Variable Efficiency Diffractive Grating Manufacturing
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Solution Overview
Problem
Current methods for fabricating height and fill factor modulated diffractive gratings, especially for inorganic materials with high refractive indices, are complex and inefficient, leading to low yield and accuracy issues in achieving maximum diffraction efficiency, particularly in mass production for applications like near-to-eye displays.
Innovation Solution
A method involving temporary elements with varying characteristics on a substrate, followed by conformal deposition and removal processes, allowing for simultaneous height and fill factor modulation of diffractive gratings using easily processable materials like inorganic oxides or nitrides, enabling precise control over diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication methods are used for height and fill factor modulated diffractive gratings, then manufacturing complexity increases and yield decreases, but diffraction efficiency control is achieved
Solution Approach 1:
The patent applies preliminary action by pre-forming temporary elements with varying heights and fill factors before the final grating material deposition. These temporary elements serve as molds that define the eventual grating structure characteristics. By preparing the pattern geometry in advance through temporary elements, the method achieves precise height and fill factor modulation without requiring complex sequential fabrication cycles for each parameter adjustment.
Solution Approach 2:
The patent uses temporary elements as intermediary structures that facilitate the transfer of pattern geometry to the final grating. These temporary elements act as mediators between the lithographic pattern and the final diffractive grating structure, allowing complex height and fill factor modulations to be achieved through a simplified conformal deposition process followed by temporary element removal.
2Manufacturing precision
If multiple fabrication cycles with alignment are used to define different element heights, then height modulation accuracy improves, but productivity decreases and overlay precision requirements increase
Solution Approach 1:
The patent performs the height variation definition in a single preliminary lithographic step by creating temporary elements with different heights and fill factors. This preliminary action captures all height modulation information in one go, eliminating the need for multiple sequential fabrication cycles. The conformal deposition that follows simply replicates this pre-defined geometry, achieving both high precision and high productivity.
3Manufacturing precision
If highly anisotropic etching is used to achieve vertical side walls, then grating profile precision improves, but process complexity and yield loss increase
Solution Approach 1:
The patent employs self-service by using conformal deposition that automatically conforms to the temporary element geometry, creating vertical side walls and precise grating profiles without requiring highly anisotropic etching. The deposition process itself serves to define the final grating structure, eliminating the need for complex etching processes and their associated complexity and yield issues.
4Manufacturing precision
If nanometer level lateral placement accuracy is required for overlay exposure, then grating alignment precision improves, but manufacturing cost and complexity increase
Solution Approach 1:
The patent performs all alignment-critical pattern definition in a single preliminary lithographic step that creates the temporary elements. By consolidating the alignment requirements into one exposure event rather than multiple overlay steps, the method achieves nanometer-level alignment precision without the cumulative complexity and cost of multi-step overlay processes.
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 high-precision, industry-scale production of modulated gratings with predictable optical properties, suitable for high refractive index materials, enhancing diffraction efficiency and optical performance in display applications.
Implementation Method 1
conformal deposition and removal processes, allowing for simultaneous height and fill factor modulation
Implementation Method 2
diffractive gratings, which can be used for example in display applications, such as near-to-eye displays
Data Source
Figure 1A~1F
Figure 2A~2B
AI summary
The invention concerns a method of manufacturing a modulated optically diffractive grating and a corresponding grating. The method comprises providing a substrate and manufacturing a plurality of temporary elements onto the substrate, the temporary elements being arranged in a periodic pattern comprising at least two periods having different element characteristics. Next, a first deposition layer is deposited so as to at least partially cover the temporary elements with the first deposition layer and the temporary elements are removed from the substrate in order to form onto the substrate a modulated diffractive grating of first grating elements made of the first deposition layer, the pattern comprising within each period a plurality of first grating elements and one more gaps between the first grating elements.The invention allows for producing high-quality gratings with locally varying diffraction efficiency.