Directional Etching of Polymer Barrier Layers for Fine Line Redistribution
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Solution Overview
Problem
Current methods for achieving fine line and space redistribution layers in silicon interposers face challenges due to the isotropic nature of chemical etchants, leading to reduced dimensions and increased side-wall roughness, and the use of polymer barrier layers with poor thermal and mechanical properties, which limits feature size and process throughput.
Innovation Solution
A method involving directional etching of barrier layers to expose seed layers while maintaining the barrier on metal layers, using etching materials with low reactivity to protect the barrier and allow precise control over seed layer removal, thereby enabling the formation of fine line redistribution layers with improved yield and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chemical etchants are used for copper seed layer etching, then the etching process is simple and cost-effective, but the isotropic nature of the etchants causes over-etching and increased side-wall roughness
Solution Approach 1:
A polymer barrier layer is introduced as an intermediary between the copper seed layer and the etchant. This barrier layer is selectively removed only at the bottom of the via holes, allowing the etchant to access and etch the copper seed layer while preventing lateral etching. The barrier layer acts as a mediator that controls the etching process to be anisotropic, maintaining vertical sidewalls and precise line widths while still using simple chemical etchants.
2Reliability
If the polymer barrier layer is made thicker to prevent etching, then the barrier protection is improved, but the minimum feature size and spacing increase
Solution Approach 1:
The polymer barrier layer is applied conformally across the entire surface, but its protective function is localized only where needed - at the bottom of the via holes. The directional removal process selectively eliminates the barrier layer from the via bottom while preserving it on vertical sidewalls. This local quality approach provides maximum barrier protection exactly where etching occurs, while allowing thin barrier layers elsewhere, thus maintaining fine feature dimensions.
3Manufacturing precision
If polymer barrier layers are used, then copper seed layer etching control is improved, but the thermal and mechanical properties deteriorate
Solution Approach 1:
The polymer barrier layer is extracted or removed after serving its protective function during the etching process. By temporarily introducing the polymer barrier for etching control and then removing it, the process achieves precise etching control without leaving the polymer in the final structure. This eliminates the thermal and mechanical property deterioration associated with permanent polymer presence, while still benefiting from the etching control during fabrication.
4Productivity
If conventional etching processes are used, then process throughput is maintained, but fine line RDL formation is limited
Solution Approach 1:
The polymer barrier layer is applied in advance before the etching process, and its selective removal is performed as a preliminary step to enable precise copper seed layer etching. This preliminary action of preparing the selective barrier configuration allows conventional chemical etchants to achieve fine line RDL formation without requiring complex etching equipment or processes, thus maintaining high throughput while improving manufacturing precision.
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 fine line redistribution layers with precise control and high yield, reducing the need for specialized equipment and extending the capabilities of existing semi-additive processes, while maintaining the integrity of the barrier layer for mechanical and electrical reliability.
Implementation Method 1
directionally etching the barrier layer from a direction orthogonal to the substrate such that at least a portion of the seed layer and the metal layer are exposed, wherein at least a portion of the barrier layer oriented parallel to the direction of the directional etching remains coated on the metal layer
Implementation Method 2
etching performed with an etching material configured to have a low reactivity with the barrier layer such that the portion of the barrier layer remains coated on the metal layer
Implementation Method 3
depositing a metal layer onto the seed layer, the metal layer being deposited in a predetermined pattern onto the seed layer
Data Source
AI summary
Disclosed herein are methods for etch barrier deposition that can include depositing a seed layer onto a substrate, depositing a metal layer onto the seed layer in a predetermined pattern, coating the metal layer with a barrier layer, directionally etching the barrier layer from a direction orthogonal to the substrate such that at least a portion of the barrier layer oriented parallel to the direction of the directional etching remains coated on the metal layer, and etching the portion of the seed layer to remove the seed layer from the substrate.