oxide free, low temperature direct bonding by novel...

Oxide free, low Temperature Direct Bonding by Novel Surface Activation Method Markus Wimplinger, Christoph Flötgen, Nasser Razek, Viorel Dragoi

Outline

Background

Experimental

Results

Summary & Outlook

EV Group Proprietary – Semicon Europa 2014 / Nanoelectronics and Healthcare Session / October 7th 2014

Background

Existing low temperature fusion bonding

technologies:

Wet chemical cleaning

Various plasma activation processes

Surface Activated Bonding (SAB)


Background

Plasma Activated Wafer Bonding (PAWB)

Wafer contacting at atmospheric

pressure results in (weak)

van-der-Waals bonds

RT covalent bonding possible,

but industrially not practical

Interfaces are only possible with

at least native oxide embedded

T. Plach, K. Hingerl, S. Tollabimazraehno, G. Hesser, V. Dragoi and M. Wimplinger, J. Appl. Phys., 113, 094905 (2013).


Background

Some emerging applications are not fully addressed,

as these demand:

Room temperature covalent bonding

Conductive / oxide-free interfaces

Minimum bulk lattice damage


Background

Process Requirements for New Technology

Dry process

Optional removal of (native) oxides

Capability to prevent re-oxidation

high vacuum processing / handling of substrates

Maintain underlying bulk lattice integrity

Amorphous layers and charge imbalances at the bonded interface

degenerate electrical device performance *

Maintain high level of cleanliness

* See: Essig S , and Dimroth F ECS J. Solid State Sci. Technol. 2013;2:Q178-Q181


Background

Advanced device applications that would benefit

from the use of the novel technology:

Heterogeneous integration

Layer transfer for advanced substrates

Optically transparent and electrically conductive

bonding interfaces

For multi-junction solar cells and

Optical devices

Improved metal/metal bonding (MEMS)


Experimental

Equipment: EVG®580 ComBond®


• Wedge error

compensation

• Top / bottom

independent temp.

control up to

400°C

• Piston force up to

60kN

Bond Module

ComBond®

Activation Module

High Vacuum Handling System

• Very flexible due

to modular setup

• Up to 5 modules

Results

• 200 mm prime Si (100) wafers manually loaded to load port cassettes in class 1000 CR

environment

• no ex situ pre-treatment

Particle Contamination Tests

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Reference 1

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Results

• Each sample was measured on > 5 points

• Consistent results on all positions

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


Results

Bonding Trials In situ bonding – inside system, wafer transfer in high vacuum

Bond strength > 2.5 J/m² (all measurement positions broken)

Example 1: thermal annealing 200°C, 1h

Example 2: room temperature


Results

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 strength ≈ bulk fracture strength without any thermal

treatment before, during or after processing.

Bonding Trials Overview

Latest results


Sample #4

Wafer 1

Wafer 2

Amorphous

layer

Wafer 1

Wafer 2

Amorphous

layer

Results – Si-Si Interface

HR-TEM Measurements

Sample #1



SRIM 2013 was used to model impact of

projectiles on amorphous layer formation J. F. Ziegler, M. D. Ziegler, and J. P. Biersack,

Nucl. Instrum. Methods Phys. Res. B., 268, 1818 (2010).

Model stack:

15 Å SiO2

Bulk Si substrate

Energetic projectile properties:

Mass

Energy

Angle of incidence

Adjusted interaction parameters Y. Kudriatsev, A. Villegas, A. Godines, R. Asomoza, Appl. Surf. Sci., 239, 273 (2005).

a

m, E

t1

t2

HR-TEM Measurements



HR-TEM Measurements sample #1- medium energy


AL thickness: t = (9.60 ± 0.13)

nm

9.2 nm

Deviation from experiment: 4%

HR-TEM Measurements sample #29 – high energy




• 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


InP

Rq = 0.63 nm GaAs

Rq = 0.093 nm

Wafer Level Bonding of III-V Compounds

InP

GaAs

Encouraging Results

AFM Measurements

TEM Measurements

EDX Measurements


Summary

Surface activation is needed to yield superior bonding quality at

low temperatures through formation of covalent bonds

Advanced applications need advanced surface activation

methods to

Remove surface oxides

Maintain maximum lattice integrity and general cleanliness

Ideally eliminate the need for thermal annealing

An equipment solution was developed that

Provides high level process flexibility through modular design

Retains wafer surface roughness after surface preparation

Introduces only minimum lattice damage to the substrates

Maintains high vacuum levels at ~ 10-8 mbar, to prevent re-oxidation

Produces real room temperature Si-Si wafer bonds with maximum

bond strength

Effectively removes surface oxides on various wafer materials (Si, SiC,

GaAs, InP…)


oxide free, low temperature direct bonding by novel...

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