Doping Technology in Semiconductors

Summary: The semiconductors are the compound which has a good electrical conductance. When a trivalent dopant like Boron is added, extra holes get formed due to the exact reverse process. Hence such dopant material creates a P-type semiconductor.

Semiconductor materials or Silicon can be single crystalline, multi-crystalline or amorphous. The key difference between these materials is the degree to which they have regular, perfectly ordered crystal structure. So, on the basis of semiconductor material, they can be classified according to crystal structure, size and material make up.

Silicon shows high resistance to the flow of electricity, and its electrical properties can be manipulated by adding elements called Dopants. Doping refers to the process of introducing impurity atoms into a semiconductor material in order to define the electrical properties of this region. The Dopant determines the type of silicon, either positive or negative. The doping allows to modify the electron and hole concentration in silicon. It is also responsible for the change in the resistivity of the silicon so that it becomes more conductive. The amount and type of dopant will determine whether the final wafer is a P-Type silicon wafer or an N-Type silicon wafer. It also determines its final resistivity as well. The carrier concentration can be varied which is used to produce built-in electric fields and PN-junctions. All electronic and optical semiconductor devices incorporate dopants as a crucial ingredient of their device structure. Therefore, all the basic MOSFET parameters are affected by the distribution of dopants in the device.

Ion Implantation Technology for Producing Specific Wafers

1. Dopant species
2. Ion beam energy
3. Implantation dose
4. Tilt and twist angles

The basic technology of ion implantation for doping semiconductors was patented by Shockley in 1957. In this process, a focused beam of ionized particles is directed towards a target wafer. Ionized particles are used in this process, because they have sufficient kinetic energy that can penetrate into the wafer upon impact. Ions can be accelerated by electric and magnetic fields in order to obtain an ion beam of well-defined energy. The wafers can be processed one at a time or in batches. These are moved in and out of the vacuum by automated handling systems.

The ion implantation process have these basic parameters:

The ion implantation technique is used to increase the production and sales volume to buy p-type silicon wafers. These wafers are manufactured with only one type of dopant called Boron. The resistivity is determined by the amount of Boron that is present in a P-Type silicon wafer. The more Boron present, the lower the resistivity and the less Boron is present, the higher the resistivity. The relative abundance of P-Type silicon wafers tends to keep their cost lower than N-Type silicon wafers.

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