Diffractive Element Wavefront Flatness via Segmented Substrate
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Solution Overview
Problem
Conventional diffractive elements face challenges in achieving high wavefront accuracy due to substrate deformation and limited thickness constraints in lithography processes, which affect their optical functionality and quality.
Innovation Solution
A method involving a stiffer, thicker carrier substrate with higher surface evenness is used to support a thinner functional substrate with a fine structure, ensuring high rigidity and flatness, and the two are permanently connected via vacuum or bonding to maintain structural integrity and optical precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick flat substrate is used to achieve high rigidity and flatness, then wavefront accuracy is improved, but the substrate thickness exceeds the limit for conventional lithography systems
Solution Approach 1:
The substrate system is segmented into two separate substrates: a thin functional substrate (few millimeters thick) that can be processed by conventional lithography systems, and a thick carrier substrate (several centimeters thick) that provides the necessary rigidity and flatness. This segmentation allows each substrate to fulfill its specific function without compromising the other.
Solution Approach 2:
The thin functional substrate is permanently attached to the thick carrier substrate, creating a nested structure where the functional substrate is supported by the carrier substrate. This nested configuration allows the thin substrate to benefit from the optical processing advantages while the thick substrate provides mechanical stability.
2Ease of manufacture
If a thin flat substrate is used to meet lithography process requirements, then ease of manufacture is improved, but wavefront accuracy deteriorates due to substrate deformation
Solution Approach 1:
The functional substrate is first processed with the fine structure using conventional lithography systems while it is thin and manageable. After the fine structure is created, the substrate is permanently attached to the carrier substrate to establish the desired flatness before final optical assembly. This preliminary processing avoids the need to handle thick substrates during delicate lithography operations.
Solution Approach 2:
The carrier substrate acts as an intermediary that transfers its flatness and rigidity to the thin functional substrate through permanent attachment. This intermediary relationship allows the thin substrate to achieve the wavefront accuracy that would otherwise require a much thicker substrate.
3Ease of operation
If the flat substrate is detached from the lithography holder, then ease of operation is improved, but the desired flatness is lost
Solution Approach 1:
The functional substrate and carrier substrate are merged through permanent attachment methods (such as bonding or fusion). This merging ensures that the flatness achieved during lithography processing is maintained permanently, eliminating the need to keep the substrate attached to the lithography holder for flatness maintenance.
Solution Approach 2:
The carrier substrate serves as a permanent copy or replica of the lithography holder's flat surface. By transferring the flatness requirement from the temporary lithography holder to the permanent carrier substrate, the functional substrate can be freely handled and detached without losing its flatness.
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 enhances wavefront accuracy and rigidity, protecting the fine structure from external influences and allowing for precise post-processing to meet stringent optical application requirements, such as deviations of less than 0.5 μm flatness.
Implementation Method 1
Holograms, diffraction gratings and/or other diffractive elements form an important component for a number of applications of such diffractive elements in the field of optics
Implementation Method 2
the thin flat substrate is brought to an adequate flatness by suitable mounting methods, such as vacuum suction or electrostatic suction on a high-level substrate holder
Implementation Method 3
the thin flat substrate is brought to an adequate flatness by suitable mounting methods, such as vacuum suction or electrostatic suction on a high-level substrate holder
Data Source
Figure 1A~1B
Figure 2A~2C
AI summary
The invention relates to the realisation of a diffractive element with high wave-front flatness. Said diffractive element comprises a flat functional substrate having a first side. A fine structure is arranged on or in said first side, and said functional substrate is arranged with its first side on a flat carrier substrate that has a higher degree of rigidity than the functional substrate.