In Situ Observation of Thin Film Ferroelectric HZO with STEM EBIC

Ferroelectric thin film hafnium oxide (HfO₂) is an especially promising candidate for next generation non-volatile memory applications because of its compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Although the metastable polar orthorhombic Pca2₁ phase is generally thought to be responsible for ferroelectricity in thin film HfO₂, this identification is not absolutely certain because multiple structurally similar phases are present in the polycrystalline films. Moreover, the mechanism stabilizing the relevant crystal phases is not fully understood. Scanning transmission electron microscopy (STEM) can identify crystal phases, but usually is insensitive to polarization. Electron-beam induced current (EBIC) imaging can map electric fields directly. Using STEM EBIC imaging along with the positive-up-negative-down (PUND) method, we map the polarization state and measure the global polarization, respectively, on a TaN/HZO/TaN capacitor. We compare the global polarization determined via transport with detailed maps showing which ferroelectric domains are switching. By varying the applied field, we identify the threshold switching fields for different domain populations.