Doping
Implanting impurities to set conductivity.
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At a glance
Inputs
- Masked wafer
- Dopant species (B, P, As, …)
- Ion beam energy
Outputs
- Wafer with defined n-type / p-type doped regions
What is it?
Introducing controlled amounts of dopant atoms (e.g. boron, phosphorus, arsenic) into specific regions of the silicon to create n-type and p-type areas — usually by ion implantation.
Why is it needed?
Doping is what makes a transistor: it defines sources, drains, wells, and channels by locally setting carrier type and concentration. Precise dose and depth control device thresholds and currents.
How does it work?
In ion implantation, dopant atoms are ionized, accelerated to high energy, and fired into the wafer; the mask (resist or oxide) blocks unwanted areas. Dose sets concentration; energy sets depth.
Implantation damages the crystal, so a high-temperature anneal follows to repair the lattice and electrically activate the dopants.
Critical parameters
- Dose
- Implant energy (depth)
- Tilt angle
- Anneal temperature
- Junction depth
Typical defects
- Incomplete activation
- Residual crystal damage
- Channeling
- Dose non-uniformity
Equipment involved
- Ion implanter
- Rapid thermal anneal (RTA) tools
- Diffusion furnace
Materials involved
- Dopant source gases
- Masking layers