Advanced profile control and the impact of sidewall angle at gate etch for critical nodes

Gate patterning is critical to the final yield and performance of logic devices. Because of this, gate linewidth control is viewed by many as the most critical application for integrated metrology on etch systems. For several years, integrated metrology and wafer-level process control have been used in high volume manufacturing of 90 and 65nm polysilicon gate etch [1], [3], [17], [22]. These wafer-level CD control systems have shown the ability to significantly reduce CD variation. With gate linewidth under control (< 2nm 3 sigma wafer-to-wafer), the next parameter to impact gate electrical performance is side wall angle (SWA). SWA had not been considered a critical control parameter due to the difficulty of measurement with conventional scanning electron microscope (SEM). With scatterometry, SWA measurement of litho and etch profiles are included with the critical dimension (CD) measurements. Recently, it has become visible that the polysilicon SWA correlates to electrical device parameters, and is thus, an important parameter to control. This paper will examine the current relationship between litho and etch profile control, determine potential limitations for future technology nodes, and introduce novel etch process control techniques based on multiple input multiple output (MIMO) modeling.