Focus Line Height Measurement for Non-Planar Milled Surfaces
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Solution Overview
Problem
Current methods for determining the shape and dimensions of semiconductor structures in 3D metrology face challenges due to non-planarity of milled surfaces, leading to inaccuracies in 3D reconstruction and critical dimension measurements, especially in high aspect ratio structures.
Innovation Solution
A dual beam device is used to obtain a milled sample with an assumed top surface shape, determine height coordinates, and employ a second beam to measure the actual milling top surface shape using optical interferometry or AFM, enabling accurate determination of structural parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of cross-section surfaces are generated to achieve precise 3D measurement, then measurement precision is improved, but measurement time increases significantly
Solution Approach 1:
The patent performs preliminary action by measuring the top surface shape before conducting the full 3D measurement process. This preliminary measurement enables the system to pre-calculate correction values for surface non-planarity, which are then applied during subsequent measurements. By addressing the surface shape issue in advance, the patent reduces the number of cross-section surfaces needed while maintaining measurement precision, thereby reducing measurement time.
2Device complexity
If the assumed milled top surface shape is used for reconstruction, then device complexity is reduced, but measurement precision deteriorates due to surface non-planarity
Solution Approach 1:
The patent implements feedback by measuring the actual top surface shape and using this information to correct the assumed surface model. The measured surface coordinates are fed back into the reconstruction algorithm to adjust and refine the 3D model, compensating for surface non-planarity effects. This feedback loop ensures high measurement precision without significantly increasing device complexity, as it uses existing measurement capabilities rather than additional hardware.
3Measurement precision
If the sampling raster resolution is reduced below the beam diameter limit, then measurement precision is improved, but the physical limitation of charged particle beam diameter restricts further resolution improvement
Solution Approach 1:
The patent introduces an intermediary approach by using optical interferometry or focus variation methods to measure surface topography. These intermediary measurement techniques bypass the charged particle beam resolution limit by using optical fields instead of particle beams for the specific task of surface shape measurement. The optical measurements provide height information with precision不受限于 the beam diameter, effectively mediating between the beam-based imaging system and the need for higher resolution surface data.
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 allows for precise reconstruction of semiconductor structures by accounting for the actual surface shape, improving measurement accuracy and reducing distortions in 3D imaging.
Implementation Method 1
employ a second beam to measure the actual milling top surface shape using optical interferometry or AFM
Implementation Method 2
employ a second beam to measure the actual milling top surface shape using optical interferometry or AFM
Implementation Method 3
A common way to generate 3D tomographic data from semiconductor samples on nm scale is the so-called slice and image approach elaborated for example by a dual beam device (DBD). In this method, a wafer is destroyed to obtain an inspection sample of block shape.
Data Source
AI summary
A method of operating a dual beam device comprises obtaining a milled sample having an assumed milled top surface shape which was obtained by milling the sample with a first ion beam of the dual beam device, and determining a plurality of height coordinates of the assumed milled top surface shape using a second beam of the dual beam device. The method also comprises determining at least one actual milling top surface shape for the milled sample based on the determined plurality of height coordinates, and determining a parameter of the sample based on the adapted milled top surface shape.