Improved Symmetry of Ferroelectric Switching in HZO Based MFM Capacitors Enabled by High Pressure Annealing

Abstract

The interface difference between HZO and the upper and lower electrodes induced by the sequence of the process flow could lead to the general asymmetry in the structure and performance of metal-ferroelectric-metal (MFM) capacitors, which may cause serious reliability problems. In this letter, we have exploited a special high pressure annealing (HPA) process, called alcohol-thermal method (ATM), to improve the symmetry of TiN/HZO/TiN capacitors. The original control device exhibits asymmetric leakage current and coercive fields. This has been significantly improved by the ATM, which was performed at temperature of 240°C and atmospheric pressure of 70 atm, in C2H6O ambient. The enhancement of ferroelectricity can be attributed to the reduction of the thickness and defects of the non-ferroelectric layers in the device. The improvement of symmetry leads to the operation ability under low voltages, which is critical to the endurance of devices. Under the electric field of 2.4 MV/cm with 10 MHz frequency, the lifetime of the TiN/ HZO/TiN device after HPA process was measured up to 1010 cycles. This work provides an effective way to improve symmetry and ferroelectricity of hafnium-based ferroelectric capacitors.