Wide area soft defect localization

A method of testing a semiconductor chip having a surface and plural circuit structures positioned beneath the surface, comprising:

• positioning moveable complementary portions of an irradiation mask for selective irradiation of a series of fractional portions of the chip surface, the irradiation mask comprising a set of overlapping upper mask portions defining a first larger variable aperture and a set of lower mask portions defining a second smaller variable aperture for mitigating diffusion of radiation beyond a target fractional portion of the chip surface area;
• selectively irradiating a series of fractional portions of the surface, the fractional portions defined via the positioning, to perturb respective circuit structures;
• and
• causing the semiconductor chip to undergo tests during the irradiation of the fractional portions to determine if a soft defect exists in the respective circuit structures of any of the fractional portions.