Optical Stress Measurement via Strain Pulse Interferometry
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Solution Overview
Problem
Current methods for determining stress in semiconductor wafers are limited by their inability to provide non-destructive, rapid, and high-resolution measurements of multidimensional stress components, especially at small areas and varying depths, with existing techniques often requiring extensive time and providing only averaged stress values over large areas.
Innovation Solution
An optical system employing short optical pulses to generate and detect mechanical strain pulses, allowing for the determination of multidimensional stress components through analysis of transient optical responses, including changes in intensity, polarization, and phase of reflected probe pulses, enabling micron or submicron resolution and depth-specific measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Raman spectroscopy is used to determine stress in wafers, then stress measurement capability is provided, but measurement time becomes excessively long
Solution Approach 1:
The patent replaces Raman spectroscopy (which relies on inelastic scattering of light and phonon interactions) with an optical interference-based measurement system. The system uses coherent light sources and interferometric detection to measure wafer curvature and stress, achieving rapid measurements without the time-consuming spectral analysis required by Raman spectroscopy.
Solution Approach 2:
The patent changes the measurement parameter from spectral frequency shift (Raman) to optical path difference and interference pattern. By measuring changes in optical interference patterns caused by wafer curvature changes, the system achieves fast stress measurement while maintaining precision.
2Measurement precision
If X-ray diffraction is used to determine stress, then stress measurement is possible, but the measurement process becomes time consuming
Solution Approach 1:
The patent substitutes X-ray diffraction (which requires complex sample preparation, alignment, and data processing) with an optical interference method. The optical system directly measures wafer curvature changes in real-time without requiring diffraction patterns or extensive data analysis, dramatically reducing measurement time.
Solution Approach 2:
The patent employs periodic optical interference measurements to continuously monitor stress changes. By using coherent light sources that produce stable interference patterns, the system can take rapid sequential measurements, achieving high temporal resolution stress monitoring.
3Measurement precision
If wafer curvature measurement is used to determine stress, then stress information is obtained, but only averaged stress over large area is provided
Solution Approach 1:
The patent divides the wafer surface into multiple measurement zones by using a scanning optical system. The interferometric measurement head can be positioned at different locations across the wafer, allowing stress to be measured at specific points rather than providing only a global average. This enables localized stress characterization.
Solution Approach 2:
The patent adds spatial resolution by implementing a two-dimensional scanning capability. Instead of a single-point measurement, the optical system can map stress distribution across the wafer surface by systematically varying the measurement position in both x and y directions, creating a stress map.
4Measurement precision
If conventional stress measurement methods are used, then stress magnitude can be estimated, but depth variation of stress cannot be determined
Solution Approach 1:
The patent uses periodic modulation of the optical path difference to probe different depths within the wafer. By varying the optical path length in a controlled periodic manner and analyzing the interference pattern responses, the system can determine stress distribution as a function of depth from the wafer surface.
Solution Approach 2:
The patent extends the measurement capability from two-dimensional surface stress mapping to three-dimensional stress characterization by adding depth resolution. The optical interference method is sensitive to path length changes, allowing the system to probe stress at different depths by controlling the optical path difference.
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
Enables the precise characterization of multidimensional stress components in semiconductor wafers, overcoming limitations of existing methods by providing detailed, non-destructive, and rapid assessments of stress distribution, particularly around through-silicon vias and at various depths, enhancing the understanding and application of stress in semiconductor fabrication.
Implementation Method 1
applying a sequence of optical pump pulses to a material, individual pulses inducing a propagating strain pulse in the material
Implementation Method 2
detecting variations in a transient optical response of the material to the optical probe pulses, the variations being due at least in part to the propagation of the strain pulse in the material
Data Source
AI summary
Methods and systems are disclosed for measuring multidimensional stress characteristics in a substrate. Generally, the methods include applying a sequence of optical pump pulses to the substrate. The optical pump pulses induce a propagating strain pulse in the substrate. Optical probe pulses are also applied. By analyzing transient optical responses caused by the propagating strain pulse, multidimensional stress components characterizing the stress in the substrate can be determined. Multidimensional stress components may also be determined at a depth of a substrate. Multidimensional stress components may also be determined at areas adjacent a through-silicon via.