ELECTRICAL-CONDUCTION IN IMPLANTED POLYCRYSTALLINE SILICON

Undoped polycrystalline silicon (poly-Si) films, 0.5 μm thick, have been prepared at 700‡C by chemical vapor deposition (CVD) onto thermally oxidized n+-Si substrates. The impurity concentration was varied by implanting with As, P, and Sb ions, accelerated to 30 keV; total doses ranged from 2×1011 to 3×1015 ions/cm2. Sheet resistance measurements, spanning 8 orders of magnitude, were made as a function of implantation dose. A reduction of 6 orders of magntiude in poly-Si sheet resistance took place within the implantation dose range between 1012 and 1014 ions/cm2. Some samples also exhibited large reductions in sheet resistance following the standard heat treatment for Al contact sintering and surface state reduction, which is normally at 450‡C for 0.5 hr in H2. Sheet resistance measurements were also made as a function of temperature in the range 0 to 315‡C. The effective activation energy for electrical conduction depends upon implantation dose. At low doses (2×1011cm-2) the poly-Si is intrinsic, with E A = 0.65 eV. At a dose of 1015 cm-2, electrical conduction is a weak function of temperature, with E A = 0.027 eV. © 1979 AIME.