Rotational Phase Plate Illumination for Speckle Reduction
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Solution Overview
Problem
Highly interferential coherent light, such as laser light, used in pattern inspection for semiconductor devices leads to speckle interference, which adversely affects inspection accuracy, particularly in LSI manufacturing where narrow line widths and high resolution are required.
Innovation Solution
An illumination apparatus comprising a light source generating laser light, a rotational phase plate with randomly arranged stepped regions to introduce a phase change, and an integrator with lenses arranged in an array, where the allowable angle of incidence is set to be at least the angle of diffraction of the first order, reducing speckles and ensuring adequate light quantity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser light is used for illumination, then resolution is improved, but speckle interference increases
Solution Approach 1:
The rotational phase plate is divided into multiple stepped regions with different phase delays (e.g., 0, π/2, π, 3π/2). These segmented regions randomly distribute the laser light into multiple diffraction orders, breaking up the coherent interference that causes speckles while maintaining the high resolution benefits of laser illumination.
2Object-generated harmful factors
If the allowable angle of incidence is increased to reduce speckles, then speckle interference is reduced, but light quantity decreases
Solution Approach 1:
The phase plate is rotated at high speed during illumination, dynamically changing the diffraction pattern over time. This temporal variation allows the system to collect light from multiple diffraction orders across different angular positions, increasing the total light quantity reaching the specimen while still achieving speckle reduction through the random phase distribution.
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 solution effectively reduces speckle interference and maintains light quantity, enhancing inspection accuracy for semiconductor devices by optimizing the phase change and incidence angle, particularly for shorter wavelengths and narrower line widths.
Implementation Method 1
a rotational phase plate having a plurality of randomly arranged stepped regions, the rotational phase plate transmitting the laser light to give a phase change to the laser light
Implementation Method 2
an allowable angle of incidence for the laser light of the lenses being set at a maximum value of or larger than an angle of diffraction of a first order of the laser light at the rotational phase plate
Data Source
AI summary
An illumination apparatus according to embodiments includes: a light source generating laser light; a rotational phase plate having a plurality of randomly arranged stepped regions, the rotational phase plate transmitting the laser light to give a phase change to the laser light; and an integrator including a plurality of lenses arranged in an array, the laser light transmitted through the rotational phase plate being incident on the integrator, an allowable angle of incidence for the laser light of the lenses being set at a maximum value of or larger than an angle of diffraction of a first order of the laser light at the rotational phase plate.