Defect formation mechanism causing increasing defect density during decreasing implant dose in low-dose SIMOX

Silicon-on-insulator material synthesized by oxygen implantation (SIMOX) is a leading candidate for advanced large scale integrated circuit applications due to thickness uniformity and moderate defect density. In the past few years, there has been a significant reduction of the defect density by optimizing processing conditions. Studies on defect formation mechanisms may suggest further modification of the processing conditions for both production cost and material quality. Recently, it was shown that through-thickness defects (TTDs) in high-dose SIMOX originated from as-implanted defects, dislocation half-loops (DHLs). On the other hand, a high density (~10⁸ cm ^-2) of defects in very low dose (0.25×10¹⁸ cm^-2) SIMOX has been observed by Nakashirna et al. (1993), but the origin of these defects has not been understood. In this paper we report on the effect of implant dose on defect formation mechanisms, and propose a defect formation mechanism in the very low-dose regime for the first time. It was found that the stacking faults generated during the initial stage of annealing are the origin of TTDs in the low-dose (<0.5×10¹⁸ cm^-2) regime, while as-implanted defects (DHL) are the origin of TTDs in the high-dose regime (>1.3×10¹⁸ cm^-2). Several approaches of process modification have been suggested for economical production of low-defect-density SIMOX