Pixel Mirror Planarity via Sacrificial Layer Etching
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Solution Overview
Problem
Conventional electronic devices with varying surface heights of metal layers, such as mirror elements, suffer from light scattering, leading to reduced image quality and contrast due to non-planarity of the mirror surfaces.
Innovation Solution
A method involving a series of sacrificial layers and etching processes is employed to form a digital micromirror device with improved planarity, where sacrificial layers are strategically used to reduce step heights and non-planarity, allowing for the formation of pixel mirrors with non-planarity no greater than 50 nm, thereby enhancing the reflecting characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional metal layer formation methods are used, then manufacturing process is simple, but surface height variation occurs leading to light scattering
Solution Approach 1:
The manufacturing process is divided into multiple sequential stages, each introducing a sacrificial layer at different levels. The first sacrificial layer is formed before the upper metal layer, the second is formed after partial removal of the upper metal layer, and the third is formed after further removal. This segmented approach allows progressive planarization at each stage, achieving high surface precision without requiring a single complex planarization step.
Solution Approach 2:
Sacrificial layers are strategically placed in advance at specific locations where height variations are anticipated. The first sacrificial layer is positioned before upper metal layer formation to prevent initial step heights, the second is positioned after partial etching to address emerging topography, and the third is positioned before final pixel mirror formation to ensure ultimate planarity. This preliminary positioning of sacrificial material allows proactive correction of surface variations.
2Reliability
If multiple sacrificial layers are used to improve planarity, then light scattering is reduced, but manufacturing steps increase
Solution Approach 1:
Each sacrificial layer serves multiple functions: it acts as a planarization element to reduce step heights, serves as a temporary support structure during subsequent processing, and provides a reference level for precise etching operations. The sacrificial layers are removed only after they have fulfilled all their functions, maximizing their utility throughout the manufacturing process.
Solution Approach 2:
The sacrificial layers act as intermediary elements that mediate between the lower metal layer structures and the upper metal layer. They fill gaps and create transitional surfaces that allow smooth integration of metal layers at different heights, preventing direct exposure of step discontinuities that would cause light scattering.
3Shape
If step heights are reduced to improve mirror planarity, then reflection angle variation decreases, but process complexity increases
Solution Approach 1:
The etching process is applied selectively at different locations and stages rather than uniformly across the entire structure. Partial etching removes metal only in specific regions where sacrificial layers need to be exposed, while leaving other regions intact. This localized etching approach reduces step heights precisely where needed without unnecessarily complicating the overall process.
Data Source
AI summary
A method of forming an electronic device includes providing a patterned lower metal layer over a substrate and a first sacrificial layer there between. A second sacrificial layer is formed over the metal layer, and a portion thereof is removed. A third sacrificial layer is formed over the second sacrificial layer, and an upper metal layer is formed over the third sacrificial layer. A portion of the upper metal layer is removed, and the first, second and third sacrificial layers are removed.