Effects of H₂ and N₂ treatment for B₂H₆ dosing process on TiN surfaces during atomic layer deposition: an ab initio...

For the development of the future ultrahigh-scale integrated memory devices, a uniform tungsten (W) gate deposition process with good conformal film is essential for improving the conductivity of the W gate, resulting in the enhancement of device performance. As the memory devices are further scaled down, uniform W deposition becomes more difficult because of the experimental limitations of the sub-nanometer scale deposition even with atomic layer deposition (ALD) W processes. Even though it is known that the B₂H₆ dosing process plays a key role in the deposition of the ALD W layer with low resistivity and in the removal of residual fluorine (F) atoms, the roles of H₂ and N₂ treatments used in the ALD W process have not yet been reported. To understand the detailed ALD W process, we have investigated the effects of H₂ and N₂ treatment on TiN surfaces for the B₂H₆ dosing process using first-principles density functional theory (DFT) calculations. In our DFT calculated results, H₂ treatment on the TiN surfaces causes the surfaces to become H-covered TiN surfaces, which results in lowering the reactivity of the B₂H₆ precursor since the overall reactions of the B₂H₆ on the H-covered TiN surfaces are energetically less favorable than the TiN surfaces. As a result, an effect of the H₂ treatment is to decrease the reactivity of the B₂H₆ molecule on the TiN surface. However, N₂ treatment on the Ti-terminated TiN (111) surface is more likely to make the TiN surface become an N-terminated TiN (111) surface, which results in making a lot of N-terminated TiN (111) surfaces, having a very reactive nature for B₂H₆ bond dissociation. As a result, the effect of N₂ treatment serves as a catalyst to decompose B₂H₆. From the deep understanding of the effect of H₂ and N₂ during the B₂H₆ dosing process, the use of proper gas treatment is required for the improvement of the W nucleation layers.