Micropad Interconnects Using CoWB Barrier and Electroless Plating
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Solution Overview
Problem
The challenge in stacking integrated circuits lies in the interconnection between different die or between die and a wafer, particularly due to issues like undercutting and oxidation of metals used in micropads during electroplating processes.
Innovation Solution
The use of a micropad with a barrier layer of cobalt/tungsten/boron (CoWB) followed by copper plating and tin immersion, employing electroless plating processes to form a robust and oxidation-resistant interconnect, which minimizes undercutting and oxidation, ensuring reliable mechanical and electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroplating is used to form micropads, then copper/tin interconnects can be formed, but undercutting and oxidation of the metals occur
Solution Approach 1:
A barrier layer is formed on the contact area before plating the copper and tin layers. This preliminary protective layer prevents oxidation of the metal interconnects and reduces undercutting during the electroplating process, thereby improving interconnect reliability while eliminating the harmful effects of oxidation and undercutting
Solution Approach 2:
The barrier layer acts as an intermediary between the contact area and the copper/tin interconnects. This intermediate layer protects the underlying contact area from oxidation and prevents undercutting of the metal layers during electroplating, resolving the contradiction between forming reliable interconnects and avoiding harmful undercutting and oxidation effects
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 enhances the reliability and strength of interconnects between stacked die and wafers by reducing oxidation and undercutting, maintaining the size of the micropads and ensuring robust bonding with higher melting temperature compounds like Cu3Sn and Cu6Sn5, thus improving the stability and functionality of the stacked integrated circuits.
Implementation Method 1
An electroless plating process is used to plate the contact area with the barrier
Implementation Method 2
Another electroless plating process is used to plate the barrier with copper
Implementation Method 3
The tin may then be formed over the copper by immersion plating for the pads to complete the pads needing the tin
Implementation Method 4
Thermocompression bonding of micropads from two different die or wafers provide both mechanical and electrical inter-strata connections of the stacked die
Data Source
AI summary
A semiconductor process is taught for performing electroless plating of copper overlying at least a portion of a layer comprising cobalt, nickel, or both cobalt and nickel. The cobalt and/or nickel comprising layer may be formed using electroless plating. For some embodiments, a tin layer is then formed overlying the copper. The tin layer may be formed using immersion plating or electroless plating. A micropad may comprise the cobalt and/or nickel comprising layer and the copper layer. In some embodiments, the micropad may also comprise the tin layer. In one embodiment, the micropad may be compressed at an elevated temperature to form a copper tin intermetallic compound which provides an interconnect between a plurality of semiconductor devices.