Silicon Nitride X-ray Window With Patterned Support
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Solution Overview
Problem
Existing x-ray radiation windows are prone to failure in harsh environments due to fragility and inability to withstand pressure differentials, temperature, and corrosive chemicals, especially in larger sizes, and require costly materials like SOI wafers that cause quality issues and manufacturing challenges.
Innovation Solution
A method using low-pressure chemical vapor deposition to form a silicon nitride film supported by a patterned silicon structure on a double-sided polished wafer, allowing for the creation of robust and consistent radiation windows with minimal absorption of x-rays, using techniques like plasma etching and wet etching to ensure a wrinkle-free and uniform film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the radiation window material thickness is reduced and lowest atomic-mass elements are used, then radiation transmission is improved, but the window's ability to withstand cracks, tears, and failures in harsh environments deteriorates
Solution Approach 1:
The patent uses silicon nitride (Si3N4) as a composite material that combines the low atomic mass properties of silicon with nitrogen to achieve both high radiation transmission and mechanical strength. The silicon nitride film is deposited on a silicon support structure, creating a composite system where the thin film provides radiation transmission while the support structure provides mechanical strength to withstand harsh environments including corrosive chemicals, high temperatures, and pressure differentials.
2Strength
If a support structure is added to reduce film failures, then the window's mechanical strength is improved, but radiation transmission is reduced due to absorption by the support structure
Solution Approach 1:
The support structure is designed with local optimization where silicon ribs or grid structures provide mechanical support only where needed to withstand pressure differentials, while minimizing the overall material volume in the radiation path. The silicon nitride film is deposited selectively on these localized support elements rather than requiring a solid continuous support, thereby reducing absorption while maintaining structural integrity.
Solution Approach 2:
The patent optimizes the geometric parameters of the support structure including rib width, spacing, and height to balance mechanical support with radiation transmission. By carefully controlling these parameters, the support structure provides sufficient strength to withstand pressure differentials while minimizing absorption of x-rays in the energy-dispersive radiation-detector applications.
3Manufacturing precision
If silicon nitride film is deposited on etched silicon wafer, then manufacturing consistency and film uniformity are improved, but manufacturing process complexity increases
Solution Approach 1:
The silicon wafer is pre-polished on both sides before deposition to create an extremely smooth base surface. The support structure pattern is etched onto the wafer in advance, creating a predefined template that guides the subsequent silicon nitride deposition. This preliminary preparation ensures that when the thin film is deposited, it forms uniformly across the support structure without wrinkles or defects, achieving high manufacturing precision.
Solution Approach 2:
The patent replaces traditional mechanical film formation methods with low-pressure chemical vapor deposition (LPCVD) to form the silicon nitride film. This deposition process allows for precise control of film thickness and uniformity through chemical reactions in the vapor phase, eliminating mechanical stresses and wrinkles that would occur with mechanical film formation methods.
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
The solution provides radiation windows with high consistency and low failure rates, capable of withstanding harsh environments and maintaining optimal x-ray transmission, while being cost-effective and avoiding the manufacturing issues associated with SOI wafers.
Implementation Method 1
performing low pressure chemical vapor deposition on a double-sided polished silicon wafer having a support structure pattern etched thereon to form a wrinkle-free film
Implementation Method 2
using techniques like plasma etching and wet etching to ensure a wrinkle-free and uniform film
Implementation Method 3
wet etching the second side of the double-sided silicon wafer to release the silicon nitride thin film and the supporting structure from the portion of the double-sided silicon wafer defined by the silicon exposure area
Data Source
AI summary
A method for producing a radiation window includes patterning a photo resist structure onto a double-sided silicon wafer, plasma etching the silicon wafer to create an etched silicon wafer having a silicon supporting structure etched upon a first side of the double-sided silicon wafer, applying a silicon nitride thin film to the etched silicon wafer, patterning a photo resist structure and plasma etching a second side of the double-sided silicon wafer to create an initial window in the silicon nitride thin film, and wet etching the second side of the double-sided silicon wafer to release the silicon nitride thin film and supporting structure from the portion of the double-sided silicon wafer defined by the initial window.