TSV Depth Measurement via Normal Incidence Reflectometry
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Solution Overview
Problem
Current measurement techniques, such as optical and infrared methods, are inadequate for reliably measuring the depth of high aspect ratio through-silicon via (TSV) structures due to signal attenuation and limited resolution, making it difficult to ensure high yield and quality in three-dimensional integrated circuit manufacturing.
Innovation Solution
An optical method using normal incidence reflectometry with a white light source, variable aperture, and automated XYZ stage to control the measurement beam's angular spectrum and spot size, allowing for non-destructive and high-throughput measurement of TSV etch depth and uniformity by maximizing the coherence of the reflected signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-section scanning electron microscopy is used to measure TSV etch depth, then measurement accuracy is improved, but measurement time increases and the process becomes destructive
Solution Approach 1:
The patent replaces the mechanical/electronic cross-section SEM measurement system with an optical reflectometry system. By using optical reflection and interference principles, the system achieves non-destructive, high-throughput measurements of TSV etch depth without requiring physical sectioning or complex electron microscopy equipment.
Solution Approach 2:
The patent creates an optical copy/reflection of the TSV structure by measuring the reflected light spectrum from the via bottom. This optical reflection serves as a non-destructive surrogate for physical cross-sectioning, allowing depth measurement without destroying the original structure.
2Measurement precision
If optical imaging techniques with high magnification objective lens are used to measure large diameter TSV, then etch depth measurement capability is improved, but measurement capability deteriorates for high aspect ratio structures due to signal attenuation
Solution Approach 1:
The patent changes the measurement parameters by using normal incidence (perpendicular) light illumination instead of oblique angles. This parameter change maximizes the coherence of reflected light from the via bottom, significantly improving signal strength and measurement reliability for high aspect ratio structures where signal attenuation is severe.
Solution Approach 2:
The patent employs spectral analysis of periodic interference patterns in the reflected light. By analyzing the oscillatory interference spectrum caused by light reflecting between the top and bottom of the via, the system can accurately determine etch depth even when direct imaging fails due to signal attenuation.
3Ease of operation
If infrared microscopy is used for backside measurement of TSV structures, then measurement accessibility is improved, but measurement precision deteriorates due to coarser resolution
Solution Approach 1:
The patent transitions from spatial resolution limitations in infrared microscopy to spectral domain analysis. By measuring the spectral interference pattern of reflected light and analyzing it in the frequency domain, the system achieves precise depth measurements without being constrained by the diffraction-limited spatial resolution of infrared optics.
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 accurate and repeatable measurements of TSV etch depth and depth uniformity for diameters ranging from 1 to 400 μm and depths up to 500 μm, improving production yield and quality by optimizing the measurement spot size and coherence of the spectral reflectance.
Implementation Method 1
An optical method using normal incidence reflectometry with a white light source, variable aperture, and automated XYZ stage to control the measurement beam's angular spectrum and spot size
Implementation Method 2
allowing for non-destructive and high-throughput measurement of TSV etch depth and uniformity by maximizing the coherence of the reflected signal
Implementation Method 3
a spectrometer equipped with a fixed grating and a linear CCD array... to determine etch depth by sequentially focusing on the top surface and bottom surface of the via
Data Source
AI summary
A system and method for measurement of high aspect ratio through silicon via structures. A preferred embodiment includes a white light source and optical components adapted to provide a measurement beam which is nearly collimated with a measurement spot size of the same order of magnitude as the diameter (or effective diameter) of the TSV. These embodiments include a white light source with a variable aperture and other optical components chosen to control the angular spectrum of the incident light. In preferred embodiments the optical components include an automated XYZ stage and a system controller that are utilized to direct the illumination light so as to illuminate the top and bottom of TSV under analysis.