Imprint Lithography

Imprint Lithography is a high-throughput wafer-level process. Using this technique, a dedicated UV-sensitive liquid material, applied to a wafer substrate, can be imprinted by mechanical casting of a stamp and subsequently can be cured with UV-light. Compared to competing alternative techniques, imprint lithography is a low-cost solution for structuring a substrate from nanometer up to millimeter scale.

As wafer level manufacturing processes are favored due to their cost reduction potential, customers in the LED manufacturing market can benefit from an additional advantageous feature offered by imprint techniques. WBS's imprint machines could offer this technology.

Standard stamps for imprint lithography can be very expensive. As a solution to overcome this, WBS implements working stamps with very low cost of ownership to reduce overall costs.

In this approach, the desired structure is transferred firstly from a master stamp to a working stamp. This stamp can then be used for repeated imprinting lithography.

UV Nano Imprint Lithography

A special UV-imprint application is UV-NIL. In this case, the UV-lacquer functions as a photoresist and will no longer be part of the product. Using UV-NIL, a substrate can be nanopatterned. The UV-NIL process differs from the imprinting process in the sense that in the former an imprint is made which serves as a mask for patterning a layer below the resist.

Typically, the UV-NIL process consists of the next steps:

On the substrate a hard mask material is applied and furthermore a UV-NIL resist layer is spin coated on top of this.
The stamp is pressed firmly into the resist. Depending on the UV-NIL technology, the filling of the features is driven by the pressing force or by the capillary force of the UV-lacquer.
When the desired final thickness is reached, the resist is UV-cured. An important aspect is that the underlayer thickness is minimal. After releasing the mold, the remaining underlayer thickness is removed using an UV-ozone etching process. The patterned resist itself now serves as a mask for the subsequent patterning of the hard mask. Usually, this is done by a Plasma ICP DRIE etch.
In the final step, the target material is etched away, which is usually carried out by another Plasma ICP DRIE etch. Then the hard mask is stripped.
Important aspects of this technology are mask selectivity, imprint homogeneity, stamp lifetime and contamination.

Other Variants

The descriptions above apply to most of the UV-imprinting applications, however, it is incomplete. Special variants like UV-imprinting without a substrate (which is more like molding), reversed imprinting (in which the material is first applied and then cured on the mold), step and repeat imprinting (for i.e. mold manufacturing) are other applications that are not further discussed here.