Investigation of lithography performance using multipass gray (MPG) with MEBES® 5000

Leading edge technologies require continually shrinking design grids due to the demands of decreasing minimum feature size and higher resolution. Using conventional raster-scanned exposure tools to place these patterns on photomasks results in longer write times, because linear decreases in address result in exponential increases in write time. This phenomenon can be compensated for by changes in writing strategies. Multipass gray (MPG) is one method of drastically improving throughput at small addresses while retaining lithographic quality. MPG was introduced with the MEBES 4500S system and takes advantage of the gray-level writing strategies of the CORE(R) and ALTA(R) exposure systems. MPG combines the use of multiple exposure passes and offset scan voting to reduce placement, butting, and scan linearity errors. Additionally, the multipass strategy allows the exposure of higher doses without impacting throughput. The added dose allows use of less sensitive resists such as DNQ/novolacs and high-molecular weight, chain scission resists such as ZEP 7000. This paper describes the MPG writing strategy and presents lithographic results. Results are based on a process using GHOST proximity effect correction (PEC), ZEP 7000 resist, and dry etch of the chrome film. Placement and butting error reduction with multipass writing, critical dimension (CD) control, CD linearity, and overall lithographic quality will be discussed.