Single-Probe Opto-Acoustic Microscopy for Fast Buried-Structure Detection
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Solution Overview
Problem
Conventional opto-acoustic metrology methods are slow due to the need for varying time delays between light pulses, limiting measurement speed and throughput in detecting buried structures in materials like semiconductor wafers.
Innovation Solution
Utilizing multiple pump beams with fixed delays and an instantaneous signal difference based on signals from two discrete delay times acquired with a single probe beam, enhancing measurement speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the time delay between light pulses in the pump and probe beams is varied through the range of time delays to obtain time resolved reflectance measurements, then measurement accuracy is improved, but measurement speed and throughput deteriorate
Solution Approach 1:
The single pump beam is segmented into multiple pump beams (first pump beam and second pump beam) with different fixed time delays. This segmentation allows simultaneous acquisition of multiple time delay measurements, converting a sequential measurement process into a parallel one, thereby improving measurement speed while maintaining the ability to obtain time-resolved reflectance information
Solution Approach 2:
The patent uses periodic modulation of the pump beams at different frequencies to encode time delay information. By modulating the first pump beam at a first frequency and the second pump beam at a second frequency, the system can distinguish and process signals from different time delays simultaneously, enabling fast acquisition of time-resolved measurements
2Productivity
If multiple pump beams with different path lengths are used to produce pump beams with two discrete delay times, then measurement speed and throughput are improved, but device complexity increases
Solution Approach 1:
Multiple pump beams with different time delays are merged and combined into a single probe beam path for simultaneous detection. This merging approach allows the system to maintain multiple measurement channels while using a single probe beam and detector, thereby improving measurement speed without proportionally increasing the complexity of the detection system
Solution Approach 2:
The single probe beam serves multiple functions by simultaneously detecting signals from multiple pump beams with different time delays. This multi-functionality allows one probe beam to extract time-resolved information from multiple pump-probe interactions, reducing the need for multiple separate detection systems and thereby limiting the increase in device complexity
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 significantly increases measurement speed and throughput while maintaining accuracy in detecting buried structures, such as voids and inclusions, in materials like semiconductor wafers.
Implementation Method 1
The light pulses in the pump beam produce an acoustic response within the sample under test that propagates to the surface of the sample, which is detected by the probe beam
Implementation Method 2
The acoustic response, for example affects the reflectivity of the material in the sample or deflection of the probe beam
Data Source
AI summary
A measuring device detects buried structures in a sample, such as voids or other underlying structures, based on an instantaneous signal difference determined from a single signal acquisition. The single signal acquisition is produced using a series of primary pump pulses and series of secondary pump pulses, which are intensity modulated and opposite in phase. The primary pump pulses and secondary pump pulses are combined to form a pump beam that is incident on the sample causing transient perturbations in material in the sample. Probe pulses are likewise incident on the sample and each probe pulse is modulated by the combined transient perturbations caused by a preceding primary pump pulse and a preceding secondary pump pulse. A series of reflected probe pulses are detected and demodulated to determine an instantaneous signal difference produced in response to the combined primary and secondary pump pulses, from which the buried structure is detected.