Lithographic Alignment System Deformation Separation
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Solution Overview
Problem
Conventional lithographic apparatuses face challenges in accurately determining the position of alignment marks on substrates due to substrate and alignment mark deformations, leading to overlay errors during the exposure of subsequent layers.
Innovation Solution
A lithographic apparatus that performs multiple alignment mark position measurements using different parameters, processes these measurements to separate substrate deformation and alignment mark deformation effects, and uses a matrix equation to determine the actual substrate deformation, enabling precise alignment of the patterned radiation beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single alignment mark position measurement is performed using conventional methods, then the measurement process is simple and fast, but the measurement precision is insufficient due to substrate and alignment mark deformations
Solution Approach 1:
The alignment measurement process is segmented into multiple independent measurements using different parameters (e.g., different wavelengths, polarizations, or focal positions). Each measurement provides partial information about the alignment mark position, and the combination of these segmented measurements enables accurate separation of substrate deformation from alignment mark deformation effects.
Solution Approach 2:
The invention changes measurement parameters (such as wavelength, polarization state, or focal position) to perform multiple alignment mark position measurements. By varying these parameters, the system captures different aspects of the alignment mark and substrate interaction, enabling precise determination of actual alignment mark position despite deformations.
2Measurement precision
If multiple alignment mark position measurements are performed using different parameters, then the measurement precision improves, but the measurement time and processing complexity increase
Solution Approach 1:
The system performs preliminary measurements using multiple parameters in quick succession before the substrate deformation changes significantly. This preliminary action captures the deformation state at a specific moment, allowing accurate alignment mark position determination without requiring excessively long measurement times.
Solution Approach 2:
The invention implements a feedback mechanism where the results from multiple measurements are processed to determine the actual alignment mark position, which then provides feedback for adjusting the exposure alignment. This feedback loop enables the system to efficiently use the information from multiple measurements to achieve precise alignment.
3Manufacturing precision
If alignment measurements are performed without separating substrate deformation and alignment mark deformation effects, then the measurement process is simple, but overlay errors occur due to inaccurate alignment mark position determination
Solution Approach 1:
The invention extracts and separates the substrate deformation effect from the alignment mark deformation effect by analyzing multiple measurements taken with different parameters. By isolating these separate effects, the system can determine the true alignment mark position on the deformed substrate, enabling accurate overlay alignment.
Solution Approach 2:
The invention exploits the asymmetry in how substrate deformation and alignment mark deformation affect measurements taken with different parameters. Since these two deformation sources affect different measurement parameters differently, the system can use this asymmetric response pattern to distinguish and separate the two effects, achieving accurate alignment mark position determination.
Data Source
AI summary
A lithographic apparatus is described, the apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the apparatus further comprises an alignment system configured to perform, for one or more alignment marks that are present on the substrate: —a plurality of alignment mark position measurements for the alignment mark by applying a respective plurality of different alignment measurement parameters, thereby obtaining a plurality of measured alignment mark positions for the alignment mark; the apparatus further comprising a processing unit, the processing unit being configured to: —determine, for each of the plurality of alignment mark position measurements, a positional deviation as a difference between an expected alignment mark position and a measured alignment mark position, the measured alignment mark position being determined based on the respective alignment mark position measurement; —define a set of functions as possible causes for the positional deviations, the set of functions including a substrate deformation function representing a deformation of the substrate, and at least one mark deformation function representing a deformation of the one or more alignment marks; —generating a matrix equation PD=M*F whereby a vector PD comprising the positional deviations is set equal to a weighted combination, represented by a weight coefficient matrix M, of a vector F comprising the substrate deformation function and the at least one mark deformation function, whereby weight coefficients associated with the at least one mark deformation function vary depending on applied alignment measurement; —determining a value for the weight coefficients of the matrix M; —determining an inverse or pseudo-inverse matrix of the matrix M, thereby obtaining a value for the substrate deformation function as a weighted combination of the positional deviations. —applying the value of the substrate deformation function to perform an alignment of the target portion with the patterned radiation beam.