Improving imaging - Partial Coherence
Photolithography steppers and scanners have evolved over the years from simple fixed illumination systems, to systems with a plethora of software controlled illumination settings that can be somewhat overwhelming e.g. Conventional, Annular, Quadrupole and Custom DOEs. However, there are compelling reasons to explore the many available illumination combinations, in particular the change in partial coherance, or sigma, which has many benefits.
ASML 5500 Yield Improvement: Improving imaging: Partial Coherence
Photolithography steppers and scanners have evolved over the years from simple fixed illumination systems, to systems with a plethora of software controlled illumination settings that can be somewhat overwhelming e.g. Conventional, Annular, Quadrupole and Custom DOEs. However, there are compelling reasons to explore the many available illumination combinations, in particular the change in partial coherance, or sigma, which has many benefits.
What is a partial coherence? Partial coherence [PC], sigma, or fill factor is the ratio of the exposure tool’s condenser numerical aperture [NAc] to the projection lens numerical aperture [NAp]. Reducing partial coherence increases the image contrast for feature sizes less than the cutoff frequency [NA Partial coherence is controlled in by adjusting the exposure tool’s source image diameter using a variable iris diaphragm or inserting a fixed aperture. Note: This type of coherence is spatial (phase) and not temporal (wavelength – frequency).
Effective use of partial coherence Using partial coherence to improve resolution for specific features such as contacts, isolated trenches, and dense linewidths has limitations that need to be evaluated, before implementing any illumination change. Decreasing partial coherence below 0.50 to improve contact resolution will increase the optical proximity effects: isolated-dense linewidth bias, interior to exterior linewidth bias, and dark area proximity exposure due to increased diffracted radiation interference effects (termed “ringing”). When implementing a partial coherence change multiple feature types besides the feature of interest need to be evaluated to avoid unexpected process excursions.
Simax has developed a custom partial coherence program for ASML 5500/xxx steppers to significantly improve specific feature imaging and depth of focus. The effective use of partial coherence has been shown to improve specific feature resolution, increase depth of focus, and increase yields by 10% . (These results are product and process sensitive.)
Isolated-Dense Linewidth Vs Partial Coherence Isolated-Dense Linewidth Bias SEM
Source: Simax
This e-mail address is being protected from spambots. You need JavaScript enabled to view it. Simax Applications Engineering for assistance in improving resolution and increasing Depth of focus for specific features using illumination control
Steve Brainerd is a Senior Applications Engineer with Simax Lithography. With over 30 years “hands-on” wafer fabrication experience concentrated in semiconductor wafer, MEMs, thick photoresist, solar, and LCD fabrication manufacturing processes, Steve uses his strong analytical skills to develop robust processes for customers. His knowledge and experience include process-equipment startup, process development, process modeling, anti-reflection coating design/modeling, cost reduction, yield improvement, and capacity increases.
ASML 5500 Yield Improvement: Improving imaging: Partial Coherence
Photolithography steppers and scanners have evolved over the years from simple fixed illumination systems, to systems with a plethora of software controlled illumination settings that can be somewhat overwhelming e.g. Conventional, Annular, Quadrupole and Custom DOEs. However, there are compelling reasons to explore the many available illumination combinations, in particular the change in partial coherance, or sigma, which has many benefits.
What is a partial coherence? Partial coherence [PC], sigma, or fill factor is the ratio of the exposure tool’s condenser numerical aperture [NAc] to the projection lens numerical aperture [NAp]. Reducing partial coherence increases the image contrast for feature sizes less than the cutoff frequency [NA Partial coherence is controlled in by adjusting the exposure tool’s source image diameter using a variable iris diaphragm or inserting a fixed aperture. Note: This type of coherence is spatial (phase) and not temporal (wavelength – frequency).
Effective use of partial coherence Using partial coherence to improve resolution for specific features such as contacts, isolated trenches, and dense linewidths has limitations that need to be evaluated, before implementing any illumination change. Decreasing partial coherence below 0.50 to improve contact resolution will increase the optical proximity effects: isolated-dense linewidth bias, interior to exterior linewidth bias, and dark area proximity exposure due to increased diffracted radiation interference effects (termed “ringing”). When implementing a partial coherence change multiple feature types besides the feature of interest need to be evaluated to avoid unexpected process excursions.
Simax has developed a custom partial coherence program for ASML 5500/xxx steppers to significantly improve specific feature imaging and depth of focus. The effective use of partial coherence has been shown to improve specific feature resolution, increase depth of focus, and increase yields by 10% . (These results are product and process sensitive.)
Isolated-Dense Linewidth Vs Partial Coherence Isolated-Dense Linewidth Bias SEM
Source: Simax
This e-mail address is being protected from spambots. You need JavaScript enabled to view it. Simax Applications Engineering for assistance in improving resolution and increasing Depth of focus for specific features using illumination control
Steve Brainerd is a Senior Applications Engineer with Simax Lithography. With over 30 years “hands-on” wafer fabrication experience concentrated in semiconductor wafer, MEMs, thick photoresist, solar, and LCD fabrication manufacturing processes, Steve uses his strong analytical skills to develop robust processes for customers. His knowledge and experience include process-equipment startup, process development, process modeling, anti-reflection coating design/modeling, cost reduction, yield improvement, and capacity increases.