Height-Modulated Diffractive Grating via Sacrificial Imprinting
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Solution Overview
Problem
Current methods for manufacturing diffractive gratings, especially those with height and fill factor modulation, are complex, require multiple fabrication cycles, and have low yield, making it difficult to achieve precise control over diffraction efficiency for mass production, particularly with inorganic materials.
Innovation Solution
A method involving the use of a sacrificial structure for imprinting, followed by conformal deposition of the final grating material and subsequent removal of the sacrificial layer to create height- and optionally fill factor-modulated gratings, reducing the need for high-precision processing and enabling industry-scale production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication methods with multiple cycles are used to achieve height and fill factor modulation, then diffraction efficiency control is improved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent applies preliminary action by first forming a sacrificial structure with the desired height and fill factor modulation pattern before depositing the final grating material. This preliminary sacrificial structure serves as a template that guides the subsequent conformal deposition, eliminating the need for multiple fabrication cycles and complex alignment steps. The sacrificial structure is removed after deposition, leaving the modulated grating pattern directly formed in the final material.
Solution Approach 2:
The patent uses a sacrificial structure as an intermediary element that temporarily holds the desired modulation pattern. This intermediary structure enables the transfer of the modulation pattern to the final grating material through conformal deposition, after which the sacrificial structure is removed. This intermediary approach simplifies the overall process by decoupling the pattern formation from the material deposition.
2Manufacturing precision
If multiple fabrication cycles with alignment are used to define different element heights, then height modulation is achieved, but productivity decreases due to low yield and time-consuming processes
Solution Approach 1:
The sacrificial structure is formed in advance with all desired height variations already present, eliminating the need for multiple sequential fabrication cycles. Each deposition cycle can now define a single element height uniformly across the substrate, significantly reducing the total number of process steps and improving manufacturing yield.
Solution Approach 2:
The patent segments the fabrication process into distinct functional steps: first forming the sacrificial structure with all height information, then performing simple conformal depositions for each grating layer. This segmentation allows parallel processing and eliminates the need for complex multi-cycle alignment operations, thereby improving productivity.
3Manufacturing precision
If highly anisotropic etching is used to achieve vertical sidewalls, then manufacturing precision is improved, but the process becomes more complex and requires nanometer-level lateral placement accuracy
Solution Approach 1:
The patent uses the sacrificial structure as a master template that is copied into the final grating material through conformal deposition. This copying approach transfers the vertical sidewall geometry directly from the sacrificial structure to the final grating, eliminating the need for highly anisotropic etching of the final material. The verticality is achieved during the sacrificial structure formation, which can use simpler, more robust processes.
4Manufacturing precision
If overlay exposure with nanometer-level lateral placement accuracy is used, then manufacturing precision is improved, but any deviations cause losses in optical performance and reduce productivity
Solution Approach 1:
The sacrificial structure serves as a physical template that is directly copied into the final grating material through conformal deposition. This copying mechanism eliminates the need for overlay exposure and nanometer-level lateral placement accuracy, as the pattern is transferred through physical conformity rather than repeated lithographic alignment. This significantly reduces sensitivity to placement errors and improves optical performance yield.
Solution Approach 2:
The sacrificial structure acts as an intermediary that physically defines the pattern geometry before material deposition. This intermediary approach replaces precision lithographic alignment with a more robust physical templating process, reducing the criticality of lateral placement accuracy and improving both yield and optical performance.
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 high-precision, cost-effective production of modulated gratings with improved diffraction efficiency, suitable for mass production, including the use of inorganic materials, and simplifies the manufacturing process by eliminating the need for multi-cycle high lateral precision processing.
Implementation Method 1
the excess amount of the final grating material and the sacrificial structure are removed in order to provide a negative of the sacrificial structure
Implementation Method 2
covering the entire structure by an excess amount of final grating material
Data Source
Figure 1A~1D
Figure 2A~2B
AI summary
The invention concerns a method of manufacturing a height-modulated optically diffractive grating. The method comprises providing a substrate and manufacturing a plurality of temporary elements of first material onto the substrate, the elements being separated by gaps and arranged as a periodic structure comprising at least two periods having different element heights. A coating layer of second material is deposited on the plurality of temporary elements such that the coating layer fills said gaps and covers said temporary elements. Then, a uniform layer of the second material is removed in order to expose said temporary elements and the first material is removed in order to form a height -modulated pattern of the second material onto the substrate as the optically diffractive grating. The invention relaxes manufacturing constraints when manufacturing gratings with locally varying diffraction efficiency.