Selective Solder Plating via Potentiostat Control
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Solution Overview
Problem
Solder alloys are not compatible with semiconductor wafer processing techniques like PECVD and RIE, making it difficult to deposit and pattern photoresist on substrates with complex structures, such as deep vias and raised features, which interferes with selective solder application.
Innovation Solution
A three-electrode electroplating cell with a potentiostat is used to maintain a predetermined voltage potential, allowing selective deposition of solder material onto metal features without covering the underlying metal layers, eliminating the need for photoresist patterning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photoresist deposition and patterning is used to selectively apply solder, then solder placement precision is improved, but device complexity and process difficulty increase due to incompatible semiconductor wafer processing techniques
Solution Approach 1:
The patent replaces the mechanical/photochemical system of photoresist deposition and patterning with an electrochemical system. Instead of using photoresist materials and photolithography processes, the invention uses electroplating with a potentiostat to control voltage potential and achieve selective solder deposition on metal features through electrochemical reactions in a plating bath.
Solution Approach 2:
The patent changes the controlling parameter from photoresist pattern geometry to electrochemical voltage potential. By maintaining a predetermined voltage potential with a potentiostat, the system selectively deposits solder on metal features based on their electrochemical properties rather than requiring complex photoresist patterning, thus simplifying the overall process.
2Productivity
If conventional electroplating is used without voltage control, then deposition speed is improved, but manufacturing precision deteriorates due to non-selective solder deposition on both metal features and metal layers
Solution Approach 1:
The patent introduces a potentiostat that provides feedback control of the voltage potential during electroplating. The potentiostat continuously monitors and adjusts the voltage to maintain a predetermined value, ensuring that solder deposition occurs only on metal features that meet specific electrochemical criteria, thereby achieving both selective precision and efficient deposition.
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
Enables efficient and precise solder deposition on metal features while avoiding the underlying layers, facilitating the sealing of recessed structures without the complexity of photoresist deposition and liftoff processes.
Implementation Method 1
immersing the structure in a plating bath contained in an electroplating cell, the plating bath comprising a selected solder material; applying a voltage potential to the structure, where the structure functions as a working electrode in combination with a reference electrode and a counter electrode that are also immersed in the plating bath; and maintaining the voltage potential at a predetermined value to deposit the selected solder material selectively only on the metal feature
Data Source
AI summary
A method provides a structure that includes a substrate having a metal layer disposed on a surface and a metal feature disposed on the metal layer. The method further includes immersing the structure in a plating bath contained in an electroplating cell, the plating bath containing a selected solder material; applying a voltage potential to the structure, where the structure functions as a working electrode in combination with a reference electrode and a counter electrode that are also immersed in the plating bath; and maintaining the voltage potential at a predetermined value to deposit the selected solder material selectively only on the metal feature and not on the metal layer. An apparatus configured to practice the method is also disclosed.