Effects of ion implantation on substrate hardening and film stress reduction and their effect on the yield of bipolar transistors

Abstract

We report evidence of the occurrence, and some salient features, of two phenomena arising from ion implantation of silicon: one is a hardening effect of the silicon substrate; the other is a stress-reduction effect in silicon nitride films. The method of indentation dislocation rosettes (IDR) was the tool used for this study. The ion species investigated included boron, arsenic, argon, oxygen, and nitrogen, as well as oxygen from recoil implantation by arsenic into a film of thermal SiO2. Arsenic is the least effective among the ions studied, producing an ∼70% increase in the critical stress-of-dislocation movement (τc), whereas boron brought about an order-of-magnitude increase in τc. Other ions are comparable to boron. A plausible explanation is that the 1×1016 ions/cm2 boron implantation at room temperature was below the critical dose for silicon amorphization (∼2×1016 ions/cm2), so that rapid defect annealing via epitaxial regrowth could not occur, leaving much residual damage. The arsenic implantation of the same dose, however, was well above the critical dose for amorphization (∼2×1014 ions/cm2). In silicon nitride films of various thicknesses, reductions of stresses caused by implanting different ion species were studied with respect to the film-edge-induced stress in the silicon substrates. The results were quantitatively indexed regarding the enhanced movements of IDR near the film edges. Finally, the effects of ion implantation on the yield of bipolar devices are also reported, with the results partly explainable in the framework of the above two phenomena.