Fabrication of Multilevel layers for Optical Printed Circuit Board by Modified Two-step Photolithography

A novel simple method is proposed to fabricate multilevel or three dimensional structures for integrated optoelectronic devices using modified two-step photolithography. First photolithographic step uses an epoxy type photoresist such as SU-8 and the second step uses a novolak type photoresist such as AZ1518. Because solubility of one photoresist to the other’s developer is different, the conventional exposure and develop process can be done consecutively without affecting the pre-existing patterns. However, flat deposition of the second novolaktype photoresist on patterned uneven surface by spin coating is difficult and in this work we suggest a method to get flat surface before the second exposure. This method has been applied successfully to prepare 3-D structures on optical printed circuit board.