Hot Embossing
Hot Embossing Lithography (HEL) is a Nanoimprint Lithography (NIL) method using temperature and pressure control during the process. Once aligned, the stamp is pressed into a thermoplastic polymer to define the desired pattern. At this stage, temperature and pressure is applied in the area underneath the stamp, using a well-designed heat & pressure cycle. After cooling, when the polymer is again below the Glass Transition temperature, the stamp is then lifted up and moved to the next imprint area.
- Unless the substrate is itself a thermoplastic material such as polycarbonate for instance, it is coated with the hot embossing material (thermoplastic resist or polymer) using Spin Coating.
- The stamp is aligned to the substrate. The accuracy of the stamp alignment with respect to the substrate depends upon the application. For some single or first level application, there is no need for alignment; a rough pre-alignment can be sufficient.
- To transfer the stamp patterns into the embossing material, the stamp and eventually the substrate are heated above the glass transition temperature of the embossing material to soften it and to minimize the force required for the polymer to flow into the stamp cavities.
- After the pattern is imprinted into the polymer, the temperature of the substrate and the stamp returns below the Glass Transition Temperature (Tg) of the embossing material and the stamp is separated from the substrate and the embossing material layer; the polymer retain the shape of the stamp patterns.
