Research departments

Photoresists


Photoresists

Resists are organic compound (generally thermoplastic polymers) whose solubility is modified by UV radiations. Several resists are available according to the desired process.


When they affect the resists, UV radiations induce different behaviours: concerning negative resists, they cause a polymerization of the exposed zones, rendering them insoluble on contact with the development solvent whereas non-exposed areas disappear in this solvent (for example, SU-8 resist). For positive resists, UV radiations chemically transform the resist so that the exposed areas become soluble in the developer (AZ9260 and S1813 resists). Image reversal resists have the possibility to change their polarity after an annealing step called reversal bake (AZ5214, TI09XR).


* Positive resists :

Insolation résine positive



* Negative resists :

Insolation résine négative



* Reversal resists :

Insolation résines inversibles



Example of use :


Photoresists are used in uniform and adhesive thin films (from a few hundred nanometres to several microns).

  • For the LIGA mould fabrication, high-viscosity resists become necessary because they provide more important thicknesses (about ten micrometers (AZ9260) up to several hundred micrometers (SU-8)). These resists are characterized by their capacity to produce high aspect ratio patterns (height over the smallest dimension ratio).

  • Particular resists for LIFT-OFF: to achieve metallic patterns, one method consists in depositing metal onto resist patterns whose sidewall slope is reversed compared to the one usually obtained in positive resist development. The final step consists in removing the polymer covered by the metal: it is called the Lift-off technique.

Méthode

"LIFT-OFF" method

Méthode

"DIRECT'' method



























Particular resist for plasma etching: specific resists like SPR220 have been developed in order to be used as masks for plasma etching, especially for BOSCH and DRIE processes.

Structures gravées_Fiche résines photosensibles

Example of Si structures etched with a SPR220 3.0 photoresist mask