Photoembossing of Periodic Relief Structures Using Polymerization- Induced Diffusion: ACombinatorial Study

Guerrero-Sanchez, Carlos; de Gans, Berend-Jan; Kozodaev, Dimitri; Alexeev, Alexander; Escuti, Michael J.; van Heesch, Chris; Bel, Thijs; Schubert, Ulrich S.; Bastiaansen, Cees W. M.; Broer, Dirk J.

Abstract:

Polymeric relief microstructures are extensively used in biosensors, cell-growth arrays, and as microelectronic and microoptical elements in displays. To generate these structures, replication methods based on physical contact are used, like embossing or cast-molding. In case of embossing, relief features are transferred by pressing a polymer film against a microstructured rigid master. Cast-molding uses a polymer precursor that is poured onto a master, cured, and released to obtain an inverse replica. Relief microstructures can also be made by lithography via a light-induced solubility change of a polymeric photoresist. A wet-etching step develops the final relief structure. Recently, a new solvent-free photolithographic technique was proposed to prepare surface-relief structures. The process that we will refer to as “photoembossing” is schematically shown in Figure 1. A photopolymer blend comprising a polymeric binder, a multireactive acrylate, and a photoinitiator is processed as a solid thin film onto a substrate. An irradiation step through a lithographic mask at room temperature (RT) generates radicals in the exposed areas. The photopolymer blend is glassy at RT, which allows the use of contact masks. Monomer diffusion and polymerization are inhibited at this stage, and a free-radical latent image of the mask is formed. A subsequent heating step enhances monomer mobility and polymerization in the irradiated areas. Consumption of monomer in these regions leads to a net flux of unreacted monomer from the unexposed to the exposed areas, resulting in a surface deformation whose final shape is determined by diffusion and surface tension. Photoembossing does not involve any wet developing step, and the mask can directly contact the photopolymer. Therefore, photoembossing is also very attractive from an industrial standpoint.

Year:

2005

Type of Publication:

Article

Journal:

Advanced Materials

Volume:

17

Pages:

2567 - 2571