P-Type Doping Observed in Silicon Implanted with High Energy Carbon Ions
Some MOSTs in which ion implantation had been used to control the threshold voltage showed unexpectedly high p-type activity if the devices were annealed to only 500°C. This had been attributed to the p-type nature of the unannealed damage. In order to examine the phenomenon carbon ions, which do not produce doping centres in silicon, were implanted at energies high enough to permit capacitance-voltage profiles of the region between the surface of the silicon and the ion range to be observed.
This paper reports on some doping concentration profiles observed following annealing in the temperature range 175–800°C. The silicon used was 20Ω cm p-type oriented a few degrees from the <111> direction. Carbon ions were implanted with energies in the range 1.5 to 4.3 MeV using the Harwell van de Graaff accelerator.
Capacitance-voltage profiles show that in unannealed specimens two p-type doping peaks are present. Following annealing at about 400°C the deeper peak can no longer be observed, and the shallower peak increases in size. Finally after annealing at about 700°C no doping centres are observed.
KeywordsDoping Profile Doping Centre Mesa Diode Doping Peak Doping Concentration Profile
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