Versatile Multilevel Soft Lithography Method with Micrometer Alignment Using All-Flexible Rubber Stamps and Moire Fringe Technique
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Soft lithography has gathered wide interest for the fabrication of unconventional micrometer and nanometersized structures and devices. Nevertheless, accurate alignment is essential to achieve multilevel soft lithography. Because of the soft nature of the stamp materials, such as soft polydimethylsiloxane, they are susceptible to mechanical distortions, which lower the registration accuracy. To reduce the distortions we backed the stamp with a polymer foil and minimized the overall forces applied to the stamp. We furthermore employed an alignment method using additive type moire fringe technique that is easy to implement and does not require extensive processing steps. The alignment results show less than 1 mu m misalignment when the stamp is brought again onto a previously structured rigid template. When performing two consecutive lithography steps by transfer printing of thin gold films, we were able to obtain average registration accuracy of 1.3 mu m over an area of 400 mm(2). This method is versatile and can be used for several soft lithography techniques. Better results can be obtained with smaller moire gratings and the use of harder materials.