Double Resist Electrodeposition Bonding for Copper Pillar Joints
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Solution Overview
Problem
Conventional bonding processes for chips on wafers, such as solder joints and solid phase diffusion bonding, face issues with thermal warping and low strength due to high temperatures, while electroless copper deposition has low strength and long bonding times, and nickel electroless deposition has inferior properties and high temperatures.
Innovation Solution
The use of a double resist structure for electrodeposition bonding, where copper pillars and pads are formed with aligned openings in resist layers, allowing copper to be deposited only on the pads and pillars, reducing undercut and stress concentration, and enabling bonding at low temperatures with high strength and low electrical resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional bonding processes (solder joints or solid phase diffusion bonding) are used, then bonding strength is achieved, but thermal warping occurs due to high temperatures over 150 degrees C
Solution Approach 1:
The invention changes the bonding temperature parameter from conventional high temperatures (>150°C) to low temperature (room temperature or below 50°C) by using electrodeposition bonding. This is achieved by applying electrical current to deposit copper metal that bonds the chip to substrate, eliminating thermal warping while maintaining bonding strength through controlled electrochemical deposition
2Strength
If electroless copper deposition is used, then bonding is achieved, but the strength is low and bonding time is long
Solution Approach 1:
The invention replaces the chemical-based electroless deposition system with an electrical-based electrodeposition system. By applying electrical current, copper ions are rapidly deposited onto the bonding surfaces, achieving both high bonding strength and short bonding time (completing in minutes rather than hours), as the electrical field drives rapid metal deposition
3Reliability
If nickel electroless deposition is used, then better joints are fabricated, but bonding temperature is high (80 degrees C) and bonding time is much longer than 0.5 hours
Solution Approach 1:
The invention changes multiple parameters simultaneously: temperature is reduced from 80°C to room temperature or below, and bonding time is reduced from over 0.5 hours to minutes. This is achieved by using copper electrodeposition instead of nickel electroless deposition, where electrical current drives rapid copper metal deposition that forms strong, reliable joints without requiring high temperature or extended time
4Manufacturing precision
If copper is deposited only on pads and pillars, then undercut and stress concentration are reduced, but precise deposition control is required
Solution Approach 1:
The invention segments the deposition process into two distinct stages using a double resist structure: first, a mandrel resist defines the basic pad/pillar patterns; second, a release resist with openings only over pads and pillars is applied. This segmentation allows precise copper deposition only on desired areas while the mandrel resist protects surrounding regions, reducing undercut and stress concentration without requiring overly complex single-step masking
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 prevents scallop-shaped joints, maintains conduction area, and facilitates bonding with high strength and low electrical resistivity, even with height variations, and prevents corrosion and oxidation by using electroless nickel and gold plating.
Implementation Method 1
electrodepositing a copper layer on outside surfaces of the first copper structures, outside surfaces of the second copper structures, bonding material receiving regions defined between the aligned first and second copper structures, and portions of the first seed layer on the outer surface of the first substrate
Data Source
AI summary
A semiconductor structure includes a wafer having a wafer outer surface; a semiconductor chip; and a plurality of copper pillars on the semiconductor chip. The pillars have curved end portions and pillar outside surfaces. Also included are a plurality of copper pads on the wafer. The pads have end portions aligned with the curved end portions of the plurality of copper pillars on the semiconductor chip, and the curved end portions of the plurality of copper pillars and the end portions of the plurality of copper pads define a plurality of bonding material receiving regions. The pads have pad outside surfaces. A copper bonding layer is on the pillar outside surfaces, the pad outside surfaces, the bonding material receiving regions, and portions of the outer surface of the wafer. The portions have an annular shape about the copper pads when viewed in plan.