Optical characterization of three-dimensional structures within a DRAM capacitor

As an alternative to completely destructive and mostly very time consuming methods non-intrusive and non-destructive Fourier Transform Infrared Spectroscopy has been chosen to enable an inline characterization chain for DRAM manufacturing. This characterization chain comprises the mold oxide etch profile and the step coverage control of high-k deposition. In our case Zirconium Aluminum Oxide deposited by Atomic Layer Deposition was used as high-k dielectric. The characterization of the different process steps was carried out by either absorption parameters based on molecule vibrations or optical path differences calculated from oscillations in the infrared spectra. For the last issue of successfully characterizing the step coverage of high-k deposition, a combination of two independent optical measurements was established. Therefore a volume related FTIR measurement in a DRAM array and an ellipsometric thickness determination of a 2-dimensional layer in a support area were combined. This method showed both, the deposition parameter dependence, like pulse time, precursor flow and deposition temperature as well as tool geometry dependence on the step coverage behavior. By the use of 300 mm mapping techniques a full characterization including spatial maps over the whole 300 mm wafers was possible.