Comparison of contact radius models for ultrashallow spreading resistance profiles

Over the years, several methods have emerged for determining the probe cont act radius in spreading resistance measurements. The methods vary from atte mpting to determine the physical area of the probe contact to the use of th e contact radius as a variable parameter determined from calibration data. The number of different methods has led to some confusion about the applica bility of the different models. In this article, we examine the validity of the different models for various ultrashallow structures typically used in current device technology. Specifically, we examine several methods of det ermining the physical contact area from the existing probe mark. These meth ods include circumscribing all visible microcontacts, determining the width of the probe mark in the measurement direction, and a summation of the con tribution from all microcontacts. We further examine various electrical mod els for determination of the probe contact, including a calibration curve f it and a determination based on a known sample profile. (C) 2000 American V acuum Society. [S0734-211X(00)00601-1].