Run-to-run control of overlay and linewidth in semiconductor manufacturing

In the manufacture of semiconductor products; overlay and linewidth are two of the most critical design specifications. Linewidth is a measure of the width of a particular feature within a given pattern, while overlay is the position of a pattern relative to underlying layers. The width of the polysilicon gate structure in Metal Oxide Semiconductor (MOS) devices is directly correlated to the performance of these devices. Overlay capability largely determines the minimum feature size that may be incorporated into semiconductor device designs. Control of these specifications, therefore, is critical to semiconductor manufacturing.; Run-to-run control refers to a class of algorithms that seek to minimize output variance and deviation from target by updating the process recipe on a run by run basis. This type of control is seeing an increased application in the industry, and is regarded as an essential tool for the production of next-generation semiconductor devices. The goal of this research was to develop a run-to-run control scheme for overlay and linewidth control. Linear Model Predictive Control (LMPC) was investigated as a robust control method capable of controlling semiconductor manufacturing processes.; Successful implementation of control in semiconductor manufacturing must account for those process conditions that impact process performance. Many factors associated with a particular wafer lot, the process to be performed on that lot, or upstream processes utilized to create underlying features may all impact process performance. This research investigated a state estimation scheme known as control threads to account for various sources of deterministic process variation. This method facilitates factory-wide control over multiple machines, which increases flexibility in tool utilization and throughput.; Both the linewidth and overlay controllers developed within this research were implemented in AMD's Fab 25 manufacturing facility as a means to validate the performance of the control algorithms. The overlay controller was applied to the photolithography process, and reduced the average, site-level, maximum overlay error for all controlled masking operations by ail average of 43%. The linewidth controller replaced an existing etch process run-to-run controller, and reduced the standard deviation of polysilicon gate linewidth error by 44%.