Dynamic mask defects in hot embossing lithography

Nanoimprint was performed in very thin layers of polystyrene (PS) in order to define a mask with minimum CD loss for a subsequent etch process at minimum etching time for opening of the mask windows after imprinting. The initial polymer layer thickness was chosen as to fill the stamp cavities with nearly no surplus of polymer material. The residual layers after imprint were in the range of 50 nm and could be cleared at 50% overetch within 90 s in an oxygen RIE step. As there was not enough polymer material available for a complete filling of the cavities when a residual layer remains, filling defects occurred. High imprint temperature and thus low viscosity led to formation of deep defects in the imprint and thus the mask to be formed by embossing. Lift off experiments revealed that within the defective regions the remaining polymer layer thickness was smaller than the imprinted residual layer. In order to avoid such mask defects the imprint temperature had to be reduced.