process control
Lithography process control enhancements using advanced light source metrology
As ArF immersion lithography is extended with multi-patterning techniques, improved process control is required to ensure stable and repeatable performance. Nakgeuon Seong,Omar Zurita, Joshua Thornes,Yookeun Won, Slava Rokitski, Bernd Burfeindt, from Cymer
Inc.describes how the addition of on-board beam metrology on the light source along with data analysis tools can provide an additional process control dimension.
M
Figure
1.Concept diagram of process control utilizing equipment process parameters
ultiple lasers in the field were monitored after installing a new on-
board metrology product called SmartPulse. We found that changes in beam parameters can be significantly reduced at major module service events when new service procedures and on-board metrology were used, while significant beam parameter shift and illumination pupil changes were observed when on-board metrology was not available at service events, causing lengthy scanner illumination pupil recalibration.
SmartPulse software from Cymer Inc. was used to monitor the variation of light source performance parameters, including critical beam parameters, at wafer level resolution.
The monitoring and control of process parameters at the process tool level has been used to improve process stability without increasing direct off-line wafer metrology, enabling fast wafer turn-around time and fab capital cost reduction. We have
identified the need to provide process monitoring capability with higher resolution and additional process parameters at the light source level to complement monitoring at the litho cell (scanner and track).
Process monitoring and control improvement
As the use of ArF immersion lithography processes for most critical layer patterning has continued for multiple technology generations, each lithographic imaging solution has become highly optimized for specific patterns to be printed. Use of different imaging solutions for different device patterns also drives different levels of control for process variables. For example, highly optimized SMO (source mask optimization) imaging solutions require tighter control of the illumination pupil than simple SDP (Spacer double pattering) with dipole illumination. Very high throughput lithography patterning processes were implemented to reduce the cost of multiple patterning processes, which are commonly used for memory device production.
It has been recognized that smaller pattern size and lower k1 imaging processes at the latest technology nodes drive tighter control of more process performance parameters of lithography tools than at previous nodes. Process parameter monitoring and control for the process tools has been adopted as a way of reducing process errors and improving process control, and minimizing added metrology capital costs.(Figure 1.)
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www.siliconsemiconductor.net Issue 2 2012
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