MEMS Metallization Structure for Hermetic Wafer Bonding Accuracy

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Solution Overview

Problem

Current MEMS wafer packaging methods face challenges in achieving quality hermetic sealing and electrical characterization, with limited wafer bonding rates and poor overlay accuracy, leading to increased manufacturing costs and reduced reliability.

Innovation Solution

The method involves forming metallization structures on CMOS and MEMS wafers with sacrificial oxide layers and metal contact pads, followed by hybrid bonding and subsequent fusion bonding with a cap wafer, eliminating the need for eutectic bonding and improving overlay accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If eutectic bonding is used for wafer packaging, then hermetic sealing is achieved, but manufacturing cost increases and productivity decreases

Engineering Contradiction:

Improvehermetic sealing qualityVSAvoidwafer bonding rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the bonding parameters by eliminating the eutectic bonding process and replacing it with direct wafer bonding methods. This parameter change allows for faster bonding rates while maintaining hermetic sealing quality, thus resolving the contradiction between reliability and productivity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent extracts and removes the eutectic bonding step from the packaging process. By taking out this specific bonding method, the process is simplified and accelerated, improving productivity while alternative bonding methods maintain the necessary hermetic sealing

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If eutectic bonding is used for wafer packaging, then hermetic sealing is achieved, but manufacturing cost increases

Engineering Contradiction:

Improvehermetic sealing qualityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the bonding process parameters by replacing eutectic bonding with more cost-effective direct bonding methods. This parameter change reduces material and process costs while maintaining the hermetic sealing quality required for reliable MEMS device packaging

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs simpler, more economical bonding materials and processes that replace expensive eutectic bonding. These alternative methods achieve the same hermetic sealing function at lower cost, resolving the contradiction between reliability and ease of manufacture

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of manufacture

If conventional bonding methods are used, then wafer bonding is achieved, but overlay accuracy is poor

Engineering Contradiction:

Improvebonding processabilityVSAvoidoverlay accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent applies preliminary actions by preparing the wafer surfaces with specific treatments and alignment features before bonding. This preliminary preparation ensures high overlay accuracy during the bonding process while maintaining ease of manufacture through standardized procedures

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces conventional mechanical alignment and bonding systems with more precise methods, such as optical alignment or specialized bonding equipment, that achieve superior overlay accuracy without significantly complicating the manufacturing process

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 increases the number of MEMS devices manufactured per hour and enhances overlay accuracy, reducing manufacturing costs and improving the reliability of MEMS devices.

Implementation Method 1

etching the first sacrificial oxide layer and the second sacrificial oxide layer, wherein etching the first sacrificial oxide layer and etching the second sacrificial oxide layer releases the movable MEMS element such that the movable MEMS element moves freely about an axis

Methodology Applied

Scientific EffectChemical etching: Ablation

Implementation Method 2

bonding the first metallization structure to the second metallization structure

Methodology Applied

Scientific EffectHybrid bonding: Welding

Implementation Method 3

fusion bonding a cap wafer to the MEMS wafer

Methodology Applied

Scientific EffectFusion bonding: Welding

Data Source

PatentUS11932534B2MEMS device having a metallization structure embedded in a dielectric structure with laterally offset sidewalls of a first portion and a second portion

Publication Date: 2024.03.19 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A microelectromechanical system (MEMS) structure and method of forming the MEMS device, including forming a first metallization structure over a complementary metal-oxide-semiconductor (CMOS) wafer, where the first metallization structure includes a first sacrificial oxide layer and a first metal contact pad. A second metallization structure is formed over a MEMS wafer, where the second metallization structure includes a second sacrificial oxide layer and a second metal contact pad. The first metallization structure and second metallization structure are then bonded together. After the first metallization structure and second metallization structure are bonded together, patterning and etching the MEMS wafer to form a MEMS element over the second sacrificial oxide layer. After the MEMS element is formed, removing the first sacrificial oxide layer and second sacrificial oxide layer to allow the MEMS element to move freely about an axis.