Beam Shaping for Wafer Inspection Sensitivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current scanning surface inspection systems face challenges in detecting defects on semiconductor wafers with high sensitivity while avoiding thermal damage, as the peak power density of laser-based illumination can damage the wafer surface, requiring significant reduction in beam power which compromises defect detection sensitivity.
Innovation Solution
A scanning surface inspection system that reshapes the beam intensity distribution of illumination light using a beam shaping element to create a flattened profile, allowing increased incident beam power without exceeding the wafer's thermal damage threshold, thereby enhancing defect sensitivity while preventing thermal damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the peak power density of laser-based illumination is increased to improve defect detection sensitivity, then the signal-to-noise ratio improves, but thermal damage to the wafer surface occurs
Solution Approach 1:
The patent applies local quality by transforming the uniform Gaussian intensity distribution into a flattened intensity distribution where different regions of the beam have optimized local intensity characteristics. This allows the beam to maintain higher overall power while ensuring that no single location exceeds the thermal damage threshold, thereby improving defect detection sensitivity without causing thermal damage.
Solution Approach 2:
The patent changes the intensity distribution parameter of the laser beam from a Gaussian profile to a flattened profile. This parameter transformation enables the system to operate at higher incident beam power levels while maintaining peak intensity below the damage threshold, thus resolving the contradiction between detection sensitivity and thermal damage prevention.
2Object-affected harmful factors
If the overall incident beam power is reduced to avoid thermal damage, then thermal damage is prevented, but defect detection sensitivity is compromised
Solution Approach 1:
By creating a flattened intensity distribution, the patent ensures that every region of the illuminated area contributes uniformly to defect detection without any single region causing thermal damage. This local quality optimization allows the system to use higher overall power while maintaining safety margins against thermal damage.
Solution Approach 2:
The transformation from Gaussian to flattened intensity distribution fundamentally changes the power utilization parameter. The system can now operate at higher incident beam power levels because the peak intensity is distributed more evenly, preventing thermal accumulation while enhancing the overall signal for defect detection.
3Device complexity
If a Gaussian beam intensity profile is used, then the illumination system is simple, but the beam power must be reduced to avoid thermal damage
Solution Approach 1:
The patent changes the intensity distribution parameter from Gaussian to flattened profile using beam shaping optics. This parameter transformation allows the system to maintain higher incident beam power while avoiding thermal damage, accepting the additional optical components as necessary for improved inspection capability.
Solution Approach 2:
The patent introduces beam shaping optical elements as intermediaries between the laser source and the wafer surface. These intermediary components transform the beam intensity distribution, enabling higher power operation while protecting the wafer from thermal damage, thus resolving the power limitation imposed by the simple Gaussian profile.
4Object-affected harmful factors
If up to 85% of beam power is dumped to avoid thermal damage, then thermal damage is prevented, but defect detection sensitivity is significantly reduced
Solution Approach 1:
The flattened intensity distribution ensures that all regions of the beam contribute effectively to defect detection without any region exceeding safe intensity limits. This eliminates the need to dump beam power, as the entire beam can be used at full power while maintaining thermal safety margins.
Solution Approach 2:
By transforming the intensity distribution parameter, the system can utilize nearly 100% of the generated beam power for inspection purposes. The flattened profile prevents thermal damage without requiring power reduction, thereby maximizing the signal strength for defect detection and eliminating the 85% power loss inherent in conventional approaches.
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 reshaped beam intensity distribution increases defect detection sensitivity by maintaining higher incident beam power within safe limits, ensuring effective inspection without damaging the wafer, with improved signal-to-noise ratio and sub-track accuracy in defect location determination.
Implementation Method 1
a beam shaping element that receives a beam of light generated by an illumination source and reshapes the beam intensity distribution of the illumination light
Implementation Method 2
An excessive amount of heat is generated by the interaction of the incident optical radiation with the wafer surface, particularly in areas of incidence subject to incident light with peak power density
Data Source
AI summary
Methods and systems for reshaping the beam intensity distribution of an illumination light supplied to a specimen under inspection are presented. A scanning surface inspection system includes a beam shaping element that flattens the beam intensity distribution of a beam of light generated by an illumination source. The reshaped illumination light is directed to the wafer surface over an illumination spot. With a flattened beam intensity distribution, the incident beam power can be increased without the beam intensity exceeding the damage threshold of the wafer at any particular location. In addition, the illumination spot is shaped by the beam shaping element to have a variable beam width in a direction parallel to the inspection track. The location of a defect within an inspection area having a variable beam width is estimated based on an analysis of the output of the detector.