Optical Attenuation Assembly for Via Depth Measurement
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Solution Overview
Problem
Current optical measurement techniques, such as spectral-reflectometry and bright-field imaging, face challenges in accurately determining the depth of high aspect ratio Through Silicon Via (TSV) structures due to the dominance of light reflections from the wafer surface over the via bottom, leading to noise-limited measurements and insufficient information about via depth.
Innovation Solution
A novel gray-field measurement approach is introduced, which selectively attenuates the specular reflection component of light to create a combined dark and bright field detection condition, allowing for a predetermined ratio between scattered and specularly reflected light portions, enabling accurate determination of via depth through spectral analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If spectral-reflectometry or bright-field imaging is used to measure via depth, then the measurement process is simple, but the measurement precision deteriorates due to dominance of surface reflection over via bottom reflection
Solution Approach 1:
The patent changes the optical parameters by introducing an attenuation assembly that selectively attenuates the specular reflection component of light. This creates a gray-field detection condition where the ratio between scattered light from the via bottom and specular reflected light from the wafer surface is optimized for accurate depth measurement, thereby improving measurement precision without significantly complicating the measurement process
Solution Approach 2:
The attenuation assembly acts as an intermediary element between the light source and the detector. It selectively attenuates the specular reflection component while allowing scattered light from the via bottom to pass through, thereby mediating the balance between surface reflection and via bottom reflection to improve depth measurement accuracy
2Device complexity
If normal-incidence bright-field imaging is used, then the setup is simple, but the visibility of depth-induced spectral oscillations deteriorates
Solution Approach 1:
The patent modifies the detection condition by introducing selective attenuation of specular reflection, transforming the detection mode from pure bright-field to gray-field. This parameter change enhances the visibility of depth-induced spectral oscillations by reducing the overwhelming surface reflection signal while preserving the scattered light containing depth information
3Measurement precision
If dark field detection mode is used to enhance via bottom signal, then the via depth information improves, but the overall light signal intensity decreases
Solution Approach 1:
The patent introduces a gray-field detection mode as an intermediate parameter between bright-field and dark-field modes. By selectively attenuating only the specular reflection component rather than all direct light, this approach maintains sufficient overall light signal intensity while still enhancing the via bottom signal visibility, thus achieving good via depth information quality without excessive signal loss
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 method enhances the visibility of depth-induced spectral oscillations, improving the measurement accuracy of via depth parameters by balancing the intensities of light reflected from the via bottom and the wafer surface, thereby overcoming the limitations of existing techniques.
Implementation Method 1
light is normally incident on the via region and specularly reflected light is detected and analyzed
Implementation Method 2
light returned from the illuminated structure includes scattered light from the via bottom and side walls
Implementation Method 3
an attenuation assembly accommodated in the illumination and detection channels and being configured and operable for selectively attenuating light propagating along the detection channel
Implementation Method 4
enhances the visibility of depth-induced spectral oscillations
Data Source
AI summary
An optical system is presented for use in measuring in patterned structures having vias. The optical system comprises an illumination channel for propagating illuminated light onto the structure being measured; a detection channel for collecting light returned from the illuminated structure to a detection unit; and an attenuation assembly accommodated in the illumination and detection channels and being configured and operable for selectively attenuating light propagating along the detection channel, the attenuation creating a predetermined condition for the selectively attenuated light, said predetermined condition being defined by a predetermined ratio between a first light portion corresponding to a dark field condition and a second light portion corresponding to a bright field condition in said selectively attenuated light, detected selectively attenuated light being therefore indicative of at least one parameter of the via being illuminated.