Cu-Sn Wafer Bonding Structure for Low-Temperature MEMS Packaging

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Solution Overview

Problem

Existing eutectic bonding methods for wafer bonding in semiconductor manufacturing face challenges with high thermal budgets and reduced pressing forces, which are unsuitable for advanced MEMS structures due to their delicacy and thermal constraints.

Innovation Solution

A Cu-Sn eutectic bond is employed with a lower bonding temperature (240-300°C) and pressing force (1-2 MPa) to form a hermetic and strong bond between silicon wafers, utilizing fusion bonding and eutectic reactions to create a Cu-Sn alloy bond.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If eutectic bonding is used for wafer bonding, then bonding strength and hermetic sealing are improved, but thermal budget and pressing force requirements become too high for advanced MEMS structures

Engineering Contradiction:

Improvebonding strengthVSAvoidbonding temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent changes the bonding temperature parameter from conventional high temperatures (>400°C) to a lower temperature range (200-300°C) by using a eutectic bonding process with specific metal composition ratios. This allows achieving strong bonding while accommodating the thermal constraints of advanced MEMS structures.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite bonding interface consisting of multiple metal layers with specific compositions (e.g., Cu-Sn, Au-Si, or Ag-Ge systems) to achieve eutectic bonding. The composite material structure enables bonding at lower temperatures while maintaining high bonding strength and hermetic sealing properties.

Inventive Principle:

Principle #40Composite materials

2Reliability

If eutectic bonding is used for wafer bonding, then bonding strength and hermetic sealing are improved, but pressing force requirements become too high for delicate MEMS structures

Engineering Contradiction:

Improvebonding strengthVSAvoidpressing force

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The patent changes the pressing force parameter from conventional high values to lower values (e.g., 0.1-10 MPa) by utilizing the eutectic reaction characteristics. The phase transformation during bonding provides self-alignment and bonding enhancement, reducing the mechanical pressing force needed while maintaining strong bonds.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent exploits the phase transition phenomenon in eutectic systems where the bonding interface undergoes a solid-to-liquid-to-solid transformation during the bonding process. This phase transition enables atomic diffusion and strong bonding at lower pressing forces, protecting delicate MEMS structures from mechanical damage.

Inventive Principle:

Principle #36Phase transitions

3Ease of manufacture

If conventional eutectic bonding materials are used, then bonding capability is sufficient, but thermal budget constraints of advanced MEMS processes are violated

Engineering Contradiction:

Improvebonding capabilityVSAvoidthermal budget

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

The patent selects eutectic material systems with specifically low melting points (e.g., Cu-Sn with eutectic temperature of 227°C, Au-Si with 363°C) to perform bonding at temperatures compatible with advanced MEMS process thermal budgets. This maintains ease of manufacture while respecting thermal constraints.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses composite metal layer structures with controlled thickness ratios to achieve the desired eutectic composition. The composite material design allows tuning of bonding characteristics and ensures compatibility with existing MEMS fabrication processes while operating within thermal budget limits.

Inventive Principle:

Principle #40Composite materials

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 Cu-Sn eutectic bond provides a robust and hermetic seal with reduced thermal stress, enabling reliable long-term operation of MEMS devices by maintaining structural integrity and electrical connectivity.

Implementation Method 1

Methodology Applied

Scientific EffectEutectic bonding: Phase Change

Implementation Method 2

Methodology Applied

Scientific EffectFusion bonding: Melting

Data Source

PatentUS12534361B2Packaging method and associated packaging structure

Publication Date: 2026.01.27 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

The present disclosure provides a packaging method, including: providing a first semiconductor substrate; forming a bonding region on the first semiconductor substrate, wherein the bonding region of the first semiconductor substrate includes a first bonding metal layer and a second bonding metal layer; providing a second semiconductor substrate having a bonding region, wherein the bonding region of the second semiconductor substrate includes a third bonding layer; and bonding the first semiconductor substrate to the second semiconductor substrate by bringing the bonding region of the first semiconductor substrate in contact with the bonding region of the second semiconductor substrate; wherein the first and third bonding metal layers include copper (Cu), and the second bonding metal layer includes Tin (Sn). An associated packaging structure is also disclosed.