Advanced MEMS Wafer Bonding Enabled by

High Vacuum Processing

Markus Wimplinger Corporate Technology Development & IP Director

“The Ultimate Goal in Wafer Bonding”

Different CTE Bulk

Materials

Very High Vacuum (<-E-5mbar)

Perfect Bond Line Uniformity (<+/-5nm)

~

Electrically Conductive

(ohmic contact or p/n junction)

Optically

Transparent

High (Bulk Equivalent)

Bond Strength

EVG® ComBond® - High Vacuum Bonding

Applic

ations f

or

Hig

h V

acuum

E

ncapsula

tion b

y W

afe

r B

ondin

g

Gyroscopes

Microbolometers

Thermally Isolated Devices Such as Atomic Clocks

Other?

EVG® ComBond® - High Vacuum Bonding

Re

quirem

ents

for

Hig

h V

acuum

E

ncapsula

tion b

y W

afe

r B

ondin

g

Effective Bake-Out Process

Dual Temperature Bake-Out

Getter Activation

Alignment in Vacuum

Formation of Hermetic Seal

EVG® ComBond® - High Vacuum Bonding

Wafers are baked out prior to aligning and clamping.

Open faced

Wafers will have a minimum of 8 mm free space above them.

Wafers stay in vacuum until bonding is completed

This increased spacing and temperature as compared to traditional

wafer bonding; where the wafers are aligned, separated with spacers

(50 µm – 500 μm) and clamped in ambient atmosphere; results in

improved desorption of water molecules from the surface of the

wafers.

Conceptual drawing of

bake out module

EVG® ComBond® - High Vacuum Bonding

• Improved getter activation due to separate preprocessing of top and

bottom wafer.

– Getter wafer can be activated at a high temperature

– Other wafer can be baked out at lower temperature if required.

EVG® ComBond® - High Vacuum Bonding

• Because of the modular tool configuration, custom

preprocessing modules can be developed and added

without redesigning the tool

• Examples:

– Reducing atmosphere; such as forming gas

– Connection to a non EVG module

– Special customer requirements

Bonding Methods Supported by EVG® ComBond®

Bonding processes other than the

yellow highlighted processes would be

supported as well, but ComBond®

typically does not offer a unique value

proposition

EVG® ComBond®

Process Flow or Direct bonding with ComBond® Activation

High Vacuum

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

Pre-Bonding Surface Characterization:

Topography AFM Measurements

p-type Si (100) Rq = 0.147 nm

p-type Si (100)

Rq = 0.092 nm p-type Si (100) Rq = 0.18 nm

p-type Si (100)

Rq = 0.066 nm

Recipe 1 Recipe 2 Recipe 3 As received

Rq < 0.5 nm for all samples / recipes

Low microroughness profiles are preserved during activation.

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

Bonding Trials Overview

Q.-Y. Tong and U. Gösele, in

Semiconductor Wafer Bonding:

Science and Technology, p. 118,

John Wiley And Sons, Inc., New

York (1999).

Reproducibly achieved bond energy ≈ bulk fracture energy without any thermal

treatment before, during or after processing.

Latest results

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

HR-TEM Measurements

sample #1- medium energy

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

HR-TEM image reveals an

amorphous layer of 2.6 nm

thickness in the bond interface.

Oxygen signal

Oxide-free!

Si/Si bond interface

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

• EDXS was performed on 3 rectangular areas.

• Spectra show the interface is most likely not composed

of SiOx.

• O and C signals have nearly the same peak intensity,

regardless at which position the spectra were taken.

• This indicates O and C contamination is due rather to

sample preparation.

keV

1

keV

2

keV

3

EDXS Measurements

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

Bonding Interface

Characterization: Uniformity C-SAM / Maszara Test

High quality bond interface

Maximum bond strength

without thermal annealing

EVG® ComBond®

Process Results: Si – Si Wafer Bonding

Bonding Interface

Characterization: Structural HR-TEM

Influence of activation power on amorphous layer thickness in

a nutshell:

High power Low power Very low power

Metal Thermo-Compression Wafer Bonding

Tem

pera

ture

Time

High melting

material

High melting

material

Metals have typically oxides on the

surfaces which can prevent perfect

bonding

Oxide

Polycrystalline

Metal

Metal Thermo-Compression Wafer Bonding:

Oxide Removal

High melting

material

High melting

material

Oxide removal by either wet

chemical, forming gas (to

enable bonding for e.g. Cu-Cu

bonding) of ComBond® for

any oxidized surface

Noble metals as e.g. Au have

no oxide formation and can

be bonded directly

Oxide free

surface

Metal Thermo-Compression : Step 1 – Contacting

Tem

pera

ture

Time

Wafers are aligned and brought into

contact

Flat surfaces needed to optimize

contact between the wafers

No grain growth

over the interface

Metal Thermo-Compression : Step 2 – Heating

Tem

pera

ture

Time

Solid-Solid Process

No liquid face at process temperature

Sill interface between the wafers as

the no grain growth over the interface

starts

Started grain growth

over the interface

Metal Thermo-Compression : Step 3 – Isothermal

Annealing

Tem

pera

ture

Time

Grains newly formed

and no more interface

Initial

interface

When the process is finished no more interface

can be detected and bulk strength is obtained

Al-Al bonding results using conventional bonding processes

Left to Right: increasing temperature 400 °C – 550 °C, ∆ = 50 °C, 60 kN

→ decreasing SAM signal with increasing bond temperature

→ increasing bond interface quality with rising bond temperature

400 °C 450 °C 500 °C 550 °C

Al-Al

EVG® ComBond®

Process Results: ComBond Al-Al Wafer Bonding

EVG® ComBond®

ComBond Platform – High Vacuum Wafer Bonding Cluster Tool

Bake

Module

ComBond

Activation

Module

(CAM)

Bond

Module

Vacuum Align

Module

Load

Locks

and

Handling

Cluster

Align & Contact

< 1µm & < 10kN

EVG® ComBond®

ComBond Platform – High Vacuum Wafer Bonding Cluster Tool

Bake

Module

ComBond

Activation

Module

(CAM)

Load

Locks

and

Handling

Cluster Removes

Surface

Contaminants

< 450°C

Removes

Native

Oxides

Bond

< 500 °C

< 100 kN

All Handling

and Modules

at

< 9E-8 mbar

EVG® ComBond®

ComBond Modules – Vacuum Align Module (VAM)

Vacuum Align Module VAM Technical Data

F2F Alignment

Back Side Alignment BSA

RIR Alignment

< 1µm

< 1µm

< 1µm

Piston force Up to 10 kN

Throughput 12 wph

Wafer Substrate 150 mm, 200 mm BSA

200 mm F2F

150 mm, 200 mm F2F with RIR

Wafer stack height < 4 mm

• Alignment Wafers Sizes

• Face to Face (200mm)

• BS Alignment (150mm & 200mm)

• RIR Alignment (150mm & 200mm)

• Force up to 10 kN

• Enhanced vacuum level of < 9 x 10-8 mbar

• Clamp mechanism to fix aligned wafer pair for wafer transfer

Summary & Conclusions

Different CTE Bulk

Materials

Very High Vacuum (<-E-5mbar)

Perfect Bond Line Uniformity (<+/-5nm)

~

Electrically Conductive

(ohmic contact or p/n junction)

Optically

Transparent

High (Bulk Equivalent)

Bond Strength

Thank you for your attention!

Please visit our booth #606 / 4F