Threshold voltage shift of n-channel Si-gate MOSFET´s

The relationship between the threshold voltage shift of the n-channel Si-gate MOSFET and the implant dose of boron ions has been examined theoretically and experimentally when these ions are implanted with an energy of 60 keV through a gate oxide of 1200 Å into a p-type silicon substrate of the acceptor concentration of 7 × 10¹⁴/cm³. The effect of high-temperature treatment after ion implantation on the threshold voltage shift has been considered. The good agreement between the theory and the experiment verifies that the model used is reasonable. The threshold voltage shift with the dose is expressed by about 5 × 10^-12V.cm²below a dose of 5 × 10¹¹ions/cm². Above this value, the increase of the threshold voltage shift becomes slow and the slope takes the value of about 2 × 10^-12V.cm²due to the maximum surface depletion layer.