Published On : 25 Apr 2018
Nanoimprint lithography refers to the process of fabricating nanometer scale patterns. It is a plain and simple nanolithography process that comes with low cost, high resolution, and high throughput. It makes a creation of patterns through mechanical deformation of imprint resist and subsequent processes. The imprint resist typically refers to a polymer or monomer formulation that is cured by UV light or heat during the time of imprinting. Adhesion between the template and the resist is controlled so as to allow proper release.
The term "Nanoimprint Lithography" (NIL) has been coined in a scientific literature of 1996, when Prof. Stephen Chou and his students published a report on the same on Science, a science journal. Though hot embossing which is now taken as a synonym of NIL, of thermoplastics had been surfacing in the patent literature for quite a few years already. Soon after the journal Science published the paper, many researchers came up with different implementations and variations. At this very point, an addition of nanoimprint lithography has been made to the International Technology Roadmap for Semiconductors (ITRS) for the 32 and 22 nm nodes.
Different Types of Nanoimprint Lithography
There exists many different types of nanoimprint lithography, but out of which three of them are most significant, namely, resist-free direct thermal nanoimprint lithography, thermoplastic nanoimprint lithography, and photo nanoimprint lithography.
Resist-free Direct Thermal Nanoimprint Lithography
Resist-free direct thermal nanoimprint is quite different from the various other types nanoimprint methods and it does not need an extra etching step in a bid to transfer patterns from imprint resists to the device layer.
Thermoplastic Nanoimprint Lithography
Thermoplastic nanoimprint lithography (T-NIL) is the earliest form of nanoimprint lithography and has been developed by Prof. Stephen Chou's group. In accordance with standard T-NIL process, a very thin layer of imprint resist (thermoplastic polymer) is spin coated onto the sample substrate. Then comes the mold, which comes with topological patterns that are predefined, and is brought into close contact with the sample and then they are pressed together closely under certain pressure. When it is heated up above the temperature of glass transition of the polymer, the pattern on the mold is then pressed into the film of softened polymer. After being cooled down, the mold is segregated from the sample and the pattern resist is then left on the substrate.
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Photo Nanoimprint Lithography
In the type of photo nanoimprint lithography (P-NIL), a photo (UV) curable liquid resist is applied on sample substrate and then the mold is generally made of transparent material such as PDMS or fused silica. After the substrate and the mold are pressed together, the resist is cured in UV light and then it becomes solid in nature. After the separation of mold, a similar pattern of transfer process can be utilized so as to make a transfer of the pattern in a bid to resist onto the underneath material. The usage of a UV-transparent mold is quite difficult in a vacuum, as a vacuum chuck to hold the mold is not possible.
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