Lithographic Metrology Illumination Switches
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Solution Overview
Problem
Current metrology systems face challenges in efficiently measuring a large number of lithographic features quickly and accurately, particularly as ICs become smaller and more densely packed.
Innovation Solution
The system incorporates an illumination system with a broadband light source, a dispersive optical element, an optical switch, and a detector. This configuration generates a plurality of light beams with narrower bandwidths, which are then transmitted to multiple alignment sensors in a sensor array, allowing for simultaneous measurements across different wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a broadband light source is used to illuminate multiple wavelengths simultaneously, then measurement speed increases, but the spectral resolution and measurement precision deteriorate
Solution Approach 1:
The broadband light beam is segmented into multiple wavelength-specific sub-beams using a dispersive element (diffraction grating or prism). Each sub-beam corresponds to a specific wavelength range and is directed to a different sensor element, enabling simultaneous multi-wavelength measurement with spectral resolution.
Solution Approach 2:
The system transitions from temporal multiplexing (sequential wavelength measurement) to spatial multiplexing (parallel wavelength measurement). By dispersing wavelengths spatially across multiple sensor elements, the system achieves both high measurement speed and spectral resolution simultaneously.
2Measurement precision
If multiple sensors are used to measure different wavelengths simultaneously, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
A single sensor array performs multiple functions by simultaneously detecting multiple wavelengths. Each sensor element is tuned to a specific wavelength range, allowing the entire array to function as both a spectrometer and a multi-channel detector, reducing the need for separate measurement systems.
Solution Approach 2:
The system replaces complex mechanical wavelength-tuning mechanisms (such as rotating filters or moving mirrors) with a static dispersive element and fixed sensor array. This eliminates moving parts while maintaining the ability to measure multiple wavelengths simultaneously.
3Measurement precision
If spectral filtering is applied to narrow bandwidth, then measurement precision improves, but light intensity and signal strength decrease
Solution Approach 1:
Instead of using narrowband filters that block most light, the dispersive element segments the broadband light into wavelength-specific beams. Each segment directs only the relevant wavelength range to its corresponding sensor, minimizing light loss while achieving spectral precision.
Solution Approach 2:
The dispersive optical element acts as an intermediary that separates wavelengths spatially without absorbing or blocking light. This mediator enables precise wavelength selection while preserving light intensity, unlike filter-based approaches that inherently block out-of-band light.
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 enables faster and more accurate measurement of lithographic features, improving the throughput of metrology systems and aligning with the increasing complexity of IC manufacturing.
Implementation Method 1
a dispersive optical element configured to receive the beam of radiation and generate a plurality of light beams having a narrower bandwidth than the broadband light source
Implementation Method 2
an optical switch configured to receive the plurality of light beams and transmit each one of the plurality of light beams to a different alignment sensor of a sensor array
Implementation Method 3
a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Implementation Method 4
measuring the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range
Data Source
AI summary
A system includes an illumination system, an optical element, a switching element and a detector. The illumination system includes a broadband light source that generates a beam of radiation. The dispersive optical element receives the beam of radiation and generates a plurality of light beams having a narrower bandwidth than the broadband light source. The optical switch receives the plurality of light 5 beams and transmits each one of the plurality of light beams to a respective one of a plurality of alignment sensor of a sensor array. The detector receives radiation returning from the sensor array and to generate a measurement signal based on the received radiation.