Increasing the fracture toughness of silicon by ion implantation

• Main Authors: Swadener, J G, Baskes, M I, Nastasi, Michael Anthony
• Format: Conference Proceeding
• Language: English
• Subjects: 08 HYDROGEN; ALPHA PARTICLES; ATOMS; CERAMICS; CRACK PROPAGATION; FRACTURE PROPERTIES; FRACTURES; HYDROGEN; ION BEAMS; ION IMPLANTATION; IRRADIATION; MATERIALS; MATERIALS SCIENCE; MODIFICATIONS; RADIATION DOSES; SILICON
• ISSN: 0168-583X; 1872-9584

This study was motivated by some earlier indications that the fracture toughness of silicon could be increased by ion implantation. The location of fracture in hydrogen implanted silicon was found to change depending on the dose of implanted ions. For relatively low doses, fracture occurred at the center of the damage region created by implantation. However, for larger doses, the fracture location switched to the deeper edge of the implanted zone. This implied that the center of the implanted region experienced toughening due to ion implantation at the higher dose level. In addition, an initial increase in fracture toughness with radiation dose has been observed experimentally in some ceramics. After the initial increase, the fracture toughness reaches a peak and then decreases with further irradiation. The toughness increases found thus far are modest (25-100%). In attempts to explain the experimental results, several toughening mechanisms (such as deflection of the crack by the irradiated damage) have been proposed. However, the proposed mechanisms predict only a 40-80% increase in fracture toughness, which does not account for the highest levels of toughness observed. Our recent molecular dynamics (MD) calculations have found a previously unknown toughening mechanism acting in silicon, which can also explain the earlier experimental observations of toughening induced by irradiation. In our MD simulations, ion implantation produced clusters of disordered atoms. The presence of these clusters allowed silicon to deform plastically as a crack approached, blunting the crack tip and arresting crack growth. The MD calculations show a factor of 3 increase in fracture toughness. We have conducted experiments with silicon implanted with a small dose (ions/cm2) of alpha particles uniformly distributed to a depth of 25 pm. A 20% increase in fracture toughness is observed. Additional experiments with higher implantation doses are planned for the immediate future.