Wafer Inspection Laser Power Control to Prevent Particle Ablation
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Solution Overview
Problem
Laser power density in defect inspection tools for semiconductors is increasing, leading to particle ablation and contamination, as well as potential damage to wafer films and the wafer itself.
Innovation Solution
A method and system for dynamically adjusting laser power during wafer inspection using a secondary laser beam to detect particles and reduce the power of the main laser beam to prevent ablation, with subsequent controlled restoration of power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser power density is increased to detect smaller particles, then measurement precision is improved, but particle ablation and contamination occur
Solution Approach 1:
The system performs preliminary detection using a low-power secondary laser beam before the main high-power laser beam inspects the wafer. When a large particle is detected by the secondary beam, the system proactively reduces the main beam power before the particle can be ablated, preventing contamination while maintaining detection capability.
Solution Approach 2:
A secondary low-power laser beam acts as an intermediary between the detection requirement and the main inspection beam. This intermediary beam identifies large particles without causing ablation, enabling the system to adjust main beam power selectively to prevent harmful effects while maintaining measurement precision.
2Measurement precision
If laser power density is increased to detect smaller particles, then measurement precision is improved, but damage to wafer films and wafer occurs
Solution Approach 1:
The system dynamically adjusts the main laser beam power in real-time based on particle detection results. The controller continuously monitors the secondary beam detection signals and modulates the main beam power accordingly, transitioning between high-power detection mode and low-power safety mode to prevent damage to sensitive wafer structures.
Solution Approach 2:
The secondary laser beam performs preliminary scanning to identify particles that could cause damage when illuminated by the main beam. This preliminary action enables preventive power reduction before the main beam can damage wafer films or the wafer substrate, protecting the object while maintaining inspection capability.
3Object-affected harmful factors
If laser power is dynamically adjusted to prevent ablation, then particle contamination is reduced, but device complexity increases
Solution Approach 1:
The laser inspection system is segmented into two independent beam paths: a low-power secondary beam for safe particle detection and a main high-power beam for detailed inspection. This segmentation allows each beam to be optimized for its specific function while the controller coordinates them to prevent ablation, managing complexity through functional separation.
Solution Approach 2:
The secondary laser beam serves as an intermediary detection mechanism that triggers main beam power adjustment. This intermediary layer simplifies the control logic by providing clear detection signals that directly control main beam power modulation, reducing the complexity of real-time power management while effectively preventing contamination.
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 effectively prevents particle ablation and contamination while maintaining the ability to detect small defects, thereby ensuring the integrity of semiconductor wafers.
Implementation Method 1
laser-scattering-based inspection tools
Implementation Method 2
Laser heating of particle defects, however, can cause the particles to explode
Data Source
AI summary
A semiconductor wafer is inspected using a main laser beam and a secondary laser beam. The secondary laser beam leads the main laser beam and has lower power than the main laser beam. Using the secondary laser beam, a particle is detected on the semiconductor wafer having a size that satisfies a threshold. In response to detecting the particle, the power of the main laser beam and the power of the secondary laser beam are reduced. The particle passes through the main laser beam with the main laser beam at reduced power. After the particle has passed through the main laser beam with the main laser beam at the reduced power, the power of the main laser beam and the power of the secondary laser beam are restored in a controlled manner that is slower than a single step.