Reflective Polarizer and Lambda-Quarter Plate for Overlay Accuracy
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Solution Overview
Problem
Conventional position measurement systems face challenges in achieving high overlay accuracy due to degradation in measurement accuracy caused by widening the wavelength band of detection light, leading to reduced contrast and flare issues with polarized beam splitters.
Innovation Solution
A measurement apparatus is designed with an illumination system and image forming system that includes a reflective polarizer and a λ/4 plate, along with additional optical members, where the reflective polarizer has higher S-polarized light reflectance than P-polarized light, and transmission polarizers in both systems optimize the separation of illumination and detection light, reducing flare and enhancing contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the wavelength band of detection light is widened to improve overlay accuracy, then the measurement system can handle diverse processes (including color filter processes), but the contrast degrades due to imperfect polarized beam splitter characteristics
Solution Approach 1:
A λ/4 plate is introduced as an intermediary optical element between the polarized beam splitter and the image forming system. This λ/4 plate converts linearly polarized light to circularly polarized light and vice versa, enabling the polarized beam splitter to effectively separate illumination light and detection light across a wide wavelength band. The combination of polarized beam splitter and λ/4 plate acts as a mediator that maintains high contrast while supporting broad wavelength coverage including near-infrared and blue wavelengths.
2Device complexity
If a conventional polarized beam splitter is used to separate illumination and detection light, then the system structure is simple, but the contrast degrades when the wavelength band is widened due to non-ideal reflectance characteristics
Solution Approach 1:
The optical system uses a composite structure combining a polarized beam splitter and a λ/4 plate. The polarized beam splitter provides wavelength-dependent reflectance characteristics (higher reflectance for S-polarized light than P-polarized light), while the λ/4 plate provides phase shift functionality. This composite optical system maintains effective light separation and high contrast across a wide wavelength band, overcoming the limitations of using either component alone.
3Measurement precision
If the polarized beam splitter has high S-polarized light reflectance and low P-polarized light reflectance for narrow wavelength band, then the separation is accurate, but this characteristic cannot be maintained when the wavelength band is widened
Solution Approach 1:
The system changes the polarization state parameter of light through the λ/4 plate, which converts linearly polarized light to circularly polarized light. This parameter transformation allows the polarized beam splitter to maintain its wavelength-dependent reflectance characteristics across a broader wavelength range. By changing the light's polarization state before it reaches the beam splitter, the system achieves both wide wavelength coverage and accurate light separation.
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 configuration improves measurement accuracy and overlay precision by effectively separating illumination and detection light, reducing flare and maintaining high contrast even with wide wavelength bands, including near-infrared and blue wavelengths.
Implementation Method 1
a reflectance of S-polarized light is higher than a reflectance of P-polarized light in the reflective polarizer
Implementation Method 2
a reflectance of S-polarized light is higher than a reflectance of P-polarized light in the reflective polarizer
Implementation Method 3
a transmittance of the P-polarized light is higher than a transmittance of the S-polarized light in the transmission polarizer included in the illumination system
Implementation Method 4
the transmittance of the S-polarized light is higher than the transmittance of the P-polarized light in the transmission polarizer included in the image forming system
Implementation Method 5
a separation system including a reflective polarizer and a λ/4 plate arranged between the illumination system and the image forming system
Data Source
AI summary
The present invention provides a measurement apparatus that measures a position of an object, including an illumination system configured to illuminate the object with illumination light, an image forming system configured to form, on a photoelectric conversion device configured to detect an image of the object, an image of detected light from the object, and a separation system including a reflective polarizer and a λ/4 plate arranged between the illumination system and the image forming system, and configured to separate the illumination light and the detected light via the reflective polarizer and the λ/4 plate, wherein the separation system includes at least one optical member arranged between the reflective polarizer and the λ/4 plate, and each of the illumination system and the image forming system includes a transmission polarizer.