Collimator Fabrication on Semiconductor X-ray Detectors
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Solution Overview
Problem
The manufacturing and alignment of collimators for semiconductor-based photon-counting CT detectors are challenging due to polarization and electronics pile-up issues, requiring small slit-shaped openings that are difficult to fabricate and align properly with detector pixels.
Innovation Solution
A method involving photolithography to pattern SU-8 photoresist and metal layers, such as lead, tungsten, or molybdenum, to create collimator structures with precise openings and alignment over cadmium zinc telluride sensors, allowing for proper attenuation and collimation while enabling multi-layer metal deposition and mass production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional manufacturing methods are used to create collimator openings, then the manufacturing process is simpler, but the alignment precision with detector pixels deteriorates
Solution Approach 1:
The patent merges the collimator structure fabrication with the detector pixel array manufacturing process by using the same photolithography and metal deposition equipment. The collimator openings are patterned simultaneously with the pixel electrode patterns, ensuring automatic alignment without requiring separate alignment steps. This integration resolves the contradiction by achieving high alignment precision through process merging rather than complex post-manufacturing alignment procedures.
Solution Approach 2:
The collimator opening patterns are defined during the initial photolithography step before metal deposition, using the pixel array pattern itself as the alignment reference. The resist is patterned to define collimator openings at precise locations corresponding to pixel boundaries, and subsequent metal layers are deposited conformally on this pre-defined pattern. This preliminary action ensures alignment precision is built into the manufacturing process rather than added through complex alignment procedures.
2Reliability
If small slit-shaped openings are fabricated to prevent polarization and pile-up, then detector performance improves, but manufacturing difficulty increases
Solution Approach 1:
The patent replaces mechanical or manual fabrication methods for creating small slit openings with a photolithography-based chemical patterning process. The collimator openings are defined by photoresist patterning and etching rather than mechanical drilling or cutting. This substitution enables precise control of small opening dimensions and shapes while using standard semiconductor manufacturing equipment, thereby improving detector performance without proportionally increasing fabrication difficulty.
Solution Approach 2:
The patent uses photolithography parameters (exposure dose, resist thickness, etch conditions) to precisely control the dimensions and shape of the collimator openings. By adjusting these process parameters, the small slit-shaped openings can be fabricated with high precision to the required specifications for preventing polarization and pile-up, while maintaining compatibility with existing manufacturing processes rather than requiring entirely new fabrication techniques.
3Reliability
If multi-layer metal deposition is used to achieve proper attenuation, then collimator effectiveness improves, but manufacturing complexity increases
Solution Approach 1:
The patent uses the same multi-layer metal deposition process that is already employed for fabricating the detector pixel electrodes and interconnect structures. The collimator openings are defined in the resist pattern, and subsequent metal layers are deposited conformally across the entire wafer, serving both as structural interconnect material and as the collimator attenuation material. This multi-functionality approach achieves proper collimator attenuation without adding separate dedicated manufacturing steps, thereby limiting the increase in manufacturing complexity.
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 enables the fabrication of collimators with precise alignment and attenuation properties, improving the performance of photon-counting CT detectors by preventing polarization and electronics pile-up, and allowing for mass production with finer control over dimensions.
Implementation Method 1
exposing the second layer of resist to ultraviolet (UV) light with a photomask to transfer a pattern from the photomask to the second layer of resist
Implementation Method 2
depositing a layer of metal in the openings and on the second layer of resist to cover the openings, the first layer of resist, the second layer of resist, and the semiconductor sensor
Data Source
AI summary
A method of fabrication of a collimator structure on a detector that includes applying a first layer of resist to a semiconductor sensor, applying a second layer of resist over the first layer of resist and the semiconductor sensor to cover both the first layer of resist and the semiconductor sensor, exposing the second layer of resist to ultraviolet (UV) light with a photomask to transfer a pattern from the photomask to the second layer of resist, removing portions of the second layer of resist corresponding to the pattern from the photomask to produce openings in the second layer of resist, which expose upper portions of the semiconductor sensor, and depositing a layer of metal in the openings and on the second layer of resist to cover the openings, the first layer of resist, the second layer of resist, and the semiconductor sensor.