Measuring a Process Parameter for a Manufacturing Process Involving Lithography

Abstract

There is disclosed a method of measuring a process parameter for a manufacturing process involving lithography. In a disclosed arrangement the method comprises performing first and second measurements of overlay error in a region on a substrate, and obtaining a measure of the process parameter based on the first and second measurements of overlay error. The first measurement of overlay error is designed to be more sensitive to a perturbation in the process parameter than the second measurement of overlay error by a known amount.

1 . A substrate comprising:
 target structures comprising a first target structure and a second target structure configured such that a first measurement of overlay error using the first target structure is more sensitive to a perturbation in a process parameter for a manufacturing process involving lithography than a second measurement of overlay error using the second target by a known amount.   
     
     
         2 . The substrate of  claim 1 , wherein the process parameter comprises an asymmetry in a feature of a target structure formed on the substrate by a lithographic process. 
     
     
         3 . The substrate of  claim 2 , wherein the asymmetry in a feature comprises an asymmetry in the cross-sectional shape of a line or trench in a line grating of the target structure, the asymmetry being defined with respect to a mirror plane cutting through the center of the line or trench when viewed along the line or trench, and extending perpendicular to the plane of the grating. 
     
     
         4 . The substrate of  claim 3 , wherein the asymmetry in a feature comprises an asymmetry in the angles of side-walls defining a line in the line grating relative to a normal to the plane of the grating. 
     
     
         5 . The substrate of  claim 3 , wherein the asymmetry in a feature comprises a tilt in the floor of a trench formed between lines of the line grating. 
     
     
         6 . The substrate of  claim 1 , wherein the first and second target structures each comprise a line grating. 
     
     
         7 . The substrate of  claim 1 , wherein the process parameter comprises a variation from a reference value of one or more of the following: etch depth of a feature formed on the substrate, thickness of a layer or feature formed on the substrate, relative permittivity of material forming a layer or feature on the substrate, or refractive index of material forming a layer or feature on the substrate. 
     
     
         8 . A substrate comprising:
 a first target structure; and   a second target structure,   wherein the first and second target structures comprise line gratings with differently biased overlay offsets, and   wherein the first and second target structures are configured such that a first measurement of overlay error using the first target structure is more sensitive to a perturbation in a process parameter for a manufacturing process involving lithography than a second measurement of overlay error using the second target by a known amount.   
     
     
         9 . The substrate of  claim 8 , wherein the first target structure comprises a first line grating with a bias of +d and a second line grating with a bias of −d. 
     
     
         10 . The substrate of  claim 8 , wherein the second target structure comprises a first line grating with a bias of +d and a second line grating with a bias of −d. 
     
     
         11 . The substrate of  claim 8 , wherein the process parameter comprises an asymmetry in a feature of a target structure formed on the substrate by a lithographic process. 
     
     
         12 . The substrate of  claim 11 , wherein the asymmetry in a feature comprises an asymmetry in the cross-sectional shape of a line or trench in a line grating of the target structure, the asymmetry being defined with respect to a mirror plane cutting through the center of the line or trench when viewed along the line or trench, and extending perpendicular to the plane of the grating 
     
     
         13 . The substrate of  claim 12 , wherein the asymmetry in a feature comprises an asymmetry in the angles of side-walls defining a line in the line grating relative to a normal to the plane of the grating. 
     
     
         14 . The substrate of  claim 12 , wherein the asymmetry in a feature comprises a tilt in the floor of a trench formed between lines of the line grating. 
     
     
         15 . The substrate of  claim 8 , wherein the process parameter comprises a variation from a reference value of one or more of the following: etch depth of a feature formed on the substrate, thickness of a layer or feature formed on the substrate, relative permittivity of material forming a layer or feature on the substrate, refractive index of material forming a layer or feature on the substrate. 
     
     
         16 . A lithographic apparatus comprising:
 an illumination system arranged to illuminate a pattern; and   a projection optical system arranged to project an image of the pattern onto a substrate,   wherein the substrate comprises a first target structure and a second target structure configured such that a first measurement of overlay error using the first target structure is more sensitive to a perturbation in a process parameter for a manufacturing process involving lithography than a second measurement of overlay error using the second target by a known amount, and   wherein the lithographic apparatus is arranged to use the process parameter in applying the pattern to the substrate or further substrates.   
     
     
         17 . The lithographic apparatus of  claim 16 , wherein the process parameter comprises an asymmetry in a feature of a target structure formed on the substrate by a lithographic process. 
     
     
         18 . The lithographic apparatus of  claim 17 , wherein the asymmetry in a feature comprises an asymmetry in the cross-sectional shape of a line or trench in a line grating of the target structure, the asymmetry being defined with respect to a mirror plane cutting through the center of the line or trench when viewed along the line or trench, and extending perpendicular to the plane of the grating 
     
     
         19 . The lithographic apparatus of  claim 18 , wherein the asymmetry in a feature comprises an asymmetry in the angles of side-walls defining a line in the line grating relative to a normal to the plane of the grating. 
     
     
         20 . The lithographic apparatus of  claim 18 , wherein the asymmetry in a feature comprises a tilt in the floor of a trench formed between lines of the line grating.