In-line control and rapid process development of nitrided gate oxides

Nitrided gate oxides on Si wafers were investigated by X-ray Photoelectron Spectroscopy (XPS) and non-contact surface voltage and surface photovoltage measurements of Corona-Oxide-Semiconductor (COS) structures. The XPS measured the physical parameters of N dose and film thickness, while the COS measured the equivalent oxide thickness and a leakage indicator. The XPS N dose, XPS thickness and the COS leakage indicator met the stability, precision, and time dependence requirements for process control, but the COS EOT was unstable possibly due to variations in substrate doping. In lot-based measurements of 65 nm node wafers, the COS leakage indicator correlated to gate leakage for two different oxide thicknesses with a correlation R ² of 0.85, whereas XPS N dose correlated for only one oxide thickness with a correlation R ² of 0.47. None of the lot-based measurements correlated to threshold voltage. The suitability of XPS, COS and single wavelength ellipsometry for rapid process development was determined by measuring pilot wafers processed alongside 65 nm node development lots. The measurements could predict threshold voltage only under variations of a limited set of process parameters. Under variations of several process parameters, only the COS leakage indicator could predict gate leakage.