Interferometric End Point Detection for Focused Ion Beam Fabrication
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Solution Overview
Problem
Conventional FIB processing systems face challenges in accurately estimating the remaining surface thickness (RST) of silicon substrates during back-side silicon integrated circuit modification, often leading to unintentional damage of circuitry due to subjective estimation methods or time-consuming and risky ex-situ measurements.
Innovation Solution
A FIB system equipped with a broadband IR light source, a narrowband IR light source, an IR optical detector, and an IR interferometer that provides real-time, in-situ navigational data, including two-dimensional IR imagery and layer thickness information, allowing operators to accurately control the ion beam and navigate the processing area while monitoring the RST.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If subjective estimation of RST by operator is used, then the process is simple and fast, but the accuracy of RST measurement deteriorates
Solution Approach 1:
The patent replaces the mechanical/optical microscopy system with interferometric measurement system. The FIB tool integrates an interferometer that uses light interference patterns to precisely measure the depth of etched features and remaining surface thickness in real-time, eliminating subjective operator estimation and providing objective, high-precision measurements during the back-side silicon processing.
Solution Approach 2:
The patent implements real-time feedback by continuously monitoring the etching process through interferometric measurements. The system provides live feedback on RST values to the operator, allowing dynamic adjustment of etching parameters to prevent circuit damage while maintaining processing efficiency.
2Measurement precision
If ex-situ measurements of RST are performed, then the measurement accuracy improves, but the time consumption increases and circuit damage risk appears
Solution Approach 1:
The patent performs preliminary action by establishing the interferometric measurement system within the FIB vacuum chamber before back-side processing begins. The system is pre-calibrated and ready to provide continuous RST measurements throughout the etching process, eliminating the need for time-consuming removal and separate measurement operations.
Solution Approach 2:
The patent merges the measurement function with the processing function by integrating the interferometer directly into the FIB tool. This combination allows simultaneous etching and real-time depth measurement to occur within the same vacuum chamber environment, eliminating the need for separate measurement steps and associated handling risks.
3Measurement precision
If pilot hole technique is used, then in-situ measurement capability is achieved, but the risk of circuit damage increases or measurement accuracy decreases
Solution Approach 1:
The patent implements a universal measurement system that can measure RST at any location on the back-side silicon substrate without requiring pilot holes. The interferometer scans the surface and provides depth measurements across the entire processing area, making the measurement capability independent of circuit layout constraints and eliminating the need for benign areas for pilot hole etching.
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
Enables precise control of the FIB processing, reducing the risk of circuit damage by providing real-time thickness data and imagery, thereby improving the accuracy of back-side silicon processing and minimizing fabrication errors.
Implementation Method 1
an IR interferometer that receives the narrowband IR light reflected from the target and outputs data indicative of a thickness of at least one layer of material at the target
Implementation Method 2
The FIB emitter emits a focused beam of ions toward a target in order to perform additive or subtractive processing of the target. For example, the FIB emitter emits the focused beam of ions such that the beam removes portions of a surface of the target over time.
Data Source
AI summary
Various technologies for providing an operator of a focused ion beam (FIB) system with navigational and processing data are described herein. An exemplary system includes a broadband light source and a narrowband light source that emit light to a target of the FIB. An optical detector receives reflections of the broadband light from the target and outputs data that is used to generate two-dimensional images of the target in a region near a location of incidence of the FIB at the target. An interferometer receives reflections of the narrowband light from the target and outputs data indicative of an interference pattern of the narrowband reflections. A computing device computes a thickness of one or more material layers that make up the target based upon the interference pattern. A two-dimensional image of the target and an indication of the computed thickness are then displayed to the operator of the FIB.