Small Spot Size Spectroscopic Ellipsometer for Nanometer Metrology
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Solution Overview
Problem
As semiconductor devices shrink to nanometer-scale dimensions, traditional optical metrology systems face challenges in maintaining measurement precision and tool-to-tool matching due to reduced signal changes from structural parameter changes, which become indistinguishable from system noise, especially for optically isotropic materials.
Innovation Solution
A small angle CD metrology system is introduced, combining small angle spectroscopic ellipsometry and reflectometry with an all-reflective objective and dynamic aperture subsystem, operating at small angles of incidence and azimuth angles to enhance measurement sensitivity and precision, and capable of complete Mueller Matrix mode operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional spectroscopic ellipsometry systems use large angles of incidence (60-70 degrees) to measure optically isotropic materials, then measurement sensitivity is improved, but spot size becomes large and measurement precision degrades for nanometer-scale dimensions
Solution Approach 1:
The patent changes the angle of incidence parameter from traditional large angles (60-70 degrees) to small angles (less than 20 degrees). This parameter change enables the use of an all-reflective objective with high numerical aperture, which focuses the beam to a small spot size while maintaining measurement sensitivity through the small angle configuration that enhances polarization state modulation.
Solution Approach 2:
The patent employs an all-reflective objective comprising multiple reflective optical surfaces (mirrors) working together in composite configuration. This composite optical system achieves both small spot size focusing and maintenance of polarization states necessary for sensitive ellipsometric measurements at small angles of incidence.
2Manufacturing precision
If critical dimensions continue to shrink to nanometer-scale, then device density and integration increase, but signal changes from structural parameter changes become indistinguishable from system noise
Solution Approach 1:
The patent changes multiple parameters simultaneously: angle of incidence (to small angles), numerical aperture (to high values through all-reflective objective), and polarization measurement mode (to complete Mueller Matrix mode). These parameter changes collectively enhance measurement sensitivity, enabling detection of signal changes from nanometer-scale structural parameters that were previously lost in system noise.
Solution Approach 2:
The patent implements dynamic aperture selection that can be adjusted during measurement. The dynamic aperture subsystem allows optimization of the measurement beam parameters in real-time, enabling the system to adapt to different nanometer-scale structures and maintain high sensitivity across varying critical dimensions.
3Area of stationary object
If small angles of incidence are used to reduce spot size, then spot size decreases, but measurement sensitivity is substantially reduced for traditional ellipsometry systems
Solution Approach 1:
The patent uses an all-reflective objective with multiple reflective surfaces configured to provide high numerical aperture at small angles of incidence. This composite optical system overcomes the traditional limitation by maintaining beam focus quality and polarization state integrity, thereby preserving measurement sensitivity even at small angles where traditional systems would fail.
Solution Approach 2:
The all-reflective objective serves multiple functions simultaneously: it focuses the beam to small spot size, maintains high numerical aperture, preserves polarization states, and enables operation at small angles of incidence. This multi-functionality resolves the contradiction between small spot size and measurement sensitivity that plagues traditional single-function optical systems.
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
The system achieves high sensitivity and precision in measuring critical dimensions with a small spot size, improving tool-to-tool matching and meeting the demands of modern semiconductor manufacturing by isolating specific angles of incidence and azimuth for improved measurement accuracy.
Implementation Method 1
A light beam with a defined polarization state is directed to a sample. After interacting with the sample, the polarization state of the incident beam is modified.
Implementation Method 2
For measurements of optically isotropic materials with typical RPSE and RCSE systems, selection of small angles of incidence results in substantially reduced measurement sensitivity.
Implementation Method 3
This modification of polarization state manifests itself as a change in the magnitude and phase of two orthogonally polarized components.
Data Source
AI summary
Methods and systems for small angle CD metrology with a small spot size are introduced to increase measurement sensitivity while maintaining adequate throughput necessary for modern semiconductor manufacture. A small angle CD metrology system includes a small angle spectroscopic ellipsometry (SE) subsystem combined with a small angle spectroscopic reflectometry system, both operated at small angles of incidence. The small angle SE subsystem is configured to operate in a complete Mueller Matrix mode to further improve measurement sensitivity. The small angle CD metrology system includes an objective having all reflective surfaces in the light path. In some embodiments, the all-reflective objective is a Schwartzschild objective having an axicon mirror element to further reduce measurement spot size. In some embodiments, the small angle CD metrology system includes a dynamic aperture subsystem to isolate specific ranges of angles of incidence and azimuth for improved measurement sensitivity.