Effect of Low Temperature Annealing on the Surface Conductivity of Si in the Si-SiO2-Al System

Studies on insulated-gate field effect devices fabricated on both n- and p-type Si have shown the existence of inversion layers on p-type surfaces and of accumulation layers on n-type surfaces. The degree of inversion or accumulation was characterized by measuring the total series capacity of the SiO
2
gate and the underlying Si as a function of an applied dc potential. The initial surface conductivity, as measured by the source to drain conductance g
sd
at zero gate bias, indicates that most of the surface charge is immobile. Prolonged heat treatments at 350°C on p-type substrates have resulted in a two order-of-magnitude increase in g
sd
accompanied by little or no change in the total surface charge density N
t
. On n-type substrates, however, the same treatment results in a factor of 5 decrease in N
t
. The effects of these treatments on the surface uniformity as well as on appropriate device parameters are reported.