Multi-Layer Substrate Metal Structure Covering via Photoresist Undercutting
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Solution Overview
Problem
Current methods for manufacturing metal structures in multi-layer substrates, such as etching and build up processes, fail to produce finer metal structures with smooth side surfaces and reliable cover metal layers, leading to increased roughness, corrosion, and reduced integration due to isotropic etching and the need for multiple photomasks.
Innovation Solution
A method involving the coating and exposure of photoresist layers with controlled undercutting to form metal structures, allowing for the formation of a single photomask-based top-cover and under-cover metal layers that cover the top, side, and under surfaces, preventing corrosion and enabling coaxial structures through vacuum coating and adhesion enhancement processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet etching method is used to form metal structures, then the manufacturing process is simple, but the side surfaces become rough and undercuts occur due to isotropic etching
Solution Approach 1:
The patent replaces the chemical wet etching process with a mechanical/physical deposition process. Specifically, it uses photoresist coating and selective removal followed by metal deposition to form metal structures with smooth side surfaces, eliminating the isotropic etching problem while maintaining manufacturing feasibility
Solution Approach 2:
Instead of forming metal structures by removing material (etching), the patent inverts the approach by forming structures through selective deposition. It coats photoresist, selectively removes portions, and deposits metal only where needed, thereby achieving smooth vertical sidewalls without undercutting
2Reliability
If multiple photomasks are used to form complete cover metal layers, then the metal structure reliability is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the formation of top-cover and under-cover metal layers into a single deposition process. By coating photoresist on the completed multi-layer substrate and selectively removing it, the patent enables simultaneous deposition of protective metal layers on both top and bottom surfaces in one operation, reducing complexity while maintaining reliability
Solution Approach 2:
The photoresist layer serves multiple functions: it acts as a mask for selective metal deposition, provides structural support during processing, and enables the formation of complete cover layers on both top and bottom surfaces. This multi-functionality reduces the need for separate photomasks and processing steps
3Reliability
If copper is used as metal structure material, then the electrical conductivity is improved, but the corrosion resistance deteriorates when polyimide is used for dielectric layer
Solution Approach 1:
The patent creates a composite protective structure by depositing cover metal layers (such as gold or other corrosion-resistant metals) over the copper metal structures. This forms a composite system where the inner copper layer provides electrical conductivity while the outer cover layer provides corrosion resistance, combining the advantages of both materials
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 results in finer, smoother metal structures with enhanced reliability and integration capabilities, overcoming the limitations of existing technologies by forming complete cover metal layers and preventing corrosion, while allowing for the creation of coaxial structures and flexible substrates.
Implementation Method 1
exposing the photoresist layer to define a predetermined position of the metal structure
Implementation Method 2
forming the metal structure at the predetermined position; forming at least one top-cover metal layer to cover a top surface and two side surfaces of the metal structure
Data Source
AI summary
Disclosed is a manufacturing method of metal structure in multi-layer substrate. The manufacturing method includes following steps: coating at least one photoresist layer on a surface of a dielectric layer; exposing the photoresist dielectric layer to define a predetermined position of the metal structure; removing the photoresist layer at the predetermined position to undercut an edge of the photoresist layer adjacent to the predetermined position by a horizontal distance of at least 0.1 μm between a top and a bottom of the edge; forming the metal structure at the predetermined position; and forming at least one top-cover metal layer to cover a top surface and two side surfaces of the metal structure. The present invention can form a cover metal layer covering the top surface and the two side surfaces by one single photomask.