Multiple-Pass Optical Metrology for 3D Semiconductor Structures
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Solution Overview
Problem
Current optical metrology systems face challenges in accurately measuring critical dimensions and film thicknesses of semiconductor structures due to limitations in sensitivity, precision, and throughput, especially as devices scale to smaller dimensions and incorporate complex three-dimensional geometries and opaque material layers.
Innovation Solution
Implementing multiple pass optical measurements with an optical subsystem configured to incident the measurement beam multiple times on the semiconductor wafer, combined with the use of optical modulation elements to enhance measurement sensitivity and break correlations between critical parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single pass optical measurements are used, then measurement throughput is maintained, but measurement sensitivity and accuracy are insufficient for complex three-dimensional semiconductor structures
Solution Approach 1:
The patent implements multiple nested optical passes through the semiconductor structure by configuring mirrors and beam paths to traverse the measurement site multiple times. Each pass contributes additional signal information, effectively nesting the measurement process within itself to amplify sensitivity without requiring separate measurement systems.
Solution Approach 2:
The measurement beam continuously interacts with the semiconductor structure across multiple passes rather than a single discrete event. The optical system maintains continuous illumination and detection throughout the multiple passes, maximizing information extraction from each photon interaction and improving signal-to-noise ratio.
2Measurement precision
If measurement beam interacts with structure multiple times, then measurement sensitivity is amplified, but optical path complexity increases
Solution Approach 1:
The optical modulation element serves multiple functions simultaneously: it modulates the measurement beam to encode structural information, provides reference signals for correlation analysis, and enables differentiation between multiple passes. This multi-functionality reduces the need for separate components for each measurement function.
Solution Approach 2:
The optical modulation element acts as an intermediary between the measurement beam and the semiconductor structure. It introduces known modulation patterns that facilitate the extraction of structural information from the complex multiple-pass optical path, effectively mediating the interaction and simplifying the interpretation of returned signals.
3Measurement precision
If conventional optical measurements are used, then system simplicity is maintained, but ability to measure deep high aspect ratio structures is insufficient
Solution Approach 1:
The measurement system employs periodic modulation of the optical beam through the semiconductor structure multiple times. This periodic action allows the system to accumulate signal information from deep structures over multiple cycles, effectively penetrating deeper into high aspect ratio features while maintaining signal detectability through rhythmic reinforcement of the measurement signal.
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 amplifies measurement signal sensitivity, leading to improved accuracy, precision, and stability, reduced measurement errors, faster measurement times, and enhanced tool-to-tool matching, while allowing for more robust and production-worthy measurements.
Implementation Method 1
the measurement beam is incident on the surface of the semiconductor wafer more than once in an optical path between the illumination source and the detector
Implementation Method 2
optical subsystem configured such that the measurement beam is incident on the surface of the semiconductor wafer
Data Source
AI summary
Methods and systems for performing multiple pass optical measurements of semiconductor structures are presented herein. A measurement beam is incident on the surface of a semiconductor wafer more than once. In some embodiments, the measurement beam is incident multiple times at the same measurement site on the semiconductor wafer in an optical path between the illumination source and the detector. In some other embodiments, the measurement beam is incident at different measurement sites on the semiconductor wafer in an optical path between the illumination source and the detector. In these embodiments, an instance of the same nominal structure under measurement is fabricated at each different measurement site. In a further aspect, an optical modulation element is disposed in the measurement path. In another further aspect, multiple pass measurements using different combinations of optical modulation targets are combined in a multi-target measurement to further enhance measurement sensitivity and break correlations.