Astigmatic Spectroscopic Instrument for Angle-Resolved Inspection

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Solution Overview

Problem

Conventional optical inspection systems, such as ellipsometers and reflectometers, face limitations in measuring ellipsometric parameters over a range of wavelengths, incident angles, and azimuth angles due to diffraction caused by slits and limited access to larger angles of incidence.

Innovation Solution

The introduction of an astigmatic element replaces the slit, allowing for the separation of the reflected probe beam as a function of angle of incidence and azimuth angle, enabling simultaneous dispersion of wavelength and angle of incidence, and the use of a two-dimensional detector array to capture more detailed information about the specimen properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a slit is used to separate the reflected probe beam, then wavelength separation is achieved, but diffraction effects are caused and angle of incidence access is limited

Engineering Contradiction:

Improvewavelength separation precisionVSAvoiddiffraction effects

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent removes the slit component from the optical path and replaces it with an astigmatic camera system. This extraction eliminates the source of diffraction effects while preserving the spectral separation function through the astigmatic optics that focus different wavelengths at different positions on the detector array.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The system changes the optical parameter from using a slit-based spatial filter to an astigmatic optical system that uses curved focal surfaces. This parameter change allows simultaneous wavelength separation and angle of incidence measurement without the diffraction limitations imposed by slit geometry.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If a slit is used for beam separation, then spectral dispersion is achieved, but the range of measurable angles of incidence is limited

Engineering Contradiction:

Improvespectral dispersion precisionVSAvoidangle of incidence range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent transitions from a one-dimensional slit-based dispersion system to a two-dimensional astigmatic imaging system. The astigmatic optics create curved focal surfaces that map both wavelength and angle of incidence onto the two-dimensional detector array, enabling simultaneous measurement across both parameters with extended angular range.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Measurement precision

If conventional ellipsometer optics are used, then polarization measurement is achieved, but sensitivity to specimen properties is reduced

Engineering Contradiction:

Improvepolarization measurement precisionVSAvoidspecimen property information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent introduces an astigmatic camera as an intermediary optical element between the specimen and the detector. This intermediary creates a magnified, astigmatic image that preserves and enhances information about specimen properties such as layer thicknesses and critical dimensions, allowing simultaneous polarization and structural analysis with improved sensitivity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 the sensitivity of measurements by retaining more information about the specimen's properties, such as layer thicknesses and critical dimensions, while reducing diffraction effects and expanding the range of measurable angles, leading to more accurate and detailed optical inspections.

Implementation Method 1

adding astigmatism to separate the reflected probe beam as a function of at least one of the angle of incidence and the azimuth angle

Methodology Applied

Scientific EffectAstigmatism:

Implementation Method 2

separating the reflected probe beam as a function of wavelength

Methodology Applied

Scientific EffectDispersion: Dispersion (of waves)

Implementation Method 3

The detector converts the reflected probe beam into signals that are analyzed by a processor

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 4

directing a probe beam onto the specimen at varying angle of incidence and azimuth angle, thereby producing a reflected probe beam

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS8643841B1Angle-resolved spectroscopic instrument

Publication Date: 2014.02.04 KLA CORP

AI summary

A method for optically inspecting a specimen by directing a probe beam onto the specimen at varying angle of incidence and azimuth angle, thereby producing a reflected probe beam, gathering the reflected probe beam, separating the reflected probe beam as a function of wavelength, adding astigmatism to separate the reflected probe beam as a function of at least one of the angle of incidence and the azimuth angle, and evaluating the specimen based at least on changes in the reflected probe beam as a function of wavelength of the reflected probe beam and at least one of the angle of incidence and the azimuth angle.