DMD Spectrometer Layout for Fast OCD Wavelength Switching
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Solution Overview
Problem
Current optical critical dimension (OCD) measuring apparatuses in semiconductor manufacturing face challenges in achieving high-speed metrology due to coupling issues and inefficiencies in wavelength conversion, particularly when dealing with complex semiconductor structures, which require a large number of floating parameters and measurements, leading to reduced throughput and limited measurement time per wafer.
Innovation Solution
A spectrometer system utilizing a collimator lens, dispersive optical element, focusing lens, and a digital micromirror device (DMD) with oblique pixel mirrors, where the DMD's substrate surface is parallel to the focusing lens's optical axis, allowing for improved light use efficiency and spectral performance by ensuring that all dispersed wavelengths are in focus, thereby enhancing wavelength conversion speed and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a monochromator is used to convert wavelengths sequentially, then wavelength conversion is achieved, but the conversion time becomes several seconds or more due to rotation of diffraction grating, significantly reducing throughput
Solution Approach 1:
The patent replaces the mechanical rotation system of the monochromator with a digital micromirror device (DMD) that uses electronic control of micro-mirrors to achieve wavelength selection. This substitution eliminates the need for mechanical rotation of diffraction gratings, reducing wavelength conversion time from several seconds to milliseconds or less, thereby significantly improving throughput while maintaining wavelength conversion capability
Solution Approach 2:
The patent introduces a dynamic wavelength selection mechanism using a DMD where individual micromirrors can be rapidly switched between ON and OFF states to select different wavelengths. This dynamic control allows for rapid wavelength changes without mechanical movement, enabling fast wavelength conversion and improving the overall speed of the OCD measuring apparatus
2Reliability
If a DMD is arranged with its surface perpendicular to the optical axis of the focusing optical system, then light is reflected toward the focusing optical system, but light dispersed out of the vicinity of the center is out of focus, degrading spectral performance
Solution Approach 1:
The patent introduces an asymmetric arrangement where the DMD surface is inclined at a specific angle relative to the optical axis of the focusing optical system. This asymmetric configuration allows light from the entire dispersed spectrum, not just the center region, to be properly focused, thereby improving spectral performance while maintaining adequate light reflection efficiency through optimized inclination angle
3Measurement precision
If SR or SE is performed on 100 or more wavelengths to avoid coupling problems, then measurement precision is improved, but measurement time increases significantly
Solution Approach 1:
The patent uses the DMD to pre-select and rapidly switch between specific wavelength combinations that are optimized for measuring complex semiconductor structures. By preparing and switching between predetermined wavelength sets, the system achieves high measurement precision with fewer wavelengths while reducing measurement time, as the DMD can quickly reconfigure wavelength selection without mechanical delays
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 significantly reduces wavelength conversion time, allowing for faster processing of multiple wavelengths and improving the overall throughput of OCD measuring apparatuses, enabling more precise and efficient semiconductor metrology within the tight time constraints of semiconductor manufacturing.
Implementation Method 1
a collimator lens configured to generate parallel light by collimating light that has passed through an incident slit
Implementation Method 2
a dispersive optical element configured to generate dispersed light by dispersing the parallel light at different angles according to wavelengths
Implementation Method 3
a focusing lens configured to generate focused light by focusing the dispersed light
Implementation Method 4
a spatial light modulator configured to generate reflective light by reflecting the focused light
Data Source
AI summary
A spectrometer and a metrology system capable of improving spectral performance are provided. The spectrometer includes a collimator lens, a focusing lens, and a spatial light modulator (SLM), wherein light reflected by the SLM is output from an output slit through the focusing lens and a dispersive optical element, and on a second plane perpendicular to a first plane including optical paths of pieces of light dispersed at different angles, an incident slit, the output slit, and a reflective plane have a conjugate relationship.