Focused Ion Beam Milling Imaging via Parallel Scanning
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Solution Overview
Problem
Current methods for milling and imaging semiconductor wafers using Focused Ion Beam (FIB) technology do not effectively capture the image of the milled face, leading to suboptimal imaging quality due to unwanted side effects like damage to fiducials and inefficient detection of radiation from deeper trench portions.
Innovation Solution
The method involves directing a focused particle beam substantially parallel to the work piece's face, scanning a single curve to mill material at varying distances, and storing data from multiple scans to define the face's direction, allowing for improved imaging of the milled surface by detecting radiation generated during milling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a focused ion beam is directed perpendicular to the wafer surface for milling, then milling efficiency is improved, but imaging quality of the milled face deteriorates due to cross-talk between surface and deeper portions
Solution Approach 1:
The patent inverts the conventional perpendicular beam direction to a substantially parallel beam direction relative to the wafer surface. This inversion resolves the contradiction by enabling both efficient milling and high-quality imaging simultaneously, as the parallel orientation reduces cross-talk between different depths while maintaining milling effectiveness through the curved scanning pattern.
Solution Approach 2:
The patent introduces a curved scanning pattern that adds a dimensional component to the beam path. Instead of simple linear or raster scanning, the beam follows a curved trajectory that optimizes both milling removal rate and imaging signal quality, effectively utilizing spatial dimensionality to resolve the efficiency-quality trade-off.
2Measurement precision
If the beam is directed parallel to the face with curved scanning, then imaging quality is improved by reducing cross-talk, but milling speed may deteriorate
Solution Approach 1:
The patent employs periodic scanning of the curved path, repeatedly traversing the same trajectory multiple times. This periodic action accumulates material removal over multiple passes while maintaining consistent imaging quality, thereby achieving both high imaging precision and acceptable milling throughput through iterative processing.
Solution Approach 2:
The curved scanning pattern ensures continuous engagement of the beam with the workpiece material along the optimized trajectory. This continuous useful action maximizes material removal efficiency during each pass while the parallel beam orientation maintains low cross-talk, resolving the speed-quality contradiction through sustained effective processing.
3Measurement precision
If repeated scanning is performed to improve signal-to-noise ratio, then imaging precision is improved, but processing time increases
Solution Approach 1:
The patent inverts the conventional raster scanning approach to a repeated curved scanning pattern. This inversion achieves superior signal-to-noise ratio improvement per unit time because the curved trajectory concentrates beam exposure on the face region of interest, reducing unnecessary scanning of irrelevant areas and thereby improving imaging precision without proportional time penalty.
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 enhances imaging quality by reducing cross-talk between the milled surface and deeper portions, enabling more accurate representation and visualization of the milled face, which is essential for precise end-point detection and further processing.
Implementation Method 1
milling in this context includes sputtering and etching
Implementation Method 2
milling in this context includes sputtering and etching
Implementation Method 3
acquiring a signal from a detector detecting radiation emerging from the work piece in response to the particle beam impinging on the work piece
Implementation Method 4
a layer of this fluid adsorbs to the surface of the wafer
Data Source
AI summary
Dual beam instruments, comprising a Scanning Electron Microscope (SEM) column for imaging and a Focused Ion Beam (FIB) column for milling, are routinely used to extract samples (lamellae) from semiconductor wafers. By observing the progress of the milling with the SEM column, end pointing of the milling process can be performed.The invention offers an alternative solution to this problem, in which an instrument with only a FIB column is used.For milling a lamella to its final thickness of, for example, 30 nm, the focused ion beam 100, is scanned repeatedly along the lamella. It is found that while milling the lamella a signal can be derived from the lamella that is sufficient for end pointing. No additional electron beam for inspection is needed.