Process improvement defines a process engineer’s value to the corporation, working to increase CD, overlay, and process latitude, with the end result being increased yield and profits.

ASML 5500/100 Yield Improvement: Exposure Latitude

Process improvement defines a process engineer’s value to the corporation. Routinely a photolithographic process engineer is working on projects to increase CD, overlay, and process latitude, with the end result being increased yield and profits.

A technique not often used to improve CD control has been to change the tools numerical aperture to increase exposure latitude. Decreasing the effect of dose on CD will improve process latitude and compensate for other process variations such as substrate reflectivity, photoresist coating thickness, illumination uniformity, hot plate bake time/temperature variations, and developer time/temperature/concentration variations. ASML 5500/100 and greater models have the ability to program defined numerical aperture values into the exposure/align job. However, there is always a trade off between exposure latitude and depth of focus when changing NA. This is also feature size dependent. We evaluated 0.36 um CDs here and increasing the NA achieved the best results

Simax has developed additional methodological techniques for functionally evaluating the impact of NA on Depth of Focus and Exposure Latitude. Increasing exposure latitude by NA optimization has been shown to increase yields by 2% and reduce reworks by 7%. (These results are product and process sensitive.)

Diagram Source: 15 year old generic data

Contact Simax Applications Engineering for assistance in developing a custom alignment mark evaluation program for your process.

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.