Planarizing Reflective Surfaces Over Cavities Using Compensatory Etching
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Solution Overview
Problem
Fabricating flat reflective surfaces for micro devices like spatial light modulators is challenging due to sagging issues when forming layers over cavities, leading to unwanted light scattering and reduced contrast and brightness in display images.
Innovation Solution
A method involving the use of sacrificial and compensatory materials, where a sacrificial material is disposed in a recess and a compensatory layer is formed over it, followed by isotropic etching to create a flat surface co-planar with the upper layer, allowing for the formation of a reflective layer with minimal height variation, thereby reducing light scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a layer is formed over a cavity using conventional techniques, then the cavity structure is created, but the layer sags and creates height variations greater than 0.1 microns leading to light scattering
Solution Approach 1:
The patent applies preliminary action by forming a compensatory layer over the cavity before forming the final reflective layer. This compensatory layer is specifically designed to offset the sagging that would otherwise occur in the reflective layer, pre-compensating for the deformation and ensuring the final surface remains flat within 0.1 microns.
Solution Approach 2:
The patent changes the physical parameters of the cavity region by introducing a compensatory layer with specific thickness and material properties. This layer modifies the local height parameter to counterbalance the sagging effect, transforming the problematic sagged surface into a flat surface that prevents light scattering.
2Manufacturing precision
If conventional techniques are used to form flat surfaces over cavities, then the cavity structure is maintained, but excessive material and time are required
Solution Approach 1:
The compensatory layer is formed in advance with the exact thickness needed to compensate for cavity sagging. This preliminary action eliminates the need for subsequent time-consuming material removal processes and reduces overall material waste by precisely controlling the final surface flatness from the beginning.
Solution Approach 2:
The patent applies local quality by placing the compensatory layer specifically over the cavity region where sagging occurs, rather than adding material uniformly across the entire substrate. This localized approach minimizes material usage while achieving the required flatness, and the compensatory layer can be selectively removed after serving its purpose.
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 the production of micro devices with flat mirror surfaces that use less material and time, reducing light scattering and enhancing contrast and brightness in spatial light modulators.
Implementation Method 1
A first portion of the compensatory material is removed using isotropic etching to form a substantially flat surface on the sacrificial material
Data Source
AI summary
A method for fabricating a micro structure includes disposing a sacrificial material in a recess formed in a lower layer and forming a layer of compensatory material on the sacrificial material in the recess. The compensatory material is higher than the upper surface of the lower layer. A first portion of the compensatory material is removed to form a substantially flat surface on the sacrificial material. The substantially flat surface is substantially co-planar with the upper surface of the lower layer. An upper layer is formed on the lower layer and the substantially flat surface.