Electrical and spectroscopic comparison of HfO2/Si interfaces on nitrided and un-nitrided Si(100)

Abstract

The interfacial chemistry of the high-k dielectric ${\mathrm{HfO}}_2$ has been investigated on nitrided and un-nitrided Si(100) using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The samples are prepared by sputter depositing Hf metal and subsequently oxidizing it. A 600 °C densification anneal is critical to completing Hf oxidation. These spectroscopic data complement electrical testing of metal oxide semiconductor capacitors fabricated with ∼50 Å ${\mathrm{HfO}}_2$ on nitrided and un-nitrided Si(100). Capacitors with interfacial nitride show reduced leakage current by a factor of 100 at a −1 V bias. Concurrently, interfacial nitride increased capacitance 12% at saturation. XPS shows that an interfacial layer composed of nonstoichiometric hafnium silicate $({\mathrm{HfSi}}_x{\mathrm{O}}_y\mathrm{),}$ forms at both the ${\mathrm{HfO}}_2/\mathrm{Si}$ and ${\mathrm{HfO}}_2/{\mathrm{SiN}}_x$ interfaces. Differences in the Si $\text{2p}$ and O $\text{1s}$ XP spectra suggest more silicate forms at the un-nitrided interface. ${\mathrm{HfO}}_2$ films on un-nitrided Si show more O $\text{1s}$ and Si $\text{2p}$ photoemission intensity characteristic of ${\mathrm{HfSi}}_x{\mathrm{O}}_y.$ SIMS depth profiles through the buried interface are consistent with interfacial silicate formation, as shown by a ${\mathrm{HfSiO}}^{+}$ ion signal, that is sandwiched between ${\mathrm{HfO}}_2$ and ${\mathrm{SiN}}_x.$ ${\mathrm{SiN}}_x$ is suggested to minimize interfacial ${\mathrm{HfSi}}_x{\mathrm{O}}_y$ formation by limiting the amount of Si available to interact with the ${\mathrm{HfO}}_2$ layer.