SHADOW MASKS AND CONTACT
MASKS FOR UV PHOTOLITHOGRAPHY

A shadow mask is used for defining the areas of a device and creating microstructures on it with precision by masking or covering part of the target surface. When a design is desired on a surface of interest, such as a silicon wafer or other substrate, a deposition process is performed using a photolithographic mask or UV photolithography and a lift-off process is performed directly.

SHADOW MASK

The shadow masks, fabricated by Scriba, represent a quick and economically cheaper alternative, compared to the application of a photolithographic process, when the size of the masks is not less than 10 µm.

Furthermore, it is good to take into consideration that the geometries produced with the laser allow to reach smaller dimensions, clearer edges and tighter tolerances than those that can be obtained by means of a chemical incision.

Another important aspect is the material with which you can create shadow masks. They can be made with unconventional materials that prevent the contamination of the substrate being studied.

Limitations related to laser production include:

  • The maximum process tolerance of ± 10 μm.
  • The minimum width of the structures that can be realized equal to 50 μm.

When we create a shadow mask, we can also make supports or frames to facilitate manipulation and alignment with the device on which they are to be integrated.

IN SCRIBA WE CAN ALSO MAKE CONTACT PHOTOLITHOGRAPHIC MASKS.

There are several ways to create a pattern on a photoresist. It is possible to write directly on the photoresist, for example using a laser, but the most common method involves the use of photolithography.

During a photolithographic process, different steps are required: first a photoresist is spin coated on a substrate and then to transfer the pattern from the mask to the substrate, a mask aligner machine is adopted. The photoresist is exposed to light radiation by means of a lamp, using selected wavelengths. In this way there is an activation of a photoactive component inside the resin. This activation will modify the local solubility properties of the resin making it soluble or not in a solvent called developer.

A photoresist is defined as positive if the exposed parts are solubilized after irradiation and denoted as negative if the unexposed parts are solubilized, for example Microchem SU-8. At the end of these steps the 3D pattern is revealed.

Basically, there are two types of photolithography masks, the rigid photolithographic masks in quartz or borosilicate glass and the soft photolithographic plastic masks.

At Scriba, we can create masks according to the customer’s requirements, which can provide the CAD drawing directly in .dxf format. Or alternatively we can also provide design support. Scriba’s team will be happy to discuss with the client of his project to guarantee assistance in every phase, from the design to the realization of the mask, always taking into consideration the final application of the client.


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