Characterization of nitrogen distribution in HfO2 with low energy secondary ion mass spectrometry

Abstract

Accurate characterization of the nitrogen distribution in a thin HfO2 film is important for process development on the nitridation of HfO2. Low energy secondary ion mass spectrometry (LESIMS) is potentially the technique of choice, thanks to the combined strength of high depth resolution and high detection sensitivity. By using a 250 eV, 60° O2+ primary beam and detecting NO−30 and O2−32 secondary ions, SIMS analysis was capable of profiling nitrogen in HfO2 with very short surface transient and minimal matrix effect across the HfO2–Si interface. This particular condition also exhibited desirable low yield of Si− secondary ions, i.e., minimal contribution of Si−30 to NO−30 through mass interference. Applications of this technique revealed incorporation of nitrogen at high levels in the top part of a HfO2 film by the modified magnetic type (MMT) plasma nitridation. The data also suggested loss of nitrogen near the top of an HfO2 film but no depletion across the interface between HfO2 and the interfacial as a result of the post nitridation anneal in O2.