Comparison of contact radius models for ultrashallow spreading resistance profiles

Over the years, several methods have emerged for determining the probe contact radius in spreading resistance measurements. The methods vary from attempting to determine the physical area of the probe contact to the use of the contact radius as a variable parameter determined from calibration data. The number of different methods has led to some confusion about the applicability 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 determining the physical contact area from the existing probe mark. These methods include circumscribing all visible microcontacts, determining the width of the probe mark in the measurement direction, and a summation of the contribution from all microcontacts. We further examine various electrical models for determination of the probe contact, including a calibration curve fit and a determination based on a known sampl...