Evaluation of different wafer charging metrology protocols for thin dielectrics

Evaluation of charging damage in thin oxides is challenging due to high tunneling currents and the lack of standard testing protocols. The problem is further complicated by the trend in the industry to modify or replace pure SiO₂ as the gate dielectric material. An effective way to evaluate the testing protocols used in characterizing ion beam induced charging damage is needed. The traditional interpretation of testing results is based on the conduction model for thick oxides in which direct tunneling is negligible. Charges injected into the oxide usually lead to catastrophic breakdown or irreversible destruction of the oxide. Around 3 nm or less, direct tunneling becomes a significant part of the current flow through the oxide and self-healing after breakdown may occur. We use antenna structure devices to detect ion beam induced charging damage. Detection sensitivity can be improved by increasing the antenna ratio. After implantation, leakage current at different stress voltages, stress voltage at 1 A/cm² , and voltage-to-breakdown (V_bd) as well as charge-to-breakdown (Q_bd) are measured. Each of the testing protocols gives a certain type of information on oxide charging damage. More complicated analysis requiring parameter extraction to fit the Fowler-Nordheim current curve has been explored. The sensitivity and effectiveness of these testing protocols are discussed