The material is exposed to ultraviolet light through a mask patterned with the outlines of cells.

ECONOMIST: REPORTS

In a process similar to printing a photograph, engineers beam high-powered light through a mask-like image of the chip, creating a duplicate on a silicon wafer.

FORBES: Trick of the Light

This involves shining light through a patterned mask and on to the surface of a chip, so as to change the chemical properties of the exposed parts of that chip.

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Obviously at 400 feet it's really quite dark but at the surface it starts off being very very light, even without a mask I can tell that.

BBC: Breakfast with Frost

It doesn't take much to tear off their flimsy mask of sweetness and light.

CENTERFORSECURITYPOLICY: Unmasking the "International Community"

Bring along an eye mask to block more light.

CNN: Sleep tips for the road-weary

The mask is designed so that light passing through its thickest region is slowed by exactly two cycles compared with that passing through its thinnest.

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