Pump-Probe Metrology Systems Using Segmented Light Pulses
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Solution Overview
Problem
Metrology systems face challenges in increasing the delay between pump and probe pulses, limiting the maximum thickness that can be measured, and inefficiencies in utilizing light pulses, leading to reduced inspection speed and accuracy.
Innovation Solution
The implementation of an extended delay stage in the probe beam path and the harvesting of previously rejected light to generate multiple measurements from a single pulse, allowing for increased delay and improved performance by splitting pulses into primary and secondary components with distinct paths and timings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the delay between pump and probe pulses is increased to measure greater thicknesses, then measurement capability is improved, but inspection time increases and productivity decreases
Solution Approach 1:
The single light pulse is segmented into multiple pulses (primary pump, primary probe, secondary pump, secondary probe) with different time delays. This allows simultaneous measurement at multiple depth ranges, resolving the contradiction by enabling both long-delay measurements for thick samples and short-delay measurements for thin samples within the same inspection cycle.
Solution Approach 2:
The system uses periodic pulsed illumination with multiple pulse pairs at different delays. By implementing periodic action with varying delay intervals, the system efficiently samples different depth ranges without requiring continuously adjustable delays, thereby maintaining high inspection speed while achieving measurement of various thicknesses.
2Productivity
If a single light pulse is used for measurement, then system simplicity is maintained, but measurement efficiency is reduced due to inability to perform multiple measurements simultaneously
Solution Approach 1:
A single input light pulse is segmented into multiple measurement channels (primary and secondary pump/probe pulses) through optical beam splitting. This segmentation enables multiple measurements from one pulse source, improving productivity while avoiding the need for multiple independent laser sources, thus controlling device complexity.
Solution Approach 2:
The single light pulse source serves multiple functions by generating both primary and secondary pump and probe pulses. This multi-functionality allows the system to perform multiple measurement tasks simultaneously, increasing measurement efficiency without requiring separate light sources for each function.
3Measurement precision
If multiple light pulses with different delays are generated, then measurement accuracy across various depths is improved, but system complexity and alignment difficulty increase
Solution Approach 1:
Optical delay lines and beam splitters serve as intermediaries to create the multiple delayed pulses from a single source. These intermediary components systematically introduce precise time delays and route the pulses to appropriate detectors, achieving high depth resolution while managing alignment complexity through standardized optical elements rather than direct mechanical adjustments.
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 enables measurement of greater thicknesses and enhances the efficiency of metrology systems by allowing multiple measurements from a single pulse, reducing inspection time and improving accuracy.
Implementation Method 1
a first pump pulse generates a first acoustic wave in a bulk of the sample
Implementation Method 2
the second pump pulse reflects of the sample and is altered by the second acoustic wave
Data Source
AI summary
Measuring or inspecting samples through non-destructive systems and methods. Multiple light pulses emitted from a light source. The light pulses are split into pump pulses and probe pulses. A first probe pulse reaches the surface of a sample after a first time duration after a first pump pulse reaches the surface. A second pump pulse reaches the surface after a time duration after the first probe pulse. When the second pump pulse reflects off the sample, the second pump pulse may be altered by an acoustic wave generated by the first probe pulse. The reflected second pump pulse may be analyzed to determine a characteristic of the sample.