Undercutting Printed Masks for Sub-20 µm Features
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Solution Overview
Problem
Digital lithography systems face limitations in producing feature sizes smaller than the minimum droplet size, typically 20-40 µm, due to the large droplet size, which is insufficient for modern micro-electronic, opto-electronic, and bio-electronic applications requiring features in the range of 5-20 µm.
Innovation Solution
A method involving the use of a printed mask formed by digital lithography where droplets of phase-change material coalesce to create features wider than the individual droplet diameter, followed by controlled development and undercutting to achieve finer feature sizes, allowing for the formation of thin film features and sub-pixel frames with widths less than the mask width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If digital lithography uses droplets of phase-change material to form masks, then the printing process is simplified and direct pattern deposition is achieved, but the minimum feature size is limited to 20-40 µm which is too large for modern applications
Solution Approach 1:
The patent applies preliminary action by first forming a mask layer with wider features (20-40 µm) using digital lithography, then performing an undercut etch to create narrower features (5-20 µm) beneath the mask. This two-step approach allows the printing process to remain simple while achieving the required precision through the preliminary mask formation followed by controlled undercutting.
Solution Approach 2:
The patent segments the feature formation process into two distinct steps: (1) mask layer formation using digital lithography droplets, and (2) undercut etching to create the final narrow features. This segmentation allows each step to be optimized independently - the printing step for ease of manufacture and the etching step for precision.
2Manufacturing precision
If droplets are made smaller to achieve finer features, then feature size precision improves, but the minimum droplet size of 20-40 µm cannot be overcome with current digital lithography technology
Solution Approach 1:
The patent transitions from two-dimensional mask features to three-dimensional undercut structures by etching beneath the mask layer. This dimensional change allows the final feature size to be determined by the undercut depth and geometry rather than the mask feature size, effectively decoupling the droplet size constraint from the final feature precision.
Solution Approach 2:
The mask layer serves as an intermediary element that is wider than the desired final features. This intermediary structure enables the use of larger droplets for mask formation while still achieving narrower final features through the undercut etching process that removes material beneath and around the mask.
3Manufacturing precision
If the mask width is reduced to match the desired feature size, then feature precision improves, but digital lithography cannot produce masks narrower than the droplet diameter
Solution Approach 1:
The patent performs preliminary action by creating an oversized mask layer that exceeds the desired final feature width. This preliminary mask structure is then used to define the region for undercut etching, allowing the final feature width to be precisely controlled by the etch process rather than constrained by the digital lithography droplet size.
Solution Approach 2:
The patent changes the controlling parameter for feature width from mask width (which is limited by droplet size) to undercut depth and geometry. By shifting the critical dimension control to the etching process parameters, the system achieves adaptability to produce narrower features than the original mask dimensions.
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 production of thin film features and sub-pixel frames with widths as small as 5-20 µm, overcoming the size limitations of traditional digital lithography and improving the precision and uniformity of microelectronic and opto-electronic device fabrication.
Implementation Method 1
Once dispensed from an ejector, a print material droplet attaches itself to the substrate through a wetting action, then proceeds to solidify in place.
Implementation Method 2
In the case of printing phase-change materials, solidification occurs when a heated and liquefied printed droplet loses its thermal energy to the substrate and/or environment and reverts to a solid form.
Implementation Method 3
The printed mask material is then used to mask a portion of a photoresist layer, and the photoresist layer is developed underneath the printed mask material.
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 1G~1J
AI summary
A print patterned mask is formed a digital lithographic process on the surface of a photoresist or similar material layer. The print patterned mask is then used as a development or etching mask, and the underlying layer overdeveloped or overetched to undercut the print patterned mask. The mask may be removed and the underlying structure used an etch mask or as a final structure. Fine feature widths, narrower the minimum width of the print patterned mask features, may be obtained while realizing the benefits of digital lithography in the manufacturing process.