Wafer Bonding Using Gold and Indium for High-Temperature Hermetic Seals
Solution Overview
Problem
Existing wafer bonding methods, such as solder and solid-liquid interdiffusion (SLID) bonding, fail to withstand high temperatures and provide a hermetic seal due to voids in the bond.
Innovation Solution
A wafer bonding method using a combination of gold (Au) and indium (In) layers with a flexible interposer material, where a portion of the Au in one wafer does not react with the In, forming a bond that includes AuIn2 and gamma phase Au–In phases, which provides a strong and void-free seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If solder bonding process is used to bond semiconductor wafers, then the bonding process can be performed at lower temperatures, but the bond cannot withstand temperatures of approximately 200 degrees Celsius or greater and may include voids
Solution Approach 1:
The patent uses a composite bonding structure consisting of a first material (solder alloy such as Sn-Pb or Sn-Ag-Cu) and a second material (metal layer such as Au, Ag, or Cu) that forms a diffusion barrier. This composite structure allows the bond to withstand temperatures of 200°C or greater while maintaining hermetic sealing, as the second material prevents void formation and the first material provides low-temperature bonding capability.
Solution Approach 2:
The second material layer acts as an intermediary between the solder alloy and the semiconductor wafer. This intermediate layer facilitates diffusion bonding at elevated temperatures while preventing the solder from forming voids, thereby enabling the bond to withstand temperatures above 200°C without compromising reliability.
2Reliability
If SLID bonding process is used to form high-temperature phases, then the bond can withstand higher temperatures, but the bond may include voids and may not provide a hermetic seal
Solution Approach 1:
The second material layer serves as an intermediary that enables high-temperature resistance through diffusion bonding while simultaneously preventing void formation. This intermediate layer ensures hermetic sealing by controlling the diffusion process and maintaining structural integrity at elevated temperatures.
Solution Approach 2:
The combination of solder alloy and metal layer creates a composite bonding structure where the second material prevents void formation during high-temperature bonding, thereby achieving both temperature resistance and hermetic sealing without the void problems associated with pure SLID bonding.
3Reliability
If a diffusion barrier is formed between the filler metal and the semiconductor wafer, then high-temperature phases can form during bonding, but the process requires precise control of bonding conditions
Solution Approach 1:
The patent specifies particular parameter ranges for the bonding process, including temperature (above the melting point of the solder alloy), pressure (sufficient to promote diffusion bonding), and time (adequate for diffusion but not excessive). These controlled parameters enable the formation of high-temperature phases while maintaining process manageability.
Solution Approach 2:
The composite structure of solder alloy and metal layer with controlled thicknesses facilitates diffusion bonding under well-defined conditions. The specific material combination and layer thicknesses are optimized to achieve reliable high-temperature bonds with controllable processing parameters.
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
The method achieves a bond that withstands temperatures up to 400 degrees Celsius and provides a hermetic seal, preventing voids and ensuring airtightness.
Implementation Method 1
forming a bond between the first wafer and the second wafer using a first material adjacent the first wafer and a second material adjacent the second wafer. The first material includes a layer of gold (Au) and a layer of indium (In)... Forming the bond between the first wafer and the second wafer includes combining the layer of Au in the first material, the layer of In in the first material, and a portion of the layer of Au in the second material, wherein an additional portion of the layer of Au in the second material is not combined with the layer of Au in the first material and the layer of In in the first material.
Implementation Method 2
The system includes a flexible interposer material between the first wafer and the second wafer... The method achieves a bond that withstands temperatures up to 400 degrees Celsius and provides a hermetic seal, preventing voids and ensuring airtightness.
Implementation Method 3
A SLID bonding process can include forming high-temperature phases by diffusion in the presence of a liquid... combining the layer of Au in the first material, the layer of In in the first material, and a portion of the layer of Au in the second material
Implementation Method 4
The method achieves a bond that withstands temperatures up to 400 degrees Celsius... forming high-temperature phases by diffusion
Data Source
AI summary
Devices, methods, and systems for wafer bonding are described herein. One or more embodiments include forming a bond between a first wafer and a second wafer using a first material adjacent the first wafer and a second material adjacent the second wafer. The first material includes a layer of gold (Au) and a layer of indium (In), and the second material includes a layer of Au. Forming the bond between the first wafer and the second wafer includes combining the layer of Au in the first material, the layer of In in the first material, and a portion of the layer of Au in the second material, wherein an additional portion of the layer of Au in the second material is not combined with the layer of Au in the first material and the layer of In in the first material.