Patterning and electrical characterization of single grain metal gate MOS capacitors

The orientation dependence of a metal work function could affect the threshold voltage of a MOS metal gate transistor. The electrical characterization of a single grain MOS capacitor is difficult to perform using an optical microscope based probe station. A ZyvexRTM Nanoprobe system was used to conduct electrical characterization (C-V, I-V) inside a dual column Focused Ion Beam (FIB) system with a field emission SEM used as the imaging tool. Exposure of a MOS structure to a high energy electron beam (5KeV) can generate positive charge near the dielectric-silicon interface. Reducing the electron beam energy to ≤1KeV eliminates the generation of Al and Si X-rays, reducing the radiation damage to the dielectric. Precise determination of the shunt capacitance is critical to determine the correct capacitance value at fF levels. We also determine the effect of measurement frequency, signal level and integration time on the signal-to-noise level to reduce the noise level to <0.5fF. We formed a thin film of isolated Al grains on SiO 2 by depositing Al at elevated substrate temperature, with different orientation isolated grains formed under these conditions. C-V measurements of single grain Al/SiO2/Si MOS capacitors at 100 kHz and 1 MHz are presented for Al grains as small as 1.2 mum2. The flat-band voltage of the micron size single crystal (111) Al gated MOS capacitors shows approximately +150 mV shift from that of polycrystalline Al gated MOS capacitors, which can be attributed to the effect of grains with different crystal orientation and grain boundaries.