Planarizing Overcoat Layer on Slanted Surface-Relief Structures
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Solution Overview
Problem
The challenge in achieving a uniform and planar overcoat layer on slanted surface-relief structures, such as slanted gratings, is exacerbated by the varying configuration of ridges and grooves, leading to inefficiencies in light coupling and refractive index variations, particularly in waveguide-based display systems for augmented reality applications.
Innovation Solution
The implementation of a method involving atomic layer deposition (ALD) followed by ion beam etching and chemical-mechanical planarization techniques to achieve a flat top surface, where the ion beam is angled to selectively remove overcoat material from non-planar surface portions, and the use of spin-coating with etching to ensure uniformity and refractive index consistency across the overcoat layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional deposition methods are used to form an overcoat layer on slanted surface-relief structures, then the grooves can be filled and ridges covered, but the resulting surface is non-planar with varying thickness and refractive index
Solution Approach 1:
The patent applies preliminary action by performing multiple cyclic deposition operations (such as ALD cycles) before the final planarization step. Each cycle deposits a thin layer that gradually fills grooves and covers ridges, preparing the surface for subsequent planarization. This preliminary buildup ensures complete coverage while setting up the surface morphology that will be refined in later steps.
Solution Approach 2:
The patent uses an intermediary planarization process (chemical-mechanical polishing or ion beam etching) as a mediator between the rough deposited overcoat layer and the final planar surface. This intermediary step removes excess material from protruding regions and fills in valleys, transforming the non-planar deposited surface into a planarized surface suitable for optical applications.
2Reliability
If the overcoat layer is deposited to completely fill grooves and cover ridges, then coverage is improved, but surface non-planarity increases leading to light scattering and refractive index variations
Solution Approach 1:
Multiple cyclic deposition operations are performed as preliminary action to ensure complete groove filling and ridge coverage before the final planarization step. This ensures that the overcoat layer achieves sufficient coverage and thickness for reliable light coupling, while the subsequent planarization corrects surface non-planarity.
Solution Approach 2:
A planarization process acts as an intermediary between deposition and final application. This intermediary step removes excess material from high points and fills valleys, maintaining the coverage benefits while eliminating surface non-planarity that would cause light scattering and refractive index variations.
3Manufacturing precision
If multiple deposition and etching cycles are performed to improve surface uniformity, then refractive index consistency improves, but processing time increases
Solution Approach 1:
The patent employs periodic action through multiple cyclic deposition operations (such as alternating ALD cycles). Each cycle deposits a thin layer uniformly across the surface, and by repeating this process multiple times, the overcoat layer achieves consistent thickness and refractive index throughout. This periodic approach builds uniformity incrementally while controlling overall processing time.
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 results in a substantially flat and even overcoat layer that enhances light coupling efficiency, reduces refractive index variations, and improves the overall performance of waveguide-based display systems by minimizing stray light paths and solvent trapping.
Implementation Method 1
removing a portion of the overcoat layer using an ion beam at a glancing angle
Implementation Method 2
ion beam etching may be utilized to improve the surface finishing of the overcoat layer
Implementation Method 3
after the grooves have been filled by an overcoat material using ALD or other cyclic deposition process
Implementation Method 4
a spin-coating operation may be performed to obtain a substantially flat surface of the overcoat layer
Implementation Method 5
chemical-mechanical planarization techniques may be used to obtain an even or flat surface after an overcoat layer has been formed on the surface-relief structures
Data Source
AI summary
Techniques for producing an overcoat layer on slanted surface-relief structures and devices obtained using the techniques are disclosed. In some embodiments, a method of planarizing an overcoat layer over a surface-relief structure includes removing a portion of the overcoat layer using an ion beam at a glancing angle. The overcoat layer includes planar surface portions and non-planar surface portions. Each of the non-planar surface portions includes a first sloped side and a second sloped side facing the first sloped side. The glancing angle is selected such that the first sloped side of each non-planar surface portion is shadowed from the ion beam by an adjacent planar surface portion such that the ion beam does not reach at least the first sloped side of each non-planar surface portion but reaches the second sloped side of each non-planar surface portion.