Photolithography is used to create a pattern on a substrate by shining light from a light source onto a photoresist that coats the surface of the substrate through a photomask and is followed by a development phase.

Depending on the complexity of a device’s design, various deposition, etching and lithography processes can be cycled through many times. This could mean that more than one photolithography stage is required, potentially dozens, and each iteration could require a new mask.

Each mask used has to be aligned perfectly to the previously processed layer if the final device is to operate as desired. To do this, photomasks are often made to feature alignment marks, but to assist with accuracy, mask aligners are commonly used to ensure things line up. These mask aligning systems also offer a great deal of control over the exposure settings and conditions in which the photolithography process takes place.