As the feature size is smaller, the overlay budget of lithography for the rigorous manufacturing control becomes so small.
And, overlay accuracy has become more important due to small overlap margin and double patterning process. Recently,
a scanner maker has developed several effective solutions to correct the errors of overlay in field. But, the error induced
by photomask still remains, so the accuracy of photomask image placement is required below than several nm for the HP
3X nm memory device generation. But, current e-beam writers don't meet this specification. There are various sources of
image placement errors. Many papers report their analysis of those errors, so we focus on e-beam charging effect and
compensation. Especially, their compensating methods are too complex to apply to production. So, it is need a simple
way to compensate to image placement errors effectively.