Pockels Cell Phase Fluctuation Correction for Wafer Inspection
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Solution Overview
Problem
The challenge lies in accurately detecting minute foreign matter on semiconductor wafers due to fluctuations in laser power caused by changes in the Pockels cell's characteristics, which can lead to excessive irradiation and damage, especially when the Pockels cell control unit is malfunctioning or temperature-dependent voltage changes occur.
Innovation Solution
An inspection device with a controller that corrects phase fluctuations in an electro-optic element like a Pockels cell using intensity modulation characteristics, ensuring stable laser power by switching voltages based on detection results and environmental conditions, thereby minimizing damage and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-power laser beam irradiation is used to improve detection sensitivity, then detection sensitivity is improved, but the specimen is damaged due to explosive fracture of large foreign matter
Solution Approach 1:
The patent applies dynamic control of laser power by switching between high-power and low-power modes based on detection results. The system first performs inspection with high-power laser beams to achieve high detection sensitivity, then switches to low-power laser beams when foreign matter is detected to prevent explosive fracture. This dynamic power adjustment resolves the contradiction between detection sensitivity and specimen damage prevention.
Solution Approach 2:
The patent implements periodic inspection cycles alternating between high-power inspection phases and low-power verification phases. During each cycle, the system performs initial inspection with high-power laser beams, detects foreign matter, and then applies low-power laser beams for further inspection or treatment. This periodic switching between power levels enables both high sensitivity detection and damage prevention.
2Measurement precision
If laser power is increased to improve detection accuracy, then scattered light intensity from foreign matter increases, but characteristics of the Pockels cell change due to long-term operation causing laser power fluctuation
Solution Approach 1:
The patent incorporates feedback control by monitoring the actual laser power and comparing it with reference values. The system measures the intensity of scattered light from foreign matter and uses this information to adjust the laser power dynamically. When foreign matter is detected, the system reduces power to prevent damage; when no foreign matter is present, it maintains high power for accurate detection. This feedback mechanism compensates for Pockels cell characteristic changes and maintains reliable operation.
Solution Approach 2:
The patent changes the laser power parameter dynamically based on detection results and environmental conditions. The system adjusts power levels by modifying the voltage applied to the Pockels cell, switching between high-power mode for detection and low-power mode for prevention. This parameter change strategy enables the system to adapt to Pockels cell characteristic changes and maintain both detection accuracy and power stability.
3Measurement precision
If high-power irradiation is used to detect minute foreign matter, then detection sensitivity is improved, but large foreign matter exceeds hundreds of nm and breaks due to explosive fracture
Solution Approach 1:
The patent applies dynamic power adjustment to maintain the structural integrity of large foreign matter while detecting minute foreign matter. The system switches from high-power mode, which provides sufficient intensity to detect minute foreign matter, to low-power mode when large foreign matter is detected, preventing explosive fracture. This dynamic control enables simultaneous achievement of high detection sensitivity and preservation of specimen integrity.
Solution Approach 2:
The patent performs preliminary detection with high-power laser beams to identify the presence and size of foreign matter before applying sustained irradiation. When large foreign matter is detected in the preliminary phase, the system prepares to switch to low-power mode to prevent explosive fracture during subsequent inspection or treatment. This preliminary action enables proactive prevention of damage while maintaining detection sensitivity.
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 solution enables high-accuracy detection of minute foreign matter while preventing specimen damage by stabilizing laser power and adapting to temperature fluctuations, even when the Pockels cell control system is malfunctioning.
Implementation Method 1
an electro-optic element which changes a phase of light incident on the electro-optic element into at least two states
Implementation Method 2
a modulation unit that modulates the emitted laser beam
Data Source
AI summary
The present invention provides an inspection device that is capable of detecting foreign matter with high accuracy, the inspection device including: a light source; an electro-optic element on which light from the light source is incident and which changes a phase of the light into at least two states; and a controller. The controller corrects a phase fluctuation of the electro-optic element itself, using intensity modulation characteristics of the eletro-optic element which are obtained by changing an applied voltage that is input to the electro-optic element.