Atomic layer deposited tungsten nitride thin film as a contact barrier layer for sub-80 nm dynamic random access memory

Tungsten nitride thin films were grown by atomic layer deposition (ALD) using alternating exposures of B₂H₆, WF₆, and NH₃ at 300 °C. The film thickness linearly increased with the number of the reaction cycles and determined growth rate was ∼ 0.28 nm/cycle with B₂H₆, WF₆ and NH₃ pulse time of 5, 0.25, and 2 s, respectively. The film had a resisitivity of ∼ 350 μΩ-cm with metallic W-N bond and density of ∼15 g/cm³ at 10 nm thickness. X-ray diffractometry analysis showed that the film had nanocrystalline grains with β-W₂N and δ-WN phase. Step coverage was approximately 100% even on the 0.14 μm diameter contact hole with 16:1 aspect ratio. ALD-WN_x film was evaluated as a barrier layer for W-plug deposition at the contact with an ultrahigh aspect ratio of about 17 for sub-80 nm dynamic random access memory. The results showed that while TiN control group has failed or has a higher contact resistance, ALD-WN_x control group showed a low contact resistance. The plan-view scanning electron microscopy images after focused ion beam milling showed that a new contact integration scheme with ALD-WN_x showed better plug filling capability due to its excellent step coverage. We also demonstrated that ALD-WN _x was successfully integrated at plate contact of polycrystalline Si or TiN and at via contact.