Replication of diffractive gratings using embossing into UV-cured photo-polymers

The original diffraction grating was fabricated using a well known Si anisotropic etching technique. By means of this micromachined Si stamper it is possible to transfer its surface-relief profile into a dry negative resist film. The transfer is performed during an embossing process which contains the following steps: In the first step, the dry photosensitive film having 1.5 mils thick, commonly used in PCB fabrication, is laminated onto a quartz UV transparent glass. After that, the protective cover sheet is removed from the laminated substrate, and the Si stamper is placed on the free surface of the photopolymer film. Next, the shimmed sandwich is loaded at the embossing temperature of 115 degrees C into a vacuum UV contact printing unit, while a moderate external pressure is applied, during aprox 5 seconds. The embossed information layer is then firmly bonded to the substrate, and the embossing is made permanent by ultraviolet radiation curing. This treatment consists of exposing the photopolymer, through the transparent substrate, at a UV broad band light source, with a hardening dose of at least 2500 mJ/cm(2). Finally, the vacuum is stopped, the sandwich is removed from the exposing unit, and the assembly is separated by slightly flexing, obtaining the permanent complementary replica of the stamper. This fabrication method, tested only for diffraction grating replicas, has also great potential in batch production of many other low-cost integrated optical components.