The Improvement of Reliability of High-k/Metal Gate pMOSFET Device with Various PMA Conditions

The oxygen and nitrogen were shown to diffuse through the TiN layer in the high-k/metal gate devices during PMA. Both the oxygen and nitrogen annealing will reduce the gate leakage current without increasing oxide thickness. The threshold voltages of the devices changed with various PMA conditions. The reliability of the devices, especially for the oxygen annealed devices, was improved after PMA treatments. 1. Introduction High-k/metal gates are needed to continuous device scaling-down. However, threshold voltage instability and performance degradation are important problems for high-k devices [1]. The defect density in the interface of gate stack is the major cause for negative bias temperature instability (NBTI) as well as mobility degradation [1]. Oxygen vacancy is known to play an important role in threshold voltage variations [2] and is a significant defect in the HfO2/Si system [3]. The influence of charge oxygen vacancies introduces a dipole offset between the gate metal and the substrate [4]. Post metallization annealing (PMA) is used to reduce the defects at the interface, such as fixed oxide charges, oxide trapped charges, and interface charges [5]. Previous work has demonstrated that oxygen vacancies can be passivated for device with noble metal gate by oxygen diffusion through the gate metal [6]. However, these suffer from high equivalent oxide thickness. In this work, we show that both oxygen and nitrogen can be diffused through thin TiN layer and passivate the oxygen vacancies without increasing the oxide thickness by using PMA with various temperatures. Negative bias instability for pFET is improved, especially for the oxygen annealed one. 2. Experimental 28？nm FET high-k/metal gate was formed on bulk Si. After interfacial SiO2 layer/high-k and TiN deposition, TiN layer was then deposited with the thickness of 100~200？？. The fabrication process of the high-k metal gate last device was sketched in Figure 1. Some of the samples were annealed at 400°C and 450°C in oxygen or nitrogen ambient for several minutes, respectively. Figure 1: The fabrication process of the high-k metal gate last device. The capacitance-voltage ( - ) curves were measured with an HP4280 precision LCR meter and the current-voltage ( - ) curves with an HP-4156B. After the basic electric measurements, the samples were then stressed by using a constant voltage of . After stressing, the samples were measured again to find out the performance of reliability. 3. Results and Discussions Figure 2 shows the？？ - curves of the samples measured with 1 MHz. The extracted EOT for