Physical characterization of ultrathin high k dielectrics

Targeting very thin equivalent oxides (<1 nm) requires the deposition of (very) thin dielectrics onto silicon surfaces with minimal interfacial oxide. Typically, high-k dielectric layers are deposited using ALD or MOCVD with, at present, a prime emphasis on Hf-based high-k dielectrics, either as pure HfO₂, as silicate or mixed with Al₂O₃. In some cases nitrogen is added to improve the high-temperature stability. Depending on the deposition conditions ALD as well as MOCVD show serious deficiencies in terms of film closure and material density for ultra thin (<3 nm) films. Various surface preparation methods and deposition conditions are used to improve the film quality.. Detailed studies on the film growth and its evolution requires the use of many analytical methods such as Rutherford backscattering spectrometry, low energy ion scattering, time-of-flight SIMS, (spectroscopic) ellipsometry and X-ray photoelectron spectroscopy. When trying to correlate the results in terms of film thickness, apparent discrepancies can be observed which relate to nonhomogeneous growth and reduced material density.