The control of the quality of the substrate surface is of the utmost importance in the production of solid state devices.
The surface should be clean, flat and show no(sub)surface damage.
Amorphous, poly and monocrystalline materials can be polished.
Glueing, thermal wax or direct bonding techniques are used both for the fixation of samples during various processes and for end products.

POLISHING

Four technologies are available for substrate bonding:

Slurry grinding 

The treatment of a substrate by a slurry on a rotating disc results  in a thinning of the sample. This process is used for lapping and trimming the thickness of the sample as a pre-treatment for subsequent polishing steps.Chemical polishing: The substrate is continuously moved over a rotating polishing pad
 while adding an etching solution. This technique is used to polish GaAs, InP, GaP, and InSb samples.
 In this technique no crystal defects are introduced.

Chemical-mechanical polishing

The sample is moved over a rotating pad while a colloidal suspension 
of silica particles of 10 - 100 nm is added. This technique allows the processing of a wide range of materials.

Planarising

The chemical-mechanical polishing technique is used for planarising the topography of wafers, which causes problems in subsequent processing steps. The technique is used in Si technology and for the processing of thin film magnetic heads.

Cleaning

The surface of samples is readily deteriorated by various treatments and during storing.
Subsequent processing requires cleaning, dependent on the material and the applications.

BONDING

Two technologies are available for substrate bonding:

Glueing

After cleaning, chemical pretreatment and primer deposition the samples are connected
 by adhesives. The technology has been developed for the SOA (Silicon On Anything) project.

Direct bonding

Two clean and flat samples are bonded together by means of Van der Waals forces
and by hydrogen bonding. The bonding becomes permanent with thermal processing.  

WAFERBONDING

Over the last few years wafer to waferbonding has increasingly become a key technology with respect to the various field related to MEMS device fabrication and packaging. It can also be used for micro-fluidics, substrate transfer and bio-chips purposes.

Since September 2006 both a wafer aligner (Suss MicroTech;BA6) as well as a waferbonder (Suss MIcroTech;SB8e) are installed and operational in the MiPlaza Cleanroom. With this equipment it is possible to perform all kind of wafer bonding techniques such as:
anodic, Si direct, adhesive, thermo compression and eutectic bonding.
These processes can take place on Si, glass or pyrex substrates.
 

Suss MicroTech;BA6

Suss MIcroTech;SB8e

At this moment processing is only possible on 6" and 8" circular substrates, but it is our intention that in the near future also other dimensions can be processed.

The most critical process parameters for waferbonding are bonding temperature, bonding pressure and bonding time and the used intermediate layer.
All these parameters are independently programmable and are well controlled with this equipment.

For more information see DTS report nr 06-012