Interferometer Phase Shift Mask Pixelated Array Resolution
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Solution Overview
Problem
Conventional phase masks in interferometry, which use 2×2 blocks of pixels, limit the lateral resolution and fail to accurately measure topography in areas with significant pattern frequency content, as they assume constant topography within each block, leading to inaccurate defect detection and surface height determination.
Innovation Solution
A phase shift mask with an array of pixels arranged in repeating horizontal and vertical linear groups, allowing all predetermined phase shifts to be included in each row and column, enabling improved interferometric measurements and defect detection by optimizing pixel groupings based on sample patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 2×2 pixel blocks are used in the phase mask, then the device structure is simple, but the lateral resolution is limited and measurement precision deteriorates in areas with pattern frequency content
Solution Approach 1:
The phase mask pixel array is segmented into multiple independent pixel groups, where each group contains pixels with different phase shifts (0, 90, 180, 270 degrees). This segmentation allows each pixel to contribute independently to the interferometric measurement, enabling single-pixel-spacing resolution while maintaining the ability to capture multiple phase states for accurate topography determination in patterned areas
Solution Approach 2:
Different pixels in the array are assigned different phase shift properties (0, 90, 180, or 270 degrees) based on their local position within pixel groups. This local differentiation of quality enables the system to resolve fine lateral features while providing sufficient phase sampling for accurate measurement in regions with varying pattern frequencies
2Measurement precision
If 2×2 pixel blocks with constant topography assumption are used, then the processing is simple, but defect detection accuracy deteriorates in areas with significant pattern frequency content
Solution Approach 1:
The pixel array is divided into multiple pixel groups, where each group independently samples the interferometric signal at different phase states. This segmentation eliminates the need to assume constant topography across a 2×2 block, as each pixel now provides independent measurement data that can be processed individually to detect defects with high accuracy even in patterned regions
Solution Approach 2:
The patent transitions from spatial blocking (2×2 groups) to a phase-dimension approach where multiple phase states are sampled across the pixel array. This dimensional change from spatial averaging to phase-space sampling enables accurate defect detection by capturing the interferometric signal's phase information at multiple states without being constrained by pattern frequency assumptions
3Measurement precision
If multiple phase samples are obtained by moving the sample or reference surface, then the phase measurement is accurate, but the measurement time increases
Solution Approach 1:
The patent merges the functions of multiple phase measurements into a single instantaneous capture. By assigning different phase shift properties to different pixels in the array, the system simultaneously records multiple phase states across the field of view in one exposure, eliminating the need for sequential mechanical scanning while maintaining the ability to accurately determine surface phase and topography
Solution Approach 2:
The patent shifts from temporal multiplexing (sequential phase measurements over time via mechanical movement) to spatial multiplexing (simultaneous phase measurements across space via pixel array). This dimensional transformation from time-domain sampling to space-domain sampling achieves the same phase measurement accuracy while dramatically improving measurement speed by capturing all phase data in a single shot
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 configuration enhances the resolution along pattern directions, improves defect detection accuracy, and allows for single pixel spacing measurements, reducing the impact of vibrations and pattern complexity on measurement accuracy.
Implementation Method 1
each pixel in the phase shift mask is adapted to produce one of a number of predetermined phase shifts between a test beam and a reference beam
Implementation Method 2
the test beam and reference beam combined to form a combined beam
Data Source
AI summary
An interferometer uses a phase shift mask that includes an array of pixels that are aligned with a corresponding array of pixels of a detector. Each pixel in the phase shift mask is adapted to produce one of a number of predetermined phase shifts between a test beam and a reference beam. For example, the pixels may be linear polarizers or phase delay elements having one of the number of polarizer orientations or phase delays to produce the predetermined phase shifts between the test beam and the reference beam. The pixels in the phase shift mask are arranged in the array to include each of the predetermined phase shifts in repeating pixel groups in rows that are one column wide, columns that are one row high, or blocks of multiple rows and columns.