Glancing Angle Milling for 3D IC Defect Analysis
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Solution Overview
Problem
Current dual beam systems face challenges in performing accurate three-dimensional defect analysis of nanoscale features due to reduced signal-to-noise ratios and the need for multiple cross-sections, which are time-consuming and may miss defects, especially in deep or buried features within 3D IC structures.
Innovation Solution
The method involves glancing angle milling, where the focused ion beam is oriented at a small angle (no greater than 10°) to the sample surface, allowing for deeper exposure on one end and enabling the formation of successive planar cross-section views that can be reconstructed into a three-dimensional model, along with the creation of three-dimensional fiducials for precise imaging and beam placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional orthogonal milling is used to expose cross-sections, then the milling process is straightforward and easy to control, but multiple cross-sections must be taken which is time-consuming and may miss defects
Solution Approach 1:
The patent transitions from conventional orthogonal cross-sectional milling to glancing angle milling, where the ion beam is directed at a shallow angle (e.g., 5-10 degrees) relative to the sample surface. This dimensional change in beam orientation allows the ion beam to travel along the surface and expose buried features in a single operation, eliminating the need for multiple cross-sections while improving defect detection reliability.
Solution Approach 2:
The patent performs preliminary glancing angle milling to expose the entire depth of buried features in a single preparatory step before imaging. By pre-exposing the full depth range of interest in one operation, the system eliminates the need for sequential cross-sectioning, thereby improving both productivity and reliability.
2Reliability
If multiple cross-sections are taken to ensure defect coverage, then defect detection reliability improves, but analysis time increases significantly
Solution Approach 1:
By changing the beam orientation from orthogonal to glancing angle, the system exposes the entire depth range of buried features in a single operation. This dimensional change allows complete defect coverage without requiring multiple cross-sections, thereby eliminating time loss while maintaining high reliability.
Solution Approach 2:
The patent merges multiple cross-sectional exposures into a single glancing angle mill operation. By combining the functionality of multiple sequential cross-sections into one continuous operation, the system achieves complete defect coverage without the time penalty of repeated milling and repositioning.
3Ease of manufacture
If conventional fiducials are used for beam placement, then the fiducial creation is simple, but the fiducials are not optimized for tilted or glancing beam operations
Solution Approach 1:
The patent creates fiducials with specific local qualities optimized for glancing angle operations. Instead of using conventional fiducials designed for orthogonal beams, the system forms fiducials with dimensions, shapes, and orientations specifically tailored to provide optimal contrast and detectability at shallow beam angles, thereby improving measurement precision.
Solution Approach 2:
The patent changes the parameters of fiducial design and formation to suit glancing angle operations. This includes modifying fiducial size, shape, orientation, and material composition, as well as changing the formation method (e.g., using focused ion beam deposition or milling at specific angles) to create fiducials that provide optimal reference signals for beam placement accuracy.
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 reduces the need for multiple milling operations, enhances the accuracy of defect analysis, and allows for faster characterization of complex structural failures by combining measurements from different depths, improving the vertical resolution and enabling precise determination of feature depths within nanoscale structures.
Implementation Method 1
a focused ion beam (FIB) exposes a cross section
Implementation Method 2
depositing a material on face 502 using electron beam 250 or ion beam 218 and known deposition methods
Implementation Method 3
detecting the interaction of the electron beam with the second surface to form images of the cross sections
Data Source
AI summary
A method for analyzing a sample with a charged particle beam including directing the beam toward the sample surface; milling the surface to expose a second surface in the sample in which the end of the second surface distal to ion source is milled to a greater depth relative to a reference depth than the end of the first surface proximal to ion source; directing the charged particle beam toward the second surface to form one or more images of the second surface; forming images of the cross sections of the multiple adjacent features of interest by detecting the interaction of the electron beam with the second surface; assembling the images of the cross section into a three-dimensional model of one or more of the features of interest. A method for forming an improved fiducial and determining the depth of an exposed feature in a nanoscale three-dimensional structure is presented.