The self-limiting deposition chemistry of ALD cannot afford a superconformal deposition where the growth rate at the bottom of a recessed feature is faster than that on the top. In this regard, Abelson and Girolami 12 have summarized several low-pressure (10 -10 -8 Pa) and low-temperature (200 -300 °C) continuous CVD approaches to deposit conformal borides (HfB2 13 , TiB2 ) and superconformal oxides (MgO 15 , HfO2 ). The fundamental approach adopted was to reduce the surface reaction probability, β, which is defined as the number of the precursor molecules that stick to the surface as a ratio of the total number of incoming molecules . A lower value of β means that the molecules arriving at the surface are more probable to be re-emitted to the gas phase rather than being chemisorbed . As a result, many of these molecules can continue diffusing along the trench without being consumed immediately at the trench opening, which in turn leads to a more conformal deposition.