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

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 A 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 A 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.