Thickness and Topography of Dielectric Dual-Sidewall Spacers on Metal Gate of DRAM Extracted by Spectroscopic Ellipsometry

As the design rule of devices decreases with shrinking gate width dimensions, the properties of sidewall layers are becoming increasingly important for controlling electrical properties, especially for processes in the nanometer-grade range. Poor control of the sidewall process can cause errors in both the implant area and length of the device channel. An optical technology has been developed and is shown here to monitor directly the width of the sidewall on the grating structure. In addition, this technology can obtain more information including the thickness of each film, optical properties, and CD's (critical dimensions) in the structure simultaneously. This nondestructive inspection technology provides accurate results with good precision, repeatability and high throughput on several user-selectable information outputs. In this study, the technology is used to measure a dual-sidewall structure on metal gate for DRAM. Good correlations are obtained when comparing the measurement results to X-SEM (cross-section SEM) and electrical property test, in particular, a 0.97 correlation with a resistance test. The technology can potentially replace traditional monitor method for dual-sidewall structure as seen in this study.