Phase Modulator with Compensatory Grating for Dispersion
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Solution Overview
Problem
Current lithographic processes face challenges in achieving high accuracy and minimizing variation in substrate alignment, particularly due to inaccuracies in creating alignment marks and substrate deformations, which affect the precise positioning and overlay of patterns on semiconductor wafers.
Innovation Solution
A phase modulator apparatus is introduced, comprising a moving grating that diffracts and Doppler shifts input radiation, and a compensatory grating element to compensate for wavelength-dependent dispersion, enabling accurate alignment and overlay measurements without the need for scanning or moving radiation beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional alignment methods are used without wavelength compensation, then device complexity is reduced, but measurement precision deteriorates due to wavelength-dependent dispersion errors
Solution Approach 1:
A compensatory grating element is introduced as an intermediary component between the moving grating and the radiation beam. This compensatory grating specifically counteracts wavelength-dependent dispersion effects, enabling precise alignment measurements across multiple wavelengths without requiring complex calibration procedures for each wavelength.
Solution Approach 2:
The system dynamically adjusts the pitch of the compensatory grating to match the pitch of the moving grating at different wavelengths. By changing the grating pitch parameter in response to wavelength variations, the system maintains wavelength-independent phase modulation and eliminates dispersion errors.
2Productivity
If alignment marks are made smaller to increase density, then productivity is improved, but measurement precision deteriorates due to reduced signal strength
Solution Approach 1:
The system replaces mechanical scanning of large alignment marks with optical phase modulation using diffraction gratings. This allows small alignment marks to be measured through interferometric phase detection of diffracted radiation, maintaining high precision even with reduced mark size and increased density.
3Measurement precision
If radiation beams are scanned across alignment marks to improve measurement accuracy, then measurement precision is improved, but productivity deteriorates due to increased measurement time
Solution Approach 1:
Instead of mechanically scanning the radiation beam across alignment marks, the system uses a moving grating to modulate the phase of diffracted radiation. This creates a time-varying phase signal that encodes position information, allowing rapid measurement without physical beam scanning and thereby maintaining high throughput.
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 solution allows for precise alignment and overlay measurements with small alignment marks, improving alignment accuracy and throughput by providing a wavelength-independent phase modulation that can detect position variations across different wavelengths, reducing errors and enhancing processing efficiency in lithographic applications.
Implementation Method 1
a first moving grating in at least an operational state for diffracting the input radiation
Implementation Method 2
Doppler shifting the frequency of the diffracted radiation
Implementation Method 3
a first compensatory grating element comprising a pitch configured to compensate for wavelength dependent dispersion of at least one diffraction order of said diffracted radiation
Data Source
AI summary
Disclosed is a phase modulator apparatus comprises at least a first phase modulator for modulating input radiation, and a metrology device comprising such a phase modulator apparatus. The first phase modulator comprises a first moving grating in at least an operational state for diffracting the input radiation and Doppler shifting the frequency of the diffracted radiation; and a first compensatory grating element comprising a pitch configured to compensate for wavelength dependent dispersion of at least one diffraction order of said diffracted radiation.