Lithography Test Pattern Monitoring for Focus and Dose Offsets
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Solution Overview
Problem
The semiconductor industry faces challenges in accurately monitoring and controlling lithography process parameters, particularly focus and dose variations, which affect the precision of feature formation on shrinking IC geometries, leading to increased complexity and costs.
Innovation Solution
A method involving the use of a test pattern with asymmetric and symmetric diffraction properties to determine lithography parameter offsets, allowing for precise adjustments in focus and dose during the exposure process, utilizing a control system to modify exposure parameters based on measurements from a scanning electron microscope.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photolithographic masks with transmissive and reflective regions are used to define IC features, then pattern transfer precision is improved, but manufacturing complexity increases due to multiple exposure steps and process parameter control requirements
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the lithography system using test patterns with known geometric features before production exposure. This allows determination of system-specific optical parameters (such as illumination coherence, numerical aperture, and wavelength) in advance, so that these parameters are stored and reused during actual IC manufacturing without requiring repeated measurements, thereby reducing process complexity while maintaining precision
Solution Approach 2:
The patent uses test patterns as simplified copies or representations of the actual IC circuit patterns. These test patterns contain representative geometric features (lines, spaces, corners) that replicate the critical dimension challenges of production patterns but are easier to manufacture and measure. By characterizing the lithography system using these test pattern copies, the complex production patterns can be exposed with optimized parameters without directly measuring each production pattern
2Quantity of substance
If multiple photoresist layers and masks are used to create layered circuit features, then functional density is improved, but process control difficulty increases due to cumulative parameter variations
Solution Approach 1:
The patent implements feedback by measuring actual critical dimensions of test patterns after each lithography exposure step and using these measurements to adjust subsequent exposure parameters. The system continuously monitors process variations and provides corrective feedback to maintain consistent feature dimensions across multiple layers, compensating for cumulative parameter variations in multi-layer processes
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting lithography exposure parameters (such as exposure dose, focus position, and illumination conditions) based on measured deviations from target critical dimensions. This allows real-time optimization of each exposure step in the multi-layer process to account for variations introduced by previous layers, maintaining overall process control
3Manufacturing precision
If lithography system parameters such as focal position are tightly controlled to maintain feature precision, then manufacturing precision is improved, but measurement and adjustment time increases
Solution Approach 1:
The patent applies preliminary action by performing comprehensive lithography system characterization using test patterns before production runs. This preliminary measurement establishes baseline parameters (optical coherence, numerical aperture, wavelength, focus characteristics) that are stored in memory and reused for subsequent production exposures, eliminating the need to repeatedly measure these stable system parameters and significantly reducing measurement time while maintaining precision
Solution Approach 2:
The patent uses test patterns as simplified copies that contain all necessary information about system performance but require much less measurement and analysis time compared to actual IC patterns. By characterizing the system using these representative test pattern copies, the full complexity of production pattern measurement is avoided while still obtaining all necessary parameter information
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate monitoring and adjustment of lithography parameters to within nanometer scales, improving the precision and efficiency of IC feature formation, reducing the complexity and cost associated with maintaining optimal process conditions.
Implementation Method 1
a test pattern is provided and exposed with asymmetric illumination to form a test pattern structure. The test pattern structure is measured to determine an amount of pattern offset. The amount of pattern offset is correlated to a defocus amount
Implementation Method 2
The test pattern is provided and exposed with asymmetric illumination to form a test pattern structure
Data Source
AI summary
A method of performing a lithography process includes providing a test pattern. The test pattern includes a first set of lines arranged at a first pitch, a second set of lines arranged at the first pitch, and further includes at least one reference line between the first set of lines and the second set of lines. The test pattern is exposed with a radiation source providing an asymmetric, monopole illumination profile to form a test pattern structure on a substrate. The test pattern structure is then measured and a measured distance correlated to an offset of a lithography parameter. A lithography process is adjusted based on the offset of the lithography parameter.