High-Reflectivity Silver Seed Layer for Microcircuit Formation
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Solution Overview
Problem
Conventional photolithography processes struggle to achieve fine pitches in microcircuit formation due to low reflectivity and high surface roughness of typical metal seed layers, leading to nonuniform circuits and defects such as the foot phenomenon and undercut, especially when trying to create circuits with pitches smaller than 14 μm.
Innovation Solution
A method is developed to form a high-reflectivity seed layer with specular reflection characteristics and low surface roughness, using a silver-based seed layer with reflectivity greater than 50% and ten-point mean roughness less than 1 μm, along with a selective etching solution to minimize damage to copper circuits, enabling precise microcircuit pattern formation and high etch factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a typical metal seed layer (copper) is used with low reflectivity, then the substrate material can be manufactured easily, but high energy is required to cure the photosensitive resin and diffuse reflection damages the photosensitive resin layer
Solution Approach 1:
The patent changes the optical parameters of the seed layer by selecting silver or aluminum materials with high reflectivity (greater than 40% at 365-405 nm wavelength) instead of conventional copper. This parameter change improves specular reflection and reduces the energy required for photosensitive resin curing, thereby enhancing curing precision and preventing foot phenomenon without significantly complicating the manufacturing process
Solution Approach 2:
The patent employs a composite structure consisting of a substrate material with a metal seed layer. By combining the substrate with a high-reflectivity metal layer (silver or aluminum), the system achieves both ease of manufacture and high curing precision. The composite material approach allows the seed layer to provide optical benefits while the substrate maintains manufacturing advantages
2Ease of manufacture
If a typical metal seed layer with high surface roughness is used, then the substrate can be manufactured with standard processes, but diffuse reflection occurs during exposure and damages the photosensitive resin layer
Solution Approach 1:
The patent changes the surface roughness parameter of the seed layer by specifying a ten-point mean roughness Rz of less than 1 μm for silver or aluminum seed layers. This parameter improvement reduces diffuse reflection during exposure, preventing damage to the photosensitive resin layer and ensuring uniform circuit patterns are formed without requiring complex additional processing steps
3Productivity
If conventional etching solution is used to remove the seed layer, then the seed layer can be etched, but copper circuit portions are also etched together causing nonuniform thickness and linewidth
Solution Approach 1:
The patent applies local quality by developing a selective etching solution that targets specific material properties. The etching solution is formulated to selectively attack silver or aluminum seed layers while leaving copper circuit portions unaffected. This localized chemical selectivity enables the seed layer to be removed with high productivity while preserving the uniformity and precision of the copper circuit dimensions
4Object-affected harmful factors
If low energy is used for exposure to avoid damaging the photosensitive resin, then the resin layer is preserved, but the underlayer is not completely cured causing undercut phenomenon
Solution Approach 1:
The patent changes the optical parameter of the seed layer by implementing high reflectivity (greater than 40%), which increases the amount of light reflected back through the photosensitive resin layer during exposure. This enhanced reflection provides sufficient energy to completely cure the underlayer at lower exposure energies, preventing undercut phenomenon while preserving the photosensitive resin layer from damage
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 allows for the creation of ultrafine microcircuit patterns smaller than 7 μm, enabling the production of lightweight, thin, and compact high-performance circuits with improved curing precision and reduced defects, and allows for selective etching of silver seed layers without damaging copper circuits.
Implementation Method 1
a conductive high-reflectivity seed layer which has a specular reflection characteristic and a reflectivity of greater than 50%
Implementation Method 2
an oxidizing agent; amines or an ammonium compound
Data Source
AI summary
The disclosure relates to a microcircuit forming method. The microcircuit forming method according to the disclosure comprises: a seed-layer forming step for forming a high-reflectivity seed layer on a substrate material by using a conductive material; a pattern-layer forming step for forming a pattern layer on the seed layer, the pattern layer having a pattern hole arranged thereon to allow the seed layer to be selectively exposed therethrough; a plating step for filling the pattern hole with a conductive material; a pattern-layer removing step for removing the pattern layer; and a seed-layer patterning step for removing a part of the seed layer which does not overlap the conductive material in the plating step, wherein the high-reflectivity seed layer has a specular reflection property.