Measurement apparatus and a method for determining a substrate grid

A method for determining a value for a process parameter measurement error obtained from measurement of a substrate subject to a manufacturing process and comprising a target having a process distortion, the process parameter measurement error being a result of the process distortion, the method comprising:

• obtaining alignment asymmetry data describing asymmetry in one or more alignment marks used for aligning the substrate;
• obtaining a model correlating alignment asymmetry data to the process parameter measurement error;
• and
• using the alignment asymmetry data and the model to obtain the value of the process parameter measurement error.

A computer program product comprising a non-transitory computer-readable medium having instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to at least:

• obtain alignment asymmetry data describing asymmetry in one or more alignment marks used for aligning a substrate;
• obtain a model correlating alignment asymmetry data to a process parameter measurement error obtained from measurement of the substrate subject to a manufacturing process, the substrate comprising a target having a process distortion and the process parameter measurement error being a result of the process distortion;
• and
• use the alignment asymmetry data and the model to obtain a value of the process parameter measurement error.

The lithocell of claim 36, wherein:

• the lithographic apparatus is configured to perform alignment measurement to obtain the alignment asymmetry data;
• the metrology apparatus is configured to measure the process parameter;
• and
• the instructions of the computer program product are further configured to cause the computer system to correct the measured process parameter using the value of the process parameter measurement error.