Ferroelectric HfO_2 thin film testing and whole wafer mapping with non-contact corona-Kelvin metrology

摘要

We present results of a non-contact, real-time feedback corona-Kelvin characterization of the ferroelectric properties of Si:HfO_2 thin films. Measurements were performed on free dielectric surfaces. The method uses corona charging pulses coupled with Kelvin probe-measured surface voltage and gives non-contact QV and CV characteristics. Analogous to voltage biasing of metal-insulator-metal (MIM) capacitors, large corona charge biasing is found to provide an effective means for poling of the ferroelectric films. Subsequent small increment corona charging is used to acquire hysteresis loops and determine the coercive field and permittivity characteristics. Negative and positive coercive fields of about ±1.2MV/cm for the 3.5mol% Si film and ±1.0MV/cm for the 4.6mol% Si film were determined from the hysteresis loops. These findings were in agreement with MIM capacitor measurements on sister wafers. Non-ferroelectric behavior was also confirmed for the 11.3 mol% Si film. Another strength of the corona-Kelvin method is the ability to perform full wafer mapping to assess spatial non-uniformities of important dielectric properties. Results of this work indicate a radial symmetry of ferroelectric film properties, such as the permittivity at the coercive field, that are consistent with processing conditions during the crystallization anneal.