CONDUCTIVITY OF BORON-IMPLANTED POLYCRYSTALLINE THIN SILICON FILMS

Sub-micron thin films of polycrystalline silicon obtained by low-press ure chemical vapor deposition, boron-implanted (amount varying from 10 (12) to 10(16) cm(-2)), and annealed at 760 degrees C for 26 h under a n oxygen ambient (dry O-2) have been characterized in terms of structu ral and electrical properties. The results obtained are correlated fir st with the Wall-effect measurements, which gives the resistivity rho, the concentration of the free carriers p and the mobility mu, and in the second part with the observations of transmission electron microsc opy (TEM), which gives the size of grains. The variations of rho, p an d mu have been studied as a function of the dopant concentration. A lo w rate of activation has been measured (40%) and a very low value of t he mobility mu has been noted (3 cm(2) V-1 s(-1)) as well as small gra in size. These results have been discussed both qualitatively and quan titatively, based on the existence of phenomena of carrier trapping an d dopant segregation at the grain boundaries.