Technology of Alignment mark in Electron Beam Lithography

Electron beam direct wring lithography has been an indispensable approach by which all sorts of novel nano-scale devices include many kinds optical devices can be fabricated. Alignment accuracy is a key factor especially to those devices which need multi-level lithography. In addition to electron beam lithography system itself the quality of alignment mark directly influences alignment accuracy. This paper introduces fundamental of alignment mark detection and discusses some techniques of alignment mark fabrication along with considerations for obtaining highly accurate alignment taking JBX5000LS and JBX6300FS e-beam lithography systems for example. The fundamental of alignment mark detection is expounded first. Many kinds of factors which can impact on the quality of alignment mark are analyzed including mark materials, depth of mark groove and influence of multi-channel process. It has been proved from experiments that material used as metal mark with higher average atomic number is better beneficial for getting high alignment accuracy. Depth of mark groove is required to 1.5 similar to 5 mu m on our experience. The more process steps alignment mark must pass through, the more probability of being damaged there will be. So the compatibility of alignment mark fabrication with the whole device process and the protection of alignment mark are both need to be considered in advance.