Wafer Profilometry with Back-Side Imaging for Buried Structure Measurement
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Solution Overview
Problem
Existing surface profilometry techniques struggle to accurately measure the flatness of layers covering components or chips that are buried or located under the surface, as they require high surface reflectivity and are prone to parasitic reflections, making it difficult to reference measurements precisely without a priori information.
Innovation Solution
A device with full-field interferometry and imaging means that acquires shape measurements and reference images through opposite surfaces, calibrating both in a common frame of reference to accurately locate and measure structures buried within the wafer, using wavelengths that penetrate non-transparent materials like silicon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional optical profilometry techniques are used to measure surface flatness, then measurement speed is improved with full-field techniques, but measurement precision deteriorates when surfaces have low reflectivity or when parasitic reflections from buried layers are present
Solution Approach 1:
The patent performs profilometry measurements from both the front and back sides of the wafer, adding a spatial dimension to the measurement approach. By measuring the back side and mathematically combining both measurements, the system overcomes the limitation of single-side measurements that are affected by low reflectivity or parasitic reflections, thereby maintaining high measurement speed while improving accuracy.
Solution Approach 2:
The patent introduces an intermediary mathematical processing step that combines front-side and back-side profilometry measurements. This intermediary calculation eliminates parasitic reflection effects and low reflectivity issues by using the back side as a reference, allowing full-field techniques to maintain both speed and precision.
2Reliability
If wavelengths that do not penetrate materials are used to avoid parasitic reflections, then measurement reliability is improved, but the ability to measure structures buried under the surface deteriorates
Solution Approach 1:
The patent inverts the measurement approach by measuring from the back side of the wafer instead of only from the front side. This inversion allows the measurement beam to access structures that are buried under the front surface, while using wavelengths that do not penetrate the material to maintain measurement reliability and avoid parasitic reflections.
Solution Approach 2:
The patent adds the back side of the wafer as an additional measurement dimension. By performing profilometry from both front and back sides and combining the measurements, the system can detect and locate buried structures while maintaining measurement reliability through the use of non-penetrating wavelengths.
3Ease of operation
If a priori information on component design is used to reference measurements, then ease of operation is improved, but measurement precision deteriorates due to imprecise positioning
Solution Approach 1:
The patent makes the measurement system self-sufficient by automatically locating buried structures through direct imaging from the back side, without requiring external a priori information about component design or manual positioning. The system performs its own referencing by capturing images of the back side and using these to precisely locate structures, thereby eliminating the need for imprecise design-based positioning.
Solution Approach 2:
The patent replaces the mechanical/manual positioning approach based on a priori design information with an optical imaging approach. By using the imaging means to directly capture and locate buried structures from the back side, the system substitutes precise optical positioning for imprecise mechanical referencing, thereby improving measurement precision while maintaining ease of operation.
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 precise surface shape measurements relative to buried components without a priori knowledge, allowing for accurate flatness control and visualization of structures through substrates, improving measurement accuracy and reducing parasitic reflections.
Implementation Method 1
interferometry techniques, which exploit interference between a measurement beam reflected by the surface to be measured and a reference beam
Implementation Method 2
using wavelengths that penetrate non-transparent materials like silicon
Data Source
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AI summary
The present invention relates to a device or apparatus for carrying out shape measurements on a first surface (13) of a wafer (12) relative to the structures (14) present under said first surface (13), which comprises (i) profilometry means (10) arranged to carry out the shape measurements on said first surface (13) of the wafer (12) according to at least one measurement field; (ii) imaging means (11) facing said profilometry means (10) and arranged to acquire a reference image of said structures (14) on or through a second surface of the wafer (12) opposite to the first surface(13) according to at least one imaging field; said profilometry means (10) and said imaging means (11) being arranged such that the measurement and the imaging fields are position-referenced in a common frame of reference (15). The invention also relates to a method implemented in said device or apparatus.