Using Hydrogen To Expand the Inherent Substrate Selectivity Window During Tungsten Atomic Layer Deposition

Area-selective thin film deposition is expected to be important in achieving sub-10 nm semiconductor devices, enabling feature patterning, alignment to underlying structures, and edge definition. Atomic layer deposition (ALD) offers advantages over common chemical vapor deposition methods, such as precise thickness control and excellent conformality. Furthermore, several ALD processes show inherent propensity for substrate-dependent nucleation. For example, tungsten ALD using SiH 4 (or Si 2 H 6 ) and WF 6 is more energetically favorable on Si than on SiO 2, but selectivity is often lost after several ALD cycles. We show that modifying the W ALD process chemistry can decrease the W nucleation rate on SiO 2, thereby expanding the ALD “selectivity window”. Specifically, we find that adding H 2 during the WF 6 dose step helps passivate SiO 2 against W nucleation without modifying W growth on silicon. Surface characterization confirms that H 2 promotes fluorine passivation of SiO 2, likely through surface reactions with HF produced in the gas phase. This passivation affords at least 10 additional W ALD cycles, corresponding to ∼6 nm of additional W growth, before substantial nucleation occurs on SiO 2 . We show that reactant modification also reduces undesirable nucleation due to substrate proximity or loading effects in patterned film growth. Further understanding of ALD reaction chemistry and film nucleation will lead to improved selective metal and dielectric film deposition, enabling ALD bottom-up patterning.