Multi-Layer Shadow Mask with Stress Gradient for Sag Mitigation
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Solution Overview
Problem
Shadow-mask deposition in semiconductor fabrication faces challenges with gravity-induced sag leading to feathering issues, limiting the minimum feature size and pattern density, especially in high-resolution applications like OLED displays and organic solar cells, where thin and large-area membranes experience significant gravity-induced variation and shadowing effects.
Innovation Solution
A multi-layer shadow mask membrane with a stress gradient is used, comprising a first layer with residual tensile stress and a second layer with residual compressive stress, positioned to counteract gravity-induced sag, allowing for a mechanically pre-biased configuration that mitigates sag and maintains deposition uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin and large-area shadow mask membrane is used to achieve high-resolution patterning, then the minimum feature size and pattern density are improved, but gravity-induced sag causes feathering effects and deposition non-uniformity
Solution Approach 1:
The patent changes the physical parameters of the shadow mask membrane by creating a stress gradient through controlled residual stresses in multi-layer structures. This modifies the membrane's mechanical properties to achieve pre-biasing that counteracts gravity-induced sag, allowing thin large-area membranes to maintain flatness while enabling high-resolution patterning
Solution Approach 2:
The patent employs composite membrane structures with multiple layers having different residual stress characteristics. By combining materials with tensile and compressive stresses in specific configurations, the composite structure creates a controlled stress gradient that generates pre-biasing forces to counteract gravitational effects on the membrane
2Area of stationary object
If the shadow mask membrane area is increased to cover large substrates, then the deposition area is improved, but gravity-induced sag and shadowing effects worsen
Solution Approach 1:
The patent modifies the mechanical parameters of large-area membranes by introducing controlled stress gradients. This allows the membrane to maintain structural stability and flatness across large areas, preventing gravity-induced sag and shadowing effects while covering extensive substrate areas for uniform deposition
Solution Approach 2:
The patent addresses the two-dimensional membrane stability problem by introducing a stress gradient dimension. The controlled distribution of residual stresses through the membrane thickness creates a three-dimensional stress state that generates pre-biasing forces, transforming the membrane's mechanical behavior to resist gravitational effects across large areas
3Manufacturing precision
If a mechanically pre-biased configuration with stress gradient is implemented, then deposition uniformity is improved, but the device complexity increases
Solution Approach 1:
The patent uses composite multi-layer membrane structures where each layer contributes specific residual stress characteristics. The complexity is managed by systematically combining layers with tensile and compressive stresses in controlled configurations, creating predictable stress gradients that achieve pre-biasing while maintaining manufacturability
Solution Approach 2:
The patent controls the complexity by precisely managing stress gradient parameters rather than creating complex geometric structures. By adjusting residual stress magnitudes and distributions through material selection and layer thickness control, the system achieves mechanical pre-biasing through parameter optimization rather than structural complexity
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 enables the direct patterning of high-resolution material layers with smaller minimum features and higher pattern density by compensating for gravity-induced sag, improving deposition uniformity and reducing feathering effects across large areas.
Implementation Method 1
the composite layer comprises a plurality of layers that includes a first layer having a first thickness and a first residual stress and a second layer having a second thickness and a second residual stress
Implementation Method 2
the first thickness, second thickness, first residual stress, and second residual stress collectively give rise to a first bending moment that is directed along a direction that is substantially normal to the first plane
Implementation Method 3
A thin layer of structural material having a pattern of apertures (i.e., openings) that matches the pattern desired for the deposited material (referred to as a 'shadow mask') is positioned just in front of (but typically not in contact with) the substrate surface. When the flow of material reaches the shadow mask, the passage of material to the substrate is blocked everywhere except at the apertures.
Data Source
AI summary
Shadow masks comprising a multi-layer membrane having a mechanical pre-bias that compensates the effect of gravity on the membrane are disclosed. A shadow mask in accordance with the present disclosure includes a membrane that is patterned with a desired pattern of apertures. The layers of the membrane are selected such that their residual stresses collectively give rise to a stress gradient that is directed normal to the plane of the membrane such that the stress gradient mitigates gravity-induced sag. In some embodiments, the membrane includes a layer pair having internal stresses that are of opposite signs to effect a tendency to bulge outward from the plane of the membrane prior to its release from the substrate. An exemplary membrane includes a layer pair comprising a layer of stoichiometric silicon dioxide that is under residual compressive stress and a layer of stoichiometric silicon nitride that is under residual tensile stress.