Rolling Mask Lithography®
Rolling Mask Lithography® (RML) is MTI’s patented manufacturing technology that offers a unique advantage in the smart materials industry. It employs massively parallel patterning scheme easily scalable to large areas of rigid substrate materials (plates and panels) and rolls of flexible films. Its nano-fabrication method combines the advantages of Soft Lithography and Near-field Optical Lithography, proved to be reliable in fabrication of nano-structures beyond the diffraction limit.
It is used to produce certain types of smart materials made from a variety of substrates such as glass, metal semiconductors, and polymer films—enabling MTI to manipulate light for a variety of outcomes: to block, absorb or enhance light. This method uses near-field phase shift photolithography which can be implemented as continuous, seamless and scalable manufacturing process. RML can be used to manufacture smart materials in a variety of shapes and sizes. With RML technology, MTI is creating a new generation of optical metamaterials that satisfy commercial requirements for nano-structured surfaces with large area and low cost. It is compatible to roll-to-plate and roll-to-roll process modes. RML is free from form-factor limitations associated with state-of-the-art projection optical lithography (steppers), pattern type limitations of holographic and self-assembly lithography’s, and process integration and yield limitations of nano-imprint lithography.
Its versatility is advancing MTI’s smart material research and helping to produce new metamaterial solutions that span from medical imaging systems to satellites orbiting the Earth.
How does RML® produce metamaterials?
In order to alter how light interacts with metamaterials, MTI uses in-house computer software to engineer a patterned nano-structure. It is modelled, optimized, and then transferred onto a soft cylindrical photomask. The RML uses the mask to pattern photosensitive materials deposited on surface such as a glass plate or plastic thin film. Then such pattern is used as an etch mask for subsequent etching a substrate (glass, semiconductor), or as template for nano-structuring metals or other functional materials. In order to create a desired pattern on the surface, the RML equipment uses ultraviolet (UV) illumination as the mask rolls across the photosensitive film. MTI uses RML due to its unique capability to create nano-structures within metamaterial films that are as small as 175 nano-meters (approximately 5000 times smaller than a human hair). Depending on the type of smart material being produced, engineers at MTI add more layers to the film to increase its functionality.
As RML is an optical lithography method, it allows fabricate both positive and negative nanopatterns from the same mask. RML also does not have a “nanoimprint residual layer”, which makes process integration (substrate etch or photoresist lift-off) much easier.