Copper Bonding With Reducing Gas for Oxide-Free Flip Chip Assembly
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Solution Overview
Problem
In semiconductor packaging, especially in flip chip and thermocompression bonding, copper structures are prone to oxidation and contamination, which can hinder effective bonding between semiconductor elements and substrates, and existing methods do not adequately address these issues during the bonding process.
Innovation Solution
The method involves using a reducing gas, such as formic acid vapor, in conjunction with localized heating to clean copper oxides and contaminants from the surfaces of electrically conductive structures, allowing for improved bonding by establishing and re-establishing contact between the semiconductor element and substrate while directing the reducing gas through a manifold angled between 10-60 degrees to ensure efficient cleaning and bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional bonding methods are used without reducing gas, then the bonding process is simpler, but copper structures undergo oxidation and contamination that hinder effective bonding
Solution Approach 1:
The patent applies an inert atmosphere principle by introducing a reducing gas environment during the bonding process. The reducing gas displaces oxygen and creates a protective atmosphere that prevents oxidation of copper structures while enabling reliable bonding. This resolves the contradiction by providing bonding reliability through atmospheric control without requiring fundamentally complex process changes.
Solution Approach 2:
The reducing gas acts as an intermediary substance between the copper structures and the oxidizing environment. It mediates the bonding process by preventing direct contact between oxygen and copper surfaces, thereby eliminating oxidation and contamination while maintaining process simplicity.
2Reliability
If reducing gas is used to prevent oxidation, then bonding reliability improves, but the complexity of the bonding process increases
Solution Approach 1:
The patent changes the atmospheric parameter by introducing reducing gas with specific flow rates and concentrations. By controlling gas flow parameters and maintaining appropriate partial pressures, the system achieves reliable oxidation prevention through quantifiable parameter control rather than complex procedural changes.
3Manufacturing precision
If high temperature is used for bonding, then bonding effectiveness improves, but copper structures may overheat and cause defects
Solution Approach 1:
The patent applies local quality by creating a reducing gas environment specifically at the bonding interface where copper structures are located. This localized protective atmosphere allows precise temperature control at the bonding zone, enabling effective bonding without excessive heating of the entire substrate, thereby achieving manufacturing precision while controlling temperature.
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 effectively removes oxidation and contamination, ensuring reliable bonding of copper structures by using a reducing gas and localized heating, maintaining substrate temperature within a controlled range and preventing excessive heating, thus enhancing the bonding process efficiency and reliability.
Implementation Method 1
providing a reducing gas in contact with each of the plurality of first electrically conductive structures and the plurality of second electrically conductive structures
Implementation Method 2
localized heating to clean copper oxides and contaminants from the surfaces of electrically conductive structures
Implementation Method 3
heat and/or pressure (and sometimes ultrasonic energy) are used to form a plurality of interconnections between (i) electrically conductive structures on a semiconductor element and (ii) electrically conductive structures on a substrate
Data Source
AI summary
A method of bonding a semiconductor element to a substrate includes: carrying a semiconductor element including a plurality of first electrically conductive structures with a bonding tool; supporting a substrate including a plurality of second electrically conductive structures with a support structure; providing a reducing gas in contact with each of the plurality of first conductive structures and the plurality of second conductive structures; establishing contact between corresponding ones of the plurality of first conductive structures and the plurality of second conductive structures; moving at least one of the semiconductor element and the substrate such that the corresponding ones of the plurality of first conductive structures and the plurality of second conductive structures are separated; re-establishing contact between the plurality of first conductive structures and the plurality of second conductive structures; and bonding the plurality of first conductive structures to the respective ones of the plurality of second conductive structures.