How many types of wafer bonding are there? This picture is finally clear!

What are the types of wafer bonding?

As shown in the picture above, let's explain the terms one by one.
Bonded permanently
The purpose is to form an irreversible mechanical structure combination, which is mostly used for 3D integration, MEMS, TSV and other device packaging.

Temporary bonding/unbonding

The purpose is to provide temporary support during device processing, which can be removed later, and is often used for ultra-thin wafer processing.

Thin wafers are bonded using temporary adhesives or intermediate support wafers (Carriers), and after completion, they are debonded by thermal/laser/chemical methods.

Permanent bonding: divided into the following two categories based on the presence of an intermediate layer:

Direct bonding without intermediate layer

1. Fusion bonding / direct or molecular bonding

Principle: Through surface flatness and hydrophilic treatment, van der Waals force bonding occurs on the surface of the two wafers, and subsequent thermal annealing promotes bonding.

Features: No intermediate materials, high bonding strength.

Applications: SOI wafer fabrication, MEMS, Si-Si, or SiO₂-SiO₂ bonding.

2. Copper-copper/oxide hybrid bonding

Principle: Copper and copper atoms are directly bonded, and the surface is assisted by a dielectric layer such as SiO₂.

Features: Suitable for high-density 3D packaging and mixed-signal ICs.

Applications: Logic-memory integration for advanced packages such as TSV, HBM, Hybrid Bonding.

3. Anode bonding

Principle: At high temperature (~300°C) and high electric field, electrostatic attraction is formed between glass and silicon and ion migration occurs.

Features: Firm bonding, suitable for glass-Si.

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Applications: MEMS devices, pressure sensor packages.

二,Indirect bonding with the intermediate layer

(1)Insulating interlayer

a. Glass paste bonding

Principle: Use a low-melting glass paste to melt and flow under heating conditions to form a bond.

Applications: Display panels, MEMS.

b. Glue bonding

Principle: Use epoxy resin, BCB and other organic glues to form bonds.

Features: Low requirements for surface flatness, low-temperature process.

Applications: Wafer-level packaging, temporary bonding.

c. Eutectic bonding

Principle: Bonding is formed using the low melting point of metal eutectic points (such as Au-Sn).

Applications: MEMS packaging, optoelectronic devices.

(2)Metal interlayer

 

a. Reflow soldering

Principle: Sn and other solder materials are used to heat and then flow back to form a bond with the pad.

Applications: Wafer-level packaging (WLP), micro-bump bonding.

b. Metal thermocompression bonding

Principle: Combine metal layers (such as Cu) under high temperature + high pressure.

Features: Used in high-density packaging, commonly found in TCB processes.

Applications: HBM stacking, COWOS, FO-WLP, etc.