Atomic Layer Deposition of Mo and MoNx Films from Chloride-based Molybdenum Precursors
The lower resistivity word line (WL) materials are very attractive to the 3DNAND device manufacturers, because they could potentially reduce the cell stack height while maintaining the same or better device speed. Current POR material of 3DNAND WL is tungsten (W) made by tungsten hexafluoride (WF6) via ALD/CVD. Molybdenum (Mo) is considered as an attractive WL material for next generation 3DNAND devices. Mo has almost same level of low bulk resistivity comparing to W, but it has smaller Electron Mean Free Path (EMFP), so the effective resistivity, a product of bulk resistivity and EMFP, is expected to be lower than W for film thickness less than 10nm. Chlorine-based Mo precursors are considered as potential materials for deposition of Mo films as fluorine free precursors.
Here, we report thermal and plasma enhanced ALD (THALD and PEALD) of Mo and molybdenum nitride (MoNx) films on PVD titanium nitride (TiN) substrates at temperatures up to 500oC employing molybdenum pentachloride (MoCl5) and molybdenum dichloride dioxide (MoO2Cl2). Hydrogen and ammonia were used as reactant gases under TH/PEALD conditions for Mo and MoNx, respectively. Thicknesses of Mo, MoNx and TiN films were measured with XRF. Sheet resistance was measured with a 4-point probe. The films have been also characterized with TEM and XPS for conformality at aspect ratio 15 trench pattern, and impurity depth profile in the film, respectively. Process conditions were identified for selective deposition of molybdenum metal on TiN substrate with almost no deposition on silicon oxide. Selective deposition of molybdenum films from molybdenum pentachloride and molybdenum dichloride dioxide will be discussed.
In this paper, we demonstrated thermal and plasma enhanced molybdenum ALD with fluorine free molybdenum precursors, which showed low etch of titanium nitride substrate, high selectivity and relatively low resistivity compared to tungsten; which are important for next 3DNAND’s WL forming application. Details of the deposition study and properties of the Mo and MoNx films will be presented.