Single Cell Grey Scatterometry Overlay Targets and Their Measurement Using Varying Illumination Parameter(s)

Abstract

Scatterometry overlay (SCOL) measurement methods, systems and targets are provided to enable efficient SCOL metrology with in-die targets. Methods comprise generating a signal matrix by: illuminating a SCOL target at multiple values of at least one illumination parameter, and at multiple spot locations on the target, wherein the illumination is at a NA (numerical aperture) >⅓ yielding a spot diameter <1μ, measuring interference signals of zeroth and first diffraction orders, and constructing the signal matrix from the measured signals with respect to the illumination parameters and the spot locations on the target; and deriving a target overlay by analyzing the signal matrix. The SCOL targets may be reduced to be a tenth in size with respect to prior art targets, as less and smaller target cells are required, and be easily set in-die to improve the accuracy and fidelity of the metrology measurements.

What is claimed is: 
     
         1 . A SCOL target comprising a single cell having periodic structures at a plurality of layers and measuring 2 μm by 2 μm or smaller. 
     
     
         2 . The SCOL target of  claim 1 , wherein the periodic structures are at most four pitch bars wide. 
     
     
         3 . The SCOL target of  claim 2 , wherein the periodic structures are two pitch bars wide. 
     
     
         4 . The SCOL target of  claim 1 , placed in-die on a corresponding wafer. 
     
     
         5 . The SCOL target of  claim 1 , wherein the periodic structures are gratings. 
     
     
         6 . The SCOL target of  claim 5 , further comprising at least one intermediate layer between the plurality of layers. 
     
     
         7 . The SCOL target of  claim 1 , wherein the single cell is configured to be illuminated with a spot diameter less than 1 μm. 
     
     
         8 . The SCOL target of  claim 7 , wherein a numerical aperture for the spot diameter is greater than ⅓. 
     
     
         9 . The SCOL target of  claim 1 , wherein the single cell is configured to be illuminated at multiple spot locations. 
     
     
         10 . The SCOL target of  claim 9 , wherein the multiple spot locations are within a pitch of at least one of the periodic structures. 
     
     
         11 . The SCOL target of  claim 1 , wherein the periodic structures are aligned. 
     
     
         12 . The SCOL target of  claim 1 , wherein the periodic structures are configured to provide zeroth and first order mixing. 
     
     
         13 . The SCOL target of  claim 1 , wherein the periodic structures are configured to provide overlap between the zeroth order and the first order in measured signals from the periodic structures.