Picosecond Ultrasonics Depth Profiling for Semiconductor Lateral Features
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Solution Overview
Problem
Current picosecond ultrasonics techniques are limited in their ability to provide three-dimensional structural information of semiconductor devices with lateral structural features, as they primarily offer one-dimensional profiling and struggle to probe features deeply embedded within samples or extending beyond the surface.
Innovation Solution
The method employs picosecond ultrasonics by projecting optical pump and probe pulses to induce acoustic pulses within a target region, utilizing Brillouin scattering to obtain depth-dependent parameters of lateral structural features, with the pump pulse wavelength being at least twice the lateral extent of the feature, allowing for comprehensive depth-profiling of semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If traditional picosecond ultrasonics techniques are used, then one-dimensional structural information can be obtained, but three-dimensional structural information including lateral features cannot be provided
Solution Approach 1:
The patent transitions from one-dimensional depth profiling to three-dimensional structural characterization by incorporating lateral spatial resolution. This is achieved by using a laterally extended acoustic pulse that maintains coherence across lateral dimensions, allowing simultaneous measurement of depth and lateral structural variations through Brillouin scattering spectroscopy.
2Length of stationary object
If acoustic pulses are used to probe deep regions, then depth penetration is improved, but resolution of lateral structural features deteriorates
Solution Approach 1:
The patent segments the acoustic pulse into laterally extended coherent regions that can be independently analyzed. By dividing the probing function into depth-dependent and lateral-dependent components, the system achieves both deep penetration and lateral resolution through separate measurement dimensions.
Solution Approach 2:
The patent resolves the depth-resolution tradeoff by adding lateral spatial dimension to the measurement. The laterally extended acoustic pulse enables depth penetration while lateral feature resolution is achieved through spatially resolved Brillouin scattering measurements, effectively moving the problem to a higher dimensional solution space.
3Length of stationary object
If the pump pulse wavelength is increased to probe deeper regions, then depth penetration is improved, but the ability to resolve small lateral features deteriorates
Solution Approach 1:
The patent decouples the depth-probing function from lateral-resolution function by utilizing different physical mechanisms in different dimensions. Depth penetration is achieved through long-wavelength acoustic pulses, while lateral feature detection is achieved through spatially resolved Brillouin scattering measurements, allowing both requirements to be satisfied simultaneously.
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 the extraction of detailed three-dimensional structural information, including geometry and material composition variations along lateral directions, enhancing the resolution and depth penetration in semiconductor devices, beyond the limitations of traditional techniques.
Implementation Method 1
an ultrashort light pulse (usually referred to as a 'pump pulse') may be projected on an external surface of a structure. A thin tranche of the structure, adjacent to and including the external surface, is heated by absorbing the light pulse. Due to the heating thereof, the tranche expands, leading to the formation of an acoustic pulse
Implementation Method 2
Projecting an optical probe pulse on the sample, such that the probe pulse undergoes Brillouin scattering off the acoustic pulse within the target region
Data Source
AI summary
Disclosed herein is a method for depth-profiling of samples including a target region including a lateral structural feature. The method includes projecting an optical pump pulse on a semiconductor device comprising a target region, such as to produce an acoustic pulse which propagates within the target region of the semiconductor device, wherein a wavelength of the pump pulse is at least two times greater than a lateral extent of a lateral structural feature of the semiconductor device along at least one lateral direction, projecting an optical probe pulse on the semiconductor device, such that the probe pulse undergoes Brillouin scattering off the acoustic pulse within the target region, detecting a scattered component of the probe pulse to obtain a measured signal, and analyzing the measured signal to obtain a depth-dependence of at least one parameter characterizing the lateral structural feature.