Substrate Transmission Imaging for High Aspect Ratio Structure Characterization
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Solution Overview
Problem
Existing techniques struggle to accurately characterize high aspect ratio structures, such as Through-Silicon Vias (TSVs) or trenches, etched in substrates, particularly in measuring the variation in lateral dimensions along the depth of these structures, which is crucial for assessing the etching process quality.
Innovation Solution
A method and system utilizing a light source to emit illumination through the substrate, combined with an imaging device positioned on the opposite side of the substrate, allowing for the acquisition of images at different longitudinal positions. These images are then processed to measure lateral dimensions and determine longitudinal data, such as taper angles or profiles, of the structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional imaging techniques are used to characterize high aspect ratio structures, then the measurement process is simple, but the measurement precision and ability to detect longitudinal variations is insufficient
Solution Approach 1:
The patent transitions from conventional 2D surface imaging to 3D volumetric characterization by acquiring images at multiple longitudinal positions (depths) through the substrate. This dimensional extension enables measurement of lateral dimension variations along the depth of high aspect ratio structures, providing longitudinal profile data that conventional single-plane imaging cannot obtain.
Solution Approach 2:
The patent uses the substrate itself as an intermediary medium to transmit light from the imaging device to the structures being characterized. By positioning the imaging device on the opposite side of the substrate and using light transmission through the substrate, the system can non-contactively access and image the lateral dimensions of deep structures without physical intervention or complex mechanical positioning systems.
2Measurement precision
If the imaging device is positioned close to the structure for detailed imaging, then the measurement precision improves, but the device complexity and positioning difficulty increase
Solution Approach 1:
The substrate serves as an optical intermediary that transmits light over long distances. This allows the imaging device to be positioned far from the structures being measured while still achieving detailed imaging of lateral dimensions at various depths, eliminating the need for complex close-proximity positioning mechanisms.
Solution Approach 2:
Instead of moving the imaging device closer to the structure in the longitudinal direction, the system compensates by acquiring images at multiple longitudinal positions (depths) and processing them to reconstruct the 3D profile. This dimensional approach maintains simple device positioning while achieving precise measurements.
3Measurement precision
If multiple images are acquired at different longitudinal positions to characterize the structure, then the measurement precision and longitudinal data accuracy improve, but the measurement time and productivity decrease
Solution Approach 1:
The system performs preliminary actions by acquiring multiple images at different longitudinal positions in advance, then processes these images to extract lateral dimension data and construct the 3D profile. This pre-acquisition approach enables efficient batch processing and reduces real-time measurement time.
Solution Approach 2:
The patent creates multiple copies (images) of the structure at different longitudinal positions, then processes these copies to extract longitudinal profile information. By working with multiple image copies rather than continuously adjusting a single view, the system achieves accurate 3D characterization through parallel image processing.
4Measurement precision
If the imaging device is positioned on the opposite side of the substrate, then the ability to characterize deep structures improves, but the light transmission quality and image clarity may deteriorate
Solution Approach 1:
The patent changes the optical parameters by selecting specific wavelengths that are transmitted through the substrate and adjusting the illumination conditions. By optimizing these parameters, the system maintains sufficient light transmission quality and image clarity even when the imaging device is positioned on the opposite side of the substrate for deep structure characterization.
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 efficient and accurate characterization of high aspect ratio structures by providing valuable longitudinal data that assesses the etching process quality and ensures the conformity of the structures, particularly useful for structures with small critical dimensions.
Implementation Method 1
a light source configured to emit an illumination beam with a wavelength adapted to be transmitted through the substrate
Data Source
Figure 1~2a
Figure 2b~3
Figure 4
AI summary
The invention relates to a method (200, 300) for characterizing a structure (104) etched in a first surface (140) of a substrate (102), such as a wafer, said structure (104) extending along a longitudinal direction, z, into the substrate (102), the method (200, 300) being implemented by a characterizing system (100) comprising a light source (130, 131) configured to emit an illumination beam with a wavelength adapted to be transmitted through the substrate (102), and an imaging device positioned to face a second surface (147) of the substrate (102) opposite to the first surface (140), the method (200, 300) comprising the following steps: - illuminating (202) at least one structure (104) with the illumination beam, - subsequently positioning (204) an object plane of the imaging device at at least two different longitudinal positions; - acquiring (206) at least one image of the structure (104) at each of the longitudinal positions, the images being acquired through the substrate (102); - measuring (210) at least one lateral data relating to a lateral dimension of the structure (104) from the at least one acquired image at each of the longitudinal positions; and determining (212) at least one longitudinal data relating to a longitudinal shape of the structure from the lateral data of at least two longitudinal positions. The invention further relates to a system implementing such a method.