Nanocalorimeter fabrication procedure and data analysis for investigations on implantation damage annealing

Abstract

Nanocalorimetry operates on similar principles as conventional differential thermal analysis, but the thinness of the system provides a mass addenda small enough to observe thermal processes in thin films or at surface, involving energies in the order of the nanojoules. The fabrication procedure of nanocalorimeters used to measure the heat released by damage after low-energy (30 keV) ion implantation in polycrystalline silicon (poly-Si) is described. Nanocalorimeters are fabricated from low-stress Si 3N x membranes (100 nm) on which a Pt strip (25 nm) is deposited which serves both as a heater and thermometer. Using Pt allows us to carry out the metallization step prior to Si anisotropic chemical etching releasing the rectangular Si 3N x membrane, so the success yield nearly reaches 100%. A 140 nm Si layer is deposited on the nanocalorimeters. Large-grain (∼75 nm) poly-Si is obtained by annealing at 900 °C for 100 s. The calculation method used to obtain heat rate curves is described, including the corrections necessary to take into account the dissimilarity between sample and reference calorimeters (baseline), and the increased heating rate and associated losses. Examples of heat release after 30 keV Si implantations are presented, showing that the total amount of heat release is characterized by a saturation above a fluence of 1 Si −/nm 2. The similarity observed in the signal shape between low and high fluence measurements also suggests that each impacting ion produces a high damage zone similar to the damage generated by high fluence irradiation. This conclusion is compatible with the annealing of damage zones proposed by molecular dynamic studies. It is also shown that the measured signal is not affected significantly by temperature non-uniformity.