Wafer Bonding Using Eutectic Alloy Reflow to Eliminate Oxide Removal
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Solution Overview
Problem
Current wafer level packaging methods require oxide removal from bonding interfaces, which is a difficult and imperfect process that reduces processing yield.
Innovation Solution
A method involving forming bond rings and standoffs on semiconductor wafers, using a layer of material with a lower reflow temperature to create a hermetic seal by heating above the reflow temperature of the second material but below the first, and optionally forming a eutectic alloy through annealing to maintain distance and prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxide removal is performed on bonding interfaces, then bonding quality is improved, but processing yield deteriorates
Solution Approach 1:
The invention extracts the oxide removal step entirely from the bonding process. Instead of removing oxides from the bonding interface, the patent uses a eutectic alloy layer that bonds directly to the oxide-containing semiconductor surfaces, eliminating the need for oxide removal and thereby maintaining high processing yield while achieving reliable bonding.
Solution Approach 2:
The eutectic alloy layer acts as an intermediary between the semiconductor wafers. This intermediate layer with specific composition and melting point enables bonding to occur on oxide-containing surfaces without requiring oxide removal, thus resolving the contradiction between bonding quality and processing yield.
2Reliability
If hermetic seal is created through traditional bonding methods, then sealing reliability is improved, but process complexity deteriorates
Solution Approach 1:
The invention changes the temperature parameter during bonding by utilizing the eutectic melting point of the alloy layer. By heating to a specific temperature range (above the eutectic melting point but below substrate damage temperature), the alloy becomes liquid and forms a hermetic seal, then solidifies upon cooling, achieving reliable sealing through controlled temperature parameter changes rather than complex mechanical or chemical processes.
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 improves wafer bonding by creating a hermetic seal without the need for oxide removal, enhancing processing yield and reliability.
Implementation Method 1
heating the first and second wafers to a temperature above the reflow temperature of the second material and below the reflow temperature of the first material causing the second material to reflow and create a hermetic seal
Implementation Method 2
annealing the first and second materials, causing the first material to diffuse into the second material to create a eutectic alloy
Data Source
AI summary
Hermetically sealed semiconductor wafer packages that include a first bond ring on a first wafer facing a complementary surface of a second bond ring on a second wafer. The package includes first and second standoffs of a first material, having a first thickness, formed on a surface of the first bond ring. The package also includes a eutectic alloy (does not have to be eutectic, typically it will be an alloy not specific to the eutectic ratio of the elements) formed from a second material and the first material to create a hermetic seal between the first and second wafer, the eutectic alloy formed by heating the first and second wafers to a temperature above a reflow temperature of the second material and below a reflow temperature of the first material, wherein the eutectic alloy fills a volume between the first and second standoffs and the first and second bond rings, and wherein the standoffs maintain a prespecified distance between the first bond ring and the second bond ring.