Method and apparatus for alignment and overlay of submicron lithographic features
OwnerSteven R. J. Brueck, Saleem H. Zaidiinventors
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Abstract
The method of measuring the relative between submicron lithographic features on a wafer having thereon a reference characteristic associated with a reference submicron grating structure of periodicity p.sub.1 onto which there may be cast from a reticle the image of a projected submicron grating structure of different periodicity p.sub.2 comprising measuring the extent of change in a moire fringe pattern produced by the superposition of the two grating structures on the wafer.
Claims13
The method of measuring the relative displacement between submicron lithographic features on a wafer after lithographic exposure of the features on the wafer, said wafer having thereon a reference characteristic associated with a reference submicron grating structure of periodicity p.sub.1 onto which there may be cast from a reticle the image of a projected submicron grating structure of periodicity p.sub.2, the periodicity p.sub.2 being sufficiently different from that of p.sub.1 that at least a substantial portion of a moire fringe pattern between the two grating periods p.sub.1 and p.sub.2 is formed across the spatial extent of the grating structures when superimposed, comprising:
- a) measuring the extent of spatial change in the moire fringe pattern produced by the relative displacement of the two grating structures on the wafer, the extent of spatial change in the moire fringe pattern being greater than the extent of relative displacement of the two grating structures when superimposed, thereby providing for measurement purposes amplification of the actual extent of relative displacement of said two grating structures.
Apparatus for enabling the measurement of the relative displacement between the submicron lithographic features established on a wafer through the photolithographic projection of an image from a reticle comprising:
- a) a first submicron grating structure on said reticle having a periodicity p.sub.1, and
- b) a second submicron grating structure on said wafer having a periodicity p.sub.2 different from p.sub.1 such that at least a substantial portion of a moire fringe pattern between the two grating periods is formed across the spatial extent of the grating structures when superimposed, whereby when the image on said reticle is projected is projected onto said wafer, a moire fringe is produced and, if there is displacement of the iamge from its desired position on the wafer, the moire fringe is changed in a manner and degree amplifying the extent to which the image is relatively displaced.
Dependencies are inferred from the claim text.