Variability of the local phi MS values over the gate area of MOS devices

The local value distributions of the effective contact potential difference (ECPD or the phi MS factor) over the gate area of Al-SiO2-Si structures were investigated for the first time. A modification of the photoelectric phi MS measurement method was developed, which allows determination of local values of this parameter in different parts of metaloxide-semiconductor (MOS) structures. It was found that the phi MS distribution was such, that its values were highest far away from the gate edge regions (e.g., in the middle of a square gate), lower in the vicinity of gate edges and still lower in the vicinity of gate corners. These results were confirmed by several independent photoelectric and electrical measurement methods. A model is proposed of this distribution in which the experimentally determined phi MS (x; y) distributions, found previously, are attributed to mechanical stress distributions in MOS structures. Model equations are derived and used to calculate phi MS (x; y) distributions for various structures. Results of these calculations remain in agreement with experimentally obtained distributions. Comparison of various characteristics calculated using the model with the results of photoelectric and electrical measurements of a wide range of Al-SiO2-Si structures support the validity of the model.