Wafer bonding for integrated optics

Physics of wafer bonding

Glass frit bondingGlass frit a slurry of fine glass particles in an appropriate carrierliquid Full sheet deposition or applied by screen printing Slurry heated to melt the glass particles Bonding upon solidification

Anodic bonding

Metallic bonding

Molecular wafer bonding

Molecular wafer bonding

Molecular wafer bonding

Molecular wafer bonding

Molecular wafer bonding

Molecular wafer bonding

Molecular wafer bonding

Molecular wafer bonding

Surface cleaning

Surface cleaning

How to get rid of these particles?

Surface cleaning

Molecular wafer bonding

Surface activation

Surface activation

Deposited SiO2 allows to bond anything to anything

Surface activation

Molecular wafer bonding

Room temperature attachment

Molecular wafer bonding

Annealing

Annealing

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive wafer bonding

Adhesive bonding

Why adhesive die to wafer bonding? Less stringent requirements on surface quality

Micro-roughness Particle contamination Other types of contamination

Low temperature bonding process Planarization of SOI topography by spin coating

DVS-BCB adhesive bonding

Why DVS-BCB as a bonding agent? Low temperature bonding process (Tbond=250C) Very good planarization properties High glass transition temperature (Tg> 350C) High resistance against chemicals Known material in IC industry (packaging)

DVS-BCB adhesive bondingChemical formula

Commercially formulated by DOW as a B-staged oligomersolution (35% pre-polymerized)

By spin-coating: layer thicknesses of 1m to 25m available For our application: much thinner bonding layers are required

Dilution of the commercially available DVS-BCB using mesitylene

Stable spin coating of layer thicknesses down to 30nm

Si

CH3

CH3

Si

CH3

CH3

O

1,3-divinyl-1,1,3,3-tetramethyldisiloxane-bisbenzocyclobutene

DVS-BCB adhesive bondingOverview of the bonding process

Si-substrate

SiO2Si

BCB BCB BCB

BCB coatingWafer cleaning

Solvent evap + prepolymerization

Die attachment

BCB

BCB curing (pressurized)

DVS-BCB adhesive bondingCleaning of the SOI wafer surface using Piranha clean Standard Clean - 1 solution Standard Clean 2 solution

Particle free hydrophilic surface

Cleaning of the InP/InGaAsP die surface by Sacrifical removal of an InP epitaxial layer using 3HCl:H2O Sacrificial removal of an InGaAs layer using H3PO4:3H2O2:H2O

Particle free hydrophilic surface

DVS-BCB adhesive bondingPlanarization properties

Double spin coating has higher DOP than single coating with the same aggregate thicknessCuring profile and density of topography important for DOP

DVS-BCB adhesive bondingDie attachment process

Aligned attachment of dies and structured SOI wafer to carrier wafers

DVS-BCB adhesive bondingDie attachment process

Mounting of the carrier wafers in bonding chamber (carrier wafers are mechanically aligned)

DVS-BCB adhesive bondingDie attachment process

Evacuation of bonding chamber and attachment of dies (150C)

DVS-BCB adhesive bondingDie attachment process

Purging of the bonding chamber evaporation or release of temporary adhesive

DVS-BCB adhesive bonding

Equipment

Bonding equipment

Bonding equipment

Characterization equipment

Characterization Equipment

Characterization Equipment

Substrate removal

Bonding equipment

Unprocessed opto-electronic layer structure

Processed SOI waveguide wafer

Die to wafer bonding Substrate removal

Processing (definition of the component)

CMOS wafer

Photonic layer

Bonding of InP/InGaAsP dies and device processing

Bonding unprocessed dies using pick and place lowers needed alignment accuracy increases throughput

After die to wafer bonding all processing steps are wafer scale processes

Fabrication of bonded devices Photodetectors

Surface illuminated photodetector

Fabrication of bonded devicesPhotodetectors

Evanescently coupled MSM photodetectors

Fabrication of bonded devicesPhotodetectors and laser diodes

Inverted adiabatic taper approach Processing of both laser diodes and photodetectors identical

InP Microdisk Laser on Silicon

Multi-wavelength Laser on Si

III-V Photodetectors on Silicon

III-V Photodetectors on Silicon

Nonlinear ring resonators

Conclusions

Wafer bonding and die-to-wafer bondingtechnology is a very versatile technology with awide range of applicationsMolecular and adhesive (die-to-) wafer bondingare enabling technologies to realize complexphotonic integrated circuitsFuture research: to scale up the integration density todemonstrate the feasibility of complexactive/passive photonic integrated circuits