface in order to alter its properties. It is performed using an ion implanter.

In a typical machine used to manufacture electronic devices, the beam energy usually ranges from 2keV up to 2MeV. An ion implanter, however, has an energy range from 0.5keV to 50keV. The ion source is a multi cusp ion source that has a SDS gas delivery system in order to create the desired beam. The beam passes through a pre acceleration section called a source extraction where the bias voltage gives the beam sufficient energy in order to permit selection of the beam species that is necessary for implementation.

Doping is the main purpose implementing ions. It is used to alter the level of conductivity and the type of semiconductor materials. This forms bases, emitters, and
resistors in bipolar devices. It also drains and sources in MOS devices, and is used to dope polysilicon layers.

In the process of ion implementation, impurity atoms are vaporized and then accelerated toward a silicon substrate. The high-energy atoms produced by this process shoot into the crystal lattice, losing their energy as they collide with silicon atoms. When they have finally come to rest, the acceleration energy can be adjusted to control the average depth of depositing the impurity atoms. Then heat treatment can be employed to anneal or repair crystal lattice disturbances, caused by the collisions as the atoms enter the lattice.

The damage that these atoms cause during the collisions of ion implementation changes the target's electrical characteristics. Multiple target atoms are displaced, producing deep electron traps which may capture mobile carriers and increase resistivity. The annealing is used to repair this and place dopant atoms in sites where electrical activity can begin once again.

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