Micrel, Incorporated

Arthur Lam

Robert W Rumsey

Hiu Fung Ip

Hui F Ip

A method for stitching a first field mask to a second field mask on a wafer includes providing a photomask with a first set of targets and a second set of targets, printing images of the first set of targets and the second set of targets onto the wafer where the photomask is applied to the wafer having no previous alignment marks formed thereon for the photomask to align to. A first set of alignment marks is formed from the first set of targets and a second set of alignment marks is formed from the second set of targets. The method includes aligning a first field mask to the first set of alignment marks and aligning a second field mask to the second set of alignment marks. The images of the first field mask and the second field mask are thereby stitched together on the wafer.

Single field zero mask for increased alignment accuracy in field stitching

A single field photomask includes a first set of targets formed on a first side of the photomask, and a second set of targets formed on a second side of the photomask, opposite the first side. In operation, the photomask is to be applied to a wafer without any alignment marks. The photomask forms a first set of alignment marks in the wafer from the first set of targets, and the photomask further forms a second set of alignment marks in the wafer from the second set of targets. The first set of alignment marks is used to align to a first field mask and the second set of alignment marks is used to align to a second field mask to stitch an image of the first field mask to an image of the second field mask.

A test structure pattern includes a first comb, a second comb, and a serpentine line. The first comb includes a first set of tines of the same orientation. The second comb includes a second set of tines of the same orientation that are interdigitated with the first set of tines. The serpentine line runs between the interdigitated tines of the first metal comb and the second metal comb. The test structure pattern forms a first metal comb, a second metal comb, and a serpentine metal line on a die. Print quality and resolution is tested by checking for electrical continuity in the serpentine metal line and bridging between the serpentine metal line and one of the first metal comb and the second metal comb.

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Fremont, CA, United States of America

Arthur Lam