TiN barrier layer formation by the two-step rapid thermal conversion process

Abstract

We formed TiN barrier layers on single-crystalline silicon substrates by thermal conversion of Ti films at various temperatures in an ammonia ambient using a rapid thermal process with a sequential two-step temperature cycle. The first-step temperatures were held in the low-temperature range of 400–450 °C for 60–300 s to minimize Ti/Si interaction while keeping reasonable interaction of Ti/NH3 and nitrogen diffusion through the Ti layer to maximize the thickness of the TiN layer. Then, the second-step was carried out at relatively high temperatures, 700–1000 °C, for 5–90 s to reduce Ti/Si interaction during the silicidation process. By the first steps of the low temperature process, sheet resistances increased with annealing time up to 60 s due to the deep penetration and high concentration of nitrogen in the Ti film, followed by saturation at 60–120 s; they steadily decreased beyond 120 s. Sheet resistance increases were dominated by the nitrogen-rich Ti layer formed during the first steps of long-time nitrogen diffusion. With the second steps of the high temperature process, nitrogen enriched Ti layers were converted to Ti-rich TiN layers, resulting in abrupt decreases in the sheet resistance due to silicidation, densification of TiN, and conversion of the remaining Ti to TiN layers. By means of a two-step rapid thermal conversion process of the 1000 Å Ti layer under long-time nitridation cycle conditions with optimal thermal conversion conditions (first step: 400 °C/90 s; second step: 700 °C/60 s), we obtained TiN/TiSi2 bilayers of 700/1500 Å thicknesses with the TiN thickness ratio relative to the totally converted layer in excess of 30%. These results indicate that the thickness ratio of the TiN layer prepared by a two-step process relative to the totally converted layer is double that obtained by a one-step process, while it also provides reduced total thickness of the thermally converted layer.