Dual-Beam Wafer Cross-Section Imaging with Adjustable Working Distance
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Solution Overview
Problem
Current dual beam devices face challenges in achieving high imaging resolution for 3D circuit pattern inspection of semiconductor wafers, particularly due to geometric constraints that limit the optimization of working distances for charged particle beam imaging columns.
Innovation Solution
The method involves providing a focused ion beam (FIB) column and a charged particle beam (CPB) imaging column in a coincidence arrangement, where the working distance of the CPB imaging column is reduced temporarily to enhance imaging resolution, while maintaining the coincidence arrangement for milling to ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the working distance of the CPB imaging column is reduced to enhance imaging resolution, then imaging resolution is improved, but the coincidence arrangement for milling cannot be maintained
Solution Approach 1:
The system dynamically adjusts the working distance of the CPB imaging column between two states: a first working distance that maintains the coincidence arrangement for accurate milling, and a second (reduced) working distance that enhances imaging resolution. This dynamic adjustment allows the system to optimize for either milling accuracy or imaging resolution depending on the operational phase.
Solution Approach 2:
The method employs periodic switching between two operational modes: during milling operations, the system uses the first working distance to maintain coincidence arrangement and ensure milling accuracy; during imaging operations, the system switches to the second working distance to achieve enhanced imaging resolution. This periodic action between different working distances resolves the contradiction between maintaining milling accuracy and achieving high imaging resolution.
2Reliability
If the working distance of the CPB imaging column is maintained at a fixed value, then the coincidence arrangement is maintained, but imaging resolution cannot be optimized
Solution Approach 1:
The system transitions from a static fixed working distance to a dynamic adjustable working distance. The working distance is now determined based on the operational phase: set to a first value during milling to maintain coincidence arrangement, and set to a second (reduced) value during imaging to optimize resolution. This dynamic approach eliminates the trade-off between maintaining coincidence arrangement and optimizing imaging resolution.
Solution Approach 2:
The method changes the working distance parameter of the CPB imaging column based on operational requirements. By adjusting this critical parameter between two distinct values (first working distance for milling, second working distance for imaging), the system can optimize both milling accuracy and imaging resolution at different times, resolving the contradiction between maintaining fixed geometric arrangement and achieving optimized imaging performance.
3Measurement precision
If the sampling raster resolution is reduced to improve lateral measurement resolution, then measurement precision is improved, but the charged particle beam diameter becomes the limiting factor
Solution Approach 1:
The patent replaces the conventional charged particle beam (such as electron beam) imaging system with a focused ion beam (FIB) imaging column. This substitution allows the use of ion beams which can achieve smaller effective diameters and better lateral measurement resolution without being constrained by the same physical limitations as electron beams. The FIB system enables direct imaging at the sample location with improved lateral resolution.
Solution Approach 2:
The focused ion beam column serves multiple functions: it performs both the milling (material removal) and the imaging functions. This multi-functionality allows the system to use the same beam for both processes, enabling the imaging function to benefit from the small beam diameter inherent to FIB systems while maintaining the coincidence arrangement for accurate correlation between milling and imaging.
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 improved imaging resolution without destroying the wafer, enabling more precise measurement and analysis of semiconductor structures, while maintaining the accuracy of the milling process.
Implementation Method 1
removing a cross section surface layer of measurement site of a wafer using the FIB column
Implementation Method 2
imaging the new cross section at the measurement site of the wafer with the CPB imaging column
Data Source
AI summary
A method comprises: providing FIB and CPB columns with FIB and CPB optical axes coinciding at a wafer surface; in the coincidence arrangement, removing a cross section surface layer of a measurement site of a wafer using the FIB column to make a new cross section accessible for imaging; reducing a working distance between the CPB imaging column and the wafer surface in a direction along the axis of the CPB imaging column; imaging the new cross section at the measurement site of the wafer with the CPB imaging column at the reduced working distance and thus not in the coincidence arrangement; and increasing the working distance between the CPB imaging column and the wafer surface in the direction along the axis of the CPB imaging column until the coincidence arrangement is reached.