Critical dimension adapted alignment for EBDW

Electron beam direct write (EBDW) promises a good solution in lithography applications, where standard optical lithography is not suitable. With shrinking dimensions in semiconductor technologies the overlay capability for the lithography has to be enhanced. The overlay depends on the tool capability as well as on the process and technology requirements and conditions. The different effects contributing are presented. We investigated a new design for alignment marks in order to improve the overlay capability. A SB320-50DW was used for the experiments. The goals were to improve the overlay to the previous lithography step and at the same time to use marks which are compatible with the standard semiconductor process. We compared gratings with double crosses regarding the achievable accuracy. All marks had the same outer shape. The gratings were varied in the width (100-240 nm) and pitch (400-640 nm) of the lines. The influence of the new mark design on signal quality, detection accuracy and achievable overlay results is discussed.