Changes in the microstructural and electrical behavior of poly-Si films subjected to ion implantation and annealing process modifications

Abstract

Polycrystalline silicon (poly-Si) films implanted with arsenic using beam currents of 500 μA (400°C) and 230 μA (room temperature) have been investigated via transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), and spreading resistance analysis (SRA). Experimental observations demonstrated the annealed high beam current-implanted poly-Si to possess inferior electrical properties compared with that implanted at a lower beam current. The reduced electrical activity of the high beam current- versus the low beam current-implanted poly-Si was directly related to the postimplant microstructure (small grains ~ 140 nm vs. amorphous) and the mechanism of the subsequent anneal (grain growth vs. recrystallization). The recrystallization mechanism augmented the electrical activation of the as dopant (decreased sheet resistivity) via a reduction of total grain boundary area. Further improvement in the electrical performance of the low beam current-implanted poly-Si, a resistivity decrease of up to 28%, was incurred via a two-step annealing process. This process induced grain growth, which in turn minimized total grain boundary area and dopant trapping.