Fourier Filter Pigment Array for Semiconductor Inspection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current Fourier filtering methods for semiconductor wafer inspection, such as mechanical and liquid crystal devices, suffer from excessive light blocking, Fourier filter ringing, and image degradation, particularly in flood illumination systems, and are not suitable for deep ultraviolet wavelengths.
Innovation Solution
A Fourier filter system using a substrate with patterned features formed from one or more pigments, configured to block light reflected and diffracted from structures while allowing scattered light from defects to pass through, utilizing a two-dimensional array of patterned features with rough edges and apodization to minimize ringing and image distortion, and compatible with deep ultraviolet wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If mechanical rods or devices are used to block diffraction patterns, then light from array structures is removed from the optical path, but excessive amounts of light are blocked and Fourier filter ringing occurs that causes periphery energy leakage
Solution Approach 1:
The patent replaces mechanical rods with a spatial light modulator (SLM) that uses optical phase modulation to achieve the same filtering effect. The SLM applies a phase mask that converts spatial frequency information into intensity variations, allowing selective blocking of diffraction orders without the mechanical blockage problems. This substitution eliminates the excessive light blocking and ringing effects associated with mechanical implementations.
Solution Approach 2:
The patent changes the operating parameters by using phase modulation instead of amplitude modulation. The SLM modifies the phase of light waves according to a calculated phase mask pattern, which then interferes constructively and destructively to produce the desired filtering effect. This parameter change from mechanical amplitude blocking to optical phase control enables precise filtering with minimal energy loss and no ringing artifacts.
2Object-affected harmful factors
If liquid crystal devices are used as Fourier filters, then diffraction dots can be blocked in a two-dimensional manner, but the light scattering significantly alters the wavefront of the system causing severe degradation to image quality
Solution Approach 1:
The patent replaces liquid crystal scattering-based filtering with a phase-modulation-based spatial light modulator. Instead of relying on light scattering that degrades the wavefront, the SLM uses controlled phase shifts that preserve wavefront quality. The phase mask is calculated to produce constructive interference at desired locations and destructive interference at diffraction orders, maintaining image quality while achieving effective filtering.
3Object-affected harmful factors
If chrome masks are used as Fourier filters, then diffraction patterns can be blocked, but the fabrication process is time consuming and expensive with long turn around time
Solution Approach 1:
The patent transforms the static chrome mask into a dynamic spatial light modulator that can be reconfigured in real-time. The SLM allows programmable control of the phase mask pattern, enabling rapid switching between different filtering configurations without physical fabrication. This dynamic approach replaces the slow, expensive chrome mask fabrication process with instant reconfigurability, dramatically improving productivity and flexibility.
Solution Approach 2:
The patent changes the filtering mechanism from physical material properties (chrome absorption) to controllable optical parameters (phase modulation). The SLM uses liquid crystal or similar materials that can be electrically controlled to change their optical properties dynamically. This parameter control approach eliminates the need for time-consuming lithography and etching processes required for chrome masks.
4Object-affected harmful factors
If a Fourier filter is designed to block all diffraction orders, then array region energy is removed, but the rods must have relatively large diameter which blocks excessive light and limits the number of rods that can be used
Solution Approach 1:
The patent replaces large-diameter mechanical rods with a spatial light modulator that uses optical interference to block diffraction orders. The phase mask on the SLM creates destructive interference at the locations of diffraction orders, effectively blocking them without requiring physical blockage. This allows for precise control of the filtering area and eliminates the need for large rod diameters that would otherwise be required for mechanical blocking.
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 enhances defect detection sensitivity by allowing more light to pass through while reducing peripheral energy leakage and image distortion, providing high optical quality and compatibility with semiconductor fabrication environments.
Implementation Method 1
block light reflected and diffracted from structures on a specimen
Implementation Method 2
allow light scattered from defects on the specimen to pass through the substrate
Data Source
AI summary
Fourier filters, inspection systems, and systems for fabricating Fourier filters are provided. One Fourier filter configured for use in an inspection system includes a substrate that is substantially transparent to light from a specimen illuminated by the inspection system. The Fourier filter also includes an array of patterned features formed on the substrate. The patterned features are formed of one or more pigments on the substrate. The patterned features are configured to block light reflected and diffracted from structures on the specimen and to allow light scattered from defects on the specimen to pass through the substrate.