Improving Depth of Focus
Photolithographic process engineers are frequently tasked with developing processes on older exposure tools that push the resolution beyond the manufacturers specifications. To achieve this the process engineer needs to be aware of the array of Reticle Enhancement Techniques and their limitations.
ASML 5500 Yield Improvement: Improving Depth of Focus for resolution exceeding the equipment’s specifications
Photolithographic process engineers are frequently tasked with developing processes on older exposure tools that push the resolution beyond the manufacturers specifications. To achieve this, the process engineer needs to be aware of the array of enhancement techniques and their limitations. These techniques are termed “RET” for Reticle Enhancement Techniques. These include: Illumination Partial Coherence (PC or sigma), Off-Axis Illumination (OAI defined by inner and outer sigma), Phase Shifted masks (PSM), mask Optical Proximity Correction (OPC), Multiple Exposure, substrate reflection control, and multi-layer photoresists. The illumination settings are the easiest RET to evaluate and implement in an existing production environment.
ASML 5500/200 and greater models have the ability to program defined illumination (PC and OAI) values into the exposure/align job. ASML 5500/100 and lower models can change the illumination by using a custom aperture (Blade) next to the illumination integrator. The optimal inner and outer sigma for OAI is dependent on the specific feature one wants to improve. This is due to different feature sizes having different diffraction angles entering the lens. OAI will increase the smaller features contrast, which increases the usable depth of focus. The worst pitch has reduced contrast resulting from the OAI 2 beam image formation phase difference, reducing depth of focus.
Simax has developed a custom aperture program for ASML 5500/100’s to improve resolution and Depth of Focus for specific features. Simax also has a program to optimize illumination setting for ASML 5500/200 models and above. Increasing depth of focus has been shown to increase yields by 10% and reduce reworks by 9%. (These results are product and process sensitive.)
Optimal OAI sigma and specific feature pitches/linewidths for ASML 248 nm exposure tool
Source: Simax
This e-mail address is being protected from spambots. You need JavaScript enabled to view it. Simax Applications Engineering for assistance in developing robust photolitographic processes
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 Depth of Focus for resolution exceeding the equipment’s specifications
Photolithographic process engineers are frequently tasked with developing processes on older exposure tools that push the resolution beyond the manufacturers specifications. To achieve this, the process engineer needs to be aware of the array of enhancement techniques and their limitations. These techniques are termed “RET” for Reticle Enhancement Techniques. These include: Illumination Partial Coherence (PC or sigma), Off-Axis Illumination (OAI defined by inner and outer sigma), Phase Shifted masks (PSM), mask Optical Proximity Correction (OPC), Multiple Exposure, substrate reflection control, and multi-layer photoresists. The illumination settings are the easiest RET to evaluate and implement in an existing production environment.
ASML 5500/200 and greater models have the ability to program defined illumination (PC and OAI) values into the exposure/align job. ASML 5500/100 and lower models can change the illumination by using a custom aperture (Blade) next to the illumination integrator. The optimal inner and outer sigma for OAI is dependent on the specific feature one wants to improve. This is due to different feature sizes having different diffraction angles entering the lens. OAI will increase the smaller features contrast, which increases the usable depth of focus. The worst pitch has reduced contrast resulting from the OAI 2 beam image formation phase difference, reducing depth of focus.
Simax has developed a custom aperture program for ASML 5500/100’s to improve resolution and Depth of Focus for specific features. Simax also has a program to optimize illumination setting for ASML 5500/200 models and above. Increasing depth of focus has been shown to increase yields by 10% and reduce reworks by 9%. (These results are product and process sensitive.)
Optimal OAI sigma and specific feature pitches/linewidths for ASML 248 nm exposure tool Source: Simax
This e-mail address is being protected from spambots. You need JavaScript enabled to view it. Simax Applications Engineering for assistance in developing robust photolitographic processes
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.