Radiation Detector Boron Layer Grid Formation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing radiation detectors, such as four-quadrant P-I-N diodes, have a 'dead zone' where low-energy backscattered electrons do not penetrate, leading to incomplete detection, and existing processes fail to form a metallic grid on thin boron layers without damaging them.
Innovation Solution
A method involving dry etching to define a conductive grid and subsequent wet etching to remove the conductive material, ensuring the boron layer remains intact, combined with the use of thin protective layers like boron nitride to enhance detection of low-energy electrons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional P-I-N diode with a standard depletion layer is used, then the device structure is simple and easy to manufacture, but low-energy backscattered electrons cannot penetrate the dead zone into the active volume, resulting in incomplete detection
Solution Approach 1:
The detector is segmented into distinct functional layers: a thin dead zone (1-5 nm), an intrinsic layer (1-10 μm), and a depleted layer. This segmentation allows low-energy electrons to pass through the thin dead zone while maintaining charge separation in the depleted layer, solving the penetration problem without excessive complexity.
Solution Approach 2:
Different regions of the detector are given different properties: the dead zone has minimal thickness to allow electron penetration, the intrinsic layer provides the active detection volume, and the depleted layer enables charge separation. This local differentiation optimizes detection while managing structural complexity.
2Manufacturing precision
If a thin boron layer (1-20 nm) is deposited to form the p+-type diffusion layer, then the dead zone becomes thin enough for low-energy electron detection, but the boron layer becomes vulnerable to damage during subsequent manufacturing processes
Solution Approach 1:
The thin boron layer is deposited first to establish the required dead zone thickness, then a protective layer is applied before subsequent processing steps. This preliminary positioning of the boron layer allows precise thickness control while the protective layer prevents damage during later manufacturing operations.
Solution Approach 2:
A protective layer is introduced as an intermediary between the thin boron layer and the manufacturing environment. This protective layer shields the vulnerable boron layer from damage during processing while allowing the boron layer to maintain its critical thin dimensions for electron detection.
3Ease of manufacture
If a metallic grid is formed directly on the thin boron layer using conventional processes, then the electrode connection is achieved, but the boron layer is damaged or removed
Solution Approach 1:
A protective layer serves as an intermediary during grid formation, allowing the metallic grid to be deposited and patterned without directly contacting and damaging the thin boron layer. The protective layer is later selectively removed to expose the boron layer for electrode connection while preserving the boron layer's integrity throughout the process.
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 approach allows for the detection of low-energy electrons by maintaining a thin depletion layer close to the surface, reducing the 'dead zone' and preventing damage to the boron layer, thereby improving the detection efficiency of radiation detectors.
Implementation Method 1
the etching comprising a first step of dry etching, the step of dry etching defining the grid but leaving a thin layer of conductive material on the part of the boron layer to be exposed
Implementation Method 2
followed by a second step of wet etching, the step of wet etching completely removing the conductive layer from the part of the boron layer to be exposed
Implementation Method 3
Because the boron layer and the silicon-boride layer are thin, e.g. 3-5 nm each, electrons with an energy of, for example, between 200 eV and 40 keV (or up to 400 keV in the case of a TEM) can enter the intrinsic layer to be detected
Data Source
AI summary
The invention discloses a process for manufacturing a radiation detector for detecting e.g. 200 eV electrons. This makes the detector suited for e.g. use in an Scanning Electron Microscope. The detector is a PIN photodiode with a thin layer of pure boron connected to the p+-diffusion layer. The boron layer is connected to an electrode with an aluminium grid to form a path of low electrical resistance between each given point of the boron layer and the electrode. The invention addresses forming the aluminium grid on the boron layer without damaging the boron layer. To that end the grid of aluminium is formed by covering the boron layer completely with a layer of aluminium and then removing part of the layer of aluminium by etching, the etching comprising a first step (304) of dry etching, the step of dry etching defining the grid but leaving a thin layer of aluminium on the part of the boron layer to be exposed, followed by a second step (308) of wet etching, the step of wet etching completely removing the aluminium from the part of the boron layer to be exposed.